Monoclonal antibodies targeting PD-1 (including pembrolizumab and nivolumab) as well as PD-L1 (including avelumab, atezolizumab, and durvalumab,) and those targeting CTLA-4 (including ipilimumab and tremelimumab) [12], have been approved by the FDA for several cancers, such as melanoma, renal cell cancer, lung cancer, and colorectal cancer [13]. Here, PDCD1 is linked to melanoma.