Optimisation of protein expression and establishment of the Wave Bioreactor for Baculovirus/insect cell culture

Protein Expression via Transient Transfection of Mammalian Cells in a WAVE Bioreactor

Large culture volumes are often required when expression constructs are particularly low-yielding or when end uses require significant amounts of material. In these cases, a single homogeneous culture is usually more convenient, in terms of both consistency of expression and labor/resource requirements, than multiple parallel cultures. Using a WAVE Bioreactor culture, volumes as high as 500L may be achieved in a single vessel. Here, we describe the transfection of Expi293F cells in a disposable 50L Cellbag on a WAVE Bioreactor platform to produce recombinant protein. The methods described herein may be adapted, with suitable optimizations, for other suspension-adapted mammalian cell lines.

Secreted Trimeric Chikungunya Virus Spikes from Insect Cells: Production, Purification, and Glycosylation Status

Chikungunya virus (CHIKV) is a rapidly emerging mosquito-borne virus that causes a severe febrile illness with long-lasting arthralgia in humans. As there is no vaccine to protect humans and limit CHIKV epidemics, the virus continues to be a global public health concern. The CHIKV envelope glycoproteins E1 and E2 are important immunogens; therefore, the aim of this study is to produce trimeric CHIKV spikes in insect cells using the baculovirus expression system. The CHIKV E1 and E2 ectodomains were covalently coupled by a flexible linker that replaces the 6K transmembrane protein. The C-terminal E1 transmembrane was replaced by a Strep-tag II for the purification of secreted spikes from the culture fluid. After production in Sf9 suspension cells (product yields of 5.8–7.6 mg/L), the CHIKV spikes were purified by Strep-Tactin affinity chromatography, which successfully cleared the co-produced baculoviruses. Bis(sulfosuccinimidyl)suberate cross-linking demonstrated that the spikes are secreted as trimers. PNGase F treatment showed that the spikes are glycosylated. LC–MS/MS-based glycoproteomic analysis confirmed the glycosylation and revealed that the majority are of the mannose- or hybrid-type N-glycans and <2% have complex-type N-glycans. The LC –MS/MS analysis also revealed three O-glycosylation sites in E1. In conclusion, the trimeric, glycosylated CHIKV spikes have been successfully produced in insect cells and are now available for vaccination studies.

Catalytically Cleavable Detergent for Membrane Protein Studies

Throughout the in vitro studies of membrane proteins (MPs), proper detergents are essential for the preparation of stable aqueous samples. To date, universally applicable detergents have not yet been reported to accommodate the distinct requirements for the highly diversified MPs and at the different stages of MP manipulation. Detergent exchange often has to be performed. We report herein the catalytically cleavable detergents (CatCDs) that can be efficiently removed to facilitate a complete exchange. To this end, functional groups, like propargyl and allyl, are introduced as branched chains or built in the hydrophobic chain close to the hydrophilic head. The representative CatCDs can be used as usual detergents in the extraction and purification of MPs and later be removed upon the addition of catalytic palladium. Mediated by CatCD-1, reconstitution of a transporter protein MsbA into a series of detergents was achieved. The extension of these designs could facilitate the future optimization of other biophysics studies.

PEI-Mediated Transient Transfection of High Five Cells at Bioreactor Scale for HIV-1 VLP Production

High Five cells are an excellent host for the production of virus-like particles (VLPs) with the baculovirus expression vector system (BEVS). However, the concurrent production of high titers of baculovirus hinder the purification of these nanoparticles due to similarities in their physicochemical properties. In this study, first a transient gene expression (TGE) method based on the transfection reagent polyethylenimine (PEI) is optimized for the production of HIV-1 VLPs at shake flask level. Furthermore, VLP production by TGE in High Five cells is successfully demonstrated at bioreactor scale, resulting in a higher maximum viable cell concentration (5.1 × 10⁶ cell/mL), the same transfection efficiency and a 1.8-fold increase in Gag-eGFP VLP production compared to shake flasks. Metabolism analysis of High Five cells indicates a reduction in the consumption of the main metabolites with respect to non-transfected cell cultures, and an increase in the uptake rate of several amino acids when asparagine is depleted. Quality assessment by nanoparticle tracking analysis and flow virometry of the VLPs produced shows an average size of 100–200 nm, in agreement with immature HIV-1 viruses reported in the literature. Overall, this work demonstrates that the High Five/TGE system is a suitable approach for the production of VLP-based vaccine candidates and other recombinant proteins.

