Plant Molecular Farming: Much More than Medicines

Optimized expression of human interleukin-15 in Nicotiana benthamiana and in vitro assessment of its activity on human keratinocytes

Human interleukin-15 (hIL-15) is a cytokine essential for immune modulation with therapeutic applications in cancer and chronic wound healing. Although hIL-15 is commercially available, large-scale production studies remain limited. With promising clinical trial results, demand for hIL-15 is expected to rise. Plant expression systems offer a sustainable, low-cost alternative for rapid biopharmaceutical production. In this study, we optimized hIL-15 expression in Nicotiana benthamiana and assessed its physicochemical properties and biological activity. We fused hIL-15 to the Fc domain of human IgG1 for efficient purification. Through optimization of the pre- and post-infiltration conditions, we achieved transient expression and recovery at 4 dpi, yielding 33.8 µg/g fresh weight. Peptide mapping confirmed 97 % overall sequence coverage of the primary structure. Treatment with plant-produced hIL-15-Fc effectively promoted human keratinocyte HaCaT cell proliferation and migration in vitro. These findings demonstrated the potential of plant-based platforms for producing therapeutic recombinant hIL-15 that support wound healing.

Protective effects of Paeonia suffruticosa callus extract in skin through anti-inflammation and repair UVB-induced damage

OBJECTIVE

The study investigated effects of peony callus extracts (PCE) on the protective efficacy against Ultraviolet B (UVB)-induced photoageing, using in vitro and in vivo studies. The research focused on PCE's ability to protect against inflammatory factors, DNA damage and accumulation of senescent cells, along with the evaluation of the extract's potential anti-photoageing benefits to skin.

METHODS

Human keratinocyte cell line (HaCaT cells), mast cells and fibroblasts were used to evaluate the role of PCE in anti-photoageing. The expression of genes of interleukin-1α (IL-1α), IL-6 and transient receptor potential vanilloid 1 (TRPV1) were tested in HaCaT cells. The histamine contents in mast cells were tested to evaluate the effect of PCE on soothing skin. Additionally, the repairment of PCE on DNA damage stimulated by UVB using comet assay was evaluated. In fibroblasts, the gene expression of matrix metalloproteinases (MMPs) and the activity of β-galactosidase were tested. In vivo test, 13 healthy volunteers were enrolled to apply a formula with 1% PCE to assess the variation in inner skin collagen contents.

RESULTS

The callus from an ancient and rare variety of tree peony (Paeoniaceae family) was successfully induced, and its ingredients were extracted. The PCE could significantly downregulate inflammation factors such as IL-1α, IL-6 and TRPV1 in HaCaT cells, and MMPs in fibroblasts which could cause the collagen degradation induced by UVB. Meanwhile, UVB-induced DNA damage was alleviated by PCE. The analysis of histamine content in mast cells revealed that PCE effectively alleviated skin sensitivity. Furthermore, the clinical trials validated a significant increase in total collagen content in vivo, following 28 days of continuous application of a cosmetic formulation containing 1% PCE measured by Raman confocal spectroscopy technology.

CONCLUSION

The PCE could downregulate the gene expression of inflammatory factors, indicating the ability of DNA repair. The number of senescent cells was also decreased after UVB stimulation. Furthermore, the results of in vivo study showed that PCE was an ideal cosmetic ingredient for promoting collagen levels.

Molecular Farming for Immunization: Current Advances and Future Prospects in Plant-Produced Vaccines

Using plants as bioreactors, molecular farming has emerged as a versatile and sustainable platform for producing recombinant vaccines, therapeutic proteins, industrial enzymes, and nutraceuticals. This innovative approach leverages the unique advantages of plants, including scalability, cost-effectiveness, and reduced risk of contamination with human pathogens. Recent advancements in gene editing, transient expression systems, and nanoparticle-based delivery technologies have significantly enhanced the efficiency and versatility of plant-based systems. Particularly in vaccine development, molecular farming has demonstrated its potential with notable successes such as Medicago's Covifenz for COVID-19, illustrating the capacity of plant-based platforms to address global health emergencies rapidly. Furthermore, edible vaccines have opened new avenues in the delivery of vaccines, mainly in settings with low resources where the cold chain used for conventional logistics is a challenge. However, optimization of protein yield and stability, the complexity of purification processes, and regulatory hurdles are some of the challenges that still remain. This review discusses the current status of vaccine development using plant-based expression systems, operational mechanisms for plant expression platforms, major applications in the prevention of infectious diseases, and new developments, such as nanoparticle-mediated delivery and cancer vaccines. The discussion will also touch on ethical considerations, the regulatory framework, and future trends with respect to the transformative capacity of plant-derived vaccines in ensuring greater global accessibility and cost-effectiveness of the vaccination. This field holds great promise for the infectious disease area and, indeed, for applications in personalized medicine and biopharmaceuticals in the near future.

Closed-loop systems for plants expressing animal proteins: a modernized framework to safeguard the future of agricultural innovation

Escalating population growth and climate change pressures on crop production necessitate agricultural innovation to ensure food security and sustainability. Plant molecular farming (PMF), which uses genetically modified (GM) plants to produce high-value proteins for food products, offers a promising solution. PMF products, particularly those that express an animal protein in seed and grain crops, have the potential to substantially benefit U.S. and global agriculture, food systems, economies, and the environment. Farmers can diversify and generate increased revenue streams, while consumers gain access to affordable proteins beyond those currently available. However, the development and commercialization of PMF products, especially those expressing allergenic animal proteins, require careful consideration of existing stewardship guidelines and best practices. Current GM plant stewardship practices must be thoroughly assessed to identify and address any gaps, ensuring that PMF products maintain identity preservation and containment throughout their lifecycle. Implementing a fit-for-purpose closed-loop system (CLS) is crucial for effectively identifying, managing, and mitigating the potential risks and liabilities associated with PMF product development, production, and processing. A CLS framework for PMF products expressing animal proteins should integrate existing best practices from Excellence Through Stewardship and applicable third-party guidelines, including by way of example ISO standards, Good Manufacturing Practices, Hazard Analysis and Risk-Based Preventive Controls, Hazard Analysis and Critical Control Points, and Safe Quality Food, as well as newly designed controls to address potential PMF-specific risks. This comprehensive approach maximizes containment, identity preservation, regulatory compliance, traceability, incident response capabilities, and continuous improvement across the product lifecycle. While customization is required based on each PMF product developer's specific product and operations, this paper examines industry best practices and describes CLS components that a PMF developer should consider in designing a robust, bespoke CLS to maintain identity preservation and product containment. Such a system will optimize for product quality and integrity while preventing commingling with commodity supplies and any associated market disruption while also addressing food safety. By implementing these rigorous systems, the PMF industry can realize its potential to contribute significantly to sustainable agriculture and food security.

Transient Expression of Zika NS2B Protein Antigen in Nicotiana benthamiana and Use for Arboviruses Diagnosis

Zika (ZIKV) and Dengue (DENV) viruses are clinically significant due to their severe neurological and hemorrhagic complications. Rapid diagnostics often rely on nonstructural proteins to generate specific antibodies. This study aimed to produce IgG antibodies from the recombinant ZIKV protein and plant-expressed NS2B protein for arbovirus detection in serum and urine samples. The NS2B protein was expressed in Nicotiana benthamiana and purified chromatographically. Validation of recombinant NS2B as an antigen in indirect immunoassays demonstrated 95% sensitivity and 100% specificity in IgM/IgG ELISA tests, enabling effective detection of ZIKV and DENV. Notably, r-ZIKV-NS2B IgG identified positive ZIKV and DENV cases in urine but failed to detect negatives, suggesting limitations in specificity for urine diagnostics. Using urine as a diagnostic medium offers a less invasive and more practical approach, broadening the test applicability. This study utilized patient-derived positive urine samples and healthy samples spiked with an exogenous virus. Findings highlight the potential of the ZIKV-NS2B protein as a robust antigen for arbovirus diagnosis and demonstrate the viability of plant-based systems for antigen production, advancing diagnostics for neglected tropical diseases.

