Comprehensive characterization of two different Nicotiana tabacum cell lines leads to doubled GFP and HA protein production by media optimization

Statistical Experimental Designs for cLTB-Syn Vaccine Production Using Daucus carota Cell Suspension Cultures

The carrot-made LTB-Syn antigen (cLTB-Syn) is a vaccine candidate against synucleinopathies based on carrot cells expressing the target antigen LTB and syn epitopes. Therefore, the development of an efficient production process is required with media culture optimization to increase the production yields as the main goal. In this study, the effect of two nitrogen sources (urea and glutamate) on callus cultures producing cLTB-Syn was studied, observing that the addition of 17 mM urea to MS medium favored the biomass yield. To optimize the MS media composition, the influence of seven medium components on biomass and cLTB-Syn production was first evaluated by a Plackett-Burman design (PBD). Then, three factors were further analyzed using a central composite design (CCD) and response surface methodology (RSM). The results showed a 1.2-fold improvement in biomass, and a 4.5-fold improvement in cLTB-Syn production was achieved at the shake-flask scale. At the bioreactor scale, there was a 1.5-fold increase in biomass and a 2.8-fold increase in cLTB-Syn yield compared with the standard MS medium. Moreover, the cLTB-Syn vaccine induced humoral responses in BALB/c mice subjected to either oral or subcutaneous immunization. Therefore, cLTB-Syn is a promising vaccine candidate that will aid in developing immunotherapeutic strategies to combat PD and other neurodegenerative diseases without the need for cold storage, making it a financially viable option for massive immunization.

Simulation and optimization of nutrient uptake and biomass formation using a multi-parameter Monod-type model of tobacco BY-2 cell suspension cultures in a stirred-tank bioreactor

Introduction

Tobacco (Nicotiana tabacum) cv Bright Yellow-2 (BY-2) cell suspension cultures enable the rapid production of complex protein-based biopharmaceuticals but currently achieve low volumetric productivity due to slow biomass formation. The biomass yield can be improved with tailored media, which can be designed either by laborious trial-and-error experiments or systematic, rational design using mechanistic models, linking nutrient consumption and biomass formation.

Methods

Here we developed an iterative experiment-modeling-optimization workflow to gradually refine such a model and its predictions, based on collected data concerning BY-2 cell macronutrient consumption (sucrose, ammonium, nitrate and phosphate) and biomass formation.

Results and discussion

The biomass formation was well predicted by an unstructured segregated mechanistic Monod-type model as long as the nutrient concentrations did not approach zero (we omitted phosphate, which was completely depleted). Multi-criteria optimization for sucrose and biomass formation indicated the best tradeoff (in a Paretian sense) between maximum biomass yield and minimum process time by reducing the initial sucrose concentration, whereas the inoculation biomass could be increased to maximize the biomass yield or minimize the process time, which we confirmed in calibration experiments. The model became inaccurate at biomass densities > 8 g L-1 dry mass when sucrose was almost depleted. We compensated for this limitation by including glucose and fructose as sucrose hydrolysis products in the model. The remaining offset between the simulation and experimental data might be resolved by including intracellular pools of sucrose, ammonium, nitrate and phosphate. Overall, we demonstrated that iterative models can be used to systematically optimize conditions for bioreactor-based processes.

Intracellular trafficking and glycosylation of hydroxyproline-O-glycosylation module in tobacco BY-2 cells is dependent on medium composition and transcriptome analysis

Expression of recombinant proteins in plant cells with a "designer" hydroxyproline (Hyp)-O-glycosylated peptide (HypGP), such as tandem repeats of a "Ser-Pro" motif, has been shown to boost the secreted protein yields. However, dramatic secretion and Hyp-O-glycosylation of HypGP-tagged proteins can only be achieved when the plant cells were grown in nitrogen-deficient SH medium. Only trace amounts of secreted fusion protein were detected in MS medium. This study aims to gain a deeper understanding of the possible mechanism underlying these results by examining the intracellular trafficking and Hyp-O-glycosylation of enhanced green fluorescent protein (EGFP) fused with a (SP)32 tag, consisting of 32 repeats of a "Ser-Pro" motif, in tobacco BY-2 cells. When cells were grown in MS medium, the (SP)32-EGFP formed protein body-like aggregate and was retained in the ER, without undergoing Hyp-O-glycosylation. In contrast, the fusion protein becomes fully Hyp-O-glycosylated, and then secreted in SH medium. Transcriptome analysis of the BY-2 cells grown in SH medium vs. MS medium revealed over 16,000 DEGs, with many upregulated DEGs associated with the microtubule-based movement, movement of subcellular component, and microtubule binding. These DEGs are presumably responsible for the enhanced ER-Golgi transport of HypGP-tagged proteins, enabling their glycosylation and secretion in SH medium.

