Best practices for cryopreserving, thawing, recovering, and assessing cells

Mesenchymal stromal cells derived from various tissues: Biological, clinical and cryopreservation aspects: Update from 2015 review

Mesenchymal stromal cells (MSCs) have become one of the most investigated and applied cells for cellular therapy and regenerative medicine. In this update of our review published in 2015, we show that studies continue to abound regarding the characterization of MSCs to distinguish them from other similar cell types, the discovery of new tissue sources of MSCs, and the confirmation of their properties and functions that render them suitable as a therapeutic. Because cryopreservation is widely recognized as the only technology that would enable the on-demand availability of MSCs, here we show that although the traditional method of cryopreserving cells by slow cooling in the presence of 10% dimethyl sulfoxide (Me2SO) continues to be used by many, several novel MSC cryopreservation approaches have emerged. As in our previous review, we conclude from these recent reports that viable and functional MSCs from diverse tissues can be recovered after cryopreservation using a variety of cryoprotectants, freezing protocols, storage temperatures, and periods of storage. We also show that for logistical reasons there are now more studies devoted to the cryopreservation of tissues from which MSCs are derived. A new topic included in this review covers the application in COVID-19 of MSCs arising from their immunomodulatory and antiviral properties. Due to the inherent heterogeneity in MSC populations from different sources there is still no standardized procedure for their isolation, identification, functional characterization, cryopreservation, and route of administration, and not likely to be a "one-size-fits-all" approach in their applications in cell-based therapy and regenerative medicine.

Cryopreservation-induced delayed injury and cell-type-specific responses during the cryopreservation of endothelial cell monolayers

The cryopreservation of endothelial cell monolayers is an important step that bridges the cryopreservation of cells in suspension to that of tissues. Previous studies have identified clear distinctions in freezing mechanisms between cells in suspension and in monolayers, as well as developed novel protocols for monolayer cryopreservation. Recently, our group has shown that human umbilical vein endothelial cell (HUVEC) and porcine corneal endothelial cell (PCEC) monolayers grown on Rinzl plastic substrate can be cryopreserved in 5% dimethyl sulfoxide, 6% hydroxyethyl starch, and 2% chondroitin sulfate, following a slow-cooling protocol (-1 °C/min) with rapid plunge into liquid nitrogen from -40 °C. However, membrane integrity assessments were done immediately post thaw, which may result in an overestimation of cell viability due to possible delayed injury responses. Here, we show that for the optimal protocol condition of plunge at the -40 °C interrupt temperature, HUVEC and PCEC monolayers exhibited no significant immediate post-thaw injuries nor delayed injury responses during the 24-h post-thaw overnight culture period. HUVEC monolayers experienced no significant impact to their natural growth rate during the post-thaw culture, while PCEC monolayers experienced significantly higher growth than the unfrozen controls. The difference in the low-temperature responses between HUVEC and PCEC monolayers was further shown under high temperature plunge conditions. At these suboptimal plunge temperatures, HUVEC monolayers exhibited moderate immediate membrane injury but a pronounced delayed injury response during the 24-h post-thaw culture, while PCEC monolayers showed significant immediate membrane injury but no additional delayed injury response during the same period. Therefore, we provide further validation of our group's previously designed endothelial monolayer cryopreservation protocol for HUVEC and PCEC monolayers, and we identify several cell-type-specific responses to the freezing process.

CellShip: An Ambient Temperature Transport and Short-Term Storage Medium for Mammalian Cell Cultures

Cell culture is a critical platform for numerous research and industrial processes. However, methods for transporting cells are largely limited to cryopreservation, which is logistically challenging, requires the use of potentially cytotoxic cryopreservatives, and can result in poor cell recovery. Development of a transport media that can be used at ambient temperatures would alleviate these issues. In this study, we describe a novel transportation medium for mammalian cells. Five commonly used cell lines, (HEK293, CHO, HepG2, K562, and Jurkat) were successfully shipped and stored for a minimum of 72 hours and up to 96 hours at ambient temperature, after which, cells were recovered into standard culture conditions. Viability (%) and cell numbers, were examined, before, following the transport/storage period and following the recovery period. In all experiments, cell numbers returned to pretransport/storage concentration within 24-48 hours recovery. Imaging data indicated that HepG2 cells were fully adherent and had established typical growth morphology following 48 hours recovery, which was not seen in cells recovered from cryopreservation. Following recovery, Jurkat cells that had been subjected to a 96 hours transport/storage period, demonstrated a 1.93-fold increase compared with the starting cell number with >95% cell viability. We conclude that CellShip® may represent a viable method for the transportation of mammalian cells for multiple downstream applications in the Life Sciences research sector.

Relevance of controlled cooling and freezing phases in T-cell cryopreservation

When cells are cryopreserved, they go through a freezing process with several distinct phases (i.e., cooling until nucleation, ice nucleation, ice crystal growth and cooling to a final temperature). Conventional cell freezing approaches often employ a single cooling rate to describe and optimize the entire freezing process, which neglects its complexity and does not provide insight into the effects of the different freezing phases. The aim of this work was to elucidate the impact of each freezing phase by varying different process parameters per phase. Hereto, spin freezing was used to freeze Jurkat T cells in either a Me2SO-based or Me2SO-free formulation. The cooling rates before ice nucleation and after total ice crystallization impacted cell viability, resulting in viability ranging from 26.7% to 52.8% for the Me2SO-free formulation, and 22.5%-42.6% for the Me2SO-based formulation. Interestingly, the degree of supercooling upon nucleation did not exhibit a significant effect on cell viability in this work. However, the rate of ice crystal formation emerged as a crucial factor, with viability ranging from 2.4% to 53.2% for the Me2SO-free formulation, and 0.3%-53.2% for the Me2SO-based formulation, depending on the freezing rate. A morphological study of the cells post-cryopreservation was performed using confocal microscopy, and it was found that cytoskeleton integrity and cell volume were impacted, depending on the formulation-process parameter combination. These findings underscore the importance of scrutinizing all cooling and freezing phases, as each phase impacted post-thaw viability in a distinct way, depending of the specific formulation used.

