Depsipeptide and its combination with daclizumab prolonged the survival of MET-1 leukemia-bearing SCID/NOD mice. At the time of the experiment, the mice had sIL-2R-α levels of 1000 to 10 000 pg/mL. The groups (13 mice/group) included those receiving intravenous PBS, 0.5 mg/kg per dose depsipeptide every other day for 2 weeks, 100 μg of daclizumab weekly for 4 weeks, and a combination of 0.5 mg/kg per dose depsipeptide every other day for 2 weeks with 100 μg of daclizumab weekly for 4 weeks. Another group receiving no tumor and no therapy was set up as a life span control for NOD/SCID mice. Event-free survival was followed for 200 days. The animals treated in depsipetide, daclizumab, and the combination of daclizumab with depsipeptide groups had significantly prolonged survivals compared with the PBS control group (P < .001). The combination of depsipeptide with daclizumab significantly prolonged the survival of leukemia-bearing mice compared with depsipeptide alone (P < .001) or daclizumab alone (P < .001).