Anti-mertk antibodies and methods of use thereof

Abstract

To provide an anti-MerTK antibodies having optimal binding characteristics (e.g., on and off rates) as well as desired biological effects, as an optimal therapy for treating, stabilizing, preventing, and / or delaying development of cancers.SOLUTION: Provided is an isolated antibody that binds to MerTK, the antibody reducing MerTK-mediated clearance of apoptotic cells.SELECTED DRAWING: Figure 21D

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Application No. 62 / 836,580, filed April 19, 2019, and No. 62 / 890,858, filed August 23, 2019, each of which is incorporated by reference in its entirety herein.

[0002] Submitting a sequence listing as an ASCII text file The contents of the following submission, an ASCII text file, are incorporated herein by reference in their entirety: Sequence Listing Computer Readable Form (CRF) (Filename: 146392047940SEQLIST.TXT, Recorded on: March 30, 2020, Size: 136KB).

[0003] The present disclosure relates to anti-MerTK antibodies and methods of use thereof. [Background technology]

[0004] Currently, most cancer immuno-oncology (IO) therapies focus on modulating the activity of T cells, the adaptive arm of the immune system, by blocking inhibitory pathways that function as immunological checkpoints. However, long-lasting responses elicited by these therapies are limited to a subpopulation of cancer patients. The relatively low response rates are caused by various immunosuppressive mechanisms in the tumor microenvironment. The innate immune system is an integral part of an effective immune response. Innate immune cells play a key role in the initiation and subsequent direction of the adaptive immune response. Targeting the innate immune system may complement adaptive immune oncology therapies (Mullard, A., Nat. Rev. Drug Discov., 17:3-5 (2018)).

[0005] Macrophages of the innate immune system are abundant in various types of solid tumors, which may contribute to the relatively low response rates to T cell-based therapy. They are versatile cells that can perform a variety of functions, including phagocytosis. Macrophages are professional phagocytes that are highly specialized in the removal of dying or dead cells and cellular debris. It is estimated that billions of cells die every day in the human body. However, due to the rapid and efficient clearance by phagocytes, it is rare to find apoptotic cells in tissues under normal physiological conditions. In homeostasis, apoptotic cells are removed at the early stage of cell death before the loss of plasma membrane integrity. Thus, in general, apoptosis is immunologically silent. In solid tumors, uncontrolled tumor growth is often accompanied by increased cell death due to hypoxia and metabolic stress. To evade immune surveillance, tumors exploit the non-immunogenic nature of apoptosis. Tumor-associated macrophages (TAMs) actively remove dying tumor cells to evade the vigilance of the immune system.

[0006] MerTK has been shown to play a role in the clearance of apoptotic cells. Therefore, reducing MerTK-mediated clearance of apoptotic cells using MerTK inhibitors is an attractive therapeutic approach in the treatment of cancer. Existing anti-MerTK antibodies have been described, but may not be suitable for therapeutic development. For example, White et al. (''MERTK-Specific Antibodies That Have Therapeutic Antitumor Activity in Mice Disrupt the Integrity of the Retinal Pigmented Epithelium in Cynomolgus Monkeys,'' presented at the American Association for Cancer Research Annual Meeting; March 31, 2019; Atlanta, GA) reported the success of two anti-MerTK antibodies, one that binds human MerTK with higher affinity (8.7 × 10 -11M;SRF1), and binds to human MerTK with lower affinity (4.4 × 10 9 ) that cross-react with mouse MerTK (SRF2). These antibodies were shown to inhibit various MerTK functions and to inhibit tumor growth in combination with an anti-PD-L1 antibody in mouse models. However, both antibodies were found to promote retinal toxicity in cynomolgus monkeys. Thus, neither antibody is acceptable as a therapeutic candidate. These findings highlight the importance of examining multiple factors, rather than simply antibody affinity, in developing effective therapeutic candidates with an acceptable safety profile.

[0007] There remains a need for optimal therapies to treat, stabilize, prevent, and / or delay the onset of various cancers, and in particular, there is a need for anti-MerTK antibodies that have optimal binding characteristics (e.g., on and off rates) and desired biological effects.

[0008] All references cited herein, including patent applications, patent publications, and UniProtKB / Swiss-Prot accession numbers, are hereby incorporated by reference in their entirety as if each individual reference was specifically and individually indicated to be incorporated by reference. Summary of the Invention

[0009] Described herein are anti-MerTK antibodies and methods of use thereof that fulfill the need for optimized therapies for treating, stabilizing, preventing and / or delaying the onset of various cancers.

[0010] In one aspect, the disclosure provides an isolated antibody that binds to MerTK, and reduces MerTK-mediated clearance of apoptotic cells. In some embodiments, the antibody reduces MerTK-mediated clearance of apoptotic cells by phagocytes. In some embodiments, the phagocytes are macrophages. In an exemplary embodiment, the macrophages are tumor-associated macrophages. In some embodiments, the clearance of apoptotic cells is reduced as measured in an apoptotic cell clearance assay at room temperature.

[0011] In some embodiments, the anti-MerTK antibodies of the present disclosure reduce ligand-mediated MerTK signaling, hi some embodiments, the antibodies induce a pro-inflammatory response, including but not limited to a type I IFN response.

[0012] In some embodiments, the anti-MerTK antibody of the present disclosure is a monoclonal antibody. In some embodiments, the antibody is a human antibody, a humanized antibody, or a chimeric antibody. In some embodiments, the antibody is an antibody fragment that binds to an antigen. In some embodiments, the antibody binds to a fibronectin-like domain or an immunoglobulin-like domain of MerTK.

[0013] In an exemplary embodiment, an anti-MerTK antibody of the present disclosure binds to the fibronectin-like domain of MerTK.

[0014] In one aspect, the disclosure provides an anti-MerTK antibody that binds to a fibronectin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 6. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 1; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 2; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 3. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 83; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 65; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 83. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 65. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 83 and a VL comprising the amino acid sequence of SEQ ID NO: 65.

[0015] In one aspect, the disclosure provides an anti-MerTK antibody that binds to a fibronectin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 84; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 66; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 84. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 66. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 84 and a VL comprising the amino acid sequence of SEQ ID NO: 66.

[0016] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 85, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 67, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 85. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 67. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 85 and a VL comprising the amino acid sequence of SEQ ID NO: 67.

[0017] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 102. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:110.

[0018] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 86, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 68, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 86. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 68. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 86 and a VL comprising the amino acid sequence of SEQ ID NO: 68.

[0019] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 103. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:111.

[0020] In one aspect, the disclosure provides an anti-MerTK antibody that binds to a fibronectin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 87; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 69; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 87. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 69. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 87 and a VL comprising the amino acid sequence of SEQ ID NO: 69.

[0021] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 88, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 70, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 88. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 70. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 88 and a VL comprising the amino acid sequence of SEQ ID NO: 70.

[0022] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 104. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:112.

[0023] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 89, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 70, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 89. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 70. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 89 and a VL comprising the amino acid sequence of SEQ ID NO: 70.

[0024] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 105. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:113.

[0025] In one aspect, the disclosure provides an anti-MerTK antibody that binds to a fibronectin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 90; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 71; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 90. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 71. In some embodiments, the antibody comprises the amino acid sequence of SEQ ID NO: 90 and a VL comprising the amino acid sequence of SEQ ID NO: 71.

[0026] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO:91, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO:72, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO:91. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO:72. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO:91 and a VL comprising the amino acid sequence of SEQ ID NO:72.

[0027] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 106. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:114.

[0028] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 92, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 73, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 92. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 73. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 92 and a VL comprising the amino acid sequence of SEQ ID NO: 73.

[0029] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 107. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:115.

[0030] In one aspect, the disclosure provides an anti-MerTK antibody that binds to a fibronectin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 29. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 26. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 93; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 74; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 93. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 74. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 93 and a VL comprising the amino acid sequence of SEQ ID NO: 74.

[0031] In one aspect, the disclosure provides an anti-MerTK antibody that binds to a fibronectin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 35. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 32. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 94; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 75; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 94. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 75. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 94 and a VL comprising the amino acid sequence of SEQ ID NO: 75.

[0032] In an exemplary embodiment, an anti-MerTK antibody of the present disclosure binds to an immunoglobulin-like domain of MerTK.

[0033] In one aspect, the disclosure provides an anti-MerTK antibody that binds to an immunoglobulin-like domain of MerTK, the anti-MerTK antibody comprising: (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; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 95; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 76; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 95. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 76. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 95 and a VL comprising the amino acid sequence of SEQ ID NO: 76.

[0034] In one aspect, the disclosure provides an anti-MerTK antibody that binds to an immunoglobulin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 46. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 96; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 77; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 96. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 77. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 96 and a VL comprising the amino acid sequence of SEQ ID NO: 77.

[0035] In one aspect, the disclosure provides an anti-MerTK antibody that binds to an immunoglobulin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 97; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 78; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 97. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 78. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 97 and a VL comprising the amino acid sequence of SEQ ID NO: 78.

[0036] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 98, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 79, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 98. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 79. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 98 and a VL comprising the amino acid sequence of SEQ ID NO: 79.

[0037] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 108. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:116.

[0038] In some embodiments, the antibody comprises (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 99, (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 80, or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 99. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 80. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 99 and a VL comprising the amino acid sequence of SEQ ID NO: 80.

[0039] In some embodiments, the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO: 109. In some embodiments, the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:117.

[0040] In one aspect, the disclosure provides an anti-MerTK antibody that binds to an immunoglobulin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 56; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 57; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 58. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 55. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 100; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 81; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 100. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 81. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 100 and a VL comprising the amino acid sequence of SEQ ID NO: 81.

[0041] In one aspect, the disclosure provides an anti-MerTK antibody that binds to an immunoglobulin-like domain of MerTK, the anti-MerTK antibody comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO: 64. In some embodiments, the antibody further comprises: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO: 61. In some embodiments, the antibody comprises: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 101; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 82; or (c) a VH such as (a) and a VL such as (b). In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 101. In some embodiments, the antibody comprises a VL comprising the amino acid sequence of SEQ ID NO: 82. In some embodiments, the antibody comprises a VH comprising the amino acid sequence of SEQ ID NO: 101 and a VL comprising the amino acid sequence of SEQ ID NO: 82.

[0042] In some embodiments, the anti-MerTK antibody of the disclosure is a full-length IgG1, IgG2, IgG3 or IgG4 antibody. In certain embodiments, the antibody is a full-length IgG1 antibody. In certain embodiments, the antibody comprises a LALAPG mutation. In some embodiments, the antibody comprises Q2 and L4 residues in the light chain variable region and I48, G49 and K71 residues in the heavy chain variable region. In some embodiments, the antibody comprises L4 and F87 in the light chain variable region and V24, I48, G49 and K71 in the heavy chain variable region. In some embodiments, the antibody comprises L4 and P43 in the light chain variable region and K71 in the heavy chain variable region. In some embodiments, the antibody comprises G49 and V78 residues in the heavy chain variable region.

[0043] In certain embodiments, the anti-MerTK antibodies provided herein bind to human MerTK with a dissociation constant (Kd) of ≦100 nM at 25° C. In certain embodiments, the anti-MerTK antibodies provided herein bind to cynomolgus monkey MerTK with a dissociation constant (Kd) of ≦100 nM at 25° C. In certain embodiments, the anti-MerTK antibodies provided herein bind to mouse MerTK with a dissociation constant (Kd) of ≦10 nM at 25° C. In certain embodiments, the anti-MerTK antibodies provided herein bind to rat MerTK with a dissociation constant (Kd) of ≦10 nM at 25° C. In certain embodiments, the anti-MerTK antibodies provided herein bind to human MerTK with a dissociation constant (Kd) of ≦10 nM, ≦5 nM, or ≦2 nM at 25° C.

[0044] In one aspect, the disclosure provides an isolated antibody that competes with a reference antibody for binding to MerTK. Such reference antibodies include an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 83 and a VL comprising the amino acid sequence of SEQ ID NO: 65; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 84 and a VL comprising the amino acid sequence of SEQ ID NO: 66; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 85 and a VL comprising the amino acid sequence of SEQ ID NO: 67; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 86 and a VL comprising the amino acid sequence of SEQ ID NO: 68; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 87 and a VL comprising the amino acid sequence of SEQ ID NO: 69; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 88 and a VL comprising the amino acid sequence of SEQ ID NO: 70; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 89 and a VL comprising the amino acid sequence of SEQ ID NO: 70; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 90 and a VL comprising the amino acid sequence of SEQ ID NO: 71; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 91 and a VL comprising the amino acid sequence of SEQ ID NO: 72; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 92 and a VL comprising the amino acid sequence of SEQ ID NO: 93; Examples of the antibody include an antibody comprising a VL comprising the amino acid sequence of SEQ ID NO: 73; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 93 and a VL comprising the amino acid sequence of SEQ ID NO: 74; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 94 and a VL comprising the amino acid sequence of SEQ ID NO: 75; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 95 and a VL comprising the amino acid sequence of SEQ ID NO: 76; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 96 and a VL comprising the amino acid sequence of SEQ ID NO: 77; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 97 and a VL comprising the amino acid sequence of SEQ ID NO: 78; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 98 and a VL comprising the amino acid sequence of SEQ ID NO: 79; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 99 and a VL comprising the amino acid sequence of SEQ ID NO: 80; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 100 and a VL comprising the amino acid sequence of SEQ ID NO: 81; and an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 101 and a VL comprising the amino acid sequence of SEQ ID NO: 82. In some embodiments, the isolated antibody binds to human MerTK. In some embodiments, the reference antibody is Y323.

[0045] In one aspect, the disclosure provides an isolated antibody that competes for binding to the same epitope on MerTK as a reference antibody. Such reference antibodies include an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 83 and a VL comprising the amino acid sequence of SEQ ID NO: 65; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 84 and a VL comprising the amino acid sequence of SEQ ID NO: 66; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 85 and a VL comprising the amino acid sequence of SEQ ID NO: 67; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 86 and a VL comprising the amino acid sequence of SEQ ID NO: 68; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 87 and a VL comprising the amino acid sequence of SEQ ID NO: 69; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 88 and a VL comprising the amino acid sequence of SEQ ID NO: 70; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 89 and a VL comprising the amino acid sequence of SEQ ID NO: 70; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 90 and a VL comprising the amino acid sequence of SEQ ID NO: 71; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 91 and a VL comprising the amino acid sequence of SEQ ID NO: 72; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 92 and a VL comprising the amino acid sequence of SEQ ID NO: 93; Examples of the antibody include an antibody comprising a VL comprising the amino acid sequence of SEQ ID NO: 73; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 93 and a VL comprising the amino acid sequence of SEQ ID NO: 74; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 94 and a VL comprising the amino acid sequence of SEQ ID NO: 75; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 95 and a VL comprising the amino acid sequence of SEQ ID NO: 76; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 96 and a VL comprising the amino acid sequence of SEQ ID NO: 77; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 97 and a VL comprising the amino acid sequence of SEQ ID NO: 78; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 98 and a VL comprising the amino acid sequence of SEQ ID NO: 79; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 99 and a VL comprising the amino acid sequence of SEQ ID NO: 80; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 100 and a VL comprising the amino acid sequence of SEQ ID NO: 81; and an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 101 and a VL comprising the amino acid sequence of SEQ ID NO: 82. In some embodiments, the isolated antibody binds to human MerTK. In some embodiments, the reference antibody is Y323.

[0046] In one aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 102 and a light chain comprising the amino acid sequence of SEQ ID NO: 110. In one aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 103 and a light chain comprising the amino acid sequence of SEQ ID NO: 111. In one aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 104 and a light chain comprising the amino acid sequence of SEQ ID NO: 112. In another aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 105 and a light chain comprising the amino acid sequence of SEQ ID NO: 113. In one aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 106 and a light chain comprising the amino acid sequence of SEQ ID NO: 114. In one aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 107 and a light chain comprising the amino acid sequence of SEQ ID NO: 115. In another aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 108 and a light chain comprising the amino acid sequence of SEQ ID NO: 116. In yet another aspect, the disclosure provides an isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO: 109 and a light chain comprising the amino acid sequence of SEQ ID NO: 117.

[0047] In some embodiments, the anti-MerTK antibodies of the present disclosure reduce MerTK-mediated clearance of apoptotic cells. In specific embodiments, the anti-MerTK antibodies reduce MerTK-mediated clearance of apoptotic cells by phagocytes. In certain embodiments, the phagocytes are macrophages. In specific embodiments, the macrophages are tumor-associated macrophages. In some embodiments, the clearance of apoptotic cells is reduced as measured by an apoptotic cell clearance assay at room temperature. In some embodiments, the anti-MerTK antibodies of the present disclosure increase circulating tumor DNA (ctDNA) in blood or plasma. In some embodiments, the anti-MerTK antibodies of the present disclosure increase cell-free DNA (cfDNA) in blood or plasma.

[0048] In some embodiments, the anti-MerTK of the present disclosure is a monoclonal antibody. In certain embodiments, the anti-MerTK antibody is a humanized or chimeric antibody. In certain embodiments, the anti-MerTK antibody is a human, humanized, or chimeric antibody. In certain embodiments, the anti-MerTK antibody is an antibody fragment that binds MerTK. In certain embodiments, the anti-MerTK antibody binds to the fibronectin-like domain or the immunoglobulin-like domain of MerTK. In certain embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK. In certain embodiments, the anti-MerTK antibody binds to the immunoglobulin-like domain of MerTK.

[0049] In one aspect, the disclosure provides an isolated nucleic acid encoding any of the anti-MerTK antibodies described herein. In another aspect, the disclosure provides a vector comprising a nucleic acid encoding any of the anti-MerTK antibodies described herein. In yet a further aspect, the disclosure provides a host cell comprising a vector suitable for expression of a nucleic acid encoding any of the anti-MerTK antibodies described herein.

[0050] Further provided herein is a method of producing an anti-MerTK antibody of the disclosure, comprising culturing a host cell comprising nucleic acid encoding the anti-MerTK antibody under conditions suitable for expression of the antibody, in some embodiments, the method further comprises recovering the anti-MerTK antibody from the cell culture.

[0051] In one aspect, the disclosure relates to an immunoconjugate comprising an anti-MerTK antibody provided herein conjugated to a cytotoxic agent. In another aspect, the disclosure relates to a pharmaceutical formulation comprising any of the anti-MerTK antibodies described above and a pharma- ceutically acceptable carrier. In another aspect, the disclosure relates to a pharmaceutical formulation comprising any of the anti-MerTK immunoconjugates described above and a pharma- ceutically acceptable carrier.

[0052] In one aspect, the disclosure provides an anti-MerTK antibody or immunoconjugate as described above for use as a medicament. In some embodiments, the use is in the treatment of cancer. In some embodiments, the use is in reducing MerTK-mediated clearance of apoptotic cells.

[0053] Further provided herein is the use of the above anti-MerTK antibody or immunoconjugate in the manufacture of a medicament. In some embodiments, the medicament is for the treatment of cancer. In some embodiments, the cancer expresses a functional STING polypeptide, a functional Cx43 polypeptide, and a functional cGAS polypeptide. In some embodiments, the cancer comprises a tumor-associated macrophage that expresses a functional STING polypeptide. In some embodiments, the cancer comprises a tumor cell that expresses a functional cGAS polypeptide. In some embodiments, the cancer comprises a tumor cell that expresses a functional Cx43 polypeptide. In certain embodiments, the cancer is colon cancer. In some embodiments, the medicament is for reducing MerTK-mediated clearance of apoptotic cells.

[0054] In some embodiments, the use may further comprise administration of an additional treatment or an effective amount of an additional therapeutic agent. In some embodiments, the additional treatment is selected from one or more of tamoxifen, letrozole, exemestane, anastrozole, irinotecan, cetuximab, fulvestrant, vinorelbine, erlotinib, bevacizumab, vincristine, imatinib mesylate, sorafenib, lapatinib, trastuzumab, cisplatin, gemcitabine, methotrexate, vinblastine, carboplatin, paclitaxel, 5-fluorouracil, doxorubicin, bortezomib, melphalan, prednisone, and docetaxel. In some embodiments, the additional therapeutic agent is an immune checkpoint inhibitor. In some embodiments, the immune checkpoint inhibitor is selected from one or more of a cytotoxic T-lymphocyte-associated protein 4 (CTLA4) inhibitor, a programmed cell death protein 1 (PD-1) binding antagonist, or a programmed death ligand 1 (PDL1) binding antagonist. In some embodiments, the immune checkpoint inhibitor is a PDL1 binding antagonist. In an exemplary embodiment, the PDL1 binding antagonist is an anti-PDL1 antibody. In some such embodiments, the anti-PDL1 antibody is atezolizumab. In some embodiments, the medicament is further used in combination with an effective amount of a chemotherapeutic agent.