Pros and Cons of Cryopreserving Allogeneic Stem Cell Products

The COVID-19 pandemic has precipitously changed the practice of transplanting fresh allografts. The safety measures adopted during the pandemic prompted the near-universal graft cryopreservation. However, the influence of cryopreserving allogeneic grafts on long-term transplant outcomes has emerged only in the most recent literature. In this review, the basic principles of cell cryopreservation are revised and the effects of cryopreservation on the different graft components are carefully reexamined. Finally, a literature revision on studies comparing transplant outcomes in patients receiving cryopreserved and fresh grafts is illustrated.

Investigating the cryoprotective efficacy of fructans in mammalian cell systems via a structure-functional perspective

Fructans have long been known with their role in protecting organisms against various stress factors due to their ability to induce controlled dehydration and support membrane stability. Considering the vital importance of such features in cryo-technologies, this study aimed to explore the cryoprotective efficacy of fructans in mammalian cell systems where structurally different fructan polymers were examined on in vitro cell models derived from organs such as the liver, frequently used in transplantation, osteoblast, and cord cells, commonly employed in cell banking, as well as human seminal fluids that are of vital importance in assisted reproductive technology. To gain insights into the fructan/membrane interplay, structural differences were linked to rheological properties as well as to lipid membrane interactions where both fluorescein leakage from unilamellar liposomes and membrane integrity of osteoblast cells were monitored. High survival rates obtained with human endothelial, osteoblast and liver cells for up to two months clearly showed that fructans could be considered as effective non-permeating cryoprotectants, especially for extended periods of cryopreservation. In trials with human seminal fluid, short chained levan in combination with human serum albumin and glycerol proved very effective in preserving semen samples across multiple patients without any morphological abnormalities.

Human Natural Killer Cells Cryopreserved without DMSO Sustain Robust Effector Responses

Natural killer (NK) cell-based immunotherapy has benefitted from the multiple strengths that NK cells offer in adoptive transfer settings, not the least of which is their safety and potential for allogeneic use. Such use, however, necessitates the cryopreservation of NK cell-based therapy products to support logistical efforts in deploying these cells in different locations, decentralized from the point of collection or manufacturing. DMSO, the most commonly used cryoprotective agent (CPA), has been effective in protecting immune cells during freezing and thawing, but its ability to induce molecular and genetic changes to immune cells as well as its toxicity has stimulated interest in alternative CPAs. However, replacing DMSO's ability to act intracellularly has been difficult, and the sensitivity of human peripheral blood-derived NK cells to freezing and thawing-induced damage has meant that investigations into the potential of replacing DMSO are lacking. As a first step toward establishing the feasibility of cryopreserving human NK cells with CPAs' alternative to DMSO, we investigate the potential of using noncell-penetrating and cell-penetrating CPAs to recover NK cells post-thaw without DMSO. Here, we find that cryoprotection using cell-penetrating CPAs can retain the viability of human peripheral blood-derived NK cells to a comparable degree to DMSO. In addition, non-DMSO-cryopreserved human NK cells were as cytotoxic as those cryopreserved with DMSO and displayed a comparable level of surface markers of activation. In summary, we present the first example of the potential of developing non-DMSO CPA formulations that could be deployed in future cell therapy regimens.

Osmotic properties of T cells determined by flow imaging microscopy in comparison to electrical sensing zone analysis

To develop cryopreservation methods for cell-based medicinal products it is important to understand osmotic responses of cells upon immersion into solutions with cryoprotective agents (CPAs) and during freezing. The aim of this study was to assess the osmotic response of T cells by using flow imaging microscopy (FIM) as a novel cell-sizing technique, and to corroborate the findings with electrical impedance measurements conducted on a Coulter counter. Jurkat cells were used as a potential model cell line for primary T cells. Cell volume responses were used to derive important cell parameters for cryopreservation such as the osmotically inactive cell volume Vb and the membrane permeability towards water and various CPAs. Unlike Coulter counter measurement, FIM, combined with Trypan blue staining can differentiate between viable and dead cells, which yields a more accurate estimation of Vb. Membrane permeabilities to water, dimethyl sulfoxide (Me2SO) and glycerol were measured for Jurkat cells at different temperatures. The permeation of Me2SO into the cells was faster in comparison to glycerol. CPA permeation decreased with decreasing temperature following Arrhenius behavior. Moreover, membrane permeability to water decreased in the presence of CPAs. Vb of Jurkat cells was found to be 49% of the isotonic volume and comparable to that of primary T cells. FIM proved to be a valuable tool to determine the membrane permeability parameters of mammalian cells to water and cryoprotective agents, which in turn can be used to rationally design CPA loading procedures for cryopreservation.

Review of Rewarming Methods for Cryopreservation

Cryopreservation is the most effective technology for the long-term preservation of biological materials, including cells, tissues, and even organs in the future. The process of cooling and rewarming is essential to the successful preservation of biological materials. One of the critical problems in the development of cryopreservation is the optimization of effective rewarming technologies. This article reviewed rewarming methods, including traditional boundary rewarming commonly used for small-volume biological materials and other advanced techniques that could be potentially feasible for organ preservation in the future. The review focused on various rewarming technique principles, typical applications, and their possible limitations for cryopreservation of biological materials. This article introduced nanowarming methods in the progressing optimization and the possible difficulties. The trends of novel rewarming methods were discussed, and suggestions were given for future development.

