Oral immunogenicity of a plant-made, subunit, tuberculosis vaccine

Immunogenicity and efficacy of recombinant subunit SARS-CoV-2 vaccine candidate in the Syrian hamster model

SARS-CoV-2 causes devastating impact on the human population and has become a major public health concern. The frequent emergence of SARS-CoV-2 variants of concern urges the development of safe and efficacious vaccine against SARS-CoV-2 variants. We developed a candidate vaccine Baiya SARS-CoV-2 Vax 1, based on SARS-CoV-2 receptor-binding domain (RBD) by fusing with the Fc region of human IgG. The RBD-Fc fusion was produced in Nicotiana benthamiana. Previously, we reported that this plant-produced vaccine is effective in inducing immune response in both mice and non-human primates. Here, the efficacy of our vaccine candidate was tested in Syrian hamster challenge model. Hamsters immunized with two intramuscular doses of Baiya SARS-CoV-2 Vax 1 induced neutralizing antibodies against SARS-CoV-2 and protected from SARS-CoV-2 challenge with reduced viral load in the lungs. These preliminary results demonstrate the ability of plant-produced subunit vaccine Baiya SARS-CoV-2 Vax 1 to provide protection against SARS-CoV-2 infection in hamsters.

Ma J, McDonald KA, Murad A, Nandi S, O’Keef B, Parthiban S, Paul MJ, Ponndorf D, Rech E, Rodrigues JC, Ruf S, Schillberg S, Schwestka J, Shah PS, Singh R, Stoger E, Twyman RM, Varghese IP, Vianna GR, Webster G, Wilbers RHP, Christou P, Oksman‐Caldentey K, Capell T. Contributions of the international plant science community to the fight against infectious diseases in humans-part 2: Affordable drugs in edible plants for endemic and re-emerging diseases

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

A Comprehensive Overview on the Production of Vaccines in Plant-Based Expression Systems and the Scope of Plant Biotechnology to Combat against SARS-CoV-2 Virus Pandemics

Many pathogenic viral pandemics have caused threats to global health; the COVID-19 pandemic is the latest. Its transmission is growing exponentially all around the globe, putting constraints on the health system worldwide. A novel coronavirus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), causes this pandemic. Many candidate vaccines are available at this time for COVID-19, and there is a massive international race underway to procure as many vaccines as possible for each country. However, due to heavy global demand, there are strains in global vaccine production. The use of a plant biotechnology-based expression system for vaccine production also represents one part of this international effort, which is to develop plant-based heterologous expression systems, virus-like particles (VLPs)-vaccines, antiviral drugs, and a rapid supply of antigen-antibodies for detecting kits and plant origin bioactive compounds that boost the immunity and provide tolerance to fight against the virus infection. This review will look at the plant biotechnology platform that can provide the best fight against this global pandemic.

Alfalfa Plants (Medicago sativa L.) Expressing the 85B (MAP1609c) Antigen of Mycobacterium avium subsp. paratuberculosis Elicit Long-Lasting Immunity in Mice

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Paratuberculosis, a contagious, untreatable, and chronic granulomatous enteritis that results in diarrhea, emaciation, and death in farmed ruminants (i.e., cattle, sheep, and goats). In this study, the Ag85B antigen from MAP was expressed in transgenic alfalfa as an attractive vaccine candidate. Agrobacterium-mediated transformation allowed the rescue of 56 putative transformed plants and transgenesis was confirmed in 19 lines by detection of the Ag85B gene (MAP1609c) by PCR. Line number 20 showed the highest Ag85B expression [840 ng Ag85B per gram of dry weight leaf tissue, 0.062% Total Soluble Protein (TSP)]. Antigenicity of the plant-made Ag85B was evidenced by its reactivity with a panel of sera from naturally MAP-infected animals, whereas immunogenicity was assessed in mice immunized by either oral or subcutaneous routes. The plant-made Ag85B antigen elicited humoral responses by the oral route when co-administered with cholera toxin as adjuvant; significant levels of anti-85B antibodies were induced in serum (IgG) and feces (IgA). Long-lasting immunity was evidenced at day 180 days post-first oral immunization. The obtained alfalfa lines expressing Ag85B constitute the first model of a plant-based vaccine targeting MAP. The initial immunogenicity assessment conducted in this study opens the path for a detailed characterization of the properties of this vaccine candidate.

