Treatment method for acute myeloid leukemia with anti-ILT3 antibody

Abstract

The present disclosure relates to a method of treating cancer in a subject confirmed to have acute myeloid leukemia (AML), comprising administering to the patient an anti-ILT3 antigen binding protein or antigen binding fragment once every three weeks (Q3W).

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 226,754, filed July 28, 2021, the entire contents of which are incorporated herein by reference.

[0002] REFERENCE TO ELECTRONICALLY SUBMITTED SEQUENCE LISTING This application contains a Sequence Listing that has been submitted electronically in XML format, which is incorporated by reference in its entirety. The XML file, created on July 19, 2022, has the name 25276-WO-PCT-SEQLIST-19JUL2022.XML and is 262,144 bytes in size on disk.

[0003] The present disclosure relates to a method for treating cancer in a subject, the method comprising administering to the subject an anti-ILT3 antigen binding protein, including an antibody or antigen-binding fragment. [Background technology]

[0004] Acute myeloid leukemia (AML) is a heterogeneous hematologic tumor characterized by the clonal proliferation of myeloblasts in bone marrow, peripheral blood, and potentially other tissues [Dohner, H., et al. 2015]. AML is the most common form of adult acute leukemia in the United States [Carter, JL, et al. 2020], with a median age at initial diagnosis of approximately 68 years [Shallis, RM, et al. 2019]. In 2021, the estimated number of new AML cases in the United States is approximately 20,240, and the estimated number of deaths from AML is approximately 11,400 [Siegel, RL, et al. 2021]. Despite an improved understanding of the underlying biology of AML and the development of several new therapies, the 5-year relative survival rate remains low, approximately 26% based on 2021 SEER estimates [American Cancer Society 2021].

[0005] Immunoglobulin-like transcript 3 (ILT3), also known as CD85k and leukocyte immunoglobulin-like receptor subfamily B member 4 (LILRB4) and leukocyte immunoglobulin-like receptor 5 (LIR-5), is a type I membrane protein containing a cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM) motif and is involved in the downregulation of immune responses (Cella et al., J Exp Med. 185(10):1743-51(1997); Samaridis et al., Eur J Immunol. 27(3):660-665(1997)). Expression of ILT3 is elevated in tolerogenic dendritic cells. The gene is a member of the leukocyte immunoglobulin-like receptor (LIR) family and is found in a gene cluster in chromosome region 19q13.4. The encoded protein belongs to the subfamily B class of LIR receptors, which contains two or four extracellular immunoglobulin domains, one transmembrane domain, and two to four ITIMs. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Cella et al., J Exp Med. 185(10):1743-51(1997) [Non-Patent Document 2] Samaridis et al., Eur J Immunol. 27(3):660-665(1997) Summary of the Invention [Problem to be solved by the invention]

[0007] ILT3 expression has been reported in dendritic cells, monocytic myeloid cells, macrophages, precursor mast cells, endothelial cells, and osteoclasts. Expression of ILT3 in myeloid and dendritic cells is thought to be involved in immunosuppression and antigen-specific immune tolerance, and contributes to the immunosuppressive tumor microenvironment in various human cancers (reviewed in Kang, 2016; [Kang, X., et al. 2016]).

[0008] Further evaluation by Li et al. [Li Z. et al. 2020] suggested that the intracellular ITIM domain of activated ILT3 recruits SHP-2, which activates NFκB. NFκB activation regulates downstream effectors such as uPAR and ARG1, inhibiting T cell proliferation and AML cell infiltration into tissues. Gui et al. developed a humanized antibody against ILT3h128-3. Disrupting ILT3 / APOE interaction using h128-3 may reverse T cell suppression in mouse models and block the development of AML [Gui, X., et al. 2019].

[0009] The ILT3 pathway may be a key regulatory element involved in the induction and maintenance of tumor immune tolerance. ILT3 inhibitors may offer an innovative and tractable approach to treat AML. [Means for solving the problem]

[0010] In a first aspect, the present disclosure provides a method of treating acute myeloid leukemia (AML) in a subject, the method comprising administering to the subject a pharmaceutical composition comprising a therapeutically effective dose of an anti-ILT3 antigen binding protein or antigen binding fragment and a pharma- ceutical acceptable excipient.

[0011] In some embodiments of the first aspect, the subject has a confirmed diagnosis of acute myelomonocytic leukemia or acute monoblastic / monocytic leukemia. In some embodiments, the subject has confirmed refractory or relapsed AML with ≧5% blasts in bone marrow or peripheral blood following chemotherapy treatment or non-ILT-3 targeted therapy. In some embodiments, the subject is human.

[0012] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment is an anti-ILT3 antibody or antigen binding fragment. In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises a heavy chain (HC) and a heavy chain variable domain (V H ) comprises a heavy chain complementarity determining region (HC-CDR) 3 having an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 42, 50, 58, 66, 74, 82, 90 and 98, or having an amino acid sequence having 3, 2 or 1 difference from an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 42, 50, 58, 66, 74, 82, 90 and 98.

[0013] In some embodiments, the anti-ILT3 antibody or antigen-binding fragment comprises: (a) a variable domain (V) comprising: a variable domain complementarity determining region (HC-CDR)1 having the amino acid sequence set forth in SEQ ID NO: 10, 40, 48, 56, 64, 72, 80, 88, or 96; a HC-CDR2 having the amino acid sequence set forth in SEQ ID NO: 11, 41, 48, 57, 64, 73, 81, 89, or 97; and a HC-CDR3 having the amino acid sequence set forth in SEQ ID NO: 16, 42, 50, 58, 66, 74, 82, 90, or 98; and a variant thereof, wherein one or more of said HC-CDRs have one, two or three amino acid substitutions, additions, deletions, or a combination thereof. Hand (b) a variable domain complementarity determining region (LC-CDR) 1 having the amino acid sequence set forth in SEQ ID NO: 20, 43, 51, 59, 67, 75, 83, 91, or 99; a LC-CDR2 having the amino acid sequence set forth in SEQ ID NO: 36, 44, 52, 60, 68, 76, 84, 92, or 100; and a LC-CDR3 having the amino acid sequence set forth in SEQ ID NO: 37, 45, 53, 61, 69, 77, 85, 93, or 101; and a light chain (LC) having a variable domain (VL) in which one or more of said LC-CDRs have one, two or three amino acid substitutions, additions, deletions, or a variant thereof having a combination thereof.

[0014] In some embodiments, (a) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 12, 13, or 14; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; and (b) the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 27, 28, 29, 30, 31, 32, 33, 34, or 35; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0015] In some embodiments, (a) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; and the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; and (b) the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 34; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0016] In some embodiments, the V H is a human V H 1. V H 2. V H 3. V H 4. V H 5 and V H6, and variants thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or combinations thereof; κ 1. V κ 2. V κ 3. V κ 4. V κ 5. V κ 6. V λ 1. V λ 2. V λ 3. V λ 4. V λ 5. V λ 6. V λ 7. V λ 8. V λ 9 and V λ 10, and variants thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions, or combinations thereof.

[0017] In some embodiments, the antibody comprises a HC having a human IgG1, IgG2, IgG3, or IgG4 HC constant domain, or a variant thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions, or a combination thereof compared to the amino acid sequence of the native IgG1, IgG2, IgG3, or IgG4 isotype constant domain.

[0018] In some embodiments, the antibody comprises a LC having a human κ or λ LC constant domain, or a variant thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions, or a combination thereof compared to the amino acid sequence of the native human κ or λ light chain constant domain.

[0019] In some embodiments, the antibody comprises: (i) a human V H 1. V H 2. V H 3. V H 4. V H 5 and V HV having a framework selected from 6 H and a human IgG1 or IgG4 HC constant domain, or a variant thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions, or a combination thereof compared to the amino acid sequence of the native IgG1 or IgG4 isotype HC constant domain; and (ii) a human V κ 1. V κ 2. V κ 3. V κ 4. V κ 5. V κ 6. V λ 1. V λ 2. V λ 3. V λ 4. V λ 5. V λ 6. V λ 7. V λ 8. V λ 9 and V λ 10, or a variant thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or a combination thereof compared to the amino acid sequence of the native human κ or λLC constant domain.

[0020] In some embodiments, the antibody or antigen-binding fragment has the amino acid sequence set forth in SEQ ID NO:8 and SEQ ID NO:9, respectively; SEQ ID NO:38 and SEQ ID NO:39, respectively; SEQ ID NO:46 and SEQ ID NO:47, respectively; SEQ ID NO:54 and SEQ ID NO:55, respectively; SEQ ID NO:62 and SEQ ID NO:63, respectively; SEQ ID NO:70 and SEQ ID NO:71, respectively; SEQ ID NO:78 and SEQ ID NO:79, respectively; SEQ ID NO:86 and SEQ ID NO:87, respectively; or SEQ ID NO:94 and SEQ ID NO:95, respectively. H and V L Includes.

[0021] In some embodiments, the antibody or antigen-binding fragment has an amino acid sequence set forth in SEQ ID NO: 110, 111, 112, 116, 117, or 118. Hand V having the amino acid sequence set forth in SEQ ID NO: 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, or 134. L Includes.

[0022] In some embodiments, the antibody or antigen-binding fragment has the amino acid sequence set forth in SEQ ID NO:111. H and V having the amino acid sequence set forth in SEQ ID NO: 133 L Includes.

[0023] In some embodiments, the antibody comprises a heavy chain (HC) constant domain comprising the amino acid sequence set forth in SEQ ID NO: 2, 3, 4, 5, or 6.

[0024] In some embodiments, the antibody comprises a light chain (LC) constant domain comprising the amino acid sequence set forth in SEQ ID NO:7.

[0025] In some embodiments, the antibody comprises a heavy chain (HC) comprising the amino acid sequence of SEQ ID NO: 135, 136, 137, 141, 142, 143, 160, 161, 162, 163, 167, 168, 169, 170, 171, 175, 176, 177, 178, 179, 180, 184, 185, or 186.

[0026] In some embodiments, the antibody comprises a light chain (LC) comprising the amino acid sequence set forth in SEQ ID NO: 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, or 159.

[0027] In some embodiments, the antibody comprises a heavy chain (HC) comprising the amino acid sequence set forth in SEQ ID NO: 136 and a light chain (LC) comprising the amino acid sequence set forth in SEQ ID NO: 158, and variants thereof wherein the HC lacks a C-terminal lysine residue or a C-terminal glycine-lysine residue.

[0028] In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is about 7.5 mg to about 2250 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is selected from the group consisting of 7.5 mg; 25 mg; 75 mg; 225 mg; 750 mg; and 2250 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is 7.5 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is 25 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is 75 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is 225 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is 750 mg. In some embodiments, the therapeutically effective amount of the anti-ILT3 antigen binding protein or antigen binding fragment is 2250 mg.

[0029] In some embodiments, the anti-ILT3 antibody or antigen-binding fragment is administered once every three weeks (Q3W) on a 21 day cycle.

[0030] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDRs) 1, 2 and 3 and light chain variable domain complementarity determining regions (LC-CDRs) 1, 2 and 3, wherein (a) the HC-CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 12; the HC-CDR3 comprises the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 36. (b) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 32; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37; (c) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10 said HC-CDR1 having the amino acid sequence set forth in SEQ ID NO: 10; said HC-CDR2 having the amino acid sequence set forth in SEQ ID NO: 13; said HC-CDR3 having the amino acid sequence set forth in SEQ ID NO: 16; said LC-CDR1 having the amino acid sequence set forth in SEQ ID NO: 33; said LC-CDR2 having the amino acid sequence set forth in SEQ ID NO: 36; said LC-CDR3 having the amino acid sequence set forth in SEQ ID NO: 37; (d) said HC-CDR1 having the amino acid sequence set forth in SEQ ID NO: 10; said HC-CDR2 having the amino acid sequence set forth in SEQ ID NO: 13; and said HC-CDR3 having the amino acid sequence set forth in SEQ ID NO: 16 wherein the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 34; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37; or (e) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 12; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 35; and the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36;The LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0031] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDRs) 1, 2 and 3 and light chain variable domain complementarity determining regions (LC-CDRs) 1, 2 and 3, wherein the HC-CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 12; the HC-CDR3 comprises the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 31; the LC-CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 comprises the amino acid sequence set forth in SEQ ID NO: 37.

[0032] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDRs) 1, 2 and 3 and light chain variable domain complementarity determining regions (LC-CDRs) 1, 2 and 3, wherein the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 32; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0033] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDRs) 1, 2 and 3 and light chain variable domain complementarity determining regions (LC-CDRs) 1, 2 and 3, wherein the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 14; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 33; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0034] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDRs) 1, 2 and 3 and light chain variable domain complementarity determining regions (LC-CDRs) 1, 2 and 3, wherein the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 34; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0035] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDRs) 1, 2 and 3 and light chain variable domain complementarity determining regions (LC-CDRs) 1, 2 and 3, wherein the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 12; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 35; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37.

[0036] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises (a) a heavy chain of SEQ ID NO: 140 and a light chain of SEQ ID NO: 149; (b) a heavy chain of SEQ ID NO: 146 and a light chain of SEQ ID NO: 151; (c) a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 150; (d) a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 163; or (e) a heavy chain of SEQ ID NO: 144 and a light chain of SEQ ID NO: 150.

[0037] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises a heavy chain of SEQ ID NO: 140 and a light chain of SEQ ID NO: 149. In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises a heavy chain of SEQ ID NO: 146 and a light chain of SEQ ID NO: 151. In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 150.

[0038] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 163. In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment comprises a heavy chain of SEQ ID NO: 144 and a light chain of SEQ ID NO: 150.

[0039] In a second aspect, the disclosure provides a pharmaceutical composition comprising 0.02 mg to 2250 mg of an anti-ILT3 antigen binding protein or antigen binding fragment and a pharma- ceutically acceptable excipient for use in a method according to any one of the above aspects and embodiments.

[0040] In another aspect, the disclosure provides for the use of a pharmaceutical composition comprising 0.02 mg to 2250 mg of an anti-ILT3 antigen binding protein or antigen binding fragment and a pharma- ceutically acceptable excipient in the manufacture of a medicament for use in any of the methods disclosed herein.

