Animal Biotechnology

RECOMBINANT VECTORED VACCINES

• It is possible to introduce genes that encode major antigens of especially virulent pathogens into a non-pathogenic or avirulent viruses or bacteria. These organism serves as a vector, replacing within the host and expressing the gene product of the pathogen. A number of organisms have been used for vector vaccines, including vaccinia virus, the canary poxvirus, attenuated poliovirus, adenoviruses, attenuated strains of Salmonella, and the BCG strain of Mycobacterium bovis.
• Vaccinia vector has widely been employed as a vector vaccine. This large, complex virus, with a genome of 200 genes, can be engineered to carry several dozen foreign genes without impairing its capacity to infect host cell and replicate. The genetically engineered vaccinia expresses high levels of the inserted gene product, which can then serve as a potent immunogen in an inoculated host.
• The canary poxvirus has recently been tried as a vector vaccine. Like its relative vaccinia, the canary poxvirus is a large virus that can be easily engineered to carry multiple genes. Unlike vaccinia, the canary poxvirus does not appear to be virulent even in individuals with severe immune suppression. Another possible vector is an attenuated strain of Salmonella typhimurium, which has been engineered with genes from the bacterium that causes cholera. The advantage of this vector vaccine is that Salmonella infects cells of the mucosal lining of the gut and therefore will induce secretory IgA production.