Combinations of Osmolytes, Including Monosaccharides, Disaccharides, and Sugar Alcohols Act in Concert During Cryopreservation to Improve Mesenchymal Stromal Cell Survival

Discovering the regulators of heat stress tolerance in Ziziphus nummularia (Burm.f) wight and walk.-arn

Ziziphus nummularia an elite heat-stress tolerant shrub, grows in arid regions of desert. However, its molecular mechanism responsible for heat stress tolerance is unexplored. Therefore, we analysed whole transcriptome of Jaisalmer (heat tolerant) and Godhra (heat sensitive) genotypes of Z. nummularia to understand its molecular mechanism responsible for heat stress tolerance. De novo assembly of 16,22,25,052 clean reads yielded 276,029 transcripts. A total of 208,506 unigenes were identified which contains 4290 and 1043 differentially expressed genes (DEG) in TGO (treated Godhra at 42 °C) vs. CGO (control Godhra) and TJR (treated Jaisalmer at 42 °C) vs. CJR (control Jaisalmer), respectively. A total of 987 (67 highly enriched) and 754 (34 highly enriched) pathways were obsorved in CGO vs. TGO and CJR vs. TJR, respectively. Antioxidant pathways and TFs like Homeobox, HBP, ARR, PHD, GRAS, CPP, and E2FA were uniquely observed in Godhra genotype and SET domains were uniquely observed in Jaisalmer genotype. Further transposable elements were highly up-regulated in Godhra genotype but no activation in Jaisalmer genotype. A total of 43,093 and 39,278 simple sequence repeats were identified in the Godhra and Jaisalmer genotypes, respectively. A total of 10 DEGs linked to heat stress were validated in both genotypes for their expression under different heat stresses using quantitative real-time PCR. Comparing expression patterns of the selected DEGs identified ClpB1 as a potential candidate gene for heat tolerance in Z. nummularia. Here we present first characterized transcriptome of Z. nummularia in response to heat stress for the identification and characterization of heat stress-responsive genes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01431-y.

Cryopreservation of organoids: Strategies, innovation, and future prospects

Organoid technology has demonstrated unique advantages in multidisciplinary fields such as disease research, tumor drug sensitivity, clinical immunity, drug toxicology, and regenerative medicine. It will become the most promising research tool in translational research. However, the long preparation time of organoids and the lack of high-quality cryopreservation methods limit the further application of organoids. Although the high-quality cryopreservation of small-volume biological samples such as cells and embryos has been successfully achieved, the existing cryopreservation methods for organoids still face many bottlenecks. In recent years, with the development of materials science, cryobiology, and interdisciplinary research, many new materials and methods have been applied to cryopreservation. Several new cryopreservation methods have emerged, such as cryoprotectants (CPAs) of natural origin, ice-controlled biomaterials, and rapid rewarming methods. The introduction of these technologies has expanded the research scope of cryopreservation of organoids, provided new approaches and methods for cryopreservation of organoids, and is expected to break through the current technical bottleneck of cryopreservation of organoids. This paper reviews the progress of cryopreservation of organoids in recent years from three aspects: damage factors of cryopreservation of organoids, new protective agents and loading methods, and new technologies of cryopreservation and rewarming.

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

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

The Effect of Cryopreservation on the Survival of Nocardia farcinica and Yersinia pestis vaccine strains

Pathogenic microorganisms are valuable biological resources, closely related to biosecurity, human health, environmental protection, and renewable energy. It is very important to properly preserve the microbial resources by methods to maintain the purity, viability, and integrity, and to avoid prolonged degradation. The present work aims to explore the cryopreservation technology of Nocardia farcinica (Gram-positive bacteria) and Yersinia pestis vaccine strains (Gram-negative bacteria). The effects of cryoprotectants (CPAs), freezing temperature, and freeze-thaw cycles on the two bacteria in the cryopreservation process were studied. The results showed that the addition of CPAs (glycerol, propylene glycol, sucrose, glucose, l-carnitine, l-proline, and skim milk) significantly enhanced the survival rates of the N. farcinica and Y. pestis vaccine strains. However, high concentrations of CPAs can produce biochemical toxicity in the two pathogens. The utilization of composite CPAs not only reduced the toxicity but also improved the survival rates of samples during cryopreservation. The optimal composite CPA for N. farcinica is 0.292 M sucrose, 0.62 M l-carnitine, and 2.82 M glycerol. The optimal composite CPA for Y. pestis is 0.62 M l-carnitine, 8.46 M glycerin, and 0.292 M sucrose. The results showed that the quality of the strains stored at -80°C and -196°C was better. For the case of freeze-thaw cycles, the two pathogens have different degrees of reduction, and the survival rate of Y. pestis decreased more than that of N. farcinica. The uniform distribution of bacteria in CPAs can form uniform nucleation sites in the solution system, which is beneficial to the cryopreservation of strains, as can be seen from the experimental results from a differential scanning calorimeter. This study may provide a reference for better preservation of precious natural biological resources of pathogenic microorganisms.

