StemCell Keep™ Is Effective for Cryopreservation of Human Embryonic Stem Cells by Vitrification

Fresh or frozen grafts for allogeneic stem cell transplantation: conceptual considerations and a survey on the practice during the COVID-19 pandemic from the EBMT Infectious Diseases Working Party (IDWP) and Cellular Therapy & Immunobiology Working Party (CTIWP)

The COVID-19 pandemic has had a significant impact on medical practices, including the delivery of allogeneic hematopoietic cell transplantation (HCT). In response, transplant centers have made changes to their procedures, including an increased use of cryopreservation for allogeneic haematopoietic progenitor cell (HPC) grafts. The use of cryopreserved grafts for allogeneic HCT has been reviewed and analysed in terms of potential benefits and drawbacks based on existing data on impact on cell subsets, hematological recovery, and clinical outcomes of approximately 2000 patients from different studies. A survey of European Society for Blood and Marrow Transplantation centers was also conducted to assess changes in practice during the pandemic and any unnecessary burdens on HPC donors. Before the pandemic, only 7.4% of transplant centers were routinely cryopreserving HPC products, but this percentage increased to 90% during the pandemic. The results of this review and survey suggest that cryopreservation of HPC grafts is a viable option for allogeneic HCT in certain situations, but further research is needed to determine long-term effects and ethical discussions are required to balance the needs of donors and patients when using frozen allografts.

Cryopreservation of Liver-Cell Spheroids with Macromolecular Cryoprotectants

Spheroids are a powerful tool for basic research and to reduce or replace in vivo (animal) studies but are not routinely banked nor shared. Here, we report the successful cryopreservation of hepatocyte spheroids using macromolecular (polyampholyte) cryoprotectants supplemented into dimethyl sulfoxide (DMSO) solutions. We demonstrate that a polyampholyte significantly increases post-thaw recovery, minimizes membrane damage related to cryo-injury, and remains in the extracellular space making it simple to remove post-thaw. In a model toxicology challenge, the thawed spheroids matched the performance of fresh spheroids. F-actin staining showed that DMSO-only cryopreserved samples had reduced actin polymerization, which the polyampholyte rescued, potentially linked to intracellular ice formation. This work may facilitate access to off-the-shelf and ready-to-use frozen spheroids, without the need for in-house culturing. Readily accessible 3-D cell models may also reduce the number of in vivo experiments.

Chemical approaches to cryopreservation

Cryopreservation of cells and biologics underpins all biomedical research from routine sample storage to emerging cell-based therapies, as well as ensuring cell banks provide authenticated, stable and consistent cell products. This field began with the discovery and wide adoption of glycerol and dimethyl sulfoxide as cryoprotectants over 60 years ago, but these tools do not work for all cells and are not ideal for all workflows. In this Review, we highlight and critically review the approaches to discover, and apply, new chemical tools for cryopreservation. We summarize the key (and complex) damage pathways during cellular cryopreservation and how each can be addressed. Bio-inspired approaches, such as those based on extremophiles, are also discussed. We describe both small-molecule-based and macromolecular-based strategies, including ice binders, ice nucleators, ice nucleation inhibitors and emerging materials whose exact mechanism has yet to be understood. Finally, looking towards the future of the field, the application of bottom-up molecular modelling, library-based discovery approaches and materials science tools, which are set to transform cryopreservation strategies, are also included.

Gene expression analysis of human induced pluripotent stem cells cryopreserved by vitrification using StemCell Keep

In recent years, regenerative medicine research using human somatic and induced pluripotent stem cells has advanced considerably, promoting clinical applications. However, it is essential that these cells are cryopreserved safely and effectively. Most cryopreservation solution agents contain dimethyl sulfoxide (DMSO), which exhibits strong toxicity and can potentially promote cell differentiation. Hence, it is important to explore substitutes for DMSO in cryoprotectant solutions. One such alternative is StemCell Keep (SCK), a DMSO-free solution that has been reported to effectively cryopreserve human induced pluripotent stem cells (hiPS cells). To clarify the effect of cryopreservation agents on cells, DNA microarray analysis is useful, as it can identify a large number of gene expression differences in cryopreserved cells, as well as functional increases in gene groups. In this study, we performed gene expression analysis of SCK-cryopreserved hiPS cells using a DNA microarray gene chip. The hiPS cells vitrified with SCK or DMSO-based vitrification solutions were thawed and cultured on Matrigel under feeder-free conditions, and RNA was extracted for DNA microarray analysis. Genes obtained from DNA microarray data were classified by the keywords of Gene Ontology Biological Process Term, and their relationships were analyzed using DAVID or the GeneMANIA database. SCK-cryopreserved hiPS cells expressed several anti-apoptotic genes, as well as genes related to cell adhesion or proliferation at levels that were nearly equivalent to those of non-frozen hiPS cells. Gene enrichment analysis with selected genes of SCK-cryopreserved hiPS cells whose expression differences were superior to those of DAP-cryopreserved showed strong interactions of negative regulation of apoptotic process, cell adhesion and positive regulation of cell proliferation in DAVID analysis. We demonstrated that SCK successfully maintained the key functions of hiPS cells, including anti-apoptosis, cell adhesion, and cell proliferation, during cryopreservation.