Plant-produced SARS-CoV-2 antibody engineered towards enhanced potency and in vivo efficacy

Prevention of severe COVID-19 disease by SARS-CoV-2 in high-risk patients, such as immuno-compromised individuals, can be achieved by administration of antibody prophylaxis, but producing antibodies can be costly. Plant expression platforms allow substantial lower production costs compared to traditional bio-manufacturing platforms depending on mammalian cells in bioreactors. In this study, we describe the expression, production and purification of the originally human COVA2-15 antibody in plants. Our plant-produced mAbs demonstrated comparable neutralizing activity with COVA2-15 produced in mammalian cells. Furthermore, they exhibited similar capacity to prevent SARS-CoV-2 infection in a hamster model. To further enhance these biosimilars, we performed three glyco- and protein engineering techniques. First, to increase antibody half-life, we introduced YTE-mutation in the Fc tail; second, optimization of N-linked glycosylation by the addition of a C-terminal ER-retention motif (HDEL), and finally; production of mAb in plant production lines lacking β-1,2-xylosyltransferase and α-1,3-fucosyltransferase activities (FX-KO). These engineered biosimilars exhibited optimized glycosylation, enhanced phagocytosis and NK cell activation capacity compared to conventional plant-produced S15 and M15 biosimilars, in some cases outperforming mammalian cell produced COVA2-15. These engineered antibodies hold great potential for enhancing in vivo efficacy of mAb treatment against COVID-19 and provide a platform for the development of antibodies against other emerging viruses in a cost-effective manner.

Production of Plant Virus-Derived Hybrid Nanoparticles Decorated with Different Nanobodies

Viral nanoparticles (VNPs) are self-assembled nanometric complexes whose size and shape are similar to those of the virus from which they are derived. VNPs are arousing great attention due to potential biotechnological applications in fields like nanomedicine and nanotechnology because they allow the presentation of polypeptides of choice linked to the virus structural proteins. Starting from tobacco etch virus (TEV), a plant plus-strand RNA virus that belongs to the genus Potyvirus (family Potyviridae), here we describe the development of recombinant hybrid VNPs in Nicotiana benthamiana plants able of exposing simultaneously different proteins on their surface. This system is based on the synergic coinfection of TEV and potato virus X (PVX; Potexvirus), in which PVX provides a second TEV CP in trans allowing a mixed assembly. We first generated genetically modified hybrid VNPs simultaneously displaying green and red fluorescent proteins on their surface. A population of decorated and nondecorated CPs resulting from the insertion of the picornavirus F2A ribosomal escape peptide was required for viral particle assembly. Correct assembly of the recombinant mosaic VNPs presenting the exogenous peptides was successfully observed by immunoelectron microscopy. We next achieved the production of hybrid VNPs expressing a nanobody against SARS-CoV-2 and a fluorescent reporter protein, whose functionality was demonstrated by ELISA and dot-blot assay. Finally, we engineered the production of hybrid multivalent VNPs carrying two different nanobodies against distinct epitopes of the same SARS-CoV-2 antigenic protein, emulating a nanobody cocktail. These plant-produced recombinant mosaic VNPs, which are filamentous and flexuous in shape, presenting two different fused proteins on the surface, represent a molecular tool with several potential applications in biotechnology.

A review and outlook on expression of animal proteins in plants

This review delves into the multifaceted technologies, benefits and considerations surrounding the expression of animal proteins in plants, emphasizing its potential role in advancing global nutrition, enhancing sustainability, while being mindful of the safety considerations. As the world's population continues to grow and is projected to reach 9 billion people by 2050, there is a growing need for alternative protein sources that can meet nutritional demands while minimizing environmental impact. Plant expression of animal proteins is a cutting-edge biotechnology approach that allows crops to produce proteins traditionally derived from animals, offering a sustainable and resource-efficient manner of producing these proteins that diversifies protein production and increases food security. In the United States, it will be important for there to be clear guidance in order for these technologies to reach consumers. As consumer demand for sustainable and alternative food sources rise, biotechnologies can offer economic opportunities, making this emerging technology a key player in the market landscape.

Bacterial growth-mediated systems remodelling of Nicotiana benthamiana defines unique signatures of target protein production in molecular pharming

The need for therapeutics to treat a plethora of medical conditions and diseases is on the rise and the demand for alternative approaches to mammalian-based production systems is increasing. Plant-based strategies provide a safe and effective alternative to produce biological drugs but have yet to enter mainstream manufacturing at a competitive level. Limitations associated with batch consistency and target protein production levels are present; however, strategies to overcome these challenges are underway. In this study, we apply state-of-the-art mass spectrometry-based proteomics to define proteome remodelling of the plant following agroinfiltration with bacteria grown under shake flask or bioreactor conditions. We observed distinct signatures of bacterial protein production corresponding to the different growth conditions that directly influence the plant defence responses and target protein production on a temporal axis. Our integration of proteomic profiling with small molecule detection and quantification reveals the fluctuation of secondary metabolite production over time to provide new insight into the complexities of dual system modulation in molecular pharming. Our findings suggest that bioreactor bacterial growth may promote evasion of early plant defence responses towards Agrobacterium tumefaciens (updated nomenclature to Rhizobium radiobacter). Furthermore, we uncover and explore specific targets for genetic manipulation to suppress host defences and increase recombinant protein production in molecular pharming.

Modulable 3D-printed plantibody-laden platform enabling microscale affinity extraction and ratiometric front-face fluorescence detection of microcystin-LR in marine waters

A 3D-printed stereolithographic platform for selective biorecognition is designed to enable convective microscale affinity extraction of microcystin-LR (MC-LR) followed by direct solid-phase optosensing exploiting ratiometric front-face fluorescence spectroscopy. For this purpose, a recombinant monoclonal plantibody (recAb) is covalently attached to a 3D-printed structure for sorptive immunoextraction, whereupon the free and unbound primary amino moieties of the recAb are derivatized with a fluorescent probe. The fluorophore-recAb-MC-LR laden device is then accommodated in the cuvette holder of a conventional fluorometer without any instrumental modification for the recording of the solid-phase fluorescence emission. Using Rodbard's four-parameter sigmoidal function, the 3D-printed bioselective platform features a limit of detection (LOD) of 28 ng L-1 using a sample volume of 500 mL, device-to-device reproducibility down to 12%, and relative recoveries ranging from 91 to 100% in marine waters. Printed prototypes are affordable, just 0.4 € per print and ≤ 10 € per device containing recAb. One of the main assets of the miniaturized immunoextraction device is that it performs comparably well in terms of analytical figures of merit with costly mass spectrometric-based analytical methodologies, such as HPLC-MS/MS. The device is readily applicable to high-matrix samples, such as seawater, as opposed to previous biosensing platforms, just applied to freshwater systems.

Production of biologically active human basic fibroblast growth factor (hFGFb) using Nicotiana tabacum transplastomic plants

MAIN CONCLUSION

We generated transplastomic tobacco lines that stably express a human Basic Fibroblast Growth Factor (hFGFb) in their chloroplasts stroma and purified a biologically active recombinant hFGFb. MAIN: The use of plants as biofactories presents as an attractive technology with the potential to efficiently produce high-value human recombinant proteins in a cost-effective manner. Plastid genome transformation stands out for its possibility to accumulate recombinant proteins at elevated levels. Of particular interest are recombinant growth factors, given their applications in animal cell culture and regenerative medicine. In this study, we produced recombinant human Fibroblast Growth Factor (rhFGFb), a crucial protein required for animal cell culture, in tobacco chloroplasts. We successfully generated two independent transplastomic lines that are homoplasmic and accumulate rhFGFb in their leaves. Furthermore, the produced rhFGFb demonstrated its biological activity by inducing proliferation in HEK293T cell lines. These results collectively underscore plastid genome transformation as a promising plant-based bioreactor for rhFGFb production.

