Scientists in the USA have shown it may be possible to isolate egg-producing stem cells from women's ovaries.

Researchers at Harvard's Massachusetts General Hospital, Boston, extracted germline stem cells capable of producing eggs from adult mouse ovaries. The stem cells spontaneously generated eggs in the laboratory, and the researchers were then able to mature the cells using human ovarian tissue grafted inside the mice.

The results, published in Nature Medicine, showed that the eggs, which appeared normal, could potentially befertilised using sperm to produce embryos.

Lead researcher, Dr Jonathan Tilly, said the study 'opens the door for development of unprecedented technologies to overcome infertility in women'.

'We might get to the point of actually having an unlimited source of human eggs', he said.

The findings, which confirm results from earlier research conducted by Dr Tilly's team, challenge the view that women have a limited number of eggs and are not able to produce more.

'Everything we teach medical students is going to have to change as a consequence of this paper', commented Dr Allan Pacey, chairman of the British Fertility Society.

Mr Stuart Lavery, a consultant gynaecologist and director of IVF Hammersmith, said the findings were 'a potentially landmark piece of research'.

Speaking to the BBC, he said: 'If this research is confirmed it may overturn one of the great asymmetries of reproductive biology - that a woman's reproductive pool of gametes may be renewable, just like a man's'.

Even if the study findings are confirmed, the research is still in its infancy and is not yet at a stage where it could be used in humans, which may be some years away.

Urging caution, David Keefe, professor of obstetrics at the NYU Langone Medical Center, New York, said: 'Humility is an absolute requirement in this field. You're dealing with people's hopes and dreams'.