Oral immunization of haemaggulutinin H5 expressed in plant endoplasmic reticulum with adjuvant saponin protects mice against highly pathogenic avian influenza A virus infection

Protein complexes from edible mushrooms as a sustainable potato protection against coleopteran pests

Protein complexes from edible oyster mushrooms (Pleurotus sp.) composed of pleurotolysin A2 (PlyA2) and pleurotolysin B (PlyB) exert toxicity in feeding tests against Colorado potato beetle (CPB) larvae, acting through the interaction with insect-specific membrane sphingolipid. Here we present a new strategy for crop protection, based on in planta production of PlyA2/PlyB protein complexes, and we exemplify this strategy in construction of transgenic potato plants of cv Désirée. The transgenics in which PlyA2 was directed to the vacuole and PlyB to the endoplasmic reticulum are effectively protected from infestation by CPB larvae without impacting plant performance. These transgenic plants showed a pronounced effect on larval feeding rate, the larvae feeding on transgenic plants being on average five to six folds lighter than larvae feeding on controls. Further, only a fraction (11%-37%) of the larvae that fed on transgenic potato plants completed their life cycle and developed into adult beetles. Moreover, gene expression analysis of CPB larvae exposed to PlyA2/PlyB complexes revealed the response indicative of a general stress status of larvae and no evidence of possibility of developing resistance due to the functional inactivation of PlyA2/PlyB sphingolipid receptors.

Plant-made vaccines against viral diseases in humans and farm animals

Plants provide not only food and feed, but also herbal medicines and various raw materials for industry. Moreover, plants can be green factories producing high value bioproducts such as biopharmaceuticals and vaccines. Advantages of plant-based production platforms include easy scale-up, cost effectiveness, and high safety as plants are not hosts for human and animal pathogens. Plant cells perform many post-translational modifications that are present in humans and animals and can be essential for biological activity of produced recombinant proteins. Stimulated by progress in plant transformation technologies, substantial efforts have been made in both the public and the private sectors to develop plant-based vaccine production platforms. Recent promising examples include plant-made vaccines against COVID-19 and Ebola. The COVIFENZ^® COVID-19 vaccine produced in Nicotiana benthamiana has been approved in Canada, and several plant-made influenza vaccines have undergone clinical trials. In this review, we discuss the status of vaccine production in plants and the state of the art in downstream processing according to good manufacturing practice (GMP). We discuss different production approaches, including stable transgenic plants and transient expression technologies, and review selected applications in the area of human and veterinary vaccines. We also highlight specific challenges associated with viral vaccine production for different target organisms, including lower vertebrates (e.g., farmed fish), and discuss future perspectives for the field.

Rapid and Highly Efficient Genetic Transformation and Application of Interleukin-17B Expressed in Duckweed as Mucosal Vaccine Adjuvant

Molecular farming utilizes plants as a platform for producing recombinant biopharmaceuticals. Duckweed, the smallest and fastest growing aquatic plant, is a promising candidate for molecular farming. However, the efficiency of current transformation methods is generally not high in duckweed. Here, we developed a fast and efficient transformation procedure in Lemna minor ZH0403, requiring 7-8 weeks from screening calluses to transgenic plants with a stable transformation efficiency of 88% at the DNA level and 86% at the protein level. We then used this transformation system to produce chicken interleukin-17B (chIL-17B). The plant-produced chIL-17B activated the NF-κB pathway, JAK-STAT pathway, and their downstream cytokines in DF-1 cells. Furthermore, we administrated chIL-17B transgenic duckweed orally as an immunoadjuvant with mucosal vaccine against infectious bronchitis virus (IBV) in chickens. Both IBV-specific antibody titer and the concentration of secretory immunoglobulin A (sIgA) were significantly higher in the group fed with chIL-17B transgenic plant. This indicates that the duckweed-produced chIL-17B enhanced the humoral and mucosal immune responses. Moreover, chickens fed with chIL-17B transgenic plant demonstrated the lowest viral loads in different tissues among all groups. Our work suggests that cytokines are a promising adjuvant for mucosal vaccination through the oral route. Our work also demonstrates the potential of duckweed in molecular farming.

