Programmed death ligand 1 (PD-L1, also known as CD274/B7-H1), a member of B7 family was identified by searching for molecules that share homology with the immunoglobulin V and C domains of B7-1 and B7-2 among the human cDNA expressed sequence tags in the National Center for Biotechnology Information database. PD-L1 is a ligand for programmed death 1 (PD-1) which belongs to the CD28/CTLA4 subfamily. Although in vitro study indicated that the cross-linking of PD-1 by PD-L1 leads to down-regulation of T-cell responses, some studies have shown that T cells stimulated with low levels of anti-CD3 and immobilized PD-L1-Ig were activated, proliferation and production of IFN-γ, GM-CSF and IL-10 from the T cells were enhanced.Synonyms: B7 homolog 1, B7H1, PD-L1, PDCD1 ligand 1, PDCD1L1, PDCD1LG1, Programmed cell death 1 ligand 1, Programmed death ligand 1