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Published on: November 5, 2019
Neisseria meningitidis serogroup X polysaccharide as a qualified antigen for multivalent meningococcal conjugate
Dan Fu1, Kang Li2, Xianhua Shi1
1Beijing Zhifei Lvzhu Biopharmaceut Co., Ltd., Beijing, China.
Background:
Meningococcal meningitis remains a severe global health threat to infants, with multivalent vaccination serving as the most effective preventive measure. In 2021, World Health Organization (WHO) released Defeating Meningitis by 2030: A Global Roadmap, highlighting an urgent demand for conjugate vaccines covering an expanded spectrum of meningococcal serogroups. Accordingly, the development of affordable and globally accessible diagnostic and preventive strategies, including protection against Neisseria meningitidis serogroup X (MenX), has become a key public health priority.
Methods:
A comprehensive multi-analytical strategy was implemented, incorporating whole-genome sequencing (WGS), electron microscopy, nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), Congo red staining assay, size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS), thermogravimetric analysis/derivative thermogravimetry (TGA/DTG), differential scanning calorimetry (DSC), immunodiffusion assays, enzyme-linked immunosorbent assay (ELISA), and serum bactericidal assay, to systematically evaluate the genetic stability of the MenX production strain, alongside the molecular structure, physicochemical properties, antigenicity, and immunogenicity of MenX polysaccharide (MenX PS).
Results:
Our study demonstrated the genomic stability of MenX CMCC 29040 strain and characterized the fermentation kinetics of capsular polysaccharide (CPS) throughout fermentation. Formaldehyde inactivation efficiently promoted the release of CPS from the bacteria while preserving bacterial cellular integrity. Furthermore, micro-morphological characterization for the first time directly visualized the optimal particle size range (100-200 nm) and polydispersity profile of purified MenX PS. In aqueous solution, free MenX PS adopted a compact, globular, random-coil conformation without triple-helix structure, exhibiting distinct structural differences compared with membrane anchored CPS. In addition, quantitative thermal analysis established the thermodynamic threshold of MenX PS, confirming a degradation temperature above 170 °C and superior thermal stability relative to Neisseria meningitidis serogroup A polysaccharide (MenA PS). Moreover, quality-qualified MenX PS exhibited specific antigenic reactivity and the MenX PS-tetanus toxoid conjugate (X-TT), prepared via reductive amination conjugation, presented robust immunogenicity and excellent batch-to-batch reproducibility. In vivo immunization confirmed that X-TT elicited high level MenX PS-specific IgG antibody responses and potent complement-dependent serum bactericidal activity.
Conclusion:
MenX PS possesses favorable physicochemical properties and specific immunogenic characteristics, supporting its eligibility as a qualified antigen component for the development of multivalent meningococcal conjugate vaccines (MMCVs).
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