Identification of meningococcal vaccine antigens using Reverse Vaccinology 2.0

Abstract

Neisseria meningitidis can cause life-threatening invasive meningococcal disease (IMD), with fatality rates of ~10% and up to a quarter of survivors suffering from long-term sequelae. Whilst effective conjugate vaccines are available for serogroups A, C, W, X and Y, the search for a serogroup B (MenB) vaccine has proved more challenging. Successful anti-meningococcal vaccines must induce bactericidal antibodies, a correlate of protection measured using serum bactericidal activity. After application of a pioneering technique called Reverse Vaccinology against MenB, a recombinant protein vaccine, 4CMenB, was produced. 4CMenB has been proven safe and effective, but does not protect against all strains of serogroup B due to antigenic variability, therefore novel vaccine candidates are still required. I have applied the Reverse Vaccinology 2.0 technique to IMD patients in order to identify novel vaccine candidates. First, fluorescent activated cell sorting was used to single-cell sort patient plasmablasts, before expression cloning. Cloned antibodies were then characterised for reactivity and functionality against N. meningitidis. Finally, the target antigen of anti-meningococcal human monoclonal antibodies (hmAbs) were elucidated using western blot, immunoprecipitation and mass spectrometry (IP-LC/MS). I successfully cloned and characterised 13 anti-meningococcal hmAbs from six patient samples, all of which have broad cross-reactivity including binding to non-4CMenB strains, suggesting novel epitopes were discovered. One of these hmAbs, P09-2F2, bound to 95% of MenB strains assessed. Four hmAbs showed the ability to recruit complement components C3b and C5b-9, suggesting potential opsonophagocytic and bactericidal roles, respectively. Six potential antigen targets for each of hmAbs P02-1A1 and P09-2F2 were identified using IP-LC/MS. Some of these targets were previously described vaccine candidates, whilst others are yet to be explored, with exciting potential as vaccine candidates. In addition, advancements to the RV2.0 methodology including an immune capture assay (ICA) using whole fluorescently labelled meningococci as antigen for sorting of pathogen-specific plasmablasts are described. The ICA increased the percentage of anti-meningococcal hmAbs cloned 1.25-fold, streamlining the RV2.0 process.