A temporally dynamic Foxp3 autoregulatory transcriptional circuit controls the effector Treg programme

Abstract

Regulatory T cells (Treg) are negative regulators of the immune response. Whilst thymic Treg generation is well studied, it is not known whether and how Foxp3 transcription is induced and regulated in the periphery during immune responses. Here we use Foxp3 Timer of cell kinetics and activity (Tocky) mice, which report real-time Foxp3 gene transcription by measuring the spontaneous maturation of Fluorescent Timer protein from Blue to Red fluorescence, to identify the flux of Foxp3-to Foxp3+ T cells within the periphery and analyse the real-time activity of Foxp3 transcription. Using a murine model of skin allergy, we show that both the flux of new Foxp3 expressors and the rate of Foxp3 transcription are increased at inflamed sites. These persistent dynamics of Foxp3 transcription determine the effector Treg programme, and are dependent on a Foxp3 autoregulatory transcriptional circuit, as evidenced by analysis of T cells lacking functional Foxp3 protein. Such reactive and persistent Foxp3 transcriptional activity controls the expression of coinhibitory molecules including CTLA-4 and effector-Treg signature genes. Using RNA-seq, we identify two groups of surface proteins based on their relationship to the temporal dynamics of Foxp3 transcription, and we show proof-of-principle for the manipulation of Foxp3 dynamics by immunotherapy: new Foxp3 flux is promoted by anti-TNFRII antibody, and high frequency Foxp3 expressors are depleted by anti-OX40 antibody. Collectively, our study dissects time-dependent mechanisms behind Foxp3-driven T cell regulation, and establishes the Foxp3-Tocky system as a tool to investigate the mechanisms behind T cell immunotherapies.