Recent developments in human oocyte, embryo and blastocyst vitrification: where are we now?

Fast and furious: pregnancy outcome with one-step rehydration in the warming protocol for human blastocysts

RESEARCH QUESTION

Do embryos warmed using a one-step rehydration protocol with a more efficient workflow result in comparable pregnancy rates to the standard multi-step rehydration protocol?

DESIGN

A retrospective cohort study of 3439 frozen embryo transfers (FET). Clinical outcomes of 833 FETs using a one-step rehydration protocol were reviewed and compared with results from the control group (2606 FETs using standard multi-step rehydration protocol). Primary outcome was ongoing pregnancy rate. Secondary outcomes were survival, positive pregnancy, clinical pregnancy, implantation and miscarriage rates.

RESULTS

Survival rates were identical between the two groups (99.5%). Clinical pregnancy rate was 63.0% in the one-step warming protocol, comparable to 59.9% in the multi-step rehydration protocol. A significant increase was observed in the ongoing pregnancy rate with 60.4% in the one-step rehydration versus 55.4% in the multi-step rehydration group (P = 0.011); implantation rate was 63.6% versus 57.0% (P = 0.0005). The miscarriage rate of 4.0% in the one-step rehydration protocol was significantly lower compared with 7.6% in the multi-step rehydration protocol (P = 0.0001). Comparable outcomes persisted even when the analysis was extended to embryos that had and had not undergone preimplantation genetic testing (PGT), as well as day of development of the blastocysts. When controlling for variables of age, PGT, blastocyst development day and embryo expansion, rapid warming significantly increased chances of an ongoing pregnancy (adjusted OR 1.264, 95% CI 1.076 to 1.484).

CONCLUSION

A one-step rehydration protocol resulted in identical survival rates and improved ongoing pregnancy rates compared with the multi-step rehydration technique.

Live birth rate following endometrial preparation with daily versus depot GnRH agonist

BACKGROUND

Gonadotrophin-releasing hormone agonist (GnRHa) downregulates gonadotropin secretion in the pituitary gland. It is used both in ovulation induction protocols and in artificial endometrium preparation. Frozen-thawed embryo transfer to artificially prepared endometrium (FET-APE) is a frequent procedure in vitro fertilization (IVF) which requires GnRHa. It can be used either as a daily low-dose injection or as a single depot injection. It is unclear which of these two regimens is superior for artificial endometrium preparation.

METHODS

We evaluated the data of 72 patients who had undergone frozen embryo transfer following the 5th day Preimplantation Genetic Test-aneuploidy (PGT-A) between 2018-2021. All embryos were genetically screened, and euploid single embryos were transferred. Group 1 (n: 36) used depot GnRHa, and Group 2 (n: 36) used single daily injections for artificial endometrial preparation. The outcomes for Beta Human Chorionic Gonadotrophin (BHCG) positivity and live birth rates (LBR) was compared.

RESULTS

The BHCG positivity for Group 1 and Group 2 was 75% and 80.6%, respectively. The LBR for Group 1 and Group 2 were found to be 58.3% and 63.9%, respectively. There was no statistically significant differences between the two groups.

CONCLUSIONS

In artificial endometrium preparation, depot GnRHa offers cheaper and more convenient alternative to single daily dose injections, particularly in busy clinical settings.

Vitrification within a nanoliter volume: oocyte and embryo cryopreservation within a 3D photopolymerized device

Purpose

Vitrification permits long-term banking of oocytes and embryos. It is a technically challenging procedure requiring direct handling and movement of cells between potentially cytotoxic cryoprotectant solutions. Variation in adherence to timing, and ability to trace cells during the procedure, affects survival post-warming. We hypothesized that minimizing direct handling will simplify the procedure and improve traceability. To address this, we present a novel photopolymerized device that houses the sample during vitrification.

Methods

The fabricated device consisted of two components: the Pod and Garage. Single mouse oocytes or embryos were housed in a Pod, with multiple Pods docked into a Garage. The suitability of the device for cryogenic application was assessed by repeated vitrification and warming cycles. Oocytes or early blastocyst-stage embryos were vitrified either using standard practice or within Pods and a Garage and compared to non-vitrified control groups. Post-warming, we assessed survival rate, oocyte developmental potential (fertilization and subsequent development) and metabolism (autofluorescence).

Results

Vitrification within the device occurred within ~ 3 nL of cryoprotectant: this volume being ~ 1000-fold lower than standard vitrification. Compared to standard practice, vitrification and warming within our device showed no differences in viability, developmental competency, or metabolism for oocytes and embryos. The device housed the sample during processing, which improved traceability and minimized handling. Interestingly, vitrification-warming itself, altered oocyte and embryo metabolism.

Conclusion

The Pod and Garage system minimized the volume of cryoprotectant at vitrification—by ~ 1000-fold—improved traceability and reduced direct handling of the sample. This is a major step in simplifying the procedure.

Supplementary information

The online version contains supplementary material available at 10.1007/s10815-022-02589-8.

Semi-automated versus manual embryo vitrification: inter-operator variability, time-saving, and clinical outcomes

PURPOSE

Does semi-automated vitrification have lower inter-operator variability and better clinical outcomes than manual vitrification?

METHODS

Retrospective analyses of 282 patients whose embryos had been cryopreserved, manually with Irvine®-CBS® (MV) or semi-automatically vitrified with the GAVI® method (AV) (from November 2017 to September 2020). Both techniques were performed during the same period by 5 operators. Inter-operator variability was statistically analyzed between operators who performed the vitrification and those who performed the warming process to compare the intact survival rate (% embryos with 100% intact blastomeres) and the positive survival rate (at least 50% intact blastomeres). Additionally, the complete vitrification time was assessed for the 2 techniques according to the number of vitrified embryos.

