MULTIPARAMETER PHENOTYPE MAPPING OF NORMAL AND POSTCHEMOTHERAPY B-LYMPHOPOIESIS IN PEDIATRIC BONE-MARROW

We studied the differentiation profiles of B cell precursors (BCP) in normal and post-chemotherapy pediatric bone marrow (BM) using multipar ameter flow cytometry. The goal of our study was to draw a comprehensi ve 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(+)CD10(lo) precursors was repeatedly observed in addit ion to the well characterized CD34(+)CD10(hl)CD19(+) majority of cells . Only two-thirds of these CD34(+)CD10(lo) cells expressed CD19. Howev er, uniformity of phenotypic features, absence of T lineage markers, a nd the regeneration kinetics after chemotherapy suggest the B lineage affiliation of the CD34(+)CD10(lo) precursors in general. In the more mature BCP, expression of CD10, CD20, cytoplasmic and surface mu chain s (c mu and s mu) was observed to overlap more than previously recogni zed. We found that CD20 and c mu appear early during B cell ontogeny ( already on CD34(+) BCP), and that CD10 is lost late, following the ons et of s mu expression. Differences between normal and post-chemotherap y BM specimens regarding the phenotypic appearance of BCP were exclusi vely due to differences in the subset composition, as post-chemotherap y samples showed a preponderance of immature stages. Our observations may build a framework for comparing leukemic cells with their normal c ounterparts to define possible leukemia-associated aberrations useful for residual disease studies.