Development of a vitrification method for preserving human myoblast cell sheets for myocardial regeneration therapy

Hypothermic and cryogenic preservation of cardiac tissue-engineered constructs

Cardiac tissue engineering (cTE) has already advanced towards the first clinical trials, investigating safety and feasibility of cTE construct transplantation in failing hearts. However, the lack of well-established preservation methods poses a hindrance to further scalability, commercialization, and transportation, thereby reducing their clinical implementation. In this study, hypothermic preservation (4 °C) and two methods for cryopreservation (i.e., a slow and fast cooling approach to -196 °C and -150 °C, respectively) were investigated as potential solutions to extend the cTE construct implantation window. The cTE model used consisted of human induced pluripotent stem cell-derived cardiomyocytes and human cardiac fibroblasts embedded in a natural-derived hydrogel and supported by a polymeric melt electrowritten hexagonal scaffold. Constructs, composed of cardiomyocytes of different maturity, were preserved for three days, using several commercially available preservation protocols and solutions. Cardiomyocyte viability, function (beat rate and calcium handling), and metabolic activity were investigated after rewarming. Our observations show that cardiomyocytes' age did not influence post-rewarming viability, however, it influenced construct function. Hypothermic preservation with HypoThermosol® ensured cardiomyocyte viability and function. Furthermore, fast freezing outperformed slow freezing, but both viability and function were severely reduced after rewarming. In conclusion, whereas long-term preservation remains a challenge, hypothermic preservation with HypoThermosol® represents a promising solution for cTE construct short-term preservation and potential transportation, aiding in off-the-shelf availability, ultimately increasing their clinical applicability.

Progress on Electro-Enhancement of Cell Manufacturing

With the long persistence of complex, chronic diseases in society, there is increasing motivation to develop cells as living medicine to treat diseases ranging from cancer to wounds. While cell therapies can significantly impact healthcare, the shortage of starter cells meant that considerable raw materials must be channeled solely for cell expansion, leading to expensive products with long manufacturing time which can prevent accessibility by patients who either cannot afford the treatment or have highly aggressive diseases and cannot wait that long. Over the last three decades, there has been increasing knowledge on the effects of electrical modulation on proliferation, but to the best of the knowledge, none of these studies went beyond how electro-control of cell proliferation may be extended to enhance industrial scale cell manufacturing. Here, this review is started by discussing the importance of maximizing cell yield during manufacturing before comparing strategies spanning biomolecular/chemical/physical to modulate cell proliferation. Next, the authors describe how factors governing invasive and non-invasive electrical stimulation (ES) including capacitive coupling electric field may be modified to boost cell manufacturing. This review concludes by describing what needs to be urgently performed to bridge the gap between academic investigation of ES to industrial applications.

Fibroblasts are the most suitable cell source for regenerative medicine due to their high intracellular fibroblast growth factor 2 content

In our previous study, we found that dry-preserved multilayered fibroblast cell sheets promoted angiogenesis and wound healing in a mouse ulcer model by releasing high levels of intracellular fibroblast growth factor 2 (FGF2), hepatocyte growth factor (HGF), and vascular endothelial growth factor (VEGF), from dried cells. In the present study, to identify which cell types are suitable for human dry-preserved cell sheets (dry sheets), we compared the intracellular FGF2 levels in seven types of cells reported as cell sheets for clinical use or preclinical studies. FGF2 levels were high in mesenchymal cells, including human oral fibroblasts (HOFs) and human dermal fibroblasts (HDFs), human dental pulp stem cells (DPSCs), and human mesenchymal stem cells (MSCs); in contrast, FGF2 levels in human umbilical vascular endothelial cells (HUVECs), human skeletal muscle myoblasts (SkMMs), and human epidermal keratinocytes (HEKs) were remarkably low, approximately 25% those in fibroblasts. In addition, we prepared dry sheets from HOFs, DPSCs, and MSCs, and analyzed the growth factors released from each dry sheet upon rehydration. High levels of FGF2, HGF, and VEGF were detected in the eluate prepared by immersing each dry sheet. In particular, FGF2 and HGF were the most abundant in HOFs. An in vitro cell proliferation assay showed that these eluates significantly enhanced HUVEC proliferation compared to control cells. Furthermore, cells incubated with HOF eluate showed significantly higher cell proliferation than cells incubated with DPSC and MSC eluates. However, this proliferative response was significantly blocked by FGF2-neutralizing antibodies. These results demonstrate that growth factors released from human dry sheets have physiological activity and that this activity is mainly mediated by the effect of FGF2. Fibroblasts are ideal for the clinical application of dry-preserved cell sheets in humans owing to their high intracellular FGF2 content, fast cell proliferation, ease of handling, availability, and low culture costs, making them the most suitable cell source for regenerative medicine, with FGF2 release as the mechanism of action.

