PDCD1 and cancer: A previous study reported that the abundance of PD-1 in patients with tumors is a prognostic factor associated with better survival after ICI therapy.8 Some studies have demonstrated the CD28-costimulation requirement for CD8 T cell rescue and have suggested an important role for the CD28/B7 pathway in PD-1 therapy in cancer patients.32,33 However, it is not yet clear whether butyrate directly regulates the expression of PD-1 and CD28 in T cells.