Long-term ovarian function in sheep after ovariectomy and transplantation of autografts stored at -196 C

Modeling the extension of ovarian function after therapeutic targeting of the primordial follicle reserve

BACKGROUND

Women are increasingly choosing to delay childbirth, and those with low ovarian reserves indicative of primary ovarian insufficiency are at risk for sub- and infertility and also the early onset of menopause. Experimental strategies that promise to extend the duration of ovarian function in women are currently being developed. One strategy is to slow the rate of loss of existing primordial follicles (PFs), and a second is to increase, or 'boost', the number of autologous PFs in the human ovary. In both cases, the duration of ovarian function would be expected to be lengthened, and menopause would be delayed. This might be accompanied by an extended production of mature oocytes of sufficient quality to extend the fertile lifespan.

OBJECTIVE AND RATIONALE

In this work, we consider how slowing physiological ovarian aging might improve the health and well-being of patients, and summarize the current state-of-the-art of approaches being developed. We then use mathematical modeling to determine how interventions are likely to influence the duration of ovarian function quantitatively. Finally, we consider efficacy benchmarks that should be achieved so that individuals will benefit, and propose criteria that could be used to monitor ongoing efficacy in different patients as these strategies are being validated.

SEARCH METHODS

Current methods to estimate the size of the ovarian reserve and its relationship to the timing of the menopausal transition and menopause were compiled, and publications establishing methods designed to slow loss of the ovarian reserve or to deliver additional ovarian PFs to patients were identified.

OUTCOMES

We review our current understanding of the consequences of reproductive aging in women, and compare different approaches that may extend ovarian function in women at risk for POI. We also provide modeling of primordial reserve decay in the presence of therapies that slow PF loss or boost PF numbers. An interactive online tool is provided that estimates how different interventions would impact the duration of ovarian function across the natural population. Modeling output shows that treatments that slow PF loss would need to be applied as early as possible and for many years to achieve significant delay of menopause. In contrast, treatments that add additional PFs should occur as late as possible relative to the onset of menopause. Combined approaches slowing ovarian reserve loss while also boosting numbers of (new) PFs would likely offer some additional benefits in delaying menopause.

WIDER IMPLICATIONS

Extending ovarian function, and perhaps the fertile lifespan, is on the horizon for at least some patients. Modeling ovarian aging with and without such interventions complements and helps guide the clinical approaches that will achieve this goal.

REGISTRATION NUMBER

Not applicable.

Treatment with trypLE before freezing improves thawing integrity and functionality of sheep ovarian tissue

OBJECTIVE

To study innovative approaches to ovarian tissue cryopreservation, a critical issue for fertility preservation in pediatric cancer patients. Despite historical attempts, recent advances in cancer treatment have underscored the urgent need for more effective and reliable ovarian tissue cryopreservation methods. Our research aims to evaluate if decreasing the rigidity of stroma before cryopreservation by investigating pre-treatments with enzymes can enhance the quality of ovarian tissue post-thawing.

DESIGN

Our research evaluated the use of five commonly used enzymes to disaggregate tissue (trypLE, collagenase, dispase, accutase and hyaluronidase) before freezing ovarian tissue to decrease rigidity and facilitate cryopreservation. Sheep ovaries, with high similarity to human ovaries, were used as an animal model. Tissue structure, cell proliferation, apoptosis and viability were assessed before and after thawing.

RESULTS

Our findings showed that enzymatic treatment with trypLE before freezing offered immediate benefits post-thawing with the highest viability values and percentage of intact follicles. A decrease in viability was observed after thawing and culturing the samples. The pretreatment with accutase damaged the tissue severely with also the lowest viability values. Ki67-positive follicles and stromal cells were observed in fresh samples, but only trypLE and hyaluronidase maintained Ki67-positive antral follicles after 2 days culture. Besides, only trypLE maintained all follicles negative to caspase-3 after thawing, and 7 days after culture primordial follicles were apoptotic in all treatments apart from trypLE.

CONCLUSION

our findings suggest that trypLE pretreatment could provide a beneficial approach for maintaining the functions and viability of cryopreserved ovaries after thawing. Further research is needed to fully understand their impact and optimize cryopreservation protocols in this important clinical context.

Ultrasound-based geometric modeling of the human ovary with applications to cryopreservation

Successful cryopreservation of the whole ovary outside of the body, while a woman undergoes cancer treatments, may help preserving fertility and regaining hormone balance during recovery. One of the key challenges in whole ovary cryopreservation is adequately loading the organ with cryoprotective agents (CPAs). Another notable challenge in developing the application is the lack of geometric data needed for designing matching thermal protocols. The objective of the current study is twofold: (i) to develop an effective geometric reconstruction method for the ovary, based on transvaginal ultrasound (TVUS) data, and (ii) to perform a pilot study on the thermal effects associated with CPA loading with application to vitrification. This study includes screening of 127 TVUS imaging datasets of ovaries from healthy ovulatory participants, reconstruction of 14 geometric models, and thermally analyzing two representative geometric models of low and high mature follicles-to-organ volume ratios. Results of this study demonstrate that the proposed reconstruction method is faster and more accurate than that facilitated by commercially available software (SonoAVC, GE Healthcare). Two extremes were investigated: (1) complete vitrification of the ovary, and (2) crystallization of mature follicles while the remaining ovarian stroma vitrifies. CPA loading into the mature follicles is considered an outstanding cryopreservation challenge, but with very little impact on long-term fertility preservation. Results of this study suggest that ovarian preservation by vitrification is feasible when sufficient CPA loading is achieved, while identifying the most suitable CPA for the task remains a challenge beyond the scope of the current study.

Human ovarian tissue xenotransplantation: advancements, challenges, and future perspectives

Ovarian tissue cryopreservation and transplantation has emerged as a promising fertility preservation technique for individuals facing premature ovarian insufficiency due to various medical conditions or treatments. Xenotransplantation, involving the transplantation of ovarian tissue into animal hosts, has played a pivotal role in refining ovarian tissue cryopreservation and transplantation techniques and addressing key challenges. This review provides a comprehensive overview of the current landscape of ovarian tissue xenotransplantation research, focusing on its applications in investigating ovarian biology, optimizing ovarian tissue cryopreservation and transplantation protocols, and assessing safety concerns. It also explores the utilization of xenografting of human ovarian tissue in mouse models in the last 10 years. Key findings from preclinical studies investigating grafting site optimization, cryopreservation protocol refinement, the development of strategies to mitigate chemotherapy-induced damage, follicle development, tissue revascularization, and the risk of malignant cell reintroduction are summarized. Moreover, the review examines the ethical considerations surrounding the use of animals in ovarian tissue xenotransplantation research and suggests emerging alternative models that aim to minimize animal use while maximizing clinical relevance.

Exploring the effect of platelet-rich plasma on vascularization and survival of follicles in xenotransplanted human ovarian tissue

RESEARCH QUESTION

Do platelet-rich plasma (PRP) products, specifically human platelet lysate (hPL) and umbilical cord plasma, enhance vascularization and follicular survival in human ovarian tissue transplanted to immunodeficient mice?

DESIGN

Human ovarian tissue was transplanted to subcutaneous pockets in nude mice, followed by daily injections for 6 days of PRP or saline at the transplantation sites. After a grafting period of 3 and 6 days, vascularization was assessed using CD-31 quantification, and gene expression of angiogenic markers (VEGF/Vegf) together with apoptosis-related genes (BAX/BCL-2), oxidative stress markers (HMOX-1/Hmox-1) and pro-inflammatory markers (Il-1β/Il-6/Tnf-α) was quantitively analysed. Follicle density was analysed in the grafts after 4 weeks. Additionally, a pilot study was conducted exploring the suitability of ultrasound scanning for assessing survival and vascularization in ovarian tissue xenografted to mice.

RESULTS

Although there was a significant increase in the CD-31 area from day 3 to day 6 post-grafting, there were no significant differences between the hPL and control groups. Gene expression analysis revealed significant down-regulation of VEGF from day 3 to day 6 for both the hPL and control groups, and significant up-regulation of BAX/BCL-2 in the hPL group compared with the controls. The follicle density showed no significant differences in the hPL group and UCP groups compared with the controls. Furthermore, ultrasound biomicroscopy provided valuable insights into graft morphology, necrotic areas and blood flow, suggesting its potential as a monitoring tool.

CONCLUSIONS

Despite the angiogenic properties of PRP, this study was unable to demonstrate a significant impact of hPL on vascularization or of hPL and UCP on follicular survival in xenotransplanted human ovarian tissue.

Prospective solutions to ovarian reserve damage during the ovarian tissue cryopreservation and transplantation procedure

Birth rates continue to decline as more women experience fertility issues. Assisted reproductive technologies are available for patients seeking fertility treatment, including cryopreservation techniques. Cryopreservation can be performed on gametes, embryos, or gonadal tissue and can be used for patients who desire to delay in vitro fertilization treatment. This review focuses on ovarian tissue cryopreservation, the freezing of ovarian cortex containing immature follicles. Ovarian tissue cryopreservation is the only available treatment for the restoration of ovarian function in patients who undergo gonadotoxic treatments, and its wide adoption has led to its recent designation as "no longer experimental" by the American Society for Reproductive Medicine. Ovarian tissue cryopreservation and subsequent transplantation can restore native endocrine function and can support the possibility of pregnancy and live birth for the patient. Importantly, there are multiple steps in the procedure that put the ovarian reserve at risk of damage. The graft is highly susceptible to ischemic reperfusion injury and mass primordial follicle growth activation, resulting in a "burnout" phenomenon. In this review, we summarize current efforts to combat the loss of primordial follicles in grafts through improvements in freeze and thaw protocols, transplantation techniques, and pharmacologic adjuvant treatments. We conducted a review of the literature, with emphasis on emergent research in the last 5 years. Regarding freeze and thaw protocols, we discuss the widely accepted slow freezing approach and newer vitrification protocols. Discussion of improved transplantation techniques includes consideration of the transplantation location of the ovarian tissue and the importance of graft sites in promoting neovascularization. Finally, we discuss pharmacologic treatments being studied to improve tissue performance postgraft. Of note, there is significant research into the efficacy of adjuvants used to reduce ischemic injury, improve neovascularization, and inhibit hyperactivation of primordial follicle growth activations. Although the "experimental" label has been removed from ovarian tissue cryopreservation and subsequent transplantation, there is a significant need for further research to better understand sources of ovarian reserve damage to improve outcomes. Future research directions are provided as we consider how to reach the most hopeful results for women globally.

