Orderly expression of B cell antigens during the in vitro differentiation of nonmalignant human pre-B cells.

Early human pre-B cells were isolated from fetal bone marrow and induced to differentiate in vitro under the stimulus of phorbol myristic acid or leukocyte-conditioned medium during a 48-hr culture period. Tritiated thymidine culture experiments substantiated that changes in surface marker phenotypes were not the results of outgrowth of subsets responsive to these stimuli. Interestingly, the addition of monoclonal antibodies directed against CALLA resulted in neither proliferation nor differentiation of the fetal lymphoid progenitor cells. Distinct changes in cell surface phenotypes were observed without evidence of cellular enrichment or depletion. The number of CALLA- and TdT-positive cells decreased, whereas the number of B1- and sIgM-positive cells increased. Moreover, a small number of pre-B cells could be driven to a more mature phenotype with the appearance of B2 and sIgG. In contrast, the pan-B B4 antigen did not alter significantly. These changes were even more pronounced when both induction stimuli were present. These studies, and previous studies on the subsets and differentiation of non-T cell acute lymphoblastic leukemias, suggest an orderly acquisition of B cell antigens during the stages of pre-B cell differentiation in man.