NHBA antibodies elicited by 4CMenB vaccination are key for serum bactericidal activity against Neisseria gonorrhoeae

The 4CMenB (Bexsero R ) vaccine contains detergent-extracted outer membrane vesicles (OMVs) from a Neisseria meningitidis ( Nm ) group B strain NZ98/254 and three recombinant Nm protein antigens: Neisseria adhesin A (NadA), Factor H binding protein (FHbp, as the C-terminal protein in the GNA2091-FHbp fusion), and Neisserial Heparin Binding Antigen (NHBA, as the N-terminal protein in the NHBA-GNA1030 fusion). Previous work has shown that 4CMenB generates serum antibodies to Nm and Neisseria gonorrhoeae ( Ng) OMV proteins and lipooligosaccharide (LOS). Mounting evidence indicates 4CMenB can partially protect against mucosal infections with Ng . The immunologic basis for Ng cross protection remains to be fully elucidated. Ten paired human sera obtained pre- and post-immunization with 4CMenB (1 month after a third vaccine dose) were used in ELISAs and in Western blots to determine IgG and IgA serum responses to OMVs from Nm strain NZ98/254 (OMV Nm ) and two Ng strains, 1291 and CNG20 (OMV Ng ), and gonococcal recombinant NHBA (rNHBA Ng ) proteins. Post 4CMenB sera, but not pre-sera, showed strong IgG and variable IgA responses to the OMV Nm but lower (2–11-fold difference in signal intensity) recognition of OMV Ng . All post (not pre) 4CMenB sera showed strong IgG, but variable IgA, recognition of rNHBA Ng by ELISAs and Western blots. Three post 4CMenB sera at 10% (v/v) concentration had serum bactericidal activity (SBA) against Ng strains 1291 and CNG20 (~30–40% killing), not seen in paired pre-sera. These data confirmed 4CMenB-induced cross-reactive functional antibody responses to Ng . In competitive SBA assays, in which sera were pre-incubated with rNHBA, minimal SBA against Nm strain NZ98/254 was titrated away. However, most of the SBA against Ng strains 1291 and CNG20 required NHBA-specific antibodies, and the Δ nhba mutants were resistant to killing by post 4CMenB sera. Removing NHBA-specific and LOS-specific OMV antibodies simultaneously decreased SBA significantly more than the sum of removing individual antibodies alone, suggesting synergy between anti-NHBA and anti-OMV antibodies. Anti- NHBA Nm antibodies induced by 4CMenB vaccination cross react with NHBA Ng and substantially contribute to the bactericidal response toward Ng induced by the vaccine.