Interwoven four-compartment capillary membrane technology for three-dimensional perfusion with decentralized mass exchange to scale up embryonic stem cell culture

Evaluating Strategies to Assess the Differentiation Potential of Human Pluripotent Stem Cells: A Review, Analysis and Call for Innovation

Pluripotent stem cells have the ability to differentiate into all cells and tissues within the human body, and as a result they are attractive resources for use in basic research, drug discovery and regenerative medicine. In order to successfully achieve this application, starting cell sources ideally require in-depth characterisation to confirm their pluripotent status and their ability to differentiate into tissues representative of the three developmental germ layers. Many different methods to assess potency are employed, each having its own distinct advantages and limitations. Some aspects of this characterisation process are not always well standardised, particularly techniques used to assess pluripotency as a function. In this article, we consider the methods used to establish cellular pluripotency and subsequently analyse characterisation data for over 1590 human pluripotent cell lines from publicly available repositories in the UK and USA. In particular, we focus on the teratoma xenograft assay, its use and protocols, demonstrating the level of variation and the frequency with which it is used. Finally, we reflect on the implications of the findings, and suggest in vitro alternatives using modern innovative technology as a way forward.

Online measurement of oxygen enables continuous noninvasive evaluation of human-induced pluripotent stem cell (hiPSC) culture in a perfused 3D hollow-fiber bioreactor

For clinical and/or pharmaceutical use of human-induced pluripotent stem cells (hiPSCs), large cell quantities of high quality are demanded. Therefore, we combined the expansion of hiPSCs in closed, perfusion-based 3D bioreactors with noninvasive online monitoring of oxygen as culture control mechanism. Bioreactors with a cell compartment volume of 3 or 17 ml were inoculated with either 10 × 10⁶ or 50 × 10⁶ cells, and cells were expanded over 15 days with online oxygen and offline glucose and lactate measurements being performed. The CellTiter-Blue® Assay was performed at the end of the bioreactor experiments for indirect cell quantification. Model simulations enabled an estimation of cell numbers based on kinetic equations and experimental data during the 15-day bioreactor cultures. Calculated oxygen uptake rates (OUR), glucose consumption rates (GCR), and lactate production rates (LPR) revealed a highly significant correlation (p < 0.0001). Oxygen consumption, which was measured at the beginning and the end of the experiment, showed a strong culture growth in line with the OUR and GCR data. Furthermore, the yield coefficient of lactate from glucose and the OUR to GCR ratio revealed a shift from nonoxidative to oxidative metabolism. The presented results indicate that oxygen is equally as applicable as parameter for hiPSC expansion as glucose while providing an accurate real-time impression of hiPSC culture development. Additionally, oxygen measurements inform about the metabolic state of the cells. Thus, the use of oxygen online monitoring for culture control facilitates the translation of hiPSC use to the clinical setting.

Effect of inoculum density on human-induced pluripotent stem cell expansion in 3D bioreactors

Objective

For optimized expansion of human‐induced pluripotent stem cells (hiPSCs) with regards to clinical applications, we investigated the influence of the inoculum density on the expansion procedure in 3D hollow‐fibre bioreactors.

Materials and Methods

Analytical‐scale bioreactors with a cell compartment volume of 3 mL or a large‐scale bioreactor with a cell compartment volume of 17 mL were used and inoculated with either 10 × 10⁶ or 50 × 10⁶ hiPSCs. Cells were cultured in bioreactors over 15 days; daily measurements of biochemical parameters were performed. At the end of the experiment, the CellTiter‐Blue^® Assay was used for culture activity evaluation and cell quantification. Also, cell compartment sections were removed for gene expression and immunohistochemistry analysis.

Results

The results revealed significantly higher values for cell metabolism, cell activity and cell yields when using the higher inoculation number, but also a more distinct differentiation. As large inoculation numbers require cost and time‐extensive pre‐expansion, low inoculation numbers may be used preferably for long‐term expansion of hiPSCs. Expansion of hiPSCs in the large‐scale bioreactor led to a successful production of 5.4 × 10⁹ hiPSCs, thereby achieving sufficient cell amounts for clinical applications.

