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

Exploring the Cryopreservation Mechanism and Direct Removal Strategy of TAPS in Red Blood Cell Cryopreservation

Cryopreservation of red blood cells (RBCs) plays an indispensable role in modern clinical transfusion therapy. Researchers are dedicated to finding cryoprotectants (CPAs) with high efficiency and low toxicity to prevent RBCs from cryopreservation injury. This study presents, for the first time, the feasibility and underlying mechanisms of a novel CPA called tris(hydroxymethyl)aminomethane-3-propanesulfonic acid (TAPS) in RBCs cryopreservation. The results demonstrated that the addition of TAPS achieved a post-thaw recovery of RBCs at 79.12 ± 0.67%, accompanied by excellent biocompatibility (above 97%). Subsequently, the mechanism for preventing RBCs from cryopreservation injury was elucidated. On one hand, TAPS exhibits a significant amount of bound water and effectively inhibits ice recrystallization, thereby reducing mechanical damage. On the other hand, TAPS demonstrates high capacity to scavenge reactive oxygen species and strong endogenous antioxidant enzyme activity, providing effective protection against oxidative damage. Above all, TAPS can be readily removed through direct washing, and the RBCs after washing showed no significant differences in various physiological parameters (SEM, RBC hemolysis, ESR, ATPase activity, and Hb content) compared to fresh RBCs. Finally, the presented mathematical modeling analysis indicates the good benefits of TAPS. In summary, TAPS holds potential for both research and practical in the field of cryobiology, offering innovative insights for the improvement of RBCs cryopreservation in transfusion medicine.

Cryopreserved leukapheresis material can be transferred from controlled rate freezers to ultracold storage at warmer temperatures without affecting downstream CAR-T cell culture performance and in-vitro functionality

Chimeric antigen receptor (CAR) T-cell therapies are increasingly adopted as a commercially available treatment for hematologic and solid tumor cancers. As CAR-T therapies reach more patients globally, the cryopreservation and banking of patients' leukapheresis materials is becoming imperative to accommodate intra/inter-national shipping logistical delays and provide greater manufacturing flexibility. This study aims to determine the optimal temperature range for transferring cryopreserved leukapheresis materials from two distinct types of controlled rate freezing systems, Liquid Nitrogen (LN2)-based and LN2-free Conduction Cooling-based, to the ultracold LN2 storage freezer (≤-135 °C), and its impact on CAR T-cell production and functionality. Presented findings demonstrate that there is no significant influence on CAR T-cell expansion, differentiation, or downstream in-vitro function when employing a transfer temperature range spanning from -30 °C to -80 °C for the LN2-based controlled rate freezers as well as for conduction cooling controlled rate freezers. Notably, CAR T-cells generated from cryopreserved leukapheresis materials using the conduction cooling controlled rate freezer exhibited suboptimal performance in certain donors at transfer temperatures lower than -60 °C, possibly due to the reduced cooling rate of lower than 1 °C/min and extended dwelling time needed to reach the final temperatures within these systems. This cohort of data suggests that there is a low risk to transfer cryopreserved leukapheresis materials at higher temperatures (between -30 °C and -60 °C) with good functional recovery using either controlled cooling system, and the cryopreserved materials are suitable to use as the starting material for autologous CAR T-cell therapies.

Preserving frozen stallion sperm on dry ice using polymers that modulate ice crystalization kinetics

Cryopreserved semen is routinely shipped in liquid nitrogen. Dry ice could serve as an alternative coolant, however, frozen storage above liquid nitrogen temperatures (LN2, -196 °C) may negatively affect shelf-life and cryosurvival. In this study, we determined critical temperatures for storage of cryopreserved stallion sperm. We evaluated: (i) effects of cooling samples to different subzero temperatures (-10 °C to -80 °C) prior to storing in LN2, (ii) stability at different storage temperatures (i.e., in LN2, dry ice, -80 °C and -20 °C freezers, 5 °C refrigerator), and (iii) sperm cryosurvival during storage on dry ice (i.e., when kept below -70 °C and during warming). Furthermore, (iv) we analyzed if addition of synthetic polymers (PVP-40, Ficoll-70) modulates ice crystallization kinetics and improves stability of cryopreserved specimens. Sperm motility and membrane intactness were taken as measures of cryosurvival, and an artificial insemination trial was performed to confirm fertilizing capacity. We found that adding PVP-40 or Ficoll-70 to formulations containing glycerol reduced ice crystal sizes and growth during annealing. Post-thaw sperm viability data indicated that samples need to be cooled below -40 °C before they can be safely plunged and stored in LN2. No negative effects of relocating specimens from dry ice to LN2 and vice versa became apparent. However, sample warming above -50 °C during transport in dry ice should be avoided to ensure preservation of viability and fertility. Moreover, addition of PVP-40 or Ficoll-70 was found to increase sperm cryosurvival, especially under non-ideal storage conditions where ice recrystallization may occur.

