Follicular growth after xenotransplantation of cryopreserved/thawed human ovarian tissue in SCID mice: dynamics and molecular aspects

To study the influence of xenotransplantation on follicular recruitment and growth in cryopreserved/thawed human ovarian tissue. Two 3-mm pieces of cryopreserved/thawed human ovarian tissue obtained from female cancer patients (n = 11) were xenotransplanted into a subcutaneous neck pouch of 6-week-old ovarectomized SCID mice (n = 33) for 4 (n = 18) and 12 (n = 15) weeks. Thirty-two out of 33 mice survived the entire observation periods. Graft recovery rate was 95.58 % (65 of 68 grafts). The percentages of primordial follicles after 4 weeks (P < 0.001) and 12 weeks (P = 0.009) of grafting were significantly lower in comparison to pregraft controls. The percentage of secondary follicle was significantly higher after 4 weeks of grafting (P = 0.018) and after 12 weeks (P = 0.001) of grafting in comparison to pregraft controls. Ki67 immunohistochemistry showed that proliferative follicles were significantly higher after 4 and 12 weeks of grafting compared to pregraft controls (P < 0.001). All follicles analyzed by TUNEL staining appeared healthy after xenotransplantation. The expression level of PTEN was reduced by 2.47-fold after 4 weeks of xenotransplantation, and this result was significant when 2(-Delta Ct) were analyzed (P = 0.042). The higher proportion of growing follicles compared to resting follicles observed after xenotransplantation is most likely due to downregulation of PTEN gene expression followed by acceleration of follicular recruitment.