Edible Vaccines: Applications, Advantages and Limitations

In this article we will discuss about Edible Vaccines:- 1. Method of Developing an Edible Vaccine 2. Candidates for Edible Vaccines 3. Applications 4. Advantages 5. Limitations.

Contents:

1. Method of Developing an Edible Vaccine
2. Candidates for Edible Vaccines
3. Applications of Edible Vaccines
4. Advantages of Edible Vaccines
5. Limitations of Edible Vaccines

1. Method of Developing an Edible Vaccine:

Gene encoding antigen from pathogenic organ­isms (virus, bacteria or parasites) that have been characterized and for which antibodies are available, can be produced in the edible parts of the plants in two ways. In one case, the entire structural gene is inserted into a plant transformation vector.

This will allow transcription and accumulation of coding se­quence in plant. In second case, epitope within the antigen are identified, DNA fragment en­coding these can be used to construct genes by fusion with a coat protein gene from plant vi­rus, e.g., TMV or CMV. The recombinant vi­rus is then used to infect stabilized plants. The resultant edible plant vaccines are utilized for further immunological studies.

2. Candidates for Edible Vaccines:

Foods under study of edible vaccines include bananas, potatoes and tomatoes as well as let­tuce, rice, wheat, soybean and corn. When choosing a plant to be used as a vaccine it is important that it is a hardy, palatable plant with high nutritive and protein content. The plant is also one that would best be indigenous to the country in which it is to be used and should be able to be transformed with relative ease.

3. Applications of Edible Vaccines:

(a) Malaria:

Malaria remains one of the most significant causes of human morbidity and mortality worldwide, with 300 to 500 mil­lion new cases of infection annually result­ing in 1.5 to 2.7 million deaths. Three an­tigens are currently being investigated for the development of a plant-based malaria vaccine, merozoite surface protein (MSP) 4 and MSP 5 from Plasmodium falcipa­rum, and MSP 4/5 from P. yoelli.

(b) Hepatitis B:

The hepatitis B virus is esti­mated to have infected 400 million people throughout the globe, making it one of the most common human pathogens. The hepatitis B surface antigen (HbsAg) is used as a vaccine against Hepatitis B.

The HbsAg subtype ayw was cloned into CaMv plasmid and the regenerated plants from the transformed cells were shown to pro­duce HbsAg. Furthermore, expression of the antigen was found to be higher in roots of the transgenic potato than in leaf tis­sues.

(c) Measles:

Measles is a highly contagious viral disease caused by the Paramyxo virus spread by air and includes symptoms such as high fever, skin rash and spots. Each year, almost one million children die from the measles and many of the survi­vors are weakened by pneumonia or en­cephalitis or become deaf.

Recent studies report expression of the Paramyxo virus surface protein haemagglutinin in tobacco, potato, rice and lettuce with satisfying re­sults.

(d) Stopping Autoimmunity:

In the past 15 years, investigators have identified several cell proteins that can elicit autoimmunity in people predisposed to Type I diabetes. The development of plant based diabetes vaccine in potato was attempted.

The de­velopment of transgenic potato and tobacco plants when fed to non-obese diabetic mice showed increased levels of IgG, an anti­body associated with cytokines that sup­press harmful immune response. Feeding of the vaccines to mouse strain that becomes diabetic helped to suppress the au­toimmune attack and to prevent the delay of high blood sugar.

4. Advantages of Edible Vaccines:

Potential advantages of plant-based vaccines are:

a. Edible means of administration.

b. Reduced need for medical personnel and sterile injection conditions.

c. Economical in mass production and trans­portation.

d. Therapeutic proteins are free of pathogens and toxins.

e. Storage near the site of use.

f. Heat stable, eliminating the need for re­frigeration.

g. Antigen protection through bio-encapsulation.

h. Subunit vaccine (not attenuated patho­gens) means improved safety.

i. Seroconversion in the presence of mater­nal antibodies.

j. Generation of systemic and mucosal im­munity.

k. Enhanced compliance (especially in chil­dren).

l. Delivery of multiple antigens.

m. Integration with other vaccine approaches.

n. Plant derived antigens assemble sponta­neously into oligomers and into virus like particles.

5. Limitations of Edible Vaccines:

a. Development of immuno tolerance to vac­cine peptide or protein.

b. Consistency of dosage form fruit to fruit, plant to plant, and generation-to-genera­tion is not similar.

c. Stability of vaccine in fruit is not known.

d. Evaluating dosage requirement is tedious.

e. Selection of best plant is difficult.

f. Certain foods like potato are not eaten raw, and cooking the food might weaken the medicine present in it.