Scalable expansion of human pluripotent stem cells in suspension culture. Nat Protoc. 2011;6:689-700. [PMID: 21527925 DOI: 10.1038/nprot.2011.318]

Chemically defined and xenogeneic-free differentiation of human pluripotent stem cells into definitive endoderm in 3D culture

In vitro differentiation of human pluripotent stem cells (hPSCs) into definitive endoderm (DE) represents a key step towards somatic cells of lung, liver and pancreas. For future clinical applications, mass production of differentiated cells at chemically defined conditions and free of xenogeneic substances is envisioned. In this study we adapted our previously published two-dimensional (2D) DE induction protocol to three-dimensional (3D) static suspension culture in the absence of the xenogeneic extracellular matrix Matrigel. Next, fetal calf serum and bovine serum albumin present in the standard medium were replaced by a custom-made and xeno-free B-27. This yielded in a chemically defined and xenogeneic-free 3D culture protocol for differentiation of hPSCs into DE at efficiencies similar to standard 2D conditions. This novel protocol successfully worked with different hPSC lines including hESCs and hiPSCs maintained in two different stem cell media prior to differentiation. DE cells obtained by our novel BSA-free 3D protocol could be further differentiated into PDX1- or NKX6.1-expressing pancreatic progenitor cells. Notably, upon DE differentiation, we also identified a CXCR4⁺/NCAM⁺/EpCAM^low cell population with reduced DE marker gene expression. These CXCR4⁺/NCAM⁺/EpCAM^low cells emerge as a result of Wnt/beta-catenin hyperactivation via elevated CHIR-99021 concentrations and likely represent misspecified DE.

Differentiation of retinal ganglion cells from induced pluripotent stem cells: a review

Glaucoma is a common optic neuropathy that is characterized by the progressive degeneration of axons and the loss of retinal ganglion cells (RGCs). Glaucoma is one of the leading causes of irreversible blindness worldwide. Current glaucoma treatments only slow the progression of RGCs loss. Induced pluripotent stem cells (iPSCs) are capable of differentiating into all three germ layer cell lineages. iPSCs can be patient-specific, making iPSC-derived RGCs a promising candidate for cell replacement. In this review, we focus on discussing the detailed approaches used to differentiate iPSCs into RGCs.

Human Pluripotent Stem Cells: Applications and Challenges for Regenerative Medicine and Disease Modeling

In recent years, human pluripotent stem (hPS) cells have started to emerge as a potential tool with application in fields such as regenerative medicine, disease modeling, and drug screening. In particular, the ability to differentiate human-induced pluripotent stem (hiPS) cells into different cell types and to mimic structures and functions of a specific target organ, resourcing to organoid technology, has introduced novel model systems for disease recapitulation while offering a powerful tool to provide a faster and reproducible approach in the process of drug discovery. All these technologies are expected to improve the overall quality of life of the humankind. Here, we highlight the main applications of hiPS cells and the main challenges associated with the translation of hPS cell derivatives into clinical settings and other biomedical applications, such as the costs of the process and the ability to mimic the complexity of the in vivo systems. Moreover, we focus on the bioprocessing approaches that can be applied towards the production of high numbers of cells as well as their efficient differentiation into the final product and further purification.

Concise Review: Towards the Clinical Translation of Induced Pluripotent Stem Cell-Derived Blood Cells-Ready for Take-Off

Since their discovery in 2006, induced pluripotent stem cells (iPSCs) have opened up a world of possibilities for regenerative medicine and novel cell‐based therapeutics. Now, over a decade later, robust reprogramming and expansion and differentiation protocols have been developed, and iPSC‐derived cells have been used in a wide variety of small and large animal models to treat many different diseases. Furthermore, the first iPSC derivatives are on their way into clinical trials. In this line, (i) GMP‐compliant generation, cultivation, and differentiation, (ii) preclinical efficacy and safety, as well as (iii) ethical and regulatory compliance of stem cell research represent important aspects that need to be evaluated for proper clinical translation of iPSCs and their derivatives. In this review article, we provide an overview of the current advances and challenges of the clinical translation of iPSC‐derived blood cells and highlight the most pressing problems that have to be overcome in the next years. stem cells translational medicine2019;8:332–339

Human Pluripotent Stem Cell Culture: Current Status, Challenges, and Advancement

Over the past two decades, human embryonic stem cells (hESCs) have gained attention due to their pluripotent and proliferative ability which enables production of almost all cell types in the human body in vitro and makes them an excellent tool to study human embryogenesis and disease, as well as for drug discovery and cell transplantation therapies. Discovery of human-induced pluripotent stem cells (hiPSCs) further expanded therapeutic applications of human pluripotent stem cells (PSCs). hPSCs provide a stable and unlimited original cell source for producing suitable cells and tissues for downstream applications. Therefore, engineering the environment in which these cells are grown, for stable and quality-controlled hPSC maintenance and production, is one of the key factors governing the success of these applications. hPSCs are maintained in a particular niche using specific cell culture components. Ideally, the culture should be free of xenobiotic components to render hPSCs suitable for therapeutic applications. Substantial efforts have been put to identify effective components, and develop culture conditions and protocols, for their large-scale expansion without compromising on quality. In this review, we discuss different media, their components and functions, including specific requirements to maintain the pluripotent and proliferative ability of hPSCs. Understanding the role of culture components would enable the development of appropriate conditions to promote large-scale, quality-controlled expansion of hPSCs thereby increasing their potential applications.

