Plant Molecular Farming: Opportunities and Challenges

Contribution of the ELRs to the development of advanced in vitro models

Developing in vitro models that accurately mimic the microenvironment of biological structures or processes holds substantial promise for gaining insights into specific biological functions. In the field of tissue engineering and regenerative medicine, in vitro models able to capture the precise structural, topographical, and functional complexity of living tissues, prove to be valuable tools for comprehending disease mechanisms, assessing drug responses, and serving as alternatives or complements to animal testing. The choice of the right biomaterial and fabrication technique for the development of these in vitro models plays an important role in their functionality. In this sense, elastin-like recombinamers (ELRs) have emerged as an important tool for the fabrication of in vitro models overcoming the challenges encountered in natural and synthetic materials due to their intrinsic properties, such as phase transition behavior, tunable biological properties, viscoelasticity, and easy processability. In this review article, we will delve into the use of ELRs for molecular models of intrinsically disordered proteins (IDPs), as well as for the development of in vitro 3D models for regenerative medicine. The easy processability of the ELRs and their rational design has allowed their use for the development of spheroids and organoids, or bioinks for 3D bioprinting. Thus, incorporating ELRs into the toolkit of biomaterials used for the fabrication of in vitro models, represents a transformative step forward in improving the accuracy, efficiency, and functionality of these models, and opening up a wide range of possibilities in combination with advanced biofabrication techniques that remains to be explored.

Molecular Farming of Pembrolizumab and Nivolumab

Immune checkpoint inhibitors (ICIs) are a class of immunotherapy agents capable of alleviating the immunosuppressive effects exerted by tumorigenic cells. The programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint is one of the most ubiquitous checkpoints utilized by tumorigenic cells for immune evasion by inducing apoptosis and inhibiting the proliferation and cytokine production of T lymphocytes. Currently, the most frequently used ICIs targeting the PD-1/PD-L1 checkpoint include monoclonal antibodies (mAbs) pembrolizumab and nivolumab that bind to PD-1 on T lymphocytes and inhibit interaction with PD-L1 on tumorigenic cells. However, pembrolizumab and nivolumab are costly, and thus their accessibility is limited in low- and middle-income countries (LMICs). Therefore, it is essential to develop novel biomanufacturing platforms capable of reducing the cost of these two therapies. Molecular farming is one such platform utilizing plants for mAb production, and it has been demonstrated to be a rapid, low-cost, and scalable platform that can be potentially implemented in LMICs to diminish the exorbitant prices, ultimately leading to a significant reduction in cancer-related mortalities within these countries.

Plant-derived natural products for drug discovery: current approaches and prospects

Nature has abundant source of drugs that need to be identified/purified for use as essential biologics, either individually or in combination in the modern medical field. These drugs are divided into small bio-molecules, plant-made biologics, and a recently introduced third category known as phytopharmaceutical drugs. The development of phytopharmaceutical medicines is based on the ethnopharmacological approach, which relies on the traditional medicine system. The concept of ‘one-disease one-target drug’ is becoming less popular, and the use of plant extracts, fractions, and molecules is the new paradigm that holds promising scope to formulate appropriate drugs. This led to discovering a new concept known as polypharmacology, where natural products from varying sources can engage with multiple human physiology targets. This article summarizes different approaches for phytopharmaceutical drug development and discusses the progress in systems biology and computational tools for identifying drug targets. We review the existing drug delivery methods to facilitate the efficient delivery of drugs to the targets. In addition, we describe different analytical techniques for the authentication and fingerprinting of plant materials. Finally, we highlight the role of biopharming in developing plant-based biologics.

Elastin-like Polypeptides in Development of Nanomaterials for Application in the Medical Field

Elastin-like polypeptides (ELPs) are biopolymers formed by amino acid sequences derived from tropoelastin. These biomolecules can be soluble below critical temperatures, forming aggregates at higher temperatures, which makes them an interesting source for the design of different nanobiomaterials. These nanobiomaterials can be obtained from heterologous expression in several organisms such as bacteria, fungi, and plants. Thanks to the many advantages of ELPs, they have been used in the biomedical field to develop nanoparticles, nanofibers, and nanocomposites. These nanostructures can be used in multiple applications such as drug delivery systems, treatments of type 2 diabetes, cardiovascular diseases, tissue repair, and cancer therapy. Thus, this review aims to shed some light on the main advances in elastin-like-based nanomaterials, their possible expression forms, and importance to the medical field.

Plant-Produced Receptor-Binding Domain of SARS-CoV-2 Elicits Potent Neutralizing Responses in Mice and Non-human Primates

The emergence of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has affected global public health and economy. Despite the substantial efforts, only few vaccines are currently approved and some are in the different stages of clinical trials. As the disease rapidly spreads, an affordable and effective vaccine is urgently needed. In this study, we investigated the immunogenicity of plant-produced receptor-binding domain (RBD) of SARS-CoV-2 in order to use as a subunit vaccine. In this regard, RBD of SARS-CoV-2 was fused with Fc fragment of human IgG1 and transiently expressed in Nicotiana benthamiana by agroinfiltration. The plant-produced RBD-Fc fusion protein was purified from the crude extract by using protein A affinity column chromatography. Two intramuscular administration of plant-produced RBD-Fc protein formulated with alum as an adjuvant have elicited high neutralization titers in immunized mice and cynomolgus monkeys. Further it has induced a mixed Th1/Th2 immune responses and vaccine-specific T-lymphocyte responses which was confirmed by interferon-gamma (IFN-γ) enzyme-linked immunospot assay. Altogether, our results demonstrated that the plant-produced SARS-CoV-2 RBD has the potential to be used as an effective vaccine candidate against SARS-CoV-2. To our knowledge, this is the first report demonstrating the immunogenicity of plant-produced SARS-CoV-2 RBD protein in mice and non-human primates.

