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Good news for gene therapy

14 June 2004
By BioNews
Appeared in BioNews 262

A French gene therapy trial halted after two participants developed leukaemia looks set to restart after a 22-month suspension, reports Nature. Scientists at the Necker hospital in Paris successfully treated nine children with an  inherited immune system disorder called X-linked severe combined immune deficiency (X-SCID). But the trial, along with similar trials in the US, was suspended while researchers investigated the cause of the blood cancer. However, the trial in France, and also one in the US, are now set to restart, researchers revealed at a recent meeting of the American Society of 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. To carry out the gene therapy treatment, the French researchers harvested bone marrow from the patients, from which they isolated blood stem cells. They then infected these cells with a retrovirus (a virus that inserts its genetic material into the host cell's DNA) carrying a working gene, before returning the modified cells back to the patients.

Eleven boys with X-linked severe combined immune deficiency (X-SCID) underwent experimental gene therapy treatment at the French hospital, but the trial was halted in October 2002, after one of the boys developed leukaemia symptoms. When a second patient developed leukaemia in January 2003, similar trials in several countries were suspended. In both cases, researchers found that the retrovirus had inserted its genetic material close to the 'on-switch' of a cancer-causing gene called LMO2. It is thought that this event caused the unregulated growth of the bone marrow cells, which in turn triggered the leukaemia, although other factors could have been involved. The two boys are reported to have responded well to chemotherapy and bone marrow transplant treatment, and are now in remission.

Scientists at Great Ormond Street Hospital in London have treated seven children with X-SCID, none of whom have developed leukaemia. Alain Fischer, who leads the French team, says he plans to minimise the risk of future side effects by only treating children older than six months, and by limiting the number of corrected cells injected during the treatment. Donald Kohn, leader of one of the US X-SCID trials, welcomed the news that the gene therapy treatment was to resume. 'No therapy is without risk, and now that we've had time to look back, we realise that this therapy, even with the risk, may be better than the current treatment', he said.

SOURCES & REFERENCES
Gene therapists hopeful as trials resume with childhood disease
Nature |  10 June 2004
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