Edible plants for oral delivery of biopharmaceuticals

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.

Recombinant MBP-pσ1 expressed in soybean seeds delays onset and reduces developing disease in an animal model of multiple sclerosis

It is estimated that multiple sclerosis (MS) affects over 2.8 million people worldwide, with a prevalence that is expected to continue growing over time. Unfortunately, there is no cure for this autoimmune disease. For several decades, antigen-specific treatments have been used in animal models of experimental autoimmune encephalomyelitis (EAE) to demonstrate their potential for suppressing autoimmune responses. Successes with preventing and limiting ongoing MS disease have been documented using a wide variety of myelin proteins, peptides, autoantigen-conjugates, and mimics when administered by various routes. While those successes were not translatable in the clinic, we have learned a great deal about the roadblocks and hurdles that must be addressed if such therapies are to be useful. Reovirus sigma1 protein (pσ1) is an attachment protein that allows the virus to target M cells with high affinity. Previous studies showed that autoantigens tethered to pσ1 delivered potent tolerogenic signals and diminished autoimmunity following therapeutic intervention. In this proof-of-concept study, we expressed a model multi-epitope autoantigen (human myelin basic protein, MBP) fused to pσ1 in soybean seeds. The expression of chimeric MBP-pσ1 was stable over multiple generations and formed the necessary multimeric structures required for binding to target cells. When administered to SJL mice prophylactically as an oral therapeutic, soymilk formulations containing MBP-pσ1 delayed the onset of clinical EAE and significantly reduced developing disease. These results demonstrate the practicality of soybean as a host for producing and formulating immune-modulating therapies to treat autoimmune diseases.

Genetic Containment for Molecular Farming

Plant molecular farming can provide humans with a wide variety of plant-based products including vaccines, therapeutics, polymers, industrial enzymes, and more. Some of these products, such as Taxol, are produced by endogenous plant genes, while many others require addition of genes by artificial gene transfer. Thus, some molecular farming plants are transgenic (or cisgenic), while others are not. Both the transgenic nature of many molecular farming plants and the fact that the products generated are of high-value and specific in purpose mean it is essential to prevent accidental cross-over of molecular farming plants and products into food or feed. Such mingling could occur either by gene flow during plant growth and harvest or by human errors in material handling. One simple approach to mitigate possible transfer would be to use only non-food non-feed species for molecular farming purposes. However, given the extent of molecular farming products in development, testing, or approval that do utilize food or feed crops, a ban on use of these species would be challenging to implement. Therefore, other approaches will need to be considered for mitigation of cross-flow between molecular farming and non-molecular-farming plants. This review summarized some of the production systems available for molecular farming purposes and options to implement or improve plant containment.

Insight of oral vaccines as an alternative approach to health and disease management: An innovative intuition and challenges

Vaccination is the most suitable and persuasive healthcare program for the prohibition of various deadly diseases. However, the higher production cost and purification strategies are out of reach for the developing nations. In this scenario, development of edible vaccine turns out to be the most promising alternative for remodeling the pharmaceutical industry with reduced production and purification costs. Generally, oral route of vaccination is mostly preferred due to its safety, compliance, low manufacturing cost and most importantly the ability to induce immunity in both systemic and mucosal sites. Genetically modified microorganisms and plants could efficiently be used as vehicles for edible vaccines. Edible vaccines are supposed to reduce the risk associated with traditional vaccines. Currently, oral vaccines are available in the market for several viral and bacterial diseases like cholera, hepatitis B, malaria, rabies etc. Herein, the review focuses on the breakthrough events in the area of edible vaccines associated with dietary microbes and plants for better control over diseases.

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.

Phase III: Randomized observer-blind trial to evaluate lot-to-lot consistency of a new plant-derived quadrivalent virus like particle influenza vaccine in adults 18-49 years of age

BACKGROUND

The global reliance on eggs to produce most influenza vaccines has several limitations and new approaches to influenza vaccine production are needed. Herein we describe a phase 3, lot-to-lot consistency trial (NCT03321968) of a quadrivalent, recombinant, virus-like particle (VLP) influenza vaccine produced in plants. This platform is based on transient expression of proteins in Nicotiana benthamiana and yields VLPs bearing hemagglutinin (HA) protein trimers that are combined in a quadrivalent vaccine (QVLP).

