Genetic immunization of mice against listeria monocytogenes using plasmid DNA encoding listeriolysin O

The development of protective immunity against many intracellular bacterial pathogens commonly requires sublethal infection with viable forms of the b acteria, Such infection results in the in vivo activation of specific cell- mediated immune responses, and both CD4(+) and CD8(+) T lymphocytes may fun ction in the induction of this protective immunity. In rodent models of exp erimental infection with Listeria monocytogenes, the expression of protecti ve immunity can be mediated solely by the immune CD8(+) T cell subset. One major target Ag of Listeria-immune CD8(+) T cells is the secreted bacterial hemolysin, listeriolysin O (LLO). In an attempt to generate a subunit vacc ine in this experimental disease model, eukaryotic plasmid DNA expression v ectors containing genes encoding either the wild-type or modified forms of recombinant LLO were generated and used for genetic vaccination of naive mi ce. Results of these studies indicate that the intramuscular immunization o f mice with specifically designed plasmid DNA constructs encoding recombina nt forms of LLO stimulates peptide-specific CD8(+) immune T cells that exhi bit in vitro cytotoxic activity. More importantly, such immunization can pr ovide protective immunity against a subsequent challenge with viable L, mon ocytogenes, demonstrating that this experimental approach may have direct a pplication in prevention of acute disease caused by intracellular bacterial pathogens.