Rice-based oral antibody fragment prophylaxis and therapy against rotavirus infection

Screening and identification of nanobody against inhibin α-subunit from a Camelus bactrianus phage display library

Background

Inhibin is a member of the transforming growth factor family that influences reproduction in animals.

Objective

The purpose of this study was to obtain nanobodies from the phage antibody library constructed by us that can specifically bind to inhibin α-subunit.

Methods

In this study, camels were immunized with Kazakh sheep inhibin-α protein that expressed in BL21 E. coli, and the camel VHH nanobody phage display library was prepared using nested PCR. The nanobodies specifically binding to inhibin α-subunit in the library were screened by three rounds of immunoaffinity screening and phage enzyme-linked immunosorbent assay (phage ELISA). The functions of the selected nanobodies were identified using molecular simulation docking, ELISA affinity test, and sheep immunity test.

Results

A nanobody display library was successfully constructed with a capacity of 1.05 × 1012 CFU, and four inhibin-α-subunit-specific nanobodies with an overall similarity of 69.34 % were screened from the library, namely, Nb-4, Nb-15, Nb-26, and Nb-57. The results of molecular simulation docking revealed that four types of nanobodies were complexed with inhibin-α protein mainly through hydrophobic bonds. Immunity tests revealed that the nanobody Nb-4 could effectively inhibit sheep inhibin A/B and could significantly improve the FSH level in sheep.

Conclusion

Four inhibin α-subunit-specific nanobodies with biological functions were successfully screened. To the best of our knowledge, this is a new reproductive immunomodulatory pathway of inhibin α-subunit, which may change the secretion of FSH in the ovary, thus changing the estrous cycle of organisms.

A Nanobody of PEDV S1 Protein: Screening and Expression in Escherichia coli

Porcine epidemic diarrhea virus (PEDV) has caused significant economic losses to the pig farming industry in various countries for a long time. Currently, there are no highly effective preventive or control measures available. Research into the pathogenic mechanism of PEDV has shown that it primarily causes infection by binding the S protein to the CD13 (APN) receptor on the membrane of porcine intestinal epithelial cells. The S1 region contains three neutralization epitopes and multiple receptor-binding domains, which are closely related to viral antigenicity and ad-sorption invasion. Nanobodies are a type of single-domain antibody that have been discovered in recent years. They can be expressed on a large scale through prokaryotic expression systems, which makes them cost-effective, stable, and less immunogenic. This study used a phage display library of nanobodies against the PEDV S1 protein. After three rounds of selection and enrichment, the DNA sequence of the highly specific nanobody S1Nb1 was successfully obtained. To obtain soluble nanobody S1Nb1, its DNA sequence was inserted into the vector Pcold and a solubility-enhancing SUMO tag was added. The resulting recombinant vector, Pcold-SUMO-S1Nb1, was then transformed into E. coli BL21(DE3) to determine the optimal expression conditions for the nanobody. Following purification using Ni-column affinity chromatography, Western blot analysis confirmed the successful purification of S1Nb1 carrying the solubility-enhancing tag. ELISA results demonstrated a strong affinity between the S1Nb1 nanobody and PEDV S1 protein.

Food-Borne Biotoxin Neutralization in Vivo by Nanobodies: Current Status and Prospects

Food-borne biotoxins from microbes, plants, or animals contaminate unclean, spoiled, and rotten foods, posing significant health risks. Neutralizing such toxins is vital for human health, especially after food poisoning. Nanobodies (Nbs), a type of single-domain antibodies derived from the genetic cloning of a variable domain of heavy chain antibodies (VHHs) in camels, offer unique advantages in toxin neutralization. Their small size, high stability, and precise binding enable effective neutralization. The use of Nbs in neutralizing food-borne biotoxins offers numerous benefits, and their genetic malleability allows tailored optimization for diverse toxins. As nanotechnology continues to evolve and improve, Nbs are poised to become increasingly efficient and safer tools for toxin neutralization, playing a pivotal role in safeguarding human health and environmental safety. This review not only highlights the efficacy of these agents in neutralizing toxins but also proposes innovative solutions to address their current challenges. It lays a solid foundation for their further development in this crucial field and propels their commercial application, thereby contributing significantly to advancements in this domain.

Single-domain antibodies applied as antiviral immunotherapeutics

Viral infections have been the cause of high mortality rates throughout different periods in history. Over the last two decades, outbreaks caused by zoonotic diseases and transmitted by arboviruses have had a significant impact on human health. The emergence of viral infections in different parts of the world encourages the search for new inputs to fight pathologies of viral origin. Antibodies represent the predominant class of new drugs developed in recent years and approved for the treatment of various human diseases, including cancer, autoimmune and infectious diseases. A promising group of antibodies are single-domain antibodies derived from camelid heavy chain immunoglobulins, or VHHs, are biomolecules with nanometric dimensions and unique pharmaceutical and biophysical properties that can be used in the diagnosis and immunotherapy of viral infections. For viral neutralization to occur, VHHs can act in different stages of the viral cycle, including the actual inhibition of infection, to hindering viral replication or assembly. This review article addresses advances involving the use of VHHs in therapeutic propositions aimed to battle different viruses that affect human health.

Orally delivered single-domain antibodies against gastrointestinal pathogens

Single-domain antibodies (sdAbs) are exceptionally stable fragments derived from the antigen-binding domains of immunoglobulins. They can withstand extreme pH, high temperature, and proteolysis, making them suitable for controlling gastrointestinal (GI) infections in humans and animals. sdAbs may function in their native soluble form, although different derived protein formats and the use of delivery vehicles can be useful for improved oral delivery. We discuss selected examples of the use of orally delivered sdAbs for protecting humans and animals against GI infections caused by pathogenic bacteria, viruses, and parasites. We finally provide perspectives on how sdAbs may be applied industrially and what challenges should be overcome for orally delivered sdAbs to reach the market.

