PDL1 (CD274), or programmed cell death-ligand 1, is a transmembrane protein expressed in B and T cells that acts as an immune checkpoint regulator by suppressing the T-cell response. The primary receptor for PDL1 is PD1 (PDCD1), and binding of PDL1 to PD1 suppresses T cell migration, proliferation, and restricts tumor cell death. High levels of expression of PDL1 are associated with poor prognosis in certain carcinomas, and expression is also associated with EGFR mutations, the onset of which may directly lead to upregulation of PDL1. Current trials involving PDL1 inhibitors have shown impressive results in treating advanced stage cancers such as melanomas. This protein is expressed in the cytoplasm and membrane in normal immune cells, placental trophoblasts, and some cancers. References: Dong, H. et al. Nat Med. 2002 Aug;8(8):793-800. Epub 2002 Jun 24; Zhang, 2016; Chen 2015; Tang 2015; Nat Med 2002(8):793