Abstract: Objective To observe the angiogenesis in the human fetal ovarian grafts one month after heterotransplantation. Methods Ovaries from 3 inevitable abortion human fetuses 22 gestational weeks of age were frozen- thawed, xenografted into the immunodeficient nu/nu mice(EM>n/EM>=18), and recovered on 2, 7, and 28 days after transplantation respectively. These grafts, together with the fresh and the frozen-thawed ovarian tissue were examined for blood vessels by immunolocalization of CD34, ultrastructure, and detection of the mRNA expression of vascular endothelial growth factor (VEGF)， Angiopientin2(Ang-2). The untransplanted tissues of the fresh and the frozenthawed ovarian were investigated exactly the same as the grafts. Results The density of the microvessel was significantly increased in the grafts on day 2, peaked on day 7, and slightly reduced on day 28, together with distended microlvessel on day 2 which turned to normal on day 7 under the light Microscope. Transmission electron microscope (TEM) showed the majority primordial follicles were well preserved. The grafts of day 2 showed some edema in stroma and vessels filled with red blood cells. As they disappeared, the microvessel was growing in the counterparts on day 7 and day 28. The mRNA levels of VEGF and Ang-2 showed the similar temporary rising on day 2 and decreasing since. Conclusion The angiogenesis of the frozen-thawed ovarian tissue from human fetus completed within one month after transplantation. The first week after transplantation was the critical time to achieve prolonged graft functionality and increased the yield

Key words: Ovary, Frozen-thawed, Xenotransplant, Angiogenesis, RT-PCR, Fetus, Human