Cryoprotection in Human Mesenchymal Stromal/Stem Cells: Synergistic Impact of Urea and Glucose

Standard freezing protocols of clinically relevant cell lines commonly employ agents such as fetal bovine serum and dimethyl sulfoxide, which are a potential concern from both a regulatory and a patient safety perspective. The aim of this work was to develop formulations with safe and well tolerated excipients for the (cryo-) preservation of cell therapy products. We evaluated the cryoprotective capabilities of urea and glucose through measurements of cell metabolic activity. Freezing of clinically relevant human mesenchymal stromal/stem cells and human dermal fibroblasts at ≤ - 65°C at equimolar ratios of urea and glucose resulted in comparable viabilities to established dimethyl sulfoxide. Pre-incubation of human mesenchymal stromal/stem cells in trehalose and addition of mannitol and sucrose to the formulation further enhanced cell viability after freeze-thaw stress. Other cell types assessed (A549 and SK-N-AS) could not satisfactorily be preserved with urea and glucose, highlighting the need for tailored formulations to sustain acceptable cryopreservation.

Development of Serum-Free Media for Cryopreservation of Hydrogel Encapsulated Cell-Based Therapeutics

Introduction

While hydrogel encapsulation of cells has been developed to treat multiple diseases, methods to cryopreserve and maintain the composite function of therapeutic encapsulated cell products are still needed to facilitate their storage and distribution. While methods to preserve encapsulated cells, and post-synthesis have received recent attention, effective preservation mediums have not been fully defined.

Methods

We employed a two-tiered screen of an initial library of 32 different cryopreservation agent (CPA) formulations composed of different cell-permeable and impermeable agents. Formulations were assayed using dark field microscopy to evaluate alginate hydrogel matrix integrity, followed by cell viability analyses and measurements of functional secretion activity.

Results

The structural integrity of large > 1 mm alginate capsules were highly sensitive to freezing and thawing in media alone but could be recovered by a number of CPA formulations containing different cell-permeable and impermeable agents. Subsequent viability screens identified two top-performing CPA formulations that maximized capsule integrity and cell viability after storage at - 80 °C. The top formulation (10% Dimethyl sulfoxide (DMSO) and 0.3 M glucose) was demonstrated to preserve hydrogel integrity and retain cell viability beyond a critical USA FDA set 70% viability threshold while maintaining protein secretion and resultant cell potency.

Conclusions

This prioritized screen identified a cryopreservation solution that maintains the integrity of large alginate capsules and yields high viabilities and potency. Importantly, this formulation is serum-free, non-toxic, and can support the development of clinically translatable encapsulated cell-based therapeutics.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00739-7.

Recent insights into polysaccharide-based hydrogels and their potential applications in food sector: A review

Hydrogels are ideal for various food applications because of their softness, elasticity, absorbent nature, flexibility, and hygroscopic nature. Polysaccharide hydrogels are particularly suitable because of the hydrophilic nature, their food compatibility, and their non-immunogenic character. Such hydrogels offer a wide range of successful applications such as food preservation, pharmaceuticals, agriculture, and food packaging. Additionally, polysaccharide hydrogels have proven to play a significant role in the formulation of food flavor carrier systems, thus diversifying the horizons of newer developments in food processing sector. Polysaccharide hydrogels are comprised of natural polymers such as alginate, chitosan, starch, pectin and hyaluronic acid when crosslinked physically or chemically. Hydrogels with interchangeable, antimicrobial and barrier properties are referred to as smart hydrogels. This review brings together the recent and relevant polysaccharide research in these polysaccharide hydrogel applications areas and seeks to point the way forward for future research and interventions. Applications in carrying out the process of flavor carrier system directly through their incorporation in food matrices, broadening the domain for food application innovations. The classification and important features of polysaccharide-based hydrogels in food processing are the topics of the current review study.

Natural Cryoprotective and Cytoprotective Agents in Cryopreservation: A Focus on Melatonin

Cryoprotective and cytoprotective agents (Cytoprotective Agents) are fundamental components of the cryopreservation process. This review presents the essentials of the cryopreservation process by examining its drawbacks and the role of cytoprotective agents in protecting cell physiology. Natural cryoprotective and cytoprotective agents, such as antifreeze proteins, sugars and natural deep eutectic systems, have been compared with synthetic ones, addressing their mechanisms of action and efficacy of protection. The final part of this article focuses melatonin, a hormonal substance with antioxidant properties, and its emerging role as a cytoprotective agent for somatic cells and gametes, including ovarian tissue, spermatozoa and spermatogonial stem cells.

Impact of Cryopreservation and Freeze-Thawing on Therapeutic Properties of Mesenchymal Stromal/Stem Cells and Other Common Cellular Therapeutics

Purpose of Review

Cryopreservation and its associated freezing and thawing procedures–short “freeze-thawing”–are among the final steps in economically viable manufacturing and clinical application of diverse cellular therapeutics. Translation from preclinical proof-of-concept studies to larger clinical trials has indicated that these processes may potentially present an Achilles heel to optimal cell product safety and particularly efficacy in clinical trials and routine use.

