Au, N. Y. T. | bioRxiv Science

bioRxiv2025

Structure-based engineering of a nutrient acquisition protein enhances neutralizing antibodies and protection for the development of a gonococcal vaccine

Gonorrhea is increasingly resistant to treatment and has been labelled an urgent threat due to the diminishing effectiveness of existing therapeutics. To address this challenge, we targeted the Neisseria gonorrhoeae transferrin binding protein B (TbpB), which is critical for iron acquisition and neisserial growth, as a vaccine target. Building on previous studies investigating the application of TbpB as an immunogen against various bacterial pathogens, we aimed to optimize this antigen for a broad protective effect. We compared the efficacy of wild type TbpB immunogens with engineered TbpB mutants that do not bind human transferrin (hTf) using infection studies in transgenic mice expressing hTf, which were required because the strict specificity of neisserial TbpB precludes its complexing with non-human transferrin. Comprehensive biophysical analyses confirmed that the introduced single residue mutations abolished hTf binding without compromising antigen structure. Immunization with the mutant antigens conferred increased resistance to infection by N. gonorrhoeae relative to that provided by the wild-type antigen in the humanized mice. When considering effector functions of the humoral response, we observed that the mutated antigen elicited more effective bactericidal and function-neutralizing activity. Through strategic mutations, we therefore enhanced vaccine effectiveness in a physiologically relevant model without significantly affecting the structure or immunogenicity of the antigen. This study highlights the use of rational structure-guided antigen design to drive effective immune responses and the potential interference of immunogen binding to host factors, and reinforces the utility of targeting TbpB in a gonococcal vaccine.

immunology↗

bioRxiv2025

Rationally designed minimized TbpB confers broad protection against meningococcal infection

Transferrin binding protein B (TbpB), an iron acquisition protein, has long been recognized as a promising vaccine candidate targeting the pathogenic Neisseria species, including Neisseria meningitidis, the cause of meningococcal disease, and Neisseria gonorrhoeae, the cause of gonorrhea. A challenge to the development of this protein as a vaccine immunogen is the extent of antigenic variability it exhibits, which complicates the selection of a single variant to elicit a broadly cross-protective immune response. We have utilized structure-informed antigen engineering to develop a minimized version of TbpB consisting of the proteins carboxy-terminal lobe with its variable surface loops removed. Here, we reveal the effectiveness of this "loopless C-lobe" as an independent immunogen, with structural characterization and stability studies to demonstrate its integrity, and murine immunization and challenge studies that establish its ability to elicit robust protective efficacy by using N. meningitidis invasive infection and nasopharyngeal colonization models. The breadth of protection provided, as measured by both in vitro analysis and cross-protection mouse challenge studies, indicate that a single loopless C-lobe elicits a broadly cross-protective immune response against the diverse panel of meningococcal strains tested, and that the cross-reactivity is superior to that offered by the intact TbpB or the native C-lobe. Together, this study demonstrates the utility of structure-informed antigen engineering towards the development of broadly efficacious protein-based vaccines. ImportanceSurface-exposed proteins on bacterial pathogens are enticing candidate vaccine targets, however their exposure to the immune system frequently leads to high levels of antigenic variation, a factor that complicates the development of broadly protective vaccines. Here, we undertake an antigen engineering approach to develop a minimized version of a surface lipoprotein, transferrin binding protein B, where variable regions of the protein have been removed to focus the immune response to conserved regions of this antigen. We combine structural studies and mouse infection models of Neisseria meningitidis, the cause of meningococcal disease, and Neisseria gonorrhoeae, the causative agent of gonorrhea, to reveal that our strategic minimizing of the protein immunogen focuses the immune response to extend the resulting breadth of cross-reactivity and cross-protection.

immunology↗