Major T cell progenitor activity in bone marrow-derived spleen colonies

Abstract

Common lymphoid progenitors (CLP) are generated in adult bone marrow (BM), but the intermediate steps leading to T cell commitment are unknown, and so is the site at which this commitment occurs. Here, we show that colonies arising in the spleen 12 days after BM injection harbor T cell precursors that are undetectable in BM. These precursors did not generate myeloid cells in vivo but repopulated the thymus and the peripheral T cell compartment much faster than did CLP. Two lineage negative (Lin-) subpopulations were distinguished, namely CD44+ Thy1- cells still capable of natural killer generation and transient low-level B cell generation, and T cell-restricted CD44- Thy1+ cells. At a molecular level, frequency of CD3ε and preTα mRNA was very different in each subset. Furthermore, only the CD44- Thy1+ subset have initiated rearrangements in the T cell receptor β locus. Thus, this study identifies extramedullary T cell progenitors and will allow easy approach to T cell commitment studies.