Bacteria-derived particles as adjuvants for non-replicating nasal vaccines

In attempts to mimic natural infections, vaccines consisting of microbial particles may be delivered directly to mucosal surfaces. In this way, the mucosal as well as the systemic immune systems can be activated. Even non-living particles of bacterial origin have been shown to elicit strong immune responses when administered intranasally. However, some particles such as formalin-inactivated influenza virus may need a mucosal adjuvant to be effective. The bacteria-derived particles seem to possess such an adjuvant activity when mixed with and given intranasally with the less immunogenic killed virus. Possibly, the bacterial particles facilitate uptake of the virus through the mucosal membranes, although an additional influence on the immune response to the virus might be mediated in the lymphoid tissue below the mucosal surface. Bacteria-derived particles in nasal vaccines may thus serve as an alternative adjuvant to derivatives of cholera toxin or the heat-labile toxin from E. coli.