Cryopreservation of Cell Sheets for Regenerative Therapy: Application of Vitrified Hydrogel Membranes

Organ transplantation is the first and most effective treatment for missing or damaged tissues or organs. However, there is a need to establish an alternative treatment method for organ transplantation due to the shortage of donors and viral infections. Rheinwald and Green et al. established epidermal cell culture technology and successfully transplanted human-cultured skin into severely diseased patients. Eventually, artificial cell sheets of cultured skin were created, targeting various tissues and organs, including epithelial sheets, chondrocyte sheets, and myoblast cell sheets. These sheets have been successfully used for clinical applications. Extracellular matrix hydrogels (collagen, elastin, fibronectin, and laminin), thermoresponsive polymers, and vitrified hydrogel membranes have been used as scaffold materials to prepare cell sheets. Collagen is a major structural component of basement membranes and tissue scaffold proteins. Collagen hydrogel membranes (collagen vitrigel), created from collagen hydrogels through a vitrification process, are composed of high-density collagen fibers and are expected to be used as carriers for transplantation. In this review, the essential technologies for cell sheet implantation are described, including cell sheets, vitrified hydrogel membranes, and their cryopreservation applications in regenerative medicine.

Recent Advances in Cell Sheet Engineering: From Fabrication to Clinical Translation

Cell sheet engineering, a scaffold-free tissue fabrication technique, has proven to be an important breakthrough technology in regenerative medicine. Over the past two decades, the field has developed rapidly in terms of investigating fabrication techniques and multipurpose applications in regenerative medicine and biological research. This review highlights the most important achievements in cell sheet engineering to date. We first discuss cell sheet harvesting systems, which have been introduced in temperature-responsive surfaces and other systems to overcome the limitations of conventional cell harvesting methods. In addition, we describe several techniques of cell sheet transfer for preclinical (in vitro and in vivo) and clinical trials. This review also covers cell sheet cryopreservation, which allows short- and long-term storage of cells. Subsequently, we discuss the cell sheet properties of angiogenic cytokines and vasculogenesis. Finally, we discuss updates to various applications, from biological research to clinical translation. We believe that the present review, which shows and compares fundamental technologies and recent advances in cell engineering, can potentially be helpful for new and experienced researchers to promote the further development of tissue engineering in different applications.

Cryopreserved allogenic fibroblast sheets: development of a promising treatment for refractory skin ulcers

