High concentration of synthetic serum, stepwise equilibration and slow cooling as an efficient technique for large-scale cryopreservation of human embryonic stem cells

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

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

Zooming in on Cryopreservation of hiPSCs and Neural Derivatives: A Dual-Center Study Using Adherent Vitrification

Human induced pluripotent stem cells (hiPSCs) are an important tool for research and regenerative medicine, but their efficient cryopreservation remains a major challenge. The current gold standard is slow‐rate freezing of dissociated colonies in suspension, but low recovery rates limit immediate post‐thawing applicability. We tested whether ultrafast cooling by adherent vitrification improves post‐thawing survival in a selection of hiPSCs and small molecule neural precursor cells (smNPCs) from Parkinson's disease and controls. In a dual‐center study, we compared the results by immunocytochemistry (ICC), fluorescence‐activated cell sorting analysis, and RNA‐sequencing (RNA‐seq). Adherent vitrification was achieved in the so‐called TWIST substrate, a device combining cultivation, vitrification, storage, and post‐thawing cultivation. Adherent vitrification resulted in preserved confluency and significantly higher cell numbers, and viability at day 1 after thawing, while results were not significantly different at day 4 after thawing. RNA‐seq and ICC of hiPSCs revealed no change in gene expression and pluripotency markers, indicating that physical damage of slow‐rate freezing disrupts cellular membranes. Scanning electron microscopy showed preserved colony integrity by adherent vitrification. Experiments using smNPCs demonstrated that adherent vitrification is also applicable to neural derivatives of hiPSCs. Our data suggest that, compared to the state‐of‐the‐art slow‐rate freezing in suspension, adherent vitrification is an improved cryopreservation technique for hiPSCs and derivatives. stem cells translational medicine2019;8:247&259

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.

Fetal bovine serum-free cryopreservation methods for clinical banking of human adipose-derived stem cells

The use of fetal bovine serum (FBS) as a cryopreservation supplement is not suitable for the banking of mesenchymal stem cells (MSCs) due to the risk of transmission of disease as well as xenogeneic immune reactions in the transplanted host. Here, we investigated if human serum albumin (HSA), human serum (HS), or knockout serum replacement (KSR) can replace FBS for the cryopreservation of MSCs. In addition, we examined the characteristics of MSCs after multiple rounds of cryopreservation. Human adipose-derived stem cells (ASCs) cryopreserved with three FBS replacements, 9% HSA, 90% HS, or 90% KSR, in combination with 10% dimethyl sulfoxide (Me₂SO) maintained stem cell properties including growth, immunophenotypes, gene expression patterns, and the potential to differentiate into adipogenic, osteogenic, and chondrogenic lineages, similar to ASCs frozen with FBS. Moreover, the immunophenotype, gene expression, and differentiation capabilities of ASCs were not altered by up to four freeze-thaw cycles. However, the performance of three or four freeze-thaw cycles significantly reduced the proliferation ability of ASCs, as indicated by the longer population doubling time and reduced colony-forming unit-fibroblast frequency. Together, our results suggest that HSA, HS, or KSR can replace FBS for the cryopreservation of ASCs, without altering their stemness, and should be processed with no more than two freeze-thaw cycles for clinical approaches.

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

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

Cryopreservation: Vitrification and Controlled Rate Cooling

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

Efficient cryopreservation of human pluripotent stem cells by surface-based vitrification

Efficient cryopreservation of human stem cells is crucial for guaranteeing a permanent supply of high-quality cell material for drug discovery or regenerative medicine. Conventionally used protocols usually employing slow freezing rates, however, result in low recovery rates for human pluripotent stem cells due to their complex colony structure. In this chapter, a surface-based vitrification protocol for pluripotent stem cells is presented based on a procedure for human embryonic stem cells developed by Beier et al. (Cryobiology 63:175-185, 2011). This simple and highly efficient cryopreservation method allows cryopreservation of large numbers of ready-to-use adherent cells that maintain pluripotency.

Human embryonic stem cells: derivation, maintenance and cryopreservation

Human embryonic stem cells (hESCs) are the most powerful candidate for the treatment of incurable diseases through the replacement of damaged cells and/or tissues in patients, although there are some obstacles to overcome for the clinical application of hESCs such as the assurance of guided differentiation and control of the immune response following cell therapy or tissue grafting. To obtain genetically stable hESCs and use them clinically, it is important to develop appropriate culture conditions. Additionally, the establishment of a hESC bank with a large number of hESC lines will be required for their clinical application because each hESC line is directed to have a different differentiation ability and immune characteristics such as HLA type. In this review, we describe the derivation and culture conditions of hESCs based on recent advances. Then, we will introduce several cryopreservation methods for hESCs, which is important for the development of cell bank.

