In vivo homing analysis of CXCR4^+/+ and CXCR4^–/– FL cells. Freshly isolated FL cells were stained with the CFSE dye as described in “In vivo homing assay.” A range of 20 × 10⁶ to 30 × 10⁶ CFSE⁺ cells for each genotype were injected in lethally syngenic irradiated and nonirradiated mice. Recipients were killed 3 and 24 hours after transplantation and BM, spleen, and blood were harvested and analyzed for the percentage of homed CFSE⁺ cells by flow cytometry. (A) Representative flow cytometry analysis of BM, spleen, and blood from control uninjected mice, CXCR4^+/+ CFSE⁺–injected mice, and CXCR4^–/– CFSE⁺–injected mice after 3 hours' homing in either irradiated or nonirradiated recipients. CFSE⁺ cell populations are shown in a gate and their relative numbers are indicated. (B) Histograms showing the percentage of recovered CFSE⁺ cells per organ (% Homing) in the BM, spleen, and blood 3 and 24 hours after transplantation. The results are calculated based on the formula described in “In vivo homing assay.” The formula is based on the percentage of homed CFSE⁺ donor cells multiplied by the cellularities of each organ recovered from mice after being lethally irradiated 24 hours before injected by CFSE⁺ donor cells and divided by the number of CFSE⁺ donor cells injected per mouse. Data representing mean ± SD of BM, spleen, and blood (n = 24 for each) cellularities (B as mentioned in the formula) were as follows: at 3 hours after injections B_marrow = 171.8 × 10⁶ ± 20.8 × 10⁶ cells, B_spleen = 4.12 × 10⁶ ± 1.4 × 10⁶ cells, and B_blood = 15.86 × 10⁶ ± 2.15 × 10⁶ cells; and at 24 hours after injections B_marrow = 30 × 10⁶ ± 10.7 × 10⁶ cells, B_spleen = 1.86 × 10⁶ ± 0.5 × 10⁶ cells, and B_blood = 1.2 × 10⁶ ± 0.3 × 10⁶ cells. Each histogram bar represents the mean ± SD of the percentage of homing obtained in 4 independent experiments (3 mice/genotype/time). *P < .01.