Edible Vaccines

EDIBLE VACCINES

Pritish Sareen

3208081

Life Sc. 3rd Year

•Discovery: Cow pox (latin Variolæ Vaccinæ) as vaccine for Small Pox by Edward Jenner in 1756.

•Successful Vaccines against diphtheria, measles, mumps, rubella and polio.

•Contains killed or attenuated microbe or its toxin.

Vaccine

•20% world infants not immunized. •Accounts for 2 million deaths annually.•Un-immunized populations can spread infections and epidemics.

Current Status

Do you think this boy is happy?

•Uneasy administration.

•Need for Skilled medical personnel

•Sterile injection conditions.

•Heat unstable vaccines, need to refrigerate.

•Expensive Production

Shortcomings of Traditional Immunization

“Let thy Food be thy Medicine”

•Scientists suggested genetically engineering plant and plant viruses to produce vaccines – Concept of Edible Vaccines.

•Introduction of desired gene into plants and then inducing these altered plants to manufacture the encoded proteins i.e. transformation to produce transgenic plants.

As Hippocrates once said-

Production

A. Entire structural gene is inserted into a plant transformation vector. This allows the transcription to take place and then the coding sequence is accumulated in the plant.

B. Epitope within the antigen are identified and DNA fragment encoding these can be used to construct genes by fusion with a coat protein gene(capsid gene) from plant virus. The recombinant virus is then used to infect plants.

Production

Methods for Transformation:

A. Agrobacterium

As we have studied, it is a naturally occurring bacterium which has the ability to induct into plants through a wound. It has a circular ‘Ti plasmid’ (tumor inducing) which enables it to infect plants, integrate into their genome and produce a hollow tumor i.e. crown gall tumor, where it can live. This ability can be exploited to insert foreign DNA into plant genome. But prior to this the plasmid needs to be disarmed by the deletion of genes for auxin and cytokine synthesis so that it does not produce tumor. After successful induction, genes for antibiotic resistance are used to select out (Selection) the transformed cells and whole plants, which contain the gene.

Methods for Transformation:

B. Biolistics (Gene Gun)

In this method, selected DNA sequences are precipitated onto metal micro particles and bombarded against the vegetable tissue with a particle gun. Micro particles penetrate the walls and release the DNA inside the cell where it will be integrated in the nuclear genome.

Methods for Transformation:

Mechanism Of ActionThe goal of oral vaccine is to stimulate both mucosal and humoral immunity against pathogens.

Edible vaccine when taken orally undergoes mastication process and the majority of the plant cell degradation occurs in the intestine as a result of action on digestive or bacterial enzymes on edible vaccines. Peyer′s Patches (PP) are an enriched source of IgA producing plasma cells and have the potential to populate mucosal tissue and serves as mucosal immune effector sites. The breakdown of edible vaccine occurs near PP, consisting of 30-40 lymphoid nodules on the outer surface of the intestine and contain follicles from which germinal centre develops upon antigenic stimulation. These follicles act as the sites from which antigen penetrates the intestinal epithelium, thereby accumulating antigen within organized lymphoid structure. The antigen then comes in contact with M-cells. It contacts with the lumen with broad membrane processes and contains a deep invagination in the basolateral plasma membrane. This pocket is filled with a cluster of B-cells, T-cells and macrophages. M-cells express class II MHC molecules and antigens transported across the mucous membrane 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 (MALT) 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

Mechanism Of Action

Edible means of administration.

Storage near the site of use.

Reduced need for medical personnel and sterile injection conditions.

Economical in mass production and transportation.

Heat stable, eliminating the need for refrigeration.

Subunit vaccine (not attenuated pathogens)

means improved safety.

Generation of systemic and mucosal immunity.

Enhanced compliance (especially in children).

Delivery of multiple antigens.

Integration with other vaccine approaches.

Advantages of Edible Vaccines

1998 - FIRST HUMAN TRIAL SHOWS THAT AN EDIBLE VACCINE IS FEASIBLE

First Human Trial By researchers supported by the National Institute of Allergy and Infectious Diseases (NIAID), US.

Potato engineered to produce the toxin of Diarrhea causing E.coli.

Blood and stool samples periodically collected.

91%- Four times rise in Serum Antibodies.

55%- Four times rise in Intestinal Antibodies.

Applications

•Malaria- 3 Antigens under testing show positive result in mice. Human application still uncertain.

•Measles- MV-H Antigen encapsulated plant vaccine induced IgA antibodies in animals. Carrot and banana can be used.

•Hepatitis B

•Diabetes

•Stopping Autoimmunity

•Cholera

Recent Developments•Second Generation Edible Vaccines- Multi antigenic vaccines. Obtained by by crossing 2 plant lines having different antigens.

•Using Alfalfa Mosaic Virus- For HIV & Rabies vaccine.

•Rabies Virus- successful expression in tomato.

•Edible Anthrax Vaccine

•Edible SARS Vaccine

•Interleukin 10 producing Tobacco

•Potato expressing Rotavirus VP7

•Possible Application for Cancer Vaccine

ChallengesScientific Challenges

•Need to consider person’s weight,age; fruit/plant size, ripeness and protein content.

•Amount to be eaten critical. Especially in infants who might spit it or eat a part of it.

•Regulatory Concerns- Lot-to-lot consistency, uniformity of dosage and purity.

•Dealing with diseases caused by multiple serotypes(dengue) or by complex life cycles of parasites(malaria) or by rapidly mutating organisms (HIV, influenza).

•Each plant- unique advantages and disadvantages.e.g. potato is not eaten raw and cooking it might weaken the medicine present in it.

•Only Small Companies undertaking Research

•Efforts under funded

•Lack of R&D personnel in Pharma Companies

•Some vaccines for e.g. diphtheria, tetanus etc. are already cheap so no incentive in R&D

Non-Scientific Challenges

Conclusion

•However with limited access to essential healthcare in much of the world and with the scientific community still struggling with complex diseases like HIV, malaria etc., a cost effective, safe and efficient delivery system in the form of edible vaccines will become an essential component in our disease-prevention arsenal.

•Edible Vaccines are the future of safer and more effective immunization. Before becoming a reality, the technical obstacles need to be overcome.

•Indian Journal of Biotechnology Vol 7, July 2008

• Indian Journal of Medical Microbiology

•www.molecularfarming.com

References