ENTPD1 and diabetes mellitus: CD39 is an ectoenzyme that hydrolyses adenosine triphosphate and adenosine diphosphate to adenosine monophosphate (AMP) and exhibits immunosuppressive effects.15, 16 Growing evidence implicates an important role for CD39 in Treg‐suppressive function.17, 18, 19 In our previous study of diabetes, the defective suppressive function of Tregs in type 1 diabetic patients is due to lowered expression of CD39 on Tregs.13 In this study, we also observed CD39 expression on Tregs to be lower in BPH patients.