This Phase 1 study will evaluate the safety and efficacy of HMI-203 gene therapy in adult male participants with MPS II currently being treated with standard-of-care idursulfase ERT or equivalent. Participants will receive a single dose of HMI-203 administered intravenously. There are 3 planned dose cohorts which will consist of 3 participants each.~Entry into the first dose cohort will be separated by a 60-day dosing interval between each participant to allow the Homology Medicines medical monitor to review safety and efficacy data prior to the second and third participants being enrolled. Enrollment of subsequent participants, in cohorts 2 and 3, will be separated by a 21-day dosing interval between each participant for review of safety and efficacy data.~Escalation to the next dose cohort will occur after 21 days of safety, efficacy, and biomarker data have been reviewed by the Homology Medicines independent DMC.~This entire study is comprised of 5 years, with the most frequent follow up visits occurring in the first year.
Phase 1, open-label, sequential ascending dose-escalation study. Designed to evaluate the safety and efficacy of a single IV infusion of investigational gene therapy HMI-203. Males, ages 18 to 45 years inclusive, with MPS II (Hunter syndrome) currently receiving idursulfase ERT (or the equivalent) are eligible to participate. Participants will be followed for safety and efficacy for 5 years.