Tissue resident memory T cells and viral immunity

Tissue resident memory T cells (T_RM) constitute a recently identified T cell lineage that is responsible for frontline defense against viral infections. In contrast to central and effector memory T cells, which constitutively recirculate between tissues and blood, T_RM reside permanently within tissues. As the main surveyors of non-lymphoid tissues, T_RM are positioned to rapidly respond upon reinfection at barrier sites. During a viral reinfection, T_RM trigger the local tissue environment to activate and recruit immune cells and establish an antiviral state. Consistent with this function, there is empirical evidence that T_RM accelerate control in the event of reinfection or possible reactivation of latent infections in solid organs and barrier tissues. Here we review recent literature highlighting the protective functions of T_RM in multiple viral challenge models and contextualize the implications of these findings for vaccine development.