Towards high-yield production of pharmaceutical proteins with plant cell suspension cultures

Alternatives of mesenchymal stem cell-derived exosomes as potential therapeutic platforms

With outstanding therapeutic potential in the tissue regeneration and anti-inflammation, mesenchymal stem cell-derived exosomes (MSC-EXOs) have emerged as a prominent therapeutic in recent. However, poor production yield and reproducibility have remained as significant challenges of their practical applications. To surmount these challenges, various alternative materials with stem cell-like functions, have been recently investigated, however, there has been no comprehensive analysis in these alternatives so far. Here, we discuss the recent progress of alternatives of MSC-EXOs, including exosomes and exosome-like nanovesicles from various biological sources such as plants, milk, microbes, and body fluids. Moreover, we extensively compare each alternative by summarizing their unique functions and mode of actions to suggest the expected therapeutic target and future directions for developing alternatives for MSC-EXOs.

Exploring the Potentiality of a Plant Platform for Monoclonal Antibody Production in Veterinary Medicine

Canine atopic dermatitis (CAD) is an allergic, inflammatory, and pruritic skin disease associated with the production of IgE antibodies against environmental allergens and mainly house dust mite allergens. This complex dermatological pathology involves Interleukin 31 (IL-31) as a central itch mediator. One of the most effective CAD treatments is a caninized monoclonal antibody (mAb) called Lokivetmab. It is produced in CHO cells and targets specifically canine IL-31 (cIL-31) and blocks its cellular messaging. This treatment has undoubtedly contributed to a breakthrough in dermatitis-related pruritus. However, its production in mammalian cells requires time-consuming procedures, high production costs, and investment. Plants are considered an emerging protein production platform for recombinant biopharmaceuticals due to their cost-effectiveness and rapidity for production. Here, we use transient expression in Nicotiana benthamiana plants to produce recombinant canine Interleukin 31 (cIL-31) and an anti-IL-31 monoclonal antibody (M1). First, we describe the production and characterization of M1 and then its activity on an IL-31-induced pruritic model in dogs compared to its commercial homolog. Dogs treated with the plant-made M1 mAb have shown similar improvements to Lokivetmab-treated ones after different challenges using canine IL-31. Furthermore, M1 injections were not associated with any side effects. These results demonstrate the safety and efficacy of this plant-made Lokivetmab biosimilar to control dogs' pruritus in a well-established model. Finally, this study shows that the plant-production platform can be utilized to produce rapidly functional mAbs and bring hope to the immunotherapy field of veterinary medicine.

Immunogenicity of a recombinant plant-produced respiratory syncytial virus F subunit vaccine in mice

Respiratory syncytial virus (RSV) is a highly infectious respiratory virus that causes serious illness, particularly in young children, elderly people, and those with immunocompromised individuals. RSV infection is the leading cause of infant hospitalization and can lead to serious complications such as pneumonia and bronchiolitis. Currently, there is an RSV vaccine approved exclusively for the elderly population, but no approved vaccine specifically designed for infants or any other age groups. Therefore, it is crucial to continue the development of an RSV vaccine specifically tailored for these populations. In this study, the immunogenicity of the two plant-produced RSV-F Fc fusion proteins (Native construct and structural stabilized construct) were examined to assess them as potential vaccine candidates for RSV. The RSV-F Fc fusion proteins were transiently expressed in Nicotiana benthamiana and purified using protein A affinity column chromatography. The recombinant RSV-F Fc fusion protein was recognized by the monoclonal antibody Motavizumab specific against RSV-F protein. Moreover, the immunogenicity of the two purified RSV-F Fc proteins were evaluated in mice by formulating with different adjuvants. According to our results, the plant-produced RSV-F Fc fusion protein is immunogenic in mice. These preliminary findings, demonstrate the immunogenicity of plant-based RSV-F Fc fusion protein, however, further preclinical studies such as antigen dose and adjuvant optimization, safety, toxicity, and challenge studies in animal models are necessary in order to prove the vaccine efficacy.

Bioreactor Systems for Plant Cell Cultivation at the Institute of Plant Physiology of the Russian Academy of Sciences: 50 Years of Technology Evolution from Laboratory to Industrial Implications

The cultivation of plant cells in large-scale bioreactor systems has long been considered a promising alternative for the overexploitation of wild plants as a source of bioactive phytochemicals. This idea, however, faced multiple constraints upon realization, resulting in very few examples of technologically feasible and economically effective biotechnological companies. The bioreactor cultivation of plant cells is challenging. Even well-growing and highly biosynthetically potent cell lines require a thorough optimization of cultivation parameters when upscaling the cultivation process from laboratory to industrial volumes. The optimization includes, but is not limited to, the bioreactor's shape and design, cultivation regime (batch, fed-batch, continuous, semi-continuous), aeration, homogenization, anti-foaming measures, etc., while maintaining a high biomass and metabolite production. Based on the literature data and our experience, the cell cultures often demonstrate cell line- or species-specific responses to parameter changes, with the dissolved oxygen concentration (pO2) and shear stress caused by stirring being frequent growth-limiting factors. The mass transfer coefficient also plays a vital role in upscaling the cultivation process from smaller to larger volumes. The Experimental Biotechnological Facility at the K.A. Timiryazev Institute of Plant Physiology has operated since the 1970s and currently hosts a cascade of bioreactors from the laboratory (20 L) to the pilot (75 L) and a semi-industrial volume (630 L) adapted for the cultivation of plant cells. In this review, we discuss the most appealing cases of the cell cultivation process's adaptation to bioreactor conditions featuring the cell cultures of medicinal plants Dioscorea deltoidea Wall. ex Griseb., Taxus wallichiana Zucc., Stephania glabra (Roxb.) Miers, Panax japonicus (T. Nees) C.A.Mey., Polyscias filicifolia (C. Moore ex E. Fourn.) L.H. Bailey, and P. fruticosa L. Harms. The results of cell cultivation in bioreactors of different types and designs using various cultivation regimes are covered and compared with the literature data. We also discuss the role of the critical factors affecting cell behavior in bioreactors with large volumes.

