Di- and tripeptidyl peptidases (EC 3.4.14.-) make up an individual class of aminopeptidases. DPP4 (EC 18.104.22.168) is also known as adenosine deaminase complexing protein 2 or CD26 (cluster of differentiation 26). It is an antigenic enzyme expressed on the surface of most cell types and is associated with immune regulation, signal transduction and apoptosis. It is an intrinsic membrane glycoprotein and a serine exopeptidase that cleaves X-proline dipeptides from the N-terminus of polypeptides. Additionally, it has been proven to be implicated in the pathogenesis of type 2 diabetes.
 Vildagliptin, a dipetidyl peptidase-IV inhibitor, improves model-assessed β-cell function in patients with type 2 diabetes. A. Mari et al. J. Clin. Endocrinol. Metab. 2005, 90, 4888-4894.