Potent cellular immune responses are crucial for the development of effective vaccines against cancer and chronic infectious diseases. Here, we formulate Nexavant (NVT), a well-characterized TLR3 agonist, into lipid nanoparticles (LNPs) using either the ionizable lipid SM-102 or the cationic lipid DOTAP, and characterize their physicochemical properties and adjuvant potential. Both formulations achieve high encapsulation efficiency and enhance cellular uptake. In contrast to the stronger in vitro potency of DOTAP-based NVT/LNPs, SM-102-based NVT/LNPs (NVT/SM-LNPs) induce greater dendritic cell activation, cytokine production, and systemic T cell responses in vivo, likely due to more efficient delivery of NVT to the spleen. As an adjuvant for peptide vaccines, NVT/SM-LNP enhances antigen-specific CD4⁺ and CD8⁺ T cell responses and demonstrates potent therapeutic efficacy across subcutaneous, orthotopic, and metastatic TC-1 and B16-OVA tumor models, while also reducing viral titers in a chronic LCMV infection model. Compared to conventional adjuvants (poly(I:C), CpG, GM-CSF, IFA) and current mRNA vaccine platforms at clinically relevant doses, NVT/SM-LNP elicits stronger T cell immunity and enables effective neoantigen responses without requiring peptide-carrier conjugation. These findings establish NVT/SM-LNP as a potent adjuvant for T cell-targeted vaccines, with the lipid composition critically influencing immune targeting and efficacy, thereby guiding the design of next-generation vaccines.
