Purification and characterization of fetal hematopoietic cells that express the common acute lymphoblastic leukemia antigen (CALLA).

Abstract

Fetal hematopoietic cells that express the common acute lymphoblastic leukemia antigen (CALLA) were purified from both fetal liver and fetal bone marrow by immune rosetting with sheep erythrocytes coated with rabbit anti-mouse immunoglobulin and by fluorescence-activated cell sorting. Dual fluorescence techniques disclosed that these cells were heterogenous with respect to the expression of a series of differentiation and activation antigens defined by monoclonal antibodies. Thus, whereas all CALLA+ cells were Ia+ and expressed two activation antigens, J2 and T10, only 30-50% expressed B1 antigen. Furthermore, using methanol-fixed cells, it could be shown that approximately 20% contained intracytoplasmic mu chains (cyto-mu) and that approximately 15% were positive for the terminal transferase enzyme (TdT) marker. The CALLA+ fetal cells thus closely resemble the childhood acute lymphoblastic leukemia cell with respect to surface marker phenotype. A population of CALLA- cells devoid of mature erythroid and myeloid surface markers was found to contain higher numbers of TdT+ cells but lower numbers of cyto-mu, B1, and Ia+ cells than the CALLA+ subset. In vitro analysis of normal, purified CALLA+ cells demonstrated that incubation at 37 degrees C with J5 monoclonal antibody specific for CALLA resulted in the specific modulation of surface antigen. Similar results have previously been obtained with CALLA+ tumor cells. Although phenotypic analysis of CALLA+ cells suggests that these cells are relatively immature lymphoid cells, CALLA+ cells do not appear to contain either myeloid precursor cells (CFU-G/M) or the earliest lymphoid stem cells.

Common acute lymphoblastic leukemia antigen expressed on leukemia and melanoma cell lines has neutral endopeptidase activity.

“…CALLA is present on hemopoietic precursors found in bone marrow and fetal liver, but not on mature B cells (9,44). The demonstration ofthe identity ofCALLA and NEP implies that this enzyme is associated with early stages in B cell ontogeny (9,44).…”

“…The demonstration ofthe identity ofCALLA and NEP implies that this enzyme is associated with early stages in B cell ontogeny (9,44). This might be linked to the production of a specific peptide whose expression is transiently needed in maturation, possibly by hydrolysis of a precursor molecule.…”

Common acute lymphoblastic leukemia antigen (CALLA) is active neutral endopeptidase 24.11 ("enkephalinase"): direct evidence by cDNA transfection analysis.

“…Subsequent studies indicated that CALLA was also expressed by certain other lymphoid malignancies with an immature phenotype (3) and by early lymphoid progenitors from fetal liver, fetal and adult bone marrow, and thymus (3)(4)(5)(6)(7). These CALLA' cells have the phenotypic characteristics of cells that are either uncommitted to B-or T-cell lineage or committed to only the earliest stages of B-cell differentiation.…”

Development of B Cell Subpopulations in Humans and its Relevance to Malignancy

“…These cells lack a number of other B cell markers such as Y29/55 [16], RFB-6, or show only cytoplasmic, but no membrane expression of RFB-4 or To15. The phenotypic features of these Tdr+ cells are similar to the blast cells seen in common acute lymphoblastic (cALL) and pre-B ALL [9,11,[15][16][17].…”

“…TdT+ cells are present in large proportions amongst the lymphoid cells of fetal liver [11,15] and fetal BM [13,15]. These cells lack a number of other B cell markers such as Y29/55 [16], RFB-6, or show only cytoplasmic, but no membrane expression of RFB-4 or To15.…”