ObjectiveTo determine whether we can safely and successfully transplant an ovary tissue allograft from a non-identical donor to her Turner syndrome sister. DesignTransplantation of cryopreserved ovary tissue, as well as fresh transplantation of ovarian tissue between identical twins, is now well established with numerous reported successful cases. However there have not yet been any ovary transplants between non-identical women requiring immunosuppression (ovary allotransplant). This could be a much more common indication for ovary tissue transplantation if safe and reliable immunosuppression were available. SubjectsA 20 year old amenorrheic woman with non-mosaic 45-XO Turner syndrome requested ovary tissue transplantation from her fertile 22 year old 46-XX sister. They were an HLA match but were ABO incompatible, a well known contra-indication to solid tissue or organ transplantation. The Turner syndrome sister strongly preferred to be able to become pregnant naturally without donor egg IVF, and to avoid HRT (hormone replacement therapy). In her religious group, that would also be important for finding a marital match. Despite the poor prognosis associated with ABO incompatibility, an ovary from her 22 year old non-identical fertile sister was transplanted to her employing the immunosuppression protocol now used for kidney transplant patients in our centers at Washington University and Johns Hopkins. Main Outcome MeasuresPost-operatively at 5 months she developed normal monthly menstrual ovarian function, and she became spontaneously pregnant with a normal baby girl. The relation between her post-op FSH and AMH levels continues to support the theory that tissue pressure controls primordial follicle recruitment. The fact that ABO incompatibility did not prevent success suggests that diffusion and not revascularization may be all that is required for successful long term ovarian cortex transplant survival with spontaneous pregnancy. ResultsOvary allotransplantation with safe immunosuppression allows natural conception, and also normal hormone function obviates the need for HRT. Orthotopic placement of the graft and surgical technique is critical for natural conception and a higher pregnancy rate. ConclusionAllotransplantation requiring safe immunosuppression, if successful, may be a much more commonly used indication for ovary transplantation in the future than frozen ovary grafts or grafts between identical twins.