Technoeconomic analysis of semicontinuous bioreactor production of biopharmaceuticals in transgenic rice cell suspension cultures

Effective parallel evaluation of molecular design, expression and bioactivity of novel recombinant butyrylcholinesterase medical countermeasures

Current medical countermeasures (MCMs) for nerve agent poisoning have limited efficacy, and can cause serious adverse effects, prompting the requirement for new broad-spectrum therapeutics. Human plasma-derived butyrylcholinseterase (huBChE) is a promising novel bioscavenger MCM which has shown potential in animal studies, however, is economically prohibitive to manufacture at scale. This study addresses current challenges for the economical production of a bioactive and long-acting recombinant huBChE (rBChE) in mammalian cells by being the first to directly compare novel rBChE design strategies. These include co-expression of a proline rich attachment domain (PRAD) and fusion of BChE with a protein partner. Additionally, a pre-purification screening method developed in this study enables parallel comparison of the expression efficiency, activity and broad-spectrum binding to nerve agents for ten novel rBChE molecular designs. All designed rBChE demonstrated functionality to act as broad-spectrum MCMs to G, V and A series nerve agents. Expression using the ExpiCHO™ Max protocol provided greatest expression levels and activity for all constructs, with most rBChE expressing poorly in Expi293™. Fc- or hSA-fused rBChE significantly outperformed constructs designed to mimic huBChE, including PRAD-BChE, and proved an effective strategy to significantly improve enzyme activity and expression. Choice of protein partner, directionality and the addition of a linker also impacted fusion rBChE activity and expression. Overall, hSA fused rBChE provided greatest expression yield and activity, with BChE-hSA the best performing construct. The purified and characterised BChE-hSA demonstrated similar functionality to huBChE to be inhibited by GD, VX and A-234, supporting the findings of the pre-screening study and validating its capacity to assess and streamline the selection process for rBChE constructs in a cost-effective manner. Collectively, these outcomes contribute to risk mitigation in early-stage development, providing a systematic method to compare rBChE designs and a focus for future development.

Enhanced efficacy of glycoengineered rice cell-produced trastuzumab

For several decades, a plant-based expression system has been proposed as an alternative platform for the production of biopharmaceuticals including therapeutic monoclonal antibodies (mAbs), but the immunogenicity concerns associated with plant-specific N-glycans attached in plant-based biopharmaceuticals has not been completely solved. To eliminate all plant-specific N-glycan structure, eight genes involved in plant-specific N-glycosylation were mutated in rice (Oryza sativa) using the CRISPR/Cas9 system. The glycoengineered cell lines, PhytoRice®, contained a predominant GnGn (G0) glycoform. The gene for codon-optimized trastuzumab (TMab) was then introduced into PhytoRice® through Agrobacterium co-cultivation. Selected cell lines were suspension cultured, and TMab secreted from cells was purified from the cultured media. The amino acid sequence of the TMab produced by PhytoRice® (P-TMab) was identical to that of TMab. The inhibitory effect of P-TMab on the proliferation of the BT-474 cancer cell line was significantly enhanced at concentrations above 1 μg/mL (****P < 0.0001). P-TMab bound to a FcγRIIIa variant, FcγRIIIa-F158, more than 2.7 times more effectively than TMab. The ADCC efficacy of P-TMab against Jurkat cells was 2.6 times higher than that of TMab in an in vitro ADCC assay. Furthermore, P-TMab demonstrated efficient tumour uptake with less liver uptake compared to TMab in a xenograft assay using the BT-474 mouse model. These results suggest that the glycoengineered PhytoRice® could be an alternative platform for mAb production compared to current CHO cells, and P-TMab has a novel and enhanced efficacy compared to TMab.