Development of Plant-Produced Recombinant ACE2-Fc Fusion Protein as a Potential Therapeutic Agent Against SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease (COVID-19) which has recently emerged as a potential threat to global public health. SARS-CoV-2 is the third known human coronavirus that has huge impact on the human population after SARS-CoV and MERS-CoV. Although some vaccines and therapeutic drugs are currently in clinical trials, none of them are approved for commercial use yet. As with SARS-CoV, SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) as the cell entry receptor to enter into the host cell. In this study, we have transiently produced human ACE2 fused with the Fc region of human IgG1 in Nicotiana benthamiana and the in vitro neutralization efficacy of the plant-produced ACE2-Fc fusion protein was assessed. The recombinant ACE2-Fc fusion protein was expressed in N. benthamiana at 100 μg/g leaf fresh weight on day 6 post-infiltration. The recombinant fusion protein showed potent binding to receptor binding domain (RBD) of SARS-CoV-2. Importantly, the plant-produced fusion protein exhibited potent anti-SARS-CoV-2 activity in vitro. Treatment with ACE2-Fc fusion protein after viral infection dramatically inhibit SARS-CoV-2 infectivity in Vero cells with an IC50 value of 0.84 μg/ml. Moreover, treatment with ACE2-Fc fusion protein at the pre-entry stage suppressed SARS-CoV-2 infection with an IC50 of 94.66 μg/ml. These findings put a spotlight on the plant-produced ACE2-Fc fusion protein as a potential therapeutic candidate against SARS-CoV-2.

Unprecedented enhancement of recombinant protein production in sugarcane culms using a combinatorial promoter stacking system

Plants represent a safe and cost-effective platform for producing high-value proteins with pharmaceutical properties; however, the ability to accumulate these in commercially viable quantities is challenging. Ideal crops to serve as biofactories would include low-input, fast-growing, high-biomass species such as sugarcane. The objective of this study was to develop an efficient expression system to enable large-scale production of high-value recombinant proteins in sugarcane culms. Bovine lysozyme (BvLz) is a potent broad-spectrum antimicrobial enzyme used in the food, cosmetics and agricultural industries. Here, we report a novel strategy to achieve high-level expression of recombinant proteins using a combinatorial stacked promoter system. We demonstrate this by co-expressing BvLz under the control of multiple constitutive and culm-regulated promoters on separate expression vectors and combinatorial plant transformation. BvLz accumulation reached 1.4% of total soluble protein (TSP) (10.0 mg BvLz/kg culm mass) in stacked multiple promoter:BvLz lines, compared to 0.07% of TSP (0.56 mg/kg) in single promoter:BvLz lines. BvLz accumulation was further boosted to 11.5% of TSP (82.5 mg/kg) through event stacking by re-transforming the stacked promoter:BvLz lines with additional BvLz expression vectors. The protein accumulation achieved with the combinatorial promoter stacking expression system was stable in multiple vegetative propagations, demonstrating the feasibility of using sugarcane as a biofactory for producing high-value proteins and bioproducts.

Plastid Transformation: How Does it Work? Can it Be Applied to Crops? What Can it Offer?

In recent years, plant genetic engineering has advanced agriculture in terms of crop improvement, stress and disease resistance, and pharmaceutical biosynthesis. Cells from land plants and algae contain three organelles that harbor DNA: the nucleus, plastid, and mitochondria. Although the most common approach for many plant species is the introduction of foreign DNA into the nucleus (nuclear transformation) via Agrobacterium- or biolistics-mediated delivery of transgenes, plastid transformation offers an alternative means for plant transformation. Since there are many copies of the chloroplast genome in each cell, higher levels of protein accumulation can often be achieved from transgenes inserted in the chloroplast genome compared to the nuclear genome. Chloroplasts are therefore becoming attractive hosts for the introduction of new agronomic traits, as well as for the biosynthesis of high-value pharmaceuticals, biomaterials and industrial enzymes. This review provides a comprehensive historical and biological perspective on plastid transformation, with a focus on current and emerging approaches such as the use of single-walled carbon nanotubes (SWNTs) as DNA delivery vehicles, overexpressing morphogenic regulators to enhance regeneration ability, applying genome editing techniques to accelerate double-stranded break formation, and reconsidering protoplasts as a viable material for plastid genome engineering, even in transformation-recalcitrant species.

Strategies for recombinant production of antimicrobial peptides with pharmacological potential

INTRODUCTION

The need to develop new drugs for the control of pathogenic microorganisms has redoubled efforts to prospect for antimicrobial peptides (AMPs) from natural sources and to characterize its structure and function. These molecules present a broad spectrum of action against different microorganisms and frequently present promiscuous action, with anticancer and immunomodulatory activities. Furthermore, AMPs can be used as biopharmaceuticals in the treatment of hospital-acquired infections and other serious diseases with relevant social and economic impacts.Areas covered: The low yield and the therefore difficult extraction and purification process in AMPs are problems that limit their industrial application and scientific research. Thus, optimized heterologous expression systems were developed to significantly boost AMP yields, allow high efficiency in purification and structural optimization for the increase of therapeutic activity.Expert opinion: This review provides an update on recent developments in the recombinant production of ribosomal and non-ribosomal synthesis of AMPs and on strategies to increase the expression of genes encoding AMPs at the transcriptional and translational levels and regulation of the post-translational modifications. Moreover, there are detailed reports of AMPs that have already reached marketable status or are in the pipeline under advanced stages of preclinical testing.

Seeds as Economical Production Platform for Recombinant Proteins

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The cost-effective production of high-quality and biologically active recombinant molecules especially proteins is extremely desirable. Seed-based recombinant protein production platforms are considered as superior choice owing to lack of human/animal pathogenic organisms, lack of cold chain requirements for transportation and long-term storage, easy scalability and development of edible biopharmaceuticals in plants with objective to be used in purified or partially processed form is desirable. This review article summarizes the exceptional features of seed-based biopharming and highlights the needs of exploiting it for commercial purposes. Plant seeds offer a perfect production platform for high-value molecules of industrial as well as therapeutic nature owing to lower water contents, high protein storage capacity, weak protease activity and long-term storage ability at ambient temperature. Exploiting extraordinarily high protein accumulation potential, vaccine antigens, antibodies and other therapeutic proteins can be stored without effecting their stability and functionality up to years in seeds. Moreover, ability of direct oral consumption and post-harvest stabilizing effect of seeds offer unique feature of oral delivery of pharmaceutical proteins and vaccine antigens for immunization and disease treatment through mucosal as well as oral route.

