Xenotransplantation of cryopreserved human ovarian tissue into murine back muscle

background: Ovarian tissue (OT) cryopreservation and transplantation are options for fertility preservation in young female cancer patients. methods: We investigated xenotransplantation of human OT into back muscle (B) of severe combined immunodeficiency mice. OT follicle content was evaluated by stereomicroscopy and pre-transplantation. Xenograft survival, follicular development (with/without FSH administration), apoptosis and vascularization were compared in B- versus K-site (under the kidney capsule) several times after grafting using histology, immunohistochemistry and magnetic resonance imaging. In vitro maturation (IVM) was also performed. results: Anastomoses which developed from existing human and invading murine vessels were seen in OT at both sites, but angiogenesis was more prominent at the B- than K-site (P , 0.001). Vascularization and follicle size were correlated in the B-group (Spearman’s coefficient 0.73; P , 0.001). FSH increased early (8 days) micro-vessel formation in B but not in K grafts (P , 0.0001, versus no FSH). B-site grafts showed a better histological morphology and survival (P ¼ 0.0084), formation of larger antral follicles (P ¼ 0.005), more metaphase-II (MII) oocytes, growing follicles (P ¼ 0.028) and slightly fewer apoptotic follicles than K grafts. One MI oocyte from B underwent IVM and reached MII stage next day. conclusions: To our knowledge, this is the first report of MII and IVM–MII oocytes obtained from B xenografts. We report the largest oval-shaped antral follicles containing an MII oocyte obtained after OT xenotransplantation to date. Xenografting in the mouse B should be further explored as a method for human OT transplantation.