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Home » Biology Homework Help » Biotechnology » Disease Prevention Vaccines
Disease Prevention Vaccines
Prevention of disease is the most desirable, most convenient and highly effective approach to health; this is achieved by vaccination or immunization using biological preparations called vaccines. Vaccines represent an invaluable contribution of biotechnology as they provide protection against even such disease for which effective cures are not yet available. The effectiveness of vaccines may be appreciated from the fact that small pox, once a dreaded disease the world over, has been completely eradicated from the world.

An ideal vaccine

An ideal vaccine or vaccination protocol should have the following features:

1. It should not be tumerogenic or toxic pr pathogenic, i.e. it should be sage.

2. It should have very low levels of side effects in normal individuals.

3. It should not cause problems in individuals with impaired immune system.

4. It should not spread either within the vaccinated individual or to other individuals (live vaccines).

5. It should not contaminate the environment.

6. It should be effective in producing long lasting humoral and cellular immunities.

7. The technique of vaccination should be simple.

8. The vaccine should be cheap so that it is generally affordable. So far, such an ideal vaccine has not been developed.

Conventional vaccines


Conventional vaccines consist of whole pathogenic organisms which may either be killed (most bacterial vaccines and some viral vaccines), or live [hence called live vaccines; the virulence of pathogens is greatly reduced (attenuation); most viral vaccines].

Purified antigen vaccines

These vaccines are based on purified antigens isolated from the concerned pathogens, i.e. these are nonrecombinant). Since they do not contain the organism, the risk of pathogenicity is avoided. However, their cost is higher due to the steps involved in purification and vaccine preparation, and many of the isolated antigens are poorly immunogenic. Successful examples of such vaccines are mostly from bacteria, e.g. vaccines based on polysaccharide antigens from the bacterial cell wall capsules of Neisseria meningitis and Streptococcus pneumonia.

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 (= proteins produced by recombinant DNA technology) 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 suppressed in E. coli or some other suitable host for a mass production of the proteins.

Recombinant polypeptide vaccines

Generally, the whole protein molecule is not necessary for immunogenicity; the immunogenic property is usually confined to a small portion of the protein molecule. For example, the immunogenicity of foot-and-mouth disease virus coat protein is due to its amino acids 114-160, and also 201-213. Segments of proteins containing either of these two amino acid sequences are effective in immunization; they induce antibodies which neutralize the virus and thereby provide protection against the foot-and-mouth disease. Similarly, the immunogenicity of coat protein of feline leukemia virus (FLV) is due to 14 amino acid long segment; this segment produced a partial immunogenic response in guinea pigs.

DNA vaccines

Recently, vaccines on DNA are being developed, and the results obtained with influenza virus are quite exciting; these are regarded as the third revolution in vaccines. The strategy of DNA vaccines is as follows. The gene encoding the relevant immunogenic protein is isolated, cloned and then integrated into a suitable expression vector. This preparation is introduced into the individual to be immunized. The gene is ultimately expressed in the vaccinated individual and the immunogenic protein is expressed in sufficient quantities to invoke both humoral and cell-mediated immunities. It may be pointed out that cell-mediated immune response is essential for recovery from infectious diseases. The various approaches for DNA vaccines are as follows: (i) injection of pure DNA (or RNA) preparation into muscle; (ii) use of vectors (e.g. vaccinia viruses, adenoviruses, retroviruses, E. coli, Salmonella typhimurium, herpesviruses etc.) for delivery of gene, (iii) reimplantation of autologous cells (cells of the individual to be vaccinated) into which the gene has been transferred, and (iv) particle gun delivery of plasmid DNA which contains the gene in an expression cassette.

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