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Novel Methods for Cryopreservation and Recovery of Female Follicles*
Site: University of Missouri
Principal Investigator: John K. Critser, PhD
Rationale
The American Cancer Society estimates that the likelihood of developing cancer in women under the age of 40 is 1 in 50; however, the overall cancer survival rate is approximately 80%, partly due to effective therapies. A large proportion of the future adult population will be cancer survivors, a prediction that has generated a significant desire for improvements in the quality of life after cancer. Namely, there is a need for the development of effective means to preserve the fertility of individuals before they undergo cancer treatments such as radiation therapy or chemotherapy.
While fertility preservation for males has been available for several decades using sperm cryopreservation, attempts to similarly preserve mature female oocytes have, in general, been disappointing. Oocyte freezing can be a physically damaging process, with the potential to irreversibly disrupt the 3-dimensional structure of the follicle necessary for the development of a fully viable mature oocyte.
Cryobiology is an interdisciplinary science that studies the physical and biological behaviors of cells and tissues at temperatures below the freezing point of water. The role of the cryobiologist working within the Oncofertility Consortium is to develop improved methods for cryopreserving oocytes, immature follicles, and ovarian tissue. It is critical to reveal the underlying barriers to the tolerance of oocytes to changes in temperature and various cryoprotective agents. New methods of cryopreservation will be evaluated in the rhesus monkey, with experimental endpoints including successful in vitro maturation of follicles, fertilization of resulting mature oocytes, and embryo development. The findings will be rapidly applied to the cryopreservation of human ovarian tissue in order to expand fertility preservation options for women at the time of diagnosis of cancer and other serious diseases.
The objectives of this project are to:
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Develop and test an optimized method for cryopreserving in vitro matured rhesus oocytes
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Develop and test an optimized method for cryopreserving immature follicles from rhesus ovaries
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Develop and test an optimized method for cryopreserving rhesus ovarian tissue
Key Experiments
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Determine the chilling sensitivity, osmotic tolerance, plasma membrane permeability to water and various cryoprotectants, and toxicity of cryoprotectants of rhesus in vitro matured oocytes to develop an optimized 3-step freezing method that is superior to current slow-cooling and vitrification procedures
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Determine the chilling sensitivity, osmotic tolerance, plasma membrane permeability of granulosa cells to water and various cryoprotectants, and toxicity of cryoprotectants to develop optimal methods for slow-cooling, 3-step freezing, and vitrification of rhesus immature follicles
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Compare the viability of rhesus ovarian cortical strips after applying optimized methods for slow-cooling, 3-step freezing and vitrification procedures
Consortium Support and Impact
The successful execution of this project and eventual application of preservation technology will require close collaboration with other members of the Oncofertility Consortium. Specifically, the project requires close cooperation with the team working to improve methods to mature primate follicles in vitro and the Biomaterials Core. In addition, a primary goal of the National Physicians Cooperative is to ultimately translate the results of these studies to the preservation of human oocytes and follicles. While the human application of methods to cryopreserve and recover ovarian tissue will fill a significant need in fertility preservation in women, it is also expected to lead to new social, legal, and ethical concerns that will impact how patients and physicians discuss infertility (see Social Science and Oncofertility), particularly with regard to pediatric cancer patients. Education of patients and physicians and training of oncofertility specialists also be necessary to ensure that cutting-edge procedures associated with follicle removal and storage become part of routine cancer care worldwide.
