The abundance of class-switched IgA antibodies with high affinities for microbial species in the gut microenvironment provides clear evidence for APC-dependent, humoral responses elicited and matured in gut-associated lymphoid tissue and/or regional lymph nodes.100,101 Such microbial-antigen-containing APCs can also cross-present their phagocytosed cargo via MHC class I to induce cellular immune responses.102,103 Furthermore, intracellular microbes present in both cancer and immune cells87 can trigger direct CD8+ T cell responses in the tumour microenvironment (TME). The gene discussed is CD8A; the disease is neoplasm.