Transgenic Plant Vaccines Research Articles

Towards Improved Use of Vaccination in the Control of Infectious Bronchitis and Newcastle Disease in Poultry: Understanding the Immunological Mechanisms.

Infectious bronchitis (IB) and Newcastle disease (ND) are two important diseases of poultry and have remained a threat to the development of the poultry industry in many parts of the world. The immunology of avian has been well studied and numerous vaccines have been developed against the two viruses. Most of these vaccines are either inactivated vaccines or live attenuated vaccines. Inactivated vaccines induce weak cellular immune responses and require priming with live or other types of vaccines. Advanced technology has been used to produce several types of vaccines that can initiate prime immune responses. However, as a result of rapid genetic variations, the control of these two viral infections through vaccination has remained a challenge. Using various strategies such as combination of live attenuated and inactivated vaccines, development of IB/ND vaccines, use of DNA vaccines and transgenic plant vaccines, the problem is being surmounted. It is hoped that with increasing understanding of the immunological mechanisms in birds that are used in fighting these viruses, a more successful control of the diseases will be achieved. This will go a long way in contributing to global food security and the economic development of many developing countries, given the role of poultry in the attainment of these goals.

Edible Transgenic Plant Vaccines for Different Diseases

Edible plant vaccines are immunogenic preparations containing antigenic proteins rather than pathogens, therefore, they sanctify situation where there is a possibility of resurgence of disease when the antigenic preparation contains the organism in any form whatsoever. Expression of antigens as vaccines and of antibodies against antigens of pathogens in transgenic plants is a convenient and inexpensive source for various bacterial, viral, helminths, protozoan and autoimmune diseases with lower capital costs. This review describes various diseases along with the production of edible transgenic plant vaccines/proteins for the same. Thus, substituting and improvising conventional immunization methods.

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.

Transgenic Plant Vaccine: A Breakthrough in Immunopharmacotherapeutics

Transgenic plant vaccines are genetically engineered plant vaccines in which a selected gene is encoded for the desired antigen and modified which when taken orally elicits a strong immune response in the body. Plant-cellproduced vaccines are inherently safe because they pose no risk of microbiologic contamination associated with animal-derived vaccines and eliminate the risk of pathogenicity, reversion to virulence and shedding. Oral delivery stimulates mucosal immunity (the first line of defense) in the tissues lining the respiratory system and eliminates injection-related hazards. Plants structure may help in maintaining the antigenic property even after degradation in intestine. Plenty of availability of plants makes the vaccine production of low cost apart from low cost in storage and transportation. They act through different mechanism of action mainly stimulating the lymphoid structure in the intestine. This review highlights the development of transgenic plant vaccine, its action, and certain important diseases of animals, poultry and humans and status of plant vaccine developed against them.

Recent Patents on Plant Transgenic Technology

Plant transformation technology plays an ever-increasing role in improving crop plant traits and addressing research questions. In recent years, a number of important patents on plant transgenic technologies have been published.These patents represent significant new progresses, many representing novel approaches in the field of plant transgenic technology. This review highlights selected as well as the most significant advancements made mostly within the past 2 years in plant transgenic research. These advancements include the improvements of plant transformation systems, development of new plant selectable markers, engineering for plant stress tolerance, production of vaccines in transgenic plants, etc. Of these, the engineering for plant stress tolerance accounts for a high percentage of the transgenic field of inventions. Some results are drastic and unexpected, having a great potential in their applications towards a wider range of plant species. This review also tries to avoid terms and languages pertaining to the patent and legal documents to ease readings.

