TOX induces T cell IL-10 production in a BATF-dependent manner
TOX is a member of the HMG-Box transcription factors and plays important roles in thymic T cell development. Outside of the thymus, however, TOX is also highly expressed by CD8 and CD4 T cells in various states of activation and in settings of cancer and autoimmune disease. In CD4 T cells, TOX has been primarily studied in T follicular helper (TFH) cells where it , along with TOX2 promotes TFH differentiation by regulating key TFH-associated genes and suppressing CD4 cytotoxic T cell differentiation. However, the role of TOX in other Th cell subtypes is less clear. In our study, we show that TOX is expressed in several physiologically-activated Th subtypes and its ectopic expression modestly enhances the in vitro differentiation of  Th2 and Treg cells. TOX overexpression also induced the expression of a small number of genes in unpolarized Th cells involved in cell activation (Pdcd1, PD-1), cellular trafficking (Ccl3, Ccl4, Xcl1) and in suppressing inflammation (Il10) that was conserved in multiple Th subtypes. We additionally show that TOX co-occupies these genes with the transcription factor BATF and that TOX-induced expression of IL-10, but not PD-1, is BATF-dependent. Based on these data, we propose a model where TOX regulates Th cell chemotactic genes involved in facilitating dendritic cell-T cell interactions and aids in the resolution or prevention of inflammation through the production of IL-10. Overall design: We transduced naïve CD4 T cells that had been activated for 2 days with EV-RV or TOX-RV under non-polarizing (i.e. anti-CD3, anti-CD28 and IL-2 only) conditions as we initially wanted to explore non-Th lineage specific effects. After 5 days of culture, we re-stimulated the cells using anti-CD3 and anti-CD28 as previously reported, sorted the GFP+ cells and performed RNA-seq on RNAs isolated from these cells