PD-L1 (also known as B7-H1 or CD274), one of the ligands of PD-1, binds to PD-1 on effector T cells for immunosuppressive functions and is widely expressed in a variety of tumor cells; the high expression of PD-L1 also predicts poor prognosis [198–200]. The gene discussed is PDCD1; the disease is neoplasm.