Recent Findings

We review the current state of the literature on how cryopreservation of cellular therapies has evolved and how the application of this technique to different cell types is interlinked with their ability to engraft and function upon transfer in vivo, in particular for hematopoietic stem and progenitor cells (HSPCs), their progeny, and therapeutic cell products derived thereof. We also discuss pros and cons how this may differ for non-hematopoietic mesenchymal stromal/stem cell (MSC) therapeutics. We present different avenues that may be crucial for cell therapy optimization, both, for hematopoietic (e.g., effector, regulatory, and chimeric antigen receptor (CAR)-modified T and NK cell based products) and for non-hematopoietic products, such as MSCs and induced pluripotent stem cells (iPSCs), to achieve optimal viability, recovery, effective cell dose, and functionality of the cryorecovered cells.

Summary

Targeted research into optimizing the cryopreservation and freeze-thawing routines and the adjunct manufacturing process design may provide crucial advantages to increase both the safety and efficacy of cellular therapeutics in clinical use and to enable effective market deployment strategies to become economically viable and sustainable medicines.

Membrane-permeable trehalose improves the freezing ability and developmental competence of in-vitro matured feline oocytes

Oocytes are highly sensitive to cryopreservation, which frequently results in an irreversible loss of developmental competence. We examined the effect of membrane-permeable trehalose on the freezing ability of feline oocytes matured in vitro. In Experiment 1, intracellular trehalose (trehalose hexaacetate; Tre-(OAc)₆) was synthesized from trehalose precursor and subjected to spectroscopic characterization. The membrane permeability of the Tre-(OAc)₆ was investigated by incubating oocytes with different concentrations of Tre-(OAc)₆ (3, 15, and 30 mM). Optimum concentration and the toxicity of Tre-(OAc)₆ were assessed in Experiment 2. The effects of Tre-(OAc)₆ on freezing ability in terms of apoptotic gene expression and developmental competence of in-vitro matured oocytes were examined in Experiments 3 and 4, respectively. The Tre-(OAc)₆ permeated into the ooplasm of cat oocytes in a dose- and time-dependent manner. The highest concentration of intracellular trehalose was detected when the oocytes were incubated for 24 h with 30 mM Tre-(OAc)₆. For the toxicity test, incubation of oocytes with 3 mM Tre-(OAc)₆ for 24 h did not affect maturation rate and embryo development. However, high doses of Tre-(OAc)₆ (15 and 30 mM) significantly reduced maturation and fertilization rates (p < 0.05). In addition, frozen-thawed oocytes treated with 3 mM Tre-(OAc)₆ significantly upregulated anti-apoptotic (BCL-2) gene expression compared with the control (0 mM) and other Tre-(OAc)₆ concentrations (15 and 30 mM). Oocyte maturation in the presence of 3 mM Tre-(OAc)₆ prior to cryopreservation significantly improved oocyte developmental competence in terms of cleavage and blastocyst rates when compared with the control group (p < 0.05). Our results lead us to infer that increasing the levels of intracellular trehalose by Tre-(OAc)₆ during oocyte maturation improves the freezing ability of feline oocytes, albeit at specific concentrations.

Cryopreservation of NK and T Cells Without DMSO for Adoptive Cell-Based Immunotherapy

Dimethylsufoxide (DMSO) being universally used as a cryoprotectant in clinical adoptive cell-therapy settings to treat hematological malignancies and solid tumors is a growing concern, largely due to its broad toxicities. Its use has been associated with significant clinical side effects-cardiovascular, neurological, gastrointestinal, and allergic-in patients receiving infusions of cell-therapy products. DMSO has also been associated with altered expression of natural killer (NK) and T-cell markers and their in vivo function, not to mention difficulties in scaling up DMSO-based cryoprotectants, which introduce manufacturing challenges for autologous and allogeneic cellular therapies, including chimeric antigen receptor (CAR)-T and CAR-NK cell therapies. Interest in developing alternatives to DMSO has resulted in the evaluation of a variety of sugars, proteins, polymers, amino acids, and other small molecules and osmolytes as well as modalities to efficiently enable cellular uptake of these cryoprotectants. However, the DMSO-free cryopreservation of NK and T cells remains difficult. They represent heterogeneous cell populations that are sensitive to freezing and thawing. As a result, clinical use of cryopreserved cell-therapy products has not moved past the use of DMSO. Here, we present the state of the art in the development and use of cryopreservation options that do not contain DMSO toward clinical solutions to enable the global deployment of safer adoptively transferred cell-based therapies.

On-demand retrieval of cells three-dimensionally seeded in injectable thioester-based hydrogels

Scaffold systems that can easily encapsulate cells and safely retrieve them at the desired time are important for the advancement of cell-based medicine. In this study, we designed and fabricated thioester-based poly(ethylene glycol) (PEG) hydrogels with injectability and on-demand degradability as new scaffold materials for cells. Hydrogels can be formed in situ within minutes via thioester cross-linking between PEG molecules and can be degraded under mild conditions in response to l-cysteine molecules through thiol exchange occurring at the thioester linkage. Various cell experiments, especially with sucrose, which enables the adjustment of the osmotic pressure around the cells, showed that the damage to the cells during encapsulation and degradation was minimal, indicating the capability of on-demand retrieval of intact cells. This hydrogel system is a versatile tool in the field of cell-based research and applications such as tissue regeneration and regenerative medicine.

Human mesenchymal stem/stromal cells can be three-dimensionally encapsulated in hydrogels cross-linked with thioester linkages. Degrading the cell-embedded hydrogels by l-cysteine molecules enables safe on-demand retrieval of the cells.

