The first comparative study on the effectiveness of slow freezing and vitrification of human ovarian tissue by xenotransplantation model in Vietnam.

Purpose: To compare the effectiveness of slow freezing (SF) and vitrification (VT) for ovarian tissue cryopreservation using a xenograft model.

Methods: From September 2020 to August 2023, ovarian tissues from patients aged 18 to 37 undergoing benign ovarian surgery were divided into three groups. Group 1: fresh tissues (FC) were immediately fixed for analysis. Group 2 (SF/VT): tissues were cryopreserved by SF or VT without transplantation. Group 3 (SF-T/VT-T): tissues were cryopreserved using SF or VT, followed by transplantation into NOD-SCID mice for one week, after which the tissues were collected and analyzed.

Results: A total of 49 ovarian tissue fragments were analyzed. Regardless of the cryopreservation technique, follicle survival, development, function, and vascularization were significantly reduced compared to the FC group, particularly after transplantation (p < 0.001). The survival rate of follicles in the SF-T group was notably higher (90.9%) than in the VT-T group (82.6%) (p < 0.001). For cell proliferation, indicated by Ki-67 positivity, the SF-T group showed a higher median number of positive follicles (2.5; range: 0-18) compared to the VT-T group (2; range: 0-11) (p = 0.04). Neo-vascularization, assessed via CD31 positivity, was significantly greater in the SF-T group (61%) than in the VT-T group (47%) (p = 0.016). Additionally, the median number of AMH-positive follicles was significantly higher in the SF-T group (3; range: 0-23) compared to the VT-T group (2; range: 0-25) (p = 0.03).

Conclusion: Both SF and VT are feasible methods for ovarian tissue cryopreservation. SF may be the preferred cryopreservation technique for fertility preservation in cases tissue transplantation is anticipated.