Towards a seamless product and process development workflow for recombinant proteins produced by plant molecular farming

Plant molecular farming (PMF) has been promoted as a fast, efficient and cost-effective alternative to bacteria and animal cells for the production of biopharmaceutical proteins. Numerous plant species have been tested to produce a wide range of drug candidates. However, PMF generally lacks a systematic, streamlined and seamless workflow to continuously fill the product pipeline. Therefore, it is currently unable to compete with established platforms in terms of routine, throughput and horizontal integration (the rapid translation of product candidates to preclinical and clinical development). Individual management decisions, limited funding and a lack of qualified production capacity can hinder the execution of such projects, but we also lack suitable technologies for sample handling and data management. This perspectives article will highlight current bottlenecks in PMF and offer potential solutions that combine PMF with existing technologies to build an integrated facility of the future for product development, testing, manufacturing and clinical translation. Ten major bottlenecks have been identified and are discussed in turn: automated cloning and simplified transformation options, reproducibility of bacterial cultivation, bioreactor integration with automated cell handling, options for rapid mid-scale candidate and product manufacturing, interconnection with (group-specific or personalized) clinical trials, diversity of (post-)infiltration conditions, development of downstream processing platforms, continuous process operation, compliance of manufacturing conditions with biosafety regulations, scaling requirements for cascading biomass.

Molecular farming for sustainable production of clinical-grade antimicrobial peptides

Antimicrobial peptides (AMPs) are emerging as next-generation therapeutics due to their broad-spectrum activity against drug-resistant bacterial strains and their ability to eradicate biofilms, modulate immune responses, exert anti-inflammatory effects and improve disease management. They are produced through solid-phase peptide synthesis or in bacterial or yeast cells. Molecular farming, i.e. the production of biologics in plants, offers a low-cost, non-toxic, scalable and simple alternative platform to produce AMPs at a sustainable cost. In this review, we discuss the advantages of molecular farming for producing clinical-grade AMPs, advances in expression and purification systems and the cost advantage for industrial-scale production. We further review how 'green' production is filling the sustainability gap, streamlining patent and regulatory approvals and enabling successful clinical translations that demonstrate the future potential of AMPs produced by molecular farming. Finally, we discuss the regulatory challenges that need to be addressed to fully realize the potential of molecular farming-based AMP production for therapeutics.

Applications of Plant-Made Fibroblast Growth Factor for Human Pluripotent Stem Cells

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) hold great potential in regenerative medicine. These cells can be expanded indefinitely in theory and are able to differentiate into different types of cells for cell therapies, drug screening, and basic biology studies. The reliable and effective propagation of hESCs and hiPSCs is important for their downstream applications. Basic fibroblast growth factor (bFGF) is critical to hESCs and hiPSCs for maintaining their pluripotency. Plant-produced growth factors are safe to use without potential contamination of infectious viruses and are less expensive to produce. In this study, we used rice cell-made basic fibroblast growth factor (RbFGF) to propagate hESCs and hiPSCs for at least eight passages. Both hESCs and hiPSCs cultured with RbFGF not only maintained the morphology but also the specific expression (OCT4, SSEA4, SOX2, and TRA-1-60) of PSCs, similar to those cultured with the commercial Escherichia coli-produced bFGF. Furthermore, both gene chip-based PluriTest and TaqMan hPSC Scorecard pluripotency analysis demonstrated the pluripotent expression profile of the hESCs cultured with RbFGF. In vitro trilineage assays further showed that these hESCs and hiPSCs cultured on RbFGF were capable of giving rise to cell derivatives of ectoderm, mesoderm, and endoderm, further demonstrating their pluripotency. Finally, chromosome stability was also maintained in hESCs cultured with RbFGF as demonstrated by normal karyotypes. This study suggests broad applications for plant-made growth factors in stem cell culture and regenerative medicine.

The advent of plant cells in bioreactors

Ever since agriculture started, plants have been bred to obtain better yields, better fruits, or sustainable products under uncertain biotic and abiotic conditions. However, a new way to obtain products from plant cells emerged with the development of recombinant DNA technologies. This led to the possibility of producing exogenous molecules in plants. Furthermore, plant chemodiversity has been the main source of pharmacological molecules, opening a field of plant biotechnology directed to produce high quality plant metabolites. The need for different products by the pharma, cosmetics agriculture and food industry has pushed again to develop new procedures. These include cell production in bioreactors. While plant tissue and cell culture are an established technology, beginning over a hundred years ago, plant cell cultures have shown little impact in biotechnology projects, compared to bacterial, yeasts or animal cells. In this review we address the different types of bioreactors that are currently used for plant cell production and their usage for quality biomolecule production. We make an overview of Nicotiana tabacum, Nicotiana benthamiana, Oryza sativa, Daucus carota, Vitis vinifera and Physcomitrium patens as well-established models for plant cell culture, and some species used to obtain important metabolites, with an insight into the type of bioreactor and production protocols.

