Programmed death receptor-1 (PD-1) is a receptor primarily expressed in T cells, while its ligands, programmed death-ligand 1 (PD-L1) and programmed death-ligand 2 (PD-L2), are expressed in various cell types, including normal lymphocytes and diverse tumor cells such as lung cancer and melanoma. Here, PDCD1LG2 is linked to lung cancer.