Synthesis of Bacterial Surface Glycans for Conjugate Vaccines

• Main Author: Haynie, Teron D.
• Format: Others
• Published: BYU ScholarsArchive 2020
• Subjects: conjugate vaccine; carbohydrate antigen; synthesis; TLR4; Physical Sciences and Mathematics
• Online Access: https://scholarsarchive.byu.edu/etd/8669; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=9669&context=etd

Bacteria are coated with repeating units of oligosaccharides that exhibit remarkable diversity. Often, glycan units of three or even two sugars are sufficient to identify a species of bacteria. Such specificity makes bacterial surface glycans attractive vaccine targets. However, efforts to create effective vaccines against carbohydrates have been hampered by poor vaccine design as well as the human immune tendency to respond to glycan antigens with non-specific, T-cell independent mechanisms. As a result, carbohydrate vaccines have historically produced only adequate memory responses in healthy individuals and poor responses in the elderly or immunocompromised. To circumvent these issues, a novel conjugate vaccine was developed that utilizes theQβ virus-like particle carrier that displays both a carbohydrate antigen as well as a Natural Killer T cell adjuvant. This unique vaccine has been reported to stimulate the production of high affinity (nanomolar) antibodies against carbohydrate antigens. To further conjugate vaccine research, the present work synthesizes two bacterial surface antigens: a trisaccharide from Streptococcus pneumoniae serotype 23F (Sp23F), and a pentasaccharide from Ruminococcus gnavus (Rg). Sp23F has been characterized as one of the more virulent and disease-causing strains of S. pneumoniae. Rg secretes highly immunostimulatory proteins and is associated with irritable bowel syndrome. The Sp23F antigen is synthesized with an alkyne at the reducing end of the sugar to facilitate coupling to Qβ. A selection reagent for Sp23F is also synthesized to enable the extraction of antibodies and B cells that bind the antigen. In conjunction with providing a conjugate vaccine antigen, the Rg pentasaccharide will be examined as a TLR4 ligand and was therefore synthesized without an alkyne. The Rg conjugate vaccine shows promise in treating irritable bowel syndrome as well as facilitating research into the role Rg plays in the human microbiome.