FDA grants fast track status to 1-time stem cell therapy for hemophilia A

The U.S. Food and Drug Administration (FDA) has granted both fast track and rare pediatric disease designations to Expression Therapeutics’ investigational stem cell therapy for hemophilia A.

Each of these designations is intended to speed development of a candidate therapy. This stem cell therapy was designed as a potentially lasting, one-time treatment for hemophilia A, a bleeding disorder marked by low or missing levels of factor VIII (FVIII), a blood-clotting protein.

Fast-track status is awarded to treatments for serious conditions that address an unmet medical need. Its benefits include more frequent interactions with the FDA and the possibility of rolling review, in which parts of an application can be submitted as they are completed. Rare pediatric disease designation, meanwhile, may make Expression eligible for a priority review voucher if the therapy is approved and other program requirements are met. That voucher would be usuable with a future drug or can be sold to another company.

Expression noted that, in an early clinical trial, its stem cell therapy was shown to completely eliminate the need for preventive treatments among participants.

“These dual FDA designations represent meaningful external validation — both of the scientific approach and of the profound unmet need this therapy is designed to address,” Krista McKerracher, a member of Expression Therapeutics’ board of directors and former VP and global franchise head, oncology global development at Novartis, said in a company press release announcing the new statuses.

“Expression Therapeutics is uniquely positioned to advance a differentiated, potentially durable treatment for hemophilia A, supported by compelling early clinical data and a well-defined regulatory pathway,” McKerracher added.

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The FDA’s decision follows positive results from a Phase 1 clinical trial (NCT05265767) involving adults with severe hemophilia A. The data showed that a single administration of the experimental therapy led to sustained FVIII expression and eliminated the need for preventive, or prophylactic, treatment.

According to the company, the stem cell therapy program is being developed in collaboration with “a world-class team” of researchers at Stanford University in California. Following the successful Phase 1 study, both parties are collaborating on a Phase 2 trial.

Bleeding rate dropped to zero for participants in earlier trial

Hemophilia A is caused by a lack of functional FVIII, which is needed for blood to clot properly. People with severe disease may experience spontaneous or prolonged bleeds, including into joints and muscles, which can cause symptoms such as pain, joint damage, and other complications over time.

Standard treatment for severe hemophilia A typically involves regular prophylactic infusions to prevent bleeds. While these treatments can reduce bleeding rates, they require lifelong management and can place a substantial physical, emotional, and financial burden on patients and families.

Expression’s investigational treatment uses a patient’s own hematopoietic, or blood-forming, stem cells. According to the company, after the patient’s stem cells are collected, they are genetically modified in the lab to carry instructions for producing FVIII, then infused back into the patient. Once they reach the bone marrow, the modified cells are intended to give rise to blood cells that continuously supply functional FVIII.

“As leaders in hemophilia and cutting-edge treatment strategies for blood and immune diseases, including gene and cellular therapies, we are excited to see this innovative approach using autologous hematopoietic stem cell-based gene therapy in hemophilia A,” said Glaivy Batsuli, MD, a pediatric hematologist and bleeding disorder physician who serves as director of hematology research at Stanford.

The Phase 1 study enrolled five people, ages 22 to 41, with severe hemophilia A. All participants had annualized bleeding rates (ABR), or the total number of bleeds per year, of at least 20 events before receiving the stem cell therapy. After treatment, the ABR dropped to zero, with no spontaneous bleeding events reported in any participant during the study, data showed.

Further, following treatment, FVIII levels increased to clinically significant levels in all five participants. Median follow-up was 14 months, or slightly longer than a year, with a range of nine to 27 months.

We are working toward the day when a child diagnosed with hemophilia A is offered a single treatment … that provides unprecedented durability and genuine freedom from the burden of lifelong infusions.

No patients developed FVIII inhibitors, which are neutralizing antibodies that can reduce the effectiveness of FVIII-based treatments. Also, no serious adverse events occurred beyond those expected. Specifically, the researchers noted that none of the participants developed neutropenia, in which levels of certain white blood cells are low, or thrombocytopenia, marked by low platelet counts.

David F. Townson, PhD, Expression’s CEO, noted that “reducing the annual bleed rate is not the finish line” for the company.

“At Expression, we are working toward the day when a child diagnosed with hemophilia A is offered a single treatment — made in the United States — that provides unprecedented durability and genuine freedom from the burden of lifelong infusions,” Townson said. “Patients deserve a therapy that addresses the physical, psychological, and financial weight of this disease for life. That is what we are building.”