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If you want to cause a long lasting alteration in DNA one of the hazards of gene therapy is a risk of cancer – caused by accidental insertion of genes into sequences prone to cause cancer. Using new virus types could reduce these events
The SCID-X1 (x-linked severe combined immune deficiency) trial in 2000 was a great success in many respects, providing beneficial in 17 of 20 boys that participated, unfortunately 5 of the 20 also developed leukaemia as a result of the therapy. This confounded scientists at the time and set the field back considerably when one of these patients sadly died. It eventually emerged that the retrovirus and retroviral genes used alongside the therapeutic gene were risky, with a tendency to integrate nearby genes called ‘proto-oncogenes’. These are genes with a capacity to induce cancer if altered in some way (usually being involved with cell division and growth). The sequences in the therapeutic DNA strands injected into infected cells contained elements that enhanced gene activity, and therefore boosted expression of these dangerous genes – triggering leukaemia in 5 of the patients. An evolving story We have learned a great many lessons since the early days of gene therapy and now utilise self inactivating vectors or even viruses that don’t integrate DNA at all; leaving a circular strand of DNA that isn’t replicated when a cell divides. This is much safer, but is also impermanent and so offers a temporary fix for a condition. In the case of monogenic diseases we really need to develop techniques that permanently fix a faulty gene by integrating into the genome itself. A team from Washington State University has been working on that problem by testing an alternative type of virus called a ‘foamy’ retrovirus.Copyright © Gowing Life Limited, 2025 • All rights reserved • Registered in England & Wales No. 11774353 • Registered office: Ivy Business Centre, Crown Street, Manchester, M35 9BG.