This is a multicenter, randomized, open-label, parallel-group study to compare mLSG15 + KW-0761 to mLSG15 in subjects with CCR4-positive adult T-cell leukemia-lymphoma (untreated primary disease). The primary variable is an efficacy of KW-0761 used as an add-on therapy to mLSG15 as measured in terms of complete response rate (CR/CRu) in the best overall response assessment for antitumor effect. The secondary variables include response rate (CR/CRu/PR) in the best overall response assessment for antitumor effect, complete or response rates by lesion site in the best overall response assessment for antitumor effect, progression-free survival and overall survival. The safety and pharmacokinetic profiles of KW-0761 will be also determined.

Inclusion Criteria:

• Subjects who have been positive for serum anti-human T-cell lymphotropic virus type I antibody
• Subjects with hematologically or pathohistologically confirmed as peripheral lymphoid tumor which surface antigen analysis has identified to be of T-cell origin
• Subjects who have been classified into acute subtype, the lymphoma subtype or chronic subtype with poor prognostic factors
• Subjects who have been positive for CCR4 by CCR4 expression analysis
• Subjects who have never been treated for adult T-cell leukemia-lymphoma
• Subjects who have presented enlarged lymph nodes, tumor nodules in extranodal organs, abnormal lymphocytes in peripheral blood or cutaneous lesions
• Subjects with a performance status of 0 to 2
• Subjects who have been negative for HBs antigen and anti-HCV antibody
• Subjects who have given written voluntary informed consent to participate in the study

Exclusion Criteria:

• Subjects who are scheduled for transplant therapy such as hematopoietic stem-cell transplantation
• Subjects who had myocardial infarction within 12 months before study enrollment or who have cardiac disease that may worsen during treatment with doxorubicin
• Subjects who have been positive for anti-HIV antibody
• Subjects with active multiple cancer
• Subjects with a history of allergic reactions to therapeutic antibodies
• Subjects who require emergency radiotherapy for treating the symptoms caused by bulky masses or who may require such radiotherapy after the start of the study
• Subjects who are pregnant, lactating or of childbearing potential, or who are planning to have children