Humanized and affinity-matured antibodies directed against FCRH5 and methods of use

Abstract

The present invention relates to anti-FcRH5 antibodies, including anti-FcRH5 antibodies comprising an FcRH5 binding domain and a CD3 binding domain (e.g., FcRH5 T cell-dependent bispecific (TDB) antibodies), and methods of using the same.

Description

HUMANIZED AND AFFINITY MATURED ANTIBODIES TO FcRH5 AND METHODS OF USESEQUENCE LISTINGThe instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on June 14, 2016, is named 50474-134W02_Sequence_Listing_6_14_16_ST25 and is 133,004 bytes in size.FIELD OF THE INVENTIONThe present invention relates to anti-FcRH5 antibodies and methods of using the same.BACKGROUND OF THE INVENTIONCell proliferative disorders, such as cancer, are characterized by the uncontrolled growth of cell subpopulations. They are the leading cause of death in the developed world and the second leading cause of death in developing countries, with over 14 million new cancer cases diagnosed and over eight million cancer deaths occurring each year. The National Cancer Institute has estimated that greater than half a million Americans will die of cancer in 2016, accounting for nearly one out of every four deaths in the country. As the elderly population has grown, the incidence of cancer has concurrently risen, as the probability of developing cancer is more than two-fold higher after the age of seventy. Cancer care thus represents a significant and ever-increasing societal burden.The Fc receptor-like 5 (FcRH5, also known as FcRL5 or IRTA2) gene belongs to a family of six recently identified genes of the immunoglobulin superfamily (IgSF). This family of genes is closely related to the Fc receptors with the conserved genomic structure, extracellular Ig domain composition, and immunoreceptor tyrosine-based inhibitory (ITIM) and immunoreceptor tyrosine-based activation (ITAM) like signaling motifs (Davis et al. Eur. J. Immunol. 35:674-80, 2005). Six members of the FcRH / IRTA receptor family have been described: FcRH1 / IRTA5, FcRH2 / IRTA4, FcRH3 / IRTA3, FcRH4 / IRTA1 ,FcRH5 / IRTA2, and FcRH6 (Poison et al. Int. Immunol. 18(9):1363-1373, 2006. The FcRH cDNAs encode type I transmembrane glycoproteins with multiple lg-like extracellular domains and cytoplasmic domains containing consensus immunoreceptor tyrosine-based activating and / or inhibitory signaling motifs. The FcRH genes are structurally related, and their protein products share 28-60% extracellular identity with each other. They also share 15-31 % identity with their closest FcR relatives. There is a high degree of homology between the different FcRHs.The ligand(s) for FcRH5 are unknown, but FcRH5 has been implicated in enhanced proliferation and downstream isotype expression during the development of antigen-primed B-cells (Dement-Brown et al. J. Leukoc. Biol. 91 :59-67, 2012). The FcRH5 locus has three major mRNA isoforms (FcRH5a, FcRH5b, and FcRHSc). The major FcRH5 protein isoforms encoded by these transcripts share a common amino acid sequence until residue 560, featuring a common signal peptide and six extracellular lg-like domains. FcRH5a represents a 759-amino acid secreted glycoprotein with eight lg-like domains followed by 13 unique, predominantly polar amino acids at its C-terminus. FcRH5b diverges from FcRH5a at amino acid residue 560 and extends for a short stretch of 32 additional residues, whose hydrophobicity is compatible with its docking to the plasma membrane via a G PI anchor. FcRHSc is the longest isoform whose sequence deviates from FcRH5a at amino acid 746. FcRH5c encodes a 977- amino acid type I transmembrane glycoprotein with nine extracellular Ig-type domains harboring eight potential N-linked glycosylate sites, a 23-amino acid transmembrane domain, and a 104-amino acid cytoplasmic domain with three consensus SH2 binding motifs having an ΙΤΊΜ consensus.The FcRH genes are clustered together in the midst of the classical FcR genes (FcyRI, FcyRII,FcyRIII, and FceRI) in the 1q21-23 region of chromosome 1. This region contains one of the most frequent secondary chromosomal abnormalities associated with malignant phenotype in hematopoietic tumors, especially in multiple myeloma (Hatzivassiliou et al. Immunity. 14:277-89, 2001). FcRH5 is expressed only in the B-cell lineage, starting as early as pre-B-cells, but does not attain full expression until the mature B-cell stage. Unlike most known other B-cell-specific surface proteins (e.g., CD20, CD19, and CD22), FcRH5 continues to be expressed in plasma cells, whereas other B-cell-specific markers are downregulated (Poison et al. Int. Immunol. 18:1363-73, 2006). In addition, FcRH5 mRNA isoverexpressed in multiple myeloma cell lines with 1q21 abnormalities as detected by oligonucleotide arrays (Inoue Am. J. Pathol. 165:71-81 , 2004). The expression pattern indicates that FcRH5 could be a target for antibody-based therapies for the treatment of multiple myeloma. Multiple myeloma is a malignancy of plasma cells characterized by skeletal lesions, renal failure, anemia, and hypercalcemia, and it is essentially incurable by current therapies. Current drug treatments for multiple myeloma include combinations of the proteosome inhibitor bortezomib (VELCADE®), the immunomodulator lenalidomide (REVLIMID®), and the steroid dexamethasone.Monoclonal antibody (mAb)-based therapy has become an important treatment modality for cancer. FcRH5c-specific antibody-based therapies and detection methods may be particularly efficacious as they specifically recognize target cell, membrane-associated FcRH5 rather than antibodies which recognize both soluble and membrane isoforms of FcRH5. However, only the last Ig-like domain of FcRH5 (Ig-like domain 9) is a unique extracellular region that differentiates between the three major isoforms of FcRH5 (e.g., FcRH5a, FcRH5b, and FcRHSc), and there is significant homology between the Ig-like domains within FcRH5. Further, the last Ig-like domain is highly conserved between FcRH1 , FcRH2, FcRH3, and FcRH5. Any antibody-based therapy that specifically targeted FcRH5 should have minimal cross-reactivity with other FcRHs to avoid adverse off-target effects (e.g., FcRH3 is expressed on normal NK cells).In view of the above, there is an unmet need in the field for safe and effective agents for use in the treatment of cell proliferative disorders (e.g., cancers, e.g., FcRH5-positive cancers, e.g., multiple myeloma).SUMMARY OF THE INVENTIONThe present invention provides anti-FcRH5 antibodies (e.g., bispecific antibodies, e.g., FcRH5 T cell-dependant bispecific (TDB) antibodies), compositions, and methods of using the same for the treatment of cell proliferative disorders (e.g., cancers, e.g., FcRH5-positive cancers, e.g., multiple myeloma).In a first aspect, the invention features an anti-Fc Receptor-like 5 (FcRH5) antibody, including a binding domain comprising the following six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 2, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 3, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 4, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 5, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 6.In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some embodiments, the binding domain comprises (a) a heavy chain variable (VH) domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 104, (b) a light chain variable (VL) domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 105, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region framework regions (FRs): (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 104. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 105. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 105.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 10, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 14, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 106, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 107, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 53, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 106. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 107. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 106 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 107.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 , (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 82, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 83, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 82. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 56, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 83. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 82 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 83.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 84, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 85, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 84. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 85. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 84 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 85.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 17, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 22. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 86, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 87, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 86. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 87. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 86 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 87.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 88, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 89, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 88. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 89. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 88 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 89.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 90, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 91 , or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 90. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 91. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 90 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 91.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 , (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 22. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 92, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 93, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 92. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 56, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 93. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 92 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 93.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 , (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 19, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 24. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 94, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 95, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 94. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 95. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 94 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 95.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 96, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 97, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 53, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 96. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 97. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 96 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 97.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 98, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 99, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 55, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 98. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 99. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 98 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 99.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 100, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 101 , or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 100. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 101. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 100 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 101.In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 , (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 102, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 103, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 102. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 56, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51. In some embodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 103. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 102 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 103.In another aspect, the invention features an anti-FcRH5 antibody including a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 32, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 33, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 34, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 35, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 36, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 110, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 111 , or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 66, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 67, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 68, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 69. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 110. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 70, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 71 , (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 72, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 73. In someembodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 111. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 110 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 111.In another aspect, the invention features an anti-FcRH5 antibody including a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41 , (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In other embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 112, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 113, or (c) a VH domain as in (a) and a VL domain as in (b). In other embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 74, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 75, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 76, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 77. In other embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 112. In other embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 78, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 79, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 80, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 81. In otherembodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 113. In other embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 112 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 113.In another aspect, the invention features an anti-FcRH5 antibody including a binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 26, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 27, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 28, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 29, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 30, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 31. In some embodiments, the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 108, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 109, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the antibody further comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 58, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 59, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 60, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 61. In some embodiments, the VH domain comprises the amino acid sequence of SEQ ID NO: 108. In some embodiments, the antibody further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 62, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 63, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 64, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 65. In someembodiments, the VL domain comprises the amino acid sequence of SEQ ID NO: 109. In some embodiments, the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 108 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 109.In some embodiments of any one of the preceding aspects, the anti-FcRH5 antibody binds to an epitope in the Ig-like domain 9 of FcRH5. In some embodiments, the epitope comprises a portion of amino acids 743-850 of SEQ ID NO: 114. In some embodiments, the binding domain binds to human FcRH5, cynomolgus monkey (cyno) FcRH5, or both. In some embodiments, the binding domain does not specifically bind to FcRH1 , FcRH2, FcRH3, and / or FcRH4. In some embodiments, the anti-FcRH5 antibody binds human FcRH5 with a KD of about 100 nM or lower. In some embodiments, the anti-FcRH5 antibody binds human FcRH5 with a KD of between about 10 pM and about 100 nM. In some embodiments, the anti-FcRH5 antibody binds human FcRH5 with a KD of between about 100 pM and about 100 nM. In some embodiments, the anti-FcRH5 antibody binds human FcRH5 with a KD of between about 1 nM and about 20 nM. In some embodiments, the anti-FcRH5 antibody binds human FcRH5 with a KD of between about 1 nM and about 10 nM. In some embodiments, the anU-FcRH5 antibody binds cyno FcRH5 with a KD of about 100 nM or lower. In some embodiments, the anti-FcRH5 antibody binds cyno FcRH5 with a KD of between about 10 pM and about 100 nM. In someembodiments, the anti-FcRH5 antibody binds cyno FcRH5 with a KD of between about 100 pM and about 100 nM. In some embodiments, the anti-FcRH5 antibody binds cyno FcRH5 with a KD of between about 1 nM and about 50 nM. In other embodiments, the anti-FcRH5 antibody comprises an aglycosylation site mutation. In some embodiments, the aglycosylation site mutation is a substitution mutation. In some embodiments, the aglycosylation site mutation reduces effector function of the anti-FcRH5 antibody. In some embodiments, the substitution mutation is at amino acid residue N297, L234, L235, D26S, and / or Ρ32Θ (EU numbering). In some embodiments, the substitution mutation is selected from the group consisting of N297G, N297A, L234A, L235A, D265A, and P329G. In some embodiments, the substitution mutation is an N297G mutation.In other embodiments, the anti-FcRH5 antibody is an IgG antibody.In some embodiments, the anti-FcRH5 antibody is an antibody fragment that binds FcRH5. In some embodiments, the antibody fragment is selected from the group consisting of bis-Fab, Fab, Fab'- SH, Fv, scFv, and (Fab")2 fragments. In some embodiments, the antibody fragment is a bis-Fab fragment.In other embodiments, the anti-FcRH5 antibody is a full-length antibody.In some embodiments, the anti-FcRH5 antibody is a monospecific antibody.In some embodiments, the anti-FcRH5 antibody is a multispecific antibody. In someembodiments, the multispecific antibody is a bispecific antibody. In some embodiments, the bispecific antibody comprises a second binding domain that binds cluster of differentiation 3 (CD3). In some embodiments, the second binding domain binds to an epitope on CD3 comprising amino acid residue Glu6 of CD3. In some embodiments, the epitope further comprises one or more additional amino acid residues selected from the group consisting of Gln1 , Asp2, and Met7 of CD3. In some embodiments, the epitope comprises amino acid residues Gln1 , Asp2, and Glu6 of CD3. In some embodiments, the epitope comprises amino acid residues Gln1 , Asp2, Glu6, and Met7 of CD3. In some embodiments, the epitope does not comprise amino acid residue Glu5 of CD3. In some embodiments, the epitope does not comprise amino acid residues Gly3 and Glu5 of CD3. In some embodiments, the epitope consists of amino acid residues Gln1 , Asp2, Glu6, and Met7 of CD3. In some embodiments, the second binding domain is capable of binding to a human CD3 polypeptide or a cyno CD3 polypeptide. In some embodiments, the human CD3 polypeptide or the cyno CD3 polypeptide is a human CD3e polypeptide or a cyno CD3e polypeptide, respectively. In some embodiments, the human CD3 polypeptide or the cyno CD3 polypeptide is a human CD3y polypeptide or a cyno CD3y polypeptide, respectively. In some embodiments, the second binding domain binds the human CD3e polypeptide with a KD of about 100 nM or lower. In some embodiments, the second binding domain binds the human CD3e polypeptide with a KD of between about 10 pM to about 100 nM. In some embodiments, the second binding domain binds the human CD3e polypeptide with a KD of between about 100 pM to about 50 nM. In some embodiments, the second binding domain binds the human CD3e polypeptide with a KD of between about 1 nM to about 10 nM.In some embodiments, the second binding domain comprises the following six HVRs: (a) anHVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 117, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 120. In some embodiments, the second binding domain comprises the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 133, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 134, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the second binding domain comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 125, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 126, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 127, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 128. In some embodiments, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 133. In some embodiments, the second binding domain further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 129, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 130, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 131 , and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 132. In some embodiments, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 134. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and(b) a VL domain comprising an amino acid sequence of SEQ ID NO: 134.In other embodiments, the second binding domain comprises the following six HVRs: (a) an HVR- H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 124. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 137, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 138, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the second binding domain comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 125, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 126, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 127, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 128. In some embodiments, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 137. In some embodiments, the second binding domain further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 129, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 130, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 131 , and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 132. In some embodiments, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 138. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 137 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 138.In other embodiments, the second binding domain comprises the following six HVRs: (a) an HVR- H1 comprising the amino acid sequence of SEQ ID NO: 139, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 140, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 141 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 142, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 143, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 144. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 153, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 154, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the second binding domain comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 145, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 146, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 147, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 148. In some embodiments, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 153. In some embodiments, the second binding domain further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 149, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 150, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 151 , and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 152. In some embodiments, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 154. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 153 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 154.In other embodiments, the second binding domain comprises the following six HVRs: (a) an HVR- H1 comprising the amino acid sequence of SEQ ID NO: 155, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 156, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 157, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 158, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 159, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 160.In some embodiments, the second binding domain comprises the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 155, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 162, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 157, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 158, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 159, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 160. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 172, (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 173, or (c) a VH domain as in (a) and a VL domain as in (b). In some embodiments, the second binding domain comprises the following heavy chain variable region FRs: (a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 164, (b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 165, (c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 166, and (d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 167. In some embodiments, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 172. In some embodiments, the second binding domain further comprises the following light chain variable region FRs: (a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 168, (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 169, (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 170, and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 171. In some embodiments, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 173. In some embodiments, the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 172 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 173.In other embodiments, the binding domain that binds FcRH5 comprises a VH domain ( VH1) comprising a charged region (CR1) and a VL domain (VL1) comprising a charged region (CR2), wherein the CR1 in the VH1 forms a charge pair with the CR2 in the VL1. In some embodiments, the CR1 comprises a basic amino acid residue and the CR2 comprises an acidic amino acid residue. In some embodiments, the CR1 comprises a Q39K substitution mutation (EU numbering). In some embodiments, the CR1 consists of the Q39K substitution mutation. In some embodiments, the CR2 comprises a Q38E substitution mutation (EU numbering). In some embodiments, the CR2 consists of the Q38E substitution mutation. In some embodiments, the second binding domain that binds CD3 comprises a VH domain (VH2) comprising a charged region (CR3) and a VL domain (VL2) comprising a charged region (CR4), wherein the CR4in the VL2 forms a charge pair with the CR3 in the VH2. In some embodiments, the CR* comprises a basic amino acid residue and the CR3 comprises an acidic amino acid residue. In some embodiments, the CR4 comprises a Q38K substitution mutation (EU numbering). In some embodiments, the CR4 consists of the Q38K substitution mutation. In some embodiments, the CR3 comprises a Q39E substitution mutation (EU numbering). In some embodiments, the CR3 consists of the Q39E substitution mutation. In some embodiments, the VL1 domain is linked to a light chain constant (CL) domain (CLt) and the VH1 is linked to a first heavy chain constant (CH1) domain (CH11), wherein the CL* comprises a charged region (CR5) and the CH11 comprises a charged region (CRe), and wherein the CR5 in the CL» forms a charge pair with the CRe in the CH11. In some embodiments, the CR5 comprises a basic amino acid residue and the CRe comprises an acidic residue. In some embodiments, the CR5 comprises a V133K substitution mutation (EU numbering). In some embodiments, the CR5 consists of the V133K substitution mutation. In some embodiments, the CRe comprises a S183E substitution mutation (EU numbering). In some embodiments, the CRe consists of the S183E substitution mutation.In other embodiments, the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises a charged region (CR7) and the CH12 comprise a charged region (CR8), and wherein the CRe in the CH12 forms a charge pair with the CR7 in the CL2. In some embodiments, the CRe comprises a basic amino acid residue and the CR7 comprises an acidic amino acid residue. In some embodiments, the CRe comprises a S183K substitution mutation (EU numbering). In some embodiments, the CR8 consists of the S183K substitution mutation. In some embodiments, the CR7 comprises a V133E substitution mutation (EU numbering). In some embodiments, the CR7 consists of the V133E substitution mutation.In other embodiments, the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein (a) the CL2 comprises one or more mutations at amino acid residues F116, L135, S174, S176, and / or T178 (EU numbering) and (b) the CH12 comprises one or more mutations at amino acid residues A141 , F170, S181 , S183, and / or V185 (EU numbering). In some embodiments, the CL.2 comprises one or more of the following substitution mutations: F116A, L135V, S174A, S176F, and / or T178V. In some embodiments, the CL2 comprises the following substitution mutations: F116A, L135V, S174A, S176F, and T178V. In some embodiments, the CH12 comprises one or more of the following substitution mutations: A141 I, F170S, S181M, S183A, and / or V185A. In some embodiments, the CH12 comprises the following substitution mutations: A141 I, F170S, S181M, S183A, and V185A.In other embodiments, the binding domain that binds FcRH5 comprises a VH domain (VHi) comprising a charged region (CR1) and a VL domain (VU) comprising a charged region (CR2), wherein the CR2 in the VU forms a charge pair with the CR1 in the VH*. In some embodiments, the CR2 comprises a basic amino acid residue and the CR1 comprises an acidic amino acid residue. In some embodiments, the CR2 comprises a Q38K substitution mutation (EU numbering). In some embodiments, the CR2 consists of the Q38K substitution mutation. In some embodiments, the CR1 comprises a Q39E substitution mutation (EU numbering). In some embodiments, the CR* consists of the Q39E substitution mutation. In some embodiments, the second binding domain that binds CD3 comprises a VH domain (VH2) comprising a charged region (CR3) and a VL domain (VL2) comprising a charged region (CR4), wherein the CR3 in the VH2 forms a charge pair with the CR4 in the VL2. In some embodiments, the CR3 comprises a basic amino acid residue and the CR* comprises an acidic amino acid residue. In some embodiments, the CR3 comprises a Q39K substitution mutation (EU numbering). In some embodiments, the CRa consists of the Q39K substitution mutation. In some embodiments, the CR* comprises a Q38E substitution mutation (EU numbering). In some embodiments, the CR* consists of the Q38E substitution mutation. In some embodiments, the VL1 domain is linked to a light chain constant (CL) domain (CL?) and the VH? is linked to a first heavy chain constant (CH1) domain (CH11), wherein the CL* comprises a charged region (CR5) and