[0055] In another aspect, provided herein is a method for treating or delaying the progression of cancer in an individual, comprising administering to the individual an effective amount of an anti-MerTK antibody or immunoconjugate thereof described in this disclosure. In some embodiments, the cancer expresses a functional STING polypeptide, a functional Cx43 polypeptide, and a functional cGAS polypeptide. In some embodiments, the cancer comprises tumor-associated macrophages that express a functional STING polypeptide. In some embodiments, the cancer comprises tumor cells that express a functional cGAS polypeptide. In some embodiments, the cancer comprises tumor cells that express a functional Cx43 polypeptide. In certain embodiments, the cancer is colon cancer.

[0056] In some embodiments, the method may further comprise administering an additional treatment or an effective amount of an additional therapeutic agent, hi some embodiments, the additional treatment is selected from one or more of tamoxifen, letrozole, exemestane, anastrozole, irinotecan, cetuximab, fulvestrant, vinorelbine, erlotinib, bevacizumab, vincristine, imatinib mesylate, sorafenib, lapatinib, trastuzumab, cisplatin, gemcitabine, methotrexate, vinblastine, carboplatin, paclitaxel, 5-fluorouracil, doxorubicin, bortezomib, melphalan, prednisone, and docetaxel.

[0057] In some embodiments, the additional therapeutic agent is an immune checkpoint inhibitor. In some embodiments, the immune checkpoint inhibitor is selected from one or more of a cytotoxic T-lymphocyte-associated protein 4 (CTLA4) inhibitor, a programmed cell death protein 1 (PD-1) binding antagonist, or a programmed death ligand 1 (PDL1) binding antagonist. In some embodiments, the immune checkpoint inhibitor is a PDL1 binding antagonist. In an exemplary embodiment, the PDL1 binding antagonist is an anti-PDL1 antibody. In some such embodiments, the anti-PDL1 antibody is atezolizumab. In some embodiments, the method may further comprise administering to the individual an effective amount of an additional chemotherapeutic agent.

[0058] In another aspect, provided herein is a method of reducing MerTK-mediated clearance of apoptotic cells in an individual, comprising administering to the individual an effective amount of an anti-MerTK antibody or immunoconjugate thereof described herein to reduce MerTK-mediated clearance of apoptotic cells. In some embodiments, clearance of apoptotic cells is reduced by about 1-10, 1-8, 1-5, 1-4, 1-3, 1-2, 2-10, 2-8, 2-5, 2-4, 2-3, 3-10, 3-8, 3-5, or 3-4 fold, or by about 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10, 3.12, 3.14, 3.16, 3.18, 3.19, 3.20, 3.21, 3.22, 3.23, 3.24, 3.25, 3.26, 3.27, 3.28, 3.29, 3.33, 3.34, 3.35, 3.36, 3.37, 3.38, 3.39, 3.40, 3.41, 3.42, 3.43, 3.44, 3.45, 3.46, 3.47, 3.48, 3.49, 4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9 or 8.0 times reduced.

[0059] It is to be understood that one, some, or all of the characteristics of the various embodiments described herein may be combined to form other embodiments of the present disclosure. These and other aspects of the present disclosure will be apparent to those skilled in the art. These and other embodiments of the present disclosure are further described in the following detailed description. [Brief description of the drawings]

[0060] [Figure 1A-1B]The light and heavy chain variable regions of each MerTK-specific antibody generated in rabbits were amplified by PCR and cloned into an expression vector for purification and sequencing. The amino acid sequences of the light chain variable region (FIG. 1A) and the heavy chain variable region (FIG. 1B) were aligned. The residue numbers referred to are consistent with the sequences defined in Kabat et al., and the CDR sequences are underlined. The sequence numbers are as follows: Rbt8F4 (SEQ ID NO: 65), Rbt9E3.FN (SEQ ID NO: 66), Rbt10C3 (SEQ ID NO: 69), Rbt10F7 (SEQ ID NO: 71), Rbt11G11 (SEQ ID NO: 76), Rbt12H4 (SEQ ID NO: 77), Rbt13B4 (SEQ ID NO: 78), Rbt13D8 (SEQ ID NO: 74), Rbt14C9 (SEQ ID NO: 81), Rbt18G7 (SEQ ID NO: 82), and Rbt22C4 (SEQ ID NO: 75). The sequence numbers in Figure 1B are as follows: Rbt8F4 (SEQ ID NO: 83), Rbt9E3.FN (SEQ ID NO: 84), Rbt10C3 (SEQ ID NO: 87), Rbt10F7 (SEQ ID NO: 90), Rbt11G11 (SEQ ID NO: 95), Rbt12H4 (SEQ ID NO: 96), Rbt13B4 (SEQ ID NO: 97), Rbt13D8 (SEQ ID NO: 93), Rbt14C9 (SEQ ID NO: 100), Rbt18G7 (SEQ ID NO: 101), and Rbt22C4 (SEQ ID NO: 94).

[0061] [Figures 2A-2D]Antibodies 10F7, 9E3, 13B4 and 10C3 were selected for humanization. The amino acid sequences of the light and heavy chain variable regions of antibody 10F7 before humanization, after phase 1 humanization (.v1) and after phase 2 humanization (.v16) were aligned (Figure 2A). The amino acid sequences of the light and heavy chain variable regions of antibody 9E3 before humanization, after phase 1 humanization (.v1) and after phase 2 humanization (.v16) were aligned (Figure 2B). The amino acid sequences of the light and heavy chain variable regions of antibody 13B4 before humanization, after phase 1 humanization (.v1) and after phase 2 humanization (.v16) were aligned (Figure 2C). The amino acid sequences of the light and heavy chain variable regions of antibody 10C3 before humanization, after phase 1 humanization (.v1) and after phase 2 humanization (.v14) were aligned (Figure 2D). Residue numbers referenced correspond to the sequences defined in Kabat et al., and CDR sequences are underlined. The sequence numbers of the light chain sequences are as follows: Rbt10F7 (SEQ ID NO: 71), h10F7.v1 (SEQ ID NO: 72), h10F7.v16 (SEQ ID NO: 73), Rbt9E3.FN (SEQ ID NO: 66), h9E3.FN.v1 (SEQ ID NO: 67), h9E3.FN.v16 (SEQ ID NO: 68), Rbt13B4 (SEQ ID NO: 78), h13B4.v1 (SEQ ID NO: 79), h13B4.v16 (SEQ ID NO: 80), Rbt10C3 (SEQ ID NO: 69), h10C3.v1, and h10C3.v14 (SEQ ID NO: 70). Overlap of Figures 2A-2D The sequence numbers of the strand sequences are as follows: Rbt10F7 (SEQ ID NO:90), h10F7.v1 (SEQ ID NO:91), h10F7.v16 (SEQ ID NO:92), Rbt9E3.FN (SEQ ID NO:84), h9E3.FN.v1 (SEQ ID NO:85), h9E3.FN.v16 (SEQ ID NO:86), Rbt13B4 (SEQ ID NO:97), h13B4.v1 (SEQ ID NO:98), h13B4.v16 (SEQ ID NO:99), Rbt10C3 (SEQ ID NO:87), h10C3.v1 (SEQ ID NO:88), and h10C3.v14 (SEQ ID NO:89).

[0062] [Diagram 3]Epitope binning was used to determine the epitope domain specificity of each anti-MerTK antibody. Antibodies 8F4, 22C4, and 13D8 raised against mouse MerTK and antibodies 10C3, 9E3.FN, 10F7, 22C4, 8F4, and 13D8 raised against human MerTK competed with each other for binding. Antibodies 12H4, 18G7, 14C9, and 11G11 raised against mouse MerTK and antibodies 13B4, 12H4, 18G7, and 11G11 raised against human MerTK competed with each other. As further described in the Examples below, antibodies 10C3, 9E3.FN, 10F7, 22C4, 8F4 and 13D8 bind to the fibronectin-like domain of MerTK, and antibodies 13B4, 12H4, 18G7 and 11G11 bind to the Ig-like domain of MerTK.

[0063] [Figure 4A-4E] To evaluate the in vitro phagocytosis inhibitory activity of anti-MerTK antibodies, an efferocytosis assay was performed. Anti-MerTK antibodies inhibited the phagocytic activity of human macrophages isolated from three different donors (Figure 4A-4C). Anti-MerTK antibody h13B4.v16 (13B4 fully humanized), an Ig domain binding antibody, was 5.2-fold more potent in inhibiting human macrophage phagocytosis compared to anti-MerTK antibody h10F7.v16 (10F7 fully humanized), a fibronectin domain binding antibody (Figure 4D). Anti-MerTK antibody 14C9 mIgG2a LALAPG was 4.8-fold more potent in inhibiting mouse macrophage phagocytosis compared to anti-MerTK antibody h10F7.v16 (10F7 fully humanized) (Figure 4E).

[0064] [Figure 5A-5C]An apoptotic cell clearance assay was performed to evaluate the in vivo activity of anti-MerTK antibodies. Apoptotic cells accumulated 8 hours after Dex treatment and were mostly gone by 24 hours (Figure 5A). 24 hours after Dex treatment, anti-MerTK (clone 14C9, mIgG2a, LALAPG) but not the control antibody anti-gp120 (mIgG2a, LALAPG) blocked the clearance of apoptotic cells in the thymus (Figure 5B). Anti-MerTK antibodies blocked the clearance of apoptotic cells compared to the anti-gp120 control (Figure 5C).

[0065] [Figures 6A-6D] To determine whether anti-MerTK antibodies affect tumor growth, a tumor efficacy study was performed in the MC-38 syngeneic tumor model. Changes in individual tumor size (Figures 6A and 6B; each line represents a single tumor) and mean tumor size (Figures 6C and 6D) were measured over time for each treatment group. In the tumor volume tracking plots, the gray lines represent tumor sizes for animals that were still in the study at the time of data collection (Figures 6A and 6B). The red lines represent animals with ulcerated or advanced tumors that were euthanized and removed from the study (Figures 6A and 6B). The red horizontal dashed line indicates the doubling of tumor volume from the start of treatment, and the green horizontal dashed line represents the minimum measurable tumor volume (Figures 6A and 6B). Animals with tumors in the area below the green dashed line were considered to have a complete response. The combination of anti-gp120 and anti-PDL1 antibody treatment did not significantly inhibit tumor growth. However, combined treatment with anti-PDL1 and anti-MerTK antibodies demonstrated enhanced anti-tumor activity (Figures 6A-6D).

[0066] [Figure 7A-7C]Schematic diagram of blockade of MerTK-dependent efferocytosis by anti-MerTK antibody (Figure 7A). To evaluate the phagocytosis inhibitory effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment, an in vitro efferocytosis assay was performed. Peritoneal macrophages treated with anti-MerTK 14C9 (mIgG2a LALAPG) antibody (green) showed approximately 8-fold less phagocytic clearance of apoptotic thymocytes (red) compared to macrophages treated with the control antibody anti-gp120 (mIgG2a LALAPG) (black) (Figure 7B). An in vivo apoptotic cell clearance assay was performed to determine the effect of anti-MerTK treatment on the clearance of apoptotic cells in the thymus. Twenty-four hours after induction of thymocyte apoptosis with dexamethasone (Dex), mice treated with anti-MerTK 14C9 (mIgG2a LALAPG) antibody accumulated approximately six-fold more apoptotic thymocytes (red) compared to mice treated with the control antibody anti-gp120 (mIgG2a LALAPG) (black) (Figure 7C).

[0067] [Figure 8A-8E]An in vitro assay to quantify the effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on ligand-mediated MerTK signaling was performed by measuring pAKT levels in macrophages incubated with the ligand hGAS6-Fc (EC50 = approx. 84 pM). Treatment of J774A.1 macrophages with increasing concentrations of anti-MerTK 14C9 (mIgG2a LALAPG) antibody blocked ligand-mediated MerTK signaling, as evidenced by lower levels of pAKT in macrophages treated with anti-MerTK 14C9 (mIgG2a LALAPG) compared to macrophages treated with an isotype control antibody (Figure 8A). To evaluate the in vivo effect of Dex on thymocytes, an apoptotic cell clearance assay was performed. Apoptotic thymocytes accumulated 8 hours after Dex treatment and were mostly gone by 24 hours (Figure 8B). The distribution of MerTK protein within MC38 tumor sections was imaged using fluorescence microscopy. MerTK protein colocalized with CD68, a marker for tumor-associated macrophages (TAMs), indicating that MerTK is specifically expressed in TAMs (Figure 8C). No background signal was observed in Mertk- / - tissue sections stained with anti-MerTK 14C9 (mIgG2a LALAPG) antibody. (Figure 8C) The distribution of MerTK expression was determined using expression data from The Cancer Genome Atlas (TCGA). MerTK expression showed a greater correlation with TAM abundance compared to other immune cell types (Figure 8D). An efferocytosis assay was performed to evaluate the inhibitory effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody on in vitro phagocytosis of apoptotic thymocytes (AC, red) by TAMs (TAM, green). Anti-MerTK 14C9 (mIgG2a LALAPG) antibody inhibited the phagocytic activity of TAMs isolated from MC38 tumors (Figure 8E).

[0068] [Figure 9A-9E]RNA sequencing experiments to evaluate the effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on gene expression patterns in MC38 TAMs. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment caused significant changes in gene expression in TAMs (Figure 9A). Gene set enrichment analysis (GSEA) was performed to reveal genes that were differentially regulated in response to treatment with anti-MerTK 14C9 (mIgG2a LALAPG) antibody. IFN-α responsive genes were enriched after anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment (Figure 9B). The effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on the expression of Ifnb1 and multiple interferon stimulated genes (ISGs) in TAMs was evaluated by qPCR. The indicated genes were more highly expressed after anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment compared to control antibody treatment (Figure 9C). Quantitative ELISA was performed to determine the effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on IFN-beta protein levels. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment resulted in significant accumulation of IFN-beta protein in MC38 tumors (Figure 9D). The effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on IFN-beta expression in the indicated MC38 tumor-derived cell types was assessed by qPCR. IFN-beta was more highly expressed in CD45+ cells and TAMs treated with anti-MerTK 14C9 (mIgG2a LALAPG) compared to cells treated with control antibody. No significant changes in IFN-beta expression were observed in CD45- cells or dendritic cells (DCs) (Figure 9E).

[0069] [Figure 10A-10E]A method for isolating TAMs from tumor-derived single cell suspensions is shown (Figure 10A). The purity of isolated TAMs was assessed by FACS (Figure 10B). Statistical analysis, shown as volcano plots, identified genes whose expression was increased, decreased, or unchanged by anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment (Figure 10C). Gene set enrichment analysis (GSEA) was performed to reveal genes that were differentially regulated in response to treatment with anti-MerTK 14C9 (mIgG2a LALAPG) antibody. The genes shown are ranked according to their enrichment after anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment (Figure 10D). qPCR analysis was performed to quantify the effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on the expression of the indicated ISGs in whole MC38 tumors. The indicated genes were more highly expressed following anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment compared to the control antibody (FIG. 10E).

[0070] [Figure 11A-11B] qPCR analysis was performed to quantify the effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on the expression of the indicated genes in MC38 tumor-derived TAMS (FIG. 11A) or total MC38 tumor homogenates (FIG. 11B). Actb, Gapdh, Rpl13a, Rpl19, Hprt, and Rpl4 were used as housekeeping genes.

[0071] [Figures 12A-12C]The effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment on antigen presentation by TAMs and dendritic cells (DCs) was evaluated using an in vivo antigen presentation assay. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment significantly increased the presentation of MC38.OVA tumor-derived SIINFEKL antigen bound to the MHC class I molecule H-2Kb by TAMs, but not by DCs (Figure 12A). The effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody on T cell activation was evaluated by quantifying the expression of CD86, a protein that promotes T cell activation. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment induced high levels of CD86 in TAMs, but not in DCs (Figure 12A). The effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment on T cell receptor (TCR) productive rearrangement and clonality was measured by genomic DNA sequencing of MC38 tumor-derived T cells. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment resulted in significantly more TCR clonality and productive rearrangement compared to control antibody (Figure 12B). The relative abundance of CD8+, CD4+, and p15e tetramer-reactive T cells in MC38 tumors was quantified to determine the effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment on anti-tumor immune responses. Anti-MerTK 14C9 (mIgG2a LALAPG) treatment significantly enhanced anti-tumor responses compared to control antibody, as evidenced by a significant increase in the relative abundance of CD8+ and p15e tetramer-reactive T cells after anti-MerTK antibody treatment (Figure 12C).

[0072] [Figures 13A-13C]Protein levels of CCL3, CCL4, CCL5, CCL7 and CCL12 were quantified in tumor homogenates to evaluate the effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment on autocrine and paracrine cytokines and chemokines. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment caused significant enrichment of all tested proteins compared to treatment with control antibody (Figure 13A). Expression of ISGs was determined by qPCR analysis in peripheral blood mononuclear cells (PBMCs) to determine the effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment. No significant differences were observed in the expression of the indicated genes after anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment compared to control antibody (Figure 13B). Quantification of the expression of the indicated cytokines and chemokines in tumors (n=10) revealed no significant effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment.

[0073] [Figures 14A-14C] Specific cell types were isolated from single cell suspensions of MC38 tumors using the gating strategy shown in the representative FACS plots in Figure 14A (Figure 14A). The frequency of TAMs and DCs over time in MC38 tumors (n=8, day 8; n=10, days 13 and 15) was quantified. TAMs were significantly more abundant than DCs in MC38 tumors, and the frequency of CD45+TAMs increased in tumors over time, whereas DCs remained constant (Figure 14B). To evaluate the effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment on CD206 expression in TAMs, flow cytometry analysis was performed and MFI, median fluorescence intensity (n=10) was reported. Anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment caused a decrease in CD206 expression on TAMs (Figure 14C).

[0074] [Figures 15A-15C]MC38 tumors were treated with either single-agent anti-MerTK 14C9 (mIgG2a LALAPG) treatment initiated at the early progression stage (Figure 15A) or combination treatment with anti-MerTK 14C9 (mIgG2a LALAPG) and anti-PD-L1 (n=10) at the established stage (Figure 15B). Single-agent anti-MerTK 14C9 (mIgG2a LALAPG) treatment inhibited the growth of early progression stage tumors (Figure 15A). Combination treatment with anti-PD-L1 and anti-MerTK 14C9 (mIgG2a LALAPG) antibodies at the established stage inhibited the growth of MC38 tumors, whereas single-agent anti-MerTK 14C9 (mIgG2a LALAPG) or anti-PD-L1 treatment had little or moderate effect, respectively (Figure 15B). Established MC38 tumors were treated with anti-MerTK 14C9 (mIgG2a LALAPG) in combination with gemcitabine (Gem) and anti-PD-1 (n=15, control Ab group; n=8, anti-PD-1 + anti-MerTK 14C9 (mIgG2a LALAPG); n=10, other groups). Anti-MerTK 14C9 (mIgG2a LALAPG) treatment in combination with gemcitabine (Gem) and anti-PD-1 inhibited tumor growth. Single agent anti-PD-1 or Gem therapy inhibited tumor growth to a lesser extent than anti-PD-1 and / or Gem combination treatment with anti-MerTK 14C9 (mIgG2a LALAPG) (Figure 15C). Both individual and LME-fit tumor growth curves for each group are shown (Figure 15A, Figure 15B, and Figure 15C).

[0075] [Figure 16A-16B]The expression of representative ISGs in tumors treated with anti-MerTK 14C9 (mIgG2a LALAPG) in the presence or absence of anti-IFNAR1 (n=5) was quantified to evaluate the impact of type 1 IFN signaling on anti-MerTK 14C9 (mIgG2a LALAPG) treatment. Anti-IFNAR1 treatment abolished the enhanced expression of the indicated ISGs caused by anti-MerTK 14C9 (mIgG2a LALAPG) (Figure 16A). The growth of MC38 tumors treated with a combination of anti-MerTK 14C9 (mIgG2a LALAPG) and anti-PD-L1 together with anti-IFNARI was evaluated to determine the effect of type 1 IFN signaling on the combined anti-MerTK 14C9 (mIgG2a LALAPG) and anti-PD-L1 treatment (n=10). Anti-IFNAR1 antibody treatment reduced the tumor-inhibitory effect of anti-MerTK 14C9 (mIgG2a LALAPG) in combination with anti-PD-L1 therapy. Both individual and LME-matched tumor growth curves for each group are shown (Figure 16B).