Membrane-based inverse-transition purification facilitates a rapid isolation of various spider-silk elastin-like polypeptide fusion proteins from extracts of transgenic tobacco

Plants can produce complex pharmaceutical and technical proteins. Spider silk proteins are one example of the latter and can be used, for example, as compounds for high-performance textiles or wound dressings. If genetically fused to elastin-like polypeptides (ELPs), the silk proteins can be reversibly precipitated from clarified plant extracts at moderate temperatures of ~ 30 °C together with salt concentrations > 1.5 M, which simplifies purification and thus reduces costs. However, the technologies developed around this mechanism rely on a repeated cycling between soluble and aggregated state to remove plant host cell impurities, which increase process time and buffer consumption. Additionally, ELPs are difficult to detect using conventional staining methods, which hinders the analysis of unit operation performance and process development. Here, we have first developed a surface plasmon resonance (SPR) spectroscopy-based assay to quantity ELP fusion proteins. Then we tested different filters to prepare clarified plant extract with > 50% recovery of spider silk ELP fusion proteins. Finally, we established a membrane-based purification method that does not require cycling between soluble and aggregated ELP state but operates similar to an ultrafiltration/diafiltration device. Using a data-driven design of experiments (DoE) approach to characterize the system of reversible ELP precipitation we found that membranes with pore sizes up to 1.2 µm and concentrations of 2-3 M sodium chloride facilitate step a recovery close to 100% and purities of > 90%. The system can thus be useful for the purification of ELP-tagged proteins produced in plants and other hosts.

Green Biologics: Harnessing the Power of Plants to Produce Pharmaceuticals

Plants are increasingly used for the production of high-quality biological molecules for use as pharmaceuticals and biomaterials in industry. Plants have proved that they can produce life-saving therapeutic proteins (Elelyso™-Gaucher's disease treatment, ZMapp™-anti-Ebola monoclonal antibodies, seasonal flu vaccine, Covifenz™-SARS-CoV-2 virus-like particle vaccine); however, some of these therapeutic proteins are difficult to bring to market, which leads to serious difficulties for the manufacturing companies. The closure of one of the leading companies in the sector (the Canadian biotech company Medicago Inc., producer of Covifenz) as a result of the withdrawal of investments from the parent company has led to the serious question: What is hindering the exploitation of plant-made biologics to improve health outcomes? Exploring the vast potential of plants as biological factories, this review provides an updated perspective on plant-derived biologics (PDB). A key focus is placed on the advancements in plant-based expression systems and highlighting cutting-edge technologies that streamline the production of complex protein-based biologics. The versatility of plant-derived biologics across diverse fields, such as human and animal health, industry, and agriculture, is emphasized. This review also meticulously examines regulatory considerations specific to plant-derived biologics, shedding light on the disparities faced compared to biologics produced in other systems.

Development of a plant-based oral vaccine candidate against the bovine respiratory pathogen Mannheimia haemolytica

Bovine respiratory disease (BRD) affects feedlot cattle across North America, resulting in economic losses due to animal treatment and reduced performance. In an effort to develop a vaccine candidate targeting a primary bacterial agent contributing to BRD, we produced a tripartite antigen consisting of segments of the virulence factor Leukotoxin A (LktA) and lipoprotein PlpE from Mannheimia haemolytica, fused to a cholera toxin mucosal adjuvant (CTB). This recombinant subunit vaccine candidate was expressed in the leaves of Nicotiana benthamiana plants, with accumulation tested in five subcellular compartments. The recombinant protein was found to accumulate highest in the endoplasmic reticulum, but targeting to the chloroplast was employed for scaling up production due the absence of post-translational modification while still producing feasible levels. Leaves were freeze dried, then orally administered to mice to determine its immunogenicity. Sera from mice immunized with leaf tissue expressing the recombinant antigen contained IgG antibodies, specifically recognizing both LktA and PlpE. These mice also had a mucosal immune response to the CTB+LktA+PlpE protein as measured by the presence of LktA- and PlpE-specific IgA antibodies in lung and fecal material. Moreover, the antigen remained stable at room temperature with limited deterioration for up to one year when stored as lyophilized plant material. This study demonstrated that a recombinant antigen expressed in plant tissue elicited both humoral and mucosal immune responses when fed to mice, and warrants evaluation in cattle.

In vitro and in vivo studies of plant-produced Atezolizumab as a potential immunotherapeutic antibody

Immune checkpoint inhibitors are a well-known class of immunotherapeutic drugs that have been used for effective treatment of several cancers. Atezolizumab (Tecentriq) was the first antibody to target immune checkpoint PD-L1 and is now among the most commonly used anticancer therapies. However, this anti-PD-L1 antibody is produced in mammalian cells with high manufacturing costs, limiting cancer patients' access to the antibody treatment. Plant expression system is another platform that can be utilized, as they can synthesize complex glycoproteins, are rapidly scalable, and relatively cost-efficient. Herein, Atezolizumab was transiently produced in Nicotiana benthamiana and demonstrated high expression level within 4-6 days post-infiltration. After purification by affinity chromatography, the purified plant-produced Atezolizumab was compared to Tecentriq and showed the absence of glycosylation. Furthermore, the plant-produced Atezolizumab could bind to PD-L1 with comparable affinity to Tecentriq in ELISA. The tumor growth inhibitory activity of plant-produced Atezolizumab in mice was also found to be similar to that of Tecentriq. These findings confirm the plant's capability to serve as an efficient production platform for immunotherapeutic antibodies and suggest that it could be used to alleviate the cost of existing anticancer products.

Molecular Farming Strategy for the Rapid Production of Protein-Based Reagents for Use in Infectious Disease Diagnostics

Recombinant proteins are a major breakthrough in biomedical research with a wide range of applications from diagnostics to therapeutics. Strategic construct design, consistent expression platforms, and suitable upstream and downstream techniques are key considerations to produce commercially viable recombinant proteins. The recombinant antigenic protein production for use either as a diagnostic reagent or subunit vaccine formulation is usually carried out in prokaryotic or eukaryotic expression platforms. Microbial and mammalian systems dominate the biopharmaceutical industry for such applications. However, there is no universal expression system that can meet all the requirements for different types of proteins. The adoptability of any expression system is likely based on the quality and quantity of the proteins that can be produced from it. The huge demand of recombinant proteins for different applications requires an inexpensive production platform for rapid development. The molecular farming scientific community has been promoting the plant system for nearly 3 decades as a cost-effective alternative to produce high-quality proteins for research, diagnostic, and therapeutic applications. Here, we discuss how plant biotechnology could offer solutions for the rapid and scalable production of protein antigens as low-cost diagnostic reagents for use in functional assays.

