PO-380 Regulatory T cells encounter pro-inflammatory immune cells in human colorectal cancer

Introduction The normal colon is facing a load of microbes, which requires a constant immunosuppression to avoid exaggerated immune responses. The immunological state within colorectal cancer (CRC) is currently not fully disclosed. Thus, we aimed at the characterisation of immune cells within normal colorectal mucosa and cancer tissue of the same surgical specimen in order to unveil alterations, and to understand the immune cell status within the tumour microenvironment. Material and methods Immune cells were analysed with immunohistochemistry to reveal their local distribution and quantity within the tissue. Furthermore, multiparameter characterisation and IFNγ production of tissue derived immune cells was assessed with flow cytometry. In situ hybridization was performed to uncover the mRNA expression of lymphocytes within the tissue. Results and discussions Our results show a shift within the lymphocyte subpopulations towards less CD8 +cytotoxic T cells and more suppressive regulatory T cells within the tumour compared to distant mucosa. Despite that, tumour lymphocytes had a higher IFNγ production capability in vitro and in situ. In accordance to that, PD-L1 levels were diminished in comparison to distant mucosa. Additionally, macrophages were decreased within the tumour and they acquired a pro-inflammatory phenotype. Conclusion : Although cytotoxic T cells and macrophages were reduced, and regulatory T cells decreased, several immunological features indicate that the microenvironment in CRC is in a pro-inflammatory state.