RESULTS

Manual vitrification involved warming 338 embryos in 266 cycles for 181 couples compared to 212 embryos in 162 AV cycles for 101 patients. The positive survival rate was higher (p < 0.05) after MV (96%; 323/338) than after AV (90%; 191/212). The intact survival rate (86 vs 84%) and the clinical pregnancy rate (27 vs 22%) were not significantly different between MV and AV. Regarding the inter-operator variability, no significant difference in positive and intact survival rate was evident between the 5 technicians, neither by vitrification nor by warming steps with MV and AV. Concerning time-saving, the MV technique proved to be quicker than AV (minus 11 ± 9 min).

CONCLUSIONS

Manual vitrification exhibited favorable total survival rates and was more time efficient, while both MV and AV cooling and warming treatments showed little operator variability.

Does longer storage of blastocysts with equal grades in a cryopreserved state affect the perinatal outcomes?

AIM

Although mammalian embryos could be preserved in liquid nitrogen for thousands of years in theoretical models, the viability of cryopreserved blastocyst with varying grades remains to be speculated. In this study, we aimed to determine whether the longer storage time of blastocysts with equal grades could negatively affect the perinatal outcomes.

MATERIALS AND METHODS

Single vitrified-warmed blastocyst was divided into four grades (AA, AB/BA, BB, BC/CB) according to the blastocyst score when freezing, and each grade of blastocyst was categorized into four storage duration categories: 28 days-1 year, 1-3 years, 3-5 years, and ≥5 years. Then the perinatal outcomes with different storage time were analyzed.

RESULTS

Our results revealed that for blastocysts with the same grade, the length of storage time had no statistical effect on blastocyst survival rate, clinical pregnancy/implantation rate, live birth rate, and abortion rate. In addition, more advanced developmental blastocyst could obtain better pregnancy outcomes regardless of the cryopreservation length. Similar neonatal outcomes were obtained over time.

CONCLUSIONS

Cryopreservation time could not negatively affect the perinatal outcomes of blastocysts with equal grades. Efficient blastocyst cryopreservation technology by vitrification can help older women obtain high-quality embryos at a young age.

Vitrification of mouse two-cell and blastocyst stage embryos in simplified closed system using either a hemi-straw or a hollow fiber device

Two-cell stage and blastocyst stage mouse embryos were equilibrated in a medium containing 7.5% ethylene glycol (EG) and 7.5% dimethyl sulfoxide (DMSO) for 8-15 min. Vitrification was performed in a medium containing 0.5 M sucrose and either 15% EG + 15% DMSO, 17.5% EG + 17.5% DMSO, or 20% EG + 20% DMSO for 30 s. They were then placed either on a hemi-straw (HS) or a hollow fiber vitrification (HFV) device and vitrified by cooled air inside a 0.5-ml straw. In two-cell embryos, a 100% survival rate was obtained from all groups except the 20% HS group (P > .05). All vitrified two-cell groups showed similar rates of blastocyst development to that of fresh control group (P > .05), except 17.5% and 20% HFV groups, which were significantly lower than the other groups (P < .05). In the blastocyst embryos, the HFV groups were divided into two subgroups (non-collapsed; HFV-NC and collapsed; HFV-C blastocyst). Re-expansion rate in 15% HFV-NC, 17.5% HFV-NC, and 15% HFV-C groups was reduced (P < .05), whereas the rest were similar to control. In conclusion, we established a simplified, reliable, and closed system for HFV vitrification applying hemi-straw, which does not require skilled practitioners.

Mouse oocyte vitrification with and without dimethyl sulfoxide: influence on cryo-survival, development, and maternal imprinted gene expression

PURPOSE

Oocytes and embryos can be vitrified with and without dimethyl sulfoxide (DMSO). Objectives were to compare no vitrification (No-Vitr), vitrification with DMSO (Vitr + DMSO), and vitrification without DMSO (Vitr - DMSO) on fresh/warmed oocyte survival, induced parthenogenetic activation, parthenogenetic embryo development, and embryonic maternal imprinted gene expression.

METHODS

In this prospective controlled laboratory study, mature B6C3F1 female mouse metaphase II oocytes were treated as: i) No-Vitr, ii) Vitr + DMSO/warmed, and iii) Vitr - DMSO/warmed with subsequent parthenogenetic activation and culture to the blastocyst stage. Oocyte cryo-survival, parthenogenetic activation and embryo development, parthenogenetic embryo maternal imprinted gene expression were outcome measures.

RESULTS

Oocyte cryo-survival was significantly improved in Vitr + DMSO versus Vitr - DMSO at initial warming and 2 h after warming. Induced parthenogenetic activation was similar between all three intervention groups. While early preimplantation parthenogenetic embryo development was similar between control, Vitr + DMSO, Vitr - DMSO oocytes, the development to blastocysts was significantly inferior in the Vitr - DMSO oocytes group compared to the control and Vitr + DMSO oocyte groups. Finally, maternal imprinted gene expression was similar between intervention groups at both the 2-cell and blastocyst parthenogenetic embryo stage.

CONCLUSION(S)

Inclusion of DMSO in oocyte vitrification solutions improved cryo-survival and developmental potential of parthenogenetic embryos to the blastocyst stage without significantly altering maternal imprinted gene expression.

Vitrification: A Simple and Successful Method for Cryostorage of Human Blastocysts

Cryopreservation is one of the keystones in clinical infertility treatment. Especially vitrification has become a well-established and widely used routine procedure that allows important expansion of therapeutic strategies when IVF is used to treat infertility. Vitrification of human blastocysts allows us to maximize the potential for conception from any one in vitro fertilization cycle and prevents wastage of embryos. This goes even further toward to best utilize a patient's supernumerary oocytes after retrieval, maximizing the use of embryos from a single stimulation cycle. The technology can even be used to eliminate fresh embryo transfers for reasons of convenience, uterine receptivity, fertility preservation, preimplantation genetic diagnosis, or emergency management. In this chapter, the application of vitrification technology for cryopreserving human blastocyst will be revealed through step-by-step protocols. The results that are presented using the described protocols underscore the robustness of the vitrification technology for embryo cryopreservation.