Bovine Pluripotent Stem Cells: Current Status and Prospects

Pluripotent stem cells (PSCs) can differentiate into three germ layers and diverse autologous cell lines. Since cattle are the most commonly used large domesticated animals, an important food source, and bioreactors, great efforts have been made to establish bovine PSCs (bPSCs). bPSCs have great potential in bovine breeding and reproduction, modeling in vitro differentiation, imitating cancer development, and modeling diseases. Currently, bPSCs mainly include bovine embryonic stem cells (bESCs), bovine induced pluripotent stem cells (biPSCs), and bovine expanded potential stem cells (bEPSCs). Establishing stable bPSCs in vitro is a critical scientific challenge, and researchers have made numerous efforts to this end. In this review, the category of PSC pluripotency; the establishment of bESCs, biPSCs, and bEPSCs and its challenges; and the application outlook of bPSCs are discussed, aiming to provide references for future research.

Developing an Allogeneic Hematopoietic Progenitor Cell Transplant Service in a Resource-Limited Country: Challenges and Outcomes

Introduction Allogeneic stem cell transplant has curative potential for many hematological disorders. Building an allogeneic hematopoietic progenitor cell transplant (HPCT) unit requires huge investment, infrastructure, equipment, medical supplies, and training of health care professionals. The key objective of this study is to share our experience of developing an allogeneic HPCT service at our tertiary care cancer hospital in a low-middle-income country. In addition, this study presents the outcomes of the first 30 allogeneic HPCTs done at our center. Methods This retrospective observational study included adult patients 18 years old or older with hematological malignancies who underwent allogeneic HPCT between July 2019 and April 2023 at Shaukat Khanum Memorial Cancer Hospital and Research Centre. Result Of the 30 patients, 24 underwent matched sibling donor (MSD) transplants in which a myeloablative-conditioning regimen (MAC) was used in 19, and a reduced conditioning regimen (RIC) was used in one. Of the six haploidentical-related donor transplants, four received MAC, and two received RIC. The median recipient age at HPCT was 23 and 21 years for MSD and Haplo-related donor transplants, respectively. The median follow-up duration was 12 months (Range: 10 days - 33 months). The overall survival rate at one year was 71.3% among all allogeneic stem cell transplant patients, whereas the disease-free survival rate at one year was 63.7%. In the acute lymphoblastic leukemia group, the disease-free survival rate at one year post allograft was 51.5%, while in the acute myeloid leukemia group, it was 78.7%. Conclusion This study demonstrates the successful development of an allogeneic bone marrow transplant unit at our hospital despite significant financial constraints. This has allowed us to provide a potentially curative and life-saving treatment to a substantial number of cancer patients. The bone marrow transplant outcomes of this study are comparable to those reported by international bone marrow transplant registries.

Microwave Sensor for the Determination of DMSO Concentration in Water-DMSO Binary Mixture

This research aims to develop a microwave sensor to accurately measure the concentration of dimethyl sulfoxide (DMSO) in water-DMSO binary mixtures. The proposed sensor will utilize microwave frequency measurements to determine the DMSO concentration, providing a non-invasive and efficient method for analyzing DMSO solutions. The research will involve the design, fabrication, and testing of the sensor, as well as the development of an appropriate calibration model. The outcomes of this study will contribute to improved monitoring and quality control in various fields, including pharmaceuticals, chemical synthesis, and biomedical research. The binary mixtures of dimethyl sulfoxide (DMSO) and water with varying concentrations were investigated in the frequency range of 1 GHz to 5 GHz at room temperature using a microwave sensor. The proposed microwave sensor design was based on an interdigital capacitor (IDC) microstrip antenna loaded with a hexagonal complementary ring resonator (HCRR). The performance of the sensor, fabricated using the print circuit board (PCB) technique, was validated through simulations and experiments. The reflection coefficient (S₁₁) and resonance frequency (F_r) of binary mixtures of DMSO and water solutions were recorded and analyzed for DMSO concentrations ranging from 0% v/v to 75% v/v. Mathematical models were developed to analyze the data, and laboratory tests showed that the sensor can detect levels of DMSO/water binary mixtures. The sensor is capable of detecting DMSO concentrations ranging from 0% v/v to 75% v/v, with a maximum sensitivity of 0.138 dB/% for S₁₁ and ΔS₁₁ and 0.2 MHz/% for F_r and ΔF_r at a concentration of 50% v/v. The developed microwave sensor can serve as an alternative for detecting DMSO concentrations in water using a simple and cost-effective technique. This method can effectively analyze a wide range of concentrations, including highly concentrated solutions, quickly and easily.

