CD274, also known as PD-L1 (Programmed Death-Ligand 1), is a gene that encodes a transmembrane protein involved in immune regulation. PD-L1 is primarily expressed on antigen-presenting cells, including dendritic cells, macrophages, and B cells, as well as on non-immune tissues, particularly under inflammatory conditions. This protein plays a critical role in immune evasion by interacting with PD-1 (Programmed Cell Death Protein 1), an inhibitory receptor expressed on T cells. The PD-L1/PD-1 interaction suppresses T-cell activation, reducing immune responses against tumors and infections. Overexpression of PD-L1 is often observed in cancers, allowing them to escape immune surveillance. As a result, PD-L1 inhibitors, such as monoclonal antibodies, have become a major focus in cancer immunotherapy, effectively restoring T-cell function and enhancing antitumor immunity.