Programmed death-ligand 1 (PD-L1) also known as cluster of differentiation 274 (CD274) or B7 homolog 1 (B7-H1) is a protein that in humans is encoded by the CD274 gene. The formation of PD-1 receptor / PD-L1 or B7.1 receptor /PD-L1 ligand complex transmits an inhibitory signal which reduces the proliferation of these CD8+ T cells at the lymph nodes. After that PD-1 is also able to control the accumulation of foreign antigen specific T cells in the lymph nodes through apoptosis, which is further mediated by a downregulation of the Bcl-2 gene.