Therapeutic efficacy of plant-produced Nivolumab in transgenic C57BL/6-hPD-1 mouse implanted with MC38 colon cancer

The therapeutic blockade of inhibitory PD-1 signaling has emerged as an effective approach for cancer immunotherapy. Nivolumab (Opdivo®), a monoclonal antibody (mAb) targeting the PD-1 immune checkpoint, is approved for treatment of several cancer indications. It functions by blocking the PD-1-mediated T-cell inhibition thus reinstating anticancer immune responses. Tremendous advances in plant biotechnology offer an alternative and economical strategy to produce therapeutic mAbs for immune-based therapies. In this study, recombinant anti-PD-1 Nivolumab was produced in Nicotiana benthamiana and the plant-produced anti-PD-1 mAb was exploited for cancer treatment in syngeneic mice model C57BL/6 mice that were used to test the antitumor efficacy of plant produced Nivolumab, along with commercial Opdivo®. C57BL/6 syngeneic mice treated with plant produced anti-PD-1 mAb exhibited reduction in the growth of established MC38 tumors. The plant produced Nivolumab treatment showed 82.9% antitumor effect in decreasing the tumor volume along with 50% tumor-free mice, whereas Opdivo® showed 90.26% reduction in volume without any tumor-free mice. Finally, plant-derived anti-PD-1 therapy was also well tolerated in tumor-bearing mice that correlated with no significant body weight changes. Overall, our plant-produced Nivolumab elicits significant inhibition of tumor growth in vivo and provides a proof-of-concept for the production of immunotherapy targeting PD-1.

Generation of multi-layered protein bodies in N. benthamiana for the encapsulation of vaccine antigens

The ability of plants to assemble particulate structures such as virus-like particles and protein storage organelles allows the direct bioencapsulation of recombinant proteins during the manufacturing process, which holds promise for the development of new drug delivery vehicles. Storage organelles found in plants such as protein bodies (PBs) have been successfully used as tools for accumulation and encapsulation of recombinant proteins. The fusion of sequences derived from 27-kDa-γ-zein, a major storage protein of maize, with a protein of interest leads to the incorporation of the chimeric protein into the stable and protected environment inside newly induced PBs. While this procedure has proven successful for several, but not all recombinant proteins, the aim of this study was to refine the technology by using a combination of PB-forming proteins, thereby generating multi-layered protein assemblies in N. benthamiana. We used fluorescent proteins to demonstrate that up to three proteinaceous components can be incorporated into different layers. In addition to 27-kDa-γ-zein, which is essential for PB initiation, 16-kDa-γ-zein was identified as a key element to promote the incorporation of a third zein-component into the core of the PBs. We show that a vaccine antigen could be incorporated into the matrix of multi-layered PBs, and the protein microparticles were characterized by confocal and electron microscopy as well as flow cytometry. In future, this approach will enable the generation of designer PBs that serve as drug carriers and integrate multiple components that can be functionalized in different ways.

Plant production of high affinity nanobodies that block SARS-CoV-2 spike protein binding with its receptor, human angiotensin converting enzyme

Nanobodies^® (V_HH antibodies), are small peptides that represent the antigen binding domain, V_HH of unique single domain antibodies (heavy chain only antibodies, HcAb) derived from camelids. Here, we demonstrate production of V_HH nanobodies against the SARS-CoV-2 spike proteins in the solanaceous plant Nicotiana benthamiana through transient expression and their subsequent detection verified through western blot. We demonstrate that these nanobodies competitively inhibit binding between the SARS-CoV-2 spike protein receptor binding domain and its human receptor protein, angiotensin converting enzyme 2. There has been significant interest and a number of publications on the use of plants as biofactories and even some reports of producing nanobodies in plants. Our data demonstrate that functional nanobodies blocking a process necessary to initiate SARS-CoV-2 infection into mammalian cells can be produced in plants. This opens the alternative of using plants in a scheme to rapidly respond to therapeutic needs for emerging pathogens in human medicine and agriculture.

Transcriptional deregulation of stress-growth balance in Nicotiana benthamiana biofactories producing insect sex pheromones

Plant biofactories are a promising platform for sustainable production of high-value compounds, among which are insect sex pheromones, a green alternative to conventional insecticides in agriculture. Recently, we have constructed transgenic Nicotiana benthamiana plants ("Sexy Plants", SxP) that successfully produce a blend of moth (Lepidoptera) sex pheromone compounds (Z)-11-hexadecen-1-ol and (Z)-11-hexadecenyl acetate. However, efficient biosynthesis of sex pheromones resulted in growth and developmental penalty, diminishing the potential for commercial use of SxP in biomanufacturing. To gain insight into the underlying molecular responses, we analysed the whole-genome transcriptome and evaluated it in relation to growth and pheromone production in low- and high-producing transgenic plants of v1.0 and v1.2 SxP lines. In our study, high-producing SxPv1.2 plants accumulated the highest amounts of pheromones but still maintained better growth compared to v1.0 high producers. For an in-depth biological interpretation of the transcriptomic data, we have prepared a comprehensive functional N. benthamiana genome annotation as well as gene translations to Arabidopsis thaliana, enabling functional information transfer by using Arabidopsis knowledge networks. Differential gene expression analysis, contrasting pheromone producers to wild-type plants, revealed that while only a few genes were differentially regulated in low-producing plants, high-producing plants exhibited vast transcriptional reprogramming. They showed signs of stress-like response, manifested as downregulation of photosynthesis-related genes and significant differences in expression of hormonal signalling and secondary metabolism-related genes, the latter presumably leading to previously reported volatilome changes. Further network analyses confirmed stress-like response with activation of jasmonic acid and downregulation of gibberellic acid signalling, illuminating the possibility that the observed growth penalty was not solely a consequence of a higher metabolic burden imposed upon constitutive expression of a heterologous biosynthetic pathway, but rather the result of signalling pathway perturbation. Our work presents an example of comprehensive transcriptomic analyses of disadvantageous stress signalling in N. benthamiana biofactory that could be applied to other bioproduction systems.

Statistical Designs to Improve Downstream Processing

The efficient extraction and purification of recombinant proteins from leaf and seed tissues is often a challenging task, involving multiple steps that must be optimized by identifying and accommodating complex parameter interactions. Conventional one-factor-at-a-time approaches fail to reveal these complex interactions and often result in sub-optimal processes with unnecessary costs. Here, we describe generic considerations to identify global optima for the extraction and purification of recombinant proteins from complex plant matrices. The corresponding experiments can help to streamline downstream processing by reducing the time, costs, and number of unit operations. The procedure involves the knowledge-based selection of factors for screening, the systematic design and analysis of experiments, and the iterative refinement of suitable conditions. The resulting descriptive models can be used to guide process scale-up and offer scientific justifications for process development decisions in negotiations with regulatory authorities.

Production of recombinant β-glucocerebrosidase in wild-type and glycoengineered transgenic Nicotiana benthamiana root cultures with different N-glycan profiles

Gaucher disease is an inherited lysosomal storage disorder caused by an insufficiency of active β-glucocerebrosidase (GCase). Exogenous recombinant GCase via enzyme replacement therapy is considered the most practical treatment for Gaucher disease. Mannose receptors mediate the efficient uptake of exogenous GCase into macrophages. Thus, terminal mannose residues on N-glycans are essential for the delivery of exogenous GCase. In this study, recombinant GCase was produced in root cultures of wild-type (WT) and glycoengineered transgenic Nicotiana benthamiana with downregulated N-acetylglucosaminyltransferase I expression. Root cultures of WT and glycoengineered transgenic N. benthamiana plants were successfully generated by the induction of plant hormones. Recombinant GCases produced in both root cultures possessed GCase enzyme activity. Purified GCases derived from both root cultures revealed different N-glycan profiles. The WT-derived GCase possessed the predominant plant-type N-glycans, which contain plant-specific sugars-linkages, specifically β1,2-xylose and α1,3-fucose residues. Notably, the mannosidic-type N-glycans with terminal mannose residues were abundant in the purified GCase derived from glycoengineered N. benthamiana root culture. This research provides a promising plant-based system for the production of recombinant GCase with terminal mannose residues on N-glycans.

