UC San Diego

During infection, naive CD8⁺ T cells differentiate into effector cells armed to eliminate pathogens and memory cells that provide protection from reinfection. How the transcriptional program regulating terminal differentiation to short-lived effector/memory cells versus long-lived memory cells is initiated and sustained is not clearly defined. Here, we identify long-lived memory precursors prior to the peak of CD8⁺ T cell expansion through the use of reporter mice that allow us to monitor expression of inhibitor-of-DNA-binding (Id)2 and Id3, key antagonists of E protein transcription factors. Id3hi long-lived memory precursors can be identified prior to expression of cell-surface receptors known to predict memory potential and display a gene- expression profile consistent with this lineage. Deficiency in Id2 or Id3 results in the loss of distinct populations of CD8⁺ effector and memory T cells, demonstrating unique roles of these transcriptional inhibitors. Furthermore, we provide a connection between inflammatory cytokines, known to influence memory subset differentiation, with the inverse regulation of Id2 and Id3 expression. These data provide novel insights into how external cues control gene expression and implicate unique roles for Id2 and Id3 in CD8⁺ T cell biology. Natural Killer T cells expressing an invariant T cell receptor (iNKT) regulate activation of both innate and adaptive immunity in many contexts. iNKT cells accumulate in the liver and rapidly produce prodigious amounts of numerous cytokines upon activation, impacting the immune response to viral infection, immunosurveillance for malignant cells and liver regeneration. However, little is known about the factors controlling iNKT homeostasis, survival and hepatic localization. Here, we report that the absence of the transcriptional regulator Id2 resulted in a severe, intrinsic defect in the accumulation of hepatic iNKT cells. Id2-deficient iNKT cells showed increased cell death in the liver, although migration and functional activity were not impaired in comparison to Id2-expressing iNKT cells. Id2-deficient iNKT cells exhibited diminished expression of CXCR6, a critical determinant of iNKT cell accumulation in the liver, and of the anti-apoptotic molecules bcl-2 and bcl-XL, compared to Id2-sufficient iNKT cells. Furthermore, survival and accumulation of iNKT cells lacking Id2 expression was rescued by deficiency in bim, a key pro-apoptotic molecule. Thus, Id2 was necessary to establish a hepatic iNKT cell population, defining a novel role for Id2 and implicating the Id targets, E protein transcription factors, in the regulation of iNKT cell homeostasis