Circulation of short-term hematopoietic reconstituting cells in CXCR4^–/– chimeras. Week-8 posttransplantation animals that were engrafted with 5 × 10⁶ FL cells were used. (A) Blood cells were stained with anti-CD45.2 mAb to identify donor-derived cells (chimerism), a cocktail of specific lineage mAbs (Lin), 7-AAD for cell viability, and the stem cell markers Sca-1 and c-Kit. Two different gates are shown in the figure: one represented CD45.2⁺ donor–derived cells and the other represented CD45.2⁺ Lin^– populations. Arrows indicate that the Sca-1/c-Kit profiles were analyzed within the CD45.2⁺ Lin^– gates. Data are representative profiles obtained for each CXCR4^+/+ (n = 6) and CXCR4^–/– (n = 5) chimera. (B) Peripheral blood was harvested from CXCR4^+/+ and CXCR4^–/– chimeras from the retro-orbital sinus. One hundred microliters of whole blood sample was mixed with 1.5 × 10⁵ Ly5.1 host–derived BM cells and transplanted in lethally irradiated C57BL/6-Ly5.1 mice (500 μL blood volume from either CXCR4^+/+ or CXCR4^–/– mice was used to engraft 5 mice per genotype). The recipients were analyzed 5 weeks after transplantation. Representative FACS profiles assayed from both groups are shown. Blood was stained with anti-CD45.2 to identify donor-derived cells. (C) These results are summarized as histogram profiles showing the mean ± SD of percentages of circulating CD45.2⁺ cells in 2 independent experiments (5 mice per genotype and per experiment). *P < .01.