In 2005, approximately 4% of cancer patients were under the age of 35 in the United States (seer.cancer.gov). With the remarkable advances in cancer therapy, survival is a realistic outcome for many (seer.cancer.gov) and the importance of minimizing off-target effects of therapy has come to the forefront in patient management. Treatment modalities such as chemotherapy and radiotherapy can have a profound and irreversible impact on fertility. As our therapies improve, an increasing number of young cancer patients survive, leading to important questions about the quality of life of the long term survivors. Preservation of reproductive ability is becoming one of the most important of these quality of life issues. The most widely used strategies to preserve fertility in young men about to undergo cancer therapy are to reduce the toxicity of the cancer therapies and cryopreservation of gametes for future assisted reproductive technology. Unfortunately, pre-pubertal boys do not produce mature sperm, so we do not have the option to cryopreserve sperm for this group. We have limited knowledge about the effects of cancer therapy on male fertility. In particular, our knowledge about the effects on pre-pubertal boys is very rudimentary. Virtually all of the laboratory work has used animal models to study the effects of cancer therapy on fertility. There are obvious pitfalls in extrapolating data from animal studies to human testis. In addition, studies on animal models have concentrated on the effects of chemotherapy on mature adult testis. In our laboratory, we have developed a unique human pre-pubertal testis model using human fetal testis transplanted into mice. The transplanted fetal testis survives and develops to become histologically very similar to pre-pubertal testis. This model provides us with the opportunity to directly study the effects of chemotherapeutic agents on pre-pubertal human testes. For the first part of the study, we will administer different concentrations of the commonly used chemotherapy agent, cyclophosphamide, to the mice with the testis transplant to study the effects of this chemotherapy on human pre-pubertal testis. The second part of our project is to induce spermatogenesis in our human testis xenotransplantation model with gonadotropin stimulation. The initiation of puberty involves a series of complex endocrine events culminating in an increase in gonadotropins and the subsequent induction of spermatogenesis. In men with low/absent gonadotropins, such as in Kallman's syndrome, have pre-pubertal testis;exogenous gonadotropins can successfully induce spermatogenesis. In this project, we intend to use a similar strategy by using exogenous gonadotropins to stimulate spermatogenesis in our human testis xenotransplantation model. If successful, this will be the first report of human germ cell maturation outside the human body. The major strength of this project is our established human fetal testis xenotransplantation model. This model is a unique and powerful system which allows us to directly probe the effects of cancer therapies on pre- pubertal testis and begin to understand how toxicity may be reduced or prevented. We also propose to use different strategies to induce spermatogenesis in this human testis model to produce a mature human testis model. This would again be an extremely powerful system for any studies on reproductive toxicology, but would also give us insights into techniques to mature pre-pubertal testis, information which will be critical to the fertility preservation of pre-pubertal boys having cancer therapy.
Our goals for this project are twofold: (1) Validate our human testis xenotransplantation model as a useful tool to study the toxic effect(s) of commonly used cancer chemotherapeutic agents on human testis and (2) hormonally stimulate per-pubertal human testis to develop towards mature sperm in our robust xenotransplantation model. If successful, we will have a direct method to evaluate the impact of any gonadotoxic agent, explore opportunities to minimize their harmful effects on human fertility, and develop the first human-mouse xenotransplant system to restore fertility in the human pre-pubescent population. vcolin 14 October 2009