High-affinity anti-MERTK antibodies and uses thereof

Abstract

The present invention discloses antibodies (e.g., humanized antibodies) that specifically bind to Mer tyrosine kinase (MERTK; e.g., human MERTK) and compositions comprising these antibodies. The present invention discloses also provides antibody-drug conjugates, which include (i) an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein and (ii) a cytotoxic agent that is directly conjugated to the antibody or conjugated to the antibody through a linker, and compositions comprising these antibody-drug conjugates. The present invention discloses also provides a method for treating cancer, which includes administering to a human subject in need thereof (a) an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein, or (b) an antibody-drug conjugate, the antibody-drug conjugate comprising (i) an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), and (ii) a cytotoxic agent that is directly conjugated to the antibody or conjugated to the antibody through a linker.

Description

1. Technical Field

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 810,841, filed on February 26, 2019, which is incorporated herein by reference in its entirety.

[0002] The present application incorporates by reference the sequence listing submitted with the present application, which is a text file in ASCII format, titled "13256-008-228_SEQ_LISTING.txt", created on February 19, 2020 and 94,274 bytes in size.

[0003] The present disclosure provides antibodies (e.g., humanized antibodies) that specifically bind to Mer tyrosine kinase (MERTK; e.g., human MERTK) and compositions comprising these antibodies. The present disclosure also provides antibody-drug conjugates, which include (i) an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein and (ii) a cytotoxic agent that is directly conjugated to the antibody or conjugated to the antibody through a linker, and compositions comprising these antibody-drug conjugates. The present disclosure also provides a method for treating cancer, which includes administering to a human subject in need thereof (a) an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein, or (b) an antibody-drug conjugate, the antibody-drug conjugate comprising (i) an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), and (ii) a cytotoxic agent that is directly conjugated to the antibody or conjugated to the antibody through a linker. 2. Background technology

[0004] Mer tyrosine kinase (MERTK), also known as c-aggregate, MER, proto-oncogene c-aggregate, receptor tyrosine kinase MerTK, tyrosine-protein kinase Mer STK kinase, RP38 or MGC133349, is a member of the TAM family of receptor tyrosine kinases, which also includes AXL and TYRO3 kinases. MERTK transduces signals from the extracellular space through activation via binding of ligands (most notably, Gas-6, a soluble protein). Gas-6 binding to MERTK induces autophosphorylation of MERTK on its intracellular domain, leading to downstream signaling activation (Cummings CT et al., (2013) Clin Cancer Res 19: 5275-5280; Verma A et al., (2011) Mol Cancer Ther 10: 1763-1773).

[0005] MERTK exists in both membrane-bound and soluble forms. The ectodomain can be cleaved to generate a soluble ectodomain, which is hypothesized to act as a decoy receptor to negatively regulate the activation of the MERTK receptor on cells by reducing the ability and / or availability of the soluble Gas-6 ligand to bind membrane-bound MERTK (Sather S et al., (2007) Blood 109: 1026-1033). Therefore, MERTK has a dual role in cancer development, angiogenesis and metastasis. On the one hand, Gas-6 activation of MERTK on endothelial cells leads to inhibition of endothelial cell recruitment by cancer cells in a co-culture system. Endothelial cell recruitment is a key feature of cancer cells that enables tumor angiogenesis, tumor growth and metastasis. Downregulation of MERTK on metastatic breast cancer cells has also been shown to inhibit endothelial cell recruitment (Png KJ et al., (2012) Nature 481: 190-194). However, on the other hand, MERTK plays the opposite role in cancer cells, where its overexpression leads to increased metastasis, which may be caused by the release of cleaved MERTK to produce soluble MERTK extracellular domain protein as a decoy receptor. In addition, ligand-dependent MERTK activation on cancer cells stimulates oncogenic pathways, including the AKT pathway (Linger RM, Cohen RA, Cummings CT, Sather S, Migdall-Wilson J, Middleton DH, Lu X, Barón AE, Franklin WA, Merrick DT, Jedlicka P, DeRyckere D, Heasley LE, Graham DK. Mer or Axl receptor tyrosine kinase inhibition promotes apoptosis, blocks growth and enhances chemosensitivity of human non-small cell lung cancer (Oncogene. 2013 Jul 18;32(29):3420-31). Therefore, tumor cells overexpress MERTK to promote oncogenic signaling. In addition, tumor cells secrete a soluble form of the extracellular MERTK receptor, which acts as a decoy receptor to reduce the ability (and / or availability) of soluble Gas-6 ligand to activate MERTK on endothelial cells, ultimately leading to endothelial cell recruitment, angiogenesis, and cancer development (Png KJ et al., (2012) Nature 481:190-194).

[0006] MERTK is also involved in regulating macrophage homeostasis and the maintenance of anti-inflammatory conditions. On macrophages, MERTK mediates the phagocytic clearance of apoptotic cells and the release of IL-10 and acute inflammatory cytokines, whose expression is stimulated by Gas6-dependent MERTK binding (Zizzo et al., (2012) J. Immunology Oct 1; 189(7): 3508-20; Cook et al., J Clin Invest. 2013; 123(8): 3231-3242).

[0007] Historically, because MERTK was thought to function only as an oncogene, efforts have been made to generate MERTK inhibitors for the treatment of cancer (e.g., compound UNC1062, a potent small molecule MERTK inhibitor developed as an anticancer compound) (Liu J et al., (2013) Eur J Med Chem 65:83-93; Cummings CT et al., (2013) Clin Cancer Res 19:5275-5280; Verma A et al., (2011) Mol Cancer Ther 10:1763-1773). In recent years, antibody-drug conjugates (ADCs) have become one of the most rapidly developing classes of cancer treatments (Beck A et al., (2017) Nat Rev Drug Discov 16:315-337; Peters C and Brown S, (2015) Biosci Rep 35:art:e00225).

[0008] Citation of references herein shall not be construed as an admission that such references are prior art to the present disclosure. 3. Summary of the invention

[0009] Disclosed herein are antibodies and antigen-binding fragments thereof that specifically bind to MERTK (e.g., human MERTK) with high affinity. In a specific embodiment of any antibody or antigen-binding fragment thereof described herein, the antibody specifically recognizes the extracellular domain of MERTK (e.g., human MERTK), and the extracellular domain comprises the amino acid sequence shown in SEQ ID NO: 132.

[0010] In a specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof specifically binds to MERTK (e.g., human MERTK) and causes MERTK to be internalized from the cell surface. In a specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof blocks AKT phosphorylation caused by Gas-6. In another specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof prevents MERTK activation. In another specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof described herein specifically recognizes the extracellular portion of human MERTK. In another specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof reduces colony formation of cancer cells. In a specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof described herein is a monoclonal. In another specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof described herein is an immunoglobulin comprising two identical light chains and two identical heavy chains. In a specific embodiment, an anti-MERTK antibody is a humanized antibody.

[0011] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:105.

[0012] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence shown in SEQ ID NO:107.

[0013] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence shown in SEQ ID NO:108.

[0014] In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence shown in SEQ ID NO:109.

[0015] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence shown in SEQ ID NO:110.

[0016] In another embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 106. In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 111.

[0017] In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises (a) a VH comprising the amino acid sequence set forth in SEQ ID NO: 105 and (b) a VL comprising the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises (a) a VH comprising the amino acid sequence set forth in SEQ ID NO: 107 and (b) a VL comprising the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises (a) a VH comprising the amino acid sequence set forth in SEQ ID NO: 108 and (b) a VL comprising the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises (a) a VH comprising the amino acid sequence set forth in SEQ ID NO: 109 and (b) a VL comprising the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises (a) a VH comprising the amino acid sequence set forth in SEQ ID NO: 110 and (b) a VL comprising the amino acid sequence set forth in SEQ ID NO: 111.

[0018] In certain embodiments, the antibody specifically bound to MERTK (e.g., human MERTK) provided herein comprises a heavy chain constant region or a light chain constant region or both. In some embodiments, the heavy chain constant region is selected from the group of human immunoglobulins consisting of IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2. In certain embodiments, the light chain constant region is selected from the group of human immunoglobulins consisting of IgGκ and IgGλ. In some embodiments, the antibody comprises a constant region with an improved binding affinity to one or more human Fcγ receptors.

[0019] In some embodiments, the antibody comprises a constant region that has reduced binding affinity for one or more human Fcγ receptors.

[0020] In a specific embodiment of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, each heavy chain comprises a variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 105. In another embodiment of this specific embodiment, each light chain comprises a variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 106.

[0021] In a specific embodiment of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, each heavy chain comprises a variable region (VH) comprising the amino acids set forth in SEQ ID NO: 107. In another embodiment of this specific embodiment, each light chain comprises a variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 106.

[0022] In a specific embodiment of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, each heavy chain comprises a variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 108. In another embodiment of this specific embodiment, each light chain comprises a variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 106.

[0023] In a specific embodiment of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, each heavy chain comprises a variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 110. In another embodiment of this specific embodiment, each light chain comprises a variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 111.

[0024] In a specific embodiment of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, each heavy chain comprises a variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 109. In another embodiment of this specific embodiment, each light chain comprises a variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 106.

[0025] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the light chain comprises a variable region (VL) comprising SEQ ID NO:106.

[0026] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the light chain comprises a variable region (VL) comprising SEQ ID NO:111.

[0027] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the heavy chain comprises a variable region (VH) comprising SEQ ID NO:105.

[0028] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the heavy chain comprises a variable region (VH) comprising SEQ ID NO:107.

[0029] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the heavy chain comprises a variable region (VH) comprising SEQ ID NO:108.

[0030] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the heavy chain comprises a variable region (VH) comprising SEQ ID NO:109.

[0031] In specific embodiments of the embodiment wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, the heavy chain comprises a variable region (VH) comprising SEQ ID NO:110.

[0032] In the specific embodiment of any antibody or its antigen-binding fragment provided herein, wherein the antibody is an immunoglobulin comprising two identical light chains and two identical heavy chains, and the antibody or its antigen-binding fragment comprises a constant region derived from humans. In another embodiment of this specific embodiment, the heavy chain constant region has an isotype selected from gamma1, gamma2, gamma3 and gamma4.

[0033] In specific embodiments of any of the antibodies or antigen-binding fragments thereof provided herein, the antibody binds to MERTK (eg, human MERTK) on cells with an EC50 in the range of about 1 nM to 15 nM (eg, 6.5 nM to 8 nM).

[0034] In a specific embodiment of any antibody or antigen-binding fragment thereof provided herein, the antibody or antigen-binding fragment reduces the expression level of MERTK on cancer cells (e.g., melanoma cell line SKMEL5). In another specific embodiment of any antibody or antigen-binding fragment thereof provided herein, the antibody or antigen-binding fragment reduces the expression level of MERTK on human M2 macrophages. In another specific embodiment of any antibody or antigen-binding fragment thereof provided herein, the antibody or antigen-binding fragment reduces the level of MERTK on human M2 macrophages differentiated in vitro.

[0035] In the specific embodiment of any antibody or antigen-binding fragment thereof provided herein, the antibody or antigen-binding fragment thereof comprises a constant region derived from a human. In another embodiment of this specific embodiment, the antibody or antigen-binding fragment thereof is a humanized immunoglobulin.

[0036] In specific embodiments of any of the antibodies or antigen-binding fragments thereof provided herein, wherein the antibody is not a monoclonal antibody or an immunoglobulin comprising two identical light chains and two identical heavy chains, the antibody or antigen-binding fragment thereof is a bispecific antibody.

[0037] In another aspect, provided herein is an immunoglobulin that specifically binds to MERTK (e.g., human MERTK), comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 105, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106.

[0038] In another aspect, provided herein is an immunoglobulin that specifically binds to MERTK (e.g., human MERTK), comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 107, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106.

[0039] In another aspect, provided herein is an immunoglobulin that specifically binds to MERTK (e.g., human MERTK), comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 108, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106.

[0040] In another aspect, provided herein is an immunoglobulin that specifically binds to MERTK (e.g., human MERTK), comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 109, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106.

[0041] In another aspect, provided herein is a humanized immunoglobulin that specifically binds to MERTK (e.g., human MERTK), comprising:

[0042] (A) (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 105, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106; or

[0043] (B) (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 107, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106, or

[0044] (C) (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 108, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106, or

[0045] (D) (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 109, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106.

[0046] In some embodiments, the antibodies provided herein are IgG. In some embodiments, the antigen-binding fragments provided herein are Fab, F(ab')2, or scFv fragments.

[0047] In another aspect, provided herein is a chimeric antibody or antigen-binding fragment thereof that binds to MERTK (e.g., human MERTK). In some embodiments, the chimeric antibody comprises a heavy chain variable region (VH) comprising the amino acids set forth in SEQ ID NO: 110. In some embodiments, the chimeric antibody comprises a light chain variable region (VL) comprising the amino acids set forth in SEQ ID NO: 111. In a specific embodiment, the chimeric antibody comprises the VH set forth in SEQ ID NO: 110 and the VL set forth in SEQ ID NO: 111.

[0048] In another specific embodiment, the antibody comprises a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112, 114, 115, 116, or 117. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a light chain comprising the amino acids set forth in SEQ ID NO: 113 or 118. In another specific embodiment, the anti-MERTK antibody comprises:

[0049] A heavy chain comprising the amino acids shown in SEQ ID NO: 112 and a light chain comprising the amino acid sequence shown in SEQ ID NO: 113; or

[0050] A heavy chain comprising the amino acids shown in SEQ ID NO: 114 and a light chain comprising the amino acid sequence shown in SEQ ID NO: 113; or

[0051] A heavy chain comprising the amino acids shown in SEQ ID NO: 115 and a light chain comprising the amino acid sequence shown in SEQ ID NO: 113; or

[0052] A heavy chain comprising the amino acids shown in SEQ ID NO: 116 and a light chain comprising the amino acid sequence shown in SEQ ID NO: 113; or

[0053] A heavy chain comprising the amino acids shown in SEQ ID NO:117 and a light chain comprising the amino acid sequence shown in SEQ ID NO:113.

[0054] In certain embodiments, the anti-MERTK antibody is a bispecific antibody comprising two different antigen binding regions, wherein one binding region specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to an antigen of interest (e.g., an immune cell receptor, a checkpoint receptor, or a tumor-associated antigen).

[0055] In a specific embodiment, the binding region that binds to MERTK comprises a variable region of a z10, z11 or z13 antibody described herein (e.g., those described in Tables 11, 12 and 13 below). In some specific embodiments, another binding region of the bispecific antibody binds to CD3. In other specific embodiments, another binding region of the bispecific antibody binds to PD-L1. In other specific embodiments, another binding region of the bispecific antibody binds to LRP1. In other specific embodiments, another binding region of the bispecific antibody binds to LPR8. In other specific embodiments, another binding region of the bispecific antibody binds to TGF-β. In other specific embodiments, another binding region of the bispecific antibody binds to ICOS. In other specific embodiments, another binding region of the bispecific antibody binds to CD40. In other specific embodiments, another binding region of the bispecific antibody binds to NKGD2. In other specific embodiments, another binding region of the bispecific antibody binds to TIGIT. In a specific embodiment, the binding region that binds to CD40 is an agonist antibody. In another specific embodiment, the binding region that binds to ICOS is an agonist antibody. In another specific embodiment, the binding region that binds to PD-L1 is a blocking antibody.

[0056] In another embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof (e.g., a humanized or human antibody or antigen-binding fragment thereof) that binds to the same MERTK (e.g., human MERTK) epitope as an anti-MERTK antibody described herein. In another embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof (e.g., a humanized or human antibody or antigen-binding fragment thereof) that competes with an anti-MERTK antibody or antigen-binding fragment thereof described herein for binding to MERTK (e.g., human MERTK). In another specific embodiment, provided herein is a first anti-MERTK antibody or antigen-binding fragment thereof that competes with an anti-MERTK antibody or antigen-binding fragment thereof described herein for binding to MERTK (e.g., human MERTK), wherein competition is exhibited because the binding of the first anti-MERTK antibody or antigen-binding fragment thereof to MERTK (e.g., human MERTK) is reduced by greater than 80% (e.g., 85%, 90%, 95%, or 98% or between 80% and 85%, 80% and 90%, 85% and 90%, or between 85% and 95%) in the presence of an anti-MERTK antibody or antigen-binding fragment thereof described herein. In a specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof that binds to the same epitope as MERTK (or competes for binding with the anti-MERTK antibody or antigen-binding fragment thereof) is not a murine antibody or antigen-binding fragment thereof.

[0057] In certain embodiments, the EC of an anti-MERTK antibody provided herein that specifically binds to MERTK (eg, human MERTK) in an assay as described herein is 50 In the range of about 1 nM to 10 nM. In some embodiments, the anti-MERTK antibody or its antigen-binding fragment specifically binds to human MERTK. In a specific embodiment, the antibody or its antigen-binding fragment provided herein does not bind or does not significantly bind to human Axl, human Tyro3 or mouse MERTK, as evaluated by an assay described therein or known to those skilled in the art. In some embodiments, the anti-MERTK antibody or its antigen-binding fragment binds to human MERTK and cynomolgus monkey MERTK. In a specific embodiment, the antibody provided herein is isolated. In a specific embodiment, the antibody provided herein is a monoclonal antibody. In a specific embodiment, the anti-MERTK antibody or its antigen-binding fragment provided herein is bivalent and can bind to two MERTK molecules (e.g., human MERTK molecules).

[0058] In another aspect, provided herein are polynucleotide sequences encoding antibodies or antigen-binding fragments thereof. In a specific embodiment, provided herein are polynucleotide sequences comprising a nucleic acid molecule encoding a heavy chain variable region, wherein the nucleic acid molecule comprises a nucleic acid sequence as set forth in SEQ ID NO: 119, SEQ ID NO: 121, SEQ ID NO: 122, or SEQ ID NO: 123. In another specific embodiment, provided herein are polynucleotide sequences comprising a nucleic acid molecule encoding a light chain variable region, wherein the nucleic acid molecule comprises a nucleic acid sequence as set forth in SEQ ID NO: 120 or SEQ ID NO: 124. In a specific embodiment, the nucleic acid molecule or polynucleotide sequence is isolated.

[0059] In another aspect, provided herein is a vector comprising a polynucleotide sequence encoding an antibody or antigen-binding fragment described herein. In certain embodiments, a vector (e.g., a separated vector) comprises a polynucleotide encoding a heavy chain variable region and / or a light chain variable region or a heavy chain and / or a light chain of an anti-MERTK antibody described herein. In certain embodiments, a host cell comprises a polynucleotide or a vector. Examples of host cells include Escherichia coli (E.coli), Pseudomonas, Bacillus, Streptomyces, yeast, 293F, CHO, YB / 20, NSO, PER-C6, HEK-293, HEK-293T, NIH-3T3, HeLa, BHK, Hep G2, SP2 / 0, R1.1, BW, LM, COS1, COS 7, BSC1, BSC40, BMT10 cells, plant cells, insect cells, and human cells in tissue culture. In a specific embodiment, provided herein is a method for producing an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (eg, human MERTK), comprising culturing a host cell, thereby expressing the polynucleotide and producing the antibody.

[0060] In another aspect, the present invention provides an ex vivo cell containing one or more polynucleotides encoding any antibody or antigen-binding fragment thereof described herein or any immunoglobulin described herein. In a specific embodiment, the ex vivo cell contains one or more polynucleotides encoding an antibody selected from the following:

[0061] a first immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 105, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0062] a second immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 107, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106; and

[0063] a third immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 108, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0064] a fourth immunoglobulin comprising (i) a heavy chain region comprising the amino acid sequence shown in SEQ ID NO: 109, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106; and

[0065] A fifth immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO:110, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO:111.

[0066] In another aspect, provided herein are ex vivo cells containing a polynucleotide encoding any of the antibody heavy chains described herein.

[0067] In another aspect, provided herein are ex vivo cells containing polynucleotides encoding any antibody light chain described herein. In another aspect, provided herein are methods for producing antibodies or antigen-binding fragments thereof, comprising culturing ex vivo cells containing one or more polynucleotides encoding any antibody or antigen-binding fragment described herein under conditions such that the cells express one or more polynucleotides to produce antibodies or antigen-binding fragments thereof encoded by the polynucleotides. In a specific embodiment, the method for producing an antibody or antigen-binding fragment thereof comprises culturing ex vivo cells containing one or more polynucleotides encoding an antibody selected from the following:

[0068] a first immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 105, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0069] a second immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 107, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0070] a third immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 108, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0071] a fourth immunoglobulin comprising (i) a heavy chain region comprising the amino acid sequence shown in SEQ ID NO: 109, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106; and

[0072] a fifth immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 110, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 111,

[0073] The method is performed under conditions such that the cell expresses the one or more polynucleotides to produce the antibody encoded by the polynucleotides.

[0074] In another aspect, provided herein is a method of producing an antibody heavy chain, comprising culturing an ex vivo cell containing a polynucleotide encoding any of the antibody heavy chains described herein under conditions such that the cell expresses the polynucleotide to produce the antibody heavy chain encoded by the polynucleotide.

[0075] In another aspect, provided herein is a method of producing an antibody light chain, comprising culturing an ex vivo cell containing a polynucleotide encoding any of the antibody light chains described herein under conditions such that the cell expresses the polynucleotide to produce the antibody light chain encoded by the polynucleotide.

[0076] In another aspect, provided herein is an antibody-drug conjugate comprising: (a) an antibody portion described herein that is an antibody or antigen-binding fragment thereof that specifically binds MERTK (e.g., human MERTK); (b) one or more drug portions, each of which is a cytotoxic agent; and (c) optionally a linker; wherein the cytotoxic agent is conjugated directly to the antibody portion or to the antibody portion through the linker.

[0077] In a specific embodiment, the molar ratio of the antibody moiety to the drug moiety is between 1:1 and 1:12.

[0078] In a specific embodiment, the molar ratio of the antibody moiety to the drug moiety is between 1:1 and 1:8.

[0079] In another specific embodiment, the molar ratio of the antibody moiety to the drug moiety is between 1:3 and 1:5.

[0080] In another specific embodiment, the molar ratio of the antibody moiety to the drug moiety is 1:9.

[0081] In a specific embodiment, the antibody-drug conjugate comprises a linker and the linker is a cleavable linker.

[0082] In another specific embodiment, the antibody-drug conjugate comprises a linker and the linker is a non-cleavable linker.

[0083] In another specific embodiment, the antibody-drug conjugate comprises a linker and the linker is maleimidocaproyl-valine-citrulline-p-aminobenzyloxycarbonyl (also known as "mc-vc-PABC") (for the structure of mc-vc-PABC; see Fig.13A In another specific embodiment, the antibody-drug conjugate comprises a linker and the linker is CL2 (for the structure of CL2, see Fig. 13B and Cardillo et al. 2011, Clin Cancer Res; 17(10); 3157-69). In another specific embodiment, the antibody-drug conjugate comprises a linker and the linker is CL2A (for the structure of CL2A, see Fig. 13B and Goldberg et al. 2018, Oncotarget;9(48);28989-29006 and Cardillo et al. 2011, Clin Cancer Res;17(10);3157-69).

[0084] In a specific embodiment, the cytotoxic agent is a small molecule, a nucleotide, a peptide, or a non-antibody protein. In another embodiment of this specific embodiment, the cytotoxic agent is a small molecule.

[0085] In another specific embodiment, the cytotoxic agent is auristatin, maytansine, pyrrolobenzodiazepine, indolinbenzodiazepine, calicheamicin, camptothecin analogs, duocantoxin, tubulin inhibitor, tubulysin or tubulysin analogs, amberstatin269, doxorubicin, antibiotics, anthracycline antibiotics, microtubule inhibitors, spliceostatin or thailanstatin. In another embodiment of this specific embodiment, the cytotoxic agent is monomethyl auristatin E (MMAE) or monomethyl auristatin F (MMAF). In another other embodiment of this specific embodiment, the cytotoxic agent is DM1 or DM4. In another other embodiment of this specific embodiment, the cytotoxic agent is SN-38.

[0086] In another aspect, provided herein is a method of producing an antibody-drug conjugate described herein in which no linker is present, the method comprising: (a) conjugating a cytotoxic agent directly to the antibody portion to produce an antibody-drug conjugate; and (b) purifying the antibody-drug conjugate.

[0087] In another aspect, provided herein is a method of producing an antibody-drug conjugate described herein wherein the antibody-drug conjugate comprises a linker, the method comprising the following steps in the order described: (a) directly conjugating the linker to the antibody portion to produce a linker-antibody portion; (b) directly conjugating the linker of the linker-antibody portion to a cytotoxic agent to produce an antibody-drug conjugate; and (c) purifying the antibody-drug conjugate.

[0088] In another aspect, provided herein is a method of producing an antibody-drug conjugate described herein wherein the antibody-drug conjugate comprises a linker, the method comprising the following steps in the order described: (a) directly conjugating the linker to a cytotoxic agent to produce a linker-cytotoxic agent portion; (b) directly conjugating the linker of the linker-cytotoxic agent portion to an antibody portion to produce an antibody-drug conjugate; and (c) purifying the antibody-drug conjugate.

