More than 80% of female cancer patients survive for at least five years after their diagnosis and many live for decades beyond treatment. However, chemotherapy or pelvic radiation can deplete the eggs within a woman’s ovaries and the young women may survive with partial or complete loss of fertility that has ramifications for the rest of their lives.
Researchers at the Oncofertility Consortium work to preserve the fertility of these women, in part, by advancing cryopreservation, or freezing, techniques of eggs, embryos, and ovarian tissue. Cryopreservation of ovarian tissue is further important as it is an important step in developing new fertility preservation techniques, such as in vitro follicle maturation (IVM). IVM is an emerging technique which involves ovarian tissue banking and the later isolation of immature eggs, called follicles, and growth in a laboratory setting. The egg from the fully grown follicle can then be extracted and fertilized with partner or donor sperm and will prove to be a valuable technique for young cancer patients.
The two primary methods for cryopreservation are slow-freezing and vitrification, a fast freezing method. Both of these techniques reduce the formation of ice crystals that may damage tissues during the thawing process. Vitrification, which comes from the Latin term for “glass” is a newer technique that has gained popularity in recent years. A recent article by scientists at Oregon National Primate Research Center, Alison Ting, Richard Yeoman, Maralee Lawson, and Mary Zelinski, compared these two freezing techniques in ovarian tissue from rhesus monkeys.
The publication entitled, “In vitro development of secondary follicles from cryopreserved rhesus macaque ovarian tissue after slow-rate freeze or vitrification,” found that the vitrification technique proved better at maintaining the structure of ovarian follicles (immature eggs) than slow freezing. For the first time in rhesus tissue, follicles from vitrified ovarian tissue were also able survive and grow in a laboratory setting. These follicles expressed markers of cellular proliferation, called phosphohistone H3 (PPH3) and bromodeoxyuridine (BrdU), and produced steroid hormones, indicating that these follicles maintained some functionality.
It is also important to note that follicles from vitrified tissues still had diminished function compared with fresh tissue. Further research will continue to advance technologies, such as cryopreservation, to make in vitro follicle maturation a reality for young cancer patients wishing to preserve their fertility. Some of this research will be discussed at CRYO 2011, the annual meeting for the Society for Cryobiology from July 24th to the 27th, 2011 in Corvallis, OR. Read the full article from the journal Human Reproduction.