These results also suggest that Th17-derived Tregs, inducible Tregs from other T-cell origins, and naturally occurring Tregs may have different stabilities 55. In support of this notion, recent studies have shown epigenetic differences between naturally occurring Tregs and induced Tregs 57. Thus, improved understanding of epigenetic and gene expression profiles in T-cell lineages is essential for studies of T-cell commitment, plasticity and reciprocity under both physiological and pathological conditions. Mounting evidence suggests that human CD4+ Tregs can differentiate into IL-17-producing Th17 cells (IL-17+FOXP3+), and that Th17 cells can express Small molecule library FOXP3 and RORγt

(RORγt+FOXP3+)

24, 25, 52. It has not previously known whether Th17 cells can be differentiated into Tregs. In addition, all these studies were performed with polyclonal CD4+ T cells purified with magnetic beads or FACS sorting, thus the purity and/or potential contamination with other cell populations could directly influence the results. To address these important issues, in the check details present study, we established Th17 clones from TILs containing high percentages of IL-17-producing cells, and we confirmed the purity of these clones by assessing TCR-Vβ expression. We then showed that these Th17 clones could significantly increase Th17+IFN-γ+ and Th17+FOXP3+ double-positive T-cell populations and could differentiate into functional Tregs following multiple rounds of unbiased TCR stimulation. Our studies further confirm the developmental plasticity of human Th17 cells at a clonal level, suggesting that Th17 cells not

only can differentiate into Th1 cells but can also convert to Tregs 21. Notably, these data implicate that Th17 cells may have dual functions, performing regulatory as well effector roles in human diseases including inflammatory disorders and cancers. The commitment of Th17 cells to Th1 and/or Treg lineages may depend on specific physiological and pathological conditions, such as the local proinflammatory cytokine milieu and pathogen- or tumor antigen-mediated stimulation. In support of our concept, recent studies have shown that FOXP3+ PtdIns(3,4)P2 Tregs can acquire an effector cell phenotype expressing T-bet and IFN-γ in the presence of strong inflammatory responses during lethal infection 58. In addition, environmental IDO can regulate the conversion of FOXP3+ Tregs to Th17-like cells in tumor-draining lymph nodes 59. Besides possessing potent suppressive function, our data also showed that these Th17-Treg differentiated T cells secreted moderate amounts of IL-10 and TGF-β1 after stimulation with OKT3 and PBMCs that may amplify their negative regulatory functions, and which is consistent with studies from other groups 14.