Investigating the candidacy of LPS-based glycoconjugates to prevent invasive meningococcal disease: conjugates based on core oligosaccharides.

In this study we have prepared glycoconjugates with core oligosaccharides (OS) from the lipopolysaccharide (LPS) of Neisseria meningitidis, thus avoiding the neo-epitopes of the deacylated lipid A region of the derived LPS molecule identified in our previous studies. A comprehensive investigation was performed with glycoconjugates prepared from the most extended to the most truncated core OS still maintaining the conserved inner core epitope. As previously, we have established reproducible bactericidal killing of the homologous antigen elaborating strain, but a failure to kill wild-type strains. In these studies it was evident that the linker molecules used in the conjugation methodologies were dominating the immune response. However, when galE core OS based conjugates were prepared without utilizing linkers, via direct reductive amination, we failed to generate an immune response to even the homologous antigen. We also identified that immunisation with the galE antigen via linker methodologies provoked an immune response that was dependent upon key residues of the conserved inner core OS structure, whereas the immune responses to lgtB and lgtA antigens did not involve the inner core OS. This comprehensive study has, despite our best efforts, cast significant doubt as to the utility of the conserved inner core region of the meningococcal LPS as a potential vaccine antigen.