Programmed cell death ligand 1 (PDL1, CD274) is a type 1 transmembrane protein with role in the regulation of cellular immune responses. PDL1 and its receptor PD-1, interacts and regulating T lymphocyte activation and immune tolerance. Blockade of PD-L1/PD-1 interaction, it enhances the antitumor activity of T lymphocytes. PDL1 is commonly expressed in many tissues and cells, eg. placenta, tonsil and histiocytes. It over expressed in many human tumors such as non-small cell lung carcinoma (NSCLC), melanoma, DLBCL, and different kind of carcinomas. The staining pattern is membranous.