The prospect of creating limitless stem-cells for treating conditions such as Parkinson’s disease, paralysis and diabetes, without destroying human embryos, has moved a step closer.

Researchers in Britain and Canada have developed a new and safer way of turning the clock back on adult skin cells so that they acquire the versatile properties of embryonic stem cells, which does not rely on viruses that could trigger cancer.

The move would also resolve some of the ethical and practical problems that have held up embryonic stem-cell research.

While these master cells have great potential for treating disease, as they can form any type of tissue for transplanting into patients, their use is controversial because they must be derived from human embryos.

There is also a shortage of the human eggs and embryos needed to produce powerful stem cells, and unless difficult cloning techniques are used, there may be a risk of rejection by the body’s immune system.

Reprogrammed skin cells promise an almost limitless source of stem cells, and as they are the patient’s own rejection would not be an issue.

A method of reprogramming human skin cells into a versatile embryo-like state was first developed in 2007 by Japanese and American teams.

The induced pluripotent stem (IPS) cells that result, which seem to have all the properties of embryonic stem cells, were named as “breakthrough of the year” by the journal Science.

The procedure, however, is unsuitable for therapeutic use, because it involves modifying four key genes with viruses, and this risks inducing genetic abnormalities that could cause cancer.

Teams led by Keisuke Kaji, of the University of Edinburgh, and Andras Nagy, of the University of Toronto, have now collaborated to develop a new approach to creating IPS cells that does not involve viruses.

Dr Kaji, who led the research, said: “It is a step towards the practical use of reprogrammed cells in medicine, perhaps even eliminating the need for human embryos as a source of stem cells. This new method will advance the field of regenerative medicine, and should help understand diseases and test new drugs.”

Other experts said that while the work is promising, there are still questions over the reprogramming technique, and that continued study of true embryonic stem cells is necessary.

Robin Lovell-Badge, of the National Institute for Medical Research in London, described the research as an “exciting step in the right direction”, but added: “we must not forget that the path is still very long and winding and full of bear traps.

“For the time being I think it rather premature to suggest that their work will remove the need to derive human embryonic stem cells from embryos. We still have a lot to learn from human embryonic stem cells about their true identity and their properties, and this knowledge is necessary in order to know whether human IPS cells are truly useful or not.”

The new procedure, which is described in two papers published in the journal Nature, came after a chance meeting between Dr Kaji and Dr Nagy, who realised that each had solved a part of the challenge.

They have now combined their techniques to develop a method that can modify all the four genes at once to reprogramme adult cells, but without leaving traces of foreign DNA that could compromise the stem cells that result.

Dr Kaji said: “I was very excited when I found stem cell-like cells in my culture dishes. Nobody, including me, thought it was really possible. Using our method, it will be possible to remove not only the inserted genes, but all traces of our genetic modification from the human IPS cells, although we still need to improve the efficiency.”

Dr Nagy said: “We hope that these stem cells will form the basis for treatment for many diseases and conditions that are currently considered incurable. We have found a highly efficient and safe way to create new cells for the human body which avoids the challenge of immune rejection.”

Professor Sir Ian Wilmut, Director of the MRC Centre for Regenerative Medicine, said: “It will still take time before these IPS cells can be given to patients. Crucially, we need to have a method to generate the desired cell types from these stem cells. But I believe the team has made great progress and combining this work with that of other scientists working on stem cell differentiation, there is hope that the promise of regenerative medicine could soon be met.”

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