Advances in renewable plant-derived protein source: The structure, physicochemical properties affected by ultrasonication

In recent years, there has been increasing interest in renewable and sustainable protein resource of plant origin. The reasons for this are summarized as follows: (1) green, low-cost, environmental friendly and sustainable concepts are deeply rooted in people's minds; (2) long-term use of animal protein can lead to high blood pressure, obesity, negative environmental impacts; (3) more and more vegetarians are emerged; (4) many consumers still do not accept food grade insect. Based on this situation, this paper links eco-innovative ultrasound technology to plant-derived sustainable proteins resource, and magnifies the advantages of both at the same time. Ultrasound is a novel, green and rapid developing environmental friendly technology, which is suitable for up scaling and improving the physicochemical properties of protein. This review summarizes the mechanisms, cavitation properties of ultrasonic field, consumption of energy, applications of spectroscopic techniques for evaluating plant-derived proteins conformation changes, effects of ultrasound on the structure and physicochemical properties of plant-derived renewable proteins, and application of ultrasound treatment proteins in food industry. Furthermore, future research to better utilize this green technology is suggested. In this way, it not only conforms to the concept of sustainable, high-efficiency, and environmental protection of the food protein industry, but also clarifies the relationship between protein structure and properties, which are conducive to the application of ultrasound in protein industrialization.

Comparison of the N-glycosylation on recombinant miraculin expressed in tomato plants with native miraculin

Miraculin is a promising protein with taste-modifying properties. Focusing on the unique function and potential of miraculin, recombinant miraculin production has been explored with the use of heterologous expression systems, but the activities of recombinant miraculins were much lower than those of native miraculin, probably due to the difference in post-translational modification, especially N-glycosylation. For practical use therefore, the differences between N-glycan of recombinant miraculin compared to that of native miraculin should be minimized. Here, to establish the platform for functional miraculin production, we expressed miraculin in tomato plants with the same taste-modifying activity as native miraculin purified from miracle fruit, and we compared the N-glycan structures with those of native miraculin. Our N-glycan structural analysis using purified miraculin, followed by hydrazynolysis, 2-pyridylamine (PA)-labeling, high-performance liquid chromatography, and a liquid chromatography tandem-mass spectrometry analysis revealed that both the native and recombinant miraculins carried an M3 structure as a predominant structure and that most of the N-glycan structures on the miraculins were pauci-mannosidic structures with a smaller amount of plant-specific α1,3-fucosylated and/or β1,2-xylosylated N-glycans and without a Lewis a epitope. These results indicate that the N-glycoform of native miraculin from miracle fruit and recombinant miraculin expressed in tomato plants are almost identical to each other with similar ratios and that, therefore, plant-specific N-glycans are essential for showing the full taste-modifying activity of miraculin.

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.

Purification and immunogenicity of hemagglutinin from highly pathogenic avian influenza virus H5N1 expressed in Nicotiana benthamiana

Highly pathogenic avian influenza (HPAI) H5N1 is an ongoing global health concern due to its severe sporadic outbreaks in Asia, Africa and Europe, which poses a potential pandemic threat. The development of safe and cost-effective vaccine candidates for HPAI is considered the best strategy for managing the disease and addressing the pandemic preparedness. The most potential vaccine candidate is the antigenic determinant of influenza A virus, hemagglutinin (HA). The present research was aimed at developing optimized expression in Nicotiana benthamiana and protein purification process for HA from the Malaysian isolate of H5N1 as a vaccine antigen for HPAI H5N1. Expression of HA from the Malaysian isolate of HPAI in N. benthamiana was confirmed, and more soluble protein was expressed as truncated HA, the HA1 domain over the entire ectodomain of HA. Two different purification processes were evaluated for efficiency in terms of purity and yield. Due to the reduced yield, protein degradation and length of the 3-column purification process, the 2-column method was chosen for target purification. Purified HA1 was found immunogenic in mice inducing H5 HA-specific IgG and a hemagglutination inhibition antibody. This paper offers an alternative production system of a vaccine candidate against a locally circulating HPAI, which has a regional significance.

Accounting for host cell protein behavior in anion-exchange chromatography

Host cell proteins (HCP) are a problematic set of impurities in downstream processing (DSP) as they behave most similarly to the target protein during separation. Approaching DSP with the knowledge of HCP separation behavior would be beneficial for the production of high purity recombinant biologics. Therefore, this work was aimed at characterizing the separation behavior of complex mixtures of HCP during a commonly used method: anion-exchange chromatography (AEX). An additional goal was to evaluate the performance of a statistical methodology, based on the characterization data, as a tool for predicting protein separation behavior. Aqueous two-phase partitioning followed by two-dimensional electrophoresis provided data on the three physicochemical properties most commonly exploited during DSP for each HCP: pI (isoelectric point), molecular weight, and surface hydrophobicity. The protein separation behaviors of two alternative expression host extracts (corn germ and E. coli) were characterized. A multivariate random forest (MVRF) statistical methodology was then applied to the database of characterized proteins creating a tool for predicting the AEX behavior of a mixture of proteins. The accuracy of the MVRF method was determined by calculating a root mean squared error value for each database. This measure never exceeded a value of 0.045 (fraction of protein populating each of the multiple separation fractions) for AEX. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1453-1463, 2016.

