A type of virus used to deliver genes to the body in gene therapy treatments could cause cell defects that may lead to cancer, according to a new US study. The findings, published in this month's Nature Genetics, follow news earlier this year that a second patient in a gene therapy trial at the Necker Hospital in Paris, France has developed leukaemia. The blood cancer affecting the two patients in the French trial is thought to have been triggered when the virus used to deliver therapeutic genes disrupted an important gene in the patient's white blood cells. In the latest study, researchers from Stanford University in California found that another type of gene-delivery virus is also prone to inserting itself into genes.
The team, lead by Mark Kay, found that when adeno-associated viruses (AAVs) were used to deliver genes to mouse livers, they tended to land in the middle of active genes, rather than in the surrounding 'non-coding' DNA. 'What this means for human trials must be assessed on a disease-by-disease basis' said Kay. 'It raises the bar of risk somewhat. But how much higher it is raised is still unclear'.
'It's a healthy development that the community realises that there are basic scientific issues that still need to be addressed' said Philip Noguchi, head of gene therapy issues at the US Food and Drug Administration. But both he and Kay think that the benefits still outweigh the risks in most gene therapy trials, reports New Scientist magazine. Kay's team, who are running a gene therapy trial for haemophilia that uses the adeno-associated virus, say they have taken numerous precautions to protect the 14 patients treated so far.
Sources and References
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Harmful potential of viral vectors fuels doubt over gene therapy
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Fresh blow for gene treatments as safety of second virus is questioned
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Modified viruses may cause cancer
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Gene therapy 'causes leukaemia'
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