Recombinant Hepatitis B Vaccine

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Chapter: Pharmaceutical Microbiology : Recombinant DNA Technology

Before the development of recombinant DNA technology, two main strategies were employed for vaccine production: the generation of inactivated vaccines consisting of chemically killed derivatives of the infectious agent, and of attenuated vaccines, which are altered viruses and bacteria that are avirulent and can no longer cause disease.


RECOMBINANT HEPATITIS B VACCINE



Before the development of recombinant DNA technology, two main strategies were employed for vaccine production: the generation of inactivated vaccines consisting of chemically killed derivatives of the infectious agent, and of attenuated vaccines, which are altered viruses and bacteria that are avirulent and can no longer cause disease. However, these vaccines were potentially dangerous as they could be contaminated with infectious organisms or revert to a virulent form. To avoid these problems, recombinant DNA technology has enabled the production of subunit vaccines consisting solely of immunogenic surface proteins which can elicit immune responses without the risk of infection.

 

The hepatitis B virus (HBV) vaccine was the first successful subunit vaccine developed. This virus infects the liver and can cause serious damage. This virus has a surface antigen, HBsAg, which is found in blood of infected patients and has been found to elicit a significant immune response. The gene coding for this antigen has been isolated from the virus and cloned into a vector that allows high expression of the HBsAg protein in yeast cells. Figure 25.11 shows the strategy currently used for the generation of recombinant HBV vaccine. In this case, as the 3.2-kb genomic sequence of the HBV virus was known, the gene coding for the HBsAg was directly cloned into a shuttle expression vector that replicates in both, E. coli for the genetic manipulation steps, and in yeasts such as Saccharomyces cerevisiae for the production of the recombinant antigen. Transcription of the gene encoding HBsAg is driven from a strong yeast promoter and is stopped by a transcriptional terminator present in the vector. The vector also has a leucine biosynthesis marker for selection in yeasts and a tetracycline resistance marker for selection in bacteria. The yeast harbouring this plasmid can grow in fermenters in the absence of leucine, generating large amounts of the antigen that can subsequently be extracted from the cells.

 


 

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