The live vector approach-viruses.

Recombinant DNA technology has made it possible to express foreign genes in viruses and bacteria. This has led to the idea of engineering live attenuated vaccines to express protective antigens from foreign pathogens. Vaccinia virus, the smallpox vaccine, has been used to ploneer this approach. Several hundred recombinants have been recorded in the literature and many of them have been shown to protect animals against challenge with the appropriate pathogen. Although mixed results have been obtained with experiments in humans and primates, and there is some concern over complications associated with vaccination, recent advances in our under-standing of the basic biology of vaccinia virus should allow these difficulties to be overcome. Whatever the final outcome of proposals to use vaccinia recombinants in humans, vaccinia has proved to be a valuable general purpose expression system and is particularly useful for studying cellular immunity. The success of field trials with a vaccinia recombinant expressing the rabies virus glycoprotein may lead to widespread use of vaccinia recombinants as animal vaccines. Therefore it seems likely that vaccinia recombinants will continue to play a useful part in the development of new vaccines for infectious disease.