Comparison between carbohydrate and salt-based macromolecular crowders for cell preservation at higher temperatures

In this investigation, the macromolecular crowding effect of a carbohydrate-based polymer, pullulan, and a salt-based polymer, poly-(4-styrenesulfonic-acid) sodium salt (PSS) was compared for the storage of A549 lung carcinoma cells, at temperatures greater than that of liquid nitrogen storage tanks. A DoE-CCD response surface model was used to optimise medium compositions comprising DMSO and a macromolecular crowder (MMC; pullulan, PSS and their combinations). The effect of adding MMCs was evaluated in terms of post-preservation viability, apoptotic population and growth curve analysis. The optimised medium consisting of 10% DMSO and 3% pullulan in the basal medium (BM) could facilitate long-term cell preservation for 90 days at - 80 °C, resulting in cell viability of ∼83%. The results also showed a significant decrease in the apoptotic population at all time points for the optimised composition of the freezing medium. These results indicated that adding 3% pullulan to the freezing medium improved the post-thaw viability and reduced the apoptotic cell population.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03571-6.

Improved cryopreservation media formulation reduces costs of maintenance while preserving function of genetically modified insect cells

Insect cell lines are an invaluable resource that facilitate various fundamental and applied research programs. Genetically engineered insect cell lines, in particular, serve as a platform through which the function of heterologously expressed proteins can be studied. However, a barrier to more widespread utilization and distribution of insect cell lines, genetically modified or not, is the technical and operational challenge associated with traditional cryopreservation methods, including their dependence on the use of liquid nitrogen facilities, animal or human serum products, and relatively high concentrations of permeating cryoprotectants (e.g., DMSO). Recent innovations in cryopreservation technologies have produced reagents with improved abilities to effectively preserve mammalian cell lines for long periods in regular laboratory deep freezers without using serum products, but their effectiveness in preserving genetically engineered insect cell lines has not yet been evaluated. In this study, we engineered Sf9 cells to express a dopamine receptor and used them as a model for evaluating the efficacy of a novel cryopreservation medium product, C80EZ^®-INSECT, in not only preserving cell viability and proliferation efficiency but also maintaining the insect cell line's "functionality" after storage at -80°C. We found that the engineered Sf9 cells frozen using C80EZ^®-INSECT with 5% DMSO alone and stored at -80°C for 6 mo displayed higher viability and growth rates than cells frozen using traditional fetal bovine serum (FBS)-based cryopreservation media with 10% DMSO that were stored at -80°C or in liquid nitrogen for the same period of time. We also found that after 6 mo of storage at -80°C or in liquid nitrogen the cells retained a responsiveness to dopamine comparable to that of the initial cell line, regardless of the cryopreservation reagent used. These results suggest that, due to the unique characteristics of C80EZ^®-INSECT in preventing ice recrystallization and reducing ice crystal size and cellular apoptosis during cryostorage procedures, it is an effective cryopreservation reagent for genetically engineered Sf9 cells, and it practically eliminates the need for liquid nitrogen-based storage facilities and FBS-based cryopreservation formulations, as well as reduces the use of permeating cryoprotectants.

Cryostorage of Mesenchymal Stem Cells and Biomedical Cell-Based Products

Mesenchymal stem cells (MSCs) manifest vast opportunities for clinical use due both to their ability for self-renewal and for effecting paracrine therapeutic benefits. At the same time, difficulties with non-recurrent generation of large numbers of cells due to the necessity for long-term MSC expansion ex vivo, or the requirement for repeated sampling of biological material from a patient significantly limits the current use of MSCs in clinical practice. One solution to these problems entails the creation of a biobank using cell cryopreservation technology. This review is aimed at analyzing and classifying literature data related to the development of protocols for the cryopreservation of various types of MSCs and tissue-engineered structures. The materials in the review show that the existing techniques and protocols for MSC cryopreservation are very diverse, which significantly complicates standardization of the entire process. Here, the selection of cryoprotectors and of cryoprotective media shows the greatest variability. Currently, it is the cryopreservation of cell suspensions that has been studied most extensively, whereas there are very few studies in the literature on the freezing of intact tissues or of tissue-engineered structures. However, even now it is possible to develop general recommendations to optimize the cryopreservation process, making it less traumatic for cells.

