Follicle survival and growth to antral stages in short-term murine ovarian cortical transplants after Cryologic solid surface vitrification or slow-rate freezing

Ultrastructure of human ovarian tissues and risk of cancer cells re-implantation after transplantation to chick embryo chorioallantois membrane (CAM) following vitrification or slow freezing

Ovarian follicle depletion and premature ovarian failure are significant challenges in cancer patients subjected to radio- or chemotherapy. Ovarian tissue (OT) cryopreservation would be an option when other fertility preservation methods are not accessible. This study aimed to analyze the structure and ultrastructure of human OTs transplanted onto chick embryo chorioallantois membrane (CAM) after cryopreservation by vitrification or slow freezing. OTs from 10 cancer patients underwent cryopreservation. CAM transplantation was done on fresh and cryopreserved OTs, to assign samples to nine study groups as follows: 1) FI-FIII = fresh, 5- and 10-days post-CAM transplantation groups; 2) VI-VIII = vitrified, 5- and 10-days post-transplantation vitrified groups; 3) SFI-SFIII: slow frozen, 5- and 10-days post-transplantation slow freezing groups. Proliferation ability, folliculogenesis, and structural and ultrastructure were analyzed. The density of primordial follicles did not change after both freezing methods, but reduced after 5 (P ≥ 0.05) and 10 days (P ≤ 0.05) post-CAM transplantation. The follicular grade significantly decreased in all transplanted tissues (P ≤ 0.0). The proliferation marker increased after cryopreservation, but reduced after transplantation (P ≤ 0.05). TEM evaluation showed better follicular ultrastructure in the fresh group, after transplantation. Stromal ultrastructure appeared more preserved after vitrification compared with slow freezing. There was no sign of malignant cell contamination after transplantation. Some follicular TEM abnormalities were found in both methods of freezing, with a better transplantation rate after vitrification. Also, enhanced follicular activation resulted in faster follicular depletion in this method. The information regarding post grafting events would improve our knowledge for longer OTs' lifespans.

Heterotopic autotransplantation of ovarian tissue in a large animal model: Effects of cooling and VEGF

Heterotopic and orthotopic ovarian tissue autotransplantation techniques, currently used in humans, will become promising alternative methods for fertility preservation in domestic and wild animals. Thus, this study describes for the first time the efficiency of a heterotopic ovarian tissue autotransplantation technique in a large livestock species (i.e., horses) after ovarian fragments were exposed or not to a cooling process (4°C/24 h) and/or VEGF before grafting. Ovarian fragments were collected in vivo via an ultrasound-guided biopsy pick-up method and surgically autografted in a subcutaneous site in both sides of the neck in each mare. The blood flow perfusion at the transplantation site was monitored at days 2, 4, 6, and 7 post-grafting using color-Doppler ultrasonography. Ovarian grafts were recovered 7 days post-transplantation and subjected to histological analyses. The exposure of the ovarian fragments to VEGF before grafting was not beneficial to the quality of the tissue; however, the cooling process of the fragments reduced the acute hyperemia post-grafting. Cooled grafts compared with non-cooled grafts contained similar values for normal and developing preantral follicles, vessel density, and stromal cell apoptosis; lower collagen type III fibers and follicular density; and higher stromal cell density, AgNOR, and collagen type I fibers. In conclusion, VEGF exposure before autotransplantation did not improve the quality of grafted tissues. However, cooling ovarian tissue for at least 24 h before grafting can be beneficial because satisfactory rates of follicle survival and development, stromal cell survival and proliferation, as well as vessel density, were obtained.

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.

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.

Development of fresh and vitrified agouti ovarian tissue after xenografting to ovariectomised severe combined immunodeficiency (SCID) mice

