Antibody‐mediated immunity induced by engineered Escherichia coli OMVs carrying heterologous antigens in their lumen

Abstract

BackgroundOuter membrane vesicles (OMVs) from Gram-negative bacteria are gaining increasing attention as vaccine platform for their built-in adjuvanticity and for their potential use as carriers of heterologous antigens. These 2 properties offer the opportunity to make highly effective, easy to produce multi-valent vaccines. OMVs can be loaded with foreign antigens by targeting protein expression either to the outer membrane or to the periplasm of the OMV-producing strain. Periplasmic expression is simple and relatively efficient but leads to the accumulation of recombinant antigens in the lumen of OMVs and the ability of OMVs carrying internalized antigens to induce antigen-specific antibody responses has been only marginally investigated and is considered to be sub-optimal.MethodsWe have systematically analyzed in qualitative and quantitative terms antibody responses induced by OMVs carrying different heterologous antigens in their lumen. Group A Streptococcus (GAS) Slo, SpyCEP, Spy0269 and Group B Streptococcus (GBS) SAM_1372 were fused to the OmpA leader sequence for secretion and expressed in Escherichia coli. OMVs from the recombinant strains were purified and tested for immunogenicity and protective activity.ResultsAll proteins were incorporated into the OMVs lumen in their native conformation. Upon mice immunization, OMVs induced high functional antibody titers against the recombinant proteins. Furthermore, immunization with Slo-OMVs and SpyCEP-OMVs protected mice against GAS lethal challenge.ConclusionsThe efficiency of antigen delivery to the vesicular lumen via periplasmic expression, and the surprisingly high immunogenicity and protective activity of OMVs carrying internalized recombinant antigens further strengthens the potential of OMVs as vaccine platform.

Immune modulation by bacterial outer membrane vesicles

“…Immunization with OMVs generates strong antigenspecific IgG and/or IgA antibody responses in the serum and in mucosal compartments 22,[76][77][78][79][80][81] . When introduced into the body, OMV antigens are presented by antigenpresenting cells (APCs) to CD4 + T cells 45,70,81,82 , which leads to the generation of antigen-specific B cell responses 45,78,82,83 .…”

“…When introduced into the body, OMV antigens are presented by antigenpresenting cells (APCs) to CD4 + T cells 45,70,81,82 , which leads to the generation of antigen-specific B cell responses 45,78,82,83 . OMVs can induce protective immune responses during infection with a variety of pathogens -including V. cholerae 81 , H. pylori 80 , S. Typhimurium 45 and Shigella flexneri 84 -and this decreases bacterial burdens [85][86][87] and protects mice from sepsis or death 25,77,79,84,88 (TABLE 1). Adoptive transfer experiments have shown that CD4 + T cells expressing IFNγ and IL-17 were required for OMV-mediated protection in an E. coli-induced sepsis model, which suggests that T helper 1 (T H 1) and T H 17 cell responses may be responsible for protection in this model 88 .…”

“…Furthermore, the ability of OMVs to activate the innate immune system 14,20,22,24,25,69,114 , together with their particulate nature, provides these nano particles with their own adjuvant activity, as they are able to enhance antibody and T cell responses to antigens 76,83,87,115 . Finally, OMVs are very versatile as they can be bioengineered to express any chosen antigen 77,112,[116][117][118] and they can be manipulated to reduce their endotoxicity [119][120][121] . Despite the enormous vaccine potential of OMVs, it has taken more than 20 years for an OMV-based vaccine to be licensed for human use.…”

Outer membrane vesicles displaying engineered glycotopes elicit protective antibodies

“…These characteristics are exemplified by OMVs isolated directly from N. meningitidis, which induce potent protective immune responses and have been incorporated successfully into several commercial vaccine formulations for use in humans (22,24,25). To expand the vaccine potential of OMVs, several groups have used genetic engineering techniques to load OMVs with foreign protein antigens by targeting expression either to the outer membrane or the periplasm of an OMV-producing host strain (26)(27)(28)(29)(30)(31)(32). These OMV-associated recombinant proteins were internalized by eukaryotic cells (26,27) and stimulated strong and specific immune responses in mice (28)(29)(30)(31)(32).…”

“…To expand the vaccine potential of OMVs, several groups have used genetic engineering techniques to load OMVs with foreign protein antigens by targeting expression either to the outer membrane or the periplasm of an OMV-producing host strain (26)(27)(28)(29)(30)(31)(32). These OMV-associated recombinant proteins were internalized by eukaryotic cells (26,27) and stimulated strong and specific immune responses in mice (28)(29)(30)(31)(32). However, although efforts to load OMVs with recombinant protein antigens are well documented (33), an analogous strategy to engineer the polysaccharide component of OMVs for specific vaccine applications has yet to be demonstrated.…”