Recent Progress in Rapid Determination of Mycotoxins Based on Emerging Biorecognition Molecules: A Review

Mycotoxins are secondary metabolites produced by fungal species, which pose significant risk to humans and livestock. The mycotoxins which are produced from Aspergillus, Penicillium, and Fusarium are considered most important and therefore regulated in food- and feedstuffs. Analyses are predominantly performed by official laboratory methods in centralized labs by expert technicians. There is an urgent demand for new low-cost, easy-to-use, and portable analytical devices for rapid on-site determination. Most significant advances were realized in the field bioanalytical techniques based on molecular recognition. This review aims to discuss recent progress in the generation of native biomolecules and new bioinspired materials towards mycotoxins for the development of reliable bioreceptor-based analytical methods. After brief presentation of basic knowledge regarding characteristics of most important mycotoxins, the generation, benefits, and limitations of present and emerging biorecognition molecules, such as polyclonal (pAb), monoclonal (mAb), recombinant antibodies (rAb), aptamers, short peptides, and molecularly imprinted polymers (MIPs), are discussed. Hereinafter, the use of binders in different areas of application, including sample preparation, microplate- and tube-based assays, lateral flow devices, and biosensors, is highlighted. Special focus, on a global scale, is placed on commercial availability of single receptor molecules, test-kits, and biosensor platforms using multiplexed bead-based suspension assays and planar biochip arrays. Future outlook is given with special emphasis on new challenges, such as increasing use of rAb based on synthetic and naïve antibody libraries to renounce animal immunization, multiple-analyte test-kits and high-throughput multiplexing, and determination of masked mycotoxins, including stereoisomeric degradation products.

Regulation of Molecular Farming Products

The regulation of molecular farming is a complex topic because plants and plant-based systems are relative newcomers among the many production platforms available for recombinant proteins. The regulations specific for different types of product (human/veterinary pharmaceuticals and medical devices, cosmetics, diagnostics, and research reagents) must therefore be overlaid with the regulations governing hitherto unfamiliar production platforms, and this must be achieved in different jurisdictions that handle genetically modified organisms (and genetically modified plants in particular) in very different ways. This chapter uses examples of different product types and production methods in three different jurisdictions (the USA, the EU, and Canada) to demonstrate some of the challenges facing the regulatory authorities.

Recombinant antibodies and their use for food immunoanalysis

Antibodies are widely employed as biorecognition elements for the detection of a plethora of compounds including food and environmental contaminants, biomarkers, or illicit drugs. They are also applied in therapeutics for the treatment of several disorders. Recent recommendations from the EU on animal protection and the replacement of animal-derived antibodies by non-animal-derived ones have raised a great controversy in the scientific community. The application of recombinant antibodies is expected to achieve a high growth rate in the years to come thanks to their versatility and beneficial characteristics in comparison to monoclonal and polyclonal antibodies, such as stability in harsh conditions, small size, relatively low production costs, and batch-to-batch reproducibility. This review describes the characteristics, advantages, and disadvantages of recombinant antibodies including antigen-binding fragments (Fab), single-chain fragment variable (scFv), and single-domain antibodies (VHH) and their application in food analysis with especial emphasis on the analysis of biotoxins, antibiotics, pesticides, and foodborne pathogens. Although the wide application of recombinant antibodies has been hampered by a number of challenges, this review demonstrates their potential for the sensitive, selective, and rapid detection of food contaminants.

Improving Recombinant Protein Recovery from Plant Tissue Using Heat Precipitation

Plants are increasingly viewed as suitable expression hosts for the production of recombinant proteins, especially when oxidative folding and/or posttranslational modification is essential for protein stability and functionality. In contrast to traditional platforms such as yeast and mammalian cells, where the product is secreted into the culture medium, recombinant proteins expressed in plants are usually retained within the cells so additional effort is required during extraction and purification. Various extraction processes are used to release soluble proteins from plant tissues, followed by clarification to remove fibers and particulates before the target protein is purified. Fermentation media generally contain few proteins, making it easier to recover a secreted product, whereas the green juice extracted from plants usually contains a large number of host proteins that interfere with target isolation and purification. In this chapter, we describe the use of heat precipitation to remove a large portion of the host cell proteins, thus improving the efficiency of subsequent purification steps and the quality of the purified recombinant protein.

An Improvised Hairy Root Transformation Method for Efficient Gene Silencing in Roots and Nodules of Arachis hypogaea

Peanut (Arachis hypogaea) is a major oilseed crop and is widely cultivated in tropical and subtropical climate zone worldwide. Peanut belongs to the Papilionoid family with an atypical nodule developmental program. In particular, rhizobia enter through developmental cracks and lead to the formation of aeschynomenoid subtype determinate nodules. Peanut nodules are efficient nitrogen-fixers and form swollen bacteroid containing symbiosomes. The allotetraploid genome and recalcitrance to stable transformation used to be the major bottleneck for peanut biologists. Recent genome sequencing of peanut cultivar Tifrunner has opened up a huge opportunity for molecular research. A composite plant contains transformed roots with a non-transformed shoot. The composite plant-based approach has already proven to be a tool of choice for high throughput studies in root biology. The available protocols failed to generate efficient hairy root transformation in the genome sequenced cultivar Tifrunner. Here we describe an efficient hairy root transformation and composite plant generation protocol for the peanut cultivar Tifrunner. Our protocol generated ~92% plant regeneration efficiency with between 21.8% and 58.6% co-transformed root regeneration. We also show that this protocol can be efficiently used for protein localization, promoter GUS analysis, monitoring hormone response, and RNAi mediated knockdown of the genes using genome sequenced cultivar Tifrunner.

Molecular Farming in Seed Crops: Gene Transfer into Barley (Hordeum vulgare ) and Wheat (Triticum aestivum )

The production of recombinant proteins in seed crops has a long history and cereal grains are now one of the platforms in commercial use. Specific advantages include excellent storage properties, a well-developed endomembrane system with a high biosynthetic capacity and well-established cultivation procedures worldwide. However, the production of transgenic cereals is a time-consuming procedure and the lack of efficient transformation systems is still a significant bottleneck. Barley can be transformed at high efficiency but the protocols are genotype-dependent. Wheat is generally more challenging to transform, but considerable progress has been made in enhancing transformation efficiencies and in controlling transgene expression. In this chapter, we describe and discuss standard procedures for generating transgenic barley and wheat for the production of recombinant proteins.

Integrating plant molecular farming and materials research for next-generation vaccines

Biologics - medications derived from a biological source - are increasingly used as pharmaceuticals, for example, as vaccines. Biologics are usually produced in bacterial, mammalian or insect cells. Alternatively, plant molecular farming, that is, the manufacture of biologics in plant cells, transgenic plants and algae, offers a cheaper and easily adaptable strategy for the production of biologics, in particular, in low-resource settings. In this Review, we discuss current vaccination challenges, such as cold chain requirements, and highlight how plant molecular farming in combination with advanced materials can be applied to address these challenges. The production of plant viruses and virus-based nanotechnologies in plants enables low-cost and regional fabrication of thermostable vaccines. We also highlight key new vaccine delivery technologies, including microneedle patches and material platforms for intranasal and oral delivery. Finally, we provide an outlook of future possibilities for plant molecular farming of next-generation vaccines and biologics.

Integrating plant molecular farming and materials research for next-generation vaccines

Biologics - medications derived from a biological source - are increasingly used as pharmaceuticals, for example, as vaccines. Biologics are usually produced in bacterial, mammalian or insect cells. Alternatively, plant molecular farming, that is, the manufacture of biologics in plant cells, transgenic plants and algae, offers a cheaper and easily adaptable strategy for the production of biologics, in particular, in low-resource settings. In this Review, we discuss current vaccination challenges, such as cold chain requirements, and highlight how plant molecular farming in combination with advanced materials can be applied to address these challenges. The production of plant viruses and virus-based nanotechnologies in plants enables low-cost and regional fabrication of thermostable vaccines. We also highlight key new vaccine delivery technologies, including microneedle patches and material platforms for intranasal and oral delivery. Finally, we provide an outlook of future possibilities for plant molecular farming of next-generation vaccines and biologics.

