The development of vaccines against pathogenic Neisseria species is challenged by antigenic variability and functional interactions between candidate antigens and host factors. Transferrin binding protein B (TbpB), a surface-exposed iron acquisition protein essential for bacterial survival, represents a promising vaccine target for both Neisseria gonorrhoeae (Ngo) and Neisseria meningitidis (Nme). However, sequence variation and TbpB's strong interaction with human transferrin and posed some initial problems for the efficacy of this putative immunogen. Here, we integrate structure-guided and phylogeny-informed strategies to optimize TbpB-based immunogens for broad and effective vaccine formulations.
For Ngo, we employed two complementary approaches. First, to address antigenic diversity, phylogenetic analysis guided the rational selection of two complementary TbpB variants, forming a bivalent vaccine that induced broadly cross-reactive antibodies against diverse gonococcal strains and reduced colonization duration in vivo. Second, structure-based engineering was used to generate TbpB variants that abolish human transferrin binding without disrupting antigen structure. These engineered immunogens elicited enhanced bactericidal and functional antibody responses and conferred improved protection in human transferrin transgenic mouse infection models, highlighting the importance of eliminating host ligand binding.
For Nme, we developed a structurally minimized TbpB immunogen consisting of a loopless C-lobe (LCL), in which variable surface loops were removed to focus immune responses on conserved epitopes and importantly, can house conserved epitopes from other important antigens such as TbpA. This LCL retained structural integrity and stability while eliciting robust and broadly protective immune responses across diverse meningococcal strains in both invasive disease and colonization models. Notably, the minimized antigen outperformed full-length TbpB in breadth of cross-protection.
Together, these findings demonstrate that combining structural engineering to remove functional or variable regions with rational antigen selection strategies can overcome key barriers to TbpB-based vaccine design. This work supports TbpB as a versatile platform for developing broadly protective vaccines against both gonococcal and meningococcal infections and provides a framework for antigen optimization targeting highly variable bacterial pathogens.