Conclusions

In conclusion, the results show a significant effect of the inoculum density on cell expansion, differentiation and production of hiPSCs, emphasizing the importance of the inoculum density for downstream applications of hiPSCs. Furthermore, the bioreactor technology was successfully applied for controlled and scalable production of hiPSCs for clinical use.

Scalable and physiologically relevant microenvironments for human pluripotent stem cell expansion and differentiation

Human pluripotent stem cells (hPSCs) are required in large numbers for various biomedical applications. However, the scalable and cost-effective culturing of high quality hPSCs and their derivatives remains very challenging. Here, we report a novel and physiologically relevant 3D culture system (called the AlgTube cell culture system) for hPSC expansion and differentiation. With this system, cells are processed into and cultured in microscale alginate hydrogel tubes that are suspended in the cell culture medium in a culture vessel. The hydrogel tubes protect cells from hydrodynamic stresses in the culture vessel and limit the cell mass smaller than 400 μm in diameter to ensure efficient mass transport, creating cell-friendly microenvironments for growing cells. This system is simple, scalable, highly efficient, defined and compatible with the current good manufacturing practices. Under optimized culture conditions, the AlgTubes enabled long-term culture of hPSCs (>10 passages, >50 days) with high cell viability, high growth rate (1000-fold expansion over 10 days per passage), high purity (>95% Oct4+) and high yield (5.0 × 10⁸ cells ml^-1), all of which offer considerable advantages compared to current approaches. Moreover, the AlgTubes enabled directed differentiation of hPSCs into various tissue cells. This system can be readily scaled to support research from basic biological study to clinical development and the future industry-scale production.

Multicompartmental Hollow-Fiber-Based Bioreactors for Dynamic Three-Dimensional Perfusion Culture

The creation of larger-scale three-dimensional tissue constructs depends on proper medium mass and gas exchange, as well as removal of metabolites, which cannot be achieved in conventional static two-dimensional petri dish culture. In cultures of tissue-density this problem can be addressed by decentral perfusion through artificial micro-capillaries. While the static medium exchange in petri dishes leads to metabolite peaks, perfusion culture provides a dynamic medium supply, thereby preventing non-physiological peaks. To overcome the limitations of conventional static two-dimensional culture, a three-dimensional perfusion bioreactor technology has been developed, providing decentral and high-performance mass exchange as well as integral oxygenation. Similar to organ systems in vivo, the perfusion with medium provides nutrition and removes waste metabolites, and the perfusion with gas delivers oxygen and carbon dioxide for pH regulation. Such bioreactors are available at various dimensions ranging from 0.2 to 800 mL cell compartment volumes (manufactured by StemCell Systems, Berlin, Germany). Here, we describe in detail the setup and maintenance of a small-scale 4-chamber bioreactor with its tubing circuit and perfusion system.

Analysis of type II diabetes mellitus adipose-derived stem cells for tissue engineering applications

To address the functionality of diabetic adipose-derived stem cells in tissue engineering applications, adipose-derived stem cells isolated from patients with and without type II diabetes mellitus were cultured in bioreactor culture systems. The adipose-derived stem cells were differentiated into adipocytes and maintained as functional adipocytes. The bioreactor system utilizes a hollow fiber–based technology for three-dimensional perfusion of tissues in vitro, creating a model in which long-term culture of adipocytes is feasible, and providing a potential tool useful for drug discovery. Daily metabolic activity of the adipose-derived stem cells was analyzed within the medium recirculating throughout the bioreactor system. At experiment termination, tissues were extracted from bioreactors for immunohistological analyses in addition to gene and protein expression. Type II diabetic adipose-derived stem cells did not exhibit significantly different glucose consumption compared to adipose-derived stem cells from patients without type II diabetes (p > 0.05, N = 3). Expression of mature adipocyte genes was not significantly different between diabetic/non-diabetic groups (p > 0.05, N = 3). Protein expression of adipose tissue grown within all bioreactors was verified by Western blotting.The results from this small-scale study reveal adipose-derived stem cells from patients with type II diabetes when removed from diabetic environments behave metabolically similar to the same cells of non-diabetic patients when cultured in a three-dimensional perfusion bioreactor, suggesting that glucose transport across the adipocyte cell membrane, the hindrance of which being characteristic of type II diabetes, is dependent on environment. The presented observation describes a tissue-engineered tool for long-term cell culture and, following future adjustments to the culture environment and increased sample sizes, potentially for anti-diabetic drug testing.

