Subunit and peptide vaccine

1. Subunit and Peptide vaccine Adnya Desai M Sc I

2. Subunit vaccine These are defined as those containing one or more pure or semi pure antigens. Usually it consist of specific, purified macromolecules derived from pathogens. e.g. HSV type 1 and 2, HIV-1, FMD, Hepatitis-B vaccine

3. Disdvantages They generally requires strong adjuvants and these adjuvants often induce tissue reaction. Duration of immunity is generally shorter than the live vaccines. They often need to be linked to the carriers to enhance immunogenicity Several doses  must be given for proper life-long immunity.

4. Peptide vaccine The vaccine in which peptide of the original pathogen is used to immunize an organism. The best known example is foot and mouth disease, where protection was achieved by immunizing animals with a linear sequence of 20 amino acids. Synthetic peptide vaccines would have many advantages. Their antigens are precisely defined and free from unnecessary components which may be associated with side effects. They are stable and relatively cheap to manufacture. Furthermore, less quality assurance is required. Changes due to natural variation of the virus can be readily accommodated, which would be a great advantage for unstable viruses such as influenza.

5. Cont……. Synthetic peptides do not readily stimulate T cells. It was generally assumed that, because of their small size, peptides would behave like haptens and would therefore require coupling to a protein carrier which is recognized by T-cells. It is now known that synthetic peptides can be highly immunogenic in their free form provided they contain, in addition to the B cell epitope, T- cell epitopes recognized by T-helper cells. Such T-cell epitopes can be provided by carrier protein molecules, foreign antigens. or within the synthetic peptide molecule itself. Synthetic peptides are not applicable to all viruses. This approach did not work in the case of polioviruses because the important antigenic sites were made up of 2 or more different viral capsid proteins so that it was in a concise 3-D conformation.  

6. Advantage of peptide vaccine Production and quality control simpler No NA or other viral or external proteins, therefore less toxic. Safer in cases where viruses are oncogenic or establish a persistent infection Feasible even if virus cannot be cultivation

7. Disadvantages May be less immunogenic than conventional inactivated whole-virus vaccines Requires adjuvant Requires primary course of injections followed by boosters Fails to elicit CMI.  

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