Improving Cell Recovery: Freezing and Thawing Optimization of Induced Pluripotent Stem Cells

Achieving good cell recovery after cryopreservation is an essential process when working with induced pluripotent stem cells (iPSC). Optimized freezing and thawing methods are required for good cell attachment and survival. In this review, we concentrate on these two aspects, freezing and thawing, but also discuss further factors influencing cell recovery such as cell storage and transport. Whenever a problem occurs during the thawing process of iPSC, it is initially not clear what it is caused by, because there are many factors involved that can contribute to insufficient cell recovery. Thawing problems can usually be solved more quickly when a certain order of steps to be taken is followed. Under optimized conditions, iPSC should be ready for further experiments approximately 4–7 days after thawing and seeding. However, if the freezing and thawing protocols are not optimized, this time can increase up to 2–3 weeks, complicating any further experiments. Here, we suggest optimization steps and troubleshooting options for the freezing, thawing, and seeding of iPSC on feeder-free, Matrigel™-coated, cell culture plates whenever iPSC cannot be recovered in sufficient quality. This review applies to two-dimensional (2D) monolayer cell culture and to iPSC, passaged, frozen, and thawed as cell aggregates (clumps). Furthermore, we discuss usually less well-described factors such as the cell growth phase before freezing and the prevention of osmotic shock during thawing.

Macromolecular cryoprotectants for the preservation of mammalian cell culture: lessons from crowding, overview and perspectives

Cryopreservation is a process used for the storage of mammalian cells at a very low temperature, in a state of 'suspended animation.' Highly effective and safe macromolecular cryoprotectants (CPAs) have gained significant attention as they obviate the toxicity of conventional CPAs like dimethyl sulfoxide (DMSO) and reduce the risks involved in the storage of cultures at liquid nitrogen temperatures. These agents provide cryoprotection through multiple mechanisms, involving extracellular and intracellular macromolecular crowding, thereby impacting the biophysical and biochemical dynamics of the freezing medium and the cryopreserved cells. These CPAs vary in their structures and physicochemical properties, which influence their cryoprotective activities. Moreover, the introduction of polymeric crowders in the cryopreservation media enables serum-free storage at low-DMSO concentrations and high-temperature vitrification of frozen cultures (-80 °C). This review highlights the need for macromolecular CPAs and describes their mechanisms of cryopreservation, by elucidating the role of crowding effects. It also classifies the macromolecules based on their chemistry and their structure-activity relationships. Furthermore, this article provides perspectives on the factors that may influence the outcomes of the cell freezing process or may help in designing and evaluating prospective macromolecules. This manuscript also includes case studies about cellular investigations that have been conducted to demonstrate the cryoprotective potential of macromolecular CPAs. Ultimately, this review provides essential directives that will further improve the cell cryopreservation process and may encourage the use of macromolecular CPAs to fortify basic, applied, and translational research.

Towards increasing stallion sperm longevity by storage at subzero temperatures in the absence of ice

The aim of cell preservation technologies is to slow down damaging reactions by lowering the storage temperature. Upon dilution in a stabilizing extender, stallion sperm can be stored at refrigerator temperatures for several days. Cryopreservation allows storage for decades, but freezing and thawing cause damage and viability losses. It is assumed that by storing cells at subzero temperatures in a non-frozen supercooled state, the damaging effects of ice formation can be avoided. In this study, we have investigated if stallion sperm can be stored at -10°C in the absence of ice, and compared viability during supercooled storage with that during storage at 5°C. We found that addition of 2% Ficoll-400 to buffered saline and covering with mineral oil depressed the sample freezing point and inhibited surface-catalyzed nucleation. This allowed storage in a supercooled state at -10°C for up to 7 days. Supplementing specimens with sperm, however, increased the incidence of sample freezing. Nonetheless, with 50×10⁶ sperm mL^-1, about 40% of the samples turned out to be non-frozen. Adding 100 mM sucrose was found to preserve sperm membrane intactness during supercooled storage, although this resulted in lower percentages as found with refrigerated storage. Sperm motility appeared to be lost during supercooled storage but could be partly restored by substituting buffered saline with a milk-based extender as base medium. Percentages of membrane intact sperm, however, were found to be lower. Supercooled storage holds promise for semen preservation, but further optimization of the storage solution is required to preserve sperm motility.

Effects of storage media, supplements and cryopreservation methods on quality of stem cells

Despite a vast amount of different methods, protocols and cryoprotective agents (CPA), stem cells are often frozen using standard protocols that have been optimized for use with cell lines, rather than with stem cells. Relatively few comparative studies have been performed to assess the effects of cryopreservation methods on these stem cells. Dimethyl sulfoxide (DMSO) has been a key agent for the development of cryobiology and has been used universally for cryopreservation. However, the use of DMSO has been associated with in vitro and in vivo toxicity and has been shown to affect many cellular processes due to changes in DNA methylation and dysregulation of gene expression. Despite studies showing that DMSO may affect cell characteristics, DMSO remains the CPA of choice, both in a research setting and in the clinics. However, numerous alternatives to DMSO have been shown to hold promise for use as a CPA and include albumin, trehalose, sucrose, ethylene glycol, polyethylene glycol and many more. Here, we will discuss the use, advantages and disadvantages of these CPAs for cryopreservation of different types of stem cells, including hematopoietic stem cells, mesenchymal stromal/stem cells and induced pluripotent stem cells.

