Anti-inflammatory drugs remodel the tumor immune environment to enhance immune checkpoint blockade efficacy

Identifying strategies to improve the efficacy of immune checkpoint blockade (ICB) remains a major clinical need. Here, we show that therapeutically targeting the COX-2/PGE2/EP2-4 pathway with widely used non-steroidal and steroidal anti-inflammatory drugs synergized with ICB in mouse cancer models. We exploited a bilateral surgery model to distinguish responders from non-responders shortly following treatment and identified acute IFN-γ-driven transcriptional remodeling in responder mice, which was also associated with patient benefit to ICB. Monotherapy with COX-2 inhibitors or EP2-4 PGE2 receptor antagonists rapidly induced this response program and, in combination with ICB, increased the intratumoral accumulation of effector T cells. Treatment of patient-derived tumor fragments from multiple cancer types revealed a similar shift in the tumor inflammatory environment to favor T cell activation. Our findings establish the COX-2/PGE2/EP2-4 axis as an independent immune checkpoint and a readily translatable strategy to rapidly switch the tumor inflammatory profile from cold to hot.