The purpose of this study was to investigate the therapeutic effect of cryopreserved allogenic fibroblast cell sheets in a mouse model of skin ulcers. It is necessary to reduce the cost of regenerative medicine for it to be widely used. We consider that cell sheets could be applied to various diseases if cryopreservation of allogenic cell sheets was possible. In this study, fibroblasts were frozen using a three-dimensional freezer. Freeze-thawed fibroblasts had ~80% cell viability, secreted ≥ 50% vascular endothelial growth factor, hepatocyte growth factor, and stromal derived factor-1α compared with non-frozen fibroblast sheets, and secreted approximately the same amount of transforming growth factor-β1. There was no difference in wound-healing rates in the skin ulcer model between non-frozen and freeze-thawed fibroblast sheets regardless of autologous and allogenic cells. The degree of angiogenesis was comparable between autologous and allogenic cells. The number of CD3-positive cells in healed tissues was larger for allogenic fibroblast sheets compared with autologous fibroblast sheets. However, histopathological images showed that the fibrosis, microvascular density, and healing phase of the wound in allogenic freeze-thawed fibroblast sheets were more similar to autologous freeze-thawed fibroblast sheets than to allogenic non-frozen fibroblast sheets. These results suggest that allogenic freeze-thawed fibroblast sheets may be a promising therapeutic option for refractory skin ulcers.

Development of a Vitrification Preservation Process for Bioengineered Epithelial Constructs

The demand for human bioengineered tissue constructs is growing in response to the worldwide movement away from the use of animals for testing of new chemicals, drug screening and household products. Presently, constructs are manufactured and delivered just in time, resulting in delays and high costs of manufacturing. Cryopreservation and banking would speed up delivery times and permit cost reduction due to larger scale manufacturing. Our objective in these studies was development of ice-free vitrification formulations and protocols using human bioengineered epithelial constructs that could be scaled up from individual constructs to 24-well plates. Initial experiments using single EpiDerm constructs in vials demonstrated viability >80% of untreated control, significantly higher than our best freezing strategy. Further studies focused on optimization and evaluation of ice-free vitrification strategies. Vitrification experiments with 55% (VS55) and 70% (VS70) cryoprotectant (CPA) formulations produced constructs with good viability shortly after rewarming, but viability decreased in the next days, post-rewarming in vitro. Protocol changes contributed to improved outcomes over time in vitro. We then transitioned from using glass vials with 1 construct to deep-well plates holding up to 24 individual constructs. Construct viability was maintained at >80% post-warming viability and >70% viability on days 1−3 in vitro. Similar viability was demonstrated for other related tissue constructs. Furthermore, we demonstrated maintenance of viability after 2−7 months of storage below −135 °C.

Trehalose glycopolymers for cryopreservation of tissue-engineered constructs

The development of an effective cryopreservation method to achieve off-the-shelf and bioactive tissue-engineered constructs (TECs) is important to meet the requirements for clinical applications. The trehalose, a non-permeable cryoprotectant (CPA), has difficulty in penetrating the plasma membranes of mammalian cells and has only been used in combination with other cell penetrating CPA (such as DMSO) to cryopreserve mammalian cells. However, the inherent cytotoxicity of DMSO results in increasing risks with respect to cryopreserved cells. Therefore, in this study, permeable trehalose glycopolymers were synthesised for cryopreservation of TECs. The trehalose glycopolymers exhibited good ice inhibiting activities and biocompatibilities. Furthermore, the viability and function of TECs after cryopreservation with 5.0 wt% S2 were similar to those of the non-cryopreserved TECs. We developed an effective preservation strategy for the off-the-shelf availability of TECs.

Droplet-based vitrification of adherent human induced pluripotent stem cells on alginate microcarrier influenced by adhesion time and matrix elasticity

