RUNX1 is required for the maintenance of leukemic growth in vivo, and Runx1 deletion in vitro results in apoptosis of leukemic cells. (A) Experimental strategy used to determine the effects of Runx1 deletion on leukemia progression in vivo. Three independent mouse T-ALLs from Tal1/Lmo2/Rosa26-CreER^T2Runx1^f/f mice were transplanted into mice and treated 1 week later with vehicle or tamoxifen for 3 days. (B) Kaplan-Meier survival curves are shown for 3 mouse T-ALLs. The difference in overall survival between the vehicle- and tamoxifen (Tam)-treated groups was assessed by the log-rank test (n = 4 for the vehicle group, n = 6 for Tam group in all 3 experiments). (C) Experimental strategy used to determine the effects of Runx1 deletion on mouse T-ALL survival in vitro. (D) Genomic DNA was isolated from mouse T-ALL cells 48 hours after EtOH or 4-OHT treatment to examine Runx1 deletion by genomic PCR. (E) Mouse T-ALL cell lines 1143 and 9895 were treated with vehicle or 4-OHT for 72 hours, stained with Annexin V-FITC and 7-AAD and analyzed by flow cytometry. The quantifications of Annexin-V–positive cells from 4 independent experiments are shown as means ± standard deviations (SD) (right). *P < .05; **P < .005; ***P < .0005; two-way analysis of variance (ANOVA) multiple comparisons test.