The revelation of experiments in which human embryos with both female and male cells were created has been condemned as 鈥渇lawed鈥� and 鈥渞evolting鈥� by both fertility scientists and anti-abortion groups.
US researcher Norbert Gleicher and colleagues took cells from three-day-old human male embryos and added them to female embryos, creating what is called a chimera. Gleicher, who unveiled the work at the European Society of Human Reproduction and Embryology鈥檚 annual conference in Madrid, says the experiments were to test a theoretical alternative to gene therapy.
Gene therapy aims to repair genetic defects by using vectors, usually viruses, to ferry new DNA into a patient鈥檚 cells. But the technique has been troubled by safety fears. Gleicher suggests that embryos carrying genetic defects might be cured by injecting early embryonic cells, called blastomeres, which carry healthy versions of the genes. This could even prevent the need to destroy embryos with faulty genes, he claims.
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But Alan Trounson, fertility expert and IVF pioneer at Monash IVF in Melbourne, Australia is scathing. 鈥淚t seems to me completely flawed,鈥� he says. 鈥淵ou can鈥檛 have half of Huntington鈥檚 disease.鈥�
Lynn Fraser, chair of ESHRE鈥檚 international scientific committee agrees. In chimeric individuals, the 鈥渂ad genes鈥� would 鈥渁ll still be there鈥�, she says. Naturally-conceived human chimeras can exist but the distribution of the cells containing the different genetic profiles is far from uniform.
Trounson adds that the work is damaging to the image of fertility science: 鈥淚t could cause some harm because it would be difficult to argue why that experiment was done to patients.鈥� Gleicher鈥檚 study is the second from the conference to cause a furore, following a report of work assessing the potential of ovarian tissue from aborted fetuses to provide eggs for IVF.
Feasible or ethical
Gleicher, at the Center for Human Reproduction in New York, and his team extracted blastomeres from 16 human male embryos. They added one, two or three of the male cells to each of 21 female embryos.
The embryos were then followed to the blastocyst stage, which occurs five to six days after fertilisation. Male cells were used because the Y chromosome is an easy marker to track in the developing embryos.
鈥淭welve of the 21 embryos reached what we considered to be perfectly normal blastocysts,鈥� says Gleicher. But four of the female embryos stopped developing after the transplantation, while five become 鈥渁bnormal blastocysts鈥�.
鈥淭his study was meant in principle to determine whether the [genetic repair] concept is possible,鈥� says Gleicher. 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�
However, he says a patent has been filed for the concept and adds: 鈥淲e believe further investigation is warranted.鈥