VLA-4 has the most prominent role in mediating homing of precursor-B ALL cells. Precursor-B ALL cells were pretreated with specific neutralizing antibodies for the specified integrins prior to injection into NOD/SCID mice. Results show percentage (compared with control = 100%) ± SE of human cells recovered from the BM of injected mice and are the average of 3 cell lines (A-1, G2, BRE) or 5 patient cells (patient nos. 1-5). Each group contains 6 or more mice. ^*P < .05 compared with both control as well as α-VLA-5 and α-LFA-1 pretreatment.