CD8A and neoplasm: Specific pathogens such as Fusobacterium nucleatum can translocate to the pancreas, where its Fap2 protein not only binds to Gal-GalNAc on PC cells to enhance their proliferative and invasive capabilities but also directly engages the TIGIT receptor on tumor-infiltrating NK cells and CD8+ T cells, suppressing their cytotoxicity and thereby establishing an immune-exempt microenvironment [189, 203].