CD274 (Programmed death-ligand 1 (PD-L1))

CD274 (Programmed death-ligand 1 (PD-L1)) is a protein that helps the body’s natural immune system defend itself against infections and diseases, including cancer. Patients with low levels of PD-L1 in their cancer typically have a poor prognosis.

The ligand of Programmed cell death protein 1 (PD-1) Programmed death-ligand 1 (PD-L1) is a member of the B7 gene family.
Freeman et al. 2000

Programmed death-ligand 1 (PD-L1) is highly expressed on the surface of tumor cells, by antigen-presenting cells , including human peripheral blood monocytes stimulated with interferon gamma , and activated human and murine dendritic cells and binds to Programmed cell death protein 1 (PD-1) on the surface of activated T cells, leading to suppression of T cells.
Freeman et al. 2000
Yin et al. 2021

In addition, Programmed death-ligand 1 (PD-L1) is expressed in nonlymphoid tissues such as heart and lung.
Freeman et al. 2000

Cancer therapy with anti-PD-1 or anti-PD-L1 antibodies is made dependent on PD-L1 (biomarker) expression in many entities. There are 5 different approved immunohistochemical assays for measuring the tumor cell surface PD-L1. However, conventional PD-L1 testing through tumor biopsy has multiple technical drawbacks. Therefore, another form of PD-L1 secreted by the tumor into the circulation (exosomal PD-L1) has emerged as a potential target. But studies are still in their preliminary stages and further testing is required
Zouein et al. 2021 Immunotherapy 13: 1053-1065

The expression of PD-L1 can serve as a potent mechanism for potentially immunogenic tumors to escape from host immune responses and that blockade of interaction between PD-1 and PD-L1 may provide a promising strategy for specific tumor immunotherapy.
Iwai et al., 2002

see also:
Anti-PD-1 Antibodies / PD-1 inhibitors & Preclinical/Clinical data
Programmed death-ligand 1 (PD-L1) & Assays