Apoptosis of KOPN-72 Ph⁺ ALL cells treated with imatinib-encapsulated liposomes. (A) Annexin V staining of KOPN-72 cells. Cells were cultured with (bottom) or without (top) 10 μM imatinib-CD19-liposomes for 48 hours. Thereafter, cells were stained with FITC-labeled Annexin V and propidium iodide (PI) and appraised by FCM. Viable cells are located in the lower left quadrant (Annexin V– and PI-negative), early apoptotic cells are located in the lower right quadrant (Annexin V–positive and PI-negative), and dead cells are found in the upper right quadrant (Annexin V– and PI-positive). The numbers in the graphs indicate the percentage of cells in each quadrant. (B) Dose response curve of Annexin V–positive cells. KOPN-72 cells were treated with the indicated imatinib-encapsulated liposomes at various concentrations of imatinib and cultured for 48 hours. The rate of Annexin V–positive cells was determined by FCM. Data represent mean of triplicate experiments.