Myeloablative conditioning results in long-term engraftment of semiallogeneic c-Kit⁺ BM progenitors administered by intravenous as well as intrathymic routes. (A) Quantification of the percentages of semiallogeneic donor cells detected within the lineage-negative BM population. Mice were either nonconditioned or preconditioned with busulphan/cyclophosphamide (cond). At 28 weeks posttransplantation, BM was isolated and the presence of donor cells within the lineage-negative progenitor gate was determined by flow cytometry. Each point represents data from a single mouse, and mean levels are indicated by a horizontal line. (B) Expression of the stem cell receptor c-Kit was assessed on lineage-negative donor progenitors in each group, and a representative histogram from 1 mouse in each group is presented.