Computational fluid dynamics analysis of mixing and gas-liquid mass transfer in wave bag bioreactor

Single use bioreactors provide an attractive alternative to traditional deep-tank stainless steel bioreactors in process development and more recently manufacturing process. Wave bag bioreactors, in particular, have shown potential applications for cultivation of shear sensitive human and animal cells. However, the lack of knowledge about the complex fluid flow environment prevailing in wave bag bioreactors has so far hampered the development of a scientific rationale for their scale up. In this study, we use computational fluid dynamics (CFD) to investigate the details of the flow field in a 20-L wave bag bioreactor as a function of rocking angle and rocking speed. The results are presented in terms of local and mean velocities, mixing, and energy dissipation rates, which are used to create a process engineering framework for the scale-up of wave bag bioreactors. Proof-of-concept analysis of mixing and fluid flow in the 20-L wave bag bioreactor demonstrates the applicability of the CFD methodology and the temporal and spatial energy dissipation rates integrated and averaged over the liquid volume in the bag provide the means to correlate experimental volumetric oxygen transfer rates (k_L a) data with power per unit volume. This correlation could be used as a rule of thumb for scaling up and down the wave bag bioreactors.

A mechanistic model for gas-liquid mass transfer prediction in a rocking disposable bioreactor

Rocking disposable bioreactors are a newer approach to smaller-scale cell growth that use a cyclic rocking motion to induce mixing and oxygen transfer from the headspace gas into the liquid. Compared with traditional stirred-tank and pneumatic bioreactors, rocking bioreactors operate in a very different physical mode and in this study the oxygen transfer pathways are reassessed to develop a fundamental mass transfer (k_L a) model that is compared with experimental data. The model combines two mechanisms, namely surface aeration and oxygenation via a breaking wave with air entrainment, borrowing concepts from ocean wave models. Experimental data for k L a across the range of possible operating conditions (rocking speed, angle, and liquid volume) confirms the validity of the modeling approach, with most predictions falling within ±20% of the experimental values. At low speeds (up to 20 rpm) the surface aeration mechanism is shown to be dominant with a k L a of around 3.5 hr^-1 , while at high speeds (40 rpm) and angles the breaking wave mechanism contributes up to 91% of the overall k L a (65 hr^-1 ). This model provides an improved fundamental basis for understanding gas-liquid mass transfer for the operation, scale-up, and potential design improvements for rocking bioreactors.

A Chemical Strategy for Amphiphile Replacement in Membrane Protein Research

Membrane mimics are indispensable tools in the structural and functional understanding of membrane proteins (MPs). Given stringent requirements of integral MP manipulations, amphiphile replacement is often required in sample preparation for various biophysical purposes. Current protocols generally rely on physical methodologies and rarely reach complete replacement. In comparison, we report herein a chemical alternative that facilitates the exhaustive exchange of membrane-mimicking systems for MP reconstitution. This method, named sacrifice-replacement strategy, was enabled by a class of chemically cleavable detergents (CCDs), derived from the disulfide incorporation in the traditional detergent n-dodecyl-β-d-maltopyranoside. The representative CCD behaved well in both solubilizing the diverse α-helical human G protein-coupled receptors and refolding of the β-barrel bacterial outer membrane protein X, and more importantly, it could also be readily degraded under mild conditions. By this means, the A_2A adenosine receptor was successfully reconstituted into a series of commercial detergents for stabilization screening and nanodiscs for electron microscopy analysis. Featured by the simplicity and compatibility, this CCD-mediated strategy would later find more applications when being integrated in other biophysics studies.

