Gene Therapy Maintains Near-Normal Levels of Clotting Factor in Hemophilia B


A single dose of an experimental gene therapy led to maintained factor levels about 30% of patients with hemophilia B.

After a single dose of a novel gene therapy, patients with hemophilia B produced and sustained near-normal levels of clotting factor IX, a recent study shows.

The updated interim phase 1/2 clinical trial data were presented at an American Society of Hematology plenary scientific session.

Included in the trial were 9 adults with hemophilia B, aged 18 to 52 years. Participants were administered a single dose of an experimental gene therapy product engineered to enter the patients’ liver cells and direct the production of the blood clotting factor IX.

“Our goal in this trial was to evaluate the safety of the gene therapy product and secondarily, to determine if we could achieve levels of factor IX that could decrease bleeding events in patients,” said lead investigator Lindsey A. George, MD. “These patients have a severe or moderate level of hemophilia, with baseline clotting factor level less than or equal to 2% of levels in healthy people. In current treatment, patients with hemophilia give themselves intravenous doses of factor IX up to a couple times a week. While generally effective, factor levels fluctuate, and patients may suffer painful, disabling joint bleeds when their clotting factor levels drop. Such a regimen requires significant planning of daily activities.”

The results of the current trial showed that patients maintained factor levels of approximately 30%, which was enough to move them out of the severe category.

“At these new levels, hemophilia patients do not typically need to self-treat with factor to avoid bleeding events,” George said. “This represents a potential dramatic improvement in their quality of life and a shift in the way we think about treating hemophilia.”

George noted that a factor level of 30% is considered near-normal, and that patients would be expected to experience bleeding only in the event of surgery or a major trauma.

Other than a single patient who self-infused 2 days after receiving the gene therapy vector, none of the patients had any bleeding events or required factor for any reason, according to the study.

As a result of the significant reduction in bleeding events and factor use, 6 of 7 patients reported an increase in physical activity and an improvement in quality of life. Two of the patients received the gene therapy product too recently to determine quality of life measures.

Prior hemophilia gene therapy trials have been hindered by the immune response to the gene therapy product. In the current trial, 2 patients experienced an immune response to the gene therapy, but it did not result in safety concerns, and was treated with steroids.

The patients are still undergoing treatment, but have maintained factor IX activity without bleeding, the study reports.

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