Follicle proliferation in cryopreserved human ovarian xenotransplants

Objective: To investigate follicle proliferation capability of cryopreserved human ovarian grafts transplanted into the chick embryo chorioallantoic membrane (CAM), in order to better understand early follicle development after ovarian cryopreservation using a low-cost, minimally invasive animal model.

Materials and methods: Forty nine frozen ovarian tissue samples obtained at Universitätklinikum Ulm from two women undergoing laparoscopic surgery to cryopreserve ovarian tissue for fertility preservation purposes were thawed and transplanted on day 5 fertilized eggs from White Leghorn chickens, with and without Follicle Stimulating Hormone (FSH) treatment. The day 10 recovered transplants were assessed for adhesion and groß vascularization by stereoscopic microscopy and for tissue integrity and ischemic injury by histology staining. Vascular integrity, neovascularization and cell proliferation were evaluated by immunohistochemistry against von Willebrand factor, desmin and Ki-67 antibodies. For each sample an ungrafted frozen-thawed control group was included.

Results: All grafts showed good adhesion, with vascular and general histology integrity, independently of the hormonal treatment. The frozen ovarian samples treated with FSH did not present a higher degree of neovascularization/cell proliferation than grafts without hormonal treatment.

Conclusions: The increasing popularity of fertility preservation leads to a greater interest in ovarian cryopreservation. Understanding follicle activation and proliferation after cryopreservation is key to a successful outcome. The results herein reported contribute to this aim by supporting CAM as a good model to study early follicle recruitment/development. They also suggest that FSH does not promote neovascularization and cell proliferation in early stages of ovarian grafting.