Risk of Contamination of Gametes and Embryos during Cryopreservation and Measures to Prevent Cross-Contamination

Cryostorage management of reproductive cells and tissues in ART: status, needs, opportunities and potential new challenges

Among the wide range of procedures performed by clinical embryologists, the cryopreservation of reproductive cells and tissues represents a fundamental task in the daily routine. Indeed, cryopreservation procedures can be considered a subspecialty of medically assisted reproductive technology (ART), having the same relevance as sperm injection or embryo biopsy for preimplantation genetic testing. However, although a great deal of care has been devoted to optimizing cryopreservation protocols, the same energy has only recently been spent on developing and implementing strategies for the safe and reliable storage and transport of reproductive specimens. Herein, we have summarized the content of the available guidelines, the risks, the needs and the future perspectives regarding the management of cryopreservation biorepositories used in ART.

Technologies for Vitrification Based Cryopreservation

Cryopreservation is a unique and practical method to facilitate extended access to biological materials. Because of this, cryopreservation of cells, tissues, and organs is essential to modern medical science, including cancer cell therapy, tissue engineering, transplantation, reproductive technologies, and bio-banking. Among diverse cryopreservation methods, significant focus has been placed on vitrification due to low cost and reduced protocol time. However, several factors, including the intracellular ice formation that is suppressed in the conventional cryopreservation method, restrict the achievement of this method. To enhance the viability and functionality of biological samples after storage, a large number of cryoprotocols and cryodevices have been developed and studied. Recently, new technologies have been investigated by considering the physical and thermodynamic aspects of cryopreservation in heat and mass transfer. In this review, we first present an overview of the physiochemical aspects of freezing in cryopreservation. Secondly, we present and catalog classical and novel approaches that seek to capitalize on these physicochemical effects. We conclude with the perspective that interdisciplinary studies provide pieces of the cryopreservation puzzle to achieve sustainability in the biospecimen supply chain.

A comprehensive review and update on human fertility cryopreservation methods and tools

The broad conceptualization of fertility preservation and restoration has become already a major concern in the modern western world since a large number of individuals often face it in the everyday life. Driven by different health conditions and/or social reasons, a variety of patients currently rely on routinely and non-routinely applied assisted reproductive technologies, and mostly on the possibility to cryopreserve gametes and/or gonadal tissues for expanding their reproductive lifespan. This review embraces the data present in human-focused literature regarding the up-to-date methodologies and tools contemporarily applied in IVF laboratories' clinical setting of the oocyte, sperm, and embryo cryopreservation and explores the latest news and issues related to the optimization of methods used in ovarian and testicular tissue cryopreservation.

Adverse events, side effects and complications in mesenchymal stromal cell-based therapies

Numerous clinical studies have shown a wide clinical potential of mesenchymal stromal cells (MSCs) application. However, recent experience has accumulated numerous reports of adverse events and side effects associated with MSCs therapy. Furthermore, the strategies and methods of MSCs therapy did not change significantly in recent decades despite the clinical impact and awareness of potential complications. An extended understanding of limitations could lead to a wider clinical implementation of safe cell therapies and avoid harmful approaches. Therefore, our objective was to summarize the possible negative effects observed during MSCs-based therapies. We were also aimed to discuss the risks caused by weaknesses in cell processing, including isolation, culturing, and storage. Cell processing and cell culture could dramatically influence cell population profile, change protein expression and cell differentiation paving the way for future negative effects. Long-term cell culture led to accumulation of chromosomal abnormalities. Overdosed antibiotics in culture media enhanced the risk of mycoplasma contamination. Clinical trials reported thromboembolism and fibrosis as the most common adverse events of MSCs therapy. Their delayed manifestation generally depends on the patient's individual phenotype and requires specific awareness during the clinical trials with obligatory inclusion in the patient' informed consents. Finally we prepared the safety checklist, recommended for clinical specialists before administration or planning of MSCs therapy.