Production of Mature Recombinant Human Activin A in Transgenic Rice Cell Suspension Culture

Activin A belongs to the transforming growth factor (TGF) family member, which exhibits a wide range of biological activities, including the regulation of cellular proliferation and differentiation and the promotion of neuronal survival. The isolation of AA from natural sources can only produce limited quantities of this bioactive protein. In this study, the whole gene of the precursor form of recombinant human activin A (rhAA) contains a signal peptide, and a pro-region and a mature region were cloned into an expression vector under the control of the rice α-amylase 3D (RAmy3D) promoter. To obtain the mature (active) form of rhAA, an enterokinase cleavage site was inserted between the pro-region and mature region of rhAA. The rice seed (Oryza sativa L. cv. Dongjin) was transformed with recombinant vectors by the Agrobacterium-mediated method, and the integration of the target gene into the plant genome was confirmed by genomic PCR. The transcript expression of rhAA in transgenic rice calli was confirmed by a Northern blot analysis of mRNA. The production of rhAA was verified by Western blot analysis and ELISA. The accumulation of secreted rhAA in the culture medium was purified by Ni2+-NTA. The mature form of AA was released from the precursor form of rhAA after proteolytically processing with enterokinase. Western blot shows that the mature AA was split into monomer and homodimer with molecular weights of 14 kDa and 28 kDa under reducing and non-reducing conditions, respectively. These results suggest that the mature form of rhAA could be produced and purified using transgenic rice cell suspension culture.

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.

The lyophilized chloroplasts store synthetic DARPin G3 as bioactive encapsulated organelles

BACKGROUND

The high cost of fermentation, purification, cold storage and transportation, short shelf life, and sterile delivery methods of biopharmaceuticals, is a matter for producers and consumers as well. Since the FDA has now approved plant cells for large-scale, cost-effective biopharmaceutical production, the isolation and lyophilization of transplastomic chloroplasts can cover concerns about limitations. DARPins are engineered small single-domain proteins that have been selected to bind to HER2 with high affinity and specificity. HER2 is an oncogene involved in abnormal cell growth in some cancers and the target molecule for cancer immunotherapy.

RESULTS

In this study, we reported the prolonged stability and functionality of DARPin G3 in lyophilized transplastomic tobacco leaves and chloroplasts. Western blot analysis of lyophilized leaves and chloroplasts stored at room temperature for up to nine months showed that the DARPin G3 protein was stable and preserved proper folding. Lyophilization of leaves and isolated chloroplasts increased DARPin G3 protein concentrations by 16 and 32-fold, respectively. The HER2-binding assay demonstrated that the chloroplast-made DARPin G3 can maintain its stability and binding activity without any affinity drop in lyophilized leaf materials throughout this study for more than nine months at room temperature.

CONCLUSION

Lyophilization of chloroplasts expressing DARPin G3 would further reduce costs and simplify downstream processing, purification, and storage. Compressed packages of lyophilized chloroplasts were much more effective than lyophilized transplastomic leaves considering occupied space and downstream extraction and purification of DARPin G3 after nine months. These methods facilitate any relevant formulation practices for these compounds to meet any demand-oriented needs.

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.

Enhancing the Production of Hydrolytic Enzymes in Elicited Tamarillo (Solanum betaceum Cav.) Cell Suspension Cultures

Plant cell suspension cultures are widely used as a tool for analyzing cellular and molecular processes, metabolite synthesis, and differentiation, bypassing the structural complexity of plants. Within the range of approaches used to increase the production of metabolites by plant cells, one of the most recurrent is applying elicitors capable of stimulating metabolic pathways related to defense mechanisms. Previous proteomics analysis of tamarillo cell lines and cell suspension cultures have been used to further characterize and optimize the growth and stress-related metabolite production under in vitro controlled conditions. The main objective of this work was to develop a novel plant-based bioreactor system to produce hydrolytic enzymes using an elicitation approach. Based on effective protocols for tamarillo micropropagation and plant cell suspension culture establishment from induced callus lines, cell growth has been optimized, and enzymatic activity profiles under in vitro controlled conditions characterized. By testing different sucrose concentrations and the effects of two types of biotic elicitors, it was found that 3% (w/v) sucrose concentration in the liquid medium enhanced the production of hydrolytic enzymes. Moreover, casein hydrolysate at 0.5 and 1.5 g/L promoted protein production, whereas yeast extract (0.5 g/L) enhanced glycosidase activity. Meanwhile, chitosan (0.05 and 0.1 g/L) enhanced glycosidases, alkaline phosphates, and protease activities.

Three Parts of the Plant Genome: On the Way to Success in the Production of Recombinant Proteins

Recombinant proteins are the most important product of current industrial biotechnology. They are indispensable in medicine (for diagnostics and treatment), food and chemical industries, and research. Plant cells combine advantages of the eukaryotic protein production system with simplicity and efficacy of the bacterial one. The use of plants for the production of recombinant proteins is an economically important and promising area that has emerged as an alternative to traditional approaches. This review discusses advantages of plant systems for the expression of recombinant proteins using nuclear, plastid, and mitochondrial genomes. Possibilities, problems, and prospects of modifications of the three parts of the genome in light of obtaining producer plants are examined. Examples of successful use of the nuclear expression platform for production of various biopharmaceuticals, veterinary drugs, and technologically important proteins are described, as are examples of a high yield of recombinant proteins upon modification of the chloroplast genome. Potential utility of plant mitochondria as an expression system for the production of recombinant proteins and its advantages over the nucleus and chloroplasts are substantiated. Although these opportunities have not yet been exploited, potential utility of plant mitochondria as an expression system for the production of recombinant proteins and its advantages over the nucleus and chloroplasts are substantiated.

Insights into the quality of recombinant proteins produced by two different Bombyx mori expression systems

The silkworm, Bombyx mori, is an attractive host for recombinant protein production due to its high expression efficiency, quality, and quantity. Two expression systems have been widely used for recombinant protein production in B. mori: baculovirus/silkworm expression system and transgenic silkworm expression system. Both expression systems enable high protein production, but the qualities of the resulting recombinant proteins have not been well evaluated. In this study, we expressed bovine interferon γ (IFN-γ) using the two systems and examined the quality of the resulting proteins in terms of N-glycosylation and protein cleavage. Both expression systems successfully produced IFN-γ as an N-glycoprotein. Although the production in the baculovirus/silkworm expression system was much more efficient than that in the transgenic silkworm expression system, unexpected variants of IFN-γ were also produced in the former system due to the different N-glycosylation and C-terminal truncations. These results indicate that while high protein production could be achieved in the baculovirus/silkworm expression system, unintentional protein modification might occur, and therefore protein expression in the transgenic silkworm expression system is preferable from the point-of-view of N-glycosylation of the recombinant protein and evasion of unexpected attack by a protease in B. mori.

The production of the first functional antibody mimetic in higher plants: the chloroplast makes the DARPin G3 for HER2 imaging in oncology

Background

Designed mimetic molecules are attractive tools in biopharmaceuticals and synthetic biology. They require mass and functional production for the assessment of upcoming challenges in the near future. The DARPin family is considered a mimetic pharmaceutical peptide group with high affinity binding to specific targets. DARPin G3 is designed to bind to the HER2 (human epidermal growth factor receptor 2) tyrosine kinase receptor. Overexpression of HER2 is common in some cancers, including breast cancer, and can be used as a prognostic and predictive tool for cancer. The chloroplasts are cost-effective alternatives, equal to, and sometimes better than, bacterial, yeast, or mammalian expression systems. This research examined the possibility of the production of the first antibody mimetic, DARPin G3, in tobacco chloroplasts for HER2 imaging in oncology.