The components of shear stress affecting insect cells used with the baculovirus expression vector system

Insect-based expression platforms such as the baculovirus expression vector system (BEVS) are widely used for the laboratory- and industrial-scale production of recombinant proteins. Thereby, major drawbacks to gain high-quality proteins are the lytic infection cycle and the shear sensitivity of infected insect cells due to turbulence and aeration. Smaller bubbles were formerly assumed to be more harmful than larger ones, but we found that cell damage is also dependent on the concentration of protective agents such as Pluronic®. At the appropriate concentration, Pluronic forms a layer around air bubbles and hinders the attachment of cells, thus limiting the damage. In this context, we used microaeration to vary bubble sizes and confirmed that size is not the most important factor, but the total gas surface area in the reactor is. If the surface area exceeds a certain threshold, the concentration of Pluronic is no longer sufficient for cell protection. To investigate the significance of shear forces, a second study was carried out in which infected insect cells were cultivated in a hollow fiber module to protect them from shear forces. Both model studies revealed important aspects of the design and scale-up of BEVS processes for the production of recombinant proteins.

Dynamic Single-Use Bioreactors Used in Modern Liter- and m(3)- Scale Biotechnological Processes: Engineering Characteristics and Scaling Up

During the past 10 years, single-use bioreactors have been well accepted in modern biopharmaceutical production processes targeting high-value products. Up to now, such processes have mainly been small- or medium-scale mammalian cell culture-based seed inoculum, vaccine or antibody productions. However, recently first attempts have been made to modify existing single-use bioreactors for the cultivation of plant cells and tissue cultures, and microorganisms. This has even led to the development of new single-use bioreactor types. Moreover, due to safety issues it has become clear that single-use bioreactors are the "must have" for expanding human stem cells delivering cell therapeutics, the biopharmaceuticals of the next generation. So it comes as no surprise that numerous different dynamic single-use bioreactor types, which are suitable for a wide range of applications, already dominate the market today. Bioreactor working principles, main applications, and bioengineering data are presented in this review, based on a current overview of greater than milliliter-scale, commercially available, dynamic single-use bioreactors. The focus is on stirred versions, which are omnipresent in R&D and manufacturing, and in particular Sartorius Stedim's BIOSTAT family. Finally, we examine development trends for single-use bioreactors, after discussing proven approaches for fast scaling-up processes.

Manufacturing of AcMNPV baculovirus vectors to enable gene therapy trials

Over the past two decades, baculoviruses have become workhorse research tools for transient transgene expression. Although they have not yet been used directly as a gene therapy vector in the clinical setting, numerous preclinical studies have suggested the highly promising potential of baculovirus as a delivery vector for a variety of therapeutic applications including vaccination, tissue engineering, and cancer treatment. As such, there is growing interest in using baculoviruses as human gene therapy vectors, which has led to advances in baculovirus bioprocessing methods. This review provides an overview of the current approaches for scaled-up amplification, concentration, purification, and formulation of AcMNPV baculoviruses, and highlights the key regulatory requirements that must be met before gene therapy clinical trials can be initiated.

Protein Expression in Insect and Mammalian Cells Using Baculoviruses in Wave Bioreactors

Many types of disposable bioreactors for protein expression in insect and mammalian cells are now available. They differ in design, capacity, and sensor options, with many selections available for either rocking platform, orbitally shaken, pneumatically mixed, or stirred-tank bioreactors lined with an integral disposable bag (Shukla and Gottschalk, Trends Biotechnol 31(3):147-154, 2013). WAVE Bioreactors™ were among the first disposable systems to be developed (Singh, Cytotechnology 30:149-158, 1999). Since their commercialization in 1999, Wave Bioreactors have become routinely used in many laboratories due to their ease of operation, limited utility requirements, and protein expression levels comparability to traditional stirred-tank bioreactors. Wave Bioreactors are designed to use a presterilized Cellbag™, which is attached to a rocking platform and inflated with filtered air provided by the bioreactor unit. The Cellbag can be filled with medium and cells and maintained at a set temperature. The rocking motion, which is adjusted through angle and rock speed settings, provides mixing of oxygen (and CO2, which is used to control pH in mammalian cell cultures) from the headspace created in the inflated Cellbag with the cell culture medium and cells. This rocking motion can be adjusted to prevent cell shear damage. Dissolved oxygen and pH can be monitored during scale-up, and samples can be easily removed to monitor other parameters. Insect and mammalian cells grow very well in Wave Bioreactors (Shukla and Gottschalk, Trends Biotechnol 31(3):147-154, 2013). Combining Wave Bioreactor cell growth capabilities with recombinant baculoviruses engineered for insect or mammalian cell expression has proven to be a powerful tool for rapid production of a wide range of proteins.