Biotechnology developments in the livestock sector in developing countries

Global meat and milk consumption is exponentially increasing due to population growth, urbanization and changes in lifestyle in the developing world. This is an excellent opportunity for developing countries to improve the livestock sector by using technological advances. Biotechnology is one of the avenues for improved production in the “Livestock revolution”. Biotechnology developments applied to livestock health, nutrition, breeding and reproduction are improving with a reasonable pace in developing countries. Simple bio-techniques such as artificial insemination have been well implemented in many parts of the developing world. However, advanced technologies including transgenic plant vaccines, marker assisted selection, solid state fermentation for the production of fibrolytic enzymes, transgenic fodders, embryo transfer and animal cloning are confined largely to research organizations. Some developing countries such as Taiwan, China and Brazil have considered the commercialization of biotechnology in the livestock sector. Organized livestock production systems, proper record management, capacity building, objective oriented research to improve farmer’s income, collaborations with the developed world, knowledge of the sociology of an area and research on new methods to educate farmers and policy makers need to be improved for the creation and implementation of biotechnology advances in the livestock sector in the developing world.

Transgenic chloroplasts are efficient sites for high‐yield production of the vaccinia virus envelope protein A27L in plant cells†

Orthopoxviruses (OPVs) have recently received increasing attention because of their potential use in bioterrorism and the occurrence of zoonotic OPV outbreaks, highlighting the need for the development of safe and cost-effective vaccines against smallpox and related viruses. In this respect, the production of subunit protein-based vaccines in transgenic plants is an attractive approach. For this purpose, the A27L immunogenic protein of vaccinia virus was expressed in tobacco using stable transformation of the nuclear or plastid genome. The vaccinia virus protein was expressed in the stroma of transplastomic plants in soluble form and accumulated to about 18% of total soluble protein (equivalent to approximately 1.7 mg/g fresh weight). This level of A27L accumulation was 500-fold higher than that in nuclear transformed plants, and did not decline during leaf development. Transplastomic plants showed a partial reduction in growth and were chlorotic, but reached maturity and set fertile seeds. Analysis by immunofluorescence microscopy indicated altered chlorophyll distribution. Chloroplast-synthesized A27L formed oligomers, suggesting correct folding and quaternary structure, and was recognized by serum from a patient recently infected by a zoonotic OPV. Taken together, these results demonstrate that chloroplasts are an attractive production vehicle for the expression of OPV subunit vaccines.

Anchorage to the cytosolic face of the endoplasmic reticulum membrane: a new strategy to stabilize a cytosolic recombinant antigen in plants

The levels of accumulation of recombinant vaccines in transgenic plants are protein specific and strongly influenced by the subcellular compartment of destination. The human immunodeficiency virus protein Nef (negative factor), a promising target for the development of an antiviral vaccine, is a cytosolic protein that accumulates to low levels in transgenic tobacco and is even more unstable when introduced into the secretory pathway, probably because of folding defects in the non-cytosolic environment. To improve Nef accumulation, a new strategy was developed to anchor the molecule to the cytosolic face of the endoplasmic reticulum (ER) membrane. For this purpose, the Nef sequence was fused to the C-terminal domain of mammalian ER cytochrome b5, a long-lived, tail-anchored (TA) protein. This consistently increased Nef accumulation by more than threefold in many independent transgenic tobacco plants. Real-time polymerase chain reaction of mRNA levels and protein pulse-chase analysis indicated that the increase was not caused by higher transcript levels but by enhanced protein stability. Subcellular fractionation and immunocytochemistry indicated that Nef-TA accumulated on the ER membrane. Over-expression of mammalian or plant ER cytochrome b5 caused the formation of stacked membrane structures, as observed previously in similar experiments performed in mammalian cells; however, Nef-TA did not alter membrane organization in tobacco cells. Finally, Nef could be removed in vitro by its tail-anchor, taking advantage of an engineered thrombin cleavage site. These results open up the way to use tail-anchors to improve foreign protein stability in the plant cytosol without perturbing cellular functions.

Sustained Expression of Human Cytomegalovirus Glycoprotein B (UL55) in the Seeds of Homozygous Rice Plants

Production of recombinant subunit vaccines in transgenic plants may be a means of reducing vaccine costs while increasing availability and safety. A plant-derived product found safe and effective for oral administration would provide additional advantages when used as a vaccine. Outstanding issues with the technology include transgene stability through successive generations and consistent bioproduction. We previously reported expression of glycoprotein B (gB) of human cytomegalovirus in seeds of transgenic tobacco. Here the goal was to determine if gB could be similarly expressed in rice, and if so, to examine expression over several plant generations. Results show that immunoreactive gB was successfully expressed in transgenic rice seeds, with sustained expression over three generations. The gB contained several neutralizing epitopes and was stable over 27 months.

