Good manufacturing practices production of a purification-free oral cholera vaccine expressed in transgenic rice plants

MucoRice-CTB line 19A, a new marker-free transgenic rice-based cholera vaccine produced in an LED-based hydroponic system

We previously established the selection-marker-free rice-based oral cholera vaccine (MucoRice-CTB) line 51A for human use by Agrobacterium-mediated co-transformation and conducted a double-blind, randomized, placebo-controlled phase I trial in Japan and the United States. Although MucoRice-CTB 51A was acceptably safe and well tolerated by healthy Japanese and U.S. subjects and induced CTB-specific antibodies neutralizing cholera toxin secreted by Vibrio cholerae, we were limited to a 6-g cohort in the U.S. trial because of insufficient production of MucoRice-CTB. Since MucoRice-CTB 51A did not grow in sunlight, we re-examined the previously established marker-free lines and selected MucoRice-CTB line 19A. Southern blot analysis of line 19A showed a single copy of the CTB gene. We resequenced the whole genome and detected the transgene in an intergenic region in chromosome 1. After establishing a master seed bank of MucoRice-CTB line 19A, we established a hydroponic production facility with LED lighting to reduce electricity consumption and to increase production capacity for clinical trials. Shotgun MS/MS proteomics analysis of MucoRice-CTB 19A showed low levels of α-amylase/trypsin inhibitor-like proteins (major rice allergens), which was consistent with the data for line 51A. We also demonstrated that MucoRice-CTB 19A had high oral immunogenicity and induced protective immunity against cholera toxin challenge in mice. These results indicate that MucoRice-CTB 19A is a suitable oral cholera vaccine candidate for Phase I and II clinical trials in humans, including a V. cholerae challenge study.

Rice-produced classical swine fever virus glycoprotein E2 with herringbone-dimer design to enhance immune responses

Pestiviruses, including classical swine fever virus, remain a concern for global animal health and are responsible for major economic losses of livestock worldwide. Despite high levels of vaccination, currently available commercial vaccines are limited by safety concerns, moderate efficacy, and required high doses. The development of new vaccines is therefore essential. Vaccine efforts should focus on optimizing antigen presentation to enhance immune responses. Here, we describe a simple herringbone-dimer strategy for efficient vaccine design, using the classical swine fever virus E2 expressed in a rice endosperm as an example. The expression of rE2 protein was identified, with the rE2 antigen accumulating to 480 mg/kg. Immunological assays in mice, rabbits, and pigs showed high antigenicity of rE2. Two immunizations with 284 ng of the rE2 vaccine or one shot with 5.12 μg provided effective protection in pigs without interference from pre-existing antibodies. Crystal structure and small-angle X-ray scattering results confirmed the stable herringbone dimeric conformation, which had two fully exposed duplex receptor binding domains. Our results demonstrated that rice endosperm is a promising platform for precise vaccine design, and this strategy can be universally applied to other Flaviviridae virus vaccines.

Production and N-glycan engineering of Varlilumab in Nicotiana benthamiana

N-glycan engineering has dramatically evolved for the development and quality control of recombinant antibodies. Fc region of IgG contains two N-glycans whose galactose terminals on Fc-glycan have been shown to increase the stability of CH2 domain and improve effector functions. Nicotiana benthamiana has become one of the most attractive production systems for therapeutic antibodies. In this study, Varlilumab, a CD27-targeting monoclonal antibody, was transiently produced in fresh leaves of soil-grown and hydroponic-grown N. benthamiana, resulted in the yield of 174 and 618 µg/gram, respectively. However, the IgG produced in wild-type N. benthamiana lacked the terminal galactose residues in its N-glycan. Therefore, N-glycan engineering was applied to fine-tune recombinant antibodies produced in plant platforms. We further co-expressed IgG together with murine β1,4-galactosyltransferase (β1,4-GALT) to modify plant N-glycan with β1,4-linked Gal residue(s) and Arabidopsis thaliana β1,3-galactosylatransferase (β1,3-GALT) to improve galactosylation. The co-expression of IgG with each of GALTs successfully resulted in modification of N-glycan structures on the plant-produced IgG. Notably, IgG co-expressed with murine β1,4-GALT in soil-grown N. benthamiana had 42.5% of N-glycans variants having galactose (Gal) residues at the non-reducing terminus and 55.3% of that in hydroponic-grown N. benthamiana plants. Concomitantly, N-glycan profile analysis of IgG co-expressed with β1,3-GALT demonstrated that there was an increased efficiency of galactosylation and an enhancement in the formation of Lewis a structure in plant-derived antibodies. Taken together, our findings show that the first plant-derived Varlilumab was successfully produced with biantennary β1,4-galactosylated N-glycan structures.

