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The Fetal Liver Counterpart of Adult Common Lymphoid Progenitors Gives Rise to All Lymphoid Lineages, CD45+CD4+CD3− Cells, As Well As Macrophages1

We identified an IL-7Rα+Sca-1lowc-Kitlow population in E14 fetal liver, which is the phenotypical analog of common lymphoid progenitors (CLP) in adult bone marrow. After transfer into newborn mice, the IL-7Rα+Sca-1lowc-Kitlow population rapidly differentiated into CD45+CD4+CD3− cells, which are candidate cells for initiating lymph node and Peyer’s patch formation. In addition, this population also gave rise to B, T, NK, and CD8α+ and CD8α− dendritic cells. The fetal liver precursors expressed a significantly lower level of the myeloid-suppressing transcription factor Pax-5, than adult CLP, and retained differentiation activity for macrophages in vitro. We propose that the transition from fetal liver IL-7Rα+Sca-1lowc-Kitlow cells to adult CLP involves a regulated restriction of their developmental potential, controlled, at least in part, by Pax-5 expression.