CD274 and cancer: PD-1 is another co-inhibitory receptor expressed on the surface of T cells upon T cell activation, which could bind to its receptor including PD-L1 and PD-L2, on the surface of tumor cells or other immune cells within the tumor environment to control the cytolytic function of effector T cells through activation of the tyrosine phosphatase SHP1/2 signaling.24,520 As such, antibodies against PD-1/PD-L1 are supposed to be effective for the treatment of cancers via the invigoration of infiltrating CD8+T cells.521 Pembrolizumab and nivolumab are the two PD-1 inhibitors approved by FDA in 2014.