Expression of two Listeria monocytogenes antigens (P60 and LLO) in Lactococcus lactis and examination for use as live vaccine vectors

Abstract

Listeria monocytogenesis a food-borne intracellular pathogen that mainly infects pregnant and immunocompromised individuals. The pore-forming haemolysin listeriolysin O (LLO), the main virulence factor ofListeria monocytogenes, allows bacteria to escape from the harsh environment of the phagosome to the cytoplasm of the infected cell. This leads to processing of bacterial antigens predominantly through the cytosolic MHC class I presentation pathway. We previously engineered the food-grade bacteriumLactococcus lactisto express LLO and demonstrated an LLO-specific CD8+response upon immunization of mice with the engineeredL. lactisvaccine strains. In the present work, we examined the immune response and protective efficacy of anL. lactisstrain co-expressing LLO and a truncated form of the listerial P60 antigen (tP60). Oral immunization revealed no significant protection against listeriosis withL. lactisexpressing LLO, tP60 or the combined LLO/tP60. In contrast, intraperitoneal vaccination induced an LLO-specific CD8+immune response with LLO-expressingL. lactisbut no significant improvement in protection was observed following vaccination with the combined LLO/tP60 expressingL. lactisstrain. This may be due to the low level of tP60 expression in the LLO/tP60 strain. These results demonstrate the necessity for improved oral vaccination strategies using LLO-expressingL. lactisvaccine vectors.