SDF-1/CXCR4 interactions activate different signaling pathways in migration and homing of precursor-B ALL and CD34⁺ cells. Migration and homing of cells following pretreatment with pertussis toxin (PTX; 100 ng/mL, 2 hours, 37°C), Toxin B (ToxB; 100 ng/mL, 20 hours, 37°C), or chelerythrine chloride (CC; 10 μM, 30-60 minutes, 37°C) were tested. (A) Results show average percentage ± SE of in vitro migration of pretreated human precursor-B ALL, CB CD34⁺, and MPB CD34⁺ cells compared with control untreated cells (= 100%). Results of migration of precursor-B ALL cells represent average of G2, BRE, and Nalm-6 cells (at least 3 experiments for each cell line). (B) Results show percentage of homing of pretreated human precursor-B ALL, CB, and MPB CD34⁺ cells to the BM 16 hours after transplantation compared with control untreated cells (= 100%). Results represent average ± SE of cell lines G2, B-1, and A-1, as well as cells from patient nos. 1, 2, 3, 4, and 6. Cell viability was greater than 90% before injection. ^*P < .05 in comparison of precursor-B ALL with normal CD34⁺ cells for each treatment. G2 cells (C) or CB CD34⁺ cells (D) were incubated with or without PTX (100 ng/mL) for 2 hours and then stimulated with increasing concentrations of SDF-1. Surface expression of CXCR4 was determined by flow cytometry. Results show average of 3 independent experiments compared with control cells not stimulated with SDF-1 (= 100%).