Effect of imatinib-encapsulated liposomes on primary Ph⁺ ALL cells. (A) Apoptosis of Ph⁺ ALL-3 cells determined by Annexin V assay. Cells were cultured with the indicated imatinib-encapsulated liposomes or free imatinib for 48 hours. The numbers in the graphs indicate the percentage of cells in each quadrant. (B) CA formation of primary leukemia cells from Ph⁺ ALL-1 patients on day 17. Primary leukemia cells were cocultured with mouse stromal cells, and cobblestone areas were formed about 2 weeks after the start of coculture (original magnification × 100). The image was acquired using an inverted microscope (Diaphot TMD300; Nikon, Tokyo, Japan) with a digital camera (DXM1200, Nikon). The type of objective lens was Plan 10 DL (Nikon), and the numerical aperture was 0.30. The acquisition and subsequent processing software were ACT-1 (Nikon) and Adobe Photoshop 5.0 (Adobe Systems), respectively. (C) Inhibition of the formation of CAs derived from primary leukemia cells from 4 patients. Cells were treated with imatinib-CD19-liposomes (bold line), imatinib-PEG-liposomes (broken line), or free imatinib (thin solid line), and CAs were counted 14 to 17 days after the start of coculture. The numbers of CAs are indicated as the percentage of CA formed in each group compared with those formed by untreated primary leukemia cells. Data represent means ± SDs of triplicate experiments.