Differences in CXCR4 expression, SDF-1–induced migration, and irradiation requirement between precursor-B ALL and CD34⁺ cells. (A) Precursor-B ALL cell line cells (5-20 × 10⁶) were injected into NOD/SCID mice, either untreated (▪) or 48 hours after total body irradiation (375 cGy; ▦). The total number (average ± SE of at least 3 experiments) of human cells that homed to the murine BM 16 hours after transplantation is shown. This was calculated according to the number of human cells per 10⁶ MNCs acquired by flow cytometry multiplied by the total number of MNCs in the BM. ^*P < .05 compared with homing into nonirradiated mice. (B) Fold increase (compared with migration to 125 ng/mL SDF-1) of spontaneous or SDF-1–induced migration (at the indicated concentrations) of precursor-B ALL (□; G2, Nalm-6, BRE cells; average ± SE of at least 3 experiments performed in duplicates for each cell line) and normal CB (▪) or MPB (▦) CD34⁺ cells. ^*P < .05 relative to migration toward 125 ng/mL SDF-1. (C) Immunofluorescence detection of intracellular (gray line), cell surface (black line), or isotype control (dotted line) expression of CXCR4 levels of normal CD34⁺ cells, G2 cells, or precursor-B ALL cells from patients with newly diagnosed disease (patient nos. 1, 3, 4, and 5). Representative experiments of at least 3 independent experiments for each group are shown.