IDENTIFICATION OF A COMMITTED T-CELL PRECURSOR POPULATION IN ADULT HUMAN PERIPHERAL-BLOOD

Here, we report data concerning the discovery in adult human periphera l blood of a precursor cell population able to differentiate into CD4( +)CD3(+)alpha beta(+) mature T cells. These cells, which represent 0.1 -0.5% of total peripheral blood mononuclear cells (PBMC), express subs tantial levels of CD4, but lack CD3 surface expression. At a molecular level, they express the pre-T cell receptor alpha (pT alpha) gene, CD 3-gamma, CD-delta and CD-epsilon, and RAG-1 recombination enzyme and h ave initiated rearrangements in the T cell receptor (TCR)-beta locus ( D-J). Moreover, low levels of CD3 epsilon protein, but not of TCR-beta chain, can be detected in their cytoplasm. Our results suggest that C D4(+)CD3(-) cells identified in peripheral blood are different from CD 3(-)CD4(+)CD8(-) thymocytes and may contain precursors of an extrathym ic T cell differentiation pathway.