Re-vascularisation in human ovarian tissue after conventional freezing or vitrification and xenotransplantation

In ovarian tissue grafts there is a massive loss of follicles during the ischaemic period until re-vascularisation is established. The aim of our study was to investigate the influence of different cryopreservation techniques on the ability for the re-vascularisation of ovarian tissue transplanted to SCID mice.

Ovarian fragments from five patients were cut into pieces (approximately 0.5 mm x 1.0 mm x 1.0 mm) and randomly distributed into three groups: fresh non-treated tissue (group A); tissue conventionally frozen in standard 0.5 ml insemination straws with 1.5 M ethylene glycol+0.1 M sucrose, with thawing in a 40 degrees C water bath and step-wise removal of cryoprotectants at room temperature in 0.5 M, 0.25 M and 0.15 M sucrose with gentle agitation (group B); tissue vitrified in 2.62 M dimethylsulphoxide+2.6 M acetamide+1.31 M propylene glycol+0.0075 M polyethylene glycol, with warming by direct plunging of solid specimens with ovarian pieces into 20 ml of 50% vitrification solution pre-warmed to 40 degrees C and dilution of cryoprotectants in a decreasing concentration of vitrification solution (25%, 12.5%) at room temperature (group C). We used a xenograft model in which ovarian tissue pieces of all three groups were subcutaneously transplanted in SCID mice. The animals were sacrificed on the third day after ovarian tissue transplantation and then weekly during 1 month to obtain the ovarian tissue grafts. These samples were examined by immunohistochemical staining with the endothelial cell-specific marker platelet endothelial cell adhesion molecule-1 (PECAM-1) to determine angiogenesis. Histological observation of tissue after explantation was performed and quality and quantity of follicles were assessed.

No PECAM-1 staining was observed in all treatment groups prior to grafting. After warming and in vivo culture of ovarian tissue, the beginning of angiogenesis in pieces from all treatment groups on the third day was detected by PECAM-1 staining. After 4 weeks of in vivo culture the overall area of PECAM-1-positive blood vessels significantly increased (P<0.05), independent of the type of cryopreservation (groups B and C vs. group A). It was found that transplantation technique had negative influence on the integrity of follicles independent of the type of treatment during in vivo culture. The duration of in vivo culture has a negative, but not statistically significant, influence on follicle quality in long-cultured transplants inside each treatment group (P>0.5).

The process of re-vascularisation of transplanted ovarian tissue is independent of the type of treatment and does not influence follicle quality.