Although
immunotherapy shows great promise for the long-term control of
cancer, many
tumors still fail to respond to treatment. To improve the outcome, the delivery of
immunostimulants to the lymph nodes draining the
tumor, where the antitumor immune response is initiated, is key. Efforts to use nanoparticles as carriers for
cancer immunotherapy have generally required targeting agents and chemical modification of the
drug, and have unfortunately resulted in low delivery and therapeutic efficiency. Here, we report on the efficacy of
gold nanoparticles with approximately 5 nm hydrodynamic diameter coated with a mixture of
1-octanethiol and 11-mercaptoundecanesulfonic
acid for the delivery of an immunostimulatory TLR7
ligand to
tumor-draining lymph nodes. The
drug was loaded without modification through nonspecific adsorption into the
ligand shell of the nanoparticles, taking advantage of their amphiphilic nature. After loading, nanoparticles retained their stability in
solution without significant premature release of the
drug, and the
drug cargo was immunologically active. Upon
subcutaneous injection into
tumor-bearing mice, the
drug-loaded particles were rapidly transported to the
tumor-draining lymph nodes. There, they induced a local immune activation and fostered a cytotoxic T-cell response that was specific for the
tumor. Importantly, the particle-delivered TLR7
ligand blocked the growth of large established
tumors and significantly prolonged survival compared to the free form of the
drug. Thus, we demonstrate for the first time that nanoparticle delivery of a TLR7
immunostimulant to the
tumor-draining lymph nodes enhances antitumor immunity and improves the outcome of
cancer immunotherapy.