Ambient analysis of leachable compounds from single-use bioreactors with desorption electrospray ionization time-of-flight mass spectrometry

RATIONALE

Trace levels of bis(2,4-di-tert-butylphenyl)phosphate (BdtbPP) leaching from single-use bioreactors (SUBs) were recently found to be highly detrimental to mammalian cell growth. The traditional approach to detect the leachable requires time-consuming solvent extraction of SUBs. To assist the qualification of SUBs and/or their manufacturing raw materials in biopharmaceutical development and manufacturing, it is essential to develop a rapid and sensitive analytical approach for detecting this leachable and related compounds, which is described in this study.

METHODS

Native films from several commercially available SUBs were directly examined by desorption electrospray ionization (DESI) time-of-flight mass spectrometry (TOFMS) without sample preparation. As a comparison, the same SUBs were also analyzed by high-performance liquid chromatography (HPLC)/ultraviolet (UV) following the solvent extraction.

RESULTS

With a suitable spray solvent selected in this study, DESI-TOFMS enabled rapid and sensitive detection of leachable compounds directly from SUBs. Accurate mass measurement from TOFMS allowed ready identification of BdtbPP, its parent analog compound, and other polymer components in the SUBs from their protonated surrogates. The relative abundances of BdtbPP in different SUBs measured by DESI-TOFMS exhibited good correlation with those from the traditional extraction-based approach with HPLC/UV.

CONCLUSIONS

A rapid and sensitive approach was developed for direct detection of BdtbPP and other leachables from SUBs using DESI-TOFMS. The results are in high accordance with those from conventional approaches, which indicates the usefulness of the proposed method as a qualification tool for SUBs in biopharmaceutical development and also its great potential in the analysis of extractables/leachables in a wide variety of materials, process components, devices and containers used in the pharmaceutical industry.

Development and evaluation of baculovirus-expressed Chikungunya virus E1 envelope proteins for serodiagnosis of Chikungunya infection

Population-based serosurveillance studies provide critical estimates on community-level immunity and the potential for future outbreaks. Currently, serological assays, such as IgG enzyme-linked immunosorbent assays (ELISAs) and indirect immunofluorescence tests (IIFT) based on the inactivated whole virus are used to determine past Chikungunya virus (CHIKV) infection. However, these commercially available tests have variable sensitivities. To develop and evaluate recombinant based CHIKV-specific IgG antibody capture ELISAs (GAC-ELISAs), baculoviruses carrying wild-type (E1-A226, named WT) or mutant (E1-A226V, named MUT) E1 envelope protein genes of CHIKV were generated. The seroreactivity of recombinant CHIKV WT and MUT envelope proteins were determined using residual blood, collected from CHIKV-confirmed patients. The sensitivities of both recombinant CHIKV envelope proteins were 83.0% as measured by GAC-ELISAs. The specificities of both recombinant proteins were 87.8%. These GAC-ELISAs were also able to detect the persistence of anti-CHIKV IgG antibodies up to 6 months after the disease onset, together with rise in sensitivities with increasing time. These results suggest that the baculovirus purified recombinant CHIKV envelope proteins react with anti-CHIKV IgG antibodies and may be useful in population-based seroprevalence surveys. In addition, these GAC-ELISAs offer good diagnostic value to determine the recent/past CHIKV infection status in non-endemic populations.

Polyethyleneimine-based transient gene expression processes for suspension-adapted HEK-293E and CHO-DG44 cells

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A brief overview of principles of TGE using mammalian cells.

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Description of TGE processes for HEK293 and CHO cells.

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Description of orbitally shaken bioreactors for suspension cell cultivation.

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Description of polyethylenime-based transfection processes.

Transient gene expression (TGE) from mammalian cells is an increasingly important tool for the rapid production of recombinant proteins for research applications in biochemistry, structural biology, and biomedicine. Here we review methods for the transfection of human embryo kidney (HEK-293) and Chinese hamster ovary (CHO) cells in suspension culture using the cationic polymer polyethylenimine (PEI) for gene delivery.

