FDA Grants Expression Fast Track and RPPD for Hemophilia A Stem Cell Therapy

Rare Daily Staff

The U.S. Food and Drug Administration has granted Fast Track and Rare Pediatric Disease designations to Expression Therapeutics for its experimental stem cell therapy for hemophilia A.

The dual designations are intended to speed regulatory interactions and, if approved, could make the company eligible for a potentially lucrative priority review voucher, which can be sold or used to expedite another drug application.

Hemophilia A is a rare genetic bleeding disorder caused by a deficiency of clotting factor VIII. It affects about one in 5,000 male births, and roughly half of patients have a severe form marked by spontaneous bleeding episodes that can lead to joint damage, chronic pain, and reduced quality of life. Standard treatment typically requires lifelong prophylactic infusions or injections of factor VIII, often multiple times per week, with annual costs that can exceed $650,000.

Expression is developing an autologous hematopoietic stem cell-based gene therapy designed as a one-time treatment. The approach involves collecting a patient’s own stem cells, genetically modifying them to produce factor VIII, and reinfusing them following conditioning. In a phase 1 study published in the New England Journal of Medicine in 2025, treated patients showed sustained factor VIII expression over multiple years and were able to discontinue prophylactic therapy, according to the company.

The company said it is working with researchers at Stanford University to advance the program into a phase 2 clinical trial. Investigators involved in the collaboration said the approach could represent a new treatment paradigm if durability and safety are confirmed in larger studies.

“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,” said David Townson, CEO of Expression Therapeutics. “Reducing the annual bleed rate is not the finish line. Patients deserve a therapy that addresses the physical, psychological, and financial weight of this disease for life. That is what we are building.”

Photo: David Townson, CEO of Expression Therapeutics