Division of labor with a workforce of one: challenges in specifying effector and memory T cell fate

In the course of the immune response against microbes, na?ve T cells proliferate and generate varied classes of effector cells, as well as memory cells with distinct properties and functions. Owing to recent technological advances, some of the most imposing questions regarding effector and memory T cell differentiation are now becoming experimentally soluble: How many classes of antigen-specific T cells exist, and how malleable are they in their fate and in their functional state? How might a spectrum of cell fates be imparted to the clonal descendants of a single lymphocyte? Where, when, and how does pathogen-associated information refine the instruction, selection, and direction of newly activated T cells as they perform their tasks in different locations and times? Some surprising new glimpses ahead on these subjects and other yet-unanswered questions are discussed.