Regenxbio’s investigational gene therapy shows promise in Hunter syndrome

Regenxbio has shared positive results from a pivotal study of its investigational gene therapy in boys aged up to five years with mucopolysaccharidosis type 2 (MPS 2), a rare genetic disease estimated to affect one in every 100,000 to 170,000 births.

The company said the results will support a regulatory submission to the US Food and Drug Administration (FDA) this year under the accelerated approval pathway.

Also known as Hunter syndrome, MPS 2 occurs when a child’s body does not properly digest certain sugar molecules. When these molecules accumulate over time, they can cause cell, tissue and organ dysfunction, including in the central nervous system (CNS).

There is currently no treatment to address fatal neuronopathic CNS disease in MPS 2.

Results from the pivotal section of the phase 1/2/3 CAMPSIITE trial, presented at this year’s WORLDSymposium, showed that MPS 2 patients treated with Regenxbio’s one-time gene therapy, RGX-121, achieved decreased levels of D2S6, a key biomarker of brain disease activity, below maximum attenuated disease levels 16 weeks after administration.

Patients receiving RGX-121 demonstrated an 86% median reduction in D2S6, which Regenxbio said is “approaching normal levels”.

The results were consistent with data from the dose-finding phase of the study, the company said, in which the majority of patients are "exceeding expectations" in neurodevelopmental function compared to natural history data up to four years.

The new long-term follow-up of those treated with RGX-121 in the dose-finding phase also showed there was a high rate of patients who were allowed to discontinue or remain naïve to standard-of-care intravenous enzyme replacement therapy.

Kenneth Mills, president and chief executive officer of Regenxbio, said: "The data from this pivotal trial supports that RGX-121 changes the course of disease by restoring the gene missing in boys with Hunter syndrome and has the potential to significantly improve vital brain function for patients living with this debilitating disease.

"We are excited about these results and working quickly to complete activities to file the biologics license application this year.”

Mills added that the company has already shared results from CAMPSIITE with FDA leadership, who have confirmed that, based on the totality of the evidence, they are “open to accelerated approval if supported by the review of full data”.