US researchers have managed to grow human eggs in the laboratory, using cells scraped from the surface of ovaries. The team, based at the University of Tennessee, Knoxville, say that the findings could lead to a new way of preserving female fertility, and also a potential new source of egg cells for embryonic stem cell (ES) research. The scientists, who published their results in the open access journal Reproductive Biology and Endocrinology, also say that the research casts doubt on the long-held belief that baby girls are born with a lifetime's supply of mature eggs.
It is thought that a woman's ovaries contain about two million egg-producing follicles at birth, but that this number falls to around 400,000 by the time she reaches puberty, and continues to drop throughout her life. However, recent studies have challenged this dogma, suggesting that new egg cells and granulosa cells (which form the wall of the ovary follicles) may originate from stem cells found on the surface of adult ovaries. To test this theory, Antonin Bukovsky and his colleagues scraped off some of these cells, known as ovarian surface epithelium (OSE) cells, and grew them in the laboratory for five to six days. They took the cells from the ovaries of five women aged 39 to 52, using a laparoscopy technique.
By growing them in the presence of the female hormone oestrogen, the scientists found that they could persuade the OSE cells to grow into mature egg cells, capable of being fertilised and developing into an embryo. The team say that the technique used to harvest the OSE cells is relatively easy, and has several potential uses in assisted reproduction. For example, OSE cells could be taken from young women about to undergo cancer treatment that could leave them infertile, and frozen for later use in IVF procedures. The approach could also help women at risk of premature menopause, and might eventually be used to delay the menopause by 10 to 12 years in fertile women, the researchers claim.
US reproductive biologist Jonathon Tilly called the study 'intriguing', and worthy of further investigation. However, he cautioned that 'making things in a dish is very different to making things in a human body'. He cited reports from three groups that have used ES cells from mice to create egg and sperm cells in the laboratory, but have not been able to produce offspring using this method - suggesting that 'whatever is being created in the dish is not normal sperm and eggs'. UK fertility expert Simon Fishel also stressed that the work was at a very early stage, but said if confirmed, 'it is possible that it could help pre-menopausal women and women coming up to their menopause having IVF, who currently have to use egg donors'.