Therapeutic cloning has potential advantages. In this technique, somatic nuclei from a patient's body — nuclei from non-reproductive cells — are fused with donated eggs (oocytes). Embryos are thereby produced from which pluripotent stem cells — those able to differentiate into any body-cell type, and genetically identical to the patient — could be generated. Cells or tissues derived from such embryonic stem cells for transplantation would not be rejected by the patient's body. The question of whether therapeutic cloning should be allowed is currently generating much heat in Britain, and elsewhere. But that is only one part of the vast field of regenerative medicine being opened up by stem cells. There is a danger that the issue of therapeutic cloning will distract politicians and the public from the wider issues and opportunities offered by embryonic stem cells for both therapeutics and basic cell biology.

The real interest of the report is in disentangling the broader range of issues. Britain is already at the far end of the moral spectrum, being one of the few countries in the world to authorize the 'utilitarian' deliberate creation of embryos for research, a practice that runs against the European Convention on Human Rights and Biomedicine. In most of Europe, and elsewhere, the fundamental question is not whether the cloning of human embryos to produce stem cells should be allowed, but whether the collection of stem cells from human embryos should be allowed at all. And it is here, in the exploration of the use of basic embryonic stem cells, rather than in somatic nuclear transfer, that the scientific promise is greatest.

Promise
Although countries opposed in principle to embryo research, such as hard-line Germany or Ireland, are unlikely to waver, the huge therapeutic promise of embryonic stem cells is likely to lead to changes in the law in countries such as France. There, a ban on human embryo research is likely to be lifted to allow embryonic stem cells to be collected, but only from the 35,000 frozen surplus embryos left over from attempts at in vitro fertilization. One need not be a Jesuit theologian to realize that the ethical argument for this is overwhelming: if such embryos are to be destroyed anyway, why not use them to relieve suffering? Obtaining consensus on whether human embryo research should be allowed is impossible, given the diversity of views. The EU report is therefore wise to leave this question up to national legislatures, rather than seeking to impose Europe-wide rules on EU research funding.

But the ethical controversy over the use of human embryos as a supply of embryonic stem cells has perhaps done science a favour. Three years ago, before human embryonic stem cells had been cultured, xenotransplantation was being pursued as the solution to cell and organ transplants (see Nature 391, 325; 1998). The breakthrough in 1998 in culturing human embryonic stem cells has now radically shifted the focus of research. In turn, whereas the use of such cells has since become the obvious way forward, the controversy over the use of embryos is now encouraging research into 'alternative' sources that might otherwise have been ignored: adult stem cells.

Use of adult cells
Stem cells from adult tissues such as bone are currently of limited use in that they do not grow as easily as embryonic stem cells, or differentiate into as many cell types. But are adult stem cells irretrievably committed to differentiating into a limited number of cell types? The past year has seen reports of blood stem cells generating muscle tissue and muscle stem cells generating blood cells. Even one year ago, few would have believed such feats possible. Brain cells, once thought irreplaceable, can now be regenerated. Might all types of brain cells be regenerated from an adult human stem cell? Why not?

Adult stem cells still appear of limited use because they cannot proliferate indefinitely. But who says they are not capable of doing so? Differentiation is a complex process, determined by the switching on and off of thousands of genes and the production of millions of proteins. The intellectual appeal of human embryonic stem cells, with their ability to divide indefinitely and potentially generate all types of cells, should not be allowed to lead to a neglect of other avenues of research, particularly given the ethical issues involved. A case-by-case approach will probably be needed — in mice, the entire blood system can now be regenerated from a single adult blood stem cell.

A cynical view of a bioethics committee is that it simply puts a brake on the introduction of new technologies until public acceptance is inevitably in place. In the EU report, ethical concerns are not only doing science a service by providing a bridge to society's legitimate concern about issues such as the rights of the human embryo, but they are also giving science an opportunity to stand back and think of alternative approaches, rather than putting all of its oocytes in one basket.

In Europe, the starkly contrasting views on embryo research are similarly having the beneficial effect of forcing the continent to debate and come to terms with fundamental ethical and scientific questions. US politicians would perhaps do well to take note of the debate in Europe. By comparison, the current US legal situation — with moral restrictions in the public sector, and almost anything allowed in the private sector — is both hypocritical and ethically incoherent.