Effect of different carboxylated poly l-lysine and dimethyl sulfoxide combinations on post thaw rabbit sperm functionality and fertility

Antifreeze proteins are biologically active substances which protect living organisms against freezing injuries. The effect of a synthetic antifreeze protein carboxylated poly l-lysine (CPLL) in the extender was evaluated in the presence of a conventional cryoprotective agent, dimethyl sulfoxide (Me₂SO), for freezing rabbit sperm cells. The experiment was conducted according to 2 × 3 factorial design including two Me₂SO (5 or 8%) and three CPLL (0, 0.5 or 1%) concentrations. CPLL supplementation improved post-thaw live and live-acrosome intact sperm rates (P<0.01) without a prominent influence on the motility (P>0.05) and live-membrane intact (P>0.05) sperm rates. The most striking effect of CPLL supplementation was seen on the DNA integrity where it reduced DNA fragmentation of sperm cells significantly by interacting Me₂SO (P < 0.01) during freezing and thawing. However, it could not replace Me₂SO in the extender and did not improve pregnancy rate. In conclusion, CPLL supplementation to the extender in the presence of Me₂SO improved sperm quality parameters and post-thaw DNA integrity.

Cryopreservation of human induced pluripotent stem cells by using a new CryoLogic vitrification method

Human induced pluripotent stem cells (hiPSCs) have the properties of differentiation potential and unlimited self-renewal. Developing efficient and highly safe methods to preserve hiPSCs is important due to they have demonstrated tremendous promise in disease etiology, drug discovery, and regenerative medicine applications. Traditionally, open systems for cell cryopreservation, such as conventional slow freezing and vitrification methods, were widespread application in the storage and transportation of hiPSCs. However, these two methods have such problems of low recovery rate and the risk of cross-contamination. Recently, closed systems for cell cryopreservation, such as CryoLogic Vitrification Method (CVM), were introduced to store and transport embryos. In this study, we developed a new friendly CVM by loading a small piece of hiPSCs colonies in the vitrification solution to the hook of Fiberplug to increase the cooling rate. To warm them, the CVM Fiberplug was immersed directly in a 37 °C warming solution for 1 min, and hiPSCs were then transferred to mTeSR1 medium. The result revealed that the new CVM had a high recovery rate and maintained the stemness and differentiation potential of hiPSCs. Our new CVM not only provide a safe way for hiPSCs preservation but also has a high survival rate in the storage of hiPSCs.

Insights into Species Preservation: Cryobanking of Rabbit Somatic and Pluripotent Stem Cells

Induced pluripotent stem cells (iPSCs) are obtained by genetically reprogramming adult somatic cells via the overexpression of specific pluripotent genes. The resulting cells possess the same differentiation properties as blastocyst-stage embryonic stem cells (ESCs) and can be used to produce new individuals by embryonic complementation, nuclear transfer cloning, or in vitro fertilization after differentiation into male or female gametes. Therefore, iPSCs are highly valuable for preserving biodiversity and, together with somatic cells, can enlarge the pool of reproductive samples for cryobanking. In this study, we subjected rabbit iPSCs (rbiPSCs) and rabbit ear tissues to several cryopreservation conditions with the aim of defining safe and non-toxic slow-freezing protocols. We compared a commercial synthetic medium (STEM ALPHA.CRYO3) with a biological medium based on fetal bovine serum (FBS) together with low (0-5%) and high (10%) concentrations of dimethyl sulfoxide (DMSO). Our data demonstrated the efficacy of a CRYO3-based medium containing 4% DMSO for the cryopreservation of skin tissues and rbiPSCs. Specifically, this medium provided similar or even better biological results than the commonly used freezing medium composed of FBS and 10% DMSO. The results of this study therefore represent an encouraging first step towards the use of iPSCs for species preservation.