Results

The chloroplast specific DARPin G3 expression cassette was constructed and transformed into N. tabacum chloroplasts. PCR and Southern blot analysis confirmed integration of transgenes as well as chloroplastic and cellular homoplasmy. The Western blot analysis and ELISA confirmed the production of DARPin G3 at the commercial scale and high dose with the rate of 20.2% in leaf TSP and 33.7% in chloroplast TSP. The functional analysis by ELISA confirmed the binding of IMAC purified chloroplast-made DARPin G3 to the extracellular domain of the HER2 receptor with highly effective picomolar affinities. The carcinoma cellular studies by flow cytometry and immunofluorescence microscopy confirmed the correct functioning by the specific binding of the chloroplast-made DARPin G3 to the HER2 receptor on the surface of HER2-positive cancer cell lines.

Conclusion

The efficient functional bioactive production of DARPin G3 in chloroplasts led us to introduce plant chloroplasts as the site of efficient production of the first antibody mimetic molecules. This report, as the first case of the cost-effective production of mimetic molecules, enables researchers in pharmaceuticals, synthetic biology, and bio-molecular engineering to develop tool boxes by producing new molecular substitutes for diverse purposes.

Establishment of the Carrot-Made LTB-Syn Antigen Cell Line in Shake Flask and Airlift Bioreactor Cultures

Carrot (Daucus carota) cells have been used to effectively manufacture recombinant biopharmaceuticals such as cytokines, vaccines, and antibodies. We generated the carrot cell line Z4, genetically modified to produce the LTB-Syn antigen, which is a fusion protein proposed for immunotherapy against synucleinopathies. In this work, the Z4 cell suspension line was cultivated to produce the LTB-Syn protein in a 250 mL shake flask and 2 L airlift bioreactor cultures grown for 45 and 30 days, respectively. Maximum biomass was obtained on day 15 in both the airlift bioreactor (35.00 ± 0.04 g/L DW) and shake flasks (17.00 ± 0.04 g/L DW). In the bioreactor, the highest LTB-Syn protein yield (1.52 ± 0.03 µg/g FW) was obtained on day 15; while the same occurred on day 18 for shake flasks (0.92 ± 0.02 µg/g FW). LTB-Syn protein levels were analyzed by GM1-ELISA and western blot. PCR analysis confirmed the presence of the transgene in the Z4 line. The obtained data demonstrate that the carrot Z4 cell suspension line grown in airlift bioreactors shows promise for a scale-up cultivation producing an oral LTB-Syn antigen.

High yield secretion of human erythropoietin from tobacco cells for ex vivo differentiation of hematopoietic stem cells towards red blood cells

Human erythropoietin (EPO) is a key cytokine in erythropoiesis by regulating differentiation of erythroid progenitor cells into red blood cells (RBCs). Plant cell cultures are considered as promising alternative bioproduction platforms for EPO. To overcome the bottlenecks of low protein productivity and secretion, EPO was expressed in tobacco BY-2 cells with a designer peptide tag, termed (SP)20 that consists of 20 tandem repeats of a "Ser-Pro" motif. This de novo designed tag directed extensive O-glycosylation on each Pro residue in plant cells and acted as a molecular carrier to promote the extracellular secretion of EPO. To facilitate the establishment of stable and high-expression BY-2 cell lines, EPO molecules were co-expressed with a reporter protein GFP, which could be used as a visual marker to monitor the protein expression during the subculture. The engineered (SP)20 glycomodule substantially increased the secreted yields of EPO up to 4.31 μg/mL. The (SP)20-tagged EPOs exhibited the expected activity in promoting the proliferation of TF-1 cells, though their EC50 was 12-fold higher than that of EPO standard. The (SP)20-tagged EPOs could also stimulate the ex vivo expansion and differentiation of hematopoietic stem cell (CD34+ cells) towards RBCs.

Development of a plant-produced recombinant monoclonal antibody against Δ-9-tetrahydrocannabinol (Δ9-THC) for immunoassay application

Δ-9-tetrahydrocannabinol (Δ9-THC) is mainly a psychoactive compound in the cannabis plant. The immunoassay, an alternative method to HPLC and GC, can be used to analyze and measure Δ9-THC. This method provides high sensitivity and specificity by using antibodies specific to the desired substances. Currently, plants provide several benefits over traditional expression platforms to produce recombinant antibodies, such as lower production costs and scalability. Therefore, this study aims to produce a recombinant anti-Δ9-THC monoclonal antibody (mAb) with transient expression using N. benthamiana. The highest expression level of the plant-produced mAb was estimated to be 0.33 ug/g leaf fresh weight. Our results demonstrate that the antibody provided in vitro affinity binding related to Δ9-THC and the metabolites of Δ9-THC, such as cannabinol (CBN). Moreover, the antibody also showed binding efficiency with Δ9-THC in cannabis extract. Moreover, plant-produced mAbs provide efficiency against Δ9-THC and can be applied for further immunoassay applications.

Process Engineering of Biopharmaceutical Production in Moss Bioreactors via Model-Based Description and Evaluation of Phytohormone Impact

The moss Physcomitrella is an interesting production host for recombinant biopharmaceuticals. Here we produced MFHR1, a synthetic complement regulator which has been proposed for the treatment of diseases associated to the complement system as part of human innate immunity. We studied the impact of different operation modes for the production process in 5 L stirred-tank photobioreactors. The total amount of recombinant protein was doubled by using fed-batch or batch compared to semi-continuous operation, although the maximum specific productivity (mg MFHR1/g FW) increased just by 35%. We proposed an unstructured kinetic model which fits accurately with the experimental data in batch and semi-continuous operation under autotrophic conditions with 2% CO₂ enrichment. The model is able to predict recombinant protein production, nitrate uptake and biomass growth, which is useful for process control and optimization. We investigated strategies to further increase MFHR1 production. While mixotrophic and heterotrophic conditions decreased the MFHR1-specific productivity compared to autotrophic conditions, addition of the phytohormone auxin (NAA, 10 µM) to the medium enhanced it by 470% in shaken flasks and up to 230% and 260%, in batch and fed-batch bioreactors, respectively. Supporting this finding, the auxin-synthesis inhibitor L-kynurenine (100 µM) decreased MFHR1 production significantly by 110% and 580% at day 7 and 18, respectively. Expression analysis revealed that the MFHR1 transgene, driven by the Physcomitrella actin5 (PpAct5) promoter, was upregulated 16 h after NAA addition and remained enhanced over the whole process, whereas the auxin-responsive gene PpIAA1A was upregulated within the first 2 hours, indicating that the effect of auxin on PpAct5 promoter-driven expression is indirect. Furthermore, the day of NAA supplementation was crucial, leading to an up to 8-fold increase of MFHR1-specific productivity (0.82 mg MFHR1/g fresh weight, 150 mg accumulated over 7 days) compared to the productivity reported previously. Our findings are likely to be applicable to other plant-based expression systems to increase biopharmaceutical production and yields.

