ASH: CSL, uniQure's gene therapy Hemgenix shows durable protection in hemophilia B

Approved just three weeks ago to treat hemophilia B, CSL Behring and uniQure’s gene therapy Hemgenix carries the highest price tag ever for a drug at $3.5 million.  

Now it is up to CSL to prove that the one-time treatment is worth it.

Over the weekend, they took a step toward that goal by presenting data showing that Hemgenix provides durable protection and sustained activity levels at 24 months. Hemgenix also reduced the rate of annual bleeding with no serious adverse events. The companies touted their therapy Saturday at the American Society of Hematology (ASH) annual meeting in New Orleans.

People with hemophilia B have a defect which prevents production of factor IX, a protein that helps blood clotting and is produced in the liver.

In the study of 54 adult male participants with severe or moderately severe hemophilia B, Hemgenix produced mean factor IX activity of 39.0 IU/dL (39%) at six months. The concentration of factor IX is expressed as a percent figure. Patients in the trial typically had less than 2% concentration of IX factor. The non-hemophilic range begins at approximately 40%, according to trial investigator Steven Pipe, M.D., of the University of Michigan.

At 18 months, there was a small drop off, with mean factor IX activity at 36.9 IU/dL (36.9%). At 24 months, the figure was a 36.7 IU/dL (36.7%).

“When you get above 5%, spontaneous bleeds are highly unusual,” Pipe said in an interview with Fierce Pharma. “Patients may still be at risk for traumatic bleeding, including bleeding into joints. But once patients get above a threshold of, probably, 15 to 20%, we would expect no spontaneous bleeding.”

Another measure that demonstrated the durability of Hemgenix treatment was the annual bleeding rate (ABR). The FDA prescribing information for Hemgenix shows that ABR was reduced 54% during months 7 to 18 after treatment. But when the study period is bumped up to 7 to 24 months from administration, the reduction in bleeding improved to 64%.

Current treatments for moderate to severe hemophilia B include life-long prophylactic infusions of factor IX to temporarily replace low levels of the blood-clotting factor. Of the 54 participants in the trial, 51 stopped use of the prophylactic infusions.

“That’s a definition of ultimate success that allows a patient to be liberated from the burden of their prophylactic therapy,” Pipe said. “They know their levels are stable, day in day out. This brings a lot of important quality of life metrics back to the patient.”