By Josh Nathan-Kazis

The biotech Rocket Pharmaceuticals said the Food and Drug Administration would allow it to continue a gene therapy trial the agency had put on hold in late May, when a patient in the trial died.

Shares of the biotech surged 20% on Wednesday. Even after that run-up, the stock price remains about 45% below where it was trading before the company disclosed the patient death earlier this year.

In the following months, investor enthusiasm for gene therapies waned even further, as what was once the biggest idea in biotech delivered even more disappointments and safety worries.

Rocket's relatively quick reprieve is good news for the stock, and suggests that the FDA remains actively supportive of gene therapy development. But investors are increasingly wary of the field, and the company still has much to prove.

Rocket's experimental gene therapy, called RP-A501, is meant to treat a rare genetic condition called Danon disease, which weakens the heart muscle and generally kills male patients in early adulthood. The patient on the therapy who died earlier this year was one of six participants in a small Phase 2 trial that was meant to be the last step before Rocket submitted the drug for FDA approval.

In late May, Rocket said two patients in the trial who had received RP-A501 had developed a serious condition called capillary leak syndrome, and that the FDA had suspended the study. Shortly after the FDA had instituted the suspension, one of the patients with capillary leak syndrome died of an acute infection.

The company said the two patients who developed capillary leak syndrome had been given a cocktail of drugs meant to tamp down their immune responses that included one new ingredient that had not been given to other patients.

On Wednesday, Rocket said the trial would continue with new patients who would receive a lower dose of RP-A501. The new ingredient that had been added to the cocktail meant to modulate patients' immune responses would be removed, the company said, and other changes would be made.

That's all good news for Rocket. Analysts said early Wednesday that the drug would likely work at the lower dose, and could at some point get approved.

"We continue to see our projected 2029 commercial launch of RP-A501 in Danon disease as reasonable," Leerink Partners analyst Mani Foroohar wrote.

The question is whether investors can be enticed back into gene therapy stocks. As Barron's wrote in June, gene therapies were the hottest idea in biotech in the years before the Covid-19 pandemic, but now, much of that enthusiasm in gone.

The past 12 months have been perhaps the worst yet for the gene therapy field, with multiple patient deaths and sinking share prices. Other high-profile patient deaths have included one in a trial of a Neurogene gene therapy for Rett Syndrome last year, and three patients who received gene therapies made by Sarepta Therapeutics. Of the Sarepta deaths, two were of patients on its approved Duchenne muscular dystrophy gene therapy Elevidys, and one in an early-stage trial of an experimental gene therapy for a condition called limb-girdle muscular dystrophy.

The Sarepta patient deaths have drawn widespread attention, amid puzzling regulatory wobbles from the FDA, political backlash, and the departure and rapid return of the top FDA official for regulating gene therapies.

The FDA said on July 18 it had stopped Sarepta's limb girdle muscular dystrophy trials, and that it had asked the company to stop shipping all doses of Elevidys. But on July 28, the FDA said Sarepta should resume shipping doses of Elevidys to some patients.

None of it has been good for the stocks. Sarepta shares are down 83% this year.

Still, there may be some hope in the lifting of the clinical hold on Rocket's gene therapy. It could be a sign that the FDA remains engaged and supportive of gene therapy development.

"The hold was lifted in under three months, signaling a collaborative and understanding CBER division led by Dr. Vinay Prasad," wrote Jefferies analyst Andrew Tsai, referring to the FDA office responsible for regulating gene therapies.

Write to Josh Nathan-Kazis at josh.nathan-kazis@barrons.com

This content was created by Barron's, which is operated by Dow Jones & Co. Barron's is published independently from Dow Jones Newswires and The Wall Street Journal.

(END) Dow Jones Newswires

August 20, 2025 11:02 ET (15:02 GMT)

Copyright (c) 2025 Dow Jones & Company, Inc.