Bacterial vaccine vectors and bacillus Calmette-Guérin

Recent advances in biotechnology now allow a more modern approach to the development of vaccines, particularly that of recombinant vaccines. Bacterial vaccine vectors have the advantage over viral vectors in that the former have the ability to express a greater number of antigens in different forms. Although no recombinant bacterial vaccines are currently in use, bacillus Calmette-Guérin (BCG), Salmonella species, and Escherichia coli are being developed as vaccine vectors. We review plasmid systems and mutant strains developed for the expression of foreign antigens, with particular emphasis on those developed for BCG. We describe the development of antigen expression systems as well as the immune response elicited by recombinant BCG vaccine strains to bacterial and human immunodeficiency virus (HIV) antigens. A modified recombinant BCG carrier with selection for the stable maintenance of rDNA is proposed.