Mammalian cell retention devices for stirred perfusion bioreactors

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.

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.

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.

Separation of Ultra-High-Density Cell Suspension via Elasto-Inertial Microfluidics

Separation of high-density suspension particles at high throughput is crucial for many chemical, biomedical, and environmental applications. In this study, elasto-inertial microfluidics is used to manipulate ultra-high-density cells to achieve stable equilibrium positions in microchannels, aided by the inherent viscoelasticity of high-density cell suspension. It is demonstrated that ultra-high-density Chinese hamster ovary cell suspension (>26 packed cell volume% (PCV%), >95 million cells mL^-1 ) can be focused at distinct lateral equilibrium positions under high-flow-rate conditions (up to 10 mL min^-1 ). The effect of flow rates, channel dimensions, and cell densities on this unique focusing behavior is studied. Cell clarification is further demonstrated using this phenomenon, from 29.7 PCV% (108.1 million cells mL^-1 ) to 8.3 PCV% (33.2 million cells mL^-1 ) with overall 72.1% reduction efficiency and 10 mL min^-1 processing rate. This work explores an extreme case of elasto-inertial particle focusing where ultra-high-density culture suspension is efficiently manipulated at high throughput. This result opens up new opportunities for practical applications of high-particle-density suspension manipulation.

Pharma 4.0 Continuous mRNA Drug Products Manufacturing

Continuous mRNA drugs manufacturing is perceived to nurture flow processes featuring quality by design, controlled automation, real time validation, robustness, and reproducibility, pertaining to regulatory harmonization. However, the actual adaptation of the latter remains elusive, hence batch-to-continuous transition would a priori necessitate holistic process understanding. In addition, the cost related to experimental, pilot manufacturing lines development and operations thereof renders such venture prohibitive. Systems-based Pharmaceutics 4.0 digital design enabling tools, i.e., converging mass and energy balance simulations, Monte-Carlo machine learning iterations, and spatial arrangement analysis were recruited herein to overcome the aforementioned barriers. The primary objective of this work is to hierarchically design the related bioprocesses, embedded in scalable devices, compatible with continuous operation. Our secondary objective is to harvest the obtained technological data and conduct resource commitment analysis. We herein demonstrate for first time the feasibility of the continuous, end-to-end production of sterile mRNA formulated into lipid nanocarriers, defining the equipment specifications and the desired operational space. Moreover, we find that the cell lysis modules and the linearization enzymes ascend as the principal resource-intensive model factors, accounting for 40% and 42% of the equipment and raw material, respectively. We calculate MSPD 1.30–1.45 €, demonstrating low margin lifecycle fluctuation.

Hydrocyclones as cell retention devices for an N-1 perfusion bioreactor linked to a continuous-flow stirred tank production bioreactor

A continuous Chinese hamster ovary (CHO) cell culture process comprised of a highly proliferative N-1 perfusion bioreactor utilizing a hydrocyclone as a cell retention device linked to a production continuous-flow stirred tank reactor (CSTR) is presented. The overflow stream from the hydrocyclone, which is only partially depleted of cells, provides a continuous source of high viability cells from the N-1 perfusion bioreactor to the 5-20 times larger CSTR. Under steady-state conditions, this linked-bioreactor system achieved a peak volumetric productivity of 0.96 g/L/day, twofold higher than the optimized fed-batch process. The linked bioreactor system using a hydrocyclone was also shown to be 1.8-3.1 times more productive than a dual, cascading CSTR system without cell retention.

