Third Generation Vaccines

Genetically Engineered Vaccines/Synthetic Vaccines/Third Generation Vaccines

	Genetically Engineered Vaccines/Synthetic Vaccines/Third Generation Vaccines These are also called synthetic vaccines or third-generation vaccines. While opting for a killed vaccine one must ensure that (i) enough material could be produced cheaply and (ii) no infectious virus survives the inactivation procedure. The recently developed DNA technology could identify the part of the viral genome that encoded the particular virus protein against which protective immunity (usually antibody) was directed.
Viral DNA, or a DNA copy of the virus that had an RNA genome, can be excised and inserted into an appropriate expression vector together with control (promoter, stop and polyadenylation) signals. Thus we have a small part of the viral genome, by definition noninfectious, which by insertion into host cells growing on an industrial scale will produce very large amounts of protein very cheaply. One even need not to grow the virus in culture, a great advantage for viruses like Hepatitis B.
What are the plus and minus points of Genetically Engineered Vaccines? Well the advantages are that they are noninfectious, their large scale production methods are available, are cheap. to produce and can use genes from noncultivable viruses. At the same time the problems likely to arise are, identification of neutralisation antigen, need for proper co and post translational modifications of viral polypeptide, need for proper assembly of viral protein to avoid poor immunogenicity, and separation of viral protein from cell constituents.
Genetic engineers are likely to utilise bacterial expression systems. However, the important human and veterinary diseases are caused by viruses of eukaryotes whose newly synthesised polypeptides undergo co translational and post translational modifications such as glycosylation and proteolytic cleavage which prokaryotic cells cannot accomplish, therefore we have to use eukaryotic cells. However, technology is well-developed for cultured cells of higher animals (including monoclonal antibody production) and bulk culture of yeast. Experimental vaccines composed of influenza virus haemogglutinin, hepatitis B virus surface (S) antigen and foot and mouth disease virus have been produced. But it has been found that genetically engineered proteins are poorly immunogenic as compared with the same antigens assembled into natural virus particles.

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