Very high density of CHO cells in perfusion by ATF or TFF in WAVE bioreactor™. Part I. Effect of the cell density on the process

Fed-batch strategies for intensified rVSV vector production in high cell density cultures of suspension HEK293 cells

Vesicular stomatitis virus (VSV) has been increasingly demonstrated as a promising viral vector platform. As the interest over this modality for vaccine and gene therapy applications increases, the need for intensified processes to produce these vectors emerge. In this study, we develop fed-batch-based operations to intensify the production of a recombinant VSV-based vaccine candidate (rVSV-SARS-CoV-2) in suspension cultures of HEK293 cells. A feeding strategy, in which a commercial concentrated medium was added to cultures based on cell growth through a fixed cell specific feeding rate (CSFR), was applied for the development of two different processes using Ambr250 modular bioreactors. Cultures operated in hybrid fed-batch/perfusion (FB/P) or fed-batch (FB) were able to sustain infections performed at 8.0 × 106 cells/mL, respectively resulting in 3.9 and 5.0-fold increase in total yield (YT) and 1.7 and 5.6-fold increase in volumetric productivity (VP) when compared with a batch reference. A maximum viral titer of 4.5 × 1010 TCID50/mL was reached, which is comparable or higher than other processes for VSV production in different cell lines. Overall, our study reports efficient fed-batch options to intensify the production of a rVSV-based vaccine candidate in suspension HEK293 cells.

Improved sieving coefficient in perfusion cell culture with reduced effective filtration length of hollow fibers

The hollow fiber filter is the primary cell-retention device used in high-density perfusion cell culture and often used in an alternating tangential flow (ATF) configuration. The limited commercially available diaphragm pumps for ATF prevent utilization of vertical space when scaling beyond 500 L. Stacking hollow fiber filters coupled with viscous cell culture imposes vacuum pressure exceeding facility capabilities. Additionally, the longer filter assembly increases the hold-up volume and exceeds the diaphragm pump's fluid exchange capacity. The conventional tangential flow filtration (TFF) configuration circumvents this issue by exchanging culture from the bioreactor and cell-retention device in a unidirectional recirculation loop; however, the increased filter length when scaled up exacerbates the TFF's inherent issue with product retention from Starling flow. Stacking commercially available 20 cm TFF filters to make up the similar single-module length TFF used for the platform 3 and 50 L perfusion process at 41.5 and 65 cm, respectively, attempts to reduce fouling caused by Starling flow. The permeate of a single-module filter is partitioned into short independent segments through serially stacked filters, each harvested separately. By partitioning the permeate, the sieving coefficient increased for both 3 and 50 L scales. Reduction of Starling flow was confirmed with lower total hydraulic membrane resistance throughout the culture. This work demonstrates a method for increasing sieving coefficient and filter capacity by stacking TFF filters with independent permeate streams.

Evaluation of various membranes at different fluxes to enable large-volume single-use perfusion bioreactors

The growing demand for biological therapeutics has increased interest in large-volume perfusion bioreactors, but the operation and scalability of perfusion membranes remain a challenge. This study evaluates perfusion cell culture performance and monoclonal antibody (mAb) productivity at various membrane fluxes (1.5-5 LMH), utilizing polyvinylidene difluoride (PVDF), polyethersulfone (PES), or polysulfone (PS) membranes in tangential flow filtration mode. At low flux, culture with PVDF membrane maintained higher cell culture growth, permeate titer (1.06-1.34 g/L) and sieving coefficients (≥83%) but showed lower permeate volumetric throughput and higher transmembrane pressure (TMP) (>1.50 psi) in the later part of the run compared to cultures with PES and PS membrane. However, as permeate flux increased, the total mass of product decreased by around 30% for cultures with PVDF membrane, while it remained consistent with PES and PS membrane, and at the highest flux studied, PES membrane generated 12% more product than PVDF membrane. This highlights that membrane selection for large-volume perfusion bioreactors depends on the productivity and permeate flux required. Since operating large-volume perfusion bioreactors at low flux would require several cell retention devices and a complex setup, PVDF membranes are suitable for low-volume operations at low fluxes whereas PES membranes can be a desirable alternative for large-volume higher demand products at higher fluxes.

Gene Delivery From Granular Scaffolds for Tunable Biologics Manufacturing

The understanding of the molecular basis for disease has generated a myriad of therapeutic biologics, including therapeutic proteins, antibodies, and viruses. However, the promise that biologics can resolve currently incurable diseases hinges in their manufacturability. These therapeutics require that their genetic material be introduced to mammalian cells such that the cell machinery can manufacture the biological components. These are then purified, validated, and packaged. Most manufacturing uses batch processes that collect the biologic a few days following genetic modification, due to toxicity or difficulty in separating product from cells in a continuous operation, limiting the amount of biologic that can be produced and resulting in yearlong backlogs. Here, a scaffold-based approach for continuous biologic manufacturing is presented, with sustained production of active antibodies and viruses for 30 days. The use of scaffold-based biologic production enabled perfusion-based bioreactors to be used, which can be incorporated into a fully continuous process.

