Stem cell engineering in bioreactors for large‐scale bioprocessing

Stem cells are promising cell sources for many biomedical applications including cell therapy, regenerative medicine, and drug discovery. However, the commonly used static tissue culture vessels can only generate a low number of cells. To provide an adequate number of stem cells for clinical applications, a scalable process based on bioreactors is needed. Stem cells can be either cultured as free cells/aggregates in suspension or as adherent cells on the solid substrates. Based on the cell property, different bioreactor configurations are developed to better expand stem cells while maintaining their differentiation capacity. In this review, several major types of bioreactor systems and their applications in stem cell engineering are discussed. Continued advancements in bioprocess and bioreactor research and development are important to engineer stem cells for their use in biomedical applications.     

Stem cell bioprocess engineering towards cGMP production and clinical applications

Stem cells, including mesenchymal stem cells and pluripotent stem cells, are becoming an indispensable tool for various biomedical applications including drug discovery, disease modeling, and tissue engineering. Bioprocess engineering, targeting large scale production, provides a platform to generate a controlled microenvironment that could potentially recreate the stem cell niche to promote stem cell proliferation or lineage-specific differentiation. This survey aims at defining the characteristics of stem cell populations currently in use and the present-day limits in their applications for therapeutic purposes. Furthermore, a bioprocess engineering strategy based on bioreactors and 3-D cultures is discussed in order to achieve the improved stem cell yield, function, and safety required for production under current good manufacturing practices.     

Effects and applications of sub-lethal ultrasound, electroporation and UV radiations in bioprocessing

Advances in bioprocess technology involving microbial cells have led to increased and improved production of beneficial new products and bioactive compounds. However, the semipermeable barrier of the cell membrane often retards the efficient productivity or reaction rate of the cells. Physical treatments such as ultrasound, electroporation and UV radiation provide an efficient approach to increase membrane permeability, leading to enhanced productivity of microbial cells. It is important to note that extensive membrane permeabilization by these physical treatments could be detrimental to cell viability leading to lower yield. An appropriate selection of sublethal dosage and intensity of these physical treatments are critical to preserve the viability of cells and at the same time maintain their bioprocess applications. Despite the promising applications of these physical treatments, safety issues related to possible genotoxicity or mutation of cells upon treatments have been raised. This genotoxic effect of physical treatments could be prevented if appropriate measures are taken, without compromising their bioprocess potentials. The current review highlights the effect of sublethal physical treatments such as ultrasound, electroporation and UV radiation on the viability of cells, their potential bioprocess applications, and the possibility of mutations.     

Cover Image,Volume 116, Number 9, September 2019

The new and rapid advancement in the complexity of biologics drug discovery has been driven by a deeper understanding of biological systems combined with innovative new therapeutic modalities, paving the way to breakthrough therapies for previously intractable diseases. These exciting times in biomedical innovation require the development of novel technologies to facilitate the sophisticated, multifaceted, high-paced workflows necessary to support modern large molecule drug discovery. A high-level aspiration is a true integration of “lab-on-a-chip” methods that vastly miniaturize cellulmical experiments could transform the speed, cost, and success of multiple workstreams in biologics development. Several microscale bioprocess technologies have been established that incrementally address these needs, yet each is inflexibly designed for a very specific process thus limiting an integrated holistic application. A more fully integrated nanoscale approach that incorporates manipulation, culture, analytics, and traceable digital record keeping of thousands of single cells in a relevant nanoenvironment would be a transformative technology capable of keeping pace with today's rapid and complex drug discovery demands. The recent advent of optical manipulation of cells using light-induced electrokinetics with micro- and nanoscale cell culture is poised to revolutionize both fundamental and applied biological research. In this review, we summarize the current state of the art for optical manipulation techniques and discuss emerging biological applications of this technology. In particular, we focus on promising prospects for drug discovery workflows, including antibody discovery, bioassay development, antibody engineering, and cell line development, which are enabled by the automation and industrialization of an integrated optoelectronic single-cell manipulation and culture platform. Continued development of such platforms will be well positioned to overcome many of the challenges currently associated with fragmented, low-throughput bioprocess workflows in biopharma and life science research.     

