Isolation of an early T-cell precursor (CFU-TL) from human bone marrow.

CD2-CD3-CD4-CD8- human bone marrow (BM) cells were previously shown to generate T-cell clones in vitro. This capacity was abolished after treatment of this population with anti-CD7 monoclonal antibody and complement. In this study, using rosetting with sheep erythrocytes, complement-dependent cytotoxicity, and specific immunoadherence method, we isolated a minor BM subset that contained more than 80% CD7+CD2-CD3-CD4-CD8- cells with small lymphoid cell morphology. They comprised most early T-cell precursors (CFU-TL) as they displayed high capacity to generate T-cell clones when cultured in limiting dilutions. CFU-TL nature of these cells was also confirmed by the sequential expression of mature T-cell specific markers on their surface after in vitro induction. This BM subset also contained 2% to 3% CFU-GM precursors. Together, these results pointed to the existence of BM CD7+CD2- precursors with high differentiation potential and showed the commitment of most of them to T-cell lineage.