Some studies have revealed that PD-1 suppresses the antitumor function of T cells primarily by inactivating CD28 signaling, indicating an important role for the CD28/B7 pathway in anti-PD-1 therapy in cancer patients.33,43 Indeed, we further found that butyrate promotes the expression of CD28 and PD-1 in cytotoxic CD8+ and Vδ2+ T cells by inducing histone 3 lysine 27 acetylation at the promoters of Cd28 and Pdcd1 genes. Here, PDCD1 is linked to cancer.