Outer membrane vesicles displaying engineered glycotopes elicit protective antibodies

Abstract

The O-antigen polysaccharide (O-PS) component of lipopolysaccharides on the surface of gram-negative bacteria is both a virulence factor and a B-cell antigen. Antibodies elicited by O-PS often confer protection against infection; therefore, O-PS glycoconjugate vaccines have proven useful against a number of different pathogenic bacteria. However, conventional methods for natural extraction or chemical synthesis of O-PS are technically demanding, inefficient, and expensive. Here, we describe an alternative methodology for producing glycoconjugate vaccines whereby recombinant O-PS biosynthesis is coordinated with vesiculation in laboratory strains of Escherichia coli to yield glycosylated outer membrane vesicles (glycOMVs) decorated with pathogen-mimetic glycotopes. Using this approach, glycOMVs corresponding to eight different pathogenic bacteria were generated. For example, expression of a 17-kb O-PS gene cluster from the highly virulent Francisella tularensis subsp. tularensis (type A) strain Schu S4 in hypervesiculating E. coli cells yielded glycOMVs that displayed F. tularensis O-PS. Immunization of BALB/c mice with glycOMVs elicited significant titers of O-PS–specific serum IgG antibodies as well as vaginal and bronchoalveolar IgA antibodies. Importantly, glycOMVs significantly prolonged survival upon subsequent challenge with F. tularensis Schu S4 and provided complete protection against challenge with two different F. tularensis subsp. holarctica (type B) live vaccine strains, thereby demonstrating the vaccine potential of glycOMVs. Given the ease with which recombinant glycotopes can be expressed on OMVs, the strategy described here could be readily adapted for developing vaccines against many other bacterial pathogens.

Novel Solutions for Vaccines and Diagnostics To Combat Brucellosis

“…Finally, the study identifies principles that can guide biotechnology approaches for creation of a genetically engineered live DIVA vaccine that exploits known OPS biosynthetic mechanisms. 37−39 …”

Differential Cultivation of Francisella tularensis Induces Changes in the Immune Response to and Protective Efficacy of Whole Cell-Based Inactivated Vaccines

“…While the dominant reactivity of anti-i Ft -BHI was to a 43 kDa protein, the anti-i Ft -MHB response was more broadly distributed among a range of Ags including Ft LPS (O-Ag). Ft LPS has been found to be an important Ag for protection against Ft infection (22). Although, at present, we do not know the significance of the differences in the Ab responses elicited by i Ft -MHB versus i Ft -BHI, further studies in this regard may reveal their impact on protection.…”

Bacterial membrane vesicles: Biogenesis, immune regulation and pathogenesis

“…Surface glycans from S. pneumoniae or C. jejuni have been expressed in non‐pathogenic E. coli OMVs that are capable of generating immune responses comparable to those induced by a commercially available pneumococcal vaccine (Price et al, ). Similarly, E. coli OMVs have been engineered to harbor Francisella tularensis O‐antigen (Chen et al, ).…”