Hemopoietic progenitors in the murine fetal liver capable of rapidly generating T cells.

We investigated the hemopoietic progenitors in fetal liver (FL) compared with those in adult bone marrow (BM) for their ability to differentiate into T, B, and myeloid cells. Lineage marker-negative (Lin-) c-kit+ cells isolated from FL and BM were used as the source of progenitors. No apparent difference was observed between FL and BM progenitors in their ability to generate B and myeloid cells when these progenitors were cultured on a monolayer of a BM-derived stromal cell line. In marked contrast, FL progenitors were able to generate T cells much more rapidly than BM progenitors in both in vivo intrathymic cell transfer and fetal thymus organ culture systems. The same type of FL progenitors were also found in the FL of congenitally athymic nu/nu mice, indicating that these progenitors arise in FL independently of the fetal thymus. The present study have provided circumstantial evidence suggesting the presence of T cell lineage-committed progenitors in FL.