Low Shear Stress Increases Recombinant Protein Production and High Shear Stress Increases Apoptosis in Human Cells

Human embryonic kidney cells HEK293 can be used for the production of therapeutic glycoproteins requiring human post-translational modifications. High cell density perfusion processes are advantageous for such production but are challenging due to the shear sensitivity of HEK293 cells. To understand the impact of hollow filter cell separation devices, cells were cultured in bioreactors operated with tangential flow filtration (TFF) or alternating tangential flow filtration (ATF) at various flow rates. The average theoretical velocity profile in these devices showed a lower shear stress for ATF by a factor 0.637 compared to TFF. This was experimentally validated and, furthermore, transcriptomic evaluation provided insights into the underlying cellular processes. High shear caused cellular stress leading to apoptosis by three pathways, i.e. endoplasmic reticulum stress, cytoskeleton reorganization, and extrinsic signaling pathways. Positive effects of mild shear stress were observed, with increased recombinant erythropoietin production and increased gene expression associated with transcription and protein phosphorylation.

Establishment and optimization of a high-throughput mimic perfusion model in ambr® 15

OBJECTIVES

To establish an automated high-throughput mimic perfusion scale-down model (SDM) in ambr^® 15 system.

RESULTS

An optimized SDM for mimic perfusion was developed in ambr^® 15 system. Cell retention in ambr^® 15 was realized by sedimentation and supernatant removal with a retention rate > 95%. Although the SDM couldn't reach the viable cell density (VCD) at a bench scale bioreactor (BR), it maintained VCD at approximately 30 × 10⁶ cells/mL with a cell bleeding rate estimated theoretically and predicted the cell specific perfusion rate (CSPR). A base-feeding strategy was developed to alleviate the pH drop during sedimentation which would adversely have an impact on cell growth, and showed an apparent cell viability improvement from 79.6% (control) to 90.1% on Day 18. The optimized SDM for mimic perfusion was employed for media screening in two cell lines.

CONCLUSIONS

A small-scale high-throughput perfusion model in ambr^® 15 was developed, optimized to improve cell viability, and as a result, utilized for media screening in two cell lines.

Application of an Inclined Settler for Cell Culture-Based Influenza A Virus Production in Perfusion Mode

Influenza viruses have been successfully propagated using a variety of animal cell lines in batch, fed-batch, and perfusion culture. For suspension cells, most studies reported on membrane-based cell retention devices typically leading to an accumulation of viruses in the bioreactor in perfusion mode. Aiming at continuous virus harvesting for improved productivities, an inclined settler was evaluated for influenza A virus (IAV) production using the avian suspension cell line AGE1.CR.pIX. Inclined settlers present many advantages as they are scalable, robust, and comply with cGMP regulations, e.g., for recombinant protein manufacturing. Perfusion rates up to 3000 L/day have been reported. In our study, successful growth of AGE1.CR.pIX cells up to 50 × 10⁶ cells/mL and a cell retention efficiency exceeding 96% were obtained with the settler cooled to room temperature. No virus retention was observed. A total of 5.4-6.5 × 10¹³ virions were produced while a control experiment with an ATF system equaled to 1.9 × 10¹³ virions. For infection at 25 × 10⁶ cells/mL, cell-specific virus yields up to 3474 virions/cell were obtained, about 5-fold higher than for an ATF based cultivation performed as a control (723 virions/cell). Trypsin activity was shown to have a large impact on cell growth dynamics after infection following the cell retention device, especially at a cell concentration of 50 × 10⁶ cells/mL. Further control experiments performed with an acoustic settler showed that virus production was improved with a heat exchanger of the inclined settler operated at 27°C. In summary, cell culture-based production of viruses in perfusion mode with an inclined settler and continuous harvesting can drastically increase IAV yields and possibly the yield of other viruses. To our knowledge, this is the first report to show the potential of this device for viral vaccine production.

