Very high cell density perfusion of CHO cells anchored in a non-woven matrix-based bioreactor

Current and future technologies for monitoring cultured meat: A review

The high population growth rate, massive animal food consumption, fast economic progress, and limited food resources could lead to a food crisis in the future. There is a huge requirement for dietary proteins including cultured meat is being progressed to fulfill the need for meat-derived proteins in the diet. However, production of cultured meat requires monitoring numerous bioprocess parameters. This review presents a comprehensive overview of various widely adopted techniques (optical, spectroscopic, electrochemical, capacitive, FETs, resistive, microscopy, and ultrasound) for monitoring physical, chemical, and biological parameters that can improve the bioprocess control in cultured meat. The methods, operating principle, merits/demerits, and the main open challenges are reviewed with the aim to support the readers in advancing knowledge on novel sensing systems for cultured meat applications.

Biosorption of process-equipment-related leachables (PERLs) in biomanufacturing: A quantitative approach to study partitioning of PERLs in a cell culture system

The assessment and potential risk of process equipment-related leachables (PERLs) in the production of biopharmaceuticals and cell therapeutics using single-use (SU) equipment has been discussed previously. However, potential interactions of cells with PERLs have not yet been considered. Here, we present a quantitative adsorption study of neutral, organic small-molecule leachable compounds - known for extractables & leachables (E&L) analysis of SU equipment - in aqueous suspensions of CHO and T cells. The solid-water partition coefficient K_d was obtained for all compounds that showed adsorption. The findings implied that hydrophobic interactions are dominant; however, there was no unambiguous correlation between the derived adsorption coefficient K_d and the octanol-water partition coefficient K_ow. Interestingly, a maximum affinity of both cell types to the leachable bis(2,4-di-tert-butylphenyl)phosphate, which is known to be detrimental to cell development, was observed. A comparison of both cell types revealed that they generally interact with the same compounds in most cases but to different extents. Using partition coefficients enables estimation of the concentrations of leachable compounds associated with the biomass phase and in the aqueous suspensions and could be used for risk assessment of SU systems in biopharmaceutical and cell therapy (CT) manufacturing processes.

The cell density effect in animal cell-based bioprocessing: Questions, insights and perspectives

One of the main challenges in the development of bioprocesses based on cell transient expression is the commonly reported reduction of cell specific productivity at increasing cell densities. This is generally known as the cell density effect (CDE). Many efforts have been devoted to understanding the cell metabolic implications to this phenomenon in an attempt to design operational strategies to overcome it. A comprehensive analysis of the main studies regarding the CDE is provided in this work to better define the elements comprising its cause and impact. Then, examples of methodologies and approaches employed to achieve successful transient expression at high cell densities (HCD) are thoroughly reviewed. A critical assessment of the limitations of the reported studies in the understanding of the CDE is presented, covering the leading hypothesis of the molecular implications. The overall analysis of previous work on CDE may offer useful insights for further research into manufacturing of biologics.

Transformation of Biopharmaceutical Manufacturing Through Single-Use Technologies: Current State, Remaining Challenges, and Future Development

Single-use technologies have transformed conventional biopharmaceutical manufacturing, and their adoption is increasing rapidly for emerging applications like antibody-drug conjugates and cell and gene therapy products. These disruptive technologies have also had a significant impact during the coronavirus disease 2019 pandemic, helping to advance process development to enable the manufacturing of new monoclonal antibody therapies and vaccines. Single-use systems provide closed plug-and-play solutions and enable process intensification and continuous processing. Several challenges remain, providing opportunities to advance single-use sensors and their integration with single-use systems, to develop novel plastic materials, and to standardize design for interchangeability. Because the industry is changing rapidly, a holistic analysis of the current single-use technologies is required, with a summary of the latest advancements in materials science and the implementation of these technologies in end-to-end bioprocesses.

