RNA-Based Immunostimulatory Liposomal Spherical Nucleic Acids as Potent TLR7/8 Modulators

Immunostimulatory spherical nucleic acids (IS-LSNAs) comprised of RNA selective for toll-like receptors (TLRs) 7/8 are synthesized and characterized. These structures consist of liposomal cores functionalized with a dense shell of RNA inserted into the wall of the lipid core via hydrophobic cholesterol moieties. IS-LSNAs potently activate TLR7/8 via NF-κΒ signaling in reporter cell lines and in primary immune cells as evidenced by cytokine production and the upregulation of costimulatory receptors. Importantly, they are preferentially taken up by plasmacytoid dendritic cells, an observation that makes them potentially useful for immunotherapy. In addition, these structures contain a core that can be loaded with antigens and used to prime T cells. In this regard, it is shown that dendritic cells treated with IS-SNAs loaded with ovalbumin peptide can prime ova specific CD8⁺ T cells. In addition to introducing the first IS-LSNAs consisting of RNA, these experiments show that one can facilitate an antigen-specific T cell response greater than that of free or cationic lipid-transfected RNA of the same sequence selective for TLR7/8. This work points toward the promise of using IS-LSNAs comprised of RNA as potent and highly tunable TLR-specific agents for the development of vaccines and other pharmaceuticals that require selective immunomodulation.