Role of cell-secreted extracellular matrix formation in aggregate formation and stability of human induced pluripotent stem cells in suspension culture

Clinical and industrial applications require large quantities of human induced pluripotent stem cells (hiPSCs); however, little is known regarding the mechanisms governing aggregate formation and stability in suspension culture. To address this, we determined differences in growth processes among hiPSC lines in suspension culture. Using an hiPSC aggregate suspension culture system, hiPSCs from different lines formed multicellular aggregates classified as large compact or small loose based on their size and morphology. Time-lapse observation of the growth processes of two different hiPSC lines revealed that the balance between cell division and the extent of subsequent cell death determined the final size and morphology of aggregates. Comparison of the cell survival and death of two hiPSC lines showed that the formation of small, loose aggregates was due to continued cell death during the exponential phase of growth, with apoptotic cells extruded from growing hiPSC aggregates by the concerted contraction of their neighbors. Western blot and immunofluorescent staining revealed that aggregate morphology and proliferative ability relied to a considerable extent upon secretion of the extracellular matrix (ECM). hiPSCs forming large compact and stable aggregates showed enhanced production of collagen type I in suspension culture at 120 h. Furthermore, these aggregates exhibited higher expression of E-cadherin and proliferation marker Ki-67 as compared with levels observed in small and loose aggregates at 120 h. These findings indicated that differences in both aggregate formation and stability in suspension culture among hiPSC lines were caused by differences in ECM secretion capacity.

Bioengineered Cardiac Tissue Based on Human Stem Cells for Clinical Application

Engineered cardiac tissue might enable novel therapeutic strategies for the human heart in a number of acquired and congenital diseases. With recent advances in stem cell technologies, namely the availability of pluripotent stem cells, the generation of potentially autologous tissue grafts has become a realistic option. Nevertheless, a number of limitations still have to be addressed before clinical application of engineered cardiac tissue based on human stem cells can be realized. We summarize current progress and pending challenges regarding the optimal cell source, cardiomyogenic lineage specification, purification, safety of genetic cell engineering, and genomic stability. Cardiac cells should be combined with clinical grade scaffold materials for generation of functional myocardial tissue in vitro. Scale-up to clinically relevant dimensions is mandatory, and tissue vascularization is most probably required both for preclinical in vivo testing in suitable large animal models and for clinical application. Graphical Abstract.

Scalable Cardiac Differentiation of Pluripotent Stem Cells Using Specific Growth Factors and Small Molecules

The envisioned routine application of human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) for therapies and industry-compliant screening approaches will require efficient and highly reproducible processes for the mass production of well-characterized CM batches.On their way toward beating CMs, hPSCs initially undergo an epithelial-to-mesenchymal transition into a primitive-streak (PS)-like population that later gives rise to all endodermal and mesodermal lineages, including cardiovascular progenies (CVPs). CVPs are multipotent and possess the capability to give rise to all major cell types of the heart, including CMs, endothelial cells, cardiac fibroblasts, and smooth muscle cells. This article provides an historical overview and describes the stepwise development of protocols that typically result in the appearance of beating CMs within 7-12 days of hPSC differentiation.We describe the development of directed and closely controlled cardiomyogenic differentiation, which now enables the induction of >90% CM purity without further lineage enrichment. Although secreted lineage specifiers (revealed from developmental biology) were initially used, we outline the advantages of chemical pathway modulators, as defined by more recent screening approaches. Subsequently, we discuss the use of defined culture media for upscaling the production of hPSC-CMs in controlled bioreactors and how this, in principle, unlimited source of human CMs can be used to progress heart regeneration and stimulate the drug discovery pipeline. Graphical Abstract.

A fully defined static suspension culture system for large-scale human embryonic stem cell production

Human embryonic stem cells (hESCs) play an important role in regenerative medicine due to their potential to differentiate into various functional cells. However, the conventional adherent culture system poses challenges to mass production of high-quality hESCs. Though scientists have made many attempts to establish a robust and economical hESC suspension culture system, there are existing limitations, including suboptimal passage methods and shear force caused by dynamic stirring. Here, we report on an efficient large-scale culture system, which enables long-term, GMP grade, single-cell inoculation, and serial expansion of hESCs with a yield of about 1.5 × 10⁹ cells per 1.5-L culture, while maintaining good pluripotency. The suspension culture system was enlarged gradually from a 100-mm dish to a 1.8-L culture bag with methylcellulose involvement to avoid sphere fusion. Under the optimal experimental protocol, this 3D system resolves current problems that limit mass production and clinical application of hESCs, and thus can be used in commercial-level hESC production for cell therapy and pharmaceutics screening in the future.

