Testing The Health And Therapeutic Potential Of In Vitro Derived Oocytes For The Restoration Of Female Fertility And The Treatment of Infertility

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The freezing and banking of very early-staged eggs within ovarian tissue has been successfully used to preserve the fertility of girls and young women who are likely to lose their ovarian function as a result of the destructive effects of cancer treatments. Small pieces of the ovary can be surgically recovered from patients and stored at liquid nitrogen temperatures for as long as required. When the patient wishes to start her family, her stored ovarian tissue is transplanted back into her body with aim of producing fertile oocytes and a pregnancy either naturally or with the help of assisted reproduction technologies such as in vitro fertilisation (IVF). Over 150 babies have now been born worldwide using this technology. However, the transplantation method for fertility restoration is not suitable for all cancer patients. For girls and women with blood diseases such as leukaemia, and/or cancers such as breast cancer there is a risk that the cancer will be restarted from the transplanted tissues. For these patients a safer option is to grow the early staged eggs from the frozen-thawed ovarian tissue to maturity in the laboratory- a technology called the in vitro growth and maturation (IVGM) of eggs. The laboratory grown eggs can then be fertilised using IVF so that healthy embryo(s) can be transferred to the patient to produce the desired pregnancy. These technologies can also be used treat healthy but infertile women who are undergoing assisted conception using donor eggs. The development of methods to grow eggs from their earliest stages in the laboratory is very challenging. Never-the-less advances are being made towards this goal. It is now possible to produce full sized, mature eggs in the laboratory in both humans and ruminant species such as cows and sheep. Two different culture approaches are showing significant promise these are: (i) a fast growth system over 21 days (FasGro); and (ii) a slow growth system over 40-60 days (SloGro). The FasGro and SloGro systems have been developed in parallel for both human and ruminant eggs. However, it is not yet clear which of these methods is best at producing healthy eggs that can be fertilised to produce embryos for future transfer to produce a pregnancy and baby. Before new technologies such as IVGM can be used to restore the fertility of cancer survivors or to treat infertile women it is essential that they are rigorously tested in a suitable animal model to prove they are both safe and effective. This project aims to test the potential of IVGM eggs to used as a treatment to restore fertility in women. Sheep ovary tissues will be used as a mimic for human ovaries. Specifically, the project will grow eggs in the laboratory from frozen-thawed sheep ovary tissues using the FasGro and SloGro methods. The project will test the health of the laboratory-grown eggs and their ability to be fertilised using IVF and to produce embryos that will implant and produce a pregnancy and live offspring. The nutritional and genetic fingerprints of laboratory-derived eggs and embryos will be combined with microscope imaging and used as health screens to confirm whether the IVGM eggs are normal when compared to similar cells grown naturally in the body. An embryo transfer trial will be conducted in sheep to establish which IVGM egg production method is most effective at delivering healthy lambs. Key measurements of health and development will be made in follow-up studies of the newborn offspring from laboratory-grown eggs. Monitoring will continue as the animals grow to adulthood and will be compared to naturally conceived animals. This research is vital to enable selection of the best IVGM method and to ensure that the technology is both efficient and safe before it is used to treat patients.