Abstract 3446: Radiation and intratumoral activation of double-stranded RNA sensors redirects myeloid cells and primes adaptive immunity
Authors: Deng Jie , Chin Scott C. , Tariveranmoshabad Mito , Graham Danielle S. , Lee Hailey R. , Quintero Marisol , Schaue Dorthe , Kalbasi Anusha 
Published: June 2022

Abstract
Background: Undifferentiated pleomorphic sarcoma (UPS) is a common aggressive sarcoma subtype for which existing therapies are ineffective. Immune checkpoint blockade (ICB) is effective in a minority of patients whose tumors harbor a pre-existing lymphocytic response. However, most UPS tumors have a myeloid infiltrate, a highly plastic cellular population with the potential to serve as a substrate for immunotherapy. Radiotherapy (RT), a standard therapy for UPS, can also drive myeloid cells into the tumor. Based on abundant expression of pattern recognition receptors (PRRs) by myeloid cells, we hypothesized that intratumoral injection of a PRR agonist would leverage pre-existing and RT-associated myeloid cells by redirecting them to prime adaptive anti-tumor immunity.
Methods: We used BO-112, a nanoplexed double-stranded ribonucleic acid that activates PRRs, most of which are not typically activated by RT. We used an ICB-resistant mouse model, in which tumor cells derived from a KrasG12D/-P53-/- model of UPS are used to establish large tumors in flanks of C57BL/6J mice. Tumor-bearing mice were treated with RT (8 Gy x 3 fractions daily) starting on day 8 ± BO-112 (30 ug/dose) on days 8 and 10. Tumor growth and survival between groups were compared by ANOVA and log-rank test, respectively. To test the role of lymphocytes, the study was repeated in RAG-/-gc-/- mice. Kinetic analysis of myeloid and T cells was performed in the tumors and lymph nodes (LN) on days 15, 21, 26 using high-dimensional flow cytometry. To evaluate the fate of monocytes, LysM-eGFP monocytes were intratumorally transferred following treatment, with subsequent analysis of tumors and LNs on days 16, 18, 21.
Results: Tumor control was significantly improved in the combination group starting from day 16 with mean tumor volume of 240 mm3 in the combination group compared to 490 mm3 in BO112, 790 mm3 in RT, and 875mm3 in mock groups (p&lt;0.0001) which translated into a maximal survival advantage in the combination group (p&lt;0.005). However, in RAG-/-gc-/- mice, this benefit of combination therapy was completely negated. This therapeutic combination appeared to drive an early reduction in Ly6ChiMHCII+ cells (p&lt;0.05) within the tumor followed by a progressive increase of the same population in the draining LN over time (p=0.01). In parallel, we observed trafficking of adoptively transferred intratumoral eGFP+ monocytes from the tumor to dLNs in response to BO-112 and RT.
Conclusions: Local-only therapy of BO-112 and RT yields a lymphocyte-dependent anti-tumor immune response in an immunotherapy-resistant model of UPS. Longitudinal analysis of locoregional immune responses and adoptive transfer experiments indicate that combination BO-112 and RT induces tumor-to-dLN myeloid trafficking that may bridge an adaptive response and confer therapeutic effect.
Citation Format: Jie Deng, Scott C. Chin, Mito Tariveranmoshabad, Danielle S. Graham, Hailey R. Lee, Marisol Quintero, Dorthe Schaue, Anusha Kalbasi. Radiation and intratumoral activation of double-stranded RNA sensors redirects myeloid cells and primes adaptive immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3446.