BackgroundTumor-derived microvesicles (TMV) or exosomes are present in body fluids of patients with cancer and might be involved in tumor progression. The frequency and suppressor functions of peripheral blood CD4+CD25highFOXP3+ Treg are higher in patients with cancer than normal controls. The hypothesis is tested that TMV contribute to induction/expansion/and activation of human Treg.Methodology/Principal FindingsTMV isolated from supernatants of tumor cells but not normal cells induced the generation and enhanced expansion of human Treg. TMV also mediated conversion of CD4+CD25neg T cells into CD4+CD25highFOXP3+ Treg. Upon co-incubation with TMV, Treg showed an increased FasL, IL-10, TGF-β1, CTLA-4, granzyme B and perforin expression (p<0.05) and mediated stronger suppression of responder cell (RC) proliferation (p<0.01). Purified Treg were resistant to TMV-mediated apoptosis relative to other T cells. TMV also increased phospho-SMAD2/3 and phospho