[0041] The above summary of the technology is non-limiting; other features and advantages of the technology will become apparent from the following detailed description and claims. [Brief description of the drawings]

[0042] [Figure 1] Figure 1 shows dot plots quantifying and comparing the percentage of 10 clusters of myeloid cell phenotypes between 52B8 and hIgG4 isotype treatment. Filled circles represent cells treated with antibody 52B8 and open circles represent cells treated with control antibody (human IgG4). Cluster 1 represents the monocytic myeloid cell phenotype and cluster 4 represents the tumor blast phenotype. [Figure 2A] Figure 1 shows graphs of mean fluorescence and standard error of the mean (SEM) for MV-4-11 luc cells inoculated into humanized mice and treated with anti-ILT3 antibody 52B8 or control human IgG4 antibody (hIgG4) and then harvested from bone marrow 7, 14, 21, 28 and 35 days post-inoculation. Filled circles represent cells treated with 52B8 at 10 mpk ip QW and open circles represent cells treated with hIgG4. [Figure 2B] FIG. 1 shows dot plots of the percentage of MV-4-11 luc cells in bone marrow cells from 52B8 and control antibody treated groups. [Figure 3A] FIG. 1 shows a bar graph of IFN-γ expression in human CD8+ T cells from two different human donors following in vitro treatment with control antibody (10 μg / mL hIgG4) or various concentrations of 52B8 antibody (10 μg / mL, 1 μg / mL, and 0.1 μg / mL). [Figure 3B] FIG. 1 shows a bar graph of IFN-γ expression in human CD8+ T cells from two different human donors following in vitro treatment with control antibody (10 μg / mL hIgG4) or various concentrations of 52B8 antibody (10 μg / mL, 1 μg / mL, and 0.1 μg / mL). [Figure 4] FIG. 1 is a schematic of the clinical trial design for treating AML patients with multiple doses of an anti-ILT3 antibody. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Definitions and Abbreviations As used throughout the specification and appended claims, the following abbreviations apply:

[0044] ADA: Anti-drug antibodies AE: Adverse event ALT: Alanine aminotransferase AML: Acute myeloid leukemia ANC: absolute neutrophil count APOE: Apolipoprotein E AST: Aspartate aminotransferase ATD: Accelerated titration design BCG: bacillus Calmette-Guerin BLI: Bioluminescence Imaging C1D1: Cycle 1, Day 1 CBC: complete blood count CDR: Complementarity determining region CDRH: Complementarity determining region in the heavy chain variable domain CDRL* Complementarity determining region in the light chain variable domain CNS: central nervous system CONSORT: Consolidated Standards for Reporting Clinical Trials CL: Clearance CrCl: Creatinine clearance CR: Complete remission CRF: Case Report Form CRi: complete remission without hematologic recovery CSF: cerebrospinal fluid CTCAE5.0: Common Terminology Criteria for Adverse Events, version 5.0 DILI: Drug-induced liver injury DL: Dose level DLT: Dose-limiting toxicity DNA: Deoxyribonucleic acid ECI: Notable Events eCRF: Electronic Case Report Form ECOG: Eastern Cooperative Oncology Group ELN: European Leukemia Network FR: Framework region GCP: Standards for conducting clinical trials of pharmaceuticals G-CSF: Granulocyte colony stimulating factor GFR: glomerular filtration rate GM-CSF: Granulocyte-macrophage colony-stimulating factor GV H D: Graft-versus-host disease HBsAg: Hepatitis B surface antigen HBV: Hepatitis B virus HCV: Hepatitis C virus HIV: Human immunodeficiency virus IDH: Isocitrate dehydrogenase Ig: immunoglobulin ILT3: immunoglobulin-like transcript 3 IP: intraperitoneal IV: Intravenous IVRS: Interactive Voice Response System IWRS: Integrated Web Response System LILRB: Leukocyte immunoglobulin-like receptor subfamily B luc: luciferase mAb: Monoclonal antibody MDSC: Myeloid-derived suppressor cells mpk: milligrams per kilogram MLFS: Morphologically free of leukemic cells MTD: maximum tolerated dose mTPI: Modified Toxicity Probability Interval NCI: National Cancer Institute NYHA: New York Heart Association OR: Objective response OTC: Over-the-counter PK: Pharmacokinetics PR: partial response Q3W: Once every three weeks RNA: Ribonucleic acid RP2D: Phase 2 recommended dose R / R: Relapsed / Refractory SAE: serious adverse event SCT: Stem cell transplant SEM: Standard error of the mean SGOT: Serum glutamic oxaloacetic transaminase SGPT: Serum glutamic-pyruvic transaminase sILT3: soluble ILT3; part or all of the ILT3 extracellular domain that is not membrane-bound TLS: Tumor lysis syndrome t1 / 2: half-life ULN: upper limit of normality V H : immunoglobulin heavy chain variable region or domain VL; immunoglobulin light chain variable region or domain WBC: white blood cell WHO: World Health Organization WOCBP: Women / women of childbearing potential.

[0045] In order to facilitate an understanding of the present invention, certain technical and scientific terms are specifically defined below. Unless specifically defined elsewhere in this document, all other technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs.

[0046] The word "or" indicates either or both possibilities, unless the context clearly dictates one of the possibilities indicated. In some cases, "and / or" is used to emphasize either or both possibilities.

[0047] As used herein, the articles a and an refer to one or to more than one (i.e., at least one) of the grammatical object of the article. As an example, "an element" means one element or more than one element. Furthermore, use of the term "including" as well as other forms such as "include," "includes," and "included" are not limiting.

[0048] The term "about," when modifying, for example, an amount (e.g., mg) of a substance or composition, or the value of a parameter characterizing a step in a method, refers to variations in the quantity that may occur, for example, due to typical measuring, handling, and sampling procedures involved in the manufacture, characterization, and / or use of the substance or composition; due to inadvertent errors in these procedures; due to differences in the manufacture, source, or purity of ingredients used in the manufacture or use of the composition or in the performance of the procedure. In certain embodiments, "about" can mean a variation of ±10%.

[0049] As used herein, the term "comprising" can include the embodiments "consisting of" and "consisting essentially of." As used herein, the terms "comprise(s), "include(s), "having," "has," "may," "contain(s)," and variations thereof, are intended to be open-ended transitional phrases, terms, or words that require the presence of the recited components / steps and permit the presence of other components / steps. However, such descriptions should also be construed as describing the composition or process as "consisting of" and "consisting essentially of" the recited components, thereby allowing for only the specified components or compounds to be present along with an acceptable carrier or fluid, and excluding other components or compounds.

[0050] As used throughout the specification and claims, "consists essentially of" and variations such as "consist essentially of" or "consisting essentially of" are intended to indicate the inclusion of the recited element or group of elements, and the optional inclusion of other elements of similar or different nature to the recited elements, that do not substantially alter the basic or novel properties of the specified administration method, method, or composition. As a non-limiting example, an anti-ILT3 antigen binding fragment consisting essentially of a recited amino acid sequence may also contain one or more amino acids that contain a substitution of one or more amino acid residues that does not substantially affect the properties of the binding compound.

[0051] "Administration" and "treatment", as they apply to an animal, human, experimental subject, cell, tissue, organ, or bodily fluid, refer to the contact of an exogenous pharmaceutical, therapeutic, diagnostic, or composition with an animal, human, subject, cell, tissue, organ, or bodily fluid. As used herein, treating or treating acute myeloid leukemia means administering an anti-ILT3 antigen binding protein (e.g., antibody) or antigen binding fragment to a subject with acute myeloid leukemia to achieve at least one positive therapeutic effect, e.g., a reduction in the number of cancer cells, a reduction in tumor size, a decrease in the rate of cancer cell invasion into peripheral organs, or a decrease in the rate of tumor metastasis or tumor growth. "Treatment" may include one or more of the following: inducing / increasing an anti-tumor immune response; reducing the number of one or more AML biomarkers; halting or slowing the growth of a tumor or hematological cancer or the progression of an ILT-3 associated disease; improving or arresting clinical symptoms of an ILT-3 associated disease; reducing the severity or duration of clinical symptoms of an ILT-3 associated disease, such as cancer; extending patient survival compared to expected survival of a similar untreated patient; and inducing complete or partial remission of the cancerous condition or other ILT-3 associated disease.

[0052] Positive therapeutic effects on cancer can be measured in several ways (see WA Weber, J. Nucl. Med. 50:1S-10S(2009)). For example, with respect to tumor growth inhibition, according to NCI criteria, T / C≦42% is the minimum level of antitumor activity. T / C<10% is considered a high level of antitumor activity, where T / C(%)=median treated tumor volume / median control tumor volume×100. In some embodiments, the treatment achieved by the therapeutically effective amount is either progression-free survival (PFS), disease-free survival (DFS) or overall survival (OS). PFS, also known as "tumor progression-free time", refers to the length of time that the cancer does not grow during and after treatment, including the amount of time that the patient experiences a complete or partial response, and the amount of time that the patient experiences stable disease. DFS refers to the length of time that the patient remains disease-free during and after treatment. OS refers to an increase in life expectancy compared to an untreated or untreated individual or patient. The therapeutic methods, compositions and use embodiments of the present invention may not be effective in achieving a positive therapeutic effect in every patient, but should do so in a statistically significant number of subjects as determined by any statistical test known in the art, e.g., Student's t-test, Chi-square test, Mann-Whitney U test. A positive therapeutic effect in leukemias such as AML may include measuring a reduction in the number of AML cells in bone marrow samples. Detection of AML cells may be achieved using flow cytometry methods to identify cellular biomarkers, detection of RNA transcripts associated with AML cells.

[0053] The terms "effective amount," "therapeutically effective amount," and "therapeutically effective dose" refer to an amount of an anti-ILT3 antigen binding protein or antigen binding fragment of the invention (e.g., an anti-ILT3 antibody) that, when administered alone or in combination with an additional therapeutic / prophylactic agent to a cell, tissue, or subject, is effective to prevent or cause a measurable improvement in one or more symptoms of the disease or condition being treated, such as a disease or condition associated with AML as disclosed herein. An effective dose further refers to an amount of an anti-ILT3 antigen binding protein or antigen binding fragment that is sufficient, alone or in combination with another compound, to result in at least partial prevention or amelioration of the symptoms of the disease or condition being treated.

[0054] The antigen binding protein or antigen binding proteins disclosed herein can be administered once or according to a dosing regimen in which multiple doses are administered at varying intervals over a given period of time. For example, doses can be administered once, twice, three times, or four times per day. Doses can be administered until a desired therapeutic effect is achieved or indefinitely to maintain a desired therapeutic effect. A suitable dosing regimen for a compound or compounds disclosed herein will depend on the pharmacokinetic properties of the compound or compounds, such as absorption, distribution, and half-life, as can be determined by one of skill in the art. Furthermore, a suitable dosing regimen for a compound or compounds disclosed herein (including the period of administration of such a regimen) will depend on factors within the knowledge and experience of the skilled artisan, such as the disease or condition being treated, the severity of the disease or condition being treated, the age and health of the subject being treated, the medical history of the subject being treated, the nature of any concurrent therapy, the desired therapeutic effect, and the like. Moreover, it will be apparent to one of skill in the art that it may be necessary to adjust a suitable dosing regimen in light of an individual subject's response to the regimen or if an individual subject requires modification over time. A typical daily dose can vary depending on the particular route of administration selected.

[0055] The term "subject" (alternatively referred to herein as a "patient" or "individual") refers to a mammal (e.g., rat, mouse, dog, cat, rabbit), most preferably a human, that can be treated with the methods and compositions of the present invention. In some embodiments, the subject is an adult subject. In other embodiments, the subject is a pediatric subject.

[0056] "Biologic agent" or "biological therapeutic agent" refers to a biological molecule, such as an antibody or a fusion protein, that blocks ligand / receptor signaling in any biological pathway that supports tumor maintenance and / or growth or suppresses anti-tumor immune responses. "Biologic therapy" or "biological therapy" refers to cancer treatment using proteins.

[0057] A "targeted agent" or "targeted therapeutic agent" refers to a therapeutic agent (either a small molecule or protein) that affects a specific protein species or class of proteins associated with the growth or spread of tumor cells within a patient's body.

[0058] "Systemic therapy" refers to cancer treatments that use therapeutic agents injected into a patient's bloodstream to affect cells throughout the patient's body, including chemotherapy, biological therapy, and targeted therapy.

[0059] "Chemotherapy" refers to anti-cancer treatment using one or more "chemotherapeutic agents." "Chemotherapeutic agents" are drugs used to treat AML, such as, but not limited to, cytarabine (also called cytosine arabinoside or ara-C); anthracyclines, such as daunorubicin (also called daunomycin) or idarubicin; cladribine (2-CdA); fludarabine; mitoxantrone; etoposide (VP-16); 6-thioguanine (6-TG); hydroxyurea; corticosteroids, such as prednisone or dexamethasone; methotrexate (MTX); 6-mercaptopurine (6-MP); azacitidine; and decitabine.

[0060] As used herein, the term "neoplastic disease" is characterized by malignant growth or, in disease states, benign hyperproliferative and hyperplastic cells. The common medical meaning of the term "neoplasia" refers to "new cell proliferation" that occurs as a result of loss of normal growth controls, e.g., responsiveness to neoplastic cell growth.

[0061] As used herein, the terms "hyperproliferative," "hyperplastic," "malignant," and "neoplastic" are used interchangeably and refer to cells in an abnormal state or condition characterized by rapid proliferation or neoplasia. The terms are meant to include all types of hyperproliferative growths, hyperplastic growths, cancerous growths or carcinogenic processes, metastatic tissues, or malignantly transformed cells, tissues, or organs, regardless of histopathological type or stage of invasion. "Hyperplasia" refers to cells undergoing an abnormally high rate of proliferation. However, as used herein, the terms neoplasia and hyperplasia may be used interchangeably, as is clear from the context, and generally refer to cells that experience an abnormal rate of cell proliferation. Neoplasia and hyperplasia may include benign, precancerous, or malignant tumors. Extramedullary leukemia (EML) refers to granulocytic, myeloid sarcoma, and chromoma tumors that may precede or accompany the development of AML (see Ohanian et al., Int J Cancer. 2013 Aug1;133(3):534-543). EML can occur during or after treatment and during remission. The incidence of EML in AML patients of all ages is estimated to be approximately 9%, and EML in children with AML is detected in 40% of patients at the time of diagnosis.

[0062] The terms "neoplasia," "hyperplasia," and "tumor" are often referred to generically as "cancer," which is a collective term for over 100 diseases characterized by uncontrolled, abnormal cell growth.

[0063] antibody As used herein, the term "antigen binding protein" refers to a polypeptide or protein that binds to an antigen, such as an ILT3 protein. Antigen binding proteins include, but are not limited to, bivalent antibody tetramers (2H+2L), monovalent antibodies (H+L), bispecific antibodies targeting an antigen and another target, Fab fragments, Fab' fragments, F(ab')2 fragments, Fv regions, and ScFvs. Unless otherwise specified, antigen binding proteins herein bind to ILT3 and inhibit its activity.

[0064] The term "antibody" refers to any form of antibody that exhibits the desired biological activity or binding activity. Thus, the term "antibody" is used in the broadest sense and specifically includes, but is not limited to, monoclonal antibodies (including full-length monoclonal antibodies), polyclonal antibodies, humanized, fully human antibodies, and chimeric antibodies. A "parent antibody" is an antibody obtained by exposure of the immune system to an antigen prior to modification of the antibody for the intended use, e.g., humanizing the antibody for use as a human therapeutic.

[0065] Generally, the basic antibody structural unit comprises a tetramer. Each tetramer comprises two identical pairs of polypeptide chains, each pair having one "light" chain (about 25 kDa) and one "heavy" chain (about 50-70 kDa). The amino-terminal portion of each chain comprises a variable region of about 100-110 or more amino acids primarily responsible for antigen recognition. The carboxy-terminal portion of the heavy chain may define a constant region primarily responsible for effector function. Typically, human light chains are classified as kappa light chains and lambda light chains. Human heavy chains are further typically classified as mu, delta, gamma, alpha or epsilon, defining the antibody's isotype as IgM, IgD, IgG, IgA and IgE, respectively. Within the light and heavy chains, the variable and constant regions are linked by a "J" region of about 12 or more amino acids, and the heavy chains also include a "D" region of about 10 or more amino acids. See generally, Fundamental Immunology Ch. 7 (Paul, W., ed., 2nd 15th ed. Raven Press, NY (1989)).

