Immunization with Salmonella enterica Serovar Typhimurium-Derived Outer Membrane Vesicles Delivering the Pneumococcal Protein PspA Confers Protection against Challenge with Streptococcus pneumoniae

Abstract

Gram-negative bacteria produce outer membrane vesicles (OMVs) that serve a variety of functions related to survival and pathogenicity. Periplasmic and outer membrane proteins are naturally captured during vesicle formation. This property has been exploited as a method to derive immunogenic vesicle preparations for use as vaccines. In this work, we constructed a Salmonella enterica serovar Typhimurium strain that synthesized a derivative of the pneumococcal protein PspA engineered to be secreted into the periplasmic space. Vesicles isolated from this strain contained PspA in the lumen. Mice intranasally immunized with the vesicle preparation developed serum antibody responses against vesicle components that included PspA and Salmonelladerived lipopolysaccharide and outer membrane proteins, while no detectable responses developed in mice immunized with an equivalent dose of purified PspA. Mucosal IgA responses developed against the Salmonella components, while the response to PspA was less apparent in most mice. Mice immunized with the vesicle preparation were completely protected against a 10؋ 50% lethal dose (LD 50 ) challenge of Streptococcus pneumoniae and significantly protected against a 200؋ LD 50 challenge, while control mice immunized with purified PspA or empty vesicles were not protected. These results establish that vesicles can be used to mucosally deliver an antigen from a Gram-positive organism and induce a protective immune response.

Outer Membrane Vesicles Induce Immune Responses to Virulence Proteins and Protect against Colonization by Enterotoxigenic Escherichia coli

“…In addition, the possibility of engineering ETEC OMV to deliver heterologous molecules (6,22) that may not normally be vesicle associated could be an attractive option in the development of a broadly protective vaccine that incorporates multiple target antigens. Such a strategy is currently being examined by combining recombinant MenB proteins with Neisseria OMV (10).…”

Decoration of Outer Membrane Vesicles with Multiple Antigens by Using an Autotransporter Approach

“…Bone marrow-derived dendritic cells (BMDCs) from C57BL/6 mice, generated in the presence of 2 ng/ml granulocyte-macrophage colony-stimulating factor, were incubated for 4 h with OMVs displaying Hbp (derivatives), purified Hbp-Ag85B CϩN -ESAT6-Rv2660c (200 g/ml), or synthetic peptide consisting of residues 241 to 260 of Ag85A (Ag85A 241-260 ) or residues 1 to 20 of ESAT6 (ESAT6 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Thereafter, the BMDCs were washed three times and cocultured overnight with C57BL/6-derived T cell hybridoma cells (DE10) (50) that recognize the 1-A b -restricted Ag85A 241-260 peptide and cross-react with an I-A b -restricted peptide in Ag85B (Ag85B 281-300 ).…”

“…An increasing body of evidence suggests that extracellular antigens evoke im-mune responses superior to those of intracellular antigens (23)(24)(25). Recently, antibody responses to a heterologous antigen packaged into the lumen of Salmonella OMVs were observed to be lower than those to endogenous vesicle OMPs and LPS (20), suggesting that surface-exposed antigens may elicit superior immune responses also in vesicles.…”

“…Several recent studies have shown that heterologous proteins can be targeted to OMVs upon production in the OM or periplasm (19,20) or as translational fusions to vesicle-associated proteins (21,22), opening up the interesting possibility of equipping OMVs with an engineered antigen repertoire. An increasing body of evidence suggests that extracellular antigens evoke im-mune responses superior to those of intracellular antigens (23)(24)(25).…”

A Burkholderia pseudomallei Outer Membrane Vesicle Vaccine Provides Protection against Lethal Sepsis

“…It may also be necessary to enrich the OMV cargo with virulence determinants specific to the intracellular stage of infection (44,45) or with antigens that induce strong T cell responses (46)(47)(48). A number of studies have shown that expression and delivery of homologous and heterologous antigens with OMVs are feasible (45,49,50). We previously showed that immunization with B. pseudomallei OMVs stimulates memory T cell responses and gamma interferon (IFN-␥) production (14).…”