Vegetable Crops as Bioreactors for Production of Edible Vaccines

Vegetable crops offers innumerable wealth to human health by providing carbohydrates, proteins, vitamins,minerals,fats (minimal amount), antioxidants and dietary fibers. In recent years, with the advancement of technology, especially, in the field of molecular biotechnology, it has summoned in new era, an era where suitable vegetable crops can be used as a manufacturer of vaccines. The concept of edible vaccines was introduced by Dr.Arntzen and his colleagues to overcome the limit of traditional vaccine production. Edible vaccines hold great promise as a cost-effective, easy-to-administer, easy-to-store, fail-safe and sociocultural readily acceptable vaccine delivery system. It involves introduction of selected desired genes into plants and then the altered plant produces the encoded proteins. Initially, thought to be useful only for preventing infectious diseases, it has also found application in prevention of autoimmune diseases, birth control, cancer therapy, etc. The added advantage of Edible vaccines is mucosal-targeted vaccines, which cause stimulation of both systematic and mucosal immune response. Agrobacterium-mediated gene transfer and transformation via genetically modified plant virus are the common methods that have been used to produce effective vaccines. New approaches have been developed to increase the efficiency of transformation such as biolistic, electroporation, agro infiltration, sonication, and polyethylene glycol treatment. The integration of gene construct into the genome i.e. nuclear and chloroplast depends on the method of transformation used. Among nuclear and chloroplast transformation, most of the recently reported plant-based vaccines are produced through chloroplast transformation. The dengue virus vaccine targeting dengue-3 serotype polyprotein (DENV3prM/E) was produced in Lactuca sativa via chloroplast transformation.

Transgenic tomato plants expressing a malaria antigen (PfCP 2.9) (a chimera of the antigens MSP1 and AMA1 of Plasmodium falciparum) was obtained using Cotyledons of seven-day old tomatoes, cultivar Summers, transformed via Agrobacterium tumefaciens .

The expression of a surface antigen from bacterium streptococcus mutants in tobacco was used for demonstration of an edible vaccines, initially .Vegetable crops like potato, tomato, carrot, lettuce have been tested and found suitable for the vaccine production. In 1997, human trial on transgenic potato containing b-subunit of the E.coli heat "labile toxin for diarrhea was undertaken. 4 fold increase in serum antibodies was reported from 10 of the 11 volunteers. In 1999, Boyce Thompson Institute at Cornell University conducted a clinical trial on potatoes containing the Norwalk virus. Immune response was elicited in 19 out of 20 volunteers. Prodigene, a biotechnology company, is developing numerous industrial and pharmaceuticals protein from plants. The patent on different technologies for edible vaccines has been claimed by various labs and universities like Biocem;Rhone-Merieux claims on Rabies vaccine expressed in tomato plant, Recombinant antigen production in lettuce and spinach by Scripps Research Institute.

Edible vaccines hold great potential, especially in Third World countries where transportation costs; poor refrigeration and needle use complicate vaccine administration. Even though plant-based vaccines provide many benefits to the vaccine industry, there are still challenges that limit the rate of successful production of these third-generation vaccines. Even with all the limitations, continuous efforts are still ongoing in order to produce efficient vaccine for many human and animals related diseases owing to its great potentials. They also offer a convenient tool against the threat of bio-terrorism.

About Author / Additional Info:
I am a PhD scholar at Indian Agricultural Research Institute, working on molecular aspects in vegetable crops.