Recent studies revealed that targeting the immune checkpoint molecules programmed cell death protein 1 (PD-1) or programmed cell death 1 ligand 1 (PD-L1) by antibodies can significantly improve T cell-mediated antitumor responses and can induce objective clinical responses in about 20–40% of patients with different tumor types [1,2,3]. The gene discussed is PDCD1; the disease is neoplasm.