| Gene therapy is a scientific marvel. By fixing flaws in our DNA, it holds the potential to treat — even cure — a wide range of devastating diseases with a single dose. But for years, the cutting-edge genetic medicine has faced a lingering question: How long does it actually last? Scientists now have an answer: a really long time. In a new study, researchers at St. Jude Children’s Research Hospital and University College London followed up with hemophilia patients who received a gene therapy treatment roughly 13 years earlier. Hemophilia is an inherited bleeding disorder that affects about 33,000 American men. It’s caused by a defective gene that limits production of a protein that’s essential for blood clotting. Surgery or even minor injuries can lead to life-threatening complications. The researchers studied 10 men who had a severe form of the condition called hemophilia B. They found those patients still had stable production of the proteins, called clotting factors, and their bleeding episodes had dropped nearly tenfold. Seven of the 10 men did not receive treatments to prevent or minimize those bleeding episodes. The study was likely the first to follow-up with gene therapy patients after that many years, according to Andrew Davidoff, a coauthor of the paper that was published in the New England Journal of Medicine. “This approach for hemophilia gives long-lasting effect,” Davidoff said in an interview. The finding is important for insurance companies footing the bill for gene therapies that can cost $3 million. Given the uncertainty, some insurers have struck deals with drugmakers to ensure they get refunds if a gene therapy’s effects fade over time. The results are also important for people with hemophilia who have so far not been that interested in gene therapy. Earlier this year, Pfizer discontinued its gene therapy for hemophilia B, citing limited interest from patients. Other gene therapies for hemophilia from CSL Behring and BioMarin Pharmaceutical have also failed to gain much traction. The gene therapy in the study was developed by scientists at St. Jude Children’s Research Hospital and University College London and work similarly to others on the market. Patients can participate in an upcoming clinical trial of the treatment being done by Ulrike Reiss, a coauthor of the paper. The treatment showed no serious side effects, which has been a problem with other gene therapies. But the study did find the men had long-lasting immunity to the virus used to deliver the treatment. That means if the gene therapy doesn’t last a lifetime, it would be difficult to give it to them again. Many hemophilia patients have avoided gene therapies in part because their condition is relatively manageable with available treatments that help with blood clotting, according to Reiss. Getting a multi-million-dollar treatment covered by insurance is not always easy. And some patients might be nervous about getting a new treatment whose long-term side effects had been unknown. Patients and insurers may be more willing to embrace the new drugs now, the coauthors said. “I think the finding that one intervention can be effective for at least 13 years may change the balance in favor of gene therapy,” Davidoff said. — Gerry Smith | 
