Mixed population approach for vaccination with live recombinant Salmonella strains.

Attenuated strains of enteropathogenic species, such as Salmonella, represent useful carries for the delivery of heterologous recombinant antigens to the immune system. A frequently encountered obstacle, however, is the negative influence of high-level antigen production on the stability of carrier strains and the maintenance of their specific properties concerning tissue colonization and viability during infection. To solve this problem we have established an expression system based on genetic variation. This generates two sub-populations of a recombinant vaccine strain, i.e., one consisting of viable cells which maintain all characteristics of the native carrier strain and generate a second population of cells producing antigen(s) of interest at a very high level. This novel expression system offers unique applications and advantages over common live recombinant vaccine approaches.