title: Antibody-mediated immunity induced by engineered Escherichia coli OMVs carrying heterologous antigens in their lumen.
abstract: BACKGROUND
  Outer 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.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  All 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Centre for Integrative Biology, University of Trento, Trento, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Fantappiè
authors.affiliation: Centre for Integrative Biology, University of Trento, Trento, Italy.
authors.forename: Micaela
authors.initials: M
authors.lastname: de Santis
authors.affiliation: Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Emiliano
authors.initials: E
authors.lastname: Chiarot
authors.affiliation: Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Carboni
authors.affiliation: Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Giuliano
authors.initials: G
authors.lastname: Bensi
authors.affiliation: Centre for Integrative Biology, University of Trento, Trento, Italy.
authors.forename: Olivier
authors.initials: O
authors.lastname: Jousson
authors.affiliation: Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Immaculada
authors.initials: I
authors.lastname: Margarit
authors.affiliation: Centre for Integrative Biology, University of Trento, Trento, Italy ; Novartis Vaccines and Diagnostics, Siena, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Grandi
keywords: Group A Streptococcus; Group B Streptococcus; heterologous antigens; outer membrane vesicles; periplasmic expression; vaccines