[0076] [Figures 17A-17C]Growth of MC38 tumors treated with single-agent anti-MerTK 14C9 (mIgG2a LALAPG) therapy together with anti-IFNARI antibody was evaluated (n=10) to determine the effect of type 1 IFN signaling on anti-MerTK 14C9 (mIgG2a LALAPG) treatment. Anti-IFNAR1 antibody treatment negated the tumor inhibitory effect of anti-MerTK 14C9 (mIgG2a LALAPG) antibody therapy (Figure 17A). The expression of representative ISGs in MC38 tumors growing in WT or Stinggt / gt mice was quantified to evaluate the effect of STING on anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment (n=9, WT host; n=10, Stinggt / gt host). STING disruption abolished the enhanced expression of the indicated ISGs caused by anti-MerTK 14C9 (mIgG2a LALAPG) (Figure 17B). The growth of MC38 tumors in WT or Stinggt / gt host mice was quantified to evaluate the effect of STING on anti-MerTK 14C9 (mIgG2a LALAPG) antibody treatment (n=10). STING disruption abolished the tumor inhibitory effect of anti-MerTK 14C9 (mIgG2a LALAPG) treatment (Figure 17C). Both individual and LME-fitted tumor growth curves for each group are shown (Figures 17A and 17C).

[0077] [Fig. 18A-18F]To evaluate the function of STING and cGAS in response to cytoplasmic DNA in macrophages, cytoplasmic DNA transfection experiments were performed. IFN-beta accumulation required both functional STING (Figure 18A) and cGAS (Figure 18B) expression in macrophages in response to DNA transfection. Western blot analysis of cGAS and STING expression in MC38 tumor cells and J774A.1 macrophages determined that J774A.1 macrophages express cGAS and STING, whereas MC38 tumor cells express only cGAS (Figure 18C). Expression of representative ISGs in WT and cGAS- / - AB22 tumors was quantified to evaluate the role of cGAS expression in tumor cells during anti-MerTK treatment. Disruption of cGAS expression in tumor cells abolished accumulation of the indicated ISGs in response to anti-MerTK treatment (Figure 18D). Growth of WT or cGAS- / - MC38 tumors was quantified to assess the effect of cGAS expression in tumor cells on anti-MerTK as a single agent or in combination with anti-PD-L1 (n=9, WT MC38 with combination treatment; n=10, other groups). Tumor growth inhibition by anti-MerTK and anti-PD-L1 combination therapy was reduced in cGAS- / - MC38 tumors. Both individual and LME-fit tumor growth curves for each group are shown (Figure 18E). Protein quantification by LC-MS / MS was used to measure cGAMP production in MC38 tumor cells, which was increased in WT tumor cells but not in cGAS- / - tumor cells after transfection with HT-DNA (Figure 18F).

[0078] [Figures 19A-19E]IFN-beta protein production was quantified from WT and Stinggt / gt BMDMs (Figure 19A), or WT and cGAS- / - J774A.1 macrophages co-cultured with UV-irradiated WT or cGAS- / - MC38 cells (Figure 19B). IFN-beta protein accumulation was dependent on cGAS expression in tumor cells and STING expression in macrophages (Figures 19A and 19B). cGAS expression in macrophages was not essential for IFN-beta protein accumulation (Figure 19B). Expression of representative ISGs in WT or cGAS- / - MC38 tumors growing in WT host mice (n=10) was quantified to assess the impact of cGAS expression in tumor cells on anti-MerTK monotherapy. cGAS disruption in tumor cells abolished the enhanced expression of the indicated ISGs in response to anti-MerTK treatment (Figure 19C). Growth of WT or cGAS- / - primary MC38 tumors grown in WT host mice was measured after single-agent anti-MerTK or anti-PD-L1 treatment (n=10). cGAS-deficient tumor cells were resistant to single-agent anti-MerTK or anti-PD-L1 treatment as measured by tumor growth inhibition. Both individual and LME-matched tumor growth curves for each group are shown (Figures 19D and 19E).

[0079] [Fig. 20A-20E]Western blot analysis was performed to confirm the loss of Cx43 protein in Cx43- / - MC38 tumor cells (Figure 20A). A schematic of the dye transfer assay measuring calcein transfer between cells through Cx43 is shown (Figure 20B). To quantify the role of Cx43 in calcein transfer between MC38 tumor cells (Figure 20C) or from macrophages to tumor cells, the dye transfer assay of Figure 20B was performed (Figure 20D). Loss of Cx43 impaired the transfer of the fluorescent dye calcein between MC38 cells (Figure 20C) and from J774A.1 macrophages to MC38 tumor cells (Figure 20D). Growth of WT or Cx43- / - MC38 tumors in WT host mice was measured after treatment with anti-MerTK and anti-PD-L1 combination therapy (n=10, WT MC38; n=8, Cx43- / - MC38). Cx43-deficient tumor cells were resistant to anti-MerTK and anti-PD-L1 combination therapy, as measured by tumor growth inhibition. Both individual and LME-matched tumor growth curves for each group are shown (Figure 20E).

[0080] [Figures 21A-21D]Schematic of gap junction-dependent import of cGAMP from MC38 cells and production of IFN-beta by macrophages (Figure 21A). IFN-beta protein production was quantified from J774A.1 macrophages in co-culture with HT-DNA transfected (+DNA) WT or Cx43- / - MC38 tumor cells. Disruption of Cx43 in tumor cells abolished the increase in IFN-beta production by macrophages caused by DNA transfection of tumor cells (Figure 21B). mRNA expression of representative ISGs in Cx43- / - MC38 tumors was quantified to determine the effect of Cx43 disruption in tumor cells on anti-MerTK treatment (n=10, control Ab; n=9, anti-MerTK). Treatment of Cx43- / - MC38 tumors with anti-MerTK did not result in significant changes in the expression of ISGs (Figure 21C). Model showing blockade of MerTK-dependent innate immune checkpoint. MerTK signaling in TAMs mediates rapid clearance of stressed or dying tumor cells, resulting in quiescent disposal of tumor-derived material without triggering immune system alarm. Treatment with anti-MerTK prevents efferocytosis, allowing for prolonged production of cGAMP by cGAS-expressing tumor cells and increased cGAMP import into host macrophages via gap junctions. IFN-beta produced by TAMs acts in an autocrine / paracrine manner to increase antigen-presenting and co-stimulatory molecule expression by antigen-presenting cells, ultimately resulting in enhanced T cell responses (Figure 21D).

[0081] [Fig. 22A-22B]Quantification of circulating tumor DNA (ctDNA) and cell-free DNA (cfDNA) in mouse MC38 tumor models treated with anti-MerTK or control antibodies. MC38 tumor cells were inoculated into C57BL / 6J mice. Anti-MerTK or control antibodies were administered after tumors were established. Three days after anti-MerTK treatment, a significant increase in ctDNA was detected in the plasma of tumor-bearing mice (Figure 22A). Anti-MerTK also increased the levels of host-derived cfDNA in the blood circulation (Figure 22B). The p-values ​​shown are based on unpaired two-tailed Student's t-tests. These results demonstrate that anti-MerTK treatment was able to block the ongoing clearance of apoptotic cells by TAMs in the tumor microenvironment.

[0082] [Diagram 23] Figure 23 shows the analysis of anti-MerTK antibody binding affinity to human MerTK using surface plasmon resonance (SPR). The binding affinity of 10 commercial antibodies and h13B4.v16 to human MerTK was determined. The binding affinities were observed as follows: 0.4 nM for Y323, 6.8 nM for A3KCAT, 7.6 nM for 590H11G1E3, 17.3 nM for MAB8912-100, and 1.6 nM for h13B4.v16. The remaining six antibodies (10g86_D21F11, 2D2, 7E5G1, 7N-20, MAB891, and MAB8911) did not show binding to human MerTK.

[0083] [Figures 24A-24C]Figures 24A-24C show the results of a competitive binding experiment examining anti-MerTK antibodies. Anti-MerTK antibodies Y323, A3KCAT, 590H11G1E3 and MAB8912-100 were tested for competition with antibody h13B4.v16 for binding to human MerTK using a classical sandwich format (Figure 24A). Antibody Y323 was found to compete with h13B4.v16 for binding to human MerTK (Figure 24B), whereas antibodies A3KCAT, 590H11G1E3 and MAB8912-100 did not compete with h13B4.v16 for binding to human MerTK (Figure 24C). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0084] I. Definition It is to be understood that the present disclosure is not limited to particular compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0085] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a "molecule" includes any combination of two or more such molecules.

[0086] The term "about" as used herein refers to a normal range of error for the respective value, which would be readily understood by one of ordinary skill in the art. Reference herein to "about" a value or parameter includes (and describes) embodiments that are directed to the value or parameter itself.

[0087] It should be understood that aspects and embodiments of the present disclosure include "comprising," "consisting," and "consisting essentially of" aspects and embodiments.

[0088] An "acceptor human framework" for the purposes of this specification is a framework that comprises 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 or may comprise amino acid sequence changes. In some embodiments, the number of amino acid changes is 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less, or 1 or less. In some embodiments, the VL acceptor human framework is identical in sequence to the VL human immunoglobulin framework sequence or the human consensus framework sequence. In some embodiments, the VH acceptor human framework is identical in sequence to the VH human immunoglobulin framework sequence or the human consensus framework sequence. In some embodiments, the VL and VH acceptor human frameworks are identical in sequence to the VL and VH human immunoglobulin framework sequences or human consensus framework sequences.

[0089] "Affinity" refers to the strength of the total non-covalent interactions between a single binding site of a molecule (e.g., an antibody) and its binding partner (e.g., an antigen). Unless otherwise specified, as used herein, "binding affinity" refers to the intrinsic binding affinity that reflects a 1:1 interaction between members of a binding pair (e.g., an antibody and an antigen). The affinity of a molecule X for its partner Y can generally be represented by a dissociation constant (Kd). Affinity can be measured by methods common in the art, including those described herein. Specific illustrative and exemplary embodiments for measuring binding affinity are described below.

[0090] An "affinity matured" antibody refers to an antibody which has one or more modifications in one or more hypervariable regions (HVRs) compared to a parent antibody which does not possess such modifications, which improve the affinity of the antibody for its antigen.

[0091] The terms "anti-MerTK antibody" and "antibody that binds to MerTK" refer to an antibody that is capable of binding to MerTK with sufficient affinity such that the antibody is useful as a diagnostic and / or therapeutic agent in targeting MerTK. In one embodiment, the extent to which an anti-MerTK antibody binds to an unrelated, non-MerTK protein is less than about 10% of the binding of the antibody to MerTK, e.g., as measured by radioimmunoassay (RIA). In certain embodiments, an antibody that binds to MerTK has an affinity of ≦1 μM, ≦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. 10 -8 M~10 -13 M, for example 10 -9 M~10 -13 M) in which the antibody binds to an epitope of MerTK that is conserved among MerTKs of different species.

[0092] The term "antibody" is used herein in the broadest sense and encompasses a variety of antibody structures, including, but not limited to, monoclonal antibodies, polyclonal antibodies, multispecific antibodies (e.g., bispecific antibodies), and antibody fragments, so long as they exhibit the desired antigen-binding activity.

[0093] "Antibody fragment" refers to a molecule other than an intact antibody that contains 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, Fv, Fab, Fab', Fab'-SH, F(ab')2, bispecific antibodies, linear antibodies, single-chain antibody molecules (e.g., scFv); and multispecific antibodies formed from antibody fragments.

[0094] 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.

[0095] The "class" of an antibody refers to the type of constant domain or region carried by its heavy chain. There are five major classes of antibodies, namely IgA, IgD, IgE, IgG, and IgM, and several of these can be further divided into "subclasses" (isotypes), e.g., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2. The heavy chain constant domains that correspond to the different classes of immunoglobulins are called α, σ, ε, γ, and μ, respectively.

[0096] As used herein, the term "cytotoxic agent" refers to a substance that inhibits or prevents cell function and / or causes cell death or destruction. Cytotoxic agents include radioisotopes (e.g., At 211 , I 131 , I 125 , Y 90 , Re 186 , Re 188 , Sm 153 , Bi 212 , P 32 , Pb 212 , and radioactive isotopes of Lu); chemotherapeutic agents or drugs (e.g., methotrexate, adriamycin, vinca alkaloids (vincristine, vinblastine, etoposide), doxorubicin, melphalan, mitomycin C, chlorambucil, daunorubicin or other intercalating agents); growth inhibitory agents; enzymes and fragments thereof, such as nucleases; 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 various anti-tumor or anti-cancer agents as disclosed below.

[0097] "Effector functions" refer to biological activities attributable to the Fc region of an antibody, which vary depending on 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 receptors), and B cell activation.

[0098] An "effective amount" of an agent, e.g., a pharmaceutical formulation, refers to an amount effective, at dosages and for periods of time necessary, to achieve a desired therapeutic or prophylactic result.

[0099] The term "Fc region" is used herein to define a C-terminal region of an immunoglobulin heavy chain that contains at least a portion of a constant region. This 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 an Fc region or constant region is according to the EU numbering system (also referred to as 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.

[0100] "Framework" or "FR" refers to variable domain residues other than hypervariable region (HVR) residues. The FR of a variable domain typically consists of four FR domains: FR1, FR2, FR3 and FR4. Thus, the HVR and FR sequences typically appear in VH (or VL) in the following order: FR1-H1(L1)-FR2-H2(L2)-FR3-H3(L3)-FR4.

[0101] The terms "full length antibody," "intact antibody," and "whole antibody" are used interchangeably herein to refer to an antibody having a heavy chain having a structure substantially similar to a native antibody structure or containing an Fc region as defined herein.

[0102] 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 original transformed cell and the progeny derived from the original transformed cell, regardless of the number of passages. The progeny may not be completely identical in nucleic acid content to the 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 in the invention.

[0103] A "human antibody" is one that possesses an amino acid sequence that corresponds to that of an antibody produced by a human or a human cell, or derived from a non-human source that utilizes a human antibody repertoire or other human antibody coding sequence. This definition of a human antibody specifically excludes humanized antibodies, which contain non-human antigen-binding residues.

[0104] A "human consensus framework" is a framework that 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 VL, the subgroup is subgroup kappa I as in Kabat et al., supra. In one embodiment, for VH, the subgroup is subgroup III as in Kabat et al., supra.

[0105] A "humanized" antibody refers to a chimeric antibody that comprises amino acid residues from non-human HVRs and amino acid residues from human FRs. In certain embodiments, a humanized antibody comprises 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 a non-human antibody and all or substantially all of the FRs correspond to a human antibody. A humanized antibody may optionally 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 been subjected to humanization.

[0106] The term "hypervariable region" or "HVR" as used herein refers to each of the regions of an antibody variable domain that are hypervariable in sequence ("complementarity determining regions" or "CDRs") and / or that structurally form defined loops ("hypervariable loops") and / or contain residues that contact the antigen ("antigen contacts"). Generally, antibodies contain six HVRs, three in the VH (H1, H2, H3) and three in the VL (L1, L2, L3). Exemplary HVRs of the invention include the following: (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 located 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 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).

[0107] In one embodiment, the HVR residues include those identified in Table 6 of the disclosure.

[0108] 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.

[0109] An "immunoconjugate" is an antibody conjugated to one or more heterologous molecules, including, but not limited to, a cytotoxic agent.

[0110] An "individual" or "subject" is a mammal. Mammals include, but are not limited to, domestic 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, an individual or subject is a human.

[0111] An "isolated antibody" is an antibody that has been separated from a component of its natural environment. In some embodiments, the antibody is purified to greater than 95% or greater than 99% purity, for example, as determined by electrophoresis (e.g., SDS-PAGE, isoelectric focusing (IEF), capillary electrophoresis) or chromatography (e.g., ion exchange or reverse phase HPLC). For a review of methods for assessment of antibody purity, see, e.g., Flatman et al., J. Chromatogr. B 848:79-87 (2007).

[0112] "Isolated nucleic acid" refers to a nucleic acid molecule that has been separated from a component of its natural environment. Isolated nucleic acid includes nucleic acid molecules that are contained in a cell that originally contained the nucleic acid molecule, but where the nucleic acid molecule is present extrachromosomally or at a chromosomal location that is different from its natural chromosomal location.

[0113] "Isolated nucleic acid encoding an anti-MerTK antibody" refers to one or more nucleic acid molecules encoding the 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) are present in one or more locations within a host cell.

[0114] The term "LALAPG mutations" as used herein refers to mutations in the Fc region of an antibody that contain the following three mutations: leucine 234 to alanine (L234A), leucine 235 to alanine (L235A), and proline 239 to glycine (P329G), which have previously been shown to reduce binding to Fc receptors and complement (see, e.g., U.S. Patent Application Publication No. 2012 / 0251531 and U.S. Patent No. 8,969,526). Numbering of amino acid residues in the Fc region or constant region follows the EU numbering system (also referred to as 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.

[0115] As used herein, the term "monoclonal antibody" refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies constituting the population are identical and / or bind to the same epitope, with the exception of possible variant antibodies that contain, for example, naturally occurring mutations or arise during the production of the monoclonal antibody preparation, which variants are generally 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 should not be construed as requiring production of the antibody by any particular method. For example, monoclonal antibodies used in accordance with the present invention can be produced by a variety of techniques, including, but not limited to, hybridoma methods, recombinant DNA methods, phage display methods, and methods utilizing transgenic animals containing all or part of the human immunoglobulin loci, and such methods and other exemplary methods for producing monoclonal antibodies are described herein.

[0116] "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.

[0117] "Native antibodies" refer to naturally occurring immunoglobulin molecules with various structures. For example, natural 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 the N-terminus to the 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 the N-terminus to the 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 (λ), based on the amino acid sequence of its constant domain.

[0118] The term "package insert" is used to refer to instructions customarily included in commercial packaging of therapeutic products that contain information about the indications, usage, dosages, administration, concomitant therapy, contraindications, and / or warnings regarding the use of such therapeutic product.

[0119] "Percentage (%) amino acid sequence identity" to a reference polypeptide sequence is defined as the percentage of amino acid residues in a candidate sequence that are identical to 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, without considering any conservative substitutions as part of the sequence identity. Alignment for purposes of determining percent amino acid sequence identity can be accomplished in a variety of ways that are within the skill of the art, for example, using known 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 required to achieve maximum alignment over the entire length of the sequences being compared. However, for purposes herein, percent amino acid sequence identity values ​​are generated using the sequence comparison computer program ALIGN-2. The ALIGN-2 sequence comparison computer program was written by Genentech, Inc., and the source code, together with user documentation, has been filed with the U.S. Copyright Office, Washington DC, 20559, where it is registered under U.S. Copyright Registration No. TXU510087. The ALIGN-2 program is publicly available from Genentech, Inc., South San Francisco, California, or may be compiled from its source code. The ALIGN-2 program should be compiled for use on UNIX operating systems, including digital UNIX V4.0D. All sequence comparison parameters are set by the ALIGN-2 program and do not vary.

[0120] In situations where ALIGN-2 is used for amino acid sequence comparisons, the % amino acid sequence identity of a given amino acid sequence A to, with, or relative to a given amino acid sequence B (alternatively, it may be written as a given amino acid sequence A having or containing a certain % amino acid sequence identity to, with, or relative to a given amino acid sequence B) is calculated as follows: 100 x fraction X / Y where X is the number of amino acid residues scored as identical matches by the sequence alignment program ALIGN-2 in its alignment of A and B, and Y is the total number of amino acid residues in B. It will be understood that if the length of amino acid sequence A is not equal to the length of amino acid sequence B, then the % amino acid sequence identity of A to B will not be equal to the % amino acid sequence identity of B to A. Unless otherwise stated, all % amino acid sequence identity values ​​used herein are obtained as described in the immediately preceding paragraph using the ALIGN-2 computer program.

[0121] The term "PD-1 axis binding antagonist" refers to a molecule that inhibits the interaction of a PD-1 axis binding partner with any one or more of its binding partners to eliminate T cell dysfunction resulting from signaling on the PD-1 signaling axis, thereby restoring or enhancing T cell function (e.g., proliferation, cytokine production, target cell killing). As used herein, PD-1 axis binding antagonists include PD-1 binding antagonists, PD-L1 binding antagonists, and PD-L2 binding antagonists.

[0122] The term "PD-1 binding antagonist" refers to a molecule that reduces, blocks, inhibits, abrogates, or prevents signaling resulting from the interaction of PD-1 with one or more of its binding partners, e.g., PD-L1 and / or PD-L2. In some embodiments, a PD-1 binding antagonist is a molecule that inhibits the binding of PD-1 to one or more of its binding partners. In certain aspects, a 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 reduce, block, inhibit, abrogate, or prevent signaling resulting from the interaction of PD-1 with PD-L1 and / or PD-L2. In one embodiment, the PD-1 binding antagonist reduces the negative costimulatory signal mediated by or through cell surface proteins expressed on T lymphocytes that mediate signaling through PD-1, rendering dysfunctional T cells less dysfunctional (e.g., enhancing the effector response to antigen recognition). In some embodiments, the PD-1 binding antagonist is an anti-PD-1 antibody. Specific examples of PD-1 binding antagonists are provided below.