[0066] The variable regions of each light / heavy chain pair form the antibody binding site. Thus, in general, an intact antibody has two binding sites. Except for bifunctional or bispecific antibodies, the two binding sites are generally identical.

[0067] Typically, both heavy and light chain variable domains contain three hypervariable regions, also called complementarity determining regions (CDRs), located within relatively conserved framework regions (FRs). The CDRs are usually aligned by the framework regions and allow binding to a specific epitope. Generally, from the N-terminus to the C-terminus, both light and heavy chain variable domains contain FR1, CDR1, FR2, CDR2, FR3, CDR3 and FR4. The assignment of amino acids to each domain generally follows the definitions in Sequences of Proteins of Immunological Interest, Kabat, et al.; National Institutes of Health, Bethesda, Md.; 5th ed.; NIH Publ. No. 91-3242 (1991); Kabat (1978) Adv. Prot. Chem. 32:1-75; Kabat, et al., (1977) J. Biol. Chem. 252:6609-6616; Chothia, et al., (1987) J Mol. Biol. 196:901-917 or Chothia, et al., (1989) Nature 342:878-883.

[0068] The term "hypervariable region" refers to the amino acid residues of an antibody which are involved in antigen binding. The hypervariable region comprises amino acid residues from the "complementarity determining regions" or "CDRs" (i.e., CDRL1, CDRL2, and CDRL3 in the light chain variable domain, and CDRH1, CDRH2, and CDRH3 in the heavy chain variable domain). See Kabat et al. (1991) Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, Md. (which defines the CDR35 region of an antibody by sequence); see also Chothia and Lesk (1987) J. Mol. Biol. 196:901-917 (which defines the CDR region of an antibody by structure). The terms "framework" or "FR" residues refer to those variable domain residues other than the hypervariable region residues defined herein as CDR residues.

[0069] Unless otherwise specified, "antibody fragment" or "antigen-binding fragment" refers to an antigen-binding fragment of an antibody, i.e., an antibody fragment that retains the ability to specifically bind to an antigen bound by the full-length antibody, e.g., a fragment that retains one or more CDR regions. Examples of antibody-binding fragments include, but are not limited to, Fab, Fab', F(ab')2, and Fv fragments.

[0070] An antibody that "specifically binds" to a particular target protein is one that exhibits preferential binding to that target relative to other proteins, although this specificity does not require absolute binding specificity. An antibody is considered to be "specific" for an intended target if the binding of the antibody is determinative of the presence of the target protein in a sample, e.g., does not result in undesirable results such as false positives. Antibodies or binding fragments thereof useful in the present invention bind to the target protein with an affinity that is at least 2-fold stronger, preferably at least 10-fold stronger, more preferably at least 20-fold stronger, and most preferably at least 100-fold stronger than the affinity for non-target proteins. As used herein, an antibody is said to specifically bind to a polypeptide that contains a given amino acid sequence, e.g., the amino acid sequence of a mature human ILT3 molecule, if it binds to a polypeptide that contains that sequence but does not bind to a protein lacking that sequence.

[0071] "Chimeric antibody" refers to an antibody in which certain portions of the heavy and / or light chains are identical to or homologous to corresponding sequences in antibodies from a particular species (e.g., human) or belonging to a particular antibody class or subclass, while the remainder of the chain(s) are identical to or homologous to corresponding sequences in antibodies from another species (e.g., mouse) or belonging to another antibody class or subclass, as well as to fragments of such antibodies, so long as they exhibit the desired biological activity.

[0072] A "human antibody" refers to an antibody that contains only human immunoglobulin protein sequences. A human antibody may contain mouse glycosylation if produced in a mouse, a mouse cell, or a hybridoma derived from a mouse cell. Similarly, a "mouse antibody" or a "rat antibody" refers to an antibody that contains only mouse or rat immunoglobulin sequences, respectively.

[0073] "Humanized antibody" refers to forms of antibodies that contain sequences from non-human (e.g., murine) antibodies as well as from human antibodies. Such antibodies contain minimal sequences derived from non-human immunoglobulins. Generally, a humanized antibody contains substantially all of at least one, and typically two, variable domains, in which all or substantially all of the hypervariable loops corresponding to those of the non-human immunoglobulin and all or substantially all of the FR regions are those of human immunoglobulin sequences. A humanized antibody may also contain at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin. The prefixes "hum," "hu," or "h" are added to antibody clone names when necessary to distinguish the humanized antibody from the parent rodent antibody. Humanized forms of rodent antibodies generally contain the same CDR sequences as those of the parent rodent antibody, but certain amino acid substitutions may be included to improve affinity, to improve the stability of the humanized antibody, or for other reasons.

[0074] "CDR" or "CDRs" means a complementarity determining region in an immunoglobulin variable region.

[0075] As used herein, "framework region" or "FR" means an immunoglobulin variable region excluding the CDR regions.

[0076] "Isolated antibody" and "isolated antibody fragment" refer to a purified state, meaning in this context that the designated molecule is substantially free of other biological molecules, such as nucleic acids, proteins, lipids, carbohydrates and other substances, such as cell debris and growth medium. In general, the term "isolated" is not intended to refer to the complete absence of such substances, or the absence of water, buffers or salts, unless present in amounts that would substantially interfere with experimental or therapeutic uses of the binding compounds described herein.

[0077] As used herein, "monoclonal antibody" or "mAb" or "Mab" refers to a population of substantially homogeneous antibodies, i.e., the amino acid sequences of the antibody molecules comprising the population are identical except for possible minor naturally occurring mutations. In contrast, conventional (polyclonal) antibody preparations typically include a large number of different antibodies having different amino acid sequences in their variable domains, particularly their CDRs, which are often specific for different epitopes. The modifier "monoclonal" indicates the character of the antibody as being obtained from a substantially homogeneous population of antibodies and is not to be construed as requiring production of the antibody by any particular method. For example, monoclonal antibodies to be used in accordance with the present invention may be made by the hybridoma method first described by Kohler et al. (1975) Nature 256:495, or may be made by recombinant DNA methods (see, e.g., U.S. Pat. No. 4,816,567). "Monoclonal antibodies" can also be isolated from phage antibody libraries using the techniques described in, for example, Clackson et al. (1991) Nature 352:624-628 and Marks et al. (1991) J. Mol. Biol. 222:581-597. See also Presta (2005) J. Allergy Clin. Immunol. 116:731.

[0078] Variable region or V region as used herein refers to the segment of an IgG chain that is variable in sequence among different antibodies. It extends to Kabat residue 109 in the light chain and 113 in the heavy chain.

[0079] A variant of a heavy chain variable region sequence or a full-length heavy chain sequence is identical to a reference sequence except for up to 17 conservative amino acid substitutions in the framework regions (i.e. outside the CDRs), preferably having fewer than 10, 9, 8, 7, 6 or 5 conservative amino acid substitutions in the framework regions. A variant of a light chain variable region sequence or a full-length light chain sequence is identical to a reference sequence except for up to 5 conservative amino acid substitutions in the framework regions (i.e. outside the CDRs), preferably having fewer than 4, 3, 2 conservative amino acid substitutions in the framework regions.

[0080] "Conservatively modified variants" or "conservative substitutions" refer to the substitution of amino acids in a protein with other amino acids having similar characteristics (e.g., charge, side chain size, hydrophobicity / hydrophilicity, main chain conformation and rigidity, etc.) such that changes can be made frequently without altering the biological activity or other desired properties of the protein, such as antigen affinity and / or specificity. Those skilled in the art recognize that single amino acid substitutions in non-essential regions of a polypeptide generally do not substantially alter biological activity (see, e.g., Watson et al. (1987) Molecular Biology of the Gene, The Benjamin / Cummings Pub. Co., p.224(4th Ed.)). Moreover, substitution of structurally or functionally similar amino acids is unlikely to destroy biological activity. Exemplary conservative substitutions are shown in Table 1. [Table 1] TIFF2024527925000003.tif43168

[0081] V H and V L The regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDRs), interspersed with regions that are more conserved, termed framework regions (FRs). H and V Lis composed of three CDR regions and four FR regions, which are located from the amino terminus to the carboxy terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. The variable regions of the heavy and light chains contain binding domains that interact with antigens. The constant region of the antibody may mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (e.g., effector cells) and the first component (C1q) of the classical complement system. The assignment of amino acids to each domain generally follows the definitions in Sequences of Proteins of Immunological Interest, Kabat, et al.; National Institutes of Health, Bethesda, Md.; 5th ed.; NIH Publ. No. 91-3242 (1991); Kabat (1978) Adv. Prot. Chem. 32:1-75; Kabat, et al., (1977) J. Biol. Chem. 252:6609-6616; Chothia, et al., (1987) J Mol. Biol. 196:901-917 or Chothia, et al., (1989) Nature 342:878-883.

[0082] The constant region of an antibody may mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (e.g., effector cells) and the first component of the classical complement system (C1q). Typically, the numbering of amino acids in the heavy chain constant domain begins at number 118 according to the Eu numbering scheme. The Eu numbering scheme is based on the amino acid sequence of human IgG1 (Eu) and is described in Edelman et al., Proc. Natl. Acad. Sci. USA. 63:78-85 (1969) and for IgG1, IgG2, IgG3, and IgG4 constant domains in Beranger, et al., Ibid.

[0083] The variable regions of the heavy and light chains contain a binding domain that contains the CDRs that interact with an antigen. Many methods are available in the art for defining the CDR sequences of antibody variable domains (see Dondelinger et al., Frontiers in Immunol. 9:Article 2278(2018)). Common numbering schemes include:

[0084] The Kabat numbering scheme is based on sequence variability and is the most commonly used (see Kabat et al. Sequences of Proteins of Immunological Interest, 5th Ed. Public Health Service, National Institutes of Health, Bethesda, Md. (1991)) (defines the CDR regions of antibodies by sequence); The Chothia numbering scheme is based on the location of structural loop regions (see Chothia & Lesk J. Mol. Biol. 196:901-917(1987);Al-Lazikani et al., J. Mol. Biol. 273:927-948(1997)); The AbM numbering scheme is a compromise between the two used in Oxford Molecular's AbM antibody modeling software (see Karu et al., ILAR Journal 37:132-141(1995)); The Contact numbering scheme is based on the analysis of available complex crystal structures (see www.bioinf.org.uk: Prof. Andrew CR Martin's Group; Abhinandan & Martin, Mol. Immunol. 45:3832-3839(2008)).

[0085] The IMGT (ImMunoGeneTics) numbering scheme is a standardized numbering system for all protein sequences of the immunoglobulin superfamily, including the variable domains of antibody light and heavy chains, and T-cell receptor chains from different species, in which residues are counted consecutively from 1 to 128 based on germline V sequence alignment (see Giudicelli et al., Nucleic Acids Res. 25:206-11(1997); Lefranc, Immunol Today 18:509(1997); Lefranc et al., Dev Comp Immunol. 27:55-77(2003)).

[0086] www.bioinf.org.uk: The following general rules, as disclosed in the group of Professor Andrew C. R Martin and reproduced below in Table 2, can be used to define CDRs in antibody sequences that contain amino acids that specifically interact with amino acids that comprise the epitope in the antigen to which the antibody binds. There are rare instances where these generally consistent features do not occur, although Cys residues are the most conserved features. [Table 2] TIFF2024527925000005.tif103170

[0087] Generally, the state of the art recognizes that in many cases the CDR3 region of the heavy chain is the primary determinant of antibody specificity, and examples of generating specific antibodies based solely on the CDR3 of the heavy chain are known in the art (e.g., Beiboer et al., J. Mol. Biol. 296:833-849(2000); Klimka, et al., British J. Cancer 83:252-260(2000); Rader et al., Proc. Natl. Acad. Sci. USA 95:8910-8915(1998); Xu et al., Immunity 13: 37-45(2000)).

[0088] Anti-ILT3 antibodies and antigen-binding fragments useful in the present invention An "anti-ILT3 antigen-binding protein or antigen-binding fragment" useful in any of the therapeutic methods, compositions and uses of the invention includes a monoclonal antibody (mAb) or antigen-binding fragment thereof that specifically binds to human ILT3. Alternative or synonymous terms for ILT3 include: LILRB4; LIR5; and CD85K. In any of the therapeutic methods, compositions and uses of the invention in which a human individual is treated, the anti-ILT3 antigen-binding protein, antibody or antigen-binding fragment binds to ILT3 and reduces the ability of MDSC to suppress T cell activation and proliferation. The anti-ILT3 antibody can be a human antibody, a humanized antibody, or a chimeric antibody and may include a human constant region. In some embodiments, the human constant region is selected from the group consisting of IgG1, IgG2, IgG3, and IgG4 constant regions, and in preferred embodiments, the human constant region is an IgG1 or IgG4 constant region. In some embodiments, the antigen-binding fragment is selected from the group consisting of Fab, Fab'-SH, F(ab')2, scFv, and Fv fragments.

[0089] The term "anti-ILT3 antigen binding protein" refers to a protein that binds to the extracellular domain (amino acids 22-259) of GenPept Accession No. Q8NHJ6.3.

