Multiparameter phenotype mapping of normal and post-chemotherapy B lymphopoiesis in pediatric bone marrow

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Abstract
We studied the differentiation profiles of B cell precursors (BCP) in normal and post-chemotherapy pediatric bone marrow (BM) using multiparameter flow cytometry. The goal of our study was to draw a comprehensive phenotypic map of the three major maturational BCP stages in BM. By correlating lineage-associated markers, CD45RA, and several adhesion molecules, the stage-specific patterns were found to differ in certain details from previously published concepts. Among the earliest BCP, a subset of CD34+CD10lo precursors was repeatedly observed in addition to the well characterized CD34+CD10hiCD19+ majority of cells. Only two-thirds of these CD34+CD10lo cells expressed CD19. However, uniformity of phenotypic features, absence of T lineage markers, and the regeneration kinetics after chemotherapy suggest the B lineage affiliation of the CD34+CD10lo precursors in general. In the more mature BCP, expression of CD10, CD20, cytoplasmic and surface μ chains (cμ and sμ) was observed to overlap more than previously recognized. We found that CD20 and cμ appear early during B cell ontogeny (already on CD34+ BCP), and that CD10 is lost late, following the onset of sμ expression. Differences between normal and post-chemotherapy BM specimens regarding the phenotypic appearance of BCP were exclusively due to differences in the subset composition, as post-chemotherapy samples showed a preponderance of immature stages. Our observations may build a framework for comparing leukemic cells with their normal counterparts to define possible leukemia-associated aberrations useful for residual disease studies.

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