Lymphoid Gene Upregulation on Circulating Progenitors Participates in Their T-Lineage Commitment

Abstract

Extrathymic T cell precursors can be detected in many tissues and represent an immediately competent population for rapid T cell reconstitution in the event of immunodeficiencies. Blood T cell progenitors have been detected, but their source in the bone marrow (BM) remains unclear. Prospective purification of BM-resident and circulating progenitors, together with RT-PCR single-cell analysis, was used to evaluate and compare multipotent progenitors (MPPs) and common lymphoid progenitors (CLPs). Molecular analysis of circulating progenitors in comparison with BM-resident progenitors revealed that CCR9+ progenitors are more abundant in the blood than CCR7+ progenitors. Second, although Flt3− CLPs are less common in the BM, they are abundant in the blood and have reduced Cd25+-expressing cells and downregulated c-Kit and IL-7Rα intensities. Third, in contrast, stage 3 MPP (MPP3) cells, the unique circulating MPP subset, have upregulated Il7r, Gata3, and Notch1 in comparison with BM-resident counterparts. Evaluation of the populations’ respective abilities to generate splenic T cell precursors (Lin−Thy1.2+CD25+IL7Rα+) after grafting recipient nude mice revealed that MPP3 cells were the most effective subset (relative to CLPs). Although several lymphoid genes are expressed by MPP3 cells and Flt3− CLPs, the latter only give rise to B cells in the spleen, and Notch1 expression level is not modulated in the blood, as for MPP3 cells. We conclude that CLPs have reached the point where they cannot be a Notch1 target, a limiting condition on the path to T cell engagement.

Gata2 +9.5 enhancer regulates adult hematopoietic stem cell self-renewal and T-cell development

“…To identify the relevant T-cell developmental stage(s), we analyzed donor-derived linage-biased MPPs and the downstream common lymphoid progenitors (CLPs) in control and +9.5 +/− recipients 8 weeks after transplant as previously described. 11 MPP1 can generate all lineages of blood cells, MPP2 loses megakaryocyte/erythroid potential, whereas MPP3 is responsible for generating downstream CLPs and lymphocytes. We found that donor-derived MPP1 and MPP2 were comparable between control and +9.5 +/− recipients ( Figure 2E ).…”