Abstract PO011: Systemic administration of Poly-ICLC promotes T cell tumor infiltration generating antitumor responses

Abstract

Background: Recent advances in immunotherapy have revolutionized cancer treatment. Immune checkpoint blockade and adoptive T cell therapy can induce durable responses in some patients. However, the majority of patients fail to respond. Absence of T cell infiltration to the tumor site in solid tumors is considered as one of the major obstacles for effective immunotherapy. Thus, strategies to enhance T cell trafficking and infiltration into the tumor parenchyma is a major research need. Methods: Using a combination of in vivo mouse tumor models and in vitro assays we compared the capacity of various formulations and routes of administration of poly-IC (a dsRNA mimic that functions as a pattern recognition receptor ligand) in enhancing T cell tumor infiltration and generating antitumor responses. Results: Our results showed that poly-ICLC (poly-IC containing poly-lysine and carboxymethylcellulose) enhanced CD8 T cell infiltration into the tumors resulting in the control of tumor growth. These effects relied both on the route of administration as well as on the formulation of poly-IC. Systemic administration (i.v. or i.m.) of poly-ICLC was significantly more effective in inducing CD8 T cell tumor infiltration as compared to intra-tumoral injections. Also, the effects poly-ICLC were substantially more pronounced as compared to unmodified poly-IC. The antitumor effect of poly-ICLC was mediated via MDA-5 and IFN-I, whereas TLR3 stimulation was not required. Interestingly, poly-ICLC stimulated IFN-I responses on tumor vascular endothelial cells (VECs) enhancing the expression of adhesion molecules (VCAM-I), production of IFN-I and T cell recruiting chemokines (CXCL9/CXCL10). Using conditional knockout mice, showed that ablation of IFNab receptors in VECs impaired the antitumor effects of poly-ICLC. IFN-I production upon MDA5 stimulation is required to enhance the secretion of (CXCL9/CXCL10) by VECs indicating that this IFN-I/CXCL9/CXCL10 regulatory axis is crucial for recruiting effector T cells into the tumor parenchyma. The T cell infiltrating effects of poly-ICLC were mainly observed in tumors and not in normal tissues. Conclusions: Systemic administration of poly-ICLC improves T cell infiltration to solid tumors in an MDA5/IFN-I dependent manner. These findings should have a strong impact on improving T cell-based treatments for solid cancers such as adoptive T cell therapy and antitumor vaccines. Citation Format: Hussein Sultan, Juan Wu, Valentyna Fesenkova, Aaron Fan, Diane Addis, Andres Salazar, Esteban Celis. Systemic administration of Poly-ICLC promotes T cell tumor infiltration generating antitumor responses [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO011.