PROJECT SUMMARY / ABSTRACT The primary objective of this proposal is to develop a localized cancer immunotherapy using particle-anchored cytokines with prolonged intratumoral retention to elicit durable anti-tumor immune responses. It is well known that immunostimulatory cytokines can elicit robust anti-tumor immune responses in preclinical studies but also exhibit severe immune-related adverse events due to systemic exposures. The current drug delivery methodology cannot sustainably supply cytokines for days to weeks, failing to fully address issues of toxicity and limited efficacy. We hypothesize that anchoring cytokines to large-sized particles for intratumoral injection would enhance the local retention of cytokines (e.g., IL-12 and IL-15) to drive tumor inhibition while avoiding the systemic exposures of such cytokines that cause adverse effects. To test this hypothesis, we develop a novel local delivery system that physically anchors the Fc-cytokine to particles having surface-decorated Fc-binding peptides. Our preliminary studies show that the intratumoral administration of our new particle-anchored cytokine significantly increases tumor retention of cytokines and markedly reduces systemic toxicity. Moreover, local treatments of our micron-meter-sized particle-anchored cytokines promote cures in poorly immunogenic tumor models, and elicit anti-tumor immunities with controls over distant untreated lesions. Overall, two specific aims will be pursued in this proposal, including: (i) to develop liposome-anchored cytokines with prolonged tumor retention over one week and minimal systemic leakage of free cytokines; and (ii) to elucidate the mechanisms by which particle-anchored cytokines elicit durable anti-tumor immunity to improve efficacies in poorly immunogenic tumors. Our simple formulation technology would fully address the dose-limiting toxicity problem in the use of cytokines in cancer immunotherapy, and provide a new and effective treatment option for difficult- to-treat solid tumors when combined with other immunotherapeutics. This work will also advance the research on drug delivery technology by elucidating crucial physicochemical characteristics to circumvent systemic leakage for local drug delivery. This work will also significantly advance our understanding of how localized immunostimulatory cytokines impact tumor microenvironments, leading to enhanced systemic anti-tumor immunity and better treatment outcomes.