AbstractReproduction is an important aspect of human life quality. However, gonadotoxic therapy can disrupt fertility in both cancer patients and patients who need to undergo total bone marrow transplantation for benign diseases. Adult patients can preserve a semen sample before starting therapy, but prepubertal boys do not have this option because complete spermatogenesis is lacking. Therefore, for these young patients, fertility preserving methods are being developed in animal models. These methods involve the cryostorage of SSCs and the transplantation of these stem cells after the patient has been cured. There are two options to retransplant the cryopreserved SSCs: either the introduction of a suspension into the seminiferous tubules or grafting of a testicular tissue piece. For patients who did not have their SSCs cryopreserved before therapy, an alternative option could be the differentiation of adult stem cells, such as BMSCs, after transplantation to the testis. Several centres worldwide have started a cryopreservation program for boys facing gonadotoxic therapy.Within a few years, these patients will return with a request for transplantation.
Currently, it is not clear which of the suggested methods will be the best strategy for restoring
rtility in these patients. Therefore, the general aim of this thesis was to explore the current
options for fertility preservation in prepubertal boys.
In the first part of this study, the best transplantation strategy was determined for patients who
have their SSCs cryopreserved before therapy. The efficiency of the initially reported SSCT
was compared with the more recently reported strategy, i.e. TTG, in a mouse model. In most
previous reports, TTG was performed to an ectopic location, i.e. the back skin. However, we
explored the testis as an alternative transplantation site, since in a clinical application
orthotopic transplantation would be more acceptable for the patient. More donor-derived
spermatogenesis was observed after intratesticular tissue grafting. Moreover, no difference
was found when fresh intratesticular tissue grafting was compared to frozen-thawed
intratesticular tissue grafting. We could conclude that intratesticular tissue grafting is a
promising fertility preserving strategy.
The feasibility of BMSCs to differentiate towards the germline was also evaluated as a
fertility restoration strategy for patients who did not cryopreserve SSCs. Differentiation
towards the germline was not observed after injection of BMSCs into the seminiferous
tubules of the tesis, neither did we observe any protective effect for SSC loss. Currently,BMSCT is thus not an option as fertility preservation strategy. Therefore, cryopreservation of SSCs should be offered to all patients facing gonadotoxic treatment before testicular maturity.
In the second part of this study, the efficiency of human intratesticular xenografting was evaluated. Meiotic activity was observed in human intratesticular xenografts from older as well as younger patients. However, the attempt to improve spermatogonial survival and induce full differentiation by the exogenous administration of FSH failed. The role of apoptosis in the spermatogonial loss, observed in xenografts was explored in the last part of this study. However, spermatogonia-specific apoptosis could not explain this spermatogonial stem cell loss. Therefore, development of the intratesticular graft and the level of global apoptosis during the first days after transplantation were explored. The first days after transplantation seem to be critical. In these first days, the blood supply to the graft needs to be established. It was observed that tubules in the centre of the graft degenerate, possibly due to a lack of blood supply. Significantly increased numbers of apoptotic tubules were observed 1 day after transplantation.
From this study we could conclude that intratesticular tissue grafting seems to be the most efficient fertility preserving strategy. However, this strategy can not be used for patients who are at risk for malignant contamination in their testicular tissue. For these patients SSCT should be performed after decontamination of the cell suspension.
|Date of Award||20 Jun 2012|
|Supervisor||Herman Tournaye (Promotor), Ellen Goossens (Co-promotor), Hilde Van De Velde (Jury), Jean De Schepper (Jury), Johan Smitz (Jury), Dirk De Rooij (Jury), Jan-Bernd Stukenborg (Jury) & Etienne Van Den Abbeel (Jury)|
- Fertility preservation