Expression of Flt3-D835Y and Flt3-ITD induces radiation-induced apoptosis resistance in myeloid cells. Cells were washed and cytokine starved in 0.5% FCS for 3 hours and exposed to 5 Gy γ irradiation. Thereafter, cells were incubated for up to 24 hours in the presence or absence of the indicated cytokines, stained with annexin V and propidium iodide, and analyzed by flow cytometry. (A) Dot plots of the flow cytometric analyses up to 24 hours after irradiation. (B) Time course of cell viability after irradiation. Cells that were negative for annexin V and propidium iodide were counted as viable cells. Viability was calculated as a percentage of these cells over the total cell population. The data shown represent the average of 3 independent experiments ± SD. The observed differences of WT versus ITD versus D835Y (left) and ITD versus WT and D835Y (middle) were statistically significant (P < .01). No significant induction of apoptosis was observed under the chosen experimental conditions in the absence of irradiation (data not shown).