Strange New World - Lab Mice
Used To 'Incubate' Human Eggs
By Roger Highfield
MICE will be used as "incubators" for human eggs in pioneering experiments to investigate whether animals can help women sterilised by cancer treatment to bear children.
Ovarian tissue from women cleared of ovary cancer, Hodgkin's disease or leukaemia will be implanted in the mice to study how animals can grow human eggs for test-tube babies and so avoid the risk of reintroducing cancer to the patients.
Research on animal incubators, started by Prof Roger Gosden of Leeds University five years ago, passed another milestone this week with the announcement by an American team that it has used the same approach to grow an elephant egg in a mouse as part of conservation efforts.
Forthcoming experiments on using mice to grow human eggs are part of research by Prof Gosden that aims to restore the fertility of young women who have been subjected to chemotherapy and radiotherapy.
Several dozen women in Britain already have had ovarian tissue stored at low temperatures. However, none has had ovarian tissue reimplanted so she can have a child. To assess the risk of reintroducing ovarian cancer by reimplanting stored ovarian tissue, Prof Gosden used animals to incubate human eggs.
His earlier experiments showed that immature eggs could be transplanted from sheep into a special strain of mice that do not reject foreign tissue. Two years ago, after then growing cat eggs in mice, the first experiments on using mice to grow human eggs were carried out.
The technique can produce mature human eggs, although the experiment was terminated when the follicles - the egg-containing sacs - were 10 days short of full maturity. Mature follicles were thought be too large for the mice and to produce mature eggs may require a larger host animal, such as a rabbit.
The latest mouse studies will investigate human egg development and the risk of passing on cancer from the stored ovarian tissue. Prof Gosden does not have a licence to fertilise these eggs and stressed that he did not intend to seek one. However, plans are already under way in America to use animal incubators to grow human eggs. Prof Gosden said that there would have to be careful research on the risk of animal diseases passing to the egg and thus to any foetus.
He sees the use of animal incubators as an interim measure. In the long term, test-tube methods would be used to ripen eggs from stored ovary tissue. Like the American team, Prof Gosden is also interested in using such methods to help to preserve a species by recovering eggs when an endangered animal dies.
At Purdue University in Indiana, John Critser announced this week that he has transplanted ovarian tissue from an African elephant into a mouse, inducing the mouse to produce successfully what appeared to be a mature elephant egg.
The results, published in the journal Animal Reproduction Science, indicate that transplanted ovarian tissue may be used to regenerate reproductive cells for a wide variety of mammals.
Mr Critser said that the elephant egg, in theory, could be fertilised in a test-tube and then transplanted into a female elephant.
However, procedures to isolate and fertilise eggs from elephants and the techniques of transferring embryos into live animals, will require additional investigation and development, he said.
Mr Critser said: "We know a great deal about a few species, such as mice, humans and sheep. But as you begin to look at the simple, fundamental reproductive biology of a tiger or a cheetah or an African elephant, very little is known."