Spotting priming-active compounds using parsley cell cultures in microtiter plates

BACKGROUND

Conventional crop protection has major drawbacks, such as developing pest and pathogen insensitivity to pesticides and low environmental compatibility. Therefore, alternative crop protection strategies are needed. One promising approach treats crops with chemical compounds that induce the primed state of enhanced defense. However, identifying priming compounds is often tedious as it requires offline sampling and analysis. High throughput screening methods for the analysis of priming-active compounds have great potential to simplify the search for such compounds. One established method to identify priming makes use of parsley cell cultures. This method relies on measurement of fluorescence of furanocoumarins in the final sample. This study demonstrates for the first time the online measurement of furanocoumarins in microtiter plates. As not all plants produce fluorescence molecules as immune response, a signal, which is not restricted to a specific plant is required, to extend online screening methods to other plant cell cultures. It was shown that the breathing activity of primed parsley cell cultures increases, compared to unprimed parsley cell cultures. The breathing activity can by monitored online. Therefore, online identification of priming-inducing compounds by recording breathing activity represents a promising, straight-forward and highly informative approach. However, so far breathing has been recorded in shake flasks which suffer from low throughput. For industrial application we here report a high-throughput, online identification method for identifying priming-inducing chemistry.

RESULTS

This study describes the development of a high-throughput screening system that enables identifying and analyzing the impact of defense priming-inducing compounds in microtiter plates. This screening system relies on the breathing activity of parsley cell cultures. The validity of measuring the breathing activity in microtiter plates to drawing conclusions regarding priming-inducing activity was demonstrated. Furthermore, for the first time, the fluorescence of the priming-active reference compound salicylic acid and of furanocoumarins were simultaneously monitored online. Dose and time studies with salicylic acid-treated parsley cell suspensions revealed a wide range of possible addition times and concentrations that cause priming. The online fluorescence measuring method was further confirmed with three additional compounds with known priming-causing activity.

CONCLUSIONS

Determining the OTR, fluorescence of the priming-active chemical compound SA and of furanocoumarins in parsley suspension cultures in MTPs by online measurement is a powerful and high-throughput tool to study possible priming compounds. It allows an in-depth screening for priming compounds and a better understanding of the priming process induced by a given substance. Evaluation of priming phenomena via OTR should also be applicable to cell suspensions of other plant species and varieties and allow screening for priming-inducing chemical compounds in intact plants. These online fluorescence methods to measure the breathing activity, furanocoumarin and SA have the potential to accelerate the search for new priming compounds and promote priming as a promising, eco-friendly crop protection strategy.

Recombinant Protein Production in Plants: A Brief Overview of Strengths and Challenges

The first recombinant proteins were produced in microbes and animal cells cultivated in bioreactors. These systems have become the standard for industrial-scale recombinant protein manufacturing. Later, the production of recombinant proteins was demonstrated in whole plants, which differ morphologically from cell-based systems and require completely different cultivation conditions. Over time, additional plant-based production platforms were established, including hairy roots and cell suspension cultures, which are more similar to conventional cell-based systems in terms of morphology, procedures, and equipment requirements. In this brief overview of the field, we explain why plant-based systems are becoming increasingly attractive for the production of valuable proteins with scientific and commercial applications, but also highlight the challenges that these systems must overcome to achieve more widespread industrial utilization. We discuss various laboratory protocols and approaches for the production of recombinant proteins in plants, as well as strategies to optimize yields, and the regulatory and legal framework.

