Ordering human CD34+CD10−CD19+pre/pro-B-cell and CD19−common lymphoid progenitor stages in two pro-B-cell development pathways

Abstract

Studies here respond to two long-standing questions: Are human “pre/pro-B” CD34⁺CD10⁻CD19⁺ and “common lymphoid progenitor (CLP)/early-B” CD34⁺CD10⁺CD19⁻ alternate precursors to “pro-B” CD34⁺CD19⁺CD10⁺ cells, and do the pro-B cells that arise from these progenitors belong to the same or distinct B-cell development pathways? Using flow cytometry, gene expression profiling, and Ig V_H-D-J_H sequencing, we monitor the initial 10 generations of development of sorted cord blood CD34^highLineage⁻ pluripotential progenitors growing in bone marrow S17 stroma cocultures. We show that (i) multipotent progenitors (CD34⁺CD45RA⁺CD10⁻CD19⁻) directly generate an initial wave of Pax5⁺TdT⁻ “unilineage” pre/pro-B cells and a later wave of “multilineage” CLP/early-B cells and (ii) the cells generated in these successive stages act as precursors for distinct pro-B cells through two independent layered pathways. Studies by others have tracked the origin of B-lineage leukemias in elderly mice to the mouse B-1a pre/pro-B lineage, which lacks the TdT activity that diversifies the V_H-D-J_H Ig heavy chain joints found in the early-B or B-2 lineage. Here, we show a similar divergence in human B-cell development pathways between the Pax5⁺TdT⁻ pre/pro-B differentiation pathway that gives rise to infant B-lineage leukemias and the early-B pathway.