3D printing human induced pluripotent stem cells with novel hydroxypropyl chitin bioink: scalable expansion and uniform aggregation

Human induced pluripotent stem cells (hiPSCs) are more likely to successfully avoid the immunological rejection and ethical problems that are often encountered by human embryonic stem cells in various stem cell studies and applications. To transfer hiPSCs from the laboratory to clinical applications, researchers must obtain sufficient cell numbers. In this study, 3D cell printing was used as a novel method for iPSC scalable expansion. Hydroxypropyl chitin (HPCH), utilized as a new type of bioink, and a set of optimized printing parameters were shown to achieve high cell survival (>90%) after the printing process and high proliferation efficiency (∼32.3 folds) during subsequent 10 d culture. After the culture, high levels of pluripotency maintenance were recognized by both qualitative and quantitative detections. Compared with static suspension culture, hiPSC aggregates formed in 3D-printed constructs showed a higher uniformity in size. Using a novel dual-fluorescent labeling method, hiPSC aggregates in the constructs were found more inclined to form by in situ proliferation rather than multicellular aggregation. This study revealed unique advantages of non-ionic crosslinking bioink material HPCH, including high gel strength and rapid temperature response in hiPSC printing, and achieved primed state hiPSC printing for the first time. Features achieved in this study, such as high cell yield, high pluripotency maintenance and uniform aggregation provide good foundations for further hiPSC studies on 3D micro-tissue differentiation and drug screening.

Large-scale production of megakaryocytes in microcarrier-supported stirred suspension bioreactors

Megakaryocytes (MKs) are the precursors of platelets (PLTs) and may be used for PLT production in vivo or in vitro, as well as a source for PLT-derived growth factors. Induced pluripotent stem cells represent an unlimited cell source for the in vitro production of MKs. This study aimed at developing an effective, xeno-free and scalable system to produce high numbers of MKs. In particular, microcarrier beads-assisted stirred bioreactors were evaluated as a means of improving MK yields. This method resulted in the production of 18.7 × 10⁷ MKs per 50 ml medium. Laminin-coated microcarriers increased MK production per iPSC by up to 10-fold. MKs obtained in this system showed typical features of mature MKs and were able to produce PLTs in vitro and in vivo. To increase safety, MKs produced in the bioreactors were irradiated; a procedure that did not affect their capability to form proPLTs and PTLs after transfusion. In vitro generated MKs represent a promising alternative to donor PLTs and open the possibility for the development of innovative MK-based cell therapies.

Towards Multi-Organoid Systems for Drug Screening Applications

A low percentage of novel drug candidates succeed and reach the end of the drug discovery pipeline, mainly due to poor initial screening and assessment of the effects of the drug and its metabolites over various tissues in the human body. For that, emerging technologies involving the production of organoids from human pluripotent stem cells (hPSCs) and the use of organ-on-a-chip devices are showing great promise for developing a more reliable, rapid and cost-effective drug discovery process when compared with the current use of animal models. In particular, the possibility of virtually obtaining any type of cell within the human body, in combination with the ability to create patient-specific tissues using human induced pluripotent stem cells (hiPSCs), broadens the horizons in the fields of drug discovery and personalized medicine. In this review, we address the current progress and challenges related to the process of obtaining organoids from different cell lineages emerging from hPSCs, as well as how to create devices that will allow a precise examination of the in vitro effects generated by potential drugs in different organ systems.

Modulating cell state to enhance suspension expansion of human pluripotent stem cells

Efficient manufacturing is critical for the translation of cell-based therapies to clinical applications. To date, high-yield expansion of human pluripotent stem cells (hPSC) in suspension bioreactors has not been reported. Here, we present a strategy to shift suspension-grown hPSC to a high-yield state without compromising their ability to differentiate to all three germ layers. In this new state, hPSC expand to densities 5.7 ± 0.2-fold higher than conventional hPSC each passage in suspension bioreactors. High-density suspension cultures enable process intensification, cost reduction, and more efficient manufacturing. This work advances cell-state engineering as a valuable tool to overcome current challenges in therapeutic cell production and processing.

The development of cell-based therapies to replace missing or damaged tissues within the body or generate cells with a unique biological activity requires a reliable and accessible source of cells. Human pluripotent stem cells (hPSC) have emerged as a strong candidate cell source capable of extended propagation in vitro and differentiation to clinically relevant cell types. However, the application of hPSC in cell-based therapies requires overcoming yield limitations in large-scale hPSC manufacturing. We explored methods to convert hPSC to alternative states of pluripotency with advantageous bioprocessing properties, identifying a suspension-based small-molecule and cytokine combination that supports increased single-cell survival efficiency, faster growth rates, higher densities, and greater expansion than control hPSC cultures. ERK inhibition was found to be essential for conversion to this altered state, but once converted, ERK inhibition led to a loss of pluripotent phenotype in suspension. The resulting suspension medium formulation enabled hPSC suspension yields 5.7 ± 0.2-fold greater than conventional hPSC in 6 d, for at least five passages. Treated cells remained pluripotent, karyotypically normal, and capable of differentiating into all germ layers. Treated cells could also be integrated into directed differentiated strategies as demonstrated by the generation of pancreatic progenitors (NKX6.1+/PDX1+ cells). Enhanced suspension-yield hPSC displayed higher oxidative metabolism and altered expression of adhesion-related genes. The enhanced bioprocess properties of this alternative pluripotent state provide a strategy to overcome cell manufacturing limitations of hPSC.

Chemically controlled aggregation of pluripotent stem cells

Heterogeneity in pluripotent stem cell (PSC) aggregation leads to variability in mass transfer and signaling gradients between aggregates, which results in heterogeneous differentiation and therefore variability in product quality and yield. We have characterized a chemical‐based method to control aggregate size within a specific, tunable range with low heterogeneity, thereby reducing process variability in PSC expansion. This method enables controlled, scalable, stirred suspension‐based manufacturing of PSC cultures that are critical for the translation of regenerative medicine strategies to clinical products.

