Since FDA approval in 2011 of the first immune checkpoint inhibitor (ICI) ipilimumab, an anti-CTLA-4 monoclonal antibody (MoAb), another six ICIs have been approved for cancer therapy: three anti-PD-1 MoAbs, nivolumab, pembrolizumab, and cemiplimab, and three anti-PD-L1 MoAbs, atezolizumab, avelumab, and durvalumab [98]. The gene discussed is PDCD1; the disease is cancer.