A novel monoclonal antibody to Neisseria meningitidis serogroup X capsular polysaccharide and its potential use in quantitation of meningococcal vaccines

Establishment of Sandwich ELISA for Quality Control in Rotavirus Vaccine Production

Non-replicating rotavirus vaccines are alternative strategies that may improve the protective efficacy of rotavirus vaccines in low- and middle-income countries. The truncated spike protein VP4 (aa26-476, VP4*)was a candidate antigen for the development of recombinant rotavirus vaccines, with higher immunogenicity and protective efficacy compared to VP8* and VP5* alone. This article describes the development of three genotype-specific sandwich ELISAs for P[4], P[6], and P[8]-VP4*, which are important for quality control in rotavirus vaccine production. Our results showed that the detection systems had good specificity for the different genotype VP4* and were not influenced by the E. coli host proteins. Moreover, the detection systems play an important role in determining whether the target protein was contaminated by VP4* proteins of other genotypes. They can also detect the adsorption rate of the adjuvant to the P[4], P[6], P[8]-VP4* protein during the process development. The three detection systems will play an important role in the quality control and process development of VP4* based rotavirus vaccines and facilitate the development of recombinant rotavirus vaccines.

Elucidating the Structural and Minimal Protective Epitope of the Serogroup X Meningococcal Capsular Polysaccharide

Despite the considerable progress toward the eradication of meningococcal disease with the introduction of glycoconjugate vaccines, previously unremarkable serogroup X has emerged in recent years, recording several outbreaks throughout the African continent. Different serogroup X polysaccharide-based vaccines have been tested in preclinical trials, establishing the principles for further improvement. To elucidate the antigenic determinants of the MenX capsular polysaccharide, we generated a monoclonal antibody, and its bactericidal nature was confirmed using the rabbit serum bactericidal assay. The antibody was tested by the inhibition enzyme-linked immunosorbent assay and surface plasmon resonance against a set of oligosaccharide fragments of different lengths. The epitope was shown to be contained within five to six α-(1–4) phosphodiester mannosamine repeating units. The molecular interactions between the protective monoclonal antibody and the MenX capsular polysaccharide fragment were further detailed at the atomic level by saturation transfer difference nuclear magnetic resonance (NMR) spectroscopy. The NMR results were used for validation of the in silico docking analysis between the X-ray crystal structure of the antibody (Fab fragment) and the modeled hexamer oligosaccharide. The antibody recognizes the MenX fragment by binding all six repeating units of the oligosaccharide via hydrogen bonding, salt bridges, and hydrophobic interactions. In vivo studies demonstrated that conjugates containing five to six repeating units can produce high functional antibody levels. These results provide an insight into the molecular basis of MenX vaccine-induced protection and highlight the requirements for the epitope-based vaccine design.