Different Impacts of Cryopreservation in Endothelial and Epithelial Ovarian Cells

The aim of our laboratory-based study was to investigate the extent of delayed-onset cell death after cryopreservation in endothelial and epithelial cell lines of ovarian origin. We found differences in percentages of vital cells directly after warming and after cultivation for 48 to 72 h. A granulosa cell line of endothelial origin (KGN) and an epithelial cell line (OvCar-3) were used. In both DMSO-containing and DMSO-free protocols, significant differences in vitality rates between the different cell lines when using open and closed vitrification could be shown (DMSO-containing: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.001; DMSO-free: KGN open vs. OvCar open, p = 0.001; KGN closed vs. OvCar closed, p = 0.031). Furthermore, there was a marked difference in the percentage of vital cells immediately after warming and after cultivation for 48 to 72 h; whereas the KGN cell line showed a loss of cell viability of 41% using a DMSO-containing protocol, the OvCar-3 cell loss was only 11% after cultivation. Using a DMSO-free protocol, the percentages of late-onset cell death were 77% and 48% for KGN and OvCar-3 cells, respectively. Our data support the hypothesis that cryopreservation-induced damage is cell type and cryoprotective agent dependent.

Sound waves for solving the problem of recrystallization in cryopreservation

Organ biobanking is the pending subject of cryopreservation. Although the problem is multifaceted, advances in recent decades have largely related it to achieving rapid and uniform rewarming of cryopreserved samples. This is a physical challenge largely investigated in past in addition to cryoprotectant toxicity studies, which have also shown a great amount of advancement. This paper presents a proof-of-principle, based on the nematode Caenorhabditis elegans, of a technology capable of performing such a function: high intensity focused ultrasound. Thus, avoiding the problem of recrystallization, this worm, in its adult state, preserved at - [Formula: see text], has been systematically brought back to life after being heated with High Intensity Focused Ultrasound (HIFU) waves. The great advantage of this technology is that it is scalable; in addition, rewarming can be monitored in real time by MRI thermography and can be controlled by acoustic interferometry. We anticipate that our findings are the starting point for a possible approach to rewarming that can be used for cryopreservation of millimeter scale systems: either alone or in combination with other promising ways of heating, like nanowarming or dielectric heating, the present technology provides new ways of solving the physical aspects of the problem of recrystallization in cryopreservation, opening the door for the long-term storage of larger samples.

Method for manufacture and cryopreservation of cartilage microtissues

The financial viability of a cell and tissue-engineered therapy may depend on the compatibility of the therapy with mass production and cryopreservation. Herein, we developed a method for the mass production and cryopreservation of 3D cartilage microtissues. Cartilage microtissues were assembled from either 5000 human bone marrow-derived stromal cells (BMSC) or 5000 human articular chondrocytes (ACh) each using a customized microwell platform (the Microwell-mesh). Microtissues rapidly accumulate homogenous cartilage-like extracellular matrix (ECM), making them potentially useful building blocks for cartilage defect repair. Cartilage microtissues were cultured for 5 or 10 days and then cryopreserved in 90% serum plus 10% dimethylsulfoxide (DMSO) or commercial serum-free cryopreservation media. Cell viability was maximized during thawing by incremental dilution of serum to reduce oncotic shock, followed by washing and further culture in serum-free medium. When assessed with live/dead viability dyes, thawed microtissues demonstrated high viability but reduced immediate metabolic activity relative to unfrozen control microtissues. To further assess the functionality of the freeze-thawed microtissues, their capacity to amalgamate into a continuous tissue was assess over a 14 day culture. The amalgamation of microtissues cultured for 5 days was superior to those that had been cultured for 10 days. Critically, the capacity of cryopreserved microtissues to amalgamate into a continuous tissue in a subsequent 14-day culture was not compromised, suggesting that cryopreserved microtissues could amalgamate within a cartilage defect site. The quality ECM was superior when amalgamation was performed in a 2% O2 atmosphere than a 20% O2 atmosphere, suggesting that this process may benefit from the limited oxygen microenvironment within a joint. In summary, cryopreservation of cartilage microtissues is a viable option, and this manipulation can be performed without compromising tissue function.

Selective Targeting and Eradication of Various Human Non-Small Cell Lung Cancer Cell Lines Using Self-Assembled Aptamer-Decorated Nanoparticles

The leading cause of cancer mortality remains lung cancer (LC), of which non-small cell lung cancer (NSCLC) is the predominant type. Chemotherapy achieves only low response rates while inflicting serious untoward toxicity. Herein, we studied the binding and internalization of S15-aptamer (S15-APT)-decorated polyethylene glycol-polycaprolactone (PEG-PCL) nanoparticles (NPs) by various human NSCLC cell lines. All the NSCLC cell lines were targeted by S15-APT-decorated NPs. Confocal microscopy revealed variable levels of NP binding and uptake amongst these NSCLC cell lines, decreasing in the following order: Adenocarcinoma (AC) A549 cells > H2228 (AC) > H1299 (large cell carcinoma) > H522 (AC) > H1975 (AC). Flow cytometry analysis showed a consistent variation between these NSCLC cell lines in the internalization of S15-APT-decorated quantum dots. We obtained a temperature-dependent NP uptake, characteristic of active internalization. Furthermore, cytotoxicity assays with APT-NPs entrapping paclitaxel, revealed that A549 cells had the lowest IC50 value of 0.03 µM PTX (determined previously), whereas H2228, H1299, H522 and H1975 exhibited higher IC50 values of 0.38 µM, 0.92 µM, 2.31 µM and 2.59 µM, respectively (determined herein). Cytotoxicity was correlated with the binding and internalization of APT-NPs in the various NSCLC cells, suggesting variable expression of the putative S15 target receptor. These findings support the development of APT-targeted NPs in precision nanomedicine for individual NSCLC patient treatment.

