Scientists have transformed mouse skin cells into embryonic stem cells and proved their potency by using the new cells to produce baby mice.

The experiments are seen as a major advance for regenerative medicine, which aims to custom-build tissues and cells to repair ailing and ageing bodies.

Scientists caution there are serious safety issues that must be resolved before the techniques could ever be used on people, but say the advance points to a new way of making embryonic stem cells for patients from their own cells.

There is no need to destroy embryos, and the procedure might allow researchers to sidestep many of the ethical objections now dogging stem-cell research.

Until now, the only way to obtain embryonic stem cells has been to take them from an embryo. Producing cells that are a genetic match for a patient would entail making a clone of that person and harvesting the cells when the cloned embryo is days old, which raises thorny ethical issues and is illegal in several countries, including Canada.

The new work promises cells free of such contentious issues.

"You could take a skin cell, or a blood cell, and reprogram it with these four genes to make embryonic stem cells," Mr. Rudnicki said. The cells could then be turned into any type of cells required for therapeutic use, be they neurons to treat Alzheimer's or insulin producers for diabetics.

He cautions that significant hurdles still need to be overcome.