The gold standard in cryopreservation is still conventional slow freezing of single cells or small aggregates in suspension, although major cell loss and limitation to non-specialised cell types in stem cell technology are known drawbacks. The requirement for rapidly available therapeutic and diagnostic cell types is increasing constantly. In the case of human induced pluripotent stem cells (hiPSCs) or their derivates, more sophisticated cryopreservation protocols are needed to address this demand. These should allow a preservation in their physiological, adherent state, an efficient re-cultivation and upscaling upon thawing towards high-throughput applications in cell therapies or disease modelling in drug discovery. Here, we present a novel vitrification-based method for adherent hiPSCs, designed for automated handling by microfluidic approaches and with ready-to-use potential e.g. in suspension-based bioreactors after thawing. Modifiable alginate microcarriers serve as a growth surface for adherent hiPSCs that were cultured in a suspension-based bioreactor and subsequently cryopreserved via droplet-based vitrification in comparison to conventional slow freezing. Soft (0.35%) versus stiff (0.65%) alginate microcarriers in concert with adhesion time variation have been examined. Findings revealed specific optimal conditions leading to an adhesion time and growth surface (matrix) elasticity dependent hypothesis on cryo-induced damaging regimes for adherent cell types. Deviations from the found optimum parameters give rise to membrane ruptures assessed via SEM and major cell loss after adherent vitrification. Applying the optimal conditions, droplet-based vitrification was superior to conventional slow freezing. A decreased microcarrier stiffness was found to outperform stiffer material regarding cell recovery, whereas the stemness characteristics of rewarmed hiPSCs were preserved.

A Roadmap to Cardiac Tissue-Engineered Construct Preservation: Insights from Cells, Tissues, and Organs

Worldwide, over 26 million patients suffer from heart failure (HF). One strategy aspiring to prevent or even to reverse HF is based on the transplantation of cardiac tissue-engineered (cTE) constructs. These patient-specific constructs aim to closely resemble the native myocardium and, upon implantation on the diseased tissue, support and restore cardiac function, thereby preventing the development of HF. However, cTE constructs off-the-shelf availability in the clinical arena critically depends on the development of efficient preservation methodologies. Short- and long-term preservation of cTE constructs would enable transportation and direct availability. Herein, currently available methods, from normothermic- to hypothermic- to cryopreservation, for the preservation of cardiomyocytes, whole-heart, and regenerative materials are reviewed. A theoretical foundation and recommendations for future research on developing cTE construct specific preservation methods are provided. Current research suggests that vitrification can be a promising procedure to ensure long-term cryopreservation of cTE constructs, despite the need of high doses of cytotoxic cryoprotective agents. Instead, short-term cTE construct preservation can be achieved at normothermic or hypothermic temperatures by administration of protective additives. With further tuning of these promising methods, it is anticipated that cTE construct therapy can be brought one step closer to the patient.

Cryopreserved skin epithelial cell sheet combined with acellular amniotic membrane as an off-the-shelf scaffold for urethral regeneration

BACKGROUND

Autologous tissue transplantation for urethral repair is often limited and causes donor site complications. Here, a cryopreserved rabbit skin epithelial cell sheet (SEC) combined with an acellular amniotic membrane (AM) was used to repair rabbit urethral defects.

METHODS

Abdominal skin was collected from 4-week-old New Zealand rabbits, and primary epithelial cells were extracted and cultured to form a cell sheet. Fresh SEC-AMs were constructed and cryopreserved. A cryopreservation system including optimized medium, two-pump perfusion, a programmed freezer and liquid nitrogen storage was established. Cell viability, mechanical strength, electron microscopy, and histological staining were performed in vitro after 1 month. Next, the sheets were transplanted subcutaneously for 2 weeks, and the graft was used to repair the rabbit urethral defect. Urinary function was measured and samples were collected for histological staining after 1 month.

RESULTS

We confirmed that cryopreservation damage of SECs was reduced by composition with acellular AMs in terms of high cell activity. The SEC mechanical strength was also enhanced by AMs, which was convenient for the operation. In in vivo experiments, we transplanted sheets into the groin area for two weeks and found that cryopreservation reduced inflammatory cell infiltration and significantly improved vascular density. In the urethral repair experiment, the near-normal passive urine flow rate, smooth mucosa of the gross specimen, intact epithelialization and abundant neovascularization were confirmed in the cryopreserved-SEC-AM group compared with the other groups.

CONCLUSIONS

Cryopreserved SEC-AMs demonstrated similar outcomes of rabbit urethral defect repair as fresh SEC-AMs, showing good clinical application prospects.