Natural deep eutectic systems for nature-inspired cryopreservation of cells

Natural deep eutectic systems (NADES) are emerging as potential cryoprotective agents (CPA) for cell preservation. In this investigation, we develop an optimized CPA formulation using trehalose-glycerol NADES (T:G) diluted in Normosol-R and supplemented with isoleucine. Differential scanning calorimetry (DSC) is used to define the thermophysical properties of NADES-based solutions, and Raman spectroscopy is used to characterize the effect of NADES on ice formation and hydrogen bonding. Jurkat cells are cryopreserved in each solution, and post-thaw cell recovery, apoptosis, and growth are quantified. Raman spectra and heat maps show that NADES suppresses both ice formation and dehydration of the nonfrozen region. Supplementing NADES with isoleucine does not affect the solution's thermophysical properties but significantly improves the cells' survival and proliferation post-thaw. The study indicates that thermophysical properties of CPA solutions alone cannot predict optimal cell survival, suggesting that stabilization of biological structures by CPAs may play a role in successful cryopreservation.

Advances and prospects in the food applications of pectin hydrogels

Pectin hydrogel is a soft hydrocolloid with multifaceted utilities in the food sector. Substantial knowledge acquired on the gelation mechanisms and structure-function relationship of pectin has led to interesting functions of pectin hydrogel. Food applications of pectin hydrogels can be categorized under four headings: food ingredients/additives, food packaging, bioactive delivery and health management. The cross-linked and tangly three-dimensional structure of pectin gel renders it an ideal choice of wall material for the encapsulation of biomolecules and living cells; as a fat replacer and texturizer. Likewise, pectin hydrogel is an effective satiety inducer due to its ability to swell under the simulated gastric and intestinal conditions without losing its gel structure. Coating or composites of pectin hydrogel with proteins and other polysaccharides augment its functionality as an encapsulant, satiety-inducer and food packaging material. Low-methoxyl pectin gel is an appropriate food ink for 3D printing applications due to its viscoelastic properties, adaptable microstructure and texture properties. This review aims at explaining all the applications of pectin hydrogels, as mentioned above. A comprehensive discussion is presented on the approaches by which pectin hydrogel can be transformed as a resourceful material by controlling its dimensions, state, and rheology. The final sections of this article emphasize the recent research trends in this discipline, such as the development of smart hydrogels, injectable gels, aerogels, xerogels and oleogels from pectin.

Raman Cryomicroscopic Imaging and Sample Holder for Spectroscopic Subzero Temperature Measurements

Raman spectroscopy has been gaining in popularity for noninvasive analysis of single cells. Raman spectra and images deliver meaningful information regarding the biochemical, biophysical, and structural properties of cells in various states. Low-temperature Raman spectroscopy has been applied to verify the presence of ice inside a frozen cell and to illustrate the distribution of both penetrating and non-penetrating cryoprotectants. This chapter delineates Raman cryomicroscopic imaging of single cells as well as sample handling for spectroscopic measurements at subzero temperature. The experimental setup is depicted with a special emphasis on a custom-built temperature-controlled cooling stage. The use of Raman cryomicroscopic imaging is demonstrated using Jurkat cells cryopreserved in a sucrose solution. Moreover, strategies for determining intracellular ice formation (IIF) and analysis of sucrose partitioning across the cell membrane are presented.

Differential Evolution for the Optimization of DMSO-Free Cryoprotectants: Influence of Control Parameters

This study presents the influence of control parameters including population (NP) size, mutation factor (F), crossover (Cr), and four types of differential evolution (DE) algorithms including random, best, local-to-best, and local-to-best with self-adaptive (SA) modification for the purpose of optimizing the compositions of dimethylsufloxide (DMSO)-free cryoprotectants. Post-thaw recovery of Jurkat cells cryopreserved with two DMSO-free cryoprotectants at a cooling rate of 1 °C/min displayed a nonlinear, four-dimensional structure with multiple saddle nodes, which was a suitable training model to tune the control parameters and select the most appropriate type of differential evolution algorithm. Self-adaptive modification presented better performance in terms of optimization accuracy and sensitivity of mutation factor and crossover among the four different types of algorithms tested. Specifically, the classical type of differential evolution algorithm exhibited a wide acceptance to mutation factor and crossover. The optimization performance is more sensitive to mutation than crossover and the optimization accuracy is proportional to the population size. Increasing population size also reduces the sensitivity of the algorithm to the value of the mutation factor and crossover. The analysis of optimization accuracy and convergence speed suggests larger population size with F > 0.7 and Cr > 0.3 are well suited for use with cryopreservation optimization purposes. The tuned differential evolution algorithm is validated through finding global maximums of other two DMSO-free cryoprotectant formulation datasets. The results of these studies can be used to help more efficiently determine the optimal composition of multicomponent DMSO-free cryoprotectants in the future.