High yield of human monoclonal antibody produced by stably transfected Drosophila schneider 2 cells in perfusion culture using wave bioreactor

Since it was first introduced in late 1990s Wave bioreactor has been used for protein production by mammalian and insect cell lines. However, using Wave bioreactor to produce human monoclonal antibody by stable Drosophila Schneider 2 (S2) cell transfectants has not been reported before. In this study, S2 cells were co-transfected with an inducible vector expressing human monoclonal antibody heavy and light chains, respectively, specific for hemagglutinin (HA) of H5N1 influenza virus. Stable S2 transfectant clone was selected by limiting dilution assay. Stable S2 transfectant clone that produce the highest amount of human monoclonal antibody was inoculated into two 2-l disposable cellbags, where cell growth and antibody production were compared between batch and perfusion cultures using Wave bioreactor. Here, we report that maximum viable cell density reached 1.06 × 10(7) cells/ml in batch culture; whereas 1.04 × 10(8) cells/ml was achieved in perfusion culture. The maximum volumetric antibody productivity in batch culture was 52 mg/l/day; while perfusion culture yielded 1,437 mg/l/day. As a result, the total antibody production was 201 mg in batch culture and 8,212 mg in perfusion culture. The antibody produced by both cultures displays full neutralizing activity. Thus, our results provide strong support for using Wave bioreactor in perfusion culture for a large-scale production of human monoclonal antibody by stable S2 cell transfectants.

Structure of the human M2 muscarinic acetylcholine receptor bound to an antagonist

The parasympathetic limb of the autonomic nervous system regulates the activity of multiple organ systems. Muscarinic receptors are G protein coupled receptors (GPCRs) that mediate the response to acetylcholine released from parasympathetic nerves.^1–5 Their role in the unconscious regulation of organ and central nervous system function makes them potential therapeutic targets for a broad spectrum of diseases. The M₂ muscarinic acetylcholine receptor (M₂ receptor) is essential for the physiologic control of cardiovascular function through activation of G protein-coupled inwardly-rectifying potassium channels, and is of particular interest because of its extensive pharmacological characterization with both orthosteric and allosteric ligands. Here we report the structure of antagonist-bound M₂ receptor, the first human acetylcholine receptor to be characterized structurally. The antagonist QNB binds in the middle of a long aqueous channel extending approximately two-thirds through the membrane. The orthosteric binding pocket is formed by amino acids that are identical in all 5 muscarinic receptor subtypes, and shares structural homology with other functionally unrelated acetylcholine binding proteins from different species. A layer of tyrosine residues forms an aromatic cap restricting dissociation of the bound ligand. A binding site for allosteric ligands has been mapped to residues at the entrance to the binding pocket near this aromatic cap. The M₂ receptor structure provides insights into the challenges of developing subtype-selective ligands for muscarinic receptors and their propensity for allosteric regulation.

Cell Culture Derived AgMNPV Bioinsecticide: Biological Constraints and Bioprocess Issues

We have studied parameters for optimizing the Spodoptera frugiperda (Sf9) cell culture and viral infection for the production of Anticarsia gemmatalis multiple nucleopolyhedrosis virus (AgMNPV) polyhedra inclusion bodies (PIBs) in shaker-Schott or spinner bottles and bioreactors. We have assayed the k(L)a of the systems, initial cell seeding, cell culture volume, dissolved oxygen (DO), multiplicity of infection (MOI), nutrients consumption, and metabolites production. The medium surface oxygen transfer was shown to be higher in shaker bottles than in spinner ones, which was in direct correlation to the higher cell density obtained. Best quantitative performances of PIBs production were obtained with a SF900II medium volume/shaker-bottle volume ratio of 15% and MOI of 0.5 to 1 performed at a cell concentration at infection (CCI) of 1 to 2.5x10(6) cells/ml in a medium containing enough glucose and glutamine. Upon infection, a decrease in the cell multiplication was observed to be dependent on the MOI used, and the muX at the exponential growth phase in infected and non-infected cultures were, respectively, of 0.2832 and 0.3914 (day(-1)). The glucose consumption and lactate production were higher in the infected cultures (muGlucose and muLactate of, respectively, 0.0248 and 0.0089x10(-8) g/cellxday in infected cultures and 0.0151 and 0.0046x10(-8) g/cellxday in non infected ones). The glutamine consumption did not differ in both cultures (muGlutamine of 0.0034 and 0.0037x10(-8) g/cellxday in, respectively, infected and non infected cultures). When a virus MOI of 0.1 to 1 was used for infection, a higher concentration of PIBs/ml was obtained. This was in direct correlation to a higher cell concentration present in these cultures, where a decrease in cell multiplication due to virus infection is minimized. When a MOI of 1 was used, a more effective decrease in cell multiplication was observed and a lower concentration of PIBs/ml was obtained, but with the best performance of PIBs/cell. Correlations between MOI and CCI indicate that a MOI 0.1 to 1.4 and a CCI of 10(6) to 2x10(6) cells/ml led to the best PIBs production performances. The virulence of PIBs produced in cultures infected at low or high MOI showed comparable DL(50). Culture and infection in scaling-up conditions, performed in a bioreactor, were shown to provide the cells with a better environment and be capable of potentially improving the shaker-Schott findings. For an accurate qualitative control of PIB virulence, hemolymph from AgMNPV infected Anticarsia gemmatalis was used as starting material for passages in Sf9 cells. These led to a loss of virulence among the PIBs with an increase in the DL(50). The loss of virulence was accompanied by a loss in budded virus titer, a decreased number of PIBs produced and an altered DNA restriction pattern, suggesting the generation of defective interference particles (DIPs). Transmission electron microscopy (TEM) studies revealed that after cell passages, PIBs lacking virions were progressively synthesized. The study described here point out the biological constraints and bioprocess issues for the preparation of AgMNPV PIBs for biological control.

