Cryopreservation by slow cooling with DMSO diminished production of Oct-4 pluripotency marker in human embryonic stem cells

The Effect of Short- and Long-Term Cryopreservation on Chicken Primordial Germ Cells

Primordial germ cells (PGCs) are the precursors of functional gametes and the only cell type capable of transmitting genetic and epigenetic information from generation to generation. These cells offer valuable starting material for cell-based genetic engineering and genetic preservation, as well as epigenetic studies. While chicken PGCs have demonstrated resilience in maintaining their germness characteristics during both culturing and cryopreservation, their handling remains a complex challenge requiring further refinement. Herein, the study aimed to compare the effects of different conditions (freezing-thawing and in vitro cultivation) on the expression of PGC-specific marker genes. Embryonic blood containing circulating PGCs was isolated from purebred Green-legged Partridgelike chicken embryos at 14-16 Hamburger-Hamilton (HH) embryonic development stage. The blood was pooled separately for males and females following sex determination. The conditions applied to the blood containing PGCs were as follows: (1) fresh isolation; (2) cryopreservation for a short term (2 days); and (3) in vitro culture (3 months) with long-term cryopreservation of purified PGCs (~2 years). To characterize PGCs, RNA isolation was carried out, followed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) to assess the expression levels of specific germ cell markers (SSEA1, CVH, and DAZL), as well as pluripotency markers (OCT4 and NANOG). The investigated genes exhibited consistent expression among PGCs maintained under diverse conditions, with no discernible differences observed between males and females. Notably, the analyzed markers demonstrated higher expression levels in PGCs when subjected to freezing than in their freshly isolated counterparts.

Optimization of Deep Eutectic Solvents Enables Green and Efficient Cryopreservation

Cryopreservation presents significant opportunities for biomedical applications including cell therapy, tissue engineering, and assisted reproduction. Dimethyl sulfoxide (DMSO), the most commonly used cryoprotectant (CPA), can be added to cells to prevent cryogenic damage. However, the toxicity of cryoprotectants restrains its further development in many areas with safety concerns such as clinical treatment. Therefore, the development of low-toxicity cryoprotectants is essential for medical research. This work reports deep eutectic solvents (DES) as naturally biocompatible osmoprotectants for green and efficient cryopreservation of human umbilical cord mesenchymal stem cells (HuMSC), which may be an ideal alternative to DMSO. The six types of DESs were explored for thermal properties, toxicity, and permeability in cells. Raman spectroscopy and viscosity studies showed that DES exhibited an improved hydrogen-bonding system as the temperature decreased. By optimizing the freezing process (cooling rate, incubation time, and loading procedure) of DES, the viability of mouse embryonic fibroblast cells (NIH-3T3) after thawing was significantly improved. The HuMSC were successfully preserved with no significant difference (p > 0.05) in cell viability (94.65%) after thawing compared with DMSO, which preserved the cell differentiation function and improved the cell proliferation rate. The mechanism of DES in cryopreservation was investigated, and it was found that DES could bind water molecules and effectively inhibit the growth of ice crystals during ice recrystallization, reducing mechanical damage to cells. This study highlights the excellent performance of DES as a low-toxicity CPA for stem cell preservation, which may be a significant advance for future clinical cell therapy.

Exploring the effect of cryopreservation in assisted reproductive technology and potential epigenetic risk

Since the birth of the first baby by in vitro fertilization in 1978, more than 9 million children have been born worldwide using medically assisted reproductive treatments. Fertilization naturally takes place in the maternal oviduct where unique physiological conditions enable the early healthy development of the embryo. During this dynamic period of early development major waves of epigenetic reprogramming, crucial for the normal fate of the embryo, take place. Increasingly, over the past 20 years concerns relating to the increased incidence of epigenetic anomalies in general, and genomic-imprinting disorders in particular, have been raised following assisted reproduction technology (ART) treatments. Epigenetic reprogramming is particularly susceptible to environmental conditions during the periconceptional period and non-physiological conditions such as ovarian stimulation, in vitro fertilization and embryo culture, as well as cryopreservation procedure, might have the potential to independently or collectively contribute to epigenetic dysregulation. Therefore, this narrative review offers a critical reappraisal of the evidence relating to the association between embryo cryopreservation and potential epigenetic regulation and the consequences on gene expression together with long-term consequences for offspring health and wellbeing. Current literature suggests that epigenetic and transcriptomic profiles are sensitive to the stress induced by vitrification, in terms of osmotic shock, temperature and pH changes, and toxicity of cryoprotectants, it is therefore, critical to have a more comprehensive understanding and recognition of potential unanticipated iatrogenic-induced perturbations of epigenetic modifications that may or may not be a consequence of vitrification.

Cryopreservation of Human Bone Marrow Derived Mesenchymal Stem Cells at High Concentration Is Feasible

Introduction: For stem cell therapies to be adopted in mainstream health care, robust, reliable, and cost-effective storage and transport processes must be developed. Cryopreservation remains the best current platform for this purpose, and freezing cells at high concentration may have many benefits, including savings on cost and storage space, facilitating transport logistics, and reducing cryoprotectant volume. Cells, such as mesenchymal stem cells (MSCs), are typically frozen at 1 million cells per milliliter (mL), but the aim of this study is to examine the post-thaw attributes of human bone marrow derived MSCs (hBM-MSCs) frozen at 1, 5, and 10 million cells per mL. Methods: Thawed cells were assessed for their morphology, phenotypic marker expression, viability, apoptosis level, metabolic activity, proliferation, and osteogenic and adipogenic differentiation. Results: In this study, for the first time, it is shown that all assessed cells expressed the typical MSC markers (CD90, CD105, and CD73) and lacked the expression of CD14, CD20, CD34, CD45, and HLA-DR. In addition, all cells showed elongated fibroblastic morphology. Post-thaw viability was retained with no difference among the three concentrations. Moreover, no significant statistical difference was observed in the post-thaw apoptosis level, metabolic activity, proliferation, and osteogenic potential, indicating that these cells are amenable to cryopreservation at higher concentrations. Conclusion: The results of this study are of paramount importance to the development of manufacturing processes around a useful freezing concentration when cells are targeted to be stored for at least 6 months.

Application-Oriented Bulk Cryopreservation of Human iPSCs in Cryo Bags Followed by Direct Inoculation in Scalable Suspension Bioreactors for Expansion and Neural Differentiation

Stem cell-based therapies are promising tools for regenerative medicine and require bulk numbers of high-quality cells. Currently, cells are produced on demand and have a limited shelf-life as conventional cryopreservation is primarily designed for stock keeping. We present a study on bulk cryopreservation of the human iPSC lines UKKi011-A and BIONi010-C-41. By increasing cell concentration and volume, compared to conventional cryopreservation routines in cryo vials, one billion cells were frozen in 50 mL cryo bags. Upon thawing, the cells were immediately seeded in scalable suspension-based bioreactors for expansion to assess the stemness maintenance and for neural differentiation to assess their differentiation potential on the gene and protein levels. Both the conventional and bulk cryo approach show comparative results regarding viability and aggregation upon thawing and bioreactor inoculation. Reduced performance compared to the non-frozen control was compensated within 3 days regarding biomass yield. Stemness was maintained upon thawing in expansion. In neural differentiation, a delay of the neural marker expression on day 4 was compensated at day 9. We conclude that cryopreservation in cryo bags, using high cell concentrations and volumes, does not alter the cells' fate and is a suitable technology to avoid pre-cultivation and enable time- and cost-efficient therapeutic approaches with bulk cell numbers.

