Recombinant live virus vaccines.

Many successful vaccines are based on live attenuated viruses. An attractive idea is to genetically engineer these live attenuated vaccines so that they express protective antigens from other pathogens. Vaccinia virus, the smallpox vaccine, can be considered as the prototype for this sort of approach. Over one hundred examples of vaccinia virus recombinants are recorded in the literature and many of these have been shown to protect animals against challenge with the appropriate pathogen. Several problems need to be overcome before these recombinants can be tested in humans; however, the potential advantages of this approach ensure vigorous study of these difficulties. Vaccinia virus recombinants can also be used to dissect the cell-mediated and humoral immune responses to pathogens, and have thus proved to be valuable laboratory tools. However, it remains to be seen if they will also be used in other than experimental situations.