Vaccination of mice with gonococcal TbpB expressed in vivo from Venezuelan equine encephalitis viral replicon particles.

We investigated the immunogenicity of gonococcal transferrin binding protein B (TbpB) expressed with and without a eukaryotic secretion signal from a nonpropagating Venezuelan equine encephalitis virus replicon particle (VRP) delivery system. TbpB was successfully expressed in baby hamster kidney (BHK) cells, and the presence of the eukaryotic secretion signal not only apparently increased the protein's expression but also allowed for extracellular localization and glycosylation. Mice immunized with VRPs produced significant amounts of serum antibody although less than the amounts produced by mice immunized with recombinant protein. The response of mice immunized with VRPs encoding TbpB was consistently more Th1 biased than the response of mice immunized with recombinant protein alone. Boosting with recombinant protein following immunization with TbpB VRPs resulted in higher specific-antibody levels without altering the Th1/Th2 bias. Most of the immunization groups produced significant specific antibody binding to the intact surface of the homologous Neisseria gonorrhoeae strain. Immunization with TbpB VRPs without a eukaryotic secretion signal generated no measurable specific antibodies on the genital mucosal surface, but inclusion of a eukaryotic secretion signal or boosting with recombinant protein resulted in specific immunoglobulin G (IgG) and IgA in mucosal secretions after TbpB VRP immunization. The TbpB VRP system has potential for an N. gonorrhoeae vaccine.

Comparison of immune responses to gonococcal PorB delivered as outer membrane vesicles, recombinant protein, or Venezuelan equine encephalitis virus replicon particles.

Porin (PorB) is a major outer membrane protein produced by all Neisseria gonorrhoeae strains and has been a focus of intense interest as a vaccine candidate. In this study, the immunogenicity of PorB in mice was investigated after several immunization regimens. Outer membrane vesicles (OMV), recombinant renatured PorB (rrPorB), and PorB-expressing Venezuelan equine encephalitis (VEE) virus replicon particles (PorB VRP) were delivered intranasally (i.n.) or subcutaneously (s.c.) into the dorsal area or the hind footpad in three-dose schedules; the PorB VRP-immunized mice were given a single additional booster dose of rrPorB in Ribi adjuvant. Different delivery systems and administration routes induced different immune responses. Mice immunized s.c. with rrPorB in Ribi had the highest levels of PorB-specific serum immunoglobulin G (IgG) by enzyme-linked immunosorbent assay. Surprisingly, there was an apparent Th1 bias, based on IgG1/IgG2a ratios, after immunization with rrPorB in Ribi in the footpad while the same vaccine given in the dorsal area gave a strongly Th2-biased response. PorB VRP-immunized mice produced a consistent Th1 response with a high gamma interferon response in stimulated splenic lymphocytes and very low IgG1/IgG2a ratios. Immunization by OMV delivered i.n. was the only regimen that resulted in a serum bactericidal response, and it generated an excellent mucosal IgA response. Serum from mice immunized with rrPorB preferentially recognized the surface of whole gonococci expressing a homologous PorB, whereas serum from PorB VRP-immunized mice had relatively low whole-cell binding activity but recognized both heterologous and homologous PorB equally. The data resulting from this direct comparison suggested that important aspects of the immune response can be manipulated by altering the form of the antigen and its delivery. This information coupled with an understanding of protective antigonococcal immune responses will enable the design of the optimal vaccine for N. gonorrhoeae.