PDCD1 and melanoma: Nivolumab, a fully human immunoglobulin G4 anti-PD-1 monoclonal antibody that was created from Chinese hamster ovary cells, is approved for multiple advanced tumors, including melanoma, non-small cell lung cancer (NSCLC), renal cell cancer, Hodgkin’s lymphoma, squamous head and neck cancer, and urothelial carcinoma [14].