Simple plant-based production and purification of the assembled human ferritin heavy chain as a nanocarrier for tumor-targeted drug delivery and bioimaging in cancer therapy

Nanoparticles are used as carriers for the delivery of drugs and imaging agents. Proteins are safer than synthetic nanocarriers due to their greater biocompatibility and the absence of toxic degradation products. In this context, ferritin has the additional benefit of inherently targeting the membrane receptor transferrin 1, which is overexpressed by most cancer cells. Furthermore, this self-assembling multimeric protein can be loaded with more than 2000 iron atoms, as well as drugs, contrast agents, and other cargos. However, recombinant ferritin currently costs ~3.5 million € g^-1 , presumably because the limited number of producers cannot meet demand, making it generally unaffordable as a nanocarrier. Because plants can produce proteins at very-large-scale, we developed a simple, proof-of-concept process for the production of the human ferritin heavy chain by transient expression in Nicotiana benthamiana. We optimized the protein yields by screening different compartments and 5'-untranslated regions in PCPs, and selected the best-performing construct for production in differentiated plants. We then established a rapid and scalable purification protocol by combining pH and heat treatment before extraction, followed by an ultrafiltration/diafiltration size-based separation process. The optimized process achieved ferritin levels of ~40 mg kg^-1 fresh biomass although depth filtration limited product recovery to ~7%. The purity of the recombinant product was >90% at costs ~3% of the current sales price. Our method therefore allows the production of affordable ferritin heavy chain as a carrier for therapeutic and diagnostic agents, which is suitable for further stability and functionality testing in vitro and in vivo.

Plant-based biopharmaceutical engineering

Plants can be engineered to recombinantly produce high-quality proteins such as therapeutic proteins and vaccines, also known as molecular farming. Molecular farming can be established in various settings with minimal cold-chain requirements and could thus ensure rapid and global-scale deployment of biopharmaceuticals, promoting equitable access to pharmaceuticals. State of the art plant-based engineering relies on rationally assembled genetic circuits, engineered to enable the high-throughput and rapid expression of multimeric proteins with complex post-translational modifications. In this Review, we discuss the design of expression hosts and vectors, including Nicotiana benthamiana, viral elements and transient expression vectors, for the production of biopharmaceuticals in plants. We examine engineering of post-translational modifications and highlight the plant-based expression of monoclonal antibodies and nanoparticles, such as virus-like particles and protein bodies. Techno-economic analyses suggest a cost advantage of molecular farming compared with mammalian cell-based protein production systems. However, regulatory challenges remain to be addressed to enable the widespread translation of plant-based biopharmaceuticals.

Design and production strategies for developing a recombinant butyrylcholinesterase medical countermeasure for Organophosphorus poisoning

Organophosphorus nerve agents represent a serious chemical threat due to their ease of production and scale of impact. The recent use of the nerve agent Novichok has re-emphasised the need for broad-spectrum medical countermeasures (MCMs) to these agents. However, current MCMs are limited. Plasma derived human butyrylcholinesterase (huBChE) is a promising novel bioscavenger MCM strategy, but is prohibitively expensive to isolate from human plasma at scale. Efforts to produce recombinant huBChE (rBChE) in various protein expression platforms have failed to achieve key critical attributes of huBChE such as circulatory half-life. These proteins often lack critical features such as tetrameric structure and requisite post-translational modifications. This review evaluates previous attempts to generate rBChE and assesses recent advances in mammalian cell expression and protein engineering strategies that could be deployed to achieve the required half-life and yield for a viable rBChE MCM. This includes the addition of a proline-rich attachment domain, fusion proteins, post translational modifications, expression system selection and optimised downstream processes. Whilst challenges remain, a combinatorial approach of these strategies demonstrates potential as a technically feasible approach to achieving a bioactive and cost effective bioscavenger MCM.

