Study details
The new report followed up on the initial trial in 134 men who were treated with a single infusion of 6 × 1013 vector genomes per kilogram of body weight.
Among the 132 subjects available for 2-year evaluation, median factor VIII activity was in the range of mild hemophilia (6%-49% of normal) with an 84.5% reduction in bleeding events from baseline.
More than 80% of participants had no bleeding events requiring treatment, and there was a 98% reduction from baseline in mean use of exogenous factor VIII.
Overall, at year 2, 4.5% of subjects had factor VIII activity consistent with severe hemophilia A; 9.1% had activity consistent with moderate disease; 59.8% had activity consistent with mild disease; and 26.5% had activity in the normal range above 40 IU/dL. The investigators estimated that the typical half-life of the transgene-derived factor VIII production system is 123 weeks.
Among the six men who resumed prophylaxis, most had fewer bleeding events than when they were on prophylaxis before the infusion, investigators noted.
All the subjects developed antibodies to the virus delivery vector, precluding retreatment.
The work was funded by valoctocogene roxaparvovec maker BioMarin Pharmaceuticals. Several investigators are employees. Others reported ties to BioMarin and other companies; Dr. Mahlangu, for instance, reported research grants from BioMarin, Roche, Novo Nordisk, Pfizer, and others. Dr. George reported a research grant from Asklepios Biopharmaceutical and having a patent licensed to the company. The full list of author disclosures can be found with the original article.
A version of this article first appeared on Medscape.com.