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Edible Vaccines - Immunization with Plants or Food

BY: Shalini Balan | Category: Healthcare | Submitted: 2011-11-04 08:09:20
 

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Biotechnology in Healthcare - EDIBLE VACCINES

Biotechnology has the potential to bring tremendous benefits, where in basic biology with the use of living organisms and bioprocesses are applied in engineering, technology, medicine and other fields. Biotechnology has various applications in healthcare, almost everybody is enthusiastic about the promise of biotechnology to cure disease and to relieve suffering and yet many people in the world are still struggling to get healing in spite of it being curable !!!!! What could be the reason?

Statistics show that around thirty millionĀ children throughout the world do not receive even the most basic immunizations each year. As a result, at least three million of these children die from diseases that are fully vaccine-preventable. The solution - to vaccinate these children - might seem simple. But, mass vaccination in developing countries has met with numerous obstacles. In many countries either the vaccines itself is too expensive to be used in a large scale or there is lack of physical infrastructure (eg.roads and refrigeration). They are costly to produce and package, provided they require trained personnel to administer injections. Clearly it would be advantage if the vaccines could be delivered inexpensively on a broad scale in edible form as a part of fruit or vegetable.

Immunizations taken with food ? Sounds more pleasant than a jab in the arm, but could it be a reality - This is one of the major inventions of biotech in field of health care. -called " EDIBLE VACCINES".

WHAT ARE EDIBLE VACCINES?

Edible vaccines Vaccination is a disease preventive measure, where the immune system of a person is boosted against a particular disease.

The introduction of a foreign DNA into the eukararyotic cells is called transfection.And the eukaryotic organism which has taken the DNA is termed as transgenic. Transgenic plants are used as recombinant protein production systems and the edible plant tissue functions as an oral vaccine.


BENEFITS OF EDIBLE VACCINE

An edible vaccine in contrast to the traditional vaccines would not require elaborate production facilities, purification, strerilization, and packaging or specialized delivery systems. Injectable vaccines are usually made by synthesizing antigenic proteins in mammalian cell culture. The process is very expensive, requiring specially-built manufacturing facilities. Complicated and time consuming procedures are necessary to purify the proteins from cell cultures. Additionally, vaccines synthesized in mammalian cells can potentially be contaminated with organisms that are pathogenic to humans - a problem that would not arise when using plants to synthesize vaccines. Fruits and vegetables carrying vaccines are also advantageous in that they can be delivered without needles, do not require refrigeration and can be made, less expensively, right in the area in which they will be delivered.

When edible vaccine is taken orally they stimulate the immune system to generate antibodies to a pathogen. The immune system keeps a record of this first encounter and, if the body is later infected with the intact pathogen, the immune system is able to mount a stronger, more effective response.

Potatoes, tomatoes, rice tobacco, lettuce, safflowers, carrots and other plants have been genetically engineered to produce insulin and certain vaccines. If future clinical trials prove successful, the advantages of edible vaccines would be enormous, especially for developing countries. The transgenic plants may be grown locally and cheaply.

To date, potato and tomato plants have been successfully modified to synthesize antigens from Norwalk virus, Vibrio cholerae, and hepatitis B virus. The results so far have been very promising. The vaccine-bearing potatoes and tomatoes produced good levels of blood serum and mucosal immunity. Researchers have also developed bananas that deliver a vaccine for hepatitis B virus. The banana vaccine is expected to cost just 2 cents a dose, as compared to the $125 cost for the currently available injectable vaccine.

TRANSFORMING PLANTS INTO VACCINE FACTORIES

The process of creating a plant that produces a vaccine begins with the first step of isolating a gene which codes for an antigenic protein of a target pathogen. This gene is then linked with a regulatory sequence that has the ability to promote high levels of gene expression. The resulting expression cassette is inserted into the plant's genome and becomes part of the genetic material present in each of the plant's cells. Plant cells with their walls removed (protoplasts), can take up foreign chromosomes or DNA directly from the environment with a very low efficiency.

The modified plant now has the ability to synthesize the foreign protein in all of the fruits or vegetables that it produces. When someone eats a fruit or vegetable from the modified plant, they are essentially eating the vaccine.

Various foreign proteins including serum albumin, human a -interferon, human erythropoetin, and murine IgG and IgA immunoglobulins have been successfully expressed in plants.

Edible plant vaccine against diarrhea, expressed in potato, and antibody against dental caries, expressed in tobacco, is already in pre-clinical human trials. Attempts are being made to express many proteins of immunotherapeutic use at high levels in plants and to use them as bio-reactors of the modern era .In the case of insulin grown in transgenic plants, it is well-established that the gastrointestinal system breaks the protein down therefore this could not currently be administered as an edible protein. However, it might be produced at significantly lower cost than insulin produced in costly bioreactors.

OVERCOMING THE HURDLES

One of the major obstacles is developing plants that deliver sufficient quantities of a vaccine. When ingested, the edible vaccine must first maneuver through the harsh environment of the gastrointestinal tract. While oral administration of proteins has proven difficult, scientists have discovered that proteins protected by fruit and vegetable materials are able to make it through the digestive system. Even with the added protection, the stomach and intestines digest some of the proteins before they reach the immune system, so it is essential that the foods contain high concentrations of the vaccine. Getting the right amount of vaccine is also critical. Too much vaccine can lead to tolerance of disease rather than immunity and too little vaccine may not provoke an effective immune response.

Many of the first edible vaccines were synthesized in potato plants. Because raw potatoes are not very appetizing, researchers tried boiling the potatoes. But, the cooking process broke down about 50% of the proteins in the vaccine. While some proteins are more tolerant of heat, for most proteins it will be necessary to amplify the amount of protein in the engineered foods if they are to be cooked before consumption.

Tomatoes are also an excellent vehicles to deliver vaccines, because they are easy to manipulate genetically and new crops can be grown quickly. While tomatoes do not grow well in the regions in which the edible vaccines are most needed, the engineered tomatoes can be dried or made into a paste to facilitate their delivery. Genetically modified bananas are also a practical option. Children tend to like bananas and banana plants grow well in the tropical areas in which the vaccines are needed.

Transgenic plants have to grown in controlled manner by making them sterile and unable to reproduce to prevent cross pollination into our normal food supply. As an a alternative, bananas are used for genetic engineering since they do not breed and therefore their genes will not escape into the environment through seeds or pollen. Still, before they can gain FDA approval, researches must show that the edible vaccines are as effective and safe as the injectable vaccines.

But still with all these disadvantages, advancements in biotech brings us one step closer to the goal that one day edible vaccines can be used to immunize all children against the 6 most threatening diseases of measles, tetanus, diphtheria, pertussis, polio and tuberculosis. Even beyond that, there is the hope that edible vaccines can be used to conquer the spread of many other serious illnesses including yellow fever, hepatitis B virus and cholera.

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