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Gene Therapy offers Remarkable Results for Hemophilia B Patients
Researchers are reporting the highest and most sustained levels to date of the essential blood-clotting factor
IX in patients with hemophilia B, an inherited bleeding disorder. After receiving a single dose of an experi- mental gene therapy in a clinical trial, patients with hemophilia B produced near-normal levels of clotting factor IX, allowing them to stop clotting factor infusions and to pursue normal activities of daily life without disabling bleeding episodes.
Lindsey A. George, MD, a hema- tologist at Children's Hospital of Philadelphia (CHOP) is the lead investigator of the Phase 1/2 clinical trial sponsored by Spark Therapeutics, Inc., and Pfizer, Inc. Updated interim trial data was presented by Katherine High, MD, a senior author of the study and Spark Therapeutics’ president and chief scientific officer, during the annual meeting of the American Society of Hematology (ASH) in December.
The clinical trial of nine adult hemo- philia B patients, aged 18 to 52 years, used a single dose of a gene therapy product engineered to enter patients’ liver cells and direct the production
of the blood clotting factor they lack. Patients participating in the trial have a severe or moderate level of hemo- philia B, with baseline clotting factor level less than or equal to 2 percent of factor levels in healthy people.
Currently, treatment of hemophilia B requires intravenous infusion of factor IX up to a couple times per week. Although generally effective, factor levels fluctuate and patients may suffer painful, disabling joint bleeds when their factor levels drop.
After receiving the gene therapy, the patients maintained factor levels of approximately 30 percent, enough to lift them out of the severe category. Dr. George said with elevated factor levels, hemophilia patients do not typically need to self-inject factor product to avoid bleeding episodes. Patients can then experience a dra- matic improvement in quality of life.
One clinical trial participant self- infused two days after receiving the gene therapy vector; beyond this, no patients had any bleeding episodes or required factor for any reason. With significant reduction in bleeding events and factor use, six of the first
seven patients reported increased physical activity and all reported im- proved quality of life. Two additional patients received the gene therapy product too recently to determine quality of life measures.
Previous hemophilia gene therapy trials have been frustrated by an immune response to the product. During the current trial, two patients experienced an immune response that did not result in safety concerns. The patients were treated with steroids and, at time of writing, have maintained factor IX activity without bleeding episodes.
Dr. George remains cautiously optimistic, acknowledging the small study size of the trial and short follow-up period. As researchers continue to monitor patients, Dr. George anticipates their next steps will include discussions with the FDA for a larger, Phase 3 trial. No gene therapies for any genetic disease have been approved for clinical use in the U.S.
Source: Children’s Hospital of Philadelphia, Hemophilia B Patients Maintain Near Normal Levels of Clotting Factor After Gene Therapy, December 5, 2016, accessed January 2017 at dddmag.com
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