Epigenetic Alterations in Cryopreserved Human Spermatozoa: Suspected Potential Functional Defects

Background: Gene set enrichment analysis (GSEA) was conducted on raw data, and alternative splicing (AS) events were found after mRNA sequencing of human spermatozoa. In this study, we aimed to compare unknown micro-epigenetics alternations in fresh and cryopreserved spermatozoa to evaluate the effectivity of cryopreservation protocols. Methods: Spermatozoa were divided into three groups: fresh spermatozoa (group 1), cryoprotectant-free vitrified spermatozoa (group 2), and conventionally frozen spermatozoa (group 3). Nine RNA samples (three replicates in each group) were detected and were used for library preparation with an Illumina compatible kit and sequencing by the Illumina platform. Results: Three Gene Ontology (GO) terms were found to be enriched in vitrified spermatozoa compared with fresh spermatozoa: mitochondrial tRNA aminoacylation, ATP-dependent microtubule motor activity, and male meiotic nuclear division. In alternative splicing analysis, a number of unknown AS events were found, including functional gene exon skipping (SE), alternative 5′ splice sites (A5SS), alternative 3′ splice sites (A3SS), mutually exclusive exon (MXE), and retained intron (RI). Conclusions: Cryopreservation of spermatozoa from some patients can agitate epigenetic instability, including increased alternative splicing events and changes in crucial mitochondrial functional activities. For fertilization of oocytes, for such patients, it is recommended to use fresh spermatozoa whenever possible; cryopreservation of sperm is recommended to be used only in uncontested situations.

Evaluation of the TMRW vapor phase cryostorage platform using reproductive specimens and in vitro extended human embryo culture

OBJECTIVE

To assess the impact of shipment and storage of sperm, oocytes, and blastocysts in vapor phase nitrogen compared with static storage in liquid phase nitrogen.

DESIGN

Prospective cohort-matched study.

SETTING

Multiple in vitro fertilization laboratories in an in vitro fertilization network.

PATIENT(S)

Fifty-eight human embryos, 32 human oocytes, 15 units of bovine semen.

INTERVENTION(S)

Vapor vs. liquid nitrogen.

MAIN OUTCOME MEASURE(S)

The postwarming survival of oocytes, sperm, and blastocysts, and the developmental potential of blastocysts during in vitro extended culture.

RESULT(S)

Custom-designed labware, for use with the TMRW platform, enables continuous temperature monitoring during shipment and/or storage in the vapor phase robotic storage system. The highest temperature recorded for specimens shipped to a domestic laboratory was -180.2 °C with a mean ± SD of -190.4 ± 0.5 °C during shipment and -181.1 ± 0.6 °C during storage. Likewise, specimens shipped internationally had a high of -180.2 °C with a mean ± SD of -193.5 ± 0.6 °C during shipment and -181.2 ± 0.7 °C during storage. Results from the extended culture assays have revealed no deleterious effect of shipment and storage in nitrogen vapor. The viability of mammalian gametes and embryos was equivalent between the vapor phase and liquid phase storage.

CONCLUSION(S)

The evaluated system did not have any deleterious effects on the postwarming survival of sperm, oocytes, and blastocysts. The postwarming developmental potential of human blastocysts during in vitro extended culture was unaffected by storage and handling in the vapor phase nitrogen TMRW platform when compared with static liquid phase nitrogen storage. Our results suggest that the vapor phase cryostorage platform is a safe system to handle and store reproductive specimens for human assisted reproductive technology.

