Gene Therapy Shows Promise for Treating Hemophilia

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Despite the vast promise of the genetic revolution in medicine, the fact remains that the hype has far outpaced the reality. Experiments with gene therapy, for instance, in which a new or corrected version of missing or damaged DNA is injected to treat disease, have been disappointing at best.

But a new study in people with hemophilia may have just resuscitated the field. Published in the New England Journal of Medicine, the study was small — just six patients who were missing the correct gene for the agent that clots blood, known as Factor IX (FIX). Patients with hemophilia need to receive infusions of FIX two to three times per week in order to prevent them from bleeding spontaneously or bleeding too much from even slight cuts and wounds — a potentially fatal condition. But in the new study, four of the six patients who received gene therapy were able to make FIX on their own, enough to stop their regular treatments. The other two patients also benefited: they weren’t able to abandon their infusions altogether, but they didn’t need as many sessions as before the gene therapy.

Led by Amit Nathwani at University College London, scientists introduced the working gene for FIX to patients by injecting them with cold viruses that were engineered to carry the gene in, infect cells, and start producing the needed clotting protein. This is the standard technique used in gene therapy, but often it fails because the immune system kills off the cold viruses before they can do their work.

Nathwani’s team was able to figure out a more efficient way to install the new genes. At the start of the study, all of the participants had less than 1% of normal levels of FIX in their blood. By the end of the study, which followed patients for as long as six to 16 months, most had FIX levels that were 3% to 11% of normal values. Two patients each received low, intermediate or high doses of the gene therapy in an IV-like infusion in the arm.

It’s not a cure, but it’s an improvement, and a promising step for the field of gene therapy, which had all but ground to a halt after the 2000 death of Jesse Gelsinger, an 18-year-old patient who underwent gene therapy to treat an inherited metabolic disorder and died from complications of the treatment. Gelsinger apparently died from an immune reaction to the virus used to deliver the disease-correcting genes to his cells, a cold virus similar to the one used in the current study. Indeed, one of the hemophilia participants receiving high doses of gene therapy showed high levels of immune-cell reaction to the viral vector, and was treated with glucocorticoids.

Experts in gene therapy were cautiously optimistic that the results would join other small victories in the field, including successful studies to treat patients with severe combined immunodeficiency disease, a genetic condition that compromises immune systems and makes people vulnerable to infections and even death from the slightest exposure to pathogens. Dr. Ron Crystal, chairman of genetic medicine at Weill Cornell Medical College and a long time researcher in the field, told the Associated Press: “I think this is a terrific advance for the field. It’s a good lesson in terms of don’t give up on good ideas.”

One of the study’s co-authors, Dr. Edward Tuddenham, director of the Hemophilia Center at the Royal Free Hospital, is even anticipating a gene therapy treatment to be available soon. The New York Times reported:

Twenty more patients will be treated to assess the best dose of the virus, the goal being the highest dose that does not set off an immune system attack, Dr. Tuddenham said. “We are pretty close to the sweet spot,” he said. If all goes well, a genetic treatment for hemophilia B “could be available for widespread use in a couple of years.”

It will take larger studies and more research to understand fully how gene therapy can be made both safer and more effective, but at least, finally, the results are moving in the right direction.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.