Listeria-based vaccines for cancer treatment.

Listeria monocytogenes is a facultative intracellular bacterium that enters professional antigen-presenting cells by active phagocytosis. As a live bacterium, it induces antigen-presenting cell maturation and strong innate immunity which may assist in the immune response to poorly immunogenic antigens, such as tumor-associated antigens. Listeria produces virulence factors that allow it to escape from the phagolysosome and colonize the cytosol of the host cell. It is thus a potent vaccine vector for the presentation of passenger antigens to the major histocompatibility complex class I and II pathways of antigen processing and presentation. Recent progress in developing this bacterium as a vaccine vector for tumor-associated antigens is reviewed. In mouse models, recombinant Listeria carrying a number of such antigens has provided therapeutic immunity directed towards established tumors. Safety issues associated with live bacterial vaccine vectors and problems to be overcome in developing Listeria as a cancer immunotherapeutic for human use are also discussed.