The Potential for Microalgae as Bioreactors to Produce Pharmaceuticals

As photosynthetic organisms, microalgae can efficiently convert solar energy into biomass. Microalgae are currently used as an important source of valuable natural biologically active molecules, such as carotenoids, chlorophyll, long-chain polyunsaturated fatty acids, phycobiliproteins, carotenoids and enzymes. Significant advances have been achieved in microalgae biotechnology over the last decade, and the use of microalgae as bioreactors for expressing recombinant proteins is receiving increased interest. Compared with the bioreactor systems that are currently in use, microalgae may be an attractive alternative for the production of pharmaceuticals, recombinant proteins and other valuable products. Products synthesized via the genetic engineering of microalgae include vaccines, antibodies, enzymes, blood-clotting factors, immune regulators, growth factors, hormones, and other valuable products, such as the anticancer agent Taxol. In this paper, we briefly compare the currently used bioreactor systems, summarize the progress in genetic engineering of microalgae, and discuss the potential for microalgae as bioreactors to produce pharmaceuticals.

Oral Delivery of Protein Drugs Bioencapsulated in Plant Cells

Plants cells are now approved by the FDA for cost-effective production of protein drugs (PDs) in large-scale current Good Manufacturing Practice (cGMP) hydroponic growth facilities. In lyophilized plant cells, PDs are stable at ambient temperature for several years, maintaining their folding and efficacy. Upon oral delivery, PDs bioencapsulated in plant cells are protected in the stomach from acids and enzymes but are subsequently released into the gut lumen by microbes that digest the plant cell wall. The large mucosal area of the human intestine offers an ideal system for oral drug delivery. When tags (receptor-binding proteins or cell-penetrating peptides) are fused to PDs, they efficiently cross the intestinal epithelium and are delivered to the circulatory or immune system. Unique tags to deliver PDs to human immune or nonimmune cells have been developed recently. After crossing the epithelium, ubiquitous proteases cleave off tags at engineered sites. PDs are also delivered to the brain or retina by crossing the blood–brain or retinal barriers. This review highlights recent advances in PD delivery to treat Alzheimer's disease, diabetes, hypertension, Gaucher's or ocular diseases, as well as the development of affordable drugs by eliminating prohibitively expensive purification, cold chain and sterile delivery.

Antibody Production in Plants and Green Algae

Monoclonal antibodies (mAbs) have a wide range of modern applications, including research, diagnostic, therapeutic, and industrial uses. Market demand for mAbs is high and continues to grow. Although mammalian systems, which currently dominate the biomanufacturing industry, produce effective and safe recombinant mAbs, they have a limited manufacturing capacity and high costs. Bacteria, yeast, and insect cell systems are highly scalable and cost effective but vary in their ability to produce appropriate posttranslationally modified mAbs. Plants and green algae are emerging as promising production platforms because of their time and cost efficiencies, scalability, lack of mammalian pathogens, and eukaryotic posttranslational protein modification machinery. So far, plant- and algae-derived mAbs have been produced predominantly as candidate therapeutics for infectious diseases and cancer. These candidates have been extensively evaluated in animal models, and some have shown efficacy in clinical trials. Here, we review ongoing efforts to advance the production of mAbs in plants and algae.

Plant Cell-Based Recombinant Antibody Manufacturing with a 200 L Orbitally Shaken Disposable Bioreactor

Tobacco BY-2 cells are an attractive platform for the manufacture of a variety of biopharmaceutical proteins, including antibodies. Here, we describe the scaled-up cultivation of human IgG-secreting BY-2 cells in a 200 L orbitally shaken disposable bioreactor, resulting in cell growth and recombinant protein yields that are proportionately comparable with those obtained from cultivations in 500 mL shake flasks. Furthermore, we present an efficient downstream process for antibody recovery from the viscous spent culture medium using expanded bed adsorption (EBA) chromatography.

Plant-produced candidate countermeasures against emerging and reemerging infections and bioterror agents

Despite progress in the prevention and treatment of infectious diseases, they continue to present a major threat to public health. The frequency of emerging and reemerging infections and the risk of bioterrorism warrant significant efforts towards the development of prophylactic and therapeutic countermeasures. Vaccines are the mainstay of infectious disease prophylaxis. Traditional vaccines, however, are failing to satisfy the global demand because of limited scalability of production systems, long production timelines and product safety concerns. Subunit vaccines are a highly promising alternative to traditional vaccines. Subunit vaccines, as well as monoclonal antibodies and other therapeutic proteins, can be produced in heterologous expression systems based on bacteria, yeast, insect cells or mammalian cells, in shorter times and at higher quantities, and are efficacious and safe. However, current recombinant systems have certain limitations associated with production capacity and cost. Plants are emerging as a promising platform for recombinant protein production due to time and cost efficiency, scalability, lack of harboured mammalian pathogens and possession of the machinery for eukaryotic post-translational protein modification. So far, a variety of subunit vaccines, monoclonal antibodies and therapeutic proteins (antivirals) have been produced in plants as candidate countermeasures against emerging, reemerging and bioterrorism-related infections. Many of these have been extensively evaluated in animal models and some have shown safety and immunogenicity in clinical trials. Here, we overview ongoing efforts to producing such plant-based countermeasures.

Stable mitotic inheritance of rice minichromosomes in cell suspension cultures

Suspension cell cultures of rice minichromosomes were established. The minichromosomes in suspension cultured cells were mitotically stable and had active gene expression, thus have the potential to be used as gene expression vectors to produce valuable bioactive products. The plant artificial chromosome (PAC) is a novel vector for plant genetic engineering to produce genetically modified crops with multiple transgenes, or to produce valuable bioactive products through the expression of multiple genes or biochemical pathways as a bioreactor. PAC is mainly constructed by engineered minichromosomes through telomere-mediated chromosome truncations. We have constructed rice minichromosomes in a previous study. Thus, the understanding of rice minichromosome inheritance under different culture conditions has potential importance for their utility in future studies and applications. In this study, we performed suspension cultures of three rice minichromosome-containing cell lines, 1004-111, 1008-100 and 1004-011. Two cell lines, 1004-111 and 1008-100, showed typical S growth pattern consisting of a lag phase, an active growing exponential phase and a stationary phase, whereas cell line 1004-011 grew very slowly and eventually died. Both 1004-111 and 1008-100 minichromosomes were stably transmitted in cell suspension cultures without any abnormality. Foreign gene expression was verified from 1004-111 and 1008-100 minichromosomes in suspension cultures. The stable mitotic inheritance of minichromosomes and gene expression from them indicated that rice minichromosomes could be maintained and propagated in cell suspension cultures. This study tested key parameters for suspension cultures of rice cell lines with minichromosomes, and proved in concept the potential for industrial use of PAC vectors as bioreactors.

