Hematopoietic progenitor cell mobilization in unperturbed CXCR4^–/– chimeras. Animals engrafted with 5 × 10⁶ FL cells were analyzed between 2 and 16 weeks after transplantation. (A) CFC potential in the peripheral blood of CXCR4^+/+ and CXCR4^–/– chimeras from 2 to 16 weeks after transplantation. Red cells were lysed and blood cells were plated in semisolid medium for CFC assay in standard conditions (control, solid line) or in the presence of 600 μg/mL G418 (G418, broken line) in duplicate. Data represent the mean ± SD number of colonies scored for CXCR4^+/+ (n = 6) and CXCR4^–/– (n = 5) blood samples in 3 independent experiments performed in duplicate. (B) CFC potential in the bone marrow of CXCR4^+/+ and CXCR4^–/– chimeras from 2 to 8 weeks after transplantation. BM cells were plated in semisolid medium for CFC assay in standard conditions (control, ▪) or in the presence of 600 μg/mL G418 (G418, ▦) in duplicate. Data represent the mean ± SD number of colonies scored for CXCR4^+/+ (n = 5) and CXCR4^–/– (n = 5) BM samples in 2 independent experiments performed in duplicate. *P < .01; **P < .001. (C) Number of CFUs-S in the peripheral blood of CXCR4^+/+ and CXCR4^+/+ chimeras by injections of 20 μL total blood for each genotype in syngeneic lethally irradiated mice (10 mice injected per blood donor). Data represent the mean ± SD number of colonies of scored CFUs-S in 2 independent experiments. **P < .001.