Oncofertility and COVID-19: At the Crossroads between Two Time-Sensitive Fields

Background: COVID-19 infection has dominated our lives and left its mark on it. The impact on fertility is major, and the long-term consequences may be disastrous. When we talk about oncofertility, we are talking about those patients worried about the delay in receiving medical services (possible cancelation of surgery, decreased availability of medical services, reorientation of medical resources) due to COVID-19. Finally, patients’ worsening biological and reproductive statuses, associated with high levels of anxiety and depression, are closely related to social restrictions, economic impact, reorientation of medical resources, health policies, and fears of SARS-CoV-2 infection. Aim: We reviewed the current literature on fertility during the COVID-19 pandemic and its effect on cancer patients. Specifically, how cancer treatment can affect fertility, the options to maintain fertility potential, and the recovery options available after treatment are increasingly common concerns among cancer patients. Methods: A systematic literature search was conducted using two main central databases (PubMed^®/MEDLINE, and Web of Science) to identify relevant studies using keywords SARS-CoV-2, COVID-19, oncofertility, young cancer patient, cryopreservation, assisted reproductive techniques (ART), psychosocial, telemedicine. Results: In the present study, 45 papers were included, centered on the six main topics related to COVID-19. Conclusions: Fertility preservation (FP) should not be discontinued, but instead practiced with adjustments to prevent SARS-CoV-2 transmission. The increased risk of SARS-CoV-2 infection in cancer patients requires screening for COVID-19 before FP procedures, among both patients and medical staff in FP clinics, to prevent infection that would rapidly worsen the condition and lead to severe complications.

Micro-straw: An efficient cryopreservation carrier for rare human spermatozoa

BACKGROUND

Many cryopreservation carriers have been introduced to freeze rare human spermatozoa, however, these carriers relative attributes and comparative effectivenesses have not yet been systematically studied.

OBJECTIVES

Is the Micro-straw cryopreservation carrier more effective for cryopreserving rare human spermatozoa compared with the Cryoplus and LSL carriers?

MATERIALS AND METHODS

This study involves ninety-three samples from healthy sperm donors and forty samples from patients diagnosed with oligospermia, asthenospermia, oligoasthenospermia, or obstructive azoospermia. we determined the optimal freeze-thaw protocol for the Micro-straw carrier. The post-thaw survival rate, normal sperm morphology, acrosome integrity, and DNA fragmentation for Micro-straw, Cryoplus, and LSL carriers were then determined. Finally, we verified the effects of freezing using these carriers by comparing the qualities of post-thaw spermatozoa from patients.

RESULTS

The highest total motility (TM) and progressive motility (PR) survival rates were obtained by placing the Micro-straw at 1 cm above the LN₂ surface for 70 s during freezing and in a 42-°C water bath for 40 s during thawing. No differences were observed in PR survival rate, acrosome integrity, and DNA fragmentation of the post-thaw spermatozoa from the three carriers. However, the normal morphology rate of spermatozoa frozen using the Micro-straw carrier was higher than for the Cryoplus carrier (p < 0.05), and the TM survival rate of spermatozoa frozen with the Micro-straw was higher than that for the LSL carrier (p < 0.01). In verification tests, there were no significant differences in the quality of post-thaw spermatozoa cryopreserved using these carriers for both rare spermatozoa or epididymal sperm.

DISCUSSION AND CONCLUSION

Micro-straw, Cryoplus, and LSL carriers are all efficient means of freezing rare human spermatozoa. However, the Micro-straw carrier is more economical, safe, and user-friendly. This article is protected by copyright. All rights reserved.

Can We Cryopreserve the Sperm of COVID-19 Patients During the Pandemic?

An extreme strain has been placed on healthcare facilities in the COVID-19 era. Initial stage of the pandemic, national and international societies for reproductive medicine suggested the suspension of new IVF treatments and non-essential cryopreservation of gametes. Accordingly, the demands of cryopreservation of semen with COVID-19 patients also was suspended by some of cryobanks to protect staff and patients from unnecessary viral exposure at the acute stage. However, the pandemic may stay with us longer than expected. In addition, there will be some male COVID-19 patients with cancer or critically illness who needs to cryopreserve their semen before medical treatments, otherwise they might loss the chance of getting their own offspring. In this document, we summarize available evidence to deepen and expand awareness of feasibility of sperm cryopreservation and propose some suggestions to help cryobanks carry out sperm preservation procedure for COVID-19 male patients.

