Impaired long-term engraftment of bystander hematopoietic cells. (A) An overall experimental design for the bystander exposure in vivo. Recipient mice of IR received 10 Gy irradiation 1 day before transplantation. (B) A cell proliferation assay. Lin⁻c-Kit⁺CFSE⁺ cells from 20 pooled mice were sorted and injected into IR or NR recipients. Seventeen hours after transplantation, the transplanted cells were analyzed for their divisions according to the intensity of CFSE by flow cytometry. Data presented were obtained from 1 of the 2 experiments with identical results. (C) Engraftment levels at different time points in blood. Homed Lin⁻c-Kit⁺ donor cells from IR and NR recipients were sorted 17 hours after transplantation and transplanted into lethally irradiated congenic recipients (1-2 × 10⁴ cells/mouse) in the cBMT model. Engraftment levels of donor cells at different time points after transplantation were represented by the frequencies of donor cells in blood. **P < .01. n = 6. This is a representative summary from 3 experiments with consistent results. (D-E) Representative ratios in blood (D) and BM (E) 20 weeks after the transplantation. The ratios of CD45.1⁺ (IR) to CD45.2⁺ (NR) in blood at whole or different lineages (D), and in BM at whole or different hematopoietic subsets (E) are shown. The figures show the representative data from 1 of 3 mice.