Effective treatment of a murine model of adult T-cell leukemia using depsipeptide and its combination with unmodified daclizumab directed toward CD25

Adult T-cell leukemia (ATL) is caused by human T-cell lymphotropic virus I (HTLV-1) and is an aggressive malignancy of CD4, CD25-expressing leukemia, and lymphoma cells. There is no accepted curative therapy for ATL. Depsipeptide, a histone deacetylase inhibitor, has demonstrated major antitumor effects in leukemias and lymphomas. In this study, we investigated the therapeutic efficacy of depsipeptide alone and in combination with daclizumab (humanized anti-Tac) in a murine model of human ATL. The Met-1 ATL model was established by intraperitoneal injection of ex vivo leukemic cells into nonobese diabetic/severe combined immunodeficiency mice. Either depsipeptide, given at 0.5 mg/kg every other day for 2 weeks, or daclizumab, given at 100 microg weekly for 4 weeks, inhibited tumor growth as monitored by serum levels of soluble IL-2R-alpha (sIL-2R-alpha) and soluble beta2-microglobulin (beta2mu) (P < .001), and prolonged survival of the leukemia-bearing mice (P < .001) compared with the control group. Combination of depsipeptide with daclizumab enhanced the antitumor effect, as shown by both sIL-2R-alpha and beta2mu levels and survival of the leukemia-bearing mice, compared with those in the depsipeptide or daclizumab alone groups (P < .001). The significantly improved therapeutic efficacy by combining depsipeptide with daclizumab supports a clinical trial of this combination in the treatment of ATL.