Stem cell cultivation in bioreactors

Cell-based therapies have generated great interest in the scientific and medical communities, and stem cells in particular are very appealing for regenerative medicine, drug screening and other biomedical applications. These unspecialized cells have unlimited self-renewal capacity and the remarkable ability to produce mature cells with specialized functions, such as blood cells, nerve cells or cardiac muscle. However, the actual number of cells that can be obtained from available donors is very low. One possible solution for the generation of relevant numbers of cells for several applications is to scale-up the culture of these cells in vitro. This review describes recent developments in the cultivation of stem cells in bioreactors, particularly considerations regarding critical culture parameters, possible bioreactor configurations, and integration of novel technologies in the bioprocess development stage. We expect that this review will provide updated and detailed information focusing on the systematic production of stem cell products in compliance with regulatory guidelines, while using robust and cost-effective approaches.     

Applications and perspectives of multi-parameter flow cytometry to microbial biofuels production processes

Conventional microbiology methods used to monitor microbial biofuels production are based on off-line analyses. The analyses are, unfortunately, insufficient for bioprocess optimization. Real time process control strategies, such as flow cytometry (FC), can be used to monitor bioprocess development (at-line) by providing single cell information that improves process model formulation and validation. This paper reviews the current uses and potential applications of FC in biodiesel, bioethanol, biomethane, biohydrogen and fuel cell processes. By highlighting the inherent accuracy and robustness of the technique for a range of biofuel processing parameters, more robust monitoring and control may be implemented to enhance process efficiency.     

Identifying analytics for high throughput bioprocess development studies

In recent years, high throughput screening (HTS) studies have been increasingly employed as an integral element of bioprocess development activities. These studies are often limited by an analytical bottleneck; they generate multiple samples for analysis and the available analytical methods cannot always cope with the added analytical burden. A potential solution to this challenge is offered by the deployment of appropriate analytics. This article outlines features of analytical methods that affect their fit to high throughput (HT) applications. These are discussed for a range of analytics frequently used in bioprocess development studies of monoclonal antibodies. It then outlines how these features need to be considered in order to classify analytical methods in terms of their particular application in high throughput scenarios. Biotechnol. Bioeng. 2013; 110: 1924–1935. © 2013 Wiley Periodicals, Inc.     

Development of a new bioprocess scheme using frozen seed train intermediates to initiate CHO cell culture manufacturing campaigns

Agility to schedule and execute cell culture manufacturing campaigns quickly in a multi‐product facility will play a key role in meeting the growing demand for therapeutic proteins. In an effort to shorten campaign timelines, maximize plant flexibility and resource utilization, we investigated the initiation of cell culture manufacturing campaigns using CHO cells cryopreserved in large volume bags in place of the seed train process flows that are conventionally used in cell culture manufacturing. This approach, termed FASTEC (Frozen Accelerated Seed Train for Execution of a Campaign), involves cultivating cells to high density in a perfusion bioreactor, and cryopreserving cells in multiple disposable bags. Each run for a manufacturing campaign would then come from a thaw of one or more of these cryopreserved bags. This article reviews the development and optimization of individual steps of the FASTEC bioprocess scheme: scaling up cells to greater than 70 × 10⁶ cells/mL and freezing in bags with an optimized controlled rate freezing protocol and using a customized rack configuration. Flow cytometry analysis was also employed to understand the recovery of CHO cells following cryopreservation. Extensive development data were gathered to ensure that the quantity and quality of the drug manufactured using the FASTEC bioprocess scheme was acceptable compared to the conventional seed train process flow. The result of offering comparable manufacturing options offers flexibility to the cell culture manufacturing network. Biotechnol. Bioeng. 2013; 110: 1376–1385. © 2012 Wiley Periodicals, Inc.     

Development of a perfusion fed bioreactor for embryonic stem cell-derived cardiomyocyte generation: oxygen-mediated enhancement of cardiomyocyte output

Cell transplantation is emerging as a promising new approach to replace scarred, nonfunctional myocardium in a diseased heart. At present, however, generating the numbers of donor cardiomyocytes required to develop and test animal models is a major limitation. Embryonic stem (ES) cells may be a promising source for therapeutic applications, potentially providing sufficient numbers of functionally relevant cells for transplantation into a variety of organs. We developed a single-step bioprocess for ES cell-derived cardiomyocyte production that enables both medium perfusion and direct monitoring and control of dissolved oxygen. Implementation of the bioprocess required combining methods to prevent ES cell aggregation (hydrogel encapsulation) and to purify for cardiomyocytes from the heterogeneous cell populations (genetic selection), with medium perfusion in a controlled bioreactor environment. We used this bioprocess to investigate the effects of oxygen on cardiomyocyte generation. Parallel vessels (250 mL culture volume) were run under normoxic (20% oxygen tension) or hypoxic (4% oxygen tension) conditions. After 14 days of differentiation (including 5 days of selection), the cardiomyocyte yield per input ES cell achieved in hypoxic vessels was 3.77 +/- 0.13, higher than has previously been reported. We have developed a bioprocess that improves the efficiency of ES cell-derived cardiomyocyte production, and allows the investigation of bioprocess parameters on ES cell-derived cardiomyogenesis. Using this system we have demonstrated that medium oxygen tension is a culture parameter that can be manipulated to improve cardiomyocyte yield.     