Increasing the Efficiency of the Accumulation of Recombinant Proteins in Plant Cells: The Role of Transport Signal Peptides

The problem with increasing the yield of recombinant proteins is resolvable using different approaches, including the transport of a target protein to cell compartments with a low protease activity. In the cell, protein targeting involves short-signal peptide sequences recognized by intracellular protein transport systems. The main systems of the protein transport across membranes of the endoplasmic reticulum and endosymbiotic organelles are reviewed here, as are the major types and structure of the signal sequences targeting proteins to the endoplasmic reticulum and its derivatives, to plastids, and to mitochondria. The role of protein targeting to certain cell organelles depending on specific features of recombinant proteins and the effect of this targeting on the protein yield are discussed, in addition to the main directions of the search for signal sequences based on their primary structure. This knowledge makes it possible not only to predict a protein localization in the cell but also to reveal the most efficient sequences with potential biotechnological utility.

Development of Plant-Based Vaccines for Prevention of Avian Influenza and Newcastle Disease in Poultry

Viral diseases, including avian influenza (AI) and Newcastle disease (ND), are an important cause of morbidity and mortality in poultry, resulting in significant economic losses. Despite the availability of commercial vaccines for the major viral diseases of poultry, these diseases continue to pose a significant risk to global food security. There are multiple factors for this: vaccine costs may be prohibitive, cold chain storage for attenuated live-virus vaccines may not be achievable, and commercial vaccines may protect poorly against local emerging strains. The development of transient gene expression systems in plants provides a versatile and robust tool to generate a high yield of recombinant proteins with superior speed while managing to achieve cost-efficient production. Plant-derived vaccines offer good stability and safety these include both subunit and virus-like particle (VLP) vaccines. VLPs offer potential benefits compared to currently available traditional vaccines, including significant reductions in virus shedding and the ability to differentiate between infected and vaccinated birds (DIVA). This review discusses the current state of plant-based vaccines for prevention of the AI and ND in poultry, challenges in their development, and potential for expanding their use in low- and middle-income countries.

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

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

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.

Systemic and Oral Immunogenicity of Porcine Epidemic Diarrhea Virus Antigen Fused to Poly-Fc of Immunoglobulin G and Expressed in ΔXT/FT Nicotiana benthamiana Plants

Porcine epidemic diarrhea virus (PEDV), a member of the Coronaviridae family has become increasingly probelmatic in the pig farming industry. Currently, there are no effective, globally applicable vaccines against PEDV. Here, we tested a recombinant PEDV vaccine candidate based on the expression of the core neutralising epitope (COE) of PEDV conjugated to polymeric immunoglobulin G scaffold (PIGS) in glycoengineered Nicotiana benthamiana plants. The biological activity of COE-PIGS was demonstrated by binding to C1q component of the complement system, as well as the surface of antigen-presenting cells (APCs) in vitro. The recombinant COE-PIGS induced humoral and cellular immune responses specific for PEDV after both systemic and mucosal vaccination. Altogether, the data indicated that PEDV antigen fusion to poly-Fc could be a promising vaccine platform against respiratory PEDV infection.

Plant-Produced N-glycosylated Ag85A Exhibits Enhanced Vaccine Efficacy Against Mycobacterium tuberculosis HN878 Through Balanced Multifunctional Th1 T Cell Immunity