the CH11 comprises a charged region (CRe), and wherein the CRe in the CH11 forms a charge pair with the CR5 in the CL1. In some embodiments, the CRe comprises a basic amino acid residue and the CR5 comprises an acidic amino acid residue. In some embodiments, the CRe comprises a S183K substitution mutation (EU numbering). In some embodiments, the CRe consists of the S183K substitution mutation. In some embodiments, the CR5 comprises a V133E substitution mutation (EU numbering). In some embodiments, the CR5 consists of the V133E substitution mutation.In other embodiments, the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to aCH1 domain (CH12), wherein the CL2 comprises a charged region (CR7) and the CH12 comprises a charged region (CRe), and wherein the CR7 in the CL2 forms a charged pair with the CRe in the CH12. In some embodiments, the CR7 comprises a basic amino acid residue and the CRe comprises an acidic residue. In some embodiments, the CR7 comprises a V133K substitution mutation (EU numbering). In some embodiments, the CR7 consists of the V133K substitution mutation. In some embodiments, the CRs comprises a S183E substitution mutation (EU numbering). In some embodiments, the CR8 consists of the S183E substitution mutation.In other embodiments, the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein (a) the CL2 comprises one or more mutations at amino acid residues F116, L135, S174, S176, and / or T178 (EU numbering) and (b) the CH12 comprises one or more mutations at amino acid residues A141 , F170, S181 , S183, and / or V185 (EU numbering). In some embodiments, the CL.2 comprises one or more of the following substitution mutations: F116A, L135V, S174A, S176F, and / or T178V. In some embodiments, the CL2 comprises the following substitution mutations: F116A, L135V, S174A, S176F, and T178V. In some embodiments, the CH12 comprises one or more of the following substitution mutations: A141 I, F170S, S181 M, S183A, and / or V185A. In some embodiments, the CH12 comprises the following substitution mutations: A141 I, F170S, S181 M, S183A, and V185A. In some embodiments, the anti-FcRH5 antibody comprises one or more heavy chain constant domains, wherein the one or more heavy chain constant domains are selected from a first CH2 domain (CH2j). a first CH3 domain (CH3i), a second CH2 domain (CH22), and a second CH3 domain (CH32). In someembodiments, at least one of the one or more heavy chain constant domains is paired with another heavy chain constant domain. In some embodiments, the CH3f and the CH32 each comprise a protuberance (Pt) or a cavity (C*), and wherein the P? or the C* in the CH3t is positionable in the Cf or the Pi, respectively, in the CH32. In some embodiments, the CH3? and the CH32 meet at an interface between the Pt and the C*. In some embodiments, the CH2? and the CH22 each comprise (P2) or a cavity (C2), and wherein the P2 or the C2 in the CH2f is positionable in the C2 or the P2, respectively, in the CH22. In some embodiments, the CH2» and the CH22 meet at an interface between the P2 and the C2.In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23, and an anti-CD3 arm comprising a second binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123, and wherein the anti-FcRH5 arm and the anti-CD3 arm each comprise an N297G substitution mutation (EU numbering), and wherein the anti-FcRH5 arm comprises a T366W substitution mutation and the anti-CD3 arm comprises T366S, L368A, and Y407V substitution mutations.In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23, and an anti-CD3 arm comprising a second binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123, and wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations, and wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations, and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23, and an anti-CD3 arm comprising a second binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123, and wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations, and wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 ami comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 ami comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations, and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23, and an anti-CD3 arm comprising a second binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123, and wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations, and wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations, and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 , (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8, (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9, (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23, and an anti-CD3 arm comprising a second binding domain comprising the following six HVRs: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115, (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116, (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 , (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118, (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119, and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123, and wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations, and wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In another aspect, the invention features an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations, and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In some embodiments of any one of the aspects of the invention, the anti-FcRH5 antibody has a clearance following intravenous injection of between about 10 ml / kg / day to about 35 ml / kg / day. In some embodiments, the anti-FcRH5 antibody has a clearance following intravenous injection of about 10 ml / kg / day to about 20 ml / kg / day in a mouse. In some embodiments, the anti-FcRH5 antibody has a clearance following intravenous injection of about 12 ml / kg / day to about 16 ml / kg / day in a mouse. In some embodiments, the anti-FcRH5 antibody has a clearance following intravenous injection of about 20 ml / kg / day to about 40 ml / kg / day in a cyno. In some embodiments, the anti-FcRH5 antibody has a clearance following intravenous injection of about 25 ml / kg / day to about 35 ml / kg / day in a cyno. In some embodiments, the anti-FcRH5 antibody has a clearance following intravenous injection of about 30 ml / kg / day to about 35 ml / kg / day in a cyno.In another aspect, the invention features an isolated nucleic acid encoding an anti-FcRH5 antibody of any one of the preceding aspects, or a portion thereof comprising a binding domain thereof that binds to FcRH5.In another aspect, the invention features a vector comprising an isolated nucleic acid of the previous aspect. In another aspect, the invention features a host cell comprising a vector of the previous aspect. In some embodiments, the host cell is a mammalian cell. In some embodiments, the mammalian cell is a Chinese hamster ovary (CHO) cell. In some embodiments, the host cell is a prokaryotic cell. In some embodiments, the prokaryotic cell is an E. coli cell.In another aspect, the invention features a method of producing an anti-FcRH5 antibody of any one of the preceding aspects of the invention, the method comprises culturing the host cell of the previous aspect in a culture medium. In some embodiments, the method further comprises recovering the anti-FcRH5 antibody from the host cell or the culture medium. In some embodiments, the method further comprising culturing a second host cell comprising a second nucleic acid encoding an anti-CD3 antibody that comprises a binding domain that binds CD3. In some embodiments, the host cells are co- cultured. In some embodiments, the method further comprises recovering the bispecific anti-FcRH5 antibody from the host cells or the culture medium.In another aspect, the invention features an immunoconjugate comprising an anti-FcRH5 antibody of any one of the previous aspects and a cytotoxic agent.In another aspect, the invention features a composition comprising an anti-FcRH5 antibody of any one of the aspects of the invention. In some embodiments, the composition further comprising a pharmaceutically acceptable excipient or diluent. In some embodiments, the pharmaceutically acceptable excipient is a buffer, carrier, stabilizer, or preservative. In some embodiments, the composition is a pharmaceutical composition. In some embodiments, the composition further comprises a PD-1 axis binding antagonist or an additional therapeutic agent.In another aspect, the invention features an anti-FcRH5 antibody of any one of the preceding aspects of the invention for use as a medicament.In another aspect, the invention features an anti-FcRH5 antibody of any one of the preceding aspects of the invention for use in treating or delaying progression of an FcRHS-positive cancer in a subject in need thereof.In another aspect, the invention features an anti-FcRH5 antibody of any one of the preceding aspects of the invention for use in enhancing immune function in a subject having an FcRH5-positive cancer. In some embodiments, the FcRH5-posrtive cancer is a B cell cancer. In another aspect, the B cell cancer is selected from the group consisting of multiple myeloma (MM), chronic lymphoid leukemia (CLL), mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), and follicular lymphoma (FL). In another embodiment, the B cell cancer is MM.In another aspect, the invention features the use of an anti-FcRH5 antibody or a composition of any one of the previous aspects in the manufacture of a medicament for treating or delaying progression of an FcRHS-positive cancer in a subject. In another aspect, the invention features the use of an anti- FcRH5 antibody or a composition of any one of the previous aspects in the manufacture of a medicament for enhancing immune function in a subject having an FcRH5-positive cancer. In some embodiments, the FcRHS-positive cancer is a B cell cancer. In some embodiments, the B cell cancer is selected from the group consisting of MM, CLL, MCL, DLBCL, and FL. In some embodiments, the B cell cancer is MM.In another aspect, the invention features a method of treating or delaying the progression of an FcRHS-positive cancer in a subject in need thereof, the method comprising administering to the subject an anti-FcRH5 antibody of any one of the preceding aspects of the invention. In another aspect, the invention features a method of enhancing immune function in a subject having an FcRH5-positive cancer, the method comprising administering to the subject an effective amount of an anti-FcRH5 antibody of any one of the preceding aspects of the invention. In some embodiments, the FcRH5-positive cancer is a B cell cancer. In some embodiments, the B cell cancer is selected from the group consisting of MM, CLL, MCL, DLBCL, and FL. In some embodiments, the B cell cancer is MM. In some embodiments, the anti- FcRH5 antibody binds to (a) an FcRH5 molecule located on a target cell and (b) a CD3 molecule located on an immune effector cell. In some embodiments, the anti-FcRH5 antibody activates the immune effector cell following binding to the FcRH5 molecule and the CD3 molecule. In some embodiments, the activated immune effector cell is capable of exerting a cytotoxic effect and / or an apoptotic effect on the target cell. In some embodiments, the target cell is a plasma cell. In some embodiments, the plasma cell is a short-lived plasma cell. In some embodiments, the plasma cell is a long-lived plasma cell. In some embodiments, the plasma cell is a myeloma cell. In some embodiments, the method comprises administering to the subject the anti-FcRH5 antibody at a dosage of about 0.01 mg / kg / wk to about 50 mg / kg / wk. In some embodiments, the method comprises administering to the subject the anti-FcRH5 antibody at a dosage of about 0.1 mg / kg / wk to about 10 mg / kg / wk. In some embodiments, the method comprises administering to the subject the anti-FcRH5 antibody at a dosage of about 1 mg / kg / wk.In other embodiments, the method further comprising administering to the subject a PD-1 axis binding antagonist and / or an additional therapeutic agent. In some embodiments, the PD-1 axis binding antagonist or additional therapeutic agent is administered prior to or subsequent to the administration of the anti-FcRH5 antibody. In some embodiments, the PD-1 axis binding antagonist or additional therapeutic agent is administered concurrently with the anti-FcRH5 antibody. In some embodiments, the PD-1 axis binding antagonist is selected from the group consisting of a PD-L1 binding antagonist, a PD-1 binding antagonist, and a PD-L2 binding antagonist. In some embodiments, the PD-1 axis binding antagonist is a PD-L1 binding antagonist. In some embodiments, the PD-L1 binding antagonist is selected from the group consisting of MPDL3280A (atezolizumab), YW243.55.S70, MDX-1105,MEDI4736 (durvalumab), and MSB0010718C (avelumab). In some embodiments, the PD-L1 binding antagonist is MPDL3280A (atezolizumab). In some embodiments, the PD-1 axis binding antagonist is a PD-1 binding antagonist. In some embodiments, the PD-1 binding antagonist is selected from the group consisting of MDX 1106 (nivolumab), MK-3475 (pembrolizumab), CT-011 (pidilizumab), MEDI-0680 (AMP-514), PDR001 , REGN2810, and BGB-108. In some embodiments, the PD-1 axis binding antagonist is a PD-L2 binding antagonist. In some embodiments, the PD-L2 binding antagonist is an antibody or an immunoadhesin. In some embodiments, the subject a steroid, an immunomodulator (IMiD), a proteosome inhibitor (PI), or a combination thereof. In some embodiments, the steroid is a glucocorticoid. In some embodiments, the glucocorticoid is dexamethasone. In some embodiments, the IMiD is lenalidomkJe. In some embodiments, the PI is bortezomib.In other embodiments, the method comprises administering the anti-FcRH5 antibody, PD-1 axis binding antagonist, steroid, IMiD, PI, or combination thereof, of any one of the preceding aspects, intravenously, subcutaneously, intramuscularly, topically, orally, transdermally, intraperitoneally, intraorbitally, by implantation, by inhalation, intrathecally, intraventricularly, or intranasally. In some embodiments, the method comprises administering the anti-FcRH5 antibody, PD-1 axis binding antagonist, steroid, IMiD, PI, or combination thereof, intravenously. In some embodiments, the method comprises administering the anti-FcRH5 antibody, PD-1 axis binding antagonist, steroid, IMiD, PI, or combination thereof, subcutaneously. In some embodiments of any one of the preceding aspects, the subject is a human.In another aspect, the invention features a method for detecting FcRH5 in a biological sample from a subject, wherein the method comprises: (a) contacting the biological sample with an anti-FcRHS antibody of any one of the aspects of the invention under conditions permissive for binding of the anti- FcRH5 antibody to a naturally occurring FcRH5 in the biological sample, and (b) detecting whether a complex is formed between the anti-FcRH5 antibody and a naturally occurring FcRH5 in the biological sample. In some embodiments, the biological sample is a blood sample. In some embodiments of this aspect, the subject is a human.In another aspect, the invention features a kit comprising an anti-FcRH5 antibody of any one of the preceding aspects of the invention and a package insert comprising instructions for using the anti- FcRH5 antibody for treating or delaying progression of an FcRH5-positive cancer in a subject. In another aspect, the invention features a kit comprising an anti-FcRH5 antibody of any one of the preceding aspects of the invention and a package insert comprising instructions for using the anti-FcRH5 antibody for enhancing immune function in a subject having an FcRH5-positive cancer. In some embodiments of these aspects, the subject is a human.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 A is a schematic diagram showing an exemplary Rational Design configuration(Configuration 1) of an FcRH5 TDB having VL, VH, CL, and CH1 domains including one or more charged regions. For Configuration 1 , the VH1, CL?, VL2, and CH12 domains contain basic charged regions, and the VL?, CH1 ?, VH2, and CL2 domains contain acidic charged regions.FIG. 1 B is a schematic diagram showing an exemplary Rational Design configuration(Configuration 2) of an FcRH5 TDB having VL, VH, CL, and CH1 domains including one or more charged regions. For Configuration 2, the VHf, CL?, VL2, and CH12 domains contain acidic charged regions, and the VL?, CH1 ?, VH2l and CL2 domains contain basic charged regions.FIG. 1C is a schematic diagram showing an exemplary Rosetta Design configuration(Configuration 1) of an FcRH5 TDB having VL, VH, CL, and CH1 domains including one or more charged regions. For Configuration 1 , the VH?, CL1, and VL2 domains contain basic charged regions, and the VL?, CH1 ?, and VH2 domains contain acidic charged regions. Additionally, the CH12 domain contains a cavity, and the CL2 domain contains a protuberance. The cavity and protuberance are depicted as a black box at the CH12 / CL2 interface.FIG. 1 D is a schematic diagram showing an exemplary Rosetta Design configuration(Configuration 2) of an FcRH5 TDB having VL, VH, CL, and CH1 domains including one or more charged regions. For Configuration 2, the VH?, CL?, and VL2 domains contain acidic charged regions, and the VL?, CH1 ?, and VH2 domains contain basic charged regions. Additionally, the CH12 domain contains a cavity, and the CL2 domain contains a protuberance. The cavity and protuberance are depicted as a black box at the CHI2 / CL2 interface.FIG. 1E is a schematic diagram showing an exemplary alternative Rosetta Design configuration (Alternative Configuration 1) of an FcRH5 TDB having VL, VH, CL, and CH1 domains including one or more charged regions. For Alternative Configuration 1 , the VL1 , VH2, and CL2 domains contain acidic charged regions, and the VH*, CH12, and VL2 domains contain basic charged regions. Additionaliy, the CH11 domain contains a cavity, and the CL1 domain contains a protuberance. The cavity and protuberance are depicted as a black box at the CHI t / CL1 interface.FIG. 1F is a schematic diagram showing an exemplary alternative Rosetta Design configuration (Alternative Configuration 2) of an FcRH5 TDB having VL, VH, CL, and CH1 domains including one or more charged regions. For Alternative Configuration 2, the VL1, VH2, and CL2 domains contain basic charged regions, and the VH?, CH12, and VL2 domains contain acidic charged regions. Additionally, the CH11 domain contains a cavity, and the CL1 domain contains a protuberance. The cavity and protuberance are depicted as a black box at the CH11 / CL1 interface.FIG. 2 is an alignment of the light chain variable (VL) domain sequences of select anti-FcRH5 antibodies. Changes from 1G7 (see U.S. Pub. No 2015-0098900, which is incorporated by reference herein in its entirety) are shown in dark boxes. Hypervariable regions (HVRs) are indicated by lines above and / or below the alignments. These VL domain sequences are also disclosed as SEQ ID NOs: 83, 85. 87, 89, 91. 93, 95, 97. 99, and 101.FIG. 3 is an alignment of the heavy chain variable (VH) domain sequences of select anti-FcRH5 antibodies. Changes from clone 1G7 (see U.S. Pub. No. 2015-0098900) are shown in dark boxes. Hypervariable regions (HVRs) are indicated by lines above and / or below the alignments. These VH domain sequences are also disclosed as SEQ ID NOs: 82, 84, 86, 88, 90, 92, 94, 96, 98, and 100.FIG. 4 is a table showing the impact on binding affinity of amino acid substitutions at position 52 of the indicated anti-FcRH5 antibodies.FIG. 5A is an alignment of the heavy chain variable (VH) domain sequences of hu1G7.v85 and hu1G7.v93. Changes from the human germline sequence hlGHV4-59*01 are shown in shaded boxes. Hypervariable regions (HVRs) are indicated by labels above the alignments. These VH domain sequences are also disclosed as SEQ ID NOs: 104 (hu1G7.v85) and 106 (hu1G7.v93).FIG. 5B is an alignment of the light chain variable (VL) domain sequences of hu1G7.v85 and hu1G7.v93. Changes from the human germline sequence hIGKVI -16*01 are shown in shaded boxes. Hypervariable regions (HVRs) are indicated by labels above the alignments. These VL domain sequences are also disclosed as SEQ ID NOs: 105 (hu1G7.v85) and 107 (hu1G7.v93).FIG. 6A is an alignment of the heavy chain variable (VH) domain sequences of hu1G7.v85. 1G7, and consensus H4. Changes from the humanized, affinity matured, and polished clone 1G7 (see U.S. Pub. No. 2015-0098900, which is incorporated by reference herein in its entirety) are shown in shaded boxes. Hypervariable regions (HVRs) are indicated by labels above the alignments. The VH domain sequence of hu1G7.v85 is disclosed as SEQ ID NO: 104. FIG. 6B is an alignment of the light chain variable (VL) domain sequences of hu1G7.v85, 1G7, and consensus Kl. Changes from the humanized, affinity matured, and polished clone 1G7 are shown in shaded boxes. The VL domain sequence of hu1G7.v8S is disclosed as SEQ ID NO: 105.FIG. 7A shows the heavy chain variable (VH) domain sequence of anti-FcRH5 antibody hu1G7.v93 (SEQ ID NO: 106).FIG. 7B shows the light chain variable (VL) domain sequence of anti-FcRH5 antibody hu1G7.v93 (SEQ ID NO: 107).FIG. 8 is a graph showing the antibody titer of 1G7.v85 and 1G7.v87 antibodies.FIG. ΘΑ is an overlay of histograms comparing the binding of FcRH5 / 38E4.v1 TDBs having different anti-FcRH5 arms (i.e., m1G7 ("1G7 TDB"), 1G7.V85 ("1G7.v85 TDB"), and 1G7.v1.4 C1G7.v1.4 TDB")) to FcRH3-overexpressing cells.FIG. 9B is a graph showing that the 1G7.v85 TDB does not deplete natural killer (NK) cells at concentrations of≤ 20 pg / mL;1G7.v85 TDB has a median EC50 of 25 ng / mL on plasma cells (PCs).FIG. 10A is a series of graphs comparing the ability of the FcRH5 TDB 1G7.v1.4 / 38E4.v1 (M G7.V1.4 TDB") to bind FcRH3, human FcRH5, and cyno FcRH5.FIG. 10B is a series of graphs comparing the ability of the 1G7.v85 TDB to bind FcRH3, human FcRH5, and cyno FcRH5.FIG. 10C is a series of graphs comparing the ability of the FcRH5 TDB 1G7 / 38E4.v1 ("1G7 TDB") to bind FcRH3, human FcRH5, and cyno FcRH5.FIG. 10D is a series of graphs comparing the ability of a control antibody to bind FcRH3, humanFcRH5, and cyno FcRH5.FIG. 11A shows the sequence of the heavy chain variable (VH) domain sequence of humanized, rabbit-derived anti-FcRH5 antibody hu7D8.L1 H2. The VH domain sequence ofhu7D8.L1H2 is disclosed as SEQ ID NO: 108.FIG. 11 B shows the sequence of the light chain variable (VL) domain sequence of humanized, rabbit-derived anti-FcRH5 antibody hu7D8.L1H2. The VL domain sequence of hu7D8.L1H2 is disclosed as SEQ ID NO: 109.FIG. 12A shows the sequence of the heavy chain variable (VH) domain sequences of mouse- derived anti-FcRH5 antibody 17B1. The VH domain sequences of 17B1 is disclosed as SEQ ID NO: 110.FIG. 12B shows the sequence of the light chain variable (VL) domain sequence of mouse- derived anti-FcRH5 antibody 17B1. The VL domain sequences of 17B1 is disclosed as SEQ ID NO: 111.FIG. 13A shows the sequence of the heavy chain variable (VH) domain sequences of mouse - derived anti-FcRH5 antibody 15G8. The VH domain sequence of 15G8 is disclosed as SEQ ID NO: 112.FIG. 13B shows the sequence of the light chain variable (VL) domain sequence of mouse- derived anti-FcRH5 antibody 15G8. The VL domain sequence of 15G8 is disclosed as SEQ ID NO: 113.FIG. 14 is a series of graphs showing the binding affinity of humanized variant of rabbit-derived anti-FcRH5 antibodies 7D8.Rb and h7D8.L1H2 to human FcRH5 and cyno FcRH5. FIG. 15 is a series of graphs showing that the FcRH5 TDBs 1G7.v85 TDB andhu1G7.v93 / 38E4.v1 ("1G7.v93 TDB") bind with comparable affinity to both human FcRH5 and cyno FcRH5.FIGS. 16A-16B are graphs showing the kinetic analysis of 1G7.v85 TDB binding to human FcRH5 and cyno FcRH5 with dissociation constants (KD) of 2.35 nM and 6.76 nM, respectively, as measured by BIACORE® in an hlgG capture format using a 1 :1 binding model of monovalent affinity.FIGS. 17A-17B are graphs demonstrating increased FcRHS-induced cell toxicity of MOLP-2 cells (i.e., human multiple myeloma cells that endogenously express FcRH5) using humanized and affinity matured variants of 1G7 formatted into T celklependent bispecific (TDB) antibodies having the CD3-binding arm of 38E4.v1 (see PCT Pub. No. WO 2015-095392 A1 , which is incorporated by reference herein in its entirety). In Fig. 17A, the 1G7 TDB, hu1G7.v1.1 / 38E4.v1 ("1G7.v1.1 TDB"), hu1G7.v1.2 / 38E4.v1 C1G7.v1.2 TDB"), hu1G7.v1.3 / 38E4.v1 C1G7.v1.3 TDB"), and 1G7.v1.4 TDB were evaluated. In Fig. 17B, the 1G7.v1.4 TDB, hu1G7.v1.5 / 38E4.v1 C1G7.v1.5" TDB), hu1G7.v1.13 / 38E4.v1 ("1G7.v1.13 TDB"), hu1G7.v1.7 / 38E4.v1 (*1G7.v1.7 TDB"), and hu1G7.v1.13.1 / 38E4.v1 ("1G7.v1.13.1") were evaluated. The 1G7.V.1.4 TDB improved target cell killing (EC50) 5- to 13-fbkJ over murine 1 G7 TDB (n=10).FIGS. 18A-18D are graphs comparing the ability of the 1 G7.v1.4 TDB and the 1 G7.v85 TDB to activate T cells (Fig. 18A), kill target MOLP-2 cells (Fig. 18B), kill target cyno plasma cells (Fig. 18C), and kill target cyno B cells (Fig. 18D).FIG. 19A is a series of histograms comparing the ability of the 1 G7.v85 TDB and thehu 1 G7.v87 / 38E4.v1 TDB ("1 G7.v87 TDB") to bind to and cross-react with mouse SVT2 cells expressing human FcRH5 (Panel 1), cyno FcRH5 (Panel 2), and human FcRH3 (Panel 3).FIGS. 19B-19D are graphs comparing the ability of the 1 G7.v85 TDB and the 1 G7.v87 TDB to kill target MOLP-2 cells (Fig. 19B), human B cells (Fig. 19C), and cyno B cells (Fig. 19D).FIGS. 20A-20D are graphs showing a reduced ability of the 1G7.v85 TDB to bind FcRH5 after undergoing either a 2,2'-azobis(2-amidopropane)dihydrochloride (AAPH) stress test (Fig. 20B) or a light stress test (Fig. 20D), as compared to unstressed respective controls (Figs. 20A and 20C).FIG. 21 A is graph showing size distribution analysis of the 1G7.v85 TDB. The 1 G7.v85 TDB lost 0.1% of the monomer peak after two weeks of stress in a his-acetate solution at pH 5.5.FIG. 21 B is a graph showing the charge heterogeneity of the 1G7.v85 TDB. The 1 G7.v85 TDB lost 7.7% of the monomer peak after two weeks of stress in a his-acetate solution at pH 5.5FIG. 22A is a graph showing that the 1G7.v85 TDB has no observable change in the reduced mass profile of the light chain mass after two weeks of stress in a his-acetate solution at pH 5.5.FIG. 22B is a graph showing that the 1G7.v85 TDB has no observable change in the reduced mass profile of the heavy chain mass after two weeks of stress in a his-acetate solution at pH 5.5.FIG. 23A is a phospho-SLP76 Western blot of a healthy donor peripheral CD8 cells stimulated with 1 pg / ml of the 1G7 / UCHT1.v9 TDB, 10A8 / UCHT1.V9 TDB (Ί 0Α8 TDB"), and anti-gD / UCI-ΠΊ .v9 TDB ("anti-gD TDB"), and cells expressing human FcRH5 with N-terminal gD expression tag. Blotting for total SLP76, indicative of TCR signaling, was used to confirm equal sample loading.FIG. 23B is a graph showing FcRH5 target cell killing with either 1G7 / UCHT1.v9 TDB or anti-gD TDB and CD8+ T cells. FIG. 23C is a schematic diagram of the truncated FcRHS construct with the gD epitope now membrane-proximal.FIG. 23D is a graph showing target cell killing using the truncated FcRH5 construct with 1G7 TDB or anti-gD TDB. The activity of the proximal 1G7 / UCHT1.v9 TDB increased by 25-fold (EC50 = 20 pM), and the anti-gD TDB was able to effectively mediate killing of cells (EC50 = 0.19 nM) when the interference caused by the ECD was removed. The truncated construct was expressed in 293 cells.FIG. 23E is a graph showing that target cell killing for five alternate FcRH5 TDBs that recognize the membrane-proximal epitope (dashed lines) are equivalent to killing mediated by the 1G7 / UCHT1.v9 TDB and significantly better than the 10A8 TDB.FIG. 24A is a histogram overlay of flow cytometry analysis of SVT2-parental, gD-FcRH5 full-length, and gD-FcRH5-domain 9 cells.FIG. 24B is a graph showing percent target cell killing by 1 G7 / UCHT1.v9 TDB, 2H7 / UCHT1.v9 TDB (*2H7 TDB"), 3G7 / UCHT1.v9 TDB ("3G7 TDB"), 10A8 TDB, and anti-gD TDB.FIG. 25A is an overlay histogram of six cell lines (SVT2-vector, SvT2-FcRH1 , SVT2-FCRH2, SVT2-FCRH3, SVT2-FcRH4, and SVT2-FcRH5), showing that the 1 G7.v85 TDB binds to FcRH5, but not to other family members.FIG. 25B is a histogram overlay of three cell lines (293 parental, 293-FcRH5 full-length, and 293- FcRH5-D9-deletion), showing that the 1G7.v85 TDB binds to the membrane proximal domain of FcRH5.FIG. 25C is an overlay histogram of three cell lines (SvT2-vector, SvT2-huFcRH5, and SVT2- cyno FcRH5), showing that the 1G7.v85 TDB binds to cyno FcRH5 and human FcRH5.FIGS. 26A-26D are overlay histograms of three cell lines (SvT2-vector, SVT2-huFcRH5, and SVT2-cyno FcRHS), showing binding of the 1G7 / 38E4.v1 TDB ("1G7 TDB") to multiple myeloma (MM) cell line and primary cells. Overlay histograms are shown for isotype-PE and 1G7 TDB for MOLP-2 cells (Fig. 26A), human CD20+ B cells (Fig. 26B), human CD38+CD138+ plasma cells (Fig. 26C), andCD38+CD138+ MM tumor cells from MM bone marrow aspirate (Fig. 26D).FIG. 27A is a graph showing dose-dependent activation of CD8+ cells upon stimulation with target cells (MOLP-2) and 1G7 TDB, detected by flow cytometry analysis.FIG. 27B is a graph showing target cell-dependent killing by 1G7 TDB. The insert shows a flow cytometry overlay of the parental Fox-NY cell line and clones transfected to express a low or a high level of human FcRH5. Error bars are standard deviation of triplicates.FIGS. 27C-27E are graphs showing that 1G7 TDB induced CD8 proliferation response (5 days), as detected by measuring CSFE fluorescence intensity dilution by flow cytometry. CFSE-labeled human CD8+ cells only (Fig. 27C), co-culture with MOLP-2 (Fig. 27D), or co-culture with MOLP-2 and 1000 ng / ml of the 1G7.V85 TDB (Fig. 27E).FIG. 27F is a graph showing target-dependent cell killing with FcRH5 TDBs containing different anthCD3 arms (e.g., UCHT1.v9, 38E4.v1 , and 40G5c) (see PCT Pub. No. WO 2015 / 095392 A1 , which is incorporated by reference herein in its entirety). The anti-CD3 arms 38E4.v1 (monovalent KD 0.5 nM, BIACORE®), UCHT1.v9 (monovalent KD = 2.5 nM, BIACORE® and Scatchard), and 40G5c (monovalent KD = 51 nM, BIACORE®) were each paired with the anti-FcRH5 arm of m1G7 (KD = 11 nm, BIACORE®) and tested for binding to purified human CD8+ cells. FIG. 27G is a graph showing target-dependent cell killing with the 1G7 TDB and 1G7 / 38E4.v1 bis-Fab ("1G7 bis-Fab").FIG. 28A is a graph showing FcRH5 expression in primary multiple myeloma tumor cells, healthy donor peripheral B cells, and bone marrow plasma cells. FcRH5 expression was analyzed by flow cytometry and normalized to expression in MOLP-2 internal and assay control. The relative level ofFcRH5 was calculated as follows: (Geometric mean of FcRH5 of "X" / Geometric mean of isotype control of "X") / (Geometric mean of FcRH5 of MOLP-2 / Geometric mean of isotype control of MOLP-2).FIG. 28B is a graph showing cytotoxic activity of the 1G7.v85 TDB on human plasma cells.Human bone marrow mononuclear cells (BMMCs) were cultured with 1G7.v85 TDB and the cell number of live CD38+CD138+ was analyzed by flow cytometry.FIG. 28C is a graph showing the cytotoxic activity of the 1G7.v85 TDB on different patient-derived primary myeloma cells. Human myeloma BMMCs were co-cultured with CD8+ T cells isolated from healthy donor and 1G7.v85 TBD.FIG. 28D is a graph showing that very low FcRH5 expression in target cells is sufficient for potent killing activity. FcRH5 copy number per cell was determined by Scatchard assay.FIG. 28E (Top) is a graph showing qRT-PCR analysis of FcRH5 mRNA levels in bone marrow biopsies from high risk myeloma patients with 1q21 gain. mRNA expression level was calculated by the delta Ct (dCt) method. Statistical analysis was done using a Mann-Whitney U test. (Bottom) Are images of FISH analysis on primary multiple myeloma biopsies showing normal diploid of 1q21 (Left) and a mixture of approximately three to six copies of 1 q21 (Right). A tumor sample was identified as 1 q21 gain when >20% of the tumor cells scored had three or more copies of the 1q21.3 locus.FIG. 29A is a histogram overlay of isotype-PE and anti-FcRH5 clone 1G7-PE, depicting the expression of FcRH5 on cyno CD20+ B cells.FIG. 29B is a histogram overlay of isotype-PE and anti-FcRH5 clone 1G7-PE, depicting the expression of FcRH5 on cyno on CD45-CD20-CD38+PC+ plasma cells.FIGS. 29C-29D are graphs showing comparable dose-dependent cytotoxic activity between cyno CD8+ T cells and human CD8+ T cells in an in vitro killing assay using SVT2-cyno-FcRH5 (Fig. 29C) and MOLP-2 (Fig. 29D) with human CD8+ T cells or cyno CD8+ T cells.FIG. 29E is a graph showing in vitro killing activity of 1G7.V85 TDB on cyno CD20+ B cells (n=14).FIG. 29F is a graph showing in vitro killing activity of 1G7.V85 TDB on CD45-CD20-CD38+PC+ plasma cells from cyno bone marrow from eight different donors (n=8).FIG. 30A is a graph showing that splenic human T cells isolated from spleens of humanized NOD / SCID gamma mice (NSG) have comparable activity to peripheral human T cells from heathy donors.FIG. 30B is a graph showing that 1 G7 TDB treatment induces regression of subcutaneous MOLP-2 xenograft tumors in humanized NSG mice. The mice were treated with a single intravenous dose of vehicle or 1G7.v85 TDB at 0.5 mg / kg. Mean tumor volume (black bold line), the individual tumor volumes (thin lines), and mean of control group (dashed line) are indicated. FIG. 31 A is a graph showing the serum concentration of FcRH5 TDB plotted over the duration of the study after single-dose administration of 1G7.v85 TDB at 1 mg / kg, 2 mg / kg, or 4 mg / kg to three animals / group. A table showing pharmacodynamics parameters is shown below.FIG. 31 B is a graph showing the serum concentration of FcRH5 TDBs (1G7.v85 TDB and 1 G7.v87 / 38E4.v1 TDB ("1 G7.v87 TDB")) plotted over the duration of study after single doseadministration of anti-gD TDB at 3 mg / kg or FcRH5 TDBs at 0.3 mg / kg or 3 mg / kg to threeanimals / group. A table showing pharmacodynamics parameters is shown below.FIGS. 31C-31D are graphs showing 1G7.v85 TDB-induced transient T cell activation in cyno peripheral blood after single-dose intravenous administration of vehicle or 1G7.v85 TDB (1 mg / kg, 2 mg / kg, or 4 mg / kg) to three animals / group.FIGS. 31E-31H are graphs showing the absolute count of CD20+ B cells in peripheral blood (Fig. 31 E), spleen (Fig. 31 F), mandibular lymph node (Fig. 31 G), and bone marrow (Fig. 31 H) in cyno after single-dose intravenous administration of vehicle or 1G7.v85 TDB (1 mg / kg, 2 mg / kg, or 4 mg / kg) to three animals / group. Figs. 31F-31H are plotted with group mean and standard error of mean (SEM).FIG. 311 is a graph showing that 1G7.v85 TDB depletes bone marrow plasma cells in cyno, with group measured SEM plotted.FIG. 31 J is a graph showing the change of cyno IgG level response to treatment, calculated using formula {(IgG level pre-dose) - (IgG level end of study)} / (IgG level pre-dose) X 100. The difference between pre-dose and after treatment is analyzed by an unpaired t-test. The data are plotted with group mean and standard error of mean (SEM).FIGS. 32A-32B are graphs showing the absolute count of CD4+ T cells in peripheral blood (Fig. 32A) and CD8+ T cells (Fig. 32B) in four groups of animals after single-dose intravenous administration of vehicle, 1G7.v85 TDB at 1 mg / kg, 1G7.v85 TDB at 2 mg / kg, or 1G7.v85 TDB at 4 mg / kg.FIG. 32C is a graph showing the decrease in the absolute count of CD20+ B cells in mesenteric lymph nodes after 1G7.v85 TDB treatment. The plot is graphed as individual animals and mean group with SEM.FIG. 32D is a graph showing FcRH5 occupancy after single-dose intravenous administration of 1G7.v85 TDB at 1 mg / kg, 2 mg / kg, or 4 mg / kg.FIGS. 33A-33F are graphs showing the change in concentration of the cytokines IL-6 (Fig. 33A), IL-2 (Fig. 33B), IFN-γ (Fig. 33C), IL-1 Ra (Fig. 33D), IL-5 (Fig. 33E), and MCP-1 (Fig. 33F) in four groups of animals after single-dose intravenous administration of vehicle, 1G7.v85 TDB at 1 mg / kg, 1G7.v85 TDB at 2 mg / kg, and 1G7.v85 TDB at 4 mg / kg.FIG. 34 is a series of plots showing that 1G7.v85 TDB treatment induces PD1 expression in human T cells. CD8+ T cells were stimulated for 48 hours with the 1G7.v85 TDB and MOLP-2 target cells and then analyzed by flow cytometry.FIG. 35A is a graph showing the percentage of PD1+ in CD8+ T cells in cyno after a single-dose intravenous administration of vehicle, 1 mg / kg, 2 mg / kg, and 4 mg / kg of 1G7.v85 TDB. 1G7.v85 TDB treatment results in induction of PD1 in cyno T cells in vivo.FIG. 35B is a graph showing the percentage of PD1+ in CD4+ T cells in cyno after single dose intravenous administration of vehicle, 1 mg / kg, 2 mg / kg, and 4 mg / kg of 1G7.v85 TDB. FIGS. 36A-36D are plots showing PD-1 expression in CD4+ T cells from blood (Fig. 36 A), CD8+T cells from spleen (Fig. 36B), CD8+T cells from lymph node (Fig. 36C), and CD8+T cells from bone marrow (Fig. 36D), as analyzed by FACS seven days after dosing with 1G7.v85 TDB or vehicle.FIGS. 37A-37B are graphs showing the ability of the 1G7.v85 TDB to redirect activity of pre- stimulated CD8+ T cells to kill HEK-293T cells expressing FcRH5 and PD-1 ("293-FcRH5-PD-L1 cells") in the presence or absence of an anti-PD-L1 or anti-PD-1 antibody. The curve in Fig. 37A is graphed with mean and standard of error (SD) of triplicates.FIG. 38A is a graph showing target cell killing of SVT2-FcRH5 by 1G7.v85 TDB in the presence and absence of dexamethasone (Dex).FIG. 38B is a series of graphs showing cytokine (i.e., IL-2, IL-6, TNF-a, and IFN-γ) release after treatment with 1 G7.v85 TDB in the presence and absence of 1 μΜ Dex.FIG. 39 is a schematic drawing showing the production of bis-Fabs from human lgG1.FIG. 40A is a graph showing the binding of FcRH5 by bis-Fabs A-D and F(ab)2 A as determined by an ELISA assay.FIG. 40B is a graph showing the binding of CD3 by bis-Fabs A-D and F(ab")2 A as determined by anELISA assay.FIG. 41 is a graph showing the amount of target-mediated T cell activation by bis-Fabs A-D and F(ab")2A. DETAILED DESCRIPTION OF THE INVENTIONI. DEFINITIONSThe term "about" as used herein refers to the usual error range for the respective value readily known to the skilled person in this technical field. Reference to "about" a value or parameter herein includes (and describes) embodiments that are directed to that value or parameter per se.An "acceptor human framework" for the purposes herein is a framework comprising the amino acid sequence of a light chain variable domain (VL) framework or a heavy chain variable domain (VH) framework derived from a human immunoglobulin framework or a human consensus framework, as defined below. An acceptor human framework "derived from" a human immunoglobulin framework or a human consensus framework may comprise the same amino acid sequence thereof, or it may contain amino acid sequence changes. In some embodiments, the number of amino acid changes are 10 or fewer, 9 or fewer, 8 or fewer, 7 or fewer, 6 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, or 2 or fewer. In some embodiments, the VL acceptor human framework is identical in sequence to the VL human immunoglobulin framework sequence or human consensus framework sequence."Affinity" refers to the strength of the sum total of noncovalent interactions between a single binding site of a molecule (e.g., an antibody) and its binding partner (e.g., an antigen). Unless indicated otherwise, as used herein, 'binding affinity" refers to intrinsic binding affinity which reflects a 1 :1 interaction between members of a binding pair (e.g., antibody and antigen). The affinity of a molecule X for its partner Y can generally be represented by the dissociation constant (KD). Affinity can be measured by common methods known in the art, including those described herein. Specific illustrative and exemplary embodiments for measuring binding affinity are described in the following.An "affinity matured" antibody refers to an antibody with one or more alterations in one or more hypervariable regions (HVRs), compared to a parent antibody which does not possess such alterations, such alterations resulting in an improvement in the affinity of the antibody for antigen.The term "anti-FcRH5 antibody" or "an antibody that binds to FcRH5" refers to an antibody that is capable of binding FcRH5 with sufficient affinity such that the antibody is useful as a diagnostic and / or therapeutic agent in targeting FcRH5. In one embodiment, the extent of binding of an anti-FcRH5 antibody to an unrelated, non-FcRH5 protein is less than about 10% of the binding of the antibody to FcRH5 as measured, e.g., by a radioimmunoassay (RIA). In certain embodiments, an antibody that binds to FcRH5 has a dissociation constant (KD) of≤ 1 μΜ,≤ 100 nM,≤ 10 nM,≤ 1 nM,≤ 0.1 nM,≤ 0.01 nM, or ≤ 0.001 nM (e.g., 10* M or less, e.g., from 10-8 M to 10-13 M, e.g., from 10-9 M to 10-13 M). In certain embodiments, an anti-FcRH5 antibody binds to an epitope of FcRH5 that is conserved among FcRH5 from different species.The terms "anthCD3 antibody" and "an antibody that binds to CD3" refer to an antibody that is capable of binding CD3 with sufficient affinity such that the antibody is useful as a diagnostic and / or therapeutic agent in targeting CD3. In one embodiment, the extent of binding of an anti-CD3 antibody to an unrelated, non-CD3 protein is less than about 10% of the binding of the antibody to CD3 as measured, e.g., by a radioimmunoassay (RIA). In certain embodiments, an antibody that binds to CD3 has a dissociation constant (Ko) of≤ 1 μΜ,≤ 100 nM,≤ 10 nM,≤ 1 nM,≤ 0.1 nM,≤ 0.01 nM, or≤ 0.001 nM (e.g., 10-8 M or less, e.g., from lO^ M to 10-13 M, e.g., from 109 M to 10 13 M). In certain embodiments, an anti- CD3 antibody binds to an epitope of CD3 that is conserved among CD3 from different species.The term "antibody" herein is used in the broadest sense and encompasses various antibody structures, including but not limited to monoclonal antibodies, polyclonal antibodies, multispecific antibodies (e.g., bispecific antibodies), and antibody fragments (e.g., bis-Fabs) so long as they exhibit the desired antigen-binding activity.An "antibody fragment" refers to a molecule other than an intact antibody that comprises a portion of an intact antibody that binds the antigen to which the intact antibody binds. Examples of antibody fragments include but are not limited to bis-Fabs; Fv; Fab; Fab, Fab'-SH; F(ab')2; diabodies; linear antibodies; single-chain antibody molecules (e.g., scFv); and multispecific antibodies formed from antibody fragments.By "binding domain" is meant a part of a compound or a molecule that specifically binds to a target epitope, antigen, ligand, or receptor. Binding domains include but are not limited to antibodies (e.g., monoclonal, polyclonal, recombinant, humanized, and chimeric antibodies), antibody fragments or portions thereof (e.g., bis-Fab fragments, Fab fragments, F(ab")2, scFv antibodies, SMIP, domain antibodies, diabodies, minibodies, scFv-Fc, affibodies, nanobodies, and VH and / or VL domains of antibodies), receptors, ligands, aptamers, and other molecules having an identified binding partner.As used herein the term "charged region" refers to a location of a polypeptide (e.g., an antibody) that includes one or more (e.g., 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10) basic or acidic amino acids that are capable of forming a charge pair with a cognate charged region having one or more (e.g., 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10) or basic or acidic amino acids, when the charged region and its cognate charged region have opposite overall relative charge.As used herein the term "charge pair" refers to the bond that is formed between two charged regions of opposite overall charge.A "chemotherapeutic agent" is a chemical compound useful in the treatment of cancer. Examples of chemotherapeutic agents include alkylating agents such as thiotepa and cyclosphosphamide(CYTOXAN®); alkyl sulfonates such as busulfan, improsulfan and piposulfan; aziridines such as benzodopa, carboquone, meturedopa, and uredopa; ethylenimines and methylamelamines including altretamine, triethylenemelamine, triethylenephosphoramide, triethylenethiophosphoramide and trimethylomelamine; acetogenins (especially bullatacin and bullatacinone); delta-9-tetrahydrocannabinol (dronabinol, MARINOL®); beta-lapachone; lapachol; colchicines; betulinic acid; a camptothecin (including the synthetic analogue topotecan (HYCAMTIN*), CPT-11 (irinotecan, CAMPTOSAR*),acetylcamptothecin, scopolectin, and 9-aminocamptothecin); bryostatin; callystatin; CC-1065 (including its adozelesin, carzelesin and bizelesin synthetic analogues); podophyllotoxin; podophyflinic acid; teniposide; cryptophycins (particularly cryptophycin 1 and cryptophycin 8); dolastatin; duocarmycin (including the synthetic analogues, KW-2189 and CB1-TM1); eleutherobin; pancratistatin; a sarcodictyin; spongistatin; nitrogen mustards such as chlorambucil, chlomaphazine, chlorophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamide, uracil mustard; nitrosoureas such as carmustine, chlorozotocin, fotemustine, lomustine, nimustine, and ranimnustine; antibiotics such as the enediyne antibiotics (e.g., calicheamicin, especially calicheamicin gammal I and calicheamicin omegall (see, e.g., Nicolaou et al. Angew. Chem Intl. Ed. Engl. 33: 183-186, 1994); CDP323, an oral alpha-4 integrin inhibitor; dynemicin, including dynemicin A; an esperamicin; as well as neocarzinostatin chromophore and related chromoprotein enediyne antibiotic chromophores), aclacinomysins, actinomycin, authramycin, azaserine, bleomycins, cactinomycin, carabicin, caminomycin, carzinophilin, chromomycins, dactinomycin, daunorubicin, detorubicin, 6-diazo-5-oxo-L-norieucine, doxorubicin (including ADRIAMYCIN®, morpholino-doxorubicin, cyanomorpholino-doxorubicin, 2-pyrrolino-doxorubicin, doxorubicin HCI liposome injection (DOXIL®), liposomal doxorubicin TLC D-99 (MYOCET®), peglylated liposomal doxorubicin (CAELYX®), and deoxydoxorubicin), epirubicin, esorubicin, idarubicin, marcellomycin, mitomycins such as mitomycin C, mycophenolic acid, nogalamycin, olivomycins, peplomycin, porfiromycin, puromycin, quelamycin, rodorubicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin; anti-metabolites such as methotrexate, gemcitabine (GEMZAR®), tegafur (UFTORAL®), capecitabine (XELODA®), an epothilone, and 5-fluorouracil (5-FU); combretastatin; folic acid analogues such as denopterin, methotrexate, pteropterin, trimetrexate; purine analogs such as fludarabine, 6-mercaptopurine, thiamiprine, thioguanine; pyrimidine analogs such as ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone; anti-adrenals such asaminoglutethimide, mitotane, trilostane; folic acid replenisher such as frolinic acid; aceglatone;akJophosphamide glycoside; aminolevulinic acid; eniluracil; amsacrine; bestrabucil; bisantrene;edatraxate; defofamine; demecolcine; diaziquone; elformithine; elliptinium acetate; an epothilone; etog lucid; gallium nitrate; hydroxyurea; lentinan; lonidainine; maytansinoids such as maytansine and ansamitocins; mitoguazone; mitoxantrone; mopidanmol; nitraerine; pentostatin; phenamet; pirarubicin; losoxantrone; 2-ethylhydrazide; procarbazine; PSK® polysaccharide complex (JHS Natural Products, Eugene, Oreg.); razoxane; rhizoxin; sizofuran; spirogermanium; tenuazonic acid; triaziquone; 2,2',2'- trichlorotriethylamine; trichothecenes (especially T-2 toxin, verracurin A, roridin A and anguidine);urethan; vindesine (ELDISINE®, FILDESIN®); dacarbazine; mannomustine; mitobronrtol; mitolactol; pipobroman; gacytosine; arabinoside ("Ara-C"); thiotepa; taxoid, e.g., paclitaxel (TAXOL®, Bristol-Myers Squibb Oncology, Princeton, N.J.), albumin-engineered nanoparticle formulation of paclitaxel(ABRAXANE™), and docetaxel (TAXOTERE®, Rhome-Poulene Rorer, Antony, France); chloranbucil; 6- thioguanine; mercaptopurine; methotrexate; platinum agents such as cisplatin, oxaliplatin (e.g.,ELOXATIN®), and carboplatin; vincas, which prevent tubulin polymerization from forming microtubules, including vinblastine (VELBAN®), vincristine (ONCOVIN®), vindesine (ELDISINE®, FILDESIN®), and vinorelbine (NAVELBINE®); etoposide (VP-16); ifosfamkJe; mitoxantrone; leucovorin; novantrone;edatrexate; daunomycin; aminopterin; ibandronate; topoisomerase inhibitor RFS 2000;difluoromethylomithine (DMFO); retinoids such as retinoic acid, including bexarotene (TARGRETIN®); bisphosphonates such as clodronate (for example, BONEFOS® or OSTAC®), etidronate (DIDROCAL®), NE-58095, zoledronic acid / zoledronate (ZOMETA®), alendronate (FOSAMAX®), pamidronate(AREDIA®), tiludronate (SKELID®), or risedronate (ACTONEL®); troxacitabine (a 1 ,3-dioxolane nucleoside cytosine analog); antisense oligonucleotides, particularly those that inhibit expression of genes in signaling pathways implicated in aberrant cell proliferation, such as, for example, PKC-alpha, Raf, H-Ras, and epidermal growth factor receptor (EGF-R) (e.g., eriotinib (Tarceva™)); and VEGF-A that reduce cell proliferation; vaccines such as THERATOPE® vaccine and gene therapy vaccines, for example, ALLOVECTIN® vaccine, LEUVECTIN® vaccine, and VAXID® vaccine; topoisomerase 1 inhibitor (e.g., LURTOTECAN®); rmRH (e.g., ABARELIX®); BAY439006 (sorafenib; Bayer); SU-11248 (sunitinib, SUTENT®, Pfizer); perifosine, COX-2 inhibitor (e.g., celecoxib or etoricoxib), proteosome inhibitor (e.g., PS341); bortezomib (VELCADE®); CCI-779; tipifamib (R11577); orafenib, ABT510; Bcl-2 inhibitor such as oblimersen sodium (GENASENSE®); pixantrone; EGFR inhibitors; tyrosine kinase inhibitors; serine-threonine kinase inhibitors such as rapamycin (sirolimus, RAPAMUNE®);farnesyltransferase inhibitors such as lonafamib (SCH 6636, SARASAR™); and pharmaceutically acceptable salts, acids or derivatives of any of the above; as well as combinations of two or more of the above such as CHOP, an abbreviation for a combined therapy of cyclophosphamide, doxorubicin, vincristine, and prednisolone; and FOLFOX, an abbreviation for a treatment regimen with oxaliplatin (ELOXATIN™) combined with 5-FU and leucovorin, and pharmaceutically acceptable salts, acids or derivatives of any of the above; as well as combinations of two or more of the above.Chemotherapeutic agents as defined herein include 'anti-hormonal agents" or "endocrine therapeutics" which act to regulate, reduce, block, or inhibit the effects of hormones that can promote the growth of cancer. They may be hormones themselves, including, but not limited to: anti-estrogens and selective estrogen receptor modulators (SERMs), including, for example, tamoxifen (includingNOLVADEX® tamoxifen), raloxifene, droloxifene, 4-hydroxytamoxifen, trioxifene, keoxifene, LY117018, onapristone, and FARESTON.cndot.toremifene; aromatase inhibitors that inhibit the enzyme aromatase, which regulates estrogen production in the adrenal glands, such as, for example, 4(5)-imidazoles, aminoglutethimide, MEGASE® megestrol acetate, AROMASIN® exemestane, formestanie, fadrozole, RIVISOR® vorozole, FEMARA® letrozole, and ARIMIDEX® anastrozole; and anti-androgens such as flutamide, nilutamide, bicalutamide, leuprolide, and goserelin; as well as troxacitabine (a 1 ,3-dioxolane nucleoside cytosine analog); antisense oligonucleotides, particularly those which inhibit expression of genes in signaling pathways implicated in abherant cell proliferation, such as, for example, PKC-alpha, Raf and H-Ras; ribozymes such as a VEGF expression inhibitor (e.g., ANGIOZYME® ribozyme) and a HER2 expression inhibitor; vaccines such as gene therapy vaccines, for example, ALLOVECTIN® vaccine, LEU VECTIN® vaccine, and VAXID® vaccine; PROLEUKIN® rlL-2; LURTOTECAN®topoisomerase 1 inhibitor; ABARELIX® rmRH; Vinorelbine and Esperamicins (see U.S. Pat. No.4,675,187), and pharmaceutically acceptable salts, acids or derivatives of any of the above; as well as combinations of two or more of the above.The term "immunomodulatory drug" or "IMiD" refers to a class of drugs that modifies the immune system response or the functioning of the immune system, such as by the stimulation of antibody formation and / or the inhibition of peripheral blood cell activity, and include, but are not limited to, thalidomide (a-N-phthalimkJo-glutarimide) and its analogues, REVLIMID® (lenalkJomide), ACTI-MID™ (pomalidomide), OTEZLA® (apremilast), and pharmaceutically acceptable salts or acids thereof.The term "chimeric" antibody refers to an antibody in which a portion of the heavy and / or light chain is derived from a particular source or species, while the remainder of the heavy and / or light chain is derived from a different source or species.The term "FcRH5," as used herein, refers to any native FcRH5 which results from the production of a FcRH5 protein in a cell. The term includes FcRH5 from any vertebrate source, including mammals such as primates (e.g., humans and cynomolgus monkeys) and rodents (e.g., mice and rats), unless otherwise indicated. The term also includes naturally occurring variants of FcRHS, e.g., splice variants or allelic variants. The amino acid sequence of an exemplary human FcRH5 protein sequence is shown in SEQ ID NO: 114. The amino acid sequence of an exemplary cynomolgus monkey FcRH5 protein is shown in SEQ ID NO: 215.The term "cluster of differentiation 3" or "CD3," as used herein, refers to any native CD3 from any vertebrate source, including mammals such as primates (e.g., humans) and rodents (e.g., mice and rats), unless otherwise indicated, including, for example, CD3e, CD3y, CD3a, and CD3p chains. The term encompasses "full-length," unprocessed CD3 (e.g., unprocessed or unmodified CD3e or CD3v), as well as any form of CD3 that results from processing in the cell. The term also encompasses naturally occurring variants of CD3, including, for example, splice variants or allelic variants. CD3 includes, for example, human CD3e protein (NCBI RefSeq No. NP_000724), which is 207 amino acids in length, and human CD3y protein (NCBI RefSeq No. NPJ300064), which is 182 amino acids in length.The "class" of an antibody refers to the type of constant domain or constant region possessed by its heavy chain. There are five major classes of antibodies: IgA, IgD, IgE, IgG, and IgM, and several of these may be further divided into subclasses (isotypes), e.g., IgGi, lgG2, IgGs, IgG*, IgAi, and IgAz. The heavy chain constant domains that correspond to the different classes of immunoglobulins are called α, δ, ε, γ, and μ, respectively. It is understood that aspects and embodiments of the invention described herein include"comprising," "consisting," and "consisting essentially of aspects and embodiments.The term "cytotoxic agent" as used herein refers to a substance that inhibits or prevents a cellular function and / or causes cell death or destruction. Cytotoxic agents include, but are not limited to, radioactive isotopes (e.g., At211, 1181, 1125, Y90, Re188, Re188, Sm153, BP12, P82, Pb212 and radioactive isotopes of Lu); chemotherapeutic agents or drugs (e.g., methotrexate, adriamicin, vinca alkaloids (vincristine, vinblastine, etoposide), doxorubicin, melphalan, mitomycin C, chlorambucil, daunorubicin or other intercalating agents); growth inhibitory agents; enzymes and fragments thereof such as nucleolytic enzymes; antibiotics; toxins such as small molecule toxins or enzymatically active toxins of bacterial, fungal, plant or animal origin, including fragments and / or variants thereof; and the various antitumor or anticancer agents disclosed below.A "disorder" is any condition that would benefit from treatment including, but not limited to, chronic and acute disorders or diseases including those pathological conditions which predispose the mammal to the disorder in question.The terms "cell proliferative disorder" and "proliferative disorder" refer to disorders that are associated with some degree of abnormal cell proliferation. In one embodiment, the cell proliferative disorder is cancer. In one embodiment, the cell proliferative disorder is a tumor.The terms "cancer" and "cancerous" refer to or describe the physiological condition in mammals that is typically characterized by unregulated cell growth / proliferation. Examples of cancer include, but are not limited to, myeloma, carcinoma, lymphoma (e.g., Hodgkin's and non-Hodgkin's lymphoma), blastema, sarcoma, and leukemia. In some embodiments, the cancer is an FcRHS-positive cancer. More particular examples of such cancers include multiple myeloma (MM), chronic lymphoid leukemia (CLL), mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), chronic myelogenous leukemia (CML), chronic myelomonocytic leukemia, acute promyelocytic leukemia (APL), chronic myeloproliferative disorder, thrombocytic leukemia, precursor B-cell acute lymphoblastic leukemia (pre-B-ALL), precursor T cell acute lymphoblastic leukemia (pre-T-ALL), mast cell disease, mast cell leukemia, mast cell sarcoma, myeloid sarcomas, lymphoid leukemia, and undifferentiated leukemia. In some embodiments, the cancer is a B cell cancer. In particular, cancer can include conditions involving the production of excess antibodies, such as monoclonal gammopathy, light chain amyloidosis, monoclonal gammopathy of undetermined significance and solitary plasmacytomas, isolated plasmacytoma and extramedullary plasmacytoma."Tumor," as used herein, refers to all neoplastic cell growth and proliferation, whether malignant or benign, and all pre- cancerous and cancerous cells and tissues. The terms "cancer," "cancerous," "cell proliferative disorder," "proliferative disorder," and "tumor" are not mutually exclusive as referred to herein."Effector functions" refer to those biological activities attributable to the Fc region of an antibody, which vary with the antibody isotype. Examples of antibody effector functions include: C1q binding and complement dependent cytotoxicity (CDC); Fc receptor binding; antibody-dependent cell-mediated cytotoxicity (ADCC); phagocytosis; down regulation of cell surface receptors (e.g., B cell receptor); and B cell activation. An "effective amount" of a compound, for example, an anti-FcRH5 antibody of the invention or a composition (e.g., pharmaceutical composition) thereof, is at least the minimum amount required to achieve the desired therapeutic or prophylactic result, such as a measurable improvement or prevention of a particular disorder (e.g., a cell proliferative disorder, e.g., cancer). An effective amount herein may vary according to factors such as the disease state, age, sex, and weight of the patient, and the ability of the antibody to elicit a desired response in the individual. An effective amount is also one in which any toxic or detrimental effects of the treatment are outweighed by the therapeutically beneficial effects. For prophylactic use, beneficial or desired results include results such as eliminating or reducing the risk, lessening the severity, or delaying the onset of the disease, including biochemical, histological and / or behavioral symptoms of the disease, its complications, and intermediate pathological phenotypes presenting during development of the disease. For therapeutic use, beneficial or desired results include clinical results such as decreasing one or more symptoms resulting from the disease, increasing the quality of life of those suffering from the disease, decreasing the dose of other medications required to treat the disease, enhancing effect of another medication such as via targeting, delaying the progression of the disease, and / or prolonging survival. In the case of cancer or tumor, an effective amount of the drug may have the effect in reducing the number of cancer cells; reducing the tumor size; inhibiting (i.e., slow to some extent or desirably stop) cancer cell infiltration into peripheral organs; inhibit (i.e., slow to some extent and desirably stop) tumor metastasis; inhibiting to some extent tumor growth; and / or relieving to some extent one or more of the symptoms associated with the disorder. An effective amount can be administered in one or more administrations. For purposes of this invention, an effective amount of drug, compound, or pharmaceutical composition is an amount sufficient to accomplish prophylactic or therapeutic treatment either directly or indirectly. As is understood in the clinical context, an effective amount of a drug, compound, or pharmaceutical composition may or may not be achieved in conjunction with another drug, compound, or pharmaceutical composition. Thus, an "effective amount" may be considered in the context of administering one or more therapeutic agents, and a single agent may be considered to be given in an effective amount if, in conjunction with one or more other agents, a desirable result may be or is achieved.The term "Fc region" herein is used to define a C-terminal region of an immunoglobulin heavy chain that contains at least a portion of the constant region. The term includes native sequence Fc regions and variant Fc regions. In one embodiment, a human IgG heavy chain Fc region extends from Cys226, or from Pro230, to the carboxyl-terminus of the heavy chain. However, the C-terminal lysine (Lys447) of the Fc region may or may not be present. Unless otherwise specified herein, numbering of amino acid residues in the Fc region or constant region is according to the EU numbering system, also called the EU index, as described in Kabat et al. Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD, 1991."Framework" or "FR" refers to variable domain residues other than hypervariable region (HVR) residues. The FR of a variable domain generally consists of four FR domains: FR1 , FR2, FR3, and FR4. Accordingly, the HVR and FR sequences generally appear in the following sequence in VH (or VL): FR1 - H1 (L1)-FR2-H2(L2)-FR3-H3(L3)-FR4. The term "FcRH5-positive cell" refers to a cell that expresses FcRH5 on its surface. In some embodiments, FcRH5 is one or more of FcRH5a, FcRH5b, FcRH5c, UniProt Identifier Q96RD9-2, and / or FcRH5d. In some embodiments, the FcRH5 is FcRH5c.The term "FcRH5-positive cancer" refers to a cancer comprising cells that express FcRH5 on their surface. For the purposes of determining whether a cell expresses FcRH5 on the surface, FcRH5 mRNA expression is considered to correlate to FcRH5 expression on the cell surface. In some embodiments, expression of FcRHS mRNA is determined by a method selected from in situ hybridization and RT-PCR (including quantitative RT-PCR). Alternatively, expression of FcRHS on the cell surface can be determined, for example, using antibodies to FcRH5 in a method such as immunohistochemistry, FACS, etc. In some embodiments, FcRH5 is one or more of FcRH5a, FcRH5b, FcRH5c, UniProt Identifier Q96RD9-2, and / or FcRHSd. In some embodiments, the FcRHS is FcRHSc.The terms "full-length antibody," "intact antibody," and *whole antibody" are used herein interchangeably to refer to an antibody having a structure substantially similar to a native antibody structure or having heavy chains that contain an Fc region as defined herein.The term "glycosylated forms of FcRHS" refers to naturally occurring forms of FcRHS that are post-translationally modified by the addition of carbohydrate residues.A "growth inhibitory agent" when used herein refers to a compound or composition which inhibits growth of a cell either in vitro or in vivo. In one embodiment, growth inhibitory agent is growth inhibitory antibody that prevents or reduces proliferation of a cell expressing an antigen to which the antibody binds. In another embodiment, the growth inhibitory agent may be one which significantly reduces the percentage of cells in S phase. Examples of growth inhibitory agents include agents that block cell cycle progression (at a place other than S phase), such as agents that induce G1 arrest and M-phase arrest. Classical M-phase blockers include the vincas (vincristine and vinblastine), taxanes, and topoisomerase II inhibitors such as doxorubicin, epirubicin, daunorubicin, etoposide, and bleomycin. Those agents that arrest G1 also spill over into S-phase arrest, for example, DNA alkylating agents such as tamoxifen, prednisone, dacarbazine, mechlorethamine, cisplatin, methotrexate, 5-fluorouracil, and ara-C. Further information can be found in Mendelsohn and Israel, eds., The Molecular Basis of Cancer, Chapter 1 , entitled "Cell cycle regulation, oncogenes, and antineoplastic drugs' by Murakami et al. (W.B. Saunders, Philadelphia, 1995), e.g., p. 13. The taxanes (paclitaxel and docetaxel) are anticancer drugs both derived from the yew tree. Docetaxel (TAXOTERE®, Rhone-Poulenc Rorer), derived from the European yew, is a semisynthetic analogue of paclitaxel (TAXOL®, Bristol-Myers Squibb). Paclitaxel and docetaxel promote the assembly of microtubules from tubulin dimers and stabilize microtubules by preventing depolymerization, which results in the inhibition of mitosis in cells.The terms "host cell," "host cell line," and "host cell culture' are used interchangeably and refer to cells into which exogenous nucleic acid has been introduced, including the progeny of such cells. Host cells include "transformants" and "transformed cells," which include the primary transformed cell and progeny derived therefrom without regard to the number of passages. Progeny may not be completely identical in nucleic acid content to a parent cell, but may contain mutations. Mutant progeny that have the same function or biological activity as screened or selected for in the originally transformed cell are included herein. A "human antibody" is one which possesses an amino acid sequence which corresponds to that of an antibody produced by a human or a human cell or derived from a non-human source that utilizes human antibody repertoires or other human antibody-encoding sequences. This definition of a human antibody specifically excludes a humanized antibody comprising non-human antigen-binding residues. Human antibodies can be produced using various techniques known in the art, including phage-display libraries. Hoogenboom and Winter. J. Mol. Biol. 227:381 ,1991 ; Marks et al. J. Mol. Biol. 222:581 ,1991. Also available for the preparation of human monoclonal antibodies are methods described in Cole et al. Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, p. 77 (1985); Boemer et al. J. Immunol., 147(1):86-95,1991. See also van Dijk and van de Winkel. Cunr. Opin. Pharmacol. 5:368-74, 2001.Human antibodies can be prepared by administering the antigen to a transgenic animal that has been modified to produce such antibodies in response to antigenic challenge, but whose endogenous loci have been disabled, e.g., immunized xenomice (see, e.g., U.S. Pat. Nos. 6,075,181 and 6,150,584 regarding XENOMOUSE™ technology). See also, for example, Li et al. Proc. Natl. Acad. Sci. USA. 103:3557-3562, 2006 regarding human antibodies generated via a human B-cell hybridoma technology.A 'human consensus framework" is a framework which represents the most commonly occurring amino acid residues in a selection of human immunoglobulin VL or VH framework sequences. Generally, the selection of human immunoglobulin VL or VH sequences is from a subgroup of variable domain sequences. Generally, the subgroup of sequences is a subgroup as in Kabat et al. Sequences of Proteins of Immunological Interest, Fifth Edition, NIH Publication 91-3242, Bethesda MD (1991), vols. 1-3. In one embodiment, for the VL, the subgroup is subgroup kappa I as in Kabat et al. supra. In one embodiment, for the VH, the subgroup is subgroup III as in Kabat et al. supra.A "humanized" antibody refers to a chimeric antibody comprising amino acid residues from non- human HVRs and amino acid residues from human FRs. In certain embodiments, a humanized antibody will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the HVRs (e.g., CDRs) correspond to those of a non-human antibody, and all or substantially all of the FRs correspond to those of a human antibody. A humanized antibody optionally may comprise at least a portion of an antibody constant region derived from a human antibody. A "humanized form' of an antibody, e.g., a non-human antibody, refers to an antibody that has undergone humanization.The term "hypervariable region" or *HVR" as used herein refers to each of the regions of an antibody variable domain which are hypervariable in sequence ("complementarity determining regions" or "CDRs") and / or form structurally defined loops ("hypervariable loops') and / or contain the antigen- contacting residues ("antigen contacts"). Generally, antibodies comprise six HVRs: three in the VH (H1 , H2, H3), and three in the VL (L1 , L2, L3). Exemplary HVRs herein include:(a) hypervariable loops occurring at amino acid residues 26-32 (L1), 50-52 (L2), 91-96 (L3), 26-32(H1), 53-55 (H2), and 96-101 (H3) (Chothia and Lesk, J. Mol. Biol. 196:901-917, 1987);(b) CDRs occurring at amino acid residues 24-34 (L1), 50-56 (L2), 89-97 (L3), 31 -35b (H1), 50- 65 (H2), and 95-102 (H3) (Kabat et al. Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, MD (1991)); (c) antigen contacts occurring at amino acid residues 27c-36 (L1), 46-55 (L2), 89-96 (L3), 30-35b (H1), 47-58 (H2), and 93-101 (H3) (MacCallum et al. J. Mol. Biol. 262: 732-745, 1996); and(d) combinations of (a), (b), and / or (c), including HVR amino acid residues 46-56 (L2), 47-56 (L2), 48-56 (L2), 49-56 (L2), 26-35 (H1), 26-35b (H1), 49-65 (H2), 93-102 (H3), and 94-102 (H3).Unless otherwise indicated, HVR residues and other residues in the variable domain (e.g., FR residues) are numbered herein according to Kabat et al. supra.An "immunoconjugate" is an antibody conjugated to one or more heterologous molecule(s), including but not limited to a cytotoxic agent.A 'subject" or an "individual* is a mammal. Mammals include, but are not limited to, domesticated animals (e.g., cows, sheep, cats, dogs, and horses), primates (e.g., humans and non-human primates such as monkeys), rabbits, and rodents (e.g., mice and rats). In certain embodiments, the subject or individual is a human.An "isolated" antibody is one which has been separated from a component of its natural environment. In some embodiments, an antibody is purified to greater than 95% or 99% purity as determined by, for example, electrophoretic (e.g., SDS-PAGE, isoelectric focusing (lEF), capillary electrophoresis) or chromatographic (e.g., ion exchange or reverse phase HPLC). For review of methods for assessment of antibody purity, see, e.g., Flatman et al. J. Chromatogr. B 848:79-87, 2007.An "isolated" nucleic acid refers to a nucleic acid molecule that has been separated from a component of its natural environment. An isolated nucleic acid includes a nucleic acid molecule contained in cells that ordinarily contain the nucleic acid molecule, but the nucleic acid molecule is present extrachromosomally or at a chromosomal location that is different from its natural chromosomal location."Isolated nucleic acid encoding an anti-FcRH5 antibody" refers to one or more nucleic acid molecules encoding antibody heavy and light chains (or fragments thereof), including such nucleic acid molecule(s) in a single vector or separate vectors, and such nucleic acid molecule(s) present at one or more locations in a host cell."Isolated nucleic acid encoding an anti-CD3 antibody" refers to one or more nucleic acid molecules encoding antibody heavy and light chains (or fragments thereof), including such nucleic acid molecule(s) in a single vector or separate vectors, and such nucleic acid molecule(s) present at one or more locations in a host cell.The term "monoclonal antibody" as used herein refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies comprising the population are identical and / or bind the same epitope, except for possible variant antibodies, e.g., containing naturally occurring mutations or arising during production of a monoclonal antibody preparation, such variants generally being present in minor amounts. In contrast to polyclonal antibody preparations, which typically include different antibodies directed against different determinants (epitopes), each monoclonal antibody of a monoclonal antibody preparation is directed against a single determinant on an antigen. Thus, the modifier "monoclonal" indicates the character of the antibody as being obtained from a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by any particular method. For example, the monoclonal antibodies to be used in accordance with the present invention may be made by a variety of techniques, including but not limited to the hybridoma method, recombinant DNA methods, phage-display methods, and methods utilizing transgenic animals containing all or part of the human immunoglobulin loci, such methods and other exemplary methods for making monoclonal antibodies being described herein.A "naked antibody" refers to an antibody that is not conjugated to a heterologous moiety (e.g., a cytotoxic moiety) or radiolabel. The naked antibody may be present in a pharmaceutical formulation."Native antibodies" refer to naturally occurring immunoglobulin molecules with varying structures. For example, native IgG antibodies are heterotetrameric glycoproteins of about 150,000 daltons, composed of two identical light chains and two identical heavy chains that are disulfide-bonded. From N- to C-terminus, each heavy chain has a variable region (VH), also called a variable heavy domain or a heavy chain variable domain, followed by three constant domains (CH1 , CH2, and CH3). Similarly, from N- to C-terminus, each light chain has a variable region (VL), also called a variable light domain or a light chain variable domain, followed by a constant light (CL) domain. The light chain of an antibody may be assigned to one of two types, called kappa (κ) and lambda (A), based on the amino acid sequence of its constant domain.The term "package insert" is used to refer to instructions customarily included in commercial packages of therapeutic products, that contain information about the indications, usage, dosage, administration, combination therapy, contraindications and / or warnings concerning the use of such therapeutic products.The term "PD-1 axis binding antagonist" refers to a molecule that inhibits the interaction of a PD-1 axis binding partner with either one or more of its binding partner, so as to remove T cell dysfunction resulting from signaling on the PD-1 signaling axis - with a result being to restore or enhance T cell function (e.g., proliferation, cytokine production, target cell killing). As used herein, a PD-1 axis binding antagonist includes a PD-1 binding antagonist, a PD-L1 binding antagonist and a PD-L2 binding antagonist.The term "PD-1 binding antagonist" refers to a molecule that decreases, blocks, inhibits, abrogates or interferes with signal transduction resulting from the interaction of PD-1 with one or more of its binding partners, such as PD-L1 , PD-L2. In some embodiments, the PD-1 binding antagonist is a molecule that inhibits the binding of PD-1 to one or more of its binding partners. In a specificembodiment, the PD-1 binding antagonist inhibits the binding of PD-1 to PD-L1 and / or PD-L2. For example, PD-1 binding antagonists include anti-PD-1 antibodies, antigen binding fragments thereof, immunoadhesins, fusion proteins, oligopeptides and other molecules that decrease, block, inhibit, abrogate or interfere with signal transduction resulting from the interaction of PD-1 with PD-L1 and / or PD- l_2. In one embodiment, a PD-1 binding antagonist reduces the negative co-stimulatory signal mediated by or through cell surface proteins expressed on T lymphocytes mediated signaling through PD-1 so as render a dysfunctional T cell less dysfunctional (e.g., enhancing effector responses to antigen recognition). In some embodiments, the PD-1 binding antagonist is an anti-PD-1 antibody. In a specific embodiment, a PD-1 binding antagonist is MDX-1106 (nivolumab). In another specific embodiment, a PD-1 binding antagonist is MK-3475 (pembrolizumab). In another specific embodiment, a PD-1 binding antagonist is CT-011 (pidilizumab). In another specific embodiment, a PD-1 binding antagonist is AMP- 224. In another specific embodiment, a PD-1 binding antagonist is MED1-0680. In another specific embodiment, a PD-1 binding antagonist is PDR001. In another specific embodiment, a PD-1 binding antagonist is REGN2810. In another specific embodiment, a PD-1 binding antagonist is BGB-108.The term "PD-L1 binding antagonist" refers to a molecule that decreases, blocks, inhibits, abrogates or interferes with signal transduction resulting from the interaction of PD-L1 with either one or more of its binding partners, such as PD-1 , B7-1. In some embodiments, a PD-L1 binding antagonist is a molecule that inhibits the binding of PD-L1 to its binding partners. In a specific embodiment, the PD-L1 binding antagonist inhibits binding of PD-L1 to PD-1 and / or B7-1. In some embodiments, the PD-L1 binding antagonists include anti-PD-L1 antibodies, antigen binding fragments thereof, immunoadhesins, fusion proteins, oligopeptides and other molecules that decrease, block, inhibit, abrogate or interfere with signal transduction resulting from the interaction of PD-L1 with one or more of its binding partners, such as PD-1 , B7-1. In one embodiment, a PD-L1 binding antagonist reduces the negative co-stimulatory signal mediated by or through cell surface proteins expressed on T lymphocytes mediated signaling through PD-L1 so as to render a dysfunctional T cell less dysfunctional (e.g., enhancing effector responses to antigen recognition). In some embodiments, a PD-L1 binding antagonist is an anti-PD-L1 antibody. In still another specific embodiment, an anti-PD-L1 antibody is MPDL3280A (atezolizumab, marketed as TECENTRIQ™ with a WHO Drug Information (International Nonproprietary Names for Pharmaceutical Substances), Recommended INN: List 74, Vol. 29, No. 3, 2015 (see page 387)). In a specific embodiment, an anti-PD-L1 antibody is YW243.55.S70. In another specific embodiment, an anti- PD-L1 antibody is MDX-1105. In another specific embodiment, an anti PD-L1 antibody is MSB0015718C. In still another specific embodiment, an anti-PD-L1 antibody is MEDI4736.The term "PD-L2 binding antagonist" refers to a molecule that decreases, blocks, inhibits, abrogates or interferes with signal transduction resulting from the interaction of PD-L2 with either one or more of its binding partners, such as PD-1. In some embodiments, a PD-L2 binding antagonist is a molecule that inhibits the binding of PD-L2 to one or more of its binding partners. In a specific embodiment, the PD-L2 binding antagonist inhibits binding of PD-L2 to PD-1. In some embodiments, the PD-L2 antagonists include anti-PD-L2 antibodies, antigen binding fragments thereof, immunoadhesins, fusion proteins, oligopeptides and other molecules that decrease, block, inhibit, abrogate or interfere with signal transduction resulting from the interaction of PD-L2 with either one or more of its binding partners, such as PD-1. In one embodiment, a PD-L2 binding antagonist reduces the negative co-stimulatory signal mediated by or through cell surface proteins expressed on T lymphocytes mediated signaling through PD-L2 so as render a dysfunctional T cell less dysfunctional (e.g., enhancing effector responses to antigen recognition). In some embodiments, a PD-L2 binding antagonist is an immunoadhesin.The term "protein," as used herein, refers to any native protein from any vertebrate source, including mammals such as primates (e.g., humans) and rodents (e.g., mice and rats), unless otherwise indicated. The term encompasses "full-length," unprocessed protein as well as any form of the protein that results from processing in the cell. The term also encompasses naturally occurring variants of the protein, e.g., splice variants or allelic variants."Percent (%) amino acid sequence identity" with respect to a reference polypeptide sequence is defined as the percentage of amino acid residues in a candidate sequence that are identical with the amino acid residues in the reference polypeptide sequence, after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent sequence identity, and not considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent amino acid sequence identity can be achieved in various ways that are within the skill in the art, for instance, using publicly available computer software such as BLAST, BLAST-2, ALIGN or Megalign (DNASTAR) software. Those skilled in the art can determine appropriate parameters for aligning sequences, including any algorithms needed to achieve maximal alignment over the full-length of the sequences being compared. For purposes herein, however, % amino acid sequence identity values are generated using the sequence comparison computer program ALIGN-2. The ALIGN-2 sequence comparison computer program was authored by Genentech, Inc., and the source code has been filed with user documentation in the U.S. Copyright Office, Washington D.C., 20559, where it is registered under U.S. Copyright Registration No. TXU510087. The ALIGN-2 program is publicly available fromGenentech, Inc., South San Francisco, California, or may be compiled from the source code. The ALIGN- 2 program should be compiled for use on a UNIX operating system, including digital UNIX V4.0D. All sequence comparison parameters are set by the ALIGN-2 program and do not vary.In situations where ALIGN-2 is employed for amino acid sequence comparisons, the % amino acid sequence identity of a given amino acid sequence A to, with, or against a given amino acid sequence B (which can alternatively be phrased as a given amino acid sequence A that has or comprises a certain % amino acid sequence identity to, with, or against a given amino acid sequence B) is calculated as follows:100 times the fraction X / Ywhere X is the number of amino acid residues scored as identical matches by the sequence alignment program ALIGN-2 in that program's alignment of A and B, and where Y is the total number of amino acid residues in B. It will be appreciated that where the length of amino acid sequence A is not equal to the length of amino acid sequence B, the % amino acid sequence identity of A to B will not equal the % amino acid sequence identity of B to A. Unless specifically stated otherwise, all % amino acid sequence identity values used herein are obtained as described in the immediately preceding paragraph using the ALIGN-2 computer program.The term "pharmaceutical formulation" refers to a preparation which is in such form as to permit the biological activity of an active ingredient contained therein to be effective, and which contains no additional components which are unacceptably toxic to a subject to which the formulation would be administered.A "pharmaceutically acceptable carrier" refers to an ingredient in a pharmaceutical formulation, other than an active ingredient, which is nontoxic to a subject. A pharmaceutically acceptable carrier includes, but is not limited to, a buffer, excipient, stabilizer, or preservative.As used herein, treatment" (and grammatical variations thereof such as "treat" or "treating") refers to clinical intervention in an attempt to alter the natural course of the individual being treated, and can be performed either for prophylaxis or during the course of clinical pathology. Desirable effects of treatment include, but are not limited to, preventing occurrence or recurrence of disease, alleviation of symptoms, diminishment of any direct or indirect pathological consequences of the disease, preventing metastasis, decreasing the rate of disease progression, amelioration or palliation of the disease state, and remission or improved prognosis. In some embodiments, antibodies of the invention are used to delay development of a disease or to slow the progression of a disease.As used herein, "delaying progression" of a disorder or disease means to defer, hinder, slow, retard, stabilize, and / or postpone development of the disease or disorder (e.g., a cell proliferative disorder, e.g., cancer). This delay can be of varying lengths of time, depending on the history of the disease and / or individual being treated. As is evident to one skilled in the art, a sufficient or significant delay can, in effect, encompass prevention, in that the individual does not develop the disease. For example, a late stage cancer, such as development of metastasis, may be delayed.The term "epitope" refers to the particular site on an antigen molecule to which an antibody binds.In some embodiments, the particular site on an antigen molecule to which an antibody binds is determined by hydroxyl radical footprinting (e.g., FcRH5 binding domain). In some embodiments, the particular site on an antigen molecule to which an antibody binds is determined by crystallography.By "reduce" or "inhibit" is meant the ability to cause an overall decrease, for example, of 20% or greater, of 50% or greater, or of 75%, 85%, 90%, 95%, or greater. In certain embodiments, reduce or inhibit can refer to the effector function of an antibody that is mediated by the antibody Fc region, such effector functions specifically including complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP).The term "variable region" or "variable domain" refers to the domain of an antibody heavy or light chain that is involved in binding the antibody to antigen. The variable domains of the heavy chain and light chain (VH and VL, respectively) of a native antibody generally have similar structures, with each domain comprising four conserved framework regions (FRs) and three hypervariable regions (HVRs). (See, e.g., Kindt et al. Kuby Immunology, 6th ed. W.H. Freeman and Co., page 91 (2007).) A single VH or VL domain may be sufficient to confer antigen-binding specificity. Furthermore, antibodies that bind a particular antigen may be isolated using a VH or VL domain from an antibody that binds the antigen to screen a library of complementary VL or VH domains, respectively. See, e.g., Portolano et al. J.Immunol. 150:880-887, 1993; Clarkson et al. Nature 352:624-628, 1991.A "variant Fc region' comprises an amino acid sequence which differs from that of a native sequence Fc region by virtue of at least one amino acid modification, preferably one or more amino acid substitution^). Preferably, the variant Fc region has at least one amino acid substitution compared to a native sequence Fc region or to the Fc region of a parent polypeptide, e.g., from about one to about ten amino acid substitutions, and preferably from about one to about five amino acid substitutions in a native sequence Fc region or in the Fc region of the parent polypeptide. The variant Fc region herein will preferably possess at least about 80% homology with a native sequence Fc region and / or with an Fc region of a parent polypeptide, and most preferably at least about 90% homology therewith, more preferably at least about 95% homology therewith.The term "vector," as used herein, refers to a nucleic acid molecule capable of propagating another nucleic acid to which it is linked. The term includes the vector as a self-replicating nucleic acid structure as well as the vector incorporated into the genome of a host cell into which it has been introduced. Certain vectors are capable of directing the expression of nucleic acids to which they are operatively linked. Such vectors are referred to herein as "expression vectors.''As used herein, "administering" is meant a method of giving a dosage of a compound (e.g., an anti-FcRH5 antibody of the invention or a nucleic acid encoding an anti-FcRH5 antibody of the invention) or a composition (e.g., a pharmaceutical composition, e.g., a pharmaceutical composition including an anti-FcRH5 antibody of the invention) to a subject. The compositions utilized in the methods described herein can be administered, for example, intramuscularly, intravenously, intradermally, percutaneously, intraarterially, intraperitoneally, intralesionally, intracranially, intraarticularly, intraprostatically, intrapleurally, intratracheally, intranasally, intravitreally, intravaginally, intrarectally, topically,intratumorally, peritoneally, subcutaneously, subconjunctivally, intra vesicularily, mucosally,intrapericardially, intraumbilically, intraoculariy, orally, topically, locally, by inhalation, by injection, by infusion, by continuous infusion, by localized perfusion bathing target cells directly, by catheter, by lavage, in cremes, or in lipid compositions. The method of administration can vary depending on various factors (e.g., the compound or composition being administered and the severity of the condition, disease, or disorder being treated).II. COMPOSITIONS AND METHODSIn one aspect, the invention is based in part on anti-FcRH5 antibodies. In certain embodiments, the anti-FcRH5 antibodies are multispecific (e.g., bispecific) and bind, in addition to FcRH5 or a fragment thereof, a second biological molecule (e.g., a cell surface antigen, e.g., a T cell marker, e.g., CD3 (e.g., CD3E and / or CD3v)). Antibodies of the invention are useful, for example, for diagnosing and / or treating or delaying the progression of a cell proliferative disorder (e.g., cancer, e.g., an FcRH5-positive cancer, e.g., multiple myeloma) in a subject. A. Exemplary Anti-FcRH5 AntibodiesIn one aspect, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 2; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 3; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 4; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 5; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 6.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some instances, the anti-FcRH5 antibody may have a heavy chain variable (VH) domain including an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 104 and / or a light chain variable (VL) domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 105. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 52, 54, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody may have a heavy chain variable (VH) domain including the amino acid sequence of SEQ ID NO: 104. In some instances, the anthFcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51 , respectively. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 105. In a particular instance, the anti-FcRH5 antibody can be 1G7.v85, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 105.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 10; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 14; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some instances, the anti-FcRH5 antibody may have a VH domain including an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 106 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 107. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NO: 53, 54, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 106. In some instances, the anti-FcRH5 further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51 , respectively. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 107. In a particular instance, the anti-FcRH5 antibody can be 1G7.v93, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 106 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 107.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 82 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 83. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 82. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 83. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1 , or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 82 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 83.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 84 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 85. In some instances, the anti-FcRH5 antibody further includes the heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 of SEQ ID NO: 52, 54, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 84. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51 , respectively. In some instances, the anU-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 85. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.1 , or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 84 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 85.In some instances, the anti-FcRH5 antibody has a binding domain comprising six hypervariable regions (HVRs) (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 17; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 22. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 86 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 87. In some instances, the anti-FcRH5 antibody further comprises further includes the heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the amino acid sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 86. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51 , respectively. In some instances, the anti-FcRH5 antibody of claim may have a VL domain comprising the amino acid sequence of SEQ ID NO: 87. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.2, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 86 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 87.In some instances, the anti-FcRH5 antibody having a binding domain comprising sixhypervariable regions (HVRs) (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In some instances, the anti-FcRH5 antibody comprises a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 88 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 89. In some instances, the anti-FcRH5 antibody further includes the heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the amino acid sequences of SEQ ID NOs: 52, 54, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 88. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, SO, and 51 , respectively. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 89. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.3, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody comprising a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 88 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 89.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some instances, the anti-FcRH5 antibody may have a binding domain including a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 90 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 91. In some instances, the anti-FcRH5 antibody further includes the heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 90. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51 , respectively. In some instances, the anti- FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 91. In a particular instance, the anti-FcRH5 antibody can be 1 G7.v1.4, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 90 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 91.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 22. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 92 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%. 89%, 90%, 91%. 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 93. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 52, 54, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 92. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51 , respectively. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 93. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.5, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 92 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 93.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 19; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 24. In some instances, The anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%. 87%, 88%, 89%. 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 94 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%. 88%, 89%, 90%, 91%, 92%, 93%, 94%. 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 95. In some instances, the anti-FcRH5 antibody includes the heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the amino acid sequences of SEQ ID NOs: 52, 54, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 94. