Gram-negative outer membrane vesicles in vaccine development.

Gram-negative bacteria naturally and constitutively release lipid bilayer vesicles from the outer membrane. Outer membrane vesicles (OMVs) range in size from approximately 20-200 nanometers in diameter and enclose many native bacterial antigens in the spherical particles. Composed of outer membrane and periplasmic constituents, the vesicles function in diverse roles that, ultimately, make them a transportable part of the bacterial arsenal and survival system. These functional roles entail mediation of bacterial envelope stress, biofilm formation, virulence, and transformation. With their immunogenic properties, self-adjuvanticity, ability to be taken up by mammalian cells, and capacity for enhancement by recombinant engineering, OMVs are attractive candidates for vaccine delivery platforms. The first OMV vaccines were shown to be protective against clonal serogroup B meningococci outbreaks in Cuba, Norway, Brazil, and New Zealand, although there is still no global vaccine against serogroup B meningococci. However, interest in OMVs as vaccine carriers is growing as research exposes more of the molecular intricacies of vesiculation and how the vesicles can be co-opted to fight infectious bacterial agents.