Expression behaviour of the fusion antigen CTB::VP60, a promising RHD-vaccine, in pea

The production of veterinary vaccines in transgenic plants appears to be an upcoming strategy. Since 15 years transgenic plants express a number of viral and bacterial antigens -amongst others VP60 (1, 2), the only structural capsid protein of the rabbit haemorrhagic disease virus (RHDV). However plantderived VP60 demonstrated very low immunogenicity compared to other production systems like baculovirus. In order to enhance the immunogenicity of plant-derived VP60 we fused the protein to the well known adjuvant CTB, the non-toxic B subunit of Cholera toxin (CTA-CTB5). The chimaric gene ctbvp60SEKDEL, regulated by the CaMV 35S promoter, was integrated into pea (Pisum sativum) by Agrobacterium-mediated transformation. Around 60 independent transgenic plant lines of the F1 generation were analysed and the protein content of CTB::VP60 was estimated using CTB-, GM1-gangliosideand VP60-dependent ELISA. Four transgenic F1 lines demonstrated detectable amount of the two complex components CTB and VP60. The heterogeneous pentamer complex could be detected by a newly developed combined GM1-VP60-ELISA Test. Additionally, we attempted to increase expression levels by analysing transgenic plant lines in the F2 and F3 generation after self pollination of the two highest expression lines. Up to 100 independent transgenic F3-lines with significant enhancement of the expression level up to 0.7 % TSP were selected to produce CTB::VP60-seeds for immunisation experiments with rabbits using mucosal and parenteral vaccination strategies.

Immunization update and hot topics in clinical immunology: How does this relate to my practice?

The prevention of infectious diseases by the use of vaccines represents one of medicine's greatest triumphs during the 20th century. This era has witnessed the global eradication of smallpox as a result of Jennerian cowpox vaccination, the elimination of paralytic poliomyelitis from the western hemisphere, and within 5-10 years the anticipated eradication of poliomyelitis worldwide as a result of the poliovirus vaccines. Next slated for worldwide eradication is measles, the great killer of infants and children, which each year extracts a global mortality of one million victims. Throughout the 20th century the percutaneous (i.e., subcutaneous or intramuscular) route has almost exclusively been the preferred way to administer vaccines. However, as a result of several important scientific discoveries made during the 20th century, including new tissue-culturing techniques, the development of recombinant DNA technology, and genetic sequencing, a whole new generation of tailor-made modern vaccines has become available, including DNA vaccines and transgenic plant vaccines. Moreover, it became apparent that alternative routes of administration of vaccines, such as by aerosol immunization might be more appropriate and more effective than immunization via the parenteral route. The overall success in vaccine development, however, has not been without cost. For every new vaccine that has been developed, an adverse effect has been seen. Thus, although modern vaccines are extremely safe and effective, they are neither completely safe nor completely effective. The goal of vaccine development, therefore, is to achieve the highest degree of protection and the lowest rate of adverse effects. This paper describes some of the recent advances in vaccine development and will focus on some hot topics relating to the recent development and use of respiratory aerosolized vaccines.

An edible vaccine for malaria using transgenic tomatoes of varying sizes, shapes and colors to carry different antigens