Optimised CO2-containing medium for in vitro culture and transportation of mouse preimplantation embryos without CO2 incubator

Conventional in vitro culture and manipulation of mouse embryos require a CO₂ incubator, which not only increases the cost of performing experiments but also hampers the transport of embryos to the other laboratories. In this study, we established and tested a new CO₂ incubator-free embryo culture system and transported embryos using this system. Using an Anaero pouch, which is a CO₂ gas-generating agent, to increase the CO₂ partial pressure of CZB medium to 4%–5%, 2-cell embryos were cultured to the blastocyst stage in a sealed tube without a CO₂ incubator at 37°C. Further, the developmental rate to blastocyst and full-term development after embryo transfer were comparable with those of usual culture method using a CO₂ incubator (blastocyst rate: 97% versus 95%, respectively; offspring rate: 30% versus 35%, respectively). Furthermore, using a thermal bottle, embryos were reliably cultured using this system for up to 2 days at room temperature, and live offspring were obtained from embryos transported in this simple and very low-cost manner without reducing the offspring rate (thermal bottle: 26.2% versus CO₂ incubator: 34.3%). This study demonstrates that CO₂ incubators are not essential for embryo culture and transportation and that this system provides a useful, low-cost alternative for mouse embryo culture and manipulation.

The effects of supplemented sericin on in vitro maturation and preimplantation development of mouse embryos: An experimental study

Background

Mouse embryo culture condition is an essential part of transgenic, reproductive and developmental biology laboratories. Mouse embryonic culture media may have a high risk of serum contamination with pathogens.

Objective

To investigate the effect of sericin as an embryo culture medium supplement on in vitro maturation (IVM), in vitro fertilization (IVF), and development of the preimplantation embryo in mice.

Materials and Methods

The effects of sericin at three concentrations (subgroups) of 0.1%, 0.5%, and 1% as a medium supplement on IVM, IVF, and in vitro development of mouse embryos were separately investigated and compared with a sericin-free (control) group. The cumulative effect of the three concentrations was evaluated for IVM + in vitro development and IVF + in vitro development as follow-up groups.

Results

In the IVM group, compared to the control group, the number of oocysts reaching the MII stage was significantly higher when 1% sericin was used (161/208 = 77.4%). No significant results were observed in the IVF and in vitro development groups with different concentrations of sericin compared to the control group. Among the follow-up groups, in the IVM + in vitro development group, the number of oocytes was higher after passing the IVM and IVF and reaching the blastocysts stage when 1% sericin was used, compared with other sericin subgroups. A significant difference was also noted when compared with the control group (p = 0.048). The IVF + in vitro development study group, on the other hand, did not show any significant relationship.

Conclusion

It can be concluded that 1% sericin can be used as a supplement in mouse embryo cultures to improve the IVM rate. Also, based on the findings, sericin appears to be an effective supplement which can have a positive effect on the development of embryos derived from IVM.

Evaluation of developmental competence of Sus scrofa domesticus (L.) oocyte-cumulus complexes after intra- and extraovarian vitrif ication

The aim of the present study was to identify the inf luence of extra- (EOV) and intraovarian vitrif ication (IOV) on mitochondrial activity (MA) and chromatin state in porcine oocytes during maturation in vitro. During EOV porcine oocytes were exposed in cryoprotective solutions (CPS): CPS-1 - 0.7 M dimethyl sulfoxide (DMSO) + 0.9 M ethylene glycol (EG); CPS-2 - 1.4 M DMSO + 1.8 M EG; CPS-3 - 2.8 M DMSO + 3.6 M EG + 0.65 M trehalose. At IOV the ovarian fragments were exposed in CPS-1 - 7.5 % EG + 7.5 % DMSO, then in CPS-2 - 15 % EG, 15 % DMSO and 0.5 M sucrose. Straws with oocytes and ovarian fragments were plunged into LN2 and stored. For devitrif ication, the EOV oocytes were washed in solutions of 0.25, 0.19 and 0.125 M of trehalose, the IOV - in 0.5 and 0.25 М trehalose. Oocytes were cultured in NCSU-23 medium with 10 % f luid of follicles, follicular walls, hormones. 0.001 % of highly dispersed silica nanoparticles (ICP named after A.A. Chuyko of the NAS of Ukraine) were added to all media. The methods of fertilization and embryo culture are presented in the guidelines developed by us. MA and chromatin state were measured by MitoTracker Orange CMTMRos and the cytogenetic method. Signif icant differences in the level of oocytes with high-expanded cumulus between control and experimental vitrif ied groups (81 % versus 59 % and 52 %, respectively, p ≤ 0.001) were observed. The percentage of pyknotic cells in native oocytes was 19 %, EOV or IOV oocytes were 39 % and 49 %, respectively. After culture, the level of matured native oocytes was 86 %, 48 % EOV and 33 % IOV cells f inished the maturation ( p ≤ 0.001). Differences were also observed in the level of MA between groups treated by EOV and IOV (89.4 ± 7.5 μA and 149.2 ± 11.3 μA, respectively, p ≤ 0.05). For the f irst time, pre-implantation embryos were obtained from oocytes treated by IOV.