Clinical practice guidelines for the care of girls and women with Turner syndrome

Turner syndrome (TS) affects 50 per 100 000 females. TS affects multiple organs through all stages of life, necessitating multidisciplinary care. This guideline extends previous ones and includes important new advances, within diagnostics and genetics, estrogen treatment, fertility, co-morbidities, and neurocognition and neuropsychology. Exploratory meetings were held in 2021 in Europe and United States culminating with a consensus meeting in Aarhus, Denmark in June 2023. Prior to this, eight groups addressed important areas in TS care: (1) diagnosis and genetics, (2) growth, (3) puberty and estrogen treatment, (4) cardiovascular health, (5) transition, (6) fertility assessment, monitoring, and counselling, (7) health surveillance for comorbidities throughout the lifespan, and (8) neurocognition and its implications for mental health and well-being. Each group produced proposals for the present guidelines, which were meticulously discussed by the entire group. Four pertinent questions were submitted for formal GRADE (Grading of Recommendations, Assessment, Development and Evaluation) evaluation with systematic review of the literature. The guidelines project was initiated by the European Society for Endocrinology and the Pediatric Endocrine Society, in collaboration with members from the European Society for Pediatric Endocrinology, the European Society of Human Reproduction and Embryology, the European Reference Network on Rare Endocrine Conditions, the Society for Endocrinology, and the European Society of Cardiology, Japanese Society for Pediatric Endocrinology, Australia and New Zealand Society for Pediatric Endocrinology and Diabetes, Latin American Society for Pediatric Endocrinology, Arab Society for Pediatric Endocrinology and Diabetes, and the Asia Pacific Pediatric Endocrine Society. Advocacy groups appointed representatives for pre-meeting discussions and the consensus meeting.

Current Fertility Preservation Steps in Young Women Suffering from Cancer and Future Perspectives

Childhood cancer incidence, especially in high-income countries, has led to a focus on preserving fertility in this vulnerable population. The common treatments, such as radiation and certain chemotherapeutic agents, though effective, pose a risk to fertility. For adult women, established techniques like embryo and egg freezing are standard, requiring ovarian stimulation. However, for prepubescent girls, ovarian tissue freezing has become the primary option, eliminating the need for hormonal preparation. This review describes the beginning, evolution, and current situation of the fertility preservation options for this young population. A total of 75 studies were included, covering the steps in the current fertility preservation protocols: (i) ovarian tissue extraction, (ii) the freezing method, and (iii) thawing and transplantation. Cryopreservation and the subsequent transplantation of ovarian tissue have resulted in successful fertility restoration, with over 200 recorded live births, including cases involving ovarian tissue cryopreserved from prepubescent girls. Despite promising results, challenges persist, such as follicular loss during transplantation, which is attributed to ischemic and oxidative damage. Optimizing ovarian tissue-freezing processes and exploring alternatives to transplantation, like in vitro systems for follicles to establish maturation, are essential to mitigating associated risks. Further research is required in fertility preservation techniques to enhance clinical outcomes in the future. Ovarian tissue cryopreservation appears to be a method with specific benefits, indications, and risks, which can be an important tool in terms of preserving fertility in younger women.

High FSH levels impair VEGF secretion of human, frozen-thawed ovarian cortical tissue in vitro

Cryopreservation and reimplantation of human ovarian tissue restore the ovarian hormonal function and fertility due to the preservation of follicles. As the success depends on proper angiogenesis, different approaches aim to support this process. In mice, pretreatment of ovarian tissue with FSH shows increased follicular numbers probably due to the supported angiogenesis by an increased vascular endothelial factor (VEGF) expression. However, in human tissue it remains completely unclear, which effect the hormonal status of the patient has at the time point of reimplantation. Frozen-thawed human ovarian cortical tissue was cultured for 48 h with 0, 1 or 10 ng/mL recombinant human FSH. VEGF-A expression was assessed by ELISA and immunohistofluorescence (IHF) analysis. By IHF, HIF-1α and FSHR expression dependency on culture and FSH concentration was analyzed. Follicles at all stages expressed VEGF-A, which increases during folliculogenesis. Frozen-thawed human ovarian cortical tissue secreted a not statistically different amount of VEGF-A, when cultured in presence of 1 ng/mL FSH (17.5 mIU/mL). However, the presence of 10 ng/mL FSH (175 mIU/mL) significantly decreased VEGF-A expression and secretion. The high FSH concentration increased especially the VEGF-A expression of already growing follicles. The presence of pre-menopausal concentrations of FSH had no significant effect on VEGF-A expression, whereas the presence of elevated FSH levels decreased cortical VEGF-A expression. A hormonal pre-treatment of women with elevated FSH concentrations prior to reimplantation might be considered to support angiogenesis. Here, we show that VEGF-A expression by follicles is affected by FSH dependent on the concentration.

Successful ovarian tissue cryopreservation with transvaginal natural orifice transluminal endoscopic surgery: A case report

Chemotherapy and radiation therapy can cause gonadal dysfunction in women of reproductive age. Ovarian tissue cryopreservation is performed to restore fertility by allowing transplantation of the patient's frozen-thawed ovarian tissue or through future in vitro maturation and in vitro fertilization of frozen-thawed oocytes. Herein, we describe our initial experience with vaginal natural orifice transluminal endoscopic surgery for ovarian tissue preservation in a young woman with malignant tumor. A 23-year-old woman with anaplastic lymphoma kinase-positive malignant lymphoma was scheduled for hematopoietic stem cell transplantation after experiencing relapse following R-cyclophosphamide, doxorubicin, vincristine, and prednisolone therapy. Ovarian tissue cryopreservation was selected as only MII2 oocytes were collected. Vaginal natural orifice transluminal endoscopic surgery was performed to excise the left ovary. Ovarian tissues were frozen using the vitrification method. The operative time was 37 min, and blood loss was minimal. Pathological examination revealed no metastatic findings of malignant lymphoma and no thermal damage to the ovarian tissue due to bipolar disorder. The patient was discharged on the first day postoperatively, and her postoperative course was uneventful. The vaginal natural orifice transluminal endoscopic surgery technique can provide a safe and effective alternative to laparoscopy or laparotomy for the cryopreservation of ovarian tissue in young patients with cancer. We believe this method has potential application in sexually mature female cancer survivors.

Significance and Influence of Suturing for Ovarian Tissue Transplantation

The purpose of this animal study was to verify the effect of suturing on graft function in ovarian tissue transplantation. Ovaries from 2-week-old rats were transplanted orthotopically into the ovaries of 8-week-old female Wistar rats. The various transplantation methods used were insertion into the ovarian bursa without suturing (group A: control), suturing with a single 6-0 Vicryl stitch (group B: 6-0*1), suturing with a single 10-0 Vicryl stitch (group C: 10-0*1), and suturing with three 10-0 Vicryl stitches (group D: 10-0*3). Two weeks after transplantation, the transplanted ovaries were evaluated histologically and for gene expression. Engraftment rates of the donor ovaries 14 days after transplantation were 62.5%, 100%, 91.7%, and 100% in groups A, B, C, and D, respectively, significantly lower in group A than in the other groups. In terms of gene expression, TNFα levels were significantly higher in group D, and GDF9 and follicle-stimulating hormone receptor (FSHR) levels were significantly lower in group D than in groups A and B. The number of primordial follicles evaluated by HE staining was significantly lower in groups B, C, and D than in group A. Compared to orthotopic transplantation without sutures, direct suturing to the host improved the engraftment rate, although increasing the number of sutures increased inflammatory marker levels and decreased the number of primordial follicles. We believe that it is important to perform ovarian tissue transplantation using optimal suture diameter for good adhesion, but with a minimum number of sutures to preserve ovarian function.

Fertility preservation in pediatric healthcare: a review

Survival rates for children and adolescents diagnosed with malignancy have been steadily increasing due to advances in oncology treatments. These treatments can have a toxic effect on the gonads. Currently, oocyte and sperm cryopreservation are recognized as well-established and successful strategies for fertility preservation for pubertal patients, while the use of gonadotropin-releasing hormone agonists for ovarian protection is controversial. For prepubertal girls, ovarian tissue cryopreservation is the sole option. However, the endocrinological and reproductive outcomes after ovarian tissue transplantation are highly heterogeneous. On the other hand, immature testicular tissue cryopreservation remains the only alternative for prepubertal boys, yet it is still experimental. Although there are several published guidelines for navigating fertility preservation for pediatric and adolescent patients as well as transgender populations, it is still restricted in clinical practice. This review aims to discuss the indications and clinical outcomes of fertility preservation. We also discuss the probably effective and efficient workflow to facilitate fertility preservation.

The effect of platelet lysate on mouse ovarian structure, function and epigenetic modifications after autotransplantation

RESEARCH QUESTION

What are the effects of platelet lysate on structure, function and epigenetic modifications of heterotopically transplanted mouse ovarian tissues?

