Inclusion Criteria:

- Males and female subjects ≥ 18 years of age

- Confirmed diagnosis of ATL (excluding smoldering subtype)

- Subjects must currently have evidence of disease in at least one of the following:

- Lymph nodes

- Extranodal masses

- Spleen or liver

- Skin

- Peripheral blood

- Bone marrow

- Relapsed or refractory after at least one prior systemic therapy regimen for ATL;

- Eastern Cooperative Oncology Group (ECOG) performance status score of ≤ 2 at study
entry

- resolution of all clinically significant toxic effects of prior cancer therapy to
grade ≤1 by the National Cancer Institute Common Terminology Criteria for Adverse
Events, version 4.0 (NCI-CTCAE, v.4.0)

- adequate hematological, hepatic and renal function

Exclusion Criteria:

- History of allogeneic transplant;

- Autologous hematopoietic stem cell transplant within 90 days of study entry;

- Untreated human immunodeficiency virus (HIV)

- Has known or tests positive for hepatitis B or C;

- Have had a malignancy in the past two years except non-melanoma skin cancers,
melanoma in situ, localized cancer of the prostate with current PSA < 0.1 µg/mL,
treated thyroid cancer or cervical carcinoma in situ or ductal/lobular carcinoma in
situ of the breast who is currently without evidence of disease;

- Clinical evidence of central nervous system (CNS) involvement or metastasis. In
subjects suspected of having CNS disease, an MRI of the brain and/or lumbar puncture
should be done to confirm;

- Psychiatric illness, disability or social situation that would compromise the
subject's safety or ability to provide consent, or limit compliance with study
requirements;

- Significant uncontrolled intercurrent illness

- Experienced allergic reactions to monoclonal antibodies or other therapeutic
proteins;

- Known active autoimmune diseases will be excluded (For example; Grave's disease;
systemic lupus erythematosus; rheumatoid arthritis; Crohn's disease);

- Is pregnant (confirmed by beta human chorionic gonadotrophin [β-HCG]) or lactating.

- Prior treatment with KW-0761;

- Initiation of treatment with systemic corticosteroids while on study is only
permitted for acute and brief complications of underlying disease (e.g.,
hypercalcemia) or for treatment related side effects (e.g., including pre-medication
for infusion reaction, nausea and vomiting). Subjects on systemic corticosteroids
prior to enrollment must be off for 7 days before initiation of study treatment,
unless specifically indicated for the treatment of hypercalcemia. (subjects may
receive inhalation corticosteroids and replacement doses of systemic corticosteroids
as needed);

- Initiation of treatment with topical corticosteroids while on study is not permitted
except to treat an acute rash;

- Have had interferon-α, zidovudine, anti-neoplastic chemotherapy, radiation,
immunotherapy, or investigational medications within 2 weeks of first study
treatment;

- Subjects on any immunomodulatory drug. Subjects on any immunomodulatory drug within 4
weeks of their first dose of KW-0761 are also excluded.