BioMarin Pharmaceutical Inc.'s three-year data in hemophilia patients treated with its experimental gene therapy, Valrox, showed signs of reduced bleeding and stabilizing factor VIII levels, the company said.

The update is part of an ongoing phase 1/2 study in six evaluated adult participants with severe hemophilia A, an inherited blood disorder, BioMarin said May 28.

Valrox, which is meant to prevent bleeding by replacing patients' deficient factor VIII levels, was tested in a 6e13 vector genomes per kilogram dose, demonstrating a median annualized bleed rate, or ABR, of 0 and mean ABR of 0.7 in the third year, indicating a 96% reduction in mean ABR over three years with Valrox, also known as valoctocogene roxaparvovec.

According to BioMarin, in the year before patients began participating in the trial, the median ABR was 16.3 and mean ABR was 16.5.

Valrox also appeared to result in study participants' factor VIII levels approaching a plateau in year three, at approximately 20% in patients.

Factor VIII levels were at 47% after one year of Valrox treatment and at 27% after two years.

Leerink analysts Joseph Schwartz and Dae Gon Ha noted that the rate of decline in factor VIII levels between years two and three appeared to slow, and factor VIII results were "stronger than expected."

In addition, BioMarin reported that 86% of patients in the third year had zero bleeds requiring factor VIII infusions. Factor VIII infusions are the current standard of care for severe hemophilia A, and patients typically receive infusions intravenously two to three times a week.

"Similar to ABRs, reductions in infusions will be key in regulatory and payor discussions," Leerink's analysts wrote following the data release.

According to BioMarin's statistical modeling, Valrox's effects would be maintained over an extended period of time of eight or more years.

However, Stifel analyst Paul Matteis said, "We do not think the durability debate for Valrox is over."

Nevertheless, Matteis wrote on May 28 that the three-year data "removes the worst case scenario from the table," and acknowledged that Valrox should provide at least five years of bleeding prevention.

BioMarin noted that Valrox was well-tolerated in the participants.

Valrox is also in ongoing phase 3 trials in the same patient population.

BioMarin said regulatory submission plans for Valrox will be announced in the third fiscal quarter of 2019. If approved, Valrox will be the first gene therapy treatment for hemophilia A.