Programmed death ligand 1 (PD-L1), also known as cluster of differentiation 274 (CD274) or B7 homolog 1 (B7-H1), is a type I transmembrane protein with a molecular weight of 40 kDa encoded by the CD274 gene.PD-L1 may play an important role in the suppression of the immune system in pregnancy, tissue transplantation, autoimmune disorders, and in other diseases such as hepatitis. Typically, the immune system responds to foreign antigens that accumulate in the lymph nodes or spleen, triggering the proliferation of antigen-specific CD8+ T cells.PD-1 receptor/PD-L1 or B7.1 receptor/PD-L1 binding transmits an inhibitory signal that suppresses the proliferation of CD8+ T cells. In contrast, there are reports suggesting that PD-L1 has a co-stimulatory effect on dormant T cells.PD-L1 may inhibit sustained T cell responses by inducing apoptosis and blocking cell cycle progression in T cells.