We have been developing a platform to optimize glycoconjugate vaccine design by determining optimal polysaccharide chain length and peptide conjugation sites. We learned that the use of a full-length polysaccharide and conjugation to the C-terminal end of the peptide induce optimal immunogenicity. When immunizing mice with such glycopeptide vaccines, we found—using GBSIII capsular polysaccharide (CPS) as a model—that these glycoconjugates induced full protection in the challenge model. We extended the platform to develop a prototype vaccine for Francisella tularensis, coupling the O polysaccharide (OPS) to an optimized peptide and observing very significant protection. Remarkably, protection with a glycoconjugate vaccine against F. tularensis had not been shown previously. Thus, we were greatly surprised when we measured antibodies to the GBSIII CPS and the OPS of F. tularensis and found that they were of very low titer but very highly protective. We have further characterized the humoral response induced by both glycoprotein and glycopeptide vaccines looking at subclasses, functionality, and relative affinity/avidity. Antibodie induced by glycopeptide vaccines showed higher relative affinity/avidity and functional activity. In the future, we are planning to expand the investigation on polysaccharide specific B cells at single cell transcriptional analysis level of as well as by hybridoma technology.
We have also extended our observations that T cell specifically recognizing carbohydrates (Tcarbs) were critical in the response to other conjugate vaccines (Salmonella Typhi, Hib, type Ib group B Streptococcus) but not group C N. meningitidis. In the latter case, digestion of the acid-sensitive group C N. meningitidis polysaccharide in the endosome resulted in a dominant CD4+ T-cell response to peptides in the context of MHCII presentation. Our results show that different mechanisms of presentation—based on the structure of the carbohydrate—are operative in responses to different glycoconjugate vaccines.
In addition, we are working on a structural investigation of the interaction between glycopeptides and MHCII molecules. We have produced two glycopeptides, using GBSIII CPS as carbohydrate source and generating oligosaccharides corresponding to a degree of polymerization (i.e. number of repeating units) of respectively 3 and 4, both conjugated to OVA peptide. Preliminary binding experiments were performed.
In the context of designing a new class of vaccines via rational approaches, we have developed a Francisella tularensis glycoconjugate vaccine by using a genetically enlarged O-antigen able to induce protective antibodies in mice. Also, we have contributed to the synthesis of Neisseria Meningitidis A carba analogues as hydrolytically stable antigens for anti-meningococcal glycoconjugate vaccines.
With regard to exploitation and dissemination, we are currently evaluating the possibility to protect the intellectual property of results generated by patents or similar mechanisms. The NEWCARBOVAX action has been presented in several conferences and symposiums, as well as exposed to Industrial, Academic and Start-up environments. So far, four publications in top-leading journals have been produced with reference to the action, and few more are expected to come in the next months.
