PDCD1 and cancer: Novel and effective immunotherapies for patients with various types of cancer are becoming a clinical reality, in part because of the remarkable clinical efficacy observed with immune checkpoint inhibitors such as programmed cell death protein 1 (PD-1, a T-cell co-inhibitory receptor) and one of this protein’s ligands, programmed cell death ligand 1 (PD-L1, also known as B7-H1 or CD274)1–12.