Empirical economic analysis shows cost-effective continuous manufacturing of cultivated chicken using animal-free medium

Cellular agriculture aims to meet the growing demand for animal products. However, current production technologies result in low yields, leading to economic projections that prohibit cultivated meat scalability. Here we use tangential flow filtration for continuous manufacturing of cultivated meat to produce biomass of up to 130 × 106 cells per ml, corresponding to yields of 43% w/v and multiple harvests for over 20 days. Continuous manufacturing was carried out in an animal-component-free culture medium for US$0.63 l-1 that supports the long-term, high density culture of chicken cells. Using this empirical data, we conducted a techno-economic analysis for a theoretical production facility of 50,000 l, showing that the cost of cultivated chicken can drop to within the range of organic chicken at US$6.2 lb-1 by using perfusion technology. Whereas other variables would also affect actual market prices, continuous manufacturing can offer cost reductions for scaling up cultivated meat production.

Dialysis rolled scaffold bioreactor allows extended production of monoclonal antibody with reduced media use

Rapidly expanding biopharmaceutical market demands more cost-effective platforms to produce protein therapeutics. To this end, novel approaches, such as perfusion culture or concentrated fed-batch, have been explored for higher yields and lower manufacturing costs. Although these new approaches produced promising results, but their wide-spread use in the industry is still limited. In this study, a dialysis rolled scaffold bioreactor was presented for long-term production of monoclonal antibodies with reduced media consumption. Media dialysis can selectively remove cellular bio-wastes without losing cells or produced recombinant proteins. The dialysis process was streamlined to significantly improve its efficiency. Then, extended culture of recombinant CHO cells for 41 days was successfully demonstrated with consistent production rate and minimal media consumption. The unique configuration of the developed bioreactor allows efficient dialysis for media management, as well as rapid media exchange to harvest produced recombinant proteins before they degrade. Taken together, it was envisioned that the developed bioreactor will enable cost-effective and long-term large-scale culture of various cells for biopharmaceutical production.

Identification of infectious viruses for risk-based virus testing of CHO unprocessed bulk using next-generation sequencing

It is important to increase manufacturing speed to make medicines more widely available. One bottleneck for CHO-based drug substance release is the in vitro viral (IVV) cell-based assay on unprocessed bulk. To increase process speed, we evaluate the suitability of replacing the IVV cell-based assay with next-generation sequencing (NGS). First, we outline how NGS is currently used in the pharmaceutical industry, and how it may apply to CHO virus testing. Second, we examine CHO virus contamination history. Since prior virus contaminants can replicate in the production bioreactor, we perform a literature search and classify 159 viruses as high, medium, low, or unknown risk based on their ability to infect CHO cells. Overall, the risk of virus contamination during the CHO manufacturing process is low. Only six viruses were reported to have contaminated CHO bioprocesses over the past several decades, and were primarily caused by fetal bovine serum or cell culture components. These virus contamination events can be mitigated through limitation and control of raw materials, combined with virus testing and virus clearance technologies. The list of CHO infectious viruses provides a starting framework for virus safety risk assessment and NGS development. Furthermore, ICH Q5A (R2) includes NGS as a molecular method for adventitious agent testing, paving a path forward for modernizing CHO virus testing.

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

A modular and multi-functional purification strategy that enables a common framework for manufacturing scale integrated and continuous biomanufacturing

Biopharmaceutical manufacture is transitioning from batch to integrated and continuous biomanufacturing (ICB). The common framework for most ICB, potentially enables a global biomanufacturing ecosystem utilizing modular and multi-function manufacturing equipment. Integrating unit operation hardware and software from multiple suppliers, complex supply chains enabled by multiple customized single-use flow paths, and large volume buffer production/storage make this ICB vision difficult to achieve with commercially available manufacturing equipment. Thus, we developed SymphonX™, a downstream processing skid with advanced buffer management capabilities, a single disposable generic flow path design that provides plug-and-play flexibility across all downstream unit operations and a single interface to reduce operational risk. Designed for multi-product and multi-process cGMP facilities, SymphonX™ can perform stand-alone batch processing or ICB. This study utilized an Apollo™ X CHO-DG44 mAb-expressing cell line in a steady-state perfusion bioreactor, harvesting product continuously with a cell retention device and connected SymphonX™ purification skids. The downstream process used the same chemistry (resins, buffer composition, membrane composition) as our historical batch processing platform, with SymphonX™ in-line conditioning and buffer concentrates. We used surge vessels between unit operations, single-column chromatography (protein A, cation and anion exchange) and two-tank batch virus inactivation. After the first polishing step (cation exchange), we continuously pooled product for 6 days. These 6 day pools were processed in batch-mode from anion exchange to bulk drug substance. This manufacturing scale proof-of-concept ICB produced 0.54 kg/day of drug substance with consistent product quality attributes and demonstrated successful bioburden control for unit-operations undergoing continuous operation.

Proteomic analysis of host cell protein fouling during bioreactor harvesting

Chinese hamster ovary (CHO) cells are among the most common cell lines used for therapeutic protein production. Membrane fouling during bioreactor harvesting is a major limitation for the downstream purification of therapeutic proteins. Host cell proteins (HCP) are the most challenging impurities during downstream purification processes. The present work focuses on identification of HCP foulants during CHO bioreactor harvesting using reverse asymmetrical commercial membrane BioOptimal™ MF-SL. In order to investigate foulants and fouling behavior during cell clarification, for the first time a novel backwash process was developed to effectively elute almost all the HCP and DNA from the fouled membrane filter. The isoelectric points (pIs) and molecular weights (MWs) of major HCP in the bioreactor harvest and fouled on the membrane were successfully characterized using two-dimensional gel electrophoresis (2D SDS-PAGE). In addition, a total of 8 HCP were identified using matrix-assisted laser desorption/ionization-mass spectroscopy (MALDI-MS). The majority of these HCP are enzymes or associated with exosomes, both of which can form submicron-sized particles which could lead to the plugging of the filters.

