Figure 1 VK2 selectively eliminates the MDS blastic population in vitro and in vivo. Upper panel: Mononuclear cells separated from the patient’s peripheral blood were cultured in RPMI 1640 containing 10% fetal bovine serum in the presence or absence of 3 or 10 mm MK4 for 72 h. Then the cells were analyzed by flow cytometry after staining with phycoerythrin-conjugated CD34 and fluorescein isothiocyanateconjugated CD33 monoclonal antibodies. Leukemic blast cells were separated as the CD34++/CD33dull+ fraction. Lower panel: After administration of MK4 (90 mg/day) for 6 weeks, the peripheral white blood cells were isolated by red blood cell lysis and analyzed as described above. The flow cytogram was compared with that obtained before treatment. Each number represents the percentage of blast cells in the whole gated area.