CD38, a differentiation antigen of B lymphocytes, is a type II integral membrane protein. It is also known as ADP-ribosyl cyclase and nicotinamide adenine dinucleotide (NAD) glycohydrolase. Through its production of cyclic ADP-ribose, CD38 modulates calcium-mediated signal transduction in various cells, including pancreatic β cells. The major enzymatic activity of CD38 is the hydrolysis of NAD. CD38 is a prognostic biomarker for acute B lymphoblastic leukemia.