Adeno-associated virus perfusion enhanced expression: A commercially scalable, high titer, high quality producer cell line process

With safety and efficacy demonstrated over hundreds of clinical trials in the last 30 years, along with at least six recent global marketing authorizations achieved since 2017, recombinant adeno-associated viruses (rAAVs) have been established as the leading therapeutic gene transfer vector for rare, monogenic diseases. Significant advances in manufacturing technology have been made in the last few decades to address challenges with GMP production of rAAV products, although yield, cost, scalability, and quality remain a challenge. With transient transfection processes established as a manufacturing platform for multiple commercial AAV products, there remains significant yield, cost, robustness, and scalability constraints that need to be resolved to enable a reliable supply of rAAV products for global patient access. The development of stable producer cell lines for rAAV products has enabled scalability and, in some cases, improvements in productivity. Herein we describe a novel AAV perfusion-enhanced expression (APEX) process, resulting in higher maximum cell densities in the production bioreactor with a 3- to 6-fold increase in volumetric productivity. This process has been successfully demonstrated across multiple serotypes in large scale cell culture with titers approaching 1 × 1012 GC/mL. The APEX production platform marks a significant leap forward in the efficient and effective manufacturing of rAAV vector products.

Platform development for high-throughput optimization of perfusion processes: Part I: Implementation of cell bleeds in microwell plates

The promise of continuous processing to increase yields and improve product quality of biopharmaceuticals while decreasing the manufacturing footprint is transformative. Developing and optimizing perfusion operations requires screening various parameters, which is expensive and time-consuming when using benchtop bioreactors. Scale-down models (SDMs) are the most feasible option for high-throughput data generation and condition screening. However, new SDMs mimicking perfusion are required, enabling experiments to be run in parallel. In this study, a method using microwell plates (MWP) operating in semi-perfusion mode with an implemented cell bleed step is presented. A CHO cell line was cultivated in a 24-well MWP (Vw = 1.2 mL) and grown at four high cell density (HCD) setpoints. Quasi steady-state condition was obtained by manually performing cell bleeds followed by a total medium exchange after centrifugation. Further, two HCD setpoints were scaled up (VW = 30 mL), comparing a squared six-well deepwell plate (DWP) to shake flasks (SF). This evaluation showed comparable results between systems (DWP vs. SF) and scales (MWP vs. DWP + SF). The results show that the well-plate-based methods are suitable to perform HCD and quasi steady-state cultivations providing a robust solution to industrially relevant challenges such as cell clone and media selection.

Continuous multi-column capture of monoclonal antibodies with convective diffusive membrane adsorbers

Downstream processing is the bottleneck in the continuous manufacturing of monoclonal antibodies (mAbs). To overcome throughput limitations, two different continuous processes with a novel convective diffusive protein A membrane adsorber (MA) were investigated: the rapid cycling parallel multi-column chromatography (RC-PMCC) process and the rapid cycling simulated moving bed (RC-BioSMB) process. First, breakthrough curve experiments were performed to investigate the influence of the flow rate on the mAb dynamic binding capacity and to calculate the duration of the loading steps. In addition, customized control software was developed for an automated MA exchange in case of pressure increase due to membrane fouling to enable robust, uninterrupted, and continuous processing. Both processes were performed for 4 days with 0.61 g L-1 mAb-containing filtrate and process performance, product purity, productivity, and buffer consumption were compared. The mAb was recovered with a yield of approximately 90% and productivities of 1010 g L-1 d-1 (RC-PMCC) and 574 g L-1 d-1 (RC-BioSMB). At the same time, high removal of process-related impurities was achieved with both processes, whereas the buffer consumption was lower for the RC-BioSMB process. Finally, the attainable productivity for perfusion bioreactors of different sizes with suitable MA sizes was calculated to demonstrate the potential to operate both processes on a manufacturing scale with bioreactor volumes of up to 2000 L.

Harnessing metabolic plasticity in CHO cells for enhanced perfusion cultivation

Chinese Hamster Ovary (CHO) cells have rapidly become a cornerstone in biopharmaceutical production. Recently, a reinvigoration of perfusion culture mode in CHO cell cultivation has been observed. However, most cell lines currently in use have been engineered and adapted for fed-batch culture methods, and may not perform optimally under perfusion conditions. To improve the cell's resilience and viability during perfusion culture, we cultured a triple knockout CHO cell line, deficient in three apoptosis related genes BAX, BAK, and BOK in a perfusion system. After 20 days of culture, the cells exhibited a halt in cell proliferation. Interestingly, following this phase of growth arrest, the cells entered a second growth phase. During this phase, the cell numbers nearly doubled, but cell specific productivity decreased. We performed a proteomics investigation, elucidating a distinct correlation between growth arrest and cell cycle arrest and showing an upregulation of the central carbon metabolism and oxidative phosphorylation. The upregulation was partially reverted during the second growth phase, likely caused by intragenerational adaptations to stresses encountered. A phase-dependent response to oxidative stress was noted, indicating glutathione has only a secondary role during cell cycle arrest. Our data provides evidence of metabolic regulation under high cell density culturing conditions and demonstrates that cell growth arrest can be overcome. The acquired insights have the potential to not only enhance our understanding of cellular metabolism but also contribute to the development of superior cell lines for perfusion cultivation.