Malaria, a disease caused by protozoan parasites of genus Plasmodium, is one of the world's biggest scourges. Over two billion individuals reside in the malaria endemic areas and the disease affects 300-500 million people annually. As a result of malarial-infection, an estimated three million lives are lost annually, among them over one million children (majority under 5 years of age). The mortality due to malaria has increased because of the spread of drug-resistant strains of the parasite, the breakdown of health services in many affected areas, the interaction of the disease with human immunodeficiency virus (HIV) infection, and possibly the effects of climate change. Infants and young children with malaria often die from severe anemia, cerebral involvement,or prostration caused by overwhelming infection; many new borns die from complications of low birth weight caused by maternal malaria during pregnancy. The scarce economic resources and lack of communication, infrastructure and adequate means of travel in the endemic areas make it extremely difficult to implement traditional infection control measures (i.e., mosquito control, preventive anti-malarial drugs and nets). To make the matter worse, both malarial parasites and its insect vectors are increasingly becoming resistant to anti-malarial agents (chloroquine) and insecticides (both DDT and melathione and related chemicals), respectively. By conventional wisdom, the immune mechanisms responsible for protection against malaria will require a multiple of 10-15 antigen targets for proper protection against various stages of malarial infection. By standard vaccination protocols, such a large number of targets would not be appropriate to be used for vaccination as a single dose due to antigenic competition. It would be almost impossible to immunize over two billion individuals who live in malaria susceptible areas with several carefully crafted immunization schedules delivered 4-6 weeks apart in the form of two different antigens as a single dose. Besides, if immunization schedules could be arranged, the stability of vaccines carrying different malarial antigens, their transport, and the logistics of vaccination would be an almost impossible task to achieve under the current fiscal constraints. We are proposing a unique way to circumvent these logistical difficulties to deliver the malaria vaccines to every susceptible home at a small fraction of a cost. We hypothesize that the anti-malaria edible vaccines in transgenic tomato plants where different transgenic plants expressing different antigenic type(s). Immunizing individuals against 2-3 antigens and against each stage of the life cycle of the multistage parasites would be an efficient, inexpensive and safe way of vaccination. Tomatoes with varying sizes, shapes and colors carrying different antigens would make the vaccines easily identifiable by lay individuals.

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.

Ethics, Biotechnology, and Global Health: The Development of Vaccines in Transgenic Plants

As compared with conventional vaccine production systems, plant-made vaccines (PMVs) are said to enjoy a range of advantages including cost of production and ease of storage for distribution in developing countries. In this article, we introduce the science of PMV production, and address ethical issues associated with development and clinical testing of PMVs within three interrelated domains: PMVs as transgenic plants; PMVs as clinical research materials; and PMVs as agents of global health. We present three conclusions: first, while many of the ethical issues raised by PMVs are familiar, PMVs add a new dimension to old issues, and raise some novel issues for ethicists and policy-makers; secondly, it is premature to promise broad applicability of PMVs across the developing world without having demonstrated their feasibility; thirdly, in particular, proponents of PMVs as a solution to global health problems must, as a condition of the ethical conduct of their research, define the commercial feasibility of PMVs for distribution in the developing world.

Risk analysis for plant-made vaccines

The production of vaccines in transgenic plants was first proposed in 1990 however no product has yet reached commercialization. There are several risks during the production and delivery stages of this technology, with potential impact on the environment and on human health. Risks to the environment include gene transfer and exposure to antigens or selectable marker proteins. Risks to human health include oral tolerance, allergenicity, inconsistent dosage, worker exposure and unintended exposure to antigens or selectable marker proteins in the food chain. These risks are controllable through appropriate regulatory measures at all stages of production and distribution of a potential plant-made vaccine. Successful use of this technology is highly dependant on stewardship and active risk management by the developers of this technology, and through quality standards for production, which will be set by regulatory agencies. Regulatory agencies can also negatively affect the future viability of this technology by requiring that all risks must be controlled, or by applying conventional regulations which are overly cumbersome for a plant production and oral delivery system. The value of new or replacement vaccines produced in plant cells and delivered orally must be considered alongside the probability and severity of potential risks in their production and use, and the cost of not deploying this technology – the risk of continuing with the status quo alternative.

