A ‘mucosal immune response’ is necessary particularly for combating infection due to bacteria/viruses invading epithelial membrane. Mucosal immune system involves production of secretory igA at mucosal surfaces such as gut and respiratory epithelia. Such a response more easily achieved by oral vaccine rather than by parenteral antigens delivery system.
Particulate antigen rather than submit or soluble antigens have been shown to be effective oral immunogens. The subunit vaccine whenever used require larger amounts of antigens and will be expensive if produced in Recombinant cell culture expression system, which will need fermentation technology.
In contrast to this, transgenic plants can be made to express the antigens in particulate form in the edible tissue, which can then be used as food, thus providing an inexpensive oral vaccine production and delivery system.