[Effect of cytokines on the growth of human B-cell precursors, purified and in the presence of stromal (CD13+) components].

As reproducible models for examining human early B-cell progenitors (BCPs) are poorly developed, the cells and molecules regulating their growth and differentiation are still incompletely characterized. We used a recently published short term culture system, using immunomagnetic beads and negative selection, in order to isolate an early BCPs enriched population from human fetal tissues that support further studies on B cell proliferation or differentiation events. This purified population was incubated with or without human recombinant Interleukin-4 (rIL4), and its capability to proliferate and differentiate was followed. We found that rIL4 did not induce either proliferation or differentiation of purified human BCPs. Furthermore in the presence of stromal cells (CD13+) it was able to enhance cy mu + cells and to induce the expression of surface Ig (sIg), surface CD22 on in vitro TdT + CD19 + CD10 + sIg-fetal liver cells. Human recombinant interleukin-7 (rIL-7) promoted the proliferation and the clonal growth of Tdt + CD19 + CD10 + fetal BCPs, confirming its critical role at early stages of human B lymphopoiesis. Furthermore rIL7 also induced growth of CFU-GM when unseparated fetal tissues or myeloid/monocytic contaminated BCPs were used as a target populations, probably by indirect mechanism. Transforming growth factor -beta (TGF-beta 1) partially inhibited the stromal cell-dependent rIL4 induced differentiation and rIL7 clonal growth and proliferation of fetal BCPs. Our study contributes to elucidate the growth factor requirements that characterize normal human B-cell ontogeny, suggesting another mechanism for the linkage between lymphopoiesis and myeloid/macrophagic micro-environment. The in vivo implications of this study are discussed.