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR- L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51 , respectively. In some instances, the anti-FcRH5 antibody includes a VL domain comprising the amino acid sequence of SEQ ID NO: 95. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.6, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody having a binding domain including (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 94 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 95.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%. 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%. 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 96 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 97. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 53, 54, 46, and 47. In some instances, the anti-FcRH5 antibody includes a VH domain comprising the amino acid sequence of SEQ ID NO: 96. In some instances, the anti-FcRH5 includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51. In some instances, the anti-FcRH5 antibody includes a VL domain comprising the amino acid sequence of SEQ ID NO: 97. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.7, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody, having a binding domain including (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 96 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 97.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%. 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 98, and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 99. In some instances, the anti-FcRH5 comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 52, 55, 46, and 47, respectively. In some instances, the anti-FcRH5 antibody includes a VH domain comprising the amino acid sequence of SEQ ID NO: 98. In some instances, the anti-FcRH5 antibody includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 99. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.13, or a derivative or clonal relative thereof. In some instances, for example, an anti-FcRH5 antibody may include a VH domain comprising an amino acid sequence of SEQ ID NO: 98 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 99.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25. In some instances, the anti-FcRH5 antibody includes (a) a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 100 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 101. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 52, 54, 46, and 47. In some instances, the anti-FcRH5 may have a VH domain comprising the amino acid sequence of SEQ ID NO: 100. In some instances, The anti-FcRH5 antibody of any one of claims 79-82, wherein the antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 57, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 101. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1.13.1 , or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody including (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 100 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 101.In some instances, the anti-FcRH5 antibody includes a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody includes (a) a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 102 and / or (b) a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 103. In some instances, the anti-FcRH5 antibody further comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 52, 54, 46, and 47, respectively. In some instances, the anti- FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 102. In some instances, the anU-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 103. In a particular instance, the anti-FcRH5 antibody can be 1G7.v87, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 102 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 103.In some instances, an anti-FcRH5 antibody may have a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 32; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 33; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 34; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 35; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 36; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In some instances, the anti-FcRH5 comprises a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 110 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 111. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 66, 67, 68, and 69, respectively. In some instances, the anti-FcRH5 antibody of claim 95, wherein the VH domain comprising the amino acid sequence of SEQ ID NO: 110. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 70, 71 , 72, and 73. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 111. In a particular instance, the anti-FcRH5 antibody can be 17B1 , or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 110 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 111.In some instances, an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 112 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 113. In some instances, the anti-FcRH5 comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NO: 74, 75, 76, and 77, respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 112. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR- L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 78, 79, 80, and 81. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 113. In a particular instance, the anti-FcRH5 antibody can be 1 SG8, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 112 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 113.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 26; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 27; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 28; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 29; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 30; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 31. In some instances, the anti-FcRH5 antibody includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 108 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 109. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 58, 59, 60, and 61 , respectively. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 108. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 62, 63, 64, and 65. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 109. In a particular instance, the anti-FcRH5 antibody can be 7D8, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti-FcRH5 antibody comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 108 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 109.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 185 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%. 84%, 85%, 86%. 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%. 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 186. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 179, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 185. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 186. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1A, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 185 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 186.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of,SEQ ID NO: 187 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%. 82%, 83%, 84%, 85%, 86%, 87%, 88%. 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%. or 99%) sequence identity to, or the sequence of, SEQ ID NO: 188. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 180, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 187. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 188. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1B, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 187 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 188.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 189 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 190. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 181 , 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 189. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 190. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1C, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 189 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 190.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 191 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 192. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 23, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 191. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 192. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1D, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 191 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 192. In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 193 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 194. In some instances, the anU-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 182, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 193. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 194. In a particular instance, the anti-FcRH5 antibody can be 1 G7.v1 E, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 193 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 194.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 175; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 195 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 196. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 195. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 196. In a particular instance, the anti-FcRH5 antibody can be 1 G7.v1 F, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 195 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 196.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 176; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 197 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 198. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 197. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 198. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1G, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 197 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 198.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 177; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 199 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%. 84%, 85%, 86%. 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%. 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 200. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 199. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 200. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1H, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 199 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 200.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 178; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 201 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%. 82%, 83%, 84%, 85%, 86%, 87%, 88%. 89%, 90%, 91%, 92%, 93%, 94%. 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 202. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 201. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 202. In a particular instance, the anti-FcRH5 antibody can be 1G7.v11, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 201 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 202.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 203 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 204. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 183, and 47. In some instances, the anthFcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 203. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 204. In a particular instance, the anti-FcRH5 antibody can be 1G7.v1 J, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 203 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 204.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 205 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 206. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 184, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 205. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 206. In a particular instance, the anti-FcRH5 antibody can be 1 G7.v1 K, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 205 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 206.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 10; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 207 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 208. In some instances, the anU-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 207. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 208. In a particular instance, the anti-FcRH5 antibody can be 1 G7.v1 L, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 207 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 208.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 14; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 209 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 210. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 209. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 210. In a particular instance, the anti-FcRH5 antibody can be 1G7.v86, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 209 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 210.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 14; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 211 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%. 82%, 83%, 84%, 85%, 86%, 87%, 88%. 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%. or 99%) sequence identity to, or the sequence of, SEQ ID NO: 212. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 53, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 211. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 212. In a particular instance, the anti-FcRH5 antibody can be 1G7.v191 , or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 211 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 212.In some instances, the invention provides an anti-FcRH5 antibody having a binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 10; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 14; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23. In some instances, the anti-FcRH5 antibody of claim may have a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%. 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%. 93%, 94%, 95%. 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 213 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 214. In some instances, the anti-FcRH5 antibody comprises at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR- H3, and FR-H4 comprising the sequences of SEQ ID NO: 52, 54, 46, and 47. In some instances, the anti-FcRH5 antibody may have a VH domain comprising the amino acid sequence of SEQ ID NO: 213. In some instances, the anti-FcRH5 antibody further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 48, 56, 50, and 51. In some instances, the anti-FcRH5 antibody may have a VL domain comprising the amino acid sequence of SEQ ID NO: 214. In a particular instance, the anti-FcRH5 antibody can be 1G7.v92, or a derivative or clonal relative thereof. In some instances, for example, the invention provides an anti- FcRH5 antibody having a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 213 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 214.In certain embodiments, an antibody provided herein is a monoclonal, human, humanized, or chimeric antibody. In some instances, the anti-FcRH5 antibody is an IgG antibody. The anti-FcRH5 may be a full-length antibody and / or a monospecific antibody. In certain embodiments, the anti-FcRH5 antibody may bind to an epitope in the Ig-like domain 9 of FcRH5. For example, the epitope may comprises a portion of amino acids 743-850 of SEQ ID NO: 114. In some instances, the anti-FcRH5 antibody binds to human FcRH5 or cynomokjus monkey (cyno) FcRH5, or both. In other instances, the binding domain does not specifically bind to FcRH1 , FcRH2, FcRH3, and / or FcRH4.In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of between about 10 ml / kg / day to about 45 ml / kg / day (e.g., about 1 ml / kg / day, 5 ml / kg / day, 10 ml / kg / day, 11 ml / kg / day, 12 ml / kg / day, 13 ml / kg / day, 14 ml / kg / day, 15 ml / kg / day, 16 ml / kg / day, 17 ml / kg / day, 18 ml / kg / day, 19 ml / kg / day, 20 ml / kg / day, 21 ml / kg / day, 22 ml / kg / day, 23 ml / kg / day, 24 ml / kg / day, 25 ml / kg / day, 26 ml / kg / day, 27 ml / kg / day, 28 ml / kg / day, 29 ml / kg / day, 30 ml / kg / day, 31 ml / kg / day, 32 ml / kg / day, 33 ml / kg / day, 34 ml / kg / day, 35 ml / kg / day, 36 ml / kg / day, 37 ml / kg / day, 38 ml / kg / day, 39 ml / kg / day, 40 ml / kg / day, 41 ml / kg / day, 42 ml / kg / day, 43 ml / kg / day, or 44 ml / kg / day).In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of about 1 ml / kg / day to about 5 ml / kg / day, about 6 ml / kg / day to about 10 ml / kg / day, about 11 ml / kg / day to about 15 ml / kg / day, about 16 ml / kg / day to about 20 ml / kg / day, about 21 ml / kg / day to about 25 ml / kg / day, about 26 ml / kg / day to about 30 ml / kg / day, about 31 ml / kg / day to about 35 ml / kg / day, about 36 ml / kg / day to about 40 ml / kg / day, about 41 ml / kg / day to about 45 ml / kg / day in a mouse. In some instances, the anti- FcRH5 antibody has a clearance following intravenous injection of about 10 ml / kg / day to about 35 ml / kg / day in a mouse. In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of about 10 ml / kg / day to about 20 ml / kg / day in a mouse. In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of about 12 ml / kg / day to about 16 ml / kg / day in a mouse.In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of about 1 ml / kg / day to about 5 ml / kg / day, about 6 ml / kg / day to about 10 ml / kg / day, about 11 ml / kg / day to about 15 ml / kg / day, about 16 ml / kg / day to about 20 ml / kg / day, about 21 ml / kg / day to about 25 ml / kg / day, about 26 ml / kg / day to about 30 ml / kg / day, about 31 ml / kg / day to about 35 ml / kg / day, about 36 ml / kg / day to about 40 ml / kg / day, about 41 ml / kg / day to about 45 ml / kg / day in cyno. In some instances, the anti- FcRH5 antibody has a clearance following intravenous injection of about 20 ml / kg / day to about 40 ml / kg / day in a cyno. In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of about 25 ml / kg / day to about 35 ml / kg / day in a cyno. In some instances, the anti-FcRH5 antibody has a clearance following intravenous injection of about 30 ml / kg / day to about 35 ml / kg / day in a cyno.In a further aspect, an anti-FcRH5 antibody according to any of the above embodiments may incorporate any of the features, singly or in combination, as described in Sections 1 -7 below.) In some instances the anti-FcRH5 antibody binds to cyno FcRH5 with a KD of≤100 nM (e.g,≤ 90 nM,≤80 nM,≤ 70 nM,≤60 nM,≤50 nM,≤40 nM,≤30 nM,≤20 nM,≤10 nM,≤5 nM,≤ 1 nM,≤ 750 pM, ≤500 pM,≤250 pM,≤100 pM,≤50 pM, ≤25 pM,≤10 pM,≤5 pM, or≤ 1 pM, e.g., from 10-» M to 10-13 M, e.g., from 109 M to 10 13 M, e.g., from 10-10 to 10-13M, e.g., from 10-" to 10 13 M, e.g., from 10 12 to 10 13 M) or lower. In some instances, the anti-FcRHS antibody binds to cyno FcRH5 with a KD of about 1 pM to about 500 nM (e.g., about 1 pM to 200 pM, 100 pM to 300 pM, 200 pM to 400 pM, 300 pM to 500 pM, 400 pM to 600 pM, 500 pM to 700 pM, 600 pM to 800 pM, 700 pM to 900 pM, 800 pM to 1 nM, 900 pM to 100 nM, 1 nM to 200 nM, 100 nM to 300 nM, 200 nM to 400 nM, or 300 nM to 500 nM). In some instances, the anti-FcRH5 antibody binds to cyno FcRH5 with a KD of about 1 pM to about 1 nM (e.g., about 1 pM to 100 pM, 50 pM to 150 pM, 100 pM to 200 pM, 150 pM to 250 pM, 200 pM to 300 pM, 250 pM to 350 pM, 300 pM to 400 pM, 350 pM to 450 pM, 400 pM to 500 pM, 450 pM to 550 pM, 500 pM to 600 pM, 550 pM to 650 pM, 600 pM to 700 pM, 650 pM to 750 pM, 700 pM to 800 pM, 750 pM to 850 pM, 800 pM to 900 pM, 850 pM to 950 pM, or 900 pM to 1 nM). In some instances, the anti-FcRH5 antibody binds to cyno FcRH5 with a KD of about 100 pM to about 500 pM (e.g., about 100 pM, 125 pM, 150 pM, 175 pM, 200 pM, 225 pM, 250 pM, 275 pM, 300 pM, 325 pM, 350 pM, 375 pM, 400 pM, 425 pM, 450 pM, 475 pM, or 500 pM). In some instances, the anti-FcRH5 antibody binds to cyno FcRH5 with a KD of about 100 pM to about 160 pM (e.g., about 100 pM, 105 pM, 110 pM, 115 pM, 120 pM, 125 pM, 130 pM, 135 pM, 140 pM, 145 pM, 150 pM, 155 pM, or 160 pM). In some instances, the anti-FcRH5 antibody binds to cyno FcRH5 with a KD of about 1 nM to about 150 nM (e.g., about 1 nM, 2 nM, 3 nM, 4 nM, 5 nM, 6 nM, 7 nM, 8 nM, 9 nM, 10 nM, 11 nM, 12, nM, 13 nM, 14 nM. 15 nM, 16 nM, 17 nM. 18 nM, 19 nM, 20 nM. 21 nM, 22 nM, 23 nM, 24 nM, 25 nM, 26 nM, 27 nM, 28 nM, 29 nM, 30 nM, 31 nM, 32 nM, 33 nM, 34 nM, 35 nM. 36 nM, 37 nM, 38 nM, 39 nM, 40 nM, 41 nM, 42 nM, 43 nM, 44 nM, 45 nM, 46 nM, 47 nM, 48 nM, 49 nM. 50 nM, 55 nM, 60 nM, 65 nM, 70 nM, 75 nM, 80 nM, 85 nM, 90 nM, 95 nM, 100 nM, 105 nM, 110 nM, 115 nM, 120 nM, 125 nM, 130 nM, 135 nM, 140 nM, 145 nM, or 150 nM).In one embodiment, KD is measured by a radiolabeled antigen binding assay (RIA). In one embodiment, an RIA is performed with the Fab version of an antibody of interest and its antigen. For example, solution binding affinity of Fabs for antigen is measured by equilibrating Fab with a minimal concentration of (125l)-labeled antigen in the presence of a titration series of unlabeled antigen, then capturing bound antigen with an anti-Fab antibody-coated plate (see, e.g., Chen .et al. J. Mol. Biol.293:865-881 , 1999). To establish conditions for the assay, MICROTITER® multi-well plates (Thermo Scientific) are coated overnight with 5 pg / ml of a capturing anti-Fab antibody (Cappel Labs) in 50 mM sodium carbonate (pH 9.6), and subsequently blocked with 2% (w / v) bovine serum albumin in PBS for two to five hours at room temperature (approximately 23°C). In a non-adsorbent plate (Nunc #269620), 100 pM or 26 pM [12Sl]-antigen are mixed with serial dilutions of a Fab of interest (e.g., consistent with assessment of the anti-VEGF antibody, Fab-12, in Presta et al. Cancer Res. 57:4593-4599, 1997). The Fab of interest is then incubated overnight; however, the incubation may continue for a longer period (e.g., about 65 hours) to ensure that equilibrium is reached. Thereafter, the mixtures are transferred to the capture plate for incubation at room temperature (e.g., for one hour). The solution is then removed and the plate washed eight times with 0.1 % polysorbate 20 (TWEEN-20*) in PBS. When the plates have dried, 150 μΙ / well of scintillant (MICROSCINT-20™; Packard) is added, and the plates are counted on a TOPCOUNT™ gamma counter (Packard) for ten minutes. Concentrations of each Fab that give less than or equal to 20% of maximal binding are chosen for use in competitive binding assays.According to another embodiment, Ko is measured using a BIACORE* surface plasmon resonance assay. For example, an assay using a BIACORE*-2000 or a BIACORE *-3000 (BIAcore, Inc., Piscataway, NJ) is performed at 25°C with immobilized antigen CM5 chips at ~10 response units (RU). In one embodiment, carboxymethylated dextran biosensor chips (CM5, BIACORE, Inc.) are activated with AA-ethyl-ZV- (3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and W-hydroxysuccinimide (NHS) according to the supplier's instructions. Antigen is diluted with 10 mM sodium acetate, pH 4.8, to 5 pg / ml (-0.2 μΜ) before injection at a flow rate of 5 μΙ / minute to achieve approximately 10 response units (RU) of coupled protein. Following the injection of antigen, 1 M ethanolamine is injected to block unreacted groups. For kinetics measurements, two-fold serial dilutions of Fab (0.78 nM to 500 nM) are injected in PBS with 0.05% polysorbate 20 (TWEEN-20™) surfactant (PBST) at 25°C at a flow rate of approximately 25 μΙ / min. Association rates (kon) and dissociation rates (kotr) are calculated using a simple one-to-one Langmuir binding model (BIACORE* Evaluation Software version 3.2) by simultaneously fitting the association and dissociation sensorgrams. The equilibrium dissociation constant (KD) is calculated as the ratio kow kon. See, for example, Chen et al. J. Mol. Biol. 293:865-881 , 1999. If the on-rate exceeds 10SM~V1 by the surface plasmon resonance assay above, then the on-rate can be determined by using a fluorescent quenching technique that measures the increase or decrease in fluorescence emission intensity (excitation = 295 nm; emission = 340 nm, 16 nm band-pass) at 25 °C of a 20 nM anti-antigen antibody (Fab form) in PBS, pH 7.2, in the presence of increasing concentrations of antigen as measured in a spectrometer, such as a stop-flow equipped spectrophometer (Aviv Instruments) or a 8000-series SLM-AMINCO™ spectrophotometer (ThermoSpectronic) with a stirred cuvette.2. Antibody FragmentsIn certain embodiments, an antibody provided herein is an antibody fragment. Antibody fragments include, but are not limited to, bis-Fabs, Fab, Fab', Fab'-SH, F(ab")2, Fv, and scFv fragments, and other fragments described below. For a review of certain antibody fragments, see Hudson et al. Nat. Med. 9:129-134, 2003. For a review of scFv fragments, see, e.g., Pluckthun, in The Pharmacology of Monoclonal Antibodies, vol. 113, Rosenburg and Moore eds., (Springer- Verlag, New York), pp. 269-315, 1994; see also WO 93 / 16185; and U.S. Patent Nos. 5,571 ,894 and 5,587,458. For discussion of Fab and F(ab*)2 fragments comprising salvage receptor binding epitope residues and having increased in vivo half- life, see U.S. Patent No. 5,869,046.Antibody fragments in which the two Fabs are linked through bis-maleimide are referred to herein as bismaleimido-(thio-Fab)2 or bis-Fabs.Diabodies are antibody fragments with two antigen-binding sites that may be bivalent or bispecific. See, for example, EP 404,097; WO 1993 / 01161 ; Hudson et al. Nat. Med. 9:129-134, 2003; and Hollinger et al. Proc. Natl. Acad. Sci. USA 90:6444-6448, 1993. Triabodies and tetrabodies are also described in Hudson et al. Nat. Med. 9:129-134, 2003.Single-domain antibodies are antibody fragments comprising all or a portion of the heavy chain variable domain or all or a portion of the light chain variable domain of an antibody. In certain embodiments, a single-domain antibody is a human single-domain antibody (Domantis, Inc., Waltham, MA; see, e.g., U.S. Patent No. 6,248,516 B1).Antibody fragments can be made by various techniques, including but not limited to proteolytic digestion of an intact antibody as well as production by recombinant host cells (e.g., E. coli or phage), as described herein.3. Chimeric and Humanized AntibodiesIn certain embodiments, an antibody provided herein is a chimeric antibody. Certain chimeric antibodies are described, e.g., in U.S. Patent No. 4,816,567; and Morrison et al. Proc. Natl. Acad. Sci. USA, 81 :6851-6855, 1984. In one example, a chimeric antibody comprises a non-human variable region (e.g., a variable region derived from a mouse, rat, hamster, rabbit, or non-human primate, such as a monkey) and a human constant region. In a further example, a chimeric antibody is a "class switched" antibody in which the class or subclass has been changed from that of the parent antibody. Chimeric antibodies include antigen-binding fragments thereof.In certain embodiments, a chimeric antibody is a humanized antibody. Typically, a non-human antibody is humanized to reduce immunogenicity to humans, while retaining the specificity and affinity of the parental non-human antibody. Generally, a humanized antibody comprises one or more variable domains in which HVRs, e.g., CDRs, (or portions thereof) are derived from a non-human antibody, and FRs (or portions thereof) are derived from human antibody sequences. A humanized antibody optionally will also comprise at least a portion of a human constant region. In some embodiments, some FR residues in a humanized antibody are substituted with corresponding residues from a non-human antibody (e.g., the antibody from which the HVR residues are derived), e.g., to restore or improve antibody specificity or affinity.Humanized antibodies and methods of making them are reviewed, e.g., in Almagro et al. Front. Biosci. 13:1619-1633, 2008, and are further described, e.g., in Riechmann et al. Nature 332:323-329, 1988; Queen et al. Proc. Natl Acad. Sci. USA 86:10029-10033, 1989; US Patent Nos. 5, 821 ,337, 7,527,791 , 6,982,321 , and 7,087,409; Kashmiri et al. Methods 36:25-34, 2005 (describing specificity determining region (SDR) grafting); Padlan Mol. Immunol. 28:489-498, 1991 (describing "resurfacing"); Dall'Acqua et al. Methods 36:43-60, 2005 (describing "FR shuffling"); and Osboum et al. Methods 36:61- 68, 2005; and Klimka et al. Br. J. Cancer, 83:252-260, 2000 (describing the "guided selection" approach to FR shuffling).Human framework regions that may be used for humanization include, but are not limited to, framework regions selected using the "best-fit" method (see, e.g., Sims et al. J. Immunol. 151 :2296, 1993); framework regions derived from the consensus sequence of human antibodies of a particular subgroup of light or heavy chain variable regions (see, e.g., Carter et al. Proc. Natl. Acad. Sci. USA, 89:4285, 1992; and Presta et al. J. Immunol. 151 :2623, 1993); human mature (somatically mutated) framework regions or human germline framework regions (see, e.g., Almagro et al. Front. Biosci.13:1619-1633, 2008); and framework regions derived from screening FR libraries (see, e.g., Baca et al. J. Biol. Chem. 272:10678-10684, 1997 and Rosok et al. J. Biol. Chem. 271 :22611-22618, 1996). 4. Human AntibodiesIn certain embodiments, an antibody provided herein is a human antibody. Human antibodies can be produced using various techniques known in the art. Human antibodies are described generally in van Dijk and van de Winkel, Cum Opin. Pharmacol. 5: 368-74, 2001 and Lonberg, Curr. Opin. Immunol. 20:450-459, 2008.Human antibodies may be prepared by administering an immunogen to a transgenic animal that has been modified to produce intact human antibodies or intact antibodies with human variable regions in response to antigenic challenge. Such animals typically contain all or a portion of the human immunoglobulin loci, which replace the endogenous immunoglobulin loci, or which are present extrachromosomally or integrated randomly into the animal's chromosomes. In such transgenic mice, the endogenous immunoglobulin loci have generally been inactivated. For review of methods for obtaining human antibodies from transgenic animals, see Lonberg, Nat. Biotech. 