Development of pneumococcal polysaccharide conjugate vaccine with long spacer arm

The Pneumococcal Polysaccharide-Tetanus Toxin Native C-Fragment Conjugate Vaccine: The Carrier Effect and Immunogenicity

The encapsulated bacteria, as Streptococcus pneumonia, Haemophilus influenzae type b, and Neisseria meningitidis, cause serious morbidity and mortality worldwide. The capsular polysaccharide (PS), which could elicit a weak T cell-independent immune response, is a vital virulence determinant. One of the strategies to improve the PS-specific immunogenicity is to conjugate PS with a nontoxic carrier protein. Tetanus toxoid (TT) and CRM₁₉₇ are the typical carrier proteins for the PS conjugate vaccines. TT is the inactivated tetanus toxin manipulated with formaldehyde, which suffers from the pollution from residual formaldehyde and the incomplete detoxification. CRM₁₉₇ has the disadvantage of low-yield purification with the requirement of sophisticated culture conditions. Thus, a novel carrier protein without these disadvantages is highly required. The tetanus toxin native C-fragment (Hc) is safe, low-cost, and highly immunogenic with easy purification, which can act as a promising carrier protein. Pneumococcal serogroups 14 and 23F were major epidemic causes of pneumococcal infections. In the present study, the capsular PSs (PS14 and PS23F) were conjugated with Hc, TT, and CRM₁₉₇, respectively. TT- and CRM₁₉₇-based conjugates acted as controls for Hc-based conjugates (PS14-Hc and PS23F-Hc). The structural properties of Hc were not fundamentally changed after conjugated with PS. PS14-Hc and PS23F-Hc could potentiate sound PS-specific antibody levels comparable to the controls. Thus, Hc exhibited a practical carrier effect to help the pneumococcal conjugate vaccines perform good immunogenicities.

The phenyl linker markedly increases the immunogenicity of the pneumococcal polysaccharide conjugate vaccine

OBJECTIVE

Capsular polysaccharide (PS) of Streptococcus pneumoniae is a key virulence factor and typically conjugated with a carrier protein. It is necessary to improve the immunogenicity of the conjugate vaccine against S. pneumoniae.

RESULTS

A phenyl linker between tetanus toxoid (TT) and S. pneumoniae Type 14 PS was used to improve the PS-specific immunogenicity of the conjugate vaccine. As compared with the one with the amyl linker (PS-TT), the conjugate with the phenyl linker (PS-phe-TT) decreased the TT-specific IgG titers and significantly increased the PS-specific IgG titers and the IL-5 level.

CONCLUSION

The phenyl linker could potentiate a robust humoral immune response to PS by decreasing the carrier-induced epitopic suppression effect. PS-phe-TT was expected to act as an effective vaccine against S. pneumoniae.