Covalent Conjugation of Small-Molecule Adjuvants to Nanoparticles Induces Robust Cytotoxic T Cell Responses via DC Activation

Abstract

Specific recognitions of pathogen associated molecular patterns by Toll-like receptors (TLRs) initiate dendritic cell (DC) activation, which is critical for coordinating innate and adaptive immune responses. Imidazoquinolines as small-molecule TLR7 agonists often suffer from prompt dissemination and short half-life in the bloodstream, preventing their localization to the corresponding receptors and effective DC activation. We postulated that covalent incorporation of imidazoquinoline moieties onto the surface of biocompatible nanoparticles (∼30 nm size) would enhance their chemical stability, cellular uptake efficiency, and adjuvanticity. The fully synthetic adjuvant-nanocomplexes led to successful DC activation at lower nanomolar doses compared with free small-molecule agonists. Once a model antigen such as ovalbumin was used for immunization, we found that the nanocomplexes promoted an unusually strong cytotoxic T lymphocyte response, revealing their unique immunostimulatory capacity benefiting from multivalency and efficient transport to endosomal TLR7.