Oral MucoRice-CTB vaccine is safe and immunogenic in healthy US adults

MucoRice-CTB is a promising cold-chain-free oral cholera vaccine candidate. Here, we report a double-blind, randomized, placebo-controlled, phase I study conducted in the USA in which vaccination with the 6-g dose of MucoRice-CTB induced cross-reactive antigen-specific antibodies against the B subunit of cholera toxin (CTB) and enterotoxigenic Escherichia coli heat-labile enterotoxin without inducing serious adverse events. This dosage was acceptably safe and tolerable in healthy men and women. In addition, it induced a CTB-specific IgA response in the saliva of two of the nine treated subjects; in one subject, the immunological kinetics of the salivary IgA were similar to those of the serum CTB-specific IgA. Antibodies from three of the five responders to the vaccine prevented CTB from binding its GM1 ganglioside receptor. These results are consistent with those of the phase I study in Japan, suggesting that oral MucoRice-CTB induces neutralizing antibodies against diarrheal toxins regardless of ethnicity.

Mucosal vaccines: wisdom from now and then

The oral and nasal cavities are covered by the mucosal epithelium that starts at the beginning of the aero-digestive tract. These mucosal surfaces are continuously exposed to environmental antigens including pathogens and allergens and are thus equipped with a mucosal immune system that mediates initial recognition of pathogenicity and initiates pathogen-specific immune responses. At the dawn of our scientific effort to explore the mucosal immune system, dental science was one of the major driving forces as it provided insights into the importance of mucosal immunity and its application for the control of oral infectious diseases. The development of mucosal vaccines for the prevention of dental caries was thus part of a novel approach that contributed to building the scientific foundations of the mucosal immune system. Since then, mucosal immunology and vaccines have gone on a scientific journey to become one of the major entities within the discipline of immunology. Here, we introduce our past and current efforts and future directions for the development of mucosal vaccines, specifically a rice-based oral vaccine (MucoRice) and a nanogel-based nasal vaccine, with the aim of preventing and controlling gastrointestinal and respiratory infectious diseases using the interdisciplinary fusion of mucosal immunology with agricultural science and biomaterial engineering, respectively.

Contributions of the international plant science community to the fight against infectious diseases in humans-part 2: Affordable drugs in edible plants for endemic and re-emerging diseases

The fight against infectious diseases often focuses on epidemics and pandemics, which demand urgent resources and command attention from the health authorities and media. However, the vast majority of deaths caused by infectious diseases occur in endemic zones, particularly in developing countries, placing a disproportionate burden on underfunded health systems and often requiring international interventions. The provision of vaccines and other biologics is hampered not only by the high cost and limited scalability of traditional manufacturing platforms based on microbial and animal cells, but also by challenges caused by distribution and storage, particularly in regions without a complete cold chain. In this review article, we consider the potential of molecular farming to address the challenges of endemic and re-emerging diseases, focusing on edible plants for the development of oral drugs. Key recent developments in this field include successful clinical trials based on orally delivered dried leaves of Artemisia annua against malarial parasite strains resistant to artemisinin combination therapy, the ability to produce clinical-grade protein drugs in leaves to treat infectious diseases and the long-term storage of protein drugs in dried leaves at ambient temperatures. Recent FDA approval of the first orally delivered protein drug encapsulated in plant cells to treat peanut allergy has opened the door for the development of affordable oral drugs that can be manufactured and distributed in remote areas without cold storage infrastructure and that eliminate the need for expensive purification steps and sterile delivery by injection.