Lactobacilli as a Vector for Delivery of Nanobodies against Norovirus Infection

Passive administration of neutralizing antibodies (Abs) is an attractive strategy for the control of gastrointestinal infections. However, an unanswered practical concern is the need to assure the stability of sufficient amounts of orally administered neutralizing Abs against intestinal pathogens (e.g., norovirus) in the harsh environment of the gastrointestinal tract. To this end, we expressed a single-domain Ab (VHH, nanobody) against norovirus on the cell surface of Lactobacillus, a natural and beneficial commensal component of the gut microbiome. First, we used intestinal epithelial cells generated from human induced pluripotent stem cells to confirm that VHH 1E4 showed neutralizing activity against GII.17 norovirus. We then expressed VHH 1E4 as a cell-wall-anchored form in Lactobacillus paracasei BL23. Flow cytometry confirmed the expression of VHH 1E4 on the surface of lactobacilli, and L. paracasei that expressed VHH 1E4 inhibited the replication of GII.17 norovirus in vitro. We then orally administered VHH 1E4-expressing L. paracasei BL23 to germ-free BALB/c mice and confirmed the presence of lactobacilli with neutralizing activity in the intestine for at least 10 days after administration. Thus, cell-wall-anchored VHH-displaying lactobacilli are attractive oral nanobody deliver vectors for passive immunization against norovirus infection.

Research progress and applications of nanobody in human infectious diseases

Infectious diseases, caused by pathogenic microorganisms, are capable of affecting crises. In addition to persistent infectious diseases such as malaria and dengue fever, the vicious outbreaks of infectious diseases such as Neocon, Ebola and SARS-CoV-2 in recent years have prompted the search for more efficient and convenient means for better diagnosis and treatment. Antibodies have attracted a lot of attention due to their good structural characteristics and applications. Nanobodies are the smallest functional single-domain antibodies known to be able to bind stably to antigens, with the advantages of high stability, high hydrophilicity, and easy expression and modification. They can directly target antigen epitopes or be constructed as multivalent nanobodies or nanobody fusion proteins to exert therapeutic effects. This paper focuses on the construction methods and potential functions of nanobodies, outlines the progress of their research, and highlights their various applications in human infectious diseases.

Maternal immune protection against infectious diseases

The maternal immune system protects developing offspring against pathogens before birth via transplacental transfer and after birth through secreted milk. This transferred maternal immunity influences each generation's susceptibility to infections and responsiveness to immunization. Thus, boosting immunity in the maternal-neonatal dyad is a potentially valuable public health strategy. Additionally, at critical times during fetal and postnatal development, environmental factors and immune stimuli influence immune development. These "windows of opportunity" offer a chance to identify both risk and protective factors that promote long-term health and limit disease. Here, we review pre- and postpartum maternal immune factors that protect against infectious agents in offspring and how they may shape the infant's immune landscape over time. Additionally, we discuss the influence of maternal immunity on the responsiveness to immunization in early life. Lastly, when maternal factors are insufficient to prevent neonatal infectious diseases, we discuss pre- and postnatal therapeutic strategies for the maternal-neonatal dyad.

Molecular farming using transgenic rice endosperm

Plant expression platforms are low-cost, scalable, safe, and environmentally friendly systems for the production of recombinant proteins and bioactive metabolites. Rice (Oryza sativa L.) endosperm is an ideal bioreactor for the production and storage of high-value active substances, including pharmaceutical proteins, oral vaccines, vitamins, and nutraceuticals such as flavonoids and carotenoids. Here, we explore the use of molecular farming from producing medicines to developing functional food crops (biofortification). We review recent progress in producing pharmaceutical proteins and bioactive substances in rice endosperm and compare this platform with other plant expression systems. We describe how rice endosperm could be modified to design metabolic pathways and express and store stable products and discuss the factors restricting the commercialization of transgenic rice products and future prospects.

Development of spirulina for the manufacture and oral delivery of protein therapeutics

The use of the edible photosynthetic cyanobacterium Arthrospira platensis (spirulina) as a biomanufacturing platform has been limited by a lack of genetic tools. Here we report genetic engineering methods for stable, high-level expression of bioactive proteins in spirulina, including large-scale, indoor cultivation and downstream processing methods. Following targeted integration of exogenous genes into the spirulina chromosome (chr), encoded protein biopharmaceuticals can represent as much as 15% of total biomass, require no purification before oral delivery and are stable without refrigeration and protected during gastric transit when encapsulated within dry spirulina. Oral delivery of a spirulina-expressed antibody targeting campylobacter-a major cause of infant mortality in the developing world-prevents disease in mice, and a phase 1 clinical trial demonstrated safety for human administration. Spirulina provides an advantageous system for the manufacture of orally delivered therapeutic proteins by combining the safety of a food-based production host with the accessible genetic manipulation and high productivity of microbial platforms.

A review of plant-based expression systems as a platform for single-domain recombinant antibody production

Monoclonal antibodies have contributed to improving the treatment of several diseases. However, limitations related to pharmacokinetic parameters and production costs have instigated the search for alternative products. Camelids produce functional immunoglobulins G devoid of light chains and CH1 domains, in which the antigenic recognition site is formed by a single domain called VHH or nanobody. VHHs' small size and similarity to the human VH domain contribute to high tissue penetration and low immunogenicity. In addition, VHHs provide superior antigen recognition compared to human antibodies, better solubility and stability. Due to these characteristics and the possibility of obtaining gene-encoding VHHs, applications of this biological tool, whether as a monomer or in related recombinant constructs, have been reported. To ensure antibody efficacy and cost-effectiveness, strategies for their expression, either using prokaryotic or eukaryotic systems, have been utilized. Plant-based expression systems are useful for VHH related constructs that require post-translational modifications. This system has exhibited versatility, low-cost upstream production, and safety. This article presents the main advances associated to the heterologous expression of VHHs in plant systems. Besides, we show insights related to the use of VHHs as a strategy for plant pathogen control and a tool for genomic manipulation in plant systems.

