Programmed death-1 (PD-1) and its ligand PD-L1 are the major members of inhibitory costimulatory molecules and express high in a variety of tumor cells and their associated cells surface,while the proportion of regulatory T cells (Tregs) are abnormally elevated in tumor infiltrating T lymphocytes cells.PD-L1 combined with PD-1 and Treg help tumors evade immune clearance,weaken immune responses and induce immune tolerance.New researches find that PD-L1 plays an important role in the development and function maintenance of inducible Treg (iTreg),and PD-L1 signal can change initial CD4 + CD25-T cells into iTreg to play a role of immunosuppression.Research on PD-1 signaling pathway can provide a new theoretical basis for the inhibition of tumor immune escape in clinical application of immunotherapy and better treatments.

Programmed death-1 (PD-1) and its ligand 1 (PD-L1) play critical roles in the identification and elimination of tumor cells evading the host's immune system.Tumor model in mice which is given anti-PD-L1 monoclonal antibody shows obviously host anti-tumor response.Currently,immunotherapy drugs of PD-1/PD-L1 signaling pathways receive good effects in a variety of tumors failure of the traditional method,and with less adverse reaction,which provide valuable clinical experiences in advanced tumor immunotherapy.