Can Cryopreservation in Assisted Reproductive Technology (ART) Induce Epigenetic Changes to Gametes and Embryos?

Since the birth of Louise Brown in 1978, more than nine million children have been conceived using assisted reproductive technologies (ARTs). While the great majority of children are healthy, there are concerns about the potential epigenetic consequences of gametes and embryo manipulation. In fact, during the preimplantation period, major waves of epigenetic reprogramming occur. Epigenetic reprogramming is susceptible to environmental changes induced by ovarian stimulation, in-vitro fertilization, and embryo culture, as well as cryopreservation procedures. This review summarizes the evidence relating to oocytes and embryo cryopreservation and potential epigenetic regulation. Overall, it appears that the stress induced by vitrification, including osmotic shock, temperature and pH changes, and toxicity of cryoprotectants, might induce epigenetic and transcriptomic changes in oocytes and embryos. It is currently unclear if these changes will have potential consequences for the health of future offspring.

Critical points for optimizing long-term culture and neural differentiation capacity of rodent and human neural stem cells to facilitate translation into clinical settings

Despite several decades of research on the nature and functional properties of neural stem cells, which brought great advances in regenerative medicine, there is still a plethora of ambiguous protocols and interpretations linked to their applications. Here, we present a whole spectrum of protocol elements that should be standardized in order to obtain viable cell cultures and facilitate their translation into clinical settings. Additionally, this review also presents outstanding limitations and possible problems to be encountered when dealing with protocol optimization. Most importantly, we also outline the critical points that should be considered before starting any experiments utilizing neural stem cells or interpreting their results.

Risk of genetic and epigenetic alteration in children conceived following ART: Is it time to return to nature whenever possible?

Assisted reproductive technology may influence epigenetic signature as the procedures coincide with the extensive epigenetic modification occurring from fertilization to embryo implantation. However, it is still unclear to what extent ART alters the embryo epigenome. In vivo fertilization occurs in the fallopian tube, where a specific and natural environment enables the embryo's healthy development. During this dynamic period, major waves of epigenetic reprogramming, crucial for the normal fate of the embryo, take place. Over the past decade, concerns relating to the raised incidence of epigenetic anomalies and imprinting following ART have been raised by several authors. Epigenetic reprogramming is particularly susceptible to environmental conditions during the periconceptional period; therefore, unphysiological conditions, including ovarian stimulation, in vitro fertilization, embryo culture, cryopreservation of gametes and embryos, parental lifestyle, and underlying infertility, have the potential to contribute to epigenetic dysregulation independently or collectively. This review critically appraises the evidence relating to the association between ART and genetic and epigenetic modifications that may be transmitted to the offspring.

Exposing intracellular molecular changes during the differentiation of human-induced pluripotent stem cells into erythropoietin-producing cells using Raman spectroscopy and imaging

The objective of this study was to explore intracellular molecular changes during the differentiation of human-induced pluripotent stem cells (iPSCs) into erythropoietin (EPO)-producing cells using Raman spectroscopy and imaging. Raman imaging data of fixed cells at four stages of cell differentiation were analyzed by a partial least squares (PLS) regression model, and the variations in the intracellular molecular compositions with cell differentiation were investigated. As a result, three biomarkers characterizing the cell phases were identified: dimethyl sulfoxide (DMSO), fatty acids with a low grade of unsaturation, and glycoproteins. The uptake of DMSO by EPO-producing cells, which was added into a culture medium as an inducer for cell differentiation, was detected, and the increase in unsaturated fatty acid concentrations was revealed that lipid metabolism changed over the course of cell differentiation. The decrease in the glycoprotein concentration after the cell phase during which iPSCs differentiated into EPO-producing cells was also made clear. Raman imaging successfully visualized chemical images of these three biomarkers in two dimensions, where the biomarker concentrations independently varied during cell differentiation. These results demonstrated the application potential of the proposed method to regenerative medicine for monitoring cell differentiation and discriminating cell maturation in situ at the molecular level.

Dimethyl sulfoxide-free cryopreservation solution containing trehalose, dextran 40, and propylene glycol for therapy with human adipose tissue-derived mesenchymal stromal cells

We evaluated a dimethyl sulfoxide (Me2SO)-free cryopreservation solution to freeze human adipose-derived mesenchymal stromal cells (hADSCs). In the first experiment, we compared the combined effects of 3% trehalose (3 T) and 5% dextran (5D) in lactated Ringer’s solution (LR) as a cryopreservation base solution containing 10% propylene glycol (PG). The cell viability of hADSCs immediately after thawing was significantly higher (p < 0.05) in LR supplemented with 3 T (LR-3 T) and with 3 T and 5D (LR-3 T-5D) than in LR. In the second experiment, we compared the cell characteristics of hADSCs freeze-thawed in LR-3 T-5D containing either 10% Me2SO or 10% PG. The cell viability, annexin V-positive ratio, colony-forming capacity, cell proliferation, cell surface antigen positivity, adipogenic differentiation, osteogenic differentiation, and genetic response to cytokine stimulation of hADSCs immediately after thawing were similar between the LR-3 T-5D containing 10% Me2SO and 10% PG. In the third experiment, we examined various concentrations of PG on the cell proliferative capacity of freeze-thawed hADSCs. The cell proliferative capacity of hADSCs frozen with LR-3 T-5D containing 2.5% to 5% PG was significantly higher (p < 0.05) than LR-3 T-5D containing 10% PG. Furthermore, the cell proliferative capacity of hADSCs frozen with LR-3 T-5D containing 4% PG was similar to that of fresh hADSCs. These results indicate that the combination of 3 T-5D in an LR solution as a basic solution is effective for post-thaw cell viability, and that the optimal concentration of PG to maintain the cell characteristics of hADSCs frozen with LR-3 T-5D is 2.5% to 5%, which is promising for cell therapy applications.