[0090] QAGPLPKPTLWAEPGSVISWGNSVTIWCQGTLEAREYRLDKEESPAPWDRQNPLEPKNKARFSIPSMTEDYAGRYRCYYRSPVGWSQPSPLELVMTGAYSKPTLSALPSPLVTSGKSVTLLCQSRSPMDTFLLIKERAAHPLLHLRSEHGAQQHQAEFPMSPVTSV H GGTYRCFSSHGFSHYLLSHPSDPLELIVSGSLEDPRPSPTRSVSTAAGPEDQPLMPTGSVPHSGLRRHWE (SEQ ID NO: 1)

[0091] Examples of mAbs that bind human ILT3 useful in the therapeutic methods and uses of the present invention are described in WO2019 / 099597 (hereby incorporated by reference) and summarized in Table 3 below. [Table 3] TIFF2024527925000007.tif254166TIFF2024527925000008.tif254165

[0092] TIFF2024527925000009.tif254165TIFF2024527925000010.tif254165TIFF2024527925000011.tif254165

[0093] TIFF2024527925000012.tif254165TIFF2024527925000013.tif254165

[0094] TIFF2024527925000014.tif254165

[0095] TIFF2024527925000015.tif254165TIFF2024527925000016.tif254165TIFF2024527925000017.tif254165TIFF2024527925000018.tif254166

[0096] TIFF2024527925000019.tif254165TIFF2024527925000020.tif254166

[0097] <h2 style=";text-align:left;direction:ltr">TIFF2024527925000021.tif254165TIFF2024527925000022.tif254165TIFF2024527925000023.tif254165TIFF2024527925000024.tif254166TIFF2024527925000025.tif254165TIFF2024527925000026.tif254166TIFF2024527925000027.tif254166TIFF2024527925000028.tif254167<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0098] <h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr"> TIFF2024527925000029.tif254166TIFF2024527925000030.tif254166TIFF2024527925000031.tif254165TIFF2024527925000032.tif254165TIFF2024527925000033.tif254165 TIFF2024527925000034.tif254166TIFF2024527925000035.tif254165TIFF2024527925000036.tif254166TIFF2024527925000037.tif254165TIFF2024527925000038.tif254165<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0099] <h2 style=";text-align:left;direction:ltr"> TIFF2024527925000039.tif254166TIFF2024527925000040.tif254165TIFF2024527925000041.t if254165TIFF2024527925000042.tif254166TIFF2024527925000043.tif254166TIFF2024527925 000044.tif254165TIFF2024527925000045.tif254165TIFF2024527925000046.tif254166TIFF20 24527925000047.tif254166TIFF2024527925000048.tif254165TIFF2024527925000049.tif25416 6TIFF2024527925000050.tif254163TIFF2024527925000051.tif254166TIFF2024527925000052. tif254166TIFF2024527925000053.tif254165TIFF2024527925000054.tif254165TIFF2024527925 000055.tif254165TIFF2024527925000056.tif254166TIFF2024527925000057.tif254166TIFF20 24527925000058.tif254165TIFF2024527925000059.tif254166TIFF2024527925000060.tif57167

[0100] In certain embodiments, the therapeutic methods and uses of the invention provide anti-ILT3 antibodies as shown in Table 4 below. H The antibodies disclosed herein bind to human ILT3, except for the antibody that comprises a replacement of the tryptophan residue at position 101 of: [Table 4] TIFF2024527925000062.tif254153

[0101] TIFF2024527925000063.tif254154TIFF2024527925000064.tif254153

[0102] TIFF2024527925000065.tif254153TIFF2024527925000066.tif254154

[0103] TIFF2024527925000067.tif254154TIFF2024527925000068.tif254152

[0104] TIFF2024527925000069.tif254153TIFF2024527925000070.tif254152

[0105] TIFF2024527925000071.tif245156

[0106] In certain embodiments of the invention, the anti-ILT3 antigen binding protein or fragment is a human or humanized anti-ILT3 antibody or antigen-binding fragment or a chimeric anti-ILT3 antibody or antigen-binding fragment comprising HC-CDR1, HC-CDR2, HC-CDR3, LC-CDR1, LC-CDR2 and LC-CDR3 of an anti-ILT3 antibody molecule disclosed herein or in Table 5 below. [Table 5] TIFF2024527925000073.tif66170

[0107] Anti-PD-1 antigen-binding proteins and antigen-binding fragments useful in the present invention An "anti-PD-1 antigen-binding protein or antigen-binding fragment" useful in any of the therapeutic methods, compositions, and uses of the invention includes a monoclonal antibody (mAb) or antigen-binding fragment thereof that specifically binds to human PD-1. Alternative or synonymous terms for PD-1 and its ligands include, for PD-1, PDCD1, PD1, CD279, and SLEB2; for PD-L1, PDCD1L1, PDL1, B7H1, B7-4, CD274, and B7-H; and for PD-L2, PDCD1L2, PDL2, B7-DC, Btdc, and CD273. In any of the therapeutic methods, compositions, and uses of the invention in which a human individual is treated, the PD-1 antigen-binding protein or antigen-binding fragment is a PD-1 antagonist that blocks the binding of human PD-L1 to human PD-L1, or blocks the binding of both human PD-L1 and PD-L2 to human PD-1. The human PD-1 amino acid sequence can be found at NCBI locus number: NP_005009. Human PD-L1 and PD-L2 amino acid sequences can be found at NCBI locus numbers: NP_054862 and NP_079515, respectively. The anti-PD-1 antibody may be a human antibody, a humanized antibody, or a chimeric antibody and may comprise a human constant region. In some embodiments, the human constant region is selected from the group consisting of IgG1, IgG2, IgG3, and IgG4 constant regions, and in preferred embodiments, the human constant region is an IgG1 or IgG4 constant region. In some embodiments, the antigen-binding fragment is selected from the group consisting of Fab, Fab'-SH, F(ab')2, scFv, and Fv fragments.

[0108] Examples of mAbs that bind human PD-1 and are useful in the therapeutic methods and uses of the invention are described in U.S. Patent No. 7,521,051, U.S. Patent No. 8,008,449, and U.S. Patent No. 8,354,509. Particular anti-human PD-1 mAbs useful as PD-1 antagonists in the therapeutic methods, compositions, and uses of the invention include pembrolizumab (formerly known as MK-3475, SCH900475, and lambrolizumab), a humanized IgG4 mAb comprising the heavy and light chain amino acid sequences shown in Figure 1, having a structure as described in WHO Drug Information, Vol.27, No.2, pp.161-162(2013), and the humanized antibodies h409A11, h409A16, and h409A17, as described in WO2008 / 156712 and Table 6.

[0109] In some embodiments of the therapeutic methods, compositions, kits, and uses of the invention, the anti-PD-1 antigen-binding protein, antibody, or antigen-binding fragment comprises (a) a light chain CDR comprising the sequence of amino acids set forth in SEQ ID NOs: 1, 2, and 3, and a heavy chain CDR comprising the sequence of amino acids set forth in SEQ ID NOs: 6, 7, and 8; or (b) a light chain CDR comprising the sequence of amino acids set forth in SEQ ID NOs: 11, 12, and 13, and a heavy chain CDR comprising the sequence of amino acids set forth in SEQ ID NOs: 14, 15, and 16. In some embodiments, the anti-PD-1 antigen-binding protein, antibody, or antigen-binding fragment is a human antibody. In other embodiments, the anti-PD-1 antigen-binding protein, antibody, or antigen-binding fragment is a humanized antibody. In other embodiments, the anti-PD-1 antigen-binding protein, antibody, or antigen-binding fragment is a chimeric antibody. In certain embodiments, the anti-PD-1 antigen-binding protein, antibody, or antigen-binding fragment is a monoclonal antibody.

[0110] In other embodiments of the therapeutic methods, compositions, kits, and uses of the invention, the anti-PD-1 antigen-binding protein, antibody, or antigen-binding fragment specifically binds to human PD-1 and comprises (a) a heavy chain variable region comprising the amino acid sequence set forth in SEQ ID NO:24, or a variant thereof, and (b) a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NO:25, or a variant thereof; SEQ ID NO:26, or a variant thereof; and SEQ ID NO:27, or a variant thereof.

[0111] In another embodiment of the therapeutic methods, compositions, kits, and uses of the invention, the anti-PD-1 antigen-binding protein or antigen-binding fragment is a monoclonal antibody that specifically binds to human PD-1 and comprises (a) a heavy chain that comprises, or consists of, the sequence of amino acids set forth in SEQ ID NO:28, or a variant thereof; and (b) a light chain that comprises, or consists of, the sequence of amino acids set forth in SEQ ID NO:29, or a variant thereof; SEQ ID NO:30, or a variant thereof; or SEQ ID NO:31, or a variant thereof.

[0112] In yet another embodiment of the therapeutic methods, compositions, and uses of the invention, the anti-PD-1 antigen-binding protein or antigen-binding fragment is a monoclonal antibody that specifically binds to human PD-1 and comprises (a) a heavy chain that comprises, or consists of, the sequence of amino acids set forth in SEQ ID NO:28 and (b) a light chain that comprises, or consists of, the sequence of amino acids set forth in SEQ ID NO:29.

[0113] Tables 6 and 7 below provide listings of exemplary anti-PD-1 mAb amino acid sequences for use in the therapeutic methods, compositions, kits and uses of the invention. [Table 6] TIFF2024527925000075.tif254162TIFF2024527925000076.tif254162TIFF2024527925000077.tif254164

[0114] [Table 7] TIFF2024527925000079.tif218169

[0115] The anti-ILT3 antigen-binding proteins or antigen-binding fragments of the present invention may be used alone or in combination with other therapies. For example, combination therapy may include compositions comprising anti-ILT3 antigen-binding proteins, antibodies or antigen-binding fragments co-formulated and / or co-administered with one or more additional therapeutic agents, such as one or more anti-cancer agents, cytotoxic or cytostatic agents, hormonal therapies, vaccines, chemotherapy and / or other immunotherapies. In other embodiments, the anti-ILT3 antigen-binding proteins, antibodies or antigen-binding fragments are administered in combination with other therapeutic methods, such as surgery, radiation, cryosurgery and / or hyperthermia. Such combination therapies may advantageously utilize lower dosages of the administered therapeutic agents, thus avoiding possible toxicities or complications associated with those various monotherapies.

[0116] "In combination with" does not imply that the therapies or therapeutic agents must be administered simultaneously and / or formulated for delivery together, although these delivery methods are within the scope described herein. The anti-ILT3 antigen binding protein, antibody or antigen binding fragment may be administered simultaneously with, prior to, or after one or more other additional therapies or therapeutic agents. The anti-ILT3 antigen binding protein, antibody or antigen binding fragment and the other agents or treatment protocols may be administered in any order. Generally, each agent will be administered at a dose and / or time schedule determined for that agent. It will further be understood that the additional therapeutic agents used in the combination may be administered together in a single composition or may be administered separately in different compositions. In general, it is expected that the additional therapeutic agents used in combination will be used at levels that do not exceed the levels at which they are used individually. In some embodiments, the levels used in combination will be lower than the levels at which they are used individually.

[0117] In certain embodiments, the anti-ILT3 antigen binding proteins or antigen binding fragments described herein are administered in combination with one or more checkpoint inhibitors or antagonists of the programmed death receptor 1 (PD-1) or its ligands PD-L1 and PD-L2. The inhibitors or antagonists can be antibodies, antigen binding fragments, immunoadhesins, fusion proteins, or oligopeptides. In some embodiments, the anti-PD-1 antibody is selected from nivolumab (OPDIVO®, Bristol Myers Squibb, New York, New York), pembrolizumab (KEYTRUDA®, Merck Sharp & Dohme Corp, Kenilworth, NJ USA), setiplimab (Regeneron, Tarrytown, NY), or pidilizumab (CT-011). In some embodiments, the PD-1 inhibitor is an immunoadhesin (e.g., an immunoadhesin comprising an extracellular or PD-1 binding portion of PD-L1 or PD-L2 fused to a constant region (e.g., an Fc region of an immunoglobulin sequence). In some embodiments, the PD-1 inhibitor is AMP-224. In some embodiments, the PD-L1 inhibitor is durvalumab (IMFINZI®, AstraZeneca, Wilmingon, DE), atezolizumab (TECENTRIQ®, Roche, Zurich, CH) or avelumab (BAVENCIO®, EMD Serono, Billerica, MA). In some embodiments, the anti-PD-L1 binding antagonist is selected from YW243.55.S70, MPDL3280A, MEDI-4736, MSB-0010718C or MDX-1105.

[0118] MDX-1105, also known as BMS-936559, is an anti-PD-L1 antibody described in WO2007 / 005874. Antibody YW243.55.S70 is an anti-PD-L1 antibody described in WO2010 / 077634 (heavy and light chain variable region sequences shown in SEQ ID NOs:20 and 21, respectively).

[0119] Nivolumab, also known as OPDIVO®, MDX-1106-04, ONO-4538 or BMS-936558, is a fully human IgG4 anti-PD-1 antibody described in WO2006 / 121168 and U.S. Pat. No. 8,008,449.

[0120] Pembrolizumab, also known as KEYTRUDA®, lambrolizumab, MK-3475 or SCH-900475, is a humanized anti-PD-1 antibody described in U.S. Pat. No. 8,354,509 and WO2009 / 114335, and disclosed, for example, in Hamid et al., New England J. Med. 369(2):134-144(2013). The heavy and light chains of prembrolizumab are represented by the amino acid sequences set forth in SEQ ID NOs:225 and 226, respectively.

[0121] Pidilizumab, also known as CT-011 (Cure Tech), is a humanized IgG1 monoclonal antibody that binds to PD-1. Pidilizumab and other humanized anti-PD-1 monoclonal antibodies are disclosed in WO2009 / 101611. Other anti-PD-1 antibodies include, among others, AMP514 (Amplimmune), including the anti-PD-1 antibodies disclosed in, for example, U.S. Patent No. 8,609,089, U.S. Patent Application Publication No. 2010028330, and U.S. Patent Application Publication No. 20120114649.

[0122] AMP-514 (MEDI0680; MedImmune LLC, Gaithersburg, MD) is a monoclonal antibody that binds to PD-1.

[0123] PDR001 (spartalizumab; Novartis) is a monoclonal antibody that binds to PD-1 and is disclosed in U.S. Patent No. 9,683,048.

[0124] BGB-A317 (tislelizumab; Beigene) is a monoclonal antibody that binds to PD-1 and is disclosed in U.S. Patent No. 8,735,553.

[0125] MDPL3280A (Genentech / Roche) is a human Fc-optimized IgG1 monoclonal antibody that binds to PD-L1. MDPL3280A, and other human monoclonal antibodies against PD-L1, are disclosed in U.S. Patent No. 7,943,743 and U.S. Patent Application Publication No. 20120039906.

[0126] MGA012 (MacroGenics, Rockville, MD) is a monoclonal antibody that binds to PD-1.

[0127] AMP-224 (B7-DCIg; Amplimmune; disclosed, for example, in WO2010 / 027827 and WO2011 / 066342) is a PD-L2 Fc fusion soluble receptor that blocks the interaction between PD-1 and B7-H1.

[0128] Other anti-PD-L1 binding agents include YW243.55.S70 (heavy and light chain variable regions are shown in SEQ ID NOs:20 and 21 in WO2010 / 077634) and MDX-1105 (also known as BMS-936559). This and other anti-PD-L1 binding agents are disclosed in WO2007 / 005874.

[0129] In some embodiments, the ILT3 antigen binding proteins or antigen binding fragments and PD-1 or PD-L1 antagonists herein may be used in combination with one or more additional therapeutic agents, such as one or more anti-cancer agents, cytotoxic or cytostatic agents, hormonal therapy, vaccines, chemotherapy, and / or other immunotherapy. In other embodiments, the anti-ILT3 antigen binding proteins, antibodies or antigen binding fragments are administered in combination with other therapies, including surgery, radiation, cryosurgery, and / or hyperthermia.

[0130] Usage / Dosage Provided herein are methods and routes of administration for treating cancer, and in certain embodiments, AML, using anti-ILT3 antigen binding proteins or antigen binding fragments (e.g., any of the mAbs in Table 4), or combinations of anti-ILT3 antigen binding proteins or antigen binding fragments (e.g., any of the mAbs in Table 4).

[0131] The anti-ILT3 antigen-binding protein or antigen-binding fragment and the anti-PD1 antigen-binding protein or antigen-binding fragment disclosed herein can be administered by continuous infusion or by doses administered, for example, simultaneously or sequentially, daily, 1-7 times per week, weekly, biweekly, every 3 weeks, 4 weeks, 5 weeks, 6 weeks, monthly, bimonthly, quarterly, semi-annually, annually, etc. The doses can be administered, for example, intravenously, subcutaneously, topically, orally, nasally, rectally, intramuscularly, intracerebrally, intraspinally, or by inhalation. In certain embodiments, the doses are administered intravenously. In certain embodiments, the doses are administered subcutaneously. The total dose over a treatment interval will generally be at least 0.05 μg / kg, more typically at least 0.2 μg / kg, 0.5 μg / kg, 1 μg / kg, 10 μg / kg, 100 μg / kg, 0.25 mg / kg, 1.0 mg / kg, 2.0 mg / kg, 5.0 mg / ml, 10 mg / kg, 25 mg / kg, 50 mg / kg or more. Doses may also be provided to achieve a predetermined target concentration of an antigen binding protein (e.g., an anti-ILT3 antibody) or antigen binding fragment in the serum of a subject, e.g., 0.1, 0.3, 1, 3, 10, 30, 100, 300 μg / mL or more. In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment is administered intravenously weekly, every other week, every three weeks, once every three weeks, once every four weeks, once every five weeks, once every six weeks, monthly, once every two months, or quarterly at 10, 20, 50, 80, 100, 200, 300, 400, 500, 1000, or 2500 mg / subject.

