ANTIVIRAL CYTOTOXIC T-CELL MEMORY BY VACCINATION WITH RECOMBINANT LISTERIA-MONOCYTOGENES

Listeria monocytogenes is a facultative intracellular bacterium that i s able to escape phagocytic vesicles and replicate in the cytoplasm of infected cells, As with viral vectors, this intracytoplasmic life cyc le provides a means for introducing foreign proteins into the major hi stocompatibility complex class I pathway of antigen presentation, Usin g recombinant L. monocytogenes (rLM) strains expressing the full lengt h nucleoprotein (NP) or a single cytotoxic T-lymphocyte (CTL) epitope from lymphocytic choriomeningitis virus (LCMV), we analyzed antiviral CTL responses induced by rLM vaccination, After vaccination, rLM was c leared from the host within 7 days while inducing an LCMV-specific ex vivo CD8(+) effector CTL response, Virus-specific CTL memory was maint ained for 6 months postvaccination, as demonstrated by vigorous second ary CTL responses after in vitro stimulation, A single immunization wi th rLM that expressed either the full-length NP gene or the CTL epitop e alone resulted in LCMV NP-specific CTL precursor frequencies of appr oximately 1/10(4) CD8(+) T cells. A second rLM vaccination resulted in enhanced virus-specific CTL activity and in vitro proliferation. rLM- vaccinated mice were protected against chronic viral infection by an a ccelerated virus-specific memory CTL response, These mice cleared infe ctious virus as well as viral antigen, suggesting that sterilizing imm unity was achieved, In contrast to mice that received mild-type LM, rL M-vaccinated mice were protected from virally induced immunosuppressio n and splenic atrophy associated with chronic LCMV infection. The abil ity to elicit long-term cell-mediated immunity is fundamental in desig ning vaccines against intracellular pathogens, and these results demon strate the efficacy of recombinant LM vaccination for inducing protect ive antiviral CTL memory.