Scalable inoculation strategies for microcarrier-based animal cell bioprocesses

Scalability is a major demand for high-yield, stable bioprocess systems in animal cell culture-based biopharmaceutical production. Increased yields can be achieved through high-density cell culture, such as in the combination of microcarrier and fluidized bed bioreactor technology. To minimize inocula volume in industrial applications of fluidized bed fermentation systems, it is crucial to increase the bed volume in the reactor during the fermentation process. We tested scale-up strategy for the production of recombinant human arylsulfatase B (ASB) enzyme used in enzyme replacement therapy in patients afflicted with mucopolysaccharidosis type VI (MPS VI). This enzyme was derived from Chinese hamster ovary (CHO) cells cultivated as adherent cell culture on Cytoline macroporous microcarriers (Amersham Biosciences, Uppsala, Sweden) using a Cytopilot Mini fluidized bed bioreactor (FBR; Amersham Biosciences, Vogelbusch, Austria). Both 1:2 expansion (herein referred to as the addition of fresh, not-yet-colonized microcarriers) and 1:6 expansion of the carrier bed were performed successfully; the cells restarted to proliferate for colonizing these newly added carriers; and the stability of the culture was not negatively affected.     

A closed,autologous bioprocess optimized for TCR-T cell therapies

Autologous cell therapy has proven to be an effective treatment for hematological malignancies. Cell therapies for solid tumors are on the horizon, however the high cost and complexity of manufacturing these therapies remain a challenge. Routinely used open steps to transfer cells and reagents through unit operations further burden the workflow reducing efficiency and increasing the chance for human error. Here we describe a fully closed, autologous bioprocess generating engineered TCR-T cells. This bioprocess yielded 5–12 × 10e9 TCR-expressing T cells, transduced at low multiplicity of infections, within 7–10 days, and cells exhibited an enriched memory T-cell phenotype and enhanced metabolic fitness. It was demonstrated that activating, transducing, and expanding leukapheresed cells in a bioreactor without any T-cell or peripheral blood mononuclear cell enrichment steps had a high level of T-cell purity (~97%). Several critical process parameters of the bioreactor, including culturing at a high cell density (7e6 cells/mL), adjusting rocking agitations during phases of scale-up, lowering glycolysis through the addition of 2-deoxy- d -glucose, and modulating interleukin-2 levels, were investigated on their roles in regulating transduction efficiency, cell growth, and T-cell fitness such as T-cell memory phenotype and resistance to activation-induced cell death. The bioprocess described herein supports scale-out feasibility by enabling the processing of multiple patients' batches in parallel within a Grade C cleanroom.     

Development of an alternating tangential flow (ATF) perfusion-based transient gene expression (TGE) bioprocess for universal influenza vaccine

An alternating tangential flow (ATF) perfusion-based transient gene expression (TGE) bioprocess has been developed using human embryonic kidney (HEK) 293 cells to produce H1-ss-np, a promising candidate for a universal influenza vaccine. Two major adjustments were taken to improve the process: (1) eliminate the interference of microbubbles during gene transfection; and (2) utilize an ATF perfusion system for a prolonged culture period. As a result, a closed-operation 9-days ATF perfusion-based TGE bioprocess was developed. The TGE bioprocess showed continuous cell growth with high cell viability and prolonged cellular productivity that achieved recombinant product level of ~270 mg/L which was more than two times that of 4-days base-line TGE bioprocess. In addition, the consumables cost per milligram for ATF perfusion-based TGE bioprocess was ~70% lower than that of the base-line TGE bioprocess suggesting high cost savings potential in vaccine manufacturing. Based on the lower contamination risk, higher productivity, and cost efficiency, the ATF perfusion-based TGE bioprocess can likely provide potential benefits to many future applications in vaccine and drug manufacturing.     

