An experimental genetic therapy that cured nine children of a deadly immune system disorder but caused leukemia in two of them should be restricted to patients who have no other option, a Food and Drug Administration advisory committee concluded Friday.
The decision represents a serious blow to the field of gene therapy, which had begun to bask in the glow of its first successes when it became clear last year that recent cases of leukemia in two toddlers were caused by the gene treatments they had received as infants. The treatment used genetically engineered viruses to deliver new genes into the children's cells.
The FDA had asked a panel of experts to look at details of the experiment, which was conducted in France, and advise the agency whether similar studies already started or poised to take place in this country should be allowed to go forward. Some researchers had hoped that close scrutiny would suggest a way to reduce the risk of leukemia while retaining the treatment's therapeutic effects.
Instead, committee members Friday expressed fears that they would face new cases of leukemia in other children who have already been treated for the disease, known as X-SCID.
"We need about two more years before I can say how safe this therapy is," said committee chairman Daniel Salomon of the Scripps Research Institute in La Jolla, referring to the apparent lag time between treatment and onset of cancer. Members of the FDA group -- the biological response modifiers advisory committee -- had been asked to focus on the narrow question of whether the agency should lift or modify the suspensions the FDA recently imposed on 30 U.S. gene therapy experiments that resemble the French experiment. But deliberations frequently digressed into a tribunal on gene therapy.
"I'm wondering if it should all go back to the lab and, instead of using people, go back to the mice," said Abbey Meyers, president of the National Organization for Rare Disorders.
The committee advised FDA officials not to allow patients into either of two pending U.S. studies whose design mirrored the French study unless the patients had no access to, or had already failed to respond to, alternative treatments.