[0132] In some embodiments, the anti-ILT3 antigen binding protein or antigen binding fragment is administered intravenously at 10, 20, 50, 80, 100, 200, 500, 1000 or 2500 mg / subject once a week, once every two weeks, once every three weeks, once every four weeks, once every five weeks, once every six weeks, once a month, once every two months or once a quarter. In some specific methods, the dose of the anti-ILT3 antigen-binding protein or antigen-binding fragment is about 0.01 mg / kg to about 50 mg / kg, about 0.05 mg / kg to about 25 mg / kg, about 0.1 mg / kg to about 10 mg / kg, about 0.2 mg / kg to about 9 mg / kg, about 0.3 mg / kg to about 8 mg / kg, about 0.4 mg / kg to about 7 mg / kg, about 0.5 mg / kg to about 6 mg / kg, about 0.6 mg / kg to about 5 mg / kg, about 0.7 mg / kg to about 4 mg / kg, about 0.8 mg / kg to about 3 mg / kg, about 0.9 mg / kg to about 2 mg / kg, about 1.0 mg / kg to about 1.5 mg / kg, about 1.0 mg / kg to about 2.0 mg / kg, about 1.0 mg / kg to about 3.0 mg / kg, or about 2.0 mg / kg to about 4.0 mg / kg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 0.2 mg to about 2 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 0.2 mg to about 2 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 0.2 mg to about 2250 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 0.2 mg to about 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 0.2 mg to about 2250 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 0.2 mg to 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 7.5 mg to about 2250 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be from about 7.5 mg to about 750 mg.In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 7.5 mg to 2250 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 7.5 mg to 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 25 mg to about 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 25 mg to 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 75 mg to about 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 75 mg to 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 225 mg to about 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 225 mg to 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 0.2 mg, about 0.7 mg, or about 2 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 7.5 mg, about 25 mg, about 75 mg, about 225 mg, about 750 mg, or about 2250 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 0.2 mg, 0.7 mg, or 2 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 7.5 mg, 25 mg, 75 mg, 225 mg, 750 mg, or 2250 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be about 750 mg. In certain methods, the dose of the anti-ILT3 antigen binding protein or antigen binding fragment can be 750 mg.

[0133] General method Standard methods in molecular biology are described in Sambrook, Fritsch and Maniatis (1982 & 1989 2nd Edition, 2001 3rd Edition) Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY; Sambrook and Russell (2001) Molecular Cloning, 3rded, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY; Wu (1993) Recombinant DNA, Vol. 217, Academic Press, San Diego, CA. Standard methods are also described in Ausbel et al. (2001) Current Protocols in Molecular Biology, VolIs. 1-4, John Wiley and Sons, Inc. New York, NY, which describes cloning and DNA mutagenesis in bacterial cells (Vol. 1), cloning in mammalian cells and yeast (Vol. 2), glycoconjugate and protein expression (Vol. 3), and bioinformatics (Vol. 4).

[0134] Methods for protein purification, including immunoprecipitation, chromatography, electrophoresis, centrifugation and crystallization have been described (Coligan et al. (2000) Current Protocols in Protein Science, Vol. 1, John Wiley and Sons, Inc., New York). Chemical analysis, chemical modification, post-translational modification, production of fusion proteins, and glycosylation of proteins are described (see, e.g., Coligan et al. (2000) Current Protocols in Protein Science, Vol. 2, John Wiley and Sons, Inc., New York; Ausubel et al. (2001) Current Protocols in Molecular Biology, Vol. 3, John Wiley and Sons, Inc., NY, NY, pp. 16.0.5-16.22.17; Sigma-Aldrich, Co. (2001) Products for Life Science Research, St. Louis, MO; pp. 45-89; Amersham Pharmacia Biotech (2001) BioDirectory, Piscataway, NJ, pp. 384-391). The production, purification, and fragmentation of polyclonal and monoclonal antibodies have been described (Coligan et al. (2001) Current Protocols in Immunology, Vol. 1, John Wiley and Sons, Inc., New York; Harlow and Lane (1999) Using Antibodies, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY; Harlow and Lane, supra). Standard techniques are available for characterizing ligand / receptor interactions (see, e.g., Coligan et al. (2001) Current Protocols in Immunology, Vol. 4, John Wiley, Inc., New York).

[0135] Monoclonal, polyclonal and humanized antibodies can be produced (see, e.g., Shepherd and Dean (eds.) (2000) Monoclonal Antibodies, Oxford Univ. Press, New York, NY; Kontermann and Dubel (eds.) (2001) Antibody Engineering, Springer-Verlag, New York; Harlow and Lane (1988) Antibodies A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, pp.139-243; Carpenter et al. (2000) J. Immunol. 165:6205; He et al. (1998) J. Immunol. 160:1029; Tang et al. (1999) J. Biol. Chem. 274:27371-27378; Baca et al. (1997) J. Biol. Chem. 272:10678-10684; Chothia et al. (1989) Nature 342:877-883; Foote and Winter (1992) J. Mol. Biol. 224:487-499; see U.S. Patent No. 6,329,511).

[0136] An alternative to humanization is to use human antibody libraries displayed on phage or in transgenic mice (Vaughan et al. (1996) Nature Biotechnol. 14:309-314; Barbas (1995) Nature Medicine 1:837-839; Mendez et al. (1997) Nature Genetics 15:146-156; Hoogenboom and Chames (2000) Immunol. Today 21:371-377; Barbas et al. (2001) Phage Display: A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York; Kay et al. (1996) Phage Display of Peptides and Proteins: A Laboratory Manual, Academic Press, San Diego, CA; de Bruin et al. (1999) Nature Biotechnol. 17:397-399).

[0137] Purification of antigens is not required for antibody production. Animals can be immunized with cells bearing the antigen of interest. Splenocytes can then be isolated from the immunized animals and fused with myeloma cell lines to generate hybridomas (see, e.g., Meyaard et al. (1997) Immunity 7:283-290; Wright et al. (2000) Immunity 13:233-242; Preston et al., supra; Kaithana et al. (1999) J. Immunol. 163:5157-5164).

[0138] The antibodies or antigen-binding fragments may be conjugated to, for example, small drug molecules, enzymes, liposomes, polyethylene glycol (PEG). Antibodies are useful for therapeutic, diagnostic, kit or other purposes, including, for example, antibodies conjugated to dyes, radioisotopes, enzymes or metals, such as colloidal gold (see, for example, Le Doussal et al. (1991) J. Immunol. 146:169-175; Gibellini et al. (1998) J. Immunol. 160:3891-3898; Hsing and Bishop (1999) J. Immunol. 162:2804-2811; Everts et al. (2002) J. Immunol. 168:883-889).

[0139] Standard histological methods for the immune system have been described (see, e.g., Muller-Harmelink (eds.) (1986) Human Thymus: Histopathology and Pathology, Springer Verlag, New York, NY; Hiatt et al. (2000) Color Atlas of Histology, Lippincott, Williams and Wilkins, Phila, PA; Louis et al. (2002) Basic Histology: Text and Atlas, McGraw-Hill, New York, NY). Software packages and databases are available for determining, e.g., antigenic fragments, leader sequences, protein folding, functional domains, glycosylation sites, and sequence alignments (e.g., GenBank, VECTOR NTI® Suite (Informax, Inc, Bethesda, MD); GCG Wisconsin Package (Accelrys, Inc., San Diego, CA); DECYPHER® (TimeLogic Corp., Crystal Bay, Nevada); Menne et al. (2000) Bioinformatics 16:741-742; Menne et al. (2000) Bioinformatics Applications Note 16:741-742; Wren et al. (2002) Comput. Methods Programs Biomed. 68:177-181; von Heijne (1983) Eur. J. Biochem. 133:17-21; von Heijne (1986) Nucleic Acids Res. 14:4683-4690). EXAMPLES

[0140] Example 1: Effect of anti-ILT3 parent antibody 52B8 on AML patient PBMCs The effect of anti-ILT3 parental antibody 52B8 on AML patient PBMCs was evaluated in vitro. AML patient PBMCs (761L), which show high ILT3 expression on myeloid cells, were treated with 52B8 or human IgG4 (hIgG4). AML PBMCs were treated in vitro for 24 hours with 52B8 or hIgG4 isotype control (1 mg / mL). Treated PBMCs were stained with Abs (see Table 8 below for a list of staining panels and antibody sources; Fluidigm, South San Francisco, CA, USA; Invitrogen, Waltham, MA, USA; eBioscience, Waltham, MA, USA; R&D Systems, Minneapolis, MN, USA) and profiled and quantified using time-of-flight cytometry (CyTOF) to detect PBMC phenotype. Table 9 below lists the CyTOF phenotypes of myeloid cell clusters 1 and 4 in AML PBMCs. [Table 8] TIFF2024527925000081.tif254142TIFF2024527925000082.tif40170

[0141] [Table 9]

[0142] Figure 1 shows dot plots quantifying and comparing the percentage of 10 clusters of myeloid cells between 52B8 and hIgG4 isotype treatment. As shown in Figure 1, treatment of AML PBMCs with 52B8 mAb (filled circles) reduced the frequency of tumor blasts (cluster 4) and increased the monocytic myeloid population (cluster 1, filled circles).

[0143] Example 2: Inhibition of AML cell proliferation in vivo by anti-ILT3 antibodies The anti-tumor efficacy of the parental anti-ILT3 antibody 52B8 as a single agent was evaluated in a systemic MV-4-11 myelomonocytic leukemia model in humanized mice. NOD.Cg-Prkdcscid Il2rgtm1Wjl / SzJ (NSG™) mice were inoculated with human PBMCs (106 cells / mouse) and MV-4-11luc cells (10 6 / mouse) were inoculated by IV injection.

[0144] For generation of MV-4-11 luc cells, live luciferase reporter virus was generated using Clontech GP2-293 packaging cells (Takara Bio, Mountain View, CA, USA) and transfected with pLXSN-Luc and pVSV-G vectors using FuGENE HD transfection reagent (Roche, Mannheim, Germany). MV-4-11 cells were infected with luciferase reporter virus and luciferase-positive cells were selected with Geneticin selection antibiotic (G418) (Invitrogen, Carlsbad, CA, USA). Luciferase activity was examined in vitro using bioluminescence imaging (BLI). Before culturing for inoculation, cells were frozen and stored in liquid nitrogen using cell culture freezing medium.

[0145] To evaluate the efficacy of 52B8, animals were assigned to two treatment groups, 10 mice / group, one week after cell inoculation. 52B8 or hIgG4 isotype control was administered intraperitoneally at 10 mg / kg on days 7, 14, 21, 28, and 35. In vivo MV-4-11 luc cell proliferation was measured by BLI using an IVIS® Spectrum In Vivo Imaging System (Perkin Elmer, Waltham, MA, USA). Measurements were performed weekly for the first 4 weeks after inoculation and twice weekly thereafter. Statistical analysis between the two groups was performed using two-way ANOVA with Geisser-Greenhouse correction. Post-hoc analysis was performed by Sidak's multiple comparison test. ** :p<0.01; *:p<0.05. Peripheral bone marrow (BM) samples from the treatment groups were profiled by CyTOF.

[0146] As shown in Figure 2A, mice receiving hIgG4 isotype control antibody starting the day after tumor cell engraftment showed a statistically significant increase in MV-4-11 luc cell proliferation. However, mice receiving 52B8 treatment starting on day 7 after tumor cell engraftment had reduced MV-4-11 proliferation in vivo. Figure 2B shows a dot plot of the percentage of MV-4-11 luc cells as a percentage of bone marrow cells from each treatment group. BM samples from mice receiving 52B8 treatment starting on day 7 after tumor cell engraftment did not show any MV-4-11 luc cells, whereas BM samples from mice treated with hIgG4 showed a high percentage of MV-4-11 luc cells.

[0147] Example 3: Anti-ILT3 antibody and IFNγ production by donor T cells The ability of anti-ILT3 antibodies to affect IFN-gamma production by T cells was examined. Anti-ILT-3 antibody c52B8 or a control human IgG4 antibody (hIgG4) was incubated with co-cultures of human CD8+ T cells from different human donors and irradiated THP-1 cells (a human monocytic cell line from a patient with acute monocytic leukemia) at a T cell:THP-1 ratio of 8:1. Control hIgG4 antibody was incubated at a concentration of 10 μg / mL, and 52B8 mAb was incubated at 10, 1, and 0.1 μg / mL. The incubated co-cultures were then stimulated with anti-CD3 / CD28 coated beads. Cell culture supernatants were then assayed for IFN-γ expression using the V-PLEX human IFN-γ assay kit (Mesoscale Discovery, Rockville, MD, USA).

[0148] Figures 3A and 3B respectively show bar graphs of IFN-γ expression in CD8+ T cells from two different donors. The anti-ILT3 antibody 52B8 significantly enhanced production of the pro-inflammatory cytokine IFN-γ, with 10 μg / mL of 52B8 causing a much higher increase in IFN-γ than the control antibody.

[0149] The following examples, using mAb No. 46 as an exemplary anti-ILT3 antibody, are for illustrative purposes and should not be construed as further limiting. The contents of the figures and all references, patents and published patent applications cited throughout this application are expressly incorporated herein by reference.

[0150] Example 4: Phase 1b study to evaluate anti-ILT3 antibodies for relapsed / refractory AML Clinical trial plan This is a multicenter, open-label, phase 1b study to evaluate the safety, tolerability, PK, and pharmacodynamics of an anti-ILT3 antibody in participants with relapsed / refractory AML. The study will enroll participants with AML subtypes of acute myelomonocytic leukemia or acute monoblastic / monocytic leukemia according to the 2016 WHO classification [Arber, DA, et al. 2016].

[0151] The study has two parts: dose escalation (part 1) and dose expansion (part 2). In part 1, initial dose escalation will be performed according to an accelerated titration design (ATD) to evaluate two low dose levels (DL): DL1 7.5 mg and DL2 25 mg, enrolling 1-3 participants in each group. Once the study passes DL2, further dose escalation will be performed according to the mTPI design [Ji, Y. et al. 2013] to evaluate dose levels of 75 mg, 225 mg, and 750 mg of anti-ILT3 antibody, respectively, according to dose levels evaluated in solid tumor studies. Higher dose levels up to 2250 mg can be considered in the study, depending on the combination of safety, PK, and available pharmacodynamic data. Each dose level under the mTPI will initially enroll 3-6 participants and can be expanded to a maximum of 10 participants. Figure 4 shows a schematic diagram of the study design. Intermediate and higher dose levels can be evaluated. The maximum treatment duration is 35 cycles (approximately 24 months). Within-participant dose escalation will be permitted for participants enrolled up to the ATD dose level of 75 mg per dose.