Effects of process intensification on homogeneity of an IgG1:κ monoclonal antibody during perfusion culture

The pharmaceutical industry employs various strategies to improve cell productivity. These strategies include process intensification, culture media improvement, clonal selection, media supplementation and genetic engineering of cells. However, improved cell productivity has inherent risk of impacting product quality attributes (PQA). PQAs may affect the products' efficacy via stability, bioavailability, or in vivo bioactivity. Variations in manufacturing process may introduce heterogeneity in the products by altering the type and extent of N-glycosylation, which is a PQA of therapeutic proteins. We investigated the effect of different cell densities representing increasing process intensification in a perfusion cell culture on the production of an IgG1-κ monoclonal antibody from a CHO-K1 cell line. This antibody is glycosylated both on light chain and heavy chain. Our results showed that the contents of glycosylation of IgG1-κ mAb increased in G0F and fucosylated type glycans as a group, whereas sialylated type glycans decreased, for the mAb whole protein. Overall, significant differences were observed in amounts of G0F, G1F, G0, G2FS1, and G2FS2 type glycans across all process intensification levels. G2FS2 and G2 type N-glycans were predominantly quantifiable from light chain rather than heavy chain. It may be concluded that there is a potential impact to product quality attributes of therapeutic proteins during process intensification via perfusion cell culture that needs to be assessed. Since during perfusion cell culture the product is collected throughout the duration of the process, lot allocation needs careful attention to process parameters, as PQAs are affected by the critical process parameters (CPPs). KEY POINTS: • Molecular integrity may suffer with increasing process intensity. • Galactosylated and sialylated N-glycans may decrease. • Perfusion culture appears to maintain protein charge structure.

Novel multimodal cation-exchange membrane for the purification of a single-chain variable fragment from Pichia pastoris supernatant

A novel salt-tolerant cation-exchange membrane, prepared with a multimodal ligand, 2-mercaptopyridine-3-carboxylic acid (MMC-MPCA), was examined for its purification properties in a bind-and-elute mode from the high conductivity supernatant of a Pichia pastoris fermentation producing and secreting a single-chain variable fragment (scFv). If successful, this approach would eliminate the need for a buffer exchange prior to product capture by ion-exchange. Two fed-batch fermentations of Pichia pastoris resulted in fermentation supernatants reaching an scFv titer of 395.0 mg/L and 555.7 mg/L, both with a purity of approximately 83 %. The MMC-MPCA membrane performance was characterized in terms of pH, residence time (RT), scFv load, and scFv concentration to identify the resulting dynamic binding capacity (DBC), yield, and purity achieved under optimal conditions. The MMC-MPCA membrane exhibited the highest DBC of 39.06 mg/mL at pH 5.5, with a residence time of 1 min, while reducing the pH below 5.0 resulted in a significant decrease of the DBC to around 2.5 mg/mL. With almost no diffusional limitations, reducing the RT from 2 to 0.2 min did not negatively impact the DBC of the MMC-MPCA membrane, resulting in a significant improvement in productivity of up to 180 mg/mL/min at 0.2 min RT. Membrane fouling was observed when reusing the membranes at 0.2 and 0.5 min RT, likely due to the enhanced adsorption of impurities on the membrane. Changing the amount of scFv loaded onto the membrane column did not show any changes in yield, instead a 10-20 % loss of scFv was observed, which suggested that some of the produced scFv were fragmented or had aggregated. When performing the purification under the optimized conditions, the resulting purity of the product improved from 83 % to approximately 92-95 %.

Bioreactors, scaffolds and microcarriers and in vitro meat production-current obstacles and potential solutions

In vitro meat production presents a potential viable alternative for meat consumption, which could provide the consumer with a product indistinguishable from the original, with very similar nutritional and culinary values. Indeed, the alternative products currently accessible often lack comparable nutritional value or culinary attributes to their animal-derived counterparts. This creates challenges for their global acceptance, particularly in countries where meat consumption holds cultural significance. However, while cultured meat research has been progressing rapidly in recent years, some significant obstacles still need to be overcome before its possible commercialization. Hence, this review summarizes the most current knowledge regarding the history of cultured meat, the currently used cell sources and methods used for the purpose of in vitro meat production, with particular focus on the role of bioreactors, scaffolds and microcarriers in overcoming the current obstacles. The authors put the potential microcarrier and scaffold-based solutions in a context, discussing the ways in which they can impact the way forward for the technology, including the use of considering the potential practical and societal barriers to implementing it as a viable food source worldwide.

WAVE-based intensified perfusion cell culture for fast process development

OBJECTIVE

This study was to evaluate the feasibility of using a rocking type bioreactor system, specifically the WAVE 25, in an intensified perfusion culture (IPC) mode for monoclonal antibody (mAb) production in Chinese hamster ovary (CHO) cell line.

METHODS

A disposable perfusion bag with floating membrane was used in the IPC process. An automated filter switching system was employed to continuously clarify the harvested post-membrane culture fluid. The overall cell culture performance, product titer, and quality were compared to those of a typical IPC conducted in a bench-top glass bioreactor.

RESULTS

The results showed that the overall trends of cell culture performance, product titer (accumulated harvest volumetric titer) were similar to those of the typical IPC conducted in the glass bioreactor, while the purity related quality were slightly better than the typical run. Furthermore, with the automated filter switching system, the harvested post-membrane culture fluid could be continuously clarified, making it suitable for downstream continuous chromatography.

