ABSTRACT
PD-1/PD-L1 signaling pathway as a T cell immune response co-stimulatory signaling pathway plays an important role in adaptive immunity. PD-1 is a major co-receptor expressing on T cells, binding with its ligands(PD-L1 and PD-L2), PD-1 can inhibit T cell activation and protect the body against the attacks from its own immune system. In addition to adjusting and maintaining autoimmune tolerance, in tumor cells PD-L1 expression is up-regulated, while in the virus-infected T cells PD-L1 expression is also upregulated. PD-1 / PD-L1 are involved in the tumor and infectious pathogen immune evasion, thus blocking the PD-1 / PD-L1 signaling pathway has become a hot research of cancer and chronic diseases. Currently, there are several anti-PD-1 or PD-L1 monoclonal antibodies approved by the FDA to enter clinical studies, which have shown significant anti-cancer effect.