February 6, 2003
T lymphoid differentiation in human bone marrow
By Florian Klein
The unique role of the thymus in the development of T cells was established more than four decades ago. In order to elucidate how uncommitted lymphoid progenitor cells are instructed to migrate from bone marrow to the thymus to undergo T lymphoid differentiation, we generated and analysed a genome-wide gene expression profile of CD7+ CD10+ human bone marrow T cell lineage precursors (TLP) using the SAGE technique. Unexpectedly, the SAGE-profile identified a high number of (pre-)TCR-related transcripts in bone marrow TLP. To determine the configuration of the TCRb locus in these cells at a quantitative level, we sorted and analysed bone marrow TLP from five donors by single-cell PCR. Similar proportions of TLP harbored TCRb germline alleles, D-J or V-DJ gene rearrangements. Thus, bone marrow TLP are heterogenous with respect to TCRb rearrangement status, suggesting an active recombination machinery consistent with expression of RAG1, RAG2 and TdT in this population. As a hallmark of ongoing TCRb V-DJ rearrangement, we could amplify broken-ended recombination-signal sequence DNA-intermediates from bone marrow TLP but not from mature T cells by ligation-mediated PCR. About the half of TCRb rearrangements were compatible with the expression of a functional pre-TCR, which is in agreement with surface expression of pre-Ta on bone marrow TLP as shown by confocal lasermicroscopy and flow cytometry. At a frequency below 0.5% of mononucleated cells in human bone marrow, this population is rare yet exemplifies T lymphoid differentiation in the human already before immigration into the thymus.
Membrane-associated clustering of of pre-Ta expression in bone marrow T lineage precursors