Therapeutic Applications of Functional Nanomaterials for Prostatitis

Prostatitis is a common disease in adult males, with characteristics of a poor treatment response and easy recurrence, which seriously affects the patient's quality of life. The prostate is located deep in the pelvic cavity, and thus a traditional infusion or other treatment methods are unable to easily act directly on the prostate, leading to poor therapeutic effects. Therefore, the development of new diagnostic and treatment strategies has become a research hotspot in the field of prostatitis treatment. In recent years, nanomaterials have been widely used in the diagnosis and treatment of various infectious diseases. Nanotechnology is a promising tool for 1) the accurate diagnosis of diseases; 2) improving the targeting of drug delivery systems; 3) intelligent, controlled drug release; and 4) multimode collaborative treatment, which is expected to be applied in the diagnosis and treatment of prostatitis. Nanotechnology is attracting attention in the diagnosis, prevention and treatment of prostatitis. However, as a new research area, systematic reviews on the application of nanomaterials in the diagnosis and treatment of prostatitis are still lacking. In this mini-review, we will highlight the treatment approaches for and challenges associated with prostatitis and describe the advantages of functional nanoparticles in improving treatment effectiveness and overcoming side effects.

Therapeutic Applications of Functional Nanomaterials for Prostatitis

Prostatitis is a common disease in adult males, with characteristics of a poor treatment response and easy recurrence, which seriously affects the patient’s quality of life. The prostate is located deep in the pelvic cavity, and thus a traditional infusion or other treatment methods are unable to easily act directly on the prostate, leading to poor therapeutic effects. Therefore, the development of new diagnostic and treatment strategies has become a research hotspot in the field of prostatitis treatment. In recent years, nanomaterials have been widely used in the diagnosis and treatment of various infectious diseases. Nanotechnology is a promising tool for 1) the accurate diagnosis of diseases; 2) improving the targeting of drug delivery systems; 3) intelligent, controlled drug release; and 4) multimode collaborative treatment, which is expected to be applied in the diagnosis and treatment of prostatitis. Nanotechnology is attracting attention in the diagnosis, prevention and treatment of prostatitis. However, as a new research area, systematic reviews on the application of nanomaterials in the diagnosis and treatment of prostatitis are still lacking. In this mini-review, we will highlight the treatment approaches for and challenges associated with prostatitis and describe the advantages of functional nanoparticles in improving treatment effectiveness and overcoming side effects.

Development of Antibody-Fragment-Producing Rice for Neutralization of Human Norovirus

Human norovirus is the leading cause of acute nonbacterial gastroenteritis in people of all ages worldwide. Currently, no licensed norovirus vaccine, pharmaceutical drug, or therapy is available for the control of norovirus infection. Here, we used a rice transgenic system, MucoRice, to produce a variable domain of a llama heavy-chain antibody fragment (VHH) specific for human norovirus (MucoRice-VHH). VHH is a small heat- and acid-stable protein that resembles a monoclonal antibody. Consequently, VHHs have become attractive and useful antibodies (Abs) for oral immunotherapy against intestinal infectious diseases. MucoRice-VHH constructs were generated at high yields in rice seeds by using an overexpression system with RNA interference to suppress the production of the major rice endogenous storage proteins. The average production levels of monomeric VHH (7C6) to GII.4 norovirus and heterodimeric VHH (7C6-1E4) to GII.4 and GII.17 noroviruses in rice seed were 0.54 and 0.28% (w/w), respectively, as phosphate buffered saline (PBS)-soluble VHHs. By using a human norovirus propagation system in human induced pluripotent stem-cell-derived intestinal epithelial cells (IECs), we demonstrated the high neutralizing activity of MucoRice expressing monomeric VHH (7C6) against GII.4 norovirus and of heterodimeric VHH (7C6-1E4) against both GII.4 and GII.17 noroviruses. In addition, MucoRice-VHH (7C6-1E4) retained neutralizing activity even after heat treatment at 90°C for 20 min. These results build a fundamental platform for the continued development of MucoRice-VHH heterodimer as a candidate for oral immunotherapy and for prophylaxis against GII.4 and GII.17 noroviruses in not only healthy adults and children but also immunocompromised patients and the elderly.

A Heterodimeric Antibody Fragment for Passive Immunotherapy Against Norovirus Infection

Human noroviruses cause an estimated 685 million infections and 200 000 deaths annually worldwide. Although vaccines against GII.4 and GI.1 genotypes are under development, no information is available regarding vaccines or monoclonal antibodies to other noroviral genotypes. Here, we developed 2 variable-domain llama heavy-chain antibody fragment (VHHs) clones, 7C6 and 1E4, against GII.4 and GII.17 human noroviruses, respectively. Although 7C6 cross-reacted with virus-like particles (VLPs) of GII.17, GII.6, GII.3, and GII.4, it neutralized only GII.4 norovirus. In contrast, 1E4 reacted with and neutralized only GII.17 VLPs. Both VHHs blocked VLP binding to human induced pluripotent stem cell-derived intestinal epithelial cells and carbohydrate attachment factors. Using these 2 VHHs, we produced a heterodimeric VHH fragment that neutralized both GII.4 and GII.17 noroviruses. Because VHH fragments are heat- and acid-stable recombinant monoclonal antibodies, the heterodimer likely will be useful for oral immunotherapy and prophylaxis against GII.4 and GII.17 noroviruses in young, elderly, or immunocompromised persons.