METHODS

The HAs targeted in this study were A/California/07/2009 H1N1, A/Hong Kong/4801/2014 H3N2, B/Brisbane/60/08 and B/Phuket/3073/2013: recommended for the 2016-2017 Northern Hemisphere season. Healthy adults 18-49 years of age (n = 1200) were randomized 1:1:1 to receive a 0.5 mL intramuscular injection of QVLP (30 μg HA/strain) from three sequential lots. Local and systemic reactions were monitored for 21 days post-vaccination and blood was collected pre-vaccination and at day 21 (D21) after vaccination to measure hemagglutination inhibition (HI) antibodies.

RESULTS

Subject demographics were similar between groups and compliance with study procedures was 96.3%. The study population was 54.8% female, the mean age (±SD) was 29.9 ± 9.01 and the racial distribution was 77.8% Caucasian, 15.6% Asian, 5.8% Black/African American and 0.8% other. The HI responses met the Center for Biologics Evaluation and Research criteria for seroconversion (SCR ≥ 40%) and seroprotection rates (SPR ≥ 70%). The geometric mean fold rise in HI titers was ≥ 2.5 for all 4 strains for each lot. Lot-to-lot consistency was met with the 95% confidence intervals of the D21 mean geometric titre ratios falling between 0.67 and 1.5 for all four strains. No safety concerns were identified. Solicited adverse events were generally mild and transient: typical for what is reported after inactivated influenza vaccines.

CONCLUSIONS

This study supported earlier findings of the safety profile and immunogenicity of the plant-derived QVLP and demonstrated the consistency with which it can be produced.

On the verge of the market - Plant factories for the automated and standardized production of biopharmaceuticals

The market for biopharmaceuticals is dominated by recombinant proteins and is driven mainly by the development of vaccines and antibodies. Manufacturing predominantly relies on fermentation-based production platforms, which have limited scalability and suffer from high upstream process costs. As an alternative, the production of recombinant proteins in whole plants (plant molecular farming) provides a scalable and cost efficient upstream process because each plant functions as a self-contained bioreactor, avoiding costs associated with single-use devices and cleaning-in-place. Despite many proof-of-concept studies and the approval of a few products as medical devices, the only approved pharmaceutical proteins manufactured in whole plants have been authorized under emergency protocols. The absence of approvals under standard clinical development pathways in part reflects the lack of standardized process equipment and unit operations, leading to industry inertia based on familiarity with fermenter systems. Here we discuss the upstream production steps of plant molecular farming by transient expression in intact plants, including seeding, plant cultivation, infiltration with Agrobacterium tumefaciens, post-infiltration incubation, and harvesting. We focus on cultivation techniques because they strongly affect the subsequent steps and overall process design. We compare the benefits and drawbacks of open field, greenhouse and vertical farm strategies in terms of upfront investment costs, batch reproducibility, and decoupling from environmental impacts. We consider process automation, monitoring and adaptive process design in the context of Industry 4.0, which can boost process efficiency and batch-to-batch uniformity to improve regulatory compliance. Finally, we discuss the costs-benefit aspects of the different cultivation systems.

Bioengineering horizon scan 2020

Horizon scanning is intended to identify the opportunities and threats associated with technological, regulatory and social change. In 2017 some of the present authors conducted a horizon scan for bioengineering (Wintle et al., 2017). Here we report the results of a new horizon scan that is based on inputs from a larger and more international group of 38 participants. The final list of 20 issues includes topics spanning from the political (the regulation of genomic data, increased philanthropic funding and malicious uses of neurochemicals) to the environmental (crops for changing climates and agricultural gene drives). The early identification of such issues is relevant to researchers, policy-makers and the wider public.