Using the Strategy of Inducing and Genetically Transforming Plant Suspension Cells to Produce High Value-Added Bioactive Substances

Plants can produce many functional bioactive substances. The suspension cell system of plants can be constructed based on its characteristics to realize the large-scale production of valuable products. In this review, we mainly talk about the main strategies, elicitation, and genetic transformation to improve the yield of active substances by using this system. Meanwhile, we focus on the challenges hiding in the practical application and the future prospects and provide new ideas and the theoretical basis for obtaining numerous bioactive substances from plants.

Analysis of N-glycan profile of Arabidopsis alg3 cell culture

N-Glycosylation is essential for protein stability, activity and characteristics, and is often needed to deliver pharmaceutical glycoproteins to target cells. A paucimannosidic structure, Man₃GlcNAc₂ (M3), has been reported to enable cellular uptake of glycoproteins through the mannose receptor (MR) in humans, and such uptake has been exploited for the treatment of certain diseases. However, M3 is generally produced at a very low level in plants. In this study, a cell culture was established from an Arabidopsis alg3 mutant plant lacking asparagine-linked glycosylation 3 (ALG3) enzyme activity. Arabidopsis alg3 cell culture produced glycoproteins with predominantly M3 and GlcNAc-terminal structures, while the amount of plant-specific N-glycans was very low. Pharmaceutical glycoproteins with these characteristics would be valuable for cellular delivery through the MR, and safe for human therapy.

Assessment of the Level of Accumulation of the dIFN Protein Integrated by the Knock-In Method into the Region of the Histone H3.3 Gene of Arabidopsis thaliana

Targeted DNA integration into known locations in the genome has potential advantages over the random insertional events typically achieved using conventional means of genetic modification. We investigated the possibility of obtaining a suspension cell culture of Arabidopsis thaliana carrying a site-specific integration of a target gene encoding modified human interferon (dIFN) using endonuclease Cas9. For the targeted insertion, we selected the region of the histone H3.3 gene (HTR5) with a high constitutive level of expression. Our results indicated that Cas9-induced DNA integration occurred with the highest frequency with the construction with donor DNA surrounded by homology arms and Cas9 endonuclease recognition sites. Among the monoclones of the four cell lines with knock-in studied, there is high heterogeneity in the level of expression and accumulation of the target protein. The accumulation of dIFN protein in cell lines with targeted insertions into the target region of the HTR5 gene does not statistically differ from the level of accumulation of dIFN protein in the group of lines with random integration of the transgene. However, one among the monoclonal lines with knock-in has a dIFN accumulation level above 2% of TSP, which is very high.

Microbial food: microorganisms repurposed for our food

Sustainable food production is a key to solve complicated and intertwined issues of overpopulation, climate change, environment and sustainability. Microorganisms, which have been routinely consumed as a part of fermented foods and more recently as probiotic dietary supplements, can be repurposed for our food to present a sustainable solution to current food production system. This paper begins with three snapshots of our future life with microbial foods. Next, the importance, possible forms, and raw materials (i.e. microorganisms and their carbon and energy sources) of microbial foods are discussed. In addition, the production strategies, further applications and current limitations of microbial foods are discussed.

Production of Human Acid-Alpha Glucosidase With a Paucimannose Structure by Glycoengineered Arabidopsis Cell Culture

Plant cell cultures have emerged as a promising platform for the production of biopharmaceutics due to their cost-effectiveness, safety, ability to control the cultivation, and secrete products into culture medium. However, the use of this platform is hindered by the generation of plant-specific N-glycans, the inability to produce essential N-glycans for cellular delivery of biopharmaceutics, and low productivity. In this study, an alternative acid-alpha glucosidase (GAA) for enzyme replacement therapy of Pompe disease was produced in a glycoengineered Arabidopsis alg3 cell culture. The N-glycan composition of the GAA consisted of a predominantly paucimannosidic structure, Man3GlcNAc2 (M3), without the plant-specific N-glycans. Supplementing the culture medium with NaCl to a final concentration of 50 mM successfully increased GAA production by 3.8-fold. GAA from an NaCl-supplemented culture showed a similar N-glycan profile, indicating that the NaCl supplementation did not affect N-glycosylation. The results of this study highlight the feasibility of using a glycoengineered plant cell culture to produce recombinant proteins for which M3 or mannose receptor-mediated delivery is desired.

Cellular engineering of plant cells for improved therapeutic protein production

In vitro cultured plant cells, in particular the tobacco BY-2 cell, have demonstrated their potential to provide a promising bioproduction platform for therapeutic proteins by integrating the merits of whole-plant cultivation systems with those of microbial and mammalian cell cultures. Over the past three decades, substantial progress has been made in improving the plant cell culture system, resulting in a few commercial success cases, such as taliglucerase alfa (Elelyso®), the first FDA-approved recombinant pharmaceutical protein derived from plant cells. However, compared to the major expression hosts (bacteria, yeast, and mammalian cells), plant cells are still largely underutilized, mainly due to low productivity and non-human glycosylation. Modern molecular biology tools, in particular RNAi and the latest genome editing technology CRISPR/Cas9, have been used to modulate the genome of plant cells to create new cell lines that exhibit desired "traits" for producing therapeutic proteins. This review highlights the recent advances in cellular engineering of plant cells towards improved recombinant protein production, including creating cell lines with deficient protease levels or humanized glycosylation, and considers potential development in the future.