The aim of the present study was to evaluate the development of fresh and vitrified agouti ovarian tissue after xenografting to C57Bl/6 severe combined immunodeficiency (SCID) female mice. Ovaries were obtained from five female agoutis and divided into 16 fragments. Five fragments were transplanted immediately to ovariectomised SCID mice and the others were vitrified, stored for 2 weeks and transplanted only after rewarming. Tissue fragments were transplanted under the kidney capsule in recipients. The return of ovarian activity in recipients was monitored by the observation of external signs of oestrus and vaginal cytology over a period of 40 days after transplantation, after which the grafts were removed and evaluated for morphology, cell proliferation and the occurrence of DNA fragmentation. Ovarian activity returned in four of five mice that received fresh ovarian tissue from agoutis and in one of six mice that had received vitrified tissue a mean (±s.e.m.) 20.6±8.6 days after xenotransplantation. After graft removal, a predominance of primordial and primary follicles was observed in all grafts. Vitrification reduced cell proliferation and increased the occurrence of DNA fragmentation in grafted agouti ovarian tissue. In conclusion, the present study demonstrates that xenografted agouti ovarian tissue, fresh or vitrified, is able to promote the return of ovarian activity in ovariectomised SCID C57B1/6 mice. However, improvements to vitrification protocols for agouti ovarian tissue are necessary.

GDF9-β promotes folliculogenesis in sheep ovarian transplantation onto the chick embryo chorioallantoic membrane (CAM) in cryopreservation programs

PURPOSE

Ovarian tissue (OT) cryopreservation is a treatment option for fertility preservation among young cancer patients. However, the procedure may involve a reduction in the GDF9-β expression and a delay in follicular growth after thawing and transplantation. The aim of this study was to evaluate whether supplementation of GDF9-β can compensate the reduction of this factor during the cryopresevation process and promote folliculogenesis after transplantation of thawed sheep ovarian tissue.

METHODS

Sheep OT was cryopreserved using two methods of vitrification and slow freezing. Fresh and thawed OTs were then transplanted onto chick embryo chorioallantoic membrane (CAM) and then divided into two groups based on the addition of GDF9-β to the grafted tissue. After 5 days of culture, both histological and immunohistological (Ki-67) assessments were performed to evaluate follicular structure, development, and proliferation. The fibrotic and necrotic areas were measured using MICROVISIBLE software.

RESULTS

Folliculogenesis took place in all culture groups, but was significantly improved only in the +GDF9-β cultured group. Also, better follicular structure was preserved in the aforementioned group (p < 0.05). When GDF9-β was supplemented to the culture medium, more neovascularization (p < 0.05) and better transplantation (p > 0.05) was observed. Furthermore, the areas of fibrosis and necrosis were lower in this group rather than the controls. Follicular proliferative activity was significantly higher only in the slow freezing +GDF9-β cultured group.

CONCLUSIONS

GDF9-β, as a stimulatory factor, not only promoted the folliculogenesis in the fresh ovarian transplant, but also compensated for its reduction during the cryopreservation process.

Conservation of somatic tissue derived from collared peccaries (Pecari tajacu Linnaeus, 1758) using direct or solid-surface vitrification techniques

Cryopreservation of somatic tissue can be applied in biodiversity conservation, especially for wild species as collared peccary. We aimed to evaluate the effect of vitrification techniques of ear tissue of collared peccary [direct vitrification in cryovials (DVC) or solid-surface vitrification (SSV)] on the layers of epidermis and dermis by conventional histology and cell ability during the in vitro culture. Thus, both the vitrification methods were able to maintain normal patterns of the epidermis as the cornea and granular layers, furthermore the intercellular space and dermal-epidermal junction of the spinous layer when compared to fresh control. Nevertheless, DVC and SSV percentage of normality decreased in the morphological integrity of cytoplasm (37.5 and 25.0%) of spinous layer, respectively, as compared to the fresh fragments (100%, p < 0.05). Moreover, other differences between the fresh control (100%) and DVC tissues were verified in the intra-epidermal cleavage of the spinous (37.5%) and basal (37.5%) layers. In general, DVC and SSV techniques were efficient for the recovery of the somatic cells according to most of the evaluated parameters for the in vitro culture (p > 0.05). In addition, only at time of 72 h (D3), in the growth curve, DVC fragments showed a reduced cell concentration than fresh control. In conclusion, SSV was found to be a more efficient method for vitrifying collared peccary skin tissue when compared to DVC. These results are relevant for the tissue cryopreservation from collared peccary and could also be useful for mammals with phylogenetic relationships.

