Eos, a member of the Ikaros family of transcription factors, is expressed by T regulatory cells (Tregs) and has been postulated to play a role in Treg suppression and maintenance of Treg stability. We demonstrate that expression of Eos was limited to a subpopulation of thymus-derived, activated Tregs and is undetectable in resting or activated T conventional cells. Eos associates with Helios and Foxp3 and binds directly to the CD25 locus at a site identical to the Foxp3-binding site, thereby enhancing CD25 expression. Studies in heterozygous female mice demonstrate that Eos is critical for Treg survival and activation. Eos+ Tregs also represent the major population of recirculating thymic Tregs, in which Eos plays a critical role in regulating their migration and suppression of Treg precursors in the thymus by competing for IL-2 and depleting MHC II from thymic dendritic cells.
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Intratumoral Tregs are key mediators of cancer immunotherapy resistance, including anti-programmed cell death (ligand) 1 [anti-PD-(L)1] immune checkpoint blockade (ICB). The mechanisms driving Treg infiltration into the tumor microenvironment (TME) and the consequence on CD8+ T cell exhaustion remain elusive. Here, we report that heat shock protein gp96 (also known as GRP94) was indispensable for Treg tumor infiltration, primarily through the roles of gp96 in chaperoning integrins. Among various gp96-dependent integrins, we found that only LFA-1 (αL integrin), and not αV, CD103 (αE), or β7 integrin, was required for Treg tumor homing. Loss of Treg infiltration into the TME by genetic deletion of gp96/LFA-1 potently induced rejection of tumors in multiple ICB-resistant murine cancer models in a CD8+ T cell-dependent manner, without loss of self-tolerance. Moreover, gp96 deletion impeded Treg activation primarily by suppressing IL-2/STAT5 signaling, which also contributed to tumor regression. By competing for intratumoral IL-2, Tregs prevented the activation of CD8+ tumor-infiltrating lymphocytes, drove thymocyte selection-associated high mobility group box protein (TOX) induction, and induced bona fide CD8+ T cell exhaustion. By contrast, Treg ablation led to striking CD8+ T cell activation without TOX induction, demonstrating clear uncoupling of the 2 processes. Our study reveals that the gp96/LFA-1 axis plays a fundamental role in Treg biology and suggests that Treg-specific gp96/LFA-1 targeting represents a valuable strategy for cancer immunotherapy without inflicting autoinflammatory conditions.

The mutualistic relationship of gut-resident microbiota and the host immune system promotes homeostasis that ensures maintenance of the microbial community and of a largely non-aggressive immune cell compartment1,2. The consequences of disturbing this balance include proximal inflammatory conditions, such as Crohn's disease, and systemic illnesses. This equilibrium is achieved in part through the induction of both effector and suppressor arms of the adaptive immune system. Helicobacter species induce T regulatory (Treg) and T follicular helper (TFH) cells under homeostatic conditions, but induce inflammatory T helper 17 (TH17) cells when induced Treg (iTreg) cells are compromised3,4. How Helicobacter and other gut bacteria direct T cells to adopt distinct functions remains poorly understood. Here we investigated the cells and molecular components required for iTreg cell differentiation. We found that antigen presentation by cells expressing RORγt, rather than by classical dendritic cells, was required and sufficient for induction of Treg cells. These RORγt+ cells-probably type 3 innate lymphoid cells and/or Janus cells5-require the antigen-presentation machinery, the chemokine receptor CCR7 and the TGFβ activator αv integrin. In the absence of any of these factors, there was expansion of pathogenic TH17 cells instead of iTreg cells, induced by CCR7-independent antigen-presenting cells. Thus, intestinal commensal microbes and their products target multiple antigen-presenting cells with pre-determined features suited to directing appropriate T cell differentiation programmes, rather than a common antigen-presenting cell that they endow with appropriate functions.
© 2022. The Author(s), under exclusive licence to Springer Nature Limited.