WHAT IS VACCINE?
- The vaccine is a biological preparation that improves immunity against a particular disease.
- It contains an agent that resembles a disease-causing microorganism and is often made from a weakened or killed form of microbe, its toxins or one of its surface proteins.
- The agent stimulates the body’s immune system to recognize foreign antigen and destroy it.
- Edward Jenner in 1796 used the first vaccine in humans which was against smallpox.
Image Source: Srinivas Bhairy
What is the Edible vaccine?
- The edible vaccine involves the introduction of selected desired genes into plants and then inducing these altered plants to manufacture the altered protein.
- The genes encoding antigens of bacterial and viral pathogens can be expressed in plants in a form in which they retain native immunogenic properties.
- Edible vaccines were initially thought to be useful only for preventing infectious diseases.
- it has also found application in the prevention of autoimmune diseases and cancer therapy.
CONCEPT OF EDIBLE VACCINE
Developed by Arntzen in 1990s
Introduce genes of interest in plants(transformation)
Genes expressed in the plant tissues edible parts(transgenic plants)
Genes encode punitively protective vaccine antigens from viral, bacterial and parasitic pathogens that cause disease in humans and animals
Ingestion of edible parts of the transgenic plant
(oral delivery of vaccine)
MECHANISM OF ACTION
- Edible vaccine when taken orally undergoes the mastication process and the majority of plant cell degradation occurs in the intestine as a result of the action of digestive or bacterial enzymes on the edible vaccine.
- 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 sites.
- The breakdown of edible vaccine near PP, consisting of the 30-40 lymphoid nodules on the outer surface of the intestine and contain follicles
- These follicles act as the site from which antigen penetrates the intestinal epithelium, thereby accumulating antigen within the organized lymphoid structure.
- The antigen then comes in contact with M-cell.
- M-cell passes the antigen to macrophages and B-cell.
- This B-cell activates the T-cell to provide an immune response.
FACTORS AFFECTING EFFICACY OF EDIBLE VACCINES
- Antigen selection.
- Efficacy in the model system.
- Choice of plant species.
- Delivery and dosing issues.
- Safety issues.
- Public perceptions and attitudes to genetic modification.
- Quality control and licensing.
PLANTS USED FOR EDIBLE VACCINE
Advantages and disadvantages of different plants
- Easily transformed.
- Easily propagated.
- Stored for long periods without refrigeration.
- Need cooking which denatures antigen
- Do not need cooking.
- Protein not destroyed even after cooking.
- Grown widely in developing countries.
- Trees take 2-3 to mature years.
- Spoils rapidly after ripening.
- Commonly used in baby food.
- High expression of the antigen.
- Grows slowly.
- Requires a glasshouse condition.
Properties of ideal vaccine
- It should be effective and affordable.
- Vaccination should be simple.
- Should not contaminate the environment.
- Long-lasting cellular and humoral immunity.
- Nontoxic or non-pathogenic.
- Very low levels of side effects.
- Do not cause problems in individuals with impaired immune systems.
DEVELOPING AN EDIBLE VACCINE
- There are two ways of developing an edible vaccine.
- In one case, the entire structural gene is inserted into the plant transformation vector between 5’ and 3’: this will allow the transcription and accumulation of encoding sequence in the plant.
- In the second case, epitope within the antigen are identified, DNA fragment encoding these can be used to construct gene by fusion with a coat protein gene from plant virus e.g. TMV or CMV.
- First human trials of a potato-based vaccine against Hepatitis B have reported encouraging results.
- The amount of HBsAg needed for one dose could be achieved in a single potato.
- Levels of specific antibodies significantly exceeded the protective level of 10mIU/mL in human
- Do not require administration by injection.
- Possible production of vaccines by low cost.
- Do not require separation and purification of vaccines from plant materials.
- Activate both mucosal and systemic immunity.
- Necessary syringe and needles not required.
- Economical in mass production and transportation.
- Heat stable, eliminating the need for refrigeration.
- Development of immunotolerance to vaccine peptide or protein.
- Consistency of dosage from fruit to fruit, plant to plant and generation-to-generation is not similar.
- The stability of the vaccine in fruit is not known.
- Dosage of vaccine would be variable.
- The selection of the best plant is difficult.
- Certain foods like potatoes are not eaten raw and cooking the food might weaken the medicine present in it.
- Not convenient for infants.
- Transgenic contamination can occur.
- Antibiotic resistance marker genes can spread from genetically modified food to pathogenic bacteria.
- Difficulty in dose maintenance.
- The edible plant-derived vaccines may lead to a future of safer and more effective immunization.