Plant-Based COVID-19 Vaccines: Current Status, Design, and Development Strategies of Candidate Vaccines

The prevalence of the coronavirus disease 2019 (COVID-19) pandemic in its second year has led to massive global human and economic losses. The high transmission rate and the emergence of diverse SARS-CoV-2 variants demand rapid and effective approaches to preventing the spread, diagnosing on time, and treating affected people. Several COVID-19 vaccines are being developed using different production systems, including plants, which promises the production of cheap, safe, stable, and effective vaccines. The potential of a plant-based system for rapid production at a commercial scale and for a quick response to an infectious disease outbreak has been demonstrated by the marketing of carrot-cell-produced taliglucerase alfa (Elelyso) for Gaucher disease and tobacco-produced monoclonal antibodies (ZMapp) for the 2014 Ebola outbreak. Currently, two plant-based COVID-19 vaccine candidates, coronavirus virus-like particle (CoVLP) and Kentucky Bioprocessing (KBP)-201, are in clinical trials, and many more are in the preclinical stage. Interim phase 2 clinical trial results have revealed the high safety and efficacy of the CoVLP vaccine, with 10 times more neutralizing antibody responses compared to those present in a convalescent patient's plasma. The clinical trial of the CoVLP vaccine could be concluded by the end of 2021, and the vaccine could be available for public immunization thereafter. This review encapsulates the efforts made in plant-based COVID-19 vaccine development, the strategies and technologies implemented, and the progress accomplished in clinical trials and preclinical studies so far.

Characterization and Specification of a Trivalent Protein-Based Pneumococcal Vaccine Formulation Using an Adjuvant-Free Nanogel Nasal Delivery System

We previously developed a safe and effective nasal vaccine delivery system using a self-assembled nanosized hydrogel (nanogel) made from a cationic cholesteryl pullulan. Here, we generated three pneumococcal surface protein A (PspA) fusion antigens as a universal pneumococcal nasal vaccine and then encapsulated each PspA into a nanogel and mixed the three resulting monovalent formulations into a trivalent nanogel-PspA formulation. First, to characterize the nanogel-PspA formulations, we used native polyacrylamide gel electrophoresis (PAGE) to determine the average number of PspA molecules encapsulated per nanogel molecule. Second, we adopted two methods-a densitometric method based on lithium dodecyl sulfate (LDS)-PAGE and a biologic method involving sandwich enzyme-linked immunosorbent assay (ELISA)-to determine the PspA content in the nanogel formulations. Third, treatment of nanogel-PspA formulations by adding methyl-β-cyclodextrin released each PspA in its native form, as confirmed through circular dichroism (CD) spectroscopy. However, when nanogel-PspA formulations were heat-treated at 80 °C for 16 h, CD spectroscopy showed that each PspA was released in a denatured form. Fourth, we confirmed that the nanogel-PspA formulations were internalized into nasal mucosa effectively and that each PspA was gradually released from the nanogel in epithelial cells in mice. Fifth, LDS-PAGE densitometry and ELISA both indicated that the amount of trivalent PspA was dramatically decreased in the heat-treated nanogel compared with that before heating. When mice were immunized nasally using the heat-treated formulation, the immunologic activity of each PspA was dramatically reduced compared with that of the untreated formulation; in both cases, the immunologic activity correlated well with the content of each PspA as determined by LDS-PAGE densitometry and ELISA. Finally, we confirmed that the trivalent nanogel-PspA formulation induced equivalent titers of PspA-specific serum IgG and mucosal IgA Abs in immunized mice. These results show that the specification methods we developed effectively characterized our nanogel-based trivalent PspA nasal vaccine formulation.

Comparative whole-genome and proteomics analyses of the next seed bank and the original master seed bank of MucoRice-CTB 51A line, a rice-based oral cholera vaccine

BACKGROUND

We have previously developed a rice-based oral vaccine against cholera diarrhea, MucoRice-CTB. Using Agrobacterium-mediated co-transformation, we produced the selection marker-free MucoRice-CTB line 51A, which has three copies of the cholera toxin B subunit (CTB) gene and two copies of an RNAi cassette inserted into the rice genome. We determined the sequence and location of the transgenes on rice chromosomes 3 and 12. The expression of alpha-amylase/trypsin inhibitor, a major allergen protein in rice, is lower in this line than in wild-type rice. Line 51A was self-pollinated for five generations to fix the transgenes, and the seeds of the sixth generation produced by T5 plants were defined as the master seed bank (MSB). T6 plants were grown from part of the MSB seeds and were self-pollinated to produce T7 seeds (next seed bank; NSB). NSB was examined and its whole genome and proteome were compared with those of MSB.

