The sensitivity of murine repopulating HSCs to TMTX in vivo. Donor C57Bl/6J mice, homozygous for the single Hbb s allele (panel A), were treated as indicated: (panel C), no drug; (panel D), 300 mg/kg TMTX ip; (panel E), 150 mg/kg 5FU intravenously; (panel F ), 150 mg/kg 5FU followed 5 days later by 150 mg/kg 5FU; (panel G), 150 mg/kg 5FU followed 5 days later by 300 mg/kg TMTX. Twenty-four hours after the final treatment BM cells were obtained for transplant. Panels (C) through (G) show the hemoglobin phenotype in recipient mice 10 weeks after transplantation. In this figure samples from two representative recipient mice are shown in each panel.