The Food and Drug Administration (FDA) has given BioMarin Pharmaceutical (NASDAQ:BMRN) a priority review for its valoctocogene roxaparvovec (valrox) gene therapy to treat patients with hemophilia A. The priority review will shave four months off of the review time for the marketing application, compared to a standard review. The agency expects to make a decision by Aug. 21, 2020.

If approved, valrox would be the first gene therapy approved to treat hemophilia A. Currently, patients are treated with a protein called Factor VIII, which has to be infused two to three times per week and still doesn't prevent patients from all bleeding events. Valrox restores expression of Factor VIII in a patient's cells, eliminating the need for the replacement therapy.

Doctor talking to a patient in an exam room

Image source: Getty Images.

The marketing application is based on results from a phase 3 clinical trial that showed 7 out of 16 patients reached or exceeded the level of Factor VIII that regulators in the U.S. and Europe wanted to see. After the data cutoff date, an additional patient also met the goal.

The study is continuing to enroll patients, so the biotech can hopefully show that valrox is superior to Factor VIII replacement therapy. Early data suggests it should meet the goal, with the 16 patients having an average annual bleed rate (ABR) of 1.5, which was 85% lower than the ABR before the study when the patients were on replacement therapy.

BioMarin and its partner ARUP Laboratories are also trying to gain approval of a companion diagnostic test for the gene therapy that will test patients for the presence of antibodies to AAV5, a virus used to deliver the gene therapy. BioMarin estimates that 20% of patients with hemophilia A in the U.S. have preexisting immunity to AAV5 that would make them ineligible for valrox.