Loss of Vav3 sensitizes p190 BCR-ABL⁺ B-cell progenitors to kinase inhibitor drug treatments in vivo and in vitro. (A) B-cell progenitor frequency (CFU-proB) of p190-BCR-ABL–transduced LDBM cells in the presence or absence of different concentrations of imatinib. Transduced LDBM cells were cultured for 9 days in methylcellulose with the indicated doses of imatinib. Results are shown as means ± SD of 2 independent experiments performed in triplicate. *P < .05. (B) Normalized B-cell progenitor cell frequency with respect to WT cells from the same cultures shown in panel A. *P < .05; **P < .01. (C) B-cell progenitor frequency (CFU-proB) pf p190-BCR-ABL–transduced LDBM cells in the presence or absence of different concentrations of dasatinib carried out as in panel A. Two independent experiments were performed in triplicate. *P < .05. (D) Normalized B-cell progenitor frequency (CFU-proB) with respect to WT cells from the same cultures shown in panel C. B-cell progenitor frequencies of WT cells are depicted by black lines (A,C) or empty bars (B,D); Vav1^−/−;Vav2^−/− are depicted by red lines (A,C) or gray bars (B,D); and Vav3^−/− are depicted by green lines (A,C) or black bars (B,D). (E) Representative example of immunoblot of p-PAK and p-CrkL in sorted B-cell progenitors from primary mouse LDBM cells transduced with p190-BCR-ABL. Sorted leukemic B-cell progenitors were pretreated with 5μM imatinib, 10nM dasatinib, or no drug (untreated) for 2 hours in vitro. β-actin expression was analyzed as a loading control (n = 2 independent experiments). (F) Kaplan-Meier survival curves of p190-BCR-ABL–induced B-ALL mice treated with either imatinib (solid lines) or dasatinib (dotted lines). WT (black solid line, n = 13) and Vav3-deficient (green solid line, n = 13), p190-BCR-ABL⁺ B-ALL mice were treated with daily doses of imatinib for up to 90 days. WT (black dotted line, n = 10) and Vav3-deficient (green dotted line, n = 15), p190-BCR-ABL⁺ B-ALL mice were treated with dasatinib for 75 days. *P < .05 between imatinib-treated WT B-ALL mice and Vav3^−/− B-ALL mice; #P < .05 between imatinib-treated WT B-ALL mice and dasatinib-treated WT B-ALL mice (log-rank test). (G) Representative examples of immunoblot of Vav3 activation (p-Vav3) and expression (Vav3) in EGFP⁺ B cells from the BM of leukemic animals transplanted with WT, p190-BCR-ABL–expressing BM cells and left untreated or treated with imatinib or dasatinib (n = 2 mice per group in 1 of 2 independent experiments).