Rational Design of a Meningococcal Antigen Inducing Broad Protective Immunity

Abstract

The sequence variability of protective antigens is a major challenge to the development of vaccines. For Neisseria meningitidis, the bacterial pathogen that causes meningitis, the amino acid sequence of the protective antigen factor H binding protein (fHBP) has more than 300 variations. These sequence differences can be classified into three distinct groups of antigenic variants that do not induce cross-protective immunity. Our goal was to generate a single antigen that would induce immunity against all known sequence variants of N. meningitidis. To achieve this, we rationally designed, expressed, and purified 54 different mutants of fHBP and tested them in mice for the induction of protective immunity. We identified and determined the crystal structure of a lead chimeric antigen that was able to induce high levels of cross-protective antibodies in mice against all variant strains tested. The new fHBP antigen had a conserved backbone that carried an engineered surface containing specificities for all three variant groups. We demonstrate that the structure-based design of multiple immunodominant antigenic surfaces on a single protein scaffold is possible and represents an effective way to create broadly protective vaccines.

Defining a protective epitope on factor H binding protein, a key meningococcal virulence factor and vaccine antigen

“…The typical antibody binding surface of an antigen covers 800-2,000 Å 2 ; therefore, it is very likely that a substantial portion of an antigen is involved in the interaction (27,30). Indeed, the HDX-MS approach not only confirmed the involvement of peptide A 238 -I 249 in binding 12C1 but also revealed additional fHbp N-terminal regions mediating the interaction.…”

“…Given this significant overlap, it is not surprising that the binding of fHbp to fH was inhibited by addition of mAb 12C1, although structural data show that Fab 12C1 is not a structural mimic of fH. Moreover, the affinity of fHbp to mAb 12C1 (K D < 0.05 nM) is remarkably higher than the affinity reported for fHbp to hfH (5-45 nM) (22,27,32,33), thus explaining the observed capacity of mAb 12C1 to displace fH from the fHbp:hfH complex. The crystal structure, together with multiple sequence alignments, also indicated a subset of fHbp residues potentially responsible for the var1 binding specificity of mAb 12C1.…”

“…A complete understanding of immunogenic B-cell epitopes is essential when trying to develop improved vaccines against pathogens displaying antigenic variability (27). Such information can be derived from several epitope mapping approaches (28).…”

Delivering vaccines to the people who need them most

“…This enables the use of structure-based design to modify antigens and make them 'better' immunogens [17]. An example of this is the surface of factor H-binding protein of meningococcus being engineered to contain non-overlapping epitopes from three meningococcal antigenic variants, which resulted in a single molecule that could induce protective antibodies against all sequence variants [18,19]. Recently, structurebased antigen design was used to stabilize the conformation of the pre-fusion form of the F protein of the respiratory syncytial virus, an excellent vaccine candidate [20].…”

A meningococcal vaccine antigen engineered to increase thermal stability and stabilize protective epitopes

“…The second licensed vaccine contains FHbp in variant group 1 and three other antigens capable of eliciting protective antibodies (7,8). Other strategies to increase the breadth of protection were to engineer FHbp antigens containing epitopes from different sequence variants (9)(10)(11).…”