Cryopreservation of Gametes and Embryos and Their Molecular Changes

The process of freezing cells or tissues and depositing them in liquid nitrogen at -196 °C is called cryopreservation. Sub-zero temperature is not a physiological condition for cells and water ice crystals represent the main problem since they induce cell death, principally in large cells like oocytes, which have a meiotic spindle that degenerates during this process. Significantly, cryopreservation represents an option for fertility preservation in patients who develop gonadal failure for any condition and those who want to freeze their germ cells for later use. The possibility of freezing sperm, oocytes, and embryos has been available for a long time, and in 1983 the first birth with thawed oocytes was achieved. From the mid-2000s forward, the use of egg vitrification through intracytoplasmic sperm injection has improved pregnancy rates. Births using assisted reproductive technologies (ART) have some adverse conditions and events. These risks could be associated with ART procedures or related to infertility. Cryopreservation generates changes in the epigenome of gametes and embryos, given that ART occurs when the epigenome is most vulnerable. Furthermore, cryoprotective agents induce alterations in the integrity of germ cells and embryos. Notably, cryopreservation extensively affects cell viability, generates proteomic profile changes, compromises crucial cellular functions, and alters sperm motility. This technique has been widely employed since the 1980s and there is a lack of knowledge about molecular changes. The emerging view is that molecular changes are associated with cryopreservation, affecting metabolism, cytoarchitecture, calcium homeostasis, epigenetic state, and cell survival, which compromise the fertilization in ART.

Microbial occurrence in liquid nitrogen storage tanks: a challenge for cryobanking?

Abstract

Modern biobanks maintain valuable living materials for medical diagnostics, reproduction medicine, and conservation purposes. To guarantee high quality during long-term storage and to avoid metabolic activities, cryostorage is often conducted in the N₂ vapour phase or in liquid nitrogen (LN) at temperatures below − 150 °C. One potential risk of cryostorage is microbial cross contamination in the LN storage tanks. The current review summarises data on the occurrence of microorganisms that may compromise the safety and quality of biological materials during long-term storage. We assess the potential for the microbial contamination of LN in storage tanks holding different biological materials based on the detection by culture-based and molecular approaches. The samples themselves, the LN, the human microbiome, and the surrounding environment are possible routes of contamination and can cause cross contaminations via the LN phase. In general, the results showed that LN is typically not the source of major contaminations and only a few studies provided evidence for a risk of microbial cross contamination. So far, culture-based and culture-independent techniques detected only low amounts of microbial cells, indicating that cross contamination may occur at a very low frequency. To further minimise the potential risk of microbial cross contaminations, we recommend reducing the formation of ice crystals in cryotanks that can entrap environmental microorganisms and using sealed or second sample packing. A short survey demonstrated the awareness for microbial contaminations of storage containers among different culture collections. Although most participants consider the risk of cross contaminations in LN storage tanks as low, they prevent potential contaminations by using sealed devices and − 150 °C freezers. It is concluded that the overall risk for cross contaminations in biobanks is relatively low when following standard operating procedures (SOPs). We evaluated the potential sources in detail and summarised our results in a risk assessment spreadsheet which can be used for the quality management of biobanks.

Key points

• Identification of potential contaminants and their sources in LN storage tanks.

• Recommendations to reduce this risk of LN storage tank contamination.

• Development of a risk assessment spreadsheet to support quality management.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11531-4.