DESIGN

Mice were divided into three groups (n = 17 per group): control (mice with no ovariectomy, grafting or treatment), autograft and autograft plus platelet lysate (3 ml/kg at the graft sites). Inflammatory markers, serum malondialdehyde (MDA) concentration and total antioxidant capacity were assessed on day 7 after transplantation. Twenty-eight days after transplantation, stereological and hormonal analyses were conducted. Chromatin immunoprecipitation and quantitative real-time polymerase chain reaction were also used to quantify the epigenetic modifications of maturation genes, parallel to their expression.

RESULTS

The total volume of the ovary, cortex and medulla, and the number of different types of follicles, the concentration of interleukin (IL)-10, progesterone and oestradiol and total antioxidant capacity significantly decreased in the autograft group compared with the control group (P < 0.001); these parameters significantly increased in the autograft plus platelet lysate group compared with the autograft group (P < 0.001). The concentrations of tumour necrosis factor alpha, IL-6 and MDA increased significantly in the autograft group compared with the control group (P < 0.001); in the autograft plus platelet lysate group, these parameters significantly decreased compared with the autograft group (P < 0.001). In the autograft plus platelet lysate group, the expression levels of Gdf-9 (P < 0.0021), Igf-1 (P < 0.0048) and Igf-2 (P < 0.0063) genes also increased along with a lower incorporation of MeCP2 in the promoter regions (P < 0.001) compared with the autograft group.

CONCLUSIONS

Platelet lysate can contribute to follicular survival by improving folliculogenesis and increasing the expression of oocyte maturation genes.

Follicle outcomes in human ovarian tissue: effect of freezing, culture, and grafting

OBJECTIVE

To study the effect of freezing, in vitro culture (IVC) and grafting to chorioallantoic membrane (CAM) on follicle outcomes in human ovarian tissue.

DESIGN

An experimental study.

SETTING

University-based research laboratory.

PATIENTS

Fresh and cryopreserved ovarian tissue from 10 patients was donated to research with their consent and institutional review board approval.

INTERVENTIONS

Fresh and frozen-thawed ovarian cortical pieces were in vitro-cultured and compared (fresh-IVC vs FT-IVC). The FT-IVC fragments were then examined against fragments grafted to CAM (FT-CAM). After both IVC and CAM grafting, ovarian cortical pieces (4×2×1 mm³) were analyzed on days 0, 1, and 6.

MAIN OUTCOME MEASURES

Follicle analyses included histology (count and classification) and immunohistochemistry (Ki67 [proliferation], caspase-3 [apoptosis], 1A and 1B light chain 3B [autophagy], p-Akt, FOXO1, and p-rpS6 [PI3K activation]). Droplet digital polymerase chain reaction further explored expression of PI3K pathway- and oocyte-related genes in tissue sections.

RESULTS

No major differences were detected between fresh-IVC and FT-IVC tissues in any conducted analyses. Although a significant drop was observed in primordial follicle (PF) proportions in the fresh-IVC and FT-IVC groups (d0 vs. d6, P<.002), they held steady in the FT-CAM group (d0 vs. d6, P>.05). The PF rates were also significantly higher in the FT-CAM group than the FT-IVC group on d6 (P=.02). Importantly, avian erythrocytes were already present in 30% of implants from d1. Apoptotic and autophagic follicle rates increased during IVC (P<.008), but remained significantly lower in the FT-CAM group (P<.01), confirming superior follicle preservation in CAM-grafted tissue. Upregulation of the PI3K/FOXO pathway was established in the IVC groups, demonstrating PF activation, whereas significant pathway downregulation was detected in the FT-CAM group (P<.03). The droplet digital polymerase chain reaction tests confirmed oocyte growth during IVC and follicle autophagy in all groups; however, the PI3K pathway appeared to be differentially modulated in tissues and follicles.

CONCLUSIONS

In vitro culture induces PF depletion with no additional impact of freezing. Grafting to CAM preserves the PF pool by curbing follicle activation, apoptosis, and autophagy, probably thanks to rapid graft revascularization and/or the circulating embryonic antimüllerian hormone. These findings highlight the importance of enhancing neoangiogenesis in ovarian grafts and investigating the potential benefits of administering antimüllerian hormone to prevent PF burnout.

A synopsis of global frontiers in fertility preservation

Since 2007, the Oncofertility Consortium Annual Conference has brought together a diverse network of individuals from a wide range of backgrounds and professional levels to disseminate emerging basic and clinical research findings in fertility preservation. This network also developed enduring educational materials to accelerate the pace and quality of field-wide scientific communication. Between 2007 and 2019, the Oncofertility Consortium Annual Conference was held as an in-person event in Chicago, IL. The conference attracted approximately 250 attendees each year representing 20 countries around the world. In 2020, however, the COVID-19 pandemic disrupted this paradigm and precluded an in-person meeting. Nevertheless, there remained an undeniable demand for the oncofertility community to convene. To maintain the momentum of the field, the Oncofertility Consortium hosted a day-long virtual meeting on March 5, 2021, with the theme of "Oncofertility Around the Globe" to highlight the diversity of clinical care and translational research that is ongoing around the world in this discipline. This virtual meeting was hosted using the vFairs ® conference platform and allowed over 700 people to participate, many of whom were first-time conference attendees. The agenda featured concurrent sessions from presenters in six continents which provided attendees a complete overview of the field and furthered our mission to create a global community of oncofertility practice. This paper provides a synopsis of talks delivered at this event and highlights the new advances and frontiers in the fields of oncofertility and fertility preservation around the globe from clinical practice and patient-centered efforts to translational research.

L-Carnitine improves follicular survival and function in ovarian grafts in the mouse

CONTEXT

Ovarian tissue transplantation is performed to preserve fertility in patients undergoing chemotherapy and radiotherapy. However, the ischemia-reperfusion injury which occurs after the ovarian tissue transplantation causes follicular depletion and apoptosis. l -Carnitine has antioxidant and anti-inflammation properties.

AIMS

Therefore, we aimed to investigate the beneficial effect of l -carnitine on mouse ovaries following heterotopic autotransplantation.

METHODS

Mice were randomly divided into three groups (six mice per group): control, autografted and autografted+l -carnitine (200mg/kg daily intraperitoneal injections). Seven days after ovary autografting, the serum levels of malondialdehyde (MDA), total antioxidant capacity, tumor necrosis factor alpha (TNF-α), interleukin (IL)-6 and IL-10 were measured. Ovary histology, serum concentrations of progesterone and estradiol were also measured 28days after autotransplantation. Data were analysed using one-way analysis of variance (ANOVA) and Tukey test, and the means were considered significantly different at P Key results: In the autografted+l -carnitine group, the total volume of the ovary, the volume of the cortex, the number of follicles, the serum concentrations of IL-10, estradiol and progesterone significantly increased compared to the autografted group. In the autografted+l -carnitine group, serum concentrations of IL-6, TNF-α and MDA were significantly decreased compared to the autografted group.

CONCLUSIONS

Our results indicated that l -carnitine can ameliorate the consequences of ischemia-reperfusion on the mice ovarian tissue following autotransplantation.

IMPLICATIONS

l -carnitine improves the structure and function of transplanted ovaries.

Cryoprotective effect of antifreeze protein III on the rabbit ovary

CONTEXT

Ovarian tissue cryopreservation is effective in preserving fertility in cancer patients who have concerns about fertility loss due to cancer treatment. However, ischemia reduces the lifespan of grafts. Microvascular transplantation of cryopreserved whole ovary may allow immediate revascularisation, but the damage incurred during the cryopreservation procedure may cause follicular depletion; hence, preventing chilling injury would help maintain ovarian function.

AIM

This study was designed to investigate the beneficial effects of antifreeze protein III (AFP III) on rabbit ovary cryopreservation.

METHODS

Ovaries (n =25) obtained from 5-month-old female rabbits (n =13) were frozen by slow freezing and vitrification. Cryoprotectant media were supplemented with and without 1mg/mL of AFP III. The experiment was divided into five groups: fresh control group (F), slow freezing group (S), slow freezing group with AFP III (AFP III-S), vitrification group (V) and vitrification group with AFP III (AFP III-V). All groups of ovaries were examined by histological characteristics analysis, ultrastructural analysis, apoptosis detection and follicle viability test.

KEY RESULTS

With slow freezing, the normal rate of change in follicle morphology, density of stromal cells and the survival rate of follicles in the AFP III supplemented group were significantly higher than those in the non-supplemented group, and a lower oocyte apoptotic rate was shown in the AFP III supplemented group. In the vitrification groups, the normal rate of change in follicle morphology and density of stromal cells in the AFP III supplemented group were significantly higher than those in the non-supplemented group, and a lower oocyte apoptotic rate was found in the AFP III supplemented group. But there was no obvious difference in the survival rate of follicles between the two groups. There was also no significant difference in the normal rate of change in follicle morphology, the survival rate of follicles and the apoptotic rate of oocytes between the vitrification and slow freezing groups (P >0.05), but the density of stromal cells in the vitrification groups was statistically higher than that of the slow freezing group (P <0.05).

CONCLUSIONS

The addition of AFP III in slow freezing and vitrification could improve the cryoprotective effect of ovaries, which was more evident in slow freezing.

IMPLICATIONS

The findings of this study provide a foundation for further research on the effects of AFP III in human ovarian tissue.

Ovarian transplantation with robotic surgery and a neovascularizing human extracellular matrix scaffold: a case series in comparison to meta-analytic data

OBJECTIVE

To report our experience with robot-assisted (RA) autologous cryopreserved ovarian tissue transplantation (ACOTT) with the use of a neovascularizing extracellular matrix scaffold.

DESIGN

Case series with meta-analytic update.

SETTING

Academic.

PATIENT(S)

Seven recipients of RA-ACOTT.

INTERVENTION(S)

Before or shortly after initiating chemotherapy, ovarian tissue was cryopreserved from 7 women, who then underwent RA-ACOTT 9.9 ± 1.8 years (range, 7-12 years) later. Perioperatively, they received transdermal estrogen and low-dose aspirin to enhance graft vascularization. Ovarian cortical pieces were thawed and sutured on an extracellular matrix scaffold, which was then robotically anastomosed to the bivalved remaining ovary in 6 cases and retroperitoneally (heterotopic) to the lower abdomen in 1 case.