Ovarian fragment sizes affect viability and morphology of preantral follicles during storage at 4°C

The method of transportation and the conditions imposed on the ovarian tissue are pivotal aspects for the success of ovarian tissue cryopreservation (OTC). The aim of this study was to evaluate the effect of the size of the ovarian tissue (e.g. whole ovary, biopsy size and transplant size) during different times of storage (0, 6, 12 and 24 h) on the structural integrity of equine ovarian tissue transported at 4°C. Eighteen pairs of ovaries from young mares (<10 years old) were harvested in a slaughterhouse and processed to simulate the fragment sizes (biopsy and transplant size groups) or kept intact (whole ovary group) and stored at 4°C for up to 24 h in α-MEM-enriched solution. The effect of the size of the ovarian tissue was observed on the morphology of preantral follicles, stromal cell density, DNA fragmentation and mitochondrial membrane potential. The results showed that (i) biopsy size fragments had more morphologically normal preantral follicles after 24 h of storage at 4°C; (ii) mitochondrial membrane potential was the lowest during each storage time when the whole ovary was used; (iii) DNA fragmentation rate in the ovarian cells of all sizes of fragments increased as storage was prolonged and (iv) transplant size fragments had increased stromal cell density during storage at cool temperature. In conclusion, the biopsy size fragment was the best to preserve follicle morphology for long storage (24 h); however, transportation/storage should be prior determined according to the distance (time of transportation) between patient and reproduction centers/clinics.

Characterisation and cryopreservation of the ovarian preantral follicle population from Spix’s yellow-toothed cavies (Galea spixii Wagler, 1831)

The aim of the present study was to characterise the ovarian preantral follicle (PF) population and to establish a solid surface vitrification (SSV) process using dimethyl sulfoxide (DMSO) as a cryoprotectant for preservation of ovarian tissue from yellow-toothed cavies (Galea spixii). Ovaries were fixed for PF population analysis or were subjected to the SSV process. The mean (± s.e.m.) PF population per ovarian pair was estimated to be 416.0 ± 342.8. There were 140.0 ± 56.0 (63.4%) and 125.0 ± 58.0 (64.0%) primary follicles on the right and left ovaries, respectively. The proportion of this follicle category was significantly greater than that of other follicle categories (P < 0.05). The diameter of follicles (123.7 ± 18.3 µm), oocytes (50.1 ± 5.0 µm) and nuclei (14.27 ± 2.01 µm) was larger for secondary ones when compared with other PFs categories. Most PFs were morphologically normal (94.6%), with light microscopy identifying only a few atretic follicles (5.4%). After SSV, there was a reduction in the proportion of morphologically normal PFs compared with the non-vitrified group (69.5% vs 91.2%, respectively). Transmission electron microscopy revealed preservation of oocytes and granulosa cell membranes and the morphological aspect of follicles; the primary change observed in some vitrified PFs was the presence of vacuoles in the oocytes and granulosa cells cytoplasm and turgid mitochondria. In conclusion, the present study provides an estimative and characterization for the PF population in ovaries of G. spixii. Moreover, we report its PFs cryopreservation using an SSV process.

Cryopreservation: Vitrification and Controlled Rate Cooling

Cryopreservation is the application of low temperatures to preserve the structural and functional integrity of cells and tissues. Conventional cooling protocols allow ice to form and solute concentrations to rise during the cryopreservation process. The damage caused by the rise in solute concentration can be mitigated by the use of compounds known as cryoprotectants. Such compounds protect cells from the consequences of slow cooling injury, allowing them to be cooled at cooling rates which avoid the lethal effects of intracellular ice. An alternative to conventional cooling is vitrification. Vitrification methods incorporate cryoprotectants at sufficiently high concentrations to prevent ice crystallization so that the system forms an amorphous glass thus avoiding the damaging effects caused by conventional slow cooling. However, vitrification too can impose damaging consequences on cells as the cryoprotectant concentrations required to vitrify cells at lower cooling rates are potentially, and often, harmful. While these concentrations can be lowered to nontoxic levels, if the cells are ultra-rapidly cooled, the resulting metastable system can lead to damage through devitrification and growth of ice during subsequent storage and rewarming if not appropriately handled.The commercial and clinical application of stem cells requires robust and reproducible cryopreservation protocols and appropriate long-term, low-temperature storage conditions to provide reliable master and working cell banks. Though current Good Manufacturing Practice (cGMP) compliant methods for the derivation and banking of clinical grade pluripotent stem cells exist and stem cell lines suitable for clinical applications are available, current cryopreservation protocols, whether for vitrification or conventional slow freezing, remain suboptimal. Apart from the resultant loss of valuable product that suboptimal cryopreservation engenders, there is a danger that such processes will impose a selective pressure on the cells selecting out a nonrepresentative, freeze-resistant subpopulation. Optimizing this process requires knowledge of the fundamental processes that occur during the freezing of cellular systems, the mechanisms of damage and methods for avoiding them. This chapter draws together the knowledge of cryopreservation gained in other systems with the current state-of-the-art for embryonic and induced pluripotent stem cell preservation in an attempt to provide the background for future attempts to optimize cryopreservation protocols.

