Intranasal Administration of Highly Conserved Influenza Antigens to Elicit Local Mucosal Responses and Enhance Cross-Subtype Protection

Abstract

Influenza causes approximately 650,000 deaths worldwide each year and remains one of the top ten causes of death in Canada. The public health burden of influenza is exacerbated by the highly variable year-to-year effectiveness of licensed vaccines. The unpredictable evolution of influenza surface antigens often leads to a mismatch between the circulating strain and the predicted vaccine strain. Additionally, current vaccines have limited ability to prevent early viral replication in the upper respiratory tract. Alternative strategies are needed to address these limitations in current influenza vaccines.

This thesis investigates the intranasal (IN) administration of conserved influenza antigens as a strategy to enhance heterosubtypic protection. By characterizing both systemic and mucosal immune responses elicited by this approach, I aim to advance our understanding of immunity against influenza viruses and to provide insights for the design of next-generation vaccines.

My research compared the protective mechanisms of intramuscular (IM) and IN delivery of a recombinant adenovirus encoding the highly conserved influenza nucleoprotein (NP), adjuvanted through fusion to CD40 ligand. While IM administration more effectively induced systemic cellular immune responses, IN immunization conferred superior cross-subtype protection through robust mucosal antibody production and pulmonary T cell responses. This thesis also evaluated the protective efficacy and immune responses elicited by an IN vaccine designed to express the consensus sequence of hemagglutinin subunit 2 (HA2) derived from all H3 strains. This approach provided cross-subtype protection against lethal H3N2 and H7N9 challenges. Further immunological analysis revealed that the vaccine induced antigen-specific pulmonary cellular and humoral immunity. Notably, a C-terminal region of the HA2 consensus sequence was identified to contain immunodominant epitopes, capable of inducing potent CD4+ and CD8+ T cell responses.

In conclusion, these studies provide mechanistic insights into the protective immune responses induced by IN administered vaccines targeting conserved influenza antigens. These findings contribute to the development of next-generation mucosal vaccines against a broad range of emerging respiratory viral pathogens.