Purpose: Currently, open systems are mainly used for cryopreservation of ovarian tissue, oocytes, and embryos, but there is a potential risk of contamination. This study was performed to assess ovarian tissue cryopreservation by a closed vitrification system (Rapid-i vitrification system™), which is already used clinically for oocyte/embryo cryopreservation.
Methods: Ovaries of C57BL/6J mice were frozen and thawed by using the Rapid-i vitrification system™ (Rapid-i) followed by implantation into recipient mice. Hematoxylin-eosin staining was performed for histological examination of the frozen-thawed ovaries to assess follicle grade. Fertility after implantation of the ovaries was assessed from the live birth rate and the number of live pups.
Results: There was no significant difference in grade 1 primary follicles between fresh ovaries (control group, 94.2 ± 2.9%) and frozen-thawed ovaries (Rapid-i group, 87.1 ± 1.8%). However, there was a significant decrease in grade 1 early and late secondary follicles in the Rapid-i group compared with the control group. The live-birth rate was significantly lower in the Rapid-i group compared with the control group (29.2 vs. 83.3%, p < 0.05). On the other hand, there was no significant difference in the average number of live pups between the control group and the Rapid-i group (3 ± 0.4 vs. 2.7 ± 0.3).
Conclusions: The Rapid-i seems to be effective for cryopreservation of mouse ovarian tissue. Under appropriate conditions, the Rapid-i could be employed for ovarian tissue cryopreservation and preservation of fertility in humans.
Keywords: Closed system; Fertility preservation; Ovarian tissue cryopreservation; Slow freezing; Vitrification.