Repeated cryopreservation process impairs embryo implantation potential but does not affect neonatal outcomes

RESEARCH QUESTION

Does repeated cryopreservation process affect embryo implantation potential and neonatal outcomes of human embryos?

DESIGN

This retrospective cohort study was conducted in the Reproductive Medicine Centre, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology. All assisted reproductive technology (ART) cycles were carried out between January 2014 and December 2018. Preferentially matched participants were divided into three groups according to the times of embryo cryopreservation: the fresh group (n = 249), the cryopreservation group (n = 244) and the re-cryopreservation group (n = 216). Embryo implantation rate, live birth rate, miscarriage rate and neonatal complication rate were compared among these three groups.

RESULTS

The embryo implantation rate, clinical pregnancy rate and live birth rate in the re-cryopreservation group were significantly lower, and the miscarriage rate also slightly increased. Logistic regression analysis indicated that embryos with repeated cryopreservation and lower trophectoderm scores were at higher risk of embryo implantation failure in single embryo transfer cycles (OR 1.79 and 1.56, respectively). No significant differences were observed in gender, gestational age, birthweight, neonatal abnormality and neonatal complications among the groups.

CONCLUSIONS

Our findings demonstrate the adverse effect of repeated cryopreservation on embryo implantation potential. The study offers embryologists and reproductive clinicians a warning of detrimental role of repeated cryopreservation. If unnecessary, it is strongly recommended to avoid repeated practice of vitrification and warming on embryos.

Using natural honey as an anti-oxidant and thermodynamically efficient cryoprotectant in embryo vitrification

Embryo cryopreservation is a common practice in reproductive biology and infertility treatments. Despite major improvements over years, the cryoprotectant solutions are still a major source of concern, mostly due to their chemical toxicity and suboptimal protection against cryoinjuries. In this work, we introduced natural honey as a non-permeating cryoprotectant to replace traditionally used sucrose in embryo vitrification. The proposed media were compared with conventional ones by evaluating vitrified/warmed mouse embryos based on their re-expansion, hatching rate and transcription pattern of selected genes involved in heat-shock response, apoptosis and oxidative stress. Despite the similar high re-expansion rate, molecular fingerprint of the cryopreservation is remarkably reduced when honey is used instead of sucrose. The biological response of the proposed media was explained from a fundamental point of view using antioxidant analysis, DSC and GC techniques. It was found that the proposed honey-based medium is less thermodynamically prone to ice formation, which along with its antioxidant capacity can control the production of oxygen radicals and minimize the stress-induced transcriptional response. Furthermore, this work tries to correlate the physico-chemical properties of the vitrification solutions with the cellular and molecular aspects of the cryopreservation and proposes the application of natural cryoprotectants in cryobiology.

Recent Advances in Fertility Preservation and Counseling for Reproductive-Aged Women with Colorectal Cancer: A Systematic Review

BACKGROUND

The incidence of colorectal cancer among reproductive-aged women is increasing. Concerns regarding future fertility are secondary only to concerns regarding survival and may significantly impact quality of life among reproductive-aged female cancer survivors. Fertility preservation counseling reduces long-term regret and dissatisfaction among cancer survivors. Health care providers counseling patients with colorectal cancer must understand the impact of cancer treatment on future reproductive potential.

OBJECTIVE

This review aims to examine the effects that colorectal cancer treatments have on female fertility and summarize existing and emerging options for fertility preservation.

DATA SOURCES

EMBASE, National Library of Medicine (MEDLINE)/PubMed, Cochrane Review Library were the data sources for this review.

STUDY SELECTION

A systematic literature review was performed using exploded MeSH terms to identify articles examining the effect of surgery, chemotherapy, and radiation, as well as fertility preservation options for colorectal cancer on female fertility. Relevant studies were included.

MAIN OUTCOME MEASURES

The primary outcome was the effect of colorectal cancer treatment on fertility.

RESULTS

There are limited data regarding the impact of colorectal surgery on fertility. The gonadotoxic effects of chemotherapy on reproductive capacity depend on age at the time of chemotherapy administration, cumulative chemotherapy, radiation dose, type of agent, and baseline fertility status. Chemotherapy-induced risks for colorectal cancers are considered low to moderate, whereas pelvic radiation with a dose of 45 to 50 Gray induces premature menopause in greater than 90% of patients. Ovarian transposition may reduce but not eliminate the damaging effect of radiation on the ovaries. Embryo and oocyte cryopreservation are considered standard of care for women desiring fertility preservation, with oocyte cryopreservation no longer being considered experimental. Ovarian tissue cryopreservation remains experimental but may be an option for select patients. The use of gonadotropin-releasing hormone agonists remains controversial and has not been definitively shown to preserve fertility.

LIMITATIONS

The limitations of this review are the lack of randomized controlled trials and high-quality studies, as well as the small sample sizes and the use of surrogate fertility markers.

CONCLUSION

Reproductive-aged women with colorectal cancer benefit from fertility preservation counseling before the initiation of cancer treatment.

Effects of Re-Vitrification of Mouse Morula and Early Blastocyst Stages on Apoptotic Gene Expression and Developmental Potential

Objective

Re-vitrification of embryos immediately after thawing or after a culture period could be used to preserve the extra embryos after embryo transfer. This study aims to clarify the effect of re-vitrification on Bax and Bcl-2 gene expressions of compact and early blastocyst stage embryos.

Materials and Methods

This experimental study was performed on mouse embryos. We collected 8-cell stage embryos (n=400) from female mature mice, 60-62 hoursafter injection of human chorionic gonadotropin (hCG). The embryos were divided into 5 groups: fresh (n=80), vitrified at the 8-cell stage (n=80), vitrified at the blastocyst stage (n=80), vitrified at the 8-cell stage, and re-vitrified at the compact (n=80) and early blastocyst stages (n=80). Embryos were vitrified by cryolock. We analyzed the developmental rates of the vitrified-warmed embryos with the chi-square test. Quantitative polymerase chain reaction (qPCR) data were analyzed with SPSS version 16 using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test. P<0.05 were considered statistically significant.