Tuberculosis (TB) is one of the deadliest infectious diseases worldwide and is caused by Mycobacterium tuberculosis (Mtb). An effective vaccine to prevent TB is considered the most cost-effective measure for controlling this disease. Many different vaccine antigen (Ag) candidates, including well-known and newly identified Ags, have been evaluated in clinical and preclinical studies. In this study, we took advantage of a plant system of protein expression using Nicotiana benthamiana to produce N-glycosylated antigen 85A (G-Ag85A), which is one of the most well-characterized vaccine Ag candidates in the field of TB vaccines, and compared its immunogenicity and vaccine efficacy with those of nonglycosylated Ag85A (NG-Ag85A) produced with an Escherichia coli system. Notably, G-Ag85A induced a more robust IFN-γ response than NG-Ag85A, which indicated that G-Ag85A is well recognized by the host immune system during Mtb infection. We subsequently compared the vaccine potential of G-Ag85A and NG-Ag85A by evaluating their immunological features and substantial protection efficacies. Interestingly, G-Ag85A yielded moderately enhanced long-term protective efficacy, as measured in terms of bacterial burden and lung inflammation. Strikingly, G-Ag85A-immunized mice showed a more balanced proportion of multifunctional Th1-biased immune responses with sustained IFN-γ response than did NG-Ag85A-immunized mice. Collectively, plant-derived G-Ag85A could induce protective and balanced Th1 responses and confer long-term protection against a hypervirulent Mtb Beijing strain infection, which indicated that plant-produced G-Ag85A might provide an excellent example for the production of an Mtb subunit vaccine Ag and could be an effective platform for the development of anti-TB vaccines.

Food Additives as Novel Influenza Vaccine Adjuvants

Influenza is a major threat to public health. Vaccination is an effective strategy to control influenza; however, the current inactivated influenza vaccine has mild immunogenicity and exhibits suboptimal efficacy in clinical use. Vaccine efficacy can be improved by the addition of adjuvants, but few adjuvants have been approved for human use. To explore novel and effective adjuvants for influenza vaccines, here we screened 145 compounds from food additives approved in Japan. Of these 145 candidates, we identified 41 compounds that enhanced the efficacy of the split influenza hemagglutinin (HA) vaccine against lethal virus challenge in a mouse model. These 41 compounds included 18 novel adjuvant candidates and 15 compounds with previously reported adjuvant effects for other antigens but not for the influenza vaccine. Our results are of value to the development of novel and effective adjuvanted influenza or other vaccines for human use.

Production of tetravalent dengue virus envelope protein domain III based antigens in lettuce chloroplasts and immunologic analysis for future oral vaccine development

Dengue fever is a mosquito (Aedes aegypti) -transmitted viral disease that is endemic in more than 125 countries around the world. There are four serotypes of the dengue virus (DENV 1-4) and a safe and effective dengue vaccine must provide protection against all four serotypes. To date, the first vaccine, Dengvaxia (CYD-TDV), is available after many decades' efforts, but only has moderate efficacy. More effective and affordable vaccines are hence required. Plants offer promising vaccine production platforms and food crops offer additional advantages for the production of edible human and animal vaccines, thus eliminating the need for expensive fermentation, purification, cold storage and sterile delivery. Oral vaccines can elicit humoural and cellular immunity via both the mucosal and humoral immune systems. Here, we report the production of tetravalent EDIII antigen (EDIII-1-4) in stably transformed lettuce chloroplasts. Transplastomic EDIII-1-4-expressing lettuce lines were obtained and homoplasmy was verified by Southern blot analysis. Expression of EDIII-1-4 antigens was demonstrated by immunoblotting, with the EDIII-1-4 antigen accumulating to 3.45% of the total protein content. Immunological assays in rabbits showed immunogenicity of EDIII-1-4. Our in vitro gastrointestinal digestion analysis revealed that EDIII-1-4 antigens are well protected when passing through the oral and gastric digestion phases but underwent degradation during the intestinal phase. Our results demonstrate that lettuce chloroplast engineering is a promising approach for future production of an affordable oral dengue vaccine.

Cost-effective production of tag-less recombinant protein in Nicotiana benthamiana