[0152] Progression from one DL to the next higher DL is based on evaluation of DLT. If grade 2 or higher treatment-related toxicity occurs, the ATD cohort will be terminated early. In that situation, dose levels will be assessed by mTPI. During dose escalation, a higher dose level cannot be initiated until the previous lower dose level has cleared the DLT.

[0153] Dose determination for Part 1 will end after 10 participants have been treated at any dose level. The pooled adjacent bilaterator algorithm [Ji, Y. et al. 2013] will be used to estimate DLT rates across doses in each treatment arm, assuming monotonicity between DLT rates and dose levels. The entire data, including safety events occurring within or beyond the DLT window, tolerability, preliminary antitumor activity, PK, and pharmacodynamics across all dose levels, will be considered before determining a preliminary RP2D for progression to Part 2. Part 1 will enroll approximately 20 participants.

[0154] Once the preliminary RP2D is confirmed in Part 1, approximately 10 participants will be enrolled in the RP2D in Part 2 with the same R / RAML subtype as in Part 1. The study will enroll approximately 30 participants.

[0155] The study will include a screening period of up to 21 days. Eligible participants will receive study treatment and will be closely monitored for safety through physical and laboratory examinations. AEs will be assessed by investigators according to NCI CTCAE 5.0.

[0156] Clinical activity will be assessed for changes in AML blasts in bone marrow and peripheral blood according to the ELN2017 response criteria listed below in Table 10. [Table 10] TIFF2024527925000085.tif254157TIFF2024527925000086.tif254160TIFF2024527925000087.tif254159TIFF2024527925000088.tif152170

[0157] Overall survival is defined for all study participants as measured from the date of clinical trial entry or diagnosis (e.g., for correlative science studies) to the date of death from any cause, and for patients not known to have died at last follow-up, censored at the date the patient was last known to be alive [Dohner, H., et al. 2017].

[0158] Within-participant dose escalation will be permitted once participants enrolled in the first two dose levels in Part 1 have completed DLT assessments and have cleared the higher dose levels for DLT if the participant does not progress.

[0159] The anti-ILT3 antibody will be administered by IV infusion in 3-week cycles. Participants will be treated until progressive disease, unacceptable toxicity, intercurrent illness that prevents administration of further therapeutic agent, investigator decision to discontinue treatment, participant withdrawal of consent, participant pregnancy, non-compliance with study intervention or procedure requirements, or administrative reasons requiring discontinuation of treatment.

[0160] Participants may receive study treatment for up to 35 cycles (24 months). Furthermore, if a participant has not achieved partial or complete remission after 6 months of study treatment, the investigator should discuss with the participant the lack of response to study treatment and other treatment options. If other alternative treatments that offer potential clinical benefit are available to the participant at that time, study treatment should be discontinued.

[0161] Participants who discontinue treatment for reasons other than documented progressive disease will be followed for disease status until disease progression, initiation of new anticancer therapy, withdrawal of consent to study participation, or loss to follow-up.

[0162] Efficacy Endpoints As this is a phase 1b study, secondary endpoints include clinical response for efficacy evaluation, including CR rate, combined CR rate (CR+CRi) and objective response rate (CR+CRi and PR). The response criteria for AML defined in the 2017 recommendations of the ELN International Expert Panel [Dohner, H., et al. 2017] have been well adapted in clinical settings around the world and include response parameters appropriate for clinical trials, such as definitions of stable disease, progressive disease and relapse. The evaluation of these parameters was developed according to the 2016 WHO Classification of Myeloid Neoplasms and Acute Leukemias [Arber, DA, et al. 2016].

[0163] Safety Endpoints The primary objective of this study is to determine the safety and tolerability characteristics of the anti-ILT3 antibody as monotherapy. The primary safety analysis will be based on participants experiencing toxicity as defined by the CTCAE version 5.0 criteria. Safety will be assessed by quantifying the toxicity and grade of toxicity experienced by participants receiving the anti-ILT3 antibody as monotherapy.

[0164] For AEs, drug attribution, time of onset, duration of the event, its resolution, and concomitant medications administered will be recorded.AEs analyzed include, but are not limited to, all AEs, SAEs, fatal AEs, and laboratory changes.

[0165] Pharmacokinetic endpoints A secondary objective of this study is to characterize the PK profile of the anti-ILT3 antibody following administration as a single agent. Serum concentrations of the drug will be used as the primary PK readout, and these data will be used to derive PK parameters for the drug. Furthermore, the results of these analyses, in combination with pharmacodynamic, safety, and exploratory endpoint data, will be used to aid in the evaluation of future dosing strategies for the anti-ILT3 antibody.

[0166] Anti-drug antibodies Formation of ADAs may confound drug exposure at therapeutic doses and contribute to subsequent infusion-related toxicity. Review anti-drug antibody responses at the start of each cycle to understand drug metabolism, exposure and safety. Evaluate and summarize incidence of ADAs and neutralizing antibodies (if applicable) over time by dose. Correlate between the presence or absence of ADA and PK positivity and pharmacodynamic markers, activity and safety of anti-ILT3 antibodies.

[0167] Pharmacodynamic endpoints The exploratory objectives of this study are to evaluate target binding used in combination with safety, PK and additional pharmacodynamic biomarker data to guide dose escalation decisions and determine the RP2D. Target binding is measured by measuring circulating CD14 in peripheral blood. +This is assessed using a receptor occupancy assay that directly measures anti-ILT3 antibodies binding to ILT3 on bone marrow cells and compares receptor occupancy before and after treatment. Additionally, receptor occupancy can be measured on bone marrow blasts if sufficient sample is available.

[0168] As preclinical evidence suggests a dose-dependent relationship between sILT3 concentration and target binding, we will measure sILT3 using an enzyme-linked immunosorbent assay and assess the correlation between sILT3 levels and anti-ILT3 antibody treatment.

[0169] Rationale for starting and maximum doses of anti-ILT3 antibodies The anti-ILT3 antibody Q3W has been evaluated as monotherapy at dose levels ranging from 0.2 mg to 2250 mg in advanced solid tumors and in combination with pembrolizumab 200 mg Q3W at dose levels ranging from 7.5 mg to 2250 mg in previous clinical trials. The anti-ILT3 antibody was well tolerated at all dose levels in monotherapy and showed an acceptable safety profile in combination with pembrolizumab.

[0170] Preliminary PK data from solid tumor clinical trials showed target-mediated drug deposition at relatively low anti-ILT3 antibody doses, but linear PK was observed at tested doses of ≥75 mg. Near-complete receptor occupancy was observed in blood samples from participants treated with anti-ILT3 antibody at dose levels ≥75 mg. Even using strict assumptions, anti-ILT3 antibody 750 mg Q3W appears to maintain complete receptor occupancy in tumors.

[0171] ADAs were observed in 16 of 62 participants with evaluable data treated with anti-ILT3 antibody doses ranging from 0.2 mg to 750 mg, but there was no clear impact of ADAs on PK or receptor occupancy. Blood samples showed a dose-dependent increase in total soluble ILT3 (sILT3) concentrations. However, internal investigations did not confirm any immunosuppressive activity of soluble ILT3.

[0172] The ILT3 target expression levels in AML patient blood compared to patients with other solid tumors are unknown. In AML patients, the safety profile resulting from ILT3 target binding is also unknown. Therefore, to eliminate unexpected adverse events, dose escalation in AML patients will start at 7.5 mg. In solid tumor patients, this dose will minimize target binding in blood at trough concentrations (approximately 20%). The study will initially enroll 3-6 participants at dose levels of 75 mg, 225 mg, and 750 mg for each cohort, and will escalate to a maximum of 10 participants as needed according to the mTPI design. Given that trough target binding increases significantly from 7.5 to 75 mg in solid tumor patients, safety evaluation in more participants is required above 25 mg.

[0173] Based on a comprehensive evaluation of data from safety, PK, and receptor occupancy, a 750mg dose of anti-ILT3 antibody was selected as the RP2D in combination with pembrolizumab for further evaluation in advanced solid tumors. This dose is expected to achieve complete target binding. However, based on actual data from dose escalation, higher dose levels can be evaluated if warranted.

[0174] Rationale for Dose Interval and Titration Once full target binding is achieved, anti-ILT3 antibodies exhibit a PK profile consistent with that of other monoclonal antibodies. Preliminary data from studies of anti-ILT3 antibodies in solid tumors suggest that the half-life of anti-ILT3 antibodies is approximately 17 days. A 3-week dosing interval is expected to be adequate to maintain full target binding at trough in AML patients.

[0175] Approximately 3-fold dose escalation is used. Although the degree of population variation in exposure in AML patients is unknown, a 3-fold difference between doses is expected to result in non-overlapping exposures between doses.

[0176] Accelerated potency test design Initial dose escalation will follow the ATD to minimize the number of participants treated with potentially sub-therapeutic doses of anti-ILT3 antibodies. A single participant will be enrolled sequentially into each of the 7.5 mg and 25 mg escalating dose levels. Transition from the ATD to mTPI will be planned at the next dose level, 75 mg.

[0177] Within-participant dose escalation may be performed for participants in the ATD. Participants may receive dose escalation up to a maximum dose level of 75 mg. Intermediate dose levels may be evaluated if warranted. The doses to be tested in each group of participants will be communicated to the Investigator or designee after the dose escalation meeting for the previous dose. Enrollment of up to three participants per dose level in the ATD will be permitted with the approval of the Sponsor's Medical Monitor or designee, provided that the first two participants receive anti-ILT3 antibody treatment at least three days apart. All participants enrolled at each dose level must complete the DLT period before the next dose level is initiated.

[0178] ATD ends when at least one of the following occurs: The highest dose level (up to 75mg) has completed the DLT evaluation period and the anti-ILT3 antibody is deemed safe and well tolerated in this cohort. Occurrence of Grade 2 or higher treatment-related toxicity by NCI CTCAE5.0 during Cycle 1 (ATD will end at that dose level).

[0179] Whenever a DLT occurs in the ATD phase, the dose level at which it occurred will be escalated at this dose according to the mTPI guidelines below. If no DLT occurs in the ATD phase, the ATD phase will progress to the mTPI phase if one of the triggers above is met.

[0180] Dose finding using a modified toxicity probability interval design Further dose titration will follow the mTPI design with a target DLT rate of 25% [Ji Y et al. 2007]. Dose escalation and de-escalation decisions will be based on the mTPI design and will depend on the number of participants enrolled and the number of DLTs observed at the current dose level.

[0181] A minimum of three participants is required for each dose. However, depending on accrual rates, three to six participants can be enrolled in an open dose level, provided that the first participants receive their first doses at least three days apart. In Table 11, the columns indicate the number of participants treated at the current dose level, and the rows indicate the number of participants who experienced DLTs. The items in the table are dose-finding decisions. E, S, D, and DU represent dose escalation, maintenance of the same dose, dose tapering, and removal of a dose from the study due to unacceptable toxicity, respectively. For example, if zero of three participants at a particular dose level develop DLTs, the dose can be increased to the next level. If two of three participants develop DLTs, the dose is reduced to the next lower dose level. If three of three participants develop DLTs, this indicates unacceptable toxicity at this dose. The dose should be de-escalated, and the current dose should not be explored further. If one of three participants develops DLTs at a particular dose level, an additional participant should be enrolled at that dose level, following the rules below:

[0182] When adding participants to a dose level in response to a "maintenance" decision, we place an upper limit on the number of additional participants enrolled to minimize exposure to doses that may exhibit unacceptable toxicity (denoted as DU in Table 11). Second, we can count the steps diagonally (down and to the right) from the current cell to the first cell marked as DU to determine how many more participants can be enrolled at that dose level. For example, if 1 of 3 participants experience a DLT at a particular dose level, no more than 3 additional participants should be enrolled at this dose level until additional DLT data are available. This dose level is considered unacceptably toxic if all 3 additional participants experience a DLT (i.e., participants with 4 / 6 DLTs in Table 11). The same principle applies whether 3, 4, 5, or 6 participants are initially enrolled at that dose level.

[0183] A decision of D or DU at the lowest dose level will stop the study. A decision of E at the highest dose level will result in remaining at that level. During dose selection, tapering to a predefined, previously untested intermediate dose may be acceptable if evaluation of toxicity at such doses is desirable. If this approach is adopted, 3-6 new participants may be enrolled at the new intermediate dose, and further enrollment at this dose level should be determined using the rules previously described.

[0184] After enrolling 10 participants at any study dose (including the intermediate dose), titration will stop if the mTPI table indicates "S" to maintain the current dose. Otherwise, up to 10 new participants may be enrolled at the lower dose if "D" or "DU" is indicated, or at the higher dose if "E" is indicated.

[0185] A pooled adjacent bilaterator algorithm [Ji, Y. et al. 2013] will be used to estimate DLT rates across doses. The dose with an estimated DLT rate closest to 25% will be treated as the preliminary MTD. However, the totality of data will be considered before deciding which doses will be carried forward into Part 2, and the titration plan may be adjusted based on pharmacodynamic, PK, and safety data emerging throughout the study.

[0186] Of note, although the target toxicity rate used to develop the guidelines in Table 11 was 25%, the percentage of participants with DLTs observed at the MTD may be slightly above or below 25%. [Table 11] TIFF2024527925000090.tif28170

[0187] Clinical criteria for early termination of the study A study or recruitment at a particular study site may be terminated due to poor adherence to the protocol, GCP, and / or other applicable regulatory requirements, procedural related problems, or excessive numbers of withdrawals for administrative reasons.

[0188] Early termination of the study will result from the criteria specified below.

[0189] 1. The incidence or severity of adverse events in this or other studies indicates a potential health hazard to participants. 2. Plans to change or discontinue development of the investigational drug.

[0190] If the sponsor decides to discontinue supplying the anti-ILT3 antibody, adequate notice will be provided.

[0191] Study population Male / female participants aged 18 years or older with relapsed or refractory AML will be enrolled in the study.

[0192] Prospective approval of protocol deviations to recruitment and enrollment criteria, also known as protocol waivers or exemptions, will not be permitted.

[0193] Selection Criteria A participant is eligible to participate in the study if he or she:

[0194] 1. Confirmed diagnosis of AML with myelomonocytic or monoblastic / monocytic differentiation according to WHO 2016 criteria and confirmed refractory or relapsed disease (i.e., ≥ 5% blasts in bone marrow or peripheral blood) following treatment with available therapies known to be beneficial for the participant's AML subtype.

[0195] 2. WBC count ≤ 20x10 within 24 hours prior to first dose of study treatment 9 Note: To the extent possible, hydroxyurea should be used to maintain white blood cell counts ≤20 × 10 / L until the first dose of study treatment. 9 / L or less.

[0196] 3. ECOG performance status of 0-2 assessed within 72 hours prior to the first dose of study treatment.

[0197] 4.Has adequate organ function as defined in Table 12 below, assessed within 72 hours prior to the first dose of study treatment. [Table 12]

[0198] 5. Male or female, aged 18 years or older at the time of providing written informed consent.

[0199] 6. You are not pregnant or breastfeeding and meet at least one of the following conditions:

[0200] ·Not WOCBP OR ·WOCBP and using highly effective contraception (failure rate <1% per year) or abstaining from heterosexual intercourse as their preferred and usual lifestyle (long-term continuous abstinence) during the intervention period and for at least 90 days after the last dose of study intervention. Investigators should assess the possibility of contraceptive failure (i.e., non-adherence, recent initiation) in relation to the first dose of study intervention.