Exposure to DMSO during infancy alters neurochemistry, social interactions, and brain morphology in long-evans rats

INTRODUCTION

Dimethyl sulfoxide (DMSO) is a widely used solvent to dissolve hydrophobic substances for clinical uses and experimental in vivo purposes. While usually regarded safe, our prior studies suggest changes to behavior following DMSO exposure. We therefore evaluated the effects of a five-day, short-term exposure to DMSO on postnatal infant rats (P6-10).

METHODS

DMSO was intraperitoneally injected for five days at 0.2, 2.0, and 4.0 ml/kg body mass. One cohort of animals was sacrificed 24 hr after DMSO exposure to analyze the neurometabolic changes in four brain regions (cortex, hippocampus, basal ganglia, and cerebellum) by hydrophilic interaction liquid chromatography. A second cohort of animals was used to analyze chronic alterations to behavior and pathological changes to glia and neuronal cells later in life (P21-P40).

RESULTS

164 metabolites, including key regulatory molecules (retinoic acid, orotic acid, adrenic acid, and hypotaurine), were found significantly altered by DMSO exposure in at least one of the brain regions at P11 (p < .05). Behavioral tests showed significant hypoactive behavior and decreased social habits to the 2.0 and 4.0 ml DMSO/kg groups (p < .01). Significant increases in number of microglia and astrocytes at P40 were observed in the 4.0 ml DMSO/kg group (at p < .015.) CONCLUSIONS: Despite short-term exposure at low, putatively nontoxic concentrations, DMSO led to changes in behavior and social preferences, chronic alterations in glial cells, and changes in essential regulatory brain metabolites. The chronic neurological effects of DMSO exposure reported here raise concerns about its neurotoxicity and consequent safety in human medical applications and clinical trials.

Sand-mediated ice seeding enables serum-free low-cryoprotectant cryopreservation of human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) possess tremendous potential for tissue regeneration and banking hiPSCs by cryopreservation for their ready availability is crucial to their widespread use. However, contemporary methods for hiPSC cryopreservation are associated with both limited cell survival and high concentration of toxic cryoprotectants and/or serum. The latter may cause spontaneous differentiation and/or introduce xenogeneic factors, which may compromise the quality of hiPSCs. Here, sand from nature is discovered to be capable of seeding ice above −10 °C, which enables cryopreservation of hiPSCs with no serum, much-reduced cryoprotectant, and high cell survival. Furthermore, the cryopreserved hiPSCs retain high pluripotency and functions judged by their pluripotency marker expression, cell cycle analysis, and capability of differentiation into the three germ layers. This unique sand-mediated cryopreservation method may greatly facilitate the convenient and ready availability of high-quality hiPSCs and probably many other types of cells/tissues for the emerging cell-based translational medicine.

•

Sand in nature is discovered to be excellent in seeding ice at high subzero temperatures.

•

The sand-mediated ice seeding enables the elimination of serum in cryopreservation solution.

•

The sand-mediated ice seeding enables the reduction of cryoprotectant by half.

•

The human iPSCs retain their intact pluripotency and differentiation capacity after cryopreservation.

Increased Cell Survival of Human Primary Conjunctival Stem Cells in Dimethyl Sulfoxide-Based Cryopreservation Media

Glycerol and dimethyl sulfoxide (DMSO) are widely used cryoprotectants for freezing human cell cultures. During the manufacturing process of ocular stem cell-based autographs, ex vivo cultivated ocular cells are cryopreserved for quality control purposes in accordance with regulatory requirements. The efficiency of the cryopreservation methods is limited by their effect on cell survival and quality. We compared two cryopreservation reagents, glycerol and DMSO, for their influence on the survival and quality of human primary conjunctival cultures. We found increased cell viability after cryopreservation in DMSO compared to cryopreservation in glycerol. The clonogenic and proliferative capacity was unaffected by the cryopreservation reagents, as shown by the colony forming efficiency and cumulative cell doubling. Importantly, the percentage of p63α- and keratin 19 (K19)-positive cells following cryopreservation in DMSO or glycerol was comparable. Taken together, our results demonstrate that cryopreservation in DMSO improves cell survival compared to cryopreservation in glycerol, with no subsequent effect on cell proliferative-, clonogenic-, or differentiation capacity. Therefore, we advise the use of a 10% DMSO-based cryopreservation medium for the cryopreservation of human primary conjunctival cells, as it will improve the number of cells available for the manufacturing of conjunctival stem cell-based autografts for clinical use.