Plants have recently received a great deal of attention as a means of producing recombinant proteins. Despite this, a limited number of recombinant proteins are currently on the market and, if plants are to be more widely used, a cost-effective and efficient purification method is urgently needed. Although affinity tags are convenient tools for protein purification, the presence of a tag on the recombinant protein is undesirable for many applications. A cost-effective method of purification using an affinity tag and the removal of the tag after purification has been developed. The family 3 cellulose-binding domain (CBM3), which binds to microcrystalline cellulose, served as the affinity tag and the small ubiquitin-related modifier (SUMO) and SUMO-specific protease were used to remove it. This method, together with size-exclusion chromatography, enabled purification of human interleukin-6 (hIL6) with a yield of 18.49 mg/kg fresh weight from leaf extracts of Nicotiana benthamiana following Agrobacterium-mediated transient expression. Plant-produced hIL6 (P-hIL6) contained less than 0.2 EU/μg (0.02 ng/mL) endotoxin. P-hIL6 activated the Janus kinase-signal transducer and activator of transcriptional pathways in human LNCaP cells, and induced expression of IL-21 in activated mouse CD4+ T cells. This approach is thus a powerful method for producing recombinant proteins in plants.

Green Therapeutic Biocapsules: Using Plant Cells to Orally Deliver Biopharmaceuticals

The use of innovative platforms to produce biopharmaceuticals cheaply and deliver them through noninvasive routes could expand their social benefits. Coverage should increase as a consequence of lower cost and higher patient compliance due to painless administration. For more than two decades of research, oral therapies that rely on genetically engineered plants for the production of biopharmaceuticals have been explored to treat or prevent high-impact diseases. Recent reports on the successful oral delivery of plant-made biopharmaceuticals raise new hopes for the field. Several candidates have shown protection in animal models, and efforts to establish their production on an industrial scale are ongoing. These advances and perspectives for the field are analyzed.

Fusion of a highly N-glycosylated polypeptide increases the expression of ER-localized proteins in plants

Plants represent promising systems for producing various recombinant proteins. One key area of focus for improving this technology is developing methods for producing recombinant proteins at high levels. Many methods have been developed to increase the transcript levels of recombinant genes. However, methods for increasing protein production involving steps downstream of transcription, including translation, have not been fully explored. Here, we investigated the effects of N-glycosylation on protein production and provide evidence that N-glycosylation greatly increases the expression levels of ER-targeted recombinant proteins. Fusion of the extracellular domain (M domain) of protein tyrosine phosphatase receptor type C (CD45), which contains four putative N-glycosylation sites to a model protein, leptin at the C-terminus, increased recombinant protein levels by 6.1 fold. This increase was specific to ER-targeted proteins and was dependent on N-glycosylation. Moreover, expression levels of leptin, leukemia inhibitory factor and GFP were also greatly increased by fusion of M domain at either the N or C-terminus. Furthermore, the increase in protein levels resulted from enhanced translation, but not transcription. Based on these results, we propose that fusing a small domain containing N-glycosylation sites to target proteins is a powerful technique for increasing the expression levels of recombinant proteins in plants.

Do microRNAs play a role in the activity of plant-based vaccines?

INTRODUCTION

An important trend in vaccinology is the development of oral vaccines based on genetically modified plants. Areas covered: Several studies have suggested that dietary microRNAs from plants and other organisms are bioavailable upon oral ingestion exerting biological events in the host such as the modulation of gene expression in several cell types. Since oral plant-based vaccines rely on whole cells as vaccine delivery vehicles, miRNAs could play a role in the immunogenic activity of this type of vaccine. In the present report, this hypothesis is discussed under the light of recent evidence on the immunomodulatory activity exerted by miRNAs using in vitro and in vivo evaluations. Expert commentary: The ways to generate new knowledge and exploit the potential of miRNAs in the development of oral vaccines are discussed.

Plant-based oral vaccines against zoonotic and non-zoonotic diseases

The shared diseases between animals and humans are known as zoonotic diseases and spread infectious diseases among humans. Zoonotic diseases are not only a major burden to livestock industry but also threaten humans accounting for >60% cases of human illness. About 75% of emerging infectious diseases in humans have been reported to originate from zoonotic pathogens. Because antibiotics are frequently used to protect livestock from bacterial diseases, the development of antibiotic-resistant strains of epidemic and zoonotic pathogens is now a major concern. Live attenuated and killed vaccines are the only option to control these infectious diseases and this approach has been used since 1890. However, major problems with this approach include high cost and injectable vaccines is impractical for >20 billion poultry animals or fish in aquaculture. Plants offer an attractive and affordable platform for vaccines against animal diseases because of their low cost, and they are free of attenuated pathogens and cold chain requirement. Therefore, several plant-based vaccines against human and animals diseases have been developed recently that undergo clinical and regulatory approval. Plant-based vaccines serve as ideal booster vaccines that could eliminate multiple boosters of attenuated bacteria or viruses, but requirement of injectable priming with adjuvant is a current limitation. So, new approaches like oral vaccines are needed to overcome this challenge. In this review, we discuss the progress made in plant-based vaccines against zoonotic or other animal diseases and future challenges in advancing this field.

