Edible vaccines

edible vaccines, advantages of edible vaccines, production of edible vaccines, examples of edible vaccines, benefits

1. Edible Vaccines by Manjusha Kondepudi M pharm (Ph D) Assistant professor Vignan Institute of Pharmaceutical technology

2. Vaccine Vaccines are biological preparations that improve our immunity. The concept of vaccination was first put forth by Edward Jenner in 1796 for small pox. Vaccines are considered as primary tools of health intervention to prevent diseases in both humans and animals.  Vaccination is the process by which the body is made ready to face and fight off new infections.

3. Disadvantages of Conventional Vaccines Production process making them expensive In accessible (especially in developing countries) Most of the vaccines are given by invasive techniques (injections) Requires refrigeration for storage and transportation

4. Search for alternatives Vaccines can be used more widely, especially in developing countries, if their cost of production can be reduced and they can be preserved without refrigeration. In developing countries certain limitations, like vaccine affordability, the need for “cold chains” from the producer to the site of use of the vaccine, and the dependence on injection, are barriers

5. Search for alternatives Hence, there is search for easily administrable, storable, fail-safe and widely acceptable bio friendly vaccines and their delivery systems especially in developing countries. Therefore, as substitutes have to be produced for traditional vaccines, it was envisaged that plants could be promising agents for efficient production system for vaccines, which in turn gave rise to the novel concept of edible vaccines (EV)

6. Production of Edible Vaccines Selection of the Desired Gene and Plant The introduction of selected desired genes into plants and then inducing these altered plants to produce the encoded proteins is the primary condition for the development of  edible vaccines . This process is known as transformation and altered plants are called  transgenic plants .

7. Production of Edible Vaccines

8. Plasmid/vector carrier system: Agrobacterium tumifaciens method One way of generating EVs depends on the microorganism species to deliver into plant cells the genetic blueprints for an infectious agent or microorganism “antigens” proteins that elicit a targeted immunologic response within the recipient. A. tumifaciens is present in soil which is employed to transfer a little phase of DNA into plant

9. The whole plant is regenerated from an individual plant cell. It has been reported that genes which are expressed successfully in experimental model plants, when given orally to animals, generate serum antibodies. Vegetable pathogens, A. tumefaciens and Agrobacterium rhizogenes , have potential to integrate their DNA (T-DNA) into the infected cell’s nuclear genome.

10. The introduction of exogenous genes into the adequately modified T-DNA of Agrobacterium cells and following infection of a vegetable tissue led to the study of gene’s stable integration in the plant’s genome and production of a transgenic protein which acts as an EV.

11. Micro projectile bombardment ( biolistics )/gene gun method The gene containing DNA-coated metal (e.g., gold and tungsten) particles are fired at the plant cells by means of the gene gun. These plant cells uptakes the DNA then permitted to grow in new plants and are cloned to supply a large amount of genetically similar crop. This technique is more often suitable to deliver DNA into cells of the plant that makes the transfer of genes independent of regeneration ability of the species. However, the limitation is that the technique is not economical because of particle gun device

12. Chimeric virus method Plant viruses are genetically modified to carry the desired genes and used to infect their natural hosts such as the edible plants where the cloned genes are expressed to varying degrees in different edible parts of the plant. Certain viruses can be redesigned to express fragments of antigenic proteins on their surfaces such as cowpea mosaic virus, alfalfa mosaic virus, tobacco mosaic virus, cauliflower mosaic virus ( CaMV ), potato virus, and tomato bushy stunt virus

13. Electroporation method The introduction of DNA into cells is done by exposing the cells for a brief period to high voltage electrical pulse that is assumed to induce transient pores within the plasmalemma (a thin layer of tissue that covers surface). The cell wall acts an efficient barrier to DNA. Hence, it has to be weakened by enzymatic treatment thus permit the entry of DNA into the cell

14. Properties of an ideal vaccine i . It should not be toxic or pathogenic, i.e., it should be safe ii. It should have very low levels of side effects in normal individuals iii. It should not cause problems in individuals with impaired immune system iv. It should produce long-lasting humoral and cellular immunities v. The vaccination technique should be simple vi. The vaccine should be less expensive vii . Contamination of the environment should not happen viii. It should be effective and affordable

15. Advantages and disadvantages of EVs Advantages i . They can be mass-produced. Hence, they are economical ii. They can be administered by eating the plant/part of the plant. Hence, the processing and purification steps can be eliminated iii. They can be stored at normal room temperature. Extensive cold storage conditions are not required iv. The process of transportation and distribution can be eliminated, if the local/native crop of a particular area is engineered to produce the vaccine V. They trigger the body’s first line of defense (immunity at the mucosal surfaces)

16. Disadvantages i . Selection of plant with stable antigen production could be a difficult task, time-consuming, and expensive ii. Lack of knowledge regarding plant biotechnology which leads to negative public opinions, stringent laws, and debates regarding intellectual property discourage pharmaceutical business investments in Evs iii. Possibility for hypersensitive reaction, development of oral tolerance to vaccines and also difficulty in the administration of the standard dose are additional limitations

17.  Mechanism of Action Most pathogens enter at mucosal surfaces lining the digestive, respiratory, and urino -productive tracts, which are collectively the largest immunologically active tissue in the body. The mucosal immune system is the first line of defense and the most effective site for vaccination against pathogens.  Nasal and oral vaccines  are most effective for mucosal infections. The goal of oral vaccine is to stimulate both mucosal and humoral immunity against pathogens.

