PDCD1 and cancer: Several notable clinical successes in cancer immunotherapy have been made over the past decade, including the FDA approval of the chimeric antigen receptor (CAR) T cell therapy and therapies with monoclonal antibodies (mAbs) targeting cytotoxic T lymphocyte antigen 4 (CTLA4), programmed cell death 1 (PD-1), or its ligand (PD-L1) as the immune checkpoint inhibitors.