Biotechnology and Bioinformatics (1+1)

4.3.8. Peptide vaccines

Peptide vaccines comprise of synthetic peptides that are able to induce protective immune response when administered into the host.

i) To produce peptide vaccines it is necessary to identify immunogenic regions, also known as ‘epitopes’ on the antigenic protein .

• The term epitope refers to a stretch of 6-8 amino acids on antigens that specifically binds to antibodies or to receptors on immune T cells.
• Those epitopes that bind to the antibody produced by specific B cells are called as B-cell epitopes while those recognized by receptors on the surface of activated T-cells are termed as T-cell epitopes.
• Monoclonal antibodies are indispensable to identify the B-cell epitopes.

ii) A region with high sequence variability among several strain s of a pathogen is also chosen as a candidate for synthetic peptide vaccine.

Epitope mapping and use of peptide vaccines against fish pathogens are still in its infancy. Some of the B-cell epitopes have been identified on some fish viral proteins such as IHNV glycoprotein.

Synthetic peptide vaccines emulsified with Freund’s complete adjuvant has induced poor neutralizing antibodies than that of the native virus fish sera, which indicates that peptides alone are less immunogenic than the native protein.

• Synthetic peptide vaccines offer the advantage of safety, purity and low cost as compared to live or inactivated vaccines.
• It is now possible to induce virus neutralizing antibody response using peptides of specific amino acid sequences.
• The peptides can be chemically synthesized in pure form or made by bacterial expression using rDNA technology. In the latter case, the peptides may be fused into other expressed proteins (fusion peptides).