CD279, also known as programmed cell death Protein 1(PD-1), is encoded by the PDCD1 gene. PD1 is a member of the immunoglobulin superfamily and belongs to the CD28 superfamily with CD28, CTLA-4 and ICOS molecules. Pd1 is mainly expressed in activated CD4+T and CD8+T cells and B cells in the form of monomers, and its ligands are B7-H1 and B7-DC. Studies have confirmed that enhancing PD-1 signaling can downregulate the response of activated T and B cells in peripheral tissues, and play an important role in maintaining peripheral T and B cell tolerance.