Poly(l-alanine-co-l-lysine)-g-Trehalose as a Biomimetic Cryoprotectant for Stem Cells

Poly(l-alanine-co-l-lysine)-graft-trehalose (PAK_T) was synthesized as a natural antifreezing glycopolypeptide (AFGP)-mimicking cryoprotectant for cryopreservation of mesenchymal stem cells (MSCs). FTIR and circular dichroism spectra indicated that the content of the α-helical structure of PAK decreased after conjugation with trehalose. Two protocols were investigated in cryopreservation of MSCs to prove the significance of the intracellularly delivered PAK_T. In protocol I, MSCs were cryopreserved at -196 °C for 7 days by a slow-cooling procedure in the presence of both PAK_T and free trehalose. In protocol II, MSCs were preincubated at 37 °C in a PAK_T solution, followed by cryopreservation at -196 °C in the presence of free trehalose for 7 days by the slow-cooling procedure. Polymer and trehalose concentrations were varied by 0.0-1.0 and 0.0-15.0 wt %, respectively. Cell recovery was significantly improved by protocol II with preincubation of the cells in the PAK_T solution. The recovered cells from protocol II exhibited excellent proliferation and maintained multilineage potentials into osteogenic, chondrogenic, and adipogenic differentiation, similar to MSCs recovered from cryopreservation in the traditional 10% dimethyl sulfoxide system. Ice recrystallization inhibition (IRI) activity of the polymers/trehalose contributed to cell recovery; however, intracellularly delivered PEG-PAK_T was the major contributor to the enhanced cell recovery in protocol II. Inhibitor studies suggested that macropinocytosis and caveolin-dependent endocytosis are the main mechanisms for the intracellular delivery of PEG-PAK_T. ¹H NMR and FTIR spectra suggested that the intracellular PEG-PAK_Ts interact with water and stabilize the cells during cryopreservation.

Fructan Improves Survival and Function of Cryopreserved Rat Islets

Cryopreservation of pancreatic islets enables their long-term storage and subsequent transplantation; however, post-cryopreservation, islets viability, and functions are reduced to a significant extent. Islet is composed of five cells (α cell, β cell, δ cell, ε cell, and PP cell), and blood vessels that carry the nutrition. Freezing technology of the organization has not developed a good method. This paper is studied using a fructan which has been found to effectively freeze protect a material of the cell. Islet transplantation has been established as an effective means of treating patients with type 1 diabetes. In this study, we demonstrated the effectiveness of using a fructan on the cryopreserved islets by showing valid results for diabetes. Isolated rat islets were cryopreserved using phosphate-buffered saline (PBS) supplemented with different concentrations of fructan and/or dimethyl sulfoxide (DMSO) in FBS. The survival rates of the islets were estimated at different time intervals, and insulin secretion function was tested in vitro. Furthermore, the in vivo function was tested by syngeneic transplantation into streptozotocin-induced diabetic rats, and the grafts were analyzed histologically and immunohistochemically. Fructan significantly increased islet survival; 30% fructan led to survival rates of more than 90% on day 3, which was significantly higher than those of the DMSO groups (p < 0.05). For both fructan and DMSO, the survival showed dose dependence, with the highest rates observed for 30% fructan and 10% DMSO, respectively (p < 0.05). The fructan groups showed a significantly increased insulin secretion volume in comparison to the DMSO groups (p < 0.05). Furthermore, cell clusters of pancreatic islets were well maintained in the fructan group, whereas margin collapse and vacuolation were observed in the DMSO group. Three days after transplantation of pancreatic islets preserved with 30% fructan, the blood glucose levels of diabetic rats were restored to the normal range, and removal of transplanted pancreatic islets from the kidney led to a profound increase in blood glucose levels. Together, these results show that a fructan is effective at cryopreserving rat pancreatic islets for subsequent transplantation.

Size and Shape Control of Ice Crystals by Amphiphilic Block Copolymers and Their Implication in the Cryoprotection of Mesenchymal Stem Cells

Precise control over the size and shape of ice crystals is a key factor to consider in designing antifreezing and cryoprotecting molecules for cryopreservation of cells. Here, we report that a poly(ethylene glycol)-poly(l-alanine) (PEG-PA) block copolymer exhibits excellent cryoprotecting properties for stem cells and antifreezing properties for water. As the molecular weight of PA increased from 500, 760, and 1750 Da (P1, P2, and P3) at the same PEG molecular weight of 5000 Da, the β-sheet content decreased and α-helix content increased. Comparing P2 (PEG-PA; 5000-760) and P4 (PEG-PA: 1000-750), β-sheets increased as the PEG block length decreased. The critical micelle concentration of the PEG-PA block copolymers was in a range of 0.5-3.0 mg/mL and was proportional to the hydrophobicity of the PEG-PA block copolymers. The P1, P2, and P3 self-assembled into spherical micelles, whereas P4 formed micelles with cylindrical morphology. The difference in the block copolymer structure affected ice recrystallization inhibition (IRI) activity and cryopreservation of cells. IRI activity was assayed via mean largest grain size (MLGS), and interactions between polymers and ice crystal surfaces were studied by dynamic ice-shaping studies. The MLGS decreased to 58 → 53 → 45 → 35 → 23% of that of PBS, as the polymer (PEG-PA 5000-500) concentration increased from 0.0 (PBS; control) → 1.0 → 5.0 → 10 → 30 → 50 mg/mL. The MLGS of PEG 5k solutions (negative control) decreased to 74 → 71 → 64 → 44 → 37% of that of PBS in the same concentration range. P3 and P4 with a longer hydrophobic PA block developed elongated ice crystals at above 30 mg/mL. The dynamic ice-shaping study exhibited that ice crystals became needle-shaped, as the hydrophobicity of the polymer increased as in P2-P4. The cell recovery in the P1 system after cryopreservation at -196 °C for 7 days was 87% of that of the dimethyl sulfoxide (DMSO) 10% system (positive control). The cell recovery was 48% for the P2 system and drastically decreased to less than 30% of that of the DMSO 10% system in the P3, P4, PEG 5k, PEG 1k, PVA 80H, and PVA 100H systems. Current studies suggest that IRI activity, round ice crystal shaping, and membrane stabilization activity of P1 cooperatively provide excellent cell recovery among the candidate systems. Recovered stem cells exhibited excellent proliferation and multilineage differentiation into osteocytes, chondrocytes, and adipocytes. To conclude, the PEG-PA (5000-500) block copolymer is suggested to be a promising antifreezing cryoprotectant for stem cells.

DMSO (Me2SO) concentrations of 1-2% in combination with pentaisomaltose are effective for cryopreservation of T cells

T cell based treatments in the setting of allogenic haematopoietic stem cell transplantation (HSCT) have been used for decades. In addition, the use of chimeric antigen receptor (CAR) T cells has been introduced as a promising cancer immunotherapy. A prerequisite for many of these treatments is the ability to cryopreserve the cells safely and efficiently. In the present study, we compared freezing media combinations containing pentaisomaltose and 1-2 % DMSO (PIM1 and PIM2, respectively) to 10 % DMSO and commercially available cryosolutions (CS2 and CS10, Cryostor® containing 2 and 10 % DMSO, respectively) for cryopreservation of T cells. T cells isolated from buffy coats from healthy donors were cryopreserved with different freezing media and analysed for 1) viability immediately post-thaw and the following 24 h, 2) recovery, 3) proliferative potential and 4) migration towards a gradient of SDF-1α. The results showed that PIM2 was superior to 10 % DMSO and comparable to CS10 when assessing viability. Furthermore, the results indicated that the T cells cryopreserved with 10 % DMSO showed the lowest proliferative potential. The expression levels of CXCR3, CXCR4 and VLA-4 were similar in T cells independent of the freezing media used; however, T cells cryopreserved with PIM2 demonstrated the highest migratory potential. In summary, the combination of pentaisomaltose and 1-2 % DMSO improves the cryoprotective properties compared to 10 % DMSO while achieving comparable results with CS10 and even showing improved migration towards SDF-1α. Thus, our results show promising potential for pentaisomaltose in combination with low amounts of DMSO for the cryopreservation of T cells.