Cryo-banking of human spermatozoa by aseptic cryoprotectants-free vitrification in liquid air: Positive effect of elevated warming temperature

Cryoprotectant-free vitrification is a common method for spermatozoa cryopreservation by direct plunging into liquid nitrogen. However, the commercial liquid nitrogen could be potentially contaminated by microorganisms. Warming temperature plays an essential role for quality of human spermatozoa after vitrification. This study aimed to evaluate comparatively a quality spermatozoa after vitrification in liquid nitrogen and clean liquid air as well as with two warming rates: at 42 °C and 45 °C. After performing of routine swim-up of normozoospermia samples, spermatozoa from the same ejaculate were divided into two groups: vitrified in liquid nitrogen (LN) and sterile liquid air (LA). Spermatozoa of LN group were warmed at 42 °C, and spermatozoa of LA groups were divided and warmed at 42 °C (LA42) and 45 °C (LA45). Then spermatozoa motility, reactive oxygen species (ROS), mitochondrial membrane potential (MMP), reactive nitrogen species (RNS), and viability were assessed. It was no found significant differences in quality of spermatozoa from LN and LA groups in the motility, ROS, MMP, RNS rates after warming at 42 °C. A tendency to obtain better spermatozoa quality was found with using of warming by 42 °C in comparison with 45 °C. It was concluded that cryoprotectant-free vitrification by direct dropping of human spermatozoa into clean liquid air can be used as an alternative to cooling in liquid nitrogen. Warming of spermatozoa at 42 °C allows to preserve the spermatozoa physiological parameters.

Fertility preservation during the COVID-19 pandemic: mitigating the viral contamination risk to reproductive cells in cryostorage

Reopening fertility care services across the world in the midst of a pandemic brings with it numerous concerns that need immediate addressing, such as the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on the male and female reproductive cells and the plausible risk of cross-contamination and transmission. Due to the novelty of the disease the literature contains few reports confirming an association of SARS-CoV-2 with reproductive tissues, gametes and embryos. Cryobanking, an essential service in fertility preservation, carries the risk of cross-contamination through cryogenic medium and thus calls for risk-mitigation strategies. This review aims to address the available literature on the presence of SARS-CoV-2 on tissues, gametes and embryos, with special reference to the possible sources of cross-contamination through liquid nitrogen. Strategies for risk mitigation have been extrapolated from reports dealing with other viruses to the current global crisis, for safety in fertility treatment services in general, and specifically for oncofertility.

Influence of Microwave-Assisted Drying on Structural Integrity and Viability of Testicular Tissues from Adult and Prepubertal Domestic Cats

Anhydrous preservation is a promising approach for storage of living biomaterials at nonfreezing temperatures. Using the domestic cat model, the objectives of this study were to characterize changes in histology, DNA integrity, and viability of testicular tissues from adult versus prepubertal individuals during microwave-assisted drying. Testes from each age group were cut into small pieces before reversible membrane permeabilization, exposure to trehalose, and microwave-assisted drying during different time periods. In Experiment 1, water content was monitored for up to 40 minutes of drying. Tissues from adult or prepubertal cats experienced similar decreases of water content during the first 10 minutes. Desiccation progressed slowly between 10 and 20 minutes and then remained stable. In Experiment 2, structural properties were explored at 5, 10, and 20 minutes of desiccation. Percentages of normal seminiferous tubules were lower after 20 minutes drying in adult (43%) than in prepubertal tissues (61%). At the same time point, the proportion of cell degeneration was higher in adult (53%) than prepubertal tissues (28%). Percentages of intact DNA in tissues remained above 85% regardless of the microwave time in both age groups. Lastly, adult and prepubertal tissues only lost 33% of viability in both age groups. Collective results demonstrated for the first time that normal morphology, incidence of degeneration, DNA integrity, and viability of testicular tissues remained at acceptable levels during microwave-assisted drying for 20 minutes. Overall, prepubertal testicular tissues appeared to be more resilient to microwave-assisted desiccations than adult tissues. Importantly, water loss in the presence of trehalose after 20 minutes of desiccation already is compatible with long-term storage of testicular tissues at temperatures above -20°C, which is one step closer to future storage at supra-zero temperatures.

