Effect of increasing concentrations of DT₃₈₈IL-3 and DT₃₈₈IL-3[K116W] on the induction of apoptosis in primary AML leukemic blasts. (A) Leukemic cells from one representative case were grown in vitro for 24 hours in the presence of either DT₃₈₈IL-3 or DT₃₈₈IL-3[K116W] and then the percentage of apoptotic cells was determined by the annexin V binding assay. ▪ indicates DT₃₈₈IL-3; ▴, DT₃₈₈IL-3[K116W]. (B) Percentage of apoptotic cells observed on the leukemic blasts of 25 patients with AML grown for 24 hours in the presence of either DT₃₈₈IL-3 or DT₃₈₈IL-3[K116W]. ▪ indicates DT₃₈₈IL-3; ▴, DT₃₈₈IL-3[K116W]. (C, D) Correlation between the percentage of apoptotic cells induced by a 24-hour incubation in the presence of either DT₃₈₈IL-3 or DT₃₈₈IL-3[K116W] and the level of IL-3Rα (C) or IL-3Rβ (D). □ indicates DT₃₈₈IL-3; ▴,DT₃₈₈IL-3[K116W].