RGX-121 Gene Therapy in Patients With MPS II (Hunter Syndrome)

  • End date
    Dec 16, 2023
  • participants needed
  • sponsor
    Regenxbio Inc.
Updated on 16 August 2021


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.


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.

Condition Hunter's Syndrome, Hunter Syndrome (MPS II)
Treatment RGX-121
Clinical Study IdentifierNCT03566043
SponsorRegenxbio Inc.
Last Modified on16 August 2021


Yes No Not Sure

Inclusion Criteria

Must meet any of the following criteria
a. Has a documented diagnosis of MPS II AND has a neurocognitive testing score 77 (Bayley or Kaufman), OR
b. 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
c. 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
d. 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

Exclusion Criteria

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 (L), absolute neutrophil count <1.3 103/L, 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
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