Integrated continuous biomanufacturing on pilot scale for acid-sensitive monoclonal antibodies

In this study, we demonstrated the first, to our knowledge, integrated continuous bioprocess (ICB) designed for the production of acid-sensitive monoclonal antibodies, prone to aggregate at low pH, on pilot scale. A high cell density perfusion culture, stably maintained at 100 x 10⁶ cells/mL, was integrated with the downstream process, consisting of a capture step with the recently developed Protein A ligand, Z_Ca ; a solvent/detergent-based virus inactivation; and two ion exchange chromatography steps. The use of a mild pH in the downstream process makes this ICB suitable for the purification of acid-sensitive monoclonal antibodies. Integration and automation of the downstream process were achieved using the Orbit software, and the same equipment and control system were used in initial small-scale trials and the pilot-scale downstream process. High recovery yields of around 90% and a productivity close to 1 g purified antibody/L/day were achieved, with a stable glycosylation pattern and efficient removal of impurities, such as host cell proteins and DNA. Finally, negligible levels of antibody aggregates were detected owing to the mild conditions used throughout the process. The present work paves the way for future industrial-scale integrated continuous biomanufacturing of all types of antibodies, regardless of acid stability. This article is protected by copyright. All rights reserved.

High-density adherent culture of CHO cells using rolled scaffold bioreactor

Rapid expansion of biopharmaceutical market calls for more efficient and reliable platforms to culture mammalian cells on a large scale. Stirred-tank bioreactors have been widely used for large-scale cell culture. However, it requires months of trials and errors to optimize culture conditions for each cell line. In this article, we extend our earlier studies on rolled scaffold (RS) bioreactors for high-density adherent cell culture and report two new implementations of RSs with greatly enhanced mass-manufacturability, termed as Mesh-RS and Fiber-RS. CHO-K1 cells were successfully expanded in Mesh-RS and Fiber-RS bioreactors with an average growth rate of 1.09 ± 0.04 1/day and 0.95 ± 0.07 1/day, which were higher than those reported in similar studies. Fiber-RS bioreactor exhibited a very high cell density of 72.8 × 10⁶  cells/ml. Besides, a dialyzer was integrated into the RS bioreactor to remove cellular waste and to replenish nutrients without disturbing the cells. By collecting the dialyzed media separately, the dialysis efficiency was significantly improved. In conclusion, the developed RS bioreactor has a strong potential to provide a highly reliable and easily scalable platform for large-scale cell culture in the biopharmaceutical industry.

Perfusion culture of Chinese Hamster Ovary cells for bioprocessing applications

Much of the biopharmaceutical industry's success over the past 30 years has relied on products derived from Chinese Hamster Ovary (CHO) cell lines. During this time, improvements in mammalian cell cultures have come from cell line development and process optimization suited for large-scale fed-batch processes. Originally developed for high cell densities and sensitive products, perfusion processes have a long history. Driven by high volumetric titers and a small footprint, perfusion-based bioprocess research has regained an interest from academia and industry. The recent pandemic has further highlighted the need for such intensified biomanufacturing options. In this review, we outline the technical history of research in this field as it applies to biologics production in CHO cells. We demonstrate a number of emerging trends in the literature and corroborate these with underlying drivers in the commercial space. From these trends, we speculate that the future of perfusion bioprocesses is bright and that the fields of media optimization, continuous processing, and cell line engineering hold the greatest potential. Aligning in its continuous setup with the demands for Industry 4.0, perfusion biomanufacturing is likely to be a hot topic in the years to come.