CONCLUSION

The study demonstrated the feasibility of using the WAVE-based rocking type bioreactor in the N stage IPC process, which increases the flexibility in adopting IPC process. The results suggest that the rocking type bioreactor system could be a viable alternative to traditional stirred tank bioreactors for perfusion culture in the biopharmaceutical industry.

Optimization of medium with perfusion microbioreactors for high density CHO cell cultures at very low renewal rate aided by design of experiments

A novel approach of design of experiment (DoE) is developed for the optimization of key substrates of the culture medium, amino acids, and sugars, by utilizing perfusion microbioreactors with 2 mL working volume, operated in high cell density continuous mode, to explore the design space. A mixture DoE based on a simplex-centroid is proposed to test multiple medium blends in parallel perfusion runs, where the amino acids concentrations are selected based on the culture behavior in presence of different amino acid mixtures, and using targeted specific consumption rates. An optimized medium is identified with models predicting the culture parameters and product quality attributes (G0 and G1 level N-glycans) as a function of the medium composition. It is then validated in runs performed in perfusion microbioreactor in comparison with stirred-tank bioreactors equipped with alternating tangential flow filtration (ATF) or with tangential flow filtration (TFF) for cell separation, showing overall a similar process performance and N-glycosylation profile of the produced antibody. These results demonstrate that the present development strategy generates a perfusion medium with optimized performance for stable Chinese hamster ovary (CHO) cell cultures operated with very high cell densities of 60 × 106 and 120 × 106  cells/mL and a low cell-specific perfusion rate of 17 pL/cell/day, which is among the lowest reported and is in line with the framework recently published by the industry.

Rapid Identification of Chinese Hamster Ovary Cell Apoptosis and Its Potential Role in Process Robustness Assessment

Currently, the assessment of process robustness is often time-consuming, labor-intensive, and material-intensive using process characterization studies. Therefore, a simple and time-saving method is highly needed for the biopharmaceutical industry. Apoptosis is responsible for 80% of Chinese hamster ovary (CHO) cell deaths and affects the robustness of the cell culture process. This study’s results showed that a more robust process can support cells to tolerate apoptosis for a longer time, suggesting that the robustness of the process could be judged by the ability of cells to resist apoptosis. Therefore, it is necessary to establish a rapid method to detect the apoptosis of CHO cells. In trying to establish a new method for detecting apoptosis in large-scale cell cultures, glucose withdrawal was studied, and the results showed that CHO cells began to apoptose after glucose was consumed. Then, the concentration of extracellular potassium increased, and a prolongation of apoptosis time was observed. Further study results showed that the process with poor robustness was associated with a higher proportion of apoptosis and extracellular potassium concentration, so potassium could be used as a biochemical index of apoptosis. The strategy we present may be used to expedite the assessment of process robustness to obtain a robust cell culture process for other biologics.

Risk control of host cell proteins in one therapeutic antibody produced by concentrated fed-batch (CFB) mode

Multiple control strategies, including a downstream purification process with well-controlled parameters and a comprehensive release or characterization for intermediates or drug substances, were implemented to mitigate the potential risk of host cell proteins (HCPs) in one concentrated fed-batch (CFB) mode manufactured product. A host cell process specific enzyme-linked immunosorbent assay (ELISA) method was developed for the quantitation of HCPs. The method was fully validated and showed good performance including high antibody coverage. This was confirmed by 2D Gel-Western Blot analysis. Furthermore, a LC-MS/MS method with non-denaturing digestion and a long gradient chromatographic separation coupled with data dependent acquisition (DDA) on a Thermo/QE-HF-X mass spectrometer was developed as an orthogonal method to help identify the specific types of HCPs in this CFB product. Because of the high sensitivity, selectivity and adaptability of the new developed LC-MS/MS method, significantly more species of HCP contaminants were able to be identified. Even though high levels of HCPs were observed in the harvest bulk of this CFB product, the development of multiple processes and analytical control strategies may greatly mitigate potential risks and reduce HCPs contaminants to a very low level. No high-risk HCP was identified and the total amount of HCPs was very low in the CFB final product.

Spontaneous immortalization of chicken fibroblasts generates stable, high-yield cell lines for serum-free production of cultured meat

Cellular agriculture could meet growing demand for animal products, but yields are typically low and regulatory bodies restrict genetic modification for cultured meat production. Here we demonstrate the spontaneous immortalization and genetic stability of fibroblasts derived from several chicken breeds. Cell lines were adapted to grow as single-cell suspensions using serum-free culture medium, reaching densities of 108 × 106 cells per ml in continuous culture, corresponding to yields of 36% w/v. We show that lecithin activates peroxisome proliferator-activated receptor gamma (PPARγ), inducing adipogenesis in immortalized fibroblasts. Blending cultured adipocyte-like cells with extruded soy protein, formed chicken strips in which texture was supported by animal and plant proteins while aroma and flavour were driven by cultured animal fat. Visual and sensory analysis graded the product 4.5/5.0, with 85% of participants extremely likely to replace their food choice with this cultured meat product. Immortalization without genetic modification and high-yield manufacturing are critical for the market realization of cultured meat.

Optimization of an adenovirus-vectored zoster vaccine production process with chemically defined medium and a perfusion system

OBJECTIVES

Cells grown in chemically defined medium are sensitive to shear force, potentially resulting in decreased cell growth. We optimized the perfusion process for HEK293 cell-based recombinant adenovirus-vectored zoster vaccine (Ad-HER) production with chemically defined medium.