Intracellular and Extracellular Antifreeze Protein Significantly Improves Mammalian Cell Cryopreservation

Cell cryopreservation is an essential part of the biotechnology, food, and health care industries. There is a need to develop more effective, less toxic cryoprotective agents (CPAs) and methods, especially for mammalian cells. We investigated the impact of an insect antifreeze protein from Anatolica polita (ApAFP752) on mammalian cell cryopreservation using the human embryonic kidney cell line HEK 293T. An enhanced green fluorescent protein (EGFP)-tagged antifreeze protein, EGFP-ApAFP752, was transfected into the cells and the GFP was used to determine the efficiency of transfection. AFP was assessed for its cryoprotective effects intra- and extracellularly and both simultaneously at different concentrations with and without dimethyl sulfoxide (DMSO) at different concentrations. Comparisons were made to DMSO or medium alone. Cells were cryopreserved at -196 °C for ≥4 weeks. Upon thawing, cellular viability was determined using trypan blue, cellular damage was assessed by lactate dehydrogenase (LDH) assay, and cellular metabolism was measured using a metabolic activity assay (MTS). The use of this AFP significantly improved cryopreserved cell survival when used with DMSO intracellularly. Extracellular AFP also significantly improved cell survival when included in the DMSO freezing medium. Intra- and extracellular AFP used together demonstrated the most significantly increased cryoprotection compared to DMSO alone. These findings present a potential method to improve the viability of cryopreserved mammalian cells.

Cryopreservation of Induced Pluripotent Stem Cell-Derived Dopaminergic Neurospheres for Clinical Application

BACKGROUND

Pluripotent stem cell (PSC)-derived dopaminergic (DA) neurons are an expected source of cell therapy for Parkinson's disease. The transplantation of cell aggregates or neurospheres, instead of a single cell suspension has several advantages, such as keeping the 3D structure of the donor cells and ease of handling. For this PSC-based therapy to become a widely available treatment, cryopreservation of the final product is critical in the manufacturing process. However, cryopreserving cell aggregates is more complicated than cryopreserving single cell suspensions. Previous studies showed poor survival of the DA neurons after the transplantation of cryopreserved fetal ventral-mesencephalic tissues.

OBJECTIVE

To achieve the cryopreservation of induced pluripotent stem cell (iPSC)-derived DA neurospheres toward clinical application.

METHODS

We cryopreserved iPSC-derived DA neurospheres in various clinically applicable cryopreservation media and freezing protocols and assessed viability and neurite extension. We evaluated the population and neuronal function of cryopreserved cells by the selected method in vitro. We also injected the cells into 6-hydroxydopamine (6-OHDA) lesioned rats, and assessed their survival, maturation and function in vivo.

RESULTS

The iPSC-derived DA neurospheres cryopreserved by Proton Freezer in the cryopreservation medium Bambanker hRM (BBK) showed favorable viability after thawing and had equivalent expression of DA-specific markers, dopamine secretion, and electrophysiological activity as fresh spheres. When transplanted into 6-OHDA-lesioned rats, the cryopreserved cells survived and differentiated into mature DA neurons, resulting in improved abnormal rotational behavior.

CONCLUSION

These results show that the combination of BBK and Proton Freezer is suitable for the cryopreservation of iPSC-derived DA neurospheres.

Efficacy of mesenchymal stem cell-delivery using perpendicular multi-needle injections to the skin: Evaluation of post-ejection cellular health and dermal delivery

AIM

Mesenchymal stem cell (MSC)-therapy is increasingly being evaluated in clinical trials. Dermal delivery is not only time consuming but also unreliable, potentially hampering the therapeutic result. Therefore, qualification of cell delivery protocols is essential. This study evaluated a clinically relevant automated multi-needle injection method for cutaneous MSC-therapy, allowing the skin to be readily and timely treated, by assessing both the cellular health post-ejection and dermal delivery.

METHODS

Following dispensation through the injector (31 G needles: 9- or 5-pin) the cellular health and potency (perceived- and long-term (12 h) viability, recovery, metabolism, adherence, proliferation and IDO1-expression) of adipose-derived stem cells (10-20-50 ×10⁶ cells/ml) were assessed in vitro in addition to dermal delivery of solution in human skin.

RESULTS

No significant detrimental effect on the perceived cell viability, recovery, metabolism, adherence or IDO1-expression of either cell concentration was observed. However, the overall long-term viability and proliferation decreased significantly regardless of cell concentration, nonetheless marginally. An injection depth above 1.0 mm resulted in all needles piercing the skin with dermal delivery from up to 89% needles and minimal reflux to the skin surface, and the results were confirmed by ultrasound and histology.

CONCLUSION

The automated injector is capable of delivering dermal cell-doses with an acceptable cell quality.

Development of a Vitrification Preservation Process for Bioengineered Epithelial Constructs

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

The preservation of synovial fluid using dimethyl sulfoxide

BACKGROUND

The Royal College of Pathologists of Australasia Quality Assurance Programs runs a Quality Assurance Program for the assessment of synovial fluid crystals. It provides aliquots of synovial fluid to various laboratories. The quality of specimens can deteriorate prior to being examined. We aimed to assess whether the addition of dimethyl sulfoxide (DMSO) to synovial fluid specimens helps maintain cellular morphology.

METHODS

Synovial fluid specimens were obtained from 15 patients. Each specimen was aliquoted into 24 samples, with half having DMSO added at a concentration of 10%. For each specimen, six samples containing DMSO and six samples not containing DMSO were stored at-80°C and room temperature. Samples from each group were examined at 1, 2, 3, 6, 7 and 8 weeks. Comparative Analysis: For each specimen, the final remaining aliquoted samples containing DMSO and not containing DMSO, which were stored at-80°C, were directly compared. Quantitative Analysis: A system for grading cellular morphology and assessing for artefacts and cellular clumping was applied by two independent assessors.

