“The history of gene therapy is a skewed history, and has been shaped partly by the field and a tendency to expect too much too quickly,” says Theodore Friedmann, a professor of pediatrics at the University of California, San Diego, and past president of the American Society of Gene Therapy.

But despite setbacks, and perhaps because of them, researchers have been moving cautiously yet steadily forward and proving gene therapy to be a viable method for treating disease. In addition to other, more successful SCID gene therapy treatments, scientists last year showed that the technique could also be used to treat a rare but fatal brain disease. The new research heralds a movement toward the use of gene therapy for more common genetic diseases. “It’s a very good piece of work, and it’s important because it extends the technology to a more widespread and worldwide disease–I’m very impressed with it,” Friedmann says.

“The results are very encouraging for the field,” says Derek Persons, an experimental hematologist at St. Jude Children’s Research Hospital in Memphis, Tennessee, who is working toward a similar therapy and plans to collaborate with Leboulch on an upcoming study. The results, he says, are the result of nearly three decades of work by multiple labs around the world–but they’re just the start. He points out that Leboulch’s patient had some functional hemoglobin production already. Not enough to survive without transfusions, but enough that the additional activity of the inserted gene brought him up to manageable levels. “If you started from zero,” where the most severe thalassemia patients are, “it would be a lot harder,” he says.

Leboulch and his collaborators will closely watch their first patient to make sure that he remains healthy and stable. They remain cautious, as the vector they used to insert the revised DNA seems to have also caused increased production of a protein associated with benign tumors. They are collaborating with a Cambridge, Massachusetts, company, Bluebird Bio, and if their first patient remains stable, they’ll start a second patient on the therapy early next year, with the goal expanding the trial to 10 patients in 2012. And because sickle-cell disease is so closely related, Leboulch hopes to use the same modified genetic vector in patients with sickle-cell anemia, also starting in 2012.

“This opens avenues to be able to treat genetic diseases in a permanent manner with one shot,” Leboulch says. “And we can also learn from this how to apply similar approaches to noninherited diseases, including cancer. It opens up a lot of possibilities.”