MAIN OUTCOME MEASURE(S)

Ovarian function return, the number of oocytes/embryos, aneuploidy %, live births, and neonatal outcomes were recorded. Graft longevity was compared with the mean from the meta-analytic data.

RESULT(S)

Ovarian function returned 13.9 ± 2.7 weeks (11-16.2 weeks) after ACOTT, and oocytes were retrieved in all cases with 12.3 ± 6.9 embryos generated. In contrast to orthotopic, the heterotopic ACOTT demonstrated low embryo quality and an 80% aneuploidy rate. A recipient did not attempt to conceive and 2 needed a surrogate, whereas 4 of 4 delivered 6 healthy children, compared with 115 of 460 (25% pregnancy rate) from the meta-analytic data (n = 79). The mean graft longevity (43.2 ± 23.6/47.4 ± 22.8 months with/without sensitivity analysis) trended longer than the meta-analytic mean (29.4 ± 22.7), even after matching age at cryopreservation.

CONCLUSION(S)

In this series, RA-ACOTT resulted in extended graft longevity, with ovarian functions restored in all cases, even when the tissues were cryopreserved after chemotherapy exposure.

Equine Chorionic Gonadotropin as an Effective FSH Replacement for In Vitro Ovine Follicle and Oocyte Development

The use of assisted reproductive technologies (ART) still requires strategies through which to maximize individual fertility chances. In vitro folliculogenesis (ivF) may represent a valid option to convey the large source of immature oocytes in ART. Several efforts have been made to set up ivF cultural protocols in medium-sized mammals, starting with the identification of the most suitable gonadotropic stimulus. In this study, Equine Chorionic Gonadotropin (eCG) is proposed as an alternative to Follicle Stimulating Hormone (FSH) based on its long superovulation use, trans-species validation, long half-life, and low costs. The use of 3D ivF on single-ovine preantral (PA) follicles allowed us to compare the hormonal effects and to validate their influence under two different cultural conditions. The use of eCG helped to stimulate the in vitro growth of ovine PA follicles by maximizing its influence under FBS-free medium. Higher performance of follicular growth, antrum formation, steroidogenic activity and gap junction marker expression were recorded. In addition, eCG, promoted a positive effect on the germinal compartment, leading to a higher incidence of meiotic competent oocytes. These findings should help to widen the use of eCG to ivF as a valid and largely available hormonal support enabling a synchronized in vitro follicle and oocyte development.

Hormonal Characteristics of Women Receiving Ovarian Tissue Transplantation with or without Endogenous Ovarian Activity

Ovarian tissue cryopreservation (OTC) and transplantation of frozen/thawed ovarian tissue (OTT) are used for fertility preservation in girls and women. Here, we evaluated the hormonal characteristics of women with or without postmenopausal levels of FSH at the time of OTT to study differences and conditions that best support the initiation of ovarian function. A total of 74 women undergoing OTT (n = 51 with menopausal levels of FSH; n = 23 with premenopausal levels) were followed by measurements of FSH, LH, AMH, and oestradiol. Concentrations of FSH and LH returned to premenopausal levels after 20 weeks on average, with a concomitant increase in oestradiol. Despite resumption of ovarian activity, AMH concentrations were in most instances below the detection limit in the menopausal group, suggesting a low ovarian reserve. Despite a higher age in the premenopausal group, they more often experienced an AMH increase than the menopausal group, suggesting that conditions in the premenopausal ovary better sustain follicle survival, perhaps due to the higher concentrations of oestradiol. Collectively, this study highlights the need for improving follicle survival after OTT. Age and the amount of tissue transplanted are important factors that influence the ability to regain ovarian activity and levels of FSH may need to be downregulated and oestradiol increased prior to OTT.

Effects of Er:YAG laser treatment on re-vascularization and follicle survival in frozen/thawed human ovarian cortex transplanted to immunodeficient mice

PURPOSE

The huge loss of ovarian follicles after transplantation of frozen/thawed ovarian tissue is considered a major drawback on the efficacy of the procedure. Here we investigate whether Er:YAG laser treatment prior to xenotransplantation can improve re-vascularization and subsequently follicle survival in human ovarian tissue.

METHODS

A total of 99 frozen/thawed human ovarian cortex pieces were included of which 72 pieces from 12 woman were transplanted to immunodeficient mice. Tissues from each woman were included in both an 8-day and an 8-week duration study and treated with either full-beam laser (L1) or fractionated laser (L2), or served as untreated controls. Vascularization of the ovarian xenografts were evaluated after 8 days by qPCR and murine Cd31 immunohistochemical analysis. Follicle densities were evaluated histologically 8 weeks after xenografting.

RESULTS

Gene expression of Vegf/VEGF was upregulated after L1 treatment (p=0.002, p=0.07, respectively), whereas Angpt1, Angpt2, Tnf-α, and Il1-β were significantly downregulated. No change in gene expression was found in Cd31/CD31, ANGPT1, ANGPT2, ANGTPL4, XBP1, or LRG1 after any of the laser treatments. The fraction of Cd31 positive cells were significantly reduced after L1 and L2 treatment (p<0.0001; p=0.0003, respectively), compared to controls. An overall negative effect of laser treatment was detected on follicle density (p=0.03).

CONCLUSIONS

Er:YAG laser treatment did not improve re-vascularization or follicle survival in human ovarian xenografts after 8 days and 8 weeks grafting, respectively. However, further studies are needed to fully explore the potential angiogenic effects of controlled tissue damage using different intensities or lasers.

Fresh and cryopreserved ovarian tissue from deceased young donors yields viable follicles

OBJECTIVE

Ovarian tissue cryopreservation is one of the crucial options for fertility preservation. Transplantation of cryopreserved ovarian tissue was proven to restore ovarian endocrine function in patients with premature ovarian insufficiency. Ovaries from deceased donors potentially serve as an excellent and readily available tissue for the translational and basic research. In this study, we used ovaries obtained from 5 deceased donors aged 18-26 years, to evaluate the number and quality of ovarian follicles isolated before and after cryopreservation.

DESIGN

Preclinical.

SETTING

Academic biomedical research laboratory.

PATIENTS

De-identified deceased human donors.

INTERVENTIONS

Slow-freeze cryopreservation and thawing.

MAIN OUTCOME MEASURES

Follicle count, follicle density, follicle viability using immunohistochemical staining (TUNEL).

RESULTS

The follicle density negatively correlated with age in both cryopreserved/thawed and fresh group. A total of 2803 follicles from fresh and 1608 follicles from cryopreserved tissues were classified and analyzed using Hematoxylin and eosin staining. There was no significant difference in the percent of morphologically normal follicles between two groups. TUNEL assay indicated no higher DNA damage in the follicles and the stroma cells after cryopreservation. Morphologically normal preantral follicles were enzymatically isolated from both fresh and cryopreserved tissue with 88.51 ± 5.93% (mean ± SD) of the isolated follicles confirmed viable using LIVE/DEAD evaluation.

CONCLUSIONS

Our results indicate the ovarian tissue from deceased donors maintain high quality after long time extracorporeal circulation and transportation from the hospital to the laboratory. High survival rate of follicles at different developmental stages suggested tolerance to the cryopreservation process. Human ovarian tissues obtained from deceased donors is an ample source tissue and can be applied to promoting research and future clinical applications.

Pharmacological inhibition of the PI3K/PTEN/Akt and mTOR signalling pathways limits follicle activation induced by ovarian cryopreservation and in vitro culture

BACKGROUND

Cryopreservation and transplantation of ovarian tissue (OTCTP) represent a promising fertility preservation technique for prepubertal patients or for patients requiring urgent oncological management. However, a major obstacle of this technique is follicle loss due to, among others, accelerated recruitment of primordial follicles during the transplantation process, leading to follicular reserve loss in the graft and thereby potentially reducing its lifespan. This study aimed to assess how cryopreservation itself impacts follicle activation.

RESULTS

Western blot analysis of the PI3K/PTEN/Akt and mTOR signalling pathways showed that they were activated in mature or juvenile slow-frozen murine ovaries compared to control fresh ovaries. The use of pharmacological inhibitors of follicle signalling pathways during the cryopreservation process decreased cryopreservation-induced follicle recruitment. The second aim of this study was to use in vitro organotypic culture of cryopreserved ovaries and to test pharmacological inhibitors of the PI3K/PTEN/Akt and mTOR pathways. In vitro organotypic culture-induced activation of the PI3K/PTEN/Akt pathway is counteracted by cryopreservation with rapamycin and in vitro culture in the presence of LY294002. These results were confirmed by follicle density quantifications. Indeed, follicle development is affected by in vitro organotypic culture, and PI3K/PTEN/Akt and mTOR pharmacological inhibitors preserve primordial follicle reserve.

CONCLUSIONS

Our findings support the hypothesis that inhibitors of mTOR and PI3K might be an attractive tool to delay primordial follicle activation induced by cryopreservation and culture, thus preserving the ovarian reserve while retaining follicles in a functionally integrated state.

Ovarian tissue damage after grafting: systematic review of strategies to improve follicle outcomes

Frozen-thawed human ovarian tissue endures large-scale follicle loss in the early post-grafting period, characterized by hypoxia lasting around 7 days. Tissue revascularization occurs progressively through new vessel invasion from the host and neoangiogenesis from the graft. Such reoxygenation kinetics lead to further potential damage caused by oxidative stress. The aim of the present manuscript is to provide a systematic review of proangiogenic growth factors, hormones and various antioxidants administered in the event of ovarian tissue transplantation to protect the follicle pool from depletion by boosting revascularization or decreasing oxidative stress. Although almost all investigated studies revealed an advantage in terms of revascularization and reduction in oxidative stress, far fewer demonstrated a positive impact on follicle survival. As the cascade of events driven by ischaemia after transplantation is a complex process involving numerous players, it appears that acting on specific molecular mechanisms, such as concentrations of proangiogenic growth factors, is not enough to significantly mitigate tissue damage. Strategies exploiting the activated tissue response to ischaemia for tissue healing and remodelling purposes, such as the use of antiapoptotic drugs and adult stem cells, are also discussed in the present review, since they yielded promising results in terms of follicle pool protection.

