Abstract 1375: Abundance of KLRB1+ (CD161) T cells in anti-PD1 non responders coupled with enhanced tumor cytotoxicity of anti-CD161 (IMT-009) with anti-PD1 makes it a rational target for combination with anti-PD-(L)1 immunotherapy

Abstract Background: Intra-tumoral CD4+ and CD8+ T cells expressing inhibitory receptor CD161 have an effector memory phenotype with high cytotoxic potential. CD161 inhibits T and NK cell function in the presence of its ligand, CLEC2D. This suppression can be recovered by treatment with IMT-009, a first in class anti-CD161 antibody. Single cell transcriptomic analysis of anti-PD1 refractory microsatellite stable colorectal tumors identified presence of CD161+ CD4+ cytotoxic T cells and CD161+ PD1+ exhausted CD8 T cells suggesting that anti-CD161 treatment may provide benefit in these tumors both as a monotherapy and in combination with anti-PD1. It was also observed that CD161+ CD4/CD8T cells are more abundant in anti-PD1/L1 non responders compared with responders in hepatocellular carcinoma, cutaneous squamous cell carcinoma, clear cell renal carcinoma and breast cancer, providing a rationale for targeting CD161. Using engineered ex-vivo tumor models and dissociated human tumors, we have demonstrated that IMT-009 reverses CLEC2D mediated inhibition and restores primary T cell function. Additionally, co-treatment of IMT-009 with anti-PD1 further enhanced T cell mediated cytotoxicity, providing rationale for studies combining IMT-009 and anti PD1 in the clinic. Methods: Using the Snakemake pipeline developed in house, we processed publicly available scRNAseq data. Cells were clustered by Louvian method followed by cell type annotation by Seurat, and gene expression and gene signature levels per cluster were plotted. For ex-vivo assays, antigen specific CD8 T cells expanded from HLA-A2: 01 donors were co-cultured with HLA-A2: 01 expressing MDA-MB 231 triple negative breast cancer cell line or Raji Burkitt Lymphoma model with HLA-A2: 01 allelic overexpression. Target tumor cells were engineered to express the ligands CLEC2D or PDL1. These cell lines were made to overexpress luciferase for monitoring target cell death using a luminescence readout. Additionally, dissociated tumor cells (DTCs) were cultured in presence of the treatment molecules. Intracellular staining of cytotoxic T cells along with detection of IFNγ, IL-2, TNFα and Granzyme B levels in culture supernatants by MSD/ELISA were used to assess activation profile of tumor infiltrated T cells. Results: Combining anti-PD1 and IMT-009 significantly enhanced cytotoxic benefit compared to individual monotherapy in both Raji and MDA-MB-231 target cell line models. IFNγ levels in supernatants of DTCs treated with this combination were elevated as compared to individual monotherapy. Together with scRNAseq data of increased abundance of KLRB1 (CD161) expressing T cells in anti PD1 non-responder patients, our data provide rationale for testing combination of IMT-009 with anti-PD1 in patients that may not respond to anti PD1 alone. Citation Format: Adwitiya Kar, Tim Nieuwenhuis, Meixue Duan, Siamak Tabrizi, Matthew Huggins, Elizabeth Scanlon, Cynthia Hession, Matthew Bernstein, Michael Ross, Ming Tang, Shruti Malu. Abundance of KLRB1+ (CD161) T cells in anti-PD1 non responders coupled with enhanced tumor cytotoxicity of anti-CD161 (IMT-009) with anti-PD1 makes it a rational target for combination with anti-PD- (L) 1 immunotherapy abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1375.