The growth of MET-1 ATL cells in NOD/SCID mice bearing the MET-1 ATL leukemia was inhibited by daclizumab, depsipeptide, and the combination of daclizumab with depsipeptide. MET-1 ATL cells were transferred into mice. The groups (13 mice/group) included those receiving PBS, 2 weeks every other day 0.5 mg/kg per dose depsipeptide, 4 weekly doses of 100 μg of daclizumab, the combination of 2 weeks every other day 0.5 mg/kg per dose depsipeptide with 4 weekly doses of 100 μg daclizumab. (A) The mean concentration of sIL-2R-α in picograms per milliliter. The animals treated in the 2-week depsipeptide, 4-week daclizumab, and the combination of 2-week depsipeptide with 4-week daclizumab groups had significantly decreased values of sIL-2R-α compared with those of the PBS control group 8 weeks after therapy (P < .001). Furthermore, the animals receiving the combination of depsipeptide with daclizumab had significantly decreased levels of sIL-2R-α compared with those of the mice in the depsipetide alone group (P < .01) and daclizumab alone group (P < .05). (B) The mean concentration of β2μ in micrograms per milliliter 8 weeks after therapy. The serum levels of β2μ were significantly lower in the depsipetide treatment alone, daclizumab treatment alone, and combination group compared with PBS group (P < .001). The animals receiving the combination of depsipeptide with daclizumab had decreased levels of β2μ compared with those of the mice in the depsipetide alone group (P < .08) and daclizumab alone group (P < .1).