Infertile men could father children if the results of experiments on mice can be repeated in humans.
Researchers in Japan have managed to get infertile male mice to father mouse pups by giving them transplants of frozen sperm stem cells - the cells which grow to become sperm.
If the treatment works with humans, it could be used on those suffering from all sorts of infertility, including that brought on by cancer therapies, said Michael Holland of the Melbourne-based Monash Institute of Reproduction and Development, a leader in infertility treatment.
Other teams have already begun work with men who provided samples of their testicular material before undergoing cancer treatments that would normally render them infertile. So far there have been no definitive results.
In the work with mice, reported today in New Scientist magazine, a team based at Kyoto University showed that those who have been given the frozen sperm stem cells can actually father mouse pups.
Although it had been shown in 1996 that infertile mice could produce sperm once implanted with the stem cells, none had created any offspring.
Sperm stem cells are the "seeds" which give rise to sperm deep inside the testes, where a complex development involving a number of different types of cells takes place.
The researchers at Kyoto University used mice that have a genetic abnormality which prevents them making sperm. Following a transplant of stem cells from a healthy animal, one of out of nine adult mice fathered young by normal sex. One of 12 adult mice that had been given anti-cancer drugs was able to father a pup following a transplant, but only by an in-vitro fertilisation technique which injected the sperm directly into the egg. "Having the ability to freeze and store the sperm stem cells might sound trivial, but it opens up a lot of therapies," Dr Holland said.