Fertility preservation in male childhood cancer

Prevention of sterility has become an important issue in reproductive medicine. For adult men, sterility after cancer treatment can be circumvented by banking sperm samples. For pre-pubertal patients, however, this is not an option, since spermatogenesis has not yet started.
Like every other adult stem cell in the human body, spermatogonial stem cells (SSCs) have the capacity to either renew themselves or to start differentiation, i.e. spermatogenesis. Due to these properties, several options for preservation and re-establishment of the spermatogenic process exist.
Currently, spermatogonial stem cell transplantation (SSCT) is considered the most promising tool for fertility restoration in pre-pubertal cancer patients. In these patients, testicular tissue could be removed and cryopreserved before starting any cancer treatment. When the boy is cured, SSCT can be applied for fertility restoration. However, before such an application can be applied, both the safety and the efficiency of the procedure have to be assured. In the mouse, we have shown that sperm obtained after SSCT were able to fertilize and produce offspring in-vivo without causing genetic anomalies or epigenetic alterations.
The efficiency of SSCT depends on the number of SSCs injected in the recipient's tubules. Since only the SSCs can relocate to the basement membrane and initiate colonization, enriching the proportion of SSCs may improve tranplantation efficiency.
Although, SSCT could prove important for fertility preservation, this technique may not be without any risk. Testicular cell suspensions from cancer patients may be contaminated with cancerous cells. It is obvious that reintroduction of malignant cells into an otherwise cured patient must be omitted. Magnetic activated cell sorting and fluorescence activated cell sorting are two strategies that can be used to decontaminate the cell suspension from malignant cells or to enrich the cell suspension for SSCs.
Intratesticular grafting is another method to preserve fertility. Pre-pubertal murine tissue could be grafted successfully, with spermatogenesis observed in almost all the grafts, but adult murine and adult human grafts were lost because of sclerosis or atrophy. Intratesticular xenografting of human pre-pubertal tissue has recently led to the first report describing differentiation up to the level of secondary spermatocytes.
When SSCT becomes available for clinical use, efficient protocols for the cryopreservation of testicular tissue will be of great benefit. By using a non-controlled freezing protocol, the structure and the function of murine prepubertal tissue could be well preserved. Similar experiments using human prepubertal tissue are ongoing.