Nanoparticulate lipid adjuvants induce robust immunity against RSV infection
Effective subunit vaccines against respiratory syncytial virus (RSV) require adjuvants that elicit both humoral and cellular immunity. Conventional adjuvants such as alum and squalene emulsions (MF59, AS03) potentiate antibody titers but fail to induce robust T cell responses, while the liposomal AS01 adjuvant, though clinically validated, relies on costly and resource-limited immunostimulants MPLA and QS21. This study introduces a nanoparticulate lipid adjuvant (NLA) platform based on ionizable lipid (IL) nanoparticles. A library of 124 structurally diverse ILs was synthesized via Ugi four-component reaction and formulated with helper lipids into 124 distinct nanoparticles. In vitro screening based on TNF-α production from splenocytes identified high-performance NLA candidates. Formulations with varied amine heads were assessed for immune cell activation, including bone marrow-derived dendritic cells and RAW264.7 macrophages. Leading NLAs upregulated TNF-α and costimulatory molecules CD80 and CD86. Co-administered with RSV pre-F antigen in mice via intramuscular injection, the optimized formulation induced robust cellular and humoral immunity, with significantly enhanced central and effector memory T cell responses. Challenge studies demonstrated superior protection against viral infection, comparable to an AS01e-like liposome adjuvant. Safety evaluations, including hematology, blood biochemistry, and histopathology, confirmed good biocompatibility. Using NLRP3 gene knockout cells, the inflammatory properties of NLAs were shown to depend primarily on the NLRP3 inflammasome pathway. These findings establish rationally designed IL-based NLAs as high-performing, accessible adjuvants for subunit vaccines.