Migration and homing of precursor-B ALL cells depend on SDF-1/CXCR4 interactions. (A) Results show average percentage ± SE of in vitro migration of untreated (control), pretreated (α-CXCR4, T22, or T140) or SDF-1–desensitized (20 hours in IMDM containing 1 μg/mL SDF-1) Nalm-6 and G2 cells to 125 ng/mL SDF-1 (at least 3 experiments for each cell line). (B) Cell surface CXCR4 expression levels of unlabeled (a), T22 pretreated (b), SDF-1–desensitized (c), or untreated (d) G2 cells were ascertained. (C) Cells (5-20 × 10⁶) from patients with newly diagnosed precursor-B ALL (patient nos. 1-5) or cell lines were injected into NOD/SCID mice either untreated, after blocking with anti-CXCR4–neutralizing antibodies (Nalm-6, G2, A1, BRE), or after 20 hours of incubation with 1 μg/mL SDF-1 (Nalm-6 and G2). Results show percentage of homing of human cells to the BM 16 hours after transplantation relative to control untreated cells (= 100%). Three or more mice were used for each cell line in each treatment. Cells from noninjected mice were used as a negative control. (D) A representative experiment showing homing of G2 cells. The number represents the number of human CD45⁺ cells per 10⁶ acquired cells. ^*P < .05 compared with control.