%0 Generic
%A Bender, Noemi
%D 2016
%F heidok:22419
%R 10.11588/heidok.00022419
%T Molecular Mechanisms of Macrophage Activation Induced by the Synergistic Effects of Low Dose Irradiation and Adoptive T Cell Therapy
%U https://archiv.ub.uni-heidelberg.de/volltextserver/22419/
%X The detection of cancerous cells by the immune system elicits spontaneous antitumour im-mune responses. Still, during their progression, tumours acquire characteristics that enable them to escape immune surveillance. Cancer immunotherapy aims to reverse tumour im-mune evasion by activating and directing the immune system against transformed tumour cells. However, the tumours’ intrinsic resistance mechanisms limit the success of many im-munotherapeutic approaches. The functionally and morphologically abnormal tumour vascu-lature forms a physical barrier and prevents the entry of tumour-reactive immune effector cells, while the immunosuppressive tumour microenvironment impairs their function. To block tumour immune evasion, therapeutic strategies are being developed that combine cancer immunotherapy with treatment modalities, such as radiotherapy, that reprogram the tumour microenvironment to increase treatment efficacies and improve clinical outcome. In various preclinical models radiotherapy was shown to enhance the efficacy of adoptive T cell therapy. Our group showed that in the RIP1-TAg5 mouse model of spontaneous insulinoma, the transfer of in vitro-activated tumour-specific T cells induces T cell infiltration and pro-motes long-term survival only in combination with neoadjuvant local low dose irradiation (LDI). These treatment effects were mediated by iNOS+ macrophages.  In this thesis, we investigated the mechanisms underlying the improved T cell infiltration and prolonged survival upon combination therapy with adoptive T cell transfer and local LDI. We demonstrate that combination therapy leads to a normalization of the aberrant tumour vas-culature and endothelial activation, an increase in intratumoural macrophages, a reduction of intratumoural myeloid derived suppressor cells and, most importantly, to tumour regres-sion. These findings suggest that this treatment inhibits tumour immune suppression but also facilitates immune effector cell infiltration through the normalization of the tumour vasculature, finally leading to tumour immune rejection. Inhibition of the inducible nitric oxide (NO) synthase (iNOS) revealed that these effects largely depend on its activity. Of note, the stimulation of human endothelial cells with low doses of the NO donor DETA NONOate activates the endothelial cells to upregulate adhesion molecules, indicating that in response to the combination therapy, iNOS-derived NO directly activates tumour endothelial cells, thereby promoting T cell infiltration and tumour immune rejection.  Moreover, adoptive transfer of low dose irradiated peritoneal macrophages into unirradiat-ed RIP1-TAg5 mice prior to adoptive T cell transfer resulted in effects corresponding to the combination treatment, which highlights the role of macrophages in this mechanism. Whole transcriptome analysis of the irradiated peritoneal macrophages revealed that LDI causes gene expression and functional changes in these cells. Specifically, LDI activated interferon signalling and induced the upregulation of interferon regulated genes. This effect is likely due to the detection of danger signals released from damaged cells, which primes macro-phages and induces a shift in their polarization state. Signal transduction and amplification of interferon responses is mediated by interferon regulatory factors like IRF7. These transcription factors induce the expression of proinflammatory genes such as Nos2. Irf7 but also Nos2 and various proinflammatory genes like tumour necrosis factor (Tnf) were upregulated in response to LDI. Since NO and TNF-α are mediators of endothelial activation, this finding represents the link between LDI and macrophage-mediated activation of the tumour endothelium.  In conclusion, the presented thesis demonstrates that macrophages with proinflammatory phenotypes are required for the activation of tumour endothelial cells, which in turn is criti-cal for the infiltration of immune effector cells and, thereby, for tumour immune destruction. Therefore these findings are of great importance for future immunotherapeutic approaches in the treatment of cancer patients.