Relaxin gene delivery modulates macrophages to resolve cancer fibrosis and synergizes with immune checkpoint blockade therapy

Cancer fibrosis serves as a major therapeutic barrier in desmoplastic tumors. Relaxin (RLN; a systemic hormone) is efficacious to decrease fibrosis, but the in vivo mechanism of action is not clear. Considering the localization of relaxin family peptide receptor type 1 (RXFP1), the receptor for RLN, on macrophages, we hypothesize that macrophages can be modulated by RLN to ameliorate cancer fibrosis. Using KPC mouse model of pancreatic ductal adenocarcinoma (PDAC), here, we report locally expressed RLN with targeted gene delivery induces increased F4/80(+)CD206(+) macrophages originating from Ly6C(+) monocytes, promoting fibrosis depletion and cytotoxic T cell infiltration. Moreover, RLN gene delivery synergizes with PD-L1 blockade for tumor inhibition by enhancing T cell–mediated tumor cell killing and macrophage phagocytosis. Collectively, our results reveal previously unidentified insights into the modulation of macrophages to regulate tumor-associated fibrosis, providing a feasible strategy to reverse the immunosuppressive environment and improve the therapeutic outcome of checkpoint immunotherapies.