Plant-derived VLP: a worthy platform to produce vaccine against SARS-CoV-2

After its emergence in late 2019 SARS-CoV-2 was declared a pandemic by the World Health Organization on 11 March 2020 and has claimed more than 2.8 million lives. There has been a massive global effort to develop vaccines against SARS-CoV-2 and the rapid and low cost production of large quantities of vaccine is urgently needed to ensure adequate supply to both developed and developing countries. Virus-like particles (VLPs) are composed of viral antigens that self-assemble into structures that mimic the structure of native viruses but lack the viral genome. Thus they are not only a safer alternative to attenuated or inactivated vaccines but are also able to induce potent cellular and humoral immune responses and can be manufactured recombinantly in expression systems that do not require viral replication. VLPs have successfully been produced in bacteria, yeast, insect and mammalian cell cultures, each production platform with its own advantages and limitations. Plants offer a number of advantages in one production platform, including proper eukaryotic protein modification and assembly, increased safety, low cost, high scalability as well as rapid production speed, a critical factor needed to control outbreaks of potential pandemics. Plant-based VLP-based viral vaccines currently in clinical trials include, amongst others, Hepatitis B virus, Influenza virus and SARS-CoV-2 vaccines. Here we discuss the importance of plants as a next generation expression system for the fast, scalable and low cost production of VLP-based vaccines.

Oral Immunization With a Plant HSP90-SAG1 Fusion Protein Produced in Tobacco Elicits Strong Immune Responses and Reduces Cyst Number and Clinical Signs of Toxoplasmosis in Mice

Plant 90kDa heat shock protein (HSP90) is a potent adjuvant that increases both humoral and cellular immune responses to diverse proteins and peptides. In this study, we explored whether Arabidopsis thaliana HSP90 (AtHsp81.2) can improve the immune effects of a Toxoplasma gondii surface antigen 1 (SAG1). We designed two constructs containing the sequence of mature antigen (SAG1m), from aa77 to aa322, and B- and T-cell antigenic epitope-containing SAG1HC, from aa221 to aa319 fused to AtHsp81.2 sequence. When comparing the transient expression in Nicotiana tabacum X-27-8 leaves, which overexpress the suppressor helper component protease HC-Pro-tobacco etch virus (TEV), to that in N. benthamiana leaves, co-agroinfiltrated with the suppressor p19, optimal conditions included 6-week-old N. benthamiana plants, 7-day time to harvest, Agrobacterium tumefaciens cultures with an OD600nm of 0.6 for binary vectors and LED lights. While AtHsp81.2-SAG1m fusion protein was undetectable by Western blot in any of the evaluated conditions, AtHsp81.2-SAG1HC was expressed as intact fusion protein, yielding up to 90μg/g of fresh weight. Besides, the AtHsp81.2-SAG1HC mRNA was strongly expressed compared to the endogenous Nicotiana tabacum elongation factor-alpha (NtEFα) gene, whereas the AtHsp81.2-SAG1m mRNA was almost undetectable. Finally, mice were orally immunized with AtHsp81.2-SAG1HC-infiltrated fresh leaves (plAtHsp81.2-SAG1HC group), recombinant AtHsp81.2-SAG1HC purified from infiltrated leaves (rAtHsp81.2-SAG1HC group), non-infiltrated fresh leaves (control group), or phosphate-buffered saline (PBS group). Serum samples from plAtHsp81.2-SAG1HC-immunized mice had significantly higher levels of IgGt, IgG2a, and IgG2b anti-SAG1HC antibodies than serum from rAtHsp81.2-SAG1HC, control, and PBS groups. The number of cysts per brain in the plAtHsp81.2-SAG1HC-immunized mice was significantly reduced, and the parasite load in brain tissue was also lower in this group compared with the remaining groups. In an immunoblot assay, plant-expressed AtHsp81.2-SAG1HC was shown to react with antibodies present in sera from T. gondii-infected people. Therefore, the plant expression of a T. gondii antigen fused to the non-pathogenic adjuvant and carrier plant HSP90 as formulations against T. gondii can improve the vaccine efficacy, and plant extract can be directly used for vaccination without the need to purify the protein, making this platform a suitable and powerful biotechnological system for immunogenic antigen expression against toxoplasmosis.

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.

Development and Optimization of an Enzyme Immunoassay to Detect Serum Antibodies against the Hepatitis E Virus in Pigs, Using Plant-Derived ORF2 Recombinant Protein

Hepatitis E is an emerging global disease, mainly transmitted via the fecal-oral route in developing countries, and in a zoonotic manner in the developed world. Pigs and wild boar constitute the primary Hepatitis E virus (HEV) zoonotic reservoir. Consumption of undercooked animal meat or direct contact with infected animals is the most common source of HEV infection in European countries. The purpose of this study is to develop an enzyme immunoassay (EIA) for the detection of anti-hepatitis E virus IgG in pig serum, using plant-produced recombinant HEV-3 ORF2 as an antigenic coating protein, and also to evaluate the sensitivity and specificity of this assay. A recombinant HEV-3 ORF2 110-610_6his capsid protein, transiently expressed by pEff vector in Nicotiana benthamiana plants was used to develop an in-house HEV EIA. The plant-derived HEV-3 ORF2 110-610_6his protein proved to be antigenically similar to the HEV ORF2 capsid protein and it can self-assemble into heterogeneous particulate structures. The optimal conditions for the in-house EIA (iEIA) were determined as follows: HEV-3 ORF2 110-610_6his antigen concentration (4 µg/mL), serum dilution (1:50), 3% BSA as a blocking agent, and secondary antibody dilution (1:20 000). The iEIA developed for this study showed a sensitivity of 97.1% (95% Cl: 89.9-99.65) and a specificity of 98.6% (95% Cl: 92.5-99.96) with a Youden index of 0.9571. A comparison between our iEIA and a commercial assay (PrioCHECK™ Porcine HEV Ab ELISA Kit, ThermoFisher Scientific, MA, USA) showed 97.8% agreement with a kappa index of 0.9399. The plant-based HEV-3 ORF2 iEIA assay was able to detect anti-HEV IgG in pig serum with a very good agreement compared to the commercially available kit.

Enhanced Ability of Plant-Derived PGT121 Glycovariants To Eliminate HIV-1-Infected Cells

The activity of broadly neutralizing antibodies (bNAbs) targeting HIV-1 depends on pleiotropic functions, including viral neutralization and the elimination of HIV-1-infected cells. Several in vivo studies have suggested that passive administration of bNAbs represents a valuable strategy for the prevention or treatment of HIV-1. In addition, different strategies are currently being tested to scale up the production of bNAbs to obtain the large quantities of antibodies required for clinical trials. Production of antibodies in plants permits low-cost and large-scale production of valuable therapeutics; furthermore, pertinent to this work, it also includes an advanced glycoengineering platform. In this study, we used Nicotiana benthamiana to produce different Fc-glycovariants of a potent bNAb, PGT121, with near-homogeneous profiles and evaluated their antiviral activities. Structural analyses identified a close similarity in overall structure and glycosylation patterns of Fc regions for these plant-derived Abs and mammalian cell-derived Abs. When tested for Fc-effector activities, afucosylated PGT121 showed significantly enhanced FcγRIIIa interaction and antibody dependent cellular cytotoxicity (ADCC) against primary HIV-1-infected cells, both in vitro and ex vivo. However, the overall galactosylation profiles of plant PGT121 did not affect ADCC activities against infected primary CD4+ T cells. Our results suggest that the abrogation of the Fc N-linked glycan fucosylation of PGT121 is a worthwhile strategy to boost its Fc-effector functionality. IMPORTANCE PGT121 is a highly potent bNAb and its antiviral activities for HIV-1 prevention and therapy are currently being evaluated in clinical trials. The importance of its Fc-effector functions in clearing HIV-1-infected cells is also under investigation. Our results highlight enhanced Fc-effector activities of afucosylated PGT121 MAbs that could be important in a therapeutic context to accelerate infected cell clearance and slow disease progression. Future studies to evaluate the potential of plant-produced afucosylated PGT121 in controlling HIV-1 replication in vivo are warranted.

