Gene therapy success

A team of French scientists at the Necker Hospital, Paris, has successfully used gene therapy to treat two babies born with a life-threatening genetic condition that affects the immune system. Usually, babies with severe combined immune deficiency (SCID) X1 have to live in sterile 'bubbles' to avoid any infections. But following the treatment, the babies are now living normal lives at home, the researchers reported in last week's issue of Science. A third baby is making similar progress after four months of the treatment.

Children with SCID X1 have no working version of a gene that controls the development of the immune system. To carry out the gene therapy treatment, the researchers first harvested bone marrow from the patients. They then isolated blood stem cells from the bone marrow, which they infected with a virus carrying a replacement gene. After three days of repeated gene transfers, the cells were transplanted back into the patients, with no prior drug treatment. 'It was important to show success in the absence of any chemotherapy' said Dr Alain Fischer, co-author of the study.

After just fifteen days, the scientists were able to detect new immune cells carrying the replacement gene in the patients' blood. The two baby boys, aged eight and eleven months, now have near-normal immune cell levels and have responded normally to routine polio, diphtheria and tetanus vaccinations.

Fischer believes the key to their success lies 'not in the technique, but in the disease itself'. Immune cells with the replacement gene seem to multiply rapidly, overwhelming cells without a working gene. 'This means that even a poorly efficient gene therapy treatment - one that only introduces a few cells with the right gene - may work as a treatment' he said.