Listeria-based anti-infective vaccine strategies

Listeria monocytogenes is a Gram-positive intracellular bacterium that has accounted for a significant proportion of human foodborne infections in recent decades. Although infection with sublethal level of L. monocytogenes generates enduring immunity, it is impractical to apply intact virulent strains as vaccine. Through use of killed, attenuated, naturally avirulent, subcellular and DNA vaccine preparations, significant protection has been achieved in experimental animals against listeriosis. Being a robust bacterium capable of eliciting all aspects of cell-mediated immunity, L. monocytogenes has the potential to become an ideal vector for vaccine delivery against other infective agents. Furthermore, with a high safety threshold, L. monocytogenes has increasingly been recognized as a vaccine vector of choice for a range of bacterial, viral and parasitic pathogens. Not surprisingly, a large number of patents have been filed in recent years that exploit attenuated or naturally avirulent L. monocytogenes strains or its listeriolysin (LLO) protein to enhance specific T cell response in the vaccine recipients or to direct vaccine molecule to the cytoplasm of host cells. Following a brief review on the key features of L. monocytogenes infection and host immune responses to listeriosis, this article summarizes the current state and recent progresses in the Listeria-based vaccine strategies that have been developed against bacterial, viral and parasitic diseases, together with a discussion on the future development trends in the utilization of L. monocytogenes as vaccine vector.