Integrin alpha4 expression inversely correlates with clinical outcomes of pre-B ALL patients and mediates adhesion-dependent chemoprotection in leukemia cells. (A) Kaplan-Meier estimates of overall survival (OS) for ALL patients negative (black) or positive (red) with MRD at the end of the induction chemotherapy cycle of flow cytometry (day 29).¹¹  (B) Analysis of the OS of MRD-positive patients (MRD⁺) (n = 67) and alpha4 expression (205885_at) separates MRD⁺ integrin alpha4^high (alpha4 expression ≥ mean; n = 34) and MRD⁺ alpha4^low expressing cases (alpha4 expression < mean, n = 33) (P = .0175, log-rank test). (C) Deletion of alpha4 induced by tamoxifen was confirmed by flow cytometry 6 days after treatment. (D) Alpha4-deleted cells (CreER^T2: red) and nondeleted control cells (Empty-ER^T2: black) were cultured with mVCAM-1(+) or without mVCAM-1 (control). Cells were then treated with standard chemotherapy VDL (0.005 µM vincristine, 0.05 nM dexamethasone, 0.005 IU/mL L-asparaginase) for 4 days. Cell viability relative to the initial viability on day 0 was assessed by Trypan blue exclusion of dead cells. *P < .05, mean ± standard deviation (SD), unpaired t test, 3 independent experiments performed in triplicate. NS, nonsignificant. (E) Colony-forming ability in primary and secondary platings. *P < .05, mean ± SD, unpaired t test, 3 independent experiments performed in triplicate. (F) Kaplan-Meier survival curve of alpha4-CreER^T2 and Empty-ER^T2 cells injected C57/BL6 Ly5.1+ recipient mice treated with or without nilotinib (NTB). MST was calculated for each group by log-rank test.