ARTIFICIAL sperm capable of fertilising an egg have been created in the laboratory for the first time, in an experiment that could bring an end to male infertility.

Scientists in the United States have successfully coaxed embryonic stem cells from mice to mature into primitive sperm, which were then injected into eggs to form normal embryos.

The advance opens a new frontier in infertility research, suggesting that it will soon be possible to manufacture sperm from scratch for men who make none of their own.

While men with low sperm counts, or those who make poor-quality sperm, can be helped by reproductive medicine, those whose testes produce no sperm at all cannot father their own genetic children. Their only option for starting a family is to use donated sperm to fertilise their partner’s eggs.

The new research, from Harvard Medical School and the Whitehead Institute for Biomedical Research, both in Boston, Massachusetts, will also assist efforts to produce artifical eggs from stem cells.

Such synthetic eggs could be used to treat women made infertile by cancer treatment or other causes, and to allow older mothers to conceive. They would also help to address the shortage of donated eggs for fertility treatment and research.

In the study, a team led by Niels Geijsen took mouse embryonic stem cells, the master cells that give rise to every type of tissue, and grew them into germ cells. These are embryonic cells that are set aside for forming reproductive cells or gametes — sperm in males and eggs in females.

After producing germ cells — in itself a significant achievement — they grew them in culture for two to three weeks, which allowed them to develop into sperm.

While these artificial sperm lacked tails, the package of DNA they carried appeared to be completely normal. When injected into mouse eggs, they fused to make embryos with full sets of chromosomes.

The team, which publishes its results today in the journal Nature, now plans to take the experiment a step further, by implanting embryos made with artificial sperm into female mice, to see how they develop.

“We will see if they make pups,” Dr Geijsen said. “This will tell us how normal the gamete really is.”

His colleague, George Daley, said: “What we would really like to know is, will these cells . . . that we formed in the dish, actually sustain the development of an embryo? If that is true and it is normal, then it opens up possibilities for novel forms of reproductive biology.”

If the next round of experiments work, and the technique proves safe and effective in people, it could be used to create sperm for men who do not make any of their own.

One approach would be to produce a line of cloned embryonic stem cells that carry the infertile man’s genes, and grow these into sperm. Scientists hope that it will eventually be possible to skip the cloning element of this procedure, and to take stem cells directly from adult bone marrow.

Dr Daley said that his team is now investigating whether the methods used to make the artifical mouse sperm will also work in humans. “Our first indications are that we are going to see the same phenomenon but it is going to take us a little while longer to work out the detail,” he said. “It could easily translate into new ways of understanding male infertility.”

The same procedure could also be used to produce eggs, though attempts to do this have not yet been as successful. Earlier this year, a team at the University of Pennsylvania led by Hans Schöler announced that it had made mouse eggs from stem cells, but these proved impossible to fertilise.

It might also be possible to create artificial sperm that carry a woman’s genes, or eggs containing a man’s DNA, which would allow gay couples to have their own genetic children. Such a step, however, remains a long way off.

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