Vav3 deficiency delays p190-BCR-ABL induced B-ALL leukemogenesis and is associated with reduced activation of Rac. (A) Circulating p190-BCR-ABL–expressing B-cell progenitors in murine B-ALL transduction/transplantation model as determined by FACS analysis. (B) Survival of mice transplanted with 3 × 10⁶ p190-BCR-ABL⁺ LDBM cells from WT (n = 22, black), Vav3^−/− (n = 19, green), or Vav1^−/−;Vav2^−/− (n = 6, red) mice. *P < .05 (log-rank test). (C) Percentage of EGFP⁺/B220⁺ cells in the peripheral blood of WT (C57Bl/10, empty bars), Vav1^−/−;Vav2^−/− (gray bars) or Vav3^−/− (black bars) mice shown in Figure 1B at different time points. (D) Representative experiment of 2 experiments with similar results, showing survival of secondary mice transplanted with sorted leukemic B-cell progenitors from primary B-ALL mice engrafted with p190-BCR-ABL WT (black) or p190-BCR-ABL, Vav3-deficient (green) cells. EGFP⁺B220⁺CD43^+, cKit^dim+ cells 4 × 10⁵) were isolated and transplanted along 5 × 10⁶ normal congenic BM cells into secondary recipients (C57Bl/10, n = 9 for each group). **P < .01 (log-rank test). (E-F) Representative examples of effector binding domain pull-down assays for total Rac, Rac2, Cdc42, and Rho (E) and Ras (F) of p190-BCR-ABL–expressing murine B-ALL BM cells (n = 3 independent experiments). Relative activation ratio (GTP-bound GTPase/total GTPase) normalized to the WT value is provided below each panel. (G) Representative example of Vav3 (effector) binding assays. Lysate from p190-BCR-ABL⁺ BaF/3 was incubated with GST alone, GST-fused Rac1, Rac2, Rac2D57N, Cdc42, or K-Ras (2 μg) and 10 μL of suspended glutathione-agarose (n = 3 independent experiments). (H) Kaplan-Meier survival curves of mice transplanted with p190 BCR-ABL–transduced LDBM cells from Rac2^−/− (n = 10, green line), Rac3^−/− (n = 22, blue line), or WT mice (n = 17, brown line). *P < .05 (log-rank test).