updated 6/20/2005 1:06:10 AM ET 2005-06-20T05:06:10

Scientists in Britain have shown that stem cells extracted from human embryos can develop in the laboratory into the early forms of cells that become eggs or sperm. The research raises the possibility that one day eggs and sperm needed for infertility treatment could be grown in a dish.

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Preliminary experiments also suggest that scientists may eventually be able to use the technique to create a supply of eggs for cloning.

But the more immediate benefit of the work could be a better understanding of why some men and women do not create their own sperm or eggs and whether toxic chemicals in the environment play a role, one of the researchers said before the start of the annual conference of the European Society of Human Reproduction and Embryology. The findings were scheduled to be presented Monday in Copenhagen.

“It may allow us to investigate the very earliest processes of how a human (ovary and testis) develops,” said Harry Moore, a professor of reproductive and developmental medicine at Sheffield University in England.

Many scientists believe that chemical pollutants, such as pesticides, that mimic the action of hormones, might interfere with human development at the stage where eggs and sperm — called germ cells — are forming and that this disruption may cause birth abnormalities, infertility and possibly cancer.

“By developing suitable tests with embryonic stem cells as they differentiate into germ cells, we can investigate the action of these chemicals in the laboratory,” Moore said.

An end to egg, sperm donors?
Stem cells are the master cells of the body, appearing when embryos are just a few days old and developing into every type of cell and tissue in the body, including sperm and eggs.

Scientists can study the stem cells by extracting them from the embryo. If the researchers create the embryo by cloning a cell from a patient, any resulting cells would be a genetic match to the patient.

The cloning technique, called cell nuclear replacement, involves emptying out the genetic material in an egg and replacing it with the genetic material of another cell, for example a skin cell from an adult. Instead of being fertilized by sperm, the newly reconstituted egg is bathed in chemical nutrients and electrocuted to shock it into dividing. It then evolves into an embryo, from which stem cells can be extracted.

For infertile couples, that approach would eliminate the need for donor sperm or eggs.

Technique faces long road
But any treatment using eggs and sperm grown from stem cells, let alone from stem cells extracted from a cloned embryo, may be many years away, Moore said.

“We would need to prove that sperm or eggs produced in this way were safe before we could contemplate using them to treat patients,” he said.

Other experts said the advance from the University of Sheffield could also raise some ethical issues.

“It opens new and challenging possibilities: because the technique can be used to generate eggs from a man’s (adult) cells, gay couples could have children genetically related to both,” said Anna Smajdor, a medical ethicist at Imperial College in London.

“These possibilities raise new questions about how we define parenthood and about how we decide who has access to these new technologies,” she said.

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