Improving Protein Quantity and Quality—The Next Level of Plant Molecular Farming

Plants offer several unique advantages in the production of recombinant pharmaceuticals for humans and animals. Although numerous recombinant proteins have been expressed in plants, only a small fraction have been successfully put into use. The hugely distinct expression systems between plant and animal cells frequently cause insufficient yield of the recombinant proteins with poor or undesired activity. To overcome the issues that greatly constrain the development of plant-produced pharmaceuticals, great efforts have been made to improve expression systems and develop alternative strategies to increase both the quantity and quality of the recombinant proteins. Recent technological revolutions, such as targeted genome editing, deconstructed vectors, virus-like particles, and humanized glycosylation, have led to great advances in plant molecular farming to meet the industrial manufacturing and clinical application standards. In this review, we discuss the technological advances made in various plant expression platforms, with special focus on the upstream designs and milestone achievements in improving the yield and glycosylation of the plant-produced pharmaceutical proteins.

An illuminated respiratory activity monitoring system identifies priming-active compounds in plant seedlings

BACKGROUND

Growing large crop monocultures and heavily using pesticides enhances the evolution of pesticide-insensitive pests and pathogens. To reduce pesticide use in crop cultivation, the application of priming-active compounds (PrimACs) is a welcome alternative. PrimACs strengthen the plant immune system and could thus help to protect plants with lower amounts of pesticides. PrimACs can be identified, for example, by their capacity to enhance the respiratory activity of parsley cells in culture as determined by the oxygen transfer rate (OTR) using the respiration activity monitoring system (RAMOS) or its miniaturized version, µRAMOS. The latter was designed for with suspensions of bacteria and yeast cells in microtiter plates (MTPs). So far, RAMOS or µRAMOS have not been applied to adult plants or seedlings, which would overcome the limitation of (µ)RAMOS to plant suspension cell cultures.

RESULTS

In this work, we introduce a modified µRAMOS for analysis of plant seedlings. The novel device allows illuminating the seedlings and records the respiratory activity in each well of a 48-well MTP. To validate the suitability of the setup for identifying novel PrimAC in Arabidopsis thaliana, seedlings were grown in MTP for seven days and treated with the known PrimAC salicylic acid (SA; positive control) and the PrimAC candidate methyl 1-(3,4-dihydroxyphenyl)-2-oxocyclopentane-1-carboxylate (Tyr020). Twenty-eight h after treatment, the seedlings were elicited with flg22, a 22-amino acid peptide of bacterial flagellin. Upon elicitation, the respiratory activity was monitored. The evaluation of the OTR course reveals Tyr020 as a likely PrimAC. The priming-inducing activity of Tyr020 was confirmed using molecular biological analyses in A. thaliana seedlings.

CONCLUSION

We disclose the suitability of µRAMOS for identifying PrimACs in plant seedlings. The difference in OTR during a night period between primed and unprimed plants was distinguishable after elicitation with flg22. Thus, it has been shown that the µRAMOS device can be used for a reliable screening for PrimACs in plant seedlings.

Plant molecular farming for the production of valuable proteins - Critical evaluation of achievements and future challenges

Recombinant proteins play an important role in many areas of our lives. For example, recombinant enzymes are used in the food and chemical industries and as high-quality proteins for research, diagnostic and therapeutic applications. The production of recombinant proteins is still dominated by expression systems based on microbes and mammalian cells, although the manufacturing of recombinant proteins in plants - known as molecular farming - has been promoted as an alternative, cost-efficient strategy for three decades. Several molecular farming products have reached the market, but the number of success stories has been limited by industrial inertia driven by perceptions of low productivity, the high cost of downstream processing, and regulatory hurdles that create barriers to translation. Here, we discuss the technical and economic factors required for the successful commercialization of molecular farming, and consider potential future directions to enable the broader application of production platforms based on plants.

Engineering Plants for the Future: Farming with Value-Added Harvest

Plants and their rich variety of natural compounds are used to maintain and to improve health since the earliest stages of civilization. Despite great advances in synthetic organic chemistry, one fourth of present-day drugs have still a botanical origin, and we are currently living a revival of interest in new pharmaceuticals from plant sources.

