Xenotransplantation of cryopreserved ovarian tissue: A realistic option for restoring fertility after cancer treatment?

Background: Xenografting of human ovarian tissue into mice has proved to be a useful model for examining ovarian function and follicle development in vivo. Moreover, with human follicles that have matured through xenografting, the possibility of cancer transmission and relapse can be eliminated, as cancer cells are not able to penetrate the zona pellucida. However it is speculated that ovarian xenotransplantation could be used for the production of fertilisable oocytes.

Method: Cryopreserved human ovarian tissue from patients with different malignance was grafted into an intramuscular pocket of the neck muscle of oophorectomized SCID mice. Follicle growth was monitored with palpation.

Results: Growing follicles were palpated in three mice during the grafting period. Two of the three mice received human chorionic gonadotropin. One metaphase II oocyte was retrieved as well as one germinal vesicle stage, which matured to an MII oocyte following culture in an in vitro maturation medium. In one mouse a MII oocyte was directly recovered without HCG administration 20 weeks after transplantation. All oocytes had morphologically a healthy appearance.

Conclusion: Maturation of oocytes in a xenograft is a technically possible option for restoring fertility that would avoid the risk of dispersal of malignant cells. Although it is not known if the so developed oocytes are competent for fertilization yet and some ethical questions are still unanswered, the xenotransplantation may be a promising method of oocyte maturation for use in human reproduction especially for cancer patients where the retransplantation of the tissue into the patient is not possible.