Eradication of tumors with pre-existing antigenic heterogeneity by vaccine-mediated co-engagement of CAR T and endogenous T cells

Chimeric Antigen Receptor (CAR) T-cell therapy can be effective in treating human cancer but, loss/downregulation of the antigen recognized by the CAR poses a major obstacle to tumor eradication. Here, we report an approach for vaccine boosting CAR T-cells, which triggers engagement of the endogenous immune system to stop antigen-negative tumor escape. Vaccine boosting enhanced CAR T-cell polyfunctionality, increased tumor antigen uptake by dendritic cells, and elicited priming of endogenous anti-tumor T cells (antigen spreading). This process required vaccine-induced enhancements in CAR T IFN-γ production and a metabolic shift in CAR T-cells toward oxidative phosphorylation. Antigen spreading induced by vaccine-boosted CAR-T therapy enabled control of solid tumors with substantial pre-existing heterogeneity, which was further enhanced by genetically amplifying CAR T IFN-γ expression. Thus, CAR T cell-derived IFN-γ plays a critical role in promoting endogenous anti-tumor immunity, and vaccine boosting provides a clinically-translatable strategy to drive such responses against solid tumors. Between 4 and 8 replicates of intratumor CAR-T cells and splenic CAR-T cells treated with and without vaccine boosting.