Nanoparticle-Mediated Intracellular Protection of Natural Killer Cells Avoids Cryoinjury and Retains Potent Antitumor Functions

The ability of natural killer (NK) cells to mediate potent antitumor immunity in clinical adoptive transfer settings relies, in large part, on their ability to retain cytotoxic function following cryopreservation. To avoid potential systemic toxicities associated with infusions of NK cells into patients in the presence of dimethylsulfoxide (DMSO), interest in alternative cryoprotective agents (CPAs) with improved safety profiles has grown. Despite the development of various sugars, amino acids, polyols, and polyampholytes as cryoprotectants, their ability to promote protection from intracellular cryodamage is limited because they mostly act outside of the cell. Though ways to shuttle cryoprotectants intracellularly exist, NK cells' high aversity to manipulation and freezing has meant they are highly understudied as targets for the development of new cryopreservation approaches. Here, the first example of a safe and efficient platform for the intracellular delivery of non-DMSO CPAs to NK cells is presented. Biocompatible chitosan-based nanoparticles are engineered to mediate the efficient DMSO-free cryopreservation of NK cells. NK cells cryopreserved in this way retain potent cytotoxic, degranulation, and cytokine production functions against tumor targets. This not only represents the first example of delivering nanoparticles to NK cells, but illustrates the clinical potential in manufacturing safer allogeneic adoptive immunotherapies "off the shelf."

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.

Understanding the freezing responses of T cells and other subsets of human peripheral blood mononuclear cells using DSMO-free cryoprotectants

BACKGROUND

This study examined the freezing responses of peripheral blood mononuclear cells (PBMCs) and specific white blood cell subsets contained therein when cryopreserved in three combinations of osmolytes composed of sugars, sugar alcohols and amino acids.

METHODS

A differential evolution algorithm with multiple objectives was used to optimize cryoprotectant composition and thus the post-thaw recoveries for both helper and cytotoxicity T cells simultaneously.

RESULTS

The screening of various formulations using a differential evolution algorithm showed post-thaw recoveries greater than 80% for the two subsets of T cells. The phenotypes and viabilities of PBMC subsets were characterized using flow cytometry. Significant differences between the post-thaw recovery for helper T cells and cytotoxic T cells were observed. Statistical models were used to analyze the importance of individual osmolytes and interactions between post-thaw recoveries of three subsets of T cell including helper T cells, cytotoxic T cells and natural killer T cells. The statistical model indicated that the preferred concentration levels of osmolytes and interaction modes were distinct between the three subsets studied. PBMCs were cultured for 72 h post-thaw to determine the stability of the cells. Because post-thaw apoptosis is a significant concern for lymphocytes, apoptosis of helper T cell and cytotoxic T cells frozen in a DMSO-free cryoprotectant was analyzed immediately post-thaw and 24 h post-thaw. Both cell types showed a decrease in cell viability 24 h post-thaw compared with immediately post-thaw. Helper T cell viability dropped 17%, and cytotoxic T cells had a 10% drop in viability. Immediately post-thaw, both cell types had >30% of cells in early apoptosis, but after 24 h the number of cells in early apoptosis decreased to below 20%.

CONCLUSION

This study helped us identify the freezing responses of different human PBMC subsets using combinations of osmolytes.

Cryopreservation of Human iPS Cell Aggregates in a DMSO-Free Solution-An Optimization and Comparative Study

Human induced pluripotent stem cells (hiPSCs) are an important cell source for regenerative medicine products. Effective methods of preservation are critical to their clinical and commercial applications. The use of a dimethyl sulfoxide (DMSO)-free solution containing all non-toxic molecules offers an effective alternative to the conventional DMSO and alleviates pain points associated with the use of DMSO in the cryopreservation of hiPSCs. Both hiPSCs and cells differentiated from them are commonly multicellular systems, which are more sensitive to stresses of freezing and thawing than single cells. In this investigation, low-temperature Raman spectroscopy visualized freezing behaviors of hiPSC aggregates in different solutions. These aggregates exhibited sensitivity to undercooling in DMSO-containing solutions. We demonstrated the ability to replace DMSO with non-toxic molecules, improve post-thaw cell survival, and reduce sensitivity to undercooling. An accelerated optimization process capitalized on the positive synergy among multiple DMSO-free molecules, which acted in concert to influence ice formation and protect cells during freezing and thawing. A differential evolution algorithm was used to optimize the multi-variable, DMSO-free preservation protocol in 8 experiments. hiPSC aggregates frozen in the optimized solution did not exhibit the same sensitivity to undercooling as those frozen in non-optimized solutions or DMSO, indicating superior adaptability of the optimized solution to different freezing modalities and unplanned deviations. This investigation shows the importance of optimization, explains the mechanisms and advantages of a DMSO-free solution, and enables not only improved cryopreservation of hiPSCs but potentially other cell types for translational regenerative medicine.

Preservation of cell-based immunotherapies for clinical trials

In the unique supply chain of cellular therapies, preservation is important to keep the cell product viable. Many factors in cryopreservation affect the outcome of a cell therapy: (i) formulation and introduction of a freezing medium, (ii) cooling rate, (iii) storage conditions, (iv) thawing conditions and (v) post-thaw processing. This article surveys clinical trials of cellular immunotherapy that used cryopreserved regulatory, chimeric antigen receptor or gamma delta T cells, dendritic cells or natural killer (NK) cells. Several observations are summarized from the given information. The aforementioned cell types have been similarly frozen in media containing 5-10% dimethyl sulfoxide (DMSO) with plasma, serum or human serum albumin. Two common freezing methods are an insulated freezing container such as Nalgene Mr. Frosty and a controlled-rate freezer at a cooling rate of -1°C/min. Water baths at approximately 37°C have been commonly used for thawing. Post-thaw processing of cryopreserved cells varied greatly: some studies infused the cells immediately upon thawing; some diluted the cells in a carrier solution of varying formulation before infusion; some washed cells to remove cryoprotective agents; and others re-cultured cells to recover cell viability or functionality lost due to cryopreservation. Emerging approaches to preserving cellular immunotherapies are also described. DMSO-free formulations of the freezing media have demonstrated improved preservation of cell viability in T lymphocytes and of cytotoxic function in natural killer cells. Saccharides are a common type of molecule used as an alternative cryoprotective agent to DMSO. Improving methods of preservation will be critical to growth in the clinical use of cellular immunotherapies.

