PDCD1 and cancer: This chimeric receptor inhibited T cell proliferation and cytokine production.81 PD-1 ITSM motif serves as docking site for SHP-1 (Src-homology region 2 domain containing phosphatase-1) and SHP-2 phosphatases.81 A mutation at this site abrogates PD-1 suppressive effect.81 However, whether cancer cells activate this immunosuppressive signaling pathway in immune cells remains to be fully clarified.