Two B7 family members, PD-L1 and programmed death ligand-2 (PD-L2), are ligands for PD-1, and while PD-L2 is primarily expressed on macrophages and dendritic cells (DCs), PD-L1 is expressed on the surface of tumor cells as well as on certain immune cells like macrophages, T cells, and DCs [23,24]. The gene discussed is PDCD1; the disease is neoplasm.