Early T cell development can be traced in rat fetal liver

The degree of T cell commitment reached by cell precursors present in the f etal liver is a controversial issue. In the present work, the occurrence of fully T cell-committed progenitors among CD45(+)Thy-1(+)CD44(+) 13-day-old rat fetal liver cells was demonstrated-when limiting numbers of these cell s in vitro reconstituted SCID mouse fetal thymic lobes providing single lin eage-containing lobes for T, natural killer or dendritic cells. in addition , expression of rat pre-TCR alpha chain mRNA was detected in the CD45(+) bu t not in the CD45(-) fetal liver cells and fully rearranged TCR V beta8-C b eta mRNA transcripts were specifically detected in the former population, d emonstrating early transcription of some rearranged TCRV beta genes in the rat fetal liver of 13 days of gestation. Finally fetal liver organ cultures provided low numbers of TCR gamma delta T cells and CD2(+)CD8(+)NKR-P1A(-) intracytoplasmic CD3(+) immature T cells, which intracellularly reacted wi th a mAb specific to the TGR alpha beta molecule. These results prove T, NK and DG cell lineage determination at a prethymic stage in the fetal liver.