[0201] WOCBP must have a negative high-sensitivity pregnancy test (urine no older than 24 hours and serum no older than 72 hours, as required by country regulations) prior to the first dose of study intervention.

[0202] A serum pregnancy test is required if a negative urine test cannot be confirmed (e.g., the result is equivocal). In such cases, if the serum pregnancy result is positive, the participant must be excluded from participation.

[0203] The investigator is responsible for reviewing medical history, menstrual history, and recent sexual activity to reduce the risk of selecting women with early undetected pregnancies.

[0204] Contraception use by women must comply with local regulations regarding contraception methods for clinical trial participants.

[0205] 7. The participant (or a legally recognized representative) has provided written informed consent for the study. Participants may also consent to future biomedical research. However, participants may participate in the main study without participating in future biomedical research.

[0206] 8. Bone marrow aspirate and biopsy samples obtained within 14 days of starting treatment.

[0207] Exclusion criteria A participant must be excluded from the study if he or she:

[0208] 1. Have active CNS leukemia. Note: Participants with clinical signs of CNS involvement or suspected CNS involvement will be required to undergo CSF ​​testing to confirm leukemic involvement.

[0209] 2. Isolated extramedullary disease, i.e., no leukemic involvement in bone marrow or peripheral blood.

[0210] 3. Have been diagnosed with acute promyelocytic leukemia.

[0211] 4. Previous allogeneic stem cell or solid organ transplant within 60 days of screening. Note: Participants who relapsed after allogeneic SCT, including those who received donor lymphocyte infusions, were excluded from the study if they had active graft-versus-host disease (GV). H D) and are either discontinued immunosuppressive therapy or taking a maintenance dose of prednisone or equivalent <10 mg / day. Note: Prior autologous transplant for AML or non-AML conditions is permitted.

[0212] 5. History of a second malignancy unless there has been no evidence of malignancy for 1 year and potentially curative treatment has not been completed. Note: This time requirement does not apply to participants who have successfully undergone curative resection for basal cell carcinoma of the skin, squamous cell carcinoma of the skin, superficial bladder cancer, or carcinoma in situ (e.g., breast carcinoma in situ, cervical carcinoma in situ, etc.).

[0213] 6. History of any of the following cardiovascular conditions within 6 months of screening: myocardial infarction, unstable angina, cerebrovascular accident, transient ischemic attack, coronary artery bypass graft, or pulmonary embolism; New York Heart Association (NYHA) class III or IV congestive heart failure.

[0214] 7. History of severe hypersensitivity reaction to mAb and / or any component of the study intervention, anti-ILT3 antibody treatment.

[0215] 8. Have an active uncontrolled infection requiring indicated therapy.

[0216] 9. Suffering from severe, immediately life-threatening complications of leukemia such as uncontrollable bleeding, pneumonia with hypoxia or shock, or disseminated intravascular coagulation.

[0217] 10. Have known HIV and / or Hepatitis B or C infection or are known to be positive for HBsAg / HBV DNA or Hepatitis C antibody or RNA. Active Hepatitis C is defined by a known positive HepC Ab result and a known quantitative HCV RNA result above the lower limit of detection of the assay.

[0218] 11. Has a known psychiatric or substance abuse disorder (verbally reported) that may interfere with the participant's ability to cooperate with the requirements of the study.

[0219] 12. Pregnant or breastfeeding, or anticipated to conceive or father a child within the anticipated study period beginning with the Screening Visit and ending 120 days after the last study intervention.

[0220] 13.Has received systemic anticancer therapy, radiation therapy, or surgery within 2 weeks prior to starting study treatment. Note: Participants must have recovered from all AEs from previous treatment to grade ≤1 or baseline.

[0221] 14.Has received hematopoietic cytokines (G-CSF, GM-CSF, or erythropoietin) within 2 weeks prior to the start of study treatment.

[0222] 15. Receipt of live or live-attenuated vaccines within 30 days prior to the first dose of study drug. Note: Killed vaccines are permitted.

[0223] 16. Previous treatment with another agent targeting ILT3.

[0224] 17. Currently participating in an investigational drug trial and receiving an investigational intervention, or have participated in an investigational drug trial and received an investigational intervention, or have used an investigational device within 28 days of receiving an anti-ILT3 antibody. Note: Participants who are in the follow-up phase of the trial may participate if 4 weeks have elapsed since their last dose of the previous investigational drug.

[0225] 18. Has been diagnosed with an immunodeficiency or is receiving chronic systemic steroid therapy (at a dose greater than 10 mg per day of prednisone equivalent) or other forms of immunosuppressive therapy within 7 days prior to the first dose of study drug. Note: Participants who require intermittent use of non-systemic steroids such as ophthalmic, inhaled, intranasal, topical steroids, or topical steroid injections will not be excluded from the study.

[0226] Screening ineligible A screen failure is defined as a participant who consents to participate in a clinical trial but subsequently does not enroll in the study. A minimum set of screen failure information is required to ensure transparent reporting of screen failure participants to meet CONSORT disclosure requirements and to address regulatory inquiries. The minimum information includes demographics, details of screen failure, eligibility criteria, and any AEs or SAEs that meet the reporting requirements outlined in the data entry guidelines.

[0227] Participant replacement strategy To fully evaluate the safety of the dose administered in this study, all enrolled participants must meet the evaluation criteria for Cycle 1. Participants will be considered ineligible for DLT evaluation if: · Allocated but not treated. A participant discontinues the study before all safety evaluations have been completed for reasons other than a treatment-related adverse event. Participants received <75% of their total anti-ILT3 antibody infusions in Cycle 1 (e.g., if the infusion had to be stopped due to an infusion reaction) and did not experience a DLT.

[0228] Participants who are not eligible for DLT assessment will be replaced unless accrual at dose level has ceased. Non-evaluable participants will not be counted in the total number of participants at the dose level for DLT assessment.

[0229] If a participant experiences a DLT in cycle 1, the study intervention may be discontinued; however, if the participant is deriving clinical benefit from the study intervention, after discussion with and approval by the sponsor, the participant may be allowed to continue.

[0230] Intervention allocation In Part 1 of the study, treatments will be assigned by non-random assignment using an IVRS / IWRS based on the dose level evaluated at that time. C1D1 treatments for the first and second enrolled participants must be separated by at least 3 days. A new dose level group will not be initiated until the previous dose level group has been evaluated for DLTs and dose escalation is indicated. Enrollment for Part 2 will begin after the RP2D dose is determined, and treatments will be assigned by non-random assignment using an IVRS / IWRS.

[0231] Acceptable Concomitant Medications All treatments that the investigator considers necessary for the participant's welfare may be administered at the investigator's discretion in accordance with local medical standards, except those prohibited as described in section 6.5.2. All concomitant medications, including all prescription, OTC, herbal supplements, and IV medications and fluids, will be recorded on the CRF. Documentation of medication dose, number, route of administration, and date may also be included on the CRF if changes occur during the study. All concomitant medications administered within 30 days prior to the first dose of study intervention and up to 30 days after the last dose of study intervention should be recorded. If the participant experiences an SAE or ECI, all concomitant medications administered after 30 days of the last dose of study intervention should be recorded.

[0232] Concomitant use of drugs Participants were prohibited from receiving the following therapies during the screening and treatment phases of the study:

[0233] Antitumor systemic chemotherapy or biological therapy Immunotherapy not specified in this protocol Chemotherapy not specified in this protocol Investigational Drugs Radiation therapy NOTE: Radiotherapy to symptomatic solitary lesions or the brain may be allowed at the investigator's discretion in consultation with the sponsor after the DLT observation period in participants deemed evaluable for DLT.

[0234] Live or attenuated vaccines prior to the first dose of the study intervention and within 30 days during study participation. Examples of live vaccines include, but are not limited to: measles, mumps, rubella, chickenpox / shingles, yellow fever, rabies, BCG, and typhoid vaccines. Injectable seasonal influenza vaccines are typically killed virus vaccines and are licensed, except intranasal influenza vaccines (such as FluMist®), which are live attenuated vaccines and are not licensed.

[0235] Systemic glucocorticoids for purposes other than controlling symptoms from AEs suspected to have an immunological etiology. The use of physiologic doses of corticosteroids may be approved after consultation with the sponsor.

[0236] Participants whose clinical management requires the use of any of the aforementioned therapies, as assessed by the investigator, must discontinue the study intervention. Participants may receive other medications as deemed medically necessary by the investigator.

[0237] General supportive care Supportive care to manage AML should be provided as needed according to institutional standards, including transfusion of leukocyte-depleted blood products (e.g., RBCs, platelets), prophylaxis and treatment of infections.9 Hydroxyurea can be administered to maintain CD4+ at 1 / L. Growth factors (GM-CSF, G-CSF) may be considered as part of postremission supportive care, but should be discontinued for at least 7 days before obtaining bone marrow for evaluation, as they may confound bone marrow evaluation.

[0238] Prevention of tumor lysis Participants at risk for developing TLS should receive prophylactic treatment with allopurinol, additional hydration, and diuretics as per institutional criteria as clinically indicated. 9 Hydroxyurea can be administered to maintain serum CO2 at 0.5 mg / L (see above). The classification of tumor lysis syndrome is summarized in Table 13 below. [Table 13] TIFF2024527925000093.tif150167

[0239] Dose-limiting toxicity All toxicities will be graded using NCI CTCAE 5.0 based on investigator assessment.

[0240] The observation window for DLT is 21 days since the first administration of study intervention (i.e., during cycle 1).

[0241] The occurrence of any of the following toxicities during Cycle 1 will be considered a DLT if assessed by the investigator as possibly, probably, or definitely related to the study intervention:

[0242] 1. Grade 4 non-hematologic toxicity (not in clinical trials) 2. Any grade 3 non-hematologic toxicity.

[0243] DLT-defined exceptions: Grade 3 fatigue lasting ≤3 days Grade 3 diarrhea, nausea, or vomiting not requiring tube feeding, total parenteral nutrition, or prolonged hospitalization Grade 3 hypersensitivity reactions that were well managed and resolved within 72 hours

[0244] 3. Grade 3 or Grade 4 non-hematological laboratory values ​​if: The participant's treatment requires a clinically significant medical intervention; or Abnormalities leading to hospitalization, or The abnormality persists for >1 week, or Electrolyte imbalance persists for more than 48 hours despite optimal treatment, or · Abnormalities cause DILI.

[0245] Exception to the DLT definition: Isolated grade 3 or grade 4 abnormality without clinical consequence that resolves to less than grade 2 in less than 72 hours, with or without intervention.

[0246] 4. Grade 4 neutropenia and / or thrombocytopenia lasting longer than 14 days in the absence of active leukemia.

[0247] 5. Prolonged delay (>2 weeks) initiation of Cycle 2 due to intervention-related toxicity.

[0248] 6. Intervention-related toxicity causing the participant to discontinue the intervention during cycle 1.

[0249] 7. Loss of >25% of the anti-ILT3 antibody dose as a result of drug-related AEs during the first cycle.

[0250] 8. Grade 5 toxicity.

[0251] Dose expansion Part 2 of the study will enroll approximately 10 additional patients with AML using the preliminary RP2D identified from Part 1.

[0252] Timing of administration Anti-ILT3 antibodies will be administered Q3W as an IV infusion. Reasons for variations in anti-ILT3 antibody dosing outside of protocol-specified windows must be documented in the participant's medical record and recorded in the eCRF.

[0253] Every effort should be made to begin the first dose of study intervention on the day of assignment or within 3 days after assignment. Subsequent doses will be administered on day 1 of each cycle with a ±3 day window.

[0254] Dose modification of anti-ILT3 antibody CTCAE 5.0 must be used to assess the severity of AEs. Investigators may attribute each toxicity event to anti-ILT3 antibodies and modify the dose according to Table 14. If a participant experiences multiple toxicities and there are conflicting recommendations, the most conservative recommendation will be followed. Exceptional circumstances that do not follow the dose modification table below may be considered in consultation with the sponsor. [Table 14] TIFF2024527925000095.tif217157

[0255] Timing of Dose Administration Dosages and schedules are summarized in Table 15 below. [Table 15]

[0256] After the first cycle, for administrative reasons, study interventions may be administered up to 3 days before or after the scheduled administration of each infusion.

[0257] On day 1 of each cycle, administer anti-ILT3 antibodies Q3W at the assigned dose level. Sites should make every effort to keep infusion timing as close to 30 minutes as possible. Given the variability of infusion pumps per site, a window of minus (-) 5 minutes to plus (+) 10 minutes is acceptable (i.e., infusion time 30 minutes, -5 minutes / +10 minutes).

[0258] Screening / Baseline AML Disease Assessment Participants' AML disease status will be assessed by the investigator based on local laboratory reports. At screening / baseline, bone marrow aspirate and biopsy, peripheral blood samples will be collected for CBC and differential, histopathological evaluation, and immunophenotyping (primarily focusing on acute myeloid and monocytic leukemia panel according to institutional criteria). To be eligible for the study, participants must have ≥5% blasts in bone marrow or peripheral blood at baseline. Blast counts include myeloblasts, monoblasts, promonocytes, and / or megakaryoblasts according to WHO AML criteria [Dohner, H., et al. 2017].

[0259] Extramedullary disease must be assessed as clinically indicated per institutional guidelines. Participants with CNS leukemia or isolated extramedullary disease (i.e., no bone marrow or peripheral disease as required per protocol) should be excluded. For eligible participants, location of extramedullary disease must be recorded on the CRF.

[0260] AML disease evaluation during study treatment Disease status during the study treatment period will be assessed by the investigator based on local clinical laboratory reports of bone marrow and peripheral blood evaluations.

[0261] Extramedullary disease will be assessed or followed as clinically indicated. Disease status will be assessed according to the ELN 2017 response criteria in AML at each protocol specified time point or as clinically indicated. Details of disease assessment will be recorded on the CRF.

[0262] Eastern Oncology Collaborative Group Performance Scale The investigator or qualified designee will assess ECOG status at screening, prior to administration of each dose of study intervention on the day of study treatment, and during the follow-up period.

[0263] Potentially Clinically Important Adverse Events (ECIs) Selected serious and non-serious AEs, also referred to as ECIs, must be reported to the Sponsor.

[0264] Adverse events considered clinically significant in this study were as follows:

[0265] Overdose of sponsored product. b. Elevation of AST or ALT laboratory values ​​≥3x the ULN and total bilirubin laboratory values ​​≥2x the ULN, with alkaline phosphatase values ​​<2x the ULN, as measured by protocol-specified or unscheduled laboratory tests. These criteria are based on available regulatory guidance documents. The purpose of the criteria is to specify thresholds for abnormal liver tests that may require further evaluation for underlying etiology.

[0266] During the period from signing of the consent form to treatment assignment, any ECI or follow-up of an ECI that occurs in a participant must be reported to the Sponsor within 24 hours if it results in the participant being removed from treatment or is the result of a protocol-specified intervention such as, but not limited to, washout or discontinuation of usual therapy, diet, or procedure.

[0267] Overdose treatment For this study, an overdose is defined as a dose exceeding the prescribed dose for the anti-ILT3 antibody by more than 20% of the designated dose. There is no specific information regarding the treatment of anti-ILT3 antibody overdose. In the event of an overdose, the anti-ILT3 antibody can be discontinued and participants should be closely observed for signs of toxicity. Appropriate supportive treatment should be provided if clinically indicated.