Anti-CfaE nanobodies provide broad cross-protection against major pathogenic enterotoxigenic Escherichia coli strains, with implications for vaccine design

Enterotoxigenic Escherichia coli (ETEC) is estimated to cause approximately 380,000 deaths annually during sporadic or epidemic outbreaks worldwide. Development of vaccines against ETEC is very challenging due to the vast heterogeneity of the ETEC strains. An effective vaccines would have to be multicomponent to provide coverage of over ten ETEC strains with genetic variabilities. There is currently no vaccine licensed to prevent ETEC. Nanobodies are successful new biologics in treating mucosal infectious disease as they recognize conserved epitopes on hypervariable pathogens. Cocktails consisting of multiple nanobodies could provide even broader epitope coverage at a lower cost compared to monoclonal antibodies. Identification of conserved epitopes by nanobodies can also assist reverse engineering of an effective vaccine against ETEC. By screening nanobodies from immunized llamas and a naïve yeast display library against adhesins of colonization factors, we identified single nanobodies that show cross-protective potency against eleven major pathogenic ETEC strains in vitro. Oral administration of nanobodies led to a significant reduction of bacterial colonization in animals. Moreover, nanobody-IgA fusion showed extended inhibitory activity in mouse colonization compared to commercial hyperimmune bovine colostrum product used for prevention of ETEC-induced diarrhea. Structural analysis revealed that nanobodies recognized a highly-conserved epitope within the putative receptor binding region of ETEC adhesins. Our findings support further rational design of a pan-ETEC vaccine to elicit robust immune responses targeting this conserved epitope.

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.

Inhibition of invasive salmonella by orally administered IgA and IgG monoclonal antibodies

Non-typhoidal Salmonella enterica strains, including serovar Typhimurium (STm), are an emerging cause of invasive disease among children and the immunocompromised, especially in regions of sub-Saharan Africa. STm invades the intestinal mucosa through Peyer's patch tissues before disseminating systemically. While vaccine development efforts are ongoing, the emergence of multidrug resistant strains of STm affirms the need to seek alternative strategies to protect high-risk individuals from infection. In this report, we investigated the potential of an orally administered O5 serotype-specific IgA monoclonal antibody (mAb), called Sal4, to prevent infection of invasive Salmonella enterica serovar Typhimurium (STm) in mice. Sal4 IgA was delivered to mice prior to or concurrently with STm challenge. Infectivity was measured as bacterial burden in Peyer's patch tissues one day after challenge. Using this model, we defined the minimal amount of Sal4 IgA required to significantly reduce STm uptake into Peyer's patches. The relative efficacy of Sal4 in dimeric and secretory IgA (SIgA) forms was compared. To assess the role of isotype in oral passive immunization, we engineered a recombinant IgG1 mAb carrying the Sal4 variable regions and evaluated its ability to block invasion of STm into epithelial cells in vitro and Peyer's patch tissues. Our results demonstrate the potential of orally administered monoclonal IgA and SIgA, but not IgG, to passively immunize against invasive Salmonella. Nonetheless, the prophylactic window of IgA/SIgA in the mouse was on the order of minutes, underscoring the need to develop formulations to protect mAbs in the gastric environment and to permit sustained release in the small intestine.

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.

A nanobody targeting the translocated intimin receptor inhibits the attachment of enterohemorrhagic E. coli to human colonic mucosa

Enterohemorrhagic E. coli (EHEC) is a human intestinal pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome. No vaccines or specific therapies are currently available to prevent or treat these infections. EHEC tightly attaches to the intestinal epithelium by injecting the intimin receptor Tir into the host cell via a type III secretion system (T3SS). In this project, we identified a camelid single domain antibody (nanobody), named TD4, that recognizes a conserved Tir epitope overlapping the binding site of its natural ligand intimin with high affinity and stability. We show that TD4 inhibits attachment of EHEC to cultured human HeLa cells by preventing Tir clustering by intimin, activation of downstream actin polymerization and pedestal formation. Furthermore, we demonstrate that TD4 significantly reduces EHEC adherence to human colonic mucosa in in vitro organ cultures. Altogether, these results suggest that nanobody-based therapies hold potential in the development of much needed treatment and prevention strategies against EHEC infection.

Currently, there is no effective treatment or vaccine against enterohemorrhagic E. coli (EHEC), a bacterial pathogen that infects human colon after the ingestion of contaminated food. It thrives in the colon thanks to its ability to attach intimately to the intestinal epithelium. Here, we have identified and characterised a small antibody fragment (nanobody) that recognises Tir, a receptor injected by the bacterium into the host cell to mediate intimate attachment. This nanobody shows higher affinity against Tir than its natural bacterial ligand (intimin) and, most importantly, blocks the intimate attachment of the pathogen to the human colonic tissue. Our results show the potential of this nanobody to prevent and treat EHEC infection.

Plant-Made Antibodies: Properties and Therapeutic Applications

BACKGROUND

A cost-effective plant platform for therapeutic monoclonal antibody production is both flexible and scalable. Plant cells have mechanisms for protein synthesis and posttranslational modification, including glycosylation, similar to those in animal cells. However, plants produce less complex and diverse Asn-attached glycans compared to animal cells and contain plant-specific residues. Nevertheless, plant-made antibodies (PMAbs) could be advantageous compared to those produced in animal cells due to the absence of a risk of contamination from nucleic acids or proteins of animal origin.

OBJECTIVE

In this review, the various platforms of PMAbs production are described, and the widely used transient expression system based on Agrobacterium-mediated delivery of genetic material into plant cells is discussed in detail.

RESULTS

We examined the features of and approaches to humanizing the Asn-linked glycan of PMAbs. The prospects for PMAbs in the prevention and treatment of human infectious diseases have been illustrated by promising results with PMAbs against human immunodeficiency virus, rotavirus infection, human respiratory syncytial virus, rabies, anthrax and Ebola virus. The pre-clinical and clinical trials of PMAbs against different types of cancer, including lymphoma and breast cancer, are addressed.

CONCLUSION

PMAb biosafety assessments in patients suggest that it has no side effects, although this does not completely remove concerns about the potential immunogenicity of some plant glycans in humans. Several PMAbs at various developmental stages have been proposed. Promise for the clinical use of PMAbs is aimed at the treatment of viral and bacterial infections as well as in anti-cancer treatment.

