PD-1 and its ligands PD-L1 PD-L2 are widely expressed on the surface of a variety cells group costimulatory molecules related to negative immune regulation. The activation PD-1/PD-L1 signaling pathway is beneficial for tumors escape from surveillance, but specific tumor mechanism not yet clear. As far as efficacy anti-PD-1 anti-PD-L1 antibodies concerned, more in-depth research mechanisms still...