RESULTS

Comparative Analysis: A significant difference was found between samples containing DMSO and not containing DMSO which were stored at -80°C (p = .000), in favour of those containing DMSO. Quantitative Analysis: Regarding the combined findings of Assessors 1 and 2 and the grading of cellular morphology, a significant difference was found according to "groups" (p = .000), in favour of those containing DMSO and stored at-80°C.

CONCLUSIONS

DMSO contributes to the maintenance of cellular morphology in synovial fluid when stored in frozen conditions.

Assessment of the Impact of Post-Thaw Stress Pathway Modulation on Cell Recovery following Cryopreservation in a Hematopoietic Progenitor Cell Model

The development and use of complex cell-based products in clinical and discovery science continues to grow at an unprecedented pace. To this end, cryopreservation plays a critical role, serving as an enabling process, providing on-demand access to biological material, facilitating large scale production, storage, and distribution of living materials. Despite serving a critical role and substantial improvements over the last several decades, cryopreservation often remains a bottleneck impacting numerous areas including cell therapy, tissue engineering, and tissue banking. Studies have illustrated the impact and benefit of controlling cryopreservation-induced delayed-onset cell death (CIDOCD) through various “front end” strategies, such as specialized media, new cryoprotective agents, and molecular control during cryopreservation. While proving highly successful, a substantial level of cell death and loss of cell function remains associated with cryopreservation. Recently, we focused on developing technologies (RevitalICE™) designed to reduce the impact of CIDOCD through buffering the cell stress response during the post-thaw recovery phase in an effort to improve the recovery of previously cryopreserved samples. In this study, we investigated the impact of modulating apoptotic caspase activation, oxidative stress, unfolded protein response, and free radical damage in the initial 24 h post-thaw on overall cell survival. Human hematopoietic progenitor cells in vitro cryopreserved in both traditional extracellular-type and intracellular-type cryopreservation freeze media were utilized as a model cell system to assess impact on survival. Our findings demonstrated that through the modulation of several of these pathways, improvements in cell recovery were obtained, regardless of the freeze media and dimethyl sulfoxide concentration utilized. Specifically, through the use of oxidative stress inhibitors, an average increase of 20% in overall viability was observed. Furthermore, the results demonstrated that by using the post-thaw recovery reagent on samples cryopreserved in intracellular-type media (Unisol™), improvements in overall cell survival approaching 80% of non-frozen controls were attained. While improvements in overall survival were obtained, an assessment on the impact of specific cell subpopulations and functionality remains to be completed. While work remains, these results represent an important step forward in the development of improved cryopreservation processes for use in discovery science, and commercial and clinical settings.

OUP accepted manuscript

Advances in regenerative medicine manufacturing continue to be a priority for achieving the full commercial potential of important breakthrough therapies. Equally important will be the establishment of distribution chains that support the transport of live cells and engineered tissues and organs resulting from these advanced biomanufacturing processes. The importance of a well-managed distribution chain for products requiring specialized handling procedures was highlighted during the COVID-19 pandemic and serves as a reminder of the critical role of logistics and distribution in the success of breakthrough therapies. This perspective article will provide insight into current practices and future considerations for creating global distribution chains that facilitate the successful deployment of regenerative medicine therapies to the vast number of patients that would benefit from them worldwide.

Bovine Fetal Mesenchymal Stem Cells Obtained From Omental Adipose Tissue and Placenta Are More Resistant to Cryoprotectant Exposure Than Those From Bone Marrow

Recent studies have shown promise for the development of cellular therapies with mesenchymal stem cells (MSCs) in livestock species, specifically bovines, and cryopreservation is highly relevant for the advancement of these applications. The use of permeable and/or non-permeable cryoprotectant solutions is necessary to reduce cell damage during freezing and thawing, but these same compounds can also cause negative effects on MSCs and their therapeutic properties. Another important factor to consider is the tissue source of MSCs, since it is now known that MSCs from different tissues of the same individual do not behave the same way, so optimizing the type and concentration of cryoprotectants for each cell type is essential to achieve a large and healthy population of MSCs after cryopreservation. Furthermore, sources of MSCs that could provide great quantities, non-invasively and without ethical concerns, such as placental tissue, have great potential for the development of regenerative medicine in livestock species, and have not been thoroughly evaluated. The objective of this study was to compare the viability of bovine fetal MSCs extracted from bone marrow (BM), adipose tissue (AT), and placenta (PT), following their exposure (15 and 30 min) to several solutions of permeable (dimethyl sulfoxide and ethylene glycol) and non-permeable (trehalose) cryoprotectants. Viability assays were performed with Trypan Blue to assess post-exposure plasma membrane integrity. The apoptotic potential was estimated analyzing the mRNA abundance of BAX and BCL-2 genes using quantitative rt-PCR. Based on the results of the study, BM-MSC exhibited significantly lower viability compared to AT-MSC and PT-MSC, at both 15 and 30 min of exposure to cryoprotectant solutions. Nevertheless, viability did not differ among treatments for any of the cell types or timepoints studied. BCL-2 expression was higher in BM-MSC compared to AT-MSC, however, BAX/BCL-2 ratio did not differ. In conclusion, AT-MSC and PT-MSC were more resistant that BM-MSC, which showed higher sensitivity to experimental conditions, regardless of the exposure times, and cryoprotectant solutions used in the study.

