Characterization of Post Natal Human Lymphoid Progenitors.

In humans, little is known about post-natal lymphoid progenitors, especially those able to circulate, colonize the thymus and generate T lymphocytes. On the basis of a previous work published by Anne Galy in 1995, we have detected in the human post-natal bone marrow up to 60 yrs of age a population of progenitors characterized by their CD34+Lin-CD10+ phenotype. Their differentiation potential analysed by culture in methylcellulose medium indicated that in contrast with their CD10− counterparts, CD10+ progenitors have lost erythroid and myeloid potential. On the other hand, CD10+ progenitors cultured on MS5 or OP9/hDL1 stroma demonstrated an enriched capacity to generate B, T and NK lymphocytes as compared to CD10− precursors. In limiting dilution assays, the high lymhoid potential of CD10+ population was confirmed, since 1 out 15 of them gave rise to T cells, 1 out 23 to B cells and 1 out 90 to NK cells. Gene expression profile shows that CD10+ cells express both B and T restricted factors, such as RAG, Gata3, Pax 5 and TdT. In addition, recombination at the IgH locus is already going on, with multiple DJ, but also VDJ recombination products detected. More importantly, CD10+ precursors circulate in the peripheral blood and are detected in the thymus where they are part of the most immature thymocytes CD34+CD1a-CD38-. Altogether, our results demonstrate for the first time the existence of a post-natal lymphoid progenitor population with a broad lymphoid potential and the ability to reach the thymus and generate efficiently T cells. On the long term, their full characterization will pave the way for their enrichment and usage in therapy of primary lymphoid immunodeficiencies.