The next 15 years: Taking plant‐made vaccines beyond proof of concept

Significant potential advantages are associated with the production of vaccines in transgenic plants; however, no commercial product has emerged. An analysis of the strengths, weaknesses, opportunities and threats for plant-made vaccine technology is provided. The use of this technology for human vaccines will require significant investment and developmental efforts that cannot be supported entirely by the academic sector and is not currently supported financially by industry. A focus on downstream aspects to define potential products, conduct of additional basic clinical testing, and the incorporation of multidisciplinary strategic planning would accelerate the potential for commercialization in this field. Estimates of production cost per dose and volume of production are highly variable for a model vaccine produced in transgenic tomato, and can be influenced by the optimization of many factors. Commercialization of plant-made vaccine technology is likely to be led by the agricultural biotechnology sector rather than the pharmaceutical sector due to the disruptive nature of the technology and the complex intellectual property landscape. The next major milestones will be conduct of a phase II human clinical trial and demonstration of protection in humans. The achievement of these milestones would be accelerated by further basic investigation into mucosal immunity, the codevelopment of oral adjuvants, and the integration of quality control standards and good manufacturing practices for the production of preclinical and clinical batch materials.

Plant-derived vaccines against diarrhoeal diseases

Transgenic plant-derived vaccines offer a new strategy for the development of safe, inexpensive vaccines against diarrhoeal diseases. In animal and Phase I clinical studies, these vaccines have been safe and immunogenic without the need for a buffer or vehicle other than the plant cell. This review examines some early attempts to develop oral transgenic plant vaccines against enteric infections such as enterotoxigenic Escherichia coli infection, cholera and norovirus infection.

Alternative routes of immunization for prevention of infectious diseases: a new paradigm for the 21st century.

The prevention of infectious diseases by the use of vaccines represents one of medicine's greatest triumphs during the 20th century. This era has witnessed the global eradication of smallpox as a result of Jennerian cowpox vaccination, the elimination of paralytic poliomyelitis from the western hemisphere, and within 5-10 years the anticipated eradication of poliomyelitis worldwide as a result of the poliovirus vaccines. Next slated for worldwide eradication is measles, the great killer of infants and children, which each year extracts a global mortality of one million victims. Throughout the 20th century the percutaneous (i.e., subcutaneous or intramuscular) route has almost exclusively been the preferred way to administer vaccines. However, as a result of several important scientific discoveries made during the 20th century, including new tissue-culturing techniques, the development of recombinant DNA technology, and genetic sequencing, a whole new generation of tailor-made modern vaccines has become available, including DNA vaccines and transgenic plant vaccines. Moreover, it became apparent that alternative routes of administration of vaccines, such as by aerosol immunization and transcutaneous skin patches, might be more appropriate and more effective than immunization via the parenteral route. This paper describes some of the recent advances relating to alternative methods of immunization and will focus primarily on the development and use of respiratory aerosolized vaccines.

Vaccine cornucopia. Transgenic vaccines in plants: new hope for global vaccination?

Vaccine cornucopia. Transgenic vaccines in plants: new hope for global vaccination?

Induction of a Protective Antibody Response to Foot and Mouth Disease Virus in Mice Following Oral or Parenteral Immunization with Alfalfa Transgenic Plants Expressing the Viral Structural Protein VP1

The utilization of transgenic plants expressing recombinant antigens to be used in the formulation of experimental immunogens has been recently communicated. We report here the development of transgenic plants of alfalfa expressing the structural protein VP1 of foot and mouth disease virus (FMDV). The presence of the transgenes in the plants was confirmed by PCR and their specific transcription was demonstrated by RT-PCR. Mice parenterally immunized using leaf extracts or receiving in their diet freshly harvested leaves from the transgenic plants developed a virus-specific immune response. Animals immunized by either method elicited a specific antibody response to a synthetic peptide representing amino acid residues 135–160 of VP1, to the structural protein VP1, and to intact FMDV particles. Additionally, the immunized mice were protected against experimental challenge with the virus. We believe this is the first report demonstrating the induction of a protective systemic antibody response in animals fed transgenic plants expressing a viral antigen. These results support the feasibility of producing edible vaccines in transgenic forage plants, such as alfalfa, commonly used in the diet of domestic animals even for those antigens for which a systemic immune response is required.