Since then, the gate of immunotherapy has been thoroughly opened, and more monoclonal antibody drugs blocking PD-1 or its ligand PD-L1 have been approved in succession by the FDA alone or in combination with other drugs to treat numerous malignancies, such as melanoma, lung cancer, lymphoma, esophageal carcinoma, gastric cancer, and hepatocellular carcinoma [11–13]. The gene discussed is PDCD1; the disease is melanoma.