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 protein's 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 models of N. meningitidis invasive infection and nasopharyngeal colonization. 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.