Inactivation of the β (1, 2)-xylosyltransferase and the α (1, 3)-fucosyltransferase gene in rice (Oryza sativa) by multiplex CRISPR/Cas9 strategy

KEY MESSAGE

CRISPR/Cas9-mediated OsXylT and OsFucT mutation caused the elimination of plant-specific β1,2-xylose and α1,3-fucose residues on glycoproteins in rice, which is the first report of OsXylT/OsFucT double KO mutation in rice. N-glycosylation pathway is the one of post-translational mechanism and is known as highly conserved in eukaryotes. However, the process for complex-N-glycan modification is different between mammals and plants. In plant-specific manner, β1,2-xylose and α1,3-fucose residues are transferred to N-glycan core structure on glycoproteins by β1,2-xylosyltransferase (β1,2-XylT) and α1,3-fucosyltransferase (α1,3-FucT), respectively. As an effort to use plants as a platform to produce biopharmaceuticals, the plant-specific N-glycan genes of rice (Oryza sativa), β1,2-xylT (OsXylT) and α1,3-FucT (OsFucT), were knocked out using multiplex CRISPR/Cas9 technology. The double knock-out lines were found to have frameshift mutations by INDELs. Both β1,2-xylose and α1,3-fucose residues in the lines were not detected in Western blot analysis. Consistently, there was no peak corresponding to the N-glycans in MALDI-TOF/MS analysis. Although α1,3-fucose and β1,2-xylose residues were not detected in the line, other plant-specific residues of β1,3-galactose and α1,4-fucose were detected. Thus, we suggest that each enzymes working on the process for complex N-glycan biosynthesis might independently act in rice, hence the double knock-out of both OsXylT and OsFucT might be not enough to humanize N-glycan structure in rice.

The effects of genotypes and media composition on callogenesis, regeneration and cell suspension culture of chamomile (Matricaria chamomilla L.)

Background

Chamomile is an important herb being used widely for medicinal purposes. Its multitherapeutic, cosmetic, and nutritional values have been established through years of traditional and scientific use and research. Increased use of medicinal plants necessitates rational use as well as sustainable production of such genetic resources. Plant in vitro micro-propagation poses unique opportunities for sustainable production of medicinal herbs, their regrowth and conservation. The present study aimed to investigate the effects of different explants, plant growth regulators (PGRs) combinations and media type on callogenesis, in vitro regeneration and cell suspension of six chamomile genotypes to enhance its sustainable production.

Methods

The shoot, lateral sprout, and leaf derived explants of six chamomile genotypes including Isfahan, Shiraz, Kazeron, Goral, Sharokashari and Presso were used for direct and indirect regeneration. For indirect regeneration various doses of NAA and kinetin were used to induce calli which were cultured on MS media containing PGRs for direct and indirect regeneration. Later, cell suspension was established and morphological characterization of CrO₃ stained cells was carried out using microscopy.

Results and Discussion

Our findings revealed that the highest callus percentage and callus volume were observed from lateral sprouts and shoots of genotype Isfahan on MS medium containing 1 mg/L NAA and 1 mg/L kinetin. The in vitro regeneration was found to be genotype dependent while 77% and 77.5% was the highest percentage for indirect and direct regeneration, respectively. Additionally, the maximum shoot number (two shoots/explant) and shoot length (2.22 cm) were also observed in Isfahan genotype. Cell suspension culture showed the highest fresh weight (18.59 g) and dry weight (1.707 g) with 0.75 g inoculum of the callus derived from lateral sprouts cultured on MS medium. Microscopy of CrO₃ stained cells was carried on each 3rd day for 27 days that revealed larger and spongier cells in the early days as compared to final days when the cell number was greater but cell size was smaller.

Conclusion

The callogenesis, organogenesis, and cell suspension culture of chamomile may be genotype dependent. Hence, optimization of media ingredients and culture conditions is of utmost importance for devising tissue culture based conservation strategy of any chamomile genotype and secondary metabolite production.

High-throughput evolutionary optimization of the induction medium towards recombinant protein production in BY-2 tobacco

Bright yellow (BY-2) tobacco cells combined with the XVE chemically inducible system are one of the most promising plant-based platforms for recombinant protein production. This offers a range of benefits, including the separation of the cell growth and heterologous gene expression, lack of risk of infecting the end product with prions and human viruses or appropriate protein glycosylation and folding. However, low protein productivity remains a major obstacle that limits the extensive commercialization of bioproduction in plants. A number of molecular, cell culture and down processing approaches have been made to overcome this problem. Media development for the specific nutritional and hormonal requirements of transgenic plant cells is one of the most efficient cell-culture approaches. We optimized the induction medium towards recombinant protein production in BY-2 and demonstrated the usefulness of evolutionary medium optimization for high-yield protein production in liquid plant cultures. A reliable XVE/GFP model, parallel conducting experiments in a microscale on 96-well plates, and dedicated Gene Game evolutionary optimization software allowed for an effective search of 7611 possible solutions of 11-component media. Within the 4608 formulations tested, the Induct X medium was found with a significant 107.14% increase in protein expression in relation to the standard BY-2 medium.

Expression and Functional Evaluation of Recombinant Anti-receptor Activator of Nuclear Factor Kappa-B Ligand Monoclonal Antibody Produced in Nicotiana benthamiana

Denosumab, an anti-receptor activator of nuclear factor-kappa B ligand antibody (anti-RANKL), is a fully human monoclonal antibody (mAb) available for the treatment of osteoporosis. In the present study, an anti-RANKL mAb was transiently expressed using the geminiviral expression system in Nicotiana benthamiana, and the functional activity of the plant-produced mAb was determined. The highest expression level of the plant-produced mAb was found at 8 days post-infiltration, and it was estimated to be 0.5 mg/g leaf fresh weight. The recombinant mAb from the plant crude extracts was purified by using Protein A affinity column chromatography. The plant-produced mAb demonstrated good in vitro affinity binding with human RANKL, as determined by RANKL-ELISA binding. The function of the plant-produced mAb was evaluated in vitro. CD14-positive cells isolated from human peripheral blood mononuclear cells (PBMCs) were cultured in vitro in the presence of human RANKL and macrophage-colony-stimulating factor (M-CSF) to stimulate osteoclastogenesis. The results demonstrated that plant-produced mAb could significantly decrease the number of osteoclasts compared to commercial denosumab. These results demonstrated that the plant-produced mAb has the potential to inhibit osteoclast differentiation and that it could be considered for osteoporosis treatment.

Production of pharmaceutical active recombinant globular adiponectin as a secretory protein in Withania Somnifera hairy root culture

Among various in vitro plant culture systems, hairy root systems seem to be one of the most appealing methods of recombinant protein production due to their advantages in combining both whole-plant cultivation and suspension cell culture platform. This is a report on production and secretion of a recombinant pharmaceutically active protein from hairy roots cultures of Withania somnifera to improve the economic potential of this plant for the production pharmaceutical compounds. In this study, we selected and synthesized a codon-optimized globular adiponectin (gAd) gene with a calreticulin signal peptide and cloned the sequence into a plant expression binary vector containing a nptII gene as a selectable marker gene. The transgenic hairy roots were produced by Agrobacterium rhizogenes-mediated transformation protocol developed by our group. Among ten established nptII positive hairy roots lines, six colons significantly accumulated gAd protein in the biomass and extracellular medium. The presence of gAd was confirmed by western blot analysis of root extracts. The maximum level of hairy root biomass, growth rate (GR), intra- and extracellular gAd expressions were obtained after 25-26 days of culture on MS medium. The maximum level of intra- and extracellular gAd proteins were found to be 15.19 μg/gFW and 215.7 μg/L, respectively, which resulted in a significant decrease in the amount of intra- and extracellular withanolide A and withaferin A production. The addition of PVP, KNO3 and NaCl significantly increased the level of extracellular gAd by approximately 13 folds. This improvement could significantly increase the amount of intra- and extracellular withanolide A and withaferin A production, too. The recombinant gAd produced from W. somnifera is functional as proved by induction the phosphorylation of ACC in C2C12 muscle cells, as its functional amount was 5.1-fold more than gAd produced from E. coli and 45 % lower than CHO cells.

