ABSTRACT: The transcription factor FoxP3 partakes dominantly in the specification and function of FoxP3+ CD4+ T regulatory cells (Tregs), but is neither strictly necessary nor sufficient to determine the characteristic Treg transcriptional signature. Computational network inference and experimental testing assessed the contribution of several other transcription factors (TFs). Enforced expression of Helios or Xbp1 elicited specific signatures, but Eos, Irf4, Satb1, Lef1 and Gata1 elicited exactly the same outcome, synergizing with FoxP3 to activate most of the Treg signature, including key TFs, and enhancing FoxP3 occupancy at its genomic targets. Conversely, the Treg signature was robust to inactivation of any single cofactor. A redundant genetic switch thus locks-in the Treg phenotype, a model which accounts for several aspects of Treg physiology, differentiation and stability. To study the impact of FoxP3 and its candidate cofactors (Eos, Gata1, Helios, Irf4, Lef1, Satb1, Xbp1) on the expression of the Treg transcriptional signature, CD4+ conventional T cells (Tconv) activated with anti-CD3+CD28 beads were retrovirally transduced with cDNAs encoding FOXP3, candidate TFs, or a combination of FOXP3 and candidate TFs. After 3 days in culture, the transduced cells were sorted into Trizol, and RNA was purified, labeled and hybridized to Affymetrix arrays.
