Exploiting immune response to intranasal Flu vaccine integrating human nasal and immune cellular in vitro models

To assess the effectiveness of mucosal vaccination, a comprehensive understanding of both local and systemic immune responses is required. Thus, we investigated the immunomodulatory properties of an anti-influenza (Flu) nasal vaccine by using two in vitro models namely air-liquid interface cultured human nasal epithelial cells (MucilAir™-pool), representing vaccine administration site, and peripheral blood mononuclear cells (PBMCs), recapitulating the immune compartment. To this aim, nasal epithelial cells and PBMCs were stimulated with Fluenz Tetra® (Astrazeneca), a live attenuated tetravalent nasal Flu vaccine based on four Flu strains: two A/strains (H1N1 and H3N2) and two B/strains (Austria and Phuket). Exposure of nasal epithelial cells to anti-Flu vaccine resulted in a poor cytotoxic effect, measured by Lactate dehydrogenase (LDH) release, and in a sustained ciliary beating frequency (CBF), determined by microscopic recording and image analysis. Also, a reduction of nasal epithelial integrity, evaluated by transepithelial electrical resistance (TEER), was observed. In both nasal epithelium and PBMC-based models an important production of cytokines, chemokines and anti-viral molecules was found upon stimulation with anti-Flu vaccine. Notably, in these conditions PBMCs only, but not nasal epithelial cells, produced high levels of the anti-viral IFN-αs. These results well correlate with the increased levels of CD86 activation marker observed in vaccine stimulated PBMCs. Together, our data offer a comprehensive in vitro framework for evaluating local and systemic effects of nasal vaccination. In particular, results from nasal epithelial cells demonstrated the ability of anti-Flu nasal vaccine to stimulate local immune responses while maintaining epithelial homeostasis, critical features for effective mucosal immunity. In parallel, PBMC data provided insights into systemic immune activation, revealing the vaccine potential to elicit controlled systemic immune responses without excessive inflammation. By integrating findings from nasal epithelial and immune cell based-models, this study improves our understanding of the mechanisms underlying responses to mucosal vaccines and supports the exploitation of this vaccine platform as a promising strategy to prevent respiratory virus infections.