Delivery of protein antigens and DNA by virulence-attenuated strains of Salmonella typhimurium and Listeria monocytogenes

Two different plasmid-vector systems were developed which allow the efficie nt production and presentation of protein antigens in antigen-presenting ce lls (APC) by means of virulence-attenuated bacteria. The first antigen-deli very system is based on the secretion machinery of the Escherichia coli hem olysin (HlyA-type I secretion system), which transports proteins, possessin g the specific HlyA secretion signal (HlyA(s)) at the C-terminus, across bo th membranes of gram-negative bacteria. This system functions in all gram-n egative bacteria that possess the TolC-analogous protein in the outer membr ane. This outer membrane protein is necessary for the stable anchoring of t he type I secretion apparatus in the cell envelope. Suitable HlyA(s)-fused antigens are secreted with high efficiency by E. coli and by virulence-atte nuated strains of Salmonella, Shigella, Vibrio cholerae and Yersinia entero colitica. The other vector system expresses the heterologous antigen under the control of an eukaryotic promoter in a similar fashion as in plasmids c ommonly used for vaccination with naked DNA. This plasmid DNA is introduced into APCs with the help of virulence-attenuated self-destructing Listeria monocytogenes mutants. After synthesis of the heterologous protein, epitope s of the antigen are presented by the APC together with MHC class I molecul es. This system functions in macrophages and dendritic cells in vitro and c an also be used in a modified form in animal models. (C) 2000 Elsevier Scie nce B.V. All rights reserved.