Flip the coin: IL-7 and IL-7R in health and disease

The cytokine IL-7 and its receptor, IL-7R, are critical for T cell and, in the mouse, B cell development, as well as differentiation and survival of naive T cells, and generation and maintenance of memory T cells. They are also required for innate lymphoid cell (ILC) development and maintenance, and consequently for generation of lymphoid structures and barrier defense. Here we discuss the central role of IL-7 and IL-7R in the lymphoid system and highlight the impact of their deregulation, placing a particular emphasis on their ‘dark side’ as promoters of cancer development. We also explore therapeutic implications and opportunities associated with either positive or negative modulation of the IL-7–IL-7R signaling axis. The cytokine IL-7 plays essential roles in lymphocyte development. In their Review, Barata, Durum and Seddon describe IL-7’s key homeostatic functions and how its dysregulation can lead to autoinflammatory disease and cancer.