Biobanked human foreskin epithelial cell sheets reduce inflammation and promote wound healing in a nude mouse model

BACKGROUND

Human epithelial cell sheets (ECSs) are used to clinically treat epithelial conditions such as burns, corneal blindness, middle ear cholesteatoma and vitiligo. As a widely used material in clinic, there is little information on the biobanking of ECSs and its repair effect after storage.

RESULTS

Two methods for biobanking foreskin ECSs were compared in a short term (7 days): 4-degree storage and programmed cryopreservation. Cell sheet integrity, viability, apoptosis, immunogenicity, mechanical properties and function were evaluated. In vivo, ECSs were directly transplanted to skin defect models and histological examination was performed at 1 week postoperatively. We successfully extracted human foreskin-derived primary epithelial cells and fabricated them into ECSs. Compared with 4-degree storage, programmed cryopreservation preserved the ECS structural integrity, enhanced the mechanical properties, decreased HLA-I expression, and increased cell viability and survival. An increased proportion of melanocytes with proliferative capacity remained in the cryopreserved sheets, and the undifferentiated epithelial cells were comparable to those of the fresh sheets. In vivo, cryopreserved ECSs could reduce inflammatory cell infiltration and promote connective tissue remodeling, epithelial cell proliferation and vascular regeneration.

CONCLUSIONS

Programmed cryopreservation of ECSs was superior and more feasible than 4-degree storage and the cryopreserved ECSs achieved satisfying skin wound healing in vivo. We anticipate that the off-the-shelf ECSs could be quickly used, such as, to repair human epithelial defect in future.

Biomedical applications of muscle-derived stem cells: from bench to bedside

INTRODUCTION

Skeletal muscle-derived stem cells (Sk-MDSCs) are considered promising sources of adult stem cell therapy. Skeletal muscle comprises approximately 40-50% of the total body mass with marked potential for postnatal adaptive response, such as muscle hypertrophy, hyperplasia, atrophy, and regenerative capacity. This strongly suggests that skeletal muscle contains various stem/progenitor cells related to muscle-nerve-vascular tissues, which would support the above postnatal events even in adulthood.

AREA COVERED

The focus of this review is the therapeutic potential of the Sk-MDSCs as an adult stem cell autograft. For this purpose, the validity of cell isolation and purification, tissue reconstitution capacity in vivo after transplantation, comparison of the results of basic mouse and preclinical human studies, potential problematic and beneficial aspects, and effective usage have been discussed following the history of clinical applications.

EXPERT OPINION

Although the clinical application of Sk-MDSCs began as a therapy for the systemic disease of Duchenne muscular dystrophy, here, through the unique local injection method, therapy for severely damaged peripheral nerves, particularly the long-gap nerve transection, has been introduced. The beneficial aspects of the use of Sk-MDSCs as the source of local tissue transplantation therapy have also been discussed.

Development of an efficient vitrification method for chondrocyte sheets for clinical application

Introduction

Regenerative therapy using chondrocyte sheets is effective for osteoarthritis. The clinical application of chondrocyte sheet therapy is expected to be further advanced by the use of a feasible cryopreservation technique. Previously, we developed a chondrocyte sheet vitrification method; however, it was too complex to be used for routine clinical application. Here, we aimed to develop a prototype method for vitrifying chondrocyte sheets for clinical practice.

Methods

We developed a “circulating vitrification bag” as a container to process cell sheets for vitrification in an efficient and sanitary fashion. Moreover, we invented the “vitrification storage box”, which is useful for the vitrification of cell sheets, long-term preservation, and transportation. These devices were used to vitrify rabbit chondrocyte sheets, which were then assessed for their structural characteristics and the viability of the component cells after rewarming.

