ESTRO 2020 Abstract book

S39 ESTRO 2020

heterotypic nature of CAFs in true in vivo circumstances, and the existence of CAF subsets possibly exerting opposing effects in the context of radiotherapy and immunotherapy needs to be carefully considered for optimized treatment strategies. OC-0082 TNFα-mediated crosstalk between regulatory T cells and monocytes limits radiotherapy efficacy M. Mondini 1 , P. Hamon 1 , P. Loyher 2 , M. Gerbé de Thoré 1 , C. Clemenson 1 , M. Laviron 2 , K. Berthelot 1 , B.L. Salomon 2 , C. Combadière 2 , A. Boissonnas 2 , E. Deutsch 3 1 Gustave Roussy, Inserm U1030, Villejuif, France ; 2 Sorbonné Université - Inserm, CIMI Paris, Paris, France ; 3 Gustave Roussy, Inserm U1030 and Departement of Radiotherapy, Villejuif, France Purpose or Objective Beyond the expected direct effects of radiation therapy (RT ) on tumor cells, several evidence support the importance of an immune response to radiotherapy. These observations foster the use of combination of immunomodulators with RT to enhance its therapeutic index. Several efforts have been put to investigate the induction of an antitumor-immunity by RT. Nevertheless, RT can also induce or amplify tumor immunosuppressive mechanisms. The balance between RT-mediated immunogenic and immunosuppressive activities deserves more attention. Infiltration of monocytes/macrophages and regulatory T cells (Tregs) into the tumor is a known factor limiting the antitumor immune response. Among the many cytokines secreted by tumor cells, CCL2 is involved in monocyte recruitment from bone marrow to the inflammatory site, as well as a subset of Tregs. We thus speculated that the CCL2/CCR2 axis might be implicated in the co-recruitment of TAMs and Tregs following RT, favoring immunosuppression. Material and Methods We used orthotopic models of oral and lung cancer in immunocompetent mice to evaluate the effects of irradiation on monocytes and Tregs recruitments to tumors. Flow cytometry and histological analysis were performed. Cytokine profiling and ELISA analyses were performed on tumor tissues and blood samples. Transgenic mice bearing fluorescent reporters allowed us to identify target cells by confocal and intravital biphoton microscopy. Mice knockout (KO) for CCL2 or CCR2 were used to investigate the respective role of the chemokine pathway in the response to radiotherapy, as well as mice selectively depleted of Tregs (Foxp3-DTR mice) to analyze their contribution to the resistance to RT. Results Radiotherapy strongly upregulated CCL2 chemokine production in tumor cells. This resulted in an accumulation of monocytes and of a subset of CCR2-positive Tregs in the tumor bed of voth oral and lung tumors, and a dynamic physical interaction between these cells was identified. CCR2-KO mice and mice conditionally depleted of Tregs had an improved response to radiotherapy. Recruited monocytes produced TNFα, which contributed to the activation of Tregs. In agreement with this observation, anti-TNFα treatment increased the efficacy of RT. Conclusion We propose that reducing radiation-induced monocyte and Trges recruitment may yield improved results in the treatment of head and neck and lung carcinomas by radiotherapy. We thus indicate CCL2/CCR2 and TNFα as potential clinical candidates to counteract the radioprotective action of monocyte-derived cells and Tregs, paving the way for effective combined immunoradiotherapies. As modulators of CCL2, CCR2 and TNFα are already being tested in clinical settings, the results from this study can be transferred into the clinic. Immunologically-augmented radiotherapy could also allow the reduction of the delivered radiation dose, thus minimizing the risk of treatment sequelae while maintaining optimal tumor control.

concurrent but brief wave of radiation-induced regulatory T cells. These early and late phase effects of RT on NK cell responses could be leveraged with checkpoint blockade therapy to achieve prolonged tumor control and, in some instances, complete regression. Conclusion NK cells may play a critical role in supporting the therapeutic capacity of RT and immunotherapy combinations, particularly in the context of high BED RT. Understanding the regulation and kinetics of radiation- induced NK cell responses reveals opportunities for optimising RT and immunotherapy strategies. OC-0081 Immuno-regulatory properties of irradiated tumor fibroblasts T. Hellevik 1 , R. Berzaghi 2 , A. Islam 2 , L. Gorchs 2 , I. Pettersen 2 , T. Stuge 3 , M.A. Akhtar 2 , I. Martinez- Zubiaurre 2 1 University Hospital of Northern Norway, Departmetn of Radiation Oncology, Tromsø, Norway ; 2 University of Tromsø, Clinical Medicine, Tromsø, Norway ; 3 University of Tromsø, Medical Biology, Tromsø, Norway Purpose or Objective Cancer-associated fibroblasts are key modulators of the tumor microenvironment, facilitating tumor initiation, tumor growth, invasion and metastasis, in addition to function as sentinel cells of the immune system. Nevertheless, the impact of the abundant and heterogeneous CAF-community towards treatment resistance is only starting to emerge. With the ultimate goal of enhancing therapeutic outcome, our laboratory is exploring how CAFs are influencing responses to radiotherapy and immunomodulation. Material and Methods Experiments were carried out with human CAFs freshly isolated from (NSCLC) lung tumor specimens. Primary CAF cultures were exposed to ionizing radiation delivered as single-high or fractionated medium-high doses. The secretory profiles of irradiated and control CAFs were compared by multiplex protein arrays and high-throughput proteomics. Immuno-regulatory properties of irradiated CAFs (iCAFs) were explored in functional in vitro assays, where different types of immune cells, such as macrophages, dendritic cells, natural killer cells or T- lymphocytes, were individually co-cultured with iCAFs or exposed to iCAF-conditioned medium or iCAF-derived exosomes. Radiation-induced events that could potentially interfere with anti-tumor immunity, including immunogenic cell death (ICD) and type-I interferon expression (IFN-I), was also explored in iCAFs. At the in vivo level, tumor development and inflammatory responses were studied upon transplantation of tumor cells admixed with irradiated or control CAFs. Results Cultured CAFs display a noticeable radio-resistant phenotype. However, exposure to high radiation doses provoke induction of cellular senescence and important phenotypic changes including persistent DDR-responses, elevated surface levels of integrins and significant changes in the secretory profile. Importantly, radiation exposure does not elicit ICD or IFN-I release in iCAFs. CAF-derived soluble factors, but not exosomes, show powerful immunosuppressive effects over activated lymphocytes, macrophages and dendritic cells, however, most of the observed effects seem to be unchanged upon radiation exposure. In vivo studies in xenografts propose that the net effect of IR on CAFs is advantageous, since the natural pro-tumorigenic effects of CAFs become abrogated. Conclusion Irradiated CAFs change substantially their phenotype upon exposure to single-high radiation doses, which could impact tumor responses to therapy. Of note, most of the studied CAF-mediated immunomodulatory functions are maintained following irradiation. However, the