PDCD1 and melanoma: Monotherapy with antagonistic antibodies targeting programmed cell death receptor 1 (PD-1, CD279) on the surface of T cells or combination therapy with antagonistic antibodies against cytotoxic T-lymphocyte-associated protein-4 (CTLA-4, CD152) are now standard-of-care treatments for patients with advanced melanoma with 5-year survival rates of approximately 50% (5).