Recent advances on host plants and expression cassettes' structure and function in plant molecular pharming

Plant molecular pharming is a promising system to produce important recombinant proteins such as therapeutic antibodies, pharmaceuticals, enzymes, growth factors, and vaccines. The system provides an interesting alternative method to the direct extraction of proteins from inappropriate source material while offering the possibility to overcome problems related to product safety and source availability. Multiple factors including plant hosts, genes of interest, expression vector cassettes, and extraction and purification techniques play important roles in the plant molecular pharming. Plant species, as a biosynthesis platform, are a crucial factor in achieving high yields of recombinant protein in plant. The choice of recombinant gene and its expression strategy is also of great importance in ensuring a high amount of the recombinant proteins. Many studies have been conducted to improve expression, accumulation, and purification of the recombinant protein from molecular pharming systems. Re-engineered vectors and expression cassettes are also pivotal tools in enhancing gene expression at the transcription and translation level, and increasing protein accumulation, stability, retention and targeting of specific organelles. In this review, we report recent advances and strategies of plant molecular pharming while focusing on the choice of plant hosts and the role of some molecular pharming elements and approaches: promoters, codon optimization, signal sequences, and peptides used for upstream design, purification and downstream processing.

Improvement in the stability and functionality of Nicotiana tabacum produced recombinant TRAIL through employment of endoplasmic reticulum expression and ascorbate buffer mediated extraction strategies

Introduction: In order to employ Nicotiana tabacum cells as a profitable natural bioreactor for production of bio-functional "Soluble human TRAIL" (ShTRAIL), endoplasmic reticulum (ER) targeted expression and innovative extraction procedures were exploited.

Methods: At first, the ShTRAIL encoding gene was sub-cloned into designed H2 helper vector to equip it with potent TMV omega leader sequences, ER sorting signal peptide, poly-histidine tag and ER retention signal peptide (KDEL). Then, the ER targeted ShTRAIL cassette was sequentially sub-cloned into "CaMV-35S" helper and "pGreen-0179" final expression vectors. Afterward, Agrobacterium mediated transformation method was adopted to express the ShTRAIL in the ER of N. tabacum . Next, the ShTRAIL protein was extracted through both phosphate and innovative ascorbate extraction buffers. Subsequently, oligomerization state of the ShTRAIL was evaluated through cross-linking assay and western blot analysis. Then, semi-quantitative western blot analysis was performed to estimate the ShTRAIL production. Finally, biological activity of the ShTRAIL was evaluated through MTT assay.

Results: The phosphate buffer extracted ShTRAIL was produced in dimmer form, whereas the ShTRAIL extracted with ascorbate buffer generated trimer form. The ER targeted ShTRAIL strategy increased the ShTRAIL’s production level up to about 20 μg/g of fresh weight of N. tabacum . MTT assay indicated that ascorbate buffer extracted ShTRAIL could prohibit proliferation of A549 cell line.

Conclusion: Endoplasmic reticulum expression and reductive ascorbate buffer extraction procedure can be employed to enhance the stability and overall production level of bio-functional recombinant ShTRAIL from transgenic N. tabacum cells.

Cloning, Transformation and Expression of Proinsulin Gene in Tomato (Lycopersicum esculentum Mill.)

BACKGROUND

Plants are among promising and suitable platform systems for production of recombinant biopharmaceutical proteins due to several features such as safety, no need for fermentation, inexpensive investment, and fast and easy scale-up. Human insulin is one of the most widely used medicines in the world. Up to now different expression systems including Escherichia coli, yeast and CHO have been exploited for producing recombinant human insulin and a variety of different recombinant insulin are extensively used.

OBJECTIVES

This study reports on the transformation and expression of proinsulin gene in tomato plants for the first time in Iran.

MATERIALS AND METHODS

This study reports the cloning, transformation and expression of proinsulin gene in tomato plants. Specific primers were designed and used for PCR amplification and cloning of the proinsulin gene in the plant expression vector pCAMBIA1304. The recombinant construct was transferred into Agrobacterium tumefaciens strain LBA4404, and used for Agrobacterium mediated stable transformation of tomato plants. Presence of the desired gene in transgenic lines was confirmed through colony PCR and sequencing. The expression of the protein in transgenic lines was confirmed by immunodot blot assay.

RESULTS

The presence of the proinsulin gene in the genomic DNA of transgenic tomato was confirmed by PCR. Also total protein of transgenic tomato was extracted and the expression of proinsulin was detected using dotblot assay.

CONCLUSIONS

This survey addresses the possibility of proinsulin gene transfer and expression in tomato transgenic lines. This study can be used as a basis for future researches to produce human proinsulin in tomato and other candidate plants.

N-glycosylation and N-glycan moieties of CTB expressed in rice seeds

Cholera toxin B subunit (CTB) is widely used as a carrier molecule and mucosal adjuvant and for the expression of fusion proteins of interest. CTB-fusion proteins are also expressed in plants, but the N-glycan structures of CTB have not been clarified. To gain insights into the N-glycosylation and N-glycans of CTB expressed in plants, we expressed CTB in rice seeds with an N-terminal glutelin signal and a C-terminal KDEL sequence and analyzed its N-glycosylation and N-glycan structures. CTB was successfully expressed in rice seeds in two forms: a form with N-glycosylation at Asn32 that included both plant-specific N-glycans and small oligomannosidic N-glycans and a non-N-glycosylated form. N-Glycan analysis of CTB showed that approximately 50 % of the N-glycans had plant-specific M3FX structures and that almost none of the N-glycans was of high-mannose-type N-glycan even though the CTB expressed in rice seeds contains a C-terminal KDEL sequence. These results suggest that the CTB expressed in rice was N-glycosylated through the endoplasmic reticulum (ER) and Golgi N-glycosylation machinery without the ER retrieval.

