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Most existing vaccines are prepared from an attenuated version of the pathogen or from inactivated disease-causing organisms or a suitable part of it e.g. a toxin. However, often the antigen to which the immune system responds is a relatively small number of amino acids or peptide.
A possible alternative approach to immunization would therefore be to identify the peptide sequences that trigger a protective immune response and to use completely synthetic versions of these as the vaccine substance. Because they would be synthetic, there would be no risk of mutation or reversion, little or no risk of contamination by pathogenic or toxic substances, and chemical manipulation of the peptide structure could possibly increase stability and decrease unwanted side effects seen in the native sequence. The number of antigens prepared this way would also increase, substituting for microorganisms that grow poorly in culture, or "exposing" parts of the antigen that are not seen by the immune system during natural infection. Due to the ease in sequencing new strains and serotypes of microorganisms, peptide antigens could be rapidly modified to generate strain-specific responses. However, the approach is not without practical and theoretical difficulties. Often the antigenic epitope is not a simple sequence of amino acids, but a structure composed of various parts of the protein sequence coming together to build a three-dimensional structure. Modelling of these structures will be needed to generate the correct antigenic site synthetically.
Synthetic Peptide Vaccine Standardization
WHO developed guidelines to provide a scientifically sound basis for the development, production and control of synthetic peptide vaccines in 1999. These include specifications for starting materials, the manufacturing processes, and quality control of final products.