Epidemiological studies in humans and experiments in mouse models have shown that gut microbiota regulate cancer onset, progression and therapy response but the precise mechanisms remain unknown. Recent breakthrough research from my lab discovered that bacterial extracellular vesicles (BEV), membrane-enclosed communicative particles containing proteins, nucleotides, lipids and metabolites, are present in the systemic circulation of cancer patients. We hypothesize that systemic BEV shape the cancer patient’s immune activity. The aim of this project is to fully identify and functionally characterize systemic BEV ecosystems with high clinical relevance to cancer, with reliable and robust methods, and to explore their use as biomarker tools for the optimization and personalization of cancer therapy. Therefore we will investigate and associate the immune composition in pre-treatment biopsy and post-treatment tumor resection specimens with the presence, composition and taxonomic classification of BEV in serial blood plasma and fecal samples of newly diagnosed triple negative breast cancer patients receiving neo-adjuvant chemotherapy. This project will provide the fundamental basis to increase our understanding of the complex interplay between the microbiota, the tumor and our immune system and to develop future larger scale BEV biomarker studies.