Expression of a cholera toxin B subunit-neutralizing epitope of the porcine epidemic diarrhea virus fusion gene in transgenic lettuce (Lactuca sativa L.)

The immunogenicity of plant-based COE-GCN4pII protein in pigs against the highly virulent porcine epidemic diarrhea virus strain from genotype 2

Porcine epidemic diarrhea virus (PEDV) is a serious infectious causative agent in swine, especially in neonatal piglets. PEDV genotype 2 (G2) strains, particularly G2a, were the primary causes of porcine epidemic diarrhea (PED) outbreaks in Vietnam. Here, we produced a plant-based CO-26K-equivalent epitope (COE) variant from a Vietnamese highly virulent PEDV strain belonging to genotype 2a (COE/G2a) and evaluated the protective efficacy of COE/G2a-GCN4pII protein (COE/G2a-pII) in piglets against the highly virulent PEDV G2a strain following passive immunity. The 5-day-old piglets had high levels of PEDV-specific IgG antibodies, COE-IgA specific antibodies, neutralizing antibodies, and IFN-γ responses. After virulent challenge experiments, all of these piglets survived and had normal clinical symptoms, no watery diarrhea in feces, and an increase in their body weight, while all of the negative control piglets died. These results suggest that the COE/G2a-pII protein produced in plants can be developed as a promising vaccine candidate to protect piglets against PEDV G2a infection in Vietnam.

Evaluation of the Immunogenicity in Mice Orally Immunized with Recombinant Lactobacillus casei Expressing Porcine Epidemic Diarrhea Virus S1 Protein

Porcine epidemic diarrhea (PED), characterized by diarrhea, vomiting, and dehydration, is an acute enteric infectious disease of pigs. The disease is caused by porcine epidemic diarrhea virus (PEDV), which infects the intestinal mucosal surface. Therefore, mucosal immunization through the oral route is an effective method of immunization. Lactic acid bacteria, which are acid resistant and bile-salt resistant and improve mucosal immunity, are ideal carriers for oral vaccines. The S1 glycoprotein of PEDV mediates binding of the virus with cell receptors and induces neutralizing antibodies against the virus. Therefore, we reversely screened the recombinant strain pPG-SD-S1/Δupp ATCC 393 expressing PEDV S1 glycoprotein by Lactobacillus casei deficient in upp genotype (Δupp ATCC 393). Mice were orally immunized three times with the recombinant bacteria that had been identified for expression, and the changes of anti-PEDV IgG and secreted immunoglobulin A levels were observed over 70 days. The results indicated that the antibody levels notably increased after oral administration of recombinant bacteria. The detection of extracellular cytokines on the 42nd day after immunization indicated high levels of humoral and cellular immune responses in mice. The above results demonstrate that pPG-SD-S1/Δupp ATCC 393 has great potential as an oral vaccine against PEDV.

Producing Vaccines against Enveloped Viruses in Plants: Making the Impossible, Difficult

The past 30 years have seen the growth of plant molecular farming as an approach to the production of recombinant proteins for pharmaceutical and biotechnological uses. Much of this effort has focused on producing vaccine candidates against viral diseases, including those caused by enveloped viruses. These represent a particular challenge given the difficulties associated with expressing and purifying membrane-bound proteins and achieving correct assembly. Despite this, there have been notable successes both from a biochemical and a clinical perspective, with a number of clinical trials showing great promise. This review will explore the history and current status of plant-produced vaccine candidates against enveloped viruses to date, with a particular focus on virus-like particles (VLPs), which mimic authentic virus structures but do not contain infectious genetic material.

