(HealthDay News) — For men with severe hemophilia A, treatment with valoctocogene roxaparvovec, an adeno-associated virus 5-based gene-therapy vector, yields a significant increase in factor VIII activity, with a reduction in treated bleeding episodes, according to a study published in the March 17 issue of the New England Journal of Medicine.

Margareth C. Ozelo, M.D., Ph.D., from the University of Campinas in São Paulo, Brazil, and colleagues conducted an open-label, phase 3 study to examine the efficacy and safety of valoctocogene roxaparvovec in men with severe hemophilia A. A total of 134 participants who had been receiving prophylaxis with factor VIII concentrate received a single infusion of 6×1013 vector genomes of valoctocogene roxaparvovec per kilogram of body weight and completed more than 51 weeks of follow-up.

The researchers found that the mean factor VIII activity level at weeks 49 through 52 had increased by 41.9 IU per deciliter among the 132 HIV-negative participants. After week 4, the mean annualized rates of factor VIII concentrate use and treated bleeding had decreased by 98.6 and 83.8 percent, respectively, after infusion among the 112 participants enrolled from a prospective nonintervention study. At least one adverse event was reported by all participants; 16.4 percent reported serious adverse events. The most common adverse event was elevations in alanine aminotransferase levels, which occurred in 85.8 percent of patients.


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“Gene therapy for hemophilia A may enable maintenance of steady, endogenous factor VIII activity without regular prophylaxis,” the authors write. “The expression of the transferred gene appears to decline over time; further study is needed to address whether repeat treatment will be necessary or possible.”

The study was funded by BioMarin Pharmaceutical, the developer of valoctocogene roxaparvovec.

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