Results

In all cell sheet samples (n = 7) vitrified by the circulating vitrification bag method, the integrity of the sheet structure was maintained, and the cell survival rate was similar to that of non-vitrified samples (91.0 ± 2.9% vs. 90.0 ± 3.0%). Proteoglycan and type II collagen, which are major components of cartilage, were densely and evenly distributed throughout the chondrocyte sheet subjected to vitrification similarly to that observed in the non-vitrified sheet. After long-term storage using the vitrification storage box, the cell sheets maintained normal structure and cell viability (survival rate: 81.2 ± 1.0% vs. 84.3 ± 1.8%) compared to the non-vitrified sheet.

Conclusion

Our results indicate that the circulating vitrification bag method is an effective approach for realizing the clinical application of vitrified chondrocyte sheets. The vitrification storage box is also useful for the long-term preservation of vitrified cell sheets, further enhancing the feasibility of the clinical application of cryopreserved chondrocyte sheets.

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We developed a new device and method for the cryopreservation of cell sheets.

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The method and device efficacy were evaluated using vitrified rabbit chondrocyte sheets.

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Our approach allows efficient clinical application of vitrified cell sheets.

High-mobility group box 1 fragment suppresses adverse post-infarction remodeling by recruiting PDGFRα-positive bone marrow cells

OBJECTIVES

High-mobility group box 1 protein (HMGB1) fragment enhances bone marrow-derived mesenchymal stem cell (BM-MSC) recruitment to damaged tissue to promote tissue regeneration. This study aimed to evaluate whether systemic injection of HMGB1 fragment could promote tissue repair in a rat model of myocardial infarction (MI).

METHODS

HMGB1 (n = 14) or phosphate buffered saline (n = 12, control) was administered to MI rats for 4 days. Cardiac performance and left ventricular remodeling were evaluated using ultrasonography and immunostaining. BM-MSC recruitment to damaged tissue in green fluorescent protein-bone marrow transplantation (GFP-BMT) models was evaluated using immunostaining.

RESULTS

At four weeks post-treatment, the left ventricular ejection fraction was significantly improved in the HMGB1 group compared to that in the control. Interstitial fibrosis and cardiomyocyte hypertrophy were also significantly attenuated in the HMGB1 group compared to the control. In the peri-infarction area, VEGF-A mRNA expression was significantly higher and TGFβ expression was significantly attenuated in the HMGB1 group than in the control. In GFP-BMT rats, GFP+/PDGFRα+ cells were significantly mobilized to the peri-infarction area in the HMGB1 group compared to that in the control, leading to the formation of new vasculature. In addition, intravital imaging revealed that more GFP+/PDGFRα+ cells were recruited to the peri-infarction area in the HMGB1 group than in the control 12 h after treatment.

CONCLUSIONS

Systemic administration of HMGB1 induced angiogenesis and reduced fibrosis by recruiting PDGFRα+ mesenchymal cells from the bone marrow, suggesting that HMGB1 administration might be a new therapeutic approach for heart failure after MI.

Effect of 'in air' freezing on post-thaw recovery of Callithrix jacchus mesenchymal stromal cells and properties of 3D collagen-hydroxyapatite scaffolds