[0123] The term "PD-L1 binding antagonist" refers to a molecule that reduces, blocks, inhibits, abrogates, or prevents signaling resulting from the interaction of PD-L1 with any one or more of its binding partners, e.g., PD-1 and / or 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 aspect, a PD-L1 binding antagonist inhibits the binding of PD-L1 to PD-1 and / or B7-1. In some embodiments, PD-L1 binding antagonists include anti-PD-L1 antibodies, antigen-binding fragments thereof, immunoadhesins, fusion proteins, oligopeptides, and other molecules that reduce, block, inhibit, abrogate, or prevent signaling resulting from the interaction of PD-L1 with one or more of its binding partners, e.g., PD-1 and / or B7-1. In one embodiment, the PD-L1 binding antagonist reduces the negative costimulatory signal mediated by or through cell surface proteins expressed on T lymphocytes that mediate signaling through PD-L1, rendering dysfunctional T cells less dysfunctional (e.g., enhancing the effector response to antigen recognition). In some embodiments, the PD-L1 binding antagonist is an anti-PD-L1 antibody. Specific examples of PD-L1 binding antagonists are provided below.

[0124] The term "PD-L2 binding antagonist" refers to a molecule that reduces, blocks, inhibits, or prevents signaling that occurs as a result of the interaction of PD-L2 with any of one or more 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 aspect, a PD-L2 binding antagonist inhibits the binding of PD-L2 to PD-1. In some embodiments, PD-L2 antagonists include anti-PD-L2 antibodies, antigen-binding fragments thereof, immunoadhesins, fusion proteins, oligopeptides, and other molecules that reduce, block, inhibit, abrogate, or prevent signaling that results from the interaction of PD-L2 with one or more of its binding partners, e.g., PD-1. In one embodiment, the PD-L2 binding antagonist reduces the negative costimulatory signal mediated by or through a cell surface protein expressed on T lymphocytes that mediates signaling through PD-L2, rendering dysfunctional T cells less dysfunctional (e.g., enhancing the effector response to antigen recognition). In some embodiments, the PD-L2 binding antagonist is an immunoadhesin.

[0125] The term "pharmaceutical formulation" refers to a preparation that is in a form such that the biological activity of the active ingredients contained in the preparation is effective, and that does not contain any additional components that are unacceptably toxic to the subject to which the formulation is administered.

[0126] A "pharmaceutically acceptable carrier" refers to an ingredient in a pharmaceutical formulation, other than an active ingredient, that is non-toxic to a subject. Pharmaceutically acceptable carriers include, but are not limited to, buffers, excipients, stabilizers, or preservatives.

[0127] The term "MerTK", as used herein, unless otherwise specified, refers to any naturally occurring MerTK of any vertebrate source, including mammals such as primates (e.g., humans) and rodents (e.g., mice and rats). The term encompasses "full-length," unprocessed MerTK, and any form of MerTK that results from processing in a cell. The term also encompasses naturally occurring variants of MerTK, such as splice variants or allelic variants. An exemplary amino acid sequence of human MerTK is described in U.S. Patent Application Publication No. 2006 / 0121562.

[0128] As used herein, "treatment" (and grammatical variants thereof, e.g., "treat" or "treating") refers to clinical intervention in an attempt to alter the natural course of the individual being treated, and can be performed prophylactically or during the course of clinical pathology. Desired effects of treatment include preventing the onset or recurrence of disease, alleviating symptoms, attenuating any direct or indirect pathological consequences of the disease, preventing metastasis, reducing the rate of disease progression, remission or alleviation of disease symptoms, and improving or improving prognosis. In some embodiments, the antibodies of the invention are used to delay the onset of disease or to slow the progression of disease.

[0129] The term "variable region" or "variable domain" refers to the domain of an antibody heavy chain or antibody light chain that is involved in the binding of the antibody to an antigen. The variable domains of the heavy and light chains of natural antibodies (VH and VL, respectively) generally have a similar structure, with each domain containing four conserved framework regions (FR) and three hypervariable regions (HVR) (see, for example, Kindt et al. Kuby Immunology, 6th ed., WH Freeman and Co., page 91 (2007)). A single VH or VL domain may be sufficient to confer antigen-binding specificity. Furthermore, antibodies that bind to a specific antigen may be isolated by screening a library of complementary VL or VH domains, respectively, using the VH or VL domain of an antibody that binds the antigen. See, e.g., Portolano et al., J. Immunol. 150:880-887 (1993); Clarkson et al., Nature 352:624-628 (1991).

[0130] 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 vectors as autonomously replicating nucleic acid structures and vectors that integrate into the genome of a host cell into which the vector is 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."

[0131] II. Anti-MerTK antibody The present disclosure is based on the discovery of a novel anti-MerTK antibody. Such novel anti-MerTK antibody finds use in the treatment of cancer.In particular, the present disclosure is based on the discovery that the anti-MerTK antibody described herein enhances the efficacy of immune checkpoint inhibitor-based therapy.

[0132] C-Mer proto-oncogene tyrosine kinase (MerTK) is a receptor tyrosine kinase that transduces extracellular signals upon binding to various ligands, such as galectin-3, protein S, and Gas6, thereby activating the expression of effector genes. The MerTK pathway regulates essential cellular processes, including cell survival, cytokine production, migration, differentiation, and phagocytosis (Cabernoy N., et al. J Cell Physio. 227(2012):401-407; Wu, G., et al. Cell Death&Disease 8(2017):e2700). Expression of MerTK is found in various hematopoietic cell types, such as macrophages, dendritic cells, and natural killer (NK) cells. Importantly, the MerTK receptor pathway is active in several solid and hematological cancers, including colon cancer (Wu, G., et al. Cell Death&Disease 8(2017):e2700).

[0133] The MerTK receptor is composed of an extracellular component, a transmembrane (TM) domain, and an intracellular component. As shown in the diagram below, the extracellular or ligand-binding region of MerTK contains two immunoglobulin (Ig)-like domains and two fibronectin (FN) type III-like domains. TIFF2025037921000002.tif20170

[0134] For example, in human MerTK, the two Ig-like domains are defined by amino acid residues 76-195 and 199-283, respectively. Furthermore, the two fibronectin-like domains of human MerTK are defined by amino acid residues 286-384 and 388-480, respectively. The intracellular region of MerTK contains a tyrosine kinase (TK) domain, which autophosphorylates specific tyrosine residues after ligand binding to the extracellular region, promoting MerTK receptor dimerization and thus activating downstream effector gene expression (Toledo, RA, et al. Clin Can. Res. 22 (2016): 2301-2312). Human MerTK comprises the following amino acid sequence:

[0135] Provided herein is an isolated antibody that binds to MerTK, the antibody having one or more of the following properties: (i) antagonizes one or more biological activities of MerTK, (ii) reduces MerTK-mediated clearance of apoptotic cells, (iii) reduces MerTK-mediated phagocytic activity, (iv) enhances tumor immunogenicity of checkpoint inhibitors, (v) binds to a fibronectin-like domain of MerTK, (vi) binds to an Ig-like domain on MerTK, (vii) specifically binds to human MerTK, (viii) binds to one or more of human, mouse and / or cynomolgus monkey MerTK, and / or (ix) has a K of less than 20 nM. D The antibody binds to MerTK at less than 10 nM, less than 5 nM, or less than 2 nM.

[0136] A. Exemplary Anti-MerTK Antibodies In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 6. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 6. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0137] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 1, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 2, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 3. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 1, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 2, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 3. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0138] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 6, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 1, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 2, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 3. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0139] In another aspect, the invention provides an antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 6, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 1, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 2, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 3. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0140] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues derived from rabbit framework region sequences, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0141] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 83. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 83. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 83, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 6. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0142] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 65. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 65. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 65, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 1, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 2, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 3. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0143] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:83 and SEQ ID NO:65, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0144] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0145] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0146] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 12, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0147] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 9. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0148] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues derived from rabbit framework region sequences, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0149] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 84. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 84. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 84, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0150] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 66. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 66. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 66, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0151] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:84 and SEQ ID NO:66, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0152] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 85. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 85. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 85, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0153] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 67. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 67. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a VL sequence of SEQ ID NO: 67, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9.

[0154] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:85 and SEQ ID NO:67, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0155] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 102. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 102. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 102, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0156] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 110. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 110. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 110, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0157] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 102 and SEQ ID NO: 110, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0158] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 86. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 86. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 86, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0159] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 68. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 68. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 68, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0160] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:86 and SEQ ID NO:68, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0161] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 103. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 103. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 103, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 12. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0162] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 111. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 111. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 111, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 9. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0163] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 103 and SEQ ID NO: 111, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0164] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0165] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0166] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 18, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0167] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 15. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0168] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues derived from rabbit framework region sequences, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0169] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 87. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 87. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 87, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0170] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 69. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 69. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 69, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0171] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:87 and SEQ ID NO:69, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0172] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 88. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 88. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 88, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0173] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 70. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 70. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a VL sequence of SEQ ID NO: 70, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0174] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:88 and SEQ ID NO:70, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0175] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 104. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 104. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 104, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0176] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 112. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 112. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 112, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0177] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 104 and SEQ ID NO: 112, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0178] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 89. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 89. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 89, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0179] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 70. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 70. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a VL sequence of SEQ ID NO: 70, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0180] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:89 and SEQ ID NO:70, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0181] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 105. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 105. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 105, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 18. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0182] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 113. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 113. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a light chain sequence of SEQ ID NO: 113, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 15. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0183] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 105 and SEQ ID NO: 113, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0184] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0185] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0186] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 24, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0187] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 21. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0188] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues derived from rabbit framework region sequences, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0189] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 90. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 90. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 90, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0190] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 71. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 71. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 71, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0191] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:90 and SEQ ID NO:71, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0192] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 91. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 91. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 91, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0193] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 72. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 72. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 72, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0194] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:91 and SEQ ID NO:72, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0195] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 106. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 106. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 106, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0196] In another aspect, an anti-MerTK antibody is provided, which comprises a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 114. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 114. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 114, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0197] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 106 and SEQ ID NO: 114, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0198] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 92. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 92. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 92, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0199] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 73. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 73. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 73, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 21. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0200] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:92 and SEQ ID NO:73, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0201] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 107. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 107. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 107, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 24. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0202] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 115. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 115. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 115, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 20. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0203] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 107 and SEQ ID NO: 115, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0204] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 29. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 29. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0205] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 26. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 26. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0206] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 29, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 26. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0207] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 29, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 26. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0208] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0209] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 93. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 93. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 93, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 29. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0210] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 74. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 74. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 74, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 26. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0211] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:93 and SEQ ID NO:74, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0212] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 35. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 35. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0213] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 32. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 32. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0214] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 35, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 32. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0215] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 35, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 32. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0216] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0217] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 94. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 94. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 94, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 35. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0218] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 75. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 75. In certain embodiments, the substitutions, insertions, or deletions occur in a region outside the HVR (i.e., in the FR). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 75, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 32. In exemplary embodiments, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0219] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:94 and SEQ ID NO:75, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0220] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0221] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0222] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 40, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In an exemplary embodiment, the anti-MerTK antibody binds to an Ig-like domain of MerTK.

[0223] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 37. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0224] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0225] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 95. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 95. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 95, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 38, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 39, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 40. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0226] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 76. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 76. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 76, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 37. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0227] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:95 and SEQ ID NO:76, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0228] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 46. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 46. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0229] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0230] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 46, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In an exemplary embodiment, the anti-MerTK antibody binds to an Ig-like domain of MerTK.

[0231] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 46, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 43. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0232] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0233] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 96. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 96. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 96, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 46. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0234] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 77. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 77. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 77, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 43. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0235] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:96 and SEQ ID NO:77, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0236] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0237] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0238] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 52, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In an exemplary embodiment, the anti-MerTK antibody binds to an Ig-like domain of MerTK.

[0239] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 49. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0240] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0241] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 97. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 97. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 97, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0242] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 78. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 78. In certain embodiments, the substitutions, insertions, or deletions occur in a region outside the HVR (i.e., in the FR). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 78, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0243] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:97 and SEQ ID NO:78, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0244] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 98. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 98. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 98, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0245] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 79. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 79. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a VL sequence of SEQ ID NO: 79, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0246] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:98 and SEQ ID NO:79, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0247] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 108. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 108. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 108, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0248] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 116. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 116. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 116, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0249] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 108 and SEQ ID NO: 116, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0250] In another aspect, an anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 99. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 99. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a VH sequence of SEQ ID NO: 99, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0251] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 80. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 80. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises a VL sequence of SEQ ID NO: 80, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0252] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO:99 and SEQ ID NO:80, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0253] In another aspect, the anti-MerTK antibody comprises a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 109. In certain embodiments, a heavy chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 109. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the heavy chain sequence of SEQ ID NO: 109, including post-translational modifications of that sequence. In certain embodiments, the heavy chain comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 50, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 51, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 52. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0254] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 117. In certain embodiments, the light chain sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but the anti-MerTK antibody comprising the sequence retains the ability to bind to MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 117. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the light chain sequence of SEQ ID NO: 117, including post-translational modifications of that sequence. In certain embodiments, the light chain comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 49. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0255] In another aspect, an anti-MerTK antibody is provided that comprises a heavy chain as in any of the embodiments set forth above and a light chain as in any of the embodiments set forth above. In one embodiment, the antibody comprises the heavy and light chain sequences of SEQ ID NO: 109 and SEQ ID NO: 117, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0256] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 56, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 57, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 58. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 56, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 57, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 58. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0257] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 55. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 55. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0258] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 56, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 57, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 58, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 55. In an exemplary embodiment, the anti-MerTK antibody binds to an Ig-like domain of MerTK.

[0259] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 56, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 57, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 58, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 55. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0260] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0261] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 100. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 100. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 100, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 56, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 57, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 58. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0262] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 81. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 81. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 81, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 55. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0263] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO: 100 and SEQ ID NO: 81, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0264] In one aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VH HVR sequences selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 64. In one embodiment, the antibody comprises (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 64. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0265] In another aspect, the invention provides an anti-MerTK antibody comprising at least one, at least two, or all three VL HVR sequences selected from: (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 61. In one embodiment, the antibody comprises (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 61. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0266] In another aspect, an anti-MerTK antibody of the invention comprises (a) a VH domain comprising at least one, at least two, or all three VH HVR sequences selected from (i) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62, (ii) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63, and (iii) HVR-H3 comprising an amino acid sequence selected from SEQ ID NO: 64, and (b) a VL domain comprising at least one, at least two, or all three VL HVR sequences selected from (i) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59, (ii) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 61. In an exemplary embodiment, the anti-MerTK antibody binds to an Ig-like domain of MerTK.

[0267] In another aspect, the invention provides an anti-MerTK antibody comprising: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63, (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 64, (d) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59, (e) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60, and (f) HVR-L3 comprising an amino acid sequence selected from SEQ ID NO: 61. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0268] In any of the above-described embodiments, the anti-MerTK antibody is humanized. In one embodiment, the anti-MerTK antibody comprises an HVR as in any of the above embodiments, and further comprises an acceptor human framework, such as a human immunoglobulin framework or a human consensus framework, optionally with up to 10 amino acid substitutions (e.g., 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid substitutions). In an exemplary embodiment, such amino acid substitutions correspond to amino acid residues from a rabbit framework region sequence, such as one or more of the following residues: Q2, L4, P43, and / or F87 in the light chain variable region framework sequence, and / or one or more of the following residues: V24, I48, G49, K71, and / or V78 in the heavy chain variable region framework sequence. Numbering of amino acid residues 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. In an exemplary embodiment, the anti-MerTK antibody binds to the fibronectin-like domain of MerTK.

[0269] In another aspect, the anti-MerTK antibody comprises a heavy chain variable domain (VH) sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 101. In certain embodiments, a VH sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising that sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 101. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VH sequence of SEQ ID NO: 101, including post-translational modifications of that sequence. In certain embodiments, the VH comprises one, two or three HVRs selected from: (a) HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62, (b) HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63, and (c) HVR-H3 comprising the amino acid sequence of SEQ ID NO: 64. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0270] In another aspect, an anti-MerTK antibody is provided, the antibody comprising a light chain variable domain (VL) having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to the amino acid sequence of SEQ ID NO: 82. In certain embodiments, a VL sequence having at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% identity contains substitutions (e.g., conservative substitutions), insertions, or deletions compared to the reference sequence, but an anti-MerTK antibody comprising the sequence retains the ability to bind MerTK. In certain embodiments, a total of 1-10 amino acids are substituted, inserted, and / or deleted in SEQ ID NO: 82. In certain embodiments, the substitutions, insertions, or deletions occur in the regions outside the HVRs (i.e., in the FRs). Optionally, the anti-MerTK antibody comprises the VL sequence of SEQ ID NO: 82, including post-translational modifications of that sequence. In certain embodiments, the VL comprises one, two, or three HVRs selected from (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59, (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60, and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO: 61. In exemplary embodiments, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0271] In another aspect, an anti-MerTK antibody is provided, wherein the antibody comprises a VH as in any of the embodiments provided above, and a VL as in any of the embodiments provided above. In one embodiment, the antibody comprises the VH and VL sequences of SEQ ID NO: 101 and SEQ ID NO: 82, respectively, including post-translational modifications of those sequences. In an exemplary embodiment, the anti-MerTK antibody binds to the Ig-like domain of MerTK.

[0272] In a further aspect, the invention provides antibodies that compete for binding to MerTK with the anti-MerTK reference antibodies provided herein. For example, in certain embodiments, antibodies are provided that compete for binding to MerTK with one or more of the following anti-MerTK reference antibodies: an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:83 and a VL comprising the amino acid sequence of SEQ ID NO:65; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:84 and a VL comprising the amino acid sequence of SEQ ID NO:66; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:85 and a VL comprising the amino acid sequence of SEQ ID NO:67; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:102 and a light chain comprising the amino acid sequence of SEQ ID NO:110; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:86 and a VL comprising the amino acid sequence of SEQ ID NO:68; a heavy chain comprising the amino acid sequence of SEQ ID NO:103 and a light chain comprising the amino acid sequence of SEQ ID NO:111; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:87 and a VL comprising the amino acid sequence of SEQ ID NO:69; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:88 and a VL comprising the amino acid sequence of SEQ ID NO:70; a heavy chain comprising the amino acid sequence of SEQ ID NO:104 and a light chain comprising the amino acid sequence of SEQ ID NO:112. an antibody comprising a heavy chain; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:89 and a VL comprising the amino acid sequence of SEQ ID NO:70; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:105 and a light chain comprising the amino acid sequence of SEQ ID NO:113; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:90 and a VL comprising the amino acid sequence of SEQ ID NO:71; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:91 and a VL comprising the amino acid sequence of SEQ ID NO:72; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:106 and a light chain comprising the amino acid sequence of SEQ ID NO:114; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:92 and a VL comprising the amino acid sequence of SEQ ID NO:73; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:107 and a light chain comprising the amino acid sequence of SEQ ID NO:115; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:93 and a VL comprising the amino acid sequence of SEQ ID NO:74; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:94 and a VL comprising the amino acid sequence of SEQ ID NO:75; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:95 and a VL comprising the amino acid sequence of SEQ ID NO:76;An antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:96 and a VL comprising the amino acid sequence of SEQ ID NO:77; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:97 and a VL comprising the amino acid sequence of SEQ ID NO:78; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:98 and a VL comprising the amino acid sequence of SEQ ID NO:79; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:108 and a light chain comprising the amino acid sequence of SEQ ID NO:116; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:99 and a VL comprising the amino acid sequence of SEQ ID NO:80; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:109 and a light chain comprising the amino acid sequence of SEQ ID NO:117; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:100 and a VL comprising the amino acid sequence of SEQ ID NO:81; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:101 and a VL comprising the amino acid sequence of SEQ ID NO:82. In some embodiments, the isolated antibody binds to human MerTK. In some embodiments, the reference antibody is commercially available Y323 (abcam catalogue no. ab52968).;

[0273] In a further aspect, the present invention provides antibodies that bind to the same epitope as the anti-MerTK antibodies provided herein. For example, in certain embodiments, an antibody is provided that binds to the same epitope as any one of the following anti-MerTK antibodies: an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:83 and a VL comprising the amino acid sequence of SEQ ID NO:65; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:84 and a VL comprising the amino acid sequence of SEQ ID NO:66; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:85 and a VL comprising the amino acid sequence of SEQ ID NO:67; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:102 and a light chain comprising the amino acid sequence of SEQ ID NO:110; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:86 and a VL comprising the amino acid sequence of SEQ ID NO:68; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:103 and a light chain comprising the amino acid sequence of SEQ ID NO:111; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:87 and a VL comprising the amino acid sequence of SEQ ID NO:69; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:88 and a VL comprising the amino acid sequence of SEQ ID NO:70; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:104. an antibody comprising a heavy chain comprising an amino acid sequence of SEQ ID NO: 107 and a light chain comprising the amino acid sequence of SEQ ID NO: 115; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 93 and a VL comprising the amino acid sequence of SEQ ID NO: 74; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO: 94 and a VL comprising the amino acid sequence of SEQ ID NO: 75. In a specific embodiment, an antibody is provided that binds to an epitope within the fibronectin-like domain of MerTK consisting of amino acid residues 286 to 384 or 388 to 480 of MerTK of SEQ ID NO:129.In some embodiments, the antibody binds to the same epitope as the antibody, Y323, which is commercially available (abcam catalog number ab52968).