Bioprocessing of cryopreservation for large-scale banking of human pluripotent stem cells

Human pluripotent stem cell (hPSC)-derived cell therapy requires production of therapeutic cells in large quantity, which starts from thawing the cryopreserved cells from a working cell bank or a master cell bank. An optimal cryopreservation and thaw process determines the efficiency of hPSC expansion and plays a significant role in the subsequent lineage-specific differentiation. However, cryopreservation in hPSC bioprocessing has been a challenge due to the unique growth requirements of hPSC, the sensitivity to cryoinjury, and the unscalable cryopreservation procedures commonly used in the laboratory. Tremendous progress has been made to identify the regulatory pathways regulating hPSC responses during cryopreservation and the development of small molecule interventions that effectively improves the efficiency of cryopreservation. The adaption of these methods in current good manufacturing practices (cGMP)-compliant cryopreservation processes not only improves cell survival, but also their therapeutic potency. This review summarizes the advances in these areas and discusses the technical requirements in the development of cGMP-compliant hPSC cryopreservation process.

Xeno-free plant-derived hydrolysate-based freezing of human embryonic stem cells

Human embryonic stem cells (hESCs) are one of the most interesting cell types for tissue engineering and cell therapy. The large-scale banking of hESCs for research and future clinical application requires economic, defined, and xeno-free cryopreservation protocols. In this study, the possibility to substitute knockout serum replacement (KO-SR) in the cryopreservation process with vegetal and synthetic hydrolysates was investigated. To our knowledge, the use of hydrolysates in hESC cryopreservation has not been yet explored. Initially, 3 different hydrolysates (Ultrapep Soy, Hypep 4601 and EX-CELL(®) CD Hydrolysate Fusion) were tested in the cryopreservation solution. A concentration of 8 mg/mL EX-CELL CD Hydrolysate Fusion in the cryopreservation solution leads to the highest recovery ratio; thus, this solution was selected for additional cryopreservation experiments. To ensure reproducibility of the results, 3 hESC lines (HS181, H9, and BG01) were used. The hESCs were collected prefreezing by application of collagenase IV and cell dissociation solution. Experiments showed that it was feasible to substitute the KO-SR in both the cryopreservation solution as the thawing solution. The obtained recovery ratios were comparable to those obtained with KO-SR (no statistical significant difference; Student's t-test, P<0.05). Further optimization protocols showed a doubling of the obtained recovery ratio after addition of Rock-inhibitor Y-27632 post-thawing. The expansion profile and pluripotency analysis revealed no changes in normal hESC behavior. We conclude that the application of vegetal or synthetic hydrolysates is suitable for xeno-free hESC cryopreservation.

Proliferation and differentiation potential of cryopreserved human skin-derived precursors

OBJECTIVES

Skin-derived precursors are recognized to be a potentially autologous and accessible source of neural precursor cells for drug screening or cell-based treatments, in many neurological disorders. Thus, it is necessary to investigate appropriate methods for cryopreservation of such human skin-derived precursors (hSKPs). The aim of this study was to evaluate different cryopreservation techniques for retention of hSKPs to discover an optimized protocol.

MATERIALS AND METHODS

We cryopreserved hSKPs treated with 0%, 10%, 20%, 30% and 40% foetal bovine serum (FBS) and three concentrations of dimethylsulphoxide (DMSO) 5%, 10% and 15%, with two different storage periods in liquid nitrogen (2 days: short-term storage; and 2 months: long-term storage). Then, we assessed survival and proliferation levels of the cells after freeze-thaw processes, by viability measurement and colony-forming assay. For detecting hSKPs, we used immunocytochemistry and RT-PCR assessments.

RESULTS

Our findings indicated that hSKPs cryopreserved in 5% DMSO without FBS, had better survival and proliferation potentials compared to other working formulations. With various concentrations of cryoprotectants over different time periods, hSKPs retained their differentiation potentiality and were able to differentiate into neurons (NFM and βΙΙΙ tubulin-positive), glial cells (GFAP-positive) and smooth muscle cells (SMA-positive).

CONCLUSIONS

  Results revealed that in only 5% DMSO, hSKPs could be cryopreserved for long-term storage with considerable survival and proliferation levels, without losing multipotency.

