Transgenic expression of mutated CD47 enables CD47-CAR T cell persistence and antitumor activity in vivo 4053

Abstract Description   CD47 is a cell surface protein that binds SIRPα on macrophages to inhibit phagocytosis. Multiple solid tumors express high levels of CD47 making it a promising target for immunotherapeutic approaches. Previously, we developed CD47-CAR T cells that downregulate cell surface CD47 to overcome fratricide and retain effector function in vitro. However, CAR T cells lacking CD47 failed to function in vivo due to rapid elimination by macrophages. To overcome this lack of efficacy in vivo, we engineered CD47-CAR T cells to express a mutated CD47 protein (mutCD47; Q31P), which avoids CAR recognition (fratricide) and retains anti-phagocytic signaling (SIRPα binding). In coculture assays, both CD47-CAR and mutCD47-CAR T cells specifically recognized and killed CD47+ target cells. In vivo, CD47-CAR T cells were rapidly eliminated post-infusion and lacked antitumor activity in multiple models. In contrast, mutCD47-CAR T cells trafficked and persisted at sites of tumor post-infusion. Further, mutCD47-CAR T cells had potent antitumor activity in both locoregional (i.p. tumor and i.p. T cells) and systemic (i.v. tumor and i.v. T cells) solid tumor models. In conclusion, expressing mutated CD47 on the surface of CD47-CAR T cells enables their persistence and antitumor activity in vivo. Future work will build upon these findings to develop CD47-CARs activated only within the tumor microenvironment to avoid off-tumor toxicities due to lower levels of CD47 expression in normal tissues. Funding Sources Assisi Foundation of Memphis; American Lebanese Syrian Associated Charities (ALSAC) Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)