Results

The expanded blastocyst formation rate showed a significant difference in re-vitrified embryos compared with fresh embryos (P<0.05). However, this result was similar between the two re-vitrified groups. Our data showed a significant difference in expression of the Bax and Bcl-2 genes between re-vitrified and fresh embryos (P<0.05). Expressions of the Bax and Bcl-2 genes showed no significant difference between the two re-vitrified groups.

Conclusion

Based on our study, re-vitrification could affect developmental rate and expressions of the Bax and Bcl2 genes.

Ice nucleating agents allow embryo freezing without manual seeding

Embryo slow freezing protocols include a nucleation induction step called manual seeding. This step is time consuming, manipulator dependent and hard to standardize. It requires access to samples, which is not always possible within the configuration of systems, such as differential scanning calorimeters or cryomicroscopes. Ice nucleation can be induced by other methods, e.g., by the use of ice nucleating agents. Snomax is a commercial preparation of inactivated proteins extracted from Pseudomonas syringae. The aim of our study was to investigate if Snomax can be an alternative to manual seeding in the slow freezing of mouse embryos. The influence of Snomax on the pH and osmolality of the freezing medium was evaluated. In vitro development (blastocyst formation and hatching rates) of fresh embryos exposed to Snomax and embryo cryopreserved with and without Snomax was assessed. The mitochondrial activity of frozen-thawed blastocysts was assessed by JC-1 fluorescent staining. Snomax didn't alter the physicochemical properties of the freezing medium, and did not affect embryo development of fresh embryos. After cryopreservation, the substitution of manual seeding by the ice nucleating agent (INA) Snomax did not affect embryo development or embryo mitochondrial activity. In conclusion, Snomax seems to be an effective ice nucleating agent for the slow freezing of mouse embryos. Snomax can also be a valuable alternative to manual seeding in research protocols in which manual seeding cannot be performed (i.e., differential scanning calorimetry and cryomicroscopy).

Transient warming events occurring after freezing impairs umbilical cord-derived mesenchymal stromal cells functionality

BACKGROUND

Mesenchymal stromal cells (MSCs) have shown promising results for the treatment of refractory acute graft-versus-host disease. While safety of MSC infusion has been demonstrated, the use of cryopreserved MSCs in clinical trials has raised concerns regarding the retention of their functional activity. This has led to the recommendation by experts in the field to use freshly harvested MSCs, even though this approach is much less practical from a logistic point of view. In the present study, we revisited the impact of cryopreservation on MSC functionality and addressed the possibility that warming events on frozen cells rather than cryopreservation per se could impact MSC functionality.

METHODS

Following controlled-rate freezing to -130°C, umbilical cord-derived MSCs were left at room temperature (RT) for 2-10 min or on dry ice for 10 min, before being transferred into liquid nitrogen (LqN₂). MSCs of each group were subsequently tested (viability, functionality and cellular damage) and compared with their freshly harvested counterparts.

RESULTS

We demonstrated that freshly harvested MSCs as well as cryopreserved MSCs that were left on dry ice following step-down freezing have comparable viability, functionality and integrity. In contrast, cryopreserved MSCs that were left at RT before being transferred into LqN₂ were functionally impaired and showed cellular damage upon thawing even though they exhibited high viability.

DISCUSSION

Warming events after freezing and not cryopreservation per se significantly impair MSC functionality, indicating that cryopreserved MSCs can be an advantageous alternative to freshly harvested cells for therapeutic purposes.

Chapter 11 Human Embryo Vitrification

Cryopreservation is one of the keystones in clinical infertility treatment. In particular vitrification has become a well-established and widely used routine procedure that has allowed important expansion of therapeutic strategies when IVF is used to treat infertility. Vitrification of human blastocysts allows us to maximize the potential for conception from any single in vitro fertilization cycle and prevents wastage of embryos. The technology may even be used to eliminate fresh embryo transfers for reasons of convenience, uterine receptivity, fertility preservation, preimplantation genetic diagnosis, or emergency management. In this chapter, the application of vitrification technology for cryopreserving human blastocysts will be revealed through step-by-step protocols. The results that are presented using the described protocols underscore the robustness of the vitrification technology for embryo cryopreservation.

Impact of Endometrial Preparation Protocols for Frozen Embryo Transfer on Live Birth Rates

BACKGROUND

It has been reported that a natural cycle (NC) is similar to or even better than hormone replacement therapy (HRT) in patients with regular cycles who undergo frozen embryo transfer (FET). Hundreds of FETs are managed yearly in our clinic. Scheduling these cycles is critical in a busy unit like ours. This is why we have to prove if a NC really shows a better outcome than other endometrium preparation protocols.

METHODS

Hence we carried out a prospective study between June 2011 and June 2012, which included 530 patients (570 FET cycles) randomly allocated to two study groups: Group 1 (n=280 cycles), artificial cycle (HRT); or group 2 (n=290 cycles), natural cycle. Natural cycles were later divided into two groups: 169 patients scheduled with human chorionic gonadotropin (hCG) and 121 with endogenous luteinizing hormone (LH) surge. The inclusion criteria were: age <39 years, regular menstrual cycles (26-35 days), and previous IVF cycle with embryo cryopreservation. The exclusion criteria were polycystic ovarian syndrome and endometriosis stage III/IV.

RESULTS

No statistical differences were found in the baseline characteristics among groups, nor between implantation or ongoing pregnancy rates (30.8% HRT group; 32.7% hCG group; 34.5% LH surge group). However, a higher miscarriage rate was observed in the HRT group when compared to hCG or LH surge (21.2% versus 12.9% versus 11.1%, P<0.01). Live birth rates were similar among groups, as were perinatal outcomes, for rates of natural delivery and weight and length of newborns.

CONCLUSIONS

We conclude that scheduling FET with HRT on weekdays and avoiding work overload at weekends prove efficient and safe in cycle outcome terms. Another reason for the convenience of an HRT protocol is having fewer visits to the clinic compared to natural cycle protocols.

