Two anti-PD-1 monoclonal antibodies (nivolumab and pembrolizumab) [25–27] and three anti-PD-L1 monoclonal antibodies (atezolizumab, avelumab, and durvalumab) [28–30] have been approved by the US Food and Drug Administration (FDA) for treating cancers, for example, melanoma, non-small cell lung cancer, and renal cell carcinoma. Here, PDCD1 is linked to melanoma.