Bloomberg News

Blindness-Busting Gene Therapy Works in Second Eye, Study Finds

February 14, 2012

Feb. 8 (Bloomberg) -- Four years ago, an experimental gene therapy improved vision in blind patients treated in one eye. Now sight has been restored to the second eye of the previously treated individuals, researchers reported today.

Three adults with a form of Leber congenital amaurosis, a rare inherited disease of the retina that appears at birth and can progress to total blindness, now have vision in dim light and can distinguish faces, researchers said. The results are published today in the journal Science Translational Medicine.

The procedure, which uses a virus to deliver a gene to offset a defective one, didn’t cause an immune response, an effect that has hampered previous gene therapy attempts, said Jean Bennett, a professor of ophthalmology at the University of Pennsylvania and a lead author on the study. The second treatment also led to a surprise benefit of improving the previously treated eye, since the two eyes could now coordinate with each other in focusing on an object, researchers said.

“After the treatment, their vision is by no means 20/20, but it’s improved to the point where they can see the faces of their children, see the teacher at a school conference, or see their child hit a home run in a baseball game,” said Bennett, who is also a scientist at Children’s Hospital of Philadelphia, in a telephone interview.

The study was a follow-on to a clinical trial conducted at Children’s Hospital whose initial data were reported in 2008 and 2009. Twelve patients, including children, were treated with an injection into the eye that had the worst vision. Each had improvements.

Retina Disorders

Leber congenital amaurosis is a collection of disorders that lead to loss of cells in the retina in the first few decades of patients’ lives, the study said. The condition affects about 3,000 people in the U.S. One of the most-common forms, LCA2, is caused by a mutation in a gene linked to generation of a vitamin A derivative necessary for capturing light and stimulating vision. About 500 people have that form of LCA, Bennett said.

The researchers were concerned about repeating the treatment in patients’ other eye because they feared the initial therapy may have primed their immune systems to react against a second dose.

“We were concerned about the possibility that readministering might activate an immune response,” Bennett said. “Analogous to what you’d see in a vaccine, where delivering something back into the body would develop an immune response, you go back a second time and it might limit the effectiveness and cause damage in the eye that had initially received the injection.”

Obstacle Course

The study, done in three adult patients before the therapy would be administered to the rest of the 12 participants in the initial trial, showed no serious side effects. The patients got the second treatment 1.7 to 3.4 years after the first. The patients’ vision in dim light improved, and two of them were able to find their way through an obstacle course they previously hadn’t been able to navigate.

The trial was funded in part by Children’s Hospital of Philadelphia. The researchers have started treating the rest of the patients in the initial part of the study, and are planning a trial for later this year in the third and final phase of tests generally required for regulatory approval, Bennett said. The program is an academic one, without involvement from any companies.

The treatment doesn’t make patients’ vision perfect. “They can’t read books or drive a car,” Bennett said. “But the improvements mean a huge amount to somebody who is blind.”

--Editors: Angela Zimm, Bruce Rule

To contact the reporter on this story: Meg Tirrell in New York at

To contact the editor responsible for this story: Reg Gale at

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