Managing and preventing blood-borne viral infection transmission in assisted reproduction: a Canadian Fertility and Andrology Society clinical practice guideline

Fertility care providers have an obligation to provide safe and effective care to patients. When a user of assisted reproductive technology (ART) is living with a blood-borne viral infection (BBVI: HIV, hepatitis C or hepatitis B), physicians and ART laboratory personnel need to know the requirements for providing quality care. Recent developments in the treatment of BBVI and understanding of transmission have changed these requirements. This guideline from the Canadian Fertility and Andrology Society (CFAS) provides comprehensive, evidence-based guidelines for reducing horizontal transmission and cross-contamination in the ART setting.

Experimental Evidence Reveals Both Cross-Infection and Cross-Contamination Risk of Embryo Storage in Liquid Nitrogen Biobanks

Simple Summary

This study was conducted to demonstrate the potential hazards of cross-infection and cross-contamination of embryos during storage in liquid nitrogen biobanks. For the harmless and successful cryopreservation of embryos, the vitrification method must be chosen meticulously to guarantee not only a high post-thaw survival of embryos, but also to reduce the risk of disease transmission when those embryos are in storage for long periods.

Abstract

In recent decades, gamete and embryo cryopreservation have become routine procedures in livestock and human assisted reproduction. However, the safe storage of germplasm and the prevention of disease transmission continue to be potential hazards of disease transmission through embryo transfer. This study aimed to demonstrate the potential risk of cross-infection of embryos from contaminated liquid nitrogen, and cross-contamination of sterile liquid nitrogen from infected embryos in naked and closed devices. Additionally, we examined the effects of antibiotic-free media on culture development of infected embryos. The study was a laboratory-based analysis using rabbit as a model. Two experiments were performed to evaluate both cross-infection (liquid nitrogen to embryos) and cross-contamination (embryos to liquid nitrogen) of artificially inoculated Salmonella Typhimurium, Staphylococcus aureus, Enterobacter aerogenes, and Aspergillus brasiliensis. Rapid cooling through vitrification was conducted on rabbit embryos, stored for a year, thawed, and cultured. In vivo produced late morulae–early blastocyst stages (72 h) embryos were used (n = 480). Embryos were cultured for 1 h in solutions with and without pathogens. Then, the embryos were vitrified and stored in naked and closed devices for one year in two liquid nitrogen biobanks (one pathogen-free and the other artificially contaminated). Embryos were warmed and cultured for a further 48 h, assessing the development and the presence of microorganism (chromogenic media, scanning electron microscopy). Embryos stored in naked devices in artificially contaminated liquid nitrogen became infected (12.5%), while none of the embryos stored in closed devices were infected. Meanwhile, storage of artificially infected embryos incurred liquid nitrogen biobank contamination (100%). Observations by scanning electron microscopy revealed that all the microorganisms were caught in the surface of embryos after the vitrification-thawed procedure. Nevertheless, embryos cultured in antibiotics and antimycotic medium developed to the hatched blastocyst stage, while artificially infected embryos cultured in antibiotic-free medium failed to develop. In conclusion, our findings support that both cross-contamination and cross-infection during embryo storage in liquid nitrogen biobanks are plausible. So, to ensure biosafety for the cryogenic storage, closed systems that avoid direct contact with liquid nitrogen must be used. Moreover, it seems essential to provide best practice guidelines for the cryogenic preservation and storage of gametes and embryos, to define appropriate quality and risk management procedures.

Human sperm vitrification: the state of the art

Sperm cryopreservation has been widely used in assisted reproductive technology (ART) and has resulted in millions of live births. Two principal approaches have been adopted: conventional (slow) freezing and vitrification. As a traditional technique, slow freezing has been successfully employed and widely used at ART clinics whereas the latter, a process to solidify liquid into an amorphous or glassy state, may become a faster alternative method of sperm cryopreservation with significant benefits in regard to simple equipment and applicability to fertility centers. Sperm vitrification has its own limitations. Firstly, small volume of load is usually plunged to liquid nitrogen to achieve high cooling rate, which makes large volume sample cryopreservation less feasible. Secondly, direct contact with liquid nitrogen increases the potential risk of contamination. Recently, new carriers have been developed to facilitate improved control over the volume and speed, and new strategies have been implemented to minimize the contamination risk. In summary, although sperm vitrification has not yet been applied in routine sperm cryopreservation, its potential as a standard procedure is growing.