Through enabling an efficient supply of cells and tissues in the health sector on demand, cryopreservation is increasingly becoming one of the mainstream technologies in rapid translation and commercialization of regenerative medicine research. Cryopreservation of tissue-engineered constructs (TECs) is an emerging trend that requires the development of practically competitive biobanking technologies. In our previous studies, we demonstrated that conventional slow-freezing using dimethyl sulfoxide (Me₂SO) does not provide sufficient protection of mesenchymal stromal cells (MSCs) frozen in 3D collagen-hydroxyapatite scaffolds. After simple modifications to a cryopreservation protocol, we report on significantly improved cryopreservation of TECs. Porous 3D scaffolds were fabricated using freeze-drying of a mineralized collagen suspension and following chemical crosslinking. Amnion-derived MSCs from common marmoset monkey Callithrix jacchus were seeded onto scaffolds in static conditions. Cell-seeded scaffolds were subjected to 24 h pre-treatment with 100 mM sucrose and slow freezing in 10% Me₂SO/20% FBS alone or supplemented with 300 mM sucrose. Scaffolds were frozen 'in air' and thawed using a two-step procedure. Diverse analytical methods were used for the interpretation of cryopreservation outcome for both cell-seeded and cell-free scaffolds. In both groups, cells exhibited their typical shape and well-preserved cell-cell and cell-matrix contacts after thawing. Moreover, viability test 24 h post-thaw demonstrated that application of sucrose in the cryoprotective solution preserves a significantly greater portion of sucrose-pretreated cells (more than 80%) in comparison to Me₂SO alone (60%). No differences in overall protein structure and porosity of frozen scaffolds were revealed whereas their compressive stress was lower than in the control group. In conclusion, this approach holds promise for the cryopreservation of 'ready-to-use' TECs.

Vitrification and storage of oral mucosa epithelial cell sheets

Shipping time and shipping delays might affect the quality of the stem cells based engineered "organs." In our laboratory, we have developed a limbal stem cell deficient (LSCD) rabbit model. To reverse the LSCD, we cultured oral mucosal epithelial cells for 2-3 weeks and engineered cultured autologous oral mucosa epithelial cell sheets (CAOMECS), which were grafted on the LSCD cornea. The purpose of this study was to vitrify CAOMECS and to store it until the CAOMECS can be grafted onto patients. CAOMECS were vitrified in LN₂ for up to 204 days. We tested two different methods of vitrification with different solutions; however, CAOMECS were only viable when they were not stored in a vitrification solution; results were only reported from this CAOMECS. On the basis of hematoxylin and eosin staining, we showed that the CAOMECS morphology was well preserved after long-term storage in LN₂ . Most of the preservation solutions maintained the CAOMECS phenotype (Ki67, proliferating cell nuclear antigen (PCNA), Beta-Catenin, ZO-1, E-Cadherin, CK3, CK4, CK13). The exception was the solution composed with ethylene glycol and Dimethyl sulfoxide (DMSO): this resulted in loss of DeltaN-p63 expression. DeltaN-p63 is an important marker for cell proliferation. The expression of proteins involved in cell-cell connection and the differentiation markers were maintained. Apoptosis was not detected in the thawed CAOMECS. We demonstrated that CAOMECS can be stored long-term in LN₂ without affecting their morphology and phenotype.

Negative air pressure treatment accelerates the penetration of permeable cryoprotectants into bovine ovarian tissue in vitrification protocol and improves cell density after vitrification

Effects of additional physical treatments during vitrification of the bovine ovarian tissue were examined for increasing of permeability of ethylene glycol (EG) and dimethyl sulfoxide (Me2SO). The concentrations of EG and Me2SO and histological changes in the ovarian tissue were evaluated. In the first equilibration step (7.5% EG and 7.5% Me2SO), all the 10-min physical treatments, i.e., negative (679 hPa) or positive (1347 hPa) air pressure applied with a disposable syringe, and shaking (60 rpm) applied with a laboratory shaker, were comparable to 25-min non-physical treatment (plain) vitrification. When effects of the negative air pressure were examined in the second equilibration step (20% EG and 20% Me2SO), its 10-min treatment was equivalent to 15-min plain vitrification (140-170 mg/g tissue). It was thus indicated that the negative air pressure treatment accelerates the penetration of permeable cryoprotectants into the ovarian tissue slices. Histological examination showed that the cell density and the amount of pan-cadherin in the tunica albuginea of the ovary was reduced by the vitrification, but was improved by the negative air pressure treatment. The amount of pan-cadherin in the tunica albuginea was recommended as a biomarker for evaluation of effectiveness of protocol for cryopreservation of bovine ovarian tissue and considered to be a candidate biomarker for human ovarian tissue cryopreservation.