Authors: Kumatkar Raghunath Bhimrao, Vivek K Singh, and Pratik I Bhoyar.
CCS Haryana Agricultural University, Hisar, Haryana, 125004.
Edible Vaccines:
Vaccines that one can eat, called edible vaccines are among the most unusual approaches for administering new vaccines. Edible vaccines are like subunit preparation, in that they are engineered to contain antigen, but bear no genes that would enable whole pathogen to form. These vaccines are mucosal-targeted vaccines, which cause stimulation of both systematic and mucosal immune response. Edible vaccines are currently being developed for a number of human and animal diseases, including measles, cholera, foot and mouse disease, and hepatitis B and C. Many of these diseases require booster vaccination or multiple antigens to induce and maintain protective immunity (Gidding et al., 2000). Plants have capacity to express more than one transgene, allowing delivery of multiple antigens for repeated inoculations (Conrad &Fiedler, 1998).
Why do we need to use Plant Vaccines:
Plant systems do not harbor human or animal pathogens and, therefore, they do not transmit such pathogens along with the target subunit vaccine (Schillberg et al., 2005). Moreover, they cost less to produce than via fermentation or bioreactors; plants can be grown in the field or in a greenhouse relatively inexpensively. When produced in edible parts of the plant, such as grain, fruit or even leaves, subunit vaccines may not require purification. Maintaining the antigenic protein within plant cells that are edible may also contribute to stability and reduce degradation. Another advantage of producing subunit vaccines in edible parts of a plant is the potential to deliver the orally rather than intramuscularly, providing a simple and easy means of administration to humans and animals (Mishra et al., 2008).
Mechanism of Action
Oral delivery stimulates mucosal immunity in the tissues lining the respiratory system and eliminates injection-related hazards. Plants structure may help in maintaining the antigenic property even after degradation in intestine. The antigens in transgenic plants are delivered through the tough outer wall of plant cells, which protects them from gastric secretions and finally break up in the intestines. The antigens are released and uptake by M cells in the intestinal lining that overlie peyer's patches and gut-associated lymphoid tissue (GALT), passed on to macrophages, other antigen-presenting cells; and local lymphocyte populations, generating serum IgG, IgE responses, local IgA response and memory cells, which would promptly neutralize the attack by the real infectious agent.
Achievements: a number of plants vaccines have been developed in many crops/plants like; transgenic potato expressing Norwalk virus antigen showed seroconversion, Cholera virus (CT-B gene) & hepatitis B in Banana, potato and vaccine for Newcastle disease in tobacco.
Advantages of Edible Vaccine:
- Reduced need for medical personnel and sterile injection conditions.
- Economical in mass production and transportation.
- Therapeutic proteins are free of pathogens and toxins.
- Heat stable, eliminating the need for refrigeration.
- Antigen protection through bioencapsulation
Limitations:
· 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.
· Stability of vaccine in fruit is not known.
· Selection of best plant is difficult.
Future prospects:
More research is being done to:
ü Determine if one vaccine can help protect against multiple diseases.
ü Determine what would be a good dose or how often vaccine would need to be taken.
ü If vaccine can cause a negative response instead of positive.
References:
Schillberg S, Twyman RM, Fischer R (2005). Opportunities for recombinant antigen and antibody expression in transgenic plants - technology assessment. Vaccine 23: 1764-1769.
Mishra N, Gupta PN, Khatri K, Goyal AK, Vyas SP (2008). Edible vaccines: A new approach to oral immunization. Indian Journal of Biotechnology 7: 283-294.
Giddings, G., Allison, G., Brooks, D. and Carter, A. (2000). Transgenic plants as factories for biopharmaceuticals. Nature Biotechnology 18, 1151-5.
Conrad, U and Fiedler, U (1998). Compartment-specific accumulation of recombinant immunoglobulins in plant cells: an essential tool for antibody production and immunomodulation of physiological functions and pathogen activity.
Plant Molecular Biology 38, 101-9.
About Author / Additional Info:
I am currently pursuing Ph.D. from CCS HAU, Hisar