Plant-Derived Trimeric CO-26K-Equivalent Epitope Induced Neutralizing Antibodies Against Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDV) is a causative agent of a highly infectious disease with a high mortality rate, especially in newborn piglets in Asian countries resulting in serious economic loss. The development of a rapid, safe, effective and cost-efficient vaccine is crucial to protect pigs against PEDV infection. The COE antigen is regarded to be a major target for subunit vaccine development against PEDV infection. The naturally assembled COE protein forms a homotrimeric structure. In the present study, we successfully produced a trimeric COE protein as a native structure by fusion with the C-terminal isoleucine zipper trimerization (GCN4pII) motif in Nicotiana benthamiana, with a high expression level shown via semi-quantified Western blots. Trimeric COE protein was purified via immobilized metal affinity chromatography (IMAC), and its trimeric structure was successfully demonstrated by a cross-linking reaction, and a native PAGE gel. A crude extract containing the COE trimer was used for evaluating immunogenicity in mice. After 1 and 2 booster immunizations, the crude extract containing trimeric COE elicited elevated PEDV-specific humoral responses, as demonstrated by ELISA and Western blot analyses. Notably, a virus-neutralizing antibody assay indicated that the neutralization activities of sera of mice vaccinated with the crude extract containing COE-GCN4pII were similar to those of mice vaccinated with a commercial vaccine. These results suggest that crude extract containing trimeric COE is a promising plant-based subunit vaccine candidate for PEDV prevention.

Recombinant adenovirus carrying a core neutralizing epitope of porcine epidemic diarrhea virus and heat-labile enterotoxin B of Escherichia coli as a mucosal vaccine

Porcine epidemic diarrhea virus (PEDV) targets the intestinal mucosa in pigs. To protect against PEDV invasion, a mucosal vaccine is utilized effectively. In this study, we generated a recombinant adenovirus vaccine encoding the heat-labile enterotoxin B (LTB) and the core neutralizing epitope (COE) of PEDV (rAd-LTB-COE). The fusion protein LTB-COE was successfully expressed by the recombinant adenovirus in HEK293 cells, and the immunogenicity of the vaccine candidate was assessed in BALB/c mice and piglets. Three intramuscular or oral vaccinations with rAd-LTB-COE at two-week intervals induced robust humoral and mucosal immune responses. Moreover, a cell-mediated immune response was promoted in immunized mice, and the neutralizing antibody inhibited both the vaccine strain and the emerging PEDV isolate. Immunization experiments in piglets revealed that rAd-LTB-COE was immunogenic and induced good immune responses in piglets. Further studies are required to evaluate the efficacy of rAd-LTB-COE against a highly virulent PEDV challenge.

Improved expression of porcine epidemic diarrhea antigen by fusion with cholera toxin B subunit and chloroplast transformation in Nicotiana tabacum

The porcine epidemic diarrhea virus (PEDV) belongs to the coronavirus family, which causes acute diarrhea in pigs with higher mortality in piglets less than 2 weeks old. The PEDV is one of the major concerns of the pig industry around the world, including Asian countries and Noth America since first identified in Europe. Currently, there is no PEDV licensed vaccine to effectively prevent this disease. This study was performed for the development of a mucosal PEDV vaccine and B subunit of cholera toxin (CTB) as a carrier was employed to surpass the tolerogenic nature of GALT and induce potent immune responses against the target antigen fused to CTB. An epitope (S1D) alone or conjugated with CTB was constructed into the tobacco chloroplasts expression vector which is controlled under the chloroplast rRNA operon promoter with T7g10 5' UTR and the psbA 3'UTR as a terminator. The homoplastomic lines were obtained by third round screening via organogenesis from the leaf tissues which were verified by PCR with antigen and chloroplast specific primers and then confirmed by Southern blot analysis. While the expression level of the S1D alone as detected by Western blotting was approximately 0.07% of total soluble protein, the CTB-S1D fusion protein was expressed up to 1.4%. The fusion protein showed binding to the intestinal membrane GM1-ganglioside receptor, demonstrating its functionality. The result shows that the highest expression of S1D could be achieved by fusion with a stable CTB protein and chloroplast transformation. Furthermore, the CTB-S1D expressed in chloroplasts of Nicotiana tabacum cv. Maryland could be assembled to pentameric form which increases the possibility to develop a mucosal vaccine against PEDV.

Porcine Epidemic Diarrhea Virus

Porcine epidemic diarrhea virus (PEDv) causes disease and mortality to piglets worldwide. Most vaccines used to combat the disease have been ineffective live attenuated virus vaccines. Research has emerged showing both the spike (S) and membrane (M) proteins of the virus have potential for use as subunit vaccines. This research has been largely undertaken using plants as expression platforms, with some promising candidates having emerged.

