PD-L1 (Programmed death-ligand 1), also known as CD274 or B7 homolog 1 (B7-H1), is encoded by the CD274 gene. PD-L1 is a class I transmembrane protein with a size of 40 kDa, with a total length of 290 amino acids, including an IgV-like region, an IgC-like region, a transmembrane hydrophobic region and an intracellular region. PD-L1 is the ligand of PD-1, which is commonly expressed in antigen-presenting cells, macrophages, activated T cells, B cells, monocytes, endothelial cells, etc.
Immune checkpoints include CTLA4-CD80, PD-1-PD-L1/PD-L2, GAL9-TIM3, etc., among which PD-1-PD-L1 has become a research hotspot in tumor immunity in recent years. PD-1 is an important negative regulatory molecule for immune cell activation. By combining with PD-L1, it produces a variety of biological effects such as inhibiting the proliferation and activation of lymphocytes, inhibiting the release of cytokines, etc., thereby exerting immunosuppressive effects. Through the high expression of PD-1 and PD-L1, tumor cells go through the three processes of clearance, balance, and escape of the immune microenvironment, and eventually may escape the body's immune system and form tumors.Studies have found that a variety of malignant tumors, such as lung cancer, melanoma, gastric cancer, breast cancer, renal cell carcinoma, etc., through the high expression of PD-L1 and the PD-1 molecule on the surface of tumor-infiltrating lymphocytes, inhibit the function of lymphocytes, and cause tumors. One of the important reasons for immune escape. By preparing PD-L1 specific antibodies to block the PD-1-PD-L1 signaling pathway, and enhance the function of CTL to kill cancer cells. Therefore, the PD-1-PD-L1 pathway has broad prospects for the treatment of malignant tumors.