[0089] In another aspect, provided herein are pharmaceutical compositions comprising an anti-MERTK antibody or antigen-binding fragment thereof described herein or an antibody-drug-conjugate described herein. In a specific embodiment, provided herein are pharmaceutical compositions comprising a therapeutically effective amount of any antibody or antigen-binding fragment described herein or any antibody-drug conjugate described herein. In a specific embodiment, the pharmaceutical composition comprises:

[0090] a first immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 105, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0091] a second immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 107, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106;

[0092] a third immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 108, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106,

[0093] a fourth immunoglobulin comprising (i) a heavy chain region comprising the amino acid sequence shown in SEQ ID NO: 109, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106; or

[0094] a fourth immunoglobulin comprising (i) a heavy chain variable region comprising the amino acid sequence shown in SEQ ID NO: 110, and (ii) a light chain variable region comprising the amino acid sequence shown in SEQ ID NO: 106,

[0095] and a pharmaceutically acceptable carrier.

[0096] In some embodiments, the pharmaceutical composition comprises a polynucleotide sequence comprising a nucleic acid sequence encoding an antibody or antigen-binding fragment thereof.

[0097] In another aspect, provided herein is a method of treating cancer in a subject in need thereof, the method comprising administering to the subject an anti-MERTK antibody or antigen-binding fragment thereof described herein or an antibody-drug conjugate described herein. In a specific embodiment, provided herein is a method of treating cancer in a subject in need thereof, the method comprising administering to the subject any pharmaceutical composition described herein.

[0098] In some embodiments, a tumor sample from the subject is evaluated for overexpression of phosphorylated MERTK prior to treatment according to the methods described herein. In certain embodiments, the subject is treated if the tumor sample overexpresses phosphorylated MERTK.

[0099] In a specific embodiment of the above aspects of the method for treating cancer, the cancer is head and neck cancer, lung cancer, breast cancer, bone cancer, ovarian cancer, stomach cancer, pancreatic cancer, laryngeal cancer, esophageal cancer, testicular cancer, liver cancer, parotid cancer, bile duct cancer, colon cancer, rectal cancer, cervical cancer, uterine cancer, endometrial cancer, kidney cancer, bladder cancer, prostate cancer or thyroid cancer. In certain embodiments of this specific embodiment, the cancer is breast cancer. In other embodiments of this certain embodiment, the cancer is triple negative breast cancer.

[0100] In a specific embodiment of the above aspects of the method for treating cancer, the cancer is a sarcoma, squamous cell carcinoma, melanoma, glioma, glioblastoma, neuroblastoma, gastric cancer, colorectal cancer, non-small cell lung cancer or Kaposi's sarcoma. In a specific embodiment of the aspects of the method for treating cancer, the cancer is a leukemia or lymphoma. In other specific embodiments, the cancer is acute myeloid leukemia. In another other specific embodiment, the cancer is acute lymphocytic leukemia. In another other embodiment, the cancer is multiple myeloma.

[0101] In a specific embodiment, the cancer treated in accordance with the methods described herein overexpresses MERTK, is associated with a constitutively active MERTK (eg, human MERTK), or both. In another specific embodiment, the cancerous cells of the cancer overexpress phosphorylated MERTK.

[0102] In a specific embodiment of the method of treating cancer, the method further comprises administering to said subject an additional therapeutic agent.

[0103] In a specific embodiment of the embodiment wherein the method further comprises administering to the subject an additional therapeutic agent, the additional therapeutic agent is used to treat cancer. The additional therapeutic agent can be administered in the same pharmaceutical composition as the anti-MERTK antibody or antigen-binding fragment thereof or antibody-drug conjugate or in a different pharmaceutical composition.

[0104] In the specific embodiment of the embodiment in which the other therapeutic agents are used to treat cancer, the other therapeutic agents are reagents for treating breast cancer, reagents for treating melanoma, immunotherapy or angiogenesis inhibitors. In one other embodiment of this specific embodiment, the other therapeutic agents are reagents for treating breast cancer, which are selected from: tamoxifen, raloxifene, paclitaxel, cyclophosphamide, docetaxel, vinblastine, fluorouracil, everolimus, trastuzumab, trastuzumab-emtansine, pertuzumab and lapatinib ditoluenesulfonate. In another other embodiment of this specific embodiment, the other therapeutic agents are reagents for treating melanoma, which are selected from BRAF inhibitors, MEK inhibitors and dacarbazine. In another other embodiment of this specific embodiment, the other therapeutic agents are reagents for blocking immune checkpoint signal transduction. In another other embodiment, the other therapeutic agents are anti-CTLA-4 antibodies, anti-PD-1 antibodies or anti-PD-L1 antibodies. In another further embodiment of this specific embodiment, the additional therapeutic agent is an angiogenesis inhibitor selected from the group consisting of a VEGF inhibitor, a VEGFR2 inhibitor, sunitinib, and sorafenib.

[0105] In a specific embodiment of the method of treating cancer, the subject is a human.

[0106] In a specific embodiment, provided herein is an antibody-drug conjugate comprising an antibody portion comprising a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the sequence shown in SEQ ID NO: 105 and the VL comprises the amino acid sequence of SEQ ID NO: 106, wherein the antibody portion is linked to MMAE via a mc-vc-PABC linker. In another specific embodiment, provided herein is an antibody-drug conjugate comprising an antibody portion comprising a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the sequence shown in SEQ ID NO: 105 and the VL comprises the amino acid sequence of SEQ ID NO: 106, wherein the antibody portion is linked to SN-38 via a CL2A linker.

[0107] In certain embodiments, the antibody-drug conjugate comprises an antibody portion that is an immunoglobulin. In some embodiments, the antibody-drug conjugate comprises an antibody portion wherein the antibody portion is an immunoglobulin and the immunoglobulin comprises a human constant region. 4. Description of the drawings

[0108] Figure 1. Determination of the dissociation rate (Kd) of humanized anti-MERTK antibodies and chimeric anti-MERTK antibodies measured using surface plasmon resonance (SPR).

[0109] Figure 2 Summary of protein purification of three humanized anti-MERTK antibodies (z10, z11 and z13) and a chimeric anti-MERTK antibody (xAb).

[0110] Figure 3A-3B . Figure 3A . Flow cytometric analysis of z10 antibody binding affinity to human MERTK expressed by melanoma cells. Figure 3B SPR measurement of the binding of the .z10 antibody to human extracellular MERTK.

[0111] Figures 4A-4D .z10 antibody specifically binds to human MERTK ( Figure 4A ), as measured in an affinity binding assay using ELISA. However, the z10 antibody did not bind to the extracellular domain of human Axl ( Figure 4B ), Tyro 3( Figure 4C ) or mouse MERTK ( Figure 4D ), as assessed in affinity binding assays using ELISA. The extracellular domains of human MERTK, human Axl and murine MERTK were conjugated to IgG Fc domains and used in ELISA.

[0112] Figure 5A-5B .z10 antibody induces degradation of human MERTK on cancer cells, specifically SKMEL5 cells. SKMEL5 cells were incubated with different concentrations of z10 antibody for 24 hours ( Figure 5A ) or incubated with 0.3 μg / mL of the antibody for different time periods ( Figure 5B ).

[0113] Figure 6A-6B .z10 antibody degrades human MERTK on in vitro differentiated human M2 macrophages. M2 macrophages were treated in vitro with 0.3 μg / mL z10 antibody or control IgG and incubated for various time periods before assessing the levels of human MERTK by immunoblot analysis. Fig. 6A Immunoblotting results are provided and Figure 6B Relative quantification of human MERTK to tubulin is provided.

[0114] Figure 7A-7BInternalization of human MERTK by SKMEL5 cells mediates degradation of human MERTK. SKMEL5 cells were incubated with control IgG or z10 antibody, both labeled with pHrodo, which is measurable only under low pH conditions, e.g., by uptake in lysosomes. Surface human MERTK was measured using a commercially available MERTK antibody. Fig. 7A shows the fluorescence over time and Figure 7B It is a representative image.

[0115] Figures 8A-8C .z10 antibody blocks Gas6-induced phosphorylation of AKT in human cancer cells. SKMEL5 cells were incubated with 0.3 μl / mL of z10 antibody or control IgG for 2 hours before incubation with 200 nM Gas6 for 10 minutes. Fig. 8A Western blot results are shown. Figure 8B The amount of human MERTK relative to tubulin is shown, and Figure 8C The amount of phosphorylated AKT on tubulin is shown.

[0116] Figures 9A-9D .z10 antibody inhibits colony formation of human cancer cells. The figure shows the reduction in the number of colonies observed after culturing 500 SKMEL5 cells for 12 days in the presence of 0.3 μg / mL or 1 μg / mL of z10 antibody relative to the number of colonies observed when 500 SKMEL5 cells were cultured with control IgG for 12 days. Fig. 9A Shown are colony formation of cancer cells after 12 days of incubation with 0.3 μg / mL z10 antibody or control IgG antibody. Fig. 9B Shown are colony formation of cancer cells after 12 days of incubation with 1 μg / mL z10 antibody or control IgG antibody. Fig. 9C The number of colonies formed after 12 days of incubation with 0.3 μg / mL z10 antibody or control IgG antibody is shown. Fig.9D The number of colonies formed after 12 days of incubation with 1 μg / mL z10 antibody or control IgG antibody is shown.

[0117] Fig.10 The .z10 antibody induced cytokine responses in M2 macrophages and CD14+ monocytes.

[0118] Fig.11A and 11B . Z10 inhibits the survival of cancer cells in vitro. 1,000 RPMI8226 multiple myeloma cells ( Fig.11A ) or 200 SKMEL5 melanoma cells ( Fig. 11B). On day 6 (RPMI8226) or day 4 (SKMel5), viability was assessed using the CellTiter-Glo 2.0 cell viability assay.

[0119] Fig. 12A and 12B .MDA-MB-231-LM2: z10 naked antibody anti-tumor efficacy. 50,000 MDA-MB-231-LM2 TNBC cells were injected into the tail vein of NSG mice. Treatment was started on the day of tumor cell inoculation and ip twice a week during the study. Fig. 12A Lung colonization by MDA-MB-231 LM2 triple-negative breast cancer cells was demonstrated using IVIS imaging. Fig. 12B Lung colonization of MDA-MB-231 LM2 triple-negative breast cancer cells was quantified. * indicates p-value less than 0.05.

[0120] Fig.13A and 13B . Fig.13A Shown is the structure of maleimidocaproyl-valine-citrulline-p-aminobenzyloxycarbonyl-monomethylauristatin E (mc-vc-PABC-MMAE) conjugated to an antibody (Ab). Fig. 13B The structure of SN-38 conjugated to an antibody (Ab) via a CL2 or CL2A linker is shown. "Ab" stands for antibody, which, by way of example and not limitation, can be z10 or a control IgG. The CL2 linker has a cathepsin B cleavage site (see Fig. 13B , when AA is phenylalanine-lysine), while the CL2A linker does not have a cathepsin B cleavage site (see Fig. 13B , when AA is lysine).

[0121] Fig.14A and 14B The results of size-exclusion high pressure liquid chromatography are shown, which measures the concentration of z10 conjugated to MMAE via a mc-vc-PABC linker (z10-MMAE, see Fig.13A , where Ab is z10)( Fig.14A ) and z10 conjugated to SN-38 via a CL2A linker (z10-SN-38, see Fig. 13B , wherein Ab is z10 and AA is lysine)( Fig. 14B ) purity.

[0122] Fig.15 : z10-ADC binds to MERTK with a Kd similar to that of z10. Fig.15Binding affinity data for z10-ADC are provided. Before adding to ELISA plates pre-coated with hMER recombinant protein, hMER recombinant protein (Mer-Fc conjugate) was equilibrated with 0.3 nM z10, z10-MMAE or z10-SN-38, respectively (50 nM-0.05 nM). Antibody binding was detected using an AP-conjugated anti-human IgG secondary antibody and developed using a GloMax microplate reader.

[0123] Fig.16A and 16B . Fig.16A and 16B Internalization of MERTK by SKMel5 cells is shown after incubation with z10, z10-MMAE, or z10-SN-38 ( Fig.16A ) and MERTK degradation ( Fig. 16B ). z10, z10-MMAE, and z10-SN-38 degraded MERTK to a similar extent. SKMel5 cells were incubated with 6.7 nM pHrodo-labeled z10, z10-MMAE, or z10-SN-38. The pHrodo signal is measurable only under low pH conditions, e.g., by uptake in lysosomes. Surface MERTK was stained with BV421-conjugated MERTK antibody. Binding was measured by flow cytometry.

[0124] Figures 17A-17E .z10-MMAE and z10-SN-38 kill cancer cells expressing MERTK. Fig.17A ) or RPMI8226( Fig. 17B ) cells and IgG control, IgG control conjugated to MMAE via a mc-mv-PABC linker (IgG-MMAE, see Fig.13A , wherein the Ab is IgG) or z10-MMAE for 7 days. Cell viability was measured using CellTiterGlo. Fig. 17C ) or RPMI8226( Fig.17D ) cells and IgG control, IgG control conjugated to SN-38 via a CL2A linker (IgG-SN-38, see Fig. 13B , wherein Ab is IgG and AA is lysine) or z10-SN-38 was incubated at the indicated concentrations for 7 days. Cell viability was measured using CellTiterGlo. Fig.17E Shown are immunoblot analyses of whole cell lysates prepared from SKMe15 or RPMI8226 cells.

[0125] Fig.18A and 18B.zl0-MMAE inhibited lung colonization of MDA-MB-231-LM2 TNBC cells. Fig.18A Lung colonization by MDA-MB-231-LM2 triple-negative breast cancer cells was demonstrated using IVIS imaging. Fig.18B Lung colonization of MDA-MB-231-LM2 triple-negative breast cancer cells was quantified. 50,000 MDA-MB-231-LM2 TNBC cells were injected into the tail vein of NSG mice. Treatment was started on the day of tumor cell inoculation, and lung metastatic colonization was monitored by bioluminescence imaging. Fig.18B The arrows in the table indicate the dosing days. ** indicates a p-value less than 0.01.

[0126] Fig.19A and 19B .z10 / z10-ADC does not affect M1 macrophages expressing MERTK ( Fig.19A ) or M2 macrophages ( Fig.19B ) survival. By dividing 8×10 4 Monocytes were cultured in PBMC medium with M-CSF (50 ng / mL) for 8 days to differentiate into M2 macrophages. 4 Monocytes were cultured in PBMC medium with GM-CSF (20 ng / mL) for 5 days and then cultured with GM-CSF (20 ng / mL), IFNg (20 ng / mL), IL-6 (20 ng / mL) and LPS (10 ng / mL) for another 3 days to differentiate M1 macrophages. M2 and M1 macrophages were treated with the indicated antibodies or ADCs in differentiation medium for 4 days and viability was assessed using the CellTiter-Glo 2.0 cell viability assay. 5. Detailed description

[0128] Provided herein are anti-MERTK antibodies (eg, monoclonal antibodies) and antigen-binding fragments thereof that specifically bind to MERTK (eg, human MERTK).

[0129] In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein specifically recognize the extracellular domain of MERTK (e.g., human MERTK). In specific embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein do not bind to human Axl, human Tyro 3 or mouse MERTK, as detected by techniques known to those of skill in the art or described herein. In specific embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein do not bind to human Axl, human Tyro3 or mouse MERTK, as evaluated by affinity binding assay using an ELISA as described in Section 6.2 below.

[0130] In a specific embodiment, the anti-MERTK antibody (e.g., humanized antibody) or antigen-binding fragment thereof described herein specifically binds to a human MERTK protein comprising the amino acid sequence set forth in SEQ ID NO: 131. In another specific embodiment, the anti-MERTK antibody (e.g., humanized antibody) or antigen-binding fragment thereof described herein specifically binds to an extracellular region of human MERTK comprising the amino acid sequence set forth in SEQ ID NO: 132. In another specific embodiment, the anti-MERTK antibody (e.g., humanized antibody) or antigen-binding fragment thereof described herein specifically binds to SEQ ID NO: 132. In a specific embodiment, the anti-MERTK antibody (e.g., humanized antibody) or antigen-binding fragment thereof described herein is bivalent. In a specific embodiment, the anti-MERTK antibody (e.g., humanized antibody) or antigen-binding fragment thereof described herein comprises two antigen binding sites that bind to MERTK (e.g., human MERTK). In a specific embodiment, the two antigen binding sites bind to the same epitope on MERTK (e.g., human MERTK). In a specific embodiment, the two antigen binding sites comprise the same CDR.

[0131] In certain embodiments, an anti-MERTK antibody (eg, a humanized antibody) or antigen-binding fragment thereof is expressed with a K of about 1 pM to 10 nM. D (as determined using techniques known to one of skill in the art or described herein) to a recombinant MERTK-Fc chimera (e.g., a recombinant human MERTK-Fc chimera). In a specific embodiment, an anti-MERTK antibody (e.g., a humanized antibody) or antigen-binding fragment thereof described herein has a K of about 1 pM to about 6 pM. DIn certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein bind to a recombinant MERTK-Fc chimera (e.g., a recombinant human MERTK-Fc chimera) (as determined using surface plasmon resonance (SPR) as described in Section 6 below). 50 Binds to MERTK (e.g., human MERTK) (using an assay described herein or known to one of skill in the art). In certain specific embodiments, an anti-MERTK antibody (e.g., a humanized antibody) or antigen-binding fragment thereof as described herein binds to MERTK (e.g., human MERTK) with a K of about 1 nM to 10 nM in an assay described in Section 6 below. D Binds to MERTK (eg, human MERTK).

[0132] In certain embodiments, an anti-MERTK antibody (eg, a humanized antibody) or antibody fragment thereof as described herein is administered at an EC of about 1 nM to 20 nM. 50 Binds to cells expressing human MERTK (e.g., human MERTK cancer cells or M2 macrophages) (as assessed by flow cytometry as described herein or known to one of skill in the art). In a specific embodiment, an anti-MERTK antibody (e.g., a humanized antibody) or antigen-binding fragment thereof as described herein is expressed at an EC of 1 nM to 10 nM. 50 Binding to cells expressing human MERTK (eg, human MERTK cancer cells or M2 macrophages) (as assessed by flow cytometry as described in Section 6.2, below).

[0133] In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein reduce the expression level of human MERTK on cancer cells, as assessed by an assay described herein (e.g., in Section 6.2, below) or an assay known to those skilled in the art. In specific embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein reduce the expression level of human MERTK on the melanoma cell line SKMEL5, as assessed by an assay described herein (e.g., in Section 6.2, below) or an assay known to those skilled in the art. In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof reduce the expression level of human MERTK on human M2 macrophages, as assessed by an assay described herein (e.g., in Section 6.2, below) or an assay known to those skilled in the art. In certain embodiments, an anti-MERTK antibody (e.g., a humanized antibody) or an antigen-binding fragment thereof reduces the expression level of human MERTK by internalization of MERTK, as assessed by an assay described herein (e.g., in Section 6.2, below) or an assay known to those of skill in the art. In certain embodiments, an anti-MERTK antibody (e.g., a humanized antibody) or an antigen-binding fragment thereof reduces the expression level of human MERTK by internalization into lysosomes, as assessed by an assay described herein (e.g., in Section 6.2, below) or an assay known to those of skill in the art.

[0134] In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein reduce Gas 6-induced AKT phosphorylation in cells expressing human MERTK (e.g., cancer cells), as assessed by an assay described herein (e.g., Section 6.2, below) or an assay known to those skilled in the art. In specific embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein prevent Gas-6-induced AKT phosphorylation in cells expressing human MERTK, such as (e.g.) melanoma SKMEL5 cells, as assessed by an assay described herein (e.g., Section 6.2, below) or an assay known to those skilled in the art. In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein reduce Gas-6-induced phosphorylation of human MERTK in cells expressing human MERTK, as assessed by an assay known to those skilled in the art. In a specific embodiment, an anti-MERTK antibody (e.g., a humanized antibody) or antigen-binding fragment thereof described herein blocks Gas-6-induced activation of MERTK in cancer cells expressing human MERTK (e.g., melanoma cells, such as, for example, SKMEL5), as assessed by assays known to those of skill in the art.

[0135] In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments described herein reduce the colony-forming ability of cancer cells, as assessed by assays described herein (e.g., in Section 6.2 below) or assays known to those of skill in the art. In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein inhibit colony formation of cancer cells (e.g., melanoma cells, such as SKMEL5).

[0136] In certain embodiments, the anti-MERTK antibodies (e.g., humanized antibodies) or antigen-binding fragments thereof described herein elicit a cytokine response in M2 macrophages, CD14+ monocytes, or both, such as Fig.10 As provided in, as assessed using assays described herein or known to those skilled in the art.

[0137] In specific embodiments, an anti-MERTK antibody (eg, a humanized antibody) or antigen-binding fragment thereof described herein is isolated.

[0138] Antibodies described herein may include monoclonal antibodies or polyclonal antibodies. In a specific embodiment, the antibody may be an immunoglobulin, a tetrameric antibody comprising two heavy chains and two light chain molecules, an antibody light chain monomer, an antibody heavy chain monomer, an antibody light chain dimer, an antibody heavy chain dimer, an antibody light chain-antibody heavy chain pair, a single domain antibody, a monovalent antibody, a single chain antibody, a single-chain Fv (scFv), a disulfide bond-connected Fv (scFv) and an anti-idiotype (anti-Id) antibody (including, for example, an anti-anti-Id antibody).

[0139] In certain embodiments, the antibodies described herein can be multi-specific or bi-specific. In certain embodiments, the antibodies described herein are bi-specific monoclonal antibodies. In certain embodiments, the antibodies described herein are monovalent. In specific embodiments, the antibodies described herein are bivalent. In specific embodiments, the antibodies described herein bind to human MERTK on cells. In some embodiments, the antibodies described herein are mono-specific. In certain embodiments, the antibodies described herein are recombinantly produced. In some embodiments, the antibodies described herein are synthetic antibodies. In specific embodiments, the antibodies described herein are humanized antibodies. In other embodiments, the antibodies described herein can be human antibodies.

[0140] The antibodies described herein can be of any type (e.g., IgG, IgE, IgM, IgD, IgA, and IgY), any class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2), or any subclass (e.g., IgG 2a or IgG 2b ). In certain embodiments, the antibodies described herein are IgG antibodies or their class or subclass. In specific embodiments, the antibodies described herein (e.g., humanized antibodies) are monoclonal antibodies. In specific embodiments, the anti-MERTK antibodies described herein are IgG antibodies.

[0141] As used herein, the terms "antigen-binding fragment", "antigen-binding region" and similar terms refer to the portion of an antibody molecule that contains amino acid residues that confer specificity to an antigen on the antibody molecule (e.g., a complementary determining region (CDR)). The antigen-binding region can be derived from any animal species, such as rodents (e.g., mice, rats, or hamsters) and humans. For example, antigen-binding fragments include Fab fragments, F(ab')2 fragments, and antigen-binding fragments of any of the antibodies described above. In a specific embodiment, the antigen-binding fragment of a humanized antibody comprises the heavy chain variable region, the light chain variable region, or both of the z10, z11, or z13 antibodies described herein.

[0142] As used herein, the terms "variable region" or "variable domain" are interchangeable and common in the art. A variable region generally refers to a portion of an antibody, typically a portion of a light chain or a heavy chain, which is widely different in sequence between antibodies and is used in the binding and specificity of a particular antibody for its specific antigen. The variability in the sequence is concentrated in those regions referred to as complementary determining regions (CDRs), while the more highly conserved regions in the variable domains are referred to as framework regions (FRs). Without wishing to be bound by any specific mechanism or theory, it is believed that the CDRs of the light and heavy chains are primarily responsible for the interaction and specificity of the antibody with the antigen.

[0143] CDRs are defined in a variety of ways in the art, including the Kabat, Chothia, AbM, contact, IMGT, and Exemplary definitions. The Kabat definition is based on sequence variability and is the most commonly used definition for predicting CDR regions (Kabat, Elvin A. et al., Sequences of Proteins of Immunological Interest. Bethesda: National Institutes of Health, 1983). The Chothia definition is based on the location of structural loop regions (Chothia et al., (1987) J Mol Biol 196: 901-917). The AbM definition, which is a compromise between the Kabat and Chothia definitions, is a suite of programs for antibody structure modeling produced by the Oxford Molecular Group (bioinf.org.uk / abs) (Martin ACR et al., (1989) PNAS 86: 9268-9272). The contact definitions are based on analysis of available complex crystal structures (bioinf.org.uk / abs) (see MacCallum RM et al. (1996) J Mol Biol 5:732-745). The IMGT definitions are from IMGT ( The international ImMunoGeneTics information system ), website: imgt.org, founder and director: Marie-Paule Lefranc, Montpellier, France). The exemplary definition is a combination of AbM and Kabat (Presta et al., (1997) Cancer Res 57:4593-4599).

[0144] In a specific embodiment, a humanized antibody or antigen-binding fragment thereof described herein comprises a heavy chain variable region, a light chain variable region, or both, wherein the heavy chain variable region, the light chain variable region, or both are the heavy chain variable region, the heavy chain variable region, or both of the z10, z11, or z12 antibodies provided in Tables 11, 12, and 13, respectively. In another specific embodiment, a humanized antibody or antigen-binding fragment described herein comprises a heavy chain variable region, a light chain variable region, or both, wherein the variable heavy chain comprises the amino acid sequence of a heavy chain variable region in Table 14, and the light chain variable region comprises the amino acid sequence of a light chain variable region in Tables 11, 12, or 13 below. In a specific embodiment, the humanized antibody is monoclonal. In some embodiments, the humanized antibody is an immunoglobulin, a tetrameric antibody comprising two heavy chains and two light chain molecules, an antibody light chain monomer, an antibody heavy chain monomer, an antibody light chain dimer and an antibody heavy chain dimer, an antibody light chain-antibody heavy chain pair, a single domain antibody, a single chain antibody, a single chain Fv, a disulfide bond-connected Fv or an anti-idiotypic antibody. The humanized antibody can be of any type (e.g., IgG, IgE, IgM, IgD, IgA or IgY), any class (IgG1, IgG2, IgG3, IgG4, IgA or IgA2) or any subclass (e.g., IgG 2a or IgG 2b In a specific embodiment, the humanized antibody described herein is IgG or its class or subclass.

