Intranasal delivery of a vasoactive intestinal peptide-based circRNA vaccine induces systemic and mucosal immunity against RSV in mice.

Respiratory syncytial virus (RSV) is a major cause of acute lower respiratory tract disease in infants and older adults; however, vaccine strategies capable of inducing robust respiratory mucosal immunity remain limited. Here, we developed a receptor-guided intranasal circular RNA (circRNA) vaccine platform based on a vasoactive intestinal peptide-nucleocapsid fusion protein (VIP-N), which enables the self-assembled delivery of circRNA encoding RSV antigens. Mechanistically, VIP-N enters cells through VIP receptor-dependent early endocytosis and preferentially enhances circRNA delivery in respiratory epithelial cells and antigen-presenting cells. In mice, intranasal immunization with VIP-N+circRNA vaccines induced serum IgG responses comparable to those elicited by intramuscular administration. VIP-N+circRNA vaccines uniquely promoted IgA responses in bronchoalveolar lavage fluid and increased T follicular helper 1 cells. Moreover, the VIP-N+circRNA vaccine encoding pre-F elicited the strongest neutralizing activity and conferred cross-protection against both RSV-A and -B subtypes, significantly reducing pulmonary viral burden and lung inflammation. Notably, the immune response was predominantly T helper type 1 (Th1) cell-skewed, without an accompanying increase in Th2 cytokines associated with vaccine-enhanced respiratory disease. Collectively, these findings suggest VIP-mediated circRNA delivery as a promising intranasal strategy to induce comprehensive immunity against RSV, potentially improving protection in vulnerable populations.