The creation of stem cells of the most versatile type without destroying human embryos has been hailed by scientists and religious groups as an ethical breakthrough.

The moral significance of the new technique for making powerful master cells without embryos, however, has been exaggerated. While it is indeed a remarkable advance, its true worth is not ethical but practical.

The method of reprogramming adult cells into an embryo-like state addresses only in part the moral objections of those who regard the embryo as a fully formed human being. And as the scientists behind it emphasised yesterday, it in no way renders future research with embryonic stem (ES) cells obsolete.

Studies of ES cells have been fundamental to the achievements of Shinya Yamanaka in Japan and Jamie Thomson in the US. Without examining the biological characteristics that give ES cells their hitherto unique ability to form every kind of human tissue, neither team would have discovered how to turn back the clock on adult cells to give them similar properties.

As Professor Thomson said: “These new lines would simply not have been derived had it not been for the past decade or so of embryonic stem-cell experiments.”

Therapies based on the new induced pluripotent stem (IPS) cells will not have involved the direct destruction of embryos, but they will ultimately owe their origins to ES cell research.

Plenty more research with ES cells will also be needed if IPS cells are to become therapeutically useful. These are not quite identical to ES cells, and further studies will have to determine whether the differences are important to their behaviour. The technique also risks inducing tumours, and will have to be refined before transplants can be attempted safely. ES cells will be critical to both lines of research, and may still be needed as a clinical fallback if either fails.

The real importance of cell reprogramming is that it should address the main concern of stem- cell researchers: the supply of the raw material.

A shortage of good-quality human embryos has so far restricted the number of ES cell lines available to scientists. Donated eggs are still scarcer, which would limit the ability to produce cloned ES cells that are genetically identical to the patient to be treated.

It should now be possible to make these cells from a much more abundant source: adult skin cells. These will first be used as models for making cell models of diseases such as Parkinson’s and for testing new drugs.

In the longer term, if safety issues are resolved, tissue grown from IPS cells could be transplanted to treat disease. As the cells would be harvested from the patient under therapy, they would be genetically matched already. Even without cloning, there would be no risk of immune rejection.

Thoughtful scientists such as Austin Smith, of the University of Cambridge, and Robin Lovell-Badge, of the National Institute for Medical Research, have never been fussy about the source of stem cells that will ultimately be used for treating patients. While they see ES cell work as critical, their preference has always been for reprogrammed adult cells in therapy.

This view, however, is founded not on any ethical objection to embryo research but on convenience: therapies based on adult cells, so long as they work, are going to be simpler. That is why these achievements are so welcome.

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