Strategies for Fertility Preservation in Female and Male Cancer Survivors

Improved survival rates and quality of life following modern cancer treatment have resulted in a growing number of patients requesting maintenance of reproductive capacity, both before and after completion of treatment. Several established options are currently available. In men, sperm banking should be offered as soon as the diagnosis of any malignant disease is established, irrespective of the expected cryosurvival rate. In such cases, conception can be achieved with frozen-thawed spermatozoa following either intrauterine insemination (IUI) or intracytoplasmic sperm injection (ICSI). In women, depending on the type of cancer, the presence of an adequate ovarian reserve, and time to delay cancer treatment, in vitro fertilization (IVF) with embryo cryopreservation constitutes a valid alternative. On the other hand, cryopreservation of mature oocytes following IVF/ICSI offers some advantages, but it is still limited by its low success rate. Emerging and exciting techniques of germ cell/gonadal tissue cryopreservation (banking) followed by autotransplantation have been clinically explored, particularly in women. Novel cryotechnologies of ovarian and testicular tissue have proven efficacious and new transplantation strategies promise improved results. However, only one live birth following autotransplanted frozen-thawed ovarian tissue has been established and there are still no pregnancies reported from autotransplanted cryopreserved testicular tissue in the human. Efficiency and safety of these techniques needs to be demonstrated. Methods for gamete in vitro maturation also need further development. Gonadal tissue cryopreservation and transplantation should be considered experimental in humans for the present time until greater evidence regarding efficacy and safety is accrued.

Increased cryosurvival of osteosarcoma cells using an amphipathic pH-responsive polymer for trehalose uptake

Amphipathic pH-responsive polymers have shown to increase the permeability of cell membranes to trehalose hence improving the cryopreservation of mammalian cells. However, the trafficking of both the polymer and trehalose across the cell membrane has not yet been thoroughly analysed. The objective of this study was to investigate the effect on cryopreservation of the trafficking of the disaccharide trehalose along PP-50, an amphipathic polymer, through an osteosarcoma cell line (SAOS-2). Confocal microscopy analysis confirmed the presence of intracellular labelled trehalose only when incubated in the presence of PP-50. Further analysis confirmed that both trehalose and PP-50 localised in the cytoplasm, accumulated mainly in the perinuclear area. Quantitative analysis of the colocalisation between trehalose and PP-50 showed Pearson and Manders coefficients of 0.862 ± 0.008 and 0.766 ± 0.033, respectively, suggesting a high degree of intracellular colocalisation between these molecules. Cryopreserved cells pre-incubated with trehalose and PP-50 showed increased cryosurvival when compared with cells pre-incubated in the absence of the polymer. PP-50 showed to be directly involved in the uptake of trehalose, a critical characteristic towards use in cryopreservation and biomedical applications.

Synchrotron X-ray diffraction to detect glass or ice formation in the vitrified bovine cumulus-oocyte complexes and morulae

Vitrification of bovine cumulus-oocyte complexes (COCs) is not as successful as bovine embryos, due to oocyte's complex structure and chilling sensitivity. Synchrotron X-ray diffraction (SXRD), a powerful method to study crystal structure and phase changes, was used to detect the glass or ice formation in water, tissue culture medium (TCM)-199, vitrification solution 2 (VS2), and vitrified bovine COCs and morulae. Data revealed Debye's rings and peaks associated with the hexagonal ice crystals at 3.897, 3.635, 3.427, 2.610, 2.241, 1.912 and 1.878 Å in both water and TCM-199, whereas VS2 showed amorphous (glassy) appearance, at 102K (−171°C). An additional peak of sodium phosphate monobasic hydrate (NaH₂PO₄.H₂O) crystals was observed at 2.064 Å in TCM-199 only. All ice and NaH₂PO₄.H₂O peaks were detected in the non-vitrified (control) and vitrified COCs, except two ice peaks (3.145 and 2.655 Å) were absent in the vitrified COCs. The intensities of majority of ice peaks did not differ between the non-vitrified and vitrified COCs. The non-vitrified bovine morulae in TCM-199 demonstrated all ice- and NaH₂PO₄.H₂O-associated Debye's rings and peaks, found in TCM-199 alone. There was no Debye's ring present in the vitrified morulae. In conclusion, SXRD is a powerful method to confirm the vitrifiability of a solution and to detect the glass or ice formation in vitrified cells and tissues. The vitrified bovine COCs exhibited the hexagonal ice crystals instead of glass formation whereas the bovine morulae underwent a typical vitrification.

Cryopreservation of embryos and oocytes in human assisted reproduction

Both sperm and embryo cryopreservation have become routine procedures in human assisted reproduction and oocyte cryopreservation is being introduced into clinical practice and is getting more and more widely used. Embryo cryopreservation has decreased the number of fresh embryo transfers and maximized the effectiveness of the IVF cycle. The data shows that women who had transfers of fresh and frozen embryos obtained 8% additional births by using their cryopreserved embryos. Oocyte cryopreservation offers more advantages compared to embryo freezing, such as fertility preservation in women at risk of losing fertility due to oncological treatment or chronic disease, egg donation, and postponing childbirth, and eliminates religious and/or other ethical, legal, and moral concerns of embryo freezing. In this review, the basic principles, methodology, and practical experiences as well as safety and other aspects concerning slow cooling and ultrarapid cooling (vitrification) of human embryos and oocytes are summarized.

Short-term storage of tripronucleated human embryos

PURPOSE

To determine the survival and subsequent in vitro development of human cleavage stage embryos and hatched blastocysts following varying periods of short-term storage at 4 °C, using tripronucleated human embryos (TPN) as a model.

METHODS

TPN cleavage embryos and hatched blastocysts short-term stored at 4 °C for 0 h (control), 24 h and 48 h. The main outcome measures were: survival rates (SR) and in vitro developmental ability (blastocyst rate and blastocyst-re-expansion rate) in each of the groups after storage.