The Antigenic Topology of Norovirus as Defined by B and T Cell Epitope Mapping: Implications for Universal Vaccines and Therapeutics

Human norovirus (HuNoV) is the leading cause of acute nonbacterial gastroenteritis. Vaccine design has been confounded by the antigenic diversity of these viruses and a limited understanding of protective immunity. We reviewed 77 articles published since 1988 describing the isolation, function, and mapping of 307 unique monoclonal antibodies directed against B cell epitopes of human and murine noroviruses representing diverse Genogroups (G). Of these antibodies, 91, 153, 21, and 42 were reported as GI-specific, GII-specific, MNV GV-specific, and G cross-reactive, respectively. Our goal was to reconstruct the antigenic topology of noroviruses in relationship to mapped epitopes with potential for therapeutic use or inclusion in universal vaccines. Furthermore, we reviewed seven published studies of norovirus T cell epitopes that identified 18 unique peptide sequences with CD4- or CD8-stimulating activity. Both the protruding (P) and shell (S) domains of the major capsid protein VP1 contained B and T cell epitopes, with the majority of neutralizing and HBGA-blocking B cell epitopes mapping in or proximal to the surface-exposed P2 region of the P domain. The majority of broadly reactive B and T cell epitopes mapped to the S and P1 arm of the P domain. Taken together, this atlas of mapped B and T cell epitopes offers insight into the promises and challenges of designing universal vaccines and immunotherapy for the noroviruses.

Therapeutics and Immunoprophylaxis Against Noroviruses and Rotaviruses: The Past, Present, and Future

Background:

Noroviruses and rotaviruses are important viral etiologies of severe gastroenteritis. Noroviruses are the primary cause of nonbacterial diarrheal outbreaks in humans, whilst rotaviruses are a major cause of childhood diarrhea. Although both enteric pathogens substantially impact human health and economies, there are no approved drugs against noroviruses and rotaviruses so far. On the other hand, whilst the currently licensed rotavirus vaccines have been successfully implemented in over 100 countries, the most advanced norovirus vaccine has recently completed phase-I and II trials.

Methods:

We performed a structured search of bibliographic databases for peer-reviewed research litera-ture on advances in the fields of norovirus and rotavirus therapeutics and immunoprophylaxis.

Results:

Technological advances coupled with a proper understanding of viral morphology and replication over the past decade has facilitated pioneering research on therapeutics and immunoprophylaxis against noroviruses and rotaviruses, with promising outcomes in human clinical trials of some of the drugs and vaccines. This review focuses on the various developments in the fields of norovirus and rotavirus thera-peutics and immunoprophylaxis, such as potential antiviral drug molecules, passive immunotherapies (oral human immunoglobulins, egg yolk and bovine colostral antibodies, llama-derived nanobodies, and anti-bodies expressed in probiotics, plants, rice grains and insect larvae), immune system modulators, probiot-ics, phytochemicals and other biological substances such as bovine milk proteins, therapeutic nanoparti-cles, hydrogels and viscogens, conventional viral vaccines (live and inactivated whole virus vaccines), and genetically engineered viral vaccines (reassortant viral particles, virus-like particles (VLPs) and other sub-unit recombinant vaccines including multi-valent viral vaccines, edible plant vaccines, and encapsulated viral particles).

Conclusions:

This review provides important insights into the various approaches to therapeutics and im-munoprophylaxis against noroviruses and rotaviruses..

Viral gastroenteritis

Enteric viruses, particularly rotaviruses and noroviruses, are a leading cause of gastroenteritis worldwide. Rotaviruses primarily affect young children, accounting for almost 40% of hospital admissions for diarrhoea and 200 000 deaths worldwide, with the majority of deaths occurring in developing countries. Two vaccines against rotavirus were licensed in 2006 and have been implemented in 95 countries as of April, 2018. Data from eight high-income and middle-income countries showed a 49-89% decline in rotavirus-associated hospital admissions and a 17-55% decline in all-cause gastroenteritis-associated hospital admissions among children younger than 5 years, within 2 years of vaccine introduction. Noroviruses affect people of all ages, and are a leading cause of foodborne disease and outbreaks of gastroenteritis worldwide. Prevention of norovirus infection relies on frequent hand hygiene, limiting contact with people who are infected with the virus, and disinfection of contaminated environmental surfaces. Norovirus vaccine candidates are in clinical trials; whether vaccines will provide durable protection against the range of genetically and antigenically diverse norovirus strains remains unknown. Treatment of viral gastroenteritis is based primarily on replacement of fluid and electrolytes.

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.

Single-Domain Antibodies As Therapeutics against Human Viral Diseases

In full-size formats, monoclonal antibodies have been highly successful as therapeutics against cancer and immune diseases. However, their large size leads to inaccessibility of some epitopes and relatively high production costs. As an alternative, single-domain antibodies (sdAbs) offer special advantages compared to full-size antibodies, including smaller size, larger number of accessible epitopes, relatively low production costs and improved robustness. Currently, sdAbs are being developed against a number of viruses, including human immunodeficiency virus-1 (HIV-1), influenza viruses, hepatitis C virus (HCV), respiratory syncytial virus (RSV), and enteric viruses. Although sdAbs are very potent inhibitors of viral infections, no sdAbs have been approved for clinical use against virial infection or any other diseases. In this review, we discuss the current state of research on sdAbs against viruses and their potential as therapeutics against human viral diseases.

Oral Administration of a Seed-based Bivalent Rotavirus Vaccine Containing VP6 and NSP4 Induces Specific Immune Responses in Mice

Rotavirus is the leading cause of severe diarrheal disease among newborns. Plant-based rotavirus vaccines have been developed in recent years and have been proven to be effective in animal models. In the present study, we report a bivalent vaccine candidate expressing rotavirus subunits VP6 and NSP4 fused with the adjuvant subunit B of E. coli heat-labile enterotoxin (LTB) in maize seeds. The RT-PCR and Western blot results showed that VP6 and LTB-NSP4 antigens were expressed and accumulated in maize seeds. The expression levels were as high as 0.35 and 0.20% of the total soluble protein for VP6 and LTB-NSP4, respectively. Oral administration of transgenic maize seeds successfully stimulated systemic and mucosal responses, with high titers of serum IgG and mucosal IgA antibodies, even after long-term storage. This study is the first to use maize seeds as efficient generators for the development of a bivalent vaccine against rotavirus.