[0274] In a further aspect, the present invention provides antibodies that bind to the same epitope as the anti-MerTK antibodies provided herein. For example, in certain embodiments, an antibody is provided that binds to the same epitope as any one of the following anti-MerTK antibodies: an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:95 and a VL comprising the amino acid sequence of SEQ ID NO:76; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:96 and a VL comprising the amino acid sequence of SEQ ID NO:77; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:97 and a VL comprising the amino acid sequence of SEQ ID NO:78; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:98 and a VL comprising the amino acid sequence of SEQ ID NO:79; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:108 and a light chain comprising the amino acid sequence of SEQ ID NO:116; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:99 and a VL comprising the amino acid sequence of SEQ ID NO:80; an antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:109 and a light chain comprising the amino acid sequence of SEQ ID NO:117; an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:100 and a VL comprising the amino acid sequence of SEQ ID NO:81; and an antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:101 and a VL comprising the amino acid sequence of SEQ ID NO:82. In a specific embodiment, an antibody is provided that binds to an epitope within the Ig-like domain of MerTK consisting of amino acid residues 76 to 195 or 199 to 283 of MerTK of SEQ ID NO:129.

[0275] In a further aspect of the invention, the anti-MerTK antibody according to any of the above embodiments is a monoclonal antibody, including a chimeric, humanized, or human antibody. In one embodiment, the anti-MerTK antibody is an antibody fragment, such as an Fv, Fab, Fab', scFv, diabody, or F(ab') 2In another embodiment, the antibody is a full-length antibody, such as an intact IgG1 antibody as defined herein, or other antibody class or isotype. In certain embodiments, the antibody comprises a mutation in the Fc region that reduces binding to Fc receptors and / or complement. In one embodiment, the antibody comprises a LALAPG mutation in the Fc region.

[0276] In further aspects, anti-MerTK antibodies according to any of the above embodiments may incorporate any of the features described in Sections 1-8 below, either alone or in combination.

[0277] 1.MerTK biological activity In some embodiments, the antibody reduces MerTK-mediated clearance of apoptotic cells by phagocytes, e.g., clearance of apoptotic cells is reduced by 1-10 fold, 1-8 fold, 1-5 fold, 1-4 fold, 1-3 fold, 1-2 fold, 2-10 fold, 2-8 fold, 2-5 fold, 2-4 fold, 2-3 fold, 3-10 fold, 3-8 fold, 3-5 fold, 3-4 fold, or 1.1 fold, 1.2 fold, 1.3 fold, 1.4 fold, 1.5 fold, 1.6 fold, 1.7 fold, 1.8 fold, 1.9 fold, 2.0 fold, 2.1 fold, 2.2 fold, 2.3 fold, 2.4 fold, 2.5 fold, 2.6 fold, 2.7 fold, 2.8 fold, 2.9 fold, 3.0 fold, 3.1 fold, x, 3.2x, 3.3x, 3.4x, 3.5x, 3.6x, 3.7x, 3.8x, 3.9x, 4.0x, 4.1x, 4.2x, 4.3x, 4 .4x, 4.5x, 4.6x, 4.7x, 4.8x, 4.9x, 5.0x, 5.1x, 5.2x, 5.3x, 5.4x, 5.5x, 5.6x, The phagocyte is reduced by 5.7-fold, 5.8-fold, 5.9-fold, 6.0-fold, 6.1-fold, 6.2-fold, 6.3-fold, 6.4-fold, 6.5-fold, 6.6-fold, 6.7-fold, 6.8-fold, 6.9-fold, 7.0-fold, 7.1-fold, 7.2-fold, 7.3-fold, 7.4-fold, 7.5-fold, 7.6-fold, 7.7-fold, 7.8-fold, 7.9-fold, or 8.0-fold. In some embodiments, the phagocyte is a macrophage. In some such embodiments, the macrophage is a tumor-associated macrophage (TAM). In humans, TAMs can be identified based on the expression of various cell surface markers, including CD14, HLA-DR (MHC class II), CD312, CD115, CD16, CD163, CD204, CD206, and CD301. Furthermore, production of certain functional biomarkers, such as matrix metalloproteinases, IL-10, inducible nitric oxide synthase (iNOS), TNF-α, or IL-12, can be combined with cell surface biomarkers to accurately identify TAM populations (Quatromoni, J., et al., Am J Transl Res. 4 (2012): 376-389.). Clearance of apoptotic cells can be measured by any assay known to those skilled in the art for such purposes. For example, for in vitro apoptotic cell clearance assays, phagocytes such as mouse peritoneal macrophages or human monocyte-derived macrophages are used.Apoptotic cells are generated by treatment with dexamethasone and labeled with a detection probe. Phagocytosis can be analyzed by microscopy or flow cytometry after incubating apoptotic cells with phagocytes. In some embodiments, the clearance of such apoptotic cells is reduced as measured in an apoptotic cell clearance assay at room temperature. For example, for an in vivo apoptosis clearance assay, mice are injected with dexamethasone to induce thymocyte death. Resident macrophages in the thymus recognize and phagocytose dead / dying cells (Seitz, HMJ Immunol. 178(9)5635-5642 (2007). In some embodiments, clearance of apoptotic cells is reduced as measured in such an apoptotic cell clearance assay in vivo. In some embodiments, the antibody reduces ligand-mediated MerTK signaling. In some embodiments, the ligand is hGAS6-Fc (EC50=about 84 pM). In some embodiments, the antibody induces a proinflammatory response. In some embodiments, the antibody induces a type I IFN response.

[0278] In some embodiments, the anti-MerTK antibodies of the present disclosure inhibit the phagocytic activity of apoptotic cells by about 10-100%, 20-100%, 30-100%, 40-100%, 50-100%, 60-100%, 70-100%, 75-100%, 80-100%, 85-100%, 90-100%, 95-100%, 10-95%, 20-95%, 30-95%, 40-95%, 50-95%, 60-95%, , 70~95%, 75~95%, 80~95%, 85~95%, 90~95%, 10~90%, 20~90%, 30~90%, 40~90%, 50~90%, 60~90%, 70~90%, 75~90%, 80~90%, 85~90%, 10~85%, 20~85%, 30~85%, 40~85%, 50~85%, 60~85%, 70~85%, 75~85%, 80~85%, 10~80%, 20~ 80%, 30~80%, 40~80%, 50~80%, 60~80%, 70~80%, 75~80%, 10~75%, 20~75%, 30~75%, 40~75%, 50~75%, 60~75%, 70~75%, 10~70%, 20~70%, 30~70%, 40~70%, 50~70%, 60~70%, 10~65%, 20~65%, 30~65%, 40~65%, 50~65%, 60~65%, A decrease of 10-60%, 20-60%, 30-60%, 40-60%, 50-60%, 10-55%, 20-55%, 30-55%, 40-55%, 50-55%, 10-40%, 20-40%, or 30-40%, or at least about 10%, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99%.In some embodiments, the anti-MerTK antibody has a half maximal inhibitory concentration (IC50) for reducing phagocytic activity of apoptotic cells of about 1 pM to 50 pM, 1 pM to 100 pM, 1 pM to 500 pM, 1 pM to 1 nM, 1 pM to 1.5 nM, 5 pM to 50 pM, 5 pM to 100 pM, 5 pM to 500 pM, 5 pM to 1 nM , 5 pM to 1.5 nM, 10 pM to 50 pM, 10 pM to 100 pM, 10 pM to 500 pM, 10 pM to 1 nM, 10 pM to 1.5 nM, 50 pM to 100 pM, 50 pM to 500 pM, 50 pM to 1 nM, 50 pM to 1.5 nM, 100 pM to 500 pM, 100 pM to 1 nM, or 100 pM to 1.5 nM. Exemplary methods for determining phagocytic activity and IC50 are described in the Examples herein below.

[0279] In certain embodiments, the anti-MerTK antibodies of the disclosure enhance the activity of a checkpoint inhibitor by about 1-2 fold, 1-5 fold, 1-10 fold, 1-15 fold, 1-20 fold, 1-25 fold, 1-30 fold, 1-50 fold, 1-75 fold, 1-100 fold, 1-150 fold, 1-200 fold, 1-250 fold, 1.5-2 fold, 1.5-5 fold, 1.5-10 fold, 1.5-15 fold, 1.5-20 fold, 1.5-25 fold, 1.5-30 fold, 1.5-50 fold, 1.5-75 fold , 1.5~100x, 1.5~150x, 1.5~200x, 1.5~250x, 2~5x, 2~10x, 2~15x, 2~20x, 2~25x, 2~30x, 2~50x, 2~75x, 2~100x, 2~15 0x, 2~200x, 2~250x, 2.5~5x, 2.5~10x, 2.5~15x, 2.5~20x, 2.5~25x, 2.5~30x, 2.5~50x, 2.5~75x, 2.5~100x, 2.5~150 times, 2.5-200 times, 2.5-250 times, 5-10 times, 5-15 times, 5-20 times, 5-25 times, 5-30 times, 5-50 times, 5-75 times, 5-100 times, 5-150 times, 5-200 times, 5-250 times, 10-15 x, 10~20x, 10~25x, 10~30x, 10~50x, 10~75x, 10~100x, 10~150x, 10~200x, 10~250x, 20~25x, 20~30x, 20~50x, 20~75x , 20-100 fold, 20-150 fold, 20-200 fold, 20-250 fold, 25-30 fold, 25-50 fold, 25-75 fold, 25-100 fold, 25-150 fold, 25-200 fold, or 25-250 fold, or at least about 1 fold, 2 fold, 5 fold, 10 fold, 15 fold, 20 fold, 25 fold, 30 fold, 40 fold, 50 fold, 60 fold, 70 fold, 75 fold, 80 fold, 90 fold, 100 fold, 125 fold, 150 fold, 200 fold, 225 fold, or 250 fold. In certain embodiments, the anti-MerTK antibodies of the present disclosure enhance the activity of a checkpoint inhibitor as determined using the assays described in the Examples herein below, for example, by determining the reduction in tumor volume in a mouse tumor model using a combination of an anti-MerTK antibody plus a checkpoint inhibitor compared to the reduction in tumor volume using the checkpoint inhibitor alone, In certain embodiments, the reduction in tumor volume is measured at least 10, 14, 20, 21, or 30 days after treatment with the therapeutic agent.In certain embodiments, the checkpoint inhibitor is an anti-PD1 axis antagonist. In an exemplary embodiment, the checkpoint inhibitor is an anti-PD-L1 antibody. In another embodiment, the checkpoint inhibitor is an anti-PD1 antibody.

[0280] In some embodiments, the anti-MerTK antibodies of the disclosure increase cell free DNA (cfDNA) and / or circulating tumor DNA (ctDNA) in, for example, a blood or plasma sample by about 1-2 fold, 1-3 fold, 1-4 fold, 1-5 fold, 1-10 fold, 1.5-2 fold, 1.5-3 fold, 1.5-4 fold, 1.5-5 fold, 1.5-10 fold, 2-3 fold, 2-4 fold, 2-5 fold, 2-10 fold, 3-5 fold, 3-10 fold, 4-5 fold, 4-10 fold, 5-10 fold, or at least about 1 fold, 2 fold, 3 fold, 4 fold, 5 fold, or 10 fold. In certain embodiments, the anti-MerTK antibodies of the present disclosure increase cell-free DNA (cfDNA) and / or circulating tumor DNA (ctDNA), as determined using the assays described in the Examples herein below, for example, by isolating cfDNA and / or ctDNA from a blood or plasma sample and detecting the levels of cfDNA and / or ctDNA using PCR and quantitative DNA electrophoresis.

[0281] 2. Antibody affinity and specificity In certain embodiments, the anti-MerTK antibodies provided herein have a cytotoxicity of about ≦1 μM, ≦100 nM, ≦10 nM, ≦1 nM, ≦0.1 nM, ≦0.01 nM, or ≦0.001 nM, or about 1 pM to 0.1 nM, 1 pM to 0.2 nM, 1 pM to 0.5 nM, 1 pM to 1 nM, 1 pM-2 nM, 1 pM to 5 nM, 1 pM to 10 nM, 1 pM to 15 nM, 5 pM ~0.1nM, 5pM~0.2nM, 5pM~0.5nM, 5pM~1nM, 5pM-2nM, 5pM~5nM, 5pM~10nM, 5pM~15nM, 10pM~0.1nM, 10pM~0.2nM, 10pM~0.5nM, 10pM~1nM, 10pM~2nM, 10pM~5nM, 10pM~10nM, 10pM~15nM, 20pM~0.1nM, 20pM~0.2nM, 20pM~0.5nM, 20pM~1nM, 20pM-2nM, 20pM~5nM, 20pM~10nM, 20pM~15nM, 25pM~0.1nM, 25pM~0.2nM, 25pM~0.5nM, 25pM~1nM, 25pM-2nM, 25pM~5nM, 25pM~10nM, 25pM~15nM, 50pM~0.1nM, The anti-MerTK antibodies disclosed herein have a dissociation constant (Kd) of 50 pM to 0.2 nM, 50 pM to 0.5 nM, 50 pM to 1 nM, 50 pM-2 nM, 50 pM to 5 nM, 50 pM to 10 nM, 50 pM to 15 nM, 100 pM to 0.2 nM, 100 pM to 0.5 nM, 100 pM to 1 nM, 100 pM-2 nM, 100 pM to 5 nM, 100 pM to 10 nM, or 100 pM to 15 nM. In certain embodiments, the Kd of the anti-MerTK antibodies disclosed herein is measured at 25° C. In certain embodiments, the Kd of the anti-MerTK antibodies disclosed herein is measured at 37° C.

[0282] In one embodiment, Kd is measured by radiolabeled antigen binding assay (RIA). In one embodiment, the RIA is performed using a Fab version of the antibody of interest and its antigen. For example, the solution binding affinity of the Fab for the antigen is determined by measuring the binding affinity of the Fab to the antigen in the presence of a titration series of unlabeled antigen at a minimal concentration of ( 125I) Fab is equilibrated with labeled antigen, and then bound antigen is measured by capturing it on a plate coated with anti-Fab antibody (see, e.g., Chen et al., J. Mol. Biol. 293:865-881 (1999)). To establish assay conditions, MICROTITER® multi-well plates (Thermo Scientific) are coated overnight with 5 μg / mL of capturing anti-Fab antibody (Cappel Labs) in 50 mM sodium carbonate (pH 9.6), and then blocked with 2% (w / v) bovine serum albumin in PBS for 2-5 hours at room temperature (approximately 23° C.). In non-adsorbent plates (Nunc #269620), 100 pM or 26 pM [ 125 I]-antigen is mixed with serial dilutions of the Fab of interest (e.g., consistent with the evaluation of anti-VEGF antibody Fab-12 in Presta et al., Cancer Res. 57:4593-4599 (1997)). The Fab of interest is then incubated overnight, although incubation can be continued for longer periods (e.g., about 65 hours) to ensure equilibrium is reached. The mixture is then transferred to a capture plate for incubation at room temperature (e.g., 1 hour). The solution is then removed and the plate is washed 8 times with 0.1% polysorbate 20 (TWEEN-20®) in PBS. Once the plate has dried, 150 μl / well of scintillant (MICROSCINT-20™, Packard) is added and the plate is counted on a TOPCOUNT™ gamma counter (Packard) for 10 minutes. Concentrations of each Fab that result in 20% or less of maximal binding are selected for use in competitive binding assays.

[0283] According to another embodiment, Kd is measured using a BIACORE® surface plasmon resonance assay. For example, an assay using a BIACORE®-2000 or BIACORE®-3000 (BIAcore, Inc., Piscataway, NJ) is performed at 25° C. with an immobilized antigen CM5 chip at approximately 10 response units (RU). In one embodiment, a carboxymethylated dextran biosensor chip (CM5, BIACORE, Inc.) is activated with N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) according to the supplier's instructions. The antigen is diluted to 5 μg / mL (approximately 0.2 μM) with 10 mM sodium acetate (pH 4.8) and then injected at a flow rate of 5 μl / min to achieve approximately 10 response units (RU) of binding protein. After injection of the antigen, 1 M ethanolamine is injected to block unreacted groups. For kinetic measurements, two-fold serial dilutions of Fab (0.78 nM-500 nM) are injected in PBS containing 0.05% polysorbate 20 (TWEEN-20™) surfactant (PBST) at 25° C. with a flow rate of approximately 25 μl / min. Association rates (kon) and dissociation rates (koff) are calculated by simultaneously fitting the association and dissociation sensograms using a simple one-to-one Langmuir binding model (BIACORE® Evaluation Software version 3.2). The equilibrium dissociation constant (Kd) is calculated as the ratio koff / kon. See, e.g., Chen et al., J. Mol. Biol. 293:865-881 (1999).If the on-rate exceeds 106 M-1 s-1 by the surface plasmon resonance assay described above, the on-rate can be determined by using a fluorescence quenching technique that measures the increase or decrease in fluorescence emission intensity (excitation = 295 nm, emission = 340 nm, 16 nm band pass) of 20 nM anti-antigen antibody (Fab form) in PBS (pH 7.2) at 25°C in the presence of increasing concentrations of antigen as measured with a spectrometer such as a spectrophotometer equipped with a stopped-flow (Aviv Instruments) or an 8000 series SLM-AMINCO™ spectrophotometer with a stirred cuvette (ThermoSpectronic).

[0284] In certain embodiments, the anti-MerTK antibodies disclosed herein bind to one or more of human MerTK, cynomolgus monkey MerTK, mouse MerTK, and / or rat MerTK. In one embodiment, the anti-MerTK antibodies disclosed herein specifically bind to human MerTK. In one embodiment, the anti-MerTK antibodies disclosed herein specifically bind to human MerTK or cynomolgus monkey MerTK. In one embodiment, the anti-MerTK antibodies disclosed herein specifically bind to human MerTK and mouse MerTK. In one embodiment, the anti-MerTK antibodies disclosed herein specifically bind to human MerTK, cynomolgus monkey MerTK, and mouse MerTK. In one embodiment, the anti-MerTK antibodies disclosed herein bind to human MerTK, cynomolgus monkey MerTK, mouse MerTK, and rat MerTK. In one embodiment, the anti-MerTK antibodies disclosed herein specifically bind to mouse MerTK.

[0285] In certain embodiments, the anti-MerTK antibodies disclosed herein bind to an Ig-like domain of MerTK. In one embodiment, an anti-MerTK antibody that binds to an Ig-like domain of MerTK binds to one or more amino acid residues in the Ig-like domain corresponding to amino acid residues 76-195 of MerTK SEQ ID NO: 129, e.g., the anti-MerTK antibody binds to at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids or 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9 or 1-10 amino acid residues of residues 76-195 of MerTK SEQ ID NO: 129. In one embodiment, an anti-MerTK antibody that binds to the Ig-like domain of MerTK binds to one or more amino acid residues in the Ig-like domain corresponding to amino acid residues 199-283 of MerTK SEQ ID NO:129, for example, the anti-MerTK antibody binds to at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acids or 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9 or 1-10 amino acid residues of residues 199-283 of MerTK SEQ ID NO:129.

[0286] In certain embodiments, an anti-MerTK antibody as disclosed herein binds to the fibronectin-like domain of MerTK. In one embodiment, an anti-MerTK antibody that binds to the fibronectin-like domain of MerTK binds to one or more amino acid residues in the fibronectin-like domain corresponding to amino acid residues 286-384 of MerTK SEQ ID NO: 129, e.g., the anti-MerTK antibody binds to at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids or 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid residues of residues 286-384 of MerTK SEQ ID NO: 129. In one embodiment, an anti-MerTK antibody that binds to the fibronectin-like domain of MerTK binds to one or more amino acid residues in the fibronectin-like domain corresponding to amino acid residues 388-480 of MerTK SEQ ID NO:129, for example, the anti-MerTK antibody binds to at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids or 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, or 1-10 amino acid residues of residues 388-480 of MerTK SEQ ID NO:129.