Production of Plant Proteases and New Biotechnological Applications: An Updated Review

An updated review of emerging plant proteases with potential biotechnological application is presented. Plant proteases show comparable or even greater performance than animal or microbial proteases for by-product valorization through hydrolysis for, for example, cheese whey, bird feathers, collagen, keratinous materials, gelatin, fish protein, and soy protein. Active biopeptides can be obtained as high added value products, which have shown numerous beneficial effects on human health. Plant proteases can also be used for wastewater treatment. The production of new plant proteases is encouraged for the following advantages: low cost of isolation using simple procedures, remarkable stability over a wide range of operating conditions (temperature, pH, salinity, and organic solvents), substantial affinity to a broad variety of substrates, and possibility of immobilization. Vegetable proteases have enormous application potential for the valorization of industrial waste and its conversion into products with high added value through low-cost processes.

A novel spray bioreactor for the proliferation of plant callus; Hyoscyamus niger and Arnebia pulchra

OBJECTIVE

Unlike plant cell suspension culture, the proliferation of callus in bioreactors has received inadequate attention. The magnificent potential of plant callus becomes more appreciated as the research unfolds and promises interesting applications including the production of valuable metabolites, therapeutic antibodies, bioactive extracts with regenerating effects, and the generation of genetically improved plants. Issues such as the lack of 3D-access of the cells to the nutrients, using an interfering gelling substance as the support matrix, and the changes in the medium formulation during the growth phase were discouraging factors for extending research on this topic. Considering the existing drawbacks, a novel open-flow spray bioreactor (OFSB) was configured to circumvent the associated problems with the solid cell culture and promote the applicability of plant callus culture via improving the feeding strategy.

METHODS

Applying similar subculture conditions, the proliferation of Arnebia pulchra and Hyoscyamus niger calli as the examples of two important plant families (Boraginaceae and Solanaceae) was studied in the OFSB in comparison with similar calli that grew in Petri dishes and jars.

RESULTS

A. pulchra and H. niger calli obtained the weight gains of (%87.3 and %106.7) in the Petri dishes, (%208.7 and %226) in the jars, and (%288.6 and %320.0) in OFSB, respectively, while no significant changes were observed in the productivity indices of the examined calli.

CONCLUSION

The simple design of OFSB bypasses most of the notorious problems associated with solid plant callus culture. OFSB technical features allow the bioreactor to be used for growth optimization of various types of plant calli in a cost-effective manner.

Contributions of the international plant science community to the fight against human infectious diseases - part 1: epidemic and pandemic diseases

Infectious diseases, also known as transmissible or communicable diseases, are caused by pathogens or parasites that spread in communities by direct contact with infected individuals or contaminated materials, through droplets and aerosols, or via vectors such as insects. Such diseases cause ˜17% of all human deaths and their management and control places an immense burden on healthcare systems worldwide. Traditional approaches for the prevention and control of infectious diseases include vaccination programmes, hygiene measures and drugs that suppress the pathogen, treat the disease symptoms or attenuate aggressive reactions of the host immune system. The provision of vaccines and biologic drugs such as antibodies is hampered by the high cost and limited scalability of traditional manufacturing platforms based on microbial and animal cells, particularly in developing countries where infectious diseases are prevalent and poorly controlled. Molecular farming, which uses plants for protein expression, is a promising strategy to address the drawbacks of current manufacturing platforms. In this review article, we consider the potential of molecular farming to address healthcare demands for the most prevalent and important epidemic and pandemic diseases, focussing on recent outbreaks of high-mortality coronavirus infections and diseases that disproportionately affect the developing world.

Immobilization of transgenic plant cells towards bioprinting for production of a recombinant biodefense agent

Transgenic rice cells (Oryza sativa) producing recombinant butyrylcholinesterase (BChE) as a prophylactic/therapeutic against organophosphate nerve agent poisoning, cocaine toxicity, and neurodegenerative diseases like Alzheimer's were immobilized in a polyethylene glycol-based hydrogel. The cells were sustained for 14 days in the semi-solid matrix, undergoing a growth phase from days 0-6, a BChE production phase in sugar-free medium from days 6-12, and a growth/recovery phase from days 12-14. Throughout this period, the cells maintained similar viability to those in suspension cultures and displayed analogous sugar consumption trends. The rice cells in the hydrogel also produced a significant amount of active BChE, comparable to the levels produced in liquid cultures. A considerable fraction of this BChE was secreted into the media, allowing for easier product separation. To the best of our knowledge, this proof-of-concept is the first report of immobilization of recombinant plant cells for continuous production of high-value heterologous proteins. This work serves as a foundation for further investigation towards plant cell bioprinting and the development of a simple, efficient, robust, modular, and potentially field-deployable bioreactor system for the manufacture of biologics. GRAPHICAL ABSTRACT AND LAY SUMMARY: Transgenic rice cells were combined with a polyethylene glycol tetra-acrylate (PEGTA) and lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) bioink and cured with UV light to construct an immobilized cell-based protein production system. The cells were maintained for 14 days in the hydrogel matrix and were induced to actively make and secrete recombinant butyrylcholinesterase, a complex enzyme that irreversibly binds to and can hydrolyze organophosphate. This proof-of-concept study showcases the use of immobilized and potentially bioprintable plant cells to produce high-value proteins with prophylactic and therapeutic applications.

