Myeloproliferative disease returns when AC220 treatment is discontinued. WBC counts are from 4 C57BL/6.CD45.1 mice repopulated with BM cells from a c-Cbl^A/− mouse (A) and three 8- to 9-month-old naturally bred c-Cbl^A/− mice (B). The mice were bled for 5 days before treatment commenced, after 6 weeks of daily dosing with vehicle or AC220, and 4 weeks after AC220 treatment was discontinued. (C) Blood films from a c-Cbl^A/− mouse (M1173) before treatment, after 6 weeks of dosing with AC220, and 4 weeks after AC220 dosing was discontinued. The images were acquired at room temperature using an Olympus BX51 microscope with a 60×/0.09 objective and photographed with an SIS 3VCU Olympus digital camera. The WBC counts are shown and the scale bar indicates 50 μm.