“A sample of frozen testicle has been used to produce live offspring in experiments on mice,” BBC News reports.
While this may seem like a strange study to conduct, the aim is to preserve the fertility of boys affected by childhood cancers such as acute lymphoblastic leukaemia.
Currently, it is not possible to preserve the fertility of pre-pubescent boys undergoing some cancer treatments, because sperm is not produced until puberty (which usually happens around the ages of 11 or 12). The aim in this particular study was to see if sperm could be grown from frozen testicular tissue samples.
The researchers froze testicular tissue samples from mice that were five days old, and then grew sperm in the laboratory. They then used this sperm to fertilise over 200 eggs. More than half of them were inserted into female mice, and eight mice were born. These mice appeared to be healthy and were able to reproduce.
This is exciting research, but there are many challenges to be faced. These include making sure that the technique works on human testicular tissue, and is able to produce normal sperm and healthy offspring
Despite the small numbers of mice involved, this animal study does provide some hope that the technique could be refined for future use in humans.
The study was carried out by researchers from Yokohama City University, the National Research Institute for Child Health and Development in Tokyo and the RIKEN Bioresource Center in Ibaraki, Japan. It was funded by Grants-in-Aid for Scientific Research on Innovative Areas from the Japan Society for the Promotion of Science, and University grants.
The study was published in the peer-reviewed medical journal Nature.
BBC News reported the study accurately, and pointed out some of the challenges that will need to be overcome when conducting human trials.
This was a laboratory study conducted on mice to see if frozen testicular tissue could be used to generate healthy sperm, which could then fertilise eggs. The researchers wanted to investigate whether they could grow testicular tissue in a laboratory to produce sperm as a method of preserving fertility for boys undergoing chemotherapy or radiotherapy. It isn’t possible to freeze a sperm sample for boys undergoing cancer treatments that might cause infertility, as sperm are not produced until a boy reaches puberty.
Other techniques that have previously been investigated in animals include freezing testicular tissue and then transplanting it back. However, these techniques could reintroduce cancer cells.
The researchers froze samples of testicular tissue from neonatal (baby) mice. They then grew the samples in the laboratory, and sperm were produced. These were used to fertilise eggs, which were implanted in female mice.
The testicular tissue of mice around 4.5 days after birth was frozen using either “slow freezing” or “vitrification” (high-speed freezing using an anti-freeze substance). After preservation in liquid nitrogen for between 7 and 223 days, they were thawed and cultured in an agarose (seaweed) gel for up to 46 days, to see if sperm would be produced.
In the second stage of tests, the sperm produced from slow freezing or vitrification was used to inseminate mice eggs, which were transferred into female mice.
In the sperm culture experiments, 17 out of 30 testicular tissue samples produced sperm. Of these, 7 samples had more than 100 sperm, and 6 samples had more than 10 sperm.
They used the sperm to fertilise 236 eggs, and then transferred 156 of them into female mice. About a third of them (n=49) implanted (attached to the womb), and 8 mice were born.
The mice appeared to grow healthily and were able to mate naturally. It is unclear how long the mice were followed.
The mice studied were born from both slow-freezing and vitrification techniques.
The researchers conclude that, “although they may not be easy and require further investigation, organ culture methods for the spermatogenesis of other animals, including humans, are expected to be successful in the future. When this goal is realised, testis tissue cryopreservation will become a practical means to preserving the reproductive capacity of pre-pubertal male cancer patients”.
This laboratory study has shown that it is possible to freeze pre-pubertal testicular tissue from mice, and that it is also possible grow viable sperm from it. However, as can be seen from the figures, the actual number of mice born was extremely small compared to the number of fertilised eggs transferred into female mice. Although the mice were able to reproduce and appeared to be healthy, this was not actually studied in depth.
In addition to this, there are challenges that need to be faced when considering using this technique in humans, including whether the technique could produce genetically normal sperm and healthy offspring.
The researchers point out other limitations in the potential for growing human testicular tissue, which include the fact that:
While the numbers were small, this experimental study does provide some hope that the technique could be refined for future use in humans.