Abstract 3531: Sensitizing immune unresponsive colorectal cancers to immune checkpoint inhibitors through MAVS overexpression

Abstract Background: The majority of colorectal carcinomas (CRCs) are insensitive to anti-PD-1/PD-L1 immune checkpoint inhibitor (ICI) antibodies. While there are many causes for ICI insensitivity, recent studies suggest that the suppression of innate immunity through a loss of innate immune adaptor expression could be a root cause of this insensitivity and an important factor in the evolution of tumor immunosuppression. Methods: We interrogated mitochondrial antiviral signaling gene (MAVS) expression through bioinformatics analyses of multiple datasets to validate its suppression in clinical samples. We then engineered MAVS expressing tumor cells and tested its ability to elicit innate and adaptive anti-tumor immunity using both in vitro and in vivo approaches, which we then confirmed using MAVS expressing viral vectors. Finally, we observed that MAVS stimulated PD-L1expression in different types of tumor cells and then assessed the combination of PD-L1 ICI antibodies with MAVS tumor expression in vivo. Results: MAVS was significantly downregulated in CRCs, but its re-expression could stimulate broad cellular interferon-related responses, in both murine and patient-derived CRCs. In vivo, local MAVS expression elicited significant anti-tumor responses in both immune-sensitive and insensitive CRC models, through the stimulation of an interferon responsive axis that elicited tumor antigen-specific adaptive immunity. Critically, we found that tumor-intrinsic MAVS expression triggered systemic adaptive immune responses that enabled abscopal CD8+ T cell cytotoxicity against distant CRCs. As MAVS also induced PD-L1 expression, we further found synergistic anti-tumor responses in combination with anti-PD-L1 ICIs. Conclusion: These data demonstrate that intratumoral MAVS expression results in local and systemic tumor antigen-specific T cell responses, which could be combined with PD-L1 ICI to permit effective anti-tumor immunotherapy in ICI resistant cancers. We are further exploring to overcome the ICI insensitivity of other types of solid tumor, with MAVS-delivery strategies other than viral vectors. Citation Format: Bin-Jin Hwang, Li-Chung Tsao, Chaitanya Acharya, Timothy Trotter, Pankaj Agarwal, Tao Wang, Junping Wei, Xiao-Yi Yang, Gang-jun Lei, Takuya Osada, Herbert Kim Lyerly, Michael A. Morse, Zachary Hartman. Sensitizing immune unresponsive colorectal cancers to immune checkpoint inhibitors through MAVS overexpression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3531.