[0287] In exemplary embodiments, anti-MerTK antibodies disclosed herein bind to the Ig-like domain of human and cynomolgus MerTK. In one embodiment, such antibodies bind to human and cynomolgus MerTK with a Kd at 37° C. that is approximately the same, e.g., the antibodies bind to cynomolgus MerTK at 37° C. with a Kd that differs by no more than 10%, 15%, or 20% from the Kd of the antibody at 37° C. for human MerTK. In certain embodiments, such antibodies bind to human and cynomolgus MerTK with a Kd at 37° C. that is at least 20-fold, 25-fold, or 50-fold better than the Kd of the antibody at 37° C. for mouse and rat MerTK.

[0288] 3. Antibody fragment In certain embodiments, the anti-MerTK antibodies provided herein are antibody fragments. Antibody fragments include Fab, Fab', Fab'-SH, F(ab') 2Antibody fragments include, but are not limited to, Fv, and scFv fragments, as well as 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. Pat. Nos. 5,571,894 and 5,587,458. Fab and F(ab') fragments that contain salvage receptor binding epitope residues and have extended half-lives in vivo. 2 For a description of fragments, see US Pat. No. 5,869,046.

[0289] Diabodies are antibody fragments with two antigen-binding sites that can be bivalent or bispecific. See, e.g., 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).

[0290] A single domain antibody is an antibody fragment that contains 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, Mass.; see, e.g., U.S. Pat. No. 6,248,516 B1).

[0291] Antibody fragments can be produced by a variety of techniques, including, but not limited to, proteolytic digestion of intact antibodies and production by recombinant host cells (e.g., E. coli or phages), as described herein.

[0292] 4. Chimeric and humanized antibodies In certain embodiments, the anti-MerTK antibody provided herein is a chimeric antibody. Certain chimeric antibodies are described, for example, in U.S. Patent No. 4,816,567; and Morrison et al., Proc. Natl. Acad. Sci. USA, 81:6851-6855 (1984). In one example, the chimeric antibody comprises a non-human variable region (e.g., a variable region from a mouse, rat, hamster, rabbit, or a non-human primate, e.g., a monkey) and a human constant region. In a further example, the chimeric antibody is a "class-switched" antibody whose class or subclass has been changed from that of the parent antibody. The chimeric antibody includes antigen-binding fragments thereof.

[0293] 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 parent non-human antibody. Generally, a humanized antibody comprises one or more variable domains in which the HVRs, e.g., CDRs (or portions thereof), are derived from a non-human antibody and the FRs (or portions thereof) are derived from a human antibody sequence. A humanized antibody optionally also comprises at least a portion of a human constant region. In some embodiments, some FR residues of the humanized antibody are replaced with the corresponding residues from the non-human antibody (e.g., the antibody from which the HVR residues are derived), e.g., to restore or improve antibody specificity or affinity.

[0294] Humanized antibodies and methods for making them are reviewed by Almagro and Fransson, Front. Biosci. 13:1619-1633 (2008), and further described in Riechmann et al., Nature 332:323-329 (1988); Queen et al., Proc. Nat'l Acad. Sci. USA 86:10029-10033 (1989); U.S. 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 Osbourn et al., Methods 36:61-68 (2005) and Klimka et al., Br. J. Cancer, 83:252-260 (2000) (describing a "guided selection approach" for FR shuffling).

[0295] 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 consensus sequences of human antibodies of particular subgroups 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 and Fransson, Front. Biosci. 13:1619-1633 (2008)); and framework regions derived from screening of FR libraries (see, e.g., Baca et al. (see, e.g., Rosok et al., J. Biol. Chem. 272:10678-10684 (1997) and Rosok et al., J. Biol. Chem. 271:22611-22618 (1996)).

[0296] 5. Human antibodies In certain embodiments, the anti-MerTK antibodies provided herein are human antibodies. Human antibodies can be produced using a variety of techniques known in the art. Human antibodies are generally described in van Dijk and van de Winkel, Curr. Opin. Pharmacol. 5:368-74 (2001) and Lonberg, Curr. Opin. Immunol. 20:450-459 (2008).

[0297] Human antibodies can be prepared by administering immunogens to transgenic animals that have been engineered to produce intact human antibodies or intact antibodies with human variable regions in response to antigen challenge. Such animals typically contain all or part of a human immunoglobulin locus that replaces the endogenous immunoglobulin locus or is present extrachromosomally or randomly integrated into the animal's chromosomes. In such transgenic mice, the endogenous immunoglobulin locus is generally inactivated. For a review of methods for obtaining human antibodies from transgenic animals, see Lonberg, Nat. Biotech. 23:1117-1125 (2005). See also, e.g., U.S. Patent Nos. 6,075,181 and 6,150,584, which describe XENOMOUSE™ technology; U.S. Patent No. 5,770,429, which describes HuMab® technology; U.S. Patent No. 7,041,870, which describes KM MOUSE® technology; and U.S. Patent Application Publication No. 2007 / 0061900, which describes VelociMouse® technology. The human variable regions from intact antibodies produced by such animals may be further modified, for example, by combining with different human constant regions.

[0298] Human antibodies can also be produced by hybridoma-based methods. Human myeloma cell lines and mouse-human heteromyeloma cell lines for producing human monoclonal antibodies have been described. (See, for example, Kozbor J.Immunol., 133:3001 (1984); Brodeur et al., Monoclonal Antibody Production Techniques and Applications, pp.51-63 (Marcel Dekker, Inc., New York, 1987); and Boerner et al., J.Immunol., 147:86 (1991)). Human antibodies generated via human B-cell hybridoma technology are also described in Li et al., Proc.Natl.Acad.Sci.USA, 103:3557-3562 (2006). Further methods include, for example, U.S. Patent No. 7,189,826, which describes the production of monoclonal human IgM antibodies from hybridoma cell lines, and Ni, Xiandai Mianyixue, 26(4):265-268 (2006), which describes human-human hybridomas. Human hybridoma technology (trioma technology) is also described in 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).

[0299] Human antibodies can also be made by isolating Fv clone variable domain sequences selected from a human-derived phage display library. Such variable domain sequences can then be combined with the desired human constant domains. Techniques for selecting human antibodies from antibody libraries are described below.

[0300] 6. Library-derived Antibodies Anti-MerTK antibodies of the invention can be isolated by screening combinatorial libraries for antibodies with the desired activity(ies). For example, various methods are known in the art for generating phage display libraries and screening such libraries for antibodies with the desired binding characteristics. Such methods are reviewed, for example, in Hoogenboom et al. in Methods in Molecular Biology 178:1-37 (O'Brien et al., ed., Human Press, Totowa, NJ, 2001), and in 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. 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).

[0301] In one particular phage display method, repertoires of VH and VL genes can be cloned separately by polymerase chain reaction (PCR), randomly recombined in a phage library, and then screened for antigen-binding phages as described by Winter et al., Ann. Rev. Immunol., 12:433-455 (1994). Phages typically display antibody fragments as either single-chain Fv (scFv) fragments or Fab fragments. Libraries from immune sources provide high affinity antibodies to the immunogen without the need to construct hybridomas. Alternatively, naive repertoires can be cloned (e.g., from humans) without immunization to provide a single source of antibodies to a wide range of non-self antigens and also self antigens, as described by Griffiths et al., EMBO J, 12:725-734 (1993). Finally, naive libraries can also be generated synthetically by cloning unrearranged V gene segments from stem cells and using PCR primers containing random sequences to encode highly variable CDR3 regions and achieve rearrangement in vitro as described in Hoogenboom and Winter, J. Mol. Biol., 227:381-388 (1992). Patent publications describing human antibody phage libraries include, for example: U.S. Pat. No. 5,750,373, and U.S. Patent Application Publication Nos. 2005 / 0079574, 2005 / 0119455, 2005 / 0266000, 2007 / 0117126, 2007 / 0160598, 2007 / 0237764, 2007 / 0292936, and 2009 / 0002360.

[0302] Antibodies or antibody fragments isolated from a human antibody library are considered herein to be human antibodies or human antibody fragments.

[0303] 7. Multispecific antibodies In certain embodiments, the anti-MerTK antibodies provided herein are multispecific antibodies, e.g., bispecific antibodies. Multispecific antibodies are monoclonal antibodies that have binding specificities for at least two different sites. In certain embodiments, one of the binding specificities is for MerTK and the other is for any other antigen. In certain embodiments, bispecific antibodies can bind to two different epitopes of MerTK. Bispecific antibodies can also be used to localize cytotoxic agents to cells expressing MerTK. Bispecific antibodies can be prepared as full-length antibodies or antibody fragments.

[0304] Techniques for making multispecific antibodies include, but are not limited to, recombinant coexpression of two immunoglobulin heavy-light chain pairs with different specificities (see Milstein and Cuello, Nature 305:537 (1983); WO 93 / 08829; and Traunecker et al., EMBO J. 10:3655 (1991)), and "knobs-into-holes" engineering (see, e.g., U.S. Pat. No. 5,731,168). Multispecific antibodies can be produced by a number of techniques, including the engineering of electrostatic steering effects to create antibody Fc-heterodimeric molecules (WO 2009 / 089004A1); cross-linking of two or more antibodies or fragments (see, e.g., U.S. Pat. No. 4,676,980, and Brennan et al., Science, 229:81 (1985)); the use of leucine zippers to produce bispecific antibodies (see, e.g., Kostelny et al., J. Immunol., 148(5):1547-1553 (1992)); the use of "diabody" technology to create bispecific antibody fragments (see, e.g., Hollinger et al., Proc. Natl. Acad. Sci. USA, 90:6444-6448 (1993)); and the use of single-chain Fv (sFv) dimers (see, e.g., Gruber et al., J. Immunol., 1997, 111:111-112 (1997)). al., J. Immunol., 152:5368 (1994); as well as, for example, as described in Tutt et al. J. Immunol. 147:60 (1991).

[0305] Engineered antibodies with three or more functional antigen binding sites, including "octopus antibodies," are also included herein (see, eg, US Patent Application Publication No. 2006 / 0025576 A1).

[0306] The antibodies or fragments herein also include "Dual Acting FAbs" or "DAFs" that contain antigen binding sites that bind to MerTK as well as another distinct antigen (see, e.g., U.S. Patent Application Publication No. 2008 / 0069820).

[0307] 8. Antibody variants In certain embodiments, amino acid sequence variants of the anti-MerTK antibodies provided herein are contemplated. For example, it may be desirable to improve the binding affinity and / or other biological properties of the anti-MerTK antibody. Amino acid sequence variants of the 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 sequence of the antibody. Any combination of deletions, insertions, and substitutions can be made to arrive at the final construct, so long as the final construct possesses the desired characteristics (e.g., antigen binding).

[0308] a) Substitution, insertion, and deletion variants In certain embodiments, antibody variants with one or more amino acid substitutions are provided. Sites of interest for substitutional mutagenesis include HVRs and FRs. Conservative substitutions are shown in Table 1 under the heading of "preferred substitutions." More substantial changes are shown in Table 1 under the heading of "exemplary substitutions" and are further described below with respect to amino acid side chain classes. Amino acid substitutions can be introduced into the antibody of interest and the products screened for the desired activity, e.g., retained / improved antigen binding, reduced immunogenicity, or improved ADCC or CDC. [Table 1]

[0309] Amino acids can be classified according to common side chain properties. (1) Hydrophobic: Norleucine, Met, Ala, Val, Leu, Ile; (2) Neutral hydrophilic: Cys, Ser, Thr, Asn, Gln; (3) Acidic: Asp, Glu, (4) Basic: His, Lys, Arg, (5) Residues that affect chain orientation: Gly, Pro, (6) Aromatic: Trp, Tyr, Phe.

[0310] Non-conservative substitutions involve exchanging a member of one of these classes for another class.

[0311] One type of substitutional variant involves the substitution of 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 testing have modified (e.g., improved) certain biological properties (e.g., increased affinity, reduced immunogenicity) compared to the parent antibody and / or have substantially retained certain biological properties of the parent antibody. An exemplary substitutional variant is an affinity matured antibody, which may be conveniently generated using, for example, phage display-based affinity maturation techniques as described herein. Briefly, one or more HVR residues are mutated and the variant antibodies are displayed on phage and screened for a particular biological activity (e.g., binding affinity).

[0312] Alterations (e.g., substitutions) may be made, for example, in HVRs to improve antibody affinity. Such modifications may be made in HVR "hot spots," i.e., residues encoded by codons that undergo frequent mutation during the somatic maturation process (see, e.g., Chowdhury, Methods Mol. Biol. 207:179-196 (2008)), and / or within residues that contact the antigen, and the resulting variants VH or VL are tested for binding affinity. Affinity maturation by construction of and reselection from secondary libraries is described, for example, 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 selected 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 generated. This library is then screened to identify any antibody variants with the desired affinity. Another method for introducing diversity involves HVR-directed approaches, where several HVR residues (e.g., 4-6 residues at a time) are randomized. HVR residues involved in antigen binding can be specifically identified, for example, using alanine scanning mutagenesis or modeling. CDR-H3 and CDR-L3 in particular are often targeted.

[0313] In certain embodiments, substitutions, insertions, or deletions may occur within one or more HVRs, so long as such modifications do not substantially reduce the ability of the antibody to bind to the antigen. For example, conservative modifications (e.g., conservative substitutions as provided herein) that do not substantially reduce binding affinity may be made in the HVRs. Such changes may, for example, be outside of the antigen contact residues within the HVRs. In certain embodiments of the variant VH and VL sequences provided above, each HVR is either unchanged or contains no more than one, two, or three amino acid substitutions.

[0314] A useful method for identifying antibody residues or regions 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, e.g., arg, asp, his, lys, and glu) are identified and replaced with neutral or negatively charged amino acids (e.g., alanine or polyalanine) to determine whether antibody-antigen interaction is affected. Further substitutions may be introduced at amino acid positions that show functional sensitivity to the initial substitution. Alternatively, or in addition, a crystal structure of an antigen-antibody complex to identify contact points between the antibody and antigen. Such contact and adjacent residues may be targeted as candidates for substitution or removed. The variants may be screened to determine whether they have the desired properties.

[0315] Amino acid sequence insertions include amino- and / or carboxyl-terminal fusions ranging in length from one residue to polypeptides containing 100 or more residues, as well as intrasequence insertions of single or multiple amino acid residues. An example of a terminal insertion is 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., in the case of ADEPT) or a polypeptide which increases the serum half-life of the antibody.

[0316] b) Glycosylation variants In certain embodiments, the anti-MerTK antibodies provided herein are altered to increase or decrease the extent to which the antibody is glycosylated. Adding or deleting glycosylation sites to an antibody can be conveniently accomplished by altering the amino acid sequence such that one or more glycosylation sites are created or removed.

[0317] If the antibody comprises an Fc region, the carbohydrate attached thereto may be modified. Natural antibodies produced by mammalian cells typically comprise branched, biantennary oligosaccharides that are generally attached to Asn297 of the CH2 domain of the Fc region by an N-linkage. See, for example, Wright et al. TIBTECH 15:26-32 (1997). The oligosaccharides may comprise a variety of carbohydrates, such as mannose, N-acetylglucosamine (GlcNAc), galactose, and sialic acid, and may comprise fucose attached to the GlcNAc at the "stem" of the biantennary oligosaccharide structure. In some embodiments, oligosaccharide modifications may be made in the antibodies of the invention to generate antibody variants with specific improved properties.

[0318] In one embodiment, antibody variants are provided that have carbohydrate structures that lack fucose attached (directly or indirectly) to the Fc region. For example, the amount of fucose in such antibodies can be 1%-80%, 1%-65%, 5%-65% or 20%-40%. The amount of fucose is determined by calculating the average amount of fucose in the glycan at Asn297 compared to the sum of all glycan structures (e.g., complex, hybrid, and high mannose structures) attached to Asn297, as measured by MALDI-TOF mass spectrometry, e.g., as described in WO 2008 / 077546. Asn297 refers to an asparagine residue located at about position 297 (Eu numbering of Fc region residues) in the Fc region, although Asn297 may be located about ±3 amino acids upstream or downstream from position 297, i.e., between positions 294 and 300, due to minor sequence variations within antibodies. Such fucosylation variants may have improved ADCC function. See, for example, US Patent Application Publication No. 2003 / 0157108 (Presta, L.); US Patent Application Publication No. 2004 / 0093621 (Kyowa Hakko Kogyo Co., Ltd). Examples of publications relating to "defucosylated" or "fucose-deficient" antibody variants include: US Patent Application Publication No. 2003 / 0157108; International Publication No. 2000 / 61739; International Publication No. 2001 / 29246; US Patent Application Publication No. 2003 / 0115614; International Publication No. 2002 / 0164328; International Publication No. 2004 / 0093621; International Publication No. 2004 / 0093621; International Publication No. 2004 / 0093622; International Publication No. 2004 / 0093623; International Publication No. 2004 / 0093624; International Publication No. 2004 / 0093621; International Publication No. 2004 / 009362 ... 132140; WO 2004 / 0110704; WO 2004 / 0110282; WO 2004 / 0109865; WO 2003 / 085119; WO 2003 / 084570; WO 2005 / 035586; WO 2005 / 035778; WO 2005 / 053742; WO 2002 / 031140; Okazaki et al. J. Mol. Biol. 336:1239-1249 (2004); Yamane-Ohnuki et al. Biotech. Bioeng. 87:614 (2004).Examples of cell lines capable of producing defucosylated antibodies include Lec13 CHO cells, which are deficient in protein fucosylation (Ripka et al. Arch. Biochem. Biophys. 249:533-545 (1986); US Patent Application Publication No. 2003 / 0157108 A1, Presta, L; and WO 2004 / 056312 A1, Adams et al., especially Example 11), and knockout cell lines, such as α-1,6-fucosyltransferase gene, FUT8, knockout CHO cells (see, e.g., Yamane-Ohnuki et al. Biotech. Bioeng. 87:614 (2004); Kanda, Y. et al., Biotechnol. Bioeng., 94(4):680-688 (2006); and WO 2003 / 085107).

[0319] Further provided are antibody variants having bisected oligosaccharides, for example, biantennary oligosaccharides attached to the Fc region of the antibody are bisected by GlcNAc. Such antibody variants may have reduced fucosylation and / or improved ADCC function. Examples of such antibody variants are described, for example, in WO 2003 / 011878 (Jean-Mairet et al.); U.S. Pat. No. 6,602,684 (Umana et al.); and U.S. Pat. App. Pub. No. 2005 / 0123546 (Umana et al.). Also provided are antibody variants having at least one galactose residue in the oligosaccharide attached to the Fc region. Such antibody variants may have improved CDC function. Such antibody variants are described, for example, in WO 1997 / 30087 (Patel et al.); WO 1998 / 58964 (Raju, S.); and WO 1999 / 22764 (Raju, S.).

[0320] c) Fc domain variants In certain embodiments, one or more amino acid modifications may be introduced into the Fc region of an anti-MerTK antibody provided herein, thereby generating an Fc region variant. The Fc region variant may comprise a human Fc region sequence (e.g., a human IgG1, IgG2, IgG3, or IgG4 Fc region) that contains an amino acid modification (e.g., substitution) at one or more amino acid positions.

[0321] In certain embodiments, the present invention contemplates antibody variants that have some, but not all, effector functions, making them desirable candidates for applications where antibody half-life in vivo is important, but where certain effector functions (e.g., complement and ADCC, etc.) are unnecessary or detrimental. In vitro and / or in vivo cytotoxicity assays can be performed to confirm reduced / lack of CDC and / or ADCC activity. For example, Fc receptor (FcR) binding assays can be performed to confirm that the antibody lacks FcγR binding (and thus likely lacks ADCC activity) but retains FcRn binding ability. NK cells, the primary cells for mediating ADCC, express only FcγRIII, while monocytes express FcγRI, FcγRII, and FcγRIII. Expression of FcR on hematopoietic cells is summarized in Table 3 on page 464 of Ravetch and Kinet, Annu. Rev. Immunol. 9:457-492 (1991). Non-limiting examples of in vitro assays to assess ADCC activity of a molecule of interest are described in U.S. Pat. No. 5,500,362 (see, e.g., Hellstrom, I. et al. Proc. Nat'l Acad. Sci. USA 83:7059-7063 (1986)), and Hellstrom, I. et al., Proc. Nat'l Acad. Sci. USA 82:1499-1502 (1985); 5,821,337 (see, Bruggemann, M. et al., J. Exp. Med. 166:1351-1361 (1987)). Alternatively, non-radioactive assay methods may be used (e.g., ACTI™ Non-Radioactive Cytotoxicity Assay for Flow Cytometry (CellTechnology, Inc. Mountain View, Calif.), and CytoTox 96® Non-Radioactive Cytotoxicity Assay (Promega, Madison, Wis.)). Useful effector cells for such assays include peripheral blood mononuclear cells (PBMC) and Natural Killer (NK) cells.Alternatively or additionally, ADCC activity of a molecule of interest can be assessed in vivo, for example in an animal model such as that disclosed in Clynes et al. Proc. Nat'l Acad. Sci. USA 95:652-656 (1998). C1q binding assays may also be performed to confirm that the antibody is unable to bind C1q and lacks CDC activity. See, for example, C1q and C3c binding ELISAs in WO 2006 / 029879 and WO 2005 / 100402. To assess complement activation, a CDC assay can be performed (see, e.g., Gazzano-Santoro et al., J. Immunol. Methods 202:163 (1996); Cragg, MS et al., Blood 101:1045-1052 (2003); and Cragg, MS and MJ Glennie, Blood 103:2738-2743 (2004)), and determination of FcRn binding and in vivo clearance / half-life can also be performed using methods known in the art (see, e.g., Petkova, SB et al., Int'l. Immunol. 18(12):1759-1769 (2006)).