Plant cell-secreted stem cell factor stimulates expansion and differentiation of hematopoietic stem cells

Ex vivo generation of red blood cells (RBCs) from hematopoietic stem cells (HSCs) used for blood transfusion represents one of the focuses in current regenerative medicine. However, massive production of HSCs-based RBCs requires a significant quantity of erythropoietic growth factors, making manufacturing at large scale cost prohibitive. Plant cell culture is proposed to be a promising bioproduction platform for functional human proteins in a safe and cost-efficient manner. This study exploited a proprietary technology, named HypGP engineering technology, for high-yield production of one of the key erythropoietic growth factors--stem cell factor (SCF)--in plant cell culture. Specifically, a designer hydroxyproline (Hyp)-O-glycosylated peptide (HypGP) comprised of 20 tandem repeats of the "Ser-Pro" motif, or (SP)_20, was engineered at either the N-terminus or C-terminus of SCF in tobacco BY-2 cells. The (SP)₂₀ tag dramatically increased the secreted yields of SCF up to 2.5 μg/ml. The (SP)₂₀-tagged SCF showed bioactivity in promoting the proliferation of the TF-1 cell line, although the SCF-(SP)₂₀ was 8.4-fold more potent than the (SP)₂₀-SCF. Both the (SP)₂₀-SCF and SCF-(SP)₂₀ exhibited desired function in stimulating the expansion and differentiation of human umbilical cord blood CD34⁺ cells towards RBCs.

Next-generation metabolic engineering approaches towards development of plant cell suspension cultures as specialized metabolite producing biofactories

Plant cell suspension culture (PCSC) has emerged as a viable technology to produce plant specialized metabolites (PSM). While Taxol® and ginsenoside are two examples of successfully commercialized PCSC-derived PSM, widespread utilization of the PCSC platform has yet to be realized primarily due to a lack of understanding of the molecular genetics of PSM biosynthesis. Recent advances in computational, molecular and synthetic biology tools provide the opportunity to rapidly characterize and harness the specialized metabolic potential of plants. Here, we discuss the prospects of integrating computational modeling, artificial intelligence, and precision genome editing (CRISPR/Cas and its variants) toolboxes to discover the genetic regulators of PSM. We also explore how synthetic biology can be applied to develop metabolically optimized PSM-producing native and heterologous PCSC systems. Taken together, this review provides an interdisciplinary approach to realize and link the potential of next-generation computational and molecular tools to convert PCSC into commercially viable PSM-producing biofactories.

Transient protein expression in tobacco BY-2 plant cell packs using single and multi-cassette replicating vectors

KEY MESSAGE

This is the first evidence that replicating vectors can be successfully used for transient protein expression in BY-2 plant cell packs. Transient recombinant protein expression in plants and recently also plant cell cultures are of increasing interest due to the speed, safety and scalability of the process. Currently, studies are focussing on the design of plant virus-derived vectors to achieve higher amounts of transiently expressed proteins in these systems. Here we designed and tested replicating single and multi-cassette vectors that combine elements for enhanced replication and hypertranslation, and assessed their ability to express and particularly co-express proteins by Agrobacterium-mediated transient expression in tobacco BY-2 plant cell packs. Substantial yields of green and red fluorescent proteins of up to ~ 700 ng/g fresh mass were detected in the plant cells along with position-dependent expression. This is the first evidence of the ability of replicating vectors to transiently express proteins in BY-2 plant cell packs.

Plant tissue culture as a perpetual source for production of industrially important bioactive compounds

Plants have been used throughout the world for its medicinal powers since ancient time. The pharmacological properties of plants are based on their phytochemical components especially the secondary metabolites which are outstanding sources of value added bioactive compounds. Secondary metabolites have complex chemical composition and are produced in response to various forms of stress to perform different physiological tasks in plants. They are used in pharmaceutical industries, cosmetics, dietary supplements, fragrances, flavors, dyes, etc. Extended use of these metabolites in various industrial sectors has initiated a need to focus research on increasing the production by employing plant tissue culture (PTC) techniques and optimizing their large scale production using bioreactors. PTC techniques being independent of climatic and geographical conditions will provide an incessant, sustainable, economical and viable production of secondary metabolites. This review article intends to assess the advantages of using plant tissue culture, distribution of important secondary metabolites in plant families, strategies involved for optimal metabolite production and the industrial importance of selected secondary metabolites.

Current state-of-the-art in the use of plants for the production of recombinant vaccines against infectious bursal disease virus

Infectious bursal disease is a widely spread threatening contagious viral infection of chickens that induces major damages to the Bursa of Fabricius and leads to severe immunosuppression in young birds causing significant economic losses for poultry farming. The etiological agent is the infectious bursal disease virus (IBDV), a non-enveloped virus belonging the family of Birnaviridae. At present, the treatment against the spread of this virus is represented by vaccination schedules mainly based on inactivated or live-attenuated viruses. However, these conventional vaccines present several drawbacks such as insufficient protection against very virulent strains and the impossibility to differentiate vaccinated animals from infected ones. To overcome these limitations, in the last years, several studies have explored the potentiality of recombinant subunit vaccines to provide an effective protection against IBDV infection. In this review, we will give an overview of these novel types of vaccines with special emphasis on current state-of-the-art in the use of plants as "biofactories" (plant molecular farming). In fact, plants have been thoroughly and successfully characterized as heterologous expression systems for the production of recombinant proteins for different applications showing several advantages compared with traditional expression systems (Escherichia coli, yeasts and insect cells) such as absence of animal pathogens in the production process, improved product quality and safety, reduction of manufacturing costs, and simplified scale-up.

Development of Systems for the Production of Plant-Derived Biopharmaceuticals

Over the last several decades, plants have been developed as a platform for the production of useful recombinant proteins due to a number of advantages, including rapid production and scalability, the ability to produce unique glycoforms, and the intrinsic safety of food crops. The expression methods used to produce target proteins are divided into stable and transient systems depending on applications that use whole plants or minimally processed forms. In the early stages of research, stable expression systems were mostly used; however, in recent years, transient expression systems have been preferred. The production of the plant itself, which produces recombinant proteins, is currently divided into two major approaches, open-field cultivation and closed-indoor systems. The latter encompasses such regimes as greenhouses, vertical farming units, cell bioreactors, and hydroponic systems. Various aspects of each system will be discussed in this review, which focuses mainly on practical examples and commercially feasible approaches.

