Genetic 'Bubble Boy' Disease Cured in Arizona Siblings

Abby and Colton [Ainslie] both had a type called SCID-ADA, which account for about 15 percent of SCID cases. Their bodies produce a faulty version of an enzyme called adenosine deaminase or ADA. Without it, immune cells die. Most patients die by the time they are about 2 from some infection, because their immune systems just can't fight off germs....

Gene therapy sounds simple. If a patient has a disease caused by a single mutated gene, just replace the bad gene and everything should be all right. But it's not so simple. For one, it's hard to get a new gene into the body, to get cells to take it up and use it. Scientists mostly use viruses to get the job done, because viruses infect by invading cells and injecting their own genetic material.

But the viruses can cause trouble, even seemingly harmless ones. In 1999, 18-year-old Jesse Gelsinger died during a gene therapy clinical trial when his immune system overreacted to the virus being used to carry the new gene into his body. And when French and British doctors first tried gene therapy for SCID a few years later, they cured a few infant boys, but five have developed leukemia as a result –although the leukemia was relatively easy to cure.

And the body doesn't always hang on to the new gene, or sometimes the gene gets inserted into a place where it doesn't work. And in the cases of kids with SCID-ADA, it wasn't clear why, but the gene therapy did not seem to be helping. Kohn's team, led by Dr. Fabio Candotti at the National Institutes of Health, was tweaking the approach. European researchers had treated 10 children with SCID-ADA but U.S. researchers had not succeeded.