[0145] The present invention application contemplates not only antibodies and antigen-binding fragments thereof (e.g., CDRs, framework regions, variable regions) comprising the sequences disclosed herein, but also antibodies and antigen-binding fragments thereof consisting of or substantially consisting of the sequences disclosed herein. For example, an antibody may include the light chain and heavy chain sequences of the z10, z11 or z13 antibodies described herein.

[0146] In a specific embodiment, provided herein is a chimeric anti-MERTK antibody or antigen-binding fragment thereof comprising a heavy chain variable region, a light chain variable region, or both, wherein the variable light chain comprises the amino acid sequence of the light chain variable region in Table 15 below, and the variable heavy chain comprises the amino acid sequence of the heavy chain variable region in Table 15 below. In a specific embodiment, the chimeric antibody is monoclonal. In some embodiments, the chimeric antibody is an immunoglobulin, a tetrameric antibody comprising two heavy chains and two light chain molecules, an antibody light chain monomer, an antibody heavy chain monomer, an antibody light chain dimer and an antibody heavy chain dimer, an antibody light chain-antibody heavy chain pair, a single domain antibody, a single chain antibody, a single chain Fv, a disulfide bond-connected Fv, or an anti-idiotypic antibody. The chimeric antibody can be of any type (e.g., IgG, IgE, IgM, IgD, IgA, or IgY), any class (IgG1, IgG2, IgG3, IgG4, IgA, or IgA2), or any subclass (e.g., IgG 2a or IgG 2b In certain embodiments, the chimeric antibodies described herein are IgG antibodies or a class or subclass thereof.

[0147] In another aspect, multi-specific antibodies and heterologous conjugate antibodies are provided herein. In a specific embodiment, a bispecific antibody comprising two different antigen binding regions is provided herein, wherein one of the binding regions binds to MERTK (e.g., human MERTK) and comprises a heavy chain variable region, a light chain variable region, or both of an antibody described herein (e.g., z10, z11, z13, or xAb antibody), and the other binding region is bound to the target antigen. In some embodiments, a bispecific antibody comprises two different antigen binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to the target antigen, and wherein the binding region specifically bound to MERTK (e.g., human MERTK) comprises a heavy chain variable region and a light chain variable region of z10, z12, or z13 antibodies described herein. In a specific embodiment, the target antigen is an immune cell receptor or a tumor-associated antigen. For bispecific antibodies, see Section 5.1.3 below.

[0148] Heteroconjugate antibodies are also provided herein. In a specific embodiment, the heteroconjugate antibody comprises two monoclonal antibodies specific for two different antigens, wherein one of the monoclonal antibodies comprises the heavy chain variable region and light chain variable region of an antibody described herein (e.g., z10, z11, z13 or xAb antibody).

[0149] Also provided are isolated nucleic acids (polynucleotides), such as complementary DNA (cDNA), encoding anti-MERTK antibodies and antigen-binding fragments thereof described herein. In certain embodiments, provided herein are polynucleotides comprising nucleic acid sequences of VH, VL, or both of z10, z11, z13, or xAb antibodies described in Tables 21, 22, 23, or 24. In some embodiments, provided herein are polynucleotides comprising heavy chains, light chains, or both of z10, z11, z13, or xAb antibodies described in Tables 25, 26, 27, or 28.

[0150] Also provided are vectors (eg, expression vectors) and cells (eg, host cells) comprising nucleic acids (polynucleotides) encoding the anti-MERTK antibodies or antigen-binding fragments thereof described herein. Also provided are methods of making these antibodies.

[0151] In another aspect, provided herein is an antibody-drug conjugate comprising: (a) an antibody portion as described herein that specifically binds to a MERTK described herein (e.g., human MERTK) or an antigen-binding fragment thereof; (b) one or more drug portions, each drug portion being a cytotoxic agent; and (c) optionally a linker; wherein the cytotoxic agent is conjugated directly to the antibody portion or to the antibody portion through the linker. The term "conjugated" as used in the present disclosure shall mean covalent binding, which may be direct or through an intermediate covalent binding structure.

[0152] In the case where the cytotoxic agent is a peptide or protein or where the cytotoxic agent and the linker (if one is present) are peptides or proteins, a nucleic acid encoding the antibody-drug conjugate is also provided. In other aspects, provided herein is a method for producing an antibody-drug conjugate comprising (i) an anti-MERTK antibody or an antigen-binding fragment thereof, and (ii) a cytotoxic agent conjugated directly to the anti-MERTK antibody or antigen-binding fragment or conjugated to the anti-MERTK antibody or antigen-binding fragment via a linker.

[0153] In another aspect, provided herein are compositions (e.g., pharmaceutical compositions) comprising an anti-MERTK antibody or antigen-binding fragment thereof as described herein. In specific embodiments, the pharmaceutical composition comprises an anti-MERTK antibody or antigen-binding fragment thereof as described herein, one or more pharmaceutically acceptable carriers, excipients, or both, and optionally one or more other therapeutic agents.

[0154] In another aspect, provided herein are compositions (e.g., pharmaceutical compositions) comprising the antibody-drug conjugates described herein. In specific embodiments, the pharmaceutical compositions comprise the antibody-drug conjugates described herein, one or more pharmaceutically acceptable carriers, excipients, or both, and optionally one or more other therapeutic agents.

[0155] In another aspect, provided herein is a method for treating cancer in a subject, the method comprising administering to the subject an effective amount of an anti-MERTK antibody or antigen-binding fragment thereof described herein, or a composition thereof. In a specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof is a humanized antibody or antigen-binding fragment described herein. In other embodiments, the anti-MERTK antibody or antigen-binding fragment thereof is a dual-specific antibody or a heteroconjugate antibody described herein. In some embodiments, the anti-MERTK antibody or antigen-binding fragment thereof is a chimeric antibody or antigen-binding fragment thereof.

[0156] In another aspect, provided herein is a method for treating cancer in a subject, comprising administering to the subject an effective amount of an antibody-drug conjugate described herein. In a specific embodiment, provided herein is a method for treating cancer in a subject, comprising administering to the subject an effective amount of an antibody-drug conjugate comprising (i) an anti-MERTK antibody or an antigen-binding fragment thereof and (ii) a cytotoxic agent conjugated directly to the anti-MERTK antibody or its antigen-binding fragment or to the anti-MERTK antibody or its antigen-binding fragment via a linker.

[0157] Antibodies

[0158] 5.1.1. Sequences and variants

[0159] The VH CDRs and VL CDRs of the anti-MERTK antibodies or antigen-binding fragments thereof as defined using different systems are provided in Tables 1 and 7 or 8, respectively, below. Tables 2, 3, 4, 5 and 6 below provide VH framework regions that can be combined with the CDRs in Table 1 as defined using different systems. In a specific embodiment, the CDRs in Table 1 are combined with a consensus sequence VH framework region 3 using a numbering system, and VH framework regions 1, 2 and 4 (provided in Tables 2, 3, 4 or 6) using the same numbering system. Tables 9 and 10 below provide VL framework regions that can be combined with the CDRs in Tables 7 or 8 as defined using different systems. Tables 11, 12, 13 and 15 provide amino acid sequences of VH and VL of specific antibodies. Table 14 provides amino acid sequences of VH that can be combined with VL provided in Tables 11, 12, 13 or 15. Tables 16, 17, 18 and 20 provide heavy and light chain amino acid sequences of specific antibodies. Table 19 provides heavy chain amino acid sequences that can be combined with the light chain amino acid sequences in Tables 16, 17 or 18. Tables 21, 22, 23 and 24 provide nucleic acid sequences encoding the variable regions of specific antibodies. Tables 25, 26, 27 and 28 provide nucleic acid sequences encoding the heavy and light chains of specific antibodies. Tables 29 and 30 provide exemplary human MERTK amino acid sequences to which the anti-MERTK antibodies or antigen-binding fragments thereof described herein can bind.

[0160] In specific embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise a VH CDR1 of an antibody in Table 1 as defined by Kabat, Chothia, AbM, Contact, IMGT, or Exemplary. In some embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise a VH CDR2 of an antibody in Table 1 as defined by Kabat, Chothia, AbM, Contact, IMGT, or Exemplary. In some embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise a VH CDR3 of an antibody in Table 1 as defined by Kabat, Chothia, AbM, Contact, IMGT, or Exemplary. In some embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise 1, 2, or all 3 VH CDRs of an antibody in Table 1 as determined by a numbering system.

[0161] In specific embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise a VL CDR1 of an antibody in Table 7 as defined by Kabat, Chothia, AbM, Contact, IMGT, or Exemplary. In some embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise a VL CDR2 of an antibody in Table 7 as defined by Kabat, Chothia, AbM, Contact, IMGT, or Exemplary. In some embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise a VL CDR3 of an antibody in Table 7 as defined by Kabat, Chothia, AbM, Contact, IMGT, or Exemplary. In some embodiments, the anti-MERTK antibodies or antigen-binding fragments thereof provided herein comprise 1, 2, or all 3 VL CDRs of an antibody in Table 7 as determined by a numbering system.

[0162] Table 1. Antibody z10 / z11 / z13 / xAb VH CDR amino acid sequences

[0163]

[0164] Table 2. Antibody z10 VH framework region amino acid sequence

[0165]

[0166] Table 3. Antibody z11 VH framework region amino acid sequence

[0167]

[0168] Table 4. Antibody z13 VH framework region amino acid sequence

[0169]

[0170] Table 5. Antibody VH FR3 consensus amino acid sequence (X1 is F or M; X2 is T or L)

[0171]

[0172] Table 6. Antibody xAb VH framework region amino acid sequence

[0173]

[0174] Table 7. Antibody z10 / z11 / z13 VL CDR amino acid sequences

[0175]

[0176] Table 8. Antibody xAb VL CDR amino acid sequences

[0177]

[0178] Table 9. Antibody z10 / z11 / z13 VL framework region amino acid sequence

[0179]

[0180] Table 10. Antibody xAb VL framework region amino acid sequence

[0181]

[0182] Table 11. Variable region amino acid sequence of antibody z10

[0183]

[0184] Table 12. Variable region amino acid sequence of antibody z11

[0185]

[0186] Table 13. Antibody z13 variable region amino acid sequence

[0187]

[0188] Table 14. Consensus amino acid sequences of antibody heavy chain variable regions (X1 is F or M; X2 is T or L)

[0189]

[0190] Table 15. Antibody xAb variable region amino acid sequence

[0191]

[0192] Table 16. Antibody z10 heavy chain and light chain amino acid sequences

[0193]

[0194] Table 17. Antibody z11 heavy chain and light chain amino acid sequences

[0195]

[0196] Table 18. Antibody z13 heavy chain and light chain amino acid sequences

[0197]

[0198] Table 19. Antibody heavy chain consensus amino acid sequence (X1 is F or M; X2 is T or L)

[0199]

[0200] Table 20. Antibody xAb heavy chain and light chain amino acid sequences

[0201]

[0202] Table 21. Antibody z10 variable region DNA sequence

[0203]

[0204] Table 22. Antibody z11 variable region DNA sequence

[0205]

[0206] Table 23. Antibody z13 variable region DNA sequence

[0207]

[0208] Table 24. Antibody xAb variable region DNA sequences

[0209]

[0210] Table 25. Antibody z10 heavy and light chain DNA sequences

[0211]

[0212] Table 26. Antibody z11 heavy and light chain DNA sequences

[0213]

[0214] Table 27. Antibody z13 heavy chain and light chain DNA sequences

[0215]

[0216] Table 28. Antibody xAb heavy and light chain DNA sequences

[0217]

[0218] Table 29. MERTK protein sequence

[0219]

[0220] In a specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Exemplary numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Exemplary numbering system. In another specific embodiment, provided herein is an anti-MERTK or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Kabat numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Kabat numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Chothia numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Chothia numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the AbM numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the AbM numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Contact numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Contact numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VHCDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the IMGT numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the IMGT numbering system.

[0221] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a heavy chain variable region (VH) CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using one numbering system, and FR1, FR2, and FR4 comprise the amino acid sequences of FR1, FR2, and FR4 set forth in Table 2, 3, or 4 using the same numbering system, and FR3 comprises the amino acid sequence of FR3 set forth in Table 5 using the same numbering system.

[0222] In a specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VHCDR3, and FR4, and wherein the VHCDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VHCDR3 set forth in Table 1 using the Exemplary numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Exemplary numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Kabat numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Kabat numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Chothia numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Chothia numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the AbM numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the AbM numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Contact numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the Contact numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the IMGT numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 2, 3, 4, or 5 using the IMGT numbering system.

[0223] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH), wherein the VH comprises a framework region (FR) 1, VH CDR1, FR2, VH CDR2, FR3, VH CDR3, and FR4, and wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using one numbering system, and FR1, FR2, and FR4 comprise the amino acid sequences of FR1, FR2, and FR4 set forth in Table 2, 3, or 4 using the same numbering system, and FR3 comprises the amino acid sequence of FR3 set forth in Table 5 using the same numbering system.

[0224] In a specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VLCDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Exemplary numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Exemplary numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VLCDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Kabat numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Kabat numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VLCDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Chothia numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Chothia numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the AbM numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the AbM numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Contact numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Contact numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the IMGT numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the IMGT numbering system.

[0225] In a specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a light chain variable region (VL), wherein the VL comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Exemplary numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Exemplary numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a light chain variable region (VL), wherein the VL comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Kabat numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Kabat numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a light chain variable region (VL), wherein the VL comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Chothia numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Chothia numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a light chain variable region (VL), wherein the VL comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the AbM numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the AbM numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a light chain variable region (VL), wherein the VL comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the Contact numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the Contact numbering system. In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a light chain variable region (VL), wherein the VL comprises a framework region (FR) 1, a light chain variable region (VL) CDR1, FR2, VL CDR2, FR3, VL CDR3, and FR4, and wherein the VLCDR1, VL CDR2, VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the IMGT numbering system, and FR1, FR2, FR3, and FR4 comprise the amino acid sequences of FR1, FR2, FR3, and FR4 set forth in Table 9 using the IGMT numbering system.

[0226] In a specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VL CDR1, VL FR2, VL CDR2, VL FR3, VL CDR3, and VLFR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Exemplary numbering system, wherein VH FR1, VH FR2, VH FR3, and VH FR4 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 2, 3, 4, or 5 using the Exemplary numbering system. The amino acid sequences of VL FR1, VH FR2, VH FR3 and VH FR4 are described in Table 9 using the Exemplary numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VL CDR1, VL FR2, VL CDR2, VL FR3, VL CDR3, and VL FR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Kabat numbering system, wherein VH FR1, VH FR2, VH FR3, and VH FR4 comprise the VH CDR1, VH CDR2, and VH CDR3 set forth in Table 2, 3, 4, or 5 using the Kabat numbering system. The amino acid sequences of VL FR1, VH FR2, VH FR3 and VH FR4 are described in Table 7 using the Kabat numbering system, and wherein the VL FR1, VL FR2, VL FR3 and VL FR4 comprise the amino acid sequences of VL FR1, VL FR2, VL FR3 and VL FR4 described in Table 9 using the Kabat numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VLCDR1, VL FR2, VL CDR2, VL FR3, VL CDR3, and VL FR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Chothia numbering system, wherein VHFR1, VH FR2, VH FR3, and VH FR4 comprises the amino acid sequence of VH FR1, VH FR2, VH FR3 and VH FR4 shown in Table 2, 3, 4 or 5 using the Chothia numbering system, wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequence of VL CDR1, VL CDR2 and VL CDR3 set forth in Table 7 using the Chothia numbering system, and wherein the VL FR1, VL FR2, VL FR3 and VL FR4 comprise the amino acid sequence of VL FR1, VL FR2, VL FR3 and VL FR4 set forth in Table 9 using the Chothia numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VL CDR1, VL FR2, VL CDR2, VLFR3, VLCDR3, and VL FR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the AbM numbering system, wherein VH FR1, VH FR2, VH FR3, and VH FR4 comprise the VH CDR1, VH CDR2, and VH CDR3 set forth in Table 2, 3, 4, or 5 using the AbM numbering system. The amino acid sequences of VL FR1, VH FR2, VH FR3 and VH FR4 are described in Table 7 using the AbM numbering system, and wherein the VL FR1, VL FR2, VL FR3 and VL FR4 comprise the amino acid sequences of VL FR1, VL FR2, VL FR3 and VL FR4 described in Table 9 using the AbM numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VL CDR1, VL FR2, VL CDR2, VL FR3, VL CDR3, and VL FR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the Contact numbering system, wherein VH FR1, VH FR2, VH FR3, and VH FR4 comprise the VH CDR1, VH CDR2, and VH CDR3 set forth in Table 2, 3, 4, or 5 using the Contact numbering system. The amino acid sequences of VL FR1, VH FR2, VH FR3 and VH FR4, wherein the VL CDR1, VL CDR2, VLCDR3 comprise the amino acid sequences of VL CDR1, VL CDR2 and VL CDR3 set forth in Table 7 using the Contact numbering system, and wherein the VL FR1, VL FR2, VL FR3 and VL FR4 comprise the amino acid sequences of VL FR1, VL FR2, VL FR3 and VL FR4 set forth in Table 9 using the Contact numbering system.In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VL CDR1, VLFR2, VL CDR2, VL FR3, VL CDR3, and VL FR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequences of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using the IMGT numbering system, wherein VH FR1, VHFR2, VH FR3, and VH FR4 comprise the VH CDR1, VH CDR2, and VH CDR3 set forth in Table 2, 3, 4, or 5 using the IMGT numbering system. The amino acid sequence of VL FR1, VH FR2, VHFR3 and VH FR4, wherein the VL CDR1, VL CDR2, VL CDR3 comprise the amino acid sequence of VL CDR1, VL CDR2 and VL CDR3 set forth in Table 7 using the IMGT numbering system, and wherein the VL FR1, VL FR2, VLFR3 and VL FR4 comprise the amino acid sequence of VL FR1, VL FR2, VL FR3 and VL FR4 set forth in Table 9 using the IMGT numbering system.

[0227] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises a VH framework region (FR) 1, VH CDR1, VH FR2, VH CDR2, VH FR3, VH CDR3, and VH FR4, wherein the VL comprises VL FR1, VL CDR1, VL FR2, VL CDR2, VL FR3, VL CDR3, and VLFR4, wherein the VH CDR1, VH CDR2, VH CDR3 comprise the amino acid sequence of VH CDR1, VH CDR2, and VH CDR3 set forth in Table 1 using one numbering system, wherein VH FR1, VH FR2, VH FR3, and VH FR4 comprise the amino acid sequence of VH FR1, VH CDR2, and VH CDR3 set forth in Table 2, 3, or 4 using the same numbering system. The invention further comprises the amino acid sequences of VH FR1, VL FR2, and VH FR4, wherein the VH FR3 comprises the amino acid sequence of VH FR3 set forth in Table 5, wherein the VL CDR1, VLCDR2, and VL CDR3 comprise the amino acid sequences of VL CDR1, VL CDR2, and VL CDR3 set forth in Table 7 using the same numbering system, and wherein the VL FR1, VLFR2, VL FR3, and VL FR4 comprise the amino acid sequences of VL FR1, VL FR2, VL FR3, and VL FR4 set forth in Table 9 using the same numbering system.

[0228] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 1, the VH CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 6, the VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO: 11, the VL CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 68, the VL CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 69, and the VL CDR3 comprises the amino acid sequence set forth in SEQ ID NO: 70.

[0229] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH CDR1 comprises the amino acid sequence set forth in SEQ ID NO:2, the VH CDR2 comprises the amino acid sequence set forth in SEQ ID NO:7, the VH CDR3 comprises the amino acid sequence set forth in SEQ ID NO:12, the VL CDR1 comprises the amino acid sequence set forth in SEQ ID NO:71, the VL CDR2 comprises the amino acid sequence set forth in SEQ ID NO:72, and the VL CDR3 comprises the amino acid sequence set forth in SEQ ID NO:73.

[0230] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH CDR1 comprises the amino acid sequence set forth in SEQ ID NO:3, the VH CDR2 comprises the amino acid sequence set forth in SEQ ID NO:8, the VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO:11, the VL CDR1 comprises the amino acid sequence set forth in SEQ ID NO:68, the VL CDR2 comprises the amino acid sequence set forth in SEQ ID NO:69, and the VL CDR3 comprises the amino acid sequence set forth in SEQ ID NO:70.

[0231] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH CDR1 comprises the amino acid sequence set forth in SEQ ID NO:4, the VH CDR2 comprises the amino acid sequence set forth in SEQ ID NO:9, the VH CDR3 comprises the amino acid sequence set forth in SEQ ID NO:13, the VL CDR1 comprises the amino acid sequence set forth in SEQ ID NO:74, the VL CDR2 comprises the amino acid sequence set forth in SEQ ID NO:75, and the VL CDR3 comprises the amino acid sequence set forth in SEQ ID NO:76.

[0232] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH CDR1 comprises the amino acid sequence set forth in SEQ ID NO:5, the VH CDR2 comprises the amino acid sequence set forth in SEQ ID NO:10, the VH CDR3 comprises the amino acid sequence set forth in SEQ ID NO:14, the VL CDR1 comprises the amino acid sequence set forth in SEQ ID NO:77, the VL CDR2 comprises the amino acid sequence set forth in SEQ ID NO:72, and the VL CDR3 comprises the amino acid sequence set forth in SEQ ID NO:70.

[0233] In another specific embodiment, provided herein is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH CDR1 comprises the amino acid sequence set forth in SEQ ID NO:3, the VH CDR2 comprises the amino acid sequence set forth in SEQ ID NO:6, the VHCDR3 comprises the amino acid sequence set forth in SEQ ID NO:11, the VL CDR1 comprises the amino acid sequence set forth in SEQ ID NO:68, the VL CDR2 comprises the amino acid sequence set forth in SEQ ID NO:69, and the VL CDR3 comprises the amino acid sequence set forth in SEQ ID NO:70.

[0234] In a specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 105. In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 107. In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO: 108. In another specific embodiment, a humanized anti-MERTK or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence shown in SEQ ID NO:109.

[0235] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a heavy chain variable region (VH) comprising the amino acid sequence set forth in SEQ ID NO:110.

[0236] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a light chain variable region (VL) comprising the amino acid sequence set forth in SEQ ID NO: 111.

[0237] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 105 and the VL comprises the amino acid sequence set forth in SEQ ID NO: 106. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 107 and the VL comprises the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 108 and the VL comprises the amino acid sequence set forth in SEQ ID NO: 106. In another embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence shown in SEQ ID NO: 110 and the VL comprises the amino acid sequence shown in SEQ ID NO: 111.

[0238] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence shown in SEQ ID NO: 109 and the VL comprises the amino acid sequence shown in SEQ ID NO: 106 or 111.

[0239] In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of VH set forth in Table 11 and the VL comprises the amino acid sequence of VL set forth in Table 11. In another specific embodiment, a humanized anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of VH set forth in Table 12 and the VL comprises the amino acid sequence of VL set forth in Table 12. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of VH set forth in Table 13 and the VL comprises the amino acid sequence of VL set forth in Table 13. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the VH set forth in Table 14 and the VL comprises the amino acid sequence of the VL set forth in Tables 11, 12, or 13.

[0240] In certain aspects, the antibodies described herein can be described by their VH domain alone or their VL domain alone. See, e.g., Rader C et al., (1998) PNAS 95:8910-8915, which is incorporated herein by reference in its entirety, which describes the humanization of mouse anti-αvβ3 antibodies by identifying complementary light chains or heavy chains from human light chain or heavy chain libraries, respectively, resulting in the production of humanized antibody variants with affinity as high or higher than that of the original antibody. See also, Clackson T et al., (1991) Nature 352:624-628, which is incorporated herein by reference in its entirety, which describes a method for producing antibodies that bind to a specific antigen by using a specific VH domain (or VL domain) and screening a library for complementary variable domains. See also, Kim SJ & Hong HJ, (2007) J Microbiol 45:572-577, which is incorporated herein by reference in its entirety, which describes a method for producing antibodies that bind to a specific antigen by using a specific VH domain and screening a library (e.g., a human VL library) for a complementary VL domain; the selected VL domain can in turn be used to guide the selection of other complementary (e.g., human) VH domains.

[0241] As used herein, the terms "immunospecific binding", "immunospecific recognition", "specific binding" and "specific recognition" are similar terms in the context of antibodies and refer to antibodies and antigen-binding fragments thereof that bind to an antigen (e.g., an epitope or an immune complex) through an antigen binding site as understood by those skilled in the art and do not exclude cross-reactivity of the antibody or antigen-binding fragment with other antigens. Any method known in the art can be used to determine whether immunospecific binding to MERTK (e.g., human MERTK) is maintained.

[0242] In a specific aspect, provided herein are anti-MERTK antibodies or antigen-binding fragments thereof comprising antibody heavy chains and / or light chains, e.g., heavy chains alone, light chains alone, or both heavy and light chains. With respect to light chains, in specific embodiments, the light chains of the anti-MERTK antibodies or antigen-binding fragments thereof described herein are kappa light chains. In another specific embodiment, the light chains of the anti-MERTK antibodies or antigen-binding fragments thereof described herein are lambda light chains. In another specific embodiment, the light chains of the anti-MERTK antibodies or antigen-binding fragments thereof described herein are human kappa light chains or human lambda light chains.

