Immune checkpoint protein inhibitors, especially antibodies against programmed cell death-1 (PD-1) and its ligand programmed death-ligand 1 (PD-L1), have elicited anti-cancer effects and long-lasting alleviation in melanoma, lymphoma, bladder cancer, non-small-cell lung cancer, RCC, and many other malignancies (87). This evidence concerns the gene PDCD1 and melanoma.