Abstract LB-071: Cross talk between T lymphocytes and macrophages promotes progression of radiation induced lung fibrosis

Background: Fractionated radiotherapy (RT) is integral part of standard treatment for locally advanced lung cancer. However radiation-induced lung disease limits the application of curative radiation doses and therapy intensification efforts of concurrent chemoradiotherapy, leading to fatal outcomes by local recurrence or metastatic disease even when accepting side effects that decrease the quality of life. So far, no predictive biomarkers exist and no mechanism-based therapies are in clinical use that prevent or treat dose-limiting pneumonitis and lung fibrosis. Own previous work revealed a pathogenic role of the immunomodulatory CD73/adenosine system and of macrophages in radiation-induced pulmonary fibrosis1,2. Moreover, clinical observations associated CD4+ T lymphocytes with adverse effects of RT in the skin and the lung of cancer patients3,4. However, the contribution of RT-induced immune changes to RT-induced lung disease require further definition. Here, we studied the functional role of lymphocytes in radiation-induced lung fibrosis, with a focus on CD4+ T cells. Methods: C57BL/6 wildtype (WT) and RAG-2 knockout (RAG-2-/-) mice received a single dose of whole thorax irradiation with 0 Gy (sham controls) or 15 Gy without or with additional adoptive transfer of CD4+ T cells. We characterized time-dependent immuno-modulation and pathogenesis of lung tissue in flow cytometry, histological and immunohistochemical as well as RNA analyses in comparison to our earlier analyses in or CD73 knockout (CD73-/-) mice. Results: CD4+ T lymphocytes, particulary Treg, accumulated in irradiated lungs of WT mice during the chronic fibrotic phase. While deficiency of B and T cells in RAG2-/- mice led to an earlier onset of fibrosis compared to WT mice, adoptive transfer of CD4+ T cells into RAG2-/- mice led to further aggravation of pulmonary fibrosis. Analysis of immune cell subtypes in adoptively transferred RAG2-/- mice revealed that CD4+ T cells were enhanced, and this was associated with a phenotypic switch in the macrophage population towards M2-like phenotypes that was not observed in CD73-/- mice. Conclusions: We conclude that a reciprocal crosstalk between CD4+ T lymphocytes and macrophages in the irradiated lung environment promotes disease progression, amongst others by regulating macrophage polarization in a microenvironment-dependent manner. 1) Wirsdorfer et al., Cancer Res 2016;76:3045-56. 2) de Leve S et al., FASEB J 2017, 31;2869-2880; Veldwijk MR et al. Clin Cancer Res., 2019, 25:562-572; Nakayama Y et al., Int J Radiat Oncol Biol Phys 1996, 34:459-467. This work was supported by grants of the University Hospital Essen (IFORES) to FW and the DFG (JE275/4-1; GRK1739/2) to VJ. Citation Format: Florian Wirsdorfer, Lena Gockeln, Simone de Leve, Martin Stuschke, Verena Jendrossek. Cross talk between T lymphocytes and macrophages promotes progression of radiation induced lung fibrosis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-071.