Edible Vaccines

Edible Vaccines - Antigens of several pathogens, e.g., enteric pathogens, produce immunogenic response when delivered orally; such antigens are good candidates for edible vaccines. The strategy, in simple terms, is as follows. The gene encoding the orally active antigenic protein is isolated from the pathogen, and a suitable construct for constitutive or tissue-specific expression of the gene is prepared.

The gene contract is introduced and stably integrated into the genome of selected plant species, and is expressed to produce the antigen. The appropriate plant parts containing the antigen may be fed raw to animals or humans to bring about immunization.

For animals, crops used as feed, e.g., alfalfa, are suitable for the expression of such antigens, while for humans fruits like banana, which are consumed raw, have to be used.

Thus edible vaccines are produced from transgenic plants in which an orally active antigen of the target pathogen is expressed and accumulated, and which is fed to animals/humans for immunization against the pathogen.

The edible vaccines are expected to alleviate the storage problems, offer an easy delivery system by feeding and would have much lower costs than the recombinant vaccines produced by bacterial fermentation. The development of edible vaccines for animals is the first objective, and would be followed by those for humans.

It may be pointed out that animals develop a tolerance to the components of their routine food, so that these become non-immunogenic in them. Therefore, edible vaccines can not be used as a regular component of animal/human food.Several genes encoding antigenic proteins have been expressed in plants where they are produced in their native immunogenic forms.

An example of an edible vaccine is provided by the E. coli heat labile enterotoxin (LT) B.subunit (LT-B) expressed in potato. Potato tubers containing LT-B were fed raw to mice. Only four feedings of 5 g tuber each induced immune response in mice, while mice fed on normal nontransgenic tubers did not show any immune response.