Cold chain and virus-free chloroplast-made booster vaccine to confer immunity against different poliovirus serotypes

The WHO recommends complete withdrawal of oral polio vaccine (OPV) type 2 by April 2016 globally and replacing with at least one dose of inactivated poliovirus vaccine (IPV). However, high-cost, limited supply of IPV, persistent circulating vaccine-derived polioviruses transmission and need for subsequent boosters remain unresolved. To meet this critical need, a novel strategy of a low-cost cold chain-free plant-made viral protein 1 (VP1) subunit oral booster vaccine after single IPV dose is reported. Codon optimization of the VP1 gene enhanced expression by 50-fold in chloroplasts. Oral boosting of VP1 expressed in plant cells with plant-derived adjuvants after single priming with IPV significantly increased VP1-IgG1 and VP1-IgA titres when compared to lower IgG1 or negligible IgA titres with IPV injections. IgA plays a pivotal role in polio eradication because of its transmission through contaminated water or sewer systems. Neutralizing antibody titres (~3.17-10.17 log2 titre) and seropositivity (70-90%) against all three poliovirus Sabin serotypes were observed with two doses of IPV and plant-cell oral boosters but single dose of IPV resulted in poor neutralization. Lyophilized plant cells expressing VP1 stored at ambient temperature maintained efficacy and preserved antigen folding/assembly indefinitely, thereby eliminating cold chain currently required for all vaccines. Replacement of OPV with this booster vaccine and the next steps in clinical translation of FDA-approved antigens and adjuvants are discussed.

The Last Ten Years of Advancements in Plant-Derived Recombinant Vaccines against Hepatitis B

Disease prevention through vaccination is considered to be the greatest contribution to public health over the past century. Every year more than 100 million children are vaccinated with the standard World Health Organization (WHO)-recommended vaccines including hepatitis B (HepB). HepB is the most serious type of liver infection caused by the hepatitis B virus (HBV), however, it can be prevented by currently available recombinant vaccine, which has an excellent record of safety and effectiveness. To date, recombinant vaccines are produced in many systems of bacteria, yeast, insect, and mammalian and plant cells. Among these platforms, the use of plant cells has received considerable attention in terms of intrinsic safety, scalability, and appropriate modification of target proteins. Research groups worldwide have attempted to develop more efficacious plant-derived vaccines for over 30 diseases, most frequently HepB and influenza. More inspiring, approximately 12 plant-made antigens have already been tested in clinical trials, with successful outcomes. In this study, the latest information from the last 10 years on plant-derived antigens, especially hepatitis B surface antigen, approaches are reviewed and breakthroughs regarding the weak points are also discussed.

Plants as Factories for Human Pharmaceuticals: Applications and Challenges

Plant molecular farming (PMF), defined as the practice of using plants to produce human therapeutic proteins, has received worldwide interest. PMF has grown and advanced considerably over the past two decades. A number of therapeutic proteins have been produced in plants, some of which have been through pre-clinical or clinical trials and are close to commercialization. Plants have the potential to mass-produce pharmaceutical products with less cost than traditional methods. Tobacco-derived antibodies have been tested and used to combat the Ebola outbreak in Africa. Genetically engineered immunoadhesin (DPP4-Fc) produced in green plants has been shown to be able to bind to MERS-CoV (Middle East Respiratory Syndrome), preventing the virus from infecting lung cells. Biosafety concerns (such as pollen contamination and immunogenicity of plant-specific glycans) and costly downstream extraction and purification requirements, however, have hampered PMF production from moving from the laboratory to industrial application. In this review, the challenges and opportunities of PMF are discussed. Topics addressed include; transformation and expression systems, plant bioreactors, safety concerns, and various opportunities to produce topical applications and health supplements.