Modern biotechnology has defined the potential of plants to be systems able to manufacture not only molecules naturally occurring in plants but also newly engineered compounds, from small to complex protein molecules, which may originate even from non-plant sources. Among these compounds, pharmaceuticals such as vaccines, antibodies and other therapeutic or prophylactic entities can be listed. For this technology, the term plant molecular farming has been coined with reference to agricultural applications due to the use of crops as biofactories for the production of high-added value molecules. In this perspective, edible plants have also been thought as a tool to deliver by the oral route recombinant compounds of medical significance for new therapeutic strategies. Despite many hurdles in establishing regulatory paths for this “novel” biotechnology, plants as bioreactors deserve more attention when considering their intrinsic advantages, such as the quality and safety of the recombinant molecules that can be produced and their potential for large-scale and low-cost production, despite worrying issues (e.g. amplification and diffusion of transgenes) that are mainly addressed by regulations, if not already tackled by the plant-made products already commercialized. The huge benefits generated by these valuable products, synthesized through one of the safest, cheapest and most efficient method, speak for themselves.

Milestone for plant-based recombinant protein production for human health use was the approval in 2012 by the US Food and Drug Administration of plant-made taliglucerase alfa, a therapeutic enzyme for the treatment of Gaucher’s disease, synthesized in carrot suspension cultures by Protalix BioTherapeutics.

In this review, we will go through the various approaches and results for plant-based production of proteins and recent progress in the development of plant-made pharmaceuticals (PMPs) for the prevention and treatment of human diseases. An analysis on acceptance of these products by public opinion is also tempted.

Parallel online determination of ethylene release rate by Shaken Parsley cell cultures using a modified RAMOS device

BACKGROUND

Ethylene is an important plant hormone that controls many physiological processes in plants. Conventional methods for detecting ethylene include gas chromatographs or optical mid-infrared sensors, which are expensive and, in the case of gas chromatographs, are hardly suitable for automated parallelized online measurement. Electrochemical ethylene sensors are cheap but often suffer from poor resolution, baseline drifting, and target gas oxidation. Thus, measuring ethylene at extremely low levels is challenging.

RESULTS

This report demonstrates the integration of electrochemical ethylene sensors into a respiration activity monitoring system (RAMOS) that measures, in addition to the oxygen transfer rate, the ethylene transfer rate in eight parallel shake flasks. A calibration method is presented that is not prone to baseline drifting and considers target gas oxidation at the sensor. In this way, changes in ethylene transfer rate as low as 4 nmol/L/h can be resolved. In confirmatory experiments, the overall accuracy of the method was similar to that of gas chromatography-mass spectrometry (GC/MS) measurements. The RAMOS-based ethylene determination method was exemplified with parsley suspension-cultured cells that were primed for enhanced defense by pretreatment with salicylic acid, methyl jasmonate or 4-chlorosalicylic acid and challenged with the microbial pattern Pep13. Ethylene release into the headspace of the shake flask was observed upon treatment with salicylic acid and methyl jasmonate was further enhanced, in case of salicylic acid and 4-chlorosalicylic acid, upon Pep13 challenge.

CONCLUSION

A conventional RAMOS device was modified for simultaneous measurement of the ethylene transfer rate in eight parallel shake flasks at nmol/L/h resolution. For the first time electrochemical sensors are used to provide a medium-throughput method for monitoring ethylene release by plants. Currently, this can only be achieved by costly laser-based detection systems and automated gas chromatographs. The new method is particularly suitable for plant cell suspension cultures. However, the method may also be applicable to intact plants, detached leaves or other plant tissues. In addition, the general principle of the technology is likely extendable to other volatiles or gases as well, such as nitric oxide or hydrogen peroxide.

