New cancer case halts US gene therapy trials
Nearly 30 US gene therapy trials were halted on Tuesday following the announcement that a second child in a pioneering French gene therapy trial has developed leukaemia following the treatment. The French trial is testing a treatment for "bubble boy" disease, or X-SCID (X-chromosome-linked Severe Combined Immunodeficiency). The initial results of the trial were hailed one of the first great successes for gene therapy. But the trial was halted in October 2002 following the first diagnosis of leukaemia in one of the boys. Three similar US gene therapy trials were suspended at the same time. A similar trial in the UK was not halted, as British doctors argued that without the treatment many of patients would certainly die.
Cure rates for childhood leukaemia can be 90 per cent, but boys with SCID almost always die within a year without a bone marrow transplant. However, the second leukaemia case has prompted the US Food and Drug Administration to suspend other trials that use the same type of virus to shuttle therapeutic genes into blood cells.
The FDA has no evidence of leukaemia caused by gene therapy in US studies, but says the suspension of trials using retroviruses is a "precautionary measure". The agency will consider specific requests to allow new patients into gene therapy trials tackling life-threatening disorders for which there are no other treatments. The UK's Gene Therapy Advisory Committee says they will maintain their position and not suspend the British X-SCID trial. However, no new patients will be treated until the evidence from the French trial has been looked at, says Stephen Cox, of Great Ormond Street Children's Hospital where the British patients are being treated. The patients have all been assessed in the last month and none shows any sign of leukaemia.
Norman Nevin, chairperson of GTAC, speculates that the adverse French results may be due to minor differences in the techniques used. "The design of the vector is not quite the same in the UK as in the French study," he told New Scientist. Philip Noguchi, head of gene therapy issues at the FDA, remains optimistic about the overall prospects of gene therapy. "We continue to see gene therapy as a promising therapy for all those who have not benefited from current technologies," he says.
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