Optimizing antibody expression: The nuts and bolts

Antibodies are extensively utilized entities in biomedical research, and in the development of diagnostics and therapeutics. Many of these applications require high amounts of antibodies. However, meeting this ever-increasing demand of antibodies in the global market is one of the outstanding challenges. The need to maintain a balance between demand and supply of antibodies has led the researchers to discover better means and methods for optimizing their expression. These strategies aim to increase the volumetric productivity of the antibodies along with the reduction of associated manufacturing costs. Recent years have witnessed major advances in recombinant protein technology, owing to the introduction of novel cloning strategies, gene manipulation techniques, and an array of cell and vector engineering techniques, together with the progress in fermentation technologies. These innovations were also highly beneficial for antibody expression. Antibody expression depends upon the complex interplay of multiple factors that may require fine tuning at diverse levels to achieve maximum yields. However, each antibody is unique and requires individual consideration and customization for optimizing the associated expression parameters. This review provides a comprehensive overview of several state-of-the-art approaches, such as host selection, strain engineering, codon optimization, gene optimization, vector modification and process optimization that are deemed suitable for enhancing antibody expression.

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.

Anti-VP6 VHH: An Experimental Treatment for Rotavirus A-Associated Disease

Species A Rotaviruses (RVA) remain a leading cause of mortality in children under 5 years of age. Current treatment options are limited. We assessed the efficacy of two VP6-specific llama-derived heavy chain antibody fragments (VHH) -2KD1 and 3B2- as an oral prophylactic and therapeutic treatment against RVA-induced diarrhea in a neonatal mouse model inoculated with virulent murine RVA (ECw, G16P[16]I7). Joint therapeutic administration of 2KD1+3B2 (200 μg/dose) successfully reduced diarrhea duration, RVA infection severity and virus shedding in feces. While the same dose of 2KD1 or 3B2 (200 μg) significantly reduced duration of RVA-induced diarrhea, 2KD1 was more effective in diminishing the severity of intestinal infection and RVA shedding in feces, perhaps because 2KD1 presented higher binding affinity for RVA particles than 3B2. Neither prophylactic nor therapeutic administration of the VHH interfered with the host's humoral immune response against RVA. When 2KD1 (200 μg) was administered after diarrhea development, it also significantly reduced RVA intestinal infection and fecal shedding. Host antibody responses against the oral VHH treatment were not detected, nor did viral escape mutants. Our findings show that oral administration of anti-VP6 VHH constitute, not only an effective prophylactic treatment against RVA-associated diarrhea, but also a safe therapeutic tool against RVA infection, even once diarrhea is present. Anti-VP6 VHH could be used complementary to ongoing vaccination, especially in populations that have shown lower immunization efficacy. These VHH could also be scaled-up to develop pediatric medication or functional food like infant milk formulas that might help treat RVA diarrhea.

Biomanufacturing of protective antibodies and other therapeutics in edible plant tissues for oral applications

Although plant expression systems used for production of therapeutic proteins have the advantage of being scalable at a low price, the downstream processing necessary to obtain pure therapeutic molecules is as expensive as for the traditional Chinese hamster ovary (CHO) platforms. However, when edible plant tissues (EPTs) are used, there is no need for exhaustive purification, because they can be delivered orally as partially purified formulations that are safe for consumption. This economic benefit is especially interesting when high doses of recombinant proteins are required throughout the treatment/prophylaxis period, as is the case for antibodies used for oral passive immunization (OPI). The secretory IgA (SIgA) antibodies, which are highly abundant in the digestive tract and mucosal secretions, and thus the first choice for OPI, have only been successfully produced in plant expression systems. Here, we cover most of the up-to-date examples of EPT-produced pharmaceuticals, including two examples of SIgA aimed at oral delivery. We describe the benefits and drawbacks of delivering partially purified formulations and discuss a number of practical considerations and criteria to take into account when using plant expression systems, such as subcellular targeting, protein degradation, glycosylation patterns and downstream strategies, all crucial for improved yield, high quality and low cost of the final product.

Fusion of the mouse IgG1 Fc domain to the VHH fragment (ARP1) enhances protection in a mouse model of rotavirus

A variable fragment of a heavy chain antibody (VHH) directed against rotavirus, also referred to as anti-rotavirus protein 1 (ARP1), was shown to confer protection against rotavirus induced diarrhea in infant mouse model of rotavirus induced diarrhea. In this study, we have fused the mouse IgG1 Fc to ARP1 to improve the protective capacity of ARP1 by inducing an Fc-mediated effector function. We have shown that the Fc-ARP1 fusion protein confers significantly increased protection against rotavirus in a neonatal mouse model of rotavirus-induced diarrhea by reducing the prevalence, duration and severity of diarrhea and the viral load in the small intestines, suggesting that the Fc part of immunoglobulins may be engaged in Fc-mediated neutralization of rotavirus. Engineered conventional-like antibodies, by fusion of the Fc part of immunoglobulins to antigen-specific heavy-chain only VHH fragments, might be applied to novel antibody-based therapeutic approaches to enhance elimination of pathogens by activation of distinct effector signaling pathways.

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.

