Efficient T-lineage progenitor activity resides within the BM Lin⁻Kit⁺Flt3^high pool 2 weeks after BMT. (A) Total Lin⁻ cells or Lin⁻ cells depleted of all Kit⁺Flt3^high cells were sorted from CD45.2 WT BM. Shown are plots of sorted populations gated on live singlets. No Kit⁺Flt3^high cells were detected in the depleted sample. (B) A total of 1.2 × 10⁵ undepleted Lin⁻ cells (left column) or Kit⁺Flt3^high-depleted Lin⁻ cells (right column) were injected into CD45.1 WT recipients that had been lethally irradiated and transplanted with 2.5 × 10⁵ host-type BM cells 2 weeks earlier. After an additional 15 days, BM and thymi of recipient mice were analyzed for donor contributions. Shown are representative plots gated on BM granulocytes (top row) and thymic DP cells (bottom row). (C) Mean donor chimerism plus or minus SEM of BM granulocytes (left panel) and mean numbers ± SEM of donor thymic DP cells (right panel). N = 3 to 6 per group.