Passive immunization of mice pups through oral immunization of dams with a plant-derived vaccine

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.

Plant production of veterinary vaccines and therapeutics

Plant-derived biologicals for use in animal health are becoming an increasingly important target for research into alternative, improved methods for disease control. Although there are no commercial products on the market yet, the development and testing of oral, plant-based vaccines is now beyond the proof-of-principle stage. Vaccines, such as those developed for porcine transmissible gastroenteritis virus, have the potential to stimulate both mucosal and systemic, as well as, lactogenic immunity as has already been seen in target animal trials. Plants are a promising production system, but they must compete with existing vaccines and protein production platforms. In addition, regulatory hurdles will need to be overcome, and industry and public acceptance of the technology are important in establishing successful products.

Induction of a protective antibody response to FMDV in mice following oral immunization with transgenic Stylosanthes spp. as a feedstuff additive

The expression of antigens in transgenic plants has increasingly been used as an alternative to the classical methodologies for the development of experimental vaccines, and it remains one of the real challenges in this field to use transgenic plant-based vaccines effectively as feedstuff additives. We report herein the development of a new oral immunization system for foot and mouth disease with the structural protein VP1 of the foot and mouth disease virus (FMDV) produced in transgenic Stylosanthes guianensis cv. Reyan II. The transgenic plantlets were identified by polymerase chain reaction (PCR), Southern blotting, and northern blotting; and the production of VP1 protein in transgenic plants was confirmed and quantified by western blotting and enzyme-linked immunosorbent assays (ELISA). Six transformed lines were obtained, and the level of the expressed protein was 0.1-0.5% total soluble protein (TSP). Mice that were orally immunized using studded feedstuff mixed with desiccated powder of the transgenic plants developed a virus-specific immune response to the structural VP1 and intact FMDV particles. To our knowledge, this is the first report of transgenic plants expressing the antigen protein of FMDV as feedstuff additives that has demonstrated the induction of a protective systemic antibody response in animals. These results support the feasibility of producing edible vaccines from transgenic forage plants, and provide proof of the possibility of using plant-based vaccines as feedstuff additives.

Crude saponins improve the immune response to an oral plant-made measles vaccine

Millions of people live in areas where infectious diseases, such as measles, are endemic and resources are scarce. Heat-stable vaccines that are delivered orally will greatly enhance vaccination programs in these areas. A stumbling block in the development of oral vaccines is the availability of safe and effective mucosal adjuvants, especially for use with subunit vaccines. The experiments presented here examine the ability of CTB/CT, LT(R192G) and crude Quillaja saponin extracts to stimulate MV-specific immune responses in mice, following oral immunisation with plant-made measles virus hemagglutinin (MV-H) protein. LT(R192G) and crude saponin extracts both functioned as potent mucosal adjuvants when ad-mixed with plant-made MV-H protein, and were more effective than CTB/CT. MV-H protein supplemented with saponin extract induced the strongest MV-specific responses, in the greatest number of mice. Crude saponins are routinely used by the food and beverage industry at concentrations greater than those required for adjuvanticity, and as such, they have a better safety profile than bacterial enterotoxins. This study demonstrates their potential as adjuvants for use with oral plant-made vaccines.

Expression systems and developments in plant-made vaccines

Delivery of vaccines to mucosal surfaces can elicit humoral and cell-mediated responses of the mucosal and systemic immune systems, evoke less pain and discomfort than parenteral delivery, and eliminate needle-associated risks. Transgenic plants are an ideal means by which to produce oral vaccines, as the rigid walls of the plant cell protect antigenic proteins from the acidic environment of the stomach, enabling intact antigen to reach the gut associated lymphoid tissue. In the past few years, new techniques (such as chloroplast transformation and food processing) have improved antigen concentration in transgenic plants. In addition, adjuvants and targeting proteins have increased the immunogenicity of mucosally administered plant-made vaccines. These studies have moved plant-made vaccines closer to the development phase.

Is there a role for plant‐made vaccines in the prevention of HIV/AIDS?

Although educational programs have had some impact, immunization against HIV will be necessary to control the AIDS pandemic. To be effective, vaccination will need to be accessible and affordable, directed against multiple antigens, and delivered in multiple doses. Plant-based vaccines that are heat-stable and easy to produce and administer are suited to this type of strategy. Pilot studies by a number of groups have demonstrated that plant viral expression systems can produce HIV antigens in quantities that are appropriate for use in vaccines. In addition, these plant-made HIV antigens have been shown to be immunogenic. However, given the need for potent cross-clade humoral and T-cell immunity for protection against HIV, and the uncertainty surrounding the efficacy of protein subunit vaccines, it is most likely that plant-made HIV vaccines will find their niche as booster immunizations in prime-boost vaccination schedules.

Development of transgenic alfalfa plants containing the foot and mouth disease virus structural polyprotein gene P1 and its utilization as an experimental immunogen

The use of transgenic plants as vectors for the expression of viral and bacterial antigens has been increasingly tested as an alternative methodology for the production of experimental vaccines. Here, we report the production of transgenic alfalfa plants containing the genes encoding the polyprotein P1 and the protease 3C of foot and mouth disease virus (FMDV). The immunogenicity of the expressed products was tested using a mouse experimental model. Parenterally immunized mice developed a strong antibody response and were completely protected when challenged with the virulent virus. This report demonstrates the possibility of using transgenic plants to express polyprotein P1 and the protease 3C of FMDV and their utilization as effective experimental immunogens.

The development of a plant-based vaccine for measles

Plant-based vaccination strategies have the potential to overcome the limitations of the current measles vaccine. The measles virus hemagglutinin (MV-H) protein has been expressed in tobacco. Oral immunisation of mice with plant-derived MV-H protein resulted in MV-specific antibodies and secretory IgA, indicative of humoral and mucosal immune responses. In addition, boosting with oral plant-derived MV-H protein following a MV-H DNA prime, resulted in a greater response than could be induced with either vaccine alone. Collectively, this research represents a significant step towards an effective oral measles vaccine that would be temperature-stable, easy to administer and amenable to inexpensive manufacture.

Application of Quillaja saponaria extracts as oral adjuvants for plant-made vaccines

Extracts from the Quillaja saponaria tree are known to provide immune potentiating responses and, hence, can be useful as adjuvants. Partial purification from the crude (food-grade) extract results in Quil A, which is contained in several veterinary vaccines. Further purification can provide concentrated saponin fractions such as QS-21, which is currently under investigation as a potential adjuvant for use in humans. Purified saponins have proven safe and effective when injected and have significantly enhanced the efficacy of some oral vaccines under clinical investigation. Toxicity of the food-grade extract from Quillaja saponaria has limited its use as a parenteral adjuvant; however, this toxicity seems to be abated when delivered orally. It is commonly used within the food and beverage industries and has no documented toxicity in humans at the present levels of consumption. Use of transgenic plants has been proposed as an alternative system for oral vaccine production and administration, and it is likely that an oral adjuvant will be required in most cases. Food-grade saponins have significant advantages for use with plant-made vaccines and are likely to provide a broad adjuvant effect due to the multiple saponin components. A review of the origin, production, biological activity, toxicity and use in the food industry is provided for Quillaja saponaria extract. Previous evaluation of this adjuvant in preclinical studies with plant made vaccines is discussed and a proposed level of experimental use in humans is provided.