Dramatic secretion of recombinant protein expressed in tobacco cells with a designer glycopeptide tag is highly impacted by medium composition

KEY MESSAGE

Cell growth medium composition has profound impacts on the O -glycosylation of a "designer" arabinogalactan protein-based module; full glycosylation is essential in directing efficient extracellular secretion of the tagged recombinant protein. Expression of recombinant proteins in plant cells as fusion with a de novo designed hydroxyproline (Hyp)-O-glycosylated peptide (HypGP) tag, termed HypGP engineering technology, resulted in dramatically increased secreted protein yields. This is due to the function of the HypGP tag as a molecular carrier in promoting efficient transport of conjoined proteins into culture media. To optimize the cell culture to achieve the best secreted protein yields, the medium effects on the cell growth and protein secretion were investigated using as a model system the tobacco BY-2 cell expressing enhanced green fluorescence protein (EGFP) fused with a (SP)32 tag (32 tandem repeats of "Ser-Pro" motif). The (SP)32 tag was found to undergo two-stage Hyp-O-glycosylation in plant cells with the dramatic secretion of the conjoined EGFP correlating with the triggering of the second-stage glycosylation. The BY-2 cell culture in SH medium generated a high secreted protein yield (125 mg/L) with a low cell biomass accumulation (~7.5 gDW/L). In contrast, very low secreted protein yields (~1.5 mg/L) with a high cell biomass accumulation (13.5 gDW/L) were obtained in MS medium. The macronutrients, specifically, the nitrogen supply greatly impacted the glycosylation of the (SP)32 tag and subsequent protein secretion. Modified MS medium with reduced nitrogen levels boosted the secreted EGFP yields to 168 mg/L. This study demonstrates the profound impacts of medium composition on the secreted yields of a HypGP-tagged protein, and provides a basis for medium design to achieve the highest productivity of the HypGP engineering technology.

"Fungal elicitors combined with a sucrose feed significantly enhance triterpene production of a Salvia fruticosa cell suspension"

Oleanolic (OA) and ursolic acid (UA) are plant secondary metabolites with diverse pharmacological properties. To reach reasonable productivities with plant cell suspension cultures, elicitation is a widely used strategy. Within the presented work, the effects of different elicitors on growth and production of OA and UA in a Salvia fruticosa cell suspension culture were examined. Beside commonly used elicitors like jasmonic acid (JA) and yeast extract, the influence of medium filtrates of the endophytic fungi Aspergillus niger and Trichoderma virens was investigated. The best eliciting effects were achieved with JA and fungal medium filtrates. Both increased the triterpene content by approximately 70 %. Since JA showed significant growth inhibition, the volumetric triterpene yield did not increase. But, adding fungal filtrates increased the volumetric triterpene yield by approximately 70 % to 32.6 mgOA l(-1) and 65.9 mgUA l(-1) for T. virens compared to the control with 19.4 mgOA l(-1) and 33.3 mgUA l(-1). An elicitation strategy combining fungal medium filtrate of T. virens with sucrose feeding significantly enhanced cell dry weight concentration to 22.2 g l(-1) as well as triterpene content by approximately 140 %. In total, this led to an approximately 500 % increase of volumetric triterpene yield referring to the control with final values of 112.9 mgOA l(-1) and 210.4 mgUA l(-1). Despite the doubled cultivation duration, productivities of 6.7 mgOA l(-1) day(-1) and 12.4 mgUA l(-1) day(-1) were reached. These results demonstrate methods by which increased productivities of triterpenes can be achieved to attain yields competing with intact plants.

Putting the Spotlight Back on Plant Suspension Cultures

Plant cell suspension cultures have several advantages that make them suitable for the production of recombinant proteins. They can be cultivated under aseptic conditions using classical fermentation technology, they are easy to scale-up for manufacturing, and the regulatory requirements are similar to those established for well-characterized production systems based on microbial and mammalian cells. It is therefore no surprise that taliglucerase alfa (Elelyso®)-the first licensed recombinant pharmaceutical protein derived from plants-is produced in plant cell suspension cultures. But despite this breakthrough, plant cells are still largely neglected compared to transgenic plants and the more recent plant-based transient expression systems. Here, we revisit plant cell suspension cultures and highlight recent developments in the field that show how the rise of plant cells parallels that of Chinese hamster ovary cells, currently the most widespread and successful manufacturing platform for biologics. These developments include medium optimization, process engineering, statistical experimental designs, scale-up/scale-down models, and process analytical technologies. Significant yield increases for diverse target proteins will encourage a gold rush to adopt plant cells as a platform technology, and the first indications of this breakthrough are already on the horizon.

