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Recombinant Vaccines -

A recombinant vaccine contains either a protein or a gene encoding a protein of a pathogen origin that is immunogenic and critical to the pathogen function; the vaccine is produced using recombinant DNA technology. The vaccines based on recombinant proteins are also called subunit vaccines.

The logic of such vaccines, in simple terms, is as follows. Proteins are generally immunogenic, and many of them are critical for the pathogenic organism. The genes encoding such proteins can be identified and isolated from a pathogen and expressed in E. coli or some other suitable host for a mass production of the proteins.

The concerned proteins are then purified and mixed with suitable stabilizers and adjuvants, if required, and used for immunization. The different steps involved in the development of a recombinant protein based vaccine may be simply summarised as follows.

(i) The first step is to identify a protein that is both immunogenic and critical for the pathogen.
(ii) The gene encoding this protein is then identified and isolated.

(iii) The gene is integrated into a suitable expression vector and introduced into a suitable host where it expresses the protein in large quantities.

(iv) The protein is then isolated and purified from the host cells.
(v) It is used for the preparation of vaccine. The host organisms used for expression of immunogenic proteins to be used as vaccines may be anyone of the following.

1. A genetically engineered microorganism, e.g., yeast for the expression of hepatitis B surface antigen (HBsAg) used as vaccine against hepatitis B virus (approved for marketing in India).

2. Cultured animal cells, e.g., HBsAg expressed in CHO (Chinese hamster ovary) cell line and C-127 cell line.

3. Transgenic plants, e.g., HBsAg, HIV-l (human immunodeficiency virus-I) epitope (in experimental stages).

4. Insect larvae; the gene is integrated into a bacculovirus genome, which is used to infect insect larvae. Often a very high quantity of the recombinant protein is produced.

So far a large number of recombinant immunogenic proteins of pathogens have been produced and evaluated. In general, a majority of such proteins are ineffective or only poorly effective in immunization.

 

 
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