Currently, there are two that are approved for the treatment of melanoma metastasis: ipilimumab, a monoclonal antibody against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and pembrolizumab or nivolumab, antibodies against programmed cell death protein 1 (PD-1) [174,175,176]. Here, PDCD1 is linked to melanoma.