Edible Plant Derived Vaccines Against Hepatitis B Virus Biology Essay



Vaccines have greatly been used in the past to fight against infectious diseases. It is through vaccines that small pox has been consigned to history and soon the case will apply to polio. In the late 90's the international campaign to immunize the world's children against the six fatal diseases reached eighty percent of infants thus reducing the death toll by approximately three million. The 20 percent of infants left out of immunization account for more than sixty percent of the three million deaths a year. This is more so in poverty stricken and remote parts of the world. There is a great risk to erode the advances made in the past few years as millions of infants continue to die of infectious diseases whose immunizations are unreliable, too costly or non-existent. This has rendered the World Health Organization to look for affordable vaccines from herbal sources (Guynup 2000).

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According to the estimates of world health organization, more than ten million children die mostly from developing countries every year for cases related to infectious diseases that may be prevented by vaccination. The existing vaccines are too costly and require experts in administration. Equipments like refrigeration to be used are also rare in developing countries thus making it even harder to administer the vaccines to the infants. This has rendered to re-use of needles making the infants vulnerable to viruses like HIV, hepatitis B and C.

How Edible Vaccines Work

Edible vaccines which are vaccines that are based on plants are cheaper, safer, can be grown, freeze dried and shipped to various global locations. Edible vaccines work in two ways: first, they initiate mucosal immunity and secondly they create systematic response to stimuli. The mucosal immunity fights germs in areas where germs first attack the body. Such areas include the mucous membranes of the genitals, gut, mouth, lungs and nose. The biggest question with regard to edible vaccines is whether the antigens they produce is recognized in the animal's immune system. The edible vaccines have to be taken raw as cooking breaks down the proteins that trigger the needed immune system response (Arntzen, 2000). According to the Word Health Organization, edible vaccines will help overcome some of the main obstacles faced in the administration of traditional vaccines as noted by Whyfiles (2002).

Edible Vaccine for Hepatitis B

Hepatitis B has been known to be among the most infectious diseases of recent times. The HBVs comes in the form of forty two nM double shelled particles that are spherical in shape but blood analysis from carriers of Hepatitis B virus show the presence of smaller twenty two nM particles that consist of viral envelopes with surface proteins. The particles have been very beneficial in the research of hepatitis B vaccine. The particles are highly immunogenic and currently used in the design of hepatitis B virus vaccine produced in yeast. The proteins form particles which are virus-like when they get expressed in yeast used for parenteral immunization.

In a research, the DNA fragment encoding hepatitis B virus antigen was added to agrobacterium tumerifacience LBA4404 and used to obtain Lupinus luteus L and Lactuca sativa L Burpee Bibb expressing envelope surface protein. The tests which were carried out on mice showed responses indicating significant levels of hepatitis B antibodies. There were human volunteers who were fed with transgenic lettuce plants expressing hepatitis B virus surface antigen. The volunteers developed specific serum IgG response to the plant produced protein.

The only economically feasible approach to vaccine mode of giving the vaccine is oral or intranasal vaccine administration. Currently, there are very few vaccines that can be administered using such methods. With the use of staple foods as vaccines, the number of vaccines that can be intranasal or orally administered is bound to be on the rise. There are quite a number of engineered pants that have biomedical substances that are important to the human immune system.

Manufacture of the Vaccine

The manufacturing process for the Hepatitis B edible vaccine kicks off by DNA cloning. All enzymatic digestions, cell transformations, litigations and other DNA manipulations are carried out according to medically accepted practices. The plasmid pROK is used as a shuttle vector incorporating HBsAg coding sequences into the A. Tumefaciens Ti-plasmid. The HBsAg is cloned from pHB614 that contains the full genome of HBV adw subtype to obtain pROK2S. The plasmid pROK2S that carries the HBsAg coding sequence is electro-porated into A. tumefaciens strains LBA4404and C58.

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The second step involves plant transformation whereby a young plant (four-day old seedling of Lupinus luteus L for example) is primarily used as a explant. The distal parts are removed and cotyledons transformed using A. tumefaciens C58. The seedlings are cultivated on antibiotic free murashige skoog (modified) medium for two days and the explants transferred to special medium for callus growth stimulation. The transgenic lines are selected and the medium supplemented with carbenicillin and kanamycin. The kanamycin calli resistant are isolated and cultured further. The cotyledons isolated from two day old lettuce seedlings are inoculated with A tumefaciens LBA4404 and the transgenic lettuce plants obtained. This is followed by protein extraction and analysis.

The protein from the plants is extracted from the transgenic tissue homogenized in phosphate buffer. The homogenate is to be centrifuged at thirty thousand times for fifteen minutes in order to remove non-homogenized cell debris. The HBsAg in the supernatant is quantitated through use of Auszyme monoclonal diagnostic kit. The amounts of antigen in the extracts of plants are calculated using a standard curve based on differential concentrations of purified HBsAg.

To test the effectiveness of the vaccine, five human volunteers aged between twenty five and sixty years who are in good health may be used. The volunteers must have had no previous HBV vaccination or history of HBV infection. Furthermore they must have no traces of anti HBv serum and anti HBs antibodies. The results of the research show that there is presence of anti-HBsAg specific anti bodies by immuno-absorbent assay.

In conclusion, there are various benefits that arise with the use of plant based vaccines. The vaccines are generally cheap and affordable. This enables a bigger population to access the vaccines especially those from remote places. The developing countries through use plant based vaccines, will be able to meet the medical needs of most of the citizens. Plant vaccines can be orally administered therefore obviating the need for injection equipment. This removes fears of unsafe injection as well as the injection associated equipments like refrigeration and coolants. Oral activity permits wider range of service providers to administer the vaccines and requires formulation and production regulations less vigorous as compared to injected products. Heat stability, mucosal effectiveness is a common nature of the edible vaccines.