Chimeric antigen receptor macrophages (CAR-M) sensitize HER2+ solid tumors to PD1 blockade

We previously developed human CAR macrophages (CAR-M) and demonstrated redirection of macrophage anti-tumor function leading to tumor control in immunodeficient xenograft models. Here, we developed clinically relevant fully immunocompetent syngeneic models to evaluate the potential for CAR-M to remodel the tumor microenvironment (TME), induce T cell anti-tumor immunity, and sensitize solid tumors to PD1/PDL1 checkpoint inhibition. In vivo, anti-HER2 CAR-M significantly reduced tumor burden, prolonged survival, remodeled the TME, increased intratumoral T cell and natural killer (NK) cell infiltration, and induced epitope spreading. CAR-M therapy protected against antigen-negative relapse in a T cell dependent fashion, confirming long-term anti-tumor immunity. In HER2+ solid tumors resistant to anti-PD1(aPD1) monotherapy, the combination of CAR-M and aPD1 significantly improved tumor growth control, survival, and remodeling of the TME. These results demonstrate synergy between CAR-M and T cell checkpoint blockade and provide a strategy to enhance response to aPD1 therapy for patients with non-responsive tumors.