Cell Viability Assessment Using Fluorescence Vital Dyes and Confocal Microscopy in Evaluating Freezing and Thawing Protocols Used in Cryopreservation of Allogeneic Venous Grafts

The authors present their contribution to the improvement of methods suitable for the detection of the freezing and thawing damage of cells of cryopreserved venous grafts used for lower limb revascularization procedures. They studied the post-thaw viability of cells of the wall of cryopreserved venous grafts (CVG) immediately after thawing and after 24 and 48 h culture at +37 °C in two groups of six CVG selected randomly for slow thawing in the refrigerator and rapid thawing in a water bath at +37 °C. The grafts were collected from multi-organ and tissue brain-dead donors, cryopreserved, and stored in a liquid nitrogen vapor phase for five years. The viability was assessed from tissue slices obtained by perpendicular and longitudinal cuts of the thawed graft samples using in situ staining with fluorescence vital dyes. The mean and median immediate post-thaw viability values above 70% were found in using both thawing protocols and both types of cutting. The statistically significant decline in viability after the 48-h culture was observed only when using the slow thawing protocol and perpendicular cutting. The possible explanation might be the “solution effect damage” during slow thawing, which caused a gentle reduction in the graft cellularity. The possible influence of this phenomenon on the immunogenicity of CVG should be the subject of further investigations.

Methods for Investigating Corneal Cell Interactions and Extracellular Vesicles In Vitro

Science and medicine have become increasingly "human-centric" over the years. A growing shift away from the use of animals in basic research has led to the development of sophisticated in vitro models of various tissues utilizing human-derived cells to study physiology and disease. The human cornea has likewise been modeled in vitro using primary cells derived from corneas obtained from cadavers or post-transplantation. By utilizing a cell's intrinsic ability to maintain its tissue phenotype in a pre-designed microenvironment containing the required growth factors, physiological temperature, and humidity, tissue-engineered corneas can be grown and maintained in culture for relatively long periods of time on the scale of weeks to months. Due to its transparency and avascularity, the cornea is an optimal tissue for studies of extracellular matrix and cell-cell interactions, toxicology and permeability of drugs, and underlying mechanisms of scarring and tissue regeneration. This paper describes methods for the cultivation of corneal keratocytes, fibroblasts, epithelial, and endothelial cells for in vitro applications. We also provide detailed, step-by-step protocols for assembling and culturing 3D constructs of the corneal stroma, epithelial- and endothelial-stromal co-cultures and isolation of extracellular vesicles. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Isolating and culturing human corneal keratocytes and fibroblasts Basic Protocol 2: Isolating and culturing human corneal epithelial cells Basic Protocol 3: Isolating and culturing human corneal endothelial cells Basic Protocol 4: 3D corneal stromal construct assembly Basic Protocol 5: 3D corneal epithelial-stromal construct assembly Basic Protocol 6: 3D corneal endothelial-stromal construct assembly Basic Protocol 7: Isolating extracellular vesicles from corneal cell conditioned medium Support Protocol: Cryopreserving human corneal fibroblasts, corneal epithelial cells, and corneal endothelial cells.

Type III antifreeze protein (AFP) improves the post-thaw quality and in vivo fertility of rooster spermatozoa

Antifreeze proteins (AFP) have the potential for improving sperm cryopreservation. We have applied Type III antifreeze protein (AFP3) on the cryopreservation of spermatozoa from broiler breeder roosters, aiming to enhance post-thawing quality and fertility. Semen was extended at 37°C in Lake's extender containing AFP3 at 0.01, 0.1, 1, 5, and 10 µg/mL (no AFP3 as control). Post-thawing sperm assessment included sperm motility (CASA), morphology, membrane functionality by hypoosmotic swelling test (HOST), lipoperoxidation as malondialdehyde (MDA) production, and sperm viability, early apoptosis (phosphatidylserine exposure as annexin V-positive staining in viable spermatozoa), and mitochondrial activity by flow cytometry. Fertility was assessed after artificial insemination (30 hens/treatment). Total and progressive motility, membrane functionality, and mitochondrial activity increased in 0.1 and 1 µg/mL AFP, compared to control and other concentrations, whereas apoptosis was significantly lower. VAP, VSL, and viability were significantly higher for 1 µg/mL AFP3 than with the other treatments except for 0.1 µg/mL (which was not always significantly different from the control or other concentrations), and with abnormal forms being significantly lower. The proportion of fertilized and hatched eggs was also higher for 1 µg/mL AFP3, with 0.1 µg/mL also showing significantly higher results than the control, and no differences with other concentrations). In conclusion, 1 µg/mL AFP3 could improve the post-thawing results of rooster spermatozoa frozen in Lake's extender. According to our results, concentrations between 1 and 0.1 µg/mL could be similarly efficient.

Forced degradation of cell-based medicinal products guided by flow imaging microscopy: Explorative studies with Jurkat cells

Cell-based medicinal products (CBMPs) offer ground-breaking opportunities to treat diseases with limited or no therapeutic options. However, the intrinsic complexity of CBMPs results in great challenges with respect to analytical characterization and stability assessment. In our study, we submitted Jurkat cell suspensions to forced degradation studies mimicking conditions to which CBMPs might be exposed from procurement of cells to administration of the product. Flow imaging microscopy assisted by machine learning was applied for determination of cell viability and concentration, and quantification of debris particles. Additionally, orthogonal cell characterization techniques were used. Thawing of cells at 5 °C was detrimental to cell viability and resulted in high numbers of debris particles, in contrast to thawing at 37 °C or 20 °C which resulted in better stability. After freezing of cell suspensions at -18 °C in presence of dimethyl sulfoxide (DMSO), a DMSO concentration of 2.5% (v/v) showed low stabilizing properties, whereas 5% or 10% was protective. Horizontal shaking of cell suspensions did not affect cell viability, but led to a reduction in cell concentration. Fetal bovine serum (10% [v/v]) protected the cells during shaking. In conclusion, forced degradation studies with application of orthogonal analytical characterization methods allow for CBMP stability assessment and formulation screening.