Transgenic barley: a prospective tool for biotechnology and agriculture

Barley (Hordeum vulgare L.) is one of the founder crops of agriculture, and today it is the fourth most important cereal grain worldwide. Barley is used as malt in brewing and distilling industry, as an additive for animal feed, and as a component of various food and bread for human consumption. Progress in stable genetic transformation of barley ensures a potential for improvement of its agronomic performance or use of barley in various biotechnological and industrial applications. Recently, barley grain has been successfully used in molecular farming as a promising bioreactor adapted for production of human therapeutic proteins or animal vaccines. In addition to development of reliable transformation technologies, an extensive amount of various barley genetic resources and tools such as sequence data, microarrays, genetic maps, and databases has been generated. Current status on barley transformation technologies including gene transfer techniques, targets, and progeny stabilization, recent trials for improvement of agricultural traits and performance of barley, especially in relation to increased biotic and abiotic stress tolerance, and potential use of barley grain as a protein production platform have been reviewed in this study. Overall, barley represents a promising tool for both agricultural and biotechnological transgenic approaches, and is considered an ancient but rediscovered crop as a model industrial platform for molecular farming.

Production of a de-novo designed antimicrobial peptide in Nicotiana benthamiana

Antimicrobial peptides are important defense compounds of higher organisms that can be used as therapeutic agents against bacterial and/or viral infections. We designed several antimicrobial peptides containing hydrophobic and positively charged clusters that are active against plant and human pathogens. Especially peptide SP1-1 is highly active with a MIC value of 0.1 μg/ml against Xanthomonas vesicatoria, Pseudomonas corrugata and Pseudomonas syringae pv syringae. However, for commercial applications high amounts of peptide are necessary. The synthetic production of peptides is still quite expensive and, depending on the physico-chemical features, difficult. Therefore we developed a plant/tobacco mosaic virus-based production system following the 'full virus vector strategy' with the viral coat protein as fusion partner for the designed antimicrobial peptide. Infection of Nicotiana benthamiana plants with such recombinant virus resulted in production of huge amounts of virus particles presenting the peptides all over their surface. After extraction of recombinant virions, peptides were released from the coat protein by chemical cleavage. A protocol for purification of the antimicrobial peptides using high resolution chromatographic methods has been established. Finally, we yielded up to 0.025 mg of peptide per g of infected leaf biomass. Mass spectrometric and NMR analysis revealed that the in planta produced peptide differs from the synthetic version only in missing of N-terminal amidation. But its antimicrobial activity was in the range of the synthetic one. Taken together, we developed a protocol for plant-based production and purification of biologically active, hydrophobic and positively charged antimicrobial peptide.

Comparative in vitro and experimental in vivo studies of the anti-epidermal growth factor receptor antibody nimotuzumab and its aglycosylated form produced in transgenic tobacco plants

A broad variety of foreign genes can be expressed in transgenic plants, which offer the opportunity for large-scale production of pharmaceutical proteins, such as therapeutic antibodies. Nimotuzumab is a humanized anti-epidermal growth factor receptor (EGFR) recombinant IgG1 antibody approved in different countries for the treatment of head and neck squamous cell carcinoma, paediatric and adult glioma, and nasopharyngeal and oesophageal cancers. Because the antitumour mechanism of nimotuzumab is mainly attributed to its ability to interrupt the signal transduction cascade triggered by EGF/EGFR interaction, we have hypothesized that an aglycosylated form of this antibody, produced by mutating the N(297) position in the IgG(1) Fc region gene, would have similar biochemical and biological properties as the mammalian-cell-produced glycosylated counterpart. In this paper, we report the production and characterization of an aglycosylated form of nimotuzumab in transgenic tobacco plants. The comparison of the plantibody and nimotuzumab in terms of recognition of human EGFR, effect on tyrosine phosphorylation and proliferation in cells in response to EGF, competition with radiolabelled EGF for EGFR, affinity measurements of Fab fragments, pharmacokinetic and biodistribution behaviours in rats and antitumour effects in nude mice bearing human A431 tumours showed that both antibody forms have very similar in vitro and in vivo properties. Our results support the idea that the production of aglycosylated forms of some therapeutic antibodies in transgenic plants is a feasible approach when facing scaling strategies for anticancer immunoglobulins.

Human granulocyte colony-stimulating factor (hG-CSF) expression in plastids of Lactuca sativa

BACKGROUND

Human granulocyte colony-stimulating factor (hG-CSF) can serve as valuable biopharmaceutical for research and treatment of the human blood cancer. Transplastomic plants have been emerged as a new and high potential candidate for production of recombinant biopharmaceutical proteins in comparison with transgenic plants due to extremely high level expression, biosafety and many other advantages.

METHODS

hG-CSF gene was cloned into pCL vector between prrn16S promoter and TpsbA terminator. The recombinant vector was coated on nanogold particles and transformed to lettuce chloroplasts through biolistic method. Callogenesis and regeneration of cotyledonary explants were obtained by Murashige and Skoog media containing 6-benzylaminopurine and 1-naphthaleneacetic acid hormones. The presence of hG-CSF gene in plastome was studied with four specific PCR primers and expression by Western immunoblotting.

RESULTS

hG-CSF gene cloning was confirmed by digestion and sequencing. Transplastomic lettuce lines were regenerated and subjected to molecular analysis. The presence of hG-CSF in plastome was confirmed by PCR using specific primers designed from the plastid genome. Western immunoblotting of extracted protein from transplastomic plants showed a 20-kDa band, which verified the expression of recombinant protein in lettuce chloroplasts.

CONCLUSIONS

This study is the first report that successfully express hG-CSF gene in lettuce chloroplast. The lettuce plastome can provide a cheap and safe expression platform for producing valuable biopharmaceuticals for research and treatment.