Modulation of transmembrane pressure in manufacturing scale tangential flow filtration N-1 perfusion seed culture

Mammalian cells were grown to high density in a 3,000 L culture using perfusion with hollow fibers operated in a tangential flow filtration mode. The high-density culture was used to inoculate the production stage of a biomanufacturing process. At constant permeate flux operation, increased transmembrane pressures (TMPs) were observed on the final day of the manufacturing batches. Small scale studies suggested that the filters were not irreversibly fouled, but rather exposed to membrane concentration polarization that could be relieved by tangential sweeping of the hollow fibers. Studies were undertaken to analyze parameters that influence the hydrodynamic profile within hollow fibers; including filter area, cell density, recirculation flow rate, and permeate flow rate. Results indicated that permeate flow rate had the greatest influence on modulating TMP. Further evaluation showed a significant decrease in TMP when permeate flow was reduced, and this occurred without any negative effect on cell growth or viability. Hence, a 30% reduction of permeate flow rate was implemented at manufacturing scale. A stable operation was achieved as TMP was successfully reduced by 75% while preserving all critical factors for performance in the perfusion bioreactor.

Screening of Media Supplements for High-Performance Perfusion Cultures by Design of Experiment

Perfusion is considered as the preferable unit operation mode for fully integrated continuous bioprocessing. However, the inherent complex process control, long process development times, and lack of suitable scale-down models for high-throughput screening are reasons why perfusion processes are still not routinely applied in cell culture technology. Advantages of perfusion are maintenance of a consistent cellular environment, a constant high-quality product flow, enhanced volumetric bioreactor productivity, and small lab footprint. Here, we provide guidelines for screening different proprietary but commercially available HyClone™ Cell Boost™ supplements in a Design of Experiment (DoE) approach to spike the HyClone™ CDM4NS0 basal media for enhanced product titers in small-scale TubeSpin models. These surrogate semi-perfusion cultures were successfully realized by a daily complete media exchange routine resulting in high viable cell densities for extended time periods at minimal media consumption. This technique was leveraged to define the potential of different perfusion media formulations.

An Introduction to "Recent Trends in the Biotechnology Industry: Development and Manufacturing of Recombinant Antibodies and Proteins"

The production of the first therapeutic proteins in the early 1980s heralded the launch of the biopharmaceuticals industry. The number of approved products has grown year on year over the past three decades to now represent a significant share of the entire pharmaceuticals market. More than 200 therapeutic proteins have been approved, approximately a quarter of which are represented by monoclonal antibodies and their derivatives. In 2016, the list of the top 15 best-selling drugs included more than eight biologics and in 2020 the trend will continue, with more than 50% of the top 20 best-selling drugs predicted to be biologics. From 1986 to 2014 several first-in-class, advance-in-class, and breakthrough designated therapeutic options were approved, with advanced therapies such as immuno-oncology and cell-based therapies being approved for several indications.

Continuous Manufacturing of Recombinant Therapeutic Proteins: Upstream and Downstream Technologies

Continuous biomanufacturing of recombinant therapeutic proteins offers several potential advantages over conventional batch processing, including reduced cost of goods, more flexible and responsive manufacturing facilities, and improved and consistent product quality. Although continuous approaches to various upstream and downstream unit operations have been considered and studied for decades, in recent years interest and application have accelerated. Researchers have achieved increasingly higher levels of process intensification, and have also begun to integrate different continuous unit operations into larger, holistically continuous processes. This review first discusses approaches for continuous cell culture, with a focus on perfusion-enabling cell separation technologies including gravitational, centrifugal, and acoustic settling, as well as filtration-based techniques. We follow with a review of various continuous downstream unit operations, covering categories such as clarification, chromatography, formulation, and viral inactivation and filtration. The review ends by summarizing case studies of integrated and continuous processing as reported in the literature.

Innovation in Cell Banking, Expansion, and Production Culture

Cell culture-based production processes enable the development and commercial supply of recombinant protein products. Such processes consist of the following elements: thaw and initiation of culture, seed expansion, and production culture. A robust cell source storage system in the form of a cell bank is developed and cells are thawed to initiate the cell culture process. Seed culture expansion generates sufficient cell mass to initiate the production culture. The production culture provides an environment where the cells can synthesize the product and is optimized to deliver the highest possible product concentration with acceptable product quality. This chapter describes the significant innovations made in these process elements and the resulting improvements in the overall efficiency, robustness, and safety of the processes and products.

