New insights on human T cell development by quantitative T cell receptor gene rearrangement studies and gene expression profiling

To gain more insight into initiation and regulation of T cell receptor (TCR) gene rearrangement during human T cell development, we analyzed TCR gene rearrangements by quantitative PCR analysis in nine consecutive T cell developmental stages, including CD34(+) lin(-) cord blood cells as a reference. The same stages were used for gene expression profiling using DNA microarrays. We show that TCR loci rearrange in a highly ordered way (TCRD-TCRG- TCRB-TCRA) and that the initiating D delta 2-D delta 3 rearrangement occurs at the most immature CD34(+)CD38(-)CD1a(-) stage. TCRB rearrangement starts at the CD34(+)CD38(+)CD1a(-) stage and complete in-frame TCRB rearrangements were first detected in the immature single positive stage. TCR beta rearrangement data together with the PTCRA ( pT alpha) expression pattern show that human TCR beta-selection occurs at the CD34(+)CD38(+)CD1a(+) stage. By combining the TCR rearrangement data with gene expression data, we identified candidate factors for the initiation/regulation of TCR recombination. Our data demonstrate that a number of key events occur earlier than assumed previously; therefore, human T cell development is much more similar to murine T cell development than reported before.