for males ages 4 months to 5 years (full criteria)
at Oakland, California and other locations
study started
estimated completion
Principal Investigator
by Dr. Paul Harmatz



RGX-121 is a gene therapy which is intended to deliver a functional copy of the iduronate-2-sulfatase (IDS) gene to the central nervous system. This study is a safety and dose ranging study to determine whether RGX-121 is safe and tolerated by patients with MPS II.

Official Title

A Phase I/II Multicenter, Open-Label Study to Evaluate the Safety, Tolerability, and Pharmacodynamics of RGX-121 in Pediatric Subjects With MPS II (Hunter Syndrome)


MPS II is a rare X-linked recessive genetic disease caused by mutations in the iduronate-2-sulfatase gene (IDS). Enzyme replacement therapy (ERT) with recombinant idursulfase (ELAPRASE®) is the only approved product for the treatment of Hunter syndrome, however, ERT as currently administered does not cross the Blood Brain Barrier and is therefore unable to address the unmet need in MPS II patients with CNS (neurocognition and behavior) involvement. RGX-121 is designed to deliver a healthy gene to cells in the CNS and iduronate-2-sulfatase (I2S) where it may be secreted by transduced cells which may cross-correct non-transduced cells by taking up the functional enzyme. This is a Phase I/II, first-in-human, multicenter, open-label, single arm dose escalation study of RGX-121. Three, one time doses of RGX-121 will be studied in approximately 12 pediatric subjects who have severe MPS II. Safety will be the primary focus for the initial 24 weeks after treatment (primary study period) whereupon, subjects will continue to be assessed (safety and efficacy) for up to a total of 104 weeks following treatment with RGX-121.-121.


Mucopolysaccharidosis Type II (MPS II) MPS II gene therapy Hunter Mucopolysaccharidosis II Mucopolysaccharidoses RGX-121 RGX-121 Dose 1 RGX-121 Dose 2 RGX-121 Dose 3


You can join if…

Open to males ages 4 months to 5 years

  • Must meet any of the following criteria:
    1. Has a documented diagnosis of MPS II AND has a neurocognitive testing score ≤ 77 (Bayley or Kaufman), OR
    1. Has a documented diagnosis of MPS II AND has a decline of ≥ 1 standard deviation on serial neurocognitive testing administered between 3 to 36 months apart (Bayley or Kaufman) OR
    1. Has a relative clinically diagnosed with severe MPS II who has the same IDS mutation as the subject AND in the opinion of a geneticist has inherited a severe form of MPS II OR
    1. Has documented mutation(s) in IDS that in the opinion of a geneticist is always known to result in a neuronopathic phenotype AND in the opinion of a clinician has a severe form of MPS II
  • Patient's legal guardian must be willing and able to provide written, signed informed consent.
  • Is ≥4 months to <5 years of age.

You CAN'T join if...

  • Has contraindications for intracisternal injection, intracerebroventricular injection, or lumbar puncture
  • Has contraindications for immunosuppressive therapy
  • Has neurocognitive deficit not attributable to MPS II or diagnosis of a neuropsychiatric condition
  • Has a (cerebral) ventricular shunt that may impact the proper dosing of the subject
  • Received hematopoietic stem cell transplantation
  • Has had prior treatment with an AAV-based gene therapy product
  • Received ELAPRASE® via intrathecal (IT) administration within 4 months of signing the ICF or experienced a serious hypersensitivity reaction to ELAPRASE®
  • Has received any investigational product within 30 days of Day 1 or 5 half-lives before signing the ICF, whichever is longer
  • Has a platelet count <100,000 per microliter (µL), absolute neutrophil count <1.3 × 103/µL, or aminotransferase (ALT) or aspartate aminotransferase (AST) >3 × upper limit of normal (ULN) or total bilirubin >1.5 × ULN at screening unless the subject has a previously known history of Gilbert's syndrome


  • University of California San Francisco, Benioff Children's Hospital accepting new patients
    Oakland California 94609 United States
  • Children's Hospital of Pittsburgh - UPMC: Program for Neurodevelopment in Rare Disorders accepting new patients
    Pittsburgh Pennsylvania 15224 United States

Lead Scientist at UCSF


accepting new patients
Start Date
Completion Date
Regenxbio Inc.
Phase 1/2
Study Type
Last Updated