A protocol to transfer a fed-batch platform process into semi-perfusion mode: The benefit of automated small-scale bioreactors compared to shake flasks as scale-down model

Continuous processes such as perfusion processes can offer advantages compared to fed‐batch or batch processes in bio‐processing: improved product quality (e.g. for labile products), increased product yield, and cost savings. In this work, a semi‐perfusion process was established in shake flasks and transferred to an automated small‐scale bioreactor by daily media exchange via centrifugation based on an existing fed‐batch process platform. At first the development of a suitable medium and feed composition, the glucose concentration required by the cells and the cell‐specific perfusion rate were investigated in shake flasks as the conventional scale‐down system. This lead to an optimized process with a threefold higher titer of 10 g/L monoclonal antibody compared to the standard fed‐batch. To proof the suitability and benefit as a small‐scale model, the established semi‐perfusion process was transferred to an automated small‐scale bioreactor with improved pH and dissolved oxygen control. The average specific productivity improved from 24.16 pg/(c*d) in the fed‐batch process and 36.04 pg/c*d in the semi‐perfusion shake flask to 38.88 pg/(c*d) in the semi‐perfusion process performed in the controlled small‐scale bioreactor, thus illustrating the benefits resulting from the applied semi‐perfusion approach, especially in combination with controlled DO and pH settings. © 2019 The Authors. Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 35: e2757, 2019.

Larger Pore Size Hollow Fiber Membranes as a Solution to the Product Retention Issue in Filtration-Based Perfusion Bioreactors

Tangential flow filtration (TFF) and alternating tangential flow (ATF) filtration technologies using hollow fiber membranes are commonly utilized in perfusion cell culture for the production of monoclonal antibodies; however, product retention remains a known and common problem with these systems. To address this issue, commercially available hollow fibers ranging from several hundred kilo-Daltons (kDa) to 0.65 μm in nominal pore size are tested and are all demonstrated to undergo moderate to severe product retention. Further investigation revealed accumulation of particles in the same size range (≈20-200 nm) as the pores. Based on the assumption that these particles contribute to product retention and membrane plugging, a hollow fiber with an unconventionally larger pore size is subsequently identified and demonstrated to drastically reduce product retention with no impact to cell clarification. Furthermore, these hollow fibers demonstrate surprisingly high membrane capacities, making them an attractive solution to the problem of product retention in perfusion reactors.

Combination of temperature shift and hydrolysate addition regulates anti-IgE monoclonal antibody charge heterogeneity in Chinese hamster ovary cell fed-batch culture

Charge heterogeneity has been broadly studied as a critical quality attribute during monoclonal antibody (mAb) production that may subsequently affect product stability and biopotency. However, the charge variation distribution is poorly controlled, so methods of more effective control need to be explored. In this study, the combined effects of temperature shift (37-34, 37-32, or 37-30 °C) and hydrolysate addition (0.100 g/L) to culture feed on the charge heterogeneity of anti-IgE mAb were investigated. The results showed that the distribution of charge variation was significantly regulated by the combination of hydrolysate addition with a highly sub-physiological temperature (34 °C). In addition, under this condition, the main peak content significantly increased, and the acidic peak content significantly decreased. Furthermore, we explored Lys variant content, which is the major basic variant content, as well as its relationship with temperature shift and hydrolysate addition. Lys variant levels were positively related to the Lys and Arg concentrations in the medium and negatively related to carboxypeptidase B and carboxypeptidase H transcript levels. The combination of temperature shift and hydrolysate addition can thus effectively improve anti-IgE mAb charge heterogeneity and significantly increase main variant levels and decrease acidic variant levels.