Potent In Vitro and In Vivo Activity of Plantibody Specific for Porphyromonas gingivalis FimA

Fimbrial protein fimbrillin (FimA), a major structural subunit of Porphyromonas gingivalis, has been suggested as a vaccine candidate to control P. gingivalis-induced periodontal disease. Previously, cDNAs encoding IgG monoclonal antibodies (MAbs) against purified FimA from P. gingivalis 2561 have been cloned, and the MAbs have been produced in rice cell suspension. Here we examined the biological activities of the plant-produced MAb specific for FimA (anti-FimA plantibody) of P. gingivalis in vitro and in vivo. The anti-FimA plantibody recognized oligomeric/polymeric forms of native FimA in immunoblot analysis and showed high affinity for native FimA (KD = 0.11 nM). Binding of P. gingivalis (10(8) cells) to 2 mg of saliva-coated hydroxyapatite beads was reduced by 53.8% in the presence of 1 μg/ml plantibody. Anti-FimA plantibody (10 μg/ml) reduced invasion of periodontal ligament cells by P. gingivalis (multiplicity of infection, 100) by 68.3%. Intracellular killing of P. gingivalis opsonized with the anti-FimA plantibody by mouse macrophages was significantly increased (77.1%) compared to killing of bacterial cells with irrelevant IgG (36.7%). In a mouse subcutaneous chamber model, the number of recoverable P. gingivalis cells from the chamber fluid was significantly reduced when the numbers of bacterial cells opsonized with anti-FimA plantibody were compared with the numbers of bacterial cells with irrelevant IgG, 66.7% and 37.1%, respectively. These in vitro and in vivo effects of anti-FimA plantibody were comparable to those of the parental MAb. Further studies with P. gingivalis strains with different types of fimbriae are needed to investigate the usefulness of anti-FimA plantibody for passive immunization to control P. gingivalis-induced periodontal disease.

Extraction and purification methods in downstream processing of plant-based recombinant proteins

During the last two decades, the production of recombinant proteins in plant systems has been receiving increased attention. Currently, proteins are considered as the most important biopharmaceuticals. However, high costs and problems with scaling up the purification and isolation processes make the production of plant-based recombinant proteins a challenging task. This paper presents a summary of the information regarding the downstream processing in plant systems and provides a comprehensible overview of its key steps, such as extraction and purification. To highlight the recent progress, mainly new developments in the downstream technology have been chosen. Furthermore, besides most popular techniques, alternative methods have been described.

Controlling Rotavirus-associated diarrhea: Could single-domain antibody fragments make the difference?

Group A Rotavirus (RVA) remains a leading cause of severe diarrhea and child mortality. The variable domain of camelid heavy chain antibodies (VHH) display potent antigen-binding capacity, have low production costs and are suitable for oral therapies. Two sets of anti-RVA VHHs have been developed: ARP1-ARP3; 2KD1-3B2. Here, we explore the potential of both sets as a prevention strategy complementary to vaccination and a treatment option against RVA-associated diarrhea in endangered populations. Both sets have been expressed in multiple production systems, showing extensive neutralizing capacity against strains of RVA in vitro. They were also tested in the neonatal mouse model with various degrees of success in preventing or treating RVA-induced diarrhea. Interestingly, mitigation of the symptoms was also achieved with freeze-dried ARP1, so that it could be applied in areas where cold chains are difficult to maintain. 3B2 was tested in a pre-clinical trial involving gnotobiotic piglets where it conferred complete protection against RVA-induced diarrhea. ARP1 was used in the first clinical trial for anti-RVA VHHs, successfully reducing stool output in infants with RVA diarrhea, with no detected side effects.

Recombinant antibody production evolves into multiple options aimed at yielding reagents suitable for application-specific needs

BACKGROUND

Antibodies have been a pillar of basic research, while their relevance in clinical diagnostics and therapy is constantly growing. Consequently, the production of both conventional and fragment antibodies constantly faces more demanding challenges for the improvement of their quantity and quality. The answer to such an increasing need has been the development of a wide array of formats and alternative production platforms. This review offers a critical comparison and evaluation of the different options to help the researchers interested in expressing recombinant antibodies in their choice.

RESULTS

Rather than the compilation of an exhaustive list of the recent publications in the field, this review intendeds to analyze the development of the most innovative or fast-growing strategies. These have been illustrated with some significant examples and, when possible, compared with the existing alternatives. Space has also been given to those solutions that might represent interesting opportunities or that investigate critical aspects of the production optimization but for which the available data as yet do not allow for a definitive judgment.

CONCLUSIONS

The take-home message is that there is a clear process of progressive diversification concerning the antibody expression platforms and an effort to yield directly application-adapted immune-reagents rather than generic naked antibodies that need further in vitro modification steps before becoming usable.

Delivery strategies to enhance oral vaccination against enteric infections

While the majority of human pathogens infect the body through mucosal sites, most licensed vaccines are injectable. In fact the only mucosal vaccine that has been widely used globally for infant and childhood vaccination programs is the oral polio vaccine (OPV) developed by Albert Sabin in the 1950s. While oral vaccines against Cholera, rotavirus and Salmonella typhi have also been licensed, the development of additional non-living oral vaccines against these and other enteric pathogens has been slow and challenging. Mucosal vaccines can elicit protective immunity at the gut mucosa, in part via antigen-specific secretory immunoglobulin A (SIgA). However, despite their advantages over the injectable route, oral vaccines face many hurdles. A key challenge lies in design of delivery strategies that can protect antigens from degradation in the stomach and intestine, incorporate appropriate immune-stimulatory adjuvants and control release at the appropriate gastrointestinal site. A number of systems including micro and nanoparticles, lipid-based strategies and enteric capsules have significant potential either alone or in advanced combined formulations to enhance intestinal immune responses. In this review we will outline the opportunities, challenges and potential delivery solutions to facilitate the development of improved oral vaccines for infectious enteric diseases.

Llama nanoantibodies with therapeutic potential against human norovirus diarrhea

Noroviruses are a major cause of acute gastroenteritis, but no vaccines or therapeutic drugs are available. Llama-derived single chain antibody fragments (also called VHH) are small, recombinant monoclonal antibodies of 15 kDa with several advantages over conventional antibodies. The aim of this study was to generate recombinant monoclonal VHH specific for the two major norovirus (NoV) genogroups (GI and GII) in order to investigate their potential as immunotherapy for the treatment of NoV diarrhea. To accomplish this objective, two llamas were immunized with either GI.1 (Norwalk-1968) or GII.4 (MD2004) VLPs. After immunization, peripheral blood lymphocytes were collected and used to generate two VHH libraries. Using phage display technology, 10 VHH clones specific for GI.1, and 8 specific for GII.4 were selected for further characterization. All VHH recognized conformational epitopes in the P domain of the immunizing VP1 capsid protein, with the exception of one GII.4 VHH that recognized a linear P domain epitope. The GI.1 VHHs were highly specific for the immunizing GI.1 genotype, with only one VHH cross-reacting with GI.3 genotype. The GII.4 VHHs reacted with the immunizing GII.4 strain and showed a varying reactivity profile among different GII genotypes. One VHH specific for GI.1 and three specific for GII.4 could block the binding of homologous VLPs to synthetic HBGA carbohydrates, saliva, and pig gastric mucin, and in addition, could inhibit the hemagglutination of red blood cells by homologous VLPs. The ability of Nov-specific VHHs to perform well in these surrogate neutralization assays supports their further development as immunotherapy for NoV treatment and immunoprophylaxis.