23:1 1 17-1 125, 2005. See also, e.g., U.S. Patent Nos. 6,075,181 and 6,150,584 describing XENOMOUSE™ technology; U.S. Patent No. 5,770,429 describing HUMAB® technology; U.S. Patent No. 7,041 ,870 describing K-M MOUSE® technology, and U.S. Patent Application Publication No. US 2007 / 0061900, describing VELOCIMOUSE® technology). Human variable regions from intact antibodies generated by such animals may be further modified, e.g., by combining with a different human constant region.Human antibodies can also be made by hybridoma-based methods. Human myeloma and mouse-human heteromyeloma cell lines for the production of human monoclonal antibodies have been described (see, e.g., Kozbor J. Immunol., 1 33: 3001 , 1984; Brodeur et al. Monoclonal AntibodyProduction Techniques and Applications, pp. 51-63 (Marcel Dekker, Inc., New York, 1987); and Boemer et al. J. Immunol., 147: 86, 1991). Human antibodies generated via human B-ceil hybridoma technology are also described in Li et al. Proc. Natl. Acad. Sci. USA, 103:3557-3562, 2006. Additional methods include those described, for example, in U.S. Patent No. 7,189,826 (describing production of monoclonal human IgM antibodies from hybridoma cell lines) and Ni, Xiandai Mianyixue, 26(4):265-268, 2006 (describing human-human hybridomas). Human hybridoma technology (Trioma technology) is also described in Vollmers and Brand lein, Histology and Histopathology, 20(3):927-937, 2005 and Vollmers and Brandlein, Methods and Findings in Experimental and Clinical Pharmacology, 27(3) :185-91 , 2005.Human antibodies may also be generated by isolating Fv clone variable domain sequences selected from human-derived phage display libraries. Such variable domain sequences may then be combined with a desired human constant domain. Techniques for selecting human antibodies from antibody libraries are described below.5. Library-Derived AntibodiesAntibodies of the invention may be isolated by screening combinatorial libraries for antibodies with the desired activity or activities. For example, a variety of methods are known in the art for generating phage display libraries and screening such libraries for antibodies possessing the desired binding characteristics. Such methods are reviewed, e.g., in Hoogenboom et al. in Methods in Molecular Biology 178:1 -37 (O'Brien et al. ed., Human Press, Totowa, NJ, 2001) and further described, e.g., in the McCafferty et al. Nature 348:552-554; Clackson et al. Nature 352: 624-628, 1991 ; Marks et al. J. Mol. Biol. 222: 581-597, 1992; Marks and Bradbury, in Methods in Molecular Biology 248: 161 -175 (Lo, ed., Human Press, Totowa, NJ, 2003); Sidhu et al. J. Mol. Biol. 338(2): 299-310, 2004; Lee et al. J. Mol. Biol. 340(5):1073-1093, 2004; Fellouse, Proc. Natl. Acad. Sci. USA 101(34): 12467-12472, 2004; and Lee et al. J. Immunol. Methods 284(1 -2):119-132, 2004.In certain phage display methods, repertoires of VH and VL genes are separately cloned by polymerase chain reaction (PCR) and recombined randomly in phage libraries, which can then be screened for antigen-binding phage as described in Winter et al. Ann. Rev. Immunol., 12: 433-455, 1994. Phage typically display antibody fragments, either as single-chain Fv (scFv) fragments or as Fab fragments. Libraries from immunized sources provide high-affinity antibodies to the immunogen without the requirement of constructing hybridomas. Alternatively, the naive repertoire can be cloned (e.g., from human) to provide a single source of antibodies to a wide range of non-self and also self antigens without any immunization as described by Griffiths et al. EMBO J, 12: 725-734, 1993. Finally, naive libraries can also be made synthetically by cloning unrearranged V-gene segments from stem cells, and using PCR primers containing random sequence to encode the highly variable CDR3 regions and to accomplish rearrangement in vHro, as described by Hoogenboom and Winter, J. Mol. Biol., 227: 381-388, 1992. Patent publications describing human antibody phage libraries include, for example: US Patent No. 5,750,373, and US Patent Publication Nos. 2005 / 0079574, 2005 / 0119455, 2005 / 0266000,2007 / 0117126, 2007 / 0160598. 2007 / 0237764, 2007 / 0292936, and 2009 / 0002360. Antibodies or antibody fragments isolated from human antibody libraries are considered human antibodies or human antibody fragments herein.6. Multispecific Antibodies, Including FcRHS T cell-dependent Bispecific (TDB) AntibodiesIn any one of the above aspects, the anti-FcRH5 antibody provided herein is a multispecific antibody, for example, a bispecific antibody. Multispecific antibodies are monoclonal antibodies that have binding specificities for at least two different sites. In certain embodiments, bispecific antibodies may bind to two different epitopes of FcRH5.In certain embodiments, one of the binding specificities is for FcRH5 and the other is for CD3 (e.g., CD3e or CD3y). Such bispecific anti-FcRH5 antibodies are also referred to as FcRH5 T cell- dependent bispecific (TDB) antibodies or FcRHS TDBs. In some instances, the second binding domain binds to an epitope on CD3 comprising amino acid residue Glu6 of CD3. In some instances, the epitope further comprises one or more additional amino acid residues selected from the group consisting of Gln1 , Asp2, and Met7 of CD3. In some instances, the epitope comprises amino acid residues Gln1 , Asp2, and Glu6 of CD3. In some instances, the epitope comprises amino acid residues Gln1 , Asp2, Glu6, and Met7 of CD3. In some instances, the epitope does not comprise amino acid residue Glu5 of CD3. In some instances, the epitope does not comprise amino acid residues Gly3 and Glu5 of CD3. In some instances, the epitope consists of amino acid residues Gln1 , Asp2, Glu6, and Met7 of CD3.In other some instances, the second binding domain is capable of binding to a human CD3 polypeptide or a cyno CD3 polypeptide. In some instances, the human CD3 polypeptide or the cyno CD3 polypeptide is a human CD3e polypeptide or a cyno CD3e polypeptide, respectively. In some instances, the human CD3 polypeptide or the cyno CD3 polypeptide is a human CD3y polypeptide or a cyno CD3y polypeptide, respectively.In particular instances, the second binding domain binds the human CD3e polypeptide with dissociation constant (Ko) of≤ 1 μΜ,≤ 100 nM,≤ 10 nM,≤ 1 nM,≤ 0.1 nM,≤ 0.01 nM, or≤ 0.001 nM (e.g., 10-8 M or less, e.g., from 10-8 M to 1 fJ-13 M, e.g., from 109 M to 10 13 M). For example, in some instances the the second binding domain binds the human CD3e polypeptide with a KD of≤100 nM (e.g,≤ 90 nM, ≤80 nM,≤ 70 nM,≤60 nM,≤50 nM,≤40 nM,≤30 nM,≤20 nM,≤10 nM,≤5 nM,≤ 1 nM,≤ 750 pM,≤500 pM,≤250 pM,≤100 pM,≤50 pM,≤25 pM,≤10 pM,≤5 pM, or≤ 1 pM) or lower.In some instances, for example, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 117; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 120.In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123. In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%. 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 133 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 134. In some instances, the anti-FcRH5 antibody includes a second binding domain comprising at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR- H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 125, 126, 127, and 128, respectively. In some instances, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 133. In some instances, the second binding domain further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 129, 130, 131 , and 132, respectively. In some instances, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 134. In some instances, the second binding domain includes a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 134.Accordingly, in some instances, a half-antibody variant of an anti-FcRH5 antibody of the invention may be paired with a half-antibody variant of anti-CD3 antibody 38E4.v1 to form an FcRH5 TDB (i.e., an anti- FcRH5 / 38E4.v1 TDB). In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 122; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123. In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 135 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 136. In some instances, the anti-FcRH5 antibody includes a second binding domain comprising at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR- H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 125, 126, 127, and 128, respectively. In some instances, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 135. In some instances, the second binding domain further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 129, 130, 131 , and 132, respectively. In some instances, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 136. In some instances, the second binding domain includes a VH domain comprising an amino acid sequence of SEQ ID NO: 135 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 136.Accordingly, in some instances, a half-antibody variant of an anti-FcRH5 antibody of the invention may be paired with a half-antibody variant of anti-CD3 antibody 38E4.v1 to form an FcRH5 TDB (i.e., an anti- FcRH5 / 38E4.v1 TDB).In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 124. In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 137 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 138. In some instances, the anti-FcRH5 antibody includes a second binding domain comprising at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR- H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 125, 126, 127, and 128, respectively. In some instances, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 137. In some instances, the second binding domain further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 129, 130, 131 , and 132, respectively. In some instances, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 138. In some instances, the second binding domain includes a VH domain comprising an amino acid sequence of SEQ ID NOs: 137 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 138. Accordingly, in some instances, a half-antibody variant of an anti-FcRH5 antibody of the invention may be paired with a half-antibody variant of anti-CD3 antibody 38E4.v11 to form an FcRH5 TDB (i.e., an anti- FcRH5 / 38E4.v11 TDB).In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 139; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 140; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 141 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 142; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 143; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 144. In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%. 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 153 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%. 87%, 88%, 89%, 90%, 91%, 92%, 93%. 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 154. In some instances, the anti-FcRH5 antibody includes a second binding domain comprising at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR- H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 145, 146, 147, and 148, respectively. In some instances, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 153. In some instances, the second binding domain further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 149, 150, 151 , and 152, respectively. In some instances, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 154. In some instances, the second binding domain includes a VH domain comprising an amino acid sequence of SEQ ID NOs: 153 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 154. Accordingly, in some instances, a half-antibody variant of an anti-FcRH5 antibody of the invention may be paired with a half-antibody variant of anti-CD3 antibody hu40G5c to form an FcRH5 TDB (i.e., an anti- FcRH5 / hu40G5c TDB).In some instances, for example, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 155; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 156; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 157; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 158; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 159; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 160.In some instances, the invention provides an anti-FcRH5 antibody, wherein the second binding domain comprises at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 155; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 162; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 157; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 158; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 159; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 160. In some instances, for example, the second binding domain includes a VH domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 172 and / or a VL domain comprising an amino acid sequence having at least 80% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 173. In some instances, for example, the anti-FcRH5 antibody includes a second binding domain comprising at least one (e.g., 1 , 2, 3, or 4) of heavy chain framework regions FR-H1 , FR-H2, FR-H3, and FR-H4 comprising the sequences of SEQ ID NOs: 164, 165, 166, and 167, respectively. In some instances, the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 172. In some instances, the second binding domain further includes at least one (e.g., 1 , 2, 3, or 4) of the light chain framework regions FR-L1 , FR-L2, FR-L3, and FR-L4 comprising the sequences of SEQ ID NOs: 168, 169, 170, and 171 , respectively. In some instances, the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 173. In some instances, the second binding domain includes a VH domain comprising an amino acid sequence of SEQ ID NOs: 172 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 173. Accordingly, in some instances, a half- antibody variant of an anti-FcRH5 antibody of the invention may be paired with a half-antibody variant of anti-CD3 antibody huUCHTI .v9 to form an FcRH5 TDB (i.e., an anti-FcRH5 / huUCHT1.v9 TDB).In some instances, for example, the invention provides an anti-FcRH5 antibody, wherein the binding domain that binds FcRH5 comprises a VH domain (VHi) comprising a charged region (CR») and a VL domain (VL?) comprising a charged region (CR2), wherein the CRj in the VH* forms a charge pair with the CR2 in the VLt. In some instances, the CRj comprises a basic amino acid residue and the CR2 comprises an acidic amino acid residue. In some instances, the CRi comprises a Q39K substitution mutation (EU numbering). In some instances, the CR» consists of the Q39K substitution mutation. In some instances, the CR2 comprises a Q38E substitution mutation (EU numbering). In some instances, the CR2 consists of the Q38E substitution mutation. In some instances, the second binding domain that binds CD3 comprises a VH domain (VH2) comprising a charged region (CR3) and a VL domain (VL2) comprising a charged region (CR<), wherein the CR* in the VL2 forms a charge pair with the CR3 in the VH2. In some instances, the CR* comprises a basic amino acid residue and the CR3 comprises an acidic amino acid residue. In some instances, the CR4 comprises a Q38K substitution mutation (EUnumbering). In some instances, the CR< consists of the Q38K substitution mutation. In some instances, the CR3 comprises a Q39E substitution mutation (EU numbering). In some instances, the CR3 consists of the Q39E substitution mutation. In some instances, the VLt domain is linked to a light chain constant (CL) domain (CLt) and the VH? is linked to a first heavy chain constant (CH1) domain (CH11), wherein the CLt comprises a charged region (CRe) and the CH11 comprises a charged region (CRe), and wherein the CR5 in the CLt forms a charge pair with the CRe in the CH11. In some instances, the CRe comprises a basic amino acid residue and the CRe comprises an acidic residue. In some instances, the CR5 comprises a V133K substitution mutation (EU numbering). In some instances, the CR5 consists of the V133K substitution mutation. In some instances, the CRe comprises a S183E substitution mutation (EU numbering). In some instances, the CRe consists of the S183E substitution mutation.In some instances, the invention provides an anti-FcRH5 antibody, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises a charged region (CR7) and the CH12 comprises a charged region (CRe), and wherein the CRe in the CH12 forms a charge pair with the CR7 in the CL2. In some instances, the CRe comprises a basic amino acid residue and the CR7 comprises an acidic amino acid residue. In some instances, the CRe comprises a S183K substitution mutation (EU numbering). In some instances, the CRe consists of the S183K substitution mutation. In some instances, the CR7 comprises a V133E substitution mutation (EU numbering). In some instances, the CR7 consists of the V133E substitution mutation.In some instances, for example, the invention provides an anti-FcRH5 antibody, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises one or more mutations at amino acid residues F116, L135, S174, S176, and / or T178 (EU numbering) and the CH12 comprises one or more mutations at amino acid residues A141 , F170, S181 , S183, and / or V185 (EU numbering). In some instances, the CL2 comprises one or more of the following substitution mutations: F116A, L135V, S174A, S176F, and / or T178V. In some instances, the CL2 comprises the following substitution mutations: F116A, L135V, S174A, S176F, and T178V. In some instances, the CH12 comprises one or more of the following substitution mutations: A1411, F170S, S181 M, S183A, and / or V185A. In some instances, the CH12 comprises the following substitution mutations: A141 I, F170S, S181M, S183A, and V185A.In some instances, the invention provides an anti-FcRH5 antibody, wherein the binding domain that binds FcRH5 comprises a VH domain (VHj) comprising a charged region (CRt) and a VL domain (VLi) comprising a charged region (CR2), wherein the CR2 in the VLt forms a charge pair with the CRj in the VH* . In some instances, the CR2 comprises a basic amino acid residue and the CR> comprises an acidic amino acid residue. In some instances, the CR2 comprises a Q38K substitution mutation (EU numbering). In some instances, the CR2 consists of the Q38K substitution mutation. In some instances, the CRt comprises a Q39E substitution mutation (EU numbering). In some instances, the CRt consists of the Q39E substitution mutation. In some instances, the second binding domain that binds CD3 comprises a VH domain (VH2) comprising a charged region (CR3) and a VL domain (VL2) comprising a charged region (CR<), wherein the CR3 in the VH2 forms a charge pair with the CR< in the VL2. In some instances, the CR3 comprises a basic amino acid residue and the CR< comprises an acidic amino acid residue. In some instances, the CR3 comprises a Q39K substitution mutation (EU numbering). In some instances, the CR3 consists of the Q39K substitution mutation. In some instances, the CR* comprises a Q38E substitution mutation (EU numbering). In some instances, the CR* consists of the Q38E substitution mutation. In some instances, the VL» domain is linked to a light chain constant (CL) domain (CLf) and the VHf is linked to a first heavy chain constant (CH1) domain (CH11), wherein the CL? comprises a charged region (CR6) and the CH11 comprises a charged region (CRe), and wherein the CRe in the CH1 ? forms a charge pair with the CRs in the CLf. In some instances, the CRe comprises a basic amino acid residue and the CRs comprises an acidic amino acid residue. In some instances, the CRe comprises a S183K substitution mutation (EU numbering). In some instances, the CRe consists of the S183K substitution mutation. In some instances, the CRs comprises a V133E substitution mutation (EU numbering). In some instances, the CRs consists of the V133E substitution mutation.In some instances, for example, the invention provides an anti-FcRH5 antibody, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises a charged region (CR7) and the CH12 comprises a charged region (CRe), and wherein the CR7 in the CL2 forms a charged pair with the CRs in the CH12. In some instances, the CR7 comprises a basic amino acid residue and the CRe comprises an acidic residue. In some instances, the CR7 comprises a V133K substitution mutation (EU numbering). In some instances, the CR7 consists of the V133K substitution mutation. In some instances, the CRs comprises a S183E substitution mutation (EU numbering). In some instances, the CRe consists of the S183E substitution mutation.In some instances, for example, the invention provides an anti-FcRH5 antibody, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises one or more mutations at amino acid residues F116, L135, S174, S176, and / or T178 (EU numbering) and the CH12 comprises one or more mutations at amino acid residues A141 , F170, S181 , S183, and / or V185 (EU numbering). In some instances, the CL2 comprises one or more of the following substitution mutations: F116A, L135V, S174A, S176F, and / or T178V. In some instances, the CL2 comprises the following substitution mutations: F116A, L135V, S174A, S176F, and T178V. In some instances, the CH12 comprises one or more of the following substitution mutations: A1411, F170S, S181 M, S183A, and / or V185A. In some instances, the CH12 comprises the following substitution mutations: A141 I, F170S, S181 M, S183A, and V185A. In some instances, the anti-FcRH5 antibody comprises one or more heavy chain constant domains, wherein the one or more heavy chain constant domains are selected from a first CH2 domain (CH2*), a first CH3 domain (CH31), a second CH2 domain (CH22), and a second CH3 domain (CH32). In some instances, at least one of the one or more heavy chain constant domains is paired with another heavy chain constant domain. In some instances, the CH3» and the CH32 each comprise a protuberance (P?) or a cavity (Ct), and the Pi or the C< in the CH3j is positionable in the C» or the Pi, respectively, in the CH32. In some instances, the CH3? and the CH32 meet at an interface between the P< and the C1. In some instances, the CH2< and the CH22 each comprise (P2) or a cavity (C2), and the P2 or the C2 in the CH2t is positionable in the C2 or the P2, respectively, in the CH22. In some instances, the CH2i and the CH22 meet at an interface between the P2 and the C2.In another aspect , the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO:121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm and the anti-CD3 arm each comprise an N297G substitution mutation (EU numbering); and wherein the anti-FcRH5 arm comprises a T366W substitution mutation and the anti-CD3 arm comprises a T366S, L368A, and Y407V substitution mutation. In some instances, the anti-FcRH5 antibody comprises an anti- FcRH5 arm comprising a first binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm and the anti-CD3 arm each comprise an N297G substitution mutation (EU numbering); and wherein the anti-FcRH5 arm comprises a T366W substitution mutation and the anti-CD3 arm comprises a T366S, L368A, and Y407V substitution mutation.In another aspect, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anthCD3 arm comprising a second binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering). In some instances, the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering).In another aspect, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 104 and a VL domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 133 and a VL domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering). In some instances, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering).In another aspect, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering). In some instances, the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 ami comprising a second binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR- H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering).In another aspect, the invention provides the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 104 and a VL domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering). In some instances, the invention provides an anti-FcRH5 antibody that binds to FcRHS and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 104, wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering).In another aspect, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181 M, S183A, V185A, and N297G substitution mutations (EU numbering). In some instances, the anti-FcRH5 antibody comprises an anti- FcRH5 arm comprising a first binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In another aspect, the invention provides the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 104 and a VL domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 105, wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering). In some instances, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In another aspect, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anti-CD3 arm comprising a second binding domain comprising at least one, two, three, four, five, or six hypervariable regions (HVRs) selected from (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181 M, S183A, V185A, and N297G substitution mutations (EU numbering). In some instances, the anti-FcRHS antibody comprises an anti- FcRH5 arm comprising a first binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; and an anthCD3 arm comprising a second binding domain comprising the six hypervariable regions (HVRs): (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116; (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ; (d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118; (e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and (0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; and wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).In another aspect, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 104 and a VL domain comprising an amino acid sequence having at least 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%) sequence identity to, or the sequence of, SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181 M, S183A, V185A, and N297G substitution mutations (EU numbering). In some instances, the invention provides an anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).7. Antibody VariantsIn certain embodiments, amino acid sequence variants of the anti-FcRH5 antibodies of the invention (e.g., bispecific anti-FcRH5 antibodies of the invention that bind to FcRH5 and a second biological molecule, e.g., CD3, such as FcRH5 TDB antibodies of the invention or variants thereof) are contemplated. For example, it may be desirable to improve the binding affinity and / or other biological properties of the antibody. Amino acid sequence variants of an antibody may be prepared by introducing appropriate modifications into the nucleotide sequence encoding the antibody, or by peptide synthesis. Such modifications include, for example, deletions from, and / or insertions into and / or substitutions of residues within the amino acid sequences of the antibody. Any combination of deletion, insertion, and substitution can be made to arrive at the final construct, provided that the final construct possesses the desired characteristics, for example, antigen-binding. a. Substitution, insertion, and deletion variantsIn certain embodiments, antibody variants having one or more amino acid substitutions are provided. Sites of interest for substitutional mutagenesis include the HVRs and FRs. Conservative substitutions are shown in Table 1 under the heading of "preferred substitutions." More substantial changes are provided in Table 1 under the heading of "exemplary substitutions," and as further described below in reference to amino acid side chain classes. Amino acid substitutions may be introduced into an antibody of interest and the products screened for a desired activity, for example, retained / improved antigen binding, decreased immunogenicity, or improved ADCC or CDC.TABLE 1. Exemplary and Preferred Amino Acid SubstitutionsAmino acids may be grouped according to common side-chain properties:(1) hydrophobic: Norleucine, Met, Ala, Val, Leu, lie;(2) neutral hydrophilic: Cys, Ser, Thr, Asn, Gin;(3) acidic: Asp, Glu;(4) basic: His, Lys, Arg;(5) residues that influence chain orientation: Gly, Pro;(6) aromatic: Trp, Tyr, Phe.Non-conservative substitutions will entail exchanging a member of one of these classes for another class.One type of substitutional variant involves substituting one or more hypervariable region residues of a parent antibody (e.g., a humanized or human antibody). Generally, the resulting variant(s) selected for further study will have modifications (e.g., improvements) in certain biological properties (e.g., increased affinity, reduced immunogenicity) relative to the parent antibody and / or will have substantially retained certain biological properties of the parent antibody. An exemplary substitutional variant is an affinity matured antibody, which may be conveniently generated, e.g., using phage display-based affinity maturation techniques such as those described herein. Briefly, one or more HVR residues are mutated and the variant antibodies displayed on phage and screened for a particular biological activity (e.g. binding affinity).Alterations (e.g., substitutions) may be made in HVRs, e.g., to improve antibody affinity. Such alterations may be made in HVR "hotspots," i.e., residues encoded by codons that undergo mutation at high frequency during the somatic maturation process (see, e.g., Chowdhury, Methods Mol. Biol.207:179-196, 2008), and / or residues that contact antigen, with the resulting variant VH or VL being tested for binding affinity. Affinity maturation by constructing and reselecting from secondary libraries has been described, e.g., in Hoogenboom et al. in Methods in Molecular Biology 178:1 -37 (O'Brien et al. ed., Human Press, Totowa, NJ, (2001).) In some embodiments of affinity maturation, diversity is introduced into the variable genes chosen for maturation by any of a variety of methods (e.g., error-prone PCR, chain shuffling, or oligonucleotide-directed mutagenesis). A secondary library is then created. The library is then screened to identify any antibody variants with the desired affinity. Another method to introduce diversity involves HVR-directed approaches, in which several HVR residues (e.g., 4-6 residues at a time) are randomized. HVR residues involved in antigen binding may be specifically identified, e.g., using alanine scanning mutagenesis or modeling. CDR-H3 and CDR-L3 in particular are often targeted.In certain embodiments, substitutions, insertions, or deletions may occur within one or more HVRs so long as such alterations do not substantially reduce the ability of the antibody to bind antigen. For example, conservative alterations (e.g., conservative substitutions as provided herein) that do not substantially reduce binding affinity may be made in HVRs. Such alterations may, for example, be outside of antigen contacting residues in the HVRs. In certain embodiments of the variant VH and VL sequences provided above, each HVR either is unaltered, or contains no more than one, two, or three amino acid substitutions.A useful method for identification of residues or regions of an antibody that may be targeted for mutagenesis is called "alanine scanning mutagenesis" as described by Cunningham and Wells (1989) Science, 244:1081-1085. In this method, a residue or group of target residues (e.g., charged residues such as arg, asp, his, lys, and glu) are identified and replaced by a neutral or negatively charged amino acid (e.g., alanine or polyalanine) to determine whether the interaction of the antibody with antigen is affected. Further substitutions may be introduced at the amino acid locations demonstrating functional sensitivity to the initial substitutions. Alternatively, or additionally, a crystal structure of an antigen- antibody complex to identify contact points between the antibody and antigen. Such contact residues and neighboring residues may be targeted or eliminated as candidates for substitution. Variants may be screened to determine whether they contain the desired properties.Amino acid sequence insertions include amino- and / or carboxyl-terminal fusions ranging in length from one residue to polypeptides containing a hundred or more residues, as well as intrasequence insertions of single or multiple amino acid residues. Examples of terminal insertions include an antibody with an N-terminal methionyl residue. Other insertional variants of the antibody molecule include the fusion to the N- or C-terminus of the antibody to an enzyme (e.g., for ADEPT) or a polypeptide which increases the serum half-life of the antibody. b. Glycosylation variantsIn certain embodiments, anti-FcRH5 antibodies of the invention can be altered to increase or decrease the extent to which the antibody is glycosylated. Addition or deletion of glycosylation sites to anti-FcRH5 antibody of the invention may be conveniently accomplished by altering the amino acid sequence such that one or more glycosylation sites is created or removed. Addition or removal of a glycosylation site may alter the effector function of an antibody, such as an anti-FcRH5 antibody (e.g., an FcRH5 TDB). In some embodiments, the anti-FcRH5 antibody (e.g., an FcRH5 TDB) may contain an aglycosylation site mutation. In some embodime...