[0322] Antibodies with reduced effector function include those containing one or more substitutions at residues 238, 265, 269, 270, 297, 327 and 329 in the Fc region (U.S. Patent No. 6,737,056). Such Fc mutants include Fc mutants with substitutions at two or more of amino acid positions 265, 269, 270, 297 and 327, including the so-called "DANA" Fc mutant in which residues 265 and 297 are substituted with alanine (U.S. Patent No. 7,332,581).

[0323] Certain antibody variants have been described with improved or diminished binding to FcRs. (See, e.g., U.S. Pat. No. 6,737,056; WO 2004 / 056312; and Shields et al. J. Biol. Chem. 9(2):6591-6604 (2001).)

[0324] In certain embodiments, the antibody variant comprises an Fc region with one or more amino acid substitutions that improve ADCC, e.g., substitutions at positions 298, 333, and / or 334 (EU numbering of residues) of the Fc region.

[0325] In some embodiments, modifications are made within the Fc region that result in altered (i.e., either improved or decreased) C1q binding and / or complement dependent cytotoxicity (CDC), e.g., as described in U.S. Pat. No. 6,194,551, WO 99 / 51642, and Idusogie et al. J. Immunol. 164:4178-4184 (2000).

[0326] Antibodies with increased half-lives and improved binding to fetal Fc receptors (FcRn) that play a role in transferring maternal IgG to the fetus (Guyer et al., J. Immunol. 117:587 (1976) and Kim et al., J. Immunol. 24:249 (1994)) are described in U.S. Patent Application Publication No. 2005 / 0014934A1 (Hinton et al.). These antibodies comprise an Fc region with one or more substitutions that improve binding of the Fc region to FcRn. Such Fc variants include those with substitutions at one or more of the following Fc region residues: 238, 256, 265, 272, 286, 303, 305, 307, 311, 312, 317, 340, 356, 360, 362, 376, 378, 380, 382, ​​413, 424 or 434, such as a substitution at Fc region residue 434 (U.S. Patent No. 7,371,826).

[0327] For other examples of Fc region variants, see also Duncan & Winter, Nature 322:738-40 (1988), U.S. Patent No. 5,648,260, U.S. Patent No. 5,624,821, and WO 94 / 29351.

[0328] In an exemplary embodiment, the anti-MerTK antibodies disclosed herein comprise a LALPG mutation in the Fc region.

[0329] d) Cysteine ​​Engineered Antibody Variants In certain embodiments, it may be desirable to generate cysteine ​​engineered antibodies, e.g., "thioMAbs," in which one or more residues of an antibody are replaced with a cysteine ​​residue. In certain embodiments, the replaced residues occur at accessible sites of the antibody. By replacing these residues with cysteine, reactive thiol groups are thereby placed at accessible sites of the antibody, which can be used to conjugate the antibody to other moieties, such as drug moieties or linker-drug moieties, to generate immunoconjugates, as further described herein. In certain embodiments, any one or more of the following residues may be replaced with cysteine: V205 (Kabat numbering) of the light chain, A118 (EU numbering) of the heavy chain, and S400 (EU numbering) of the heavy chain Fc region. Cysteine ​​engineered antibodies can be generated, for example, as described in U.S. Pat. No. 7,521,541.

[0330] e) Antibody derivative In certain embodiments, the anti-MerTK antibodies provided herein may be further modified to contain additional non-proteinaceous moieties that are known in the art and readily available. Moieties suitable for derivatization of antibodies include, but are not limited to, water-soluble polymers. Non-limiting examples of water-soluble polymers include, but are not limited to, polyethylene glycol (PEG), ethylene glycol / propylene glycol copolymers, carboxymethylcellulose, dextran, polyvinyl alcohol, polyvinylpyrrolidone, poly-1,3-dioxolane, poly-1,3,6-trioxane, ethylene / maleic anhydride copolymers, polyamino acids (either homopolymers or random copolymers), and dextran or poly(n-vinylpyrrolidone) polyethylene glycol, polypropylene glycol homopolymer, polypropylene oxide / ethylene oxide copolymer, polyoxyethylated polyols (e.g., glycerol), polyvinyl alcohol, and mixtures thereof. Polyethylene glycol propionaldehyde may be advantageous in manufacturing due to its stability in water. The polymer may be of any molecular weight and may be branched or unbranched. The number of polymers attached to the antibody can vary, and when multiple polymers are attached, they can be the same molecule or different molecules. In general, the number and / or type of polymers used for derivatization can be determined based on considerations including, but not limited to, the particular property or function of the antibody to be improved, whether the antibody derivative will be used in a therapy under a given condition, etc.

[0331] In another embodiment, a conjugate of an antibody and a non-proteinaceous moiety is provided that can be selectively heated by exposure to radiation. In one embodiment, the non-proteinaceous moiety is a carbon nanotube (Kam et al., Proc. Natl. Acad. Sci. USA 102:11600-11605 (2005)). The radiation can be of any wavelength, including but not limited to wavelengths that are not harmful to normal cells, but heat the non-proteinaceous moiety to a temperature that kills cells proximal to the antibody-non-proteinaceous moiety.

[0332] B. Recombinant Methods and Compositions The antibodies may be produced using recombinant methods and compositions described, for example, in U.S. Patent No. 4,816,567. In one embodiment, an isolated nucleic acid is provided encoding an anti-MerTK antibody described herein. Such a nucleic acid may encode an amino acid sequence comprising a VL and / or an amino acid sequence comprising an antibody VH (e.g., an antibody light chain and / or heavy chain). In a further embodiment, one or more vectors (e.g., expression vectors) comprising such a nucleic acid are provided. In a further embodiment, a host cell comprising such a nucleic acid is provided. In one such embodiment, the host cell comprises (e.g., has been transformed with): (1) a vector comprising a nucleic acid encoding an amino acid sequence comprising an antibody VL and an amino acid sequence comprising an antibody VH, or (2) a first vector comprising a nucleic acid encoding an amino acid sequence comprising an antibody VL and a second vector comprising a nucleic acid encoding an amino acid sequence comprising an antibody VH. In one embodiment, the host cell is eukaryotic, for example, a Chinese Hamster Ovary (CHO) cell or a lymphoid cell (e.g., a Y0, NS0, Sp20 cell). In one embodiment, a method of making an anti-MerTK antibody is provided, comprising culturing a host cell comprising nucleic acid encoding the antibody under conditions suitable for expression of the antibody, and, optionally, recovering the antibody from the host cell (or host cell culture).

[0333] For recombinant production of an anti-MerTK antibody, nucleic acid encoding the antibody, such as those described above, is isolated and inserted into one or more vectors for further cloning and / or expression in a host cell. Such nucleic acid may be readily isolated and sequenced using conventional procedures (e.g., by using oligonucleotide probes capable of binding specifically to genes encoding the antibody heavy and light chains).

[0334] Suitable host cells for cloning or expressing antibody-encoding vectors include prokaryotic or eukaryotic cells as described herein. For example, antibodies may be produced in bacteria, particularly if glycosylation and effector functions are not required. For expression of antibody fragments and polypeptides in bacteria, see, e.g., U.S. Patent Nos. 5,648,237, 5,789,199, and 5,840,523. (See also Charlton, Methods in Molecular Biology, Vol. 248 (BKC Lo, ed., Humana Press, Totowa, NJ, 2003), pp. 245-254, which describes the expression of antibody fragments in E. coli.) After expression, the antibodies of the invention may be isolated in a soluble fraction from the bacterial cell paste or may be further purified.

[0335] In addition to prokaryotes, eukaryotic organisms such as filamentous fungi and yeast are suitable as cloning or expression hosts for antibody-encoding vectors, including bacterial and yeast strains that have been "humanized" in their glycosylation pathways to result in the production of antibodies with partially or fully human glycosylation patterns. See Gerngross, Nat. Biotech. 22:1409-1414 (2004), and Li et al., Nat. Biotech. 24:210-215 (2006).

[0336] Suitable host cells for expressing glycosylated antibodies are also derived from multicellular organisms (invertebrates and vertebrates). Examples of invertebrate cells include plant cells and insect cells. Numerous baculovirus strains have been identified and can be used in conjunction with insect cells, particularly for transfection of Spodoptera frugiperda cells.

[0337] Plant cell cultures can also be used as hosts, see, e.g., U.S. Patent Nos. 5,959,177, 6,040,498, 6,420,548, 7,125,978, and 6,417,429 (describing PLANTIBODIES™ technology for producing antibodies in transgenic plants).

[0338] Vertebrate cells may also be used as hosts. For example, mammalian cell lines adapted to grow in suspension may be useful. Other examples of useful mammalian host cell lines are the monkey kidney CV1 line transformed with SV40 (COS-7); human embryonic kidney lines (e.g., Graham et al., J. Gen Virol. 36:59 (1977)). Error! Bookmark is not defined. 293 or 293 cells described in Mather et al., Annals NYAcad. Sci. 383:44-68 (1982); baby hamster kidney cells (BHK); mouse Sertoli cells (e.g., TM4 cells described in Mather, Biol. Reprod. 23:243-251 (1980); monkey kidney cells (CV1); African green monkey kidney cells (VERO-76); human cervical carcinoma cells (HELA); canine kidney cells (MDCK); buffalo rat liver cells (BRL 3A); human lung cells (W138); human hepatocytes (Hep G2); mouse mammary tumor (MMT 060562); TRI cells described in Mather et al., Annals NYAcad. Sci. 383:44-68 (1982); MRC 5 cells; and FS4 cells. Other useful mammalian host cell lines include DHFR - Examples of suitable host cell lines include Chinese hamster ovary (CHO) cells, including CHO cells (Urlaub et al., Proc. Natl. Acad. Sci. USA 77:4216 (1980)), and myeloma cell lines such as Y0, NS0, and Sp2 / 0. For a review of certain mammalian host cell lines suitable for antibody production, see, for example, Yazaki and Wu, Methods in Molecular Biology, Vol. 248 (BKC Lo, ed., Humana Press, Totowa, NJ), pp. 255-268 (2003);

[0339] C. Assay The anti-MerTK antibodies provided herein may be identified, screened, or characterized for their physical / chemical properties and / or biological activity by various assays known in the art.

[0340] In one embodiment, the antibodies of the invention are tested for their antigen binding activity by known methods, such as ELISA, Western blot, etc.

[0341] In another aspect, a competition assay can be used to identify antibodies that compete with one or more of the anti-MerTK antibodies disclosed herein for binding to MerTK. In certain embodiments, such competing antibodies bind to the same epitope (e.g., a linear or conformational epitope) bound by one or more of the anti-MerTK antibodies disclosed herein. Detailed exemplary methods for mapping antibody-binding epitopes are provided in Morris (1996) "Epitope Mapping Protocols," in Methods in Molecular Biology vol. 66 (Humana Press, Totowa, NJ).

[0342] In an exemplary competitive assay, immobilized MerTK is incubated in a solution containing a first labeled antibody that binds to MerTK and a second unlabeled antibody that is being tested for its ability to compete with the first antibody for binding to MerTK. The second antibody can be present in hybridoma supernatant. As a control, immobilized MerTK is incubated in a solution containing the first labeled antibody but not the second unlabeled antibody. After incubation under conditions that allow binding of the first antibody to MerTK, excess unbound antibody is removed and the amount of label associated with immobilized MerTK is measured. If the amount of label associated with immobilized MerTK is substantially reduced in the test sample compared to the control sample, this indicates that the second antibody competes with the first antibody for binding to MerTK. See Harlow and Lane (1988) Antibodies: A Laboratory Manual ch.14 (Cold Spring Harbor Laboratory, Cold Spring Harbor, NY).

[0343] In another aspect, assays are provided to identify anti-MerTK antibodies having biological activity, which may include, for example, reducing MerTK-mediated phagocytic activity, reducing MerTK-mediated clearance of apoptotic cells, and / or enhancing tumor immunogenicity of checkpoint inhibitors. Antibodies having such biological activity in vivo and / or in vitro are also provided.

[0344] In certain embodiments, the antibodies of the invention are tested for such biological activities. Examples of suitable assays for measuring such biological activities are further described herein, including in the Exemplification section below.

[0345] D. Immunoconjugates The present invention also provides immunoconjugates comprising an anti-MerTK antibody herein conjugated to one or more cytotoxic agents, such as a chemotherapeutic agent or drugs, a growth inhibitory agent, a toxin (e.g., a protein toxin, an enzymatically active toxin of bacterial, fungal, plant, or animal origin, or fragments thereof), or a radioactive isotope.

[0346] In one embodiment, the immunoconjugate is an antibody that is capable of binding to a compound selected from the group consisting of maytansinoids (see U.S. Pat. Nos. 5,208,020, 5,416,064, and EP 0 425 235); auristatins, such as monomethylauristatin drug moieties DE and DF (MMAE and MMAF) (see U.S. Pat. Nos. 5,635,483, 5,780,588, and 7,498,298); dolastatins; calicheamicin or derivatives thereof (see U.S. Pat. Nos. 5,712,374, 5,714,586, 5,739,116, 5,767,285, 5,770,701, 5,770,710, 5,773,001, and 5,877,296; Hinman et al. al., Cancer Res. 53:3336-3342 (1993); and Cancer Res. 58:2925-2928 (1998)); anthracyclines such as daunomycin or doxorubicin (Kratz et al., Current Med. Chem. 13:477-523 (2006); Jeffrey et al., Bioorganic & Med. Chem. Letters 16:358-362 (2006); Torgov et al., Bioconj. Chem. 16:717-721 (2005); Nagy et al., Proc. Natl. Acad. Sci. USA 97:829-834 (2000); Dubowchik et al., Bioorg. & Med. Chem. Letters 16:358-362 (2006); 12:1529-1532 (2002); King et al., J. Med. Chem. 45:4336-4343 (2002); and U.S. Patent No. 6,630,579); methotrexate; vindesine; taxanes such as docetaxel, paclitaxel, larotaxel, tesetaxel, and ortataxel; trichothecenes; and antibody-drug conjugates (ADCs) conjugated to one or more agents, including, but not limited to, CC1065.

[0347] In another embodiment, the immunoconjugate comprises an antibody as described herein conjugated to an enzymatically active toxin or fragment thereof, including, but not limited to, diphtheria A chain, nonbinding active fragment of diphtheria toxin, exotoxin A chain (from Pseudomonas aeruginosa), ricin A chain, abrin A chain, modeccin A chain, alpha-sarcin, Aleurites fordii protein, dianthin protein, Phytolaca americana proteins (PAPI, PAPII, and PAP-S), momordica charantia inhibitor, curcin, crotin, sapaonaria officinalis inhibitor, gelonin, mitogellin, restrictocin, phenomycin, enomycin, and the trichothecenes.

[0348] In another embodiment, the immunoconjugate comprises an antibody as described herein conjugated to a radioactive atom to form a radioconjugate. A variety of radioisotopes are available for the production of radioconjugates. Examples include At 211 , I 131 , I 125 , Y 90 , Re 186 , Re 188 , Sm 153 , Bi 212 , P 32 , Pb 212 , and radioisotopes of Lu. When a radioactive substance is used for detection, it may comprise a radioactive atom, such as tc99m or I123, for scintigraphy studies, or a spin label, such as iodine-123 again, iodine-131, indium-111, fluorine-19, carbon-13, nitrogen-15, oxygen-17, gadolinium, manganese or iron, for nuclear magnetic resonance (NMR) imaging (also known as magnetic resonance imaging, MRI).

[0349] Conjugates ...

Claims

1. An isolated antibody that binds to MerTK and reduces MerTK-mediated clearance of apoptotic cells.

2. The antibody of claim 1 , wherein the antibody reduces MerTK-mediated clearance of apoptotic cells by phagocytes.

3. The antibody of claim 2 , wherein the phagocyte is a macrophage.

4. The antibody of claim 3, wherein the macrophage is a tumor-associated macrophage.

5. The antibody of any one of claims 1 to 4, wherein the clearance of apoptotic cells is reduced as measured in an apoptotic cell clearance assay at room temperature.

6. The antibody of any one of claims 1 to 4, wherein the antibody reduces ligand-mediated MerTK signaling.

7. The antibody of any one of claims 1 to 5, wherein the antibody induces a pro-inflammatory response or a type I IFN response.

8. The antibody according to any one of claims 1 to 7, wherein the antibody is a monoclonal antibody.

9. The antibody according to any one of claims 1 to 8, wherein the antibody is a human antibody, a humanized antibody, or a chimeric antibody.

10. The antibody according to any one of claims 1 to 9, wherein the antibody is an antibody fragment that binds MerTK.

11. The antibody of any one of claims 1 to 10, wherein the antibody binds to a fibronectin-like domain or an immunoglobulin-like domain of MerTK.

12. The antibody of any one of claims 1 to 11, wherein the antibody binds to the fibronectin-like domain of MerTK.

13. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 4; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 5; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

6.

14. The antibody of claim 13, further comprising: (a) an HVR-L1 having the amino acid sequence of SEQ ID NO: 1; (b) an HVR-L2 having the amino acid sequence of SEQ ID NO: 2; and (c) an HVR-L3 having the amino acid sequence of SEQ ID NO:

3.

15. 15. The antibody of claim 13 or 14, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 83; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 65; or (c) a VH such as (a) and a VL such as (b).

16. The antibody of claim 15, comprising a VH comprising the amino acid sequence of SEQ ID NO:

83.

17. The antibody of claim 15 or 16, comprising a VL comprising the amino acid sequence of SEQ ID NO:

65.

18. VH comprising the amino acid sequence of SEQ ID NO:83 and VL comprising the amino acid sequence of SEQ ID NO:

65.

19. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 10; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 11; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

12.

20. The antibody of claim 19, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 7; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 8; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

9.

21. 21. The antibody of claim 19 or 20, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 84; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 66; or (c) a VH such as (a) and a VL such as (b).

22. The antibody of claim 21, comprising a VH comprising the amino acid sequence of SEQ ID NO:

84.

23. The antibody of claim 21 or 22, comprising a VL comprising the amino acid sequence of SEQ ID NO:

66.

24. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:84 and a VL having the amino acid sequence of SEQ ID NO:

66.

25. 21. The antibody of claim 19 or 20, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 85; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 67; or (c) a VH such as (a) and a VL such as (b).

26. The antibody of claim 25, comprising a VH comprising the amino acid sequence of SEQ ID NO:

85.

27. The antibody of claim 25, comprising a VL comprising the amino acid sequence of SEQ ID NO:

67.

28. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:85 and a VL having the amino acid sequence of SEQ ID NO:

67.

29. The antibody of any one of claims 25 to 28, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

102.

30. The antibody of any one of claims 25 to 29, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

110.

31. 21. The antibody of claim 19 or 20, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 86; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 68; or (c) a VH such as (a) and a VL such as (b).

32. The antibody of claim 31 , comprising a VH comprising the amino acid sequence of SEQ ID NO:

86.

33. The antibody of claim 31 or 32, comprising a VL comprising the amino acid sequence of SEQ ID NO:

68.

34. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:86 and a VL having the amino acid sequence of SEQ ID NO:

68.

35. The antibody of any one of claims 31 to 34, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

103.

36. The antibody of any one of claims 31 to 35, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

111.

37. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 16; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 17; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

18.

38. The antibody of claim 37, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 13; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

15.

39. 39. The antibody of claim 37 or 38, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 87; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 69; or (c) a VH such as (a) and a VL such as (b).

40. The antibody of claim 39, comprising a VH comprising the amino acid sequence of SEQ ID NO:

87.

