An Extension Study of JR-141 to Evaluate the Long-term Safety and Efficacy in Mucopolysaccharidosis Type II (Hunter Syndrome) Male Subjects

Open to males

1. A subject who participated in the Parent Study (JR-141-GS31) and completed the Week 105 visit in Cohort A and Week 53 visit in Cohort B, and in the opinion of the principal investigator has no safety concerns to enter this study OR A subject who participated in Cohort A in the Parent Study (JR-141-GS31) and changed study intervention from idursulfase to JR-141 after data at Week 53 were collected.
2. A subject from whom an IRB or IEC-approved written informed consent can be obtained, which is voluntarily signed. If the subject is aged under 18 years (aged under 16 years in the UK) at the time of enrollment or willingness to participate in the study cannot be confirmed due to MPS II-related intellectual disability, the subject's legally acceptable representative (e.g., his parents or guardians) may sign the ICF on behalf of the subject. Written informed assent should be obtained from the subject, wherever possible.
3. Male subjects whose partners are of child-bearing potential agree to use a medically accepted, highly effective method of contraception being a condom plus an approved method of effective contraception from the time of signing the ICF.

The following methods are acceptable:

- Partner's use of combined (estrogen and progestogen-containing) hormonal contraception associated with inhibition of ovulation: - oral - intravaginal - transdermal - Partner's use of progestogen-only hormonal contraception: - oral - injectable/implantable - IUS - Partner's use of implantable IUD - Surgical sterilization (for example, vasectomy or bilateral tubal occlusion) - Partner's use of female cap or diaphragm (double barrier). Alternatively, true abstinence is acceptable when it is in line with the subject's preferred and usual lifestyle. If a subject is usually not sexually active but becomes active, they, with their partner, must comply with the contraceptive requirements detailed above.

1. For subjects with hearing impairment requiring hearing aid(s), every effort will be made to encourage compliance with the use of functioning hearing aid(s). Subject or/and parent/legally acceptable representative agrees to wearing them during the study and on neurocognitive testing days.

1. A subject who has received gene therapy treatment at any point.
2. Refusal to sign the ICF.
3. A subject who is judged by the principal investigator as being unable to undergo lumbar puncture, including those who has difficulties in attaining the required position for lumbar puncture due to joint contracture or those who is likely experience breathing difficulties during the lumbar puncture process.
4. A subject who switched from JR-141 to idursulfase during the treatment period in the Parent Study (JR-141-GS31).
5. A subject who is unable to comply with the protocol (e.g., is unable to return for safety evaluations or is otherwise unlikely to complete the study) as determined by the principal investigator.
6. A subject who is judged by the principal investigator to be ineligible to participate in the study due to a history of serious drug allergy or sensitivity including to anesthesia or hypersensitivity to any component of JR-141.
7. A subject who has a known or suspected local or general chronic infection or is at risk of abnormal bleeding due to medical conditions* or therapies.
8. A subject who otherwise is judged by the principal investigator to be ineligible to participate in the study.

Medical Conditions:

1. Clinically significant multiple or severe drug allergies, intolerance to topical corticosteroids, or severe post-treatment hypersensitivity reactions (including, but not limited to, erythema multiforme major, linear IgA, toxic epidermal necrolysis, and exfoliative dermatitis)
2. Evidence or history of significant active bleeding or coagulation disorder or use of non steroidal anti-inflammatory drugs or other drugs that affect coagulation or platelet function within 14 days prior to lumbar catheter insertion
3. Allergy to lidocaine (Xylocaine®) or its derivatives