Plant-derived protein bodies as delivery vehicles for recombinant proteins into mammalian cells

The encapsulation of biopharmaceuticals into micro- or nanoparticles is a strategy frequently used to prevent degradation or to achieve the slow release of therapeutics and vaccines. Protein bodies (PBs), which occur naturally as storage organelles in seeds, can be used as such carrier vehicles. The fusion of the N-terminal sequence of the maize storage protein, γ-zein, to other proteins is sufficient to induce the formation of PBs, which can be used to bioencapsulate recombinant proteins directly in the plant production host. In addition, the immunostimulatory effects of zein have been reported, which are advantageous for vaccine delivery. However, little is known about the interaction between zein PBs and mammalian cells. To better understand this interaction, fluorescent PBs, resulting from the fusion of the N-terminal portion of zein to a green fluorescent protein, was produced in Nicotiana benthamiana leaves, recovered by a filtration-based downstream procedure, and used to investigate their internalization efficiency into mammalian cells. We show that fluorescent PBs were efficiently internalized into intestinal epithelial cells and antigen-presenting cells (APCs) at a higher rate than polystyrene beads of comparable size. Furthermore, we observed that PBs stimulated cytokine secretion by epithelial cells, a characteristic that may confer vaccine adjuvant activities through the recruitment of APCs. Taken together, these results support the use of zein fusion proteins in developing novel approaches for drug delivery based on controlled protein packaging into plant PBs.

Molecular farming - The slope of enlightenment

Molecular farming can be defined as the use of plants to produce recombinant protein products. The technology is now >30 years old. The early promise of molecular farming was based on three perceived advantages: the low costs of growing plants, the immense scalability of agricultural production, and the inherent safety of plants as hosts for the production of pharmaceuticals. This resulted in a glut of research publications in which diverse proteins were expressed in equally diverse plant-based systems, and numerous companies were founded hoping to commercialize the new technology. There was a moderate degree of success for companies producing non-pharmaceutical proteins, but in the pharmaceutical sector the anticipation raised by promising early research was soon met by the cold hard reality of industrial pragmatism. Plants did not have a track record of success in pharmaceutical protein manufacturing, lacked a regulatory framework, and did not perform as well as established industry platforms. Negative attitudes towards genetically modified plants added to the mix. By the early 2000s, major industry players started to lose interest and pharmaceutical molecular farming fell from a peak of expectation into a trough of disillusionment, just as predicted by the Gartner hype cycle. But many of the pioneers of molecular farming have refocused their activities and have worked to address the limitations that hampered the first generation of technologies. The field has now consolidated around a smaller number of better-characterized platforms and has started to develop standardized methods and best practices, mirroring the evolution of more mature industry sectors. Likewise, attention has turned from proof-of-principle studies to realistic techno-economic modeling to capture significant niche markets, replicating the success of the industrial molecular farming sector. Here we argue that these recent developments signify that pharmaceutical molecular farming is now climbing the slope of enlightenment and will soon emerge as a mature technology.

Plant Virus Nanoparticles for Vaccine Applications

In the rapidly evolving field of nanotechnology, plant virus nanoparticles (pVNPs) are emerging as powerful tools in diverse applications ranging from biomedicine to materials science. The proteinaceous structure of plant viruses allows the capsid structure to be modified by genetic engineering and/or chemical conjugation with nanoscale precision. This means that pVNPs can be engineered to display peptides and proteins on their external surface, including immunodominant peptides derived from pathogens allowing pVNPs to be used for active immunization. In this context, pVNPs are safer than VNPs derived from mammalian viruses because there is no risk of infection or reversion to pathogenicity. Furthermore, pVNPs can be produced rapidly and inexpensively in natural host plants or heterologous production platforms. In this review, we discuss the use of pVNPs for the delivery of peptide antigens to the host immune in pre-clinical studies with the final aim of promoting systemic immunity against the corresponding pathogens. Furthermore, we described the versatility of plant viruses, with innate immunostimulatory properties, in providing a huge natural resource of carriers that can be used to develop the next generation of sustainable vaccines.