Induced Pluripotent Stem Cells for Cardiovascular Disease Modeling and Precision Medicine: A Scientific Statement From the American Heart Association

Induced pluripotent stem cells (iPSCs) offer an unprece-dented opportunity to study human physiology and disease at the cellular level. They also have the potential to be leveraged in the practice of precision medicine, for example, personalized drug testing. This statement comprehensively describes the provenance of iPSC lines, their use for cardiovascular disease modeling, their use for precision medicine, and strategies through which to promote their wider use for biomedical applications. Human iPSCs exhibit properties that render them uniquely qualified as model systems for studying human diseases: they are of human origin, which means they carry human genomes; they are pluripotent, which means that in principle, they can be differentiated into any of the human body's somatic cell types; and they are stem cells, which means they can be expanded from a single cell into millions or even billions of cell progeny. iPSCs offer the opportunity to study cells that are genetically matched to individual patients, and genome-editing tools allow introduction or correction of genetic variants. Initial progress has been made in using iPSCs to better understand cardiomyopathies, rhythm disorders, valvular and vascular disorders, and metabolic risk factors for ischemic heart disease. This promising work is still in its infancy. Similarly, iPSCs are only just starting to be used to identify the optimal medications to be used in patients from whom the cells were derived. This statement is intended to (1) summarize the state of the science with respect to the use of iPSCs for modeling of cardiovascular traits and disorders and for therapeutic screening; (2) identify opportunities and challenges in the use of iPSCs for disease modeling and precision medicine; and (3) outline strategies that will facilitate the use of iPSCs for biomedical applications. This statement is not intended to address the use of stem cells as regenerative therapy, such as transplantation into the body to treat ischemic heart disease or heart failure.

Therapeutic Application of Pluripotent Stem Cells: Challenges and Risks

Stem-cell-based therapies are considered to be promising and innovative but complex approaches. Induced pluripotent stem cells (iPSCs) combine the advantages of adult stem cells with the hitherto unique characteristics of embryonic stem cells (ESCs). Major progress has already been achieved with regard to reprogramming technology, but also regarding targeted genome editing and scalable expansion and differentiation of iPSCs and ESCs, in some cases yielding highly enriched preparations of well-defined cell lineages at clinically required dimensions. It is noteworthy, however, that for many applications critical requirements such as the targeted specification into distinct cellular subpopulations and a proper cell maturation remain to be achieved. Moreover, current hurdles such as low survival rates and insufficient functional integration of cellular transplants remain to be overcome. Nevertheless, PSC technologies obviously have come of age and matured to a stage where various clinical applications of PSC-based cellular therapies have been initiated and are conducted.

A novel three-dimensional tumorsphere culture system for the efficient and low-cost enrichment of cancer stem cells with natural polymers

Cancer stem cells (CSCs) are considered to serve a key role in tumor progression, recurrence and metastasis. Tumorsphere culture is the most important method for enriching CSCs and is widely used in basic research and drug screening. However, the traditional suspension cell culture system has several disadvantages, including low efficiency, high cost and difficult procedure, making it difficult to produce tumorspheres on a large scale. In the present study, two biomaterials, methylcellulose (MC) and gellan gum (GG), were used to construct a novel culture system based on the traditional system. Subsequently, the characteristics of the novel three-dimensional (3D) culture system were evaluated, the design scheme was optimized, and the morphological and biological features of the tumorspheres cultured in this 3D system were compared with the traditional system. The results revealed that the tumorspheres cultured in the novel 3D system presented a higher seeding density and improved morphology, while maintaining stem-like properties. This evidence suggests that a simple, efficient and low-cost culture system that produces tumorspheres on a large scale was successfully constructed, which can be widely used in various aspects of stem cell research.

Efficient Large-Scale 2D Culture System for Human Induced Pluripotent Stem Cells and Differentiated Cardiomyocytes

Cardiac regenerative therapies utilizing human induced pluripotent stem cells (hiPSCs) are hampered by ineffective large-scale culture. hiPSCs were cultured in multilayer culture plates (CPs) with active gas ventilation (AGV), resulting in stable proliferation and pluripotency. Seeding of 1 × 10⁶ hiPSCs per layer yielded 7.2 × 10⁸ hiPSCs in 4-layer CPs and 1.7 × 10⁹ hiPSCs in 10-layer CPs with pluripotency. hiPSCs were sequentially differentiated into cardiomyocytes (CMs) in a two-dimensional (2D) differentiation protocol. The efficiency of cardiac differentiation using 10-layer CPs with AGV was 66%–87%. Approximately 6.2–7.0 × 10⁸ cells (4-layer) and 1.5–2.8 × 10⁹ cells (10-layer) were obtained with AGV. After metabolic purification with glucose- and glutamine-depleted and lactate-supplemented media, a massive amount of purified CMs was prepared. Here, we present a scalable 2D culture system using multilayer CPs with AGV for hiPSC-derived CMs, which will facilitate clinical applications for severe heart failure in the near future.

