Recalling the year in memory T cells.

The memory immune response forms the basis for protective immunity and is orchestrated by long-lived memory T lymphocytes. Memory T cells mediate potent and rapid effector function upon secondary challenge, and migrate to diverse peripheral sites, resulting in efficacious clearance of pathogens before the onset of disease. However, these robust memory T cell functions and diverse homing capacities can also lead to immunopathology in viral infections, autoimmunity, and transplantation. Elucidating mechanisms controlling memory T cell generation and recall responses therefore has broad clinical and immunological relevance. In this review, we highlight advances in the past year on dissecting the processes of memory generation, recall capacity, and regulation of memory T cell responses. We discuss the past year's studies focused on identifying pathways and precursors for memory development at both the priming and effector stage, and how the earliest events in T cell activation may have far-ranging influences on the resultant memory T cell population. We also describe results on the biochemical and molecular control of the distinct and immediate effector functions of memory T cells and their implications for immunotherapies. Finally, we present recent technological advances in T cell tracking and imagery and how they may be applied to provide new insight into the complex nature of the memory immune response.