Chimera embryos spark controversy

Dr Kirsty Horsey

Progress Educational Trust

04 July 2003

| | | |

[BioNews, London] Experiments in which cells from one early human embryo were mixed with those from another triggered a heated debate last week. The studies of mixed, or chimera embryos (dubbed 'she-males' by the media as they contained cells from one male and one female embryo), were presented at the annual conference of the European Society of Human Reproduction and Embryology in Madrid.

Scientists from the Centers for Human Reproduction in New York and Chicago say they created the chimeras to investigate the possibility that cells from a healthy embryo could be used to treat a genetically defective one. They stressed that their work was not ready for clinical application and that the embryos were destroyed after a few days. But other fertility experts at the meeting called the experiments 'completely flawed', and potentially damaging for the reputation of other fertility researchers around the world.

Norbert Gleicher and his team took 21 three-day old female embryos, and injected them with cells taken from early male embryos. Twelve of the embryos continued to develop normally, and these were then grown in the laboratory for three further days. The researchers then studied the make-up of the chimeras, using the Y-chromosome as a 'marker' to track the male cells, and found that the male cells had spread evenly throughout the embryos.

Gleicher said the work was carried out with the approval of an in-house ethical committee, and was not done with the intention of implanting embryos into a womb, but to investigate possible treatments for genetic disease. 'If you had an afflicted embryo and if you are able to introduce just 15 per cent healthy cells, you may be able to treat single gene disorders' he told the conference.

However, other scientists at the meeting thought that the experiments were flawed, since there is no way of ensuring that the healthy cells would go on to form the organs or tissues affected by the gene defect. For example, to treat the genetic condition cystic fibrosis, the researchers would need to get the healthy cells into the parts of the early embryo destined to form the lungs and the pancreas.

'It is essentially trivial science that shouldn't be done' said Australian fertility researcher Alan Trounson, adding that 'it is difficult to argue why it should be done, to the public'. UK scientist Lyn Fraser, chair of ESHRE's scientific committee, also criticised the study, calling it a 'non-starter'. She added that the production of chimeric embryos to make babies was 'expressly forbidden' in the UK, and that it was unlikely that the Human Fertilisation and Embryology Authority would permit any research on human chimeric embryos.

Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.