Process Simulation and Techno-Economic Analysis of Large-Scale Bioproduction of Sweet Protein Thaumatin II

There are currently worldwide efforts to reduce sugar intake due to the various adverse health effects linked with the overconsumption of sugars. Artificial sweeteners have been used as an alternative to nutritive sugars in numerous applications; however, their long-term effects on human health remain controversial. This led to a shift in consumer preference towards non-caloric sweeteners from natural sources. Thaumatins are a class of intensely sweet proteins found in arils of the fruits of the West-African plant Thaumatococcus daniellii. Thaumatins' current production method through aqueous extraction from this plant and uncertainty of the harvest from tropical rainforests limits its supply while the demand is increasing. Despite successful recombinant expression of the protein in several organisms, no large-scale bioproduction facilities exist. We present preliminary process design, process simulation, and economic analysis for a large-scale (50 metric tons/year) production of a thaumatin II variant using several different molecular farming platforms.

Alpha-1 antitrypsin deficiency and recombinant protein sources with focus on plant sources: Updates, challenges and perspectives

Alpha-1 antitrypsin deficiency (A1ATD) is an autosomal recessive disease characterized by low plasma levels of A1AT, a serine protease inhibitor representing the most abundant circulating antiprotease normally present at plasma levels of 1-2 g/L. The dominant clinical manifestations include predispositions to early onset emphysema due to protease/antiprotease imbalance in distal lung parenchyma and liver disease largely due to unsecreted polymerized accumulations of misfolded mutant A1AT within the endoplasmic reticulum of hepatocytes. Since 1987, the only FDA licensed specific therapy for the emphysema component has been infusions of A1AT purified from pooled human plasma at the 2020 cost of up to US $200,000/year with the risk of intermittent shortages. In the past three decades various, potentially less expensive, recombinant forms of human A1AT have reached early stages of development, one of which is just reaching the stage of human clinical trials. The focus of this review is to update strategies for the treatment of the pulmonary component of A1ATD with some focus on perspectives for therapeutic production and regulatory approval of a recombinant product from plants. We review other competitive technologies for treating the lung disease manifestations of A1ATD, highlight strategies for the generation of data potentially helpful for securing FDA Investigational New Drug (IND) approval and present challenges in the selection of clinical trial strategies required for FDA licensing of a New Drug Approval (NDA) for this disease.

Production of recombinant butyrylcholinesterase from transgenic rice cell suspension cultures in a pilot-scale bioreactor

Producing recombinant proteins in transgenic plant cell suspension cultures in bioreactors provides controllability, reproducibility, scalability, and low-cost production, although low yields remain the major challenge. The studies on scaling-up to pilot-scale bioreactors, especially in conventional stainless-steel stirred tank bioreactors (STB), to produce recombinant proteins in plant cell suspension cultures are very limited. In this study, we scaled-up the production of rice recombinant butyrylcholinesterase (rrBChE), a complex hydrolase enzyme that can be used to prophylactically and therapeutically treat against organophosphorus nerve agents and pesticide exposure, from metabolically regulated transgenic rice cell suspension cultures in a 40-L pilot-scale STB. Employing cyclical operation together with a simplified-process operation (controlling gas sparging rate rather than dissolved oxygen and allowing natural sugar depletion) identified in lab-scale (5 L) bioreactor studies, we found a consistent maximum total active rrBChE production level of 46-58 µg/g fresh weight in four cycles over 82 days of semicontinuous operation. Additionally, maintaining the overall volumetric oxygen mass transfer coefficient (k_L a) in the pilot-scale STB to be equivalent to the lab-scale STB improves the maximum total active rrBChE production level and the maximum volumetric productivity to 85 µg/g fresh weight and 387 µg L^-1  day^-1 , respectively, which are comparable to the lab-scale culture. Here, we demonstrate pilot-scale bioreactor performance using a metabolically regulated transgenic rice cell culture for long-term, reproducible, and sustained production of rrBChE.