Plant-made oral vaccines against human infectious diseases-Are we there yet?

Although the plant-made vaccine field started three decades ago with the promise of developing low-cost vaccines to prevent infectious disease outbreaks and epidemics around the globe, this goal has not yet been achieved. Plants offer several major advantages in vaccine generation, including low-cost production by eliminating expensive fermentation and purification systems, sterile delivery and cold storage/transportation. Most importantly, oral vaccination using plant-made antigens confers both mucosal (IgA) and systemic (IgG) immunity. Studies in the past 5 years have made significant progress in expressing vaccine antigens in edible leaves (especially lettuce), processing leaves or seeds through lyophilization and achieving antigen stability and efficacy after prolonged storage at ambient temperatures. Bioencapsulation of antigens in plant cells protects them from the digestive system; the fusion of antigens to transmucosal carriers enhances efficiency of their delivery to the immune system and facilitates successful development of plant vaccines as oral boosters. However, the lack of oral priming approaches diminishes these advantages because purified antigens, cold storage/transportation and limited shelf life are still major challenges for priming with adjuvants and for antigen delivery by injection. Yet another challenge is the risk of inducing tolerance without priming the host immune system. Therefore, mechanistic aspects of these two opposing processes (antibody production or suppression) are discussed in this review. In addition, we summarize recent progress made in oral delivery of vaccine antigens expressed in plant cells via the chloroplast or nuclear genomes and potential challenges in achieving immunity against infectious diseases using cold-chain-free vaccine delivery approaches.

Expression of H3N2 nucleoprotein in maize seeds and immunogenicity in mice

Oral administration of maize-expressed H3N2 nucleoprotein induced antibody responses in mice showing the immunogenicity of plant-derived antigen and its potential to be utilized as a universal flu vaccine. Influenza A viruses cause influenza epidemics that are devastating to humans and livestock. The vaccine for influenza needs to be reformulated every year to match the circulating strains due to virus mutation. Influenza virus nucleoprotein (NP) is a multifunctional RNA-binding protein that is highly conserved among strains, making it a potential candidate for a universal vaccine. In this study, the NP gene of H3N2 swine origin influenza virus was expressed in maize endosperm. Twelve transgenic maize lines were generated and analyzed for recombinant NP (rNP) expression. Transcript analysis showed the main accumulation of rNP in seed. Protein level of rNP in T1 transgenic maize seeds ranged from 8.0 to 35 µg of NP/g of corn seed. The level increased up to 70 µg of NP/g in T3 seeds. A mouse study was performed to test the immunogenicity of one line of maize-derived rNP (MNP). Mice were immunized with MNP in a prime-boost design. Oral gavage administration showed that a humoral immune response was elicited in the mice treated with MNP indicating the immunogenicity of MNP. NP-specific antibody responses in the MNP group showed comparable antibody titer with the groups receiving positive controls such as Vero cell-derived NP (VNP) or alphavirus replicon particle-derived NP (ANP). Cytokine analysis showed antigen-specific stimulation of IL-4 cytokine elicited in splenocytes from mice treated with MNP further confirming a TH2 humoral immune response induced by MNP administration.

The increasing value of plant-made proteins

The production of high-value proteins in plants is maturing, as shown by the recent approval of innovative products and the latest studies that showcase plant-based production systems using technologies and approaches that are well established in other fields. These include host cell engineering, medium optimization, scalable unit operations for downstream processing (DSP), bioprocess optimization and detailed cost analysis. Product-specific benefits of plant-based systems have also been exploited, including bioencapsulation and the mucosal delivery of minimally processed topical and oral products with a lower entry barrier than pharmaceuticals for injection. Success stories spearheaded by the FDA approval of Elelyso developed by Protalix have revitalized the field and further interest has been fueled by the production of experimental Ebola treatments in plants.