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CD39, also known as ectonucleoside triphosphate diphosphohydrolase-1 （ENTPD1）, is a membrane-bound enzyme that hydrolyzes extracellular nucleotides such as ATP and ADP into AMP in a Ca2?- and Mg2?-dependent manner. It plays a crucial role in regulating immune responses and vascular function. In the tumor microenvironment, CD39 works with CD73 to convert ATP into adenosine, an immunosuppressive molecule that inhibits the activity of effector immune cells while promoting the function of regulatory immune cells, thus contributing to tumor immune evasion. This protein is highly expressed in various cell types within the tumor microenvironment, including tumor cells, stromal cells, endothelial cells, and immune cells. CD39 is also involved in thromboregulation and has been identified as a potential therapeutic target for cancer immunotherapy.