Tuberculosis: Current Status, Diagnosis, Treatment and Development of Novel Vaccines

Tuberculosis (TB) is an infectious disease that mainly affects the lungs and spreads to other organs of the body through the haematogenous route. It is one of the ten major causes of mortality worldwide. India has the highest incidence of new- and multidrug-resistant (MDR) - TB cases in the world. Bacille Calmette-Guerin (BCG) is the vaccine commonly available against TB. BCG does offer some protection against serious forms of TB in childhood but its protective effect wanes with age. Many new innovative strategies are being trailed for the development of effective and potent vaccines like mucosal- and epitope-based vaccines, which may replace BCG or boost BCG responses. The use of nanotechnology for diagnosis and treatment of TB is also in the pipeline along with many other vaccines, which are under clinical trials. Further, in-silico models were developed for finding new drug targets and designing drugs against Mycobacterium tuberculosis (Mtb). These models offer the benefit of computational experiments which are easy, inexpensive and give quick results. This review will focus on the available treatments and new approaches to develop potent vaccines for the treatment of TB.

Use of the Human Vaccine, Mycobacterium bovis Bacillus Calmette Guérin in Deer

The only vaccine ever approved for human tuberculosis was developed a century ago from an isolate of Mycobacterium bovis derived from a tuberculous cow. Initial safety and efficacy studies of an attenuated version of this isolate were conducted in cattle and other animals. In 1921 the first human, an infant, was orally dosed with this attenuated strain that came to be known as M. bovis bacillus Calmette-Guérin (BCG); named for Albert Calmette and Camille Guérin, the two French scientists that developed the strain. Since 1921, billions of people have been vaccinated with BCG making it the oldest, most widely used, and safest vaccine in use today. It is also the tuberculosis vaccine most studied for use in wildlife, including deer. While BCG vaccination of deer may not reliably prevent infection, it consistently decreases lesion severity, minimizing large, necrotic lesions, which often contain large numbers of bacilli. It is believed that decreased lesion severity correlates with decreased disease transmission; however, this hypothesis remains to be proven. Safety studies in white-tailed deer show BCG may persist in lymphoid tissues for up to 12 months; a factor to be considered in deer used for food. Beyond efficacy and safety, methods of vaccine delivery to free-ranging deer are also under investigation, both in the laboratory and in the field. The ideal delivery method is effective, efficient and safe for non-target species, including livestock. Ingestion of BCG by cattle is of special concern as such cattle may present as "false positives" using currently approved diagnostic methods, thus interfering with efforts by animal health agencies to monitor cattle for tuberculosis. An effective BCG vaccine for deer would be of value in regions where free-ranging deer represent a potential source of M. bovis for livestock. Such a vaccine would also be beneficial to farmed deer where M. bovis represents a serious threat to trade and productivity.

Successes and failures in human tuberculosis vaccine development

INTRODUCTION

Tuberculosis (TB) is an infectious disease caused mainly by Mycobacterium tuberculosis. In 2016, the WHO estimated 10.5 million new cases and 1.8 million deaths, making this disease the leading cause of death by an infectious agent. The current and projected TB situation necessitates the development of new vaccines with improved attributes compared to the traditional BCG method. Areas covered: In this review, the authors describe the most promising candidate vaccines against TB and discuss additional key elements in vaccine development, such as animal models, new adjuvants and immunization routes and new strategies for the identification of candidate vaccines. Expert opinion: At present, around 13 candidate vaccines for TB are in the clinical phase of evaluation; however, there is still no substitute for the BCG vaccine. One major impediment to developing an effective vaccine is our lack of understanding of several of the mechanisms associated with infection and the immune response against TB. However, the recent implementation of an entirely new set of technological advances will facilitate the proposal of new candidates. Finally, development of a new vaccine will require a major coordination of effort in order to achieve its effective administration to the people most in need of it.

