Survival of human CD34⁺ hematopoietic cells expressing mutant Ras. CD34⁺ cells expressing mutant Ras or GFP control were incubated in serum-free, growth factor–free medium for 48 hours and stained with annexin V and 7-AAD. Annexin V⁻ and 7-AAD⁻ cells were defined as viable. (Ai) Typical flow cytometric plots obtained at start of incubation and after 48-hour incubation with percentage of viable cells indicated. (Aii) Bar chart representing survival averaged over 3 experiments. (B) Viability of CD34⁺ cells expressing H-Ras^G12V or GFP control while decreasing cell-culture density. (C) Normal (control) CD34⁺ cells were cocultured with an increasing proportion of CD34⁺ H-Ras^G12V cells coexpressing DsRed, enabling analysis of CD34⁺ control cell viability in mixed culture by flow cytometry. Some experiments were carried out in the presence of catalase. (D) CD34⁺ cells expressing mutant Ras or GFP were cultured at a cell density of 5 × 10⁴ cells/mL in the presence of purified catalase. (E) Whole-cell lysates were analyzed by Western blot, using antibodies recognizing phospho-Akt (S473) or total Akt protein. GAPDH was used as a loading control. Data represent mean ± 1 SD (n = 3). Statistical significance was calculated by ANOVA using Tukey honestly significant differences or Mann-Whitney test. †P < .001; *P < .05; **P < .01.