Intranasal Adenoviral Vector Vaccination Induces Durable Antibody and T Cell Responses in the Respiratory Tract

Background/Objectives: Respiratory pathogens such as influenza virus and SARS-CoV-2 pose major threats to global public health. Current vaccines provide limited mucosal protection against respiratory infection, while vaccine-induced immunity can wane over time. Intranasal vaccination has emerged as a promising approach to induce mucosal immunity, however relatively low immunogenicity and limited durability remain major challenges. Various strategies have therefore been explored to improve intranasal vaccine efficacy, including mucosal adjuvants and alternative vaccine platforms. In this study, we evaluated the magnitude and durability of systemic and mucosal immune responses induced by an adenoviral vector vaccine. Methods: Six-week-old female C57BL/6 mice were immunized intranasally or intramuscularly with a single dose of an adenoviral vector vaccine and compared with mice receiving one or two doses of an intranasal CpG-adjuvanted protein vaccine. Humoral immune responses in serum and BALF, as well as cellular immune responses in the mLNs, lungs, and blood, were evaluated. We further assessed Ova-specific CD8 T cells with a lung-resident phenotype by class I MHC-peptide tetramer staining combined with intravascular labeling, allowing their direct ex vivo identification. Results: A single dose of intranasal adenoviral vector vaccination elicited potent serum IgG and BALF IgA responses, together with antigen-specific CD8 T cell responses in the blood, mLNs, and lungs. Notably, these systemic and respiratory mucosal immune responses were sustained for up to 4 months after vaccination, with lung-resident CD8 T cell responses detected at this time point. In contrast, intramuscular adenoviral vector vaccination predominantly induced systemic immunity. Intranasal CpG-adjuvanted protein vaccination induced weaker responses after a single dose, while booster vaccination enhanced systemic antibody and cellular responses but showed limited induction of mucosal immunity. Conclusions: A single intranasal dose of Ad5-Ova induced systemic and respiratory mucosal immune responses comparable to those observed after two-dose Ova+CpG vaccination, while maintaining these responses for up to 4 months. These findings suggest adenoviral vectors as a promising platform for inducing long-lasting respiratory mucosal immunity.