Magnetic heating of nanoparticles as a scalable cryopreservation technology for human induced pluripotent stem cells

Scale-up of production is needed for industrial applications and clinical translation of human induced pluripotent stem cells (hiPSCs). However, in cryopreservation of hiPSCs, successful rewarming of vitrified cells can only be achieved by convective warming of small volumes (generally 0.2 mL). Here, we present a scalable nano-warming technology for hiPSC cryopreservation employing inductive heating of magnetic nanoparticles under an alternating magnetic field. The conventional method by water bath heating at 37 °C resulted in a decrease of cell viability owing to devitrification caused by slow warming of samples with large volumes (≥ 20 mL). Nano-warming showed uniform and rapid rewarming of vitrified samples and improved viability of hiPSCs in the 20-mL system. In addition to single cells, hiPSC aggregates prepared using a bioreactor-based approach were successfully cryopreserved by the nano-warming technique. These results demonstrate that nano-warming is a promising methodology for cryopreservation in mass production of hiPSCs.

Canine amniotic membrane mesenchymal stromal/stem cells: Isolation, characterization and differentiation

The amniotic membrane can be considered as one of the sources of isolation of these cells, since it is found in the fetal maternal interface and has low immunogenicity. Mesenchymal stromal/stem cells (MSCs) have not been identified in canine amniotic membrane (AMC). Therefore, our objective was to isolate, culture, characterize and differentiate cells derived from canine amniotic membrane (AMC) and to verify its immunological and tumorigenic potential. For this, 12 dogs fetuses of each gestational age 32, 43 and 55 days were used, and the isolation and culture of the AMC were performed. We observed that the cells presented fibroblastoid morphology and high confluence even after freezing. We also observed that, when induced, they were able to differentiate into osteogenic, adipogenic, and chondrogenic cells, as well as being CD34- and CD105+. Regarding the immunological markers, we found that IL-1, IL-2, IL-6, IL-10 and MHC II were not expressed, whereas MHC I was expressed. After application of AMC cells in nude mice we can verify that there was no tumor formation. Based on this, we conclude that canine amniotic membrane is a good and accessible source for obtaining MSCs of low immunogenic and tumorigenic potential for veterinary therapeutic applications.

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

BACKGROUND

Tissue-engineered cardiac constructs have potential in the functional recovery of heart failure; however, the preservation of these constructs is crucial for the development and widespread application of this treatment. We hypothesized that tissue-engineered skeletal myoblast (SMB) constructs may be preserved by vitrification to conserve biological function and structure.

RESULTS

Scaffold-free cardiac cell-sheet constructs were prepared from SMBs and immersed in a vitrification solution containing ethylene glycol, sucrose, and carboxyl poly-L-lysine. The cell sheet was wrapped in a thin film and frozen rapidly above liquid nitrogen to achieve vitrification (vitrification group, n = 8); fresh, untreated SMB sheets (fresh group, n = 8) were used as the control. The cryopreserved SMB sheets were thawed at 2 days, 1 week, 1 month, and 3 months after cryopreservation for assessment. Thawed, cryopreserved SMB sheets were transplanted into rat hearts in a myocardial infarction nude rat model, and their effects on cardiac function were evaluated. Cell viability in the cardiac constructs of the vitrification group was comparable to that of the fresh group, independent of the period of cryopreservation (p > 0.05). The structures of the cell-sheet constructs, including cell-cell junctions such as desmosomes, extracellular matrix, and cell membranes, were maintained in the vitrification group for 3 months. The expression of cytokine genes and extracellular matrix proteins (fibronectin, collagen I, N-cadherin, and integrin α5) showed similar levels in the vitrification and fresh groups. Moreover, in an in vivo experiment, the ejection fraction was significantly improved in animals treated with the fresh or cryopreserved constructs as compared to that in the sham-treated group (p < 0.05).

CONCLUSIONS

Overall, these results show that the vitrification method proposed here preserves the functionality and structure of scaffold-free cardiac cell-sheet constructs using human SMBs after thawing, suggesting the potential clinical application of this method in cell-sheet therapy.

Cryopreservation: Vitrification and Controlled Rate Cooling

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