Effects of pre-transplant estradiol treatment on ovarian reserve preservation and endocrine recovery in xenotransplanted human ovarian tissue

Abstract Background Early follicle loss caused by ischemic–hypoxic injury limits the efficacy of ovarian tissue transplantation. Estradiol acts directly on vascular endothelial cells, but whether recipient estradiol conditioning before transplantation improves graft adaptation and ovarian reserve preservation remains unknown. We evaluated pre-transplant estradiol priming and compared it with continuous treatment following human ovarian tissue xenotransplantation. Methods Eighty bilaterally ovariectomized female BALB/c nude mice were randomized to pre-transplant estradiol priming (Pre-ERT), continuous estradiol treatment (C-ERT), no estradiol treatment (No-ERT), or non-grafted ovariectomized control groups (n = 20 each). Frozen–thawed human ovarian cortical tissue was xenografted beneath the renal capsule in the three transplantation groups. A 0.72-mg 17β-estradiol slow-release pellet was implanted 7 days before transplantation and removed at transplantation in Pre-ERT or retained until graft retrieval in C-ERT. Blood and grafts were collected on post-transplantation Days 7 and 21 (n = 10/group/time point). Serum estradiol (E2), human anti-Müllerian hormone (AMH), and follicle-stimulating hormone (FSH) were measured. Follicle counts were assessed histologically, microvessel density by CD31 immunofluorescence, proliferative activity by Ki-67 immunofluorescence, and DNA fragmentation by TUNEL assay. Results At Day 7, both estradiol-treated groups had lower serum FSH and higher E2 and human AMH than No-ERT (all P < 0.05). At Day 21, E2 and human AMH remained higher in both estradiol-treated groups than in No-ERT (all P < 0.05). At both time points, Pre-ERT and C-ERT showed higher total and primordial follicle counts, greater CD31-positive MVD, higher Ki-67 positivity, and lower TUNEL positivity than No-ERT (all P < 0.05). At Day 21, growing follicle counts were higher in C-ERT than in No-ERT. No tissue-level outcome differed significantly between Pre-ERT and C-ERT. Conclusions Pre-transplant estradiol priming improved primordial follicle preservation and supported endocrine recovery following human ovarian tissue xenotransplantation. The accompanying changes in microvascular density, Ki-67 positivity, and TUNEL-detected DNA fragmentation were consistent with improved early graft adaptation. Continuous treatment provided no statistically detectable additional tissue-level benefit over pre-transplant priming during the 21-day observation period.