PROJECT SUMMARY This proposal addresses the significant, unmet need to develop and translate new therapies for children with advanced, high-risk neuroblastoma. Neuroblastoma (NB) is the third most common pediatric cancer and the most common extracranial solid tumor of childhood, accounting for 15% of all pediatric cancer deaths each year despite an intensive, multimodal, and toxic treatment regimen. Immunotherapy offers the potential for selective targeting and killing of cancer cells and represents an appealing alternative for eradicating recurrent, metastatic disease and achieving durable cures with minimal toxicity. However, NB has proven poorly responsive to most immunotherapeutic modalities, notably including immune checkpoint blockade and CAR T cell therapy. Therefore, novel immunotherapies for NB must be developed. The objective of this proposal is to advance and mature STING-activating nanoparticles (STANs), a promising experimental immunotherapeutic nanomedicine for enhancing immunotherapy responses in NB, towards clinical translation. To accomplish this, we will directly address potential barriers to the clinical advancement of STANs by further optimizing their physiochemical and biological properties via a scalable manufacturing process, elucidating key immunopharmacological parameters in rigorous NB mouse models, and establishing rationally-designed immunotherapy regimens that generate robust and durable responses. We will accomplish this through the following Specific Aims. First, we will employ an integrated polymer and materials science approach to reproducibility fabricate STANs with optimized properties via a facile and scalable flash nanoprecipitation nanofabrication strategy. Second, we will evaluate the pharmacokinetics, biodistribution, pharmacodynamics, safety, and therapeutic efficacy of STANs in a rigorous immunocompetent NB that mimic human disease. Third, we will evaluate and optimize rationally-designed immunotherapy regimens combining STANs with immune checkpoint blockade and NB-targeted CAR T cells. We expect the proposed work to address several critical preclinical gaps that, when filled, will accelerate STANs toward clinical translation. Therefore, this research addresses a problem of high clinical urgency by advancing a next-generation nanotechnology for enhancing immunotherapy responses in NB.