Gonorrhea is the second most diagnosed sexually transmitted disease in the United States, and untreated infections can lead to severe complications including pelvic inflammatory disease and ectopic pregnancy in women and prostatitis in men. Due to the rise of antibiotic resistance found in Neisseria gonorrhoeae (Ng) isolates, newer intervention options such as vaccines are needed to combat untreatable gonorrhea. VesiVax®, developed by Molecular Express, is a nanoparticle liposomal delivery system that allows native presentation of recombinant outer membrane proteins (OMP) in conjunction with immunostimulatory adjuvants. Previously, we showed that the gonococcal multidrug-resistant efflux pump (MtrE) presented in the VesiVax® system elicited robust antibody and T cell responses in mice.
Here, we evaluated two additional Ng integral membrane vaccine candidate antigens in the VesiVax® system in mice as single antigens or as combination antigens co-expressed with or without MtrE. After confirming proper orientation of the OMPs in the VesiVax® liposomes, we immunized BALB/c female mice with three doses of each vaccine formulation containing monophosphoryl lipid A (MPL) adjuvant; control mice were immunized with VesiVax® containing MPL or buffer alone. We characterized the humoral and cellular immune responses by measurement of total antibody titers in ELISA, functional antibodies in serum bactericidal activity (SBA) assays, and characterization of T cells by flow cytometry.
All VesiVax®-MPL vaccine formulations were immunogenic, eliciting high IgG, IgG1 and IgG2a antibody titers against the immunizing antigen(s) and whole cell Ng strain FA1090 compared to controls. SBA varied according to gonococcal test strain and immunizing group. Splenocytes from mice stimulated ex vivo with unadjuvanted VesiVax®-OMP formulations demonstrated Th1, Th2, or Th17 responses that were dependent on both the immunizing and stimulating antigens, suggesting antigen-specific induction of immune memory.
Our studies demonstrate that VesiVax®-MPL-OMP formulations are immunogenic when presented natively in the VesiVax® system. Notably, immune responses to the majority of the combined antigen formulations were not reduced in comparison to mice administered single antigens alone, demonstrating the utility of the VesiVax® system in generating a multi-component recombinant antigen vaccine.