FDA Halts Rocket’s Gene Therapy Trial After Patient Death

Highlights

• The FDA has placed a clinical hold on Rocket Pharmaceuticals’ pivotal gene therapy trial after a patient death.
• The patient developed capillary leak syndrome and later died of an acute systemic infection.
• Rocket attributes the adverse event to the addition of a C3 inhibitor in the pretreatment regimen.
• The biotech is in discussions with the FDA but has not provided a timeline for resuming the trial.
• Rocket is refocusing its investments to extend its financial runway into 2027.
• Other pipeline programs remain on track and unaffected by the hold.
• Company shares dropped 63%, though analysts see a potential recovery with safety modifications.

Regulatory Action Follows Patient Death in Danon Disease Study

Rocket Pharmaceuticals has encountered a major regulatory and clinical setback following the death of a patient in its pivotal gene therapy trial for Danon disease. The U.S. Food and Drug Administration (FDA) issued a clinical hold on the trial, prompting the New Jersey-based biotechnology firm to suspend dosing and reassess its approach.

The trial, designed to evaluate RP-A501—a gene therapy intended to restore heart function by delivering the LAMP2B transgene using an AAV9 vector—was being conducted in 12 patients with the rare cardiac condition. Initially slated for completion by mid-2026, Rocket has since withdrawn this target date and outlined cost-control measures to prolong its financial runway.

Adverse Events Linked to Modified Pretreatment Protocol

The patient who died experienced capillary leak syndrome shortly after infusion. According to Rocket CEO Gaurav Shah, M.D., “There were other medical complications and procedural complications in the week or so afterwards, and actually the patient was at that time stable and doing potentially well enough that we were cautiously optimistic over recovery and the capillary leak was improving.” Unfortunately, the patient’s condition worsened due to an acute systemic infection, leading to their death.

Notably, the FDA imposed the clinical hold “before the patient died, to enable evaluation of the causes of the adverse event.” Rocket traced the issue to the recent addition of a C3 inhibitor in its pretreatment regimen. The drug was originally introduced to counter complement activation and prevent thrombotic microangiopathy (TMA)—a serious blood vessel complication seen in earlier patients. While this adjustment appeared to reduce the incidence of TMA, it coincided with new cases of capillary leak syndrome in the two patients who received the C3 inhibitor.

Investigating a Path Forward

Shah indicated that lessons from the first patient’s case informed changes in the care of the second, stating Rocket took action “so that we didn’t see the same events happening in the second patient.” Despite the complications, Shah affirmed Rocket’s commitment to RP-A501 and expressed confidence that “there is a path forward” in discussions with the FDA. However, no definitive timeline has been provided for resolving the clinical hold.

The FDA’s response has been characterized as “more responsive and more collaborative and faster” than in previous engagements, according to Shah. Nevertheless, Rocket must await regulatory clearance before resuming dosing, with multiple patients currently in a holding pattern.

Strategic Adjustments and Financial Outlook

As part of its revised strategy, Rocket will prioritize investments in its adeno-associated virus (AAV) platform and conduct an internal review to enhance pipeline value. The company reported having $318.2 million in cash as of the end of March. These measures are expected to extend Rocket’s financial runway into 2027, a year beyond its prior projection.

Meanwhile, Rocket confirmed that its other gene therapy programs—RP-A601 for Plakophilin-2 associated arrhythmogenic cardiomyopathy and its BAG3 and PKP2 programs—remain unaffected by the hold. The AAVrh74 vector used in RP-A601 differs from RP-A501’s and does not include the controversial C3 inhibitor.

Market Reaction and Analyst Perspective

The news triggered a sharp market response, with Rocket shares plummeting 63% to $2.29 in premarket trading. Despite investor concerns about trial safety and resolution timelines, analysts at William Blair offered a measured outlook: “We continue to believe there is a path forward for the program once a modified safety plan is implemented.”

The firm also emphasized that the adverse developments in the RP-A501 trial do not appear to impact Rocket’s other cardiovascular programs, particularly RP-A601, due to their differing vectors and immunosuppressive approaches.