Process intensification to produce a difficult-to-express therapeutic enzyme by high cell density perfusion or enhanced fed-batch

Intensified bioprocesses have caught industrial interest in the field of biomanufacturing in recent years. Thanks to new technology, intensified processes can support high cell densities, higher productivities and longer process times, which together can offer lower cost of goods. In this study two different intensified process modes, high cell density perfusion and enhanced fed-batch, were evaluated and compared with a conventional fed-batch process for a difficult-to-express therapeutic enzyme. The intensified process modes were cultivated with a target cell density of 100 × 10⁶  cells/ml and with alternating tangential flow filtration, ATF, as cell retention device. The processes were designed to resemble an established optimized fed-batch process using the knowledge of this process without new dedicated optimization for the intensified modes. The design strategy included decision of the ratio of feed concentrate to base medium and glucose supplementation, which were based on target cell-specific consumption rates of key amino acids and glucose, using a targeted feeding approach (TAFE). A difficult-to-express therapeutic enzyme with multiple glycosylation sites was expressed and analyzed in the different production processes. The two new intensified processes both achieved 10 times higher volumetric productivity (mg/L/day) with retained protein quality and minor changes to the glycan profile compared to the fed-batch process. The study demonstrates the potential of using intensified processes for sensitive complex enzymes. It is shown here that it is possible to transfer a developed fed-batch process into high cell density processes either in intensified fed-batch or steady-state perfusion without new dedicated optimization. The results demonstrated as well that these intensified modes significantly increase the productivity while maintaining the desired product quality, for instance the same amount of product was obtained in 1 day during the perfusion process than in a whole fed-batch run. Without any prior optimization of the perfusion rate, the high cell density perfusion process resulted in only 1.2 times higher medium cost per gram produced protein.

A Scalable Suspension Platform for Generating High-Density Cultures of Universal Red Blood Cells from Human Induced Pluripotent Stem Cells

Universal red blood cells (RBCs) differentiated from O-negative human induced pluripotent stem cells (hiPSCs) could find applications in transfusion medicine. Given that each transfusion unit of blood requires 2 trillion RBCs, efficient bioprocesses need to be developed for large-scale in vitro generation of RBCs.

We have developed a scalable suspension agitation culture platform for differentiating hiPSC-microcarrier aggregates into functional RBCs and have demonstrated scalability of the process starting with 6 well plates and finally demonstrating in 500 mL spinner flasks. Differentiation of the best-performing hiPSCs generated 0.85 billion erythroblasts in 50 mL cultures with cell densities approaching 1.7 × 10⁷ cells/mL. Functional (oxygen binding, hemoglobin characterization, membrane integrity, and fluctuations) and transcriptomics evaluations showed minimal differences between hiPSC-derived and adult-derived RBCs.

The scalable agitation suspension culture differentiation process we describe here could find applications in future large-scale production of RBCs in controlled bioreactors.

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Scalable process for differentiating hiPSC-microcarrier aggregates into RBCs

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Erythroid differentiation potential of multiple hiPSC lines was evaluated

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hiPSC RBCs and adult RBCs revealed minor differences functionally and transcriptionally

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Co-culture of hiPSC RBCs with OP9 cells (2D and 3D) promoted improved enucleation

Control of IgG glycosylation in CHO cell perfusion cultures by GReBA mathematical model supported by a novel targeted feed, TAFE

The N-linked glycosylation pattern is an important quality attribute of therapeutic glycoproteins. It has been reported by our group and by others that different carbon sources, such as glucose, mannose and galactose, can differently impact the glycosylation profile of glycoproteins in mammalian cell culture. Acting on the sugar feeding is thus an attractive strategy to tune the glycan pattern. However, in case of feeding of more than one carbon source simultaneously, the cells give priority to the one with the highest uptake rate, which limits the usage of this tuning, e.g. the cells favor consuming glucose in comparison to galactose. We present here a new feeding strategy (named 'TAFE' for targeted feeding) for perfusion culture to adjust the concentrations of fed sugars influencing the glycosylation. The strategy consists in setting the sugar feeding such that the cells are forced to consume these substrates at a target cell specific consumption rate decided by the operator and taking into account the cell specific perfusion rate (CSPR). This strategy is applied in perfusion cultures of Chinese hamster ovary (CHO) cells, illustrated by ten different regimes of sugar feeding, including glucose, galactose and mannose. Applying the TAFE strategy, different glycan profiles were obtained using the different feeding regimes. Furthermore, we successfully forced the cells to consume higher proportions of non-glucose sugars, which have lower transport rates than glucose in presence of this latter, in a controlled way. In previous work, a mathematical model named Glycan Residues Balance Analysis (GReBA) was developed to model the glycosylation profile based on the fed carbon sources. The present data were applied to the GReBA to design a feeding regime targeting a given glycosylation profile. The ability of the model to achieve this objective was confirmed by a multi-round of leave-one-out cross-validation (LOOCV), leading to the conclusion that the GReBA model can be used to design the feeding regime of a perfusion cell culture to obtain a desired glycosylation profile.