Camelid nanobodies with high affinity for broad bean mottle virus: a possible promising tool to immunomodulate plant resistance against viruses

Worldwide, plant viral infections decrease seriously the crop production yield, boosting the demand to develop new strategies to control viral diseases. One of these strategies to prevent viral infections, based on the immunomodulation faces many problems related to the ectopic expression of specific antibodies in planta. Camelid nanobodies, expressed in plants, may offer a solution as they are an attractive tool to bind efficiently to viral epitopes, cryptic or not accessible to conventional antibodies. Here, we report a novel, generic approach that might lead to virus resistance based on the expression of camelid specific nanobodies against Broad bean mottle virus (BBMV). Eight nanobodies, recognizing BBMV with high specificity and affinity, were retrieved after phage display from a large 'immune' library constructed from an immunized Arabic camel. By an in vitro assay we demonstrate how three nanobodies attenuate the BBMV spreading in inoculated Vicia faba plants. Furthermore, the in planta transient expression of these three selected nanobodies confirms their virus neutralizing capacity. In conclusion, this report supports that plant resistance against viral infections can be achieved by the in vivo expression of camelid nanobodies.

Next biotech plants: new traits, crops, developers and technologies for addressing global challenges

Most of the genetically modified (GM) plants currently commercialized encompass a handful of crop species (soybean, corn, cotton and canola) with agronomic characters (traits) directed against some biotic stresses (pest resistance, herbicide tolerance or both) and created by multinational companies. The same crops with agronomic traits already on the market today will continue to be commercialized, but there will be also a wider range of species with combined traits. The timeframe anticipated for market release of the next biotech plants will not only depend on science progress in research and development (R&D) in laboratories and fields, but also primarily on how demanding regulatory requirements are in countries where marketing approvals are pending. Regulatory constraints, including environmental and health impact assessments, have increased significantly in the past decades, delaying approvals and increasing their costs. This has sometimes discouraged public research entities and small and medium size plant breeding companies from using biotechnology and given preference to other technologies, not as stringently regulated. Nevertheless, R&D programs are flourishing in developing countries, boosted by the necessity to meet the global challenges that are food security of a booming world population while mitigating climate change impacts. Biotechnology is an instrument at the service of these imperatives and a wide variety of plants are currently tested for their high yield despite biotic and abiotic stresses. Many plants with higher water or nitrogen use efficiency, tolerant to cold, salinity or water submergence are being developed. Food security is not only a question of quantity but also of quality of agricultural and food products, to be available and accessible for the ones who need it the most. Many biotech plants (especially staple food) are therefore being developed with nutritional traits, such as biofortification in vitamins and metals. The main international seed companies continue to be the largest investors in plant biotechnology R&D, and often collaborate in the developing world with public institutions, private entities and philanthropic organizations. These partnerships are particularly present in Africa. In developed countries, plant biotechnology is also used for non-food purposes, such as the pharmaceutical, biofuel, starch, paper and textile industries. For example, plants are modified to specifically produce molecules with therapeutic uses, or with an improved biomass conversion efficiency, or producing larger volumes of feedstocks for biofuels. Various plant breeding technologies are now used in the entire spectrum of plant biotechnology: transgenesis producing proteins or RNAi. Cisgenesis (transgenes isolated from a crossable donor plant) and intragenesis (transgenes originate from the same species or a crossable species), null segregants are also used. To date, the next generation precision gene editing tools are developed in basic research. They include: clustered regularly interspaced short palindromic repeats (CRISPR), oligonucleotide-directed mutagenesis (ODM), transcription activator-like effects nucleases (TALENs) and zinc-finger nuclease (ZFN).

Recent developments in therapeutic protein expression technologies in plants

Infectious diseases and cancers are some of the commonest causes of deaths throughout the world. The previous two decades have witnessed a combined endeavor across various biological sciences to address this issue in novel ways. The advent of recombinant DNA technologies has provided the tools for producing recombinant proteins that can be used as therapeutic agents. A number of expression systems have been developed for the production of pharmaceutical products. Recently, advances have been made using plants as bioreactors to produce therapeutic proteins directed against infectious diseases and cancers. This review highlights the recent progress in therapeutic protein expression in plants (stable and transient), the factors affecting heterologous protein expression, vector systems and recent developments in existing technologies and steps towards the industrial production of plant-made vaccines, antibodies, and biopharmaceuticals.

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.

The mucosal immune system: From dentistry to vaccine development

The oral cavity is the beginning of the aero-digestive tract, which is covered by mucosal epithelium continuously under the threat of invasion of pathogens, it is thus protected by the mucosal immune system. In the early phase of our scientific efforts for the demonstration of mucosal immune system, dental science was one of major driving forces due to their foreseeability to use oral immunity for the control of oral diseases. The mucosal immune system is divided functionally into, but interconnected inductive and effector sites. Intestinal Peyer's patches (PPs) are an inductive site containing antigen-sampling M cells and immunocompetent cells required to initiate antigen-specific immune responses. At effector sites, PP-originated antigen-specific IgA B cells become plasma cells to produce polymeric IgA and form secretory IgA by binding to poly-Ig receptor expressed on epithelial cells for protective immunity. The development of new-generation mucosal vaccines, including the rice-based oral vaccine MucoRice, on the basis of the coordinated mucosal immune system is a promising strategy for the control of mucosal infectious diseases.