Evaluation of the Pichia pastoris expression system for the production of GPCRs for structural analysis

Background

Various protein expression systems, such as Escherichia coli (E. coli), Saccharomyces cerevisiae (S. cerevisiae), Pichia pastoris (P. pastoris), insect cells and mammalian cell lines, have been developed for the synthesis of G protein-coupled receptors (GPCRs) for structural studies. Recently, the crystal structures of four recombinant human GPCRs, namely β₂ adrenergic receptor, adenosine A_2a receptor, CXCR4 and dopamine D3 receptor, were successfully determined using an insect cell expression system. GPCRs expressed in insect cells are believed to undergo mammalian-like posttranscriptional modifications and have similar functional properties than in mammals. Crystal structures of GPCRs have not yet been solved using yeast expression systems. In the present study, P. pastoris and insect cell expression systems for the human muscarinic acetylcholine receptor M2 subtype (CHRM2) were developed and the quantity and quality of CHRM2 synthesized by both expression systems were compared for the application in structural studies.

Results

The ideal conditions for the expression of CHRM2 in P. pastoris were 60 hr at 20°C in a buffer of pH 7.0. The specific activity of the expressed CHRM2 was 28.9 pmol/mg of membrane protein as determined by binding assays using [³H]-quinuclidinyl benzilate (QNB). Although the specific activity of the protein produced by P. pastoris was lower than that of Sf9 insect cells, CHRM2 yield in P. pastoris was 2-fold higher than in Sf9 insect cells because P. pastoris was cultured at high cell density. The dissociation constant (Kd) for QNB in P. pastoris was 101.14 ± 15.07 pM, which was similar to that in Sf9 insect cells (86.23 ± 8.57 pM). There were no differences in the binding affinity of CHRM2 for QNB between P. pastoris and Sf9 insect cells.

Conclusion

Compared to insect cells, P. pastoris is easier to handle, can be grown at lower cost, and can be expressed quicker at a large scale. Yeast, P. pastoris, and insect cells are all effective expression systems for GPCRs. The results of the present study strongly suggested that protein expression in P. pastoris can be applied to the structural and biochemical studies of GPCRs.

Experimental characterization of flow conditions in 2- and 20-L bioreactors with wave-induced motion

Quantifying the influence of flow conditions on cell viability is essential for a successful control of cell growth and cell damage in major biotechnological applications, such as in recombinant protein and antibody production or vaccine manufacturing. In the last decade, new bioreactor types have been developed. In particular, bioreactors with wave-induced motion show interesting properties (e.g., disposable bags suitable for cGMP manufacturing, no requirement for cleaning and sterilization of cultivation vessels, and fast setup of new production lines) and are considered in this study. As an additional advantage, it is expected that cultivations in such bioreactors result in lower shear stress compared with conventional stirred tanks. As a consequence, cell damage would be reduced as cell viability is highly sensitive to hydrodynamic conditions. To check these assumptions, an experimental setup was developed to measure the most important flow parameters (liquid surface level, liquid velocity, and liquid and wall shear stress) in two cellbag sizes (2 and 20 L) of Wave Bioreactors®. The measurements confirm in particular low shear stress values in both cellbags, indicating favorable hydrodynamic conditions for cell cultivation.

