Targeting innate immune sensors for intranasal vaccine adjuvant design

While injectable vaccines can prevent respiratory pathogens from causing severe disease, their ability to elicit protective local immunity in the respiratory mucosa is more limited. For viral pathogens, infection outcome is often determined at the site of entry, where innate immune sensing within the airway mucosa precedes and conditions adaptive immune responses. At these surfaces, epithelial cells and antigen-presenting cells express a wide repertoire of pattern recognition receptors (PRRs), positioning innate immune activation as a central determinant of vaccine efficacy and durability of mucosal immunity. Recent advances in mucosal immunology facilitate the progression of mucosal vaccine development from empirical formulation toward mechanism-informed targeting of innate immune pathways. This review highlights emerging evidence supporting targeted engagement of cytosolic and endosomal PRRs to enhance intranasal vaccine efficacy. We focus on the cyclic GMP-AMP synthase-stimulator of interferon genes (STING) pathway, highlighting how spatially and temporally constrained STING activation can drive interferon-mediated antiviral immunity, enhance antigen presentation and promote tissue-resident T cells. We also discuss how complementary targeting of endosomal PRRs, including TLR3 and TLR9, further reinforces antiviral programming and adaptive immunity at mucosal sites.