BioNews reporting from ESHRE conference, Copenhagen: Human embryonic stem cells (ES cells) may be capable of growing into egg and sperm cells in the laboratory, UK scientists say. Behrouz Aflatoonian, part of a team based at the University of Sheffield, told the annual conference of the European Society of Human Reproduction and Embryology (ESHRE) that human ES cells can develop into 'primordial germ cells' (PGCs) - the cells that eventually become eggs or sperm. The work suggests that mature eggs and sperm could eventually be produced in the laboratory and used to treat infertility. Such cells could also be used in 'therapeutic cloning' research, to create more embryo stem cell lines.
A US study reported in 2003 showed that mouse ES cells can be used to grow sperm cells in the laboratory, which can then be used to fertilise mouse eggs. Another US group has shown that mouse embryo cells grown in the laboratory can be coaxed into making eggs and egg-nurturing cells similar to those found in the body. However, as yet, none of these laboratory-produced eggs have been successfully fertilised with mouse sperm to make healthy embryos.
In the latest study, which has not yet been published, the researchers studied several human ES cell lines, which they grew into collections of cells called 'embryoid bodies' in the laboratory. Within two weeks, a 'very tiny proportion' of these cells showed gene activity typical of PGCs. Some cells also 'switched on' genes only usually active in maturing sperm cells. This suggests that human ES cells 'may have the ability to develop into PGCs and early gametes as has been shown previously for mouse embryonic stem cells', said Aflatoonian.
Mr Alflatoonian stressed that much more work needed to be done, since embryoid bodies can develop into all sorts of tissue types. 'We need to choose cells that are going to develop into PGCs and then work out how we can encourage them to grow into gametes', he said in a press release. As well as allowing researchers to study early egg and sperm development, the ability to grow egg and sperm in the laboratory will also allow scientists to study the effects of chemicals thought to disrupt this process - so-called 'endocrine disrupting' substances.
Eventually, it might be possible to produce sperm and eggs for use in assisted conception treatments, although, according to team leader Professor Harry Moore, 'this is a long way off'. He said that such an approach would not be reproductive cloning, as fertilisation would involve only one set of gametes produced this way, producing a unique embryo. Eggs produced from ES cells could also potentially overcome the shortage of eggs for therapeutic cloning research - the use of ES cells to create tissue-matched cell therapies for a range of diseases.
Commenting on the research, ethicist Anna Smajdor said that the technique could be used by gay couples to have children genetically related to both. 'Single men could even produce a child using their own sperm and an engineered egg', she said, adding 'these possibilities raise new questions about how we define parenthood'.
Allan Pacey, of the British Fertility Society, described the work as 'a really exciting step forward', saying 'we still don't really understand why some men and women can't produce sperm and eggs of their own'. He added that 'if we could better understand the basic biology then we might be in a better position to help them one day'.