Abstract 1540: The dendritic cell receptor DNGR-1 shapes immunity to cancer

Abstract Background: Central to the success of CD8+ T cell-mediated anti-cancer response are type 1 conventional dendritic cells (cDC1s), acting as professional antigen presenting cells. In both mouse and human, DNGR-1 (a.k.a. CLEC9A) is a dedicated cDC1 receptor that, upon binding to its physiological ligand filamentous-actin (F-actin) exposed upon cell death, prime cytotoxic CD8+ T cells specifically against dead cell-associated antigens. Here, we interrogate the role of DNGR-1 in shaping the tumor microenvironment during carcinogenesis. Methods: We utilized two models of chemical carcinogenesis: 3-methylcholanthrene (MCA)-induced sarcoma, and azoxymethane (AOM) and dextran sodium sulfate colitis (DSS)-associated carcinoma. Rag1−/- (no B and T cells), Clec9agfp/gfp, Clec9acre/cre and WT (wildtype) mice on C57BL/6 background were used. Primary MCA-sarcoma cell lines were generated and subsequently tested in a series of transplantation experiments in naïve syngeneic WT mice. Whole exome and RNA sequencing were performed to elucidate the mutational landscape and decipher the immunopeptidome of these primary cell lines. Results: Upon challenge with MCA, there is shorter latency for tumorigenesis in DNGR-1-deficient mice (n=46), like in Rag1−/− mice (n=43), in contrast to immunocompetent WT hosts (n=59) (median: 95 vs 113 days, hazard ratio: 1.72, 95% CI 1.11-2.68, p=0.008). DNGR-1-deficient mice also display increased susceptibility to AOM-DSS carcinogenesis compared to co-housed WT mice. Majority (n=16/24, 68%) of MCA-induced primary sarcoma cell lines derived from DNGR-1-deficient hosts are highly immunogenic and were controlled/rejected at a similar rate, upon challenge in secondary naïve WT recipients, like those derived from Rag1−/− mice (n=13/19, 68%). Whole-exome sequencing of cell lines derived from DNGR-1-deficient hosts revealed that they harbor high mutational burden, including mutations in F-actin-binding proteins that have been previously associated with better survival outcomes in patients with cancer (Giampazolias et al. Cell, 2021). Collectively, these data argue that DNGR-1 protects against carcinogenesis and selects for less immunogenic tumor cells. To evaluate the degree of immunoediting which occurred in the respective primary host mice, we applied the evolutionary metric based on the ratio of nonsynonymous to synonymous mutations (dN/dS), and found that they are less immunoedited compared to cell lines derived from WT hosts. Conclusion: Our findings highlight DNGR-1 as a novel immune checkpoint that couples cell death sensing and (neo-)antigen cross-presentation to functional tumor-specific CD8+ T cell responses during cancer immunoediting. Understanding the mechanism by which DNGR-1 sculpts the mutational landscape of tumors may further inform the dynamics of cancer evolution and may have translational therapeutic implications in directing effective immunotherapy strategies. Citation Format: Kok Haw Lim, Evangelos Giampazolias, Bruno Frederico, Neil C. Rogers, Probir Chakravarty, Gavin Kelly, Ana Cardoso, Emma Nye, Alejandro Suárez-Bonnet, Simon Priestnall, Robert Goldstone, Cell Services Science Technology Platform, Sonia Lee, Oliver Schulz, Jessica Strid, Luis Zapata, Caetano Reis e Sousa. The dendritic cell receptor DNGR-1 shapes immunity to cancer [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(6_Suppl):Abstract nr 1540.