RESULTS

Cleavage-stage TPN survived at comparable rates to controls, regardless of storage time (average: 97.3 %). The in vitro development of cleavage-stage TPN stored for 24 h was comparable to that of controls (average 64.7 %), but was significantly impaired when storage lasted 48-h (20.8 %). After artificial shrinkage, SR was comparable in 24-h-stored and non-stored hatched blastocysts (85.7 %; p > 0.05), but was significantly impaired in the 48-h-stored group (20.0 %). Following 24-h storage, the re-expansion rate of hatched blastocysts was similar to that of controls (average: 57.1 %; p > 0.05), but was higher than that of the 48-h-stored group (15.0 %; p < 0.05).

CONCLUSIONS

TPN human cleavage embryos and blastocysts can be successfully stored short-term for up to 24 h at 4 °C without using cryoprotectants without any significant negative impact on survival or subsequent in vitro development.

Is vitrification of oocytes useful for fertility preservation for age-related fertility decline and in cancer patients?

The aim of this review is to provide current knowledge on oocyte cryopreservation, with special emphasis on vitrification as a means to preserve fertility in different indications. Major advancements achieved in the past few years in the cryolaboratory have facilitated major changes in our practice. Areas such as fertility preservation for social or oncologic reasons, the possibility to create oocyte banks for egg donation programs, the opportunity to avoid ovarian hyperstimulation syndrome, or to accumulate oocytes in low-yield patients, or even to offer treatment segmentation by stimulating the ovaries, vitrifying, and then transferring in a natural cycle are some of the options that are now available with the development of cryopreservation. We present general experience from our group and others on fertility preservation for age-related fertility decline as well as in oncologic patients, confirming that oocyte vitrification is a standardized, simple, reproducible, and efficient option.

The effect of vitrification on maturation and viability capacities of immature human oocytes

BACKGROUND

15 % of oocytes collected from Assisted Reproductive Technology (ART) cycles are immature. These oocytes may be matured following in vitro maturation (IVM) program. It is possible to cryopreserve the immature oocytes for further use in ART after application of IVM.

OBJECTIVE

The aim was to determine the maturation rate and viability of human oocytes that were matured in vitro after vitrification program.

MATERIALS AND METHODS

63 women (19-43 years old) who underwent controlled ovarian stimulation for ART were included in this study. 53 immature oocytes were used for fresh group (fIVM) and 50 immature oocytes for vitrification group (vIVM). The maturation medium was Ham's F10 supplemented with 0.75 IU FSH, 0.75 IU LH and 40 % human follicular fluid (HFF). After 36 h, maturation and morphology of all oocytes were assessed. Also, the oocyte viability was assessed using PI/Hoechst immunostaining technique.

RESULTS

The maturation rates were reduced in vIVM group (56.0 %) in comparison to fIVM group (88.7 %; P < 0.001). Oocyte viability rate were also reduced in vIVM group (56.0 %) in comparison to fIVM (86.8 %, P < 0.007).

CONCLUSIONS

Cryopreservation via vitrification reduced both the maturation capacity and viability of human oocytes in IVM technology. It is, therefore, recommended to apply IVM on fresh immature oocytes, instead.

Survival and post-warming in vitro competence of human oocytes after high security closed system vitrification

PURPOSE

To compare two vitrification methods and two warming methods for human oocyte vitrification using a high security closed device in terms of survival, fertilization and embryo development.

METHODS

For vitrification, oocytes were (1) immediately placed in equilibration solution or (2) they were gradually exposed to the cryoprotectants. For warming, oocytes were placed (1) in a 25 μl preheated (37 °C) thawing solution droplet that was put at room temperature for 1 min once the oocytes were inside or (2) in a 150 μl droplet for 1 minute at 37 °C.

RESULTS

Survival and preimplantation development were significantly lower when warming was performed in a small preheated droplet. There was no significant difference in survival and embryo development between the gradual or direct exposure to cryoprotectants.

CONCLUSIONS

Using this high security closed vitrification device a 90 % survival rate can be achieved when the oocytes are immediately warmed in a large volume at 37 °C.

Blastocyst transfer in frozen-thawed cycles

OBJECTIVE

It is well known that fresh blastocyst transfer results in better pregnancy outcomes with a smaller number of transferred embryos compared with cleavage stage embryo transfer. However, in terms of frozen-thawed blastocyst transfer, only a few studies are available. We aimed to evaluate clinical outcomes of frozen-thawed embryo transfer (FET) with blastocysts.

METHODS

Retrospective analysis of FET cycles with blastocysts (B-FET) between Jan 2007 and June 2009 was performed. Age-matched FET cycles with cleavage stage embryos (C-FET) during the same period were collected as controls. A total of 58 B-FET cycles were compared with 172 C-FET cycles and also compared with those of post-thaw extended culture blastocysts from frozen pronuclear stage embryos (22 cycles).

RESULTS

There was no difference in the patient characteristics of each group. The embryos' survival rates after thawing were comparable (>90%) and there was no difference in the implantation rate or clinical and ongoing pregnancy rate among the three groups.

CONCLUSION

In FET, blastocyst transfers may not present better pregnancy outcomes than cleavage stage embryo transfers. A further large-scale prospective study is needed.

Outcomes of day 3 embryo transfer with vitrification using Cryoleaf: a 3-year follow-up study

OBJECTIVE

To compare success rates of vitrified-warmed with fresh and frozen-thawed ETs

DESIGN

Retrospective.

SETTING

Public fertility center.

PATIENT(S)

Cryopreserved- thawed/warmed ETs were included in this study. Fresh cycles, in which supernumerary embryos were cryopreserved, were set as the fresh control group.

INTERVENTION(S)

Supernumerary day 3 embryos were cryopreserved by slow-freezing or vitrification and transferred after thawing or warming.

MAIN OUTCOME MEASURE(S)

Comparison of two cryopreservation techniques with respect to post-thaw survival of embryos, implantation and pregnancy rates, neonatal outcome, and congenital birth defects.

