FL + IL-7–stimulated Lin^−/loSca1⁺c-kit⁺ cells support lymphoid-restricted reconstitution in vivo. A total of 1,000 Lin^−/loSca1⁺c-kit⁺ cells from B6SJL mice (Ly5.1, donor) was either transplanted directly or cultured in the presence of FL + IL-7 for 14 days before transplantation into lethally irradiated C57Bl/6 mice (Ly5.2, recipient), together with 150,000 (Ly5.2) fresh BM cells. Peripheral blood was analyzed for the presence of donor and recipient-derived cells and lineage distribution 6 and 10 weeks after transplantation. Similar results were obtained at both time points. The CD3 and B220 reconstitution (only from Ly5.1 donor cells) from 1 typical mouse is shown for fresh, as well as FL + IL-7–cultured cells. In addition, for FL + IL-7–cultured cells, the coexpression of B220 and IgM on circulating B cells is shown. The percentage in each quadrant shows the mean from 2 or 3 mice (in 1 of 2 representative experiments) in the fresh Lin^−/loSca1⁺c-kit⁺ and FL + IL-7–culture group, respectively. B220⁻CD3⁻ cells detected when transplanting fresh Lin^−/loSca1⁺c-kit⁺cells were practically all Gr1/Mac1⁺ myeloid cells (J.A. and S.E.W.J., unpublished observations, February 1999).