Embryo-free stem cells on the horizon

Ethical concerns about research using human embryos and political pressure from Washington has been driving the search for alternative ways to derive stem cells in the United States. Now the possibility of 'reprogramming' adult skin cells into embryonic stem (ES) cells may be within reach in the next few years, US researchers say.

At the June meeting of the International Society for Stem Cell Research in San Francisco, Kevin Eggan of the Harvard University Stem Cell Institute revealed that his lab had fused a human ES cell with an adult skin cell. The stem cell then 'reprogrammed' the skin cell's nucleus, causing it to behave like an ES cell. The fused cells stopped expressing genes that characterised the adult cell and instead expressed the same genes as the ES cell. They could also be made to transform into the major cell types of the body.

The research moves scientists a step closer to the goal of making human ES cell lines tailored to individual patients without having to create a cloned embryo of the patient. Skin cells contain all of the same genes as ES cells, but different sets of genes are turned on in each type of cell. Scientists think that if they can discover how to control gene expression with enough precision, they will be able to turn a normal skin cell back into an ES cell, as if they were rebooting a computer. 'In 10 to 15 years, we will induce transformation directly and will no longer need embryos or oocytes at all,' predicts Eggan.

This isn't possible yet. Eggan's hybrid cells still contain twice the normal amount of DNA, a nucleus from each of the two fused cells, so they can't be used for therapy. Other scientists think that it will be difficult to overcome this problem. 'It will be important to see whether he can get rid of the extra nucleus,' says Rudolf Jaenisch of MIT. 'I think it might be pretty tough to do.'

If that hurdle can be overcome, Eggan's new technique could mean that scientists in the future would be able to avoid some of the practical and ethical pitfalls that plague stem cell research. 'These logistical and moral concerns are not going to go away,' he says. 'Our work points to a potential solution to these issues.'

While most scientists welcome these advances, and the new funding which could come as a result, they caution that it should not distract researchers from the techniques that are known to work today, using human embryos. 'You move ahead on all fronts,' said George Daly of Harvard Medical School. 'Scientists will in the end use what works best.'