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.

Molecular Design of Polyampholytes for Vitrification-Induced Preservation of Three-Dimensional Cell Constructs without Using Liquid Nitrogen

Current slow-freezing methods are too inefficient for cryopreservation of three-dimensional (3D) tissue constructs. Additionally, conventional vitrification methods use liquid nitrogen, which is inconvenient and increases the chance of cross-contamination. Herein, we have developed polyampholytes with various degrees of hydrophobicity and showed that they could successfully vitrify cell constructs including spheroids and cell monolayers without using liquid nitrogen. The polyampholytes prevented ice crystallization during both cooling and warming, demonstrating their potential to prevent freezing-induced damage. Monolayers and spheroids vitrified in the presence of polyampholytes yielded high viabilities post-thawing with monolayers vitrified with PLL-DMGA exhibiting more than 90% viability. Moreover, spheroids vitrified in the presence of polyampholytes retained their fusibilities, thus revealing the propensity of these polyampholytes to stabilize 3D cell constructs. This study is expected to open new avenues for the development of off-the-shelf tissue engineering constructs that can be prepared and preserved until needed.

Me2SO- and serum-free cryopreservation of human umbilical cord mesenchymal stem cells using electroporation-assisted delivery of sugars

Cryopreservation is the universal technology used to enable long-term storage and continuous availability of cell stocks and tissues for regenerative medicine demands. The main components of standard freezing media are dimethyl sulfoxide (hereinafter Me₂SO) and fetal bovine serum (FBS). However, for manufacturing of cells and tissue-engineered products in accordance with the principles of Good Manufacturing Practice (GMP), current considerations in regenerative medicine suggest development of Me₂SO- and serum-free biopreservation strategies due to safety concerns over Me₂SO-induced side effects and immunogenicity of animal serum. In this work, the effect of electroporation-assisted pre-freeze delivery of sucrose, trehalose and raffinose into human umbilical cord mesenchymal stem cells (hUCMSCs) on their post-thaw survival was investigated. The optimal strength of electric field at 8 pulses with 100 μs duration and 1 Hz pulse repetition frequency was determined to be 1.5 kV/cm from permeabilization (propidium iodide uptake) vs. cell recovery data (resazurin reduction assay). Using sugars as sole cryoprotectants with electroporation, concentration-dependent increase in cell survival was observed. Irrespective of sugar type, the highest cell survival (up to 80%) was achieved at 400 mM extracellular concentration and electroporation. Cell freezing without electroporation yielded significantly lower survival rates. In the optimal scenario, cells were able to attach 24 h after thawing demonstrating characteristic shape and sugar-loaded vacuoles. Application of 10% Me₂SO/90% FBS as a positive control provided cell survival exceeding 90%. Next, high glass transition temperatures determined for optimal concentrations of sugars by differential scanning calorimetry (DSC) suggest the possibility to store samples at -80 °C. In summary, using electroporation to incorporate cryoprotective sugars into cells is an effective strategy towards Me₂SO- and serum-free cryopreservation and may pave the way for further progress in establishing clinically safe biopreservation strategies for efficient long-term biobanking of cells.

The roles of reactive oxygen species and antioxidants in cryopreservation

Cryopreservation has facilitated advancement of biological research by allowing the storage of cells over prolonged periods of time. While cryopreservation at extremely low temperatures would render cells metabolically inactive, cells suffer insults during the freezing and thawing process. Among such insults, the generation of supra-physiological levels of reactive oxygen species (ROS) could impair cellular functions and survival. Antioxidants are potential additives that were reported to partially or completely reverse freeze-thaw stress-associated impairments. This review aims to discuss the potential sources of cryopreservation-induced ROS and the effectiveness of antioxidant administration when used individually or in combination.

Survivability of rabbit amniotic fluid-derived mesenchymal stem cells post slow-freezing or vitrification

This work aimed to evaluate the effect of two distinct cryopreservation procedures - conventional slow-freezing and vitrification, on survivability and mesenchymal marker expression stability of rabbit amniotic fluid-derived mesenchymal stem cells (rAF-MSCs). Cells at passage 2 were slowly frozen, using 10% of dimethylsulfoxide, or vitrified, using 40% of ethylene glycol, 0.5 M sucrose and 18% Ficoll 70. After three months storage in liquid nitrogen, viability, chromosomal stability, ultrastructure, surface and intracellular marker expression and differentiation potential of cells were evaluated immediately post-thawing/warming and after additional culture for 48-72 h. Our results showed decreased (P ≤ 0.05) viability of cells post-thawing/warming. However, after additional culture, the viability was similar to those in fresh counterparts in both cryopreserved groups. Increase (P ≤ 0.05) in the population doubling time of vitrified cells was observed, while doubling time of slow-frozen cells remained similar to non-cryopreserved cells. No changes in karyotype (chromosomal numbers) were observed in frozen/vitrified AF-MSCs, and histological staining confirmed similar differentiation potential of fresh and frozen/vitrified cells. Analysis of mesenchymal marker expression by qPCR showed that both cryopreservation approaches significantly affected expression of CD73 and CD90 surface markers. These changes were not detected using flow cytometry. In summary, the conventional slow-freezing and vitrification are reliable and effective approaches for the cryopreservation of rabbit AF-MSCs. Nevertheless, our study confirmed affected expression of some mesenchymal markers following cryopreservation.

Pentaisomaltose, an Alternative to DMSO. Engraftment of Cryopreserved Human CD34+ Cells in Immunodeficient NSG Mice

Hematopoietic stem cell transplantation often involves the cryopreservation of stem cell products. Currently, the standard cryoprotective agent (CPA) is dimethyl sulfoxide (DMSO), which is known to cause concentration-related toxicity and side effects when administered to patients. Based on promising in vitro data from our previous study using pentaisomaltose (a 1 kDa subfraction of Dextran 1) as an alternative to DMSO for cryopreservation of hematopoietic progenitor cells (HPCs) from apheresis products, we proceeded to a preclinical model and compared the two CPAs with respect to engraftment of human hematopoietic stem and progenitor cells (HSPCs) in the immunodeficient NSG mouse model. Human HPCs from apheresis products were cryopreserved with either pentaisomaltose or DMSO, and the following outcomes were measured: (1) the post-thaw recovery of cryopreserved cells and clonogenic potential of CD34⁺ cells and (2) hematopoietic engraftment in NSG mice. We found that recovery and colony-forming cells data were comparable between pentaisomaltose and DMSO. The engraftment data revealed comparable human CD45⁺ levels in peripheral blood at 8 weeks and bone marrow at 16 weeks post transplantation. Additionally, the frequencies of CD34⁺CD38^low/negative and myeloid/lymphoid cells in the bone marrow were comparable. We here demonstrated that long-term engrafting HSPCs were well preserved in pentaisomaltose and comparable to cells cryopreserved with DMSO. Although a clinical trial is necessary to translate these results into human use, the present data represent an important step toward the replacement of DMSO with a non-toxic alternative.