Three dimensional in vitro culture of preantral follicles following slow-freezing and vitrification of mouse ovarian tissue

To evaluate the effects slow-freezing and vitrification on three dimensional in vitro culture of preantral follicles, ovaries of 12-14 days old female NMRI mice were isolated and randomly assigned to fresh control, slow-freezing and vitrification groups. Slow-freezing was performed using programmable freezer. Vitrification was carried out in a medium consisting of ethylene glycol (EG) and dimethyl sulphoxide (Me2SO) by needle immersion method. middle sized preantral follicles were mechanically isolated and cultured for 12 days in 0.7% sodium alginate gel. The follicles development and quantitative expression of oocyte specific genes (Bmp15, Gdf9, Fgf8) and the growth related genes (Igf1, Kit, Kit-l) were assessed after 1, 8 and 12 days of culture. Both cryopreserved groups showed reduction of follicular survival rates compared to the control group on days 8 and 12 of culture (P < 0.05). Antrum formation rates reduced in slow-freezing after 12 days of culture (P < 0.05). Evaluation of gene expression showed reduction of Bmp15, Gdf9, Fgf8, Kit and Kit-l during 12 days of culture (P < 0.05). Kit and Kit-l expression in slow-freezing group significantly reduced on day 8 of culture (p < 0.05). Igf1 expression was lower in slow-freezing group on 1st day of culture than vitrification and control groups (P < 0.05). Finally, intergroup comparison showed same expression pattern of genes after 12 days of culture. Thus, cryopreservation of mouse ovaries by both methods can preserve most developmental parameters and expression of maturation genes. However, vitrification is a better method for cryopreservation of mouse ovaries due to greater antrum formation and expression of growth related markers.

Interaction between differential gene expression profile and phenotype in bovine blastocysts originating from oocytes exposed to elevated non-esterified fatty acid concentrations

Maternal metabolic disorders linked to lipolysis are major risk factors for reproductive failure. A notable feature of such disorders is increased non-esterified fatty acid (NEFA) concentrations in the blood, which are reflected in the ovarian follicular fluid. Elevated NEFA concentrations impact on the maturing oocyte and even alter subsequent embryo physiology. The aetiological mechanisms have not been fully elucidated. Therefore, in the present study, bovine in vitro maturing cumulus-oocyte complexes were exposed (24 h) to three different maturation treatments containing: (1) physiological (72 µM) NEFA concentrations (=control); (2) elevated (75 µM) stearic acid (SA) concentrations (=HIGH SA); and (3) elevated (425 µM) NEFA concentrations (=HIGH COMBI). Zygotes were fertilised and cultured following standard procedures. Transcriptomic analyses in resulting Day 7.5 blastocysts revealed that the major pathways affected are related to lipid and carbohydrate metabolism in HIGH COMBI embryos and to lipid metabolism and cell death in HIGH SA embryos. Furthermore, lower glutathione content and a reduced number of lipid droplets per cell were observed in HIGH SA-exposed oocytes and resulting morulae, respectively, compared with their HIGH COMBI-exposed counterparts. Vitrified embryos originating from HIGH SA-exposed oocytes tended to exhibit lower survival rates compared with controls. These data suggest possible mechanisms explaining why females across species suffering lipolytic disorders experience difficulties in conceiving.

Effects of neutral red assisted viability assessment on the cryotolerance of isolated bovine preantral follicles

PURPOSE

Fertility preservation strategies warrant non-invasive viability assessment of preantral follicles (PAF) such as staining with Neutral Red (NR) that is incorporated by viable follicles. To optimize the procedure, we firstly determined the lowest concentration and shortest exposure time needed for optimal viability screening of isolated bovine PAF. Secondly, we combined this protocol to a vitrification procedure to assess cryotolerance of the stained follicles.

