RegenXBio gets FDA support for Hunter syndrome gene therapy's accelerated review filing—in 2024

It’s going to be a long wait, but RegenXBio is already waving a flag to show that the Hunter syndrome gene therapy RGX-121 is headed for an accelerated approval request at the FDA.

The company has been given the go-ahead from the FDA to file its biologics license application for the therapy under the accelerated review pathway, which allows drugs for conditions with an unmet need to reach patients sooner. But in this case, sooner means 2024, which is when RegenXBio plans to officially submit the application.

CEO Kenneth Mills said the company’s plans to seek accelerated approval were supported by the FDA based on recent conversations with the agency. This pathway allows companies to submit drugs based on surrogate endpoint data, rather than clinical efficacy, for conditions that do not have a lot of options.

It’s been a flashpoint of debate over the past year, after the FDA approved the Alzheimer’s disease drug Aduhelm under the pathway and granted Biogen nine years to conduct a required confirmatory study. FDA Commissioner Robert Califf, M.D., has been mulling over changes to the program but has indicated support for the continued use of the pathway.

Hunter syndrome, also known as mucopolysaccharidosis type II, is a rare inherited disorder in which the body is unable to break down sugar molecules. This leads to buildup in the organs and can cause damage over time that affects patients’ physical and mental abilities.

RGX-121 is a gene therapy working its way through a pivotal phase 1/2/3 trial for children up to five years old called CAMPSIITE. The open label study is currently enrolling patients.

RegenXBio hopes to use endpoint data from this study to support the FDA filing, particularly changes from baseline of glycosaminoglycans (GAGs) in the cerebrospinal fluid at four months. The buildup of GAGs has been associated with clinical manifestations of Hunter syndrome, including neurodevelopmental deficits, so the company believes this endpoint can be used to support the accelerated review.