Study On The Chemical Modification And Immunological Properties Change Of Meningococcal Group A Polysaccharide Conjugate Vaccine

Neisseria meningitidis can cause severe diseases such as meningitis in children. As a key virulence determinant, meningococcal capsular polysaccharide(PS) is poorly immunogenic that can not induce immunological memory. In recent years, the development of conjugate vaccines has solved the problem to a certain extent. Compared to conventional polysaccharide vaccine, as a T cell-dependent antigen, conjugate vaccine of polysaccharide to protein has a better protective effect on infants under two years old and can induce immunological memory. However, a dose-dependent carrier priming of the Neisseria meningitidis group C polysaccharide-TT conjugate vaccine was observed. Increase in the anti-polysaccharide antibody response could be obtained for Men CTT with low-dose carrier priming(0.025 to 0.25μg). Suppression of the anti-polysaccharide antibody response was observed with high-dose(25μg) carrier priming. That is, when overloaded the pre-immune carrier protein, immunogenicity of polysaccharide may be inhibited(CIES phenomenon). Meanwhile, when injected a multivalent vaccine with the same carrier protein, one or more components can not fully play its role in immune response. It was not clear whether suppressing or enhancing protein-specific immunogenicity could improve the PS-specific immunogenicity of conjugate vaccine. In addition, carrier protein has carrier specificity. So studying the influence of carrier on the immunogenicity of the polysaccharide plays an important role in the development of the polysaccharide conjugate vaccine.This experiment used the linear PEG approved by FDA and tetanus toxoid as modifier to prepare three meningococcal capsular polysaccharide conjugate vaccine. The method comprises the following steps:(1)activates of meningococcal polysaccharide with cyanogen bromide, then the heterobifunctional reagent N-2- amine ethyl maleimide reacts with activated meningococcal polysaccharide;(2) thiolation of the carrier protein;(3) bind the meningococcal polysaccharide to thiolated carrier protein(4) modification with PEG and carrier protein;When the mass ratio of PEG to PS is 3: 10, 10: 10, and the mass ratio TT to PS is 1: 1, the carrier-specific Ig G antibody titer of the three conjugates(PS-TT-P1, PS-TT-P2, PS-TT-TT) are respectively 0.89 times, 0.49 times, 1.61 times that of PS-TT. PS-specific Ig G antibody titers are 2.6 times, 0.63 times, and 0.56 times that of PS-TT.Presumably, when the mass ratio of PEG to PS is 3: 10, PEG appropriately suppresses the immunogenicity of carrier. It contributes to the immunogenicity improvement of the polysaccharide. Excessive PEGylation strongly suppressed the immunogenicity of carrier and was not conducive to the formation of APC-MHCII-TCR. It probably led to insufficient activation of T helper cell and mature B cells. As a result, the anti-polysaccharide immunogenicity declined. When TT modified carrier, antigen epitopes of carrier greatly increased, and competed with the polysaccharide hapten for mature B cells. It turned out oligomerization of carrier produces strong carrier-specific immunogenicity and weakens the polysaccharide-specific immunogenicity. Mild PEGylated meningitis polysaccharide conjugate can be developed to new, efficient polysaccharide conjugate vaccine for prevention the infection caused by epidemic Neisseria meningitidis. This article can be used to optimize the combination vaccine immunization program and design the ideal carrier protein.