CD274 and neoplasm: The interaction of these “immune checkpoint” molecules with their ligands, B7.1/B7.2 and PD-L1/PD-L2 expressed on antigen-presenting cells and tumor cells, respectively, inhibits positive signals mediated by the T-cell receptor (TCR) or the costimulatory receptor CD28 and thereby leads to suppression of T-cell responses [2–5].