Abstract A18: Personalized RNA nanoparticles remodel the HNSCC immunologic milieu to unlock immunotherapeutic activity

Introduction: Immunotherapy is promising for patients with treatment-refractory head and neck squamous cell carcinoma (HNSCC). However, greater than 80% do not respond to checkpoint inhibitors, suggesting that the highly immunosuppressive immune microenvironment of HNSCC mediates therapeutic resistance. Our group has developed a novel treatment platform utilizing clinically translatable RNA-nanoparticles (NPs) to remodel the systemic and intratumoral HNSCC immune microenvironment to enable potent immunotherapeutic activity. Objective: The purpose of this study is to examine the immunologic effects and antitumor efficacy of tumor-derived RNA-NPs in murine models of oral cavity squamous cell carcinoma (OCSCC). Materials and Methods: Tumor-derived RNA-NPs were prepared by complexing in vitro transcribed mRNA from MOC1 cells (syngeneic murine oral cavity squamous cell carcinoma cell line) with nanoliposomes. These complexes were injected into MOC1 tumor-bearing C57BL/6 mice. Immunogenicity was determined from spleens and tumors by multiparameter flow cytometry and qPCR analysis. Efficacy was assessed based on subcutaneous tumor volume measurements. Results: Personalized tumor RNA-NPs mediated significant increases in systemic and tumor-infiltrating lymphocytes (TILs). Compared to control animals, RNA-NPs increased peripheral CD8+ T cells (p=0.0007) and decreased regulatory immune cells [CD4+CD25+FoxP3+ (Tregs)] (p=0.0043). WIthin the tumor microenvironment, RNA-NPs increased intratumoral CD3+CD8+ T cells (p =0.0278) and CD3+CD4+ T cells (p=0.0307). qPCR on MOC1 tumors revealed elevated expression of the effector cytokine interferon-γ (NP alone vs. RNA-NP; fold change 1.309 vs. 90.13) and reduced gene expression of arginase-1 (NP alone vs. RNA-NP; fold change 1.29 vs. 0.005), suggesting that RNA-NPs can attenuate the immunosuppressive microenvironment. Compared to control animals or mice receiving PD-L1 monotherapy, RNA-NPs mediated significantly greater antitumor efficacy based on subcutaneous tumor volume measurements (p Conclusion: RNA-NPs reprogram the peripheral and intratumoral HNSCC immune microenvironments and unlock antitumor activity in preclinical models. We have successfully generated tumor-derived RNA-NPs as a renewable resource that can be made readily available for HNSCC patients from a small tissue sample. FDA-IND enabling studies are currently under way in preparation for first-in-human trials. Citation Format: Natalie L. Silver, Rekha R. Garg, Hector R. Mendez-Gomez, Kristianna Fredenberg, Spencer Barnes, Frances L. Weidert, Peter Dziegielewski, Sayour J. Elias, Duane A. Mitchell. Personalized RNA nanoparticles remodel the HNSCC immunologic milieu to unlock immunotherapeutic activity [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr A18.