At age 8, Corey Haas stood at square one of a floor maze at the Children’s Hospital of Philadelphia. Black and white squares covered the ground, with an arrow on each to show him the correct path. He took a few steps and then paused. “This is being really hard,” he told the adults in the room. After about a minute, they nudged him in the right direction. After a couple more timid steps, he stopped again, frustrated. “I can’t even see anything.”

Corey has Leber’s congenital amaurosis (LCA), a rare inherited disease in which a genetic glitch damages cells in the retina, causing blindness. On that fall day in 2008, he was tackling the maze as the youngest of 12 patients who had received an experimental therapy for LCA. Ninety days before, a surgeon had injected a healthy version of a gene called RPE65 into the back of Corey’s left eye. His eye cells began pumping out the protein that he was born without, allowing him to see.

In that first, frustrating maze, Corey was relying on his untreated eye, wearing a patch over the newly treated left eye. About an hour later, he did the maze again, this time using his left eye to guide him. He cruised through it in about 20 seconds. The spectators burst into applause.

The trial’s participants ranged from 8 to 44 years old, and the therapy worked, to varying degrees, for all of them. When the results were published, in November 2009, it was a boon to the gene therapy field, which has had highly publicized ups and downs since its debut in the late 1980s (see gene therapy timeline). The general pattern: scientists would see fantastic results when testing gene therapy on animals. But when they used it on people, they came up against two major obstacles: the new gene would be expressed only for a short time or the immune system would reject the therapy outright.

Read more at…

HHMI Bulletin, August 2011.