CD31⁺ Sca-1^– progenitors do not give rise to multilineage hematopoiesis in a competitive repopulation assay. Lethally irradiated recipient mice received transplants of either 500 CD31⁺ KSL cells (□) or 25 000 CD31⁺ Lin^– c-kit⁺ Sca-1^– cells (▪) in addition to unfractionated host-type bone marrow carrier cells (1 × 105). (A) Peripheral blood analysis was performed at the time points indicated, and the level of total donor engraftment was determined. (B) At 26 weeks, donor-derived cells were either B220⁺ B cells or CD3⁺ T cells. A representative FACS plot gated on donor-derived cells is shown in middle and right panels. Error bars indicate SEM; n = 6 mice. Percentages of donor-derived cell populations are shown in each panel.