Impact of Pluronic® F68 on hollow fiber filter-based perfusion culture performance

High cell density is an important factor in achieving high bioreactor productivity. To meet the oxygen demand with density at >100 × 10⁶ cells/mL, a frit sparger is often used. In this study, the impact of Pluronic^® F68 on a perfusion process using a frit sparger was studied. The perfusion process was developed using an alternating tangential flow device with a 0.2 µm PES hollow fiber filter. Pluronic^® F68 at 2 g/L was sufficient in preventing cell damage at gas flow rate of ~0.20 vvm from a drilled hole sparger (0.5 mm) but inadequate at ~0.025 vvm from a frit sparger (20 µm). Increase of Pluronic^® F68 concentration to 5 g/L prevented cell death at up to ~0.10 vvm from the frit sparger and was able to maintain high cell density at high viability in the range of 60-80 × 10⁶ cells/mL. Such positive effect was demonstrated in both 3- and 200-L bioreactors. Supplementing additional Pluronic^® F68 was also effective in restoring cell growth/viability from low viability cultures. Increased Pluronic^® F68 concentration had no adverse impact on target antibody, HCP, and Pluronic^® F68 transmissions.

Nutrient Regulation by Continuous Feeding for Large-scale Expansion of Mammalian Cells in Spheroids

In this demonstration, spheroids formed from the β-TC6 insulinoma cell line were cultured as a model of manufacturing a mammalian islet cell product to demonstrate how regulating nutrient levels can improve cell yields. In previous studies, bioreactors facilitated increased culture volumes over static cultures, but no increase in cell yields were observed. Limitations in key nutrients such as glucose, which were consumed between batch feedings, can lead to limitations in cell expansion. Large fluctuations in glucose levels were observed, despite the increase in glucose concentrations in the media. The use of continuous feeding systems eliminated fluctuations in glucose levels, and improved cell growth rates when compared with batch fed static and SSB culture methods. Additional increases in growth rates were observed by adjusting the feed rate based on calculated nutrient consumption, which allowed the maintenance of physiological glucose over three weeks in culture. This method can also be adapted for other cell types.

Separation of suspensions and emulsions via ultrasonic standing waves - a review

Ultrasonic standing waves (USW) separation is an established technology for micro scale applications due to the excellent control to manipulate particles acoustically achieved when combining high frequency ultrasound with laminar flow in microchannels, allowing the development of numerous applications. Larger scale systems (pilot to industrial) are emerging; however, scaling up such processes are technologically very challenging. This paper reviews the physical principles that govern acoustic particle/droplet separation and the mathematical modeling techniques developed to understand, predict, and design acoustic separation processes. A further focus in this review is on acoustic streaming, which represents one of the major challenges in scaling up USW separation processes. The manuscript concludes by providing a brief overview of the state of the art of the technology applied in large scale systems with potential applications in the dairy and oil industries.

Configuration of bioreactors

Lab-scale stirred-tank bioreactors (0.2-20 l) are used for fundamental research on animal cells and in process development and troubleshooting for large-scale production. In this chapter, different configurations of bioreactor systems are shortly discussed and setting up these different configurations is described. In addition, online measurement and control of bioreactor parameters is described, with special attention to controller settings (PID) and online measurement of oxygen consumption and carbon dioxide production. Finally, methods for determining the oxygen transfer coefficient are described.

Production of high-titer human influenza A virus with adherent and suspension MDCK cells cultured in a single-use hollow fiber bioreactor

Hollow fiber bioreactors (HFBRs) have been widely described as capable of supporting the production of highly concentrated monoclonal antibodies and recombinant proteins. Only recently HFBRs have been proposed as new single-use platforms for production of high-titer influenza A virus. These bioreactors contain multiple hollow fiber capillary tubes that separate the bioreactor in an intra- and an extra-capillary space. Cells are usually cultured in the extra-capillary space and can grow to a very high cell concentration. This work describes the evaluation of the single-use hollow fiber bioreactor PRIMER HF (Biovest International Inc., USA) for production of influenza A virus. The process was setup, characterized and optimized by running a total of 15 cultivations. The HFBRs were seeded with either adherent or suspension MDCK cells, and infected with influenza virus A/PR/8/34 (H1N1), and the pandemic strain A/Mexico/4108/2009 (H1N1). High HA titers and TCID₅₀ of up to 3.87 log₁₀(HA units/100 μL) and 1.8 × 10(10)virions/mL, respectively, were obtained for A/PR/8/34 influenza strain. Influenza virus was collected by performing multiple harvests of the extra-capillary space during a virus production time of up to 12 days. Cell-specific virus yields between 2,000 and 8,000 virions/cell were estimated for adherent MDCK cells, and between 11,000 and 19,000 virions/cell for suspension MDCK.SUS2 cells. These results do not only coincide with the cell-specific virus yields obtained with cultivations in stirred tank bioreactors and other high cell density systems, but also demonstrate that HFBRs are promising and competitive single-use platforms that can be considered for commercial production of influenza virus.