[0268] References 1.[American Cancer Society 2021] American Cancer Society. Cancer facts and figures, 2021. Atlanta (GA): American Cancer Society (ACS);2021. p.17. 2.[Arber, D. A., et al. 2016] Arber DA et al. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood. 2016 May 19;127(20):2391-405. 3.[Carter, J. L., et al. 2020] Carter JL et al. Targeting multiple signaling pathways: the new approach to acute myeloid leukemia therapy. Signal Transduct Target Ther. 2020;5:288. 4.[Cella, M., et al. 1997] Cella M et al. A novel inhibitory receptor (ILT3) expressed on monocytes, macrophages, and dendritic cells involved in antigen processing. J Exp Med. 1997 May 19;185(10):1743-51. 5.[Dohner, H., et al. 2015] Dohner H et al. Acute myeloid leukemia. N Engl J Med.2015 Sep 17;373(12):1136-52. 6.[Dohner, H., et al. 2017] Dohner H et al. Diagnosis and management of AML in adults: 2017 ELN recommendations from an international expert panel. Blood.2017 Jan 26;129(4):424-47. 7.[Gui, X., et al. 2019] Gui X et al. Disrupting LILRB4 / APOE interaction by an efficacious humanized antibody reverses T-cell suppression and blocks AML development. Cancer Immunol Res.2019 Aug;7(8):1244-57. 8.[Howard, S. C., et al. 2011] Howard SC et al. The tumor lysis syndrome. N Engl J Med 2011;364:1844-54. 9.[Ji Y et al. 2007] Ji Y et al. Dose-finding in phase l clinical trials based on toxicity probability intervals. Clin Trials 2007;4:235-44. 10. [Ji, Y. et al. 2013] Ji Y et al. Modified toxicity probability interval design: a safer and more reliable method than the 3+3 design for practical phase I trials. J Clin Oncol 2013;31:1-12. 11.[Ji, Y., et al. 2010] Ji Y et al. A modified toxicity probability interval method for dose-finding trials. Clin Trials.2010;7:653-63. 12.[Kang, X., et al. 2016] Kang X et al. Inhibitory leukocyte immunoglobulin-like receptors: immune checkpoint proteins and tumor sustaining factors. Cell Cycle. 2016;15(1):25-40. 13.[Li, Z., et al.2020] Li Z et al. LILRB4 ITIMs mediate the T cell suppression and infiltration of acute myeloid leukemia cells. Cell Mol Immunol. 2020;17:272-82. Erratum in: Cell Mol Immunol. 2020;17:302-4. 14.[Shallis, R. M., et al. 2019] Shallis RM et al. Epidemiology of acute myeloid leukemia: recent progress and enduring challenges. Blood Rev. 2019;36:70-87. 15.[Siegel, R. L., et al. 2021] Siegel RL et al. Cancer statistics, 2021. CA Cancer J Clin. 2021 Jan-Feb;71(1):7-33.

[0269] The disclosed subject matter is not limited in scope by the specific embodiments and examples described herein. Indeed, various modifications of the present disclosure in addition to those described will become apparent to those skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to be within the scope of the appended claims.

[0270] All references (e.g., publications or patents or patent applications) cited herein are incorporated by reference in their entirety and in all respects to the same extent as if each individual reference (e.g., publication, patent, or patent application) was specifically and individually indicated to be incorporated by reference in its entirety in all respects. Other embodiments are within the scope of the appended claims.

Claims

1. A pharmaceutical composition for the treatment of acute myeloid leukemia (AML) in a subject, comprising a therapeutically effective amount of an anti-ILT3 antigen-binding protein or antigen-binding fragment and a pharmaceutically acceptable excipient.

2. The subject has a confirmed diagnosis of acute myelomonocytic leukemia or acute monoblastic / monocytic leukemia, wherein the subject may have established refractory or relapsed AML with ≧5% blasts in the bone marrow or peripheral blood after chemotherapy treatment or after non-ILT-3 targeted treatment. The pharmaceutical composition according to claim 1.

3. The anti-ILT3 antigen-binding protein or antigen-binding fragment is an anti-ILT3 antibody or antigen-binding fragment. The pharmaceutical composition according to claim 1.

4. The anti-ILT3 antigen-binding protein or antigen-binding fragment comprises a heavy chain (HC), The heavy chain variable domain (V Ｈ ) has an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 42, 50, 58, 66, 74, 82, 90, and 98, or has an amino acid sequence having 3, 2, or 1 difference from the amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 42, 50, 58, 66, 74, 82, 90, and 98, and comprises a heavy chain complementarity determining region (HC-CDR) 3. The pharmaceutical composition according to claim 2.

5. The anti-ILT3 antibody or antigen-binding fragment, Variable domain complementarity determining region (HC-CDR) 1 having the amino acid sequence set forth in SEQ ID NO: 10, 40, 48, 56, 64, 72, 80, 88, or 96; HC-CDR 2 having the amino acid sequence set forth in SEQ ID NO: 11, 41, 48, 57, 64, 73, 81, 89, or 97; and HC-CDR 3 having the amino acid sequence set forth in SEQ ID NO: 16, 42, 50, 58, 66, 74, 82, 90, or 98; and variants thereof having one or more of said HC-CDRs having 1, 2 or 3 amino acid substitutions, additions, deletions or combinations thereof, comprising a variable domain (V Ｈ ), having a heavy chain (HC); and (b) A variable domain complementarity determining region (LC-CDR) 1 having the amino acid sequence set forth in SEQ ID NO: 20, 43, 51, 59, 67, 75, 83, 91, or 99; an LC-CDR 2 having the amino acid sequence set forth in SEQ ID NO: 36, 44, 52, 60, 68, 76, 84, 92, or 100; and an LC-CDR 3 having the amino acid sequence set forth in SEQ ID NO: 37, 45, 53, 61, 69, 77, 85, 93, or 101; and variants thereof having one or more of said LC-CDRs having 1, 2, or 3 amino acid substitutions, additions, deletions, or combinations thereof, comprising a variable domain (V Ｌ ) having a light chain (LC) according to claim 4, a pharmaceutical composition according to claim 4.

6. (a) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 12, 13, or 14; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; and (b) the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 27, 28, 29, 30, 31, 32, 33, 34, or 35; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO:

37. The pharmaceutical composition according to claim 5.

7. (a) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; and the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; and (b) the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 34; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO:

37. The pharmaceutical composition according to claim 6.

8. Said V Ｈ is human V Ｈ 1, V Ｈ 2, V Ｈ 3, V Ｈ 4, V Ｈ 5 and V Ｈ 6, and, frameworks selected from the group consisting of those variants having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or combinations thereof; and Said V Ｌ is human V κ 1, V κ 2, V κ 3, V κ 4, V κ 5, V κ 6, V λ 1, V λ 2, V λ 3, V λ 4, V λ 5, V λ 6, V λ 7, V λ 8, V λ 9 and V λ 10, and, 1, 2, 3 Comprising a framework selected from the group consisting of variants having 4, 5, 6, 7, 8, 9, or 10 amino acid substitutions, additions, deletions, or combinations thereof. The pharmaceutical composition according to claim 5.

9. The pharmaceutical composition according to claim 5, wherein the antibody comprises an HC having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or combinations thereof as compared to the amino acid sequence of the human IgG1, IgG2, IgG3, or IgG4 HC constant domain or the native IgG1, IgG2, IgG3, or IgG4 isotype constant domain.

10. The pharmaceutical composition according to claim 8, wherein the antibody comprises an LC having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or combinations thereof as compared to the amino acid sequence of the human κ or λ LC constant domain or the native human κ or λ light chain constant domain.

11. The antibody is (i) Human V Ｈ 1. V Ｈ 2. V Ｈ 3. V Ｈ 4. V Ｈ 5 and V Ｈ V having a framework selected from 6 Ｈ , and variants thereof having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or combinations thereof as compared to the amino acid sequence of the human IgG1 or IgG4 HC constant domain or the native IgG1 or IgG4 isotype HC constant domain; and (ii) Human V κ 1. V κ 2. V κ 3. V κ 4. V κ 5. V κ 6. V λ 1. V λ 2. V λ 3. V λ 4. V λ 5. V λ 6. V λ 7. V λ 8. V λ 9 and V λ V having a framework selected from 10 Ｌ , and, a human κ or λ LC constant domain or those variants having 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acid substitutions, additions, deletions or combinations thereof as compared to the amino acid sequence of said native human κ or λ LC constant domain, the pharmaceutical composition according to claim 7

12. The antibody or antigen-binding fragment has the amino acid sequences set forth in SEQ ID NO: 8 and SEQ ID NO: 9; SEQ ID NO: 38 and SEQ ID NO: 39; SEQ ID NO: 46 and SEQ ID NO: 47; SEQ ID NO: 54 and SEQ ID NO: 55; SEQ ID NO: 62 and SEQ ID NO: 63; SEQ ID NO: 70 and SEQ ID NO: 71; SEQ ID NO: 78 and SEQ ID NO: 79; SEQ ID NO: 86 and SEQ ID NO: 87; or SEQ ID NO: 94 and SEQ ID NO: 95, respectively, for V Ｈ and V Ｌ The pharmaceutical composition according to claim 7, comprising

13. The antibody or antigen-binding fragment thereof has a V having the amino acid sequence set forth in SEQ ID NO: 110, 111, 112, 116, 117, or 118 Ｈ and a V having the amino acid sequence set forth in SEQ ID NO: 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, or 134 Ｌ The pharmaceutical composition according to claim 7, comprising the same.

14. The antibody or antigen-binding fragment thereof has a V having the amino acid sequence set forth in SEQ ID NO: 111 Ｈ and a V having the amino acid sequence set forth in SEQ ID NO: 133 Ｌ The pharmaceutical composition according to claim 13, comprising the same.

15. The pharmaceutical composition according to claim 11, wherein the antibody comprises a heavy chain (HC) constant domain comprising the amino acid sequence set forth in SEQ ID NO: 2, 3, 4, 5, or 6.

16. The pharmaceutical composition according to claim 11, wherein the antibody comprises a light chain (LC) constant domain comprising the amino acid sequence set forth in SEQ ID NO:

7.

17. The pharmaceutical composition according to claim 11, wherein the antibody comprises a heavy chain (HC) comprising the amino acid sequence of SEQ ID NO: 135, 136, 137, 141, 142, 143, 160, 161, 162, 163, 167, 168, 169, 170, 171, 175, 176, 177, 178, 179, 180, 184, 185, or 186.

18. The pharmaceutical composition according to claim 11, wherein the antibody comprises a light chain (LC) comprising the amino acid sequence set forth in SEQ ID NO: 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, or 159.

19. The pharmaceutical composition according to claim 11, wherein the antibody comprises a heavy chain (HC) comprising the amino acid sequence set forth in SEQ ID NO: 136 and a light chain (LC) comprising the amino acid sequence set forth in SEQ ID NO: 158, and variants thereof in which the HC lacks a C-terminal lysine residue or C-terminal glycine-lysine.

20. The pharmaceutical composition according to claim 1, wherein a therapeutically effective amount of the anti-ILT3 antigen-binding protein or antigen-binding fragment is from about 7.5 mg to about 2250 mg.

21. A therapeutically effective amount of the anti-ILT3 antigen-binding protein or antigen-binding fragment is 7.5 mg; The pharmaceutical composition according to claim 1, wherein the therapeutically effective amount is selected from the group consisting of 7.5 mg; 25 mg; 75 mg; 225 mg; 750 mg; and 2250 mg.

22. The pharmaceutical composition according to claim 1, wherein the anti-ILT3 antibody or antigen-binding fragment is administered once every three weeks (Q3W) in a 21-day cycle.

23. The anti-ILT3 antigen-binding protein or antigen-binding fragment comprises heavy chain variable domain complementarity determining regions (HC-CDR) 1, 2, and 3 and light chain variable domain complementarity determining regions (LC-CDR) 1, 2, and 3, (a) the HC-CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 12; the HC-CDR3 comprises the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 comprises the amino acid sequence set forth in SEQ ID NO: 31; the LC-CDR2 comprises the amino acid sequence set forth in SEQ ID NO: 36; the LC-CDR3 comprises the amino acid sequence set forth in SEQ ID NO: 37; (b) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 32; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37; (c) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 14; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 33; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37; (d) the HC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 13; the HC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC-CDR1 has the amino acid sequence set forth in SEQ ID NO: 34; the LC-CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; the LC-CDR3 has the amino acid sequence set forth in SEQ ID NO: 37; or (e) the HC - CDR1 has the amino acid sequence set forth in SEQ ID NO: 10; the HC - CDR2 has the amino acid sequence set forth in SEQ ID NO: 12; the HC - CDR3 has the amino acid sequence set forth in SEQ ID NO: 16; the LC - CDR1 has the amino acid sequence set forth in SEQ ID NO: 35; the LC - CDR2 has the amino acid sequence set forth in SEQ ID NO: 36; and the LC - CDR3 has the amino acid sequence set forth in SEQ ID NO: 37, the pharmaceutical composition according to claim 1.

24. The anti - ILT3 antigen - binding protein or antigen - binding fragment is (a) a heavy chain of SEQ ID NO: 140 and a light chain of SEQ ID NO: 149; (b) a heavy chain of SEQ ID NO: 146 and a light chain of SEQ ID NO: 151; (c) a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 150; (d) a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 163; or (e) a heavy chain of SEQ ID NO: 144 and a light chain of SEQ ID NO: 150, the pharmaceutical composition according to claim 22.

25. (i) the anti - ILT3 antigen - binding protein or antigen - binding fragment comprises a heavy chain of SEQ ID NO: 140 and a light chain of SEQ ID NO: 149; (ii) the anti - ILT3 antigen - binding protein or antigen - binding fragment comprises a heavy chain of SEQ ID NO: 146 and a light chain of SEQ ID NO: 151; (iii) the anti - ILT3 antigen - binding protein or antigen - binding fragment comprises a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 150; (iv) the anti - ILT3 antigen - binding protein or antigen - binding fragment comprises a heavy chain of SEQ ID NO: 141 and a light chain of SEQ ID NO: 163; or, (v) the anti - ILT3 antigen - binding protein or antigen - binding fragment comprises a heavy chain of SEQ ID NO: 144 and a light chain of SEQ ID NO: 150, the pharmaceutical composition according to claim 24.

26. The pharmaceutical composition according to claim 2, comprising 0.02 mg to 2250 mg of an anti - ILT3 antigen - binding protein or antigen - binding fragment and a pharmaceutically acceptable excipient.

27. Use of a pharmaceutical composition comprising 0.02 mg to 2250 mg of an anti - ILT3 antigen - binding protein or antigen - binding fragment and a pharmaceutically acceptable excipient in the manufacture of a medicament for the treatment of acute myeloid leukemia (AML) in a subject, wherein the subject has a confirmed diagnosis of acute myelomonocytic leukemia or acute monoblastic / monocytic leukemia, Use, wherein the subject may have established refractory or relapsed AML with ≧ 5% blasts in the bone marrow or peripheral blood after chemotherapy treatment or after non-ILT-3 targeted treatment.

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