Opportunities and challenges related to the implementation of sperm cryopreservation into breeding of salmonid fishes

The main aim of the present review is to present the opportunities and challenges associated with the application of cryopreserved sperm, which may improve the breeding of salmonid fishes. Cryopreservation of sperm has been used as a strategy for the conservation of biodiversity of fishes populations, the preservation of sperm from the most valuable breeding individuals and facilitate transportation of genomes, and providing a biological source of sperm regardless of the synchronisation of the maturity of broodstocks. Cryopreserved sperm can be used for the genetic improvement of salmonid fishes based on the programs of individual crossing of selected males with individual females. However, these opportunities have not yet been fully implemented at the conditions of hatchery practice. Despite the significant progress concerning the standardization of cryopreservation procedures, there are still more challenges than opportunities related to the implementation of sperm cryopreservation into breeding of salmonid fishes. The main challenge concerns the scaling up of the method towards fulfilling the requirements of fishes-breeders, in particular mass production of eyed eggs and fry. The present review shows knowledge gaps that should be considered in further studies, including development of methods to obtain sufficient amounts of sperm from numerous species of salmonids, scaling up the methods towards cryopreservation of high volumes of sperm and towards thawing high number of straws, and optimizing artificial fertilization in which oocytes are fertilized with high numbers of frozen/thawed sperm. Moreover, the implementation of technologies into hatchery practice will require special consideration to counteract the risk of sperm infection and its transmission to offsprings during cryopreservation and storage in liquid nitrogen.

Science of cryopreservation in reproductive medicine - Embryos and oocytes as exemplars

The modern successes of reproductive medicine are based on the achievements in the fields of artificial fertilization and cryobiology over the last 50years. Cryopreservation of oocytes makes it possible to preserve their reproductive potential after surgical interventions, treatment of cancer, for delayed pregnancy and to use cells for donation. Cryopreservation of embryos allows not only to reduce the multiple pregnancies rate and to increase the cumulative pregnancy rate as a result of embryo transfer in the following favorable cycles of the patient, but is also a necessary procedure in case of genetic diagnosis or in the case of contraindications for embryo transfer in the stimulated cycle due to possible complications. However, the viability of cryopreserved oocytes and embryos depends on the degree of their cryo damage during the process of freeze-warming. In this regard, it is very important to develop such freezing protocols that minimize the damages caused by the intra- and extracellular ice crystal formation, toxic effect of high concentrations of cryoprotectants and osmotic stresses. The effectiveness of cryopreservation of gametes and embryos is assessed on the basis of morphological, functional and genetic changes in the cells after warming. Special attention should be paid to the ethical issues of assisted reproductive technology, including cryobiotech technologies, which in many countries remain open and in need of settlement.

Comparison of two closed carriers for vitrification of human blastocysts in a donor program

The survival of human blastocysts to vitrification with two different carriers is compared. Both vitrification carriers used in this study are in the category of closed carriers, as they completely isolate the samples from direct contact with liquid nitrogen or its vapours during cooling and storage, until warming. This characteristic is appealing because it reduces or eliminates the theoretical risk of cross-contamination during that period of time. The two closed vitrification systems used present very different design and features: in the High Security Vitrification device, the carrier straw containing the embryos is encapsulated inside an external straw before plunging in liquid nitrogen, resulting in thermal insulation during cooling. On the other hand, in the SafeSpeed carrier embryos are loaded in a thin-walled, narrow capillary designed to maximize the thermal transference. Both closed carriers achieved comparable outcomes in terms of survival of blastocysts to the vitrification process, with 97.5% vs. 96.1% survival with HSV and SafeSpeed, respectively. In conclusion, the cooling and warming rates at which these carriers operate, in combination with the cytosolic solute concentration in the cells of the cryopreserved blastocysts attained after a cryoprotectant-loading protocol, result in successful vitrification of human blastocysts for human assisted reproduction.