High cell density cultivation and recombinant protein production with Escherichia coli in a rocking-motion-type bioreactor

Background

Single-use rocking-motion-type bag bioreactors provide advantages compared to standard stirred tank bioreactors by decreased contamination risks, reduction of cleaning and sterilization time, lower investment costs, and simple and cheaper validation. Currently, they are widely used for cell cultures although their use for small and medium scale production of recombinant proteins with microbial hosts might be very attractive. However, the utilization of rocking- or wave-induced motion-type bioreactors for fast growing aerobic microbes is limited because of their lower oxygen mass transfer rate. A conventional approach to reduce the oxygen demand of a culture is the fed-batch technology. New developments, such as the BIOSTAT^® CultiBag RM system pave the way for applying advanced fed-batch control strategies also in rocking-motion-type bioreactors. Alternatively, internal substrate delivery systems such as EnBase^® Flo provide an opportunity for adopting simple to use fed-batch-type strategies to shaken cultures. Here, we investigate the possibilities which both strategies offer in view of high cell density cultivation of E. coli and recombinant protein production.

Results

Cultivation of E. coli in the BIOSTAT^® CultiBag RM system in a conventional batch mode without control yielded an optical density (OD₆₀₀) of 3 to 4 which is comparable to shake flasks. The culture runs into oxygen limitation. In a glucose limited fed-batch culture with an exponential feed and oxygen pulsing, the culture grew fully aerobically to an OD₆₀₀ of 60 (20 g L^-1 cell dry weight). By the use of an internal controlled glucose delivery system, EnBase^® Flo, OD₆₀₀ of 30 (10 g L^-1 cell dry weight) is obtained without the demand of computer controlled external nutrient supply. EnBase^® Flo also worked well in the CultiBag RM system with a recombinant E. coli RB791 strain expressing a heterologous alcohol dehydrogenase (ADH) to very high levels, indicating that the enzyme based feed supply strategy functions well for recombinant protein production also in a rocking-motion-type bioreactor.

Conclusions

Rocking-motion-type bioreactors may provide an interesting alternative to standard cultivation in bioreactors for cultivation of bacteria and recombinant protein production. The BIOSTAT^® Cultibag RM system with the single-use sensors and advanced control system paves the way for the fed-batch technology also to rocking-motion-type bioreactors. It is possible to reach cell densities which are far above shake flasks and typical for stirred tank reactors with the improved oxygen transfer rate. For more simple applications the EnBase^® Flo method offers an easy and robust solution for rocking-motion-systems which do not have such advanced control possibilities.

New baculovirus expression tools for recombinant protein complex production

Most eukaryotic proteins exist as large multicomponent assemblies with many subunits, which act in concert to catalyze specific cellular activities. Many of these molecular machines are only present in low amounts in their native hosts, which impede purification from source material. Unraveling their structure and function at high resolution will often depend on heterologous overproduction. Recombinant expression of multiprotein complexes for structural studies can entail considerable, sometimes inhibitory, investment in both labor and materials, in particular if altering and diversifying of the individual subunits are necessary for successful structure determination. Our laboratory has addressed this challenge by developing technologies that streamline the complex production and diversification process. Here, we review several of these developments for recombinant multiprotein complex production using the MultiBac baculovirus/insect cell expression system which we created. We also addressed parallelization and automation of gene assembly for multiprotein complex expression by developing robotic routines for multigene vector generation. In this contribution, we focus on several improvements of baculovirus expression system performance which we introduced: the modifications of the transfer plasmids, the methods for generation of composite multigene baculoviral DNA, and the simplified and standardized expression procedures which we delineated using our MultiBac system.