Trehalose to cryopreserve human pluripotent stem cells

The successful exploitation of human pluripotent stem cells (hPSCs) for research, translational or commercial reasons requires the implementation of a simple and efficient cryopreservation method. Cryopreservation is usually performed with dimethylsulphoxide (DMSO), in addition to animal proteins. However, even at sub-toxic levels, DMSO diminishes the pluripotency capacity of hPSCs and affects their epigenetic system by acting on the three DNA methyltransferases (Dnmts) and histone modification enzymes. Our study aimed to test trehalose-based cryosolutions containing ethylene glycol (EG) or glycerol (GLY) on hESCs RC17, hiPSCs CTR2#6 and long-term neuroepithelial-like stem cells (lt-NES) AF22. Here, we demostrate the effectiveness of these cryosolutions in hPSCs by showing an acceptable rate of cell viability and high stability compared to standard 10% DMSO freezing medium (CS10). All cell lines retained their morphology, self renewal potential and pluripotency, and none of the cryosolutions affected their differentiation potential. Genotoxicity varied among different stem cells types, while trehalose-based cryopreservation did not sensibly alter the homeostasis of endoplasmic reticulum (ER). This study provides evidence that pluripotent and neural stem cells stored in trehalose alone or with other cryoprotectants (CPAs) maintain their functional properties, indicating their potential use in cell therapies if produced in good manufacturing practice (GMP) facility.

Directional freezing for the cryopreservation of adherent mammalian cells on a substrate

Successfully cryopreserving cells adhered to a substrate would facilitate the growth of a vital confluent cell culture after thawing while dramatically shortening the post-thaw culturing time. Herein we propose a controlled slow cooling method combining initial directional freezing followed by gradual cooling down to -80°C for robust preservation of cell monolayers adherent to a substrate. Using computer controlled cryostages we examined the effect of cooling rates and dimethylsulfoxide (DMSO) concentration on cell survival and established an optimal cryopreservation protocol. Experimental results show the highest post-thawing viability for directional ice growth at a speed of 30 μm/sec (equivalent to freezing rate of 3.8°C/min), followed by gradual cooling of the sample with decreasing rate of 0.5°C/min. Efficient cryopreservation of three widely used epithelial cell lines: IEC-18, HeLa, and Caco-2, provides proof-of-concept support for this new freezing protocol applied to adherent cells. This method is highly reproducible, significantly increases the post-thaw cell viability and can be readily applied for cryopreservation of cellular cultures in microfluidic devices.

Evaluation of changes arising in the pig mesenchymal stromal cells transcriptome following cryopreservation and Trichostatin A treatment

Cryopreservation is an important procedure in maintenance and clinical applications of mesenchymal stem/stromal cells (MSCs). Although the methods of cell freezing using various cryoprotectants are well developed and allow preserving structurally intact living cells, the freezing process can be considered as a severe cellular stress associated with ice formation, osmotic damage, cryoprotectants migration/cytotoxicity or rapid cell shrinkage. The cellular response to freezing stress is aimed at the restoring of homeostasis and repair of cell damage and is crucial for cell viability. In this study we evaluated the changes arising in the pig mesenchymal stromal cell transcriptome following cryopreservation and showed the vast alterations in cell transcriptional activity (5,575 genes with altered expression) suggesting the engagement in post-thawing cell recovery of processes connected with cell membrane tension regulation, membrane damage repair, cell shape maintenance, mitochondria-connected energy homeostasis and apoptosis mediation. We also evaluated the effect of known gene expression stimulator—Trichostain A (TSA) on the frozen/thawed cells transcriptome and showed that TSA is able to counteract to a certain extent transcriptome alterations, however, its specificity and advantages for cell recovery after cryopreservation require further studies.

Exploring the Potential of Biocompatible Osmoprotectants as Highly Efficient Cryoprotectants

Cryoprotectants (CPAs) are critical to successful cryopreservation because they can protect cells from cryoinjuries. Because of the limitations of current CPAs, especially the toxicity, the search for new effective CPAs is attracting increasing attention. In this work, we reported that natural biocompatible osmoprotectants, which could protect cells from osmotic injury in various biological systems, might also be ideal candidates for CPAs. Three representative biocompatible osmoprotectants (proline, glycine, and taurine) were tested and compared. It was found that, aside from presenting a different ability to prevent osmotic injury, these biocompatible osmoprotectants also possessed a different ability to inhibit ice formation and thus mitigate intra-/extracellular ice injury. Because of the strongest ability to prevent the two types of injuries, we found that proline performed the best in cryopreserving five different types of cells. Moreover, the natural osmoprotectants are intrinsically biocompatible with the cells, superior to the current state-of-the-art CPA, dimethyl sulfoxide (DMSO), which is a toxic organic solvent. This work opens a new window of opportunity for DMSO-free cryopreservation, and sheds light on the applications of osmoprotectants in cryoprotection, which may revolutionize the current cryopreservation technologies.

Cryopreservation of Human Mesenchymal Stem Cells in an Allogeneic Bioscaffold based on Platelet Rich Plasma and Synovial Fluid

Transplantation of mesenchymal stem cells (MSCs) has emerged as an alternative strategy to treat knee osteoarthritis. In this context, MSCs derived from synovial fluid could provide higher chondrogenic and cartilage regeneration, presenting synovial fluid as an appropriate MSCs source. An allogeneic and biomimetic bioscaffold composed of Platelet Rich Plasma and synovial fluid that preserve and mimics the natural environment of MSCs isolated from knee has also been developed. We have optimized the cryopreservation of knee-isolated MSCs embedded within the aforementioned biomimetic scaffold, in order to create a reserve of young autologous embedded knee MSCs for future clinical applications. We have tested several cryoprotectant solutions combining dimethyl sulfoxide (DMSO), sucrose and human serum and quantifying the viability and functionality of the embedded MSCs after thawing. MSCs embedded in bioscaffolds cryopreserved with DMSO 10% or the combination of DMSO 10% and Sucrose 0,2 M displayed the best cell viabilities maintaining the multilineage differentiation potential of MSCs after thawing. In conclusion, embedded young MSCs within allogeneic biomimetic bioscaffold can be cryopreserved with the cryoprotectant solutions described in this work, allowing their future clinical use in patients with cartilage defects.

