Researchers hope the technique can be used to preserve the fertility of boys undergoing cancer treatment, who are not able to provide a sperm sample. Some forms of cancer treatment may reduce men's fertility, so they can opt to have their sperm cryogenically frozen, but this is not a possibility for children yet to undergo puberty.
'The cryopreservation of testicle tissue may be a realistic measure for preserving fertility', the researchers wrote in Nature Communications.
The team, from Yokohama City University, took 30 tissue samples from the testes of five-day-old mice, then cryopreserved them. After thawing the tissue and growing it in the lab, mature sperm cells began to develop in 17 of the samples.
The sperm cells, and immature sperm precursors called spermatids, were then injected into mouse egg cells. The 156 resulting embryos were transferred into female mice, and eight healthy mouse pups were born. These mice were healthy, able to mate normally and produced their own offspring.
The researchers noted that samples of rat testicles could not successfully produce sperm in the lab after being thawed, so it is possible that the technique does not work in other animals. However, the team are now beginning to develop a method that will work for human samples.
'We are now working on human samples, which are very different from mice tissue, I have to find some trick to make it work, so it's very difficult to predict how long that will take'.
Dr Allan Pacey, andrology lecturer from the University of Sheffield, told the BBC: 'We would need to check that lab-made sperm were genetically normal and that any babies born are going to be healthy and fertile themselves. But based on this research in mice, the data looks encouraging and I hope that proper trials in humans will soon begin'.