Fes-Deficient Macrophages Prime CD8+ T Cells to Stimulate Anti-tumor Immunity and Improve Immunotherapy Efficacy

Homeostatic immunoregulatory mechanisms that prevent adverse effects of immune overaction can serve as barriers to successful anti-cancer immunity, representing attractive targets to improve cancer immunotherapy. Here, we demonstrated the role of the non-receptor tyrosine kinase Fes, abundantly expressed in immune cells, as an innate intracellular immune checkpoint. Host Fes-deficiency delayed tumor onset in a gene dose-dependent manner and improved tumor control, survival, doxorubicin efficacy, and anti-PD-1 therapy sensitization in murine triple-negative breast cancer and melanoma models. These effects were associated with a shift to an anti-tumorigenic immune microenvironment. Fes-deficient macrophages displayed increased Toll-like receptor signaling, proinflammatory cytokine production, antigen presentation to and activation of T cells, leading to increased cancer cell killing in vitro and tumor control in vivo. This study highlights Fes as an innate immune checkpoint with potential as a therapeutic target and a predictive biomarker to guide immune checkpoint inhibitor treatment.