Interfacial Interactions of Sucrose during Cryopreservation Detected by Raman Spectroscopy

There is considerable interest in the use of sugars to preserve cells. In this study, low temperature Raman spectroscopy was used to characterize the behaviors of sucrose during freezing. The hydrogen bond network between sucrose and water was investigated at -10 °C and -50 °C, and the Raman spectra showed strengthened sucrose-water and sucrose-sucrose hydrogen bonds in more concentrated sucrose solution at -50 °C. The concentration of sucrose at the ice interface increased as the ice density decreased, and it plateaued across a narrow channel of nonfrozen sucrose solution before it decreased toward the next ice interface. The biophysical environment at interfaces between the cell and nonfrozen sucrose solution and between the cell and extracellular ice was also studied. A thin layer of nonfrozen sucrose solution was observed at the interface between the cell and extracellular ice. The extracellular concentration of sucrose at this interface was generally lower than that of bulk nonfrozen sucrose solution. The variation of sucrose concentration outside different regions of the cell membrane suggests that the chemical environment around the cell during freezing may be more heterogeneous than previously thought. Raman spectra and images also showed colocalization of nonfrozen sucrose solution and the cell, which implied that direct interaction between sucrose and cell membrane might be responsible for protective properties of sucrose. Sucrose was predominantly distributed outside the cell, and the observation of strong partitioning of sucrose across the cell membrane is consistent with substantial cell dehydration detected by the Raman spectra. This work enhances our understanding of the behaviors of sucrose solution and its interactions with cells at low temperature and can improve cryopreservation protocols of cells frozen in a sucrose-based media.

The role of preservation in the variability of regenerative medicine products

Regenerative medicine (RM) has the potential to restore or establish normal function of cells, tissues and organs that have been lost due to age, disease or injury. It is common for the site of raw material collection, site of manufacture and site of clinical use to be different for RM products, and at the same time cells must remain viable and functional during transportation among different sites. Freezing products down to cryogenic temperatures along with cold chain transportation has become an effective method of preserving RM products. The quality of RM products along this supply chain represents the cumulative effects of all of the processing steps and all of the reagents used in the process. A variety of sources of variability in the preservation of RM products can result in both cell losses and greater variability in the quality of RM products. The purpose of this article is to review the sources of variability in the preservation process as well as the methods by which variability can be controlled or avoided.

Characterizing modes of action and interaction for multicomponent osmolyte solutions on Jurkat cells

This study examined the post-thaw recovery of Jurkat cells cryopreserved in three combinations of five osmolytes including trehalose, sucrose, glycerol, mannitol, and creatine. Cellular response was characterized using low-temperature Raman spectroscopy, and variation of post-thaw recovery was analyzed using statistical modeling. Combinations of osmolytes displayed distinct trends of post-thaw recovery, and a nonlinear relationship between compositions and post-thaw recovery was observed, suggesting interactions not only between different solutes but also between solutes and cells. The post-thaw recovery for optimized cryoprotectants in different combinations of osmolytes at a cooling rate of 1°C/min was comparable to that measured with 10% dimethyl sulfoxide. Statistical modeling was used to understand the importance of individual osmolytes as well as interactions between osmolytes on post-thaw recovery. Both higher concentrations of glycerol and certain interactions between sugars and glycerol were found to typically increase the post-thaw recovery. Raman images showed the influence of osmolytes and combinations of osmolytes on ice crystal shape, which reflected the interactions between osmolytes and water. Differences in the composition also influenced the presence or absence of intracellular ice formation, which could also be detected by Raman. These studies help us understand the modes of action for cryoprotective agents in these osmolyte solutions.

Osmolytes resist against harsh osmolarity: Something old something new

From the halophilic bacteria to human, cells have to survive under the stresses of harsh environments. Hyperosmotic stress is a process that triggers cell shrinkage, oxidative stress, DNA damage, and apoptosis and it potentially contributes to a number of human diseases. Remarkably, by high salts and organic solutes concentrations, a variety of organisms struggle with these conditions. Different strategies have been developed for cellular osmotic adaptations among which organic osmolyte synthesis/accumulation is a conserved once. Osmolytes are naturally occurring solutes used by cells of several halophilic (micro) organisms to preserve cell volume and function. In this review, the osmolytes diversity and their protective roles in harsh hyperosmolar environments from bacteria to human cells are highlighted. Moreover, it provides a close look at mammalian kidney osmoregulation at a molecular level. This review provides a concise view on the recent developments and advancements on the applications of osmolytes. Identification of disease-related osmolytes and their targeted-delivery may be used as a therapeutic measurement for treatment of the pathological conditions and the inherited diseases related to protein misfolding and aggregation. The molecular and cellular aspects of cell adaptation against harsh environmental osmolarity will benefit the development of effective drugs for many diseases.

