Abstract

Chimeric Antigen Receptor (CAR) T-cell therapy can be effective in treating human cancer but loss of the antigen recognized by the CAR poses a major obstacle. Here, we report an approach for vaccine boosting CAR T-cells, which triggers engagement of the endogenous immune system to circumvent antigen-negative tumor escape. Vaccine-boosted CAR T-cells promoted dendritic cell (DC) recruitment to tumors, increased tumor antigen uptake by DCs, and elicited priming of endogenous anti-tumor T-cells (antigen spreading). This process was accompanied by a shift in toward oxidative phosphorylation in CAR T-cells and was critically dependent on CAR-T-derived IFN-{gamma}. Antigen spreading induced by vaccine-boosted CAR-T enabled a proportion of complete responses even when the initial tumor was 50% CAR-antigen-negative, and heterogenous tumor control was further enhanced by genetically amplifying CAR-T IFN-{gamma} expression. Thus, CAR T-cell-derived IFN-{gamma} plays a critical role in promoting antigen spreading, and vaccine boosting provides a clinically-translatable strategy to drive such responses against solid tumors.