The rational structure-based design of a protein nanoparticle presenting a chimeric MenB antigen
Bacterial infection by the gram-negative diplococcus Neisseria meningitidis serogroup B (MenB) is a leading cause of meningitis and septicaemia. Vaccines rank amongst the most important public health interventions for combatting these diseases. As vaccine development orientates towards more minimalist subunit antigen-based vaccines, new adjuvant systems are increasingly needed to boost immunogenicity. The application of nanoparticles in vaccine formulations has the potential to drive the
... ment of next generation adjuvant systems that improve antigen presentation and overall vaccine immunogenicity. In addition, advances in structural and computational biology have enabled a new era of vaccine design and discovery, Structural Vaccinology, which seeks the rational structure-based design of improved vaccine antigens measured in terms of epitope presentation, stability and ease of production. In this project, a structural vaccinology approach is adopted toward the rational design of a self-assembling ferritin nanoparticle system displaying a chimeric protein antigen to stimulate broad and efficacious immunogenicity against MenB. This chimeric antigen, incorporating epitopes from the NadA3 and PorA MenB antigens seeks to confer broader MenB strain coverage, while its incorporation into a self-assembling ferritin-based nanoparticle system sees the chimeric NadA3-PorA presented in a multicopy format on the ferritin surface, enhancing the immunogenicity. The first part of the thesis describes the in silico design of a feasible protein nanoparticle system using X-ray crystallography data. This NadA3-PorA-Ferritin was then expressed and purified, before its epitope presentation was characterised by a range of structural and biochemical approaches, including cryo-electron microscopy (cryo-EM). The immunogenicity of the NadA3-PorA-Ferritin was assessed in vivo, revealing that recombinant nanoparticle presentation of the NadA3-PorA enhanced the humoral responses raised against the subunit antigen. Different adjuvant systems to deliver the NadA3-PorA-Ferritin were also examined, demonstrating that an inhouse, cationic liposome formulation produced by benchtop microfluidics generated a similar level of immunogenicity as a commercially available MF59-based emulsion adjuvant. Further serological assays were performed to gauge the bactericidal titre resulting from immunisation with the nanoparticle. The work within this project exemplifies a structural vaccinology approach towards the design of a chimeric protein antigen-presenting self-assembling nanoparticle system that is able to confer broad and efficacious protection against MenB.