Defect of in vivo homing of BM cells from 8- to 10-day-old TGF-β1^−/− mice. Total BM cells from TGF-β1^+/+ and TGF-β1^−/− mice were stained with CFSE dye as described in “In vivo homing assay.” CFSE⁺ cells were injected in lethally irradiated mice (15 × 10⁶/mouse). Recipients were killed 3 and 24 hours after injection. Peripheral blood (A), BM (B), and spleen (C) were harvested, and the percentage of homed CFSE⁺ cells was analyzed by flow cytometry. Shown are flow cytometric profiles for a representative analysis and histograms showing the mean ± SD of 3 independent experiments with 4 mice per experiment (*P < .05). (D) Percentage of CFSE⁺ Lin⁻ cells in BM. Irradiated mice were injected as above and killed after 3 hours. Cells were stained with antibodies against lineage markers, and CFSE⁺ Lin⁻ cells were analyzed by flow cytometry. The histogram represents the mean ± SD of 3 independent experiments with 4 mice per experiment; *P < .05.