Stem cell discovery raises prospect of treating genetic disorders in the womb

The prospect of treating genetic disorders in three-month-old foetuses came a step closer yesterday with a study showing gene therapy might be possible inside the womb of a pregnant woman.

A team of British scientists has identified stem cells – the "master" cells of the body – that circulate in the blood of a developing foetus and that can be engineered easily using gene therapy.

The findings suggest it might be possible to extract the stem cells of an early foetus with a genetic defect, insert a correct gene into the cells in the laboratory and inject them back into the embryo to correct the abnormality.

Professor Nick Fisk, of Imperial College, London, who led the team, said early tests had shown it was possible to engineer the so-called mesenchymal stem cells found in foetal blood with a success rate of 99 per cent. "It raises the concept or idea that we may be able to collect these mesenchymal stem cells in the first three months of pregnancy," Professor Fisk said yesterday.

"The big advantage of these stem cells is that they are circulating in the blood of the foetus so it may be possible to take them out, stick in a normal gene to replace the gene that is not working, and put them back at an early enough stage of development that they can be taken up by the foetus without fear of rejection.

"The great advantage is that because you're taking them out of the same foetus you are putting them back into, you're not going to suffer from the problems of tissue rejection."

Stem cells are invaluable tools because they have the power of developing into a range of fully specialised tissues, such as muscles, bones or nerves.

Mesenchymal stem cells are half-way between the stem cells of early embryos – which can develop into any tissue of the body – and adult stem cells, which seem to be more restricted in the range of tissues they can become, Professor Fisk said.

In the tests on human mesenchymal stem cells taken from early foetuses, the scientists engineered them with a gene for a protein that lights in the dark to see how many could be successfully altered in the laboratory using a virus to inject the gene into the cell. The 99 per cent success rate was better than previous attempts at gene therapy using different kinds of stem cells, the researchers report in the Journal of Obstetrics and Gynaecology.

There are many genetic disorders that could benefit from this approach, such as muscular dystrophy and a range of hereditary bone diseases where early treatment in the womb might prevent the disability from being severe.

But Professor Fisk emphasised that it would take at least five years, and more likely 10 years, before the approach could lead to the first clinical trials. The procedure would mostly benefit families with a history of inherited disorders and where there is a high risk of a baby being affected by the abnormal gene.