PDCD1 and melanoma: It should be emphasized that cytotoxic T CD8+ cells are considered the most powerful effectors of the anticancer response among the immune repertoire being the backbone of cancer immunotherapy with immune checkpoint inhibitors anti-CTLA-4 (cytotoxic T-lymphocyte associated protein 4) or anti-PD-1 (programmed cell death protein 1), including melanoma [73,74].