Gene Therapy Nearly Eliminates Hemophilia B Bleeding Episodes, Trial Shows

A hemophilia gene therapy developed by Spark Therapeutics and Pfizer nearly eliminated bleeding episodes in 10 patients who took part in a Phase 1/2 trial.

The treatment, SPK-9001, worked so well in eight of the 10 that they were able to stop taking clotting factor replacements.

Researchers published the preliminary trial findings in The New England Journal of Medicine. The study is titled “Hemophilia B Gene Therapy with a High-Specific-Activity Factor IX Variant.”

“The data suggest a one-time infusion of SPK-9001 has the potential to safely sustain factor IX coagulant activity level,” Dr. Katherine A. High, Spark’s president, said in a press release. In fact, the therapy may eliminate the need for preventive “factor infusions, significantly reduce bleeding, and nearly eliminate the need for exogenous factor IX concentrate infusions,” said High, the study’s senior author.

The trial (NCT02484092) covered 10 men with hemophilia B who had experienced bleeding episodes despite factor replacement infusions.

All received a single administration of the gene therapy, which is composed of a harmless virus carrying the factor IX gene. It triggered an increase in factor IX coagulant activity that averaged 34 percent of normal.

Before the treatment, the group averaged 11 bleeding episodes a year. The therapy reduced the number of episodes to 0.4 a year — a 97 percent drop.

Only one patient experienced bleeding after the treatment. He had four episodes.

Meanwhile, eight out of the 10 were able to stop taking factor infusions. One patient with severe joint disease had a factor replacement infusion after doctors suspected a bleeding episode. But his factor use dropped by 91 percent after the gene therapy, researchers said.

“People who live with hemophilia today face a lifelong need for vigilant monitoring and recurrent factor concentrate infusions to prevent spontaneous, potentially life-threatening bleeds and to protect their joints,” High said. “The discipline required to execute the usual prophylactic [preventive] regimen can exact a heavy toll on quality of life, and these regimens result in significant costs to patients, families and the healthcare system.”

Although the trial showed how effective gene therapy is, its main objective was to determine how safe the treatment is. There was good news on that front: None of the participants experienced a severe adverse event. Researchers saw no blood clot formations, and no patients developed antibodies blocking the newly produced factor IX.

Two patients had increases in liver enzymes. But they did not lead to symptoms and researchers resolved them with temporary corticosteroid treatment.

Considering that hemophilia B patients usually require recurrent clotting factor infusions, the potential of a one-time treatment for the disease is an exciting development — largely because it has the potential to improve patients’ quality of life.

The trial is still going on in the United States, Canada, and Australia, with researchers seeking more participants.

In November 2017, the companies announced that they would include a few more patients to try a new version of the treatment, produced with a different manufacturing process.

For more information about the study, including how to enroll, see the trial’s registration webpage.