Listeria monocytogenes: a live vector able to deliver heterologous protein within the cytosol and to drive a CD8 dependent T cell response.

After an introduction on the entry and lifestyle of Listeria monocytogenes within mammalian eucaryotic cells, this chapter gives a brief overview of murine experimental listeriosis. Among the main characteristics of this murine model of infectious/pathogenic processes initiated by a facultative intracellular bacteria, we point out two main recent advances. One relates to Listeria monocytogenes-induced production of cytokines as local, and transient signals able to direct the immune responses along a type 1 pathway of CD4/CD8 T cell differentiation. The other relates (a) to the recognition of L. monocytogenes-reactive CD8+ T lymphocytes as effectors able, once recruited within infected loci, to critically contribute to the complete clearance of the bacteria, and (b) to the recently recognized specificity of some of these CD8 lymphocytes in BALB/c mice. In this paper, we also briefly review (a) the readout assays presently used to monitor the outcome of the infectious/pathogenic processes and the related development and expression of immune responses induced by intravenous inoculation of wild-type virulent or attenuated L. Monocytogenes, (b) why all this information allows us to consider the use of L monocytogenes of attenuated virulence as relevant live recombinant vectors in order to deliver heterologous proteins to the class I processing and presentation pathway, and to induce CD8 T cells along the type 1 pathway.