An Alternative Perfusion Approach for the Intensification of Virus-Like Particle Production in HEK293 Cultures

Virus-like particles (VLPs) have gained interest over the last years as recombinant vaccine formats, as they generate a strong immune response and present storage and distribution advantages compared to conventional vaccines. Therefore, VLPs are being regarded as potential vaccine candidates for several diseases. One requirement for their further clinical testing is the development of scalable processes and production platforms for cell-based viral particles. In this work, the extended gene expression (EGE) method, which consists in consecutive media replacements combined with cell retransfections, was successfully optimized and transferred to a bioreactor operating in perfusion. A process optimization using design of experiments (DoE) was carried out to obtain optimal values for the time of retransfection, the cell specific perfusion rate (CSPR) and transfected DNA concentration, improving 86.7% the previously reported EGE protocol in HEK293. Moreover, it was successfully implemented at 1.5L bioreactor using an ATF as cell retention system achieving concentrations of 6.8·10¹⁰ VLP/mL. VLP interaction with the ATF hollow fibers was studied via confocal microscopy, field emission scanning electron microscopy, and nanoparticle tracking analysis to design a bioprocess capable of separating unassembled Gag monomers and concentrate VLPs in one step.

Rapid process development of serum-free pseudorabies virus production with the Quality by Design approach

This study described a successful application of the Quality by Design (QbD) approach to pseudorabies virus (PRV) production process development in a fixed-bed bioreactor using the serum-free medium (SFM). The innovated tube-fixed-bed bioreactor was used as a scale-down model of the fixed-bed bioreactor for process development. Risk analysis was performed using Ishikawa diagram combined with failure mode effects analysis (FMEA). The comparative experiment was performed to screen proper medium for adherent African green monkey kidney (Vero) cells from three commercially available SFMs (VP-SFM, ProVERO-1 and Vero-A). The Vero-A medium showed as an outstanding one for further study. The PRV titer in harvest medium was consider as Critical Quality Attribute (CQA) and the Critical Process Parameters (CPPs) [time of infection (TOI), multiplicity of infection (MOI) and initial inoculation cell density] ranked high with risk priority number (RPN) were taken into design of experiment (DoE) methodology. Then prediction model of PRV production process was established and a robust PRV production process was explored. Under the robust setpoint conditions, the Xcell 1 L laboratory-scale fixed-bed bioreactor yielded PRV titer up to 7.87 log₁₀ TCID₅₀/mL at 3 dpi, which was comparable with that in the tube-fixed-bed bioreactor. Combination of the tube-fixed-bed bioreactor and QbD approach could further accelerate the development of a robust virus production process.

Development of rolled scaffold for high-density adherent cell culture

Bioreactors for large-scale culture of mammalian cells are playing vital roles in biotechnology and bioengineering. Various bioreactors have been developed, but their capacity and efficiency are often limited by insufficient mass transfer rate and high shear stress. A rolled scaffold (RS) is a fully defined scaffold for high-density adherent culture of mammalian cells. The RS is a polymer film with spacers, that is rolled into a cylinder with a pre-determined gap between each turn. Cells are cultured on its inner surfaces, while media flows through the gap. The RS exhibits high surface-area-to-volume ratio over 100 cm²/mL and can transport nutrients and gases with significantly reduced shear stress via convection in a unidirectional laminar flow, rather than diffusion and random turbulent flow as in stirred-tank bioreactors. In this paper, we expanded Chinese Hamster Ovary cells with RS bioreactors and demonstrated cell culture density over 60 million cells/mL with a growth rate higher than conventional suspension culture. Besides, murine embryonic stem cells were successfully expanded without losing their pluripotency. The RS will provide an affordable, scalable, and reliable platform for large-scale culture of recombinant cells in biopharmaceutical industries and shear-sensitive stem cells for tissue engineering.

