I-12: Follicular Loss of Cryopreserved CanineOvary after Xenotransplantation and its Solution

Advances in the diagnosis and treatment of cancer have resulted in a growing population of adolescent and adult long-term survivors of malignancies with infertility problems due to induced premature ovarian failure. Although several options are currently available to preserve fertility in cancer patients, cryopreservation of ovarian tissue is the only option available for prepubertal girls and women in need of immediate chemotherapy. On the other hand, the cryopreservation of ovarian tissues is a potentially significant technology for the preservation of the genetic resources of working dogs as well as other target animals. However, it has been reported that a large proportion of follicles are lost during the initial ischemia which occurs after transplantation of mouse, sheep and human ovaries. In addition, we have shown that the effect of cryopreservation and subsequent xenotransplantation on the follicular reserve of the canine ovary by using NOD-SCID mice. When vitrified-warmed canine ovarian tissues were placed into the ovarian bursa, and then were removed and subjected to histological examination at 4 weeks after the transplantation, over 30% of primordial follicles and 65% of early primary follicles survived after cryopreservation. However, regardless of breed or age, percentages of survived primordial follicles and early primary follicles after the transplantation ranged from 0-7% and from 0-15%, respectively. These results indicate that the majority of primordial follicles and early primary follicles in vitrified-warmed canine ovarian tissues disappear after xenotransplantation. Thus, the main drawback of ovarian cryopreservation followed by transplantation is that a large proportion of follicles are lost after transplantation. Several attempts have been made to prevent or at least decrease the follicular loss of cryopreserved ovarian tissues after transplantation. However, an effective solution has not been found to date. It has been reported that functional vessels within the graft were detected when rat ovaries were transplanted into the muscles of castrated nude mice. Treatment with vitamin E improved the survival of follicles in ovarian grafts. More recently, we have shown that the administration of asialo EPO was effective for enhancing the survival of transplanted cryopreserved ovarian follicles. The increasing number of early primary follicles in the frozen-thawed ovarian tissues treated with asialo EPO indicates a growth promoting effect of asialo EPO for primordial follicles. In addition, positive effect of hyperbaric oxygen therapy on the follicular reserve of ovarian tissues after transplantation was founded.