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

Safe and stable cryopreservation is critical for research involving human embryonic stem cells (hESCs). Dimethyl sulfoxide (DMSO) is a popular cryoprotective agent; however, its cytotoxicity cannot be ignored. Thus, there is a need for an alternate cryoprotectant. We reported previously that a novel cryopreservation reagent, StemCell Keep™ (SCK), was effective for cryopreserving human induced pluripotent stem cells (hiPSCs) by vitrification. Because hESCs and hiPSCs are not identical, the current study examined the use of SCK on hESCs. hESCs cryopreserved with SCK were thawed and cultured on SNL 76/7 cells, which were derived from a mouse fibroblast STO cell line transformed with neomycin resistance and murine LIF genes. After cryopreservation, cultured hESCs were assessed for their attachment ability and characterized by alkaline phosphatase (AP) and immunocytochemical (ICC) staining, fluorescence-activated cell sorting (FACS), reverse transcription polymerase chain reaction (RT-PCR), and karyotyping. The proliferation of SCK-cryopreserved hESCs cultured on SNL cells, or in feeder-free conditions, was higher than that of cells preserved in a solution of 2 M DMSO, 1 M acetamide, and 3 M propylene glycol (DAP). The cell number with SCK-cryopreserved hESCs was about twice that of hESCs cryopreserved in DAP. The pluripotency of SCK-cryopreserved hESCs was similar to that of DAP-cryopreserved hESCs based on AP staining. Data from ICC, FACS, and RT-PCR analyses showed that stem cell markers were continually expressed on SCK-cryopreserved hESCs. The teratoma assay showed that SCK-cryopreserved hESCs differentiated into three germ layers. Furthermore, SCK-cryopreserved hESCs had normal karyotypes. These data indicate that SCK was effective for cryopreservation of hESCs by vitrification.

Long-term culture-induced phenotypic difference and efficient cryopreservation of small intestinal organoids by treatment timing of Rho kinase inhibitor

AIM

To investigate a suitable long-term culture system and optimal cryopreservation of intestinal organoid to improve organoid-based therapy by acquiring large numbers of cells.

METHODS

Crypts were isolated from jejunum of C57BL/6 mouse. Two hundred crypts were cultured in organoid medium with either epidermal growth factor/Noggin/R-spondin1 (ENR) or ENR/CHIR99021/VPA (ENR-CV). For subculture, organoids cultured on day 7 were passaged using enzyme-free cell dissociation buffer (STEMCELL Technologies). The passage was performed once per week until indicated passage. For cryopreservation, undissociated and dissociated organoids were resuspended in freezing medium with or without Rho kinase inhibitor subjected to different treatment times. The characteristics of intestinal organoids upon extended passage and freeze-thaw were analyzed using EdU staining, methyl thiazolyl tetrazolium assay, qPCR and time-lapse live cell imaging.

RESULTS

We established a three-dimensional culture system for murine small intestinal organoids using ENR and ENR-CV media. Both conditions yielded organoids with a crypt-villus architecture exhibiting Lgr5⁺ cells and differentiated intestinal epithelial cells as shown by morphological and biochemical analysis. However, during extended passage (more than 3 mo), a comparative analysis revealed that continuous passaging under ENR-CV conditions, but not ENR conditions induced phenotypic changes as observed by morphological transition, reduced numbers of Lgr5⁺ cells and inconsistent expression of markers for differentiated intestinal epithelial cell types. We also found that recovery of long-term cryopreserved organoids was significantly affected by the organoid state, i.e., whether dissociation was applied, and the timing of treatment with the Rho-kinase inhibitor Y-27632. Furthermore, the retention of typical morphological characteristics of intestinal organoids such as the crypt-villus structure from freeze-thawed cells was observed by live cell imaging.

CONCLUSION

The maintenance of the characteristics of intestinal organoids upon extended passage is mediated by ENR condition, but not ENR-CV condition. Identified long-term cryopreservation may contribute to the establishment of standardized cryopreservation protocols for intestinal organoids for use in clinical applications.

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.

Natural zwitterionic betaine enables cells to survive ultrarapid cryopreservation

Cryoprotectants (CPAs) play a critical role in cryopreservation because they can resist the cell damage caused by the freezing process. Current state-of-the-art CPAs are mainly based on an organic solvent dimethyl sulfoxide (DMSO), and several DMSO-cryopreserved cell products have been brought to market. However, the intrinsic toxicity and complex freezing protocol of DMSO still remain as the bottleneck of the wide use for clinical applications. Herein, we reported that betaine, a natural zwitterionic molecule, could serve as a nontoxic and high efficient CPA. At optimum concentration of betaine, different cell types exhibited exceptional post-thaw survival efficiency with ultrarapid freezing protocol, which was straightforward, cost efficient but difficult to succeed using DMSO. Moreover, betaine showed negligible cytotoxicity even after long-term exposure of cells. Mechanistically, we hypothesized that betaine could be ultra-rapidly taken up by cells for intracellular protection during the freezing process. This technology unlocks the possibility of alternating the traditional toxic CPAs and is applicable to a variety of clinical applications.

Efficient long-term cryopreservation of pluripotent stem cells at -80 °C

Current long term cryopreservation of cell stocks routinely requires the use of liquid nitrogen (LN₂), because commonly used cryopreservation media containing cell membrane permeating cryoprotectants are thermally unstable when frozen at higher storage temperatures, e.g. -80 °C. This instability leads to ice recrystallization, causing progressive loss of cell viability over time under the storage conditions provided by most laboratory deep freezers. The dependency on LN₂ for cell storage significantly increases operational expense and raises issues related to impaired working efficiency and safety. Here we demonstrate that addition of Ficoll 70 to cryoprotectant solutions significantly improves system thermal stability at the working temperature (~-80 °C) of laboratory deep freezers. Moreover, a medium comprised of Ficoll 70 and dimethyl sulfoxide (DMSO) in presence or absence of fetal bovine serum (FBS) can provide reliable cryopreservation of various kinds of human and porcine pluripotent stem cells at -80 °C for periods that extend up to at least one year, with the post-thaw viability, plating efficiency, and full retention of pluripotent phenotype comparable to that achieved with LN₂ storage. These results illustrate the practicability of a promising long-term cryopreservation method that completely eliminates the need for LN₂.

The effect of Me2SO overexposure during cryopreservation on HOS TE85 and hMSC viability, growth and quality

With the cell therapy industry continuing to grow, the ability to preserve clinical grade cells, including mesenchymal stem cells (MSCs), whilst retaining cell viability and function remains critical for the generation of off-the-shelf therapies. Cryopreservation of MSCs, using slow freezing, is an established process at lab scale. However, the cytotoxicity of cryoprotectants, like Me₂SO, raises questions about the impact of prolonged cell exposure to cryoprotectant at temperatures >0 °C during processing of large cell batches for allogenic therapies prior to rapid cooling in a controlled rate freezer or in the clinic prior to administration. Here we show that exposure of human bone marrow derived MSCs to Me₂SO for ≥1 h before freezing, or after thawing, degrades membrane integrity, short-term cell attachment efficiency and alters cell immunophenotype. After 2 h's exposure to Me₂SO at 37 °C post-thaw, membrane integrity dropped to ∼70% and only ∼50% of cells retained the ability to adhere to tissue culture plastic. Furthermore, only 70% of the recovered MSCs retained an immunophenotype consistent with the ISCT minimal criteria after exposure. We also saw a similar loss of membrane integrity and attachment efficiency after exposing osteoblast (HOS TE85) cells to Me₂SO before, and after, cryopreservation. Overall, these results show that freezing medium exposure is a critical determinant of product quality as process scale increases. Defining and reporting cell sensitivity to freezing medium exposure, both before and after cryopreservation, enables a fair judgement of how scalable a particular cryopreservation process can be, and consequently whether the therapy has commercial feasibility.