METHODS

We first studied the pseudo-continuous strategies in shake flasks as a mimic of the bioreactor equipped with perfusion systems. Using design of experiment (DoE) in shake flasks, we obtained the regression models between Ad-HER titer/virus input-output ratio and three production process parameters: time of infection (TOI), multiplicity of infection (MOI), and virus production pH (pH). We then confirmed the effect of Pluronic F68 (PF-68) at 3.0 g/L on HEK293 cell growth and Ad-HER production in shake flasks and a 2 L benchtop bioreactor.

RESULTS

The optimized process was scale-up to a 2 L benchtop bioreactor with the PATFP perfusion system, which yielded cell density of 7.4 × 10⁶ cells/mL and Ad-HER titer of 9.8 × 10⁹ IFU/mL at 2 dpi, comparable to the bioreactor with a ATF2 system.

CONCLUSION

This optimization strategy could be used to develop a robust process with stable cell culture performance and adenovirus titer. Increasing PF-68 concentration in chemically defined medium could protect cells from shear stress generated by perfusion system.

Model predictive control for steady-state performance in integrated continuous bioprocesses

Perfusion bioreactors are commonly used for the continuous production of monoclonal antibodies (mAb). One potential benefit of continuous bioprocessing is the ability to operate under steady-state conditions for an extended process time. However, the process performance is often limited by the feedback control of feed, harvest, and bleed flow rates. If the future behavior of a bioprocess can be adequately described, predictive control can reduce set point deviations and thereby maximize process stability. In this study, we investigated the predictive control of biomass in a perfusion bioreactor integrated to a non-chromatographic capture step, in a series of Monte-Carlo simulations. A simple algorithm was developed to estimate the current and predict the future viable cell concentrations (VCC) of the bioprocess. This feature enabled the single prediction controller (SPC) to compensate for process variations that would normally be transported to adjacent units in integrated continuous bioprocesses (ICB). Use of this SPC strategy significantly reduced biomass, product concentration, and harvest flow variability and stabilized the operation over long periods of time compared to simulations using feedback control strategies. Additionally, we demonstrated the possibility of maximizing product yields simply by adjusting perfusion control strategies. This method could be used to prevent savings in total product losses of 4.5-10% over 30 days of protein production.

Application of bioreactor technology for cell culture-based viral vaccine production: Present status and future prospects

Bioreactors are widely used in cell culture-based viral vaccine production, especially during the coronavirus disease 2019 (COVID-19) pandemic. In this context, the development and application of bioreactors can provide more efficient and cost-effective vaccine production to meet the global vaccine demand. The production of viral vaccines is inseparable from the development of upstream biological processes. In particular, exploration at the laboratory-scale is urgently required for further development. Therefore, it is necessary to evaluate the existing upstream biological processes, to enable the selection of pilot-scale conditions for academic and industrial scientists to maximize the yield and quality of vaccine development and production. Reviewing methods for optimizing the upstream process of virus vaccine production, this review discusses the bioreactor concepts, significant parameters and operational strategies related to large-scale amplification of virus. On this basis, a comprehensive analysis and evaluation of the various process optimization methods for the production of various viruses (SARS-CoV-2, Influenza virus, Tropical virus, Enterovirus, Rabies virus) in bioreactors is presented. Meanwhile, the types of viral vaccines are briefly introduced, and the established animal cell lines for vaccine production are described. In addition, it is emphasized that the co-development of bioreactor and computational biology is urgently needed to meet the challenges posed by the differences in upstream production scales between the laboratory and industry.

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.

Seed Train Intensification Using an Ultra-High Cell Density Cell Banking Process

A current focus of biopharmaceutical research and production is seed train process intensification. This allows for intermediate cultivation steps to be avoided or even for the direct inoculation of a production bioreactor with cells from cryovials or cryobags. Based on preliminary investigations regarding the suitability of high cell densities for cryopreservation and the suitability of cells from perfusion cultivations as inoculum for further cultivations, an ultra-high cell density working cell bank (UHCD-WCB) was established for an immunoglobulin G (IgG)-producing Chinese hamster ovary (CHO) cell line. The cells were previously expanded in a wave-mixed bioreactor with internal filter-based perfusion and a 1 L working volume. This procedure allows for cryovial freezing at 260 × 106 cells mL−1 for the first time. The cryovials are suitable for the direct inoculation of N−1 bioreactors in the perfusion mode. These in turn can be used to inoculate subsequent IgG productions in the fed-batch mode (low-seed fed-batch or high-seed fed-batch) or the continuous mode. A comparison with the standard approach shows that cell growth and antibody production are comparable, but time savings of greater than 35% are possible for inoculum production.

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.

