To date, thirteen FDA-approved agents targeting PD-1, PD-L1 or CTLA-4 are used in the treatment of multiple cancer types, including melanoma, lung cancer, lymphoma, gastric cancer, Merkel cell carcinoma, head and neck cancer, hepatocellular carcinoma, cervical cancer, urothelial cancer, renal cell cancer, biliary tract cancer, cutaneous squamous cell cancer, endometrial cancer, breast cancer, and sarcoma (Table 1). Here, PDCD1 is linked to melanoma.