Vaccines - Recombinant DNA technology - Viral Agents - Types of Antigens

A vaccine is a preparation which contains an antigen composed of whole disease causing organisms or parts of such organisms. Vaccines are used to confer immunity against the antigen. The Vaccines currently in use have three types of antigens:

Dead microorganisms: Vaccines with bacterial or viral agents inactivated by various methods in order to preserve their antigen capacity.

Live or attenuated organisms: Living vaccines developed through exhaustive selection of mutant strains.

Toxiods: Some bacteria exert their pathogenic effects through the secretion of toxic proteins that act in various tissues of the host. These proteins are transformed into toxoids in order to make them lose their toxic activity but still retain their antigenic specificity. These toxoids induce the production of antibodies capable of neutralizing the native toxins by blocking their active sites.

Recombinant DNA technology can be used to clone the gene protective antigen protein. Small peptides may be synthesized, conjugated to carrier molecules and utilized as the sole antigen source for eliciting a protective immune response. Recombinant DNA technology has yielded remarkable results in the development of antimalarial vaccine. A number of vaccines against viruses have been developed using recombinant DNA technology.

Vaccines may also be developed using recombinant vaccinia virus genome. In this method DNA for surface antigen epitopes from viruses such as Influenza A or Hepatitis B are cloned into the vaccinia viral genome to the vacccinia derived and recombinant antigens and mounts a protective immune response to them. This results in a polyvalent vaccine.

Through Recombinant DNA technologies, it has become possible to identify the DNA sequences that codes pathogenecity determinants e.g. production of toxins. By eliminating those specific sequences, it is possible to transform the microorganism into an attenuated variant that retains all other characteristics and can be used as an immunization agent.

Vaccines can be elaborated against the surface structure of the microorganism. Those structures, usually proteins, are extremely important in the initial stages of infections and are specific for each microorganism. Those proteins can be produced on large scale by DNA fragments cloned in E.coli having the sequence coding adhesion structures.