Abstract P030: Making cold tumors hot: Multi-faceted immune ignition by USP6
Authors: Henrich Ian C. , Jain Kanika , Quick Laura , Young Robert , Chou Margaret M. 
Published: January 2022

Abstract
Ewing sarcoma (ES) is the second most common bone cancer, affecting predominantly children and young adults. While patients with localized disease have a five-year survival rate of ~75%, this plummets to 20% for metastatic and recurrent patients. Immunotherapy has had limited success in ES, in large part because it is considered immunologically cold, with few tumor-infiltrating T lymphocytes (TILs). However, TILs actually vary significantly, and high levels portend greatly improved survival. In ES, TIL abundance correlates with the interferon (IFN)g-inducible chemokines CXCL9/CXCL10/CCL5. These immune features (i.e. IFNg response, CXCL9/10 production, and high CD8+ TIL recruitment) define a hot TME, and predict both improved overall survival and response to immune checkpoint inhibitors (ICIs) across many malignancies. However, the tumor-intrinsic factors that confer this favorable immune phenotype, in ES or any other cancer, are largely unknown, and their identification represents a window of opportunity for therapeutic intervention to improve patient outcomes.
We have discovered that high USP6 expression in ES patients is associated with dramatically improved overall survival. Our work has revealed that USP6 has potent and multi-faceted immunostimulatory properties: not only is it capable of triggering all hallmark features of a hot TME, but its expression in ES cells directly activates the cytolytic function of NK cells, and also induces secretion of a complex array of immune-activating, anti-tumorigenic chemokines that affect both innate and adaptive immune lineages. In vivo, USP6 inhibits growth of human ES cell xenografts in nude mice, and enhances intratumoral infiltration/activation of natural killer (NK) cells and myeloid lineages. We hypothesize that USP6 improves ES patient outcome due to these pleiotropic immunostimulatory functions, which engender a hot TME with resultant activation of multiple cytolytic immune lineages that effect tumor cell elimination.
We have sought to harness the multi-faceted immune-igniting properties of USP6 into a novel immunotherapeutic by delivering USP6 mRNA using lipid nanoparticles (LNPs) customized for in vivo delivery into ES cells. Preliminary data validate the efficacy of intratumorally administered USP6 LNPs in stimulating immune cell recruitment and activation, and suppressing xenograft growth, with a fraction of tumors undergoing complete regression. Furthermore, we have observed that intratumoral expression of USP6 can trigger systemic activation of the immune system, including increased levels and activation NK cells. Notably, increased circulating levels of NK cells have been associated with improved patient prognosis.
Despite the success of CAR-T cells and ICIs, there are significant hurdles limiting their efficacy, and it is essential to pursue therapeutics that engender an immunologically hospitable TME, as well as activate other cytolytic immune lineages, such as NK cells, both of which are encompassed by USP6 LNP therapy.
Citation Format: Ian C. Henrich, Kanika Jain, Laura Quick, Robert Young, Margaret M. Chou. Making cold tumors hot: Multi-faceted immune ignition by USP6 [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P030.