Implication of HIF-1α in hypoxia-related T-ALL chemoresistance. (A) Relative mRNA expression of HIF-1α, Glut3, VEGF, and CXCR4 genes in shHIF-1α/T-ALL reported to levels measured in shCTL/T-ALL controls. Every dot represents gene levels of 1 experiment compared with β2m reporter gene levels. Tested on T-ALL #1, T-ALL #3, T-ALL #5, Jurkat, and DND41 cell lines. Shown are results of a total of 8 experiments. (B) Number of shCTL/T-ALL and shHIF-1α/T-ALL cells after 4 days of coculture with MS5-DL1 stromal cells in normoxia or in hypoxia. Data are expressed as fold variation compared with control (shCTL 21%). Tested in triplicate in every experiment. T-ALL #1, n = 6exp (i); and T-ALL #3, n = 2exp (ii). (C) Decreased HIF-1α modifies T-ALL cycling in hypoxia. Shown is the proportion of shCTL/T-ALL and shHIF-1α/T-ALL cells in G0 phase in normoxia or in hypoxia. Shown are mean ± SEM of cultures with T-ALL #1 and T-ALL #3, n = 4exp. (D) Decreased HIF1α increases chemosensitivity of T-ALL in hypoxia. Shown are the percentages of lived shCTL/T-ALL and shHIF-1α/T-ALL cells recovered after treatment during 72 hours with vincristine compared with nontreated cells. Every experiment was done in triplicate. Shown are mean ± SEM of cultures with T-ALL #1 and T-ALL #3, n = 8exp. (E) Leukemic cell production after 7 days in normoxia without treatment, following shCTL/T-ALL and shHIF-1α/T-ALL cell treatment with vincristine in normoxia or hypoxia. Shown are mean ± SEM of technical triplicates of 1 experiment on T-ALL #1. (F) Survival of mice transplanted with 1000 shCTL/T-ALL or shHIF-1α/T-ALL cells isolated after cultures in normoxia or in hypoxia in presence of 10 nM vincristine. T-ALL #1, 5 mice per condition. Statistics were determined using the Wilcoxon test (A, C) or Friedman test (D-E) and the log-rank (Mantel-Cox) test for mice survival: **P < .01, ***P < .001. exp, experiment.