Mucosal-associated invariant T (MAIT) cells are evolutionary conserved innate-like T cells comprising up to 10% of circulating T cells. MAIT cells express a semi-invariant and MR1 restricted TCR that recognizes antigens derived from microbial vitamin B synthesis. MAIT cells are enriched in mucosal tissues within the body and can rapidly produce Th1 and/or Th17 cytokine responses. Their role barrier function is not defined, however their response to microbes suggests a potential role in mucosal immune homeostasis. The lung and bowel are the largest mucosal organs and cancers of these organs have high mortality rates in Australia. These mucosal cancers and pre-cancerous lesions involve a breach of mucosal barriers that allows entry of microbiota. We have found that patients with bowel or lung cancer have a decrease in peripheral blood MAIT cell frequency, but the importance of MAIT cells to the cancer microenvironment is unknown. To investigate this, we have characterised the location and function of MAIT cells within human bowel and lung tissue and evaluated MAIT cell differences between non-cancerous and cancerous tissues. We hypothesise that MAIT cells are contributing to the evolution and progression of lung and bowel cancers as a result of their response to microbiota.