Nivolumab, a fully human PD-1 blocking antibody, has been developed, and a durable clinical response (43, 44) together with increased survival has been reported in a large phase I trial recruiting patients with different tumor types, including melanoma, renal cell carcinoma, colorectal cancer, and non-small-cell lung cancer (NSCLC) (45). Here, PDCD1 is linked to melanoma.