Claims

CLAIMSWhat is claimed is:

1. An anti-Fc Receptor-like 5 (FcRH5) antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six hypervariable regions (HVRs):(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 2;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 3;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 4;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 5; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 6.

2. The anti-FcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23.

3. The anti-FcRH5 antibody of claim 2, wherein the binding domain comprises (a) a heavy chain variable (VH) domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 104; (b) a light chain variable (VL) domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 105; or (c) a VH domain as in (a) and a VL domain as in (b).

4. The anti-FcRH5 antibody of claim 2 or 3, wherein the antibody further comprises the following heavy chain variable region framework regions (FRs):(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

5. The anti-FcRH5 antibody of claim 4, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 104.

6. The anti-FcRH5 antibody of any one of claims 2-5, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48; (b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

7. The anti-FcRH5 antibody of claim 6, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 105.

8. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 105.

9. The anti-FcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 10;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 14;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23.

10. The anti-FcRH5 antibody of claim 9, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 106; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 107; or (c) a VH domain as in (a) and a VL domain as in (b).

11. The anti-FcRH5 antibody of claim 9 or 10, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 53;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

12. The anti-FcRH5 antibody of claim 11 , wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 106.

13. The anti-FcRH5 antibody of any one of claims 9-12, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57; (c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

14. The anti-FcRH5 antibody of claim 13, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 107.

15. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 106 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 107.

16. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20.

17. The anti-FcRH5 antibody of claim 16, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 82; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 83; or (c) a VH domain as in (a) and a VL domain as in (b).

18. The anti-FcRH5 antibody of claim 16 or 17, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

19. The anti-FcRH5 antibody of claim 18, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 82.

20. The anti-FcRH5 antibody of any one of claims 16-19, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 56;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and (d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

21. The anti-FcRH5 antibody of claim 20, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 83.

22. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 82 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 83.

23. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21.

24. The anti-FcRH5 antibody of claim 23, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 84; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 85; or (c) a VH domain as in (a) and a VL domain as in (b).

25. The anti-FcRH5 antibody of claim 23 or 24, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

26. The anti-FcRH5 antibody of claim 25, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 84.

27. The anti-FcRH5 antibody of any one of claims 23-26, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

28. The anti-FcRH5 antibody of claim 27, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 85.

29. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 84 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 85.

30. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 17; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 22.

31. The anti-FcRH5 antibody of claim 30, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 86; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 87; or (c) a VH domain as in (a) and a VL domain as in (b).

32. The anti-FcRH5 antibody of claim 30 or 31 , wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

33. The anti-FcRH5 antibody of claim 32, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 86.

34. The anti-FcRH5 antibody of any one of claims 30-33, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

35. The anti-FcRH5 antibody of claim 34, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 87.

36. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 86 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 87.

37. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21.

38. The anti-FcRH5 antibody of claim 37, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 88; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 89; or (c) a VH domain as in (a) and a VL domain as in (b).

39. The anti-FcRH5 antibody of claim 37 or 38, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

40. The anti-FcRH5 antibody of claim 39, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 88.

41. The anti-FcRH5 antibody of any one of claims 37-40, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

42. The anti-FcRH5 antibody of claim 41 , wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 89.

43. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 88 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 89.

44. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23.

45. The anti-FcRH5 antibody of claim 44, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 90; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 91 ; or (c) a VH domain as in (a) and a VL domain as in (b).

46. The anti-FcRH5 antibody of claim 44 or 45, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

47. The anti-FcRH5 antibody of claim 46, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 90.

48. The anti-FcRH5 antibody of any one of claims 44-47, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

49. The anti-FcRH5 antibody of claim 48, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 91.

50. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 90 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 91.

51. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 22.

52. The anti-FcRH5 antibody of claim 51 , wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 92; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 93; or (c) a VH domain as in (a) and a VL domain as in (b).

53. The anti-FcRH5 antibody of claim 51 or 52, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

54. The anti-FcRH5 antibody of claim 53, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 92.

55. The anti-FcRH5 antibody of any one of claims 51 -54, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 56;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

56. The anti-FcRH5 antibody of claim 55, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 93.

57. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 92 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 93.

58. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 19; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 24.

59. The anti-FcRH5 antibody of claim 58, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 94; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 95; or (c) a VH domain as in (a) and a VL domain as in (b).

60. The anti-FcRH5 antibody of claim 58 or 59, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

61. The anti-FcRH5 antibody of claim 60, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 94.

62. The anti-FcRH5 antibody of any one of claims 58-61 , wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

63. The anti-FcRH5 antibody of claim 62, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 95.

64. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 94 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 95.

65. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25.

66. The anti-FcRH5 antibody of claim 65, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 96; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 97; or (c) a VH domain as in (a) and a VL domain as in (b).

67. The anti-FcRH5 antibody of claim 65 or 66, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 53;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

68. The anti-FcRH5 antibody of claim 67, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 96.

69. The anti-FcRH5 antibody of any one of claims 65-68, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

70. The anti-FcRH5 antibody of claim 69, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 97.

71. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 96 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 97.

72. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25.

73. The anti-FcRH5 antibody of claim 72, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 98; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 99; or (c) a VH domain as in (a) and a VL domain as in (b).

74. The anti-FcRH5 antibody of claim 72 or 73, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 55;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

75. The anti-FcRH5 antibody of claim 74, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 98.

76. The anti-FcRH5 antibody of any one of claims 72-75, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

77. The anti-FcRH5 antibody of claim 76, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 99.

78. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 98 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 99.

79. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 7;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 18; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 25.

80. The anti-FcRH5 antibody of claim 79, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 100; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 101 ; or (c) a VH domain as in (a) and a VL domain as in (b).

81. The anti-FcRH5 antibody of claim 79 or 80, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

82. The anti-FcRH5 antibody of claim 81 , wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 100.

83. The anti-FcRH5 antibody of any one of claims 79-82, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 57;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

84. The anti-FcRH5 antibody of claim 83, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 101.

85. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 100 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 101.

86. The anthFcRH5 antibody of claim 1 , wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 11 ;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 15; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20.

87. The anti-FcRH5 antibody of claim 86, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 102; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 103; or (c) a VH domain as in (a) and a VL domain as in (b).

88. The anti-FcRH5 antibody of claim 86 or 87, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 52;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 54;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 46; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 47.

89. The anti-FcRH5 antibody of claim 88, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 102.

90. The anti-FcRH5 antibody of any one of claims 86-89, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 48;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 56;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 50; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 51.

91. The anti-FcRH5 antibody of claim 90, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 103.

92. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 102 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 103.

93. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 32;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 33;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 34;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 35;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 36; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37.

94. The anti-FcRH5 antibody of claim 93, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 110; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 111 ; or (c) a VH domain as in (a) and a VL domain as in (b).

95. The anti-FcRH5 antibody of claim 93 or 94, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 66;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 67;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 68; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 69.

96. The anti-FcRH5 antibody of claim 95, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 110.

97. The anti-FcRH5 antibody of any one of claims 93-96, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 70;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 71 ;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 72; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 73.

98. The anti-FcRH5 antibody of claim 97, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 111.

99. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 110 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 111.

100. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41 ;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43.

101. The anti-FcRH5 antibody of claim 100, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 112; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 113; or (c) a VH domain as in (a) and a VL domain as in (b).

102. The anti-FcRH5 antibody of claim 100 or 101 , wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 74;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 75;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 76; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 77.

103. The anti-FcRH5 antibody of claim 102, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 112.

104. The anti-FcRH5 antibody of any one of claims 100-103, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 78;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 79;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 80; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 81.

105. The anti-FcRH5 antibody of claim 104, wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 113.

106. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 112 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 113.

107. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 26;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 27;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 28;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 29;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 30; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 31.

108. The anti-FcRH5 antibody of claim 107, wherein the binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 108; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 109; or (c) a VH domain as in (a) and a VL domain as in (b).

109. The anti-FcRH5 antibody of claim 107 or 108, wherein the antibody further comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 58;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 59;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 60; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 61.

110. The anti-FcRH5 antibody of claim 109, wherein the VH domain comprises the amino acid sequence of SEQ ID NO: 108.

111. The anti-FcRH5 antibody of any one of claims 107-110, wherein the antibody further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 62;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 63;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 64; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 65.

112. The anti-FcRH5 antibody of claim 111 , wherein the VL domain comprises the amino acid sequence of SEQ ID NO: 109.

113. An anti-FcRH5 antibody, wherein the anti-FcRH5 antibody comprises a binding domain comprising (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 108 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 109.

114. The anthFcRH5 antibody of any one of claims 1-113, wherein the anti-FcRH5 antibody binds to an epitope in the Ig-like domain 9 of FcRH5.

115. The anthFcRH5 antibody of claim 114, wherein the epitope comprises a portion of amino acids 743-850 of SEQ ID NO: 114.

116. The anti-FcRH5 antibody of claim 114 or 115, wherein the binding domain binds to human FcRH5 or cynomolgus monkey (cyno) FcRH5 or both.

117. The anti-FcRH5 antibody of claim 116, wherein the binding domain does not specifically bind to FcRH1 , FcRH2, FcRH3, and / or FcRH4.

118. The anti-FcRH5 antibody of claim 116 or 117, wherein the anti-FcRH5 antibody binds human FcRH5 with a Ko of about 100 nM or lower.

119. The anti-FcRH5 antibody of claim 118, wherein the anti-FcRH5 antibody binds human FcRH5 with a Ko of between about 10 pM and about 100 nM.

120. The anti-FcRH5 antibody of claim 119, wherein the anti-FcRH5 antibody binds human FcRH5 with a Ko of between about 100 pM and about 100 nM.

121. The anti-FcRH5 antibody of claim 120, wherein the anti-FcRH5 antibody binds human FcRH5 with a Ko of between about 1 nM and about 20 nM.

122. The anti-FcRH5 antibody of claim 121 , wherein the anti-FcRH5 antibody binds human FcRH5 with a Ko of between about 1 nM and about 10 nM.

123. The anthFcRH5 antibody of any one of claims 118-122, wherein the anti-FcRH5 antibody binds cyno FcRH5 with a Ko of about 100 nM or lower.

124. The anthFcRH5 antibody of claim 123, wherein the anti-FcRH5 antibody binds cyno FcRH5 with a Ko of between about 10 pM and about 100 nM.

125. The anti-FcRH5 antibody of claim 124, wherein the anti-FcRH5 antibody binds cyno FcRH5 with a KD of between about 100 pM and about 100 nM.

126. The anti-FcRH5 antibody of claim 125, wherein the anti-FcRH5 antibody binds cyno FcRH5 with a KD of between about 1 nM and about 50 nM.

127. The anti-FcRH5 antibody of any one of claims 1-126, wherein the anti-FcRH5 antibody comprises an aglycosylation site mutation.

128. The anthFcRH5 antibody of claim 127, wherein the aglycosylation site mutation is a substitution mutation.

129. The anti-FcRH5 antibody of claim 127 or 128, wherein the aglycosylation site mutation reduces effector function of the anti-FcRH5 antibody.

130. The anti-FcRH5 antibody of claim 128 or 129, wherein the substitution mutation is at amino acid residue N297, L234, L235, D265, and / or P329 (EU numbering).

131. The anti-FcRH5 antibody of claim 130, wherein the substitution mutation is selected from the group consisting of N297G, N297A, L234A, L235A, D265A, and P329G.

132. The anti-FcRH5 antibody of claim 131 , wherein the substitution mutation is an N297G mutation.

133. The anti-FcRH5 antibody of any one of claims 1-132, wherein the anti-FcRH5 antibody is a monoclonal, human, humanized, or chimeric antibody.

134. The anti-FcRH5 antibody of any one of claims 1-133, wherein the anti-FcRH5 antibody is an IgG antibody.

135. The anti-FcRH5 antibody of any one of claims 1-134, wherein the anti-FcRH5 antibody is an antibody fragment that binds FcRH5.

136. The anti-FcRH5 antibody of claim 135, wherein the antibody fragment is selected from the group consisting of bis-Fab, Fab, Fab'-SH, Fv, scFv, and (Fab*)2 fragments.

137. The anthFcRH5 antibody of claim 136, wherein the antibody fragment is a bis-Fab fragment.

138. The anthFcRH5 antibody of any one of claims 1-134, wherein the anti-FcRH5 antibody is a full- length antibody.

139. The anti-FcRH5 antibody of any one of claims 1-138, wherein the anti-FcRH5 antibody is a monospecific antibody.

140. The anti-FcRH5 antibody of any one of claims 1-138, wherein the anti-FcRH5 antibody is a multispecific antibody.

141. The anti-FcRH5 antibody of claim 140, wherein the multispecific antibody is a bispecific antibody.

142. The anthFcRH5 antibody of claim 141 , wherein the bispecific antibody comprises a second binding domain that binds cluster of differentiation 3 (CD3).

143. The anti-FcRH5 antibody of claim 142, wherein the second binding domain binds to an epitope on CD3 comprising amino acid residue Glu6 of CD3.

144. The anti-FcRH5 antibody of claim 143, wherein the epitope further comprises one or more additional amino acid residues selected from the group consisting of Gln1 , Asp2, and Met7 of CD3.

145. The anti-FcRH5 antibody of claim 143 or 144, wherein the epitope comprises amino acid residues Gln1 , Asp2, and Glu6 of CD3.

146. The anti-FcRH5 antibody of any one of claims 143-145, wherein the epitope comprises amino acid residues Gln1 , Asp2, Glu6, and Met7 of CD3.

147. The anti-FcRH5 antibody of any one of claims 143-146, wherein the epitope does not comprise amino acid residue Glu5 of CD3.

148. The anti-FcRH5 antibody of any one of claims 143-147, wherein the epitope does not comprise amino acid residues Gly3 and Glu5 of CD3.

149. The anti-FcRH5 antibody of any one of claims 143-148, wherein the epitope consists of amino acid residues Gln1 , Asp2, Glu6, and Met? of CD3.

150. The anti-FcRH5 antibody of any one of claims 143-149, wherein the second binding domain is capable of binding to a human CD3 polypeptide or a cyno CD3 polypeptide.

151. The anthFcRH5 antibody of claim 150, wherein the human CD3 polypeptide or the cyno CD3 polypeptide is a human CD3e polypeptide or a cyno CD3E polypeptide, respectively.

152. The anti-FcRH5 antibody of claim 150, wherein the human CD3 polypeptide or the cyno CD3 polypeptide is a human CD3y polypeptide or a cyno CD3y polypeptide, respectively.

153. The anti-FcRH5 antibody of any one of claims 142-152, wherein the second binding domain binds the human CD3e polypeptide with a Ko of about 100 nM or lower.

154. The anti-FcRH5 antibody of claim 153, wherein the second binding domain binds the human CD3e polypeptide with a KD of between about 10 pM to about 100 nM.

155. The anthFcRH5 antibody of claim 154, wherein the second binding domain binds the human CD3e polypeptide with a KD of between about 100 pM to about 50 nM.

156. The anti-FcRH5 antibody of claim 155, wherein the second binding domain binds the human CD3e polypeptide with a KD of between about 1 nM to about 10 nM.

157. The anti-FcRH5 antibody of any one of claims 142-156, wherein the second binding domain comprises the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 117;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 120.

158. The anti-FcRH5 antibody of claim 157, wherein the second binding domain comprises the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123.

159. The anti-FcRH5 antibody of claim 158, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 133; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 134; or (c) a VH domain as in (a) and a VL domain as in (b).

160. The anti-FcRH5 antibody of claim 158 or 159, wherein the second binding domain comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 125;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 126;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 127; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 128.

161. The anthFcRH5 antibody of claim 160, wherein the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 133.

162. The anthFcRH5 antibody of any one of claims 158-161 , wherein the second binding domain further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 129;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 130;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 131 ; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 132.

163. The anti-FcRH5 antibody of claim 162, wherein the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 134.

164. The anti-FcRH5 antibody of any one of claims 158-163, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 134.

165. The anti-FcRH5 antibody of claim 157, wherein the second binding domain comprises the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 124.

166. The anti-FcRH5 antibody of claim 165, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 137; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 138; or (c) a VH domain as in (a) and a VL domain as in (b).

167. The anti-FcRH5 antibody of claim 165 or 166, wherein the second binding domain comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 125;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 126;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 127; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 128.

168. The anthFcRH5 antibody of claim 167, wherein the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 137.

169. The anthFcRH5 antibody of any one of claims 165-168, wherein the second binding domain further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 129;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 130;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 131 ; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 132.

170. The anti-FcRH5 antibody of claim 169, wherein the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 138.

171. The anti-FcRH5 antibody of any one of claims 165-170, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 137 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 138.

172. The anti-FcRH5 antibody of any one of claims 142-156, wherein the second binding domain comprises the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 139;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 140;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 141 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 142;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 143; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 144.

173. The anti-FcRH5 antibody of claim 172, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 153; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 154; or (c) a VH domain as in (a) and a VL domain as in (b).

174. The anti-FcRH5 antibody of claim 172 or 173, wherein the second binding domain comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 145;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 146;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 147; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 148.

175. The anthFcRH5 antibody of claim 174, wherein the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 153.

176. The anthFcRH5 antibody of any one of claims 172-175, wherein the second binding domain further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 149;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 150;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 151 ; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 152.

177. The anti-FcRH5 antibody of claim 176, wherein the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 154.

178. The anti-FcRH5 antibody of any one of claims 172-177, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 153 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 154.

179. The anti-FcRH5 antibody of any one of claims 142-156, wherein the second binding domain comprises the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 155;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 156;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 157;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 158;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 159; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 160.

