Imagine a scenario where a child could be vaccinated against several major diseases, including measles, hepatitis B, and cholera, by merely eating a banana. This might seem a bit far-fetched at the moment, but in the near future, edible vaccines could be the preferred immunization delivery system. Plant-based, edible vaccines not only have the advantage of being more accessible at a world-wide level, but could also be cheaper to produce and safer than other types of oral and needle-based vaccines. Before edible vaccines are commercially available, however, several challenges must be overcome, including conducting more clinical trials in order to assess their safety, and achieving general acceptance from the public.
Edible Vaccines – Products of Transgenic Organisms
Vaccines are preparations that contain either weakened microorganisms, viruses, or parts of them, usually proteins. When the body’s immune system recognizes the foreign compounds, certain types of cells attack the invading bodies. The next time the same type of foreign proteins are detected in the body, the immune system is ready to attack before the pathogens have the chance to multiply. Conventional methods of producing vaccines include growing viruses or their recombinant proteins in animal, human or bacterial cells. The next step involves purifying the viruses or proteins and making them inactive.
Edible vaccines, on the other hand, are produced via genetically modified, or transgenic, organisms. In other words, foreign genes are inserted into plants so that they can produce viral proteins or antigens. There are two main methods of producing plant-based, edible vaccines. The first one involves using a gene gun to bombard plasmids containing foreign genes into embryonic cell cultures. The second method involves infecting plant tissues with Agrobacterium tumefaciens, a bacteria that contains a T-plasmid that is integrated into the plant’s genome in order to produce tumors in which it can then live. Prior to infection, the genes that generate the tumors are inactivated from the plasmid and both viral and antibiotic resistance genes are inserted. In this way, screening can be done to select the cells that are resistant to the specific antibiotic.
The Advantages of Edible Vaccines
Wider Accessibility – Vaccines in Bananas: Amongst the many advantages that edible vaccines have over conventional vaccine delivery methods, being accessible to more people stands out as the top one. Edible vaccines not only eliminate the inconvenience of syringes, but they can be more easily accessible for people living in remote areas. It is estimated that about 20% of infants are not vaccinated against major diseases, thus causing over 2 million deaths every year. (Sharma, et. al., 2007) This could easily be prevented by the production of transgenic plants, such as bananas, potatoes, or even grains, genetically engineered to produce vaccines.
Safety of Edible Vaccines Due to Being Antigenic Subunit Vaccines: Another important advantage of edible vaccines is that they all are antigenic subunit vaccines, meaning that they do not contain the pathogen’s DNA, but merely proteins, making them safer to administer. On the other hand, the elimination of needles further increases the safety of edible vaccines by preventing contamination with external pathogens.
Increased Efficiency and Reduced Costs of Edible Vaccines: Edible vaccines are more efficient than conventional vaccine delivery methods since they are able to induce mucosal immunity. In other words, as soon as the antigens make contact with mucous membranes, a fast immune response is generated. Edible vaccines could also be cheaper to produce because they would not require extensive purification, unlike conventional vaccines. This is due to the fact that plant viruses cannot infect humans; whereas vaccines generated in human, animal, or bacterial cells can be contaminated with external pathogens. (Sharma, et. al., 2009) On the other hand, edible vaccines could not only be easier to produce, but to store and transport as well, thus eliminating the high costs associated with cold-distribution chains.
Current Status in the Development of Plant-Based, Edible Vaccines
Several clinical trials involving edible vaccines are currently underway, with a couple already in phase III. A wide variety of plants have been deemed as effective transgenic organisms for the production of viral antigens, including potato, banana, spinach, tomato, tobacco, and papaya. Successful clinical trials involve more than 90% of enrolled patients producing antibodies against diarrhea-causing Escherichia coli and Norwalk Virus. On the other hand, phase I clinical trials have reported good results of a potato-based vaccine against hepatitis B. (Thanavala, et. al., 2000)
Potential Applications of Edible Vaccines – HIV Vaccines and Cancer Vaccines
Obstacles Against Edible Vaccines
Before they can be commercially available, edible vaccines must overcome several hurdles. In the first place, a dosage problem might occur, as the production of antigens is likely to vary from plant to plant. A possible way to overcome this would involve processing the transgenic plants into concentrated forms, so that dosing could be uniform. More studies need to be performed in order to determine the safety of edible vaccines, especially since horizontal gene transfer may occur, thus increasing the risk of creating new strains of viruses.
Perhaps the greatest hurdle that edible vaccines face is to gain acceptance from the majority of the public. In some countries, there is a strong resistance against transgenic organisms; however, a minority of people possess the adequate knowledge regarding this controversial topic. In the end, people must be well-informed before passing judgment about edible vaccines, especially because they could potentially save millions of lives each year.
