Local immunity by tissue-resident CD8+ memory T cells

Microbial infection primes a CD8(+) cytotoxic T cell response that gives rise to a long-lived population of circulating memory cells able to provide protection against systemic reinfection. Despite this, effective CD8(+) T cell surveillance of barrier tissues such as skin and mucosa typically wanes with time, resulting in limited T cell-mediated protection in these peripheral tissues. However, recent evidence suggests that a specialized subset of CD103(+) memory T cells can permanently lodge and persist in peripheral tissues, and that these cells can compensate for the loss of peripheral immune surveillance by circulating memory T cells. Here, we review evolving concepts regarding the generation and long-term persistence of these tissue-resident memory T cells (T-RM) in epithelial and neuronal tissues. We further discuss the role of T-RM cells in local infection control and their contribution to localized immune phenomena, in both mice and humans.