Dimethyl sulfoxide-free cryopreservation for cell therapy: A review

Cell-based therapeutics promise to transform the treatment of a wide range of diseases including cancer, genetic and degenerative disorders, or severe injuries. Many of the commercial and clinical development of cell therapy products require cryopreservation and storage of cellular starting materials, intermediates and/or final products at cryogenic temperature. Dimethyl sulfoxide (Me₂SO) has been the cryoprotectant of choice in most biobanking situations due to its exceptional performance in mitigating freezing-related damages. However, there is concern over the toxicity of Me₂SO and its potential side effects after administration to patients. Therefore, there has been growing demand for robust Me₂SO-free cryopreservation methods that can improve product safety and maintain potency and efficacy. This article provides an overview of the recent advances in Me₂SO-free cryopreservation of cells having therapeutic potentials and discusses a number of key challenges and opportunities to motivate the continued innovation of cryopreservation for cell therapy.

Trehalose-Based Polyethers for Cryopreservation and Three-Dimensional Cell Scaffolds

The capability to slow ice growth and recrystallization is compulsory in the cryopreservation of cells and tissues to avoid injuries associated with the physical and chemical responses of freezing and thawing. Cryoprotective agents (CPAs) have been used to restrain cryoinjury and improve cell survival, but some of these compounds pose greater risks for the clinical application of cryopreserved cells due to their inherent toxicity. Trehalose is known for its unique physicochemical properties and its interaction with the phospholipids of the plasma membrane, which can reduce cell osmotic stress and stabilized the cryopreserved cells. Nonetheless, there has been a shortage of relevant studies on the synthesis of trehalose-based CPAs. We hereby report the synthesis and evaluation of a trehalose-based polymer and hydrogel and its use as a cryoprotectant and three-dimensional (3D) cell scaffold for cell encapsulation and organoid production. In vitro cytotoxicity studies with the trehalose-based polymers (poly(Tre-ECH)) demonstrated biocompatibility up to 100 mg/mL. High post-thaw cell membrane integrity and post-thaw cell plating efficiencies were achieved after 24 h of incubation with skin fibroblast, HeLa (cervical), and PC3 (prostate) cancer cell lines under both controlled-rate and ultrarapid freezing protocols. Differential scanning calorimetry and a splat cooling assay for the determination of ice recrystallization inhibition activity corroborated the unique properties of these trehalose-based polyethers as cryoprotectants. Furthermore, the ability to form hydrogels as 3D cell scaffolds encourages the use of these novel polymers in the development of cell organoids and cryopreservation platforms.

Assessment of Post-thaw Quality of Dental Mesenchymal Stromal Cells After Long-Term Cryopreservation by Uncontrolled Freezing

Cryopreservation abilities of dental tissue-derived mesenchymal stromal cells (DMSCs) including dental pulp stem cells (DPSCs) and dental follicle stem cells (DFSC) play an important role in the applications of these cells in clinical settings. In this context, we checked whether storage at - 80 °C in 10% DMSO for a longer period has any adverse effect on the functionality and genetic stability. We carried our studies on DPSC and DFSC samples that were revived after a maximum of 5 years of cryopreservation. We observed that even after long-term uncontrolled freezing at - 80 °C, these cells survived and proliferated efficiently. The assessment was made based on their post-thaw morphology, immunophenotypes, differentiation potential, growth kinetics, and genetic features. These cells retained the expression of stemness markers, differentiation ability and maintained their normal karyotype. Our results indicated no significant morphological or immunophenotypic differences between the cryopreserved DMSCs and the fresh DMSCs. Our study implies that mesenchymal stromal cells derived from the dental tissue origin are very robust and do not require any sophisticated preservation protocols. Thus, these can be an ideal source for research, stem cell banking, as well as successful clinical applications in tissue engineering and cell-based therapeutics. Graphical Abstract Schematic diagram showing the cryopreservation of DMSCs by uncontrolled freezing at -80 c has no adverse effects on their functionality and genetic stability.