Recent Advancements in Engineered Biomaterials for the Regeneration of Female Reproductive Organs

Various gynecologic diseases and chemoradiation or surgery for the management of gynecologic malignancies may damage the uterus and ovaries, leading to clinical problems such as infertility or early menopause. Embryo or oocyte cryopreservation-the standard method for fertility preservation-is not a feasible option for patients who require urgent treatment because the procedure requires ovarian stimulation for at least several days. Hormone replacement therapy (HRT) for patients diagnosed with premature menopause is contraindicated for patients with estrogen-dependent tumors or a history of thrombosis. Furthermore, these methods cannot restore the function of the uterus and ovaries. Although autologous transplantation of cryopreserved ovarian tissue is being attempted, it may re-introduce malignant cells after cancer treatment. With the recent development in regenerative medicine, research on engineered biomaterials for the restoration of female reproductive organs is being actively conducted. The use of engineered biomaterials is a promising option in the field of reproductive medicine because it can overcome the limitations of current therapies. Here, we review the ideal properties of biomaterials for reproductive tissue engineering and the recent advancements in engineered biomaterials for the regeneration of female reproductive organs.

Current and Future Perspectives for Improving Ovarian Tissue Cryopreservation and Transplantation Outcomes for Cancer Patients

Although advances in cancer treatment and early diagnosis have significantly improved cancer survival rates, cancer therapies can cause serious side effects, including ovarian failure and infertility, in women of reproductive age. Infertility following cancer treatment can have significant adverse effects on the quality of life. However, established methods for fertility preservation, including embryo or oocyte cryopreservation, are not always suitable for female cancer patients because of complicated individual conditions and treatment methods. Ovarian tissue cryopreservation and transplantation is a promising option for fertility preservation in pre-pubertal girls and adult patients with cancer who require immediate treatment, or who are not eligible to undergo ovarian stimulation. This review introduces various methods and strategies to improve ovarian tissue cryopreservation and transplantation outcomes, to help patients and clinicians choose the best option when considering the potential complexity of a patient's situation. Effective multidisciplinary oncofertility strategies, involving the inclusion of a highly skilled and experienced oncofertility team that considers cryopreservation methods, thawing processes and devices, surgical procedures for transplantation, and advances in technologies, are necessary to provide high-quality care to a cancer patient.

N-acetylcysteine protects ovarian follicles from ischemia-reperfusion injury in xenotransplanted human ovarian tissue

STUDY QUESTION

Can antioxidant treatment with N-acetylcysteine (NAC) protect ovarian follicles from ischemia-reperfusion injury in xenotransplanted human ovarian tissue?

SUMMARY ANSWER

Daily administration of NAC for 7-12 days post-transplantation reduced ischemia-reperfusion injury and increased follicle survival in human ovarian xenografts by upregulating the antioxidant defense system and exerting anti-inflammatory and antiapoptotic effects.

WHAT IS KNOWN ALREADY

Freezing of human ovarian tissue is performed with high follicular survival rates but up to 70% of follicles appear to be lost due to hypoxia and ischemia-reperfusion injury during ovarian tissue transplantation (OTT). NAC has been demonstrated to possess antioxidant and antiapoptotic properties, and studies in rodents have shown that intraperitoneal administration of NAC reduces ischemia-reperfusion injury and increases follicle survival in autotransplanted murine ovaries.

STUDY DESIGN, SIZE, DURATION

Pieces of frozen-thawed human ovarian tissue from 28 women aged 23-36 years were transplanted to immunodeficient mice in short- and long-term xenograft studies or cultured in vitro. Three short-term xenograft studies (1-week duration) were performed, in which saline or 150 mg/kg NAC was administered for 7 days post-transplantation (n = 12 patients per group). Two long-term xenograft studies (4 weeks of duration) were performed. In one of these studies, saline or 150 mg/kg NAC was administered for 12 days (n = 12 patients per group), while in the other study 50, 150 or 300 mg/kg NAC was administered for 7 days (n = 8 patients per group). In addition, human ovarian tissue (n = 12 pieces from three patients per group) was cultured with increasing concentrations of NAC (0, 5, 25 and 75 mM) for 4 days in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Donated ovarian tissue was obtained from women who had undergone ovarian tissue cryopreservation for fertility preservation at the University Hospital of Copenhagen. Cortical tissue pieces (5 × 5 × 1 mm) were transplanted subcutaneously to immunodeficient mice and NAC or saline was injected intraperitoneally. Grafts were retrieved after 1 or 4 weeks and follicle density was assessed. Gene expression analysis of antioxidant defense markers (superoxide dismutase; Sod1/SOD1, heme oxygenase-1; Hmox1/HMOX1, catalase; Cat/CAT), proinflammatory cytokines (tumor necrosis factor-alpha; Tnf-α, interleukin-1-beta; Il1-β, interleukin 6; Il6), apoptotic factors (B-cell lymphoma 2; Bcl2/BCL2, Bcl-2-associated X protein; Bax/BAX) and angiogenic factors (vascular endothelial growth factor A; Vegfa/VEGFA, angiopoietin-like 4; Angptl4/ANGPTL4) was performed in 1-week-old human ovarian xenografts and in cultured human ovarian tissue. Grafts retrieved after 4 weeks were histologically processed and analyzed for vascularization by CD31 immunohistochemical staining, fibrosis by Masson's Trichrome staining and apoptosis by immunofluorescence using cleaved caspase-3.

MAIN RESULTS AND THE ROLE OF CHANCE

After 1-week grafting, the relative expression of Sod1, Hmox1 and Cat was significantly higher in the group receiving 150 mg/kg NAC (NAC150-treated group) compared to controls (P = 0.04, P = 0.03, and P = 0.01, respectively), whereas the expression levels of Tnf-α, Il1-β and Il6 were reduced. The Bax/Bcl2 ratio was also significantly reduced in the NAC150-treated group (P < 0.005). In vitro, the relative gene expression of SOD1, HMOX1 and CAT increased significantly in the human ovarian tissue with increasing concentrations of NAC (P < 0.001 for all genes). However, the expression of VEGFA and ANGPTL4 as well as the BAX/BCL2 ratio decreased significantly with increasing concentrations of NAC (P < 0.02, P < 0.001 and P < 0.001, respectively). After 4-week grafting, fibrosis measured by collagen content was similar in the NAC150-treated group compared to controls (control: 56.6% ± 2.2; NAC150: 57.6% ± 1.8), whereas a statistically significant reduction in the CD31-positive vessel area was found (control: 0.69% ± 0.08; NAC150: 0.51% ± 0.07; P < 0.02). Furthermore, a reduced immunoreactivity of cleaved caspase-3 was observed in follicles of the NAC150-treated xenografts compared to controls. Follicle density (follicles/mm3, mean ± SD) was higher in the NAC150-treated group compared to the control group in the 1-week xenografts (control: 19.5 ± 26.3; NAC150: 34.2 ± 53.5) and 4-week xenografts (control: 9.3 ± 11.0; NAC150: 14.4 ± 15.0). Overall, a 2-fold increase in follicle density was observed in the NAC150-group after 1-week grafting where fold changes in follicle density were calculated in relation to grafts from the same patient. Around a 5-fold increase in follicle density was observed in the NAC150 and NAC300 groups after 4-week grafting.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Follicle density in the human ovarian cortex is highly heterogeneous and can vary 100-fold between cortex pieces from the same woman. 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. While intraperitoneal injections of NAC appeared to reduce ischemia-reperfusion injury in human ovarian xenografts, different administration routes should be investigated in order to optimize NAC for potential clinical use.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study to demonstrate the antioxidant, anti-inflammatory and antiapoptotic properties of NAC in xenotransplanted human ovarian tissue. Therefore, NAC appears to be a promising candidate for protecting ovarian follicles from ischemia-reperfusion injury. This provides the initial steps toward clinical application of NAC, which could potentially reduce the loss of ovarian follicles following OTT.

STUDY FUNDING/COMPETING INTEREST(S)

We are grateful to the Danish Childhood Cancer Foundation, Hørslev Foundation, Aase and Einar Danielsen's Foundation (grant number: 10-001999), Dagmar Marshalls Foundation, Else and Mogens Wedell-Wedellsborgs Foundation, Knud and Edith Eriksens Mindefond, and Fabrikant Einar Willumsens Mindelegat for funding this study. None of the authors have any competing interests to declare.

The Effectiveness of Anti-Apoptotic Agents to Preserve Primordial Follicles and Prevent Tissue Damage during Ovarian Tissue Cryopreservation and Xenotransplantation

The purpose of this study is to investigate the effectiveness of sphingosine-1-phosphate (S1P) and Z-VAD-FMK (Z-VAD) as anti-apoptotic agents to preserve ovarian function and prevent tissue damage during ovarian tissue cryopreservation and transplantation. This study consisted of two steps, in vitro and in vivo. In the first step, human ovarian tissues were cryopreserved using slow-freezing media alone, S1P, or Z-VAD (control, S1P, Z-VAD group); based on the outcomes in these groups, Z-VAD was selected for subsequent xenotransplantation. In the second step, human frozen/thawed ovarian tissues were grafted into fifty mice divided into three groups: slow-freezing/thawing and transplantation without an anti-apoptotic agent (Trans-control) and xenotransplantation with or without Z-VAD injection (Trans-Z-VAD-positive and Trams-Z-VAD-negative groups, respectively). In the first step, the Z-VAD group had a significantly higher primordial follicular count than the S1P (p = 0.005) and control groups (p = 0.04). Transplanted ovarian tissues were obtained 4 weeks after transplantation (second step). Angiogenesis was significantly increased in the Z-VAD-negative (p = 0.03) and -positive (p = 0.04) groups compared to the control group. This study demonstrated that slow-freezing and transplantation with Z-VAD is an effective method for preserving primordial follicle counts, decreasing double-strand DNA breaks, and increasing angiogenesis in a mouse model. Further molecular and clinical studies are needed to confirm these results.