[0243] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a light chain, wherein the light chain comprises a light chain variable region (VL) and a kappa light chain constant region amino acid sequence, wherein the VL comprises the amino acid sequence shown in SEQ ID NO: 106 or SEQ ID NO: 111. As used herein, the terms "constant region" or "constant domain" are interchangeable and have their common meanings in the art. The constant region is an antibody portion that is not directly involved in the binding of the antibody to the antigen, but can exhibit a variety of effector functions, such as interaction with an Fc receptor, for example, the carboxyl terminal portion of the light chain and / or heavy chain. The constant region of an immunoglobulin molecule generally has a more conserved amino acid sequence relative to the immunoglobulin variable domain.

[0244] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a light chain, wherein the light chain comprises a light chain variable region (VL) and a human kappa or lambda light chain constant region, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106 or SEQ ID NO: 111. Non-limiting examples of human constant region sequences have been described in the art, e.g., see Kabat EA et al., (1991).

[0245] In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK) comprises a light chain, wherein the light chain comprises the amino acid sequence shown in SEQ ID NO:113 or SEQ ID NO:118.

[0246] With respect to the heavy chain, in specific embodiments, the heavy chain of the anti-MERTK antibody or antigen-binding fragment thereof described herein can be a human α, δ, ε, γ or μ heavy chain. In specific embodiments, the anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain, wherein the heavy chain comprises a constant region or a portion thereof described herein or known in the art (e.g., C H 1. C H 2 or C H 3 or a combination thereof) and a heavy chain variable region (VH) of an anti-MERTK antibody described herein (e.g., SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 108, 109, or SEQ ID NO: 110).

[0247] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain, wherein the heavy chain comprises a heavy chain variable region (VH) of an anti-MERTK antibody described herein (e.g., SEQ ID NO: 105, 107, 108, 109, or 110) and a constant region of a human gamma heavy chain constant region variable region or a portion thereof (e.g., C H 1. C H 2 or C H 3 or a combination thereof). In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequence set forth in SEQ ID NO: 112, SEQ ID NO: 114, SEQ ID NO: 115, SEQ ID NO: 116, or SEQ ID NO: 117. Non-limiting examples of human constant region sequences have been described in the art, e.g., see Kabat EA et al., (1991) supra.

[0248] In a specific embodiment, the anti-MERTK antibody described herein that specifically binds to MERTK (e.g., human MERTK) comprises (i) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 and (ii) a light chain comprising the amino acids set forth in SEQ ID NO: 113. In a specific embodiment, the anti-MERTK antibody described herein that specifically binds to MERTK (e.g., human MERTK) comprises (i) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 114 and (ii) a light chain comprising the amino acids set forth in SEQ ID NO: 113. In a specific embodiment, the anti-MERTK antibody described herein that specifically binds to MERTK (e.g., human MERTK) comprises (i) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 115 and (ii) a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113. In a specific embodiment, the anti-MERTK antibody described herein that specifically binds to MERTK (e.g., human MERTK) comprises (i) a heavy chain comprising the amino acid sequence shown in SEQ ID NO: 116 and (ii) a light chain comprising the amino acids shown in SEQ ID NO: 113. In a specific embodiment, the anti-MERTK antibody described herein that specifically binds to MERTK (e.g., human MERTK) comprises (i) a heavy chain comprising the amino acid sequence shown in SEQ ID NO: 117 and (ii) a light chain comprising the amino acids shown in SEQ ID NO: 118.

[0249] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that immunospecifically binds to MERTK (e.g., human MERTK) as described herein comprises a heavy chain variable region (VH) and a light chain variable region (VL) comprising any amino acid sequence described herein, and wherein the constant region comprises the amino acid sequence of a constant region of a human IgG, IgE, IgM, IgD, IgA, or IgY immunoglobulin molecule. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that immunospecifically binds to MERTK (e.g., human MERTK) as described herein comprises a VH and a VL comprising any amino acid sequence described herein, and wherein the constant region comprises a human IgG, IgE, IgM, IgD, IgA, or IgY immunoglobulin molecule, any class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1, and IgA2) or any subclass (e.g., IgG 2a and IgG 2b ) (e.g., those described in Tables 11, 12, 13 or 15).

[0250] In certain embodiments, 1, 2 or more mutations (eg, amino acid substitutions) are introduced into the Fc region of an anti-MERTK antibody or antigen-binding fragment thereof described herein to alter one or more functionalities of the antibody.

[0251] In some embodiments, 1, 2 or more mutations (e.g., amino acid substitutions) are introduced into the Fc region (e.g., C H 2 domain (residues 231-340 of human IgG1) and / or C H The 3 domains (residues 341-447 of human IgG1) and / or hinge regions, wherein the numbering is according to the Kabat numbering system (e.g., the EU index in Kabat)) to increase or decrease the affinity of the antibody or its antigen-binding fragment for an Fc receptor on the surface of an effector cell (e.g., an activated Fc receptor). Mutations in the Fc region of an anti-MERTK antibody or its antigen-binding fragment that decrease or increase the affinity of the antibody for an Fc receptor and techniques for introducing these mutations into the Fc receptor or its fragment are known to those skilled in the art. Examples of mutations in the Fc receptor of an anti-MERTK antibody or antigen-binding fragment thereof that can be prepared to alter the affinity of the antibody or antigen-binding fragment thereof for the Fc receptor are described in, e.g., Smith P et al., (2012) PNAS 109:6181-6186, U.S. Pat. No. 6,737,056, and International Patent Publication Nos. WO 02 / 060919; WO 98 / 23289; and WO 97 / 34631, which are incorporated herein by reference.

[0252] In some embodiments, the antibodies or antigen-binding fragments thereof described herein comprise a glycosylated constant region. In some embodiments, the antibodies or antigen-binding fragments thereof described herein comprise a non-glycosylated constant region. It has been reported that antibodies with reduced fucose content have increased affinity for Fc receptors, such as (for example) FcγRIIIa. Therefore, in certain embodiments, the antibodies or antigen-binding fragments thereof described herein have reduced fucose content or no fucose content. These antibodies or antigen-binding fragments thereof can be produced using techniques known to those skilled in the art. For example, the antibodies or antigen-binding fragments thereof can be expressed in cells with defective or lacking fucosylation ability. In a specific example, a cell line in which two alleles of α1,6-fucosyltransferase are knocked out can be used to produce antibodies with reduced fucose content. The Lonza system is an example of such a system that can be used to produce antibodies or antigen-binding fragments thereof with reduced fucose content. Alternatively, antibodies or antigen-binding fragments with reduced fucose content or without fucose content can be produced by, for example, (i) culturing cells under conditions that prevent or reduce fucosylation; (ii) removing fucose post-translationally (e.g., using a fucosidase); (iii) adding the desired carbohydrate post-translationally, for example, after recombinant expression of a non-glycosylated glycoprotein; or (iv) purifying the glycoprotein to select for antibodies or antigen-binding fragments thereof that are not fucosylated. For methods of producing antibodies or antigen-binding fragments thereof with no or reduced fucose content, see, for example, Longmore GD & Schachter H (1982) Carbohydr Res 100: 365-92 and Imai-Nishiya H et al., (2007) BMC Biotechnol. 7: 84.

[0253] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain or a light chain, wherein (i) the heavy chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 108 or SEQ ID NO: 109, and (b) a heavy chain constant domain comprising the amino acid sequence of the constant domain of human IgG; or (ii) the light chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 106, and (b) a light chain constant domain comprising the amino acid sequence of the constant domain of a human light chain.

[0254] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain and a light chain, wherein (i) the heavy chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 108 or SEQ ID NO: 109, and (b) a heavy chain constant domain comprising the amino acid sequence of the constant domain of human IgG; and (ii) the light chain comprises a variable region comprising the amino acid sequence shown in SEQ ID NO: 106, and (b) a light chain constant domain comprising the amino acid sequence of the constant domain of a human kappa light chain.

[0255] In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain or a light chain, wherein (i) the heavy chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 110, and (b) a heavy chain constant domain comprising the amino acid sequence of the constant domain of human IgG; or (ii) the heavy chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 111, and (b) a light chain constant domain comprising the amino acid sequence of the constant domain of a human κ light chain. In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain and a light chain, wherein (i) the heavy chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 110, and (b) a heavy chain constant domain comprising the amino acid sequence of the constant domain of human IgG; and (ii) the light chain comprises (a) a variable region comprising the amino acid sequence shown in SEQ ID NO: 111, and (b) a light chain constant domain comprising the amino acid sequence of the constant domain of a human kappa light chain.

[0256] The determination of percent identity between two sequences (e.g., amino acid sequences or nucleic acid sequences) can also be accomplished using a mathematical algorithm. A specific, non-limiting example of a mathematical algorithm for the comparison of two sequences is the algorithm described by Karlin S & Altschul SF (1990) PNAS 87: 2264-2268, modified by Karlin S & Altschul SF (1993) PNAS 90: 5873-5877. This algorithm was incorporated into the NBLAST and XBLAST programs of Altschul SF et al., (1990) J Mol Biol 215: 403. BLAST nucleotide searches can be performed with the NBLAST nucleotide program parameters set to, for example, score = 100, wordlength = 12 to obtain nucleotide sequences identical to the nucleic acid molecules described herein. BLAST protein searches can be performed with the XBLAST program parameters set to, for example, score 50, wordlength = 3 to obtain protein sequences identical to the protein molecules described herein. To obtain gapped alignments for comparison purposes, Gapped BLAST can be used as described in Altschul SF et al., (1997) Nuc Acids Res 25:3389-3402. Alternatively, PSI BLAST can be used to perform an iterated search that detects more distant relationships between molecules (supra). When using BLAST, Gapped BLAST, and PSI Blast programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used (see, e.g., the National Center for Biotechnology Information (NCBI) on the World Wide Web at ncbi.nlm.nih.gov). Another specific, non-limiting example of a mathematical algorithm used for sequence comparison is the algorithm of Myers and Miller, 1988, CABIOS 4:11-17. This algorithm is incorporated into the ALIGN program (version 2.0) that is part of the GCG sequence alignment software package. When using the ALIGN program to compare amino acid sequences, a PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used.

[0257] The percent identity between two sequences can be determined using techniques similar to those described above, with or without allowing gaps. In calculating percent identity, typically only complete matches are counted.

[0258] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises a VH having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of the VH set forth in SEQ ID NO: 105, SEQ ID NO: 107, or SEQ ID NO: 108, or SEQ ID NO: 109. In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof comprises a VH having at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of the VH set forth in SEQ ID NO: 110.

[0259] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that immunospecifically binds to MERTK (e.g., human MERTK) comprises a VL having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of VL set forth in SEQ ID NO: 106. In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof comprises a VL having at least 99% sequence identity to VH set forth in SEQ ID NO: 111.

[0260] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises: (i) a VH domain having at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98% or at least 99% sequence identity to the amino acid sequence of the VH domain set forth in SEQ ID NO: 105, SEQ ID NO: 107, or SEQ ID NO: 108 or SEQ ID NO: 109; and (ii) a VL domain having at least 80%, at least 85%, at least 90%, at least 95% or at least 98% sequence identity to the amino acid sequence of the VL domain set forth in SEQ ID NO: 106.

[0261] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) comprises (i) a VH domain having at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the VH domain set forth in SEQ ID NO: 110, and (ii) a VL domain having at least 99% sequence identity to the VL domain set forth in SEQ ID NO: 111.

[0262] In another aspect, as antibodies described herein, antibodies that bind the same or overlapping epitopes of MERTK (e.g., human MERTK) are provided herein. As used herein, "epitope" is a term in the art and refers to a local region of an antigen to which an antibody can specifically bind. An epitope can be, for example, the adjacent amino acids (straight or adjacent epitopes) of a polypeptide, or an epitope can be, for example, from two or more non-adjacent regions (conformation, non-straight, discontinuous or non-adjacent epitopes) of a polypeptide together. In some embodiments, the epitope of an antibody can be determined by, for example, NMR spectroscopy, X-ray diffraction crystal research, ELISA assay, hydrogen / deuterium exchange coupling mass spectrometry (e.g., MALDI mass spectrometry), array-based oligopeptide scanning assays and / or mutation localization (e.g., site-directed mutation localization). For X-ray crystallography, crystallization can be achieved using any method known in the art (e.g., Giege R et al., (1994) Acta Crystallogr D Biol Crystallogr 50(Pt 4):339-350; McPherson A (1990) Eur J Biochem 189:1-23; Chayen NE (1997) Structure 5:1269-1274; McPherson A (1976) J Biol Chem 251:6300-6303). Antibody: antigen crystals can be studied using well-known X-ray diffraction techniques and can be refined using computer software such as X-PLOR (Yale University, 1992, distributed by Molecular Simulations, Inc.; see, e.g., Meth Enzymol (1985) Vol. 114 & 115, edited by Wyckoff HW et al.; U.S. Patent Application No. 2004 / 0014194) and BUSTER (Bricogne G (1993) Acta Crystallogr D Biol Crystallogr 49 (Pt 1): 37-60; Bricogne G (1997) Meth Enzymol 276A: 361-423, edited by Carter CW; Roversi P et al., (2000) Acta Crystallogr D Biol Crystallogr 56 (Pt 10): 1316-1323). Mutation mapping studies can be performed using any method known to those skilled in the art. For a description of mutagenesis techniques, including alanine scanning mutagenesis techniques, see, for example, Champe M et al., (1995) and Cunningham BC & Wells JA (1989).In addition, antibodies that recognize and bind to the same or overlapping epitopes of MERTK (e.g., human MERTK) can be identified using conventional techniques, such as immunoassays, for example, by showing the ability of one antibody to block the binding of another antibody to a target antigen, i.e., competitive binding assays. Competitive binding assays can also be used to determine whether two antibodies have similar binding specificities for an epitope. Competitive binding can be determined in an assay in which a tested immunoglobulin inhibits specific binding of a reference antibody to a common antigen, such as MERTK. Various types of competitive binding assays are known, for example: solid phase direct or indirect radioimmunoassay (RIA), solid phase direct or indirect enzyme immunoassay (EIA), sandwich competition assay (see Stahli C et al., (1983) Methods Enzymol 9:242-253); solid phase direct biotin-avidin EIA (see Kirkland TN et al., (1986) J Immunol 137:3614-9); solid phase direct labeling assay, solid phase direct labeling sandwich assay (see Harlow E & Lane D, (1988) Antibodies: A Laboratory Manual, Cold Spring Harbor Press); solid phase direct labeling RIA using I-125 labeling (see Morel GA et al., (1988) Mol Immunol 25(1):7-15); solid phase direct biotin-avidin EIA (Cheung RC et al., (1990) Virology 176:546-52); and direct label RIA (Moldenhauer G et al., (1990) Scand J Immunol 32:77-82). Typically, such assays involve the use of a purified antigen (e.g., MERTK (e.g., human MERTK)) bound to a solid surface or cell with any of these unlabeled test immunoglobulins and labeled reference immunoglobulins. Competitive inhibition can be measured by determining the amount of label bound to the solid surface or cell in the presence of the test immunoglobulin. Typically, the test immunoglobulin is present in excess. Typically, when the competing antibody is present in excess, it inhibits specific binding of the reference antibody to the common antigen by at least 50-55%, 55-60%, 60-65%, 65-70%, 70-75% or more. The competitive binding assay can be configured in a variety of different formats using either the labeled antigen or the labeled antibody. In a common format of such an assay, the antigen is immobilized on a 96-well plate. The ability of the unlabeled antibody to block the binding of the labeled antibody to the antigen is then measured using either a radioactive or enzymatic label.For additional details, see, e.g., Wagener C et al., (1983) J Immunol 130:2308-2315; Wagener C et al., (1984) J Immunol Methods 68:269-274; Kuroki M et al., (1990) Cancer Res 50:4872-4879; Kuroki M et al., (1992) Immunol Invest 21:523-538; Kuroki M et al., (1992) Hybridoma 11:391-407 and Antibodies: A Laboratory Manual, Harlow E & Lane D, eds., supra, pp. 386-389.

[0263] In certain aspects, competitive binding assays can be used to determine whether another antibody competitively blocks an antibody in, for example, a dose-dependent manner, e.g., when the two antibodies recognize the same or spatially overlapping epitopes in a competitive binding assay that can be configured in some different formats using either a labeled antigen or a labeled antibody, such as a competition ELISA assay, an antibody binds to substantially the same epitope or an overlapping epitope as a reference antibody. In specific embodiments, an antibody can be tested in a competitive binding assay using an antibody described herein (e.g., antibody z10, z11, or z13).

[0264] In another aspect, provided herein are antibodies that compete (e.g., in a dose-dependent manner) with an anti-MERTK antibody described herein (e.g., z10, z11, z13, or xAb) for binding to MERTK (e.g., human MERTK) as determined using an assay known to those of skill in the art or as described herein (e.g., an ELISA competitive assay or surface plasmon resonance). In another aspect, provided herein are antibodies that competitively inhibit (e.g., in a dose-dependent manner) the binding of an anti-MERTK antibody described herein (e.g., z10, z11, z13, or xAb) to MERTK (e.g., human MERTK) as determined using an assay known to those of skill in the art or as described herein (e.g., an ELISA competitive assay or suspension array or surface plasmon resonance).

[0265] In certain embodiments, provided herein are anti-MERTK antibodies that compete with an antibody described herein for binding to MERTK (e.g., human MERTK) to the same extent that an antibody described herein self-competes for binding to MERTK (e.g., human MERTK). In certain embodiments, provided herein are first antibodies that compete with an anti-MERTK antibody described herein for binding to MERTK (e.g., human MERTK), wherein competition is shown as a greater than 80% reduction in binding of the first antibody to MERTK (e.g., human MERTK) (e.g., 85%, 90%, 95%, or 98% or between 80% and 85%, 80% and 90%, 85% and 90%, or between 85% and 95%).

[0266] In specific aspects, provided herein are anti-MERTK antibodies that compete (e.g., in a dose-dependent manner) for specific binding to MERTK (e.g., human MERTK) with an antibody comprising a VH domain comprising the amino acid sequence set forth in SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 108, SEQ ID NO: 109, or SEQ ID NO: 110 and a VL domain comprising the amino acid sequence set forth in SEQ ID NO: 106 or SEQ ID NO: 111.

[0267] In a specific embodiment, an anti-MERTK antibody (e.g., a humanized antibody or a human antibody) or an antigen-binding fragment thereof specifically binds to the same or overlapping epitope of an antibody comprising a VH domain having an amino acid sequence as set forth in SEQ ID NO: 105 and a VL domain having an amino acid sequence as set forth in SEQ ID NO: 106. In another specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof described herein immunospecifically binds to the same or overlapping epitope of an antibody comprising a VH domain having an amino acid sequence as set forth in SEQ ID NO: 107 and a VL domain having an amino acid sequence as set forth in SEQ ID NO: 106. In another specific embodiment, an anti-MERTK antibody or an antigen-binding fragment thereof described herein immunospecifically binds to the same or overlapping epitope of an antibody comprising a VH domain having an amino acid sequence as set forth in SEQ ID NO: 108 and a VL domain having an amino acid sequence as set forth in SEQ ID NO: 106. In another specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein immunospecifically binds to the same or overlapping epitope of an antibody comprising a VH domain having an amino acid sequence as shown in SEQ ID NO: 110 and a VL domain having an amino acid sequence as shown in SEQ ID NO: 111. Assays known to those of skill in the art or described herein (e.g., X-ray crystallography, ELISA assays, etc.) can be used to determine whether two antibodies bind to the same epitope. In a specific embodiment, the antibody or antigen-binding fragment thereof that competes with the antibody described herein for binding to MERTK (e.g., human MERTK) is not a mouse antibody. In a specific embodiment, the antibody or antigen-binding fragment thereof that binds to the same or overlapping epitope of an antibody described herein (e.g., human MERTK) is not a mouse antibody.

[0268] Affinity can be measured and / or expressed in a number of ways known in the art, including but not limited to the equilibrium dissociation constant (K D ) and equilibrium binding constant (K A ). K can be determined by techniques known to those skilled in the art. D , such as biofilm interferometry or surface plasmon resonance.

[0269] In certain embodiments, an anti-MERTK antibody (e.g., a humanized antibody) or antigen-binding fragment thereof described herein that competes with an antibody described herein for binding to MERTK (e.g., human MERTK) or an anti-MERTK antibody or antigen-binding fragment thereof that binds to the same or overlapping epitope of an anti-MERTK antibody described herein has a K of about 8 nM, 7 nM, 6 nM, 5 nM, 4.5 nM, 4 nM, 3.5 nM, 3 nM, 2.5 nM, 2 nM, 1.5 nM, 1 nM, 0.75 nM, 0.5 nM, 0.25 nM, or 0.1 nM. D Binding to MERTK (e.g., human MERTK). In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein that competes with an antibody described herein for binding to MERTK (e.g., human MERTK) or an anti-MERTK antibody or antigen-binding fragment thereof that binds to the same or overlapping epitope of an antibody described herein has a K of 0.1 nM to 10 nM, 0.5 nM to 10 nM, 1 nM to 10 nM, 2 nM to 10 nM, 2 nM, 5 nM, 4 nM to 10 nM in an assay as described herein or known to one of skill in the art. D Binds to MERTK (e.g., human MERTK). In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein that competes with an antibody described herein for binding to MERTK (e.g., human MERTK) or an anti-MERTK antibody or antigen-binding fragment thereof that binds to the same or overlapping epitope of an antibody described herein has a K of about 2 pM to 8 pM using an assay described herein or known to one of skill in the art. D Avidity binds to MERTK (eg, human MERTK).

[0270] In a specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein have a K of about 3 nM in an assay described herein or known to one of skill in the art. D Binds to MERTK (e.g., human MERTK). In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein binds to MERTK (e.g., human MERTK) with a K of about 1 pM to 15 pM in an assay described herein or known in the art. D In another specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein bind to MERTK (e.g., human MERTK) with a K of about 1.46 nM in an assay described herein or known to one of skill in the art. DIn another specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein bind to MERTK (e.g., human MERTK) with a K of about 5.74 pM in an assay described herein or known to one of skill in the art. D In another specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein bind to MERTK (e.g., human MERTK) with a K of about 3.68 pM in an assay described herein or known to one of skill in the art. D In another specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein bind to MERTK (e.g., human MERTK) with a K of about 2.99 pM in an assay described herein or known to one of skill in the art. D Avidity binds to MERTK (eg, human MERTK). As used herein, the term "about" when used to modify a numerical value or numerical range means that deviations of 5% to 10% above and 5% to 10% below the stated value or range are still within the intended meaning of the recited value or range.

[0271] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof binds to MERTK (e.g., human MERTK) with an EC50 of 1 nM to 20 nM as assessed by an assay described herein or known in the art. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof binds to MERTK (e.g., human MERTK) with an EC50 of 1 nM to 10 nM as assessed by an assay described herein or known in the art. In another specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof binds to MERTK (e.g., human MERTK) with an EC50 of about 1 nM, about 2 nM, about 3 nM, about 4 nM, about 5 nM, about 6 nM, about 7 nM, about 8 nM, about 9 nM, or about 10 nM as assessed by an assay described herein or known in the art.

[0272] In a specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof is an antibody described in Section 6, below.

[0273] 5.1.2. Functional characteristics

[0274] In some aspects, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) reduces the expression level of human MERTK on cancer cells (e.g., SKMEL5 melanoma cells) by more than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% as assessed by an assay known to one of skill in the art or described herein. In some aspects, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to human MERTK described herein reduces the expression level of human MERTK on human M2 macrophages by more than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, as assessed by an assay known to those of skill in the art or described herein. In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof binds to MERTK (e.g., human MERTK, but not human Axl, human Tyro3 or mouse MERTK), as assessed by methods described herein or known in the art.

[0275] In some embodiments, the anti-MERTK antibody or antigen-binding fragment thereof binds to human MERTK and cynomolgus monkey MERTK.

[0276] In some aspects, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) induces a cytokine secretion response by M2 macrophages, CD14+ monocytes, or both, such as Fig.10 In some respects, such as Fig.10 As shown, the anti-MERTK antibody or antigen-binding fragment thereof changes the expression of certain cytokines by M2 macrophages, CD14+ monocytes, or both (e.g., the antibody or antigen-binding fragment thereof increases the expression of certain cytokines) by more than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, as assessed by an assay known to those of skill in the art or described herein.

[0277] In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) blocks (e.g., partially or completely) the level of MERTK phosphorylation induced by Gas-6 in cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells), M2 macrophages, or both, in an assay known to those of skill in the art. In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) reduces the level of human MERTK phosphorylation induced by Gas-6 in cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells), M2 macrophages, or both, by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% in an assay known to those of skill in the art.

[0278] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) causes degradation of human MERTK on cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells), M2 macrophages, or both. In specific embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) reduces the level of human MERTK on the surface of cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells), M2 macrophages, or both, by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% in an assay described herein or known to one of skill in the art.

[0279] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) causes internalization of human MERTK on cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells), M2 macrophages, or both. In specific embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) increases internalization of human MERTK by cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells), M2 macrophages, or both, by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85% in an assay described herein or known to one of skill in the art.

