Anti-CD26 antibodies are reagents directed against CD26 encoded by the gene DPP4, or 'dipeptidyl peptidase 4' in humans. The 766-amino acid protein is a member of the Peptidase S9B family, DPPIV subfamily. The cellular localization is predicted to be membrane-associated and secreted. Glycosylation sites have been reported. The CD26 antigen is a documented cancer stem cell marker.