RESULTS

We re-sequenced the transgenes of NSB and MSB and confirmed the positions of the three CTB genes inserted into chromosomes 3 and 12. The DNA sequences of the transgenes were identical between NSB and MSB. Using whole-genome sequencing, we compared the genome sequences of three NSB with three MSB samples, and evaluated the effects of SNPs and genomic structural variants by clustering. No functionally important mutations (SNPs, translocations, deletions, or inversions of genic regions on chromosomes) between NSB and MSB samples were detected. Analysis of salt-soluble proteins from NSB and MSB samples by shot-gun MS/MS detected no considerable differences in protein abundance. No difference in the expression pattern of storage proteins and CTB in mature seeds of NSB and MSB was detected by immuno-fluorescence microscopy.

CONCLUSIONS

All analyses revealed no considerable differences between NSB and MSB samples. Therefore, NSB can be used to replace MSB in the near future.

Development of Systems for the Production of Plant-Derived Biopharmaceuticals

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

Alternative Methods of Vaccine Delivery: An Overview of Edible and Intradermal Vaccines

Vaccines are recognized worldwide as one of the most important tools for combating infectious diseases. Despite the tremendous value conferred by currently available vaccines toward public health, the implementation of additional vaccine platforms is also of key importance. In fact, currently available vaccines possess shortcomings, such as inefficient triggering of a cell-mediated immune response and the lack of protective mucosal immunity. In this regard, recent work has been focused on vaccine delivery systems, as an alternative to injectable vaccines, to increase antigen stability and improve overall immunogenicity. In particular, novel strategies based on edible or intradermal vaccine formulations have been demonstrated to trigger both a systemic and mucosal immune response. These novel vaccination delivery systems offer several advantages over the injectable preparations including self-administration, reduced cost, stability, and elimination of a cold chain. In this review, the latest findings and accomplishments regarding edible and intradermal vaccines are described in the context of the system used for immunogen expression, their molecular features and capacity to induce a protective systemic and mucosal response.

A Fruitful Decade Using Synthetic Promoters in the Improvement of Transgenic Plants

Advances in plant biotechnology provide various means to improve crop productivity and greatly contributing to sustainable agriculture. A significant advance in plant biotechnology has been the availability of novel synthetic promoters for precise spatial and temporal control of transgene expression. In this article, we review the development of various synthetic promotors and the rise of their use over the last several decades for regulating the transcription of various transgenes. Similarly, we provided a brief description of the structure and scope of synthetic promoters and the engineering of their cis-regulatory elements for different targets. Moreover, the functional characteristics of different synthetic promoters, their modes of regulating the expression of candidate genes in response to different conditions, and the resulting plant trait improvements reported in the past decade are discussed.

Challenges in developing mucosal vaccines and antibodies against infectious diarrhea in children

Infectious diarrhea in children can be life-threatening and imposes a large economic burden on healthcare systems, therefore more effective prophylactic and therapeutic drugs are needed urgently. Because most of the pathogens responsible for childhood diarrhea infect the gastrointestinal mucosa, providing protective immunity at the mucosal surface is an ideal way to control pathogen invasion and toxic activity. Mucosal (e.g. oral, nasal) vaccines are superior to systemic (subcutaneous or intramuscular) vaccination for conferring both mucosal and systemic pathogen-specific immune responses. Therefore, great efforts has been focused on the development of cost-effective mucosal vaccines for the past 50 years. Recent progress in plant genetic engineering has revolutionized the production of inexpensive and safe recombinant vaccine antigens. For example, rice plant biotechnology has facilitated the development of a cold-chain-free rice-based oral subunit vaccine against Vibrio cholerae. Furthermore, this technology has led to the creation of a rice-based oral antibody for prophylaxis and treatment of rotavirus gastroenteritis. This review summarizes current perspectives regarding the mucosal immune system and the development of mucosal vaccines and therapeutic antibodies, particularly rice-based products, and discusses future prospects regarding mucosal vaccines for children.

An overview on the strategies to exploit rice endosperm as production platform for biopharmaceuticals

Cereal seed has been utilized as production platform for high-value biopharmaceutical proteins. Especially, protein bodies (PBs) in seeds are not only natural specialized storage organs of seed storage proteins (SSPs), but also suitable intracellular deposition compartment for recombinant proteins. When various recombinant proteins were produced as secretory proteins by attaching N terminal ER signal peptide and C terminal KDEL endoplasmic reticulum (ER) retention signal or as fusion proteins with SSPs, high amounts of recombinant proteins can be predominantly accumulated in the PBs. Recombinant proteins bioencapsulated in PBs exhibit high resistance to digestive enzymes in gastrointestinal tract than other intracellular compartments and are highly stable at ambient temperature, thus allowing oral administration of PBs containing recombinant proteins as oral drugs or functional nutrients in cost-effective minimum processed formulation. In this review, we would like to address key factors determining accumulation levels of recombinant proteins in PBs. Understanding of bottle neck parts and improvement of specific deposition to PBs result in much higher levels of production of high quality recombinant proteins.

