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FDA clears Rocket to resume testing gene therapy for a rare heart disease

Rocket’s program has been in limbo since early May, when the company surprised investors and analysts with news of the trial’s stoppage.

That announcement stalled what had been steady progress for Rocket, which went public via a reverse merger in 2017 and has since become one of the most valuable gene therapy developers, surpassing more established companies like Bluebird bio and UniQure.

Rocket has one of the broader pipelines in gene therapy, with programs in development for a number of rare diseases. But the biotech’s gene therapy for Danon — a deadly disease with no approved treatments for its underlying cause — is its largest opportunity. The disease causes weakness in the heart and skeletal muscles that leads to cognitive impairment, heart transplants and often death at an early age.

Rocket’s treatment is meant to restore cardiac function, though the biotech has so far proven only that treatment can lead to a decline in markers of heart failure in some young adult patients. A couple are showing signs of disease stabilization or improvement compared to historical controls.

There have been some safety concerns, however. Last year, one patient on a higher dose had an immune response that needed to be treated with the Alexion Pharmaceuticals drug Soliris. That patient went on to receive a heart transplant after the disease worsened, but is “currently doing well clinically,” CEO Gaurav Shah said on a conference call last week. Shah added that the patient’s case highlights “the importance of the right timing in order for the gene therapy to be fully effective,” rather than a safety issue.

Still, Rocket has more closely monitored patients since the incident. And though no new adverse events related to treatment have emerged, the FDA suspended testing in May and asked for new risk mitigation measures.

The clinical hold was one of several for gene therapies over the past year, a pileup of negative news that led the FDA to schedule an unusual advisory committee meeting next month. Rocket investors were concerned the fate of the Danon program would be tied to the outcome of that meeting, according to a note from Dae Gon Ha, an analyst at the investment bank Stifel.

Rocket may have sidestepped some of those concerns, however, by coming to an agreement with the FDA beforehand. The September meeting will now be “more of an informative discussion forum rather than a determinant for [Rocket’s] most important asset,” he wrote.

As part of its agreement with the agency, Rocket will no longer test the higher dose of its gene therapy, and is enrolling patients who are younger and whose disease isn’t as advanced. The company also modified its use of immune-suppressing drugs to “bolster safety guardrails,” Shah said on the conference call last week. The company didn’t provide any additional specifics in its announcement Monday.

Rocket will disclose more data from its Phase 1 trial later this year. Results in pediatric patients should come in 2022.