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.
Programmed death-ligand 1 (PD-L1) is a 40kDa type 1 transmembrane protein that contributes to tumor immunosuppression during particular events such as pregnancy, tissue allografts, autoimmune disease and other disease states such as hepatitis.
Normally the immune system reacts to foreign antigens where there is some accumulation in the lymph nodes or spleen which triggers a proliferation of antigen-specific CD8+ T cells. The binding of PD-L1 to PD-1 or B7.1 transmits an inhibitory signal which reduces the addition of these CD8+ T cells at the lymph nodes and supplementary to 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 lower regulation of the gene Bcl-2.
Chen et al. revealed a novel mechanism of how PD-L1 regulates epithelial-mesenchymal-transition (EMT) of cancer cells, namely STAT1/IFIT2 signal pathway is required in PD-L1 mediated EMT in human esophageal cancer 1)
Famoso et al. reported the first patient with a pineal melanoma to be managed by targeting PD-L1. Furthermore, she achieved the second longest overall survival and the longest progression-free survival reported in the literature 2).