Enhanced secretion of human α1-antitrypsin expressed with a novel glycosylation module in tobacco BY-2 cell culture

Expression of recombinant proteins fused to a novel glycomodule tag, termed hydroxyproline (Hyp)-O-glycosylated peptides (HypGP), was earlier found to boost secreted protein yields up to 500-fold in plant cell culture. Here, this technology was applied to the expression of human protease inhibitor α1-antitrypsin (AAT) in tobacco BY-2 cell culture. A designer HypGP tag composed of a 'Ala-Pro' motif of 20 units, or (AP)20, was engineered either at the N- or C-terminal end of AAT. The (AP)20 tag substantially increased the secreted yields of the recombinant AAT up to 34.7 mg/L. However, the (AP)20-tagged AAT products were frequently subjected to proteolytic processing. The intact AAT-(AP)20 along with some of the truncated AAT domains exhibited desired biological activity in inhibiting elastase. The results from this research demonstrated that the designer (AP)20 module engineered in BY-2 cells could function as a molecular carrier to substantially enhance the secreted yields of the recombinant AAT.

Production of recombinant proteins through sequestration in chloroplasts: a strategy based on nuclear transformation and post-translational protein import

Recently, plants have emerged as a lucrative alternative system for the production of recombinant proteins, as recombinant proteins produced in plants are safer and cheaper than those produced in bacteria and animal cell-based production systems. To obtain high yields in plants, recombinant proteins are produced in chloroplasts using different strategies. The first strategy is based on chloroplast transformation, followed by gene expression and translation in chloroplasts. This has proven to be a powerful approach for the production of proteins at high levels. The second approach is based on nuclear transformation, followed by post-translational import of proteins from the cytosol into chloroplasts. In the nuclear transformation approach, foreign genes are stably integrated into the nuclear genome or transiently expressed in the nucleus by non-integrating T-DNA. Although this approach also has great potential for protein production at high levels, it has not been thoroughly investigated. In this review, we focus on nuclear transformation-based protein expression and its subsequent sequestration in chloroplasts, and summarize the different strategies used for high-level production of recombinant proteins. We also discuss future directions for further improvements in protein production in chloroplasts through nuclear transformation-based gene expression.

Production of Human IFNγ Protein in Nicotiana benthamiana Plant through an Enhanced Expression System Based on Bamboo mosaic Virus

Plant-based systems are safe alternatives to the current platforms for the production of biologically active therapeutic proteins. However, plant-based expression systems face certain major challenges, including the relatively low productivity and the generation of target proteins in biologically active forms. The use of plant virus-based expression systems has been shown to enhance yields, but further improvement is still required to lower the production cost. In this study, various strategies were employed to increase the yields of an important therapeutic protein, human interferon gamma (IFNγ), in Nicotiana benthamiana through modifications of expression vectors based on potexviruses. Among these, the vector based on a coat protein (CP)-deficient Bamboo mosaic virus (BaMV), pKB△CHis, was shown to exhibit the highest expression level for the unmodified IFNγ. Truncation of the N-terminal signal peptide of IFN (designated mIFNγ) resulted in a nearly seven-fold increase in yield. Co-expression of a silencing suppressor protein by replacing the coding sequence of BaMV movement protein with that of P19 led to a 40% increase in mIFNγ accumulation. The fusion of endoplasmic reticulum (ER) retention signal with mIFNγ significantly enhanced the accumulation ratio of biologically active dimeric mIFNγ to 87% relative to the non-active monomeric form. The construct pKB19mIFNγER, employing the combination of all the above enhancement strategies, gave the highest level of protein accumulation, up to 119 ± 0.8 μg/g fresh weight, accounting for 2.5% of total soluble protein (TSP) content. These findings advocate the application of the modified BaMV-based vector as a platform for high-level expression of therapeutic protein in N. benthamiana.

Engineering 'designer' glycomodules for boosting recombinant protein secretion in tobacco hairy root culture and studying hydroxyproline-O-glycosylation process in plants

The key technical bottleneck for exploiting plant hairy root cultures as a robust bioproduction platform for therapeutic proteins has been low protein productivity, particularly low secreted protein yields. To address this, we engineered novel hydroxyproline (Hyp)-O-glycosylated peptides (HypGPs) into tobacco hairy roots to boost the extracellular secretion of fused proteins and to elucidate Hyp-O-glycosylation process of plant cell wall Hyp-rich glycoproteins. HypGPs representing two major types of cell wall glycoproteins were examined: an extensin module consisting of 18 tandem repeats of 'Ser-Hyp-Hyp-Hyp-Hyp' motif or (SP4)18 and an arabinogalactan protein module consisting of 32 tandem repeats of 'Ser-Hyp' motif or (SP)32 . Each module was expressed in tobacco hairy roots as a fusion to the enhanced green fluorescence protein (EGFP). Hairy root cultures engineered with a HypGP module secreted up to 56-fold greater levels of EGFP, compared with an EGFP control lacking any HypGP module, supporting the function of HypGP modules as a molecular carrier in promoting efficient transport of fused proteins into the culture media. The engineered (SP4)18 and (SP)32 modules underwent Hyp-O-glycosylation with arabino-oligosaccharides and arabinogalactan polysaccharides, respectively, which were essential in facilitating secretion of the fused EGFP protein. Distinct non-Hyp-O-glycosylated (SP4)18 -EGFP and (SP)32 -EGFP intermediates were consistently accumulated within the root tissues, indicating a rate-limiting trafficking and/or glycosylation of the engineered HypGP modules. An updated model depicting the intracellular trafficking, Hyp-O-glycosylation and extracellular secretion of extensin-styled (SP4)18 module and AGP-styled (SP)32 module is proposed.

Bioreactor-based advances in plant tissue and cell culture: challenges and prospects

Bioreactors are engineered systems capable of supporting a biologically active situation for conducting aerobic or anaerobic biochemical processes. Stability, operational ease, improved nutrient uptake capacity, time- and cost-effectiveness, and large quantities of biomass production, make bioreactors suitable alternatives to conventional plant tissue and cell culture (PTCC) methods. Bioreactors are employed in a wide range of plant research, and have evolved over time. Such technological progress, has led to remarkable achievements in the field of PTCC. Since the classification of bioreactors has been extensively reviewed in numerous reviews, the current article avoids repeating the same material. Alternatively, it aims to highlight the principal advances in the bioreactor hardware s used in PTCC rather than classical categorization. Furthermore, our review summarizes the most significant steps as well as current state-of-the-art of PTCC carried out in various types of bioreactor.

