Understanding The MHC-II Presentation Mechanism For The Rational Design Of Glycoconjugate Vaccines

Despite the great advantages in using glycoconjugates for generating a protective immunity, the molecular mechanism of T cell epitope recruitment and MHC-II presentation has to be clarified. Dissecting the mechanism that controls glycoconjugates/peptide-MHC-II interactions will allow defining a rational for a better design of glycoconjugate vaccines. It is well accepted that polysaccharides function as T cell–independent antigens, since they fail to induce T cell–mediated immune responses (IgM to IgG class switching, booster antibody response and T cell memory). On the contrary, when a polysaccharide is linked to a carrier protein, the protein provides the T cell epitopes that engage the T cell receptor (TCR) and trigger the release of cytokines that help the B cell to differentiate and proliferate. With the aim to analyze glycoconjugate/MHC-II interactions and evaluating the efficacy of glycoconjugate MHC-II processing and presentation, different glycoconjugates were synthesized. ß-1,3-glucans oligosaccharides were covalently linked to the lysine side chains of recombinant proteins from Neisseria meningitidis and Streptococcus pneumoniae. Testing the glycoconjugates in mice, we highlighted differences in the immune response probably due to different pattern of glycosylation that can lead to a different MHC-II peptide interaction. Using proteomic and glycoproteomic approaches, we evidenced differences in the pattern and extent of conjugation. Mutated recombinant carriers lacking the identified conjugation-sites were produced, conjugated, and tested as carrier in mice. This represents a first step in the design of experiments that will provide insight in the understanding of the peptide/glycopeptide-MHC-II interaction.