Promises and challenges of adoptive T-cell therapies for solid tumours

Cancer is a leading cause of death worldwide and, despite new targeted therapies and immunotherapies, many patients with advanced-stage- or high-risk cancers still die, owing to metastatic disease. Adoptive T-cell therapy, involving the autologous or allogeneic transplant of tumour-infiltrating lymphocytes or genetically modified T cells expressing novel T-cell receptors or chimeric antigen receptors, has shown promise in the treatment of cancer patients, leading to durable responses and, in some cases, cure. Technological advances in genomics, computational biology, immunology and cell manufacturing have brought the aspiration of individualised therapies for cancer patients closer to reality. This new era of cell-based individualised therapeutics challenges the traditional standards of therapeutic interventions and provides opportunities for a paradigm shift in our approach to cancer therapy. Invited speakers at a 2020 symposium discussed three areas-cancer genomics, cancer immunology and cell-therapy manufacturing-that are essential to the effective translation of T-cell therapies in the treatment of solid malignancies. Key advances have been made in understanding genetic intratumour heterogeneity, and strategies to accurately identify neoantigens, overcome T-cell exhaustion and circumvent tumour immunosuppression after cell-therapy infusion are being developed. Advances are being made in cell-manufacturing approaches that have the potential to establish cell-therapies as credible therapeutic options. T-cell therapies face many challenges but hold great promise for improving clinical outcomes for patients with solid tumours.

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

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

Intracellular delivery of trehalose renders mesenchymal stromal cells viable and immunomodulatory competent after cryopreservation

Trehalose is a nontoxic disaccharide and a promising cryoprotection agent for medically applicable cells. In this study, the efficiency of combining trehalose with reversible electroporation for cryopreservation of two types of human mesenchymal stromal cells was investigated: adipose-derived stromal cells, and umbilical-cord-derived stromal cells. Comparable results to standard dimethyl sulfoxide cryopreservation protocols were achieved, even without extensive electroporation parameters and protocol optimization. The presence of high extracellular trehalose resulted in comparable cell viabilities without and with electroporation. According to the determination of trehalose concentrations, 250 mM extracellular trehalose resulting in, 20 mM to 50 mM intracellular trehalose were sufficient for successful cryopreservation of cells. With electroporation, higher (i.e. 50 mM to 90 mM) intracellular trehalose was achieved after cryopreservation, although cell survival was not improved significantly. To evaluate the impact of electroporation and cryopreservation on cells, stress and immune-activation-related gene expression were analyzed. Electroporation and/or cryopreservation resulted in increased SOD2 and HSPA1A expression. Despite the increased stress response, the high up-regulation by mesenchymal stromal cells of immunomodulatory genes in the inflammatory environment was not affected. Highest expression was seen for the IDO1 and TSG6 genes. In conclusion, cryopreservation of mesenchymal stromal cells in trehalose results in comparable characteristics to their cryopreservation using dimethyl sulfoxide.

Cryopreserved Spontaneous Spheroids from Compact Bone-Derived Mesenchymal Stromal Cells for Bone Tissue Engineering

Spontaneously formed spheroids from mouse compact bone-derived mesenchymal stromal cells (CB-MSCs) possess enhanced stemness and superior plasticity. In this study, the effect of cryopreservation on viability, stemness, and osteogenic differentiation capability of spontaneous CB-MSC spheroids were investigated. CB-MSCs were isolated from mouse femur and tibia. Spheroids were cryopreserved with various concentrations of dimethyl sulfoxide (DMSO). After thawing, the number of living and dead cells was measured. The expression levels of stem cell markers and osteogenic marker genes were analyzed. The cryopreserved and noncryopreserved spheroids were transplanted in mice with a beta-tricalcium phosphate as a scaffold to evaluate the in vivo bone-forming capability. The percentage of living cells was highest when 5% DMSO was used as a cryoprotectant, confirmed by the number of dead cells. The expression of stem cell marker genes and osteogenic differentiation capability were maintained after cryopreservation with 5% DMSO. The cryopreserved spontaneous CB-MSC spheroids showed remarkable new bone formation in vivo, identical to that of the noncryopreserved spheroids even without osteogenic induction. The cryopreserved spontaneous CB-MSC spheroids retained stemness and osteogenic differentiation capability and highlight the utility of spontaneous CB-MSC spheroids as ready-to-use tissue-engineered products for bone tissue engineering.

Towards a method for cryopreservation of mosquito vectors of human pathogens

Mosquito-borne diseases are responsible for millions of human deaths every year, posing a massive burden on global public health. Mosquitoes transmit a variety of bacteria, parasites and viruses. Mosquito control efforts such as insecticide spraying can reduce mosquito populations, but they must be sustained in order to have long term impacts, can result in the evolution of insecticide resistance, are costly, and can have adverse human and environmental effects. Technological advances have allowed genetic manipulation of mosquitoes, including generation of those that are still susceptible to insecticides, which has greatly increased the number of mosquito strains and lines available to the scientific research community. This generates an associated challenge, because rearing and maintaining unique mosquito lines requires time, money and facilities, and long-term maintenance can lead to adaptation to specific laboratory conditions, resulting in mosquito lines that are distinct from their wild-type counterparts. Additionally, continuous rearing of transgenic lines can lead to loss of genetic markers, genes and/or phenotypes. Cryopreservation of valuable mosquito lines could help circumvent these limitations and allow researchers to reduce the cost of rearing multiple lines simultaneously, maintain low passage number transgenic mosquitoes, and bank lines not currently being used. Additionally, mosquito cryopreservation could allow researchers to access the same mosquito lines, limiting the impact of unique laboratory or field conditions. Successful cryopreservation of mosquitoes would expand the field of mosquito research and could ultimately lead to advances that would reduce the burden of mosquito-borne diseases, possibly through rear-and-release strategies to overcome mosquito insecticide resistance. Cryopreservation techniques have been developed for some insect groups, including but not limited to fruit flies, silkworms and other moth species, and honeybees. Recent advances within the cryopreservation field, along with success with other insects suggest that cryopreservation of mosquitoes may be a feasible method for preserving valuable scientific and public health resources. In this review, we will provide an overview of basic mosquito biology, the current state of and advances within insect cryopreservation, and a proposed approach toward cryopreservation of Anopheles stephensi mosquitoes.

