Grotesque. Horrific. Revolting. Two studies presented at the conference had the columnists scrabbling for adjectives. One group examined the possibility of obtaining eggs from aborted fetuses. The other looked at whether adding normal cells to an embryo with a genetic defect could make up for that defect.
Norbert Gleicher at the Center for Human Reproduction in New York thinks the latter could be an alternative to genetic engineering to correct defects. To make it easy to follow the fate of the added cells, his team added up to three male cells to 21 female embryos. Twelve developed into normal embryos. 鈥淭his study was to determine whether the concept is possible,鈥� Gleicher said. 鈥淚t is not meant to support in any way that the clinical application of this kind of concept at the present time is either feasible or ethically acceptable.鈥�
The scientific term for an individual composed of populations of genetically distinct cells is a 鈥渃himera鈥�. Thousands of human chimeras already exist, though most probably go unnoticed. Chimeras form when two embryos fuse instead of becoming non-identical twins. Depending on which cells end up where, male-female chimeras may be infertile or have genital abnormalities, but many are completely normal.
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Regardless of the ethics, the practical problem with creating chimeras to correct genetic defects is that you cannot control which cells will form which tissues. So if the method was used to try to prevent muscular dystrophy, for example, and none of the added cells contributed to muscle tissue, that individual would still develop muscular dystrophy.
Nevertheless, some experts believe the technique is at least feasible. 鈥淲hen you introduce embryonic stem cells into early-stage embryos, they do contribute to some, if not all of the tissues,鈥� says Robert Lanza of Advanced Cell Technology of Massachusetts. Others disagree. 鈥淚t seems to me completely flawed,鈥� says Alan Trounson, an IVF pioneer at Monash IVF in Melbourne.
Even if it did work, where would doctors obtain the normal cells? Would parents really want a child who was partly theirs and partly consisted of donor cells? Researchers also question why Gleicher鈥檚 team experimented with human embryos. 鈥淲hy didn鈥檛 they try it in mice first?鈥� asks Lanza. 鈥淭here was no need to go leaping into humans.鈥�
The other controversial study involved growing ovarian tissue from seven human fetuses aborted after 22 to 33 weeks. Some cells showed early signs of maturing into eggs after a month, claimed Tal Biron-Shental of the Meir Hospital-Sapir Medical Center in Israel. She believes the method could help solve the acute shortage of donor eggs. 鈥淚 am fully aware of the controversy about this, but probably, in some places, it will be ethically acceptable.鈥�
However, it is far from clear whether the technique really could provide viable eggs. Suitable ovarian tissue can only be taken from fetuses after about 16 weeks鈥� gestation, but most abortions take place long before this, making the tissue rare. What鈥檚 more, it takes six months for a human egg to mature, and all attempts to grow eggs in the lab have failed because it has proved impossible to keep the cells alive and healthy this long.
鈥淚f they had thought it through, they鈥檇 have realised there are other sources that are more ethically sound and medically feasible,鈥� adds Lanza. For instance, recent work suggests it may be possible to grow eggs from embryonic stem cells (New 杏吧原创, 10 May, p 4).
Ethically, the idea of creating children from aborted fetuses has been widely condemned. 鈥淚t would be difficult for any child to come to terms with being created by aborted fetuses,鈥� says Suzi Leather of the UK鈥檚 Human Fertilisation and Embryology Authority. The technique would also be illegal in some countries, including the UK, she pointed out.