Oxygen transfer rate identifies priming compounds in parsley cells

BACKGROUND

In modern agriculture, the call for an alternative crop protection strategy increases because of the desired reduction of fungicide and pesticide use and the continuously evolving resistance of pathogens and pests to agrochemicals. The direct activation of the plant immune system does not provide a promising plant protection measure because of high fitness costs. However, upon treatment with certain natural or synthetic compounds, plant cells can promote to a fitness cost-saving, primed state of enhanced defense. In the primed state, plants respond to biotic and abiotic stress with faster and stronger activation of defense, and this is often associated with immunity and abiotic stress tolerance. Until now, the identification of chemical compounds with priming-inducing activity (so-called plant activators) relied on tedious and invasive approaches, or required the late detection of secreted furanocoumarin phytoalexins in parsley cell cultures. Thus, simple, fast, straightforward, and noninvasive techniques for identifying priming-inducing compounds for plant protection are very welcome.

RESULTS

This report demonstrates that a respiration activity-monitoring system (RAMOS) can identify compounds with defense priming-inducing activity in parsley cell suspension in culture. RAMOS relies on the quasi-continuous, noninvasive online determination of the oxygen transfer rate (OTR). Treatment of parsley culture cells with the known plant activator salicylic acid (SA), a natural plant defense signal, resulted in an OTR increase. Addition of the defense elicitor Pep13, a cell wall peptide of Phythophthora sojae, induced two distinctive OTR peaks that were higher in SA-primed cells than in unprimed cells upon Pep13 challenge. Both, the OTR increase after priming with SA and the Pep13 challenge were dose-dependent. Furthermore, there was a close correlation of a compound's activity to enhance the oxygen consumption in parsley cells and its capacity to prime Pep13-induced furanocoumarin secretion as evaluated by fluorescence spectroscopy.

CONCLUSIONS

RAMOS noninvasively determines the OTR as a measure of the metabolic activity of plant cells. Chemical enhancement of oxygen consumption by salicylic derivatives in parsley cell suspension cultures correlates with the induction of the primed state of enhanced defense that enhances the quantity of Pep13-induced furanocoumarin phytoalexins. Treatment with the priming-active compounds methyl jasmonate and pyraclostrobin also resulted in an enhanced respiration activity. Thus, RAMOS is a novel technology for identifying priming-inducing compounds for agriculture.

High-value products from plants: the challenges of process optimization

Plants can be used to produce a diverse repertoire of complex small-molecule compounds and recombinant proteins that are valuable as industrial and pharmaceutical products. But as we move from proof-of-principle experiments and begin to consider the realistic prospects of commercial production, the focus must shift from the achievement of target molecule production and move towards quality, purity and yield aspects that determine commercial feasibility. This review describes some of the recent advances that have been implemented to improve the development of integrated production processes for high-value molecules expressed in plants, including the introduction of novel procedures to increase the likelihood of regulatory acceptance.

Accumulation of secreted antibodies in plant cell cultures varies according to the isotype, host species and culture conditions

Nicotiana tabacum suspension cells have been widely used to produce monoclonal antibodies, but the yield of secreted antibodies is usually low probably because of proteolytic degradation. Most IgGs that have been expressed in suspension cells have been of the human IgG1 isotype. In this study, we examined whether other isotypes displayed the same sensitivity to proteolytic degradation and whether the choice of plant host species mattered. Human serum IgG displayed different degradation profiles when incubated in spent culture medium from N. tabacum, Nicotiana benthamiana or Arabidopsis thaliana suspension cells. Zymography showed that the protease profile was host species dependent. Three human isotypes, IgG1, IgG2 and IgG4, and a mouse IgG2a were provided with the same heavy- and light-chain variable regions from an anti-human IgM antibody and expressed in N. tabacum cv. BY-2 and A. thaliana cv. Col-0 cells. Although all tested isotypes were detected in the extracellular medium using SDS-PAGE and a functional ELISA, up to 10-fold differences in the level of intact antibody were found according to the isotype expressed, to the host species and to the culture conditions. In the best combination (BY-2 cells secreting human IgG1), we reported accumulation of more than 30 mg/L of intact antibody in culture medium. The possibility of using IgG constant regions as a scaffold to allow stable accumulation of antibodies with different variable regions was demonstrated for human IgG2 and mouse IgG2a.