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Efficient mass production of hiPSCs by multilayer culture plates with AGV

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Efficient mass production of hiPSC-CMs using a massive 2D culture system with AGV

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Mass production of pure hiPSC-CMs via metabolic selection

Microfluidic generation of egg-derived protein microcarriers for 3D cell culture and drug delivery

Microcarriers have a demonstrated value for biomedical applications, in particular for drug delivery and three-dimensional cell culture. Attempts to develop this technique tend to focus on the fabrication of functional microparticles by using convenient methods with innovative but accessible materials. Inspired by the process of boiling eggs in everyday life, which causes the solidification of egg proteins, we present a new microfluidic "cooking" approach for the generation of egg-derived microcarriers for cell culture and drug delivery. As the egg emulsion droplets are formed with exquisite precision during the microfluidic emulsification, the resultant egg microcarriers present highly monodisperse and uniform morphologies at the size range of hundred microns to one millimeter. Benefiting from the excellent biocompatibility of the egg protein components, the obtained microcarriers showed good performances of cell adherence and growth. In addition, after a freezing treatment, the egg microcarriers were shown to have interconnected porous structures throughout their whole sphere, could absorb and load different kinds of drugs or other active molecules, and work as microcarrier-based delivery systems. These features point to the potential value of the microfluidic egg microcarriers in biomedicine.

Clump-passaging-based efficient 3D culture of human pluripotent stem cells under chemically defined conditions

Large-scale production of human pluripotent stem cells (hPSCs) in an efficient and safe manner is crucial to the successful application of hPSCs in biomedical research and regenerative medicine. Three-dimensional culture methods for hPSCs have been extensively studied using single-cell passaging approaches; however, these techniques have been challenged by the induction of massive cell death and accumulation of genomic abnormalities. In this work, we developed and optimized a novel, simple clump-passaging method for in vitro hPSCs 3-dimensional (3D) culture that can be exploited for large-scale production. Fully grown hPSC spheroids were dissociated into smaller-sized spheroid clumps by simple treatment with enzyme-free dissociation buffer, and clumped hPSCs were inoculated and maintained for 3D suspension culture. Our clump-passaging method effectively increased the hPSCs survival rate after subculture and supported scalable hPSCs 3D expansion. We also tested and selected chemically defined media formulations that are suitable for 3D culture and commercially available. Overall, our clump-passaging and expansion method demonstrated high survival and expansion rates for hPSC spheroids compared with conventional methods and may also have the advantage of maintaining genomic stability.

Sensitivity of human pluripotent stem cells to insulin precipitation induced by peristaltic pump-based medium circulation: considerations on process development

Controlled large-scale production of human pluripotent stem cells (hPSCs) is indispensable for their envisioned clinical translation. Aiming at advanced process development in suspension culture, the sensitivity of hPSC media to continuous peristaltic pump-based circulation, a well-established technology extensively used in hydraulically-driven bioreactors, was investigated. Unexpectedly, conditioning of low protein media (i.e. E8 and TeSR-E8) in a peristaltic pump circuit induced severe viability loss of hPSCs cultured as aggregates in suspension. Optical, biochemical, and cytological analyses of the media revealed that the applied circulation mode resulted in the reduction of the growth hormone insulin by precipitation of micro-sized particles. Notably, in contrast to insulin depletion, individual withdrawal of other medium protein components (i.e. bFGF, TGFβ1 or transferrin) provoked minor reduction of hPSC viability, if any. Supplementation of the surfactant glycerol or the use of the insulin analogue Aspart did not overcome the issue of insulin precipitation. In contrast, the presence of bovine or human serum albumin (BSA or HSA, respectively) stabilized insulin rescuing its content, possibly by acting as molecular chaperone-like protein, ultimately supporting hPSC maintenance. This study highlights the potential and the requirement of media optimization for automated hPSC processing and has broad implications on media development and bioreactor-based technologies.

Size- and time-dependent growth properties of human induced pluripotent stem cells in the culture of single aggregate

Aggregate culture of human induced pluripotent stem cells (hiPSCs) is a promising method to obtain high number of cells for cell therapy applications. This study quantitatively evaluated the effects of initial cell number and culture time on the growth of hiPSCs in the culture of single aggregate. Small size aggregates ((1.1 ± 0.4) × 10¹-(2.8 ± 0.5) × 10¹ cells/aggregate) showed a lower growth rate in comparison to medium size aggregates ((8.8 ± 0.8) × 10¹-(6.8 ± 1.1) × 10² cells/aggregate) during early-stage of culture (24-72 h). However, when small size aggregates were cultured in conditioned medium, their growth rate increased significantly. On the other hand, large size aggregates ((1.1 ± 0.2) × 10³-(3.5 ± 1.1) × 10³ cells/aggregate) showed a lower growth rate and lower expression level of proliferation marker (ki-67) in the center region of aggregate in comparison to medium size aggregate during early-stage of culture. Medium size aggregates showed the highest growth rate during early-stage of culture. Furthermore, hiPSCs proliferation was dependent on culture time because the growth rate decreased significantly during late-stage of culture (72-120 h) at which point collagen type I accumulated on the periphery of aggregate, suggesting blockage of diffusive transport of nutrients, oxygen and metabolites into and out of the aggregates. Consideration of initial cell number and culture time are important to maintain balance between autocrine factors secretion and extracellular matrix accumulation on the aggregate periphery to achieve optimal growth of hiPSCs in the culture of single aggregate.