RESULTS

A total of 962 fresh, 151 freezing-thawed and 300 vitrified-warmed cycles were included in this study. The survival and intact cell rates in the vitrification group were significantly higher compared with those in the slow freezing group (88.5 % vs 74.5 % and 86.6 % vs 64.0 %). The implantation, clinical pregnancy and live birth rates of the vitrification group were similar to the fresh and significant higher than slow freezing group. There were no significant differences in mean gestational age, birth weight, stillbirth, birth defects and the prevalence of neonatal diseases among three groups.

CONCLUSION

Vitrified-warmed ETs yield comparable outcomes with fresh ETs and is superior to frozen-thawed ETs regarding the survival rate and clinical outcomes.

In vitro development and gene expression of frozen-thawed 8-cell stage mouse embryos following slow freezing or vitrification

Objective

This study was performed to compare the efficiency of slow freezing and vitrification based on survival, development to blastocysts, and cell numbers of blastocysts. Changes in embryonic gene expression in fresh and frozen-thawed embryos were also examined.

Methods

Eight-cell stage embryos were collected from superovulated female BDF1 mice. The collected embryos were randomly divided into three groups. One group was maintained as fresh controls (n=42), one was frozen by slow freezing (n=43), and one was cooled by vitrification (n=43). After thawing or cooling, survival rates, development to blastocyst, and cell numbers and inner cell mass (ICM) cell numbers of blastocysts were compared with those of the control group. The expressions of eight genes (Rbm3, Birc5, Sod1, Sod2, Cirbp, Caspase3, Trp53, Hsp70.1) were examined by real time-quantitative polymerase chain reaction in the fresh and frozen-thawed embryos.

Results

There were no significant differences in the slow freezing and vitrification groups' survival rate after thawing (88.4% vs. 88.4%), development to blastocyst (100% vs. 97.4%), cell numbers (107.0±21.0 vs. 115.0±19.7), or ICM cell numbers of blastocysts (11.3±5.2 vs. 11.1±3.7). Cell numbers of blastocysts were significantly (p<0.05) lower in the frozen-thawed embryos than the fresh embryos. There were no significant differences in the slow freezing and the vitrification groups' expressions of the eight genes. The expressions of CirbP and Hsp70.1 were higher in the frozen-thawed embryos than in the fresh embryos but there were no significant differences.

Conclusion

These results suggest that there were no significant differences between embryos that underwent slow freezing and vitrification.

Mouse ovarian follicle cryopreservation using vitrification or slow programmed cooling: assessment of in vitro development, maturation, ultra-structure and meiotic spindle organization

AIM

To compare different outcomes of vitrification and slow freezing of isolated pre-antral follicles and to evaluate different cryo-devices for vitrification of isolated follicles.

METHODS

Pre-antral follicles were isolated from mouse ovaries and cryopreserved using vitrification and slow freezing. A preliminary experiment was carried out to select the optimal cryo-device for vitrification of isolated follicles. A total of 414 follicles were randomly distributed among four groups: control (CT) fresh (n=100), nylon mesh (n=96), electron microscopy grid (n=102), and micro-capillary tips (n=116). Subsequently, a total of 979 follicles were randomly assigned to three different groups: CT fresh (n=256), vitrification (n=399) and slow freezing (n=324). CT and cryopreserved/thawed follicles were cultured in vitro and examined daily for development. Final maturation was triggered with human chorionic gonadotrophin and rates of oocyte maturation were calculated. The ultra-structure of cryopreserved/thawed follicles was studied using electron microscopy. Meiotic spindle presence and organization in mature oocytes were examined using the Oosight imaging system.

RESULTS

  Micro-capillary tips resulted in poor immediate post-warming survival but no differences were observed in the subsequent in vitro development characteristics between different cryo-devices. Nylon mesh proved to be the easiest carrier, particularly when large numbers of follicles were to be vitrified. Compared to vitrification, slow freezing resulted in a significantly lower number of intact follicles at the end of the culture period (P<0.0001). However all other outcome measures were comparable between both techniques.

CONCLUSIONS

Isolated follicles were more vulnerable to cryodamage after slow freezing as compared to vitrification.

In situ cryopreservation of human embryonic stem cells in gas-permeable membrane culture cassettes for high post-thaw yield and good manufacturing practice

The development of efficient and robust methods for the cryopreservation of human embryonic stem cells (hESCs) is important for the production of master and working cell banks for future clinical applications. Such methods must meet requirements of good manufacturing practice (GMP) and maintain genetic stability of the cell line. We investigated the culture of four Shef hESC lines in gas permeable 'culture cassettes' which met GMP compliance. hESCs adhered rapidly to the membrane and colonies displayed good proliferation and expansion. After 5-7 days of culture, hESCs were cryopreserved in situ using 10% dimethyl sulphoxide in foetal calf serum at approximately 1 degrees C/min. This method was compared with a control of standard flask culture and cryopreservation in vials. Post-thaw cassette culture displayed relative proliferation ratios (fold increase above flask/cryovial culture) of 114 (Shef 4), 8.2 (Shef 5), 195 (shef 6) and 17.5 (Shef 7). The proportion of cells expressing pluripotency markers after cryopreservation was consistently greater in cassette culture than for the control with the markers SSEA3 and SSEA4 exhibiting a significant increase (P> or =0.05). The efficiency of cell line culture in cassette was associated with the overall passage number of the cell line. The procedure enables cryopreservation of relatively large quantities of hESCs in situ, whilst returning high yields of viable, undifferentiated stem cells, thereby increasing capacity to scale up with greater efficacy.

An effective serum- and xeno-free chemically defined freezing procedure for human embryonic and induced pluripotent stem cells

BACKGROUND

Both human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) bear a great potential in regenerative medicine. In addition to optimized clinical grade culture conditions, efficient clinical grade cryopreservation methods for these cells are needed. Obtaining good survival after thawing has been problematic.

METHODS

We used a novel, chemically defined effective xeno-free cryopreservation system for cryostorage and banking of hESCs and iPSCs. The earlier established slow freezing protocols have, even after recent improvements, resulted in low viability and thawed cells had a high tendency to differentiate. The medium is a completely serum and animal substance free product containing dimethylsulfoxide, anhydrous dextrose and a polymer as cryoprotectants. The cells were directly frozen at -70 degrees C, without a programmed freezer.