The efficient development of a novel recombinant adenovirus zoster vaccine perfusion production process

The adenovirus vector vaccines induce humoral and cellular immune responses and have been used to develop vaccines for effective prevention of life-threating viruses, such as Ebola and Coronaviruses. High demand of vaccines worldwide requires optimization of the production process. Perfusion process increases cell concentration and volumetric productivity, so that it becomes the commonly used strategy in vaccine production In this study, we optimized and developed a perfusion process for the adenovirus-based zoster vaccine production efficiently. We first tested different perfusion strategies in shake flasks, showing semi-continuous strategies for optimal HEK 293 cell growth. We then evaluated three empirical key process parameters (cell concentration at the time of infection (VCC), multiplicity of infection (MOI), virus production pH) by the design of experiment (DoE) method, from which the robust setpoint (VCC 1.04 × 10⁷ cells/mL, MOI 9, and virus production pH 7.17) was confirmed in both shake flask and 2 L benchtop bioreactor. In the bioreactor, we compared the performances of two perfusion systems, the commercially-available XCell ATF® system and a novel peristaltic pump-driven alternating tangential flow perfusion system (PATFP system) that we developed. During cell cultivation stage, both perfusion systems have comparable performances regarding viable cell concentration and cell viability. At 2 dpi, the PATFP system resulted in an adenovirus titer of 2.1 × 10¹⁰ IFU/mL and cell-specific virus yield of 2,062 IFU/cell, reaching 75% and 77% of values for XCell ATF® system. This study demonstrates the perfusion process to be superior strategy for adenovirus-based vaccine production compared to the batch-mode strategy (1,467 IFU/cell). Furthermore, our PATFP system shows potential to be comparable to the XCell ATF® system, and it would become an alternative perfusion strategy for the vaccine production.

Enablers of continuous processing of biotherapeutic products

The benefits of continuous processing over batch manufacturing are widely acknowledged across the biopharmaceutical industry, primary of which are higher productivity and greater consistency in product quality. Furthermore, the reduced equipment and facility footprint lead to significantly lower capital costs. Technology enablers have a major role in this migration from batch to continuous processing. In this review, we highlight the various enablers that are facilitating adoption of continuous upstream and downstream bioprocessing. This includes new bioreactors and cell retention devices for upstream operations, and on-column and continuous flow refolding, novel continuous chromatography, and single-pass filtration systems for downstream processes. We also elucidate the significant roles of process integration and control as well as of data analytics in these processes.

Large-scale cultured meat production: Trends, challenges and promising biomanufacturing technologies

Food systems of the future will need to face an increasingly clear reality - that a protein-rich diet is essential for good health, but traditional meat products will not suffice to ensure safety, sustainability, and equity of food supply chains at a global scale. This paper provides an in-depth analysis of bioprocess technologies needed for cell-based meat production and challenges in reaching commercial scale. Specifically, it reviews state-of-the-art bioprocess technologies, current limitations, and opportunities for research across four domains: cell line development, cell culture media, scaffolding, and bioreactors. This also includes exploring innovations to make cultured meat a viable protein alternative across numerous key performance indicators and for specific applications where traditional livestock is not an option (e.g., local production, space exploration). The paper explores tradeoffs between production scale, product quality, production cost, and footprint over different time horizons. Finally, a discussion explores various factors that may impact the ability to successfully scale and market cultured meat products: social acceptance, environmental tradeoffs, regulatory guidance, and public health benefits. While the exact nature of the transition from traditional livestock to alternative protein products is uncertain, it has already started and will likely continue to build momentum in the next decade.

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.

Optimized process operations reduce product retention and column clogging in ATF-based perfusion cell cultures

Product retention in hollow fibers is a common issue in ATF-based cell culture system. In this study, the effects of four major process factors on product (therapeutic antibody/recombinant protein) retention were investigated using Chinese hamster ovary cell. Hollow fibers made of polysulfone presented a product retention rate from 15% ± 8 to 43% ± 18% higher than those made of polyether sulfone varying with specific processes. Higher harvest flowrate and ATF exchange rate increased product retention by 13% ± 10% and up to 31% ± 13%, respectively. Hollow fibers with larger pore sizes (0.65 μm) appeared to have increased product retention by 38% ± 7% compared with smaller ones (0.2 μm) in this study. Further investigation revealed that the effects of pore size on retention could be correlated to the particle size distribution in the cell culture broth. A hollow fiber with a larger pore size (>0.5 μm) may reduce protein retention when small particles (approximately 0.01-0.2 μm in diameter) are dominant in the culture. However, if majority of the particles are larger than 0.2 μm in diameter, hollow fiber with smaller pore sizes (0.2 μm) could be a solution to reducing product retention. Alternatively, process optimization may modulate particle size distribution towards reduced production retention with selected ATF hollow fibers. This study for the first time highlights the importance of matching proper pore sizes of hollow fibers with the cell culture particles distribution and offers methods to reducing product retention and ATF column clogging in perfusion cell cultures. KEY POINTS: The material of ATF column could impact product retention during perfusion culture. Higher harvest flowrate and ATF exchange rate increased product retention. Matching culture particle size and ATF pore size is critical for retention modulation.

The design basis for the integrated and continuous biomanufacturing framework

An 8 ton per year manufacturing facility is described based on the framework for integrated and continuous bioprocessing (ICB) common to all known biopharmaceutical implementations. While the output of this plant rivals some of the largest fed-batch plants in the world, the equipment inside the plant is relatively small: the plant consists of four 2000 L single-use bioreactors and has a maximum flow rate of 13 L/min. The equipment and facility for the ICB framework is described in sufficient detail to allow biopharmaceutical companies, vendors, contract manufacturers to build or buy their own systems. The design will allow the creation of a global ICB ecosystem that will transform biopharmaceutical manufacturing. The design is fully backward compatible with legacy fed-batch processes. A clinical production scale is described that can produce smaller batch sizes with the same equipment as that used at the commercial scale. The design described allows the production of as little as 10 g to nearly 35 kg of drug substance per day.