Bioreactors addressing diabetes mellitus

The concept of bioreactors in biochemical engineering is a well-established process; however, the idea of applying bioreactor technology to biomedical and tissue engineering issues is relatively novel and has been rapidly accepted as a culture model. Tissue engineers have developed and adapted various types of bioreactors in which to culture many different cell types and therapies addressing several diseases, including diabetes mellitus types 1 and 2. With a rising world of bioreactor development and an ever increasing diagnosis rate of diabetes, this review aims to highlight bioreactor history and emerging bioreactor technologies used for diabetes-related cell culture and therapies.

Teratoma formation of human embryonic stem cells in three-dimensional perfusion culture bioreactors

Teratoma formation in mice is today the most stringent test for pluripotency that is available for human pluripotent cells, as chimera formation and tetraploid complementation cannot be performed with human cells. The teratoma assay could also be applied for assessing the safety of human pluripotent cell-derived cell populations intended for therapeutic applications. In our study we examined the spontaneous differentiation behaviour of human embryonic stem cells (hESCs) in a perfused 3D multi-compartment bioreactor system and compared it with differentiation of hESCs and human induced pluripotent cells (hiPSCs) cultured in vitro as embryoid bodies and in vivo in an experimental mouse model of teratoma formation. Results from biochemical, histological/immunohistological and ultrastuctural analyses revealed that hESCs cultured in bioreactors formed tissue-like structures containing derivatives of all three germ layers. Comparison with embryoid bodies and the teratomas revealed a high degree of similarity of the tissues formed in the bioreactor to these in the teratomas at the histological as well as transcriptional level, as detected by comparative whole-genome RNA expression profiling. The 3D culture system represents a novel in vitro model that permits stable long-term cultivation, spontaneous multi-lineage differentiation and tissue formation of pluripotent cells that is comparable to in vivo differentiation. Such a model is of interest, e.g. for the development of novel cell differentiation strategies. In addition, the 3D in vitro model could be used for teratoma studies and pluripotency assays in a fully defined, controlled environment, alternatively to in vivo mouse models.

The multiparametric effects of hydrodynamic environments on stem cell culture

Stem cells possess the unique capacity to differentiate into many clinically relevant somatic cell types, making them a promising cell source for tissue engineering applications and regenerative medicine therapies. However, in order for the therapeutic promise of stem cells to be fully realized, scalable approaches to efficiently direct differentiation must be developed. Traditionally, suspension culture systems are employed for the scale-up manufacturing of biologics via bioprocessing systems that heavily rely upon various types of bioreactors. However, in contrast to conventional bench-scale static cultures, large-scale suspension cultures impart complex hydrodynamic forces on cells and aggregates due to fluid mixing conditions. Stem cells are exquisitely sensitive to environmental perturbations, thus motivating the need for a more systematic understanding of the effects of hydrodynamic environments on stem cell expansion and differentiation. This article discusses the interdependent relationships between stem cell aggregation, metabolism, and phenotype in the context of hydrodynamic culture environments. Ultimately, an improved understanding of the multifactorial response of stem cells to mixed culture conditions will enable the design of bioreactors and bioprocessing systems for scalable directed differentiation approaches.

