Combined and Novel Adjuvant Strategies to Enhance and Direct Immune Responses to Influenza A Virus Vaccines

Vaccines have been a tremendous breakthrough by preventing illness and death due to infectious disease. However, many relevant pathogens, including influenza A virus (IAV), do not have effective vaccines. Therefore, investigation of strategies to improve vaccination is essential. One such strategy is the use of adjuvants, which are additives that enhance vaccine-induced immune responses. Examination of new adjuvant strategies will contribute to development of improved vaccines. This dissertation investigated two adjuvant strategies, combined pattern recognition receptor (PRR) agonists and the biomaterial chitosan (CS). PRR agonists studied here included monophosphoryl lipid A (MPL) and unmethylated CpG oligodeoxynucleotides (CpG). MPL and CpG are currently used as adjuvants in human vaccines but are not used in combination. It was hypothesized that incorporating combined CpG+MPL into an IAV vaccine would increase B and T cell responses and enhance protection over individual agonists. In vitro, CpG+MPL induced distinct antiviral transcription in antigen presenting cells (APCs). When delivered intramuscularly, CpG+MPL and MPL alone resulted in similar levels of protection from morbidity. Intranasally delivered vaccines containing combined CpG+MPL resulted in improved protection compared to unadjuvanted vaccines but not individual agonists or intramuscular vaccines. CS, a partially deacylated derivative of chitin, was examined for its adjuvant potential, and in particular the role of molecular weight (MW) in CS adjuvanticity was studied. Two CS variants, low MW (LMW, 50-190 kDa) and high MW (HMW, 310-375 kDa), were tested. LMW and HMW CS induced cytokine responses in vitro in APCs and, in an IAV vaccine, reduced morbidity following infection compared to unadjuvanted vaccination. However, CS appeared to induce a T helper 2 response and mice receiving CS experienced significant morbidity following challenge. Taken together, the results described here provide insights into the use of CpG+MPL and CS as adjuvants. Although, neither adjuvant strategy is optimized for an IAV vaccine, information gained about the advantages and limitations of each strategy has potential to inform future investigations of novel adjuvants