Anti CD161 Antibody IMT-009 Is a Novel Immunotherapeutic Agent That Effectively Blocks the Inhibitory CLEC2D/CD161 Axis in CLEC2D+ B Cell Hematological Malignancies Reinvigorating T and NK Cell Function Leading to Anti-Tumor Benefit

Background: The CLEC2D/CD161 axis is a ligand-receptor pathway that has been shown to inhibit both T and NK cell function 1,2. CD161 is a C-type lectin-like receptor, which is expressed on NK cells and subsets of both CD4 + and CD8 + T cells. The tumor infiltrating CD161+ T cells have high cytotoxic potential and display an NK cell-like signature 2. Its ligand CLEC2D is expressed on the surface of both malignant cells and immune cells including germinal center B cells, activated T cells and tumor associated macrophages. Owing to its expression in germinal center B cells, CLEC2D is highly expressed in multiple types of B cell lymphomas including Diffuse Large B Cell Lymphoma (DLBCL), Follicular Lymphoma and Burkitt lymphoma 3. Furthermore, subset of infiltrated T cells in these lymphomas are CD161+ making this axis a promising novel target for immunotherapeutic intervention in hematological malignancies (Fig1). Immunitas has developed IMT-009, a monoclonal, Fc silent, fully human IgG1, high affinity antibody to CD161 that selectively blocks its interaction with CLEC2D. We show that IMT-009 effectively reverses CLEC2D-mediated inhibition and restores NK cell and T cell functions, including antigen specific T cell mediated cytotoxicity to lymphoma cell lines. Furthermore, IMT-009 shows monotherapy benefit in reducing tumor burden in a human B cell lymphoma model engrafted in humanized mice in vivo. IMT-009 is currently being evaluated in a Phase 1/2a clinical trial in both solid tumors and heme malignancies. Results: IMT-009 is a highly selective antibody to CD161 that strongly blocks its interaction with CLEC2D. In presence of CLEC2D-expressing target cells, NK cell degranulation, cytokine production and cellular cytotoxicity towards lymphoma tumor targets is highly suppressed which is overcome by treatment with IMT-009. Similarly, IMT-009 reversed CLEC2D-mediated inhibition and restored T cell activity (TCR signaling, cytokine production) in a Jurkat cell reporter system, and enhanced polyfunctionality of primary antigen-specific human T cells shown by secretion of TNF-α, IL-2, and IFN-γ, and direct T cell mediated cytotoxicity. IMT-009 also released CD161-mediated suppression of antigen recall response by PBMC derived effector memory CD161+ CD4+ T cells, resulting in an increased frequency of CD161+ IFN-γ+ cells and an increase in their proliferation. These data together show that IMT-009 is highly effective in overcoming CLEC2D mediated suppression of both T and NK cell functions. To prioritize indications that will likely benefit from IMT-009, we performed IHC for CLEC2D in a diverse set of tumor indications and found that B cell lymphomas of various subtypes have high CLEC2D protein expression by H score. Also, DLBCL was found to have the second highest median RNA expression of CLEC2D in TCGA. Furthermore, analysis of publicly available single-cell RNA-sequencing (scRNA-seq) data from B cell lymphoma including CNS lymphoma revealed CLEC2D to be highly expressed within the B lineage cells including the abundant malignant cell population (Fig2). KLRB1 (gene encoding for CD161) was also found to be expressed on a subset of tumor infiltrating CD4 and CD8 T cells in these datasets (Fig2). To confirm this, we tested CD161 expression in B cell lymphomas by immunofluorescence. Results showed CD161+ cells infiltrated in Hodgkin Lymphoma, and post-R-CHOP treated DLBCL, highlighting the potential sensitivity of these malignancies to IMT-009 treatment. Together, these results indicate that B cell lymphomas may exhibit an immunosuppressive environment mediated by the CLEC2D/CD161 axis. To test the anti-tumor benefit of IMT-009 in a human B cell lymphoma model, we treated CD34+ humanized mice implanted with Raji, a Burkitt lymphoma cell line with IMT-009. The group of mice treated with IMT-009 had a mean tumor growth inhibition of 35% and the anti-tumor response correlated with increased frequency of CD161+ T and NK cells. We further show that IMT-009 can synergize with Rituximab in NK cell mediated killing of B cell lymphoma cell lines in vitro. Conclusion: B cell malignancies tend to respond poorly to anti-PD-1 therapy 4,5. This lack of efficacy could be driven by a highly immunosuppressive environment mediated by the CLEC2D/CD161 axis. Our results support evaluation of IMT-009 as a novel cancer immunotherapy to disrupt CLEC2D/CD161 signaling, with strong therapeutic potential in lymphomas.