[0280] In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) (e.g., partially or completely) inhibits colony formation by cancer cells (e.g., melanoma cells) in an assay described herein or known to one of skill in the art. In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) reduces the level of colony formation by cancer cells (e.g., melanoma cells) by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% in an assay described herein or known to one of skill in the art. In some aspects, an anti-MERTK antibody or antigen-binding fragment thereof described herein that immunospecifically binds to MERTK (e.g., human MERTK) reduces the colony forming ability of cancer cells (e.g., SKMEL5 melanoma cells) by more than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% as assessed by an assay known to one of skill in the art or described herein.

[0281] In some aspects, in an assay described herein or known in the art, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) prevents Gas6-induced AKT phosphorylation. In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) competes with Gas-6 (e.g., human Gas-6) for binding to human MERTK. In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein inhibits (e.g., completely inhibits or only partially inhibits) the binding of Gas-6 to human MERTK. In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) inhibits the binding of Gas-6 (e.g., human or mouse Gas-6) to human MERTK by more than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%, as assessed by an assay known to one of skill in the art or described herein. In a specific embodiment, the assay for assessing the inhibition of binding of Gas-6 (e.g., human Gas-6) to human MERTK in the presence of an anti-MERTK antibody or antigen-binding fragment thereof described herein is an antibody capture ELISA known to one of skill in the art, such as described in International Patent Publication No. WO2016 / 106221 (e.g., Example 1 of International Patent Publication No. WO2016 / 106221).

[0282] In some embodiments, an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) reduces the level of AKT phosphorylation induced by Gas-6 in cancer cells (e.g., melanoma cells) expressing human MERTK by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% in an assay described herein or known to one of skill in the art.

[0283] In a specific embodiment, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) inhibits angiogenesis in a tumor. In some embodiments, the inhibition of angiogenesis is at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%. In a specific embodiment, the inhibition of angiogenesis is at least 50%, 55%, 60%, 65% or 70%. The inhibition of angiogenesis can be evaluated by methods described herein and / or known to those skilled in the art. The inhibition can be relative to the level of angiogenesis without any antibody or using an irrelevant antibody (e.g., an antibody that does not immunospecifically bind to MERTK).

[0284] In certain embodiments, an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (e.g., human MERTK) inhibits tumor development. The inhibition of tumor development is at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%. Tumor development can be evaluated by methods known to those skilled in the art. The tumor development can be relative to the cancer state without any antibody or using an irrelevant antibody (e.g., an antibody that does not specifically bind to human MERTK). In a specific embodiment, the anti-MERTK antibody or antigen-binding region thereof has 1, 2, 3 or more of the antibody characteristics described in Section 6 below.

[0285] 5.1.3. Dual-specific antibodies

[0286] In a specific aspect, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to human MERTK and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) is an anti-MERTK antibody or antigen-binding fragment thereof described herein. In a specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the heavy chain variable region of an anti-MERTK antibody or antigen-binding fragment thereof described herein. In another specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the heavy chain variable region amino acid sequence of antibody z10 described in Table 11. In another specific embodiment, provided herein are dual-specific antibodies comprising two different binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the heavy chain variable region amino acid sequence of antibody z11 described in Table 12. In another specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the heavy chain variable region amino acid sequence of antibody z13 described in Table 13. In another specific embodiment, provided herein are dual-specific antibodies comprising two different binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises a heavy chain variable region comprising the amino acid sequence described in Table 14.

[0287] In another specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the light chain variable region of an anti-MERTK antibody or antigen-binding fragment thereof described herein. In another specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequence of the light chain variable region of antibody z10 described in Table 11. In another specific embodiment, provided herein is a bispecific antibody comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequence of the light chain variable region of antibody z11 described in Table 12. In another specific embodiment, provided herein is a bispecific antibody comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequence of the light chain variable region of antibody z13 described in Table 13. In another specific embodiment, provided herein is a bispecific antibody comprising two different binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises a light chain variable region, wherein the light chain variable region comprises the amino acid sequence of VL described in Table 11, 12 or 13.

[0288] In another specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the light chain variable region and the heavy chain variable region of the anti-MERTK antibody or antigen-binding fragment thereof described herein. In another specific embodiment, provided herein are dual-specific antibodies comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequences of the light chain variable region and the heavy chain variable region of the antibody z10 described in Table 11. In another specific embodiment, provided herein is a dual-specific antibody comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequences of the light chain variable region and the heavy chain variable region of antibody z11 described in Table 12. In another specific embodiment, provided herein is a dual-specific antibody comprising two different antigen-binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises the amino acid sequences of the light chain variable region and the heavy chain variable region of antibody z13 described in Table 13. In another specific embodiment, provided herein is a dual-specific antibody comprising two different antigen binding regions, wherein one of the binding regions specifically binds to MERTK (e.g., human MERTK) and the other binding region binds to another target antigen, and wherein the binding region that specifically binds to MERTK (e.g., human MERTK) comprises a light chain variable region and a heavy chain variable region, wherein the heavy chain variable region comprises the amino acid sequence described in Table 14 and the light chain variable region comprises the VL amino acid sequence described in Table 11, 12 or 13.

[0289] In certain embodiments, the target antigen bound by another binding region of the bispecific antibody described herein is an antigen presented on an immune cell (e.g., a T cell, a NK cell, or a dendritic cell). In some embodiments, the target antigen bound by another binding region of the bispecific antibody described herein is an immune checkpoint receptor (e.g., PD-1, PD-L1, CTLA-4, LAG3, Tim3, ICOS, CD40, GITR, or OX40). In a specific embodiment, another binding region of the bispecific antibody described herein comprises an agonist anti-GITR antibody, an agonist anti-OX40 antibody, or an agonist anti-CD40 antibody. In a specific embodiment, another binding region of the bispecific antibody comprises a blocking antibody or an antigen-binding fragment thereof that binds to PD-1, PD-L1, CTLA-4, or LAG3. In certain embodiments, the target antigen bound by another binding region of the bispecific antibody described herein is a T cell receptor. In a specific embodiment, the target antigen bound by another binding region of the bispecific antibody described herein is CD3, PD-L1, LRP1, LRP8, TGF-β, NKGD2, or TIGIT. In some embodiments, the target antigen is a tumor-associated antigen.

[0290] In a specific embodiment, another binding region of the bispecific antibodies described herein is nivolumab or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is lanlozumab or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is MEDI-4736 or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is plimumab or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is MPDL-3280A or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is pidilizumab or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is avelumab or an antigen-binding fragment thereof. In another specific embodiment, another binding region of the bispecific antibodies described herein is pembrolizumab or an antigen-binding fragment thereof.

[0291] 5.2. Antibody-drug conjugates

[0292] Provided herein are antibody-drug conjugates comprising: (a) an antibody portion that is an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein; (b) one or more drug portions, each of which is a cytotoxic agent; and (c) optionally a linker; wherein the cytotoxic agent is conjugated directly to the antibody portion or to the antibody portion through the linker. The term "conjugated" as used in the disclosure of the present invention shall mean covalent binding, which may be direct or through an intermediate covalent binding structure. The antibody portion of the antibody-drug conjugates provided herein may be an antibody as described in Section 5.1 or 6. The antibody-drug conjugate may be an antibody-drug conjugate as described in Section 6.

[0293] In certain embodiments, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is between 1:1 and 1:20. In a specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is between 1:1 and 1:15. In a specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is between 1:1 and 1:12. In a specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is between 1:1 and 1:8. In a preferred embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is between 1:3 and 1:5. In a specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is 1:3. In another specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is 1:4. In another specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugates provided herein is 1:5. In another specific embodiment, the molar ratio of the antibody portion to the drug portion of the antibody-drug conjugate provided herein is 1:9.

[0294] The drug moiety is conjugated to one or more chains of the antibody portion. In some embodiments, the drug moiety is conjugated to one chain of the antibody portion (e.g., when the antibody portion is a scFv or when the antibody portion is a multi-chain antibody, such as an immunoglobulin or an antigen-binding fragment thereof (as a tetramer). In other embodiments, the drug moiety is conjugated to two or more chains of the antibody portion (when the antibody portion is a multi-chain antibody, such as an immunoglobulin or an antigen-binding fragment thereof). In a specific embodiment, the drug moiety is conjugated to two identical chains of an immunoglobulin, for example, a heavy chain or a light chain. In other embodiments, the drug moiety is conjugated to all chains of the antibody portion (when the antibody portion is a multi-chain antibody, such as an immunoglobulin or an antigen-binding fragment thereof). In some embodiments, the drug moiety is conjugated to the antibody by the method described in Section 6.4 below.

[0295] In a specific embodiment, the drug moiety is conjugated to one or more sites in the constant region of an antibody. In a specific embodiment, the drug moiety is conjugated to one or more sites in the variable region of an antibody. In a specific embodiment, the drug moiety is conjugated to one or more lysine residues in the antibody. In a specific embodiment, the drug moiety is conjugated to one or more cysteine ​​residues in the antibody, for example, when MMAE is the drug moiety. In a specific embodiment, the drug moiety is conjugated to the Fc region of an antibody that is an immunoglobulin. In a specific embodiment, the drug moiety is a peptide or protein fused to the N-terminus or C-terminus of one or more chains of the antibody moiety (directly or through a linker that is a peptide or protein).

[0296] For example, when the antibody portion is an scFv, the drug portion can be fused to the N- or C-terminus of the scFv (directly or through a linker that is a peptide or protein). In a specific embodiment, when the antibody portion is a multi-chain antibody or an antigen-binding fragment thereof, the drug portion can be fused to one of the chains of the antibody portion (directly or through a linker that is a peptide or protein). In the case of antibodies that are immunoglobulins, in a specific embodiment, two heavy chains can be fused to the drug portion (directly or through a linker that is a peptide or protein), and / or two light chains can be fused to the drug portion (directly or through a linker that is a peptide or protein). In these specific embodiments, provided herein is a vector (e.g., an expression vector) comprising a polynucleotide comprising a nucleotide sequence encoding a fusion protein for recombinant expression in a host cell, preferably in a mammalian cell, the fusion protein consisting of the drug portion and the antibody portion or its chain and a linker (if one exists) between the drug portion and the antibody portion. Also provided herein are ex vivo host cells containing these vectors for recombinantly expressing fusion proteins, the fusion proteins consisting of the drug portion and the antibody portion or its chain and a joint (if one) between the drug portion and the antibody portion. The features and methods for producing these vectors and ex vivo host cells can be the same as those described below for anti-MERTK antibodies. Also provided herein are methods for producing a fusion protein consisting of the drug portion and the antibody portion or its chain and a joint (if one) between the drug portion and the antibody portion, comprising culturing such ex vivo host cells under conditions such that a polynucleotide comprising a nucleotide sequence encoding the fusion protein is expressed by an ex vivo host cell to produce the fusion protein. Antibody-drug conjugates described herein can be produced by methods known in the art or as described in Section 6 below.

[0297] In some embodiments, the antibody-drug conjugate has Fig.13A or Fig. 13B , and specifically Fig.13A The structure shown in . Fig.13A Shown is the structure of MMAE linked to an antibody (Ab) via a mc-vc-PABC linker. Fig. 13B The structures of SN38 connected to an antibody (Ab) via a CL2 or CL2A linker are shown. Fig. 13B The "AA" in is phenylalanine-lysine, then Fig. 13B The antibody is shown linked to SN-38 via a CL2 linker (which contains a cathepsin B cleavage site). Fig. 13B The "AA" in is lysine, then Fig. 13BThe antibody is shown linked to SN-38 via a CL2A linker (which does not contain a cathepsin B cleavage site).

[0298] In a specific embodiment, the antibody portion of the antibody-drug conjugate comprises the variable region of antibody z10. In a specific embodiment, the antibody-drug conjugate provided herein comprises an antibody portion comprising a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the sequence shown in SEQ ID NO: 105 and the VL comprises the amino acid sequence of SEQ ID NO: 106, wherein the antibody portion is conjugated to MMAE via a mc-vc-PABC linker. In another specific embodiment, the antibody-drug conjugate provided herein comprises an antibody portion comprising a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the sequence shown in SEQ ID NO: 105 and the VL comprises the amino acid sequence of SEQ ID NO: 106, wherein the antibody portion is conjugated to SN-38 via a CL2A linker.

[0299] In alternative embodiments of the antibody-drug conjugates described throughout the disclosure, the drug moiety need not be a cytotoxic agent. For example, the drug moiety may be any drug known in the art suitable for use, and may include, but is not limited to, those described in Sections 5.2-3 below, or, for example, for the purpose of diagnosing or monitoring disease, may be an imaging agent.

[0300] In preferred embodiments of the antibody-drug conjugates described throughout this disclosure, the drug moiety is conjugated to the antibody moiety via a linker.

[0301] 5.2.1. Functional characteristics of antibody-drug conjugates

[0302] In certain embodiments, the antibody-drug conjugates described herein have a K of about 8 nM, 7 nM, 6 nM, 5 nM, 4.5 nM, 4 nM, 3.5 nM, 3 nM, 2.5 nM, 2 nM, 1.5 nM, 1 nM, 0.75 nM, 0.5 nM, 0.25 nM, 0.17 nM, 0.1 nM, 0.081 nM, or 0.021 nM. DBind to MERTK (e.g., human MERTK). In some aspects, the antibody-drug conjugates provided herein reduce the expression level of human MERTK on cancer cells (e.g., SKMEL5 melanoma cells) by greater than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, as evaluated by a determination known to those skilled in the art or described herein, e.g., as described in Section 6 below. In a specific embodiment, the antibody-drug conjugates provided herein bind to MERTK (e.g., bind to human MERTK, but not human Axl, human Tyro3 or mouse MERTK), as evaluated by methods described herein or known in the art. In certain embodiments, the antibody-drug conjugates provided herein include an antibody portion in which the antibody-drug conjugate binds to MERTK with an affinity greater than that of the non-conjugated antibody portion.

[0303] In certain embodiments, the antibody-drug conjugates provided herein cause cell death in vitro of cells expressing MERTK (e.g., human MERTK) (e.g., M2 macrophages, cancer cells, or both). In some specific embodiments, at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% of cells expressing MERTK cultured for a period of time in the presence of the antibody-drug conjugates described herein die at the end of the period of time, as assessed by methods known to those skilled in the art for measuring cell death in vitro. In other specific embodiments, when cultured for a period of time in the presence of an antibody-drug conjugate described herein, the percentage of MERTK-expressing cells (e.g., M2 macrophages, cancer cells, or both) that undergo cell death is at least 50%, 100%, 2-fold, 3-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1000-fold greater relative to when cultured in the absence of the antibody-drug conjugate (e.g., culture without any antibody-drug conjugate or culture with an antibody-drug conjugate comprising an unrelated antibody (e.g., an antibody that does not immunospecifically bind to MERTK (e.g., human MERTK)) or culture with an unconjugated anti-MERTK antibody or unconjugated anti-MERTK antigen-binding fragment described herein). The period of time can be, for example, about 1 hour, 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, or 1 week.

[0304] In some embodiments, the antibody-drug conjugates provided herein do not affect the viability of macrophages expressing MERTK, as evaluated by methods known to those skilled in the art for measuring cell death in vitro or as described herein (e.g., Section 6, below). In some embodiments, the antibody-drug conjugates provided herein do not affect the viability of M1 macrophages, as evaluated by methods known to those skilled in the art for measuring cell death in vitro or as described herein (e.g., Section 6, below). In some embodiments, the antibody-drug conjugates provided herein do not affect the viability of M2 macrophages, as evaluated by methods known to those skilled in the art for measuring cell death in vitro or as described herein (e.g., Section 6, below).

[0305] In certain embodiments, the antibody-drug conjugates provided herein cause degradation of MERTK on cells expressing MERTK, such as, for example, cancer cells (e.g., melanoma cells). In specific embodiments, the antibody-drug conjugates provided herein reduce the level of human MERTK on the surface of cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells) by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% in assays described herein or known to those skilled in the art. In certain embodiments, the antibody-drug conjugates provided herein cause greater degradation of MERTK on cells expressing MERTK than the unconjugated antibody portion, as evaluated in assays described herein or known in the art.

[0306] In certain embodiments, the antibody-drug conjugates provided herein cause internalization of MERTK on cells expressing MERTK, such as, for example, cancer cells (e.g., melanoma cells). In specific embodiments, the antibody-drug conjugates provided herein increase the internalization of human MERTK by cells expressing human MERTK, such as, for example, cancer cells (e.g., melanoma cells) by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85% in assays described herein or known to those skilled in the art. In certain embodiments, the antibody-drug conjugates provided herein include an antibody portion, and the antibody-drug causes greater internalization of cells expressing MERTK than the unconjugated antibody portion, as assessed by assays described herein or known to those skilled in the art.

[0307] In certain embodiments, the antibody-drug conjugates provided herein inhibit tumor development. Tumor development is inhibited by at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%. Tumor development can be evaluated by methods known to those skilled in the art. Tumor development can be a cancer state relative to no antibody treatment, treatment with an unrelated antibody (e.g., an antibody that does not specifically bind to human MERTK), treatment with SN-38, treatment with MMAE, or treatment with the unconjugated antibody portion of the antibody-drug conjugate. In a specific embodiment, the anti-MERTK antibody or its antigen-binding region has one, two, three or more of the antibody characteristics described in Section 6 below.

[0308] In a specific embodiment, the antibody-drug conjugates described herein inhibit angiogenesis in tumors. In some embodiments, the inhibition of angiogenesis is at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%. In a specific embodiment, the inhibition of angiogenesis is at least 50%, 55%, 60%, 65% or 70%. The inhibition of angiogenesis can be evaluated by methods described herein and / or known to those skilled in the art. The inhibition can be relative to the angiogenesis level without the antibody-drug conjugate (e.g., culture without any antibody-drug conjugate or culture with an antibody-drug conjugate containing an unrelated antibody (e.g., an antibody that does not specifically bind to MERTK (e.g., human MERTK)) or culture with an unconjugated anti-MERTK antibody or unconjugated anti-MERTK antigen-binding fragment described herein).

[0309] In certain embodiments, the antibody-drug conjugates described herein inhibit the development of tumors (e.g., human breast cancer tumors). The inhibition of tumor development is at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%. Tumor development can be evaluated by methods known to those skilled in the art. The tumor development can be relative to the cancer state without the antibody-drug conjugate (e.g., culture without any antibody-drug conjugate or culture with an antibody-drug conjugate containing an unrelated antibody (e.g., an antibody that does not specifically bind to MERTK (e.g., human MERTK)) or culture with an unconjugated anti-MERTK antibody or unconjugated anti-MERTK antigen-binding fragment described herein). In a specific embodiment, the assay for evaluating tumor development is a murine tumor transplant model.

[0310] 5.2.2. Antibody

[0311] The antibody-drug conjugates provided herein can include any anti-MERTK antibody provided herein. For examples of antibody portions of antibody-drug conjugates provided herein, see, e.g., Section 5.1.1. In a specific embodiment, the antibody portion is an immunoglobulin, e.g., an immunoglobulin or a humanized immunoglobulin comprising a human constant domain. In another specific embodiment, the antibody portion is a scFv, e.g., an scFv comprising the VH and VL domains of the antibody described in Section 5.1.1 herein.

[0312] In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety optionally conjugated through a linker to an antibody portion comprising a VH disclosed herein, e.g., a VH described in Section 5.1.1. In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety optionally conjugated through a linker to an antibody portion comprising a VL disclosed herein, e.g., a VL described in Section 5.1.1. In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety optionally conjugated through a linker to an antibody portion comprising a VH and VL of an antibody disclosed herein, e.g., a VH and VL of an antibody as described in Section 5.1.1.

[0313] In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety conjugated, optionally via a linker, to an antibody portion comprising a VH comprising the amino acid sequence set forth in SEQ ID NO: 105. In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety conjugated, optionally via a linker, to an antibody portion comprising a VL comprising the amino acid sequence set forth in SEQ ID NO: 106. In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety conjugated, optionally via a linker, to an antibody portion comprising (i) a VH comprising the amino acid sequence set forth in SEQ ID NO: 105 and (ii) a VL comprising the amino acid sequence set forth in SEQ ID NO: 106.

[0314] In some embodiments, the antibody-drug conjugates provided herein comprise MMAE conjugated to an antibody portion comprising VH via a linker, wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 105. In some embodiments, the antibody-drug conjugates provided herein comprise MMAE conjugated to an antibody portion comprising VL via a linker, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106. In some embodiments, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody portion comprising VH via a linker, wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 105. In some embodiments, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody portion comprising VL via a linker, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106.

[0315] In a specific embodiment, the antibody-drug conjugates provided herein comprise MMAE conjugated to an antibody portion comprising VH and VL via a linker, wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 105 and the VL comprises the amino acid sequence set forth in SEQ ID NO: 106. In another specific embodiment, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody portion comprising VH and VL via a linker, wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 105 and the VL comprises the amino acid sequence set forth in SEQ ID NO: 106.

[0316] In some embodiments, the antibody-drug conjugates provided herein include a drug moiety conjugated to an antibody portion comprising a heavy chain provided herein, e.g., a heavy chain described in Section 5.1.1, through a linker. In some embodiments, the antibody-drug conjugates provided herein include MMAE conjugated to an antibody portion comprising a heavy chain provided herein, e.g., a heavy chain described in Section 5.1.1, through a linker. In some embodiments, the antibody-drug conjugates provided herein include SN-38 conjugated to an antibody portion comprising a heavy chain provided herein, e.g., a heavy chain described in Section 5.1.1, through a linker. In some embodiments, the antibody-drug conjugates provided herein include a drug moiety conjugated to an antibody portion comprising a light chain provided herein, e.g., a light chain described in Section 5.1.1, through a linker. In some embodiments, the antibody-drug conjugates provided herein include MMAE conjugated to an antibody portion comprising a light chain provided herein, e.g., a light chain described in Section 5.1.1, through a linker. In some embodiments, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody portion comprising a light chain provided herein, e.g., a light chain described in Section 5.1.1, through a linker. In some embodiments, the antibody-drug conjugates provided herein comprise a drug portion conjugated to an antibody portion through a linker, the antibody portion comprising (i) a heavy chain provided herein and (ii) a light chain provided herein, e.g., a heavy chain and a light chain described in Section 5.1.1. In some embodiments, the antibody-drug conjugates provided herein comprise MMAE conjugated to an antibody portion through a linker, the antibody portion comprising (i) a heavy chain provided herein and (ii) a light chain provided herein, e.g., a heavy chain and a light chain described in Section 5.1.1. In some embodiments, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody portion through a linker, the antibody portion comprising (i) a heavy chain provided herein and (ii) a light chain provided herein, e.g., a heavy chain and a light chain described in Section 5.1.1.

[0317] In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety conjugated to an antibody portion comprising a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 via a linker. In some specific embodiments, the antibody-drug conjugates provided herein comprise MMAE conjugated to an antibody portion comprising a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 via a linker. In some specific embodiments, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody portion comprising a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 via a linker. In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety conjugated to an antibody portion comprising a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113 via a linker. In some specific embodiments, the antibody-drug conjugates provided herein comprise MMAE conjugated to a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113 via a linker. In some specific embodiments, the antibody-drug conjugates provided herein comprise SN-38 conjugated to a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113 via a linker. In some embodiments, the antibody-drug conjugates provided herein comprise a drug moiety conjugated to an antibody moiety via a linker, the antibody moiety comprising (i) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 and (ii) a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113. In a specific embodiment, the antibody-drug conjugates provided herein comprise MMAE conjugated to an antibody moiety via a linker, the antibody moiety comprising (i) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 and (ii) a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113. In another specific embodiment, the antibody-drug conjugates provided herein comprise SN-38 conjugated to an antibody moiety via a linker, the antibody moiety comprising (i) a heavy chain comprising the amino acid sequence set forth in SEQ ID NO: 112 and (ii) a light chain comprising the amino acid sequence set forth in SEQ ID NO: 113.

[0318] 5.2.3. Drug moiety and linker

[0319] The cytotoxic agents used in antibody-drug conjugates are also often referred to as payloads or warheads. Most cytotoxic agents used in antibody-drug conjugates target DNA or microtubules and have high cytotoxic potency (IC 50 In about 10 -10 Up to 10 -12M) (see Beck A et al., (2017) Nat Rev Drug Discov 16: 315-337). However, less potent cytotoxic agents may also be used. The cytotoxic agent may be a small molecule, a nucleotide, a peptide, or a non-antibody protein. In a specific embodiment, the cytotoxic agent is a small molecule. In another specific embodiment, the cytotoxic agent is a non-antibody protein. Non-limiting exemplary cytotoxic agents that can be used in the antibody-drug conjugates according to the present invention are described in Beck A et al., (2017) Nat Rev Drug Discov 16:315-337; Peters C and Brown S, (2015) Biosci Rep 35:art:e00225; McCombs JR and Owen SC (2015) The AAPS Journal 17:339-351; Jackson DY (2016) Org Process Res Dev 20:852-866; and Olivier KJ and Hurvitz SA, eds., (2016) Antibody-Drug Coniugates: Fundamentals, Drug Development, and Clinical, Wiley.

