SO-23 The influence of the microbiome on the tumour-immune microenvironment in colorectal cancer

The immune microenvironment in colorectal cancer (CRC) has a huge impact on progression. Among the consensus molecular subtypes (CMS) of CRC, CMS1 and CMS4 are both characterized with infiltrates, yet is considered to have good prognosis while opposite. Although CRC subtyping been useful way characterizing manifestations this heterogenous disease, contributions microbiome seldom discussed. We aimed determine paradoxical effects we see immune-infiltrated subtypes, CMS4. carried out RNA-sequencing 260 tumour samples, subtyped samples into respective CMS, obtained human gene expression microbial abundance profiles. then identified enriched sets corresponding relatively abundant microbes subtypes. Based relationships between bacteria, lipopolysaccharide (LPS) from particular bacterial species as potential modifiers tumour-immune microenvironment. Using peripheral blood mononuclear cells (PBMCs) an vitro model, sought investigate different LPS molecules secreted cytokine expression. In addition previously described characteristics tumours, “lipopolysaccharide binding” was set, suggesting relationship LPS. Fusobacterium Bacteroides spp. Porphyromomas bacteria that may affect activation Treatment PBMCs these showed opposing immunomodulatory secretion. Different not only increase activity but also immunosuppressive effect. balance tumour-resident influence important implications for