Parenteral-Oral Immunization with Plant-Derived HBcAg as a Potential Therapeutic Vaccine against Chronic Hepatitis B

Chronic hepatitis B (CHB) is the cause of severe liver damage, cirrhosis, and hepatocellular carcinoma for over 240 million people worldwide. Nowadays, several types of treatment are being investigated, including immunotherapy using hepatitis B core antigen (HBcAg) assembled into highly immunogenic capsid-like particles (CLPs). Immunogenicity of plant-produced and purified HBcAg, administered parenterally or intranasally, was previously reported. In this study, a novel parenteral-oral vaccination scheme is proposed using plant-derived HBcAg preparations. The antigen for injection was obtained via transient expression in Nicotiana benthamiana. HBcAg-producing transgenic lettuce was lyophilized and used as an orally delivered booster. The intracellular location of plant-produced HBcAg CLPs implies additional protection in the digestive tract during oral immunization. BALB/c mice were intramuscularly primed with 10 µg of the purified antigen and orally boosted twice with 5 or 200 ng of HBcAg. A long-lasting and significant systemic response after boosting with 200 ng HBcAg was induced, with anti-HBc titer of 25,000. Concomitantly, an insignificant mucosal response was observed, with an S-IgA titer of only 500. The profile of IgG isotypes indicates a predominant Th1 type of immune response, supplemented by Th2, after injection-oral vaccination. The results demonstrate that a low dose of parenteral-oral immunization with plant-derived HBcAg can elicit a specific and efficient response. This study presents a potential new pathway of CHB treatment.

Vaccine and antibody production in plants: developments and computational tools

Plants as bioreactors have been widely used to express efficient vaccine antigens against viral, bacterial and protozoan infections. To date, many different plant-based expression systems have been analyzed, with a growing preference for transient expression systems. Antibody expression in diverse plant species for therapeutic applications is well known, and this review provides an overview of various aspects of plant-based biopharmaceutical production. Here, we highlight conventional and gene expression technologies in plants along with some illustrative examples. In addition, the portfolio of products that are being produced and how they relate to the success of this field are discussed. Stable and transient gene expression in plants, agrofiltration and virus infection vectors are also reviewed. Further, the present report draws attention to antibody epitope prediction using computational tools, one of the crucial steps of vaccine design. Finally, regulatory issues, biosafety and public perception of this technology are also discussed.

Plant-made E2 glycoprotein single-dose vaccine protects pigs against classical swine fever

Classical Swine Fever Virus (CSFV) causes classical swine fever, a highly contagious hemorrhagic fever affecting both feral and domesticated pigs. Outbreaks of CSF in Europe, Asia, Africa and South America had significant adverse impacts on animal health, food security and the pig industry. The disease is generally contained by prevention of exposure through import restrictions (e.g. banning import of live pigs and pork products), localized vaccination programmes and culling of infected or at-risk animals, often at very high cost. Current CSFV-modified live virus vaccines are protective, but do not allow differentiation of infected from vaccinated animals (DIVA), a critical aspect of disease surveillance programmes. Alternatively, first-generation subunit vaccines using the viral protein E2 allow for use of DIVA diagnostic tests, but are slow to induce a protective response, provide limited prevention of vertical transmission and may fail to block viral shedding. CSFV E2 subunit vaccines from a baculovirus/insect cell system have been developed for several vaccination campaigns in Europe and Asia. However, this expression system is considered expensive for a veterinary vaccine and is not ideal for wide-spread deployment. To address the issues of scalability, cost of production and immunogenicity, we have employed an Agrobacterium-mediated transient expression platform in Nicotiana benthamiana and formulated the purified antigen in novel oil-in-water emulsion adjuvants. We report the manufacturing of adjuvanted, plant-made CSFV E2 subunit vaccine. The vaccine provided complete protection in challenged pigs, even after single-dose vaccination, which was accompanied by strong virus neutralization antibody responses.

