Sammy Navarre, Maki N. Ishibashi, Achuth Nair, Ivan Reyes-Torres, Meriem Belabed, Laszlo Halasz, Matthew D. Park, Raphaël Mattiuz, Merouane Ounadjela, Gertrude Gunset, Jorge Mansilla-Soto, Judith Feucht, Annalisa Cabriolu, Jessica Le Berichel, Alexander Birbrair, Justin Eyquem, Brian D. Brown, Miriam Merad, Michel Sadelain, Jalal Ahmed
Metastatic solid tumors remain the principal cause of cancer mortality worldwide. High tumor burden impairs responses to chimeric antigen receptor (CAR) T cell therapy, yet off-tumor toxicity limits the doses that can be safely delivered. Strategies to selectively enhance CAR T cell activity at tumor sites could widen the therapeutic window. Using syngeneic models of extensive metastatic lung adenocarcinoma and melanoma, we show that 8 Gy of tumor irradiation significantly enhanced CAR T cell persistence in a manner critically dependent on dendritic cells (DCs). Irradiation promoted trogocytic antigen dressing of tumor antigens onto DCs, which then expanded CAR T cells through the chimeric receptor. Without functional DCs, irradiation failed to sustain CAR T cell persistence and tumors relapsed. Irradiation increased CAR T cell numbers within tumors but not in adjacent normal lung tissue that also expressed target antigen, conferring robust control of tumor without increased toxicity. These data define a mechanistic basis and rationale for combining radiotherapy with CAR T cell therapy.