The US Food and Drug Administration (FDA) has recommended that gene therapy treatments for an inherited immune disorder are limited to those who have no alternative. The move follows news that a third child in a similar French trial has developed leukaemia. The trial for X-linked severe combined immunodeficiency disorder (X-SCID), based at the Necker Hospital in Paris, was halted in January. In the UK, the Gene Therapy Advisory Committee (GTAC) is set to carry out a safety review of an X-SCID trial underway at the Institute of Child Health.
Eleven patients affected by X-SCID have been treated in the French trial so far. While most have responded extremely well to the therapy, the trial was suspended in late 2002, after two patients developed symptoms of leukaemia. One of these boys is now in remission, but the other has since died. The AFSSAPS (French Agency for Health Product Safety) gave permission for the trial to restart in May 2004, but suspended the experimental treatment last month, after a third child developed symptoms of leukaemia.
The latest patient to develop side effects received gene therapy treatment at the age of eight months, and was diagnosed with 'lymphoproliferation' - overgrowth of white blood cells - about five weeks ago. Study leader Alain Fischer immediately stopped the study again, and notified the FDA, as well as the AFSSAPS. According to a report in the Washington Post, the FDA does not usually tell the public about clinical trials that it has suspended, but US researchers involved in trials similar to the French one say that the agency has recently told them to suspend their studies. At a meeting held last week, an advisory panel told the FDA that they didn't want to hold up therapy for the small number of children who had failed to respond to bone marrow transplants. It also recommended that gene therapy trials for another type of immune disorder, called ADA-SCID, be allowed to continue.
Fischer says that the recently diagnosed boy is responding well to chemotherapy, and that he is doing well, as are the other trial participants. 'They can cope with infections. That tells us efficacy is there', he said, adding 'there is a future in gene therapy'. Children affected by SCID have a faulty gene that means they have no working immune system, so their bodies cannot fight infections. This life-threatening condition is sometimes called 'bubble boy' disease, as unless they can be successfully treated with a matched bone marrow transplant, patients must spend their lives in a sterile environment.
In the UK, seven children and one adult affected by X-SCID have been successfully treated with gene therapy. A spokesman for the Department of Health said: 'Without treatment, babies with X-SCID rarely survive beyond their first birthday', adding that for children with no matched bone marrow donor, 'gene therapy offers an alternative treatment'. The Committee on Safety of Medicines and GTAC will meet this month to review all X-SCID studies data, the Daily Telegraph reports.