In addition, Th17 cells can be converted into Th1 cells in different animal

models 21, 22. Furthermore, human CD4+ Tregs can be converted to a Th2 cell lineage subsequent to decreased FOXP3 expression 23. More recent studies have shown that CD4+ Tregs can also differentiate into IL-17-producing Th17 cells (IL-17+FOXP3+), and Th17 cells can co-express FOXP3 and RORγt (RoRγt+FOXP3+) 24, 25. Although these studies have focused on Th17 and Treg commitment and plasticity, whether Th17 cells can reciprocally convert into Tregs has not been described. In addition, the majority of studies demonstrating the plasticity of T-cell development have been based on observations in mixed cell populations without clear proof that this occurs buy PF-02341066 at the single-cell level. Further precise investigations of

plasticity and the intimate links between T-cell lineages at a homogeneous cell clonal level will be critical for better understanding of T-cell-mediated immunity. To further explore the phenotypic and functional features of human Th17 cells, we have recently generated Th17 clones from tumor-infiltrating T lymphocytes (TILs) which were characterized by their transcriptional factor expression, cytokine and chemokine receptor expression profiles, and their effector function. During the course of procedures intended to maintain the stability of Th17 clones for future studies, we

unexpectedly found that these Th17 clones could differentiate into IFN-γ-producing and Ivacaftor chemical structure FOXP3+ cells after in vitro stimulation with OKT3 and allogeneic peripheral blood mononuclear cells (PBMCs). Further studies showed that this Th17-to-Treg differentiation was specifically due to T-cell receptor (TCR) stimulation and was associated with FOXP3 demethylation and reprogramming of gene expression signatures, including lineage-specific transcriptional factor and cytokine genes, in Th17 cells following TCR stimulation and expansion. In addition to the expression of IFN-γ and FOXP3, these Th17 clones exhibited potent suppressive function following three rounds of repetitive stimulations and expansions with OKT3 and allogeneic PBMCs, suggesting their differentiation into Tregs. We also demonstrated that these Th17-derived Tregs RAS p21 protein activator 1 were resistant to Th17 reconversion in the presence of Th17 differentiation cytokines, including IL-2, IL-1β, IL-6 and IL-23. These results further indicate the substantial developmental plasticity of human Th17 cells and provide the first evidence that human Th17 cells can differentiate into Tregs at a T-cell clonal level. In the course of studies to examine the role of TIL subsets in anti-tumor immunity, we observed increased numbers of CD4+ Th17 cell populations in tumors of melanoma, ovarian, breast and colon cancers 26, 27.