The evaluation of xenotransplantation of feline ovarian tissue vitrified by needle immersed vitrification technique into male immunodeficient mice

In this study, the efficiency of the “Needle Immersed Vitrification” technique was tested on cryopreserved feline ovarian tissue. For vitrification, ovarian fragments (0.5–1.5 mm²) from each ovary were collected; the grafts were exposed to 7.5–15% ethylene glycol and 7.5–15% dimethyl sulfoxide at room temperature and stored in liquid nitrogen at least 1 week. Morphologic examinations, expression of genes such as B cell lymphoma 2, B-cell lymphoma-2-associated X protein, Bone morphogenetic protein 15, zone of polarizing activity, zona pellucida C protein and DNA (cytosine-5)-methyltransferase 1, ultrastructural analysis and viability tests were carried out from collected grafts. Light microscopy examinations revealed the percentage of morphologically normal primordial follicles in a fresh group which was significantly higher than the treatment groups (p < 0.001). Terminal deoxynucleotidyl transferase dUTP nick end labeling and anti-caspase-3 staining observed in oocytes, follicle cells, interstitial tissue showed higher rates of apoptosis for post-vitrification and -transplantation groups than freshly grafted ovarian tissues. Furthermore, we observed significant downregulation of zone of polarizing activity and zona pellucida C protein gene expression in vitrified ovarian tissue grafts than in the fresh grafts (p < 0.05). In conclusion, we suggest that the needle immersed vitrification method is a convenient, cheap, and feasible vitrification method for cat ovarian tissues. However, further studies need to be performed to determine more optimal vitrification solutions and equilibration times for the needle immersed vitrification method in order to adapt it for cat ovaries.