Hiding in Plain Sight: Virtually Unrecognizable Memory Phenotype CD8 T cells.

Virtual memory T (T) cells are a recently described population of conventional CD8 T cells that, in spite of their antigen inexperience, express markers of T cell activation. T cells exhibit rapid responsiveness to both antigen-specific and innate stimuli in youth but acquire intrinsic antigen-specific response defects in the elderly. In this article, we review how the identification of T cells necessitates a re-evaluation of accepted paradigms for conventional memory T (T) cells, the potential for heterogeneity within the T population, and the defining characteristics of T cells. Further, we highlight recent literature documenting the development of T cells as a distinct CD8 T cell lineage as well their biological significance in the context of disease.