Cloning of a novel cell type from human fetal liver expressing cytoplasmic CD3 δ and ε but not membrane CD3

Seventeen-week human fetal liver cells cultured with a feeder cell mixture of irradiated PBL, irradiated JY cells (an EBV-transformed B cell line) and PHA contained a subpopulation of CD3- cells in addition to a major population of T cells with the mature phenotype. After 12 days in culture, CD3- CD16- cells were sorted and cloned by limiting dilution. Two representative clones, FL121 and FL125, were expanded and characterized. They shared the phenotype of CD2+CD3-CD4-CD5-CD6+CD16-CD56+. FL121 did not express CD8 whereas FL125 expressed CDα but not CD8β. Both clones were found to express cytoplasmic CD3δ and CD3ε Ag while CD3- NK clones isolated from PBL were negative for them. These results indicate that FL121 and FL125 were committed to the T-cell lineage. Southern blot analysis showed that the TCRβ genes and the TCRγ genes of these clones were in the germ-line configuration. The establishment of FL121 and FL125 may provide a novel insight into the earliest stage of T-cell development in man.