Washington

Clinical trials of a gene therapy for a rare disorder of the immune system should be allowed to continue in the United States, according to the panel that advises the National Institutes of Health (NIH) on the safety of gene transfer.

Regulators in five countries halted such studies earlier this year, after a French boy being treated for severe combined immunodeficiency disease (SCID) developed a leukaemia-like illness (see Nature 420, 116–118; 2002). Most researchers now agree the gene therapy was a cause of his cancer.

The US Food and Drug Administration (FDA) has been working with investigators to determine how the country's own trials could proceed. Many researchers are now calling for extra precautions to check for cancer in certain patients undergoing gene therapy.

The NIH's Recombinant DNA Advisory Committee (RAC), which met in Bethesda, Maryland, on 4–6 December, recommended that the US trials should proceed with appropriate monitoring and informed consent. But the RAC deferred any rulings on monitoring patients after such trials.

Scientists suspect that the retrovirus vector used to deliver the genetic material to the French patient caused his cancer. But the RAC did not comment on any US gene-therapy trials using retroviruses apart from those to treat SCID. It is still unclear how the FDA will deal with the other studies.

Current NIH guidelines do not require researchers conducting gene-therapy trials to follow their patients' health for any set period of time. But the FDA has already told investigators that they should make plans to follow their patients long after the studies are over. At least one scientist running a SCID gene-therapy trial told the RAC that he has been advised by the FDA to plan on tracking his patients for the rest of their lives.

RAC member David Sidransky, a cancer geneticist at Johns Hopkins University School of Medicine in Baltimore, says that it would be expensive and impractical to require more than a handful of investigators to undertake life-long monitoring. He adds that two of the French boy's close relatives had childhood cancers, so he may have inherited a genetic defect that raises his risk of developing cancer.

“The question is would I rather spend $100 million on monitoring, when we may not see another leukaemia in the next 100 years, or would I rather spend $100 million treating sick patients,” Sidransky says. “I'm not ready to commit to a major monitoring programme based on information from one patient.”

Theodore Friedmann, a gene-therapy researcher at the University of California, San Diego, and chair of the RAC, says that the committee will take up the issue at its next meeting in March, and then draw up guidelines on how researchers should monitor their subjects. The FDA is expected to take the RAC's recommendations into consideration as it decides what to require from scientists who want to conduct gene-transfer studies in the future. “I hope that the language we come up with will be relevant not just to SCID, but to gene-transfer trials more generally,” Friedmann says.