It is therefore possible that reduced Trm priming is a general mechanism underlying the hygiene hypothesis in immune-mediated disease, and associations of microbiota with tumour development and cancer therapy.50,51 Memory CD8 T cells migrate to multiple tissues and escape homeostatic control mechanisms that limit their numbers in the circulation,52 so numbers of Trm can accumulate throughout life in response to immunological experiences. This evidence concerns the gene CD8A and neoplasm.