Recent advances in the production of proteins in insect and mammalian cells for structural biology

The production of proteins in sufficient quantity and of appropriate quality is an essential pre-requisite for structural studies. Escherichia coli remains the dominant expression system in structural biology with nearly 90% of the structures in the Protein Data Bank (PDB) derived from proteins produced in this bacterial host. However, many mammalian and eukaryotic viral proteins require post-translation modification for proper folding and/or are part of large multimeric complexes. Therefore expression in higher eukaryotic cell lines from both invertebrate and vertebrate is required to produce these proteins. Although these systems are generally more time-consuming and expensive to use than bacteria, there have been improvements in technology that have streamlined the processes involved. For example, the use of multi-host vectors, i.e., containing promoters for not only E. coli but also mammalian and baculovirus expression in insect cells, enables target genes to be evaluated in both bacterial and higher eukaryotic hosts from a single vector. Culturing cells in micro-plate format allows screening of large numbers of vectors in parallel and is amenable to automation. The development of large-scale transient expression in mammalian cells offers a way of rapidly producing proteins with relatively high throughput. Strategies for selenomethionine-labelling (important for obtaining phase information in crystallography) and controlling glycosylation (important for reducing the chemical heterogeneity of glycoproteins) have also been reported for higher eukaryotic cell expression systems.

Disposable bioreactors: the current state-of-the-art and recommended applications in biotechnology

Disposable bioreactors have increasingly been incorporated into preclinical, clinical, and production-scale biotechnological facilities over the last few years. Driven by market needs, and, in particular, by the developers and manufacturers of drugs, vaccines, and further biologicals, there has been a trend toward the use of disposable seed bioreactors as well as production bioreactors. Numerous studies documenting their advantages in use have contributed to further new developments and have resulted in the availability of a multitude of disposable bioreactor types which differ in power input, design, instrumentation, and scale of the cultivation container. In this review, the term "disposable bioreactor" is defined, the benefits and constraints of disposable bioreactors are discussed, and critical phases and milestones in the development of disposable bioreactors are summarized. An overview of the disposable bioreactors that are currently commercially available is provided, and the domination of wave-mixed, orbitally shaken, and, in particular, stirred disposable bioreactors in animal cell-derived productions at cubic meter scale is reported. The growth of this type of reactor system is attributed to the recent availability of stirred disposable benchtop systems such as the Mobius CellReady 3 L Bioreactor. Analysis of the data from computational fluid dynamic simulation studies and first cultivation runs confirms that this novel bioreactor system is a viable alternative to traditional cell culture bioreactors at benchtop scale.

Evaluation of a novel Wave Bioreactor cellbag for aerobic yeast cultivation

The Wave Bioreactor is widely used in cell culture due to the benefits of disposable technology and ease of use. A novel cellbag was developed featuring a frit sparger to increase the system's oxygen transfer. The purpose of this work was to evaluate the sparged cellbag for yeast cultivation. Oxygen mass transfer studies were conducted in simulated culture medium and the sparged system's maximum oxygen mass transfer coefficient (kLa) was 38 h(-1). These measurements revealed that the sparger was ineffective in increasing the oxygen transfer capacity. Cultures of Saccharomyces cerevisiae were successfully grown in oxygen-blended sparged and oxygen-blended standard cellbags. Under steady state conditions for both cellbag designs, kLa values as high as 60 h(-1) were obtained with no difference in growth characteristics. This is the first report of a successful cultivation of a microbe in a Wave Bioreactor comparing conventional seed expansion in shake flasks and stirred tank bioreactors.

Bag bioreactor based on wave-induced motion: characteristics and applications

Today wave-mixed bag bioreactors are common devices in modern biotechnological processes where simple, safe and flexible production has top priority. Numerous studies that have been published on ex vivo generation of cells, viruses and therapeutic agents during the last 10 years have confirmed their suitability and even superiority to stirred bioreactors made from glass or stainless steel for animal as well as plant cell cultivations. In these studies the wave-mixed bag bioreactors enabled middle to high cell density and adequate productivity in laboratory and pilot scale. This mainly results from low-shear conditions and highly efficient oxygen transfer for cell cultures, as demonstrated for the widely used BioWave((R)).Starting with an overview of wave-mixed bag bioreactors and their common operation strategies, this chapter delineates engineering aspects of BioWave((R)), which like Wave Reactor and BIOSTAT((R))CultiBag RM originates from the prototype of a wave-mixed bag bioreactor introduced in 1998. Subsequently, the second part of the chapter focuses on reported BioWave((R)) applications. Conditions and results from cultivations with animal cells, plant cells, microbial cells and nematodes are presented and discussed.