In summary, we have shown that Th17 cells can differentiate into IFN-γ-producing and FOXP3+ T cells after repetitive in vitro stimulation with OKT3 and PBMCs. We further demonstrated that this differentiation was due to TCR stimulation, resulting in epigenetic modification of FOXP3 and reprogramming of the gene expression signatures,

including lineage-specific transcriptional factors and cytokines. In addition to the expression of IFN-γ and FOXP3, we showed that these Th17 cells after differentiation into cells with a Treg phenotype mediated potent suppressive function. These results indicate that human Th17 cells exhibit substantial developmental plasticity and can differentiate into Tregs. In addition, our data provide novel information regarding T-cell-mediated immunity, which may have clinical implications for the development of target therapies. Tumor tissue samples of melanoma, Gefitinib price ovarian, breast and colon cancers and patient data were obtained from hospitalized

patients undergoing surgery at St. Louis University Hospital, as approved by the Institutional Review Board and ethics committee of the institution. SB203580 price Buffy coats from healthy donors were obtained from the Saint Louis Red Cross. PBMCs were purified from buffy coats using Ficoll-Paque. Bulk and naïve CD4+ T cells were isolated by either positive or negative selection with microbeads (Miltenyi Biotec) according to the manufacturer’s instructions. CD4+CD25+ Tregs

were further purified from CD4+ T cells by FACS sorting after staining with anti-CD25-PE antibody (BD Bioscience). Tumor-infiltrating lymphocytes (TILs) were generated from various tumor tissues, as previously described 28. Briefly, tissues were minced into small pieces followed by digestion with collagenase type IV, hyaluronidase and deoxyribonuclease. After digestion, the cells were washed in RPMI1640, and then cultured in RPMI1640 containing 10% human serum supplemented Phosphatidylinositol diacylglycerol-lyase with L-glutamine, 2-mercaptethanol and 50 U/mL of IL-2 for the generation of T cells. The percentages of CD4+ Th17 cells were determined from bulk T cells by FACS analysis after intracellular staining for IL-17. Th17 cell clones were generated from TILs by a limiting dilution cloning method, as previously described 27, 28. Briefly, CD4+ TILs were diluted in U bottom 96-well plates at a 0.3-cell/well concentration and then co-cultured with irradiated allogeneic PBMCs in the presence of soluble anti-CD3 antibody (OKT3, 100 ng/mL) for 10–14 days. Th17 clones were screened by determining IL-17 secretion in cell supernatants by ELISA (eBioscience) after stimulation with plate-bound anti-CD3 antibody (2 μg/mL). The expression markers on T cells were determined by FACS analysis after surface staining or intracellular staining with specific anti-human antibodies conjugated with either PE or FITC.