Cell fiber-based three-dimensional culture system for highly efficient expansion of human induced pluripotent stem cells

Human pluripotent stem cells are a potentially powerful cellular resource for application in regenerative medicine. Because such applications require large numbers of human pluripotent stem cell-derived cells, a scalable culture system of human pluripotent stem cell needs to be developed. Several suspension culture systems for human pluripotent stem cell expansion exist; however, it is difficult to control the thickness of cell aggregations in these systems, leading to increased cell death likely caused by limited diffusion of gases and nutrients into the aggregations. Here, we describe a scalable culture system using the cell fiber technology for the expansion of human induced pluripotent stem (iPS) cells. The cells were encapsulated and cultured within the core region of core-shell hydrogel microfibers, resulting in the formation of rod-shaped or fiber-shaped cell aggregations with sustained thickness and high viability. By encapsulating the cells with type I collagen, we demonstrated a long-term culture of the cells by serial passaging at a high expansion rate (14-fold in four days) while retaining its pluripotency. Therefore, our culture system could be used for large-scale expansion of human pluripotent stem cells for use in regenerative medicine.

Biomanufacturing of Therapeutic Cells: State of the Art, Current Challenges, and Future Perspectives

Stem cells and other functionally defined therapeutic cells (e.g., T cells) are promising to bring hope of a permanent cure for diseases and disorders that currently cannot be cured by conventional drugs or biological molecules. This paradigm shift in modern medicine of using cells as novel therapeutics can be realized only if suitable manufacturing technologies for large-scale, cost-effective, reproducible production of high-quality cells can be developed. Here we review the state of the art in therapeutic cell manufacturing, including cell purification and isolation, activation and differentiation, genetic modification, expansion, packaging, and preservation. We identify current challenges and discuss opportunities to overcome them such that cell therapies become highly effective, safe, and predictively reproducible while at the same time becoming affordable and widely available.

Defined and Scalable Differentiation of Human Oligodendrocyte Precursors from Pluripotent Stem Cells in a 3D Culture System

Oligodendrocyte precursor cells (OPCs) offer considerable potential for the treatment of demyelinating diseases and injuries of the CNS. However, generating large quantities of high-quality OPCs remains a substantial challenge that impedes their therapeutic application. Here, we show that OPCs can be generated from human pluripotent stem cells (hPSCs) in a three-dimensional (3D), scalable, and fully defined thermoresponsive biomaterial system. We used CRISPR/Cas9 to create a NKX2.2-EGFP human embryonic stem cell reporter line that enabled fine-tuning of early OPC specification and identification of conditions that markedly increased the number of OLIG2⁺ and NKX2.2⁺ cells generated from hPSCs. Transplantation of 50-day-old OPCs into the brains of NOD/SCID mice revealed that progenitors generated in 3D without cell selection or purification subsequently engrafted, migrated, and matured into myelinating oligodendrocytes in vivo. These results demonstrate the potential of harnessing lineage reporter lines to develop 3D platforms for rapid and large-scale production of OPCs.

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A defined and scalable 3D system accelerates the differentiation of OPCs from hPSCs

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A NKX2.2-EGFP hESC reporter line enables optimization of OPC differentiation

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3D-derived OPCs engraft, migrate, and mature after implantation into NOD/SCID mice

Impact of fluidic agitation on human pluripotent stem cells in stirred suspension culture

The success of human pluripotent stem cells (hPSCs) as a source of future cell therapies hinges, in part, on the availability of a robust and scalable culture system that can readily produce a clinically relevant number of cells and their derivatives. Stirred suspension culture has been identified as one such promising platform due to its ease of use, scalability, and widespread use in the pharmaceutical industry (e.g., CHO cell-based production of therapeutic proteins) among others. However, culture of undifferentiated hPSCs in stirred suspension is a relatively new development within the past several years, and little is known beyond empirically optimized culture parameters. In particular, detailed characterizations of different agitation rates and their influence on the propagation of hPSCs are often not reported in the literature. In the current study, we systematically investigated various agitation rates to characterize their impact on cell yield, viability, and the maintenance of pluripotency. Additionally, we closely examined the distribution of cell aggregates and how the observed culture outcomes are attributed to their size distribution. Overall, our results showed that moderate agitation maximized the propagation of hPSCs to approximately 38-fold over 7 days by keeping the cell aggregates below the critical size, beyond which the cells are impacted by the diffusion limit, while limiting cell death caused by excessive fluidic forces. Furthermore, we observed that fluidic agitation could regulate not only cell aggregation, but also expression of some key signaling proteins in hPSCs. This indicates a new possibility to guide stem cell fate determination by fluidic agitation in stirred suspension cultures. Biotechnol. Bioeng. 2017;114: 2109-2120. © 2017 Wiley Periodicals, Inc.