Bioreactor-Based Production of Glycoproteins in Plant Cell Suspension Cultures

Recombinant glycoproteins such as monoclonal antibodies have a major impact on modern healthcare systems, e.g., as the active pharmaceutical ingredients in anticancer drugs. A specific glycan profile is often necessary to achieve certain desirable activities, such as the effector functions of an antibody, receptor binding or a sufficient serum half-life. However, many expression systems produce glycan profiles that differ substantially from the preferred form (usually the form found in humans) or produce a diverse array of glycans with a range of in vivo activities, thus necessitating laborious and costly separation and purification processes. In contrast, protein glycosylation in plant cells is much more homogeneous than other systems, with only one or two dominant forms. Additionally, these glycan profiles tend to remain stable when the process and cultivation conditions are changed, making plant cells an ideal expression system to produce recombinant glycoproteins with uniform glycan profiles in a consistent manner. This chapter describes a protocol that uses fermentations using plant cell cultures to produce glycosylated proteins using two different types of bioreactors, a classical autoclavable STR 3-L and a wave reactor.

Methyl Jasmonate Increases Isoflavone Production in Soybean Cell Cultures by Activating Structural Genes Involved in Isoflavonoid Biosynthesis

Isoflavonoids are a class of biologically active natural products that accumulate in soybean ( Glycine max L.) seeds during development, play vital roles in plant defense, and act as phytoestrogens with important human health benefits. Plant cell suspension cultures represent an excellent source of biologically important secondary metabolites. We found that methyl jasmonate (MJ) treatment increased isoflavone production in soybean suspension cell cultures. To investigate the underlying mechanism, we examined the expression of structural genes ( CHS6, CHS7, CHI1, IFS1, IFS2, IFMaT, and HID) in the isoflavonoid biosynthesis pathways in soybean suspension cells under various abiotic stress conditions. MJ treatment had the most significant effect on gene expression and increased the production of three glycosidic isoflavones (daidzin, malonyldaidzin, and malonylgenistin), with the maximum total isoflavone production (∼10-fold increase) obtained on day 9 after MJ application. MJ treatment significantly increased total phenolic contents and upregulated isoflavonoid biosynthesis genes, shedding light on the underlying mechanism.

Platforms for Plant-Based Protein Production

Plant molecular farming depends on a diversity of plant systems for production of useful recombinant proteins. These proteins include protein biopolymers, industrial proteins and enzymes, and therapeutic proteins. Plant production systems include microalgae, cells, hairy roots, moss, and whole plants with both stable and transient expression. Production processes involve a narrowing diversity of bioreactors for cell, hairy root, microalgae, and moss cultivation. For whole plants, both field and automated greenhouse cultivation methods are used with products expressed and produced either in leaves or seeds. Many successful expression systems now exist for a variety of different products with a list of increasingly successful commercialized products. This chapter provides an overview and examples of the current state of plant-based production systems for different types of recombinant proteins.

Glyco-Engineering of Plant-Based Expression Systems

Most secreted proteins in eukaryotes are glycosylated, and after a number of common biosynthesis steps the glycan structures mature in a species-dependent manner. Therefore, human therapeutic proteins produced in plants often carry plant-like rather than human-like glycans, which can affect protein stability, biological function, and immunogenicity. The glyco-engineering of plant-based expression systems began as a strategy to eliminate plant-like glycans and produce human proteins with authentic or at least compatible glycan structures. The precise replication of human glycans is challenging, owing to the absence of a pathway in plants for the synthesis of sialylated proteins and the necessary precursors, but this can now be achieved by the coordinated expression of multiple human enzymes. Although the research community has focused on the removal of plant glycans and their replacement with human counterparts, the presence of plant glycans on proteins can also provide benefits, such as boosting the immunogenicity of some vaccines, facilitating the interaction between therapeutic proteins and their receptors, and increasing the efficacy of antibody effector functions. Graphical Abstract Typical structures of native mammalian and plant glycans with symbols indicating sugar residues identified by their short form and single-letter codes. Both glycans contain fucose, albeit with different linkages.

Vanilla (Vanilla planifolia Jacks.) cell suspension cultures: establishment, characterization, and applications

The establishment and characterization of cell suspension cultures are an in vitro culture technique very useful for various plant biotechnological applications (production of secondary metabolites, mass micropropagation, protoplast isolation and fusion, gene transfer and the investigation of cell pathways). The objective of this study was to establish and characterization of cell suspension cultures of V. planifolia by inducing friable calluses. For that, friable calluses were obtained from immature seeds cultivated in MS medium supplemented with 0.45 µM thidiazuron (TDZ). The effect of benzyladenine (BA) in different concentrations was evaluated. Cultures were incubated under photoperiod at continuous stirring at 120 rpm on an orbital shaker. The optimal condition found for biomass growth in suspension cultures was 0.5 g of inoculum density (fresh weight) in MS liquid, supplemented with 8.88 µM BA. The growth kinetics of the cell suspension culture revealed a maximum cell growth (exponential growth phase) at day 16 and an 80% cell viability. The establishment and characterization of cell suspension cultures of V. planifolia constitute the bases of future studies and above all a better biotechnological use of this crop.

Metabolic engineering of CHO cells for the development of a robust protein production platform

Chinese hamster ovary (CHO) cells are the most preferred mammalian host used for the bio-pharmaceutical production. A major challenge in metabolic engineering is to balance the flux of the tuned heterogonous metabolic pathway and achieve efficient metabolic response in a mammalian cellular system. Pyruvate carboxylase is an important network element for the cytoplasmic and mitochondrial metabolic pathway and efficiently contributes in enhancing the energy metabolism. The lactate accumulation in cell culture can be reduced by re-wiring of the pyruvate flux in engineered cells. In the present work, we over-expressed the yeast cytosolic pyruvate carboxylase (PYC2) enzyme in CHO cells to augment pyruvate flux towards the TCA cycle. The dual selection strategy is adopted for the screening and isolation of CHO clones containing varying number of PYC2 gene load and studied their cellular kinetics. The enhanced PYC2 expression has led to enhanced pyruvate flux which, thus, allowed reduced lactate accumulation up to 4 folds and significant increase in the cell density and culture longevity. With this result, engineered cells have shown a significant enhanced antibody expression up to 70% with improved product quality (~3 fold) as compared to the parental cells. The PYC2 engineering allowed overall improved cell performance with various advantages over parent cells in terms of pyruvate, glucose, lactate and cellular energy metabolism. This study provides a potential expression platform for a bio-therapeutic protein production in a controlled culture environment.

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

Background

The ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014–2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle.

Results

In this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized.

Conclusions

This study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0745-2) contains supplementary material, which is available to authorized users.