Oral Delivery of Probiotics Expressing Dendritic Cell-Targeting Peptide Fused with Porcine Epidemic Diarrhea Virus COE Antigen: A Promising Vaccine Strategy against PEDV

Porcine epidemic diarrhea virus (PEDV), an enteric coronavirus, is the causative agent of porcine epidemic diarrhea (PED) that damages intestinal epithelial cells and results in severe diarrhea and dehydration in neonatal suckling pigs with up to 100% mortality. The oral vaccine route is reported as a promising approach for inducing protective immunity against PEDV invasion. Furthermore, dendritic cells (DCs), professional antigen-presenting cells, link humoral and cellular immune responses for homeostasis of the intestinal immune environment. In this study, in order to explore an efficient oral vaccine against PEDV infection, a mucosal DC-targeting oral vaccine was developed using Lactobacillus casei to deliver the DC-targeting peptide (DCpep) fused with the PEDV core neutralizing epitope (COE) antigen. This probiotic vaccine could efficiently elicit secretory immunoglobulin A (SIgA)-based mucosal and immunoglobulin G (IgG)-based humoral immune responses via oral vaccination in vivo. Significant differences (p < 0.05) in the immune response levels were observed between probiotics expressing the COE-DCpep fusion protein and COE antigen alone, suggesting better immune efficiency of the probiotics vaccine expressing the DC-targeting peptide fused with PEDV COE antigen. This mucosal DC-targeting oral vaccine delivery effectively enhances vaccine antigen delivery efficiency, providing a useful strategy to induce efficient immune responses against PEDV infection.

Transformation of Lettuce with rol ABC Genes: Extracts Show Enhanced Antioxidant, Analgesic, Anti-Inflammatory, Antidepressant, and Anticoagulant Activities in Rats

Lettuce is an edible crop that is well known for dietary and antioxidant benefits. The present study was conducted to investigate the effects of rol ABC genes on antioxidant and medicinal potential of lettuce by Agrobacterium-mediated transformation. Transgene integration and expression was confirmed through PCR and real-time RT-PCR, respectively. The transformed plants showed 91-102 % increase in total phenolic contents and 53-65 % increase in total flavonoid contents compared to untransformed plants. Total antioxidant capacity and total reducing power increased up to 112 and 133 % in transformed plants, respectively. Results of DPPH assay showed maximum 51 % increase, and lipid peroxidation assay exhibited 20 % increase in antioxidant activity of transformed plants compared to controls. Different in vivo assays were carried out in rats. The transgenic plants showed up to 80 % inhibition in both hot plate analgesic assay and carrageenan-induced hind paw edema test, while untransformed plants showed only 45 % inhibition. Antidepressant and anticoagulant potential of transformed plants was also significantly enhanced compared to untransformed plants. Taken together, the present work highlights the use of rol genes to enhance the secondary metabolite production in lettuce and improve its analgesic, anti-inflammatory, antidepressant, and anticoagulatory properties.

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.

Immunogenicity of an S1D epitope from porcine epidemic diarrhea virus and cholera toxin B subunit fusion protein transiently expressed in infiltrated Nicotiana benthamiana leaves

Porcine epidemic diarrhea virus (PEDV) belongs to the Coronaviridae family and causes acute enteritis in pigs. A fragment of the large spike glycoprotein, termed the S1D epitope (aa 636-789), alone and fused with cholera toxin B subunit, were independently cloned into plant expression vectors, yielding plasmids pMYV717 and pMYV719, respectively. Plant expression vectors were transformed into Agrobacterium tumefaciens and subsequently infiltrated into Nicotiana benthamiana leaves. The highest expression level of S1D was found at 2 days post infiltration (dpi), reached 0.04 % of total soluble protein, and rapidly decreased thereafter. The expression and assembly of CTB-S1D fusion protein were confirmed by Western blot and GM1-ELISA. The highest expression level of CTB-S1D fusion protein was 0.07 % of TSP at 4 dpi, with a rapid decrease thereafter. In the presence of p19 protein from tomato bushy stunt virus, the S1D and CTB-S1D protein levels peaked at 6 dpi and were fourfold to sevenfold higher than in the absence of p19, respectively. After oral administration of transiently expressed CTB-S1D fusion protein, or with bacterial cholera toxin or rice callus expressing mutant cholera toxin 61F, mice exhibited significantly greater serum IgG and sIgA levels against bacterial CTB and S1D antigen, peaking at week 6. Transiently expressed CTB-S1D fusion protein will be administered orally to pigs to assess the immune response against PEDV.

