Testicular tissue frozen for 20 years can still produce viable sperm, according to a new study published in PLOS Biology. After implanting decades-old frozen rat tissue into mice and comparing it with tissue just a few months old, the researchers discovered that the older tissue could resume sperm production even after being frozen for so long – a discovery that may help childhood cancer survivors become fertile again.
Should a young boy develop cancer, the most common of which is leukemia, aggressive chemotherapy is often needed to maximize the chance of survival. A devastating and lasting impact of this treatment is lower fertility in adult life, as the chemotherapy drugs also target testes tissue.
One option for these children is for a sample of testicular tissue to be taken and frozen, then reimplanted after the cancer goes into remission. However, it can sometimes take years and even decades before the patient is ready for implantation. As survival rates are increasing, side effects of aggressive cancer treatments are becoming a growing issue, and researchers are looking at ways to increase the quality of life for survivors in the long term.
In the paper, which comes from researchers at the University of Pennsylvania, the team wished to determine just how long sperm-producing stem cells can be frozen while still being viable for transplantation. They already had a sample of spermatogenic stem cells (SSCs) – which are integral in sperm production – from 23 years ago, in a rat colony line that has since been maintained. This allowed them to take a sample from the same colony recently, before implanting them into mice with lessened immune systems (to prevent rejection).
The results showed that, following transplantation, the mice could produce all the required cell types even after the tissue was frozen for over 20 years. However, while the tissue was still viable for increasing fertility, it produced worse results when compared to the tissue that was only frozen for a few months. So, while the tissue was still usable, it appears the sooner the better when looking at reimplantation.
“Our study showed that rat spermatogonial stem cells can be successfully frozen for over 20 years, transplanted into an infertile recipient animal and regenerate the ability to produce sperm, albeit at a reduced rate,” said Eoin Whelan, lead author, in a statement.
“This could provide a method to recover the loss of fertility in prepubertal boys treated for cancer.”
Assuming the results translate to humans (which is a big assumption), it suggests extensive testing needs to be done on the potential of stem cells before they are taken to get the best outcome, and may also open doors in understanding how fertility potential is lost over time at cryogenic temperatures.