Protein kinase A inhibitor, H89, significantly enhances survival rate of dissociated human embryonic stem cells following cryopreservation

OBJECTIVES

Human embryonic stem cells (hESCs) have huge potential for establishment of disease models and for treating degenerative diseases. However, the extremely low survival level of dissociated hESCs following cryopreservation is been a tremendous problem to allow for their rapid expansion, genetic manipulation and future medical applications. In this study, we have aimed to develop an efficient strategy to improve survival of dissociated hESCs after cryopreservation.

MATERIALS AND METHODS

Human embryonic stem cells (H9 line), dissociated into single cells, were cryopreserved using the slow-freezing method. Viable cells and their colony numbers in culture after cryopreservation were evaluated when treated with protein kinase A inhibitor H89. Western blotting was carried out to investigate mechanisms of low survival levels of dissociated hESCs following cryopreservation. Immunofluorescence, reverse transcription-polymerase chain reaction (RT-PCR), in vitro and in vivo differentiation were performed to testify to pluripotency and differentiation ability of hte cryopreserved cells treated with H89.

RESULTS

H89 significantly improved survival level of dissociated hESCs after cryopreservation through ROCK inhibition. H89-treated cells still maintained their pluripotency and differentiation capacity.

CONCLUSIONS

This new approach for cryopreservation of single hESCs, using H89, can promote potential use of hESCs in regenerative medicine in the future.

Effects of Cryopreservation on Canine Multipotent Stromal Cells from Subcutaneous and Infrapatellar Adipose Tissue

Adipose derived multipotent stromal cells (ASCs) isolated from brown versus white adipose tissues, may have distinct in vitro properties, including response to cryopreservation, due to differences in tissue physiology. This study was designed to determine the ultrastructure, immunophenotype, in vitro expansion capabilities and multipotentiality of paired canine ASCs harvested from subcutaneous (SUB) and infrapatellar (IFP) adipose tissue up to cell passage (P) 3 before and after cryopreservation. Adipocyte and ASC ultrastructure from the same tissue were distinct, and morphologies of both differed between tissue sources and with cryopreservation. Cell expansion and colony forming unit frequencies were similar between ASCs from both tissue sources before and after cryopreservation. Most fresh cells were CD29+, CD44+, CD90+ and CD34- up to P3. Cryopreserved P1 and P3 cells had lower percentages of CD29+ and 44+ cells, respectively, compared to fresh. Peroxisome proliferator-activated receptor γ (PPAR-γ) gene expression and sex determining region Y-box 2 (SOX2), CD29 and CD44 protein expression was lower in cryopreserved versus fresh P3 ASCs. Both PPAR-γ and osteopontin (OPN) protein expression increased in fresh and cryopreserved P3 ASCs cultured in adipogenic and osteogenic induction medium, respectively, while SOX2 decreased. Based on the study findings, in vitro expansion and multipotentiality are not distinct among canine SUB and IFP ASCs before or after cryopreservation. However, cryopreservation alters ASC ultrastructure, immunophenotype and transcription factor expression from both tissue sources. Future studies are necessary to determine the impact of cryopreservation on cell potential for therapy and de novo tissue generation.

Low-molecular-weight carbohydrate Pentaisomaltose may replace dimethyl sulfoxide as a safer cryoprotectant for cryopreservation of peripheral blood stem cells

BACKGROUND

Cryopreserved hematopoietic stem cell products are widely used for certain hematologic malignancies. Dimethyl sulfoxide (DMSO) is the most widely used cryoprotective agent (CPA) today, but due to indications of cellular toxicity, changes of the cellular epigenetic state, and patient-related side effects, there is an increasing demand for DMSO-free alternatives. We therefore investigated whether Pentaisomaltose (PIM), a low-molecular-weight carbohydrate (1 kDa), can be used for cryopreservation of peripheral blood stem cells, more specifically hematopoietic progenitor cell apheresis (HPC(A)) product.

STUDY DESIGN AND METHODS

We cryopreserved patient or donor HPC(A) products using 10% DMSO or 16% PIM and quantified the recovery of CD34+ cells and CD34+ subpopulations by multicolor flow cytometry. In addition, we compared the frequency of HPCs after DMSO and PIM cryopreservation using the colony-forming cells (CFCs) assay.

RESULTS

The mean CD34+ cell recovery was 56.3 ± 23.7% (11.4%-97.3%) and 58.2 ± 10.0% (45.7%-76.9%) for 10% DMSO and 16% PIM, respectively. The distribution of CD34+ cell subpopulations was similar when comparing DMSO or PIM as CPA. CFC assay showed mean colony numbers of 70.7 ± 25.4 (range, 37.8-115.5) and 67.7 ± 15.7 (range, 48-86) for 10% DMSO and 16% PIM, respectively.

CONCLUSION

Our findings demonstrate that PIM cryopreservation of HPC(A) products provides recovery of CD34+ cells, CD34+ subpopulations, and CFCs similar to that of DMSO cryopreservation and therefore may have the potential to be used for cryopreservation of peripheral blood stem cells.

Phenotypic and functional characterization of long-term cryopreserved human adipose-derived stem cells

Cryopreservation represents an effective technique to maintain the functional properties of human adipose-derived stem cells (ASCs) and allows pooling of cells via long-term storage for clinical applications, e.g., cell-based therapies. It is crucial to reduce freezing injury during the cryopreservation process by loading the ASCs with the optimum concentration of suitable cryoprotective agents (CPAs). In this study, human ASCs were preserved for 3 months in different combinations of CPAs, including 1) 0.25 M trehalose; 2) 5% dimethylsulfoxide (DMSO); 3) 10% DMSO; 4) 5% DMSO + 20% fetal bovine serum (FBS); 5) 10% DMSO + 20% FBS; 6) 10% DMSO + 90% FBS. Interestingly, even with a reduction of DMSO to 5% and without FBS, cryopreserved ASCs maintained high cell viability comparable with standard cryomedium (10% DMSO + 90% FBS), with normal cell phenotype and proliferation rate. Cryopreserved ASCs also maintained their differentiation capability (e.g., to adipocytes, osteocytes and chondrocytes) and showed an enhanced expression level of stemness markers (e.g., NANOG, OCT-4, SOX-2 and REX-1). Our findings suggest that 5% DMSO without FBS may be an ideal CPA for an efficient long-term cryopreservation of human ASCs. These results aid in establishing standardized xeno-free long-term cryopreservation of human ASCs for clinical applications.

