Pfizer's investigational gene therapy, giroctocogene fitelparvovec, has demonstrated sustained bleed control in patients with moderately severe to severe hemophilia A, according to full data from the Phase 3 AFFINE clinical trial presented at the American Society of Hematology (ASH) Annual Meeting. The data showed that nearly two-thirds of patients who received a single infusion of the gene therapy were free of bleeding episodes for a median of almost three years.
AFFINE Trial Results
The AFFINE trial (NCT04370054) enrolled 75 adult men with moderately severe or severe hemophilia A, characterized by factor VIII (FVIII) activity levels no greater than 1% of normal. Participants had previously completed at least six months of treatment in a lead-in Phase 3 clinical trial (NCT03587116) involving standard-of-care prophylaxis. Upon entering the AFFINE trial, patients discontinued prophylaxis and received a single infusion of giroctocogene fitelparvovec and are being monitored for up to 5 years, and then for as long as 15 years in a longer-term follow-up study.
The primary endpoint of the trial was the annualized bleed rate (ABR) assessed from three months post-infusion up to at least 15 months. Results from the main efficacy population (50 men) showed a significant reduction in mean total ABR after gene therapy compared to the lead-in period (1.24 vs. 4.73, p<0.0001). The mean ABR for bleeds requiring treatment also dropped significantly from 4.08 pre-infusion to 0.07 post-infusion.
A sensitivity analysis, excluding a single patient with inconsistent bleed reporting, further supported these findings, demonstrating a significant reduction in mean total ABR with giroctocogene fitelparvovec compared to routine prophylaxis (0.26 vs. 4.65).
Clinical Impact and Safety
According to Pfizer, 64% of participants experienced no bleeding events over a median follow-up of 33.6 months after receiving the gene therapy, and 88% had no treated bleeds during that time. The annualized infusion rate of FVIII replacement products also decreased significantly, from a mean of 124.39 pre-treatment to 0.21 post-treatment. Most participants (84%) achieved FVIII activity levels greater than 5% of normal by 15 months post-infusion, with mean FVIII activity levels reaching more than 50% of normal by about a year after the gene therapy and remaining relatively stable thereafter.
The treatment was generally well-tolerated. About three-quarters of participants experienced infusion-related reactions, and two-thirds saw temporary elevations in liver enzymes, but these were usually mild and manageable. Approximately half of the participants experienced temporary FVIII elevations greater than 150% in the initial months post-treatment; however, no thrombotic events were reported except in one patient with a history of blood clots.
Expert Commentary
Andrew Leavitt, MD, lead investigator of AFFINE and a professor at the University of California San Francisco, highlighted the potential benefits of the gene therapy, stating, "A one-time treatment with giroctocogene fitelparvovec significantly reduced bleeding events for both total and treated bleeds, demonstrating the potential to lessen disease and treatment burden for appropriate patients living with hemophilia A."
Mechanism of Action
Giroctocogene fitelparvovec is designed to deliver a shortened but functional version of the F8 gene to the body’s cells, enabling continuous production of FVIII. The therapy uses a viral vector to deliver the gene to liver cells, where FVIII is produced. This approach aims to provide long-term bleed prevention with a single infusion, reducing the need for frequent intravenous infusions or injections associated with standard-of-care prophylaxis.
