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Stereotactic body radiation therapy (SBRT) allows the administration of ablative doses and is used for the management of a proportion of non-small cell lung cancer (NSCLC) patients. SBRT allows high fractional doses (≥ 8 Gy), which may result in a fundamentally different biological effect from conventional radiotherapy (RT). The effects of SBRT are mediated by cytotoxic, inflammatory and immunomodulatory mechanisms. The latter are of particular interest and their understanding is the key to potentiating the local effect and synergy with immunotherapies. Several studies have shown the involvement of the immune system in the antitumor efficacy of RT, but these studies were mainly conducted in subcutaneous murine tumor models using conventional doses of RT. In contrast, the effects of ablative irradiation (IR) doses on the infiltration and activity of immune cells are poorly understood, especially in orthotopic models.Here we used a murine orthotopic model of NSCLC to evaluate the effects of high doses of RT, delivered using a small animal radiation platform (SARRP) that allows stereotactic IR with a millimetric precision. Mice were subjected to a trans-pleural injection with Lewis lung carcinoma cells expressing luciferase (LLC-Luc) and irradiated at doses ranging from 8Gy to 60Gy in 1-3 fractions. Our results show that orthotopic LLC tumors, which correctly develop as single tumor mass within the lung parenchyma, are resistant to SBRT, with no complete tumor regression observed even after 60Gy IR. The characterization of the tumor environment by at the clinically relevant dose of 20Gy showed transient (by day 3 post-IR) increased CD8+ T cells and inflammatory monocytes within the tumor bed but not in the juxtatumor tissue. Resident alveolar macrophages where mostly detected in the juxtatumor tissue and were depleted by RT. Although RT did not affect interstitial tumor-associated macrophages (TAM) number, we observed that the fraction of CD206+ TAM was decreased together with an increased proportion of MHC class II+ TAM. At later time points, Treg harboring increased CD69 accumulated in the tumor bed and TAM recovered a similar phenotype compared to non-irradiated mice. The analysis of the tumor cytokinome revealed the modulation of several cytokines and chemokines including CCL-5, CXCL-10, LIF (Leukemia Inhibitory Factor) and Eotaxin. Altogether, these results argue that high IR doses induce transient and localized activation of the tumor immune environment that is rapidly dampened by anti-inflammatory cell recovery, such as Tregs and CD206 TAMs. The ongoing analyses using a single-cell RNAseq approach on sorted CD45+ cells will allow a precise evaluation of the composition and phenotype of the tumor immune populations.The results of this project will guide the design of therapeutic combinations with immunomodulatory agents to optimize the tumor response to SBRT. Citation Format: Céline Clémenson, Morgane Dos Santos, Maxime Petit, Jeremy Lavigne, Winchygn Liu, Marina Milic, Georges Tarlet, Agnès François, Alexandre Boissonnas, Fabien Milliat, Michele Mondini, Eric Deutsch. Modulation of the immune environment in a preclinical orthotopic model of non-small cell lung cancer exposed to ablative doses of radiation [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 1307. |
