Altered Viruses Reversed Progressive Blindness, Studies Say
Monday, April 28, 2008
Three young adults barely able to see because of a congenital and progressive form of blindness have regained modest amounts of vision after getting genetically engineered viruses injected into their eyes, the leaders of two independent studies reported yesterday.
The results were something short of miraculous. Three other patients showed no increase in visual acuity, and the three who improved are still legally blind.
But to get any improvement at all during such an early phase of the research suggests that the approach has promise for people with gene-based forms of blindness, researchers said. The work could also provide a boost for the field of gene therapy, which for 15 years has tried and mostly failed to treat diseases by giving people new genes -- and in a few high-profile cases has sickened or even killed them.
"We're learning things as we go along," said Jean Bennett of the University of Pennsylvania, who with Albert M. Maguire led one of the two studies. "We were not really going for a cure. But we do view it as a success in that their vision has improved. I'd call it a dramatic response."
Others took a more conservative view, noting that some of the key measures of improvement were subjective and could not be conclusively linked to the therapy. In an editorial to appear in the New England Journal of Medicine along with the study results, Joan W. Miller of the Massachusetts Eye and Ear Infirmary called the results "suggestive of efficacy."
Still, videos of some of the experimental subjects trying to navigate through a dimly lit obstacle course show notable improvement in the weeks and months after the injections. Scientists said they are hopeful that the treatment will prove even more beneficial in younger patients, whose retinas have only begun to degenerate.
"If we can get any benefits in people with such advanced disease, then when we start to treat children, and when we treat a greater part of the retina and give a higher dose, the expectation is we can get even better results," said Robin R. Ali of University College London, who led the other study.
Both teams are moving ahead with tests in younger patients and at higher doses.
The experiments involve patients with Leber's congenital amaurosis, a rare disease caused by a defect in a single gene that is crucial to the retina's ability to convert light into signals to the brain. Affected children have impaired vision from birth and are typically blind by age 30.
The British and Pennsylvania teams took somewhat different approaches. Each involved what are known as adeno-associated viruses, popular among gene-therapy researchers because of their ability to deliver new genes to cells.
In this case, the teams used genetic engineering techniques to load the viruses with healthy versions of the rpe65 gene, the gene that is faulty in people with Leber's. Then they injected tens of billions of the viruses into the tiny space behind the retina.
They treated just one eye of each patient, in part so as not to put both eyes at risk of side effects but also to allow for comparisons of visual acuity after the treatment.