%0 Journal Article %T Continuous activity of Foxo1 is required to prevent anergy and maintain the memory state of CD8+ T cells %J JEM | The Journal of Experimental Medicine %D 2018 %R 10.1084/jem.20170697 %X Upon infection with an intracellular pathogen, cytotoxic CD8+ T cells develop diverse differentiation states characterized by function, localization, longevity, and the capacity for self-renewal. The program of differentiation is determined, in part, by FOXO1, a transcription factor known to integrate extrinsic input in order to specify survival, DNA repair, self-renewal, and proliferation. At issue is whether the state of T cell differentiation is specified by initial conditions of activation or is actively maintained. To study the spectrum of T cell differentiation, we have analyzed an infection with mouse cytomegalovirus, a persistent-latent virus that elicits different cytotoxic T cell responses characterized as acute resolving or inflationary. Our results show that FOXO1 is continuously required for all the phenotypic characteristics of memory-effector T cells such that with acute inactivation of the gene encoding FOXO1, T cells revert to a short-lived effector phenotype, exhibit reduced viability, and manifest characteristics of anergy. %U http://jem.rupress.org/content/215/2/575