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Regenxbio Plans to Launch Pivotal Trial of DMD Gene Therapy in Second Half of 2024

NEW YORK – Regenxbio on Tuesday shared encouraging interim safety and efficacy data from the open-label Phase I/II AFFINITY DUCHENNE trial of its experimental Duchenne muscular dystrophy gene therapy, which the firm said puts it on track to initiate a pivotal study in the second half of the year.

The US Food and Drug Administration last year approved the first gene therapy to treat Duchenne muscular dystrophy, Sarepta Therapeutics' Elevidys (delandistrogene moxeparvovec), which uses an adeno-associated virus (AAV) vector to deliver a gene that encodes for microdystrophin, a protein Sarepta developed to carry out the normal functions of dystrophin, the protein lacking in patients with the condition. Mutations in the DMD gene can hinder production of the dystrophin protein, which is necessary to maintain muscle structure.

Rockville, Maryland-based Regenxbio's gene therapy candidate, called RGX-202, uses an AAV serotype 8 vector to deliver a gene for a novel microdystrophin that it says has functional elements of the C-terminal domain found in naturally occurring dystrophin. Based on a three-month assessment, the first patient who received a higher dose of RGX-202 has demonstrated "robust" microdystrophin expression up about 76 percent compared to baseline, according to Regenxbio, with early evidence of improved strength and motor function. That patient was 12 years of age.

Four patients between ages 4 and 10 years old, all with three months of follow-up data, also demonstrated improved microdystrophin expression up anywhere from 11 percent to 83 percent.

Regenxbio said it expects to decide on the dose it will use in a pivotal trial midyear, with plans to initiate the study in the second half of 2024. The company said it expects to pursue accelerated approval with the FDA, using microdystrophin expression as a surrogate endpoint to support a biologics license application.

Regenxbio on Wednesday also said it intends to raise funds by selling $125 million of its common stock in an underwritten public offering, subject to market and other conditions. Morgan Stanley, Goldman Sachs, Barclays, and Stifel are joint bookrunning managers of the offering.

For Elevidys, which was granted accelerated approval based on increased expression of its microdystrophin protein, the FDA opted to limit the indication to patients between 4 and 5 years old based on available evidence. Cambridge, Massachusetts-based Sarepta is currently seeking to expand the indication to all ages and convert its accelerated approval to traditional approval.