P-450 Mechanical injury improves follicle survival in xenotransplanted human ovarian cortex
Authors: Olesen H.Ø , Pors S.E , Adrados C.S , Zeuthen M.C , Mamsen L.S , Kristensen S.G 
Published: June 2022

Abstract

Study question
Can mechanical injury by needle puncturing of frozen thawed human ovarian cortex tissue prior to transplantation increase revascularization of xenografts and improve follicle survival?

Summary answer
Mechanical injury caused by needle puncture prior to transplantation improved follicle survival 2-fold in human ovarian cortex tissue after 4 weeks xenografting.

What is known already
Cryopreservation and autotransplantation of ovarian tissue is an established fertility preservation method which has resulted in numerous live births worldwide. However, the efficiency of the method is hampered by a critical follicle loss after transplantation. Faster revascularization of the transplanted graft would shorten the ischemic period and could potentially improve follicle survival. Controlled tissue damage by laser or needles can induce local angiogenesis by initiating the wound healing mechanisms and has been applied clinically in cardiovascular surgery for decades. Whether controlled mechanical tissue damage could be used to improve grafting of human ovarian cortex tissue has not yet been investigated.

Study design, size, duration
A total of 32 frozen-thawed human ovarian cortex pieces were cut in halves; one half serving as the untreated control and the other half was punctured approximately 200 times with a 29G needle immediately after thawing. The cortical pieces were transplanted subcutaneously to 10 immunodeficient mice. Ovarian grafts were retrieved after 3, 6 and 10 days (n = 8) to analyse graft revascularization and gene expression, and after 4 weeks to assess follicle density (n = 8).

Participants/materials, setting, methods
Ovarian cortex was donated by 16 women (aged 24-36 years) undergoing ovarian tissue cryopreservation for fertility preservation at a University Hospital. Gene expression analysis of proinflammatory cytokines (Tnf-α), apoptotic factors (Bcl2 and Bax), and angiogenic factors (Vegfa, Angptl4, Ang1, and Ang2) were performed by qPCR. Follicle density after 4 weeks xenografting were evaluated histologically. Graft-revascularization was assessed using immunohistochemical detection of murine Cd31.

Main results and the role of chance
Our results showed that the ovarian grafts which had been punctured with needles prior to transplantation contained a larger number of surviving follicles per mm3 compared to the untreated control (control group: 2.9 ± 0.6 (mean±SEM) follicles/mm3; needle group: 6.4 ± 2.4 follicles/mm3). Follicle densities between patients and groups varied from 0.8 to 26 follicles/mm3. Overall, a 2.3-fold increase in follicle density was found in the needle group compared to control, though this finding was not significantly different (p-value = 0.1182). The relative gene expression of Tnf-α and the Bax/Bcl2 ratio after 6 days grafting was similar in the needle and control group, indicating that the mechanical injury did not induce an additional inflammatory or apoptotic response in the grafts. The relative gene expression of Vegf, Angptl4, and Ang2 after 6 days grafting was highest in the needle group compared to the control group, though not significant (p&gt;0.1). Results of the gene expression analysis from Day 3 and 10 are awaited, and so are the quantification of the Cd31 positive vessel area and vascular density from Day 3, 6, and 10, which will provide valuable insight into the initial graft revascularization.

Limitations, reasons for caution
The ovarian follicles are highly heterogeneously distributed in the ovarian cortex and can vary 100-fold between cortex pieces from the same woman and between patients. A high variability in follicle density within and between treatment groups and patients was found in the current study. Thus, solid conclusions cannot be made.

Wider implications of the findings
Our findings suggest a positive effect of mechanical injury on human ovarian grafts as needle puncturing prior to transplantation improved follicle survival after xenotransplantation. Clinically, this technique would be easy to implement since it is performed during the thawing process and does not involve any additional treatment of the patient.

Trial registration number
Not applicable