Differentiation of cardiomyocytes and generation of human engineered heart tissue

Since the advent of the generation of human induced pluripotent stem cells (hiPSCs), numerous protocols have been developed to differentiate hiPSCs into cardiomyocytes and then subsequently assess their ability to recapitulate the properties of adult human cardiomyocytes. However, hiPSC-derived cardiomyocytes (hiPSC-CMs) are often assessed in single-cell assays. A shortcoming of these assays is the limited ability to characterize the physiological parameters of cardiomyocytes, such as contractile force, due to random orientations. This protocol describes the differentiation of cardiomyocytes from hiPSCs, which occurs within 14 d. After casting, cardiomyocytes undergo 3D assembly. This produces fibrin-based engineered heart tissues (EHTs)-in a strip format-that generate force under auxotonic stretch conditions. 10-15 d after casting, the EHTs can be used for contractility measurements. This protocol describes parallel expansion of hiPSCs; standardized generation of defined embryoid bodies, growth factor and small-molecule-based cardiac differentiation; and standardized generation of EHTs. To carry out the protocol, experience in advanced cell culture techniques is required.

Transplantation of purified iPSC-derived cardiomyocytes in myocardial infarction

Background

Induced pluripotent stem cells (iPSC) can be differentiated into cardiomyocytes and represent a possible autologous cell source for myocardial repair. We analyzed the engraftment and functional effects of murine iPSC-derived cardiomyocytes (iPSC-CMs) in a murine model of myocardial infarction.

Methods and results

To maximize cardiomyocyte yield and purity a genetic purification protocol was applied. Murine iPSCs were genetically modified to express a Zeocin^™ resistance gene under control of the cardiac-specific α-myosin heavy chain (α-MHC, MYH6) promoter. Thus, CM selection was performed during in vitro differentiation. iPSC-CM aggregates (“cardiac bodies”, CBs) were transplanted on day 14 after LAD ligation into the hearts of previously LAD-ligated mice (800 CBs/animal; 2-3x10⁶ CMs). Animals were treated with placebo (PBS, n = 14) or iPSC-CMs (n = 35). Myocardial remodeling and function were evaluated by magnetic resonance imaging (MRI), conductance catheter (CC) analysis and histological morphometry. In vitro and in vivo differentiation was investigated. Follow up was 28 days (including histological assessment and functional analysis). iPSC-CM purity was >99%. Transplanted iPSC-CMs formed mature grafts within the myocardium, expressed cardiac markers and exhibited sarcomeric structures. Intramyocardial transplantation of iPSC-CMs significantly improved myocardial remodeling and left ventricular function 28 days after LAD-ligation.

Conclusions

We conclude that iPSCs can effectively be differentiated into cardiomyocytes and genetically enriched to high purity. iPSC derived cardiomyocytes engraft within the myocardium of LAD-ligated mice and contribute to improve left ventricular function.

Dinaciclib potently suppresses MCL-1 and selectively induces the cell death in human iPS cells without affecting the viability of cardiac tissue

Induced pluripotent stem (iPS) cells hold great potential for being a major source of cells for regenerative medicine. One major issue that hinders their advancement to clinic is the persistence of undifferentiated iPS cells in iPS-derived tissue. In this report, we show that the CDKs inhibitor, Dinaciclib, selectively eliminates iPS cells without affecting the viability of cardiac cells. We found that low nanomolar concentration of dinaciclib increased DNA damage and p53 protein levels in iPSCs. This was accompanied by negative regulation of the anti-apoptotic protein MCL-1. Gene knockdown experiments revealed that p53 downregulation only increased the threshold of dinaciclib induced apoptosis in iPS cells. Dinaciclib also inhibited the phosphorylation of Serine 2 of the C-terminal domain of RNA Polyemrase II through CDK9 inhibition. This resulted in the inhibition of transcription of MCL-1 and the pluripotency genes, NANOG and c-MYC. Even though dinaciclib caused a slight downregulation of MCL-1 in iPS-derived cardiac cells, the viability of the cells was not significantly affected, and beating iPS-derived cardiac cell sheet could still be fabricated. These findings suggest a difference in tolerance of MCL-1 downregulation between iPSCs and iPS-derived cardiac cells which could be exploited to eliminate remaining iPS cells in bioengineered cell sheet tissues.

Stem Cell Spheroids and Ex Vivo Niche Modeling: Rationalization and Scaling-Up

Improved protocols/devices for in vitro culture of 3D cell spheroids may provide essential cues for proper growth and differentiation of stem/progenitor cells (S/PCs) in their niche, allowing preservation of specific features, such as multi-lineage potential and paracrine activity. Several platforms have been employed to replicate these conditions and to generate S/PC spheroids for therapeutic applications. However, they incompletely reproduce the niche environment, with partial loss of its highly regulated network, with additional hurdles in the field of cardiac biology, due to debated resident S/PCs therapeutic potential and clinical translation. In this contribution, the essential niche conditions (metabolic, geometric, mechanical) that allow S/PCs maintenance/commitment will be discussed. In particular, we will focus on both existing bioreactor-based platforms for the culture of S/PC as spheroids, and on possible criteria for the scaling-up of niche-like spheroids, which could be envisaged as promising tools for personalized cardiac regenerative medicine, as well as for high-throughput drug screening.