Construction of a bivalent DNA vaccine co-expressing S genes of transmissible gastroenteritis virus and porcine epidemic diarrhea virus delivered by attenuated Salmonella typhimurium

Porcine transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) can cause severe diarrhea in newborn piglets and led to significant economic losses. The S proteins are the main structural proteins of PEDV and TGEV capable of inducing neutralizing antibodies in vivo. In this study, a DNA vaccine SL7207 (pVAXD-PS1-TS) co-expressing S proteins of TGEV and PEDV delivered by attenuated Salmonella typhimurium was constructed and its immunogenicity in piglets was investigated. Twenty-day-old piglets were orally immunized with SL7207 (pVAXD-PS1-TS) at a dosage of 1.6 × 10(11) CFU per piglet and then booster immunized with 2.0 × 10(11) CFU after 2 weeks. Humoral immune responses, as reflected by virus neutralizing antibodies and specific IgG and sIgA, and cellular immune responses, as reflected by IFN-γ, IL-4, and lymphocyte proliferation, were evaluated. SL7207 (pVAXD-PS1-TS) simultaneously elicited immune responses against TGEV and PEDV after oral immunization. The immune levels started to increase at 2 weeks after immunization and increased to levels statistically significantly different than controls at 4 weeks post-immunization, peaking at 6 weeks and declined at 8 weeks. The humoral, mucosal, and cellular immune responses induced by SL7207 (pAXD-PS1-TS) were significantly higher than those of the PBS and SL7207 (pVAXD) (p < 0.01). In particular, the levels of IFN-γ and IL-4 were higher than those induced by the single-gene vaccine SL7207 (pVAXD-PS1) (p < 0.05). These results demonstrated that SL7207 (pVAXD-PS1-TS) possess the immunological functions of the two S proteins of TGEV and PEDV, indicating that SL7207 (pVAXD-PS1-TS) is a candidate oral vaccine for TGE and PED.

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

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

Enhanced heterologous expression of biologically active human granulocyte colony stimulating factor in transgenic tobacco BY-2 cells by localization to endoplasmic reticulum

Tobacco Bright Yellow-2 (BY-2) cells, one of the best characterized cell lines is an attractive expression system for heterologous protein expression. However, the expression of foreign proteins is currently hampered by their low yield, which is partially the result of proteolytic degradation. Human granulocyte colony stimulating factor (hG-CSF) is a hematopoietic cytokine. Recombinant hG-CSF is successfully being used for the treatment of chemotherapy-induced neutropenia in cancer patients. Here, we describe a simple strategy for producing biologically active hG-CSF in tobacco BY-2 cells, localized in the apoplast of BY-2 cells, as well as targeted to the endoplasmic reticulum (ER). ER targeting significantly enhanced recombinant production which scaled to 17.89 mg/l from 4.19 mg/l when expressed in the apoplasts. Southern blotting confirmed the stable integration of hG-CSF in the BY-2 nuclear genome, and the expression of hG-CSF was analysed by Western blotting. Total soluble protein containing hG-CSF isolated from positive calli showed proliferative potential when tested on HL-60 cell lines by MTT assay. We also report the potential of a Fluorescence-activated cell sorting approach for an efficient sorting of the hG-CSF-expressing cell lines, which will enable the generation of homogenous high-producing cell lines.

Expression of cholera toxin B subunit-lumbrokinase in edible sunflower seeds-the use of transmucosal carrier to enhance its fusion protein's effect on protection of rats and mice against thrombosis

Lumbrokinase (LK) is a group of serine proteases with strong fibrinolytic and thrombolytic activities and is useful for treating diseases caused by thrombus. Cholera toxin B subunit (CTB) has been widely used to facilitate antigen delivery by serving as an effective mucosal carrier molecule for the induction of oral tolerance. We investigate here the application of CTB as a transmucosal carrier in enhancing its fusion protein-LKs effect to protect rats against thrombosis. Thus, in this study, CTB-LK fusion gene separated by a furin cleavage site was expressed in seeds of Helianthus annuus L. The activity of recombinant protein in seeds of transgenic sunflower was confirmed by Western blot analysis, fibrin plate assays and GM1 -ganglioside ELISA. The thrombosis model of rats and mice revealed that the oral administration of peeled seeds of sunflower expressing CTB-LK had a more significant anti-thrombotic effect on animals compared with that administration of peeled seeds of sunflower expressing LK. It is possible to conclude that CTB can successfully enhance its fusion protein to be absorbed in rats or mice thrombosis model. The use of CTB as a transmucosal carrier in the delivery of transgenic plant-derived oral therapeutic proteins was supported. In addition, for the purpose of that recombinant CTB-LK was designed for oral administration, thus the expression of CTB-LK in edible sunflower seeds eliminated the need for downstream processing of proteins.

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

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

Plant-derived pharmaceuticals for the developing world

Plant-produced vaccines and therapeutic agents offer enormous potential for providing relief to developing countries by reducing the incidence of infant mortality caused by infectious diseases. Vaccines derived from plants have been demonstrated to effectively elicit an immune response. Biopharmaceuticals produced in plants are inexpensive to produce, require fewer expensive purification steps, and can be stored at ambient temperatures for prolonged periods of time. As a result, plant-produced biopharmaceuticals have the potential to be more accessible to the rural poor. This review describes current progress with respect to plant-produced biopharmaceuticals, with a particular emphasis on those that target developing countries. Specific emphasis is given to recent research on the production of plant-produced vaccines toward human immunodeficiency virus, malaria, tuberculosis, hepatitis B virus, Ebola virus, human papillomavirus, rabies virus and common diarrheal diseases. Production platforms used to express vaccines in plants, including nuclear and chloroplast transformation, and the use of viral expression vectors, are described in this review. The review concludes by outlining the next steps for plant-produced vaccines to achieve their goal of providing safe, efficacious and inexpensive vaccines to the developing world.

Recent advances and safety issues of transgenic plant-derived vaccines

Transgenic plant-derived vaccines comprise a new type of bioreactor that combines plant genetic engineering technology with an organism's immunological response. This combination can be considered as a bioreactor that is produced by introducing foreign genes into plants that elicit special immunogenicity when introduced into animals or human beings. In comparison with traditional vaccines, plant vaccines have some significant advantages, such as low cost, greater safety, and greater effectiveness. In a number of recent studies, antigen-specific proteins have been successfully expressed in various plant tissues and have even been tested in animals and human beings. Therefore, edible vaccines of transgenic plants have a bright future. This review begins with a discussion of the immune mechanism and expression systems for transgenic plant vaccines. Then, current advances in different transgenic plant vaccines will be analyzed, including vaccines against pathogenic viruses, bacteria, and eukaryotic parasites. In view of the low expression levels for antigens in plants, high-level expression strategies of foreign protein in transgenic plants are recommended. Finally, the existing safety problems in transgenic plant vaccines were put forward will be discussed along with a number of appropriate solutions that will hopefully lead to future clinical application of edible plant vaccines.

Rapid and scalable plant-based production of a cholera toxin B subunit variant to aid in mass vaccination against cholera outbreaks

INTRODUCTION

Cholera toxin B subunit (CTB) is a component of an internationally licensed oral cholera vaccine. The protein induces neutralizing antibodies against the holotoxin, the virulence factor responsible for severe diarrhea. A field clinical trial has suggested that the addition of CTB to killed whole-cell bacteria provides superior short-term protection to whole-cell-only vaccines; however, challenges in CTB biomanufacturing (i.e., cost and scale) hamper its implementation to mass vaccination in developing countries. To provide a potential solution to this issue, we developed a rapid, robust, and scalable CTB production system in plants.

METHODOLOGY/PRINCIPAL FINDINGS

In a preliminary study of expressing original CTB in transgenic Nicotiana benthamiana, the protein was N-glycosylated with plant-specific glycans. Thus, an aglycosylated CTB variant (pCTB) was created and overexpressed via a plant virus vector. Upon additional transgene engineering for retention in the endoplasmic reticulum and optimization of a secretory signal, the yield of pCTB was dramatically improved, reaching >1 g per kg of fresh leaf material. The protein was efficiently purified by simple two-step chromatography. The GM1-ganglioside binding capacity and conformational stability of pCTB were virtually identical to the bacteria-derived original B subunit, as demonstrated in competitive enzyme-linked immunosorbent assay, surface plasmon resonance, and fluorescence-based thermal shift assay. Mammalian cell surface-binding was corroborated by immunofluorescence and flow cytometry. pCTB exhibited strong oral immunogenicity in mice, inducing significant levels of CTB-specific intestinal antibodies that persisted over 6 months. Moreover, these antibodies effectively neutralized the cholera holotoxin in vitro.

CONCLUSIONS/SIGNIFICANCE

Taken together, these results demonstrated that pCTB has robust producibility in Nicotiana plants and retains most, if not all, of major biological activities of the original protein. This rapid and easily scalable system may enable the implementation of pCTB to mass vaccination against outbreaks, thereby providing better protection of high-risk populations in developing countries.

Construction of recombinant lactobacilli expressing the core neutralizing epitope (COE) of porcine epidemic diarrhea virus and a fusion protein consisting of COE and Escherichia coli heat-labile enterotoxin B, and comparison of the immune responses by orogastric immunization

The core neutralizing epitope (COE) region of porcine epidemic diarrhea virus (PEDV) plays an important role in the development of the subunit vaccine against PEDV infection. To enhance the vaccine's immunogenicity, Escherichia coli heat-labile enterotoxin B (LTB) has usually been adopted as a molecular adjuvant. In this study, the COE and LTB-COE genes were engineered into the Lactobacillus -Escherichia coli shuttle vectors pSAPG1 (surface-displaying) and pSAPG2 (secreting) followed by electrotransformation into Lactobacillus casei (Lc) to yield the following recombinant strains: Lc:PG1-LTB-COE, Lc:PG2-LTB-COE, Lc:PG1-COE, and Lc:PG2-COE. Our results showed that mice immunized orogastrically with L. casei expressing COE or LTB-COE produced secretory immunoglobulin A and immunoglobulin G with the ability to neutralize PEDV in sera and mucus. Moreover, higher levels of interleukin-4 and gamma interferon were also exhibited compared with negative control. These data displayed the tendency of Lc:PG2-LTB-COE > Lc:PG1-LTB-COE > Lc:PG2-COE > Lc:PG1-COE at the same time point. Taken together, LTB-COE is more suitable for Lactobacillus expressing system to engineer mucosal vaccine against PEDV infection.

Immunogenicity of a neutralizing epitope from porcine epidemic diarrhea virus: M cell targeting ligand fusion protein expressed in transgenic rice calli

To increase immune responses of plant-based vaccines in intestine mucosal immune systems, a synthetic neutralizing epitope (sCOE) gene of porcine epidemic diarrhea virus (PEDV) was fused with M cell-targeting ligand (Co1) and introduced into a plant expression vector under the control of rice amylase 3D promoter. The sCOE-Co1 fusion gene was introduced into rice calli via the particle bombardment-mediated transformation method. The stable integration and transcriptional expression of the sCOE-Co1 fusion gene was confirmed by genomic DNA PCR amplification and Northern blot analysis, respectively. The expression of the COE-Co1 fusion protein was confirmed by immunoblot analysis. The highest expression level of the COE-Co1 fusion protein reached 0.083 % of the total soluble protein according to quantitative densitometry of Western blot analysis. Mice immunized with transgenic rice calli protein extracts induced significant serum IgG and fecal IgA antibody levels against purified bacterial COE. The systemic and mucosal immune responses were confirmed by measuring COE-specific IgG and IgA antibody-secreting cells in the lymphocytes extracted from the spleen and COE-specific IgA antibody-secreting cells in the Peyer's patches from immunized mice. These results indicated that oral immunization of plant-produced COE-Co1 fusion protein could elicit efficient systemic and mucosal immune responses against the COE antigen. Key message Neutralizing epitope from porcine epidemic diarrhea virus-M cell targeting ligand fusion protein was produced in transgenic rice calli and elicited systemic and mucosal immune responses by oral administration in mice.

The use of plants for the production of therapeutic human peptides

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