Robust protocol for feeder-free adaptation of cryopreserved human pluripotent stem cells

Human pluripotent stem cells (hPSCs) are conventionally maintained on mouse embryonic fibroblast (MEF) feeder layers. However, downstream applications, such as directed differentiation protocols, are primarily optimized for feeder-free cultures. Therefore, hPSCs must often be adapted to feeder-free conditions. Here we propose a novel feeder-free adaptation protocol using StemFlex medium, which can be directly applied to thawed hPSC lines.The direct feeder-free adaptation protocol using StemFlex culture medium on Geltrex coating led to robust hPSC cultures in approximately 2 weeks. This approach was tested with three human embryonic stem cell (hESC) lines. All lines were confirmed to be pluripotent, expressing POU5F1, SOX2, and NANOG. No chromosomal imbalances were induced by the feeder-free adaptation.StemFlex medium enabled the efficient adaptation of hPSCs to feeder-free conditions directly after thawing. This protocol is easy to implement in laboratories that perform feeder-free cultures, allowing more convenient adaptation and more robust expansion of cryopreserved hPSCs, even in cases when sample quality is low or unknown.

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.

Hair-follicle-associated pluripotent stem cells derived from cryopreserved intact human hair follicles sustain multilineage differentiation potential

The bulge area of the hair follicle contains hair-follicle-associated pluripotent (HAP) stem cells. Here, we present effective cryopreservation procedures of the human hair follicle that preserve the differentiation potential of HAP stem cells. Whole hair follicles isolated from human scalp were cryopreserved by a slow-rate cooling medium and stored in liquid nitrogen. A careful thawing method was used to collect the upper parts of the human hair follicles which were cultured for four weeks in a Dulbecco’s Modified Eagle’s Medium with fetal bovine serum (FBS). Proliferating hair follicle cells were then shifted to DMEM/Ham’s Nutrient Mixture F-12 medium without FBS and allowed to grow for one week. These proliferating cells were able to produce HAP stem cell colonies with multilineage differentiation capacity. They produced keratinocytes, smooth muscle cells, cardiac muscle cells, neurons and glial cells. Interestingly, these cryopreserved hair follicles produced pluripotent HAP stem cell colonies similar to fresh follicles. These findings suggest that the cryopreserved whole human hair follicle preserves the ability to produce HAP stem cells, which will enable any individual to preserve a bank of these stem cells for personalized regenerative medicine.

Technical Considerations in the Freezing, Low-Temperature Storage and Thawing of Stem Cells for Cellular Therapies

The commercial and clinical development of cellular therapy products will invariably require cryopreservation and frozen storage of cellular starting materials, intermediates and/or final product. Optimising cryopreservation is as important as optimisation of the cell culture process in obtaining maximum yield and a consistent end-product. Suboptimal cryopreservation can lead not only to batch-to-batch variation, lowered cellular functionality and reduced cell yield, but also to the potential selection of subpopulations with genetic or epigenetic characteristics divergent from the original cell line. Regulatory requirements also impact on cryopreservation as these will require a robust and reproducible approach to the freezing, storage and thawing of the product. This requires attention to all aspects of the application of low temperatures: from the choice of freezing container and cryoprotectant, the cooling rate employed and its mode of de-livery, the correct handling of the frozen material during storage and transportation, to the eventual thawing of the product by the end-user. Each of these influences all of the others to a greater or lesser extent and none should be ignored. This paper seeks to provide practical insights and alternative solutions to the technical challenges faced during cryopreservation of cells for use in cellular therapies.

DMSO induces drastic changes in human cellular processes and epigenetic landscape in vitro

Though clinical trials for medical applications of dimethyl sulfoxide (DMSO) reported toxicity in the 1960s, later, the FDA classified DMSO in the safest solvent category. DMSO became widely used in many biomedical fields and biological effects were overlooked. Meanwhile, biomedical science has evolved towards sensitive high-throughput techniques and new research areas, including epigenomics and microRNAs. Considering its wide use, especially for cryopreservation and in vitro assays, we evaluated biological effect of DMSO using these technological innovations. We exposed 3D cardiac and hepatic microtissues to medium with or without 0.1% DMSO and analyzed the transcriptome, proteome and DNA methylation profiles. In both tissue types, transcriptome analysis detected >2000 differentially expressed genes affecting similar biological processes, thereby indicating consistent cross-organ actions of DMSO. Furthermore, microRNA analysis revealed large-scale deregulations of cardiac microRNAs and smaller, though still massive, effects in hepatic microtissues. Genome-wide methylation patterns also revealed tissue-specificity. While hepatic microtissues demonstrated non-significant changes, findings from cardiac microtissues suggested disruption of DNA methylation mechanisms leading to genome-wide changes. The extreme changes in microRNAs and alterations in the epigenetic landscape indicate that DMSO is not inert. Its use should be reconsidered, especially for cryopreservation of embryos and oocytes, since it may impact embryonic development.

