Identifying regulators of CAR-T cell survival and adaptation in the tumor microenvironment 3676

Abstract Description Chimeric antigen receptor T (CAR-T) cell therapy can lead to durable responses in patients with some hematologic malignancies yet remains largely ineffective in solid tumors. Impaired persistence of CAR-T cells and the immunosuppressive tumor microenvironment (TME) are important barriers to overcome to improve efficacy against solid tumors. To test how T cell mode of tumor recognition affects fate and persistence, we developed a tumor model to compare tumor-specific CAR-T cells and T cells with a transgenic T cell receptor (TCR) side-by-side. While these cells had similar survival and proliferative capacity in vitro, CD8 CAR-T cells had a survival disadvantage in vivo compared to TCR-T cells in the same TME, suggesting that CAR expression reduced CD8 T cell fitness in the TME. To probe regulators of CAR-T cell survival, we used an in vivo CRISPR screen of cell death-related genes. Deletion of Il2ra gave CAR-T cells a fitness disadvantage in vitro but those CAR-T cells ultimately had a fitness advantage in vivo in the TME. This may be due to attenuation of strong IL-2 signaling in vitro, suggesting the possibility that CAR-T cells become dependent on IL-2 for survival during in vitro expansion and this leads to impaired survival upon transfer in vivo where IL-2 can be limiting. Future studies will investigate IL-2 signaling and metabolic dependencies of CAR-T cells, with the goal of identifying strategies to mitigate this dependency and improve survival and function in vivo. Funding Sources Supported by T32AI138932 and R01CA217987 Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)