Design of a Type-1 Diabetes Vaccine Candidate Using Edible Plants Expressing a Major Autoantigen

Type-1 diabetes (T1D) is a metabolic disease involving the autoimmune destruction of insulin-producing pancreatic beta cells. It is often diagnosed by the detection of autoantibodies, typically those recognizing insulin itself or the 65-kDa isoform of glutamic acid decarboxylase (GAD65). Oral insulin can be used to induce systemic immunological tolerance and thus prevent or delay the onset of T1D, suggesting that combination treatments with other autoantigens such as GAD65 could be even more successful. GAD65 has induced oral tolerance and prevented T1D in preclinical studies but it is difficult to produce in sufficient quantities for clinical testing. Here we combined edible plant systems, namely spinach (Spinacia oleracea cv Industra) and red beet (Beta vulgaris cv Moulin Rouge), with the magnICON^® expression system to develop a safe, cost-effective and environmentally sustainable platform for the large-scale production of GAD65. The superior red beet platform was extensively characterized in terms of recombinant protein yields and bioequivalence to wild-type plants, and the product was tested for its ability to resist simulated gastric digestion. Our results indicate that red beet plants are suitable for the production of a candidate oral vaccine based on GAD65 for the future preclinical and clinical testing of T1D immunotherapy approaches.

Plant-made vaccines and reagents for the One Health initiative

The One Health initiative is increasingly becoming a prominent discussion topic in animal and human health, with its focus on prevention of spread of zoonotic diseases, both in animals, and from animals to humans. An important part of One Health is that diagnostics and vaccines for diseases may be the same thing - and be used for both humans and animals. One potential problem standing in the way of wider adoption of One Health principles, though, is that use of conventional cell fermentation systems for production of the recombinant proteins that could be used as diagnostics or vaccines is often expensive and is not easily scalable. A solution to this may be the use of plants or plant cells as bioreactors: molecular farming, or the production of biologics in plants, is now a well-established science with many proofs of principle and important proofs of efficacy for especially animal vaccines. This review discusses how molecular farming could enable important advances in One Health, using as examples plant-made vacccines, reagents and therapeutics for influenza viruses, ebolaviruses, rabies virus, bunyaviruses and flaviviruses.

Disease Prevention: An Opportunity to Expand Edible Plant-Based Vaccines?

The lethality of infectious diseases has decreased due to the implementation of crucial sanitary procedures such as vaccination. However, the resurgence of pathogenic diseases in different parts of the world has revealed the importance of identifying novel, rapid, and concrete solutions for control and prevention. Edible vaccines pose an interesting alternative that could overcome some of the constraints of traditional vaccines. The term “edible vaccine” refers to the use of edible parts of a plant that has been genetically modified to produce specific components of a particular pathogen to generate protection against a disease. The aim of this review is to present and critically examine “edible vaccines” as an option for global immunization against pathogenic diseases and their outbreaks and to discuss the necessary steps for their production and control and the list of plants that may already be used as edible vaccines. Additionally, this review discusses the required standards and ethical regulations as well as the advantages and disadvantages associated with this powerful biotechnology tool.

Edible plants for oral delivery of biopharmaceuticals

Molecular farming is the use of plants for the production of high value recombinant proteins. Over the last 25 years, molecular farming has achieved the inexpensive, scalable and safe production of pharmaceutical proteins using a range of strategies. One of the most promising approaches is the use of edible plant organs expressing biopharmaceuticals for direct oral delivery. This approach has proven to be efficacious in several clinical vaccination and tolerance induction trials as well as multiple preclinical studies for disease prevention. The production of oral biopharmaceuticals in edible plant tissues could revolutionize the pharmaceutical industry by reducing the cost of production systems based on fermentation, and also eliminating expensive downstream purification, cold storage and transportation costs. This review considers the unique features that make plants ideal as platforms for the oral delivery of protein-based therapeutics and describes recent developments in the production of plant derived biopharmaceuticals for oral administration.