Published online 27 June 2005 | Nature | doi:10.1038/news050627-1

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Rebooted cells tackle ethical concerns

Fusion technique resets adult skin cells to embryonic state.

Come together: a stem cell fused to a skin cell can reprogramme it back to an embryonic state.Come together: a stem cell fused to a skin cell can reprogramme it back to an embryonic state.© Getty Images

Scientists who want to study the special properties of stem cells may be able to use a new technique to avoid some of the practical and ethical pitfalls of stem-cell research.

On 24 June, Kevin Eggan of the Harvard Stem Cell Institute told an international scientific meeting that his lab has fused a human embryonic stem cell to an adult skin cell. Eggan showed that the embryonic stem cell ‘reprogrammed’ the skin cell’s nucleus, causing the skin cell to start behaving like a youthful, embryonic stem cell.

Eggan’s work raises the possibility that scientists may one day be able to make human embryonic stem-cell lines tailored to individual patients without first having to create an embryo clone of the patient: researchers could simply reprogramme a patient’s skin cells.

But this isn’t possible yet. The hybrid cells made by Eggan contain twice the amount of DNA found in normal cells, and so can’t be transplanted into the body for therapy. Eggan thinks it should be possible to overcome this problem.

Other scientists at the third annual meeting of the International Society for Stem Cell Research in San Francisco, say the research is promising, but caution that it might not be easy to remove the extra DNA from the hybrids.

“It’s nice that he’s shown reprogramming, but it will be important to see whether he can get rid of the extra nucleus,” says Rudolf Jaenisch, a biologist at the Massachusetts Institute of Technology. “I think it might be pretty tough to do.”

Reboot

In an embryo, stem cells have the ability to grow into any of the cell types in the body. As we grow older, our cells lose this flexibility. So, scientists think the best way to create new cells for a patient is to create a cloned embryo of that patient, extract the stem cells, and nurture these cells so that they grow into the desired cell type.

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But this process involves using human eggs and creating an embryo that is later destroyed. “These logistical and moral concerns are not going to go away,” Eggan says. “Our work points to a potential solution to these issues.”

Scientists think that adult stem cells still have a deep-rooted ability to turn into other cells, but that this is obscured by adult programming that tells the cell which genes to switch on and off. If the cell can be reprogrammed, in the same way that a computer can be reformatted, it should regain the flexibility that it had as an embryonic cell.

Eggan says he has achieved this with his hybrids. The fused cells stopped expressing the genes that characterized the adult cell, he reports, and instead expressed the same genes as the embryonic stem cells. They could also transform themselves into the major cell types of the body, such as neurons, hair follicles and muscle cells.

Although the original stem cells used in this process came from an embryo, more stem-cell lines could be created without having to use further embryos or eggs. These cell lines could then be used to study many of the same scientific questions as embryonic stem-cell lines, but without the ethical difficulties, Eggan says.