41. 41. The antibody of claim 39 or 40, comprising a VL comprising the amino acid sequence of SEQ ID NO:

69.

42. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:87 and a VL having the amino acid sequence of SEQ ID NO:

69.

43. 39. The antibody of claim 37 or 38, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 88; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 70; or (c) a VH such as (a) and a VL such as (b).

44. The antibody of claim 43, comprising a VH comprising the amino acid sequence of SEQ ID NO:

88.

45. The antibody of claim 43 or 44, comprising a VL comprising the amino acid sequence of SEQ ID NO:

70.

46. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:88 and a VL having the amino acid sequence of SEQ ID NO:

70.

47. The antibody of any one of claims 43 to 46, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

104.

48. The antibody of any one of claims 43 to 47, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

112.

49. 39. The antibody of claim 37 or 38, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 89; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 70; or (c) a VH such as (a) and a VL such as (b).

50. The antibody of claim 49, comprising a VH comprising the amino acid sequence of SEQ ID NO:

89.

51. 51. The antibody of claim 49 or 50, comprising a VL comprising the amino acid sequence of SEQ ID NO:

70.

52. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:89 and a VL having the amino acid sequence of SEQ ID NO:

70.

53. The antibody of any one of claims 49 to 52, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

105.

54. The antibody of any one of claims 49 to 53, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

113.

55. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 22; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 23; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

24.

56. The antibody of claim 55, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 19; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 20; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

21.

57. 57. The antibody of claim 55 or 56, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 90; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 71; or (c) a VH such as (a) and a VL such as (b).

58. The antibody of claim 57, comprising a VH comprising the amino acid sequence of SEQ ID NO:

90.

59. 59. The antibody of claim 57 or 58, comprising a VL comprising the amino acid sequence of SEQ ID NO:

71.

60. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:90 and a VL having the amino acid sequence of SEQ ID NO:

71.

61. 57. The antibody of claim 55 or 56, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 91; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 72; or (c) a VH such as (a) and a VL such as (b).

62. The antibody of claim 61, comprising a VH comprising the amino acid sequence of SEQ ID NO:

91.

63. 63. The antibody of claim 61 or 62, comprising a VL comprising the amino acid sequence of SEQ ID NO:

72.

64. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:91 and a VL having the amino acid sequence of SEQ ID NO:

72.

65. The antibody of any one of claims 61 to 64, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

106.

66. The antibody of any one of claims 61 to 65, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

114.

67. 57. The antibody of claim 55 or 56, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 92; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 73; or (c) a VH such as (a) and a VL such as (b).

68. The antibody of claim 67, comprising a VH comprising the amino acid sequence of SEQ ID NO:

92.

69. The antibody of claim 67 or 68, comprising a VL comprising the amino acid sequence of SEQ ID NO:

73.

70. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:92 and a VL having the amino acid sequence of SEQ ID NO:

73.

71. The antibody of any one of claims 67 to 70, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

107.

72. The antibody of any one of claims 67 to 71, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

115.

73. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 27; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 28; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

29.

74. The antibody of claim 73, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 25; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

26.

75. 75. The antibody of claim 73 or 74, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 93; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 74; or (c) a VH such as (a) and a VL such as (b).

76. The antibody of claim 75, comprising a VH comprising the amino acid sequence of SEQ ID NO:

93.

77. The antibody of claim 75 or 76, comprising a VL comprising the amino acid sequence of SEQ ID NO:

74.

78. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:93 and a VL having the amino acid sequence of SEQ ID NO:

74.

79. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 33; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 34; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

35.

80. (a) HVR-L1 comprising the amino acid sequence of SEQ ID NO: 30; (b) HVR-L2 comprising the amino acid sequence of SEQ ID NO: 31; and (c) HVR-L3 comprising the amino acid sequence of SEQ ID NO:

32.

81. 81. The antibody of claim 79 or 80, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 94; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 75; or (c) a VH such as (a) and a VL such as (b).

82. The antibody of claim 81, comprising a VH comprising the amino acid sequence of SEQ ID NO:

94.

83. The antibody of claim 81 or 82, comprising a VL comprising the amino acid sequence of SEQ ID NO:

75.

84. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:94 and a VL having the amino acid sequence of SEQ ID NO:

75.

85. The antibody of any one of claims 1 to 11, wherein the antibody binds to the immunoglobulin-like domain of MerTK.

86. An isolated antibody that binds to MerTK, comprising: (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; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

40.

87. The antibody of claim 86, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 36; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 14; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

37.

88. 88. The antibody of claim 86 or 87, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 95; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 76; or (c) a VH such as (a) and a VL such as (b).

89. The antibody of claim 88, comprising a VH comprising the amino acid sequence of SEQ ID NO:

95.

90. The antibody of claim 88 or 89, comprising a VL comprising the amino acid sequence of SEQ ID NO:

76.

91. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:95 and a VL having the amino acid sequence of SEQ ID NO:

76.

92. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 44; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 45; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

46.

93. The antibody of claim 92, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 41; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 42; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

43.

94. 94. The antibody of claim 92 or 93, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 96; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 77; or (c) a VH such as (a) and a VL such as (b).

95. The antibody of claim 94, comprising a VH comprising the amino acid sequence of SEQ ID NO:

96.

96. The antibody of claim 94 or 95, comprising a VL comprising the amino acid sequence of SEQ ID NO:

77.

97. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:96 and a VL having the amino acid sequence of SEQ ID NO:

77.

98. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO:50; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO:51; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

52.

99. The antibody of claim 98, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 47; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 48; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

49.

100. 100. An antibody according to claim 98 or 99, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 97; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 78; or (c) a VH such as (a) and a VL such as (b).

101. The antibody of claim 100, comprising a VH comprising the amino acid sequence of SEQ ID NO:

97.

102. The antibody of claim 100 or 101, comprising a VL comprising the amino acid sequence of SEQ ID NO:

78.

103. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:97 and a VL having the amino acid sequence of SEQ ID NO:

78.

104. 100. The antibody of claim 98 or 99, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 98; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 79; or (c) a VH such as (a) and a VL such as (b).

105. The antibody of claim 104, comprising a VH comprising the amino acid sequence of SEQ ID NO:

98.

106. The antibody of claim 104 or 105, comprising a VL comprising the amino acid sequence of SEQ ID NO:

79.

107. An antibody comprising a VH having the amino acid sequence of SEQ ID NO:98 and a VL having the amino acid sequence of SEQ ID NO:

79.

108. The antibody of any one of claims 104 to 107, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

108.

109. The antibody of any one of claims 104 to 108, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

116.

110. 100. The antibody of claim 98 or 99, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 99; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 80; or (c) a VH such as (a) and a VL such as (b).

111. The antibody of claim 110, comprising a VH comprising the amino acid sequence of SEQ ID NO:

99.

112. The antibody of claim 110 or 111, comprising a VL comprising the amino acid sequence of SEQ ID NO:

80.

113. An antibody comprising a VH comprising the amino acid sequence of SEQ ID NO:99 and a VL comprising the amino acid sequence of SEQ ID NO:

80.

114. The antibody of any one of claims 110 to 113, wherein the antibody comprises a heavy chain comprising the amino acid sequence of SEQ ID NO:

109.

115. The antibody of any one of claims 110 to 114, wherein the antibody comprises a light chain comprising the amino acid sequence of SEQ ID NO:

117.

116. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO:56; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO:57; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

58.

117. The antibody of claim 116, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 53; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 54; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

55.

118. 118. The antibody of claim 116 or 117, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 100; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 81; or (c) a VH such as (a) and a VL such as (b).

119. The antibody described in claim 118, comprising a VH comprising the amino acid sequence of SEQ ID NO:

100.

120. The antibody of claim 118 or 119, comprising a VL comprising the amino acid sequence of SEQ ID NO:

81.

121. An antibody comprising a VH having the amino acid sequence of SEQ ID NO: 100 and a VL having the amino acid sequence of SEQ ID NO:

81.

122. An isolated antibody that binds to MerTK, comprising: (a) an HVR-H1 comprising the amino acid sequence of SEQ ID NO: 62; (b) an HVR-H2 comprising the amino acid sequence of SEQ ID NO: 63; and (c) an HVR-H3 comprising the amino acid sequence of SEQ ID NO:

64.

123. The antibody of claim 122, further comprising: (a) an HVR-L1 comprising the amino acid sequence of SEQ ID NO: 59; (b) an HVR-L2 comprising the amino acid sequence of SEQ ID NO: 60; and (c) an HVR-L3 comprising the amino acid sequence of SEQ ID NO:

61.

124. An antibody described in claim 122 or 123, comprising: (a) a heavy chain variable domain (VH) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 101; (b) a light chain variable domain (VL) comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 82; or (c) a VH such as (a) and a VL such as (b).

125. The antibody of claim 124, comprising a VH comprising the amino acid sequence of SEQ ID NO:

101.

126. The antibody of claim 124 or 125, comprising a VL comprising the amino acid sequence of SEQ ID NO:

82.

127. An antibody comprising a VH having the amino acid sequence of SEQ ID NO: 101 and a VL having the amino acid sequence of SEQ ID NO:

82.

128. 20. An isolated antibody that competes with a reference antibody comprising the antibody of claim 18 for binding to MerTK.

129. 20. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 18.

130. 25. An isolated antibody that competes with a reference antibody comprising the antibody of claim 24 for binding to MerTK.

131. 25. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 24.

132. 30. An isolated antibody that competes with a reference antibody comprising the antibody of claim 28 for binding to MerTK.

133. 29. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 28.

134. 35. An isolated antibody that competes with a reference antibody comprising the antibody of claim 34 for binding to MerTK.

135. 35. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 34.

136. 43. An isolated antibody that competes with a reference antibody comprising the antibody of claim 42 for binding to MerTK.

137. 43. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 42.

138. 47. An isolated antibody that competes with a reference antibody comprising the antibody of claim 46 for binding to MerTK.

139. 47. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 46.

140. 53. An isolated antibody that competes with a reference antibody comprising the antibody of claim 52 for binding to MerTK.

141. 53. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 52.

142. 61. An isolated antibody that competes with a reference antibody comprising the antibody of claim 60 for binding to MerTK.

143. 61. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 60.

144. 65. An isolated antibody that competes with a reference antibody comprising the antibody of claim 64 for binding to MerTK.

145. 65. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 64.

146. 71. An isolated antibody that competes with a reference antibody comprising the antibody of claim 70 for binding to MerTK.

147. 71. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 70.

148. 80. An isolated antibody that competes with a reference antibody comprising the antibody of claim 78 for binding to MerTK.

149. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 78.

150. 85. An isolated antibody that competes with a reference antibody comprising the antibody of claim 84 for binding to MerTK.

151. 85. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 84.

152. 92. An isolated antibody that competes with a reference antibody comprising the antibody of claim 91 for binding to MerTK.

153. 92. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 91.

154. 98. An isolated antibody that competes with a reference antibody comprising the antibody of claim 97 for binding to MerTK.

155. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 97.

156. An isolated antibody that competes with a reference antibody comprising the antibody of claim 103 for binding to MerTK.

157. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 103.

158. An isolated antibody that competes with a reference antibody comprising the antibody of claim 107 for binding to MerTK.

159. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 107.

160. An isolated antibody that competes with a reference antibody comprising the antibody of claim 113 for binding to MerTK.

161. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 113.

162. An isolated antibody that competes with a reference antibody comprising the antibody of claim 121 for binding to MerTK.

163. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody of claim 121.

164. An isolated antibody that competes with a reference antibody comprising the antibody of claim 127 for binding to MerTK.

165. An isolated antibody that binds to the same epitope on MerTK as a reference antibody comprising the antibody described in claim 127.

166. The isolated antibody of any one of claims 128-165, wherein the antibody binds to human MerTK.

167. The antibody of any one of claims 1 to 166, wherein the antibody is a full-length IgG1 antibody, an IgG2 antibody, an IgG3 antibody or an IgG4 antibody.

168. The antibody of claim 167, wherein the antibody is a full-length IgG1 antibody.

169. The antibody of claim 167 or 168, wherein the antibody comprises a LALAPG mutation.

170. The antibody of any one of claims 1 to 11, wherein the antibody comprises Q2 and L4 residues in the light chain variable region, and I48, G49 and K71 residues in the heavy chain variable region.

171. The antibody according to any one of claims 1 to 11, wherein the antibody comprises L4 and F87 in the light chain variable region and V24, I48, G49 and K71 in the heavy chain variable region.

172. The antibody according to any one of claims 1 to 11, wherein the antibody comprises L4 and P43 in the light chain variable region and K71 in the heavy chain variable region.

173. The antibody of any one of claims 1 to 11, wherein the antibody comprises a G49 residue and a V78 residue in the heavy chain variable region.

174. The antibody of any one of claims 1-115 and 122-127, wherein the antibody binds to human MerTK with a dissociation constant of ≦100 nM at 25° C.

175. 128. The antibody of any one of claims 1-97 and 122-127, wherein the antibody binds to cynomolgus MerTK with a dissociation constant of ≦100 nM at 25° C.

176. The antibody of any one of claims 1-97 and 116-127, wherein the antibody binds to mouse MerTK with a dissociation constant of ≦10 nM at 25° C.

177. The antibody of any one of claims 1-97 and 116-127, wherein the antibody binds to rat MerTK with a dissociation constant of ≦10 nM at 37° C.

178. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:102 and a light chain comprising the amino acid sequence of SEQ ID NO:

110.

179. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:103 and a light chain comprising the amino acid sequence of SEQ ID NO:

111.

180. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:104 and a light chain comprising the amino acid sequence of SEQ ID NO:

112.

181. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:105 and a light chain comprising the amino acid sequence of SEQ ID NO:

113.

182. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:106 and a light chain comprising the amino acid sequence of SEQ ID NO:

114.

183. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:107 and a light chain comprising the amino acid sequence of SEQ ID NO:

115.

184. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:108 and a light chain comprising the amino acid sequence of SEQ ID NO:

116.

185. An isolated antibody that binds to MerTK, the antibody comprising a heavy chain comprising the amino acid sequence of SEQ ID NO:109 and a light chain comprising the amino acid sequence of SEQ ID NO:

117.

186. The isolated antibody of any one of claims 13-84 or 86-185, wherein the antibody reduces MerTK-mediated clearance of apoptotic cells.

187. The antibody of claim 186, wherein the antibody reduces MerTK-mediated clearance of apoptotic cells by phagocytes.

188. The antibody of claim 187, wherein the phagocyte is a macrophage.

189. The antibody of claim 188, wherein the macrophage is a tumor-associated macrophage.

190. The antibody of any one of claims 186 to 189, wherein the clearance of apoptotic cells is reduced as measured in an apoptotic cell clearance assay at room temperature.

191. The antibody of any one of claims 13 to 190, wherein the antibody is a monoclonal antibody.

192. The antibody of any one of claims 186 to 138 or 178 to 185, wherein the antibody is a humanized antibody or a chimeric antibody.

193. The antibody of any one of claims 128 to 185, wherein the antibody is a human antibody, a humanized antibody, or a chimeric antibody.

194. The antibody of any one of claims 13 to 193, wherein the antibody is an antibody fragment that binds MerTK.

195. The antibody of any one of claims 13 to 194, wherein the antibody binds to a fibronectin-like domain or an immunoglobulin-like domain of MerTK.

196. The antibody of claim 195, wherein the antibody binds to the fibronectin-like domain of MerTK.

197. The antibody of claim 195, wherein the antibody binds to an immunoglobulin-like domain of MerTK.

198. An isolated nucleic acid encoding the antibody of any one of claims 1 to 197.

199. A vector comprising the nucleic acid of claim 198.

200. A host cell comprising the vector of claim 199.

201. 201. A method for producing an anti-MerTK antibody, comprising culturing the host cell of claim 200 in a cell culture under conditions suitable for expression of the antibody.

202. The method of claim 201, further comprising recovering the anti-MerTK antibody from the cell culture.

203. An immunoconjugate comprising an antibody according to any one of claims 1 to 197 attached to a cytotoxic agent.

204. 204. A pharmaceutical formulation comprising an antibody according to any one of claims 1 to 197 or an immunoconjugate according to claim 203, and a pharma- ceutically acceptable carrier.

205. An antibody according to any one of claims 1 to 197 or an immunoconjugate according to claim 203 for use as a medicament.

206. An antibody according to any one of claims 1 to 197 or an immunoconjugate according to claim 203 for use in the treatment of cancer.

207. An antibody according to any one of claims 1 to 197 or an immunoconjugate according to claim 203 for use in reducing MerTK mediated clearance of apoptotic cells.

208. Use of an antibody according to any one of claims 1 to 197 or an immunoconjugate according to claim 203 in the manufacture of a medicament.

209. The use described in claim 208, wherein the medicament is for the treatment of cancer.

210. The use of claim 209, wherein the cancer expresses a functional STING polypeptide, a functional Cx43 polypeptide, and a functional cGAS polypeptide.

211. 210. The use of claim 209, wherein the cancer is colon cancer.

212. 207. Use of an antibody according to any one of claims 1 to 197 or an immunoconjugate according to claim 203 in the manufacture of a medicament for reducing MerTK mediated clearance of apoptotic cells.

213. The use according to any one of claims 208 to 212, wherein the medicament is used in combination with an effective amount of an additional therapeutic agent.

214. 214. The use of claim 213, wherein the additional therapeutic agent is selected from one or more of tamoxifen, letrozole, exemestane, anastrozole, irinotecan, cetuximab, fulvestrant, vinorelbine, erlotinib, bevacizumab, vincristine, imatinib mesylate, sorafenib, lapatinib, trastuzumab, cisplatin, gemcitabine, methotrexate, vinblastine, carboplatin, paclitaxel, 5-fluorouracil, doxorubicin, bortezomib, melphalan, prednisone, and docetaxel.

215. The use of claim 213, wherein the additional therapeutic agent is an immune checkpoint inhibitor.

216. 216. The use of claim 215, wherein the immune checkpoint inhibitor is selected from the group consisting of a cytotoxic T-lymphocyte associated protein 4 (CTLA4) inhibitor, a programmed cell death protein 1 (PD-1) binding antagonist, or a programmed death ligand 1 (PDL1) binding antagonist.

217. The use of claim 216, wherein the immune checkpoint inhibitor is a PDL1 binding antagonist.

218. The use of claim 217, wherein the PDL1 binding antagonist is an anti-PDL1 antibody.

219. The use of claim 218, wherein the anti-PDL1 antibody is atezolizumab.

220. The use according to any one of claims 215 to 219, wherein the medicament is further used in combination with an effective amount of a chemotherapeutic agent.

221. 20. A method of treating an individual having cancer comprising administering to said individual an effective amount of an antibody of any one of claims 1 to 197 or an effective amount of the immunoconjugate of claim 203.

222. The method of claim 221, wherein the cancer expresses a functional STING polypeptide, a functional Cx43 polypeptide, and a functional cGAS polypeptide.

223. 222. The method of claim 221 or 221, further comprising administering an additional therapeutic agent to the individual.

224. 224. The method of claim 223, wherein the additional therapeutic agent is selected from one or more of tamoxifen, letrozole, exemestane, anastrozole, irinotecan, cetuximab, fulvestrant, vinorelbine, erlotinib, bevacizumab, vincristine, imatinib mesylate, sorafenib, lapatinib, trastuzumab, cisplatin, gemcitabine, methotrexate, vinblastine, carboplatin, paclitaxel, 5-fluorouracil, doxorubicin, bortezomib, melphalan, prednisone, and docetaxel.

225. 224. The method of claim 223, wherein the additional therapeutic agent is an immune checkpoint inhibitor.

226. 226. The method of claim 225, wherein said immune checkpoint inhibitor is selected from the group consisting of a cytotoxic T-lymphocyte-associated protein 4 (CTLA4) inhibitor, a programmed cell death protein 1 (PD-1) binding antagonist, and a programmed death ligand 1 (PDL1) binding antagonist.

227. The method of claim 226, wherein the immune checkpoint inhibitor is a PDL1 binding antagonist.

228. The method of claim 227, wherein the PDL1 binding antagonist is an anti-PDL1 antibody.

229. The method of claim 228, wherein the anti-PDL1 antibody is atezolizumab.

230. 230. The method of any one of claims 225-229, further comprising administering to said individual an effective amount of an additional chemotherapeutic agent.

231. 231. The method of any one of claims 216 to 230, wherein the cancer is colon cancer.

232. A method of reducing MerTK-mediated clearance of apoptotic cells in an individual, comprising administering to the individual an effective amount of an antibody of any one of claims 1 to 195 or an immunoconjugate of claim 201, thereby reducing MerTK-mediated clearance of apoptotic cells.

233. 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 233. The method of claim 232, wherein the concentration of 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9 or 8.0 fold is reduced.

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