18. Edible vaccines  when taken orally undergo mastication, and degradation of plant cells occurs in the intestine due to the action of digestive enzymes. Peyer’s patches are an enriched source of IgA producing plasma cells and have the potential to populate mucosal tissue and serve as mucosal immune effector site. The breakdown of edible vaccine occurs near Peyer’s patches, which consist of 30–40 lymphoid nodules on the outer surface of the intestine and also contain follicles from which the germinal center develops after antigenic stimulation. 

19. These follicles act as a site for the penetration of antigens in intestinal epithelium. The antigen then comes in contact with M-cells. M-cells express class-2 major histocompatibility complex molecules, and antigens transported across the mucous membranes by M-cells can activate B-cells within these lymphoid follicles. The activated B-cells leave the lymphoid follicles and migrate to diffuse mucosal associated lymphoid tissue where they differentiate into plasma cells that secrete the IgA class of antibodies. These  IgA antibodies  are transported across the epithelial cells into secretions of the lumen where they can interact with antigens present in the lumen

20. Most popular edible vaccines produced by plants  Plant/Fruit Advantage Disadvantage Tobacco •Good model for evaluating recombinant proteins •Low cost preserving system •Easy purification of antibodies stored in the seeds •Large harvests •Produces toxic compounds *  (toxic alkaloids incompatible w/oral delivery) •Potential for outcrossing in field Potato •Dominated clinical trials •Easily manipulated/transformed •Easily propagated from its “eyes” •Stored for long periods without refrigeration •Relatively low tuber protein content •Unpalatable in raw form ** ; cooking may cause denaturation and p

21. Banana •Does not need cooking •Proteins not destroyed even if cooked •Inexpensive •Grown widely in developing countries •Trees take 2–3 years to mature and transformed trees take about 12 months to bear fruit •Fruits spoil rapidly after ripening and contain very little protein, so unlikely to produce large amounts of recombinant proteins Tomato •Grows quickly •Cultivated broadly •High content of vitamin A may boost immune response •Overcomes the spoilage problem by freeze-drying technology •Heat-stable, antigen-containing powders † , made into capsules •Different batches blended to give uniform doses of antigen •Relatively low fruit protein content •Acidic fruit may be incompatible with some antigens or for delivery to infants •No  in vitro   sy

22. Rice •Commonly used in baby food because of low allergenic potential •High expression of proteins/antigens •Easy storage/transportation •Expressed protein is heat stable •Grows slowly •Requires specialized glasshouse conditions Lettuce •Fast growing •Direct consumption •Spoils readily

23. * Soybean and alfalfa •Relatively efficient transformation system •High protein content in leaves •Leaves edible uncooked •Ideal system for animal vaccines •Potential for outcrossing in field •Deep root system problematic for cleaning field Legumes or cereals •Production technology widely established •High protein content in seeds •Stable protein in stored seeds •Well suited for animal vaccines •Industrial seed processing well established •Inefficient transformation systems •Heating or cooking for human use may cause denaturation and poor immunogenicity of vaccine (corn meal is exception) •Potential for outcrossing in field for some species

24. Glance of Benefits Benefit Characteristics Oral delivery The plant cell wall, consisting essentially of cellulose and sugars, provides protection in the stomach and gradual release of the antigen in the gut Use as raw food or dry powder The vaccinogenic plant tissue may be used as raw food or, alternatively, proteins may be partially or fully purified and administered in capsules as dry powder No need for “cold chain” The vaccinogenic plant parts or plant extracts can be stored and shipped at room temperature

25. Mucosal and serum immune response Plant-derived vaccines are primarily designed to trigger the mucosal immune system (IgA) Cost efficiency Production cost will be reduced 100–1000 times as compared with that of traditional vaccines Optimized expression system Plants may be engineered to accumulate the antigen in convenient intracellular compartments (endoplasmic reticulum, chloroplast) Ease of genetic manipulation Procedures essentially rely on established molecular and genetic manipulation protocols; these are already available

26. Ease of production and scale-up GM plants can be stored as seeds. Unlimited vaccine quantity can be produced from these in limited time; production and management are suitable for developing countries Safer than conventional vaccines Lack of contamination with mammalian pathogens Ideal to face bioweapons Safety and cost efficiency plant-derived vaccines act as an ideal tool to face bioterrorism Ideal for veterinary use Cost affordable and ready for use as food additive

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