Delaying Reproductive Aging by Ovarian Tissue Cryopreservation and Transplantation: Is it Prime Time?

Ovarian tissue cryopreservation and autotransplantation can restore ovarian endocrine function and fertility and recently were changed from experimental to fertility preservation procedures for medical indications by the American Society of Reproductive Medicine. Such advances have resulted in discussions around the utility of ovarian cryopreservation in healthy women to preserve fertility and delay menopause or as a hormone replacement approach. Such 'elective' use of ovarian tissue cryopreservation requires a risk-benefit assessment. Here, we review evidence for and against the utility of ovarian tissue harvesting in healthy women, scrutinize recent and needed advances to enhance the feasibility of such an approach, and provide practice and future research guidelines.

Ovaries of patients recently treated with alkylating agent chemotherapy indicate the presence of acute follicle activation, elucidating its role among other proposed mechanisms of follicle loss

OBJECTIVE

To investigate mechanisms of primordial follicle (PMF) loss in vivo in human ovaries shortly after alkylating agent (AA) chemotherapy.

DESIGN

Cohort study.

SETTING

Tertiary university medical center.

PATIENT(S)

Ninety-six women aged 15-39 years who underwent ovarian tissue cryopreservation for fertility preservation.

INTERVENTION(S)

Fresh ovarian tissue samples were harvested from women treated with AA (n = 24) or non-AA (n = 24) chemotherapy <6 months after treatment and age-matched untreated women (n = 48).

MAIN OUTCOME MEASURE(S)

Differential follicle counts, time from chemotherapy exposure, immunostaining for apoptosis (cleaved caspase-3) and FOXO3A on tissue harvested within ultrashort time intervals (4-12 days), collagen (Sirius red) and neovascularization (CD34).

RESULT(S)

AA-treated ovaries had significant loss of PMFs, and significant increase in absolute numbers of growing follicles compared with untreated control ovaries. The number of growing follicles was inversely correlated with time from chemotherapy. Representative staining for FOXO3A observed decreased nuclear localization in PMF oocytes in AA-treated ovaries removed within the ultrashort time interval compared with untreated ovaries. Neither significant loss of PMFs, increase in growing follicles, nor decrease in nuclear FOXO3A were observed in non-AA-treated ovaries. No increased expression of cleaved caspase-3 was seen in PMFs within the ultrashort time interval after AA or non-AA chemotherapy. Significant stromal fibrosis and neovascularization were observed in AA-treated ovaries only after follicle loss had already occurred (4-6 months).

CONCLUSION(S)

Follicle activation occurs in vivo in ovaries of patients treated with AA, indicating a pathologic mechanism which may contribute to chemotherapy-induced follicle loss.

Defining the gonadotrophin requirement for the selection of a single dominant follicle in cattle

The aim was to define the pattern and physiological concentrations of FSH and LH required for the selection of a single dominant follicle in mono-ovulatory species. A series of five experiments was carried out using gonadotrophin-releasing hormone agonist-induced hypogonadal heifers. Animals were infused with different patterns of either FSH and/or LH followed by an ovulatory dose of human chorionic gonadotrophin. Follicular response was monitored by ultrasound scanning and blood samples were collected to measure concentrations of FSH, LH, oestradiol and progesterone. The main findings were: (1) physiological concentrations of FSH given as a continuous infusion and for an adequate duration, in the presence of basal LH, with or without LH pulses, are capable of inducing a superovulatory response, (2) initial exposure to FSH followed by LH pulses alone stimulate the development of multiple preovulatory follicles, confirming that ovarian follicles are capable of transferring dependence on gonadotrophins from FSH to LH, (3) while LH pulses appear not to have a major effect on the pattern of preovulatory follicle development, adequate LH pulsatile support is required for full oestradiol synthesis and (4) the duration of initial exposure to FSH and the ability to transfer the dependence from FSH to LH are critical for the selection of a single dominant follicle. In conclusion, this experimental series confirms that the duration of initial exposure to FSH and the ability of the selected follicle to transfer its gonadotrophic dependence from FSH to LH are critical for the selection of a single dominant follicle in cattle.

Ovarian tissue cryopreservation and novel bioengineering approaches for fertility preservation

PURPOSE OF REVIEW

Breast cancer patients who cannot delay treatment or for whom hormone stimulation and egg retrieval are contraindicated require alternative methods of fertility preservation prior to gonadotoxic treatment. Ovarian tissue cryopreservation is an alternative approach that may offer patients the opportunity to preserve fertility and carry biologically-related children later in life. Various experimental approaches are being explored to obtain mature gametes from cryopreserved and thawed ovarian tissue for fertilization and implantation using biomimetic tissue culture in vitro. Here we review the most recent developments in ovarian tissue cryopreservation and exciting advances in bioengineering approaches to in vitro tissue and ovarian follicle culture.

RECENT FINDINGS

Slow freezing is the most widely accepted method for ovarian tissue cryopreservation, but efforts have been made to modify vitrification for this application as well. Numerous approaches to in vitro tissue and follicle culture are in development, most prominently two-step culture systems for ovarian cortical tissue and encapsulation of ovarian follicles in biomimetic matrices for in vitro culture.

SUMMARY

Refinements to slow freeze and vitrification protocols continue to address challenges associated with cryopreservation, such as ice crystal formation and damage to the stroma. Similarly, improvements to in vitro tissue and follicle culture show promise for utilizing patients' cryopreserved tissues to obtain mature gametes after disease treatment and remission. Development of an effective and reproducible culture system for human ovarian follicles will serve as a broad assisted reproductive technology for cancer survivors who cryopreserved tissue prior to treatment.

Optimizing ovarian tissue quality before cryopreservation: comparing outcomes of three decortication methods on stromal and follicular viability

OBJECTIVE

To evaluate whether specific ovarian decortication techniques vary in promoting ovarian cortex cryopreservation and transplant outcomes.

DESIGN

Experimental design.

SETTING

University hospital.

ANIMAL(S)

Nonobese diabetic (NOD)/severe combined immunodeficiency (SCID) female mice.

INTERVENTION(S)

Human ovarian biopsy samples allocated to one of the following decortication procedures: scratching with scalpel blade (B), cutting with microsurgical scissors (M), separation with slicer (S), or no-separation (control, C). Parallel, in vivo experiment: decortication techniques combined with slow freezing (SF) and vitrification (VT) before xenograft into immunodeficient mice.

MAIN OUTCOME MEASURE(S)

Follicular counts, apoptosis, shear stress, Hippo pathway and inflammation. In vivo: recovered grafts analyzed for follicular counts, angiogenesis, proliferation, and fibrosis.

RESULT(S)

There were no differences in follicular density or number of damaged follicles between the decortication techniques in the in vitro study. Nevertheless, the M samples showed statistically significantly increased stromal damage compared with the controls and S samples, and up-regulation of Hsp60 shear stress gene expression. Decortication by both M and S inhibited the Hippo pathway, promoting gene expression changes. In the 21-day xenograft, total follicular density statistically significantly decreased compared with the nongrafted controls in all groups. Nevertheless, no differences were observed between the decortication techniques. Ovarian stroma vascularization was increased in the vitrified samples, but among the slow-freezing samples, the B samples had the lowest microvessel density. The M decorticated xenografts had increased fibrosis.

CONCLUSION(S)

Decortication with a slicer causes less damage to ovarian tissue than other commonly used methods although microsurgical scissors seem to preserve slightly increased follicular numbers. Nevertheless, blade decortication seems to be a reliable technique for maintaining acceptable follicular conditions without inducing serious stromal impairment.

Whole Ovary Cryopreservation and Transplantation: A Systematic Review of Challenges and Research Developments in Animal Experiments and Humans

Ovarian tissue cryopreservation and transplantation is the only fertility preservation option that enables both restoration of fertility and resumption of ovarian endocrine function, avoiding the morbidity associated with premature menopause. It is also the only technique available to prepubertal patients and those whose treatment cannot be delayed for life-threatening reasons. Ovarian tissue cryopreservation can be carried out in two different ways, either as ovarian cortical fragments or as a whole organ with its vascular pedicle. Although use of cortical strips is the only procedure that has been approved by the American Society for Reproductive Medicine, it is fraught with drawbacks, the major one being serious follicle loss occurring after avascular transplantation due to prolonged warm ischemia. Whole ovary cryopreservation involves vascular transplantation, which could theoretically counteract the latter phenomenon and markedly improve follicle survival. In theory, this technique should maintain endocrine and reproductive functions much longer than grafting of ovarian cortical fragments. However, this procedure includes a number of critical steps related to (A) the level of surgical expertise required to accomplish retrieval of a whole ovary with its vascular pedicle, (B) the choice of cryopreservation technique for freezing of the intact organ, and (C) successful execution of functional vascular reanastomosis upon thawing. The aim of this systematic review is to shed light on these challenges and summarize solutions that have been proposed so far in animal experiments and humans in the field of whole ovary cryopreservation and transplantation.