Freezing of dendritic cells with trehalose as an additive in the conventional freezing medium results in improved recovery after cryopreservation

BACKGROUND

Dendritic cell (DC) vaccination involves administration of multiple doses. Cryopreservation of tumor antigen-pulsed DCs can provide a ready to use vaccine source and eliminate the need of frequent withdrawal of the patient's blood for vaccine preparation. The aim of this study was to assess the effect of addition of trehalose in the freezing medium on the recovery of DCs after cryopreservation.

STUDY DESIGN AND METHODS

DCs were generated from mononuclear cells from apheresis samples of healthy donors. For long-term storage of 6 months, cells were frozen with a rate-controlled programmable freezer and stored in liquid nitrogen. For short-term storage of 1 month, cells were frozen and stored at -80°C. DCs frozen with Iscove's Modified Dulbecco's Medium + 10% dimethyl sulfoxide + 20% fetal bovine serum served as the control group, while the test group was additionally supplemented with 50 μg/mL of trehalose. After revival of control and test DCs, they were assessed for viability, morphology, phenotype, and functions.

RESULTS

The addition of trehalose to the conventional freezing medium helped to preserve the viability and functionality of DCs better than dimethyl sulfoxide alone in both long- and short-term cryopreservation. Trehalose also protected the mitochondrial membrane potential and cytoskeleton integrity of DCs, which are necessary for their functionality. Mediators of the intrinsic apoptotic pathway like Caspase-9 and Bim-1 were found to be low in the test.

CONCLUSION

Supplementation of conventional freezing medium with trehalose results in better quality of DCs revived after cryopreservation. This finding could help improve DC vaccine preparation for cancer immunotherapy.

Characterizing the "sweet spot" for the preservation of a T-cell line using osmolytes

This study examined the post-thaw recovery of Jurkat cells cryopreserved in single osmolyte solutions containing sucrose, glycerol or isoleucine, as well as in a combination of the three osmolytes. Cell response was determined using low temperature Raman Spectroscopy and variation in post-thaw recovery with composition was analyzed using statistical modeling. Post-thaw recovery of Jurkat cells in single osmolyte was low. A combination of the osmolytes displayed a non-linear relationship between composition and post-thaw recovery, suggesting that interactions exist between the different solutes. The post-thaw recovery for an optimized multicomponent solution was comparable to that observed using 10% dimethyl sulfoxide and a cooling rate of 1 °C/min. Statistical modeling was used to characterize the importance of each osmolyte in the combination and test for interactions between osmolytes. Higher concentrations of glycerol increase post-thaw recovery and interactions between sucrose and glycerol, as well as sucrose and isoleucine improve post-thaw recovery. Raman images clearly demonstrated that damaging intracellular ice formation was observed more often in the presence of single osmolytes as well as non-optimized multi-component solution compositions.

Changes of soluble sugars and ATP content during DMSO droplet freezing and PVS3 droplet vitrification of potato shoot tips

The potato's great genetic diversity needs to be maintained for future agricultural applications and can be preserved at ultra-low temperatures. To decipher detailed physiological processes, the aim of the study was to analyze the regrowth in 28 gene bank accessions and to reveal metabolite changes in a subset of four accessions that showed pronounced differences after shoot tip cryopreservation using DMSO droplet freezing and PVS3 droplet vitrification. Regrowth varied in all 28 genotypes ranging from 5% ('Kagiri') to 100% ('Karakter') and was higher after PVS3 droplet vitrification (71 ± 19%) than after cryopreservation using DMSO (54 ± 17%). Sucrose, glucose, and fructose were analyzed and showed significant increases after pre-culture in combination with PVS3 or DMSO and liquid nitrogen treatment and were reduced during regeneration. In contrast, adenosine triphosphate (ATP) reached its minimum concentration after cryoprotection and liquid nitrogen treatment and recovered most quickly after PVS3 droplet vitrification. A shortening of the explant pre-culture period reduced dramatically the regrowth after PVS3 vitrification. However, correlations between the shoot tip regrowth and sugar concentration were absent and significant at a low extent with ATP (r = 0.4, P < 0.01). Interestingly, several sub-cultivations of the donor plants from the previous stock affected negatively the regrowth. In conclusion, the cryopreservation protocol, genotypes, pre-culture period and number of sub-cultures affect the regrowth ability of explants, which was best estimated by the ATP concentration after low-temperature treatment. Due to the superior performance of PVS3, the routine potato cryopreservation at the Gatersleben gene bank was changed to PVS3 droplet vitrification.

