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Human-cow chimeric embryos for stem cell research

7 November 2006   |   News story

Two research teams from Newcastle University and Kings College, London, have applied to the Human Fertilisation and Embryology Authority (HFEA) for licenceto create embryos by fusing human DNA with cow eggs, a technique known as nuclear transfer or therapeutic cloning. A third application is expected to be submitted from Edinburgh University. Bovine oocytes would have the nucleus (containing the majority of the bovine DNA) removed before being fused with human cell nuclei; the resulting chimeric human-bovine embryos would be grown for six days, then harvested for stem cells. All embryos would be required to be destroyed by 14 days.

The stem cells would be used for research purposes. The purpose of the application is supposedly to make up for the limited supply of human eggs by using cow eggs instead; genetically, the human-cow embryos would be largely human because only extra-nuclear bovine genetic material would be present. The Newcastle team, led by Dr Lyle Armstrong, wants to analyse the process of cellular genetic reprogramming following nuclear transfer, in the hope of learning how to make embryonic stem cells without an animal egg. Dr Armstrong said: “At the moment we don’t know if the nuclear transfer process works well enough in humans to create useful embryonic stem cells. We need to carry out many tests to establish this and, as animal eggs are freely available, it makes sense to use these as a source of material for our laboratory work” (see Newcastle press release).

Dr Stephen Minger, who leads the King's College application, wants to use the chimeric embryos to continue current work to produce disease-specific stem cells from humans with genetic neurodegenerative diseases. He said that they considered it appropriate to use “non-human oocytes from livestock as a surrogate” rather than human ooctyes from women. Dr Minger also stated: “Once the nucleus of the animal egg is removed it essentially no longer has a species identity and when replaced with a human nucleus, the resulting embryo and cell line will have human genetic identity” (see King’s press release). However, this is not strictly correct, as although the vast majority of genetic identity would be human, heritable extra-nuclear genetic material such as that present in the cellular structures mitochondria would be bovine in origin.

Critics of the plans have slated the application to the HFEA as potentially dangerous, as well as unethical. Calum MacKellar of the Scottish Council on Human Bioethics said: "In this kind of procedure, you are mixing at a very intimate level animal eggs and human chromosomes, and you may begin to undermine the whole distinction between humans and animals…If that happens, it might also undermine human dignity and human rights" (see BBC news report).

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