Production of functional human fetal hemoglobin in Nicotiana benthamiana for development of hemoglobin-based oxygen carriers

Hemoglobin-based oxygen carriers have long been pursued to meet clinical needs by using native hemoglobin (Hb) from human or animal blood, or recombinantly produced Hb, but the development has been impeded by safety and toxicity issues. Herewith we report the successful production of human fetal hemoglobin (HbF) in Nicotiana benthamiana through Agrobacterium tumefaciens-mediated transient expression. HbF is a heterotetrameric protein composed of two identical α- and two identical γ-subunits, held together by hydrophobic interactions, hydrogen bonds, and salt bridges. In our study, the α- and γ-subunits of HbF were fused in order to stabilize the α-subunits and facilitate balanced expression of α- and γ-subunits in N. benthamiana. Efficient extraction and purification methods enabled production of the recombinantly fused endotoxin-free HbF (rfHbF) in high quantity and quality. The transiently expressed rfHbF protein was identified by SDS-PAGE, Western blot and liquid chromatography-tandem mass spectrometry analyses. The purified rfHbF possessed structural and functional properties similar to native HbF, which were confirmed by biophysical, biochemical, and in vivo animal studies. The results demonstrate a high potential of plant expression systems in producing Hb products for use as blood substitutes.

Efficient gene targeting in Nicotiana tabacum using CRISPR/SaCas9 and temperature tolerant LbCas12a

Nicotiana tabacum is a non-food herb that has the potential to be utilized as bio-factory for generating medicines, vaccines or valuable small metabolites. To achieve these goals, the improvement of genetic tools for pre-designed genome modifications is indispensable. The development of CRISPR/Cas nucleases allows the induction of site-specific double-strand breaks to enhance homologous recombination-mediated gene targeting (GT). However, the efficiency of GT is still a challenging obstacle for many crops including tobacco. Recently, studies in several plant species indicated that by replacing SpCas9 with other CRISPR/Cas-based nucleases, GT efficiencies might be enhanced considerably. Therefore, we tested SaCas9 as well as a temperature-insensitive version of LbCas12a (ttLbCas12a) for targeting the tobacco SuRB gene. At the same time, we also optimized the protocol for Agrobacterium-mediated tobacco transformation and tissue culture. In this way, we could improve GT efficiencies to up to a third of the inoculated cotyledons when using ttLbCas12a, which outperformed SaCas9 considerably. In addition, we could show that the conversion tract length of the GT reaction can be up to 606 bp long and in the majority of cases, it is longer than 250 bp. We obtained multiple heritable GT events, mostly heterozygous, but also biallelic GT events and some without T-DNA integration. Thus, we were not only able to obtain CRISPR/Cas-based heritable GT events in allotetraploid Nicotiana tabacum for the first time, but our results also indicate that ttLbCas12a might be a superior alternative for gene editing and GT in tobacco as well as in other crops.

A Comprehensive Overview on the Production of Vaccines in Plant-Based Expression Systems and the Scope of Plant Biotechnology to Combat against SARS-CoV-2 Virus Pandemics

Many pathogenic viral pandemics have caused threats to global health; the COVID-19 pandemic is the latest. Its transmission is growing exponentially all around the globe, putting constraints on the health system worldwide. A novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), causes this pandemic. Many candidate vaccines are available at this time for COVID-19, and there is a massive international race underway to procure as many vaccines as possible for each country. However, due to heavy global demand, there are strains in global vaccine production. The use of a plant biotechnology-based expression system for vaccine production also represents one part of this international effort, which is to develop plant-based heterologous expression systems, virus-like particles (VLPs)-vaccines, antiviral drugs, and a rapid supply of antigen-antibodies for detecting kits and plant origin bioactive compounds that boost the immunity and provide tolerance to fight against the virus infection. This review will look at the plant biotechnology platform that can provide the best fight against this global pandemic.

Wolffia arrhiza as a promising producer of recombinant hirudin

The production of recombinant proteins in transgenic plants is becoming an increasingly serious alternative to classical biopharming methods as knowledge about this process grows. Wolffia arrhiza, an aquatic plant unique in its anatomy, is a promising expression system that can grow in submerged culture in bioreactors. In our study 8550 explants were subjected to Agrobacterium-mediated transformation, and 41 independent hygromycin-resistant Wolffia lines were obtained, with the transformation efficiency of 0.48%. 40 of them contained the hirudin-1 gene (codon-optimized for expression in plants) and were independent lines of nuclear-transformed Wolffia, the transgenic insertion has been confirmed by PCR and Southern blot analysis. We have analyzed the accumulation of the target protein and its expression has been proven in three transgenic lines. The maximum accumulation of recombinant hirudin was 0.02% of the total soluble protein, which corresponds to 775.5 ± 111.9 ng g^-1 of fresh weight of the plant. The results will be used in research on the development of an expression system based on Wolffia plants for the production of hirudin and other recombinant pharmaceutical proteins.

In situ vaccine application of inactivated CPMV nanoparticles for cancer immunotherapy

Cowpea mosaic virus (CPMV) is currently in the development pipeline for multiple biomedical applications, including cancer immunotherapy. In particular the application of CPMV as in situ vaccine has shown promise; here the plant viral nanoparticle is used as an adjuvant and is injected directly into a tumor to reverse immunosuppression and prime systemic anti-tumor immunity. Efficacy of this CPMV-based cancer immunotherapy has been demonstrated in multiple tumor mouse models and canine cancer patients. However, while CPMV is non-infectious to mammals, it is infectious to legumes and therefore, from a safety perspective, it is desired to develop non-infectious CPMV formulations. Non-infectious virus-like particles of CPMV devoid of nucleic acids have been produced; nevertheless, efficacy of such empty CPMV nanoparticles does not match efficacy of nucleic acid-laden CPMV. The multivalent capsid activates the innate immune system through pathogen pattern recognition receptors (PRRs) such as toll-like receptors (TLRs); the RNA cargo provides additional signaling through TLR-7/8, which boosts the efficacy of this adjuvant. Therefore, in this study, we set out to develop RNA-laden, but non-infectious CPMV. We report inactivation of CPMV using UV light and chemical inactivation using β-propiolactone (βPL) or formalin. 7.5 J cm^-2 UV, 50 mM βPL or 1 mM formalin was determined to be sufficient to inactivate CPMV and prevented plant infection. We compared the immunogenicity of native CPMV and inactivated CPMV formulations in vitro and in vivo using RAW-Blue™ reporter cells and a murine syngeneic, orthotropic melanoma model (using B16F10 cells and C57BL6 mice). While the in vitro assay indicated activation of the RAW-Blue™ reporter cells by formaldehyde and UV-inactivated CPMV at levels comparable to native CPMV; βPL-inactivated CPMV appeared to have diminished activity. Tumor mouse model experiments indicate potent efficacy of the chemically-inactivated CPMV (UV-treated CPMV was not tested) leading to tumor regression and increased survival; efficacy was somewhat reduced when compared to CPMV, however these samples outperformed the empty CPMV nanoparticles. These results will facilitate the translational development of safe and potent CPMV-based cancer immunotherapies.

