Intratumoral Localization of Pattern Recognition Receptor Signaling Informs CAR T Cell Design

Abstract

Abstract Immune therapies have significantly improved outcomes for cancer patients with poor prognosis, but mechanisms that underlie response or resistance to therapy remain elusive. Type I and Type II interferon signaling is required for immune activation but is also known to drive programs of tumor-intrinsic resistance. We propose that activation of pattern recognition receptor (PRR) signaling in specific cellular compartments underlies this seemingly contradictory observation. We have recently identified the highly structured RNA RN7SL1 (7SL) as a novel intratumoral PAMP (pathogen associated molecular pattern) capable of activating PRR signaling. When over-expressed in tumor cells, the resulting tumors are resistant to immune checkpoint blockade (ICB) therapy. However, 7SL is stimulatory to primary human DCs, and improves T cell priming in vitro. Furthermore, direct intratumoral injection of 7SL improves immune activation and response to ICB in vivo. Thus, we propose the localization of PAMP recognition and PRR signaling may represent an important determinant of response to ICB therapy. Based on this finding, we have developed a CAR T cell capable of producing 7SL in the tumor microenvironment, as well as a fully syngeneic B16 solid tumor model for CAR T cell therapy. Murine 7SL-CAR T cells control tumors more robustly than controls and synergize with ICB. Importantly, this effect is dependent on endogenous T cells, indicating that 7SL-CAR T cells are jump-starting an endogenous polyclonal anti-tumor immune response. In total, this represents a novel insight into the role of PRR signaling in tumors and leverages the findings to create a therapy with potential to serve patients that are currently refractory to CAR-T or ICB therapies alone.