Toward Preclinical Predictive Drug Testing for Metabolism and Hepatotoxicity by Using In Vitro Models Derived from Human Embryonic Stem Cells and Human Cell Lines — A Report on the Vitrocellomics EU-project

Drug-induced liver injury is a common reason for drug attrition in late clinical phases, and even for post-launch withdrawals. As a consequence, there is a broad consensus in the pharmaceutical industry, and within regulatory authorities, that a significant improvement of the current in vitro test methodologies for accurate assessment and prediction of such adverse effects is needed. For this purpose, appropriate in vivo-like hepatic in vitro models are necessary, in addition to novel sources of human hepatocytes. In this report, we describe recent and ongoing research toward the use of human embryonic stem cell (hESC)-derived hepatic cells, in conjunction with new and improved test methods, for evaluating drug metabolism and hepatotoxicity. Recent progress on the directed differentiation of human embryonic stem cells to the functional hepatic phenotype is reported, as well as the development and adaptation of bioreactors and toxicity assay technologies for the testing of hepatic cells. The aim of achieving a testing platform for metabolism and hepatotoxicity assessment, based on hESC-derived hepatic cells, has advanced markedly in the last 2–3 years. However, great challenges still remain, before such new test systems could be routinely used by the industry. In particular, we give an overview of results from the Vitrocellomics project (EU Framework 6) and discuss these in relation to the current state-of-the-art and the remaining difficulties, with suggestions on how to proceed before such in vitro systems can be implemented in industrial discovery and development settings and in regulatory acceptance.

Hepatic differentiation of human embryonic stem cells is promoted by three-dimensional dynamic perfusion culture conditions

The developmental potential of human embryonic stem cells (hESCs) holds great promise to provide a source of human hepatocytes for use in drug discovery, toxicology, hepatitis research, and extracorporeal bioartificial liver support. There are, however, limitations to induce fully functional hepatocytes on conventional two-dimensional (2D) static culture. It had been shown that dynamic three-dimensional (3D) perfusion culture is superior to induce maturation in fetal hepatocytes and prolong hepatic functions of primary adult hepatocytes. We investigated the potential of using a four-compartment 3D perfusion culture to induce hepatic differentiation in hESC. Undifferentiated hESC were inoculated into hollow fiber-based 3D perfusion bioreactors with integral oxygenation. Hepatic differentiation was induced with a multistep growth factor cocktail protocol. Parallel controls were operated under equal perfusion conditions without the growth factor supplementations to allow for spontaneous differentiation, as well as in conventional 2D static conditions using growth factors. Metabolism, hepatocyte-specific gene expression, protein expression, and hepatic function were evaluated after 20 days. Significantly upregulated hepatic gene expression was observed in the hepatic differentiation 3D culture group. Ammonia metabolism activity and albumin production was observed in the 3D directed differentiation culture. Drug-induced cytochrome P450 gene expression was increased with rifampicin induction. Using flow cytometry analysis the mature hepatocyte marker asialoglycoprotein receptor was found on up to 30% of the cells in the 3D system with directed hepatic differentiation. Histological and immunohistochemical analysis revealed structural formation of hepatic and biliary marker-positive cells. In contrast to 2D culture, the 3D perfusion culture induced more functional maturation in hESC-derived hepatic cells. 3D perfusion bioreactor technologies may be useful for further studies on generating hESC-derived hepatic cells.

Optimization of a serum-free culture medium for mouse embryonic stem cells using design of experiments (DoE) methodology

The in vitro culture behaviour of embryonic stem cells (ESC) is strongly influenced by the culture conditions. Current culture media for expansion of ESC contain some undefined substances. Considering potential clinical translation work with such cells, the use of defined media is desirable. We have used Design of Experiments (DoE) methods to investigate the composition of a serum-free chemically defined culture medium for expansion of mouse embryonic stem cells (mESC). Factor screening analysis according to Plackett-Burman revealed that insulin and leukaemia inhibitory factor (LIF) had a significant positive influence on the proliferation activity of the cells, while zinc and L: -cysteine reduced the cell growth. Further analysis using minimum run resolution IV (MinRes IV) design indicates that following factor adjustment LIF becomes the main factor for the survival and proliferation of mESC. In conclusion, DoE screening assays are applicable to develop and to refine culture media for stem cells and could also be employed to optimize culture media for human embryonic stem cells (hESC).