Common Acute Lymphocytic Leukemia Antigen

Common acute lymphocytic leukemia antigen (CALLA' ; CD10) is an important cell surface marker in the diagnosis of human acute lymphocytic leukemia (ALL) (references 1-8) . It is present on leukemic cells of pre-B phenotype, which represent 85% of cases of ALL, and is absent from normal PBMC. However, CALLA is not restricted to leukemic cells and is found on a variety of normal tissues (9-14) . It is particularly abundant in kidney, where it is present on the brush border of proximal tubules and on glomerular epithelium (2, 9, 10) . CALLA is a glycoprotein of Mr 9.4 x 104-10 5 (4-11, 14-19) for which no functional activity has yet been described . We report on the cloning of a cDNA coding for CALLA, and show that the amino acid sequence deduced from the cDNA sequence is identical to that of human membrane-associated neutral endopeptidase (NEP; EC 3.4.24.11), also known as enkephalinase. NEP cleaves peptides at the amino side of hydrophobic residues (21, 22) and inactivates several peptide hormones including glucagon, enkephalins, substance P, neurotensin, oxytocin, bradykinin, and the chemotactic peptide fMLF (20-24) .