The demonstration that the technique, which was pioneered on mouse cells, also works on human skin cells raises the prospect of new treatments for incurable illnesses, from Parkinson's to heart disease, based on regenerating diseased organs in situ from a patient's own stem cells.

Although there is no intention to create human embryos from skin cells, scientists believe that it could, theoretically, be possible to do so given that entire mouse embryos have already been effectively created from the re-engineered blood cells of laboratory mice.

Creating the mouse embryos was the final proof the scientists needed to demonstrate that the stem cells were "pluripotent", and so capable of developing into any specialised tissue of an adult animal, including the "germ cells" that make sperm and eggs.

Pluripotent stem cells could usher in a new age of medicine based on regenerating diseased organs or tissues with injections of tissue material engineered from a patient's own skin or blood, which would pose few problems in terms of tissue rejection.

However, the technique also has the potential to be misused for cloning babies, although stem cell scientists believe there are formidable technical, legal and ethical obstacles that would make this effectively impossible.

A team of Japanese and American scientists converted human skin cells into stem cells using the same simple approach that had astonished scientists around the world last month when they announced that they had converted blood cells of mice into stem cells by bathing them in a weak solution of citric acid for 30 minutes.

The scientist who instigated the research programme more than a decade ago said that he now has overwhelming evidence that the same technique can be used to create embryonic-like stem cells from human skin cells.

Charles Vacanti, a tissue engineer at Brigham and Women's Hospital in Boston, Massachusetts, said that the same team of researchers has generated stem cells from human dermal fibroblasts skin cells which came from a commercial source of human tissues sold for research purposes.

"The process was very similar to the one we used on mouse cells, but we used human dermal fibroblasts that we purchased commercially," Dr Vacanti said. "I can confirm that stem cells were made when we treated these human cells. They do the same thing [as the mouse cells].

"They revert back to stem cells, and we believe the stem cells are not a contamination in the sample that we were inadvertently sent by the company, but that they are being made, although we still have to do the final tests to prove this," he added.

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