CD274 and neoplasm: PD-1 is another inhibitory T-cell receptor that is engaged by its two known ligands PD-L1 (also known as B7-H1 or CD274) and PD-L2 (also known as B7-DC or CD273) primarily within the tumor microenvironment, and increased PD-1 and PD-L1 expression appeared to increased immune suppressive signals, which was related to inhibition of the effector phase of T cell responses and reduced antitumor activity[20].