Expansion of phenotypic KSL cells by IFN-γ without expansion of functional HSCs. (A) IFN-γ injection (10 µg per mouse; n = 9) caused a significant increase in the proportion of KSL cells relative to untreated controls (n = 9). (B) When B6 BM cells were cultured for 6 days with IFN-γ (50 ng/mL; n = 10), there was a significant increase in KSL cell proportion. (C) In a competitive repopulation assay with KSL:competitor BM cell ratio of 180:3 × 105, KSL cells from IFN-γ-treated donors (solid circles) contributed very little to recipient mature blood cells relative to KSL cells form normal donors (open circles). This was confirmed in a second competitive repopulation assay at KSL:competitor BM cell ratio of 4800:4.8 × 105 in which IFN-γ-expanded KSL cells (solid circles) had significantly lower donor contributions than normal KSL cells (open circles), shown as representative flow cytometry dot plots and means with standard errors. APC, allophycocyanin; FITC, fluorescein isothiocyanate; PE, phycoerythrin. **P < .01; ****P < .0001.