Application of Polysaccharide-Based Hydrogels as Probiotic Delivery Systems

Polysaccharide hydrogels have been increasingly utilized in various fields. In this review, we focus on polysaccharide-based hydrogels used as probiotic delivery systems. Probiotics are microorganisms with a positive influence on our health that live in the intestines. Unfortunately, probiotic bacteria are sensitive to certain conditions, such as the acidity of the gastric juice. Polysaccharide hydrogels can provide a physical barrier between encapsulated probiotic cells and the harmful environment enhancing the cells survival rate. Additionally, hydrogels improve survivability of probiotic bacteria not only under gastrointestinal track conditions but also during storage at various temperatures or heat treatment. The hydrogels described in this review are based on selected polysaccharides: alginate, κ-carrageenan, xanthan, pectin and chitosan. Some hydrogels are obtained from the mixture of two polysaccharides or polysaccharide and non-polysaccharide compounds. The article discusses the efficiency of probiotic delivery systems made of single polysaccharide, as well as of systems comprising more than one component.

Freezing Responses in DMSO-Based Cryopreservation of Human iPS Cells: Aggregates Versus Single Cells

Inadequate preservation methods of human induced pluripotent stem cells (hiPSCs) have impeded efficient reestablishment of cell culture after the freeze-thaw process. In this study, we examined roles of the cooling rate, seeding temperature, and difference between cell aggregates (3-50 cells) and single cells in controlled rate freezing of hiPSCs. Intracellular ice formation (IIF), post-thaw membrane integrity, cell attachment, apoptosis, and cytoskeleton organization were evaluated to understand the different freezing responses between hiPSC single cells and aggregates, among cooling rates of 1, 3, and 10°C/min, and between seeding temperatures of -4°C and -8°C. Raman spectroscopy images of ice showed that a lower seeding temperature (-8°C) did not affect IIF in single cells, but significantly increased IIF in aggregates, suggesting higher sensitivity of aggregates to supercooling. In the absence of IIF, Raman images showed greater variation of dimethyl sulfoxide concentration across aggregates than single cells, suggesting cryoprotectant transport limitations in aggregates. The ability of cryopreserved aggregates to attach to culture substrates did not correlate with membrane integrity for the wide range of freezing parameters, indicating inadequacy of using only membrane integrity-based optimization metrics. Lower cooling rates (1 and 3°C/min) combined with higher seeding temperature (-4°C) were better at preventing IIF and preserving cell function than a higher cooling rate (10°C/min) or lower seeding temperature (-8°C), proving the seeding temperature range of -7°C to -12°C from literature to be suboptimal. Unique f-actin cytoskeletal organization into a honeycomb-like pattern was observed in postpassage and post-thaw colonies and correlated with successful reestablishment of cell culture.

Characterizing Intracellular Ice Formation of Lymphoblasts Using Low-Temperature Raman Spectroscopy

Raman microspectroscopy was used to quantify freezing response of cells to various cooling rates and solution compositions. The distribution pattern of cytochrome c in individual cells was used as a measure of cell viability in the frozen state and this metric agreed well with the population-averaged viability and trypan blue staining experiments. Raman imaging of cells demonstrated that intracellular ice formation (IIF) was common and did not necessarily result in cell death. The amount of intracellular ice as well as ice crystal size played a role in determining whether or not ice inside the cell was a lethal event. Intracellular ice crystals were colocated to the sections of cell membrane in close proximity to extracellular ice. Increasing the distance between extracellular ice and cell membrane decreased the incidence of IIF. Reducing the effective stiffness of the cell membrane by disrupting the actin cytoskeleton using cytochalasin D increased the amount of IIF. Strong intracellular osmotic gradients were observed when IIF was present. These observations support the hypothesis that interactions between the cell membrane and extracellular ice result in IIF. Raman spectromicroscopy provides a powerful tool for observing IIF and understanding its role in cell death during freezing, and enables the development, to our knowledge, of new and improved cell preservation protocols.

Improved Post-Thaw Function and Epigenetic Changes in Mesenchymal Stromal Cells Cryopreserved Using Multicomponent Osmolyte Solutions

Current methods for freezing mesenchymal stromal cells (MSCs) result in poor post-thaw function, which limits the clinical utility of these cells. This investigation develops a novel approach to preserve MSCs using combinations of sugars, sugar alcohols, and small-molecule additives. MSCs frozen using these solutions exhibit improved post-thaw attachment and a more normal alignment of the actin cytoskeleton compared to cells exposed to dimethylsulfoxide (DMSO). Osteogenic and chondrogenic differentiation assays show that cells retain their mesenchymal lineage properties. Genomic analysis indicates that the different freezing media evaluated have different effects on the levels of DNA hydroxymethylation, which are a principal epigenetic mark and a key step in the demethylation of CpG doublets. RNA sequencing and quantitative real time-polymerase chain reaction validation demonstrate that transcripts for distinct classes of cytoprotective genes, as well as genes related to extracellular matrix structure and growth factor/receptor signaling are upregulated in experimental freezing solutions compared to DMSO. For example, the osmotic regulator galanin, the antiapoptotic marker B cell lymphoma 2, as well as the cell surface adhesion molecules CD106 (vascular cell adhesion molecule 1) and CD54 (intracellular adhesion molecule 1) are all elevated in DMSO-free solutions. These studies validate the concept that DMSO-free solutions improve post-thaw biological functions and are viable alternatives for freezing MSCs. These novel solutions promote expression of cytoprotective genes, modulate the CpG epigenome, and retain the differentiation ability of MSCs, suggesting that osmolyte-based freezing solutions may provide a new paradigm for therapeutic cell preservation.