Seed Metabolome Analysis of a Transgenic Rice Line Expressing Cholera Toxin B-subunit

Plant-based human vaccines have been actively developed in recent years, and rice (Oryza sativa L.) is one of the best candidate crops for their production and delivery. By expressing a modified cholera toxin B (CTB) subunit, we previously developed MucoRice-CTB, a rice-based vaccine against cholera, which is caused by infection of the intestine with the bacteria Vibrio cholerae. MucoRice-CTB lines have been extensively characterized by whole-genome sequencing and proteome analyses to evaluate the mutation profiles and proteome status, respectively. Here, we report non-targeted metabolomic profiling of the MucoRice-CTB transgenic rice line 51A (MR-CTB51A), MucoRice-RNAi (MR-RNAi), and their non-transgenic parent line by using gas chromatography-time-of-flight mass spectrometry. The levels of several amino acids, organic acids, carbohydrates, lipids, and secondary metabolites were significantly increased in MR-CTB51A compared with the non-transgenic parent line. These metabolomics results complement essential information obtained by genome sequencing and proteomics approaches, thereby contributing to comprehensive understanding of the properties of MucoRice-CTB as a plant-based vaccine.

Corn-based vaccines: current status and prospects

Corn is an attractive host for vaccine production and oral delivery. The present review provides the current outlook and perspectives for this field. Among seed-crops, corn represents a key source of biomass for food, fuel production, and other applications. Since the beginning of the development of plant-based vaccines, corn was explored for the production and delivery of vaccines. About a dozen of pathogens have been studied under this technology with distinct degrees of development. A vaccine prototype against enterotoxigenic Escherichia coli was evaluated in a phase I clinical trial and several candidates targeting bacterial and viral diseases are under preclinical evaluation. The present review provides an updated outlook on this topic highlighting the employed expression strategies; perspectives for the field are also provided.

Oral immunisation of mice with transgenic rice calli expressing cholera toxin B subunit fused to consensus dengue cEDIII antigen induces antibodies to all four dengue serotypes

Dengue virus (DENV) infection is an emerging global health threat. DENV consists of four distinct serotypes, necessitating a tetravalent vaccine. In this study, expression of consensus envelope protein domain III (cEDIII) fused to cholera toxin B subunit (CTB) in transgenic rice calli was improved using the luminal binding protein BiP at the N-terminus and the SEKDEL signal sequences at the C-terminus, targeting the recombinant protein to endoplasmic reticulum (ER). We found that the fusion protein showed higher levels of expression when compared to the fusion proteins using rice amylase 3D (RAmy3D) or CTB native signal sequence only. The CTB-cEDIII fusion protein was evaluated as an oral dengue vaccine candidate in mice. Serotype specific systemic IgG antibodies and specific IgA response in feces were detected and furthermore, T cell proliferation and high frequency antibody-secreting B cells were detected in the spleen. These results suggest the possible use of plant-based dengue tetravalent vaccine targeted to the mucosal immune system for induction of systemic and mucosal immune responses to DENV infection.

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.

Plant-Based Vaccines: Production and Challenges

Plant-based vaccine technologies involve the integration of the desired genes encoding the antigen protein for specific disease into the genome of plant tissues by various methods. Agrobacterium-mediated gene transfer and transformation via genetically modified plant virus are the common methods that have been used to produce effective vaccines. Nevertheless, with the advancement of science and technology, new approaches have been developed to increase the efficiency of former methods such as biolistic, electroporation, agroinfiltration, sonication, and polyethylene glycol treatment. Even though plant-based vaccines provide many benefits to the vaccine industry, there are still challenges that limit the rate of successful production of these third-generation vaccines. Even with all the limitations, continuous efforts are still ongoing in order to produce efficient vaccine for many human and animals related diseases owing to its great potentials. This paper reviews the existing conventional methods as well as the development efforts by researchers in order to improve the production of plant-based vaccines. Several challenges encountered during and after the production process were also discussed.