Nanoparticle-based vaccine for mucosal protection against Shigella flexneri in mice.

Shigellosis is one of the leading causes of diarrhea worldwide with more than 130 million cases annually. Hence, the research of an effective vaccine is still a priority. Unfortunately, a safe and efficacious vaccine is not available yet. We have previously demonstrated the capacity of outer membrane vesicles (OMVs) to protect mice against an experimental infection with Shigella flexneri. Now, we present results on the capacity of this antigenic complex to confer a longer-term protection by oral or nasal routes when encapsulated into nanoparticles. OMVs were encapsulated in poly(anhydride) nanoparticles (NP) prepared by a solvent displacement method with the copolymer poly methyl vinyl ether/maleic anhydride. OMVs loaded into nanoparticles (NP-OMVs) were homogeneous and spherical in shape, with a size of 148nm (PdI=0.2). BALB/c mice were immunized with OMVs either free or encapsulated in nanoparticles by nasal (20µg or 10µg of OMVs) or oral route (100µg or 50µg of OMVs). All immunized animals remained in good health after administration. Challenge infection was performed intranasally on week 8th with a lethal dose of 5×10(7)CFU/mouse of S. flexneri 2a. The number of dead mice after challenge was recorded daily. Results confirmed the value of OMVs as a vaccine. By oral route, the OMV-vaccine was able to protect independently either the dose or the formulation. When vaccine was delivered by nasal route, encapsulation into NPs resulted beneficial in increasing protection from 40% up to 100% when low dose was administered. These results are extraordinary promising and put in relevance the positive effect of nanoencapsulation of the OMV subcellular vaccine.