METHODS

Isolated PAF (900, divided over 6 replicates) were cultured in DMEM/Ham's F12 (Culture Medium - Cm) for 4 days (38.5 °C, 5% CO2). On D0, D2 and D4, follicles were stained, by adding NR medium (NRm = Cm with different concentrations NR) after which viability was assessed by counting stained/non-stained PAF every 30 min for a period of 2 h.

RESULTS

Following a binary logistic regression analysis with staining as a result (yes/no) versus log-concentration, a probability model could be fitted, indicating that the proportion of stained follicles remained stable after 30 min when 15 μg/ml NR was used, without compromising follicular health and viability. Consequently, using this protocol, no significant effect of staining prior to vitrification, was found on PAF viability immediately after warming or following 4 days of culture.

CONCLUSIONS

In conclusion, we propose NR staining as a non-invasive, non-detrimental viability assessment tool for PAF, when applied at 15 μg/ml for 30 min, being perfectly compatible with PAF vitrification.

Characterization of freshly retrieved preantral follicles using a low-invasive, mechanical isolation method extended to different ruminant species

Due to the increased interest in preantral follicular physiology, non-invasive retrieval and morphological classification are crucial. Therefore, this study aimed: (1) to standardize a minimally invasive isolation protocol, applicable to three ruminant species; (2) to morphologically classify preantral follicles upon retrieval; and (3) to describe morphological features of freshly retrieved follicles compared with follicle characteristics using invasive methods. Bovine, caprine and ovine ovarian cortex strips were retrieved from slaughterhouse ovaries and dispersed. This suspension was filtered, centrifuged, re-suspended and transferred to a Petri dish, to which 0.025 mg/ml neutral red (NR) was added to assess the viability of the isolated follicles. Between 59 and 191 follicles per follicle class and per species were collected and classified by light microscopy, based on follicular cell morphology. Subsequently, follicle diameters were measured. The proposed isolation protocol was applicable to all three species and showed a significant, expected increase in diameter with developmental stage. With an average diameter of 37 ± 5 μm for primordial follicles, 47 ± 6.3 μm for primary follicles and 67.1 ± 13.1 μm for secondary follicles, no significant difference in diameter among the three species was observed. Bovine, caprine and ovine follicles (63, 59 and 50% respectively) were graded as viable upon retrieval. Using the same morphological characteristics as determined by invasive techniques [e.g. haematoxylin–eosin (HE) sections], cumulus cell morphology and follicle diameter could be used routinely to classify freshly retrieved follicles. Finally, we applied a mechanical, minimally invasive, follicle isolation protocol and extended it to three ruminant species, yielding viable preantral follicles without compromising further in vitro processing and allowing routine follicle characterization upon retrieval.

Vitrified-warmed ovarian tissue autotransplantation into ovariectomized mice restores sufficient ovarian function to support full-term pregnancy

Purpose

Our previous study demonstrated that heterotopic autotransplantation of fresh ovarian tissue followed by transfer of blastocysts supported full-term pregnancy in the mouse. In the present study, to address whether vitrified-warmed ovarian tissue has the potential to support uterine preparation for implantation and subsequent pregnancy to full term, we examined vitrified-warmed ovarian tissue autotransplantation (VOAT) in mice.

Methods

VOAT into kidney capsules was performed for sexual cycle-ceased mice after 7 days of ovariectomy. Uterine potential of decidualization was examined by oil infusion on day 4 of pseudopregnancy. Immunohistochemical analysis was performed to examine the potential in VOAT ovarian tissues. Blastocysts were transferred into uteri on day 4 of pseudopregnancy.

Results

In VOAT mice, uterine decidualization on day 8 of pseudopregnancy was the same as that in intact mice. Blastocyst transfer into the pseudopregnant VOAT mice showed the same rates of pregnancy and live birth pups as intact mice, while less steroidogenesis in the corpus luteum was detected in VOAT mice.

Conclusions

The autotransplantation of vitrified-warmed ovarian tissues after 7 days of ovariectomy restored their sexual cycle and then supported their pregnancy and production of offspring.

