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Spermatogonial stem cells. An update on spermatogonial stem cell banking and transplantation
Tijdschriftbijdrage - Tijdschriftartikel
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.
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. 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 and after assisted reproduction. However, it was also observed that fertilizing potential was lower with transplanted males compared to control mice. Moreover, the litter sizes were smaller and the fetal length and weight were significantly lower in the first-generation offspring from transplanted animals, whereas subsequent generations did not show those abnormalities. This observation may be suggestive for imprinting disorders. 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 Fluoresence 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.
Xenogeneic transplantation and xenografting are two other hypothetical methods to preserve fertility. Until now, human spermatogonial stem cells are reported only to survive in the murine testis and differentiation to spermatozoa has not yet been observed. 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. Although xenografting of human pre-pubertal tissue may be within reach, xenogeneic transplantation and xenografting should not be used in a clinical application because of the ethical and biological concerns inherent to these approaches. These techniques could however be useful to test the risk of malignant contamination of the testicular tissue.
When SSCT becomes available for clinical use, efficient protocols for the cryopreservation of SSCs and testicular tissue will be of great benefit. By using a non-controlled freezing protocol, the survival rate of SSCs was higher compared with other testicular cells, which resulted in an enrichment of SSCs in the final suspension, but an important loss of functionality of spermatogonial stem cells was found after freezing and thawing. An alternative way to preserve SSCs is to freeze the whole testicular tissue instead of cell suspensions. The structure of the tissue can be well preserved and especially the spermatogonia survive.
An alternative to cryopreservation could be in-vitro culture of SSCs. This approach may be applied to generate spermatozoa in-vitro from cultured spermatogonial stem cells, which, in turn, could be used for intracytoplasmic sperm injection. Recently, it was reported that mouse SSCs could be expanded in-vitro with maintenance of functionality. When this approach would be feasible with human SSCs, it may improve the efficiency of cryopreservation, either by increasing the number of SSCs before freezing or after thawing. Since mouse SSCs can be cultured over long time periods, long-term in-vitro culture may even become an alternative to cryostorage.
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. 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 and after assisted reproduction. However, it was also observed that fertilizing potential was lower with transplanted males compared to control mice. Moreover, the litter sizes were smaller and the fetal length and weight were significantly lower in the first-generation offspring from transplanted animals, whereas subsequent generations did not show those abnormalities. This observation may be suggestive for imprinting disorders. 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 Fluoresence 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.
Xenogeneic transplantation and xenografting are two other hypothetical methods to preserve fertility. Until now, human spermatogonial stem cells are reported only to survive in the murine testis and differentiation to spermatozoa has not yet been observed. 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. Although xenografting of human pre-pubertal tissue may be within reach, xenogeneic transplantation and xenografting should not be used in a clinical application because of the ethical and biological concerns inherent to these approaches. These techniques could however be useful to test the risk of malignant contamination of the testicular tissue.
When SSCT becomes available for clinical use, efficient protocols for the cryopreservation of SSCs and testicular tissue will be of great benefit. By using a non-controlled freezing protocol, the survival rate of SSCs was higher compared with other testicular cells, which resulted in an enrichment of SSCs in the final suspension, but an important loss of functionality of spermatogonial stem cells was found after freezing and thawing. An alternative way to preserve SSCs is to freeze the whole testicular tissue instead of cell suspensions. The structure of the tissue can be well preserved and especially the spermatogonia survive.
An alternative to cryopreservation could be in-vitro culture of SSCs. This approach may be applied to generate spermatozoa in-vitro from cultured spermatogonial stem cells, which, in turn, could be used for intracytoplasmic sperm injection. Recently, it was reported that mouse SSCs could be expanded in-vitro with maintenance of functionality. When this approach would be feasible with human SSCs, it may improve the efficiency of cryopreservation, either by increasing the number of SSCs before freezing or after thawing. Since mouse SSCs can be cultured over long time periods, long-term in-vitro culture may even become an alternative to cryostorage.
Tijdschrift: Journal of Internal Medicine
ISSN: 0954-6820
Issue: 16
Volume: 15
Pagina's: 22-24
Jaar van publicatie:2008
Trefwoorden:spermatogonia, stamceltransplantatie, fertility