US Gene Therapy Trials Halted After Illness

After undergoing gene therapy, a boy in France developed a condition resembling leukemia, the US Food and Drug Administration (FDA, Bethesda, MD, USA; www.fda.gov) recently halted 27 US trials of gene therapy. Last year, an infant in France in the same trial also developed the leukemia-like condition.

The trial in France involved 11 boys with a fatal immune disorder often called "bubble-boy” disease. Their therapy involved the use of a retrovirus to carry a gene into blood-forming stem cells. Following the treatment, nine of the boys became well enough to leave the hospital and resume more normal lives. The trial was considered a success until the two boys developed the leukemia-like condition.

According to scientists, the use of retroviruses to insert genes into blood-forming stem cells offers a theoretical risk that a cancer-causing gene may be turned on by a nearby retrovirus. Most researchers believe, however, that the benefits of gene therapy are worth the risk. Now, a US doctor working with the French researchers says both cases of a leukemia-like condition appear to have been caused by a gene accidentally landing near or on a cancer-causing gene.

The trials halted by the FDA represented around 15% of the gene trials being conducted and about half of those that involved the use of retroviruses. The American Society of Gene Therapy and the gene therapy advisory committee of the US National Institutes of Health have announced they are taking steps to study the situation. An FDA advisory committee has planned a meeting in February for the same purpose.