Cryopreservation of Human Stem Cells for Clinical Application: A Review

SUMMARY: Stem cells have been used in a clinical setting for many years. Haematopoietic stem cells have been used for the treatment of both haematological and non-haematological disease; while more recently mesenchymal stem cells derived from bone marrow have been the subject of both laboratory and early clinical studies. Whilst these cells show both multipotency and expansion potential, they nonetheless do not form stable cell lines in culture which is likely to limit the breadth of their application in the field of regenerative medicine. Human embryonic stem cells are pluripotent cells, capable of forming stable cell lines which retain the capacity to differentiate into cells from all three germ layers. This makes them of special significance in both regenerative medicine and toxicology. Induced pluripotent stem (iPS) cells may also provide a similar breadth of utility without some of the confounding ethical issues surrounding embryonic stem cells. An essential pre-requisite to the commercial and clinical application of stem cells are suitable cryopreservation protocols for long-term storage. Whilst effective methods for cryopreservation and storage have been developed for haematopoietic and mesenchymal stem cells, embryonic cells and iPS cells have proved more refractory. This paper reviews the current state of cryopreservation as it pertains to stem cells and in particular the embryonic and iPS cell.

Live offspring from vitrified blastocysts derived from fresh and cryopreserved ovarian tissue grafts of adult mice

Ovarian tissue cryopreservation and transplantation can be used to preserve fertility for cancer patients. In this study, we assessed the viability and function of ovarian tissue from adult mice that was cryopreserved by solid surface vitrification or traditional slow-cooling using variousin vitroandin vivotechniques, including allotransplantation,in vitrooocyte maturation, embryo culturein vitro, blastocyst cryopreservation, embryo transfer, and development. The importance of cumulus cells for oocyte maturation, fertilization, and embryo development was investigated. Graft recovery, follicle survival, and oocyte retrieval was similar in control, vitrified, and slow-cooled groups. High rates of oocyte maturation, cleavage, and blastocyst formation were achieved, with no significant differences between the control, vitrified or slow-cooled ovarian tissue grafts. The presence of cumulus cells was important for oocyte maturation, fertilization, and subsequent development. Cumulus–oocyte complexes with no surrounding cumulus cells (N-COCs) or with an incomplete layer (P-COCs) had significantly lower rates of oocyte maturation and blastocyst formation than cumulus–oocyte complexes with at least one complete layer of cumulus cells (F-COCs; maturation rate: 63, 78 vs 94%; blastocyst rate: 29, 49 vs 80%). Live births were achieved using vitrified blastocysts derived from oocytes taken from vitrified and slow-cooled ovarian tissue heterotypic allografts. Successful production of healthy offspring from these vitrified blastocysts suggests that this technique should be considered as a useful stage to pause in the assisted reproduction pathway. This provides an alternative protocol for restoring fertility and offering cancer patients a better indication of their chances of pregnancy and live birth.

Orthotopic and heterotopic ovarian tissue transplantation

BACKGROUND

Transplantation of ovarian tissue is, at present, the only clinical option available to restore fertility using cryopreserved ovarian tissue. More than 30 transplantations of cryopreserved tissue have been reported, and six babies have been born, worldwide, following this procedure. Despite these encouraging results, it is essential to optimize the procedure by improving the follicular survival, confirming safety and developing alternatives. Here, we review the different factors affecting follicular survival and growth after grafting.

METHODS

Relevant studies were identified by searching Pubmed up to January 2009 with English language limitation. The following key words were used: (ovarian tissue or whole ovary) AND (transplantation) AND (cryopreservation or pregnancy). Using the literature and personal experience, we examined relevant data on the different exogenous and clinical factors affecting follicular development after grafting.

RESULTS

Clinical factors such as the patient's age and the transplantation sites influenced the lifespan of the graft. A heterotopic transplantation site is not optimal but offers some advantages and it may also promote the hormonal environment after a combined heterotopic and orthotopic transplantation. Exogenous factors such as antioxidants, growth factors or hormones were tested to improve follicular survival; however, their efficiency regarding further follicular development and fertility potential remains to be established.

CONCLUSION

Additional evidence is required to define optimal conditions for ovarian tissue transplantation. Alternatives such as whole ovary or isolated follicles transplantations require further investigation but are likely to be successful in humans in the future.