Risk and mechanism of glucose metabolism disorder in the offspring conceived by female fertility maintenance technology

Although female fertility maintenance technology (FFMT) provides an effective option for preserving fertility in patients with cancer suffering from fertility loss due to cancer treatment, previous studies have shown that the technique has certain potential risks and requires an assessment of the health status of the offspring since FFMT may lead to glucose metabolism disorder in offspring mice. The present animal study examined the glucose metabolism of adult mice offspring born from ovarian tissue cryopreservation and orthotopic allotransplantation. The mice were divided into three groups: normal, fresh ovary transplantation, and cryopreserved ovary transplantation. We recorded fasting blood glucose, glucose tolerance, and fasting serum insulin level for six months. Liver DNA, RNA, and proteins were extracted to detect the interaction between DNA methylation and Grb10 expression and insulin signaling pathway factors such as P-IGF1R, P-IRS2, P-AKT, and Grb10. Female recipient mice that received FFMT could successfully give birth after mating. The average litter size and total litter size of the cryopreserved and fresh groups showed marked differences compared with the normal group. Compared with the normal group, the fasting blood glucose and fasting serum insulin levels were higher in the cryopreserved and fresh groups. The mRNA and protein expressions of Grb10 were higher in the fresh and cryopreserved groups. Compared with the normal group, the DNA methylation status of four of the 11 sites of the Grb10 promoter was lower in the cryopreserved group. Grb10 overexpression inhibited the downstream phosphorylation protein factor expression (p-IGF-1R, p-IRS2, and p-Akt) of the IGF-1R signaling pathway. Female fertility maintenance technology (FFMT), including ovarian tissue cryopreservation (OTC), and orthotopic allotransplantation techniques might lead to glucose metabolism disorders in offspring mice.

Altered expression of activator proteins that control follicle reserve after ovarian tissue cryopreservation/transplantation and primordial follicle loss prevention by rapamycin

PURPOSE

We investigated whether expression of activator proteins that control follicle reserve and growth change after ovarian tissue vitrification and re-transplantation. Moreover, we assessed whether inhibition of mTOR signaling pathway by rapamycin would protect primordial follicle reserve after ovarian tissue freezing/thawing and re-transplantation.

METHODS

Fresh control, frozen/thawed, fresh-transplanted, frozen/thawed and transplanted, rapamycin/control, rapamycin fresh-transplanted, and rapamycin frozen-thawed and transplanted groups were established in rats. After freezing and thawing process, two ovaries were transplanted into the back muscle of the same rat. After 2 weeks, grafts were harvested, fixed, and embedded into paraffin block. Normal and atretic primordial/growing follicle count was performed in all groups. Ovarian tissues were evaluated for the dynamic expressions of Gdf-9, Bmp-15, KitL, Lif, Fgf-2, and p-s6K using immunohistochemistry, and H-score analyses were done.

RESULTS

Primordial follicle reserve reduced almost 50% after ovarian tissue re-transplantation. Expression of Gdf-9 and Lif increased significantly in primordial and growing follicles in frozen-thawed, fresh-transplanted, and frozen/thawed and transplanted groups, whereas expression of Bmp-15, KitL, and Fgf-2 decreased in primordial follicles. Freezing and thawing of ovarian tissue solely significantly increased p-s6K expression in primordial follicles, and on the other hand, suppression of mTORC1 pathway using rapamycin preserved the primordial follicle pool.

CONCLUSION

Altered expressions of activator proteins that regulate primordial follicle reserve and growth may lead to primordial follicle loss and rapamycin treatment can protect ovarian reserve after ovarian tissue cryopreservation/transplantation.

Investigation on revascularization time and initial damage after transplantation of fresh and cryopreserved ovarian tissue in domestic cats

The present study evaluated revascularization time of fresh and cryopreserved cat ovarian tissue after transplantation to subcutaneous tissue. Ovaries of five cats were used and eight pieces of ovarian tissue were taken from each pair of ovaries. Immediately after removal, three pieces were transplanted and one fixed for fresh control. The remaining four pieces were cryopreserved and, after thawing, one was fixed for cryopreservation control and three were transplanted. Grafts were recovered on days 2 (D2), 4 (D4) and 6 (D6) post-transplantation. Blood vessels were identified by immunohistochemistry and doppler ultrasound. Immunohistochemistry showed that the percentages of total tissue area occupied by blood vessels were similar (P > 0.05) in fresh and cryopreserved tissues. In both cases, blood vessel area was significantly higher (P < 0.05) on D4 and D6 compared to D0. Ultrasound analysis showed vascularization improvement on the periphery of grafts from D2 to D4 and from D4 to D6, both in fresh and cryopreserved tissue samples. Nonetheless, there was a significant decrease (P < 0.05) in the percentage of morphologically normal follicles (MNF) after transplantation compared to non-transplanted tissue (D0), both for fresh and cryopreserved samples. Moreover, the number of follicles found in samples was considerably smaller after grafting. In conclusion, revascularization of ovarian tissue autotransplanted to subcutaneous tissue in domestic cats occurs within 4 days after transplantation, both for fresh and cryopreserved tissue. However, large follicular loss has been observed in the first days post-transplantation, especially in cryopreserved tissues.

Adipose tissue-derived stem cells boost vascularization in grafted ovarian tissue by growth factor secretion and differentiation into endothelial cell lineages

Adipose tissue-derived stem cells (ASCs) have multilineage differentiation potential, proangiogenic properties, and the ability to enhance vascularization in xenografted human ovarian tissue. The aim of the present study was to identify the mechanisms behind the proangiogenic effects of ASCs. For this purpose, severe combined immunodeficient (SCID) mice were grafted with frozen-thawed human ovarian tissue. ASCs were labeled by lentiviral transfection for expression of enhanced green fluorescent protein (eGFP), and human ovarian tissue was grafted using a previously described two-step procedure. In the control group, ovarian tissue was transplanted using the standard one-step approach. Samples were collected and analyzed after 7 days. Detection of the eGFP antigen by immunofluorescence showed ASCs surrounding and infiltrating ovarian tissue grafts. Significantly higher vessel density was observed in the ASC group (P = 0.0182 versus control) on Day 7. Co-expression of eGFP, CD34 and CD31 was demonstrated in human vessels, confirming ASC differentiation into human endothelial cell lineages. Increased gene expression of vascular endothelial growth factor (VEGF) was also shown in the ASC group (P = 0.0182 versus control). Immunohistochemistry targeting anti-human VEGF revealed significantly higher expression levels in the ASC group (P = 0.033 versus control), while VEGF and eGFP immunofluorescence showed greater growth factor expression in areas surrounding ASCs. In conclusion, ASCs differentiate into human vessels and promote secretion of VEGF when transplanted together with human ovarian tissue to SCID mouse peritoneum using a two-step ovarian tissue grafting procedure. This is a promising step towards potentially improving ovarian tissue quality and lifespan. Long-term studies should be conducted to investigate ASC safety and efficacy in the context of ovarian tissue transplantation.

Fertility preservation for young adults, adolescents, and children with cancer

Options for fertility preservation (FP) through cryopreservation methods are currently available for young adults, adolescents, and children. Guidelines for FP have been provided by international clinical societies, and emergency procedures aimed at FP have been implemented into clinical practice worldwide. In this article, we review the current data on clinical standards of emergency FP in patients who are facing gonadotoxic effects of cancer treatment, and we also describe the methods that are still under development, usually denoted as experimental. In Sweden, programmes for FP have been established at large university hospitals, thus covering the whole country. The Swedish publicly financed health care covers both assisted reproduction for treatment of infertility and the cryopreservation of gametes or gonadal tissue when there is a medical indication, such as the risk to become infertile due to oncologic treatment; hence the access to FP is ensured for the whole population. At our centre at Karolinska University Hospital in Stockholm, methods for FP have been offered since 1988. In this article, we also review the oncologic indications for FP in our patient cohort of >3000 individuals during the period 1988-2018.

Vitrification technique for female germinative tissue cryopreservation and banking

Objective

To report on a device designed for the vitrification of germinative tissue, and a systematic vitrification/warming protocol.

Methods

We obtained six fragments of cortical germinative tissue from a human ovary. We randomly chose two fragments and sent them to histological analysis. We vitrified four test samples and stored them for one week in liquid nitrogen (LN), and warmed one week later. We sent the vitrified/warmed fragments to the pathology laboratory, where they analyzed them morphologically under an optical microscope (10-40X). They analyzed the nuclear and cytoplasmic characteristics of the follicular cells, luteal layer, and stroma. The primordial and primary follicles in the fresh and vitrified/warmed fragments were counted and compared with the Mann-Whitney test (p<0.05).

Results

There were ovarian follicles in different phases of maturation in both fresh and vitrified/warmed fragments, with a predominance of healthy-looking primordial and primary follicles. In the test fragments, the fusocellular architecture supporting the stromal cells exhibited some foci of edema, and were associated with cells with hydropic degeneration, with cytoplasmic fragmentation and eosinophilia. However, there were no signs of tissue necrosis or autolysis. There was no statistically significant difference between the number of follicles found in the control and test tissue fragments (p>0.05).

Conclusions

There were no significant morphological changes between fresh and vitrified/warmed germinative tissue. The vitrification device and protocol tested were effective in the preservation of human follicles, and should be considered for the banking germinative tissue for the restoration of fertility of women who are submitted to life-saving sterilizing treatments.

