Anti-PorA antibodies elicited by immunization with peptides conjugated to P64k

Effect of conjugation methodology on the immunogenicity and protective efficacy of meningococcal group C polysaccharide-P64k protein conjugates

Neisseria meningitidis serogroup C polysaccharide (CCPS) was conjugated to the carrier protein P64k using two different conjugation procedures, condensation mediated by carbodiimide with adipic acid dihydrazide as spacer and the reductive amination method. BALB/c mice were immunized with the resultant polysaccharide-protein conjugates and the immune response was evaluated. All conjugates assayed generated at least 10-fold higher antibody titers than the free polysaccharide. The reductive amination method rendered the best conjugate (CCPS-P64kR) that was able to elicit antibody titers statistically higher than the titer elicited by the plain CCPS (P<0.001). The sera of the group immunized with CCPS-P64kR showed a three-fold higher bactericidal response than the sera of the group immunized with the plain CCPS and they were able to protect against challenge with meningococci in the infant rat protection model. In addition, three different conjugates were obtained from polysaccharides with molecular relative sizes of 2000-4000 Da, 4000-10,000 Da or 10,000-50,000 Da, but no differences were detected in the immune response obtained against the three conjugates. Our experiments demonstrate that it is possible to generate a protective, T-cell-dependent response against CCPS using the P64k protein as carrier.

Effect of P64k presensitization on its efficacy as an immunological carrier in mice

Recently, we have successfully employed the meningococcal P64k protein as a carrier for weak immunogens. Here, we study if presensitization with it can affect the murine antibody response against the hapten chemically coupled to P64k. We found that priming with 10 microg of P64k did not induce epitope-specific suppression against two out of three synthetic peptides, from viral proteins, conjugated to this carrier. Depending on the anti-carrier antibody titers elicited in the presensitized mice, we observed or not a suppressed immune response against the third peptide. Presensitization with 100 microg of P64k resulted in epitope-specific suppression when lower doses of conjugate were administered. In summary, as described for other protein carriers, P64k could induce epitope-specific suppression in mice, but it depends on the hapten and the extent of carrier-specific immunity. Furthermore, this suppression can be overcome by increasing the amount of conjugate administered per dose in the presensitized animals.