In Vitro Insect Muscle for Tissue Engineering Applications

Tissue engineering is primarily associated with medical disciplines, and research has thus focused on mammalian cells. For applications where clinical relevance is not a constraint, it is useful to evaluate the potential of alternative cell sources to form tissues in vitro. Specifically, skeletal muscle tissue engineering for bioactuation and cultured foods could benefit from the incorporation of invertebrate cells because of their less stringent growth requirements and other versatile features. Here, we used a Drosophila muscle cell line to demonstrate the benefits of insect cells relative to those derived from vertebrates. The cells were adapted to serum-free media, transitioned between adherent and suspension cultures, and manipulated with hormones. Furthermore, we analyzed edible scaffolds to support cell adhesion and assayed cellular protein and minerals to evaluate nutrition potential. The insect muscle cells exhibited advantageous growth patterns and hold unique functionality for tissue engineering applications beyond the medical realm.

Bioreactors for high cell density and continuous multi-stage cultivations: options for process intensification in cell culture-based viral vaccine production

With an increasing demand for efficacious, safe, and affordable vaccines for human and animal use, process intensification in cell culture-based viral vaccine production demands advanced process strategies to overcome the limitations of conventional batch cultivations. However, the use of fed-batch, perfusion, or continuous modes to drive processes at high cell density (HCD) and overextended operating times has so far been little explored in large-scale viral vaccine manufacturing. Also, possible reductions in cell-specific virus yields for HCD cultivations have been reported frequently. Taking into account that vaccine production is one of the most heavily regulated industries in the pharmaceutical sector with tough margins to meet, it is understandable that process intensification is being considered by both academia and industry as a next step toward more efficient viral vaccine production processes only recently. Compared to conventional batch processes, fed-batch and perfusion strategies could result in ten to a hundred times higher product yields. Both cultivation strategies can be implemented to achieve cell concentrations exceeding 10(7) cells/mL or even 10(8) cells/mL, while keeping low levels of metabolites that potentially inhibit cell growth and virus replication. The trend towards HCD processes is supported by development of GMP-compliant cultivation platforms, i.e., acoustic settlers, hollow fiber bioreactors, and hollow fiber-based perfusion systems including tangential flow filtration (TFF) or alternating tangential flow (ATF) technologies. In this review, these process modes are discussed in detail and compared with conventional batch processes based on productivity indicators such as space-time yield, cell concentration, and product titers. In addition, options for the production of viral vaccines in continuous multi-stage bioreactors such as two- and three-stage systems are addressed. While such systems have shown similar virus titers compared to batch cultivations, keeping high yields for extended production times is still a challenge. Overall, we demonstrate that process intensification of cell culture-based viral vaccine production can be realized by the consequent application of fed-batch, perfusion, and continuous systems with a significant increase in productivity. The potential for even further improvements is high, considering recent developments in establishment of new (designer) cell lines, better characterization of host cell metabolism, advances in media design, and the use of mathematical models as a tool for process optimization and control.

Observation of Chinese Hamster Ovary Cells retained inside the non-woven fiber matrix of the CellTank bioreactor

This data article shows how the recombinant Chinese Hamster Ovary (CHO) cells are located in the interstices of the matrix fibers of a CellTank bioreactor after completion of a perfusion culture, supporting the article entitled "Very high cell density perfusion of CHO cells anchored in a non-woven matrix-based bioreactor" by Zhang et al. [1]. It provides a visualization of the cell distribution in the non-woven fiber matrix in a deeper view.