[0320] In certain embodiments, the cytotoxic agent is one of the agents listed in Table 30 or 31. In specific embodiments, the cytotoxic agent used in the antibody-drug conjugate is an auristatin (such as monomethyl auristatin E (MMAE), monomethyl auristatin F (MMAF), Aur0101, PF06380101, auristatin W or auristatin F) or a derivative thereof, a maytansine (such as DM1 or DM4), a pyrrolobenzodiazepine (PBD) (such as SGD1882 or SG3199), an indolinbenzodiazepine (such as DGN462 or DGN549), a calicheamicin (ozogamicin) (such as CM1), a camptothecin analog (such as SN38, DX-8951f or a DX-8951f derivative In some embodiments, the cytotoxic agent used in the antibody-drug conjugate is MMAE or MMAF. In some embodiments, the cytotoxic agent used in the antibody-drug conjugate is MMAE (see, e.g., MMAF). In some embodiments, the cytotoxic agent used in the antibody-drug conjugate is MMAE (see, e.g., Fig.13A ). In another specific embodiment, the cytotoxic agent used in the antibody-drug conjugate is DM1 or DM4. In another specific embodiment, the cytotoxic agent used in the antibody-drug conjugate is SN-38. In another specific embodiment, the cytotoxic agent used in the antibody-drug conjugate is Fig. 13B SN-38 shown.

[0321] Table 30: Examples of drug moieties

[0322]

[0323]

[0324]

[0325]

[0326]

[0327] Table 31: Other examples of drug moieties.

[0328]

[0329]

[0330] As used herein, the term "small molecule" refers to an organic or inorganic compound (which may be, for example, a heteroorganic or organometallic compound) having a molecular weight of less than about 10,000 grams per mole. In specific embodiments, the small molecule has a molecular weight of less than about 5,000 grams per mole, or less than about 2,000 grams per mole, or less than about 1,000 grams per mole, or less than about 500 grams per mole, or less than about 100 grams per mole.

[0331] In some embodiments, the cytotoxic agent is directly conjugated to the antibody portion. In other embodiments, the cytotoxic agent is conjugated to the antibody portion via a linker. Linkers suitable for use according to the present invention are preferably stable in the bloodstream to limit off-target toxicity and unstable at the cancer site to allow release of the cytotoxic agent (see Peters C and Brown S, (2015) Biosci Rep 35:art:e00225). Non-limiting exemplary linkers that can be used according to the present invention are described in Beck A et al., (2017) Nat Rev Drug DiscoV 16: 315-337; Peters C and Brown S, (2015) Biosci Rep 35: art: e00225; McCombs JR and Owen SC (2015) The AAPS Journal 17: 339-351; Jackson DY (2016) Org Process Res Dev 20: 852-866; and Olivier KJ and Hurvitz SA, eds., (2016) Antibody-Drug Conjugates: Fundamentals, Drug Development, and Clinical, Wiley. In some embodiments, the linker is a cleavable linker, for example, having a motif sensitive to lysosomal proteases (e.g., cathepsin B), a motif sensitive to acidic pH (e.g., hydrazone), or a motif containing a disulfide bridge that can be reduced by glutathione. In other embodiments, the linker is a non-cleavable linker. By way of example and not limitation, the linker can be a small molecule, a nucleotide, a peptide, or a non-antibody protein. In a specific embodiment, the linker is a small molecule. In a specific embodiment, the linker used in the antibody-drug conjugate is cathepsin B, hydrazone, succinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC), maleimidocaproic acid (mc), valine-citrulline (vc), N-hydroxysuccinimidyl 4-(2-pyridyldithio)-2-sulfobutyrate (sulfo-SPDB), N-hydroxysuccinimidyl 4-(2-pyridyldithio)butyrate (SPDB), N-succinimidyl 4-(2-pyridyldithio)pentanoic acid (SPP), valine-alanine (va), polyethylene glycol 8-valine-citrulline (PEG8-va), mb-vc, CL2A, a cleavable vc-based linker or a flexible polymer linker. In a specific embodiment, the linker selected for use in the antibody-drug conjugate described herein does not interfere with the binding of the antibody portion to its antigen, cytotoxic agent, or both.In a specific embodiment, the linker selected for use in the antibody-drug conjugates described herein is maleimidocaproyl-valine-citrulline-p-aminobenzyloxycarbonyl (mc-vc-PABC). In other specific embodiments, the linker selected for use in the antibody-drug conjugates described herein is CL2. In other specific embodiments, the linker selected for use in the antibody-drug conjugates described herein is CL2A. In some specific embodiments, the linker selected for use in the antibody-drug conjugates described herein is such as. Fig.13A In other specific embodiments, the linker selected for use in the antibody-drug conjugates described herein is as shown in Fig. 13B In other specific embodiments, the linker selected for use in the antibody-drug conjugates described herein is as shown in Fig. 13B In a specific embodiment, the antibody-drug conjugate comprises a linker and the linker is maleimidocaproyl-valine-citrulline-p-aminobenzyloxycarbonyl (also known as "mc-vc-PABC") (for the structure of mc-vc-PABC; see Fig.13A In another specific embodiment, the antibody-drug conjugate comprises a linker and the linker is CL2 (for the structure of CL2, see Fig. 13B and Cardillo et al. 2011, Clin Cancer Res; 17(10); 3157-69). In another specific embodiment, the antibody-drug conjugate comprises a linker and the linker is CL2A (for the structure of CL2A, see Fig. 13B and Goldberg et al. 2018, Oncotarget;9(48);28989-29006 and Cardillo et al. 2011, Clin Cancer Res;17(10);3157-69).

[0332] In some embodiments, the linker selected for use in the antibody-drug conjugates described herein comprises one or more cleavage sites. In specific embodiments, the linker selected for use in the antibody-drug conjugates described herein comprises a cathepsin B protease site. In other specific embodiments, the linker selected for use in the antibody-drug conjugates described herein comprises a cathepsin B protease site and a pH-dependent cleavage site.

[0333] Non-limiting exemplary linker-drug moiety pairs that can be used in the antibody-drug conjugates described herein are described in Beck A et al., (2017) Nat Rev Drug Discov 16:315-337; Peters C and Brown S, (2015) Biosci Rep 35:art:e00225; McCombs JR and Owen SC (2015) The AAPS Journal 17:339-351; Jackson DY (201 6) Org Process Res Dev 20:852-866; and Olivier KJ and Hurvitz SA, eds., (201 6) Antibody-Drug Conjugates: Fundamentals, Drug Development, and Clinical, Wiley. In a specific embodiment, the linker-drug moiety pair in the antibody-drug conjugate is vc-MMAE, mc-MMAF, SMCC-DM1, sulfo-SPDB-DM4, SPDB-DM4, SPP-DM1, va-SGD1882, polyethylene glycol 8 (PEG8)-va-SG3199, sulfo-SPDB-DGN462, hydrazone-CM1, vc-seco-DUBA, mb-vc-MGBA, CL2A-SN-38, a peptide linker with a DX-8951 derivative, hydrazone-doxorubicin, a cleavable vc-based linker with Aur0101, vc-PF06380101, a flexible polymer linker with auristatin F, a cleavable linker-tubulin inhibitor or vc-rifalogue. In a specific embodiment, the linker-drug moiety pair in the antibody-drug conjugate is mc-vc-PABC-MMAE (such as Fig.13A In other specific embodiments, the linker-drug moiety pair in the antibody-drug conjugate is CL2-SN-38 (as shown in Fig. 13B In other specific embodiments, the linker-drug moiety pair in the antibody-drug conjugate is CL2A-SN-38 (as shown in Fig. 13B , where AA is lysine).

[0334] In specific embodiments, the drug moiety of the antibody-drug conjugates described herein does not interfere with the binding of the antibody moiety to its antigen (eg, MERTK (eg, human MERTK)).

[0335] 5.3. Antibody production

[0336] 5.3.1. Production and screening of antibodies

[0337] In another aspect, provided herein are methods of producing an anti-MERTK antibody or antigen-binding fragment thereof described herein that specifically binds to MERTK (eg, human MERTK).

[0338] The antibodies or their antigen-binding fragments described herein can be produced by any method known in the art for antibody synthesis, for example, by chemical synthesis or by recombinant expression technology. Unless otherwise indicated, the methods described herein use conventional techniques in molecular biology, microbiology, gene analysis, recombinant DNA, organic chemistry, biochemistry, PCR, oligonucleotide synthesis and modification, nucleic acid hybridization, and related fields within the technical scope of the art. These techniques are described in, for example, the references cited herein and are fully explained in the literature. See, e.g., Maniatis T et al., (1982) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press; Sambrook J et al., (1989) Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press; Sambrook J et al., (2001) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY; Ausubel FM et al., Current Protocols in Molecular Biology, John Wiley & Sons (1987 and annual updates); Current Protocols in Immunology, John Wiley & Sons (1987 and annual updates); Gait (ed.) (1984) Oligonucleotide Synthesis: A Practical Approach, IRL Press; Eckstein (ed.) (1991) Oligonucleotides and Analogues: A Practical Approach, IRL Press; Birren et al., Current Protocols in Immunology, John Wiley & Sons (1987 and annual updates); B et al. (eds.) (1999) Genome Analysis: A Laboratory Manual, Cold Spring Harbor Laboratory Press.

[0339] In a specific embodiment, the antibodies described herein are antibodies (e.g., recombinant antibodies) prepared, expressed, produced, or isolated by any means including production, for example, by synthesis of DNA sequences, production by genetic engineering. In certain embodiments, such antibodies comprise sequences encoded by DNA sequences that are not naturally present in vivo in the antibody germline repertoire of an animal or mammal (e.g., human). In a specific embodiment, the antibodies described herein are prepared by a method including using human MERTK (SEQ ID NO: 131) or its extracellular domain (SEQ ID NO: 132) as an immunogen.

[0340] In a certain aspect, provided herein is a method for preparing an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), the method comprising culturing a cell or host cell described herein. In a certain aspect, provided herein is a method for preparing an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), the method comprising expressing (e.g., recombinantly expressing) the antibody or antigen-binding fragment thereof using a cell or host cell described herein (e.g., a cell or host cell comprising a polynucleotide encoding an antibody described herein). In a specific embodiment, the cell is an isolated cell. In a specific embodiment, an exogenous polynucleotide has been introduced into the cell. In a specific embodiment, the method further comprises a step of purifying the antibody or antigen-binding fragment thereof obtained from the cell or host cell.

[0341] Methods for producing polyclonal antibodies are known in the art (see, e.g., Chapter 11 in Short Protocols in Molecular Biology, (2002) 5th edition, Ausubel FM et al., eds., John Wiley and Sons, New York).

[0342] The term "monoclonal antibody" as used herein is not limited to antibodies produced by hybridoma technology. Monoclonal antibodies can be prepared using a variety of techniques known in the art, including the use of hybridoma, recombinant and phage display technology or a combination thereof. For example, monoclonal antibodies can be produced from host cells that exogenously express antibodies as described herein or fragments thereof, for example, the light chain and / or heavy chain of the antibody. Methods for preparing clonal cell lines and monoclonal antibodies expressed thereby are well known in the art (see, e.g., Chapter 11, Short Protocols in Molecular Biology, (2002) Fifth Edition, Ausubel FM et al., as above). For example, monoclonal antibodies can be produced using hybridoma technology, including those known and taught in the art, such as Harlow E & Lane D, Antibodies: A Laboratory Manual (Cold Spring Harbor Laboratory Press, 2nd edition 1988); Hammerling GJ et al., Monoclonal Antibodies and T-Cell Hybridomas 563 681 (Elsevier, NY, 1981); and Kohler G & Milstein C (1975) Nature 256: 495. Methods for producing and screening specific antibodies using hybridoma technology are routine and well known in the art. In some embodiments, mice (or other animals, such as rats, monkeys, donkeys, pigs, sheep, hamsters or dogs) can be immunized with an antigen (e.g., human), and once an immune response is detected, for example, antibodies specific to the antigen are detected in the mouse serum, the mouse spleen is harvested and spleen cells are isolated. The spleen cells are then fused to any suitable myeloma cells, e.g., from the American Type Culture Collection (ATCC), by well-known techniques. Hybridomas were formed by using cells of the cell line SP2 / 0 of ) (Manassas, VA). Hybridomas were selected and cloned by limiting dilution.

[0343] The hybridoma cells thus prepared are inoculated and grown in a suitable culture medium that preferably contains one or more substances that inhibit the growth or survival of the unfused parental myeloma cells. The culture medium in which the hybridoma cells are grown is assayed for the production of monoclonal antibodies against MERTK (e.g., human MERTK). After hybridoma cells that produce antibodies with the desired specificity, affinity and / or activity are identified, the clones can be subcloned, grown and separated from the culture medium by standard methods (Goding JW (ed.), Monoclonal Antibodies: Principles and Practice, supra). The binding specificity of the monoclonal antibodies produced by the hybridoma cells is determined by methods known in the art, for example, immunoprecipitation or by in vitro binding assays, such as radioimmunoassay (RIA) or enzyme-linked immunosorbent assay (ELISA).

[0344] In specific embodiments, disclosed herein are monoclonal antibodies produced by a single cell (e.g., a hybridoma or host cell producing a recombinant antibody), wherein the antibody immunospecifically binds to MERTK (e.g., human MERTK), as determined, for example, by ELISA or other antigen-binding or competitive binding assays known in the art or as described in Section 6 herein. In certain embodiments, the monoclonal antibody is a monovalent antibody or a multivalent (e.g., bivalent) antibody. In specific embodiments, the monoclonal antibody is a monospecific or a multispecific antibody (e.g., a bispecific antibody).

[0345] Antibody fragments that recognize MERTK (e.g., human MERTK) can be produced by any technique known to those skilled in the art. For example, the Fab and F(ab')2 fragments described herein can be produced by proteolytic cleavage of immunoglobulin molecules using enzymes such as papain (to produce Fab fragments) or pepsin (to produce F(ab')2 fragments). The Fab fragment corresponds to one of the two identical arms of the antibody molecule and contains a complete light chain paired with the VH and CH1 domains of the heavy chain. The F(ab')2 fragment contains two antigen-binding arms of the antibody molecule connected by a disulfide bond in the hinge region.

[0346] In addition, various phage display methods known in the art can also be used to produce anti-MERTK antibodies or antigen-binding fragments described herein. In the phage display method, functional antibody domains are displayed on the surface of phage particles with polynucleotide sequences encoding them. Specifically, DNA sequences encoding VH and VL domains are amplified from animal cDNA libraries (e.g., human or murine cDNA libraries of affected tissues). DNA encoding VH and VL domains are recombined with scFv joints by PCR and cloned into phagemid vectors. The vector is electroporated to Escherichia coli (E. coli) cells and infected with helper phages. The phage used in these methods is typically a filamentous phage comprising fd and M13, and VH and VL domains are usually recombinantly fused to any one of phage gene III or gene VIII. Antigens can be used, for example, using labeled antigens or antigens bound or captured to a solid surface or a bead to select or identify phages expressing antigen binding domains bound to a specific antigen. Examples of phage display methods that can be used to prepare the antibodies described herein include those described in Brinkman U et al. (1995) J Immunol Methods 182:41-50; Ames RS et al. (1995) J Immunol Methods 184:177-186; Kettleborough CA et al. (1994) Eur J Immunol 24:952-958; Persic L et al. (1997) Gene 187:9-18; Burton DR & Barbas CF (1994) Advan Immunol 57:191-280; PCT Patent Application No. PCT / GB91 / 001134; International Patent Publication Nos. WO 90 / 02809, WO 91 / 10737, WO 92 / 01047, WO 92 / 18619, WO 93 / 11236, WO 95 / 15982, WO 95 / 20401 and WO 97 / 13844; and those disclosed in U.S. Patent Nos. 5,698,426, 5,223,409, 5,403,484, 5,580,717, 5,427,908, 5,750,753, 5,821,047, 5,571,698, 5,427,908, 5,516,637, 5,780,225, 5,658,727, 5,733,743 and 5,969,108.

[0347] As described in the above references, after phage selection, the antibody coding regions from the phage can be isolated and used to produce complete antibodies, including humanized antibodies, chimeric antibodies or any other desired antigen-binding fragments, and expressed in any desired host, including mammalian cells, insect cells, plant cells, yeast and bacteria, for example, as described in detail below. Using methods known in the art, techniques for recombinant production of antibody fragments, such as Fab, Fab' and F(ab')2 fragments, such as those disclosed in PCT Patent Publication No. WO 92 / 22324; Mullinax RL et al., (1992) BioTechniques 12(6):864-9; Sawai H et al., (1995) Am J Reprod Immunol 34:26-34; and Better M et al., (1988) Science 240:1041-1043 can also be used.

[0348] In one aspect, to produce a complete antibody, PCR primers can be used to amplify VH or VL sequences from a template, e.g., scFv clones, and the PCR primers include VH or VL nucleotide sequences, restriction sites, and flanking sequences protecting the restriction sites. Using cloning techniques known to those skilled in the art, the PCR-amplified VH domains can be cloned into a vector expressing a VH constant region, and the PCR-amplified VL domains can be cloned into a vector expressing a VL constant region, e.g., a human kappa or lambda constant region. The VH and VL domains can also be cloned into a vector expressing the necessary constant region. Then, using techniques known to those skilled in the art, the heavy chain conversion vector and the light chain conversion vector are co-transfected into a cell line to produce a stable or transient cell line expressing a full-length antibody, e.g., IgG.

[0349] Chimeric antibodies are molecules in which different parts of an antibody are derived from different immunoglobulin molecules. For example, a chimeric antibody may contain the variable region of a mouse or rat monoclonal antibody fused to the constant region of a human antibody. Methods for producing chimeric antibodies are known in the art. See, e.g., Morrison SL (1985) Science 229: 1202-7; Oi VT & Morrison SL (1986) BioTechniques 4: 214-221; Gillies SD et al., (1989) J Immunol Methods 125: 191-202; and U.S. Pat. Nos. 5,807,715, 4,816,567, 4,816,397 and 6,331,415. In a specific embodiment, a chimeric antibody comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH and VL respectively comprise the amino acid sequences of the VH and VL described in Table 13, respectively.

[0350] Humanized antibodies can be bound to a predetermined antigen and comprise a framework region having substantially the amino acid sequence of a human immunoglobulin and a CDR having substantially the amino acid sequence of a non-human immunoglobulin (e.g., mouse immunoglobulin). In a specific embodiment, the humanized antibody also comprises at least a portion of an immunoglobulin constant region (Fc), typically at least a portion of a constant region of a human immunoglobulin. The antibody may also include CH1, hinge, CH2, CH3, and CH4 regions of a heavy chain. The humanized antibody may be selected from any class of immunoglobulins, including IgM, IgG, IgD, IgA, and IgE, and any isotype, including IgG1, IgG2, IgG3, and IgG4. Humanized antibodies can be produced using a variety of techniques known in the art, including, but not limited to, CDR-grafting (European Patent No. EP 239400; International Patent Publication No. WO 91 / 09967; and U.S. Pat. Nos. 5,225,539, 5,530,101, and 5,585,089), veneering or resurfacing (European Patent Nos. EP 592106 and EP 519596; Padlan EA (1991) Mol Immunol 28(4 / 5):489-498; Studnicka GM et al., (1994) Prot Engineering 7(6):805-814; and Roguska MA et al., (1994) PNAS 91:969-973), chain shuffling (U.S. Pat. No. 5,565,332) and (e.g.) U.S. Pat. No. 6,407,213, U.S. Pat. No. 5,766,886, International Patent Publication No. WO 93 / 17105; Tan P et al. (2002) J Immunol 169:1119-25; Caldas C et al. (2000) Protein Eng. 13(5):353-60; Morea V et al. (2000) Methods 20(3):267-79; Baca M et al. (1997) J Biol Chem 272(16):10678-84; Roguska MA et al. (1996) Protein Eng 9(10):895904; Couto JR et al. (1995) Cancer Res. 55(23 Supp):5973s-5977s; Couto JR et al., (1995) Cancer Res 55(8):1717-22; Sandhu JS (1994) Gene 150(2):409-10 and Pedersen JT et al., (1994) J Mol Biol 235(3):959-73.See also the technology disclosed in U.S. Patent Application Publication No. US 2005 / 0042664 Al (February 24, 2005), which is incorporated herein by reference in its entirety.

[0351] In a specific embodiment, a humanized antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) comprises the VH and VL of antibody z10 (see Table 11), the VH and VL of antibody z11 (see Table 12), or the VH and VL of antibody z13 (see Table 13). Methods for preparing multispecific (e.g., bispecific antibodies) have been described, see, e.g., U.S. Pat. Nos. 7,951,917; 7,183,076; 8,227,577; 5,837,242; 5,989,830; 5,869,620; 6,132,992 and 8,586,713.

[0352] Single domain antibodies, e.g., antibodies lacking light chains, can be produced by methods well known in the art. See Riechmann L & Muyldermans S (1999) J Immunol 231: 25-38; Nuttall SD et al., (2000) Curr Pharm Biotechnol 1(3): 253-263; Muyldermans S, (2001) J Biotechnol 74(4): 277-302; U.S. Pat. No. 6,005,079; and International Patent Publication Nos. WO 94 / 04678, WO 94 / 25591, and WO 01 / 44301.

[0353] Furthermore, antibodies that immunospecifically bind to a MERTK (e.g., human MERTK) antigen can be used, in turn, to generate anti-idiotypic antibodies that "mimic" the antigen using techniques well known to those skilled in the art (see, e.g., Greenspan NS & Bona CA (1989) FASEB J 7(5): 437-444; and Nissinoff A (1991) J Immunol 147(8): 2429-2438).

[0354] In a specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein bind to a MERTK (e.g., human MERTK) epitope that is identical or overlapping with the anti-MERTK antibodies or antigen-binding fragments thereof described herein. In a specific embodiment, the antibodies described herein that competitively block (e.g., in a dose-dependent manner) the binding of any one of the antibodies described herein (e.g., z10, z11 or z13 or xAb) to MERTK (e.g., human MERTK) are human anti-MERTK antibodies or antigen-binding fragments thereof. Human antibodies can be produced using any method known in the art. For example, transgenic mice that cannot express functional endogenous immunoglobulins but can express human immunoglobulin genes can be used. Specifically, human heavy chain and light chain immunoglobulin gene complexes can be introduced into mouse embryonic stem cells randomly or by homologous recombination. Alternatively, in addition to human heavy chain and light chain genes, human variable regions, constant regions, and diversity regions can be introduced into mouse embryonic stem cells. By introducing human immunoglobulin loci through homologous recombination, mouse heavy chain and light chain immunoglobulin genes can be rendered non-functional, either alone or simultaneously. Specifically, homozygous deletions in the JH region prevent endogenous antibody production. Modified embryonic stem cells are expanded and microinjected into blastocysts to produce chimeric mice. Then, chimeric mice are bred to produce homozygous offspring expressing human antibodies. In a normal manner, transgenic mice are immunized by selected antigens, for example, all or part of an antigen (e.g., MERTK). Using conventional hybridoma technology, monoclonal antibodies against the antigen can be obtained from immunized transgenic mice. The human immunoglobulin transgene possessed by transgenic mice is rearranged during B cell differentiation, and subsequently undergoes class switching and somatic mutation. Therefore, using this technology, it is possible to produce IgG, IgA, IgM and IgE antibodies for therapeutic use. For a review of this technology for producing human antibodies, see, for example, Lonberg N & Huszar D (1995) Int Rev Immunol 13: 65-93. For a detailed discussion of this technology for producing human antibodies and human monoclonal antibodies and procedures for producing such antibodies, see, e.g., International Patent Publication Nos. WO 98 / 24893, WO 96 / 34096, and WO 96 / 33735; and U.S. Pat. Nos. 5,413,923, 5,625,126, 5,633,425, 5,569,825, 5,661,016, 5,545,806, 5,814,318, and 5,939,598. Examples of mice capable of producing human antibodies include the Xenomouse TM (Abgenix, Inc.; U.S. Patent Nos. 6,075,181 and 6,150,184), HuAb-Mouse TM(Mederex, Inc. / Gen Pharm; U.S. Patent Nos. 5,545,806 and 5,569,825), Trans Chromo Mouse TM (Kirin) and KM Mouse TM (Medarex / Kirin).

[0355] Human antibodies that specifically bind to MERTK (e.g., human MERTK) can be prepared by a variety of methods known in the art, including the above-described phage display methods using antibody libraries derived from human immunoglobulin sequences. See also U.S. Patent Nos. 4,444,887, 4,716,111, and 5,885,793; and International Patent Publication Nos. WO 98 / 46645, WO 98 / 50433, WO 98 / 24893, WO 98 / 16654, WO 96 / 34096, WO 96 / 33735, and WO 91 / 10741.

[0356] In some embodiments, mouse-human hybridomas can be used to produce human antibodies. For example, human peripheral blood mononuclear cells transformed with Epstein-Barr virus (EBV) can be fused with mouse myeloma cells to produce mouse-human hybridomas that secrete human monoclonal antibodies, and these mouse-human hybridomas can be screened to determine those mice that secrete human monoclonal antibodies that immunospecifically bind to target antigens (e.g., human MERTK). These methods are known and described in the art, see, e.g., Shinmoto H et al., (2004) Cytotechnology 46: 19-23; Naganawa Y et al., (2005) Human Antibodies 14: 27-31.

[0357] In a specific embodiment, methods of screening and selecting antibodies or antigen-binding fragments thereof described herein that specifically bind to MERTK (eg, human MERTK) are described in Example 1 below.

[0358] Once the anti-MERTK antibodies or antigen-binding fragments thereof described herein are produced, they can be purified by any method known in the art for purification of immunoglobulin molecules, for example, by chromatography (e.g., ion exchange chromatography, affinity chromatography, specifically by affinity and size exclusion chromatography for specific antigens after Protein A), centrifugation, differential solubility, or by any other standard technique for protein purification. In addition, the antibodies described herein can be fused to heterologous polypeptide sequences described herein or otherwise known in the art to aid purification.

