Intramuscular self-amplifying RNA and adenoviral RSV vaccines program distinct systemic and respiratory mucosal immune architectures.

Respiratory syncytial virus (RSV) remains a major cause of severe lower respiratory tract disease in infants, older adults, and immunocompromised individuals, underscoring the need for vaccine strategies that balance systemic protection with frontline respiratory immunity. Although adenoviral and RNA-based RSV are both promising platforms, how the platform itself shapes systemic versus respiratory mucosal immunity under the same antigenic context remains insufficiently defined. We conducted a head-to-head comparison of an LNP-delivered saRNA vaccine (LNP-RSV-preF saRNA) and a recombinant Ad5-vectored vaccine (Ad5-RSV-preF) in mice using intramuscular prime-boost immunization. The two platforms drove distinct immune architectures rather than just differences in response magnitude. LNP-RSV-preF saRNA preferentially promoted respiratory mucosal immunity, including elevated BALF IgG, pulmonary antibody-secreting cells, CD69+ T cells, and lung-resident memory T (TRM) cells, as well as cycling and memory-associated CD8+ T-cell states and durable lung IgA memory. In contrast, Ad5-RSV-preF induced stronger systemic immunity, featured by higher early serum IgG, splenic polyfunctional effector T cells, enhanced germinal center/TFH responses, and effector-polarized CD8 + T cells, with sustained systemic humoral memory. Ad5-vectored and LNP-saRNA vaccine platforms induce distinct compartmentalized immune responses to the same RSV preF antigen. This study establishes a framework for rational platform selection in RSV vaccine design, enabling tailored strategies to balance systemic immunity and respiratory mucosal memory.