Freezing Technology: Control of Freezing, Thawing, and Ice Nucleation

From early dry-ice-based freezers and passive coolers, cryopreservation devices have come a long way. With increasing interest in the field of cryobiology from new scientific applications, the importance of reliable, traceable, and reproducible cold chain devices is sure to increase, ensuring more precise cryopreservation and enabling better post-thaw outcomes, both for the user and for biological samples. As with any cryopreservation process, it is important to optimize each part of the cold chain for each lab's biological samples, cryocontainers used, and logistical restraints. In this chapter we describe how freezing technology can be used for cryopreservation of cells.

Logistics of an advanced therapy medicinal product during COVID-19 pandemic in Italy: successful delivery of mesenchymal stromal cells in dry ice

Background

During the coronavirus disease-2019 (COVID-19) pandemic, Italian hospitals faced the most daunting challenges of their recent history, and only essential therapeutic interventions were feasible. From March to April 2020, the Laboratory of Advanced Cellular Therapies (Vicenza, Italy) received requests to treat a patient with severe COVID-19 and a patient with acute graft-versus-host disease with umbilical cord-derived mesenchymal stromal cells (UC-MSCs). Access to clinics was restricted due to the risk of contagion. Transport of UC-MSCs in liquid nitrogen was unmanageable, leaving shipment in dry ice as the only option.

Methods

We assessed effects of the transition from liquid nitrogen to dry ice on cell viability; apoptosis; phenotype; proliferation; immunomodulation; and clonogenesis; and validated dry ice-based transport of UC-MSCs to clinics.

Results

Our results showed no differences in cell functionality related to the two storage conditions, and demonstrated the preservation of immunomodulatory and clonogenic potentials in dry ice. UC-MSCs were successfully delivered to points-of-care, enabling favourable clinical outcomes.

Conclusions

This experience underscores the flexibility of a public cell factory in its adaptation of the logistics of an advanced therapy medicinal product during a public health crisis. Alternative supply chains should be evaluated for other cell products to guarantee delivery during catastrophes.

Cryopreservation as a Key Element in the Successful Delivery of Cell-Based Therapies-A Review

Cryopreservation is a key enabling technology in regenerative medicine that provides stable and secure extended cell storage for primary tissue isolates and constructs and prepared cell preparations. The essential detail of the process as it can be applied to cell-based therapies is set out in this review, covering tissue and cell isolation, cryoprotection, cooling and freezing, frozen storage and transport, thawing, and recovery. The aim is to provide clinical scientists with an overview of the benefits and difficulties associated with cryopreservation to assist them with problem resolution in their routine work, or to enable them to consider future involvement in cryopreservative procedures. It is also intended to facilitate networking between clinicians and cryo-researchers to review difficulties and problems to advance protocol optimization and innovative design.

Analyses of human granulosa cell vitality by fluorescence activated cell sorting after rapid cooling

In reproductive medicine, the technique of rapid cooling becomes increasingly important for the preservation of tissue and cells. In order to protect the cells, incubation in different cryopreservation solutions is essential. The speed of the cooling process also makes a pivotal contribution to the success of this method. Using Flourescence Activated Cell Sorting (FACS), we investigated the impact of an open rapid and a closed rapid cooling technique on the vitality of human granulosa cells. Furthermore, we examined effects of the different solutions used for rapid cooling and warming before and after rapid cooling. We found a significant lower proportion of vital cells after rapid cooling compared to untreated controls independently of the technique and the tube size. However, we did not find any significant differences between open and closed rapid cooling. In both, a lower proportion of vital granulosa cells were found after incubation in rapid cooling solution only compared to warming solution only. Our results lend support to the conclusion that the difference of cooling-speed between open and closed rapid cooling is, in our settings, not crucial for the success of the procedure and that cryoprotective agents in the rapid cooling solutions have a higher potential to cause severe cell damage than agents used for warming.

Formulation of Cell-Based Medicinal Products: A Question of Life or Death?

The formulation of cell-based medicinal products (CBMPs) poses major challenges because of their complexity, heterogeneity, interaction with their environment (e.g., the formulation buffer, interfaces), and susceptibility to degradation. These challenges can be quality, safety, and efficacy related. In this commentary we discuss the current status in formulation strategies of off-the-shelf and non-off-the-shelf (patient-specific) CBMPs and highlight advantages and disadvantages of each strategy. Analytical tools for the characterization and stability assessment of CBMP formulations are addressed as well. Finally, we discuss unmet needs and make some recommendations regarding the formulation of CBMPs.

How does temperature play a role in the storage of extracellular vesicles?

Extracellular vesicles (EVs) contain specific proteins, lipids, and nucleic acids that can be passed to other cells as signal molecules to alter their function. However, there are many problems and challenges in the conversion and clinical application of EVs. Storage and protection of EVs is one of the issues that need further research. To adapt to potential clinical applications, this type of problem must be solved. This review summarizes the storage practices of EVs in recent years, and explains the impact of temperature on the quality and stability of EVs during storage based on current research, and explains the potential mechanisms involved in this effect as much as possible.

Improving CAR T cell therapy by optimizing critical quality attributes

Whether as a cure or bridge to transplant, chimeric antigen receptor (CAR)-T cell therapies have shown dramatic outcomes for the treatment of hematologic malignancies, and particularly relapsed/refractory B cell leukemia and lymphoma. However, these therapies are not effective for all patients, and are not without toxicities. The challenge now is to optimize these products and their manufacture. The manufacturing process is complex and subject to numerous variabilities at each step. These variabilities can affect the critical quality attributes of the final product, and this can ultimately impact clinical outcomes. This review will focus on optimizing the manufacturing variables that can impact the safety, purity, potency, consistency and durability of CAR-T cells.

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.