[0359] In a specific embodiment, the anti-MERTK antibody or antigen-binding fragment thereof described herein is isolated or purified. Generally, an isolated antibody is an antibody that is substantially free of other antibodies having an antigenic specificity different from that of the isolated antibody. For example, in a specific embodiment, the preparation of the antibodies described herein is substantially free of cellular material and / or chemical precursors. The language "substantially free of cellular material" includes the preparation of antibodies, wherein the antibodies are separated from the cellular components of the cells from which the antibodies are isolated or recombinantly produced. Therefore, antibodies substantially free of cellular material include the preparation of antibodies having less than about 30%, 20%, 10%, 5%, 2%, 1%, 0.5% or 0.1% (by dry weight) of heterologous proteins (also referred to herein as "contaminating proteins") and / or antibody variants, for example, post-translationally modified forms of antibodies or other different forms of antibodies (e.g., antibody fragments). When the antibody is recombinantly produced, it is also generally substantially free of culture medium, i.e., the culture medium accounts for less than about 20%, 10%, 2%, 1%, 0.5% or 0.1% of the volume of the protein preparation. When an antibody is produced by chemical synthesis, it is generally substantially free of chemical precursors or other chemicals, i.e., it is separated from chemical precursors or other chemicals involved in protein synthesis. Thus, these antibody preparations have less than about 30%, 20%, 10% or 5% (by dry weight) of chemical precursors or compounds other than the antibody of interest. In specific embodiments, the antibodies described herein are isolated or purified.

[0360] 5.3.2. Polynucleotides

[0361] In certain aspects, provided herein are polynucleotides comprising nucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof that specifically bind to a MERTK (e.g., human MERTK) antigen as described herein, and vectors, e.g., vectors comprising these polynucleotides for their efficient expression in host cells (e.g., E. coli and mammalian cells). In some embodiments, the polynucleotides are isolated or purified.

[0362] As used herein, "isolated" polynucleotide or nucleic acid molecule is a polynucleotide or nucleic acid molecule isolated from other nucleic acid molecules present in the natural source of the nucleic acid molecule (for example, in mice or people). In addition, "isolated" nucleic acid molecule, such as cDNA molecules, when produced by recombinant technology, can be substantially free of other cell materials or culture medium, or when chemosynthesized, can be substantially free of chemical precursors or other chemicals. For example, language "substantially free of" includes having less than about 15%, 10%, 5%, 2%, 1%, 0.5% or 0.1% other materials, for example, cell materials, culture medium, other nucleic acid molecules, chemical precursors and / or other chemicals polynucleotide or nucleic acid molecule preparation.

[0363] In a specific aspect, provided herein are polynucleotides comprising nucleotide sequences encoding the anti-MERTK antibodies or antigen-binding fragments thereof described herein, which specifically bind to a MERTK (e.g., human MERTK) polypeptide and comprise an amino acid sequence as described herein, as well as antibodies that compete with these antibodies for binding to a MERTK (e.g., human MERTK) polypeptide (e.g., in a dose-dependent manner) or bind to the same or overlapping epitope as these antibodies.

[0364] In certain aspects, provided herein are polynucleotides comprising a nucleotide sequence encoding a light chain or a heavy chain of an antibody described herein.

[0365] In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising an amino acid sequence described herein (SEQ ID NO: 105, SEQ ID NO: 107, SEQ ID NO: 108, or SEQ ID NO: 109). In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) described herein, wherein the anti-MERTK antibody or antigen-binding fragment thereof comprises a light chain variable region comprising an amino acid sequence described herein (SEQ ID NO: 106 or SEQ ID NO: 111). In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 105 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106. In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 107 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106. In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK) as described herein, wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 108 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106. In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 110 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 111.In certain embodiments, the polynucleotides described herein comprise a nucleotide sequence encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein the antibody or antigen-binding fragment thereof comprises a heavy chain variable region comprising the amino acids set forth in SEQ ID NO: 109 and a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106.

[0366] In certain embodiments, the polynucleotides described herein encode VH, wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 119, SEQ ID NO: 121, SEQ ID NO: 122, or SEQ ID NO: 123. In certain embodiments, the polynucleotides described herein encode VL, wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 120 or SEQ ID NO: 124. In a specific embodiment, the polynucleotides described herein encode VH and VL, wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 119, and wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 120. In another specific embodiment, the polynucleotides described herein encode VH and VL, wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 121, and wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 120. In another specific embodiment, the polynucleotides described herein encode VH and VL, wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 122, and wherein the polynucleotide comprises the nucleic acid sequence set forth in SEQ ID NO: 120. In another embodiment, the polynucleotide described herein encodes VH and VL, wherein the polynucleotide comprises the nucleic acid shown in SEQ ID NO:123, and wherein the polynucleotide comprises the nucleic acid sequence shown in SEQ ID NO:124.

[0367] In a specific aspect, polynucleotides are provided herein, comprising a nucleotide sequence encoding an antibody comprising a light chain and a heavy chain, e.g., an isolated light chain and a heavy chain. For a light chain, in a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody as described herein, comprising a human kappa light chain or a human lambda light chain.

[0368] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody light chain, wherein the nucleotide sequence comprises a light chain variable region as shown in SEQ ID NO: 106 and a human light chain constant region nucleotide sequence of a human kappa or lambda light chain. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody light chain, wherein the light chain comprises a light chain variable region as shown in SEQ ID NO: 111 and a human light chain constant region of a human kappa or lambda light chain.

[0369] In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises a light chain, and wherein the amino acid sequence of the light chain variable region may comprise any one of the amino acid sequences shown in SEQ ID NO: 106 or SEQ ID NO: 111, and wherein the constant region of the light chain comprises the amino acid sequence of a human kappa light chain constant region. In another specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and comprises a light chain, wherein the amino acid sequence of the light chain variable region may comprise any one of the amino acid sequences shown in SEQ ID NO: 106 or SEQ ID NO: 111, and wherein the light chain constant region comprises the amino acid sequence of a human lambda light chain constant region. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody light chain, wherein the light chain comprises the amino acid sequence shown in SEQ ID NO: 113 or 118. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding a light chain of an antibody that specifically binds to MERTK (eg, human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 126 or 130.

[0370] In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 105 and a heavy chain constant region. In another specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 107 and a heavy chain constant region. In another specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 108 and a heavy chain constant region. In another specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 109 and a heavy chain constant region. In another specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (eg, human MERTK) and comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence shown in SEQ ID NO: 110 and a heavy chain constant region.

[0371] In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 112. In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 114. In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 115. In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 116. In a specific embodiment, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody described herein that specifically binds to MERTK (eg, human MERTK), wherein the antibody comprises a heavy chain, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO:117.

[0372] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK (e.g., human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 119 and a human heavy chain constant region nucleotide sequence. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK, wherein the nucleotide sequence comprises SEQ ID NO: 125.

[0373] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK (e.g., human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 121 and a human heavy chain constant region nucleotide sequence. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK, wherein the nucleotide comprises SEQ ID NO: 127.

[0374] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK (e.g., human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 122 and a human heavy chain constant region nucleotide sequence. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK (e.g., human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 128.

[0375] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK (e.g., human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 123 and a human heavy chain constant region nucleotide sequence. In another aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody heavy chain that specifically binds to MERTK (e.g., human MERTK), wherein the nucleotide sequence comprises SEQ ID NO: 129.

[0376] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding a light chain of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding a heavy chain of the antibody, wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 119 and a human heavy chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 120 and a human heavy chain constant region nucleotide sequence. In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding a light chain of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding a heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 120 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 121 and a human heavy chain constant region nucleotide sequence. In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding a light chain of an antibody that specifically binds to MERTK (e.g., human MERTK) as described herein and a nucleotide sequence encoding a heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 120 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 122 and a human heavy chain constant region nucleotide sequence. In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding a light chain of an antibody that specifically binds to MERTK (e.g., human MERTK) as described herein and a nucleotide sequence encoding a heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 124 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 123 and a human heavy chain constant region nucleotide sequence.

[0377] In a specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises: (1) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 105 and a human heavy chain constant region; and (2) a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106 and a human light chain constant region. In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises: (1) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 107 and a human heavy chain constant region; and (2) a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106 and a human light chain constant region. In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises: (1) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 108 and a human heavy chain constant region; and (2) a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106 and a human light chain constant region. In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises: (1) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 110 and a human heavy chain constant region; and (2) a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 111 and a human light chain constant region.

[0378] In another specific aspect, the polynucleotides provided herein comprise a nucleotide sequence encoding an antibody that specifically binds to MERTK (e.g., human MERTK), wherein the antibody comprises: (1) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 109 and a human heavy chain constant region; and (2) a light chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 106 and a human light chain constant region.

[0379] In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and another nucleotide sequence encodes the light chain of the antibody, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 125, and the nucleotide sequence encoding the light chain comprises SEQ ID NO: 126. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and another nucleotide sequence encodes the light chain of the antibody, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 127, and the nucleotide sequence encoding the light chain comprises SEQ ID NO: 126. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and another nucleotide sequence encodes the light chain of the antibody, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 128, and the nucleotide sequence encoding the light chain comprises SEQ ID NO: 126. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and another nucleotide sequence encodes the light chain of the antibody, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 129, and the nucleotide sequence encoding the light chain comprises SEQ ID NO: 130.

[0380] In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and the other encodes the light chain of the antibody, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 112 and the light chain comprises the amino acid sequence set forth in SEQ ID NO: 113. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and the other encodes the light chain of the antibody, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 114 and the light chain comprises the amino acid sequence set forth in SEQ ID NO: 113. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and the other encodes the light chain of the antibody, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 115 and the light chain comprises the amino acid sequence set forth in SEQ ID NO: 113. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and the other encodes the light chain of the antibody, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 116 and the light chain comprises the amino acid sequence set forth in SEQ ID NO: 113. In another specific embodiment, the polynucleotides provided herein comprise nucleotide sequences encoding an anti-MERTK antibody or an antigen-binding fragment thereof that specifically binds to MERTK (e.g., human MERTK), wherein one nucleotide sequence encodes the heavy chain of the antibody and the other encodes the light chain of the antibody, wherein the heavy chain comprises the amino acid sequence set forth in SEQ ID NO: 117 and the light chain comprises the amino acid sequence set forth in SEQ ID NO: 118.

[0381] In certain embodiments, polynucleotides, nucleic acids or nucleotides include deoxyribonucleic acids, ribonucleic acids, ribonucleotides and polymeric forms thereof. In some embodiments, polynucleotides, nucleic acids or nucleotides are single-stranded or double-stranded. In specific embodiments, polynucleotides, nucleic acids or nucleotide sequences are cDNA sequences.

[0382] In some embodiments, the polynucleotide sequences (e.g., nucleic acid sequences) encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein are codon optimized using methods known to those skilled in the art. In certain embodiments, the optimized polynucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein (e.g., VH domains and / or VL domains) can be hybridized to the antisense (e.g., complementary) polynucleotides of the unoptimized polynucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein (e.g., VH domains and / or VL domains). In a specific embodiment, the optimized nucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein hybridize to the antisense polynucleotides of the unoptimized polynucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein under high stringency conditions. In a specific embodiment, the optimized nucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof hybridize to the antisense polynucleotides of the unoptimized nucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein under high stringency, medium or low stringency hybridization conditions. Information regarding hybridization conditions has been described, see, for example, U.S. Patent Application Publication No. US2005 / 0048549 (eg, paragraphs 72-73), which is incorporated herein by reference.

[0383] Polynucleotides can be obtained and the nucleotide sequence of the polynucleotides can be determined by any method known in the art. The nucleotide sequences encoding the antibodies described herein and modified forms of these antibodies can be determined using methods well known in the art, i.e., nucleotide codons known to encode specific amino acids are assembled in this manner to produce nucleic acid sequences encoding the antibodies. Such polynucleotides encoding the antibodies can be assembled from chemically synthesized oligonucleotides (e.g., as described in Kutmeier G et al., (1994), BioTechniques 17: 242-6), briefly, this includes the synthesis of overlapping oligonucleotides containing sequence portions encoding the antibodies, annealing and connection of those oligonucleotides, and then amplification of the connected oligonucleotides by PCR.

[0384] Alternatively, polynucleotides encoding antibodies described herein can be generated from nucleic acids from suitable sources (e.g., hybridomas) using methods well known in the art (e.g., PCR and other molecular cloning methods). For example, PCR amplification using synthetic primers that can hybridize to the 3' and 5' ends of a known sequence can be implemented using genomic DNA from hybridoma cells that produce target antibodies. These PCR amplification methods can be used to obtain nucleic acids containing sequences encoding light chains and / or heavy chains of antibodies. These PCR amplification methods can be used to obtain nucleic acids containing sequences encoding light chain variable regions and / or heavy chain variable regions of antibodies. The amplified nucleic acids can be cloned into vectors for expression in host cells and for further cloning, for example, to produce humanized antibodies.

[0385] If a clone containing a nucleic acid sequence encoding a particular antibody is not available, but the sequence of the antibody molecule is known, the nucleic acid encoding the immunoglobulin can be obtained from a suitable source (e.g., an antibody cDNA library or cDNA library generated from any tissue or cell expressing the antibody (e.g., a hybridoma cell selected to express an antibody described herein), or nucleic acid isolated from any tissue or cell expressing the antibody, preferably poly A+RNA) by chemical synthesis or by PCR amplification using synthetic primers that hybridize to the 3' and 5' ends of the sequence or by cloning using oligonucleotide probes specific for a particular gene sequence to, for example, identify cDNA clones from a cDNA library encoding the antibody. The amplified nucleic acid generated by PCR can then be cloned into a replicable cloning vector using any method well known in the art.

[0386] DNA encoding the anti-MERTK antibodies described herein can be readily isolated and sequenced using conventional procedures (e.g., by using oligonucleotide probes that are capable of binding specifically to genes encoding the heavy and light chains of the anti-MERTK antibodies). Hybridoma cells can be used as a source of such DNA. Once isolated, the DNA can be placed into expression vectors and then transfected into host cells, such as Escherichia coli (E. coli) cells, simian COS cells, Chinese hamster ovary (CHO) cells (e.g., from CHO GS System TM (Lonza) CHO cells), 293F cells, HEK293 cells, or myeloma cells that do not otherwise produce immunoglobulin to obtain synthesis of MERTK agonistic antibodies in the recombinant host cells.

[0387] In order to produce a complete antibody, PCR primers can be used to amplify the VH or VL sequence in the scFv clone, and the PCR primers include VH or VL nucleotide sequences, restriction sites, and flanking sequences protecting the restriction sites. Using cloning techniques known to those skilled in the art, the VH domain amplified by PCR can be cloned into a vector expressing a heavy chain constant region, for example, a human γ4 constant region, and the VL domain amplified by PCR can be cloned into a vector expressing a light chain constant region, for example, a human K or λ constant region. In certain embodiments, the vector for expressing the VH or VL domain comprises a promoter, a secretion signal, a cloning site for the variable domain, a constant domain, and a selection marker. The VH and VL domains can also be cloned into a vector for expressing the necessary constant region. Then, using techniques known to those skilled in the art, the heavy chain conversion vector and the light chain conversion vector are co-transfected into a cell line to produce a stable or transient cell line expressing a full-length antibody, for example, IgG.

[0388] The DNA may also be modified, for example, by replacing the murine sequences with coding sequences for human heavy and light chain constant domains or by covalently linking all or part of the coding sequence for a non-immunoglobulin polypeptide to the immunoglobulin coding sequence.

[0389] Also provided are polynucleotides that hybridize to polynucleotides encoding antibodies or antigen-binding fragments thereof described herein under high stringency, medium or low stringency hybridization conditions. In specific embodiments, the polynucleotides described herein hybridize to polynucleotides encoding VH (SEQ ID NO: 119, 121, 122 or 123) and / or VL (SEQ ID NO: 120 or 124) provided herein under high stringency, medium or low stringency hybridization conditions.

[0390] Hybridization conditions have been described in the art and are known to those skilled in the art. For example, hybridization under stringent conditions may include hybridization to filter-bound DNA in 6× sodium chloride / sodium citrate (SSC) at about 45° C., followed by one or more washes in 0.2×SSC / 0.1% SDS at about 50-65° C.; hybridization under highly stringent conditions may include hybridization to filter-bound nucleic acids in 6×SSC at about 45° C., followed by one or more washes in 0.1×SSC / 0.2% SDS at about 68° C. Other hybridization under stringent hybridization conditions are known to those skilled in the art and have been described, see, for example, Ausubel FM et al., eds., (1989) Current Protocols in Molecular Biology, Vol. I, Green Publishing Associates, Inc. and John Wiley & Sons, Inc., New York, pp. 6.3.1-6.3.6 and 2.10.3.

[0391] 5.3.3. Cells and vectors

[0392] In certain aspects, provided herein are vectors (e.g., expression vectors) containing polynucleotides containing nucleotide sequences encoding anti-MERTK antibodies or antigen-binding fragments thereof described herein for recombinant expression in host cells, preferably in mammalian cells. The expression vector can be, for example, a plasmid or a viral vector (such as Newcastle disease virus, adenovirus, adenovirus-associated virus, vaccinia, etc.). Also provided herein are host cells containing these vectors for recombinant expression of anti-MERTK antibodies or antigen-binding fragments thereof described herein.

[0393] The recombinant expression of antibodies (e.g., full-length antibodies, heavy and / or light chains of antibodies, or single-chain antibodies described herein) that specifically bind to MERTK (e.g., human MERTK) described herein includes the construction of expression vectors containing polynucleotides encoding the antibodies. Once the polynucleotides encoding antibody molecules, heavy and / or light chains of antibodies, or antigen-binding fragments thereof (e.g., heavy and / or light chain variable regions) described herein have been obtained, vectors for antibody molecule production can be generated by DNA recombinant technology using techniques well known in the art. Thus, methods for preparing proteins by expressing polynucleotides containing nucleotide sequences encoding antibodies or antibody fragments (e.g., light chains or heavy chains or both) are described herein. Methods that are well known to those skilled in the art can be used to construct expression vectors containing antibody or antibody fragment (e.g., light chains or heavy chains or both) coding sequences and suitable transcriptional and translational control signals. These methods include, for example, in vitro recombinant DNA techniques, synthetic techniques, and in vivo genetic recombination. Also provided are replicable vectors comprising nucleotide sequences encoding antibody molecules described herein, heavy or light chains of antibodies, or heavy or light chain variable domains of anti-MERTK antibodies, or antigen-binding fragments thereof, operably linked to a promoter. These vectors may, for example, include nucleotide sequences encoding constant regions of antibody molecules (see, e.g., International Patent Publication Nos. WO 86 / 05807 and WO 89 / 01036; and U.S. Patent No. 5,122,464), and the variable domains of the antibodies may be cloned into the vector for expression of the entire heavy chain, the entire light chain, or both the entire heavy chain and the light chain.

[0394] The expression vector can be transferred to a cell (e.g., a host cell) by conventional techniques, and the resulting cells are then cultured by conventional techniques to produce an anti-MERTK antibody or antigen-binding fragment thereof as described herein. Therefore, a host cell is provided herein, which contains a polynucleotide encoding an antibody or antigen-binding fragment thereof, or a heavy chain or light chain or fragment thereof, or a single-chain antibody as described herein, operably linked to a promoter for expression of these sequences in a host cell. As used herein, the term "host cell" can be any type of cell, for example, a primary cell, a cell in culture, or a cell from a cell line. In a specific embodiment, the term "host cell" refers to a cell transfected with a nucleic acid molecule and the progeny or potential progeny of such a cell. Due to mutations or environmental influences that may occur in the successful generation or integration of a nucleic acid molecule into a host cell genome, the progeny of such a cell may be different from the parental cell transfected with the nucleic acid molecule.

[0395] A variety of host-expression vector systems can be used to express the antibody molecules described herein. These host-expression systems represent vehicles by which the target coding sequence can be produced and subsequently purified, and also represent cells that can in situ express the antibody molecules described herein when transformed or transfected with suitable nucleotide coding sequences. These include, but are not limited to, microorganisms, such as bacteria (e.g., E. coli and Bacillus subtilis) transformed with recombinant bacteriophage DNA, plasmid DNA or cosmid DNA expression vectors containing antibody coding sequences; yeast (e.g., Pichia pastoris) transformed with recombinant yeast expression vectors containing antibody coding sequences; insect cell systems infected with recombinant virus expression vectors (e.g., baculovirus) containing antibody coding sequences; plant cell systems (e.g., green algae, such as Chlamydomonas reinhardtii) infected with recombinant virus expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or transformed with recombinant plasmid expression vectors (e.g., Ti plasmid) containing antibody coding sequences. reinhardtii)); or a mammalian cell system (e.g., COS (e.g., COS1 or COS), CHO, BHK, MDCK, HEK 293, NS0, PER.C6, VERO, CRL7030, HsS78Bst, HeLa and NIH 3T3, HEK-293T, 293F, HepG2, SP210, R1.1, BW, LM, BSC1, BSC40, YB / 20 and BMT10 cells) with a recombinant expression construct containing a promoter derived from mammalian cells (e.g., a metallothionein promoter) or a promoter derived from a mammalian virus (e.g., adenovirus late promoter; vaccinia virus 7.5K promoter). In a specific embodiment, the cell used to express the antibody or antigen-binding fragment thereof described herein is a CHO cell, for example, a CHO GS System TM In a specific embodiment, the cells used to express the antibodies described herein are human cells, e.g., human cell lines. In a specific embodiment, the mammalian expression vector is pOptiVEC TMOr pcDNA3.3. In a specific embodiment, bacterial cells, such as Escherichia coli, or eukaryotic cells (e.g., mammalian cells) are used for the expression of recombinant antibody molecules, particularly for the expression of complete recombinant antibody molecules. For example, mammalian cells, such as Chinese hamster ovary (CHO) cells, combined with vectors, such as the major intermediate early gene promoter element from human cytomegalovirus are effective expression systems for antibodies (Foecking MK & Hofstetter H (1986) Gene 45: 101-5; and Cockett MI et al., (1990) Biotechnology 8 (7): 662-7). In certain embodiments, the antibodies described herein are produced by CHO cells or NS0 cells. In a specific embodiment, the expression of the nucleotide sequence encoding the antibody described herein that immunospecifically binds to MERTK (e.g., human MERTK) is regulated by a constitutive promoter, an inducible promoter, or a tissue-specific promoter.

[0396] In bacterial systems, some expression vectors may be advantageously selected based on the intended use of the antibody molecule to be expressed. For example, when large quantities of such antibodies are produced, vectors that direct high-level expression of fusion protein products that are easily purified may be desirable for the production of pharmaceutical compositions of the antibody molecule. These vectors include, but are not limited to, the E. coli expression vector pUR278 (Ruether U & Mueller-Hill B (1983) EMBO J 2: 1791-1794), to which the antibody coding sequence can be ligated individually in frame with the lac Z coding region to produce a fusion protein; pIN vectors (Inouye S & Inouye M (1985) Nuc Acids Res 13: 3101-3109; Van Heeke G & Schuster SM (1989) J Biol Chem 24: 5503-5509); etc. For example, pGEX vectors can also be used to express exogenous polypeptides as fusion proteins with glutathione 5-transferase (GST). Typically, these fusion proteins are soluble and can be easily purified from lysed cells by adsorption and binding to matrix glutathione agarose beads followed by elution in the presence of free glutathione. pGEX vectors are designed to include thrombin or factor Xa protease cleavage sites so that the cloned target gene product can be released from the GST moiety.

[0397] In insect systems, for example, Autographa californica nuclear polyhedrosis virus (AcNPV) can be used as a vector to express foreign genes. The virus is grown in Spodoptera frugiperda cells. The antibody coding sequence can be cloned separately into non-essential regions of the virus (e.g., the polyhedrin gene) and placed under the control of the AcNPV promoter (e.g., the polyhedrin promoter).

[0398] In mammalian host cells, some virus-based expression systems can be used. If adenovirus is used as an expression vector, the target antibody coding sequence can be connected to an adenovirus transcription / translation control complex, such as a late promoter and a tripartite leader sequence. Then, this chimeric gene can be inserted into the adenovirus genome by in vitro or in vivo recombination. Insertion in the non-essential region of the viral genome (e.g., E1 or E3 region) will result in the production of a recombinant virus that survives in an infected host and can express the antibody molecule (e.g., see Logan J & Shenk T (1984) PNAS 81 (12): 3655-9). For the effective translation of the inserted antibody coding sequence, specific initiation signals may also be required. These signals include an ATG initiation codon and adjacent sequences. In addition, the initiation codon must be in phase with the reading frame of the desired coding sequence to ensure translation of the entire insert. These exogenous translation control signals and initiation codons can be of a variety of sources, i.e., both natural and synthetic sources. The expression efficiency can be increased by including appropriate transcription enhancer elements, transcription terminators, etc. (see, for example, Bitter G et al., (1987) Methods Enzymol. 153: 516-544).

[0399] In addition, host cell strains that regulate the expression of inserted sequences or modify and process gene products in a desired specific manner can be selected. These modifications (e.g., glycosylation) and processing (e.g., cutting) of protein products can be important for protein function. Different host cells have characteristic and specific mechanisms for post-translational processing and modification of proteins and gene products. Suitable cell lines or host systems can be selected to ensure the correct modification and processing of expressed foreign proteins. For this reason, eukaryotic host cells with appropriate processing of primary transcripts, glycosylation of gene products and phosphorylated cellular mechanisms can be used. These mammalian host cells include, but are not limited to, CHO, VERO, BHK, Hela, MDCK, HEK293, NIH 3T3, W138, 293F, BT483, Hs578T, HTB2, BT2O and T47D, NSO (a murine myeloma cell line that does not endogenously produce any immunoglobulin chains), CRL7O3O, COS (e.g., COS1 or COS), PER.C6 VERO, HsS78Bst, HEK-293T, HEK293, HepG2, SP210, R1.1, BW, LM, BSC1, BSC40, YB / 20, BMT10 and HsS78Bst cells. In certain embodiments, the anti-MERTK antibodies described herein are produced in mammalian cells, such as CHO cells.

