Due to not achieving the primary outcome.

The objective of this study is to assess the efficacy and safety of KW-0761 after intravenous injections in subjects with HTLV-1 associated myelopathy (HAM) in Japan.

The effects of KW-0761 (0.3 mg/kg) on the Osame's motor disability score (OMDS) of subjects with HTLV-1 associated myelopathy (HAM).

Inclusion Criteria:

1. Voluntary written informed consent to participate in the study

2. Diagnosis as HAM according to the second edition of HAM Treatment Manual

3. At least 1-year history of HAM

4. Ongoing medication*1 for HAM, with no changes in 3 months before enrollment; or inadequate response or intolerance to prior medication,*2 which must have been discontinued for at least 3 months before enrollment. Subjects on maintenance therapy with steroids must have been receiving ≤ 10 mg/day prednisolone equivalent continuously for at least 3 months before enrollment.

   • 1 Steroids, salazosulfapyridine, or ≥ 1.5 g/day vitamin C
   • 2 Steroids, Interferon-α, salazosulfapyridine, or ≥ 1.5 g/day vitamin C

5. No change in the degree of motor dysfunction for at least 3 months before the date of screening, as judged by the investigator or subinvestigator

6. A OMDS of ≥3 at screening and able to walk ≥10 m at screening (use of a single cane or double canes is allowed)

Exclusion Criteria:

1. Any of the following significant concomitant diseases:

   Type 1 diabetes mellitus, Poorly controlled type 2 diabetes mellitus (HbA1c (NGSP) > 8.5%), Congestive heart failure (Class II to IV of the New York Heart Association Functional Classification), Myocardial infarction within 1 year before enrollment, Unstable angina within 1 year before enrollment, Poorly controlled hypertension (systolic blood pressure > 150 mm Hg and diastolic blood pressure > 90 mm Hg at screening), Sever chronic lung disease requiring oxygen therapy, Multiple sclerosis or any other demyelinating disease, Epilepsy requiring treatment with antiepileptics (with the exception of epilepsy controlled by antiepileptics, with no occurrence of seizures for at least 3 years before informed consent), and Active malignancy (including ATL); or onset of malignancy or previous treatment for malignancy (with the exception of resected or surgically cured intraepithelial carcinoma of the uterine cervix, basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or ductal breast carcinoma) within 5 years before informed consent

2. Active infection

3. Concurrent spinal cord compression lesion (e.g., cervical spine diseases, disk herniation, or ossification of the ligamentum flavum) , with the exception of conditions that would not affect efficacy evaluation in the study, as judged by the investigator or subinvestigator

4. Concurrent dementia

5. Concurrent psychiatric disorder, with the exception of conditions that would not affect obtaining informed consent or efficacy evaluation in the study, as judged by the investigator or subinvestigator

6. History of or current alcohol or drug dependence

7. Planned surgery during the study period

8. Any other conditions unsuitable for participation in the study in the opinion of the investigator or subinvestigator