The Food and Drug Administration has suspended several U.S. gene therapy experiments after learning that a third child who underwent treatment in France has developed cancer as a result, a development that has cast a pall over the struggling research field.
Adding to the gloom, researchers are due to report today that a monkey has died of cancer caused by a gene therapy experiment six years ago. That suggests the treatments may carry long-term as well as near-term risks, said scientists who will be discussing the issue at an FDA meeting.
Library of Life: Interactive graphic shows the makeup of human genes. (Flash Required)
The events are the latest in a series of setbacks for a field that a decade ago seemed poised to revolutionize medicine by replacing defective genes with healthy ones -- fixing the molecular underpinnings of disease instead of simply treating its symptoms.
After thousands of efforts, the treatments appear to have cured only about a dozen patients, all of them children in Europe who were born with a severe immune system disorder. With three of those children having developed cancer from the treatment and one recently dying of it, even the field's most ardent supporters are discouraged.
"We want to continue, but of course there is a safety issue," said Alain Fischer of the Necker Hospital in Paris, leader of the French study. The details are to be discussed at today's meeting of the FDA's Cellular, Tissue and Gene Therapies Advisory Committee.
The latest cancer case appeared a few weeks ago, in a 3-year-old boy Fischer treated in the summer of 2002. Like the other children in the study, the boy was born with X-linked severe combined immunodeficiency, or X-SCID. The disease, which affects only boys and disables the immune system, was made famous in the 1970s by David Vetter, the Texas "bubble boy," who lived his 12 years in a plastic tent to protect him from everyday infections that for him could prove fatal.
The only other way to cure the disease is a perfectly matched bone marrow transplant, but such matches are rare, and recipients of unmatched transplants do not fare well. The experimental alternative involves infusions of mouse viruses engineered to carry the immune system gene that patients lack.
The viruses infect the patients' immune system cells to deliver the needed gene. But the viruses sometimes disturb healthy genes -- including genes that, when disrupted, can cause cancer.
The first case arose in September 2002, triggering a suspension of all similar experiments. A second treated boy was diagnosed with cancer in December of that year. Both had been treated while infants and developed leukemia about 2 1/2 years later.
Although both appeared to respond well to chemotherapy, one of the boys died this past October, after the experiments were resumed with new safeguards.