A method to simplify bioreactor processing for recombinant protein production in rice cell suspension cultures

Transgenic plant cell suspension culture is a promising platform for recombinant protein production. Rice cell suspension culture is one of the systems that has been developed due to its unique metabolically-regulated promoter, rice alpha-amylase 3D (RAmy3D), that is up-regulated in sugar-deprived medium. Using the RAmy3D promoter system in transgenic rice cell suspensions results in two phases of the culture, the growth phase and the induction phase. Conventionally, medium exchange is performed to remove residual sugar and induce recombinant protein. In this work, a simplified production process is demonstrated in a 5-L bioreactor, including reduction of sugar concentration in the initial culture medium, elimination of the media exchange operation, and uncontrolled dissolved oxygen (DO) with constant aeration. The simplified method significantly improves the accumulation level of a recombinant protein, protein purity, and productivity compared to the conventional method. This method also reduces costs associated with material and labor.

• The method of simplified bioreactor processing includes single-stage culture, uncontrolled dissolved oxygen (DO) but controlled inlet air flowrate, and lower (50% reduction) initial sucrose concentration in the culture medium.

• This method improves recombinant protein production level and productivity compared to the conventional method.

• This method reduces material and labor costs.

Effects of Kifunensine on Production and N-Glycosylation Modification of Butyrylcholinesterase in a Transgenic Rice Cell Culture Bioreactor

The production and N-glycosylation of recombinant human butyrylcholinesterase (BChE), a model highly glycosylated therapeutic protein, in a transgenic rice cell suspension culture treated with kifunensine, a strong α-mannosidase I inhibitor, was studied in a 5 L bioreactor. A media exchange was performed at day 7 of cultivation by removing spent sugar-rich medium (NB+S) and adding fresh sugar-free (NB-S) medium to induce the rice α-amylase 3D (RAmy3D) promoter to produce rice recombinant human BChE (rrBChE). Using a 1.25X-concentrated sugar-free medium together with an 80% reduced working volume during the media exchange led to a total active rrBChE production level of 79 ± 2 µg (g FW)^-1 or 7.5 ± 0.4 mg L^-1 in the presence of kifunensine, which was 1.5-times higher than our previous bioreactor runs using normal sugar-free (NB-S) media with no kifunensine treatment. Importantly, the amount of secreted active rrBChE in culture medium was enhanced in the presence of kifunensine, comprising 44% of the total active rrBChE at day 5 following induction. Coomassie-stained SDS-PAGE gel and Western blot analyses revealed different electrophoretic migration of purified rrBChE bands with and without kifunensine treatment, which was attributed to different N-glycoforms. N-Glycosylation analysis showed substantially increased oligomannose glycans (Man5/6/7/8) in rrBChE treated with kifunensine compared to controls. However, the mass-transfer limitation of kifunensine was likely the major reason for incomplete inhibition of α-mannosidase I in this bioreactor study.

The Emergency Response Capacity of Plant-Based Biopharmaceutical Manufacturing-What It Is and What It Could Be

Several epidemic and pandemic diseases have emerged over the last 20 years with increasing reach and severity. The current COVID-19 pandemic has affected most of the world's population, causing millions of infections, hundreds of thousands of deaths, and economic disruption on a vast scale. The increasing number of casualties underlines an urgent need for the rapid delivery of therapeutics, prophylactics such as vaccines, and diagnostic reagents. Here, we review the potential of molecular farming in plants from a manufacturing perspective, focusing on the speed, capacity, safety, and potential costs of transient expression systems. We highlight current limitations in terms of the regulatory framework, as well as future opportunities to establish plant molecular farming as a global, de-centralized emergency response platform for the rapid production of biopharmaceuticals. The implications of public health emergencies on process design and costs, regulatory approval, and production speed and scale compared to conventional manufacturing platforms based on mammalian cell culture are discussed as a forward-looking strategy for future pandemic responses.