PDCD1 and cancer: Drugs targeting this negative immune regulatory pathway, including the anti-PD-1 monoclonal antibodies (mAbs) nivolumab (5), pembrolizumab (6), and cemiplimab (7) and the anti-PD-L1 mAbs atezolizumab (8), avelumab (9), and durvalumab (10) have been approved for the treatment of various cancer types.