An efficient, economical slow-freezing method for large-scale human embryonic stem cell banking

Human embryonic stem cells (hESCs) are one of the most interesting cell types for tissue engineering, cell therapy, basic scientific research, and drug screening. Fast advancement in these areas requires the availability of large amounts of safe and well-characterized hESCs from hESC banks. Therefore, optimized freezing protocols, allowing the cryopreservation of large amounts of hESC without direct contact with liquid nitrogen, need to be established. In this study, 6 different cryoprotector combinations [dimethylsulfoxide (DMSO), ethylene glycol, and hydroxyethylstarch (HES)] combined with 2 different application methods were screened with the VUB01 cell line, to establish a new slow-freezing protocol with high recovery rates and a good expansion capacity. Our best conditions were confirmed in 4 other hESC lines: H1, H9, 181, and UGent2. To our knowledge, this is the first time that HES is evaluated as a cryoprotector for hESCs. The use of 5% DMSO+5% HES combined with a new detachment protocol leads to efficient hESC cryopreservation. This protocol involves treating the hESC colonies with cell dissociation solution, a mild dissociation solution uncommonly used for hESC culture. A recovery ratio ranging from 45.5% to 168.2% was obtained, and these were significantly different from the other tested conditions (Student's t-test, P<0.05). The cryopreserved hESCs were morphologically comparable to control cells, exhibited a good expansion profile, were positive for pluripotent expression markers, and could still differentiate into the 3 germ layers. This new protocol allows efficient and economical hESC cryopreservation, ideal for hESC banking.

Cryopreservation of Human Stem Cells for Clinical Application: A Review

SUMMARY: Stem cells have been used in a clinical setting for many years. Haematopoietic stem cells have been used for the treatment of both haematological and non-haematological disease; while more recently mesenchymal stem cells derived from bone marrow have been the subject of both laboratory and early clinical studies. Whilst these cells show both multipotency and expansion potential, they nonetheless do not form stable cell lines in culture which is likely to limit the breadth of their application in the field of regenerative medicine. Human embryonic stem cells are pluripotent cells, capable of forming stable cell lines which retain the capacity to differentiate into cells from all three germ layers. This makes them of special significance in both regenerative medicine and toxicology. Induced pluripotent stem (iPS) cells may also provide a similar breadth of utility without some of the confounding ethical issues surrounding embryonic stem cells. An essential pre-requisite to the commercial and clinical application of stem cells are suitable cryopreservation protocols for long-term storage. Whilst effective methods for cryopreservation and storage have been developed for haematopoietic and mesenchymal stem cells, embryonic cells and iPS cells have proved more refractory. This paper reviews the current state of cryopreservation as it pertains to stem cells and in particular the embryonic and iPS cell.

Current technology for the derivation of pluripotent stem cell lines from human embryos

Technology for the derivation, propagation, and characterization of pluripotent stem cell lines from the human embryo has undergone considerable refinement and improvement since the first published description of human embryonic stem cells in 1998. In particular, there has been extensive effort to optimize protocols and develop defined culture systems with a view toward future clinical applications of embryonic stem cell-derived products. Here, we review the current status of methodology for human embryonic stem cell derivation and culture, and we highlight the challenges that remain for workers in the field.

Evaluation of 28 Human Embryonic Stem Cell Lines for Use as Unrelated Donors in Stem Cell Therapy: Implications of HLA and ABO Genotypes

For human embryonic stem cells (hESCs) to be used clinically, it is imperative that immune responses evoked by hESCs and their derivates after transplantation should be prevented. Human leukocyte antigens (HLA) and ABO blood group antigens are important histocompatibility factors in graft rejection. HLA matching between recipient and unrelated donors, in particular, is important in improving outcomes in hematopoietic cell transplantation (HCT). We have established and successfully maintained 29 hESC lines and analyzed the HLA and ABO genotypes of these lines. HLA-A, -B, -C and -DR (DRB1) genotyping was performed by polymerase chain reaction (PCR) sequence-based typing and ABO genotyping was carried out by PCR restriction fragment length polymorphism methods. To determine what proportion of the Korean population would be covered by these cell lines in organ transplantation, 27 cell lines with HLA-A, -B, and -DR data were evaluated for HCT (cord blood) donors and 28 cell lines with HLA-DR and ABO data were evaluated for solid organ (kidney) transplantation donors, and then compared the data with those from 6,740 donated cord bloods. When 2 HLA mismatches are allowed for HCT, as currently accepted for cord blood transplantation, it was estimated that about 16% and 25% of the possible recipients can find one or more donor cell lines with ≤2 mismatches at A, B, DRB1 allele level and at A, B antigen/DRB1 allele level, respectively. When HLA-DR antigen level matching and ABO compatibility was considered for solid organ (kidney) transplantation, it was estimated that about 29% and 96% of the possible recipients can find one or more ABO-compatible donor cell lines with 0 and 1 DR mismatches, respectively. We provided the first report on the HLA and ABO genotypes of hESC lines, and estimated the degree of HLA and ABO matching in organ transplantation for the Korean population.