Knockdown of Ape1 expression in day-3 EB cells or sorted CD34⁺ day-10 EB cells did not trigger apoptosis. (A) Day-3 or (B) CD34⁺ day-10 EB cells were transfected with control siRNA or Ape1 siRNA, and after 48 hours of transfection, cells were harvested and stained with annexin V and PI. Double annexin V– and PI–positive cells in staining were scored as apoptotic cells in FACS analysis. In a separate group, cells were treated with IFN-γ (500 IU) as positive control in apoptosis induction. (A-B) *P < .01. Bars represent mean ± SD of triplicate experiments.