Viral and bacterial vectors of immunogenes.

A recent development in the production of experimental vaccines has been the use of the smallpox vaccine virus (vaccinia virus) as a carrier (vector) of the genes (immunogenes) which code for the protection-inducing proteins (immunogens) of unrelated viruses. The potential of these vector vaccines lies in the hope that such a vaccine would be cheaper, safer and/or more effective than existing vaccines to some pathogens. Vaccinia virus as a vector has attracted most attention to date because: several immunogenes can be inserted into its genome without destroying its infectivity; the immunogens appear to be produced normally; vaccinia virus has been used highly successfully to eradicate smallpox; and it has a wide host-range and thus might find veterinary as well as human medical application. Experimental vaccines, successfully tested in animals, have been prepared using immunogenes from influenza virus, hepatitis B virus and herpes simplex virus. Apathogenic enteric bacteria have some potential as vectors, most probably against enteric pathogens, although the potential of viral vectors is likely to be realized first. Parasitic worms and protozoa devastate millions of people. When the immunogens of these organisms have been identified there will be added impetus to investigate the potential of vector vaccines against these pathogens.