What the trial was testing
The trial enrolled 25 patients with hemophilia a. The study was sponsored by Spark Therapeutics and tracked outcomes across the full group of patients who matched the trial's eligibility profile.
It was an early-stage trial — researchers are still confirming safety and getting an early look at how well the treatment works. Trials at this stage are designed to produce evidence regulators and physicians can act on — not just observations to follow up later.
What the results showed
Bleeding rates dropped 91.5% over the median three years of follow-up.
New England Journal of Medicine · 2021 · NCT03003533
These findings — that in annual bleeding rate after a one-time gene therapy infusion in 16 of 18 men — were published in the New England Journal of Medicine and represent the headline result of the study.
Researchers tracked outcomes across 25 patients enrolled in the trial. The result was consistent enough across the group that the team felt confident reporting it.
What this means for patients
For patients with hemophilia a, this result changes the calculus on what to ask their care team about. Whether it changes day-to-day care depends on factors like disease subtype, prior treatments, and where the patient is in their care journey.
What you can do now
This gene therapy (SPK-8011) is still in development and not yet FDA-approved. A different hemophilia A gene therapy (Roctavian/valoctocogene roxaparvovec) was approved by the FDA in 2023. Ask your hematologist about open trials and approved gene therapies if standard prophylaxis is not working for you.
Eligibility for the treatments mentioned above depends on specific test results and clinical history. Bring this summary, the trial name, and your most recent labs or pathology report to your next visit.
Open hemophilia a trials
A Clinical Study to Evaluate the Effects of NXT007 Compared to Factor VIII Prophylaxis in Participants With Hemophilia A
The purpose of this study is to evaluate the efficacy, safety, pharmacokinetics and pharmacodynamics of NXT007 prophylaxis compared with Factor VIII (FVIII) prophylaxis in participants with severe or moderate congenital hemophilia A without FVIII inhibitors. The study will include people aged ≥12 years old who have been on FVIII prophylaxis treatment prior to study entry.
Liver Biopsy In Haemophilia Gene Therapy
To perform a liver biopsy in haemophilia A and B patients with endogenous FVIII:C/FIX:C expression at \>1% any time after gene transfer following AAV mediated gene transfer. This is to obtain tissue for analysis, to understand if FIX/FVIII transgenic protein expression is mediated by AAV proviral DNA that is integrated into the host cell DNA or if stable expression in humans is mediated by episomal maintained AAV genome.