180. The anti-FcRH5 antibody of claim 179, wherein the second binding domain comprises the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 155;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 162;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 157;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 158;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 159; and (f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 160.

181. The anti-FcRH5 antibody of claim 180, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 172; (b) a VL domain comprising an amino acid sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 173; or (c) a VH domain as in (a) and a VL domain as in (b).

182. The antt-FcRH5 antibody of claim 180 or 181 , wherein the second binding domain comprises the following heavy chain variable region FRs:(a) an FR-H1 comprising the amino acid sequence of SEQ ID NO: 164;(b) an FR-H2 comprising the amino acid sequence of SEQ ID NO: 165;(c) an FR-H3 comprising the amino acid sequence of SEQ ID NO: 166; and(d) an FR-H4 comprising the amino acid sequence of SEQ ID NO: 167.

183. The anti-FcRH5 antibody of claim 182, wherein the second binding domain comprises a VH domain comprising the amino acid sequence of SEQ ID NO: 172.

184. The anti-FcRH5 antibody of any one of claims 180-183, wherein the second binding domain further comprises the following light chain variable region FRs:(a) an FR-L1 comprising the amino acid sequence of SEQ ID NO: 168;(b) an FR-L2 comprising the amino acid sequence of SEQ ID NO: 169;(c) an FR-L3 comprising the amino acid sequence of SEQ ID NO: 170; and(d) an FR-L4 comprising the amino acid sequence of SEQ ID NO: 171.

185. The anti-FcRH5 antibody of claim 184, wherein the second binding domain comprises a VL domain comprising the amino acid sequence of SEQ ID NO: 173.

186. The anti-FcRH5 antibody of any one of claims 180-185, wherein the second binding domain comprises (a) a VH domain comprising an amino acid sequence of SEQ ID NO: 172 and (b) a VL domain comprising an amino acid sequence of SEQ ID NO: 173.

187. The anti-FcRH5 antibody of any one of claims 142-186, wherein the binding domain that binds FcRH5 comprises a VH domain (VH?) comprising a charged region (CR<) and a VL domain (VL<) comprising a charged region (CR2), wherein the CR< in the VH» forms a charge pair with the CR2 in the VL,.

188. The anti-FcRH5 antibody of claim 187, wherein the CRj comprises a basic amino acid residue and the CR2 comprises an acidic amino acid residue.

189. The anti-FcRH5 antibody of claim 188, wherein the CR1 comprises a Q39K substitution mutation (EU numbering).

190. The anti-FcRH5 antibody of claim 189, wherein the CR1 consists of the Q39K substitution mutation.

191. The antt-FcRH5 antibody of any one of claims 187-190, wherein the CR2 comprises a Q38E substitution mutation (EU numbering).

192. The anti-FcRH5 antibody of claim 191 , wherein the CR2 consists of the Q38E substitution mutation.

193. The anti-FcRH5 antibody of any one of claims 187-192, wherein the second binding domain that binds CD3 comprises a VH domain (VH2) comprising a charged region (CR3) and a VL domain (VL2) comprising a charged region (CR*), wherein the CR<in the VL2 forms a charge pair with the CR3 in the VH2.

194. The anti-FcRH5 antibody of claim 193, wherein the CR* comprises a basic amino acid residue and the CR3 comprises an acidic amino acid residue.

195. The anti-FcRH5 antibody of claim 194, wherein the CR< comprises a Q38K substitution mutation (EU numbering).

196. The anti-FcRH5 antibody of claim 195, wherein the CR< consists of the Q38K substitution mutation.

197. The anti-FcRH5 antibody of any one of claims 193-196, wherein the CR3 comprises a Q39E substitution mutation (EU numbering).

198. The anti-FcRH5 antibody of claim 197, wherein the CR3 consists of the Q39E substitution mutation.

199. The anti-FcRH5 antibody of any one of claims 187-198, wherein the VU domain is linked to a light chain constant (CL) domain (CU) and the VH» is linked to a first heavy chain constant (CH1) domain (CH11), wherein the CL< comprises a charged region (CR5) and the CH11 comprises a charged region (CRe), and wherein the CR5 in the CU forms a charge pair with the CRe in the CH11.

200. The anthFcRH5 antibody of claim 199, wherein the CRs comprises a basic amino acid residue and the CRe comprises an acidic residue.

201. The anti-FcRH5 antibody of claim 200, wherein the CR5 comprises a V133K substitution mutation (EU numbering).

202. The anti-FcRH5 antibody of claim 201 , wherein the CR5 consists of the V133K substitution mutation.

203. The antt-FcRH5 antibody of any one of claims 199-202, wherein the CRe comprises a S183E substitution mutation (EU numbering).

204. The anti-FcRH5 antibody of claim 203, wherein the CRe consists of the S183E substitution mutation.

205. The anti-FcRH5 antibody of any one of claims 199-204, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises a charged region (CR7) and the CH12 comprise a charged region (CRe), and wherein the CRe in the CH12 forms a charge pair with the CR7 in the CL2.

206. The anti-FcRH5 antibody of claim 205, wherein the CRe comprises a basic amino acid residue and the CR7 comprises an acidic amino acid residue.

207. The anti-FcRH5 antibody of claim 206, wherein the CR8 comprises a S183K substitution mutation (EU numbering).

208. The anti-FcRH5 antibody of claim 207, wherein the CRe consists of the S183K substitution mutation.

209. The anti-FcRH5 antibody of any one of claims 205-208, wherein the CR7 comprises a V133E substitution mutation (EU numbering).

210. The anti-FcRH5 antibody of claim 209, wherein the CR7 consists of the V133E substitution mutation.

211. The anthFcRH5 antibody of any one of claims 199-204, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein (a) the CL2 comprises one or more mutations at amino acid residues F116, L135, S174, S176, and / or T178 (EU numbering) and (b) the CH12 comprises one or more mutations at amino acid residues A141 , F170, S181 , S183, and / or V185 (EU numbering).

212. The anti-FcRH5 antibody of claim 211 , wherein the CL2 comprises one or more of the following substitution mutations: F116A, L135V, S174A, S176F, and / or T178V.

213. The anti-FcRH5 antibody of claim 212, wherein the CL2 comprises the following substitution mutations: F116A, L135V, S174A, S176F, and T178V.

214. The antt-FcRH5 antibody of any one of claims 211 -213, wherein the CH12 comprises one or more of the following substitution mutations: A141 I, F170S, S181 M, S183A, and / or V185A.

215. The anti-FcRH5 antibody of claim 214, wherein the CH12 comprises the following substitution mutations: A141 I, F170S, S181M, S183A, and V185A.

216. The antt-FcRH5 antibody of any one of claims 142-186, wherein the binding domain that binds FcRH5 comprises a VH domain (VH?) comprising a charged region (CRi) and a VL domain (VU) comprising a charged region (CR2), wherein the CR2 in the VU forms a charge pair with the CR< in the VH,.

217. The anti-FcRH5 antibody of claim 216, wherein the CR2 comprises a basic amino acid residue and the CRt comprises an acidic amino acid residue.

218. The anti-FcRH5 antibody of claim 217, wherein the CR2 comprises a Q38K substitution mutation (EU numbering).

219. The anti-FcRH5 antibody of claim 218, wherein the CR2 consists of the Q38K substitution mutation.

220. The anti-FcRH5 antibody of any one of claims 216-219, wherein the CRt comprises a Q39E substitution mutation (EU numbering).

221. The anti-FcRH5 antibody of claim 220, wherein the CR» consists of the Q39E substitution mutation.

222. The anti-FcRH5 antibody of any one of claims 216-221 , wherein the second binding domain that binds CD3 comprises a VH domain (VH2) comprising a charged region (CR3) and a VL domain (VL2) comprising a charged region (CR4), wherein the CR3 in the VH2 forms a charge pair with the CR* in the VL2.

223. The anti-FcRH5 antibody of claim 222, wherein the CR3 comprises a basic amino acid residue and the CR< comprises an acidic amino acid residue.

224. The anti-FcRH5 antibody of claim 223, wherein the CR3 comprises a Q39K substitution mutation (EU numbering).

225. The anti-FcRH5 antibody of claim 224, wherein the CR3 consists of the Q39K substitution mutation.

226. The anti-FcRH5 antibody of any one of claims 222-225, wherein the CR4 comprises a Q38E substitution mutation (EU numbering).

227. The anti-FcRH5 antibody of claim 225, wherein the CR4 consists of the Q38E substitution mutation.

228. The anti-FcRH5 antibody of any one of claims 216-227, wherein the VL1 domain is linked to a light chain constant (CL) domain (CLt) and the VHt is linked to a first heavy chain constant (CH1) domain (CH11), wherein the CLt comprises a charged region (CR5) and the CH11 comprises a charged region (CRs), and wherein the CR5 in the CH11 forms a charge pair with the CR5 in the CL1.

229. The anti-FcRH5 antibody of claim 228, wherein the CRe comprises a basic amino acid residue and the CRs comprises an acidic amino acid residue.

230. The anti-FcRH5 antibody of claim 229, wherein the CRe comprises a S183K substitution mutation (EU numbering).

231. The anti-FcRH5 antibody of claim 230, wherein the CRe consists of the S183K substitution mutation.

232. The anti-FcRH5 antibody of any one of claims 228-231 , wherein the CRs comprises a V133E substitution mutation (EU numbering).

233. The anti-FcRH5 antibody of claim 232, wherein the CRs consists of the V133E substitution mutation.

234. The anti-FcRH5 antibody of any one of claims 228-233, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein the CL2 comprises a charged region (CR7) and the CH12 comprises a charged region (CRs), and wherein the CR7 in the CU forms a charged pair with the CR8 in the CH12.

235. The anti-FcRH5 antibody of claim 234, wherein the CR7 comprises a basic amino acid residue and the CR8 comprises an acidic residue.

236. The anti-FcRH5 antibody of claim 235, wherein the CR7 comprises a V133K substitution mutation (EU numbering).

237. The anti-FcRH5 antibody of claim 236, wherein the CR7 consists of the V133K substitution mutation.

238. The anti-FcRH5 antibody of any one of claims 234-237, wherein the CR8 comprises a S183E substitution mutation (EU numbering).

239. The anti-FcRH5 antibody of claim 238, wherein the CR8 consists of the S183E substitution mutation.

240. The anti-FcRH5 antibody of any one of claims 228-233, wherein the VL2 domain is linked to a CL domain (CL2) and the VH2 is linked to a CH1 domain (CH12), wherein (a) the CL2 comprises one or more mutations at amino acid residues F116, L135, S174, S176, and / or T178 (EU numbering) and (b) the CH12 comprises one or more mutations at amino acid residues A141 , F170, S181 , S183, and / or V185 (EU numbering).

241. The anti-FcRH5 antibody of claim 240, wherein the CL2 comprises one or more of the following substitution mutations: F116A, L135V, S174A, S176F, and / or T178V.

242. The anti-FcRH5 antibody of claim 241 , wherein the CL2 comprises the following substitution mutations: F116A, L135V, S174A, S176F, and T178V.

243. The anti-FcRH5 antibody of any one of claims 240-242, wherein the CH12 comprises one or more of the following substitution mutations: A141 I, F170S, S181 M, S183A, and / or V185A.

244. The anti-FcRH5 antibody of claim 243, wherein the CH12 comprises the following substitution mutations: A141 I, F170S, S181 M, S183A, and V185A.

245. The anti-FcRH5 antibody of any one of claims 187-244, wherein the anti-FcRH5 antibody comprises one or more heavy chain constant domains, wherein the one or more heavy chain constant domains are selected from a first CH2 domain (CH2»), a first CH3 domain (CH3<), a second CH2 domain (CH22), and a second CH3 domain (CH32).

246. The anti-FcRH5 antibody of claim 245, wherein at least one of the one or more heavy chain constant domains is paired with another heavy chain constant domain.

247. The anti-FcRH5 antibody of claim 246, wherein the CH3» and the CH32 each comprise a protuberance (P1) or a cavity (Ct), and wherein the P< or the C» in the CH3? is positionable in the Ci or the P1, respectively, in the CH32.

248. The anti-FcRH5 antibody of claim 247, wherein the CH3f and the CH32 meet at an interface between the Pi and the Ct .

249. The anti-FcRH5 antibody of any one of claims 245-249, wherein the CH2f and the CH22 each comprise (P2) or a cavity (C2), and wherein the P2 or the C2 in the CH2t is positionable in the C2 or the P2, respectively, in the CH22.

250. The anti-FcRH5 antibody of claim 249, wherein the CH2? and the CH22 meet at an interface between the P2 and the C2.

251. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; andan anti-CD3 arm comprising a second binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; andwherein the anti-FcRH5 arm and the anti-CD3 arm each comprise an N297G substitution mutation (EU numbering); andwherein the anti-FcRH5 arm comprises a T366W substitution mutation and the anti-CD3 arm comprises T366S, L368A, and Y407V substitution mutations.

252. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; andan anti-CD3 arm comprising a second binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; andwherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; andwherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering).

253. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises:(a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and(b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations (EU numbering).

254. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; andan anti-CD3 arm comprising a second binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(0 an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; andwherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering).

255. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises:(a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and(b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations (EU numbering).

256. An anU-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; andan anti-CD3 arm comprising a second binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; andwherein the anti-FcRH5 arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; andwherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).

257. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises: (a) an anti-FcRHS arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRHS arm comprises a light chain comprising Q38E and V133K substitution mutations and a heavy chain comprising Q39K, S183E, and N297G substitution mutations; and(b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38K, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39E, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).

258. An anU-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises an anti-FcRH5 arm comprising a first binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 1 ;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 8;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 9;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 12;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 16; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 23; andan anti-CD3 arm comprising a second binding domain comprising the following six HVRs:(a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 115;(b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 116;(c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 121 ;(d) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 118;(e) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 119; and(f) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 123; andwherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; andwherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L135V, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181M, S183A, V185A, and N297G substitution mutations (EU numbering).

259. An anti-FcRH5 antibody that binds to FcRH5 and CD3, wherein the anti-FcRH5 antibody comprises:(a) an anti-FcRH5 arm comprising a first binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 104 and a VL domain comprising an amino acid sequence of SEQ ID NO: 105, wherein the anti-FcRH5 arm comprises a light chain comprising Q38K and V133E substitution mutations and a heavy chain comprising Q39E, S183K, and N297G substitution mutations; and (b) an anti-CD3 arm comprising a second binding domain comprising a VH domain comprising an amino acid sequence of SEQ ID NO: 133 and a VL domain comprising an amino acid sequence of SEQ ID NO: 134, wherein the anti-CD3 arm comprises a light chain comprising Q38E, F116A, L13SV, S174A, S176F, and T178V substitution mutations and a heavy chain comprising Q39K, A141 I, F170S, S181M, S183A, V18SA, and N297G substitution mutations (EU numbering).

260. The anti-FcRH5 antibody of any one of claims 1-8, 114-164, and 187-259, wherein the anti- FcRH5 antibody has a clearance following intravenous injection of between about 10 ml / kg / day to about 35 ml / kg / day.

261. The anthFcRH5 antibody of claim 260, wherein the anti-FcRH5 antibody has a clearance following intravenous injection of about 10 ml / kg / day to about 20 ml / kg / day in a mouse.

262. The anti-FcRH5 antibody of claim 261 , wherein the anti-FcRH5 antibody has a clearance following intravenous injection of about 12 ml / kg / day to about 16 ml / kg / day in a mouse.

263. The anti-FcRH5 antibody of any one of claims 260-262, wherein the anti-FcRH5 antibody has a clearance following intravenous injection of about 20 ml / kg / day to about 40 ml / kg / day in a cyno.

264. The anti-FcRH5 antibody of claim 263, wherein the anti-FcRH5 antibody has a clearance following intravenous injection of about 25 ml / kg / day to about 35 ml / kg / day in a cyno.

265. The anti-FcRH5 antibody of claim 264, wherein the anti-FcRH5 antibody has a clearance following intravenous injection of about 30 ml / kg / day to about 35 ml / kg / day in a cyno.

266. An isolated nucleic acid encoding the anti-FcRH5 antibody of any one of claims 1 -265, or a portion thereof comprising a binding domain thereof that binds to FcRH5.

267. A vector comprising the isolated nucleic acid of claim 266.

268. A host cell comprising the vector of claim 267.

269. The host cell of claim 268, wherein the host cell is a mammalian cell.

270. The host cell of claim 269, wherein the mammalian cell is a Chinese hamster ovary (CHO) cell.

271. The host cell of claim 268, wherein the host cell is a prokaryotic cell.

272. The host cell of claim 271 , wherein the prokaryotic cell is an E. coli cell.

273. A method of producing the anti-FcRH5 antibody of any one of claims 1-265, the method comprising culturing the host cell of claim 268 in a culture medium.

274. The method of claim 273, wherein the method further comprises recovering the anti-FcRH5 antibody from the host cell or the culture medium.

275. The method of claim 273, further comprising culturing a second host cell comprising a second nucleic acid encoding an anti-CD3 antibody that comprises a binding domain that binds CD3.

276. The method of claim 275, wherein the host cells are co-cultured.

277. The method of claim 275 or 276, wherein the method further comprises recovering the bispecific anti-FcRH5 antibody from the host cells or the culture medium.

278. An immunoconjugate comprising the anti-FcRH5 antibody of any one of claims 1-265 and a cytotoxic agent.

279. A composition comprising the anti-FcRH5 antibody of any one of claims 1-265.

280. The composition of claim 279, further comprising a pharmaceutically acceptable excipient or diluent.

281. The composition of claim 280, wherein the pharmaceutically acceptable excipient is a buffer, carrier, stabilizer, or preservative.

282. The composition of claim 281 , wherein the composition is a pharmaceutical composition.

283. The composition of any one of claims 279-282, wherein the composition further comprises a PD-1 axis binding antagonist or an additional therapeutic agent.

284. The anti-FcRH5 antibody of any one of claims 1-265 for use as a medicament.

285. The anti-FcRH5 antibody of any one of claims 1-265 for use in treating or delaying progression of an FcRHS-positive cancer in a subject in need thereof.

286. The anti-FcRH5 antibody of any one of claims 1-265 for use in enhancing immune function in a subject having an FcRHS-positive cancer.

287. The anti-FcRH5 antibody of claim 285 or 286, wherein the FcRH5-positive cancer is a B cell cancer.

288. The anti-FcRH5 antibody of claim 287, wherein the B cell cancer is selected from the group consisting of multiple myeloma (MM), chronic lymphoid leukemia (CLL), mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), and follicular lymphoma (FL).

289. The anti-FcRH5 antibody of claim 288, wherein the B cell cancer is MM.

290. Use of the anti-FcRH5 antibody of any one of claims 1-265 or the composition of any one of claims 279-283 in the manufacture of a medicament for treating or delaying progression of an FcRH5- positive cancer in a subject.

291. Use of the anti-FcRH5 antibody of any one of claims 1 -265 or the composition of any one of claims 279-283 in the manufacture of a medicament for enhancing immune function in a subject having an FcRH5-positive cancer.

292. The use of claim 290 or 291 , wherein the FcRH5-posrtive cancer is a B cell cancer.

293. The use of claim 292, wherein the B cell cancer is selected from the group consisting of MM, CLL, MCL. DLBCL, and FL.

294. The use of claim 293, wherein the B cell cancer is MM.

295. A method of treating or delaying the progression of an FcRH5-positive cancer in a subject in need thereof, the method comprising administering to the subject the anti-FcRH5 antibody of any one of claims 1-265.

296. A method of enhancing immune function in a subject having an FcRH5-positive cancer, the method comprising administering to the subject an effective amount of the anti-FcRH5 antibody of any one of claims 1-265.

297. The method of claim 295 or 296, wherein the FcRH5-positive cancer is a B cell cancer.

298. The method of claim 297, wherein the B cell cancer is selected from the group consisting of MM, CLL, MCL, DLBCL, and FL.

299. The method of claim 298, wherein the B cell cancer is MM.

300. The method of any one of claims 295-299, wherein the anti-FcRH5 antibody binds to (a) an FcRH5 molecule located on a target cell and (b) a CD3 molecule located on an immune effector cell.

301. The method of claim 300, wherein the anti-FcRH5 antibody activates the immune effector cell following binding to the FcRH5 molecule and the CD3 molecule.

302. The method of claim 301 , wherein the activated immune effector cell is capable of exerting a cytotoxic effect and / or an apoptotic effect on the target cell.

303. The method of any one of claims 300-302, wherein the target cell is a plasma cell.

304. The method of claim 303, wherein the plasma cell is a short-lived plasma cell.

305. The method of claim 303, wherein the plasma cell is a long-lived plasma cell.

306. The method of any one of claims 303-305, wherein the plasma cell is a myeloma cell.

307. The method of any one of claims 295-306, wherein the method comprises administering to the subject the anti-FcRH5 antibody at a dosage of about 0.01 mg / kg / wk to about 50 mg / kg / wk.

308. The method of claim 307, wherein the method comprises administering to the subject the anti- FcRH5 antibody at a dosage of about 0.1 mg / kg / wk to about 10 mg / kg / wk.

309. The method of claim 308, wherein the method comprises administering to the subject the anti- FcRH5 antibody at a dosage of about 1 mg / kg / wk.

310. The method of any one of claims 295-309, further comprising administering to the subject a PD- 1 axis binding antagonist and / or an additional therapeutic agent.

311. The method of claim 310, wherein the PD-1 axis binding antagonist or additional therapeutic agent is administered prior to or subsequent to the administration of the anti-FcRH5 antibody.

312. The method of claim 311 , wherein the PD-1 axis binding antagonist or additional therapeutic agent is administered concurrently with the anti-FcRH5 antibody.

313. The method of any one of claims 310-312, wherein the PD-1 axis binding antagonist is selected from the group consisting of a PD-L1 binding antagonist, a PD-1 binding antagonist, and a PD-L2 binding antagonist.

314. The method of claim 313, wherein the PD-1 axis binding antagonist is a PD-L1 binding antagonist.

315. The method of claim 314, wherein the PD-L1 binding antagonist is selected from the group consisting of MPDL3280A (atezolizumab), YW243.55.S70, MDX-1105, MEDI4736 (durvalumab), and MSB0010718C (avelumab).

316. The method of claim 315, wherein the PD-L1 binding antagonist is MPDL3280A (atezolizumab).

317. The method of claim 313, wherein the PD-1 axis binding antagonist is a PD-1 binding antagonist.

318. The method of claim 317, wherein the PD-1 binding antagonist is selected from the group consisting of MDX 1106 (nivolumab), MK-3475 (pembrolizumab), CT-011 (pidilizumab), MEDI-0680 (AMP-514), PDR001 , REGN2810, and BGB-108.

319. The method of claim 313, wherein the PD-1 axis binding antagonist is a PD-L2 binding antagonist.

320. The method of claim 319, wherein the PD-L2 binding antagonist is an antibody or an immunoadhesin.

321. The method of any one of claims 295-320, further comprising administering to the subject a steroid, an immunomodulator (IMiD), a proteosome inhibitor (PI), or a combination thereof.

322. The method of claim 321 , wherein the steroid is a glucocorticoid.

323. The method of claim 322, wherein the glucocorticoid is dexamethasone.

324. The method of claim 321 , wherein the IMiD is lenalidomide.

325. The method of claim 321 , wherein the PI is bortezomib.

326. The method of any one of claims 295-325, wherein the method comprises administering the anti-FcRH5 antibody, PD-1 axis binding antagonist, steroid, IMiD, PI, or combination thereofintravenously, subcutaneously, intramuscularly, topically, orally, transdermally, intraperitoneally, intraorbitally, by implantation, by inhalation, intrathecally, intraventriculariy, or intranasally.

327. The method of claim 326, wherein the method comprises administering the anti-FcRH5 antibody, PD-1 axis binding antagonist, steroid, IMiD, PI, or combination thereof intravenously.

328. The method of claim 326, wherein the method comprises administering the anti-FcRH5 antibody, PD-1 axis binding antagonist, steroid, IMiD, PI, or combination thereof subcutaneously.

329. The method of any one of claims 295-328, wherein the subject is a human.

330. A method for detecting FcRH5 in a biological sample from a subject, wherein the method comprises:(a) contacting the biological sample with the anti-FcRH5 antibody of any one of claims 1-265 under conditions permissive for binding of the anti-FcRH5 antibody to a naturally occurring FcRH5 in the biological sample, and(b) detecting whether a complex is formed between the anti-FcRH5 antibody and a naturally occurring FcRH5 in the biological sample.

331. The method of claim 330, wherein the biological sample is a blood sample.

332. The method of claim 330 or 331 , wherein the subject is a human.

333. A kit comprising the antibody of any one of claims 1-265 and a package insert comprising instructions for using the antibody for treating or delaying progression of an FcRH5-positive cancer in a subject.

334. A kit comprising the antibody of any one of claims 1-265 and a package insert comprising instructions for using the antibody for enhancing immune function in a subject having an FcRH5-positive cancer.

335. The kit of claim 333 or 334, wherein the subject is a human.