Nutrient regulation by continuous feeding removes limitations on cell yield in the large-scale expansion of Mammalian cell spheroids

Cellular therapies are emerging as a standard approach for the treatment of several diseases. However, realizing the promise of cellular therapies across the full range of treatable disorders will require large-scale, controlled, reproducible culture methods. Bioreactor systems offer the scale-up and monitoring needed, but standard stirred bioreactor cultures do not allow for the real-time regulation of key nutrients in the medium. In this study, β-TC6 insulinoma cells were aggregated and cultured for 3 weeks as a model of manufacturing a mammalian cell product. Cell expansion rates and medium nutrient levels were compared in static, stirred suspension bioreactors (SSB), and continuously fed (CF) SSB. While SSB cultures facilitated increased culture volumes, no increase in cell yields were observed, partly due to limitations in key nutrients, which were consumed by the cultures between feedings, such as glucose. Even when glucose levels were increased to prevent depletion between feedings, dramatic fluctuations in glucose levels were observed. Continuous feeding eliminated fluctuations and improved cell expansion when compared with both static and SSB culture methods. Further improvements in growth rates were observed after adjusting the feed rate based on calculated nutrient depletion, which maintained physiological glucose levels for the duration of the expansion. Adjusting the feed rate in a continuous medium replacement system can maintain the consistent nutrient levels required for the large-scale application of many cell products. Continuously fed bioreactor systems combined with nutrient regulation can be used to improve the yield and reproducibility of mammalian cells for biological products and cellular therapies and will facilitate the translation of cell culture from the research lab to clinical applications.

Continuous production and recovery of itaconic acid in a membrane bioreactor

This study presents the fermentative production of the platform chemical itaconic acid using the fungus Ustilago maydis. The innovative aspect here is that the fermentation is run continuously with integrated cell retention and product recovery using membranes. Unlike conventional membrane processes, we use the recently introduced "reverse-flow diafiltration" which prevents performance loss by periodically reversing the flow direction. Results show that filtration stability can be (1) significantly improved compared to conventional membrane processes and (2) product recovery was constantly high at highly dynamic conditions. This is especially remarkable when taking into account the complex nature of fungi cells which tend to block surfaces rapidly.

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

High cell density perfusion process of antibody producing CHO cells was developed in disposable WAVE Bioreactor™ using external hollow fiber filter as cell separation device. Both "classical" tangential flow filtration (TFF) and alternating tangential flow system (ATF) equipment were used and compared. Consistency of both TFF- and ATF-based cultures was shown at 20-35 × 10(6) cells/mL density stabilized by cell bleeds. To minimize the nutrients deprivation and by-product accumulation, a perfusion rate correlated to the cell density was applied. The cells were maintained by cell bleeds at density 0.9-1.3 × 10(8) cells/mL in growing state and at high viability for more than 2 weeks. Finally, with the present settings, maximal cell densities of 2.14 × 10(8) cells/mL, achieved for the first time in a wave-induced bioreactor, and 1.32 × 10(8) cells/mL were reached using TFF and ATF systems, respectively. Using TFF, the cell density was limited by the membrane capacity for the encountered high viscosity and by the pCO2 level. Using ATF, the cell density was limited by the vacuum capacity failing to pull the highly viscous fluid. Thus, the TFF system allowed reaching higher cell densities. The TFF inlet pressure was highly correlated to the viscosity leading to the development of a model of this pressure, which is a useful tool for hollow fiber design of TFF and ATF. At very high cell density, the viscosity introduced physical limitations. This led us to recommend cell densities under 1.46 × 10(8) cell/mL based on the analysis of the theoretical distance between the cells for the present cell line.