Immobilized Growth of the Peridinin-Producing Marine Dinoflagellate Symbiodinium in a Simple Biofilm Photobioreactor

Products from phototrophic dinoflagellates such as toxins or pigments are potentially important for applications in the biomedical sciences, especially in drug development. However, the technical cultivation of these organisms is often problematic due to their sensitivity to hydrodynamic (shear) stress that is a characteristic of suspension-based closed photobioreactors (PBRs). It is thus often thought that most species of dinoflagellates are non-cultivable at a technical scale. Recent advances in the development of biofilm PBRs that rely on immobilization of microalgae may hold potential to circumvent this major technical problem in dinoflagellate cultivation. In the present study, the dinoflagellate Symbiodinium voratum was grown immobilized on a Twin-Layer PBR for isolation of the carotenoid peridinin, an anti-cancerogenic compound. Biomass productivities ranged from 1.0 to 11.0 g m^?2 day^?1 dry matter per vertical growth surface and a maximal biomass yield of 114.5 g m^?2, depending on light intensity, supplementary CO₂, and type of substrate (paper or polycarbonate membrane) used. Compared to a suspension culture, the performance of the Twin-Layer PBRs exhibited significantly higher growth rates and maximal biomass yield. In the Twin-Layer PBR a maximal peridinin productivity of 24 mg m^?2 day^?1 was determined at a light intensity of 74 μmol m^?2 s^?1, although the highest peridinin content per dry weight (1.7 % w/w) was attained at lower light intensities. The results demonstrate that a biofilm-based PBR that minimizes hydrodynamic shear forces is applicable to technical-scale cultivation of dinoflagellates and may foster biotechnological applications of these abundant marine protists.     

Differentiation and lineage selection of mouse embryonic stem cells in a stirred bench scale bioreactor with automated process control

It is well established that embryonic stem (ES) cells can differentiate into functional cardiomyocytes in vitro. ES-derived cardiomyocytes could be used for pharmaceutical and therapeutic applications, provided that they can be generated in sufficient quantity and with sufficient purity. To enable large-scale culture of ES-derived cells, we have developed a robust and scalable bioprocess that allows direct embryoid body (EB) formation in a fully controlled, stirred 2 L bioreactor following inoculation with a single cell suspension of mouse ES cells. Utilizing a pitched-blade-turbine, parameters for optimal cell expansion as well as efficient ES cell differentiation were established. Optimization of stirring conditions resulted in the generation of high-density suspension cultures containing 12.5 x 10(6) cells/mL after 9 days of differentiation. Approximately 30%-40% of the EBs formed in this process vigorously contracted, indicating robust cardiomyogenic induction. An ES cell clone carrying a recombinant DNA molecule comprised of the cardiomyocyte-restricted alpha myosin heavy chain (alphaMHC) promoter and a neomycin resistance gene was used to establish the utility of this bioprocess to efficiently generate ES-derived cardiomyocytes. The genetically engineered ES cells were cultured directly in the stirred bioreactor for 9 days, followed by antibiotic treatment for another 9 days. The protocol resulted in the generation of essentially pure cardiomyocyte cultures, with a total yield of 1.28 x 10(9) cells in a single 2 L bioreactor run. This study thus provides an important step towards the large-scale generation of ES-derived cells for therapeutic and industrial applications.     

Integration of biocatalyst and process engineering for sustainable and efficient n‐butanol production

Recent environmental economic developments generate a need for sustainable and cost‐effective (microbial) processes for the production of high‐volume, low‐priced bulk chemicals. As an example, n‐butanol has, as a second‐generation biofuel, beneficial characteristics compared to ethanol in liquid transportation fuel applications. The industrial revival of the classic n‐butanol (ABE) fermentation requires process and strain engineering solutions for overcoming the main process limitations: product toxicity and low space–time yield. Reaction intensification on the biocatalyst, fermentation, and bioprocess level can be based on economic and ecologic evaluations using quantifiable constraints. This review describes the means of process intensification for biotechnological processes. A quantitative approach is then used for the comparison of the massive literature on n‐butanol fermentation. A comprehensive literature study—including key fermentation performance parameters—is presented and the results are visualized using the window of operation methodology. The comparison allowed the identification of the key constraints, high cell densities, high strain stability, high specific production rate, cheap in situ product removal, high n‐butanol tolerance, to operate in situ product removal efficiently, and cheap carbon source. It can thus be used as a guideline for the bioengineer during the combined biocatalyst, fermentation, and bioprocess development and intensification.     