Nano-on-micro fibrous extracellular matrices for scalable expansion of human ES/iPS cells

Human pluripotent stem cells (hPSCs) hold great potential for industrial and clinical applications. Clinical-grade scaffolds and high-quality hPSCs are required for cell expansion as well as easy handling and manipulation of the products. Current hPSC culture methods do not fulfill these requirements because of a lack of proper extracellular matrices (ECMs) and cell culture wares. We developed a layered nano-on-micro fibrous cellular matrix mimicking ECM, named "fiber-on-fiber (FF)" matrix, which enables easy handling and manipulation of cultured cells. While non-woven sheets of cellulose and polyglycolic acid were used as a microfiber layer facilitating mechanical stability, electrospun gelatin nanofibers were crosslinked on the microfiber layer, generating a mesh structure with connected nanofibers facilitating cell adhesion and growth. Our results showed that the FF matrix supports effective hPSC culture with maintenance of their pluripotency and normal chromosomes over two months, as well as effective scaled-up expansion, with fold increases of 54.1 ± 15.6 and 40.4 ± 8.4 in cell number per week for H1 human embryonic stem cells and 253G1 human induced pluripotent stem cells, respectively. This simple approach to mimick the ECM may have important implications after further optimization to generate lineage-specific products.

Thicker three-dimensional tissue from a "symbiotic recycling system" combining mammalian cells and algae

In this paper, we report an in vitro co-culture system that combines mammalian cells and algae, Chlorococcum littorale, to create a three-dimensional (3-D) tissue. While the C2C12 mouse myoblasts and rat cardiac cells consumed oxygen actively, intense oxygen production was accounted for by the algae even in the co-culture system. Although cell metabolism within thicker cardiac cell-layered tissues showed anaerobic respiration, the introduction of innovative co-cultivation partially changed the metabolism to aerobic respiration. Moreover, the amount of glucose consumption and lactate production in the cardiac tissues and the amount of ammonia in the culture media decreased significantly when co-cultivated with algae. In the cardiac tissues devoid of algae, delamination was observed histologically, and the release of creatine kinase (CK) from the tissues showed severe cardiac cell damage. On the other hand, the layered cell tissues with algae were observed to be in a good histological condition, with less than one-fifth decline in CK release. The co-cultivation with algae improved the culture condition of the thicker tissues, resulting in the formation of 160 μm-thick cardiac tissues. Thus, the present study proposes the possibility of creating an in vitro “symbiotic recycling system” composed of mammalian cells and algae.

Expansion of 3D human induced pluripotent stem cell aggregates in bioreactors: Bioprocess intensification and scaling-up approaches

Human induced pluripotent stem cells (hiPSC) are attractive tools for drug screening and disease modeling and promising candidates for cell therapy applications. However, to achieve the high numbers of cells required for these purposes, scalable and clinical-grade technologies must be established. In this study, we use environmentally controlled stirred-tank bioreactors operating in perfusion as a powerful tool for bioprocess intensification of hiPSC production. We demonstrate the importance of controlling the dissolved oxygen concentration at low levels (4%) and perfusion at 1.3day^-1 dilution rate to improve hiPSC growth as aggregates in a xeno-free medium. This strategy allowed for increased cell specific growth rate, maximum volumetric concentrations (4.7×10⁶cell/mL) and expansion factors (approximately 19 in total cells), resulting in a 2.6-fold overall improvement in cell yields. Extensive cell characterization, including whole proteomic analysis, was performed to confirm that cells' pluripotent phenotype was maintained during culture. A scalable protocol for continuous expansion of hiPSC aggregates in bioreactors was implemented using mechanical dissociation for aggregate disruption and cell passaging. A total expansion factor of 1100 in viable cells was obtained in 11days of culture, while cells maintained their proliferation capacity, pluripotent phenotype and potential as well as genomic stability after 3 sequential passages in bioreactors.

Efficient generation of hPSC-derived midbrain dopaminergic neurons in a fully defined, scalable, 3D biomaterial platform

Pluripotent stem cells (PSCs) have major potential as an unlimited source of functional cells for many biomedical applications; however, the development of cell manufacturing systems to enable this promise faces many challenges. For example, there have been major recent advances in the generation of midbrain dopaminergic (mDA) neurons from stem cells for Parkinson's Disease (PD) therapy; however, production of these cells typically involves undefined components and difficult to scale 2D culture formats. Here, we used a fully defined, 3D, thermoresponsive biomaterial platform to rapidly generate large numbers of action-potential firing mDA neurons after 25 days of differentiation (~40% tyrosine hydroxylase (TH) positive, maturing into 25% cells exhibiting mDA neuron-like spiking behavior). Importantly, mDA neurons generated in 3D exhibited a 30-fold increase in viability upon implantation into rat striatum compared to neurons generated on 2D, consistent with the elevated expression of survival markers FOXA2 and EN1 in 3D. A defined, scalable, and resource-efficient cell culture platform can thus rapidly generate high quality differentiated cells, both neurons and potentially other cell types, with strong potential to accelerate both basic and translational research.

Choices for Induction of Pluripotency: Recent Developments in Human Induced Pluripotent Stem Cell Reprogramming Strategies

The ability to generate human induced pluripotent stem cells (iPSCs) from somatic cells provides tremendous promises for regenerative medicine and its use has widely increased over recent years. However, reprogramming efficiencies remain low and chromosomal instability and tumorigenic potential are concerns in the use of iPSCs, especially in clinical settings. Therefore, reprogramming methods have been under development to generate safer iPSCs with higher efficiency and better quality. Developments have mainly focused on the somatic cell source, the cocktail of reprogramming factors, the delivery method used to introduce reprogramming factors and culture conditions to maintain the generated iPSCs. This review discusses the developments on these topics and briefly discusses pros and cons of iPSCs in comparison with human embryonic stem cells generated from somatic cell nuclear transfer.