An experimental gene therapy from Pfizer performed well in a Phase 3 trial involving people with hemophilia A, despite previous safety issues that caused the trial to be halted for almost 12 months. The therapy is a one-time infusion of giroctocogene fitelparvovec, designed to help patients produce enough of a protein known as Factor VIII, which is required for blood clotting. Currently, patients diagnosed with hemophilia A manage the condition through regular injections of Factor VIII.
The study findings offer a promising future for patients who want to avoid the frequent injections of Factor VIII. However, there are still some questions about the treatment. It is not yet clear how long the effects of Pfizer’s therapy will last or if it will permanently reduce the need for Factor VIII injections. Pfizer, founded in New York, plans to track patients who have received the treatment for up to 15 years.
Regulators will focus on the subset of patients whose Factor VIII levels increased to 150% or more during the study, which accounted for nearly half of the participants. Issues with clot formation in some of these patients led the Food and Drug Administration (FDA) to halt the trial in November last year.
Pfizer addressed all the FDA’s concerns and resumed the trial in September 2022 with a new format. In response to the elevated Factor VIII levels, Pfizer stated that they were temporary and did not impact the efficacy and safety outcomes. Regulators are expected to engage in further discussions about the treatment in the coming months, according to the company.
Gene therapy developers for hemophilia have had a tumultuous relationship with the FDA. In 2020, the FDA surprised the industry by rejecting BioMarin’s therapy and requesting more information. BioMarin eventually gained approval, but sales have not met investors’ expectations.
Pfizer collaborated with Sangamo Therapeutics to develop a hemophilia A therapy. The company’s other gene therapy projects have shown mixed results. Pfizer received approval for a hemophilia B gene therapy in April but experienced a research setback in June with its Duchenne muscular dystrophy therapy. In 2023, Pfizer sold its primary gene therapy projects to AstraZeneca.