Equipment design considerations for large scale cell culture

Equipment design is frequently recognized as a key component in the success of GMP biologics manufacturing, but is not always implemented with full appreciation of the processing implications. In the case of mammalian cell culture, there are some recognized issues and risks that develop when transitioning to a large scale of operation. The developing demand for cell culture production capacity in the biopharmaceutical industry has led to a progressive increase in the scale of operation in the last decade. This review will provide a high level summary of the documented process difficulties unique to serum-free large scale (LS) cell culture, analyze the engineering constraints typical of these processes, and suggest some practical equipment design considerations to enhance the productivity, reliability and operability of such systems under GMP manufacturing conditions. A systems approach will be used to establish a good LS bioreactor design practice, providing a discussion on gas distribution, agitation, vessel design, SIP/CIP and control issues.

CFD-aided cell settler design optimization and scale-up: effect of geometric design and operational variables on separation performance

The inclined multiplate (lamella) gravity settler has proven to be an effective cell retention device in industrial perfusion cell culture applications. Investigations on the effects of geometric design and operational variables of the cell settler are crucial to understanding how to best improve the settler performance. Maximizing the harvest/perfusion flow rate while minimizing viable cell loss out of the harvest is the primary challenge for optimization of the settler design. This study demonstrated that computational fluid dynamics (CFD) can be utilized to accurately model and evaluate the settler separation performance for near-monodisperse suspensions and therefore aid in the design optimization of the settler under these baseline conditions. With the preferred geometric features that were identified from CFD modeling results, we proposed design guidelines for the scale-up of these multiplate settler systems. With these guidelines and performance verification using the CFD model, a new large-scale settler was designed and fabricated for a perfusion cell culture process using a minimally aggregating production cell line. Perfusion cell culture runs with this particular cell line were performed with this settler, and the CFD model was able to predict the initial ramp-up performance, proving it to be a valuable scale-up design tool for this production process.

A Perfusion Culture System Using a Stirred Ceramic Membrane Reactor for Hyperproduction of IgG2a Monoclonal Antibody by Hybridoma Cells

A novel perfusion culture system for efficient production of IgG2a monoclonal antibody (mAb) by hybridoma cells was developed. A ceramic membrane module was constructed and used as a cell retention device installed in a conventional stirred-tank reactor during the perfusion culture. Furthermore, the significance of the control strategy of perfusion rate (volume of fresh medium/working volume of reactor/day, vvd) was investigated. With the highest increasing rate (deltaD, vvd per day, vvdd) of perfusion rate, the maximal viable cell density of 3.5 x 10(7) cells/mL was obtained within 6 days without any limitation and the cell viability was maintained above 95%. At lower deltaD's, the cell growth became limited. Under nutrient-limited condition, the specific cell growth rate (mu) was regulated by deltaD. During the nonlimited growth phase, the specific mAb production rate (qmAb) remained constant at 0.26 +/- 0.02 pg/cell x h in all runs. During the cell growth-limited phase, qmAb was regulated by deltaD within the range of 0.25-0.65 vvdd. Under optimal conditions, qmAb of 0.80 and 2.15 pg/cell x h was obtained during the growth-limited phase and stationary phase, respectively. The overall productivity and yield were 690 mg/L x day and 340 mg/L x medium, respectively. This study demonstrated that this novel perfusion culture system for suspension mammalian cells can support high cell density and efficient mAb production and that deltaD is an important control parameter to regulate and achieve high mAb production.