Applications of nanobodies in plant science and biotechnology

Present review summarizes the current applications of nanobodies in plant science and biotechnology, including plant expression of nanobodies, plant biotechnological applications, nanobody-based immunodetection, and nanobody-mediated resistance against plant pathogens. Nanobodies (Nbs) are variable domains of heavy chain-only antibodies (HCAbs) isolated from camelids. In spite of their single domain structure, nanobodies display many unique features, such as small size, high stability, and cryptic epitopes accessibility, which make them ideal for sophisticated applications in plants and animals. In this review, we summarize the current applications of nanobodies in plant science and biotechnology, focusing on nanobody expression in plants, plant biotechnological applications, determination of plant toxins and pathogens, and nanobody-mediated resistance against plant pathogens. Prospects and challenges of nanobody applications in plants are also discussed.

Transient Production of Human β-Glucocerebrosidase With Mannosidic-Type N-Glycan Structure in Glycoengineered Nicotiana benthamiana Plants

Gaucher disease is an inherited lysosomal storage disorder caused by a deficiency of functional enzyme β-glucocerebrosidase (GCase). Recombinant GCase has been used in enzyme replacement therapy to treat Gaucher disease. Importantly, the terminal mannose N-glycan structure is essential for the uptake of recombinant GCase into macrophages via the mannose receptor. In this research, recombinant GCase was produced using Agrobacterium-mediated transient expression in both wild-type (WT) and N-acetylglucosaminyltransferase I (GnTI) downregulated Nicotiana benthamiana (ΔgntI) plants, the latter of which accumulates mannosidic-type N-glycan structures. The successfully produced functional GCase exhibited GCase enzyme activity. The enzyme activity was the same as that of the conventional mammalian-derived GCase. Notably, N-glycan analysis revealed that a mannosidic-type N-glycan structure lacking plant-specific N-glycans (β1,2-xylose and α1,3-fucose residues) was predominant in all glycosylation sites of purified GCase produced from ΔgntI plants. Our research provides a promising alternative plant line as a host for the production of recombinant GCase with a mannosidic-type N-glycan structure. This glycoengineered plant might be applicable to the production of other pharmaceutical proteins, especially mannose receptor targeted protein, for therapeutic uses.

Growth years and post-harvest processing methods have critical roles on the contents of medicinal active ingredients of Scutellaria baicalensis

Optimizing the processing technology is an effective way to improve the yield of active ingredients for the industrial production of medicinal crops. Baikal Skullcap (Scutellaria baicalensis Georgi) is a perennial herb in the Lamiaceae family and its dried root is used as a famous traditional Chinese medicine (TCM). Modern pharmacological studies have shown that the active ingredients of S. baicalensis have important pharmacological effects including anti-oxidation, anti-bacterial, anti-viral, anti-tumor, and anti-inflammation. Specifically, it is recently found that S. baicalensis has significant curative effects on the treatment of corona virus disease 2019 (COVID-19). In recent years, the market demand for the medicinal products of S. baicalensis is increasing because of its great medicinal values. However, the annual yield of active ingredients originated from the root of S. baicalensis is limited due to that little progress has been made on the traditional processing technology used in the extraction process. A pressing issue faced by both herbalists and scientists is how to improve the processing efficiency, thereby obtaining the maximum yield of products for S. baicalensis. In this study, a systematic analysis on the effects of growth years and post-harvest processing on the contents of medicinal active ingredients of S. baicalensis was conducted. The contents of eight active ingredients (baicalin, wogonoside, baicalein, wogonin, scutellarin, scutellarein, apigenin, and chrysin) in roots of S. baicalensis of different growth years (ranging from 1 year to 15 years) were estimated using high performance liquid chromatography (HPLC) and further analyzed to determine the optimal harvest period. In particular, the contents of six active ingredients in different parts (cortex and stele) of the root of S. baicalensis were estimated and compared. Meanwhile, the dynamic changes of the contents of active ingredients in fresh-crush and fresh-cut roots of S. baicalensis at room temperature were compared and analyzed to reveal the influence of post-harvest treatment on the contents of active ingredients. In addition, the effects of six different post-harvest treatments on the contents of active ingredients were systematically designed and compared to determine the best primary processing technology. The results showed that the best harvesting period for S. baicalensis should be determined as 2-3 years based on comprehensive evaluation of active ingredient content, annual yield increment, and land use efficiency. The contents of active ingredients including baicalin, wogonoside, baicalein, and wogonin in cortex were significantly higher than those in stele (P ≤  0.05). The contents of baicalin, wogonoside, and scutellarin in fresh roots of S. baicalensis significantly reduced as the storage time increased, but the reduction of fresh-cutting was significantly lower than that of fresh-crushing. For the effects of different processing treatments, the contents of four main active ingredients (baicalin, wogonoside, baicalein, and wogonin) under drying (D) and cutting-drying (C-D) treatments were significantly higher than those of the other four treatments (P ≤  0.05). Collectively, the above results will not only provide novel processing methods that will improve the yield of active ingredients for S. baicalensis, but also shed light on the optimization of processing technology for the industrial production of medicinal crops.

Co-expression of human calreticulin significantly improves the production of HIV gp140 and other viral glycoproteins in plants

Plant molecular farming (PMF) is rapidly gaining traction as a viable alternative to the currently accepted paradigm of producing biologics. While the platform is potentially cheaper and more scalable than conventional manufacturing systems, expression yields and appropriate post-translational modifications along the plant secretory pathway remain a challenge for certain proteins. Viral fusion glycoproteins in particular are often expressed at low yields in plants and, in some cases, may not be appropriately processed. Recently, however, transiently or stably engineering the host plant has shown promise as a strategy for producing heterologous proteins with more complex maturation requirements. In this study we investigated the co-expression of a suite of human chaperones to improve the production of a human immunodeficiency virus (HIV) type 1 soluble gp140 vaccine candidate in Nicotiana benthamiana plants. The co-expression of calreticulin (CRT) resulted in a dramatic increase in Env expression and ameliorated the endoplasmic reticulum (ER) stress response - as evidenced by lower transcript abundance of representative stress-responsive genes. The co-expression of CRT similarly improved accumulation of glycoproteins from Epstein-Barr virus (EBV), Rift Valley fever virus (RVFV) and chikungunya virus (CHIKV), suggesting that the endogenous chaperone machinery may impose a bottleneck for their production. We subsequently successfully combined the co-expression of human CRT with the transient expression of human furin, to enable the production of an appropriately cleaved HIV gp140 antigen. These transient plant host engineering strategies are a promising approach for the production of high yields of appropriately processed and cleaved viral glycoproteins.

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.

RAP Tag and PMab-2 Antibody: A Tagging System for Detecting and Purifying Proteins in Plant Cells

An affinity tag system requires both high affinity and specificity. The RAP tag epitope DMVNPGLEDRIE, derived from rat podoplanin (PDPN), is specifically recognized by PMab-2 monoclonal antibodies in rats. Here, we demonstrated that high levels of PMab-2 can be produced in Nicotiana benthamiana and plant-derived PMab-2 possesses similar activity to CHO-derived PMab-2, and the RAP tag presents a useful tagging system for detecting and purifying proteins from plant cells. The heavy chain of PMab-2 fused with KDEL, an endoplasmic reticulum retention sequence, and the light chain of the antibody were introduced into N. benthamiana by agroinfiltration. The expression of PMab-2 peaked 4 days after agroinfiltration, and approximately 0.3 mg/g fresh weight of the antibody was accumulated. After purification, the plant-derived PMab-2 successfully recognized rat PDPN expressed in CHO-K1 cells and exhibited almost the same binding activity as CHO-derived PMab-2. The RAP-tagged proteins expressed in plant cells were specifically recognized by PMab-2. These results indicate that PMab-2 can accumulate at high levels in N. benthamiana and is easily purified and that the RAP tagging system presents a useful tool for detecting and purifying proteins of interest in plant cells.