Cryopreservation of Hematopoietic Stem Cells: Emerging Assays, Cryoprotectant Agents, and Technology to Improve Outcomes

Hematopoietic stem cell (HSC) therapy is widely used to treat a growing number of hematological and non-hematological diseases. Cryopreservation of HSCs allows for cells to be transported from the site of processing to the site of clinical use, creates a larger window of time in which cells can be administered to patients, and allows sufficient time for quality control and regulatory testing. Currently, HSCs and other cell therapies conform to the same cryopreservation techniques as cells used for research purposes: cells are cryopreserved in dimethyl sulfoxide (DMSO) at a slow cooling rate. As a result, HSC therapy can result in numerous adverse symptoms in patients due to the infusion of DMSO. Efforts are being made to improve the cryopreservation of HSCs for clinical use. This review discusses advances in the cryopreservation of HSCs from 2007 to the present. The preclinical development of new cryoprotectants and new technology to eliminate cryoprotectants after thawing are discussed in detail. Additional cryopreservation considerations are included, such as cooling rate, storage temperature, and cell concentration. Preclinical cell assessment and quality control are discussed, as well as clinical studies from the past decade that focus on new cryopreservation protocols to improve patient outcomes.

Electric ultrafreezer (- 150 °C) as an alternative for zebrafish sperm cryopreservation and storage

Zebrafish sperm cryopreservation is a fundamental methodology to manage and back-up valuable genetic resources like transgenic and mutant strains. Cryopreservation usually requires liquid nitrogen for storage, which is expensive and hazardous. Our objective was to evaluate if electric ultrafreezers (- 150 °C) are a viable alternative for zebrafish sperm storage. Zebrafish sperm was cryopreserved in the same conditions (- 20 °C/min), stored either in liquid nitrogen or in an ultrafreezer, and thawed after 1 week, 1 month, and 3 months. Sperm motility, membrane integrity, and fertilization ability were assessed. There were no significant differences in motility and hatching rate throughout storage time. Additionally, we aimed at understanding if cryopreservation directly in an ultrafreezer (- 66 °C/min) could improve post-thaw sperm quality. Freezing at - 20 °C/min was performed as before, and compared to samples cryopreserved with a fast cooling rate by placing directly in an ultrafreezer (- 66 °C/min). Sperm quality was assessed according to motility, viability, DNA fragmentation, and apoptosis (annexin V). The - 66 °C/min cooling rate showed significantly higher membrane and DNA integrity, and lower number of cells in late apoptosis in comparison to the other treatments. This study showed that zebrafish sperm cryopreservation and storage in an ultrafreezer system is possible and a fast cooling rate directly in ultrafreezer improves post-thaw sperm quality.

Storage stability of liposomes stored at elevated subzero temperatures in DMSO/sucrose mixtures

Cryopreservation of biological materials is predominantly done using liquid nitrogen, and its application involves high maintenance costs and the need for periodical refilling of liquid nitrogen. Stable storage in mechanical freezers at −80°C would eliminate these issues and allow for shipment of frozen specimens using dry ice. In this work, the possibility of increasing the storage temperature of cryopreserved samples to −80°C by using combinations of DMSO and sucrose has been studied. Preservation efficacy was studied by measuring stability of liposomes encapsulated with carboxyfluorescein during storage at −150, −80 and −25°C for up to three months. Thermal and molecular mobility properties of the different DMSO-sucrose formulations were measured using differential scanning calorimetry, whereas hydrogen bonding interactions of the formulations were probed by Fourier transform infrared spectroscopy. It was found that addition of sucrose to DMSO solutions increases the T_g, and decreases molecular mobility in the glassy state at a particular temperature. Although it was expected that storage above or close to T_g at −80°C would affect liposome stability, stability was found to be similar compared to that of samples stored at −150°C. Higher molecular mobility in the glassy state could not be associated with faster CF-leakage rates. Distinct differences in storage stability at −25°C, far above T_g, were found among the sucrose/DMSO formulations, which were explained by the differences in permeability of sucrose and DMSO resulting in different levels of osmotic stress in the formulations.

Advances in the slow freezing cryopreservation of microencapsulated cells

Over the past few decades, the use of cell microencapsulation technology has been promoted for a wide range of applications as sustained drug delivery systems or as cells containing biosystems for regenerative medicine. However, difficulty in their preservation and storage has limited their availability to healthcare centers. Because the preservation in cryogenic temperatures poses many biological and biophysical challenges and that the technology has not been well understood, the slow cooling cryopreservation, which is the most used technique worldwide, has not given full measure of its full potential application yet. This review will discuss the different steps that should be understood and taken into account to preserve microencapsulated cells by slow freezing in a successful and simple manner. Moreover, it will review the slow freezing preservation of alginate-based microencapsulated cells and discuss some recommendations that the research community may pursue to optimize the preservation of microencapsulated cells, enabling the therapy translate from bench to the clinic.