Anti-CD13 antibodies are directed against the CD13 antigen. The CD13 protein is a reported synonym for the human gene ANPEP, encoding alanyl aminopeptidase, membrane. The full-length protein is 109,540 daltons in mass and has been noted to be membrane-associated. This protein is reported to contain sites of glycosylation. The CD13 antigen is a documented cancer and mesenchymal stem cell marker.