Metabolic engineering of apoptosis in cultured animal cells: implications for the biotechnology industry

Animal cells have been widely used to obtain a wide range of products for human and animal healthcare applications. However, the extreme sensitivity of these cells in respect to changes experienced in their environment is evidenced by the activation of a gene-encoded program known as apoptosis, resulting in their death and destruction. From the bioprocess angle, losses in cell viability bring lower productivities and higher risks of product degradation. Consequently, many research efforts have been devoted to the development of apoptosis protective mechanisms, including the metabolic engineering of apoptosis pathways, that has proven effective in diminishing programmed cell death in a variety of biotechnological relevant cell lines. This review is focused especially in the encouraging initial results obtained with the over-expression of cloned anti-apoptosis genes, from both endogenous and viral origin interfering at mitochondrial and initiator caspases levels.     

动物细胞代谢工程进展

动物细胞被越来越广泛地用于工业生产,一些现代化企业已采用分子生物学技术,将一些比较重要的基因导入动物细胞,生产具有医用价值的药物。但该技术并未成熟,主要是因为体外培养的细胞,其生长代谢及生理模式都比较复杂,而且细胞的应答机制还受外界因素的影响。因此,采用细胞代谢工程手段,提高体外培养细胞的生长率、产品产率及有效性,成为人们追求的新目标。我们从细胞代谢中心途径、抑制细胞调亡的因素、细胞生长周期的控制及其相关代谢、多基因共表达代谢工程及糖基化代谢工程等方面对代谢工程进行阐述,为动物细胞的培养提供新的思路。     

Automated maintenance of embryonic stem cell cultures

Embryonic stem cell (ESC) technology provides attractive perspectives for generating unlimited numbers of somatic cells for disease modeling and compound screening. A key prerequisite for these industrial applications are standardized and automated systems suitable for stem cell processing. Here we demonstrate that mouse and human ESC propagated by automated culture maintain their mean specific growth rates, their capacity for multi-germlayer differentiation, and the expression of the pluripotency-associated markers SSEA-1/Oct-4 and Tra-1-60/Tra-1-81/Oct-4, respectively. The feasibility of ESC culture automation may greatly facilitate the use of this versatile cell source for a variety of biomedical applications.     

Single-cell bioelectrical impedance platform for monitoring cellular response to drug treatment

The response of cells to a chemical or biological agent in terms of their impedance changes in real-time is a useful mechanism that can be utilized for a wide variety of biomedical and environmental applications. The use of a single-cell-based analytical platform could be an effective approach to acquiring more sensitive cell impedance measurements, particularly in applications where only diminutive changes in impedance are expected. Here, we report the development of an on-chip cell impedance biosensor with two types of electrodes that host individual cells and cell populations, respectively, to study its efficacy in detecting cellular response. Human glioblastoma (U87MG) cells were patterned on single- and multi-cell electrodes through ligand-mediated natural cell adhesion. We comparatively investigated how these cancer cells on both types of electrodes respond to an ion channel inhibitor, chlorotoxin (CTX), in terms of their shape alternations and impedance changes to exploit the fine detectability of the single-cell-based system. The detecting electrodes hosting single cells exhibited a significant reduction in the real impedance signal, while electrodes hosting confluent monolayer of cells showed little to no impedance change. When single-cell electrodes were treated with CTX of different doses, a dose-dependent impedance change was observed. This enables us to identify the effective dose needed for this particular treatment. Our study demonstrated that this single-cell impedance system may potentially serve as a useful analytical tool for biomedical applications such as environmental toxin detection and drug evaluation.     

Designing a blueprint for next-generation stem cell bioprocessing development

The creation of a blueprint for stem cell bioprocess development that it is easily readable and shareable among those involved in the construction of the bioprocess is a necessary step toward full-fledged bioprocess integration. The blueprint provides the culturing tools and methodologies, designed to highlight knowledge gaps within biological sciences and bioengineering. This review highlights a blueprint for stem cell bioprocessing development using a landscape architecture approach that can aid the development of culture technologies and tools that satisfy the demands for stem cell-derived products for use in clinical and industrial applications. This work is intended to provide insights to cell biologists, geneticists, bioengineers, and clinicians seeking knowledge outside of their field of expertise and fosters a leap from a reductionist approach to one, that is, globally integrated in stem cell bioprocessing.