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 (similar to 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.