for males ages 18-45 (full criteria)
at Oakland, California and other locations
study started
estimated completion
Principal Investigator
by Paul Harmatz, MD



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.

Official Title

A Phase 1 Open-Label Dose Escalation Study to Evaluate the Safety and Efficacy of HMI-203 in ERT-Treated Adults With Mucopolysaccharidosis Type II (MPS II) (juMPStart Trial)


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 HMI 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 HMI independent DMC. This entire study is comprised of 5 years, with the most frequent follow up visits occurring in the first year.


Mucopolysaccharidosis II, MPS II, Hunter syndrome, Mucopolysaccharidoses, Genetic HMI-203


You can join if…

Open to males ages 18-45

  • Adult males 18-45 years of age at the time of informed consent
  • Has capacity, is able to understand the purpose and risks of the study, is willing and able to comply with all study procedures for a total of 5 years after gene therapy administration
  • Diagnosis of MPS II based on presence of IDS pathogenic variant
  • KBIT2 score ≥ 80
  • Compliance with regular treatments of ERT for MPS II for at least 12 months prior to enrollment
  • Clinically stable relative to urinary GAG levels, ambulation, and cardiopulmonary status for 12 months preceding enrollment
  • Able to complete the 6MWT

You CAN'T join if...

  • Multiple sulfatase disorder as determined by abnormal activity of another lysosomal sulfatase
  • Unresponsive and/or intolerant to idursulfase treatment
  • History of BMT, stem cell transplant, or gene therapy
  • Presence of anti-neutralizing antibodies
  • ALT and AST > ULN; Total and Direct bilirubin > ULN
  • International normalized ratio (INR) >1.2 ULN
  • Hematology values below the normal range
  • Hemoglobin A1c ≥ 6.5% or fasting glucose ≥126 mg/dL
  • Contraindication to corticosteroid use
  • Any condition that would not allow the potential participant to complete follow up examinations during the course of the study or, in the opinion of the investigator, makes the potential participant unsuitable for the study


  • UCSF Benioff Children's Hospital Oakland accepting new patients
    Oakland California 94609 United States
  • University of Utah Pediatric Genetic & Metabolism Clinic not yet accepting patients
    Salt Lake City Utah 84113 United States

Lead Scientist at UCSF

  • Paul Harmatz, MD
    Professor, Pediatrics, School of Medicine. Authored (or co-authored) 205 research publications


accepting new patients
Start Date
Completion Date
Homology Medicines, Inc
Phase 1 research study
Study Type
Expecting 9 study participants
Last Updated