Molecular strategies to engineer transgenic rice seed compartments for large-scale production of plant-made pharmaceuticals

The use of plants as bioreactors for the large-scale production of recombinant proteins has emerged as an exciting area of research. The current shortages in protein therapeutics due to the capacity and economic bottlenecks faced with modern protein production platforms (microbial, yeast, mammalian) has driven considerable attention towards molecular pharming. Utilizing plants for the large-scale production of recombinant proteins is estimated to be 2-10% the cost of microbial platforms, and up to 1,000-fold more cost effective than mammalian platforms (Twyman et al. Trends Biotechnol 21:570-578, 2003; Sharma and Sharma, Biotechnol Adv 27:811-832, 2009). In order to achieve an economically feasible plant production host, protein expression and accumulation must be optimized. The seed, and more specifically the rice seed has emerged as an ideal candidate in molecular pharming due to its low protease activity, low water content, stable protein storage environment, relatively high biomass, and the molecular tools available for manipulation (Lau and Sun, Biotechnol Adv 27:1015-1022, 2009).

Recombinant hHscFv-RC-RNase protein derived from transgenic tobacco acts as a bifunctional molecular complex against hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common clinical primary malignant tumor; however, efficient drugs for the treatment of HCC are still lacking at the present time. To develop a new approach for liver cancer therapy, we designed a chimeric gene (his-HR) encoding a single-chain variable fragment of human HAb25 (hHscFv) fused to a cytotoxic ribonuclease from Rana catesbeiana (RC-RNase) and expressed the corresponding fusion protein in transgenic tobacco (Nicotiana tabacum). Eleven positive transgenic plant lines were identified from 204 regenerated tobacco plants by PCR and Southern blot analysis, and the immunocompetence of the recombinant his-HR protein was confirmed by Western blotting. The expression levels of his-HR protein ranged from 0.75 to 1.99 µg/g in the fresh tobacco leaves. To characterize the bifunction of the expressed his-HR protein in tobacco, binding specificity and cell toxicity to several cell lines were examined by the indirect immunocytochemical streptavidin-biotin complex method and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay. Data indicated that the his-HR protein had stronger specific binding affinity to HepG2 (human liver HCC cell line) than to the other tumor cell lines and normal liver cell line, and the capacity to kill the HCC cell lines SMMC7721 and HepG2 with an half maximal inhibiting concentration of 2.0 and 2.4 nM, respectively. The results suggest that recombinant bifunctional his-HR protein derived from transgenic plants may provide a novel strategy to treat HCC in the future.

Coloring genetically modified soybean grains with anthocyanins by suppression of the proanthocyanidin genes ANR1 and ANR2

Detection and quantification of the levels of adventitious presence of genetically modified (GM) soybeans in non-GM grain shipments currently requires sophisticated tests that can have issues with their reproducibility. We show here that pigment biosynthesis in the soybean seed coat can be manipulated to provide a distinct color that would enable the simple visible detection of the GM soybean grain. We observed that a distinct red-brown grain color could be engineered by the simultaneous suppression of two proanthocyanidin (PA) genes, ANTHOCYANIDIN REDUCTASE1 (ANR1) and ANR2. Multiple reaction monitoring by liquid chromatography tandem mass spectrometry was used to quantify differentially accumulated seed coat metabolites, and revealed the redirection of metabolic flux into the anthocyanin pigment pathway and unexpectedly the flavonol-3-O-glucoside pathway. The upregulations of anthocyanin isogenes (DFR1 and GST26) and the anthocyanin/flavonol-3-O-glycosyltransferase (UGT78K2) were identified by quantitative RT-PCR to be endogenous feedback and feedforward responses to overaccumulation of upstream flavonoid intermediates resulting from ANR1 and ANR2 suppressions. These results suggested the transcription of flavonoid genes to be a key component of the mechanism responsible for the redirection of metabolite flux. This report identifies the suppression of PA genes to be a novel approach for engineering pigmentation in soybean grains.

Pharmaceutical prospects: biopharming and the geography of technological expectations

The paper explores the role of imagined geographies in the shaping of new technologies. I argue that the role of place in future-oriented visions of technoscience is a neglected topic in studies of the social shaping of technology. The paper proposes an approach that combines the sociology of expectations with the geography of science. It focuses on the interplay between envisaged and current geographies to highlight the recursive dynamics of place and imagination. To illustrate this approach, the paper discusses the example of biopharming, the production of biopharmaceuticals using genetically modified crops. I argue that expectations for biopharming bear the imprint of place, or rather of the places in which they are imagined, as well as those they imagine, and ultimately those they produce. I use this example to suggest how social studies of science and technology can usefully investigate the spaces, places and scales of technological development.

The use of plants for the production of therapeutic human peptides

Peptides have unique properties that make them useful drug candidates for diverse indications, including allergy, infectious disease and cancer. Some peptides are intrinsically bioactive, while others can be used to induce precise immune responses by defining a minimal immunogenic region. The limitations of peptides, such as metabolic instability, short half-life and low immunogenicity, can be addressed by strategies such as multimerization or fusion to carriers, to improve their pharmacological properties. The remaining major drawback is the cost of production using conventional chemical synthesis, which is also difficult to scale-up. Over the last 15 years, plants have been shown to produce bioactive and immunogenic peptides economically and with the potential for large-scale synthesis. The production of peptides in plants is usually achieved by the genetic fusion of the corresponding nucleotide sequence to that of a carrier protein, followed by stable nuclear or plastid transformation or transient expression using bacterial or viral vectors. Chimeric plant viruses or virus-like particles can also be used to display peptide antigens, allowing the production of polyvalent vaccine candidates. Here we review progress in the field of plant-derived peptides over the last 5 years, addressing new challenges for diverse pathologies.

Production of camel-like antibodies in plants

Transgenic plants for the production of high-value recombinant complex and/or glycosylated proteins are a promising alternative for conventional systems, such as mammalian cells and bacteria. Many groups use plants as production platform for antibodies and antibody fragments. Here, we describe how bivalent camel-like antibodies can be produced in leaves and seeds. Camel-like antibodies are fusions of the antigen-binding domain of heavy chain camel antibodies (VHH) with an Fc fragment of choice. Transient expression in Nicotiana benthamiana leaves allows the production of VHH-Fc antibodies within a few days after the expression plasmid has been obtained. Generation of stable Arabidopsis thaliana transformants allows production of scalable amounts of VHH-Fc antibodies in seeds within a year. Further, we describe how the in planta-produced VHH-Fc antibodies can be quantified by Western blot analysis with Fc-specific antibodies.

