Federal authorities have temporarily suspended three gene therapy experiments after news that in a similar French study, a third child has developed leukemia and one of the three has died.
A Food and Drug Administration advisory panel is meeting in suburban Washington today in an effort to determine whether the French cases are an isolated incident or a precursor of problems that will affect all gene therapy attempts.
Experts don't expect an immediate consensus from the advisory panel, but there appears to be a growing feeling among researchers that the problem is of limited scope and reflects the combination of the virus and gene used by the French.
Most of the researchers involved will be gathering in Washington on March 15 for a separate meeting sponsored by the National Institutes of Health's Recombinant DNA Advisory Committee. They are scheduled to discuss their results to date. Despite the three leukemia cases, the results have been promising.
The experiments in question have involved treatments for severe combined immunodeficiency disease, or SCID, a potentially fatal genetic disorder that leaves its victims susceptible to life-threatening infections. David, the Houston "Bubble Boy" who lived for 12 years in a sterile enclosure to keep infections out, suffered from the disease.
Dr. Alain Fischer of Necker Hospital in Paris has been treating patients with so-called X-linked SCID, which is caused by a defective gene called GammaC. Fischer put a healthy form of the gene in a modified mouse leukemia virus, which was used to insert the gene into embryonic blood cells that are then infused into the patient.
Fischer has so far treated 17 patients, and virtually all have shown major improvement - if not a cure. But two years ago, Fischer said that two of the patients had developed leukemia, presumably as a result of the treatment.
The FDA temporarily suspended 27 gene therapy trials in the United States but eventually allowed them to proceed again after concluding that there were special circumstances in the cancer victims. Both were under the age of 2 and had received large doses of cells.
In recent weeks, Fischer revealed that one of the two original leukemia victims had died of the disease and that a third child had apparently contracted it. That child was older than the first two and received a lower dose of altered cells.
Some experts think the virus inserts the gene at a specific site within the blood cells, called Lmo-2, that triggers leukemia.
Concern escalated when Betty Dunbar of the National Heart, Lung and Blood Institute revealed last month that one of 42 monkeys that had undergone gene therapy experiments using the same virus had developed cancer.
The cancer was found about three years after the monkey was treated, about the same period of time that had elapsed in the French children.
The FDA has not formally announced the suspensions of the gene therapy experiments, but it has temporarily shut down three studies examining treatments for SCID. One is run by doctors at the National Institute of Allergy and Infectious Diseases. The other two are run by doctors at the Keck School of Medicine at USC.
The Johns Hopkins School of Medicine has 15 active gene therapy studies under way, spokeswoman Joanna Downer said. The University of Maryland School of Medicine is not conducting any gene therapy trials, a spokeswoman said.
Sun staff writer Erika Niedowski contributed to this article. The Los Angeles Times is a Tribune Publishing newspaper.