RESULTS

The number of frozen colonies versus the number of surviving colonies differed significantly for both HS293 (chi(2) = 9.616 with one degree of freedom and two-tailed P = 0.0019) and HS306 (chi(2) = 8.801 with one degree of freedom and two-tailed P = 0.0030). After thawing, the cells had a high viability (90-96%) without any impact on proliferation and differentiation, compared with the standard freezing procedure where viability was much lower (49%). The frozen-thawed hESCs and iPSCs had normal karyotype and maintained properties of pluripotent cells with corresponding morphological characteristics, and expressed pluripotency markers after 10 passages in culture. They formed teratomas containing tissue components of the three germ layers.

CONCLUSION

The defined freezing-thawing system described here offers an excellent simple option for banking of hESCs and iPSCs.

Clinical pregnancy and live births after transfer of embryos vitrified on day 3

Human embryo vitrification is a promising new technology but clinical outcome data is needed to gauge its effectiveness and safety. While pregnancy and live-birth data is available for blastocyst vitrification, such information is lacking for human embryo vitrification at the 6- to 8-cell stage. The current work presents clinical and obstetric outcomes from the transfer of embryos vitrified on day 3 at the cleavage stage. A total of 270 transfers were performed. The clinical pregnancy and implantation rates for patients under 38 years of age (n=200) were 45% and 24%, respectively. Corresponding rates in patients 38-42 years old declined to 29% and 13% (n=70). Embryonic compaction and/or blastulation by the time of transfer were excellent prognostic indicators of a successful pregnancy outcome. Of the 66 deliveries, 12 (18.2%) were twin pregnancies and nine were preterm (13.6%). The mean birthweight for singletons was 3281+/-644 g, compared with 2506+/-549 g in the twin pregnancies. A total of 78 infants have been born with no major congenital malformations. These data attest to the efficacy and safety of the vitrification technique for cryopreservation of human embryos at the 6- to 8-cell stage.

Clinical outcomes resulting from the transfer of vitrified human embryos using a new device for cryopreservation (plastic blade)

PURPOSE

We attempted clinical application of a plastic blade, which is a novel cryopreservation device, for vitrification of human embryos and blastocysts.

METHODS

Between February 2003 and December 2007, a total of 4,430 Day 3 embryos from 898 patients (Day 3 group) and 55 blastocysts from 29 patients (blastocyst group) were vitrified and cryopreserved with a plastic device, and subsequently thawed for embryo transfer. Clinical outcomes after thawing and transfer of vitrified embryos and blastocysts were evaluated.

RESULTS

In the Day 3 group, all embryos resulting from 1,441 oocyte retrieval cycles were recovered, and the thawed embryo survival rate was 98.4%. In the blastocyst group, the survival rate after thawing was 100%. A total of 3,026 day 3 embryos and 46 blastocysts were transferred. The pregnancy and implantation rates in the Day 3 group were 25.0% and 15.5%, respectively, and in the blastocyst group the rates were 24.2% and 26.1%, respectively. The miscarriage rates in the Day 3 and blastocyst groups were 18.3% and 50.0%, respectively.

CONCLUSIONS

A plastic blade is a useful novel device in cryopreservation of vitrified human embryos.

Vitrification of human embryos subjected to blastomere biopsy for pre-implantation genetic screening produces higher survival and pregnancy rates than slow freezing

PURPOSE

Cryopreservation of blastocysts, especially those subjected to the trauma due to blastomere biopsy for the purposes of pre-implantation genetic screening (PGS), requires significant optimization. Laboratory and clinical outcomes were compared to determine the effect of two different cryopreservation techniques on the development of human pre-implantation embryos that underwent blastomere biopsy and blastocoel drainage prior to cryopreservation.

DESIGN

Retrospective clinical study.

PATIENT(S)

Women who requested cryotransfer of supernumerary blastocysts were analyzed by FISH.

RESULTS

The main outcome measures were post-thaw survival (SR), pregnancy (PR), and implantation (IR). The SR of slowly frozen blastocysts was 83% compared to 97% for vitrified blastocysts. In 160 cases where biopsied embryos were cryotransferred, the results for slowly frozen versus vitrified blastocysts were: SR (71% vs. 95%), PR (23% vs. 37%), and IR (26% vs. 36%, P < 0.05), respectively.

CONCLUSION

The results revealed that vitrified blastocysts provided higher SR, PR and IR as compared to slowly frozen counterparts.

Slow freezing, vitrification and ultra-rapid freezing of human embryos: a systematic review and meta-analysis

Embryo cryopreservation is an important aspect of assisted reproduction. Many methods have been described, but they have been poorly investigated in randomized trials, highlighting the need for a systematic review of the literature. Meticulous electronic/hand searches were performed to locate randomized trials (RCT) comparing embryo cryopreservation methods. Primary outcomes were clinical pregnancy rate (CPR) and incidence of congenital abnormalities. Secondary outcomes included live-birth (LBR), ongoing pregnancy (OPR), implantation (IR), and miscarriage (MR) rates. Data were extracted to allow for an intention-to-treat analysis and analysed using a random-effects model. Literature search revealed 11 RCT, of which five were excluded. The quality of the included studies was variable, but generally poor. There was a significantly higher CPR, OPR and IR with vitrification compared with slow freezing (odds ratio (OR)=1.55, 95% confidence interval (CI)=1.03-2.32, OR=1.82, 95% CI=1.04-3.20 and OR=1.49, 95% CI=1.03-2.15, respectively). In addition, there was a significantly lower CPR and OPR with embryo ultra-rapid freezing compared with slow freezing (OR=0.35, 95% CI=0.16-0.76 and OR=0.37, 95% CI=0.17-0.81, respectively). Vitrification is superior to slow freezing, which in turn is superior to ultra-rapid freezing. However, more well-designed and powered studies are needed to further corroborate these findings.