Scale-up economics for cultured meat

This analysis examines the potential of "cultured meat" products made from edible animal cell culture to measurably displace the global consumption of conventional meat. Recognizing that the scalability of such products must in turn depend on the scale and process intensity of animal cell production, this study draws on technoeconomic analysis perspectives in industrial fermentation and upstream biopharmaceuticals to assess the extent to which animal cell culture could be scaled like a fermentation process. Low growth rate, metabolic inefficiency, catabolite inhibition, and shear-induced cell damage will all limit practical bioreactor volume and attainable cell density. Equipment and facilities with adequate microbial contamination safeguards have high capital costs. The projected costs of suitably pure amino acids and protein growth factors are also high. The replacement of amino-acid media with plant protein hydrolysates is discussed and requires further study. Capital- and operating-cost analyses of conceptual cell-mass production facilities indicate economics that would likely preclude the affordability of their products as food. The analysis concludes that metabolic efficiency enhancements and the development of low-cost media from plant hydrolysates are both necessary but insufficient conditions for displacement of conventional meat by cultured meat.

Process intensification for the production of yellow fever virus-like particles as potential recombinant vaccine antigen

Yellow fever (YF) is a life-threatening viral disease endemic in parts of Africa and Latin America. Although there is a very efficacious vaccine since the 1930s, YF still causes 29,000-60,000 annual deaths. During recent YF outbreaks there were issues of vaccine shortage of the current egg-derived vaccine; rare but fatal vaccine adverse effects occurred; and cases were imported to Asia, where the circulating mosquito vector could potentially start local transmission. Here we investigated the production of YF virus-like particles (VLPs) using stably transfected HEK293 cells. Process intensification was achieved by combining sequential FACS (fluorescence-activated cell sorting) rounds to enrich the stable cell pool in terms of high producers and the use of perfusion processes. At shaken-tube scale, FACS enrichment of cells allowed doubling VLP production, and pseudoperfusion cultivation (with daily medium exchange) further increased VLP production by 9.3-fold as compared to batch operation mode. At perfusion bioreactor scale, the use of an inclined settler as cell retention device showed operational advantages over an ATF system. A one-step steric exclusion chromatography purification allowed significant removal of impurities and is a promising technique for future integration of upstream and downstream operations. Characterization by different techniques confirmed the identity and 3D-structure of the purified VLPs.

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.

End-to-end continuous bioprocessing: Impact on facility design, cost of goods, and cost of development for monoclonal antibodies

This article presents a systematic approach to evaluate the business case for continuous processing that captures trade-offs between manufacturing and development costs for monoclonal antibodies (mAbs). A decisional tool was built that integrated cost of goods (COG) with the cost of development models and new equipment sizing equations tailored to batch, hybrid, and end-to-end continuous processes. The COG analysis predicted that single-use continuous facilities (sized using a dedicated downstream processing train per bioreactor) offer more significant commercial COG savings over stainless steel batch facilities at annual demands of 100-500 kg (~35%), compared to tonnage demands of 1-3 tons (~±10%) that required multiple parallel continuous trains. Single-use batch facilities were found to compete with continuous options on COG only at 100 kg/year. For the scenarios where batch and continuous facilities offered similar COG, the analysis identified the windows of operation required to reach different COG savings with thresholds for the perfusion rate, volumetric productivity, and media cost. When considering the project lifecycle cost, the analysis indicated that while end-to-end continuous facilities may struggle to compete on development costs, they become more cost-effective than stainless steel batch facilities when considering the total out-of-pocket cost across both drug development and commercial activities.

Antibody capture process based on magnetic beads from very high cell density suspension

Cell clarification represents a major challenge for the intensification through very high cell density in the production of biopharmaceuticals such as monoclonal antibodies (mAbs). The present report proposes a solution to this challenge in a streamlined process where cell clarification and mAb capture are performed in a single step using magnetic beads coupled with protein A. Capture of mAb from non-clarified CHO cell suspension showed promising results; however, it has not been demonstrated that it can handle the challenge of very high cell density as observed in intensified fed-batch cultures. The performances of magnetic bead-based mAb capture on non-clarified cell suspension from intensified fed-batch culture were studied. Capture from a culture at density larger than 100 × 10⁶ cells/ml provided an adsorption efficiency of 99% and an overall yield of 93% with a logarithmic host cell protein (HCP) clearance of ≈2-3 and a resulting HCP concentration ≤≈5 ppm. These results show that direct capture from very high cell density cell suspension is possible without prior processing. This technology, which brings significant benefits in terms of operational cost reduction and performance improvements such as low HCP, can be a powerful tool alleviating the challenge of process intensification.

Trends in Monoclonal Antibody Production Using Various Bioreactor Syst

Monoclonal antibodies are widely used as diagnostic reagents and for therapeutic purposes, and their demand is increasing extensively. To produce these proteins in sufficient quantities for commercial use, it is necessary to raise the output by scaling up the production processes. This review describes recent trends in high-density cell culture systems established for monoclonal antibody production that are excellent methods to scale up from the lab-scale cell culture. Among the reactors, hollow fiber bioreactors contribute to a major part of high-density cell culture as they can provide a tremendous amount of surface area in a small volume for cell growth. As an alternative to hollow fiber reactors, a novel disposable bioreactor has been developed, which consists of a polymer-based supermacroporous material, cryogel, as a matrix for cell growth. Packed bed systems and disposable wave bioreactors have also been introduced for high cell density culture. These developments in high-density cell culture systems have led to the monoclonal antibody production in an economically favourable manner and made monoclonal antibodies one of the dominant therapeutic and diagnostic proteins in biopharmaceutical industry.