Zonula occludens toxin as a new promising adjuvant for mucosal vaccines

Cholera toxin (CT) and CT-related molecules have been known since a long time to act as powerful mucosal adjuvants. We have studied the stimulatory effects of CT on human dendritic cells and its inhibitory activity on T lymphocytes. We have also identified a third bacterial enterotoxin, Zonula occludens toxin (Zot) that acts as an effective mucosal adjuvant. Zonula occludens toxin is produced by Vibrio cholerae and has the property to increase intestinal mucosa permeability by reversibly affecting the structure of tight junctions. We found that recombinant ZOT induces long lasting and protective immunity to intranasally delivered antigens and is effective also through other mucosal routes. Furthermore, ZOT is highly efficacious when compared to the mucosal adjuvant LT (Escherichia coli heat-labile enterotoxin) but has a much lower immunogenicity. By using an octapeptide representing the putative binding site of Zot and of its endogenous analogue Zonulin, we provided evidence that Zot may bind a receptor on the nasal mucosa and may mimic an endogenous regulator of tight junctions to deliver antigens in the submucosa. Finally, we are testing recombinant fragments of ZOT for their mucosal adjuvant activity. In conclusion, Zot and its derivatives are very promising tools for the development of needle-free mucosal vaccines.