Researchers have isolated egg-producing stem cells from the ovaries of reproductive age women and shown these can produce what appear to be normal egg cells or oocytes, according to a new study.

The discovery "opens the door for development of unprecedented technologies to overcome infertility in women" according to the scientist who led the study.

Jonathan Tilly, of Massachusetts General Hospital in the United States, said: "The primary objective of the current study was to prove that oocyte-producing stem cells do in fact exist in the ovaries of women during reproductive life, which we feel this study demonstrates very clearly."

The researchers developed a precise cell-sorting technique to isolate oocyte producing stem cells (OSCs) without contamination from other cells, according to an article in the March issue of Nature Medicine.

The cells were able, in the laboratory, to form cells spontaneously with characteristic features of oocytes. Further experiments on mice showed such eggs could be fertilised.

Dr Tilly's team is exploring potential clinical applications from its findings which include the establishment of human OSC banks - since these cells, unlike human oocytes, can be frozen and thawed without damage - and the development of mature human oocytes from OSCs for in vitro fertilisation, plus other approaches to improve the outcomes of IVF and other infertility treatments.

In 2004 a report from Dr Tilly's team challenged the fundamental belief, held since the 1950s, that female mammals are born with a finite supply of eggs that is depleted throughout life and exhausted at menopause.

Dr Tilly said: "The discovery of oocyte precursor cells in adult human ovaries, coupled with the fact that these cells share the same characteristic features of their mouse counterparts that produce fully functional eggs, opens the door for development of unprecedented technologies to overcome infertility in women and perhaps even delay the timing of ovarian failure."

Dr Allan Pacey, a fertility expert at the University of Sheffield, told the BBC: "This is a nice study which shows quite convincingly that women's ovaries contain stem cells that can divide and make eggs.

"Not only does this re-write the rule book, it opens up a number of exciting possibilities for preserving the fertility of women undergoing treatment for cancer, or just maybe for women who are suffering infertility by extracting these cells and making her new eggs in the lab."

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Stem cell boost in fertility study