CD274 and neoplasm: Additionally, PD-1 interacts with its ligands, programmed death-ligand 1 (PD-L1) (B7-H1; CD274) and programmed death-ligand 2 (PD-L2) (B7-DC; CD273), which are expressed on antigen-presenting cells (APCs) and, in some cases, tumor cells to mediate immunosuppression [7,8].