Embryos created by 'virgin conception'

Each embryo came about as a result of parthenogenesis, when an egg divides without being fertilised into a ball of cells that develops in effect into an early embryo called a blastocyst.

Paul de Souza, the study's principal investigator at the Roslin Institute in Edinburgh, said that although the aim was to harvest stem cells from the embryos, efforts to do this had so far not been successful. "We've made half a dozen blastocysts. We have not at present got embryonic stem cells, that continues to be our ambition," Dr de Souza told the British Association for the Advancement of Science meeting in Dublin.

Parthenogenesis - which literally means virgin birth - is a common form of asexual reproduction in many animals but not in mammals, the group to which humans belong.

Dr de Souza said there was no intention of implanting the embryos into the womb of a woman and that his government licence from the Human Fertilisation and Embryology Authority was strictly for research. "If we don't put these artificial conceptuses into a uterus, they will go nowhere. They will not result in a foetus, they will not result in a life," he said.

The announcement of the first human embryos created by parthenogenesis is likely to be criticised by "pro-life" groups who oppose all research that involves creating human embryos for research purposes, he said.

The scientists at the Roslin Institute, where Dolly the sheep was cloned, used about 300 eggs taken from the ovaries of women undergoing an operation to make them sterile who had given their consent. About half the eggs matured successfully in the laboratory and about 5 per cent of these divided several times to produce a blastocyst, he said.

"We need a blastocyst to recover embryo stem cells and our success rate in recovering embryo stem cells is about one in ten," Dr de Souza said. "I think it's more of a technical challenge [to get stem cells] as distinct from a biological challenge."

Normally eggs and sperm have only half the genetic material and chromosomes of other cells in the body but the scientists have developed a technique whereby the eggs are stimulated to retain all their chromosomes before developing into a pathenogenic embryo.

"We can manipulate that process where normally genetic information is expelled, so that we can create eggs and embryos whose genetic constitution is identical to the mother," Dr de Souza said.

"The tissue we can derive from such an embryo would presumably be compatible for transplantation.

"There are in existence parthenogenic stem cell lines from non-human primates but to date no one has cracked that in humans. I think it's just a matter of the supply of tissue with which to be able to engage in experimentation," he added.

At present only women could benefit from parthenogenic embryos as men cannot produce eggs but scientists are also working on the possibility of using genetic material from sperm to create a parthenogenic embryo.

"Based on experiments in mice we could create what are called androgenotes where we would replace the egg's genetic information with the genetic information from a sperm," Dr de Souza said.

"We could put in two sperms if we wanted to to create a full genetic complement. Androgenotes would be a little more problematic in terms of how exactly matched that tissue would be to the donor because those sperm could have been created through a process where there would have been an expulsion of genetic material," Dr de Souza said.

Parthenogenic embryos offer an alternative way of creating stem cells than cloned embryos, which are created by transfering the nucleus of a skin cell into an egg with its own nucleus removed. Dr de Souza said: "It is possible that the cloned stem cell lines that are produced will not be suitable for therapeutic purposes or not suitable for use as models of genetic diseases.

"We don't know whether any one of them is going to lead to where to want to go and therapy is not the only objective. We also want these cell lines for research," he added.