Cryopreservation of embryonic stem cell-derived multicellular neural aggregates labeled with micron-sized particles of iron oxide for magnetic resonance imaging

Magnetic resonance imaging (MRI) provides an effective approach to track labeled pluripotent stem cell (PSC)-derived neural progenitor cells (NPCs) for neurological disorder treatments after cell labeling with a contrast agent, such as an iron oxide derivative. Cryopreservation of pre-labeled neural cells, especially in three-dimensional (3D) structure, can provide a uniform cell population and preserve the stem cell niche for the subsequent applications. In this study, the effects of cryopreservation on PSC-derived multicellular NPC aggregates labeled with micron-sized particles of iron oxide (MPIO) were investigated. These NPC aggregates were labeled prior to cryopreservation because labeling thawed cells can be limited by inefficient intracellular uptake, variations in labeling efficiency, and increased culture time before use, minimizing their translation to clinical settings. The results indicated that intracellular MPIO incorporation was retained after cryopreservation (70-80% labeling efficiency), and MPIO labeling had little adverse effects on cell recovery, proliferation, cytotoxicity and neural lineage commitment post-cryopreservation. MRI analysis showed comparable detectability for the MPIO-labeled cells before and after cryopreservation indicated by T2 and T2* relaxation rates. Cryopreserving MPIO-labeled 3D multicellular NPC aggregates can be applied in in vivo cell tracking studies and lead to more rapid translation from preservation to clinical implementation.

The microenvironment of embryoid bodies modulated the commitment to neural lineage postcryopreservation

Neural progenitor cells are usually derived from pluripotent stem cells (PSCs) through the formation of embryoid bodies (EBs), the three-dimensional (3D) aggregate-like structure mimicking embryonic development. Cryo-banking of EBs is a critical step for sample storage, process monitoring, and preservation of intermediate cell populations during the lengthy differentiation procedure of PSCs. However, the impact of microenvironment (including 3D cell organization and biochemical factors) of EBs on neural lineage commitment postcryopreservation has not been well understood. In this study, intact EBs (I-E) and dissociated EBs (D-E) were compared for the recovery and neural differentiation after cryopreservation. I-E group showed the enhanced viability and recovery upon thaw compared with D-E group due to the preservation of extracellular matrix, cell-cell contacts, and F-actin organization. Moreover, both I-E and D-E groups showed the increased neuronal differentiation and D-E group also showed the enhanced astrocyte differentiation after thaw, probably due to the modulation of cellular redox state indicated by the expression of reactive oxygen species. In addition, mesenchymal stem cell secretome, known to bear a broad spectrum of protective factors, enhanced EB recovery. Taken together, EB microenvironment plays a critical role in the recovery and neural differentiation postcryopreservation.

Detailed method description for noninvasive monitoring of differentiation status of human embryonic stem cells

The (non)differentiation status of human embryonic stem cells (hESCs) is usually analyzed by determination of key pluripotency defining markers (e.g., OCT4, Nanog, SOX2) by means of reverse transcription quantitative polymerase chain reaction (RT-qPCR), flow cytometry (FC), and immunostaining. Despite proven usefulness of these techniques, their destructive nature makes it impossible to follow up on the same hESC colonies for several days, leading to a loss of information. In 2003, an OCT4-eGFP knock-in hESC line to monitor OCT4 expression was developed and commercialized. However, to the best of our knowledge, the use of fluorescence microscopy (FM) for monitoring the OCT4-eGFP expression of these cells without sacrificing them has not been described to date. Here, we describe such a method in detail, emphasizing both its resolving power and its complementary nature to FC as well as the potential pitfalls in standardizing the output of the FM measurements. The potential of the method is demonstrated by comparison of hESCs cultured in several conditions, both feeder free (vitronectin, VN) and grown on feeder cells (mouse embryonic fibroblasts, MEFs).

Long-term and transgenerational effects of cryopreservation on rabbit embryos

The short-term effects of cryopreservation and embryo transfer are well documented (reduced embryo viability, changes in pattern expression), but little is known about their long-term effects. We examined the possibility that embryo vitrification and transfer in rabbit could have an impact on the long-term reproductive physiology of the offspring and whether these phenotypes could be transferred to the progeny. Vitrified rabbit embryos were warmed and transferred to recipient females (F0). The offspring of the F0 generation were the F1 generation (cryopreserved animals). Females from F1 generation offspring were bred to F1 males to generate an F2 generation. In addition, two counterpart groups of noncryopreserved animals were bred and housed simultaneously to F1 and F2 generations (CF1 and CF2, respectively). The reproductive traits studied in all studied groups were litter size (LS), number born alive at birth (BA), and postnatal survival at Day 28 (number of weaned/number born alive expressed as percentage). The reproductive traits were analyzed using Bayesian methodology. Features of the estimated marginal posterior distributions of the differences between F1 and their counterparts (F1 - CF1) and between F2 and their counterparts (F2 - CF2) in reproductive characters found that vitrification and transfer procedures cause a consistent increase in LS and BA between F1 and CF1 females (more than 1.4 kits in LS and more than 1.3 BA) and also between F2 and CF2 females (0.96 kits in LS and 0.94 BA). We concluded that embryo cryopreservation and transfer procedures have long-term effects on derived female reproduction (F1 females) and transgenerational effects on female F1 offspring (F2 females).

Amphipathic polymer-mediated uptake of trehalose for dimethyl sulfoxide-free human cell cryopreservation

For stem cell therapy to become a routine reality, one of the major challenges to overcome is their storage and transportation. Currently this is achieved by cryopreserving cells utilising the cryoprotectant dimethyl sulfoxide (Me₂SO). Me₂SO is toxic to cells, leads to loss of cell functionality, and can produce severe side effects in patients. Potentially, cells could be frozen using the cryoprotectant trehalose if it could be delivered into the cells at a sufficient concentration. The novel amphipathic membrane permeabilising agent PP-50 has previously been shown to enhance trehalose uptake by erythrocytes, resulting in increased cryosurvival. Here, this work was extended to the nucleated human cell line SAOS-2. Using the optimum PP-50 concentration and media osmolarity, cell viability post-thaw was 60 ± 2%. In addition, the number of metabolically active cells 24 h post-thaw, normalised to that before freezing, was found to be between 103 ± 4% and 91 ± 5%. This was found to be comparable to cells frozen using Me₂SO. Although reduced (by 22 ± 2%, p = 0.09), the doubling time was found not to be statistically different to the non-frozen control. This was in contrast to cells frozen using Me₂SO, where the doubling time was significantly reduced (by 41 ± 4%, p = 0.004). PP-50 mediated trehalose delivery into cells could represent an alternative cryopreservation protocol, suitable for research and therapeutic applications.