[0400] In a specific embodiment, the antibodies or antigen-binding fragments thereof described herein have reduced fucose content or no fucose content. These antibodies can be produced using techniques known to those skilled in the art. For example, the antibodies are expressed in cells that are defective or lacking in fucosylation ability. In a specific example, a cell line in which both alleles of α1,6-fucosyltransferase are knocked out can be used to produce antibodies or antigen-binding fragments thereof with reduced fucose content. The TRANSPAREN(R) system (Lonza) is an example of such a system that can be used to generate antibodies or antigen-binding fragments thereof with reduced fucose content.

[0401] For long-term, high-yield production of recombinant proteins, stable expressing cells can be generated. For example, cell lines that stably express an anti-MERTK antibody or antigen-binding fragment thereof described herein or a chimeric anti-MERTK antibody or antigen-binding fragment thereof described herein can be engineered. In a specific embodiment, the cells provided herein stably express a light chain / light chain variable domain and a heavy chain / heavy chain variable domain that bind to form an antibody or antigen-binding fragment thereof described herein.

[0402] In certain aspects, instead of using an expression vector containing a viral origin of replication, a host cell can be transformed with a DNA controlled by suitable expression control elements (e.g., promoters, enhancers, sequences, transcription terminators, polyadenylation sites, etc.) and selectable markers. After the introduction of exogenous DNA / polynucleotides, the engineered cells can be allowed to grow in an enriched medium for 1-2 days and then transferred to a selection medium. The selectable marker in the recombinant plasmid confers selection tolerance and allows cells to stably integrate the plasmid into their chromosomes and grow to form foci that can in turn be cloned and amplified as cell lines. This method can be advantageously used for engineering cell lines expressing humanized anti-MERTK antibodies described herein or antigen-binding fragments thereof or chimeric anti-MERTK antibodies described herein or antigen-binding fragments thereof. These engineered cell lines can be particularly useful in the screening and evaluation of compositions that interact directly or indirectly with antibody molecules.

[0403] Several selection systems can be used, including but not limited to herpes simplex virus thymidine kinase (Wigler M et al., (1977) Cell 11(1):223-32), xanthine guanine phosphoribosyltransferase (Szybalska EH & Szybalski W (1962) PNAS 48(12):2026-2034), and adenine phosphoribosyltransferase (Lowy I et al., (1980) Cell 22(3):817-23) genes, which can be used in tk-, hgprt- or aprt- cells, respectively. In addition, antimetabolite resistance can be used as the basis for selection for the following genes: dhfr, which confers resistance to methotrexate (Wigler M et al., (1980) PNAS 77(6):3567-70; O'Hare K et al., (1981) PNAS 78:1527-31); gpt, which confers resistance to mycophenolic acid (Mulligan RC & Berg P (1981) PNAS 78(4):2072-6); neo, which confers resistance to the aminoglycoside G-418 (Wu GY & Wu CH (1991) Biotherapy 3:87-95; Tolstoshev P (1993) Ann Rev Pharmacol Toxicol 32:573-596; Mulligan RC (1993) Science 260:926-932; and Morgan RA & Anderson WF (1993) Ann Rev Biochem 62: 191-217; Nabel GJ & Felgner PL (1993) Trends Biotechnoll 1(5): 211-5); and hygro, which confers resistance to hygromycin (Santerre RF et al., (1984) Gene 30(1-3): 147-56).Methods generally known in the field of DNA recombinant technology can be routinely applied to select desired recombinant clones, and these methods are described in, for example, Ausubel FM et al. (eds.), Current Protocols in Molecular Biology, John Wiley & Sons, NY (1993); Kriegler M, Gene Transfer and Expression, A Laboratory Manual, Stockton Press, NY (1990); and in Chapters 12 and 13, Dracopoli NC et al. (eds.), Current Protocols in Human Genetics, John Wiley & Sons, NY (1994); Colbère-Garapin F et al., (1981) J Mol Biol 150: 1-14, the entire contents of which are incorporated herein by reference.

[0404] The expression level of antibody molecules can be increased by vector amplification (for review, see Bebbington CR & Hentschel CCG, The use of vectors based on gene amplification for the expression of cloned genes in mammalian cells in DNA cloning, Vol. 3 (Academic Press, New York, 1987)). When the marker in the vector system expressing the antibody is amplifiable, the increase in the inhibitor level present in the host cell culture will increase the copy number of the marker gene. Since the amplified region is associated with the antibody gene, the production of the antibody will also be increased (Crouse GF et al., (1983) Mol Cell Biol 3: 257-66).

[0405] Host cells can be co-transfected with two or more expression vectors described herein, wherein the first vector encodes a polypeptide derived from a heavy chain and the second vector encodes a polypeptide derived from a light chain. The two vectors can contain the same selectable marker, which makes the expression of heavy and light chain polypeptides equal. Host cells can be co-transfected with two or more expression vectors of different amounts. For example, any of the following first expression vector and second expression vector ratios can be used to transfect host cells: 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:12, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45 or 1:50.

[0406] In a specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding a light chain variable region (VL) of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding a heavy chain variable region (VH) of the antibody, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106, and wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 105. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding a light chain of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding a heavy chain of the antibody, wherein the light chain comprises a light chain variable region comprising the amino acids set forth in SEQ ID NO: 106 and a human light chain constant region, and wherein the heavy chain comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 105 and a human heavy chain constant region.

[0407] In a specific aspect, a host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding a light chain variable region (VL) of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding a heavy chain variable region (VH) of the antibody, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106, and wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 109. In another specific aspect, a host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding a light chain of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding a heavy chain of the antibody, wherein the light chain comprises a light chain variable region comprising the amino acids set forth in SEQ ID NO: 106 and a human light chain constant region, and wherein the heavy chain comprises a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO: 109 and a human heavy chain constant region.

[0408] In a specific aspect, a host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the VL of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding the VH of the antibody, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106, and wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 107. In another specific aspect, a host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the light chain of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding the heavy chain of the antibody, wherein the light chain comprises a VL comprising the amino acid sequence set forth in SEQ ID NO: 106 and a human light chain constant region, and wherein the heavy chain comprises a VH comprising the amino acid sequence set forth in SEQ ID NO: 107 and a human heavy chain constant region.

[0409] In a specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the VL of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding the VH of the antibody, wherein the VL comprises the amino acid sequence set forth in SEQ ID NO: 106, and wherein the VH comprises the amino acid sequence set forth in SEQ ID NO: 108. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the light chain of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding the heavy chain of the antibody, wherein the light chain comprises a light chain variable region set forth in SEQ ID NO: 108 and a human light chain constant region, and wherein the heavy chain comprises a heavy chain variable region nucleotide sequence set forth in SEQ ID NO: 105 and a human heavy chain constant region.

[0410] In a specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the VL of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding the VH of the antibody, wherein the VL comprises the amino acid sequence shown in SEQ ID NO: 111, and wherein the VH comprises the amino acid sequence shown in SEQ ID NO: 110.

[0411] In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the light chain of an antibody that specifically binds to MERTK (e.g., human MERTK) described herein and a nucleotide sequence encoding the heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 120 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 119 and a human heavy chain constant region nucleotide sequence.

[0412] In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the light chain of an antibody that specifically binds to MERTK (e.g., human MERTK) as described herein and a nucleotide sequence encoding the heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 120 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 121 and a human heavy chain constant region nucleotide sequence. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the light chain of an antibody that specifically binds to MERTK (e.g., human MERTK) as described herein and a nucleotide sequence encoding the heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 120 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 122 and a human heavy chain constant region nucleotide sequence. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the light chain of an antibody that specifically binds to MERTK (e.g., human MERTK) described herein and a nucleotide sequence encoding the heavy chain of the antibody, wherein the nucleotide sequence encoding the light chain comprises SEQ ID NO: 124 and a human light chain constant region nucleotide sequence, and wherein the nucleotide sequence encoding the heavy chain comprises SEQ ID NO: 123 and a human heavy chain constant region nucleotide sequence.

[0413] In a specific aspect, the host cell provided herein comprises a first vector and a second vector, wherein the first vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the second vector comprises the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 105, and wherein the light chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a first vector and a second vector, wherein the first vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the second vector comprises the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 107, and wherein the light chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a first vector and a second vector, wherein the first vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody that specifically binds to MERTK (e.g., human MERTK) as described herein, wherein the second vector comprises the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence shown in SEQ ID NO: 108, and wherein the light chain variable region comprises the amino acid sequence shown in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a first vector and a second vector, wherein the first vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody that specifically binds to MERTK (e.g., human MERTK) as described herein, wherein the second vector comprises the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence shown in SEQ ID NO: 109, and wherein the light chain variable region comprises the amino acid sequence shown in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a first vector and a second vector, wherein the first vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK), wherein the second vector comprises the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence shown in SEQ ID NO: 110, and wherein the light chain variable region comprises the amino acid sequence shown in SEQ ID NO: 111. In some embodiments, the first vector comprises a heavy chain constant region and / or the second vector comprises a light chain constant region.

[0414] Alternatively, a single vector can be used that encodes and is capable of expressing both heavy and light chain polypeptides. In such an expression vector, transcription of both genes can be driven by a common promoter, but translation of the mRNA from the first gene can be by a cap-dependent scanning mechanism, while translation of the mRNA from the second gene can be by a cap-independent mechanism, e.g., by IRES.

[0415] In a specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide encoding the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 105, and wherein the light chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide encoding the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 107, and wherein the light chain variable region comprises the amino acid sequence set forth in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide encoding the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence shown in SEQ ID NO: 108, and wherein the light chain variable region comprises the amino acid sequence shown in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide encoding the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence shown in SEQ ID NO: 109, and wherein the light chain variable region comprises the amino acid sequence shown in SEQ ID NO: 106. In another specific aspect, the host cell provided herein comprises a vector, wherein the vector comprises a nucleotide sequence encoding the heavy chain variable region of an antibody described herein that specifically binds to MERTK (e.g., human MERTK) and a nucleotide sequence encoding the light chain variable region of the antibody, wherein the heavy chain variable region comprises the amino acid sequence shown in SEQ ID NO: 110, and wherein the light chain variable region comprises the amino acid sequence shown in SEQ ID NO: 111. In some embodiments, the vector comprises a heavy chain constant region and / or a light chain constant region.

[0416] In a specific embodiment, the host cells described herein (e.g., in vitro host cells) are cultured under conditions where the antibody or antigen-binding fragment thereof is encoded by a polynucleotide sequence contained in the host cell using techniques known in the art. In certain embodiments, the antibody or antigen-binding fragment thereof is isolated or purified from the host cell using techniques known in the art.

[0417] 5.4. Production of Antibody-Drug Conjugates

[0418] In another aspect, provided herein is a method for producing an antibody-drug conjugate described herein in which a linker is not present, the method comprising: (a) directly conjugating a cytotoxic agent to an antibody portion to produce an antibody-drug conjugate; and (b) purifying the antibody-drug conjugate. Examples of methods for producing antibody-drug conjugates are described in Section 6 (e.g., in Example 4).

[0419] In another aspect, provided herein is a method of producing an antibody-drug conjugate described herein wherein the antibody-drug conjugate comprises a linker, the method comprising the following steps in the order described: (a) directly conjugating the linker to the antibody portion to produce a linker-antibody portion; (b) directly conjugating the linker of the linker-antibody portion to a cytotoxic agent to produce an antibody-drug conjugate; and (c) purifying the antibody-drug conjugate.

[0420] In another aspect, provided herein is a method of producing an antibody-drug conjugate described herein wherein the antibody-drug conjugate comprises a linker, the method comprising the following steps in the order described: (a) directly conjugating the linker to a cytotoxic agent to produce a linker-cytotoxic agent portion; (b) directly conjugating the linker of the linker-cytotoxic agent portion to an antibody portion to produce an antibody-drug conjugate; and (c) purifying the antibody-drug conjugate.

[0421] The conjugation and purification steps can be performed by methods known in the art for producing antibody-drug conjugates, such as Beck A et al., (2017) Nat Rev Drug Discov 16: 315-337; Peters C and Brown S, (2015) Biosci Rep 35: art: e00225; McCombs JR and Owen SC (2015) The AAPS Journal 17: 339-351; Jackson DY (2016) Org Process Res Dev 20: 852-866; or the methods described in Olivier KJ and Hurvitz SA, eds., (2016) Antibody-Drug Conjugates: Fundamentals, Drug Development, and Clinical, Wiley. In some embodiments, the drug moiety is conjugated to one chain of the antibody portion (e.g., when the antibody portion is a scFv or when the antibody portion is a multi-chain antibody, such as an immunoglobulin or an antigen-binding fragment thereof (as a tetramer). In other embodiments, the drug moiety is conjugated to two or more chains of the antibody portion (when the antibody portion is a multi-chain antibody, such as an immunoglobulin or an antigen-binding fragment thereof). In a specific embodiment, the drug moiety is conjugated to two identical chains of an immunoglobulin, e.g., a heavy chain or a light chain. In other embodiments, the drug moiety is conjugated to all chains of the antibody portion (when the antibody portion is a multi-chain antibody, such as an immunoglobulin or an antigen-binding fragment thereof). In a specific embodiment, the antibody-drug conjugates described herein are purified by chromatography. In another specific embodiment, the antibody-drug conjugates described herein are purified by centrifugation.By way of example and not limitation, conjugation chemistries that can be used to generate antibody-drug conjugates can be thiol plus maleimide, thiol plus autohydrolyzable maleimide, thiol plus phenyloxadiazole sulfone, oxime linkage, alkoxyamine-to-keto reaction, strain-induced azide-alkynyl cycloaddition (SPAAC), copper-free click chemistry, cysteine ​​oxidation to formylglycine, hydrazine-iso-Pictet-Spengler (HIPS) linkage, linkage of a γ-amide group from a glutamine residue to a primary amine, linkage of LPETG to a primary amine of a polyglycine motif, maleimide plus 6-thiofucose, fucose-specific conjugation of hydrazide, periodate oxidation (aldehyde) plus amino-oxy-payload, strain-induced alkynyl-azide cycloaddition, C2-keto-galactose moiety oximation (C2-keto-galactose moiety oximation) oximation), site-selective aldehyde oxidation plus oxime ligation, oxime ligation NH2 plus indol-yl 5-difluoro-2,4-dinitrobenzene derivatives, thiols plus bis-sulfones, thiols plus dibromomaleimide, thiols plus maleimide followed by pH 9.2 treatment (45°C, 48 hours), or thiols plus arylpropionitrile (see Beck A et al., (2017) Nat Rev Drug Discov 16: 315-337).

[0422] The anti-MERTK antibodies or antigen-binding fragments thereof described herein can be generated as described in 5.3 below. In a specific embodiment, the anti-MERTK antibodies or antigen-binding fragments thereof described herein are engineered or modified by methods known in the art to facilitate conjugation to a drug moiety, specifically to facilitate site-specific conjugation to a drug moiety, for example, by methods described in Beck A et al., (2017) Nat Rev Drug Discov 16:315-337; Peters C and Brown S, (2015) Biosci Rep 35:art:e00225; McCombs JR and Owen SC (2015) The AAPS Journal 17:339-351; Jackson DY (2016) Org Process Res Dev 20:852-866; or Olivier KJ and Hurvitz SA, eds., (2016) Antibody-Drug Conjugates: Fundamentals, Drug Development, and Clinical, Wiley. Non-limiting exemplary methods that can be used to engineer or modify an anti-MERTK antibody or antigen-binding fragment thereof (see Beck A et al., (2017) Nat Rev Drug Discov 16: 315-337) to facilitate conjugation to a drug moiety include adding one or more additional cysteines or selenocysteine ​​residues, non-natural amino acid engineering, adding one or more amino acid tags recognizable by certain enzymes that can facilitate conjugation, glycan remodeling, adding an amino-terminal serine, and natural cysteine ​​bridging.

[0423] The linker and cytotoxic agent may be produced by any method known in the art for linkers and cytotoxic agents, respectively.

[0424] 5.5. Pharmaceutical Compositions

[0425] Provided herein are pharmaceutical compositions comprising (a) an anti-MERTK antibody (e.g., a humanized antibody) or an antigen-binding fragment thereof described herein and (b) a pharmaceutically acceptable carrier. In a specific embodiment, the antibody or antigen-binding fragment thereof is purified. In a specific embodiment, the antibody or antigen-binding fragment thereof is present in the pharmaceutical composition in a therapeutically effective amount. In a specific embodiment, the pharmaceutical composition comprises an anti-MERTK antibody or antigen-binding fragment thereof comprising a VH comprising the amino acid sequence shown in SEQ ID NO: 105 and a VL comprising the amino acid sequence shown in SEQ ID NO: 106 (e.g., antibody z10). In another specific embodiment, the pharmaceutical composition comprises an anti-MERTK antibody or antigen-binding fragment thereof comprising a VH comprising the amino acid sequence shown in SEQ ID NO: 107 and a VL comprising the amino acid sequence shown in SEQ ID NO: 106 (e.g., antibody z11). In another specific embodiment, the pharmaceutical composition comprises an anti-MERTK antibody or an antigen-binding fragment thereof, which comprises a VH comprising the amino acid sequence of SEQ ID NO: 108 and a VL comprising the amino acid sequence of SEQ ID NO: 106 (e.g., antibody z13). In another specific embodiment, the pharmaceutical composition comprises an anti-MERTK antibody or an antigen-binding fragment thereof, which comprises a VH comprising the amino acid sequence of SEQ ID NO: 108 and a VL comprising the amino acid sequence of SEQ ID NO: 106.

[0426] Also provided herein is a pharmaceutical composition comprising (a) a chimeric anti-MERTK antibody or antigen-binding fragment thereof described herein and (b) a pharmaceutically acceptable carrier. In a specific embodiment, the antibody or antigen-binding fragment thereof is purified. In a specific embodiment, the antibody or antigen-binding fragment thereof is present in the pharmaceutical composition in a therapeutically effective amount. In a specific embodiment, the pharmaceutical composition comprises a chimeric antibody or antigen-binding fragment thereof containing a VH comprising the amino acid sequence shown in SEQ ID NO: 110 and a VL comprising the amino acid sequence shown in SEQ ID NO: 111 (e.g., antibody xAb). Also provided herein is a pharmaceutical composition comprising a polynucleotide or vector described herein and a pharmaceutically acceptable carrier.

[0427] Also provided herein is a pharmaceutical composition comprising (a) an antibody-drug conjugate described herein and (b) a pharmaceutically acceptable carrier. In a specific embodiment, the antibody-drug conjugate is present in the pharmaceutical composition in a therapeutically effective amount.

[0428] Also provided herein are pharmaceutical compositions comprising a bispecific antibody that binds to MERTK (e.g., human MERTK) and another target antigen (e.g., as described herein) and (b) a pharmaceutically acceptable carrier. In a specific embodiment, the bispecific antibody is purified. In a specific embodiment, the bispecific antibody is present in the pharmaceutical composition in a therapeutically effective amount.

[0429] In a specific embodiment, the population of antibody-drug conjugates contained in the pharmaceutical composition has a drug-antibody ratio (DAR) between 1 and 20. DAR is the average number of cytotoxic agents conjugated to the antibody. In another specific embodiment, the population of antibody-drug conjugates contained in the pharmaceutical composition has a DAR between 1 and 15. In another specific embodiment, the population of antibody-drug conjugates contained in the pharmaceutical composition has a DAR between 1 and 12. In another specific embodiment, the population of antibody-drug conjugates contained in the pharmaceutical composition has a DAR between 1 and 8. In another specific embodiment, the population of antibody-drug conjugates contained in the pharmaceutical composition has a DAR between 3 and 5. In another specific embodiment, the population of antibody-drug conjugates contained in the pharmaceutical composition has a DAR between 3.5 and 4.

[0430] Acceptable carriers, which may be excipients or stabilizers, are nontoxic to recipients at the dosages and concentrations employed and include, but are not limited to, buffers such as phosphates, citrates, and other organic acids; antioxidants including ascorbic acid and methionine; preservatives (such as octadecyldimethylbenzyl ammonium chloride; hexamethonium chloride; benzalkonium chloride, benzethonium chloride; phenol, butyl alcohol, or benzyl alcohol; alkyl parabens such as methyl or propyl paraben; catechol; resorcinol; cyclohexanol; 3-pentanol; and m-cresol); low molecular weight (less than about 10 residues) polypeptides; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers, such as polyvinylpyrrolidone; amino acids, such as glycine, glutamine, asparagine, histidine, arginine, or lysine; monosaccharides, disaccharides, and other carbohydrates, including glucose, mannose, or dextrins; chelating agents, such as EDTA; sugars, such as sucrose, mannitol, trehalose, or sorbitol; salt-forming counterions, such as sodium; metal complexes (e.g., Zn-protein complexes); and / or nonionic surfactants, such as TWEEN®. TM 、PLURONICS TM Or polyethylene glycol (PEG).

[0431] In specific embodiments, the pharmaceutical composition comprises an anti-MERTK antibody or antigen-binding fragment thereof described herein and optionally one or more other prophylactic or therapeutic agents in a pharmaceutically acceptable carrier. In specific embodiments, the pharmaceutical composition comprises an effective amount of an anti-MERTK antibody or antigen-binding fragment thereof described herein and optionally one or more other prophylactic or therapeutic agents in a pharmaceutically acceptable carrier. In specific embodiments, the pharmaceutical compositions and / or antibodies or antigen-binding fragments thereof described herein can be combined with a therapeutically effective amount of any other therapeutic agent described herein (see Section 5.4.2 below).

[0432] In a specific embodiment, the pharmaceutical composition comprises an antibody-drug conjugate described herein and optionally one or more other prophylactic or therapeutic agents in a pharmaceutically acceptable carrier. In a specific embodiment, the pharmaceutical composition comprises an effective amount of an antibody-drug conjugate described herein and optionally one or more other prophylactic or therapeutic agents in a pharmaceutically acceptable carrier. In a specific embodiment, the pharmaceutical composition and / or antibody-drug conjugate described herein can be combined with a therapeutically effective amount of any other therapeutic agent described herein (see Section 5.4.2 below).

[0433] In some embodiments, the antibody-drug conjugate is the only active ingredient included in the pharmaceutical composition.

[0434] In some embodiments, the anti-MERTK antibody is the only active ingredient included in the pharmaceutical composition. In a specific embodiment, the humanized antibody or antigen-binding fragment thereof described herein is the only active ingredient included in the pharmaceutical composition. In another embodiment, a polynucleotide or vector encoding an antibody or antigen-binding fragment thereof is the only active ingredient included in the pharmaceutical composition.

[0435] The pharmaceutical compositions described herein can be used to treat cancer.The pharmaceutical compositions can be formulated for any route of administration (eg, parenteral, topical, intratumoral, etc.).

[0436] The drug-usable carriers used in parenteral preparations include aqueous vehicles, non-aqueous vehicles, antimicrobial agents, isotonic agents, buffers, antioxidants, local anesthetics, suspending agents and dispersants, emulsifiers, multivalent...

Claims

1. An antibody or antigen-binding fragment thereof that specifically binds to human Mer tyrosine kinase (MERTK), wherein the antibody or antigen-binding fragment comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence shown in SEQ ID NO: 105 and the VL comprises the amino acid sequence shown in SEQ ID NO:

106.

2. An antibody or antigen-binding fragment thereof that specifically binds to human MERTK, wherein the antibody or antigen-binding fragment comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence shown in SEQ ID NO: 107 or 108 and the VL comprises the amino acid sequence shown in SEQ ID NO:

106.

3. An antibody or antigen-binding fragment thereof that specifically binds to human MERTK, wherein the antibody or antigen-binding fragment comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the sequence shown in SEQ ID NO: 108 or 109 and the VL comprises the amino acid sequence shown in SEQ ID NO:

106.

4. An antibody or antigen-binding fragment thereof that specifically binds to human MERTK, wherein the antibody or antigen-binding fragment comprises a heavy chain variable region (VH) and a light chain variable region (VL), wherein the VH comprises the amino acid sequence of the sequence shown in SEQ ID NO: 110 and the VL comprises the amino acid sequence shown in SEQ ID NO:

120. 5 . The antibody or antigen-binding fragment thereof according to claim 1 , wherein the antibody is a monoclonal antibody. 6 . The antibody or antigen-binding fragment thereof according to any one of claims 1 to 5 , wherein the antibody is an immunoglobulin comprising two identical heavy chains and two identical light chains. 7 . The antibody or antigen-binding fragment thereof according to any one of claims 1 to 6 , wherein the antibody comprises heavy and light chain constant regions of human origin.

8. The antibody or antigen-binding fragment thereof according to any one of claims 1 to 7, wherein the antibody is IgG. 9 . The antibody or antigen-binding fragment thereof according to claim 1 , wherein the antibody comprises a portion of human-derived heavy and light chain constant regions.

10. The antibody or antigen-binding fragment thereof according to any one of claims 1 to 9, wherein the antigen-binding fragment is a Fab or F(ab')2 fragment.

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