PD-1 signaling negatively regulates the common cytokine receptor γ chain via MARCH5-mediated ubiquitination and degradation to suppress anti-tumor immunity.

Combination therapy with PD-1 blockade and IL-2 substantially improves anti-tumor efficacy comparing to monotherapy. The underlying mechanisms responsible for the synergistic effects of the combination therapy remain enigmatic. Here we show that PD-1 ligation results in BATF-dependent transcriptional induction of the membrane-associated E3 ubiquitin ligase MARCH5, which mediates K27-linked polyubiquitination and lysosomal degradation of the common cytokine receptor γ chain (γ). PD-1 ligation also activates SHP2, which dephosphorylates γ, leading to impairment of γ family cytokine-triggered signaling. Conversely, PD-1 blockade restores γ level and activity, thereby sensitizing CD8 T cells to IL-2. We also identified Pitavastatin Calcium as an inhibitor of MARCH5, which combined with PD-1 blockade and IL-2 significantly improves the efficacy of anti-tumor immunotherapy in mice. Our findings uncover the mechanisms by which PD-1 signaling antagonizes γ family cytokine-triggered immune activation and demonstrate that the underlying mechanisms can be exploited for increased efficacy of combination immunotherapy of cancer.