Plant production of anti-β-glucan antibodies for immunotherapy of fungal infections in humans

There is an increasing interest in the development of therapeutic antibodies (Ab) to improve the control of fungal pathogens, but none of these reagents is available for clinical use. We previously described a murine monoclonal antibody (mAb 2G8) targeting β-glucan, a cell wall polysaccharide common to most pathogenic fungi, which conferred significant protection against Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans in animal models. Transfer of this wide-spectrum, antifungal mAb into the clinical setting would allow the control of most frequent fungal infections in many different categories of patients. To this aim, two chimeric mouse-human Ab derivatives from mAb 2G8, in the format of complete IgG or scFv-Fc, were generated, transiently expressed in Nicotiana benthamiana plants and purified from leaves with high yields (approximately 50 mg Ab/kg of plant tissues). Both recombinant Abs fully retained the β-glucan-binding specificity and the antifungal activities of the cognate murine mAb against C. albicans. In fact, they recognized preferentially β1,3-linked glucan molecules present at the fungal cell surface and directly inhibited the growth of C. albicans and its adhesion to human epithelial cells in vitro. In addition, both the IgG and the scFv-Fc promoted C. albicans killing by isolated, human polymorphonuclear neutrophils in ex vivo assays and conferred significant antifungal protection in animal models of systemic or vulvovaginal C. albicans infection. These recombinant Abs represent valuable molecules for developing novel, plant-derived immunotherapeutics against candidiasis and, possibly, other fungal diseases.

Transgênicos - Plantas Produtoras de Fármacos (PPF)

As Plantas Produtoras de Fármacos (PPF) representam a 4ª onda de vegetais geneticamente modificados. Neste caso, com a tecnologia sendo empregada para desenvolver e produzir vacinas e/ou produtos farmacêuticos, a partir de plantas transgênicas. Esta tecnologia, como todas as inovações científicas, vem acompanhada de riscos. Porém, o conhecimento atual disponível sobre seu uso não permite ainda conclusões definitivas sobre o caráter dos riscos, sua significância e sua probabilidade de causar, ou não, sérios danos. A análise de risco deve servir de base para a implementação de inovações tecnocientíficas. Os parâmetros devem ser avaliados, precauções especiais devem ser tomadas, a pesquisa deve ser conduzida de forma detalhada e também precisa ter amplo alcance quanto aos riscos potenciais por ser uma inovação. O presente artigo revisou a aplicabilidade desta nova tecnologia com relação ao gerenciamento do risco e a uma contenção que vise a segurança de uso, a manipulação e o comércio para os seres humanos.

Production of the 42-kDa fragment of Plasmodium falciparum merozoite surface protein 1, a leading malaria vaccine antigen, in Arabidopsis thaliana seeds

Malaria is widely associated with poverty, and a low-cost vaccine against malaria is highly desirable for implementing comprehensive vaccination programmes in developing countries. Production of malaria antigens in plants is a promising approach, but its development has been hindered by poor expression of the antigens in plant cells. In the present study, we targeted plant seeds as a low-cost vaccine production platform and successfully expressed the Plasmodium falciparum 42-kDa fragment of merozoite surface protein 1 (MSP1₄₂), a leading malaria vaccine candidate, at a high level in transgenic Arabidopsis seeds. We overcame hurdles of transcript and protein instabilities of MSP1₄₂ in plants by synthesizing a plant-optimized MSP1₄₂ cDNA and either targeting the recombinant protein to protein storage vacuoles or fusing it with a stable plant storage protein. An exceptional improvement in MSP1₄₂ expression, from an undetectable level to 5% of total extractable protein, was achieved with these combined strategies. Importantly, the plant-derived MSP1₄₂ maintains its natural antigenicity and can be recognized by immune sera from malaria-infected patients. Our results provide a strong basis for the development of a plant-based, low-cost malaria vaccine.

Advances in plant molecular farming

Plant molecular farming (PMF) is a new branch of plant biotechnology, where plants are engineered to produce recombinant pharmaceutical and industrial proteins in large quantities. As an emerging subdivision of the biopharmaceutical industry, PMF is still trying to gain comparable social acceptance as the already established production systems that produce these high valued proteins in microbial, yeast, or mammalian expression systems. This article reviews the various cost-effective technologies and strategies, which are being developed to improve yield and quality of the plant-derived pharmaceuticals, thereby making plant-based production system suitable alternatives to the existing systems. It also attempts to overview the different novel plant-derived pharmaceuticals and non-pharmaceutical protein products that are at various stages of clinical development or commercialization. It then discusses the biosafety and regulatory issues, which are crucial (if strictly adhered to) to eliminating potential health and environmental risks, which in turn is necessary to earning favorable public perception, thus ensuring the success of the industry.

Recombinant human GAD65 accumulates to high levels in transgenic tobacco plants when expressed as an enzymatically inactive mutant

The 65-kDa isoform of glutamic acid decarboxylase (GAD65) is the major autoantigen implicated in the development of type 1 diabetes mellitus (T1DM). The bulk manufacture of GAD65 is a potential issue in the fight against T1DM but current production platforms are expensive. We show that a catalytically inactive form of GAD65 (GAD65mut) accumulates at up to 2.2% total soluble protein in transgenic tobacco leaves, which is more than 10-fold the levels achieved with active GAD65, yet the protein retains the immunogenic properties required to treat T1DM. This higher yield was found to be a result of a higher rate of protein synthesis and not transcript availability or protein stability. We found that targeting GAD65 to the endoplasmic reticulum, a strategy that increases the accumulation of many recombinant proteins expressed in plants, did not improve production of GAD65mut. The production of a catalytically inactive autoantigen that retains its immunogenic properties could be a useful strategy to provide high-quality therapeutic protein for treatment of autoimmune T1DM.