History, Evolution and Current State of Ovarian Tissue Auto-Transplantation with Cryopreserved Tissue: a Successful Translational Research Journey from 1999 to 2020

The loss of fertility and early menopause are common after gonadotoxic therapies and radical pelvic surgery. The strategy of ovarian tissue cryopreservation and auto-transplantation was introduced to prevent this significant quality of health issue. Ovarian transplantation with cryopreserved tissue has gone through remarkable evolution in the last 20 years. In this review, we detail the history and evolution of ovarian transplantation with cryopreserved tissue from its origins to the present. Ovarian cryopreservation and transplantation approach was first tested with animal models. The approach was then validated in human ovarian xenografting models before being applied to patients in pioneering clinical studies. The first orthotopic and heterotopic approaches to ovarian transplantation was developed by Oktay et al. who reported the first successful restoration of ovarian function with these approaches beginning in 2000 with first embryo development in 2004. Controversy remains on when the first live birth occurred after orthotopic ovarian transplantation with cryopreserved tissue as the patient was ovulating with elevated progesterone levels in the case reported in 2004; first live birth is likely to be the one reported by Meirow et al. in 2005. Nevertheless, the technique has evolved to reach a level where most recent live birth rates are exceeding 35% and the procedure is no longer considered experimental by many.

Ovarian tissue vitrification is more efficient than slow freezing to preserve ovarian stem cells in CF-1 mice

OBJECTIVE

The aim of this study was to investigate the efficacy of protocols for mice ovary cryopreservation to compare the differences in Mouse Vasa Homologue expression (a germline cell marker) and ovarian viability after vitrification or slow freezing.

METHODS

Female CF1 mice aged 40-45 days were randomly divided into three groups: Control, vitrification or slow freezing. Their ovaries were surgically removed, rinsed in saline solution and cryopreserved. For vitrification, we used a commercial protocol and for slow freeze, we used 1.5 M ethylene glycol (EG) as cryoprotectant. After that, the ovaries were processed for histological an immunohistochemical analysis, and counting of primordial, primary, pre-antral and antral follicles.

RESULTS

No significant difference was found in the proportion of high-quality primordial, primary and pre-antral follicles after thawing/warming in the slow freezing and vitrification groups. The immunohistochemistry for MVH antibody demonstrated that the slow freeze group had a higher number of unmarked cells (p=0.012), indicating a harmful effect on the MVH expression in the ovarian tissue, where the cell structure is complex.

CONCLUSION

Although both protocols indicated similar results in the histological analysis of follicular counts, the vitrification protocol was significantly better to preserve ovarian stem cells, an immature germ cell population. These cells are able to self-renew having regeneration potential, and may be effective for the treatment of ovarian failure and consequently infertility.

Influence of graft size, histocompatibility,and cryopreservation on reproductive outcome following ovary transplantation in mice

Purpose

Transplantation of ovarian tissue is a valuable method to rescue mouse strains with fertility problems and to revitalize archived strains. The purpose of this study was to investigate the effect of (i) different sizes of transplanted ovary pieces on reproductive outcome, (ii) use of immunodeficient recipients to overcome the limitation of histocompatibility, and (iii) to compare different protocols for cryopreservation of ovarian tissue.

Methods

Halves, quarters, and eights of mouse ovaries were transplanted. Half ovaries from B6 donors were transferred into immunodeficient mice. Halves of ovaries were frozen according to four different protocols, thawed and transferred.

Results

Pregnancy rate after transplantation of ovarian tissue was high (90–100%) independent of the transplant size. Although, the average litter size was significantly lower for recipients of quarters and eights (4.4 and 4.6 vs. 6.5), the total number of offspring produced per donor ovary was higher compared with recipients of halves. Pregnancy rate of immunodeficient recipients was 40% (mean 4.7 offspring per litter). All four cryopreservation protocols used were able to preserve functionality of the ovarian tissue.

Conclusions

Transplantation of ovarian tissue smaller than halves resulted in reduced litter sizes. The distribution of ovarian tissue of one donor female to 4 or 8 recipients will therefore yield in a higher total number of offspring in a certain time period. The use of immunodeficient recipients is an option for non-histocompatible donors. Cryopreservation of ovarian tissue is generally feasible but the function of frozen-thawed ovary halves after transplantation differs depending on the freezing protocol used.

Current state and future possibilities of ovarian tissue transplantation

BACKGROUND

As a result of recent developments in cancer treatment, cancer survivorship and survivors' quality of life have been emphasized. Although ovarian tissue cryopreservation (OTC) is an experimental technique, it would be the sole technique for fertility preservation treatment for girls with malignant disease. Indeed, OTC requires ovarian tissue transplantation (OTT) for conception. As for OTC, there is room to investigate OTT. The present review focused on the current state and progress of OTT.

METHOD

The literature regarding OTT, which is currently under development, was reviewed.

MAIN FINDINGS

To improve the outcome of OTT, both efficacy and safety are important. Good surgical technique and the optimal site are important surgical factors, with orthotopic transplantation increasing. Treatment of growth factors, gonadotropins, antioxidants, apoptosis suppression factors, and cell therapy may improve the efficacy of OTT by inducing neo-angiogenesis and preventing damage. Artificial ovaries, complete in vitro primordial follicle culture technique, and non-invasive ovarian imaging techniques, such as optical coherence tomography, to select the best ovarian tissue are future possibilities.

CONCLUSION

Improving neo-angiogenesis and preventing damage with optimization, as well as investigation of future techniques, may bring us to the next stage of a fertility preservation strategy.

A simple method to quantify follicle survival in cryopreserved human ovarian tissue

STUDY QUESTION

Can follicle survival in frozen-thawed human ovarian tissue be quantified in situ using the dye Neutral Red (NR) to stain viable follicles specifically?

SUMMARY ANSWER

A follicle survival rate within ovarian tissue can be calculated using NR followed by histological evaluation and evidence for a consistently high follicle survival in a series of ovarian tissue from 25 Danish girls and women undergoing ovarian tissue cryopreservation (OTC) was obtained.

WHAT IS KNOWN ALREADY

Securing follicle survival in cryopreserved ovarian tissue is crucial for proper quality control when centers wish to implement OTC. The only established technique for validation of follicle survival is xenografting of thawed ovarian tissue to immunodeficient mice. However, this functional test is expensive, time consuming, requires animal facilities and only provides a qualitative-not quantitative-measure for follicle survival.

STUDY DESIGN SIZE, DURATION

Quantification of follicle survival in human ovarian tissue donated from 30 girls and women having tissue cryopreserved for fertility preservation from 2000 to 2015 at the Laboratory of Reproductive Biology in Copenhagen, Denmark.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Cryopreserved ovarian cortex was donated from 25 girls and young women aged 10-36 years (mean age: 25 years) and the average storage time in liquid nitrogen was 9.1 ± 5.6 years, ranging from 1.6 to 17.9 years. In 12 of the cases, the ovarian tissue was collected from the local hospital and in the other 13 cases the ovarian tissue was transported on ice up to 6 h prior to freezing. Donated fresh ovarian surplus tissue was obtained from five women aged 23-34 years (mean age: 27 years). Ovarian tissues were chopped into small fragments and incubated in culture medium containing 50 mg/ml NR for 3-4 h. Fragments of ovarian tissue containing clearly NR-stained follicles were selected for counting, encapsulated in 4% agar and were processed for histology to calculate a follicular survival rate.

MAIN RESULTS AND THE ROLE OF CHANCE

The mean follicle survival rate in the 25 patients after freezing and thawing was 84% ± 11 (mean ±SD), ranging from 50% to 98%. The high follicle survival rate in this clinical series of patients reflects a constant high-quality service performed in our center and confirms the robustness of the slow freezing protocol. No significant association between follicle survival rates and storage time was found using linear regression analysis, suggesting that storage in liquid nitrogen does not affect viability of the tissue. No significant association in follicle survival rates was found between ovarian tissues collected at the local hospital compared to tissues transported on ice prior to freezing, supporting that prolonged cooling does not seem to greatly affect the follicle survival. For the fresh ovarian tissue, the average follicle survival rate was 91% ± 5 (mean ± SD) in five patients, ranging from 81% to 95%.

LIMITATIONS, REASONS FOR CAUTION

Even though the NR staining requires active incorporation of the dye, the test is merely a short in situ test that cannot completely replace the functional value of xenografting studies in which the integrity and developmental potential of the ovarian follicles are assessed.

WIDER IMPLICATIONS OF THE FINDINGS

OTC is now being employed around the world but to date it has been difficult for centers to evaluate the effectiveness of their program and perform proper quality control. NR staining combined with histological evaluation is the first quantitative method to provide a survival rate for follicles in frozen-thawed human ovarian tissue and offer a valuable and easily applicable tool to validate the cryopreservation procedure when implementing OTC or as routine quality control for the overall freezing performance within tissue banking facilities.

STUDY FUNDING/COMPETING INTEREST(S)

The Research Pools of Rigshospitalet, the Danish Cancer Foundation, Dagmar Marshalls Foundation, and the Novo Nordic Foundation are thanked for having funded this study. The authors have no conflicts of interest.

Is the pre-antral ovarian follicle the 'holy grail'for female fertility preservation?

Fertility preservation is not only a concern for humans with compromised fertility after cancer treatment. The preservation of genetic material from endangered animal species or animals with important genetic traits will also greatly benefit from the development of alternative fertility preservation strategies. In humans, embryo cryopreservation and mature-oocyte cryopreservation are currently the only approved methods for fertility preservation. Ovarian tissue cryopreservation is specifically indicated for prepubertal girls and women whose cancer treatment cannot be postponed. The cryopreservation of pre-antral follicles (PAFs) is a safer alternative for cancer patients who are at risk of the reintroduction of malignant cells. As PAFs account for the vast majority of follicles in the ovarian cortex, they represent an untapped potential, which could be cultivated for reproduction, preservation, or research purposes. Vitrification is being used more and more as it seems to yield better results compared to slow freezing, although protocols still need to be optimized for each specific cell type and species. Several methods can be used to assess follicle quality, ranging from simple viability stains to more complex xenografting procedures. In vitro development of PAFs to the pre-ovulatory stage has not yet been achieved in humans and larger animals. However, in vitro culture systems for PAFs are under development and are expected to become available in the near future. This review will focus on recent developments in (human) fertility preservation strategies, which are often accomplished by the use of in vitro animal models due to ethical considerations and the scarcity of human research material.