Outer Membrane Vesicle Induction and Isolation for Vaccine Development

Abstract

Gram-negative bacteria release vesicular structures from their outer membrane, so called outer membrane vesicles (OMVs). OMVs have a variety of functions such as waste disposal, communication, and antigen or toxin delivery. These vesicles are the promising structures for vaccine development since OMVs carry many surface antigens that are identical to the bacterial surface. However, isolation is often difficult and results in low yields. Several methods to enhance OMV yield exist, but these do affect the resulting OMVs. In this review, our current knowledge about OMVs will be presented. Different methods to induce OMVs will be reviewed and their advantages and disadvantages will be discussed. The effects of the induction and isolation methods used in several immunological studies on OMVs will be compared. Finally, the challenges for OMV-based vaccine development will be examined and one example of a successful OMV-based vaccine will be presented.

Keywords: Bordetella pertussis; Neisseria meningitidis; host defense peptides; induction; isolation; outer membrane vesicles; vaccine development.

Figure 1

Gram-negative bacterial membrane during OMV formation and functions of resulting OMVs. OMVs have been implicated in many different processes. Depicted here are the different functions OMVs have been shown to be involved in such as transport of toxins, waste removal, or communication between bacteria. LPS: lipopolysaccharide, PL: phospholipid, OM: outer membrane, PG: peptidoglycan, IM: inner membrane.

Figure 2

Schematic overview of different induction methods for OMVs including characteristics of resulting OMVs. No stimulation: these vesicles are most similar to spontaneous vesicles released in vivo (sOMVs). Genetic manipulation may alter OMV cargo (gOMVs). Detergent isolation of OMVs results in OMVs lacking LPS (dOMVs), an important immunogenic molecule. Sonication of bacteria disrupts the entire membrane, resulting in impurities in the vesicles’ fraction due to cell lysis (lOMVs). Extraction with membrane destabilizing molecules may alter vesicle composition (nOMVs), but they are more representative of the OM. OMV induction by peptides or antibiotics may alter membrane stability and may result in the peptide or antibiotic being present in the resulting OMV (pOMVs/aOMVs). A new technique researched to induce OMVs is heat-shock, resulting in hOMVs, but this technique is not yet established and therefore not included in this figure.