Cryopreserved male testicular tissue can be reinstituted and produce viable sperm after more than 20 years, according to a new study in rodents published in the open-access journal PLOS Biology by Eoin Whelan of the University of Pennsylvania School of Veterinary Medicine and colleagues.
What is Cryopreservation?
The term cryopreservation, from the Greek cryo (cold) and the Latin servare (protect, save, preserve), means the freezing and storage of formed cells and tissues.
They are stored (freeze-free) in liquid nitrogen for years at minus 196 degrees Celsius without damage or aging. It is a special procedure in which tissues are preserved by certain liquids and frozen slowly so as not to damage the cells. Cryopreservation plays an important role in fertility medicine and continues to gain importance.
If we go back to our article;
However, compared to tissue that is frozen only for a short time, prolonged latency results in decreased fertility. The findings could have major implications for the treatment of men with cancer who could benefit from harvesting and freezing testicular tissue prior to chemotherapy.
The survival rate for childhood cancers has increased dramatically over the past few decades, but a serious side effect of treatment is decreased fertility later in life.
A potential treatment would be to harvest, freeze, and replant testicular tissue containing stem cells, a procedure recently demonstrated in the macaque model to restore fertility after at least short-term freezing.
Reimplantation may not be possible for prepubertal children with cancer for a decade or more after tissue retrieval, raising the question of how long frozen spermatogenic stem cells (SSCs) can survive.
To find out, the researchers thawed rat spermatogenic stem cells that had been cryopreserved for more than 23 years in their lab and inserted them into nude mice that lacked an immune response to reject foreign tissue.
They compared the ability of long-frozen spermatogenic stem cells to produce viable sperm with spermatogenic stem cells frozen for just a few months and freshly harvested spermatogenic stem cells from a single rat colony, all preserved for several decades.
According to the researchers, long frozen sscs colonized the mouse testis. He then produced SSCs from any of the recently collected tissue samples, as well as all the cell types necessary for efficient sperm production.
While the long-frozen spermatogenic stem cells had similar profiles of gene expression changes compared to other samples, they produced fewer elongated spermatids, which continued to form swimming sperm.
These results have several important implications.
First, they point to the importance of testing SSC viability in situ rather than relying on biochemical or cellular biomarkers to determine the potential of cryopreserved cells, which may not reflect the true loss of stem cell potential over time.
Second, while there are currently no protocols capable of expanding human spermatogenic stem cells for reimplantation – a requirement for the clinical development of this therapy – such protocols may need to take into account the time-dependent degradation of viability, assuming that human SSCs mimic those of rats.
Finally, and that's the good news.
No viability is lost during prolonged cryopreservation, suggesting that it may be possible to identify and reduce key factors of viability loss to improve reproductive options for boys who have been successfully treated for childhood cancers.
Finally, and this good news, the lack of viability during prolonged cryopreservation hints that it may be possible to identify and reduce the main drivers of viability to improve reproductive prospects in men with successfully treated childhood malignancies.
“Our study showed that rat spermatogonial stem cells can be effectively maintained for more than 20 years, transplanted into an infertile recipient animal, and regain the ability to make sperm, albeit at a reduced rate,” continues Whelan.
"This could be a way to restore fertility in prepubertal men undergoing cancer treatment."