Molecular farming in tobacco hairy roots by triggering the secretion of a pharmaceutical antibody

Recombinant pharmaceutical proteins expressed in hairy root cultures can be secreted into the medium to improve product homogeneity and to facilitate purification, although this may result in significant degradation if the protein is inherently unstable or particularly susceptible to proteases. To address these challenges, we used a design of experiments approach to develop an optimized induction protocol for the cultivation of tobacco hairy roots secreting the full-size monoclonal antibody M12. The antibody yield was enhanced 30-fold by the addition of 14 g/L KNO3 , 19 mg/L 1-naphthaleneacetic acid and 1.5 g/L of the stabilizing agent polyvinylpyrrolidone. Analysis of hairy root cross sections revealed that the optimized medium induced lateral root formation and morphological changes in the inner cortex and pericycle cells, indicating that the improved productivity was at least partially based on the enhanced efficiency of antibody secretion. We found that 57% of the antibody was secreted, yielding 5.9 mg of product per liter of induction medium. Both the secreted and intracellular forms of the antibody could be isolated by protein A affinity chromatography and their functionality was confirmed using vitronectin-binding assays. Glycan analysis revealed three major plant complex-type glycans on both forms of the antibody, although the secreted form was more homogeneous due to the predominance of a specific glycoform. Tobacco hairy root cultures therefore offer a practical solution for the production of homogeneous pharmaceutical antibodies in containment.

Correlation between mass transfer coefficient kLa and relevant operating parameters in cylindrical disposable shaken bioreactors on a bench-to-pilot scale

Background

Among disposable bioreactor systems, cylindrical orbitally shaken bioreactors show important advantages. They provide a well-defined hydrodynamic flow combined with excellent mixing and oxygen transfer for mammalian and plant cell cultivations. Since there is no known universal correlation between the volumetric mass transfer coefficient for oxygen k_La and relevant operating parameters in such bioreactor systems, the aim of this current study is to experimentally determine a universal k_La correlation.

Results

A Respiration Activity Monitoring System (RAMOS) was used to measure k_La values in cylindrical disposable shaken bioreactors and Buckingham’s π-Theorem was applied to define a dimensionless equation for k_La. In this way, a scale- and volume-independent k_La correlation was developed and validated in bioreactors with volumes from 2 L to 200 L. The final correlation was used to calculate cultivation parameters at different scales to allow a sufficient oxygen supply of tobacco BY-2 cell suspension cultures.

Conclusion

The resulting equation can be universally applied to calculate the mass transfer coefficient for any of seven relevant cultivation parameters such as the reactor diameter, the shaking frequency, the filling volume, the viscosity, the oxygen diffusion coefficient, the gravitational acceleration or the shaking diameter within an accuracy range of +/− 30%. To our knowledge, this is the first k_La correlation that has been defined and validated for the cited bioreactor system on a bench-to-pilot scale.

Optimization of BY-2 cell suspension culture medium for the production of a human antibody using a combination of fractional factorial designs and the response surface method

We have developed a strategy for the optimization of plant cell suspension culture media using a combination of fractional factorial designs (FFDs) and response surface methodology (RSM). This sequential approach was applied to transformed tobacco BY-2 cells secreting a human antibody (M12) into the culture medium, in an effort to maximize yields. We found that the nutrients KNO₃, NH₄NO₃ and CaCl₂ and the hormones 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (BAP) had the most significant impact on antibody accumulation. The factorial screening revealed strong interactions within the nutrients group (KNO₃, NH₄NO₃ and CaCl₂) and also individually between 2,4-D and three other components (KNO₃, NH₄NO₃ and BAP). The RSM design resulted in a fivefold increase in the antibody concentration after 5 days and a twofold reduction in the packed cell volume (PCV). Longer cultivation in the optimized medium led to the further accumulation of antibody M12 in the culture medium (up to 107 μg/mL, day 10). Because the packed cell volume was reduced in the optimized medium, this enhanced the overall yield by 20-fold (day 7) and 31-fold (day 10) compared to the conventional MS medium.