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

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

Plant-based vaccines against respiratory diseases: current status and future prospects

INTRODUCTION

Respiratory infections have an enormous, worldwide epidemiologic impact on humans and animals. Among the prophylactic measures, vaccination has the potential to neutralize this impact. New technologies for vaccine production and delivery are of importance in this field since they offer the potential to develop new immunization approaches overriding the current limitations that comprise high cost, safety issues, and limited efficacy. Areas covered: In the present review, the state of the art in developing plant-based vaccines against respiratory diseases is presented. The review was based on the analysis of current biomedical literature. Expert commentary: Preclinical and clinical evaluations of several vaccine candidates against influenza, tuberculosis, respiratory syncytial virus, pneumonia, anthrax and asthma are discussed and placed in perspective.

Transgenic carrot expressing fusion protein comprising M. tuberculosis antigens induces immune response in mice

Tuberculosis remains one of the major infectious diseases, which continues to pose a major global health problem. Transgenic plants may serve as bioreactors to produce heterologous proteins including antibodies, antigens, and hormones. In the present study, a genetic construct has been designed that comprises the Mycobacterium tuberculosis genes cfp10, esat6 and dIFN gene, which encode deltaferon, a recombinant analog of the human γ-interferon designed for expression in plant tissues. This construct was transferred to the carrot (Daucus carota L.) genome by Agrobacterium-mediated transformation. This study demonstrates that the fusion protein CFP10-ESAT6-dIFN is synthesized in the transgenic carrot storage roots. The protein is able to induce both humoral and cell-mediated immune responses in laboratory animals (mice) when administered either orally or by injection. It should be emphasized that M. tuberculosis antigens contained in the fusion protein have no cytotoxic effect on peripheral blood mononuclear cells.

An overview of tuberculosis plant-derived vaccines

Tuberculosis (TB) is a leading fatal infectious disease to which the current BCG vaccine has a questionable efficacy in adults. Thus, the development of improved vaccines against TB is needed. In addition, decreasing the cost of vaccine formulations is required for broader vaccination coverage through global vaccination programs. In this regard, the use of plants as biofactories and delivery vehicles of TB vaccines has been researched over the last decade. These studies are systematically analyzed in the present review and placed in perspective. It is considered that substantial preclinical trials are still required to address improvements in expression levels as well as immunological data. Approaches for testing additional antigenic configurations with higher yields and improved immunogenic properties are also discussed.

Production of a plant-derived immunogenic protein targeting ApoB100 and CETP: toward a plant-based atherosclerosis vaccine

In an effort to initiate the development of a plant-based vaccination model against atherosclerosis, a cholera toxin B subunit (CTB)-based chimeric protein was designed to target both ApoB100 and CETP epitopes associated with immunotherapeutic effects in atherosclerosis. Epitopes were fused at the C-terminus of CTB to yield a protein called CTB:p210:CETPe. A synthetic gene coding for CTB:p210:CETPe was successfully transferred to tobacco plants with no phenotypic alterations. Plant-derived CTB:p210:CETPe was expressed and assembled in the pentameric form. This protein retained the target antigenic determinants, as revealed by GM1-ELISA and Western blot analyses. Higher expresser lines reached recombinant protein accumulation levels up to 10 µg/g fresh weight in leaf tissues and these lines carry a single insertion of the transgene as determined by qPCR. Moreover, when subcutaneously administered, the biomass from these CTB:p210:CETPe-producing plants was able to elicit humoral responses in mice against both ApoB100 and CETP epitopes and human serum proteins. These findings evidenced for the first time that atherosclerosis-related epitopes can be expressed in plants retaining immunogenicity, which opens a new path in the molecular farming field for the development of vaccines against atherosclerosis.

Oral Immunogenicity of plant-made Mycobacterium tuberculosis ESAT6 and CFP10

Two lines of transgenic carrot plants producing Mycobacterium tuberculosis proteins (ESAT6 and CFP10) have been constructed. The target proteins are present in carrot storage roots at a level not less than 0.056% of the total storage protein (TSP) for ESAT6 and 0.002% of TSP for CFP10. As has been shown, oral immunization of mice induces both the cell-mediated and humoral immunities. These data suggest that the proteins in question are appropriate as a candidate edible vaccine against tuberculosis.

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.

Production of pharmaceutical proteins in solanaceae food crops

The benefits of increased safety and cost-effectiveness make vegetable crops appropriate systems for the production and delivery of pharmaceutical proteins. In particular, Solanaceae edible crops could be inexpensive biofactories for oral vaccines and other pharmaceutical proteins that can be ingested as minimally processed extracts or as partially purified products. The field of crop plant biotechnology is advancing rapidly due to novel developments in genetic and genomic tools being made available today for the scientific community. In this review, we briefly summarize data now available regarding genomic resources for the Solanaceae family. In addition, we describe novel strategies developed for the expression of foreign proteins in vegetable crops and the utilization of these techniques to manufacture pharmaceutical proteins.

The effect of plant tissue and vaccine formulation on the oral immunogenicity of a model plant-made antigen in sheep

Antigen-specific antibody responses against a model antigen (the B subunit of the heat labile toxin of enterotoxigenic Escherichia coli, LTB) were studied in sheep following oral immunisation with plant-made and delivered vaccines. Delivery from a root-based vehicle resulted in antigen-specific immune responses in mucosal secretions of the abomasum and small intestine and mesenteric lymph nodes. Immune responses from the corresponding leaf-based vaccine were more robust and included stimulation of antigen-specific antibodies in mucosal secretions of the abomasum. These findings suggest that oral delivery of a plant bioencapsulated antigen can survive passage through the rumen to elicit mucosal and systemic immune responses in sheep. Moreover, the plant tissue used as the vaccine delivery vehicle affects the magnitude of these responses.

Protective efficacy against Chlamydophila psittaci by oral immunization based on transgenic rice expressing MOMP in mice

Avian chlamydiosis is caused by Chlamydophila psittaci (Cp. psittaci) and major outer membrane protein (MOMP) of Cp. psittaci is an excellent vaccine candidate. In this study, the MOMP gene was expressed in rice callus by the Agrobacterium tumefaciens vector. The production of protein in transgenic rice seeds was confirmed and quantified by Western-blot and ELISA, the results demonstrating that the antigen was expressed stably. The transgenic rice seeds expressing the MOMP protein were administered by the oral route to BALB/c mice, which developed MOMP-specific serum IgG and fecal IgA antibodies and a splenocyte MOMP-specific proliferative response and significant levels of IFN-γ, IL-2, IL-4, IL-5 and TGF-β production. Immunization with MOMP transgenic seeds induced partial protection (50%) against a lethal challenge with the highly virulent Cp. psittaci 6BC strain. Lung function after challenge was less affected compared non-MOMP immunized animals. The results demonstrate the feasibility of using transgenic rice seeds as an oral vaccine to generate protective immunity and reduce the lung lesions in mice against virulent Cp. psittaci 6BC strain. This finding has implications for further development of an oral vaccine against avian chlamydiosis.

Flagellin produced in plants is a potent adjuvant for oral immunization

The aim of this study was to produce adjuvant with high biosafety, efficacy and low cost. Towards this goal, the plant Nicotiana benthamiana transient expression system was successfully used to express Salmonella typhimurium's flagellin (FljB). The yield of the expressed FljB was 280 mg per kg of fresh weight (FW) leaves. The lyophilized plant powder containing plant expressing FljB was mixed with ovalbumin (OVA) and used for oral immunization of BALB/c mice. The ELISA analysis showed higher and accelerated OVA-specific serum antibody responses in mice given the mixture when compared to animals receiving OVA alone. Furthermore, FljB elicited a mixed Th1/Th2 response as shown by the presence of specific anti-OVA IgG1, IgG2a and IgG2b isotypes. OVA-specific IgAs were also detected in mice given the mixture. Cell-mediated immune response to OVA was induced by FljB as determined by a spleen lymphocyte specific proliferation test. No immune response was generated against FljB. In conclusion, our results showed for the first time the production of FljB in plants and the efficient use of the crude lyophilized extract as an adjuvant for oral immunization.

Two decades of plant-based candidate vaccines: a review of the chimeric protein approaches

Genetic engineering revolutionized the concept of traditional vaccines since subunit vaccines became reality. Additionally, over the past two decades plant-derived antigens have been studied as potential vaccines with several advantages, including low cost and convenient administration. More specifically, genetic fusions allowed the expression of fusion proteins carrying two or more components with the aim to elicit immune responses against different targets, including antigens from distinct pathogens or strains. This review aims to provide an update in the field of the production of plant-based vaccine, focusing on those approaches based on the production of chimeric proteins comprising antigens from human pathogens, emphasizing the case of cholera toxin/E. coli enterotoxin fusions, chimeric viruses like particles approaches as well as the possible use of adjuvant-producing plants as expression hosts. Challenges for the near future in this field are also discussed.

Evaluation of the immunogenicity of a transgenic tobacco plant expressing the recombinant fusion protein of GP5 of porcine reproductive and respiratory syndrome virus and B subunit of Escherichia coli heat-labile enterotoxin in pigs

Escherichia coli heat-labile enterotoxin B subunit (LTB) can be used as an adjuvant for co-administered antigens. Our previous study showed that the expression of neutralizing epitope GP5 of porcine reproductive and respiratory syndrome virus (PRRSV) in transgenic tobacco plant (GP5-T) could induce PRRSV-specific immune responses in pigs. A transgenic tobacco plant co-expressing LTB and PRRSV GP5 as a fusion protein (LTB-GP5-T) was further constructed and its immunogenicity was evaluated. Pigs were given orally three consecutive doses of equal concentration of recombinant GP5 protein expressed in leaves of LTB-GP5-T or GP5-T at a 2-week interval and challenged with PRRSV at 7 weeks post-initial immunization. Pigs receiving LTB-GP5-T or GP5-T developed PRRSV-specific antibody- and cell-mediated immunity and showed significantly lower viremia and tissue viral load and milder lung lesions than wild type tobacco plant (W-T). The LTB-GP5-T-treated group had relatively higher immune responses than the GP5-T-treated group, although the differences were not statistically significant.

In planta production of plant-derived and non-plant-derived adjuvants

Recombinant antigen production in plants is a safe and economically sound strategy for vaccine development, particularly for oral/mucosal vaccination, but subunit vaccines usually suffer from weak immunogenicity and require adjuvants that escort the antigens, target them to relevant sites and/or activate antigen-presenting cells for elicitation of protective immunity. Genetic fusions of antigens with bacterial adjuvants as the B subunit of the cholera toxin have been successful in inducing protective immunity of plant-made vaccines. In addition, several plant compounds, mainly plant defensive molecules as lectins and saponins, have shown strong adjuvant activities. The molecular diversity of the plant kingdom offers a vast source of non-bacterial compounds with adjuvant activity, which can be assayed in emerging plant manufacturing systems for the design of new plant vaccine formulations.

Improved immunogenicity of recombinant Mycobacterium bovis bacillus Calmette-Guérin strains expressing fusion protein Ag85A-ESAT-6 of Mycobacterium tuberculosis

Early secretory antigen target 6 (ESAT-6) is a dominant target for cell-mediated immunity in the early phase of tuberculosis (TB) in patients with TB, causing T-cell proliferation and gamma interferon (IFN-γ) production, which has been considered to be a protective antigen that can be used for future vaccine development. Ag85A is the most essential component for bacterial survival within macrophages and has been used in numerous vaccine preparations, which can induce strong cellular immune responses. In this study, we constructed a new recombinant bacilli Calmette-Guérin (BCG) strain (rBCG-AE) that could express fusion protein Ag85A-ESAT-6 of Mycobacterium tuberculosis and evaluated its immunogenicity in BALB/c mice. There was no evidence for increased virulence of this rBCG. Our experiments illustrated that the rBCG-AE was able to induce higher titer of antibody and elicit more long-lasting and stronger Th1 type cellular immune responses than the parental BCG strain, or rBCG-A (expressing Ag85A) strain, or rBCG-E (expressing ESAT-6) strain, which are characterized by the strong antibody response, the proliferation rate of splenocytes, the ratio of CD4(+) T and CD8(+) T cells stimulated by tuberculin-purified protein derivative and elevated levels of IFN-γ in antigen-stimulated splenocyte cultures. The results show that rBCG-AE is an improved TB vaccine for further study.

Development of plant-based mucosal vaccines against widespread infectious diseases

Mucosal vaccination is a perspective for the control of infectious diseases, since it is capable of inducing humoral and cell-mediated responses. In addition, the delivery of vaccines to mucosal surfaces makes immunization practice safe and acceptable, and eliminates needle-associated risks. Transgenic plants can be used as bioreactors for the production of mucosally delivered protective antigens. This technology shows great promise to simplify and decrease the cost of vaccine delivery. Herein, we review the development of mucosally administered vaccines expressed in transgenic plants. In particular, we evaluate the advantages and disadvantages of using plants for the production of mucosal vaccines against widespread infectious diseases such as HIV, hepatitis B and TB.

Immunogenicity of recombinant GP5 protein of porcine reproductive and respiratory syndrome virus expressed in tobacco plant

The aim of the study was to evaluate the immunogenicity of the ORF5-encoded major envelop glycoprotein 5 (GP5) of porcine reproductive and respiratory syndrome virus (PRRSV) expressed in tobacco plant as a potential pig oral vaccine in protection against PRRSV infection. Six-week-old PRRSV-free pigs were fed four times orally with 50g of chopped fresh GP5 transgenic tobacco leaves (GP5-T) (GP5 reaching 0.011% of total soluble protein) or wild-type tobacco leaves (W-T) each on days 0, 14, 28, and 42. Samples of serum, saliva, and peripheral blood mononuclear cells (PBMCs) were collected on days -1, 6, 13, 20, 27, 34, 41, and 48 after the initial oral vaccination. A similar vaccination-dependent gradual increase in the responses of serum and saliva anti-PRRSV total IgG and IgA, respectively, and in the levels of PRRSV-specific blastogenic response of PBMCs was seen in GP5-T-treated pigs; all statistically significant elevations occurred after the 2nd vaccination and were revealed after 20 days post-initial oral vaccination (DPIOV). Pigs fed on GP5-T also developed serum neutralizing antibodies to PRRSV at a titer of 1:4-1:8 after the 4th vaccination by 48 DPIOV. No detectable anti-PRRSV antibody responses and PRRSV-specific blastogenic response were seen in W-T-treated pigs. The present study has demonstrated that pigs fed on GP5-T could develop specific mucosal as well as systemic humoral and cellular immune responses against PRRSV. The results also support that transgenic plant as GP5-T can be an effective system for oral delivery of recombinant subunit vaccines in pigs.

Plant-made vaccines for humans and animals

The concept of using plants to produce high-value pharmaceuticals such as vaccines is 20 years old this year and is only now on the brink of realisation as an established technology. The original reliance on transgenic plants has largely given way to transient expression; proofs of concept for human and animal vaccines and of efficacy for animal vaccines have been established; several plant-produced vaccines have been through Phase I clinical trials in humans and more are scheduled; regulatory requirements are more clear than ever, and more facilities exist for manufacture of clinic-grade materials. The original concept of cheap edible vaccines has given way to a realisation that formulated products are required, which may well be injectable. The technology has proven its worth as a means of cheap, easily scalable production of materials: it now needs to find its niche in competition with established technologies. The realised achievements in the field as well as promising new developments will be reviewed, such as rapid-response vaccines for emerging viruses with pandemic potential and bioterror agents.

Expression and immunogenicity of the mycobacterial Ag85B/ESAT-6 antigens produced in transgenic plants by elastin-like peptide fusion strategy

This study explored a novel system combining plant-based production and the elastin-like peptide (ELP) fusion strategy to produce vaccinal antigens against tuberculosis. Transgenic tobacco plants expressing the mycobacterial antigens Ag85B and ESAT-6 fused to ELP (TBAg-ELP) were generated. Purified TBAg-ELP was obtained by the highly efficient, cost-effective, inverse transition cycling (ICT) method and tested in mice. Furthermore, safety and immunogenicity of the crude tobacco leaf extracts were assessed in piglets. Antibodies recognizing mycobacterial antigens were produced in mice and piglets. A T-cell immune response able to recognize the native mycobacterial antigens was detected in mice. These findings showed that the native Ag85B and ESAT-6 mycobacterial B- and T-cell epitopes were conserved in the plant-expressed TBAg-ELP. This study presents the first results of an efficient plant-expression system, relying on the elastin-like peptide fusion strategy, to produce a safe and immunogenic mycobacterial Ag85B-ESAT-6 fusion protein as a potential vaccine candidate against tuberculosis.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

Tuberculosis subunit vaccine development: Impact of physicochemical properties of mycobacterial test antigens

Tuberculosis caused by Mycobacterium tuberculosis continues to be one of the major public health problems in the world. The eventual control of this disease will require the development of a safe and effective vaccine. One of the approaches receiving a great deal of attention recently is subunit vaccination. An efficacious antituberculous subunit vaccine requires the identification and isolation of key components of the pathogen that are capable of inducing a protective immune response. Clues to identify promising subunit vaccine candidates may be found in their physicochemical and immunobiological properties. In this article, we review the evidence that the physicochemical properties of mycobacterial components can greatly impact the induction of either protective or deleterious immune response and consequently influence the potential utility as an antituberculous subunit vaccine.

Tuberculosis subunit vaccine design: the conflict of antigenicity and immunogenicity

The attempts to find an effective antituberculous subunit vaccine are based on the assumption that it must drive a Th1 response. In the absence of effective correlates of protection, a vast array of mycobacterial components are being evaluated worldwide either on the basis of their ability to be recognized by T lymphocytes in in vitro assays during early stage of animal or human infection (antigenicity) or their capacity to induce T cell response following immunization in animal models (immunogenicity). The putative vaccine candidates selected using either of these strategies are then subjected to challenge studies in different animal models to evaluate the protective efficacy. Here we review the outcome of this current scheme of selection of vaccine candidates using an 'antigenicity' or 'immunogenicity' criterion on the actual protective efficacy observed in experimental animal models. The possible implications for the success of some of the leading vaccine candidates in clinical trials will also be discussed.

Induction of protective immune responses against the challenge of Actinobacillus pleuropneumoniae by the oral administration of transgenic tobacco plant expressing ApxIIA toxin from the bacteria

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia. Among the virulence factors, ApxIIA, a bacterial exotoxin, is reportedly expressed in many serotypes and is considered as a candidate for the development of a vaccine against the bacterial infection. Previously, we isolated a field strain of A. pleuropneumoniae serotype 2 in Korea and characterized its exotoxins to develop an oral vaccine. In this study, we initially confirmed the immunogenicity of ApxIIA expressed in Escherichia coli. We then developed transgenic tobacco expressing ApxIIA and tested its efficacy to induce a protective immune response against A. pleuropneumoniae infection after oral administration of the plant powder. We observed that protective immune responses were induced in mice after oral administration of the plant powder once a week for 4 weeks. Immunoassays revealed that the levels of antigen-specific immunoglobulin G against ApxIIA increased in mice that were fed a powder made from the transgenic plant, but not in mice fed a powder made from wild-type tobacco. Additionally, mice fed the transgenic plant powder were protected from an injection of a lethal dose of A. pleuropneumoniae. These results support that the transgenic plant may be a suitable candidate for an oral vaccine that could be used effectively against A. pleuropneumoniae infection.

Immunogenicity of a plant-derived edible rotavirus subunit vaccine transformed over fifty generations

Major efforts have been put forth for the development of effective rotavirus vaccines including transgenic plant vaccines. Previous studies have reported that rotavirus VP7 maintains its neutralizing immunity when it is transformed into the potato genome. The present study was aimed at investigating the hereditary stability of VP7-transformed potatoes over fifty generations. The VP7 gene was stably transcribed and expressed in potato cells as detected by RT-PCR and Western blotting. Humeral and mucosal responses were successfully induced in BALB/c mice fed with the fiftieth generation transformed potato tubers. There were no significant differences in serum IgG and fecal IgA between the mice fed with the first and fiftieth generation potatoes (P>0.05). Profiles of cytokines such as IFN-gamma, IL-2, IL-4, IL-5 and TGF-beta in immunized mice showed a naive T-cells bias to Th1 and Th3 polarization. Moreover, specific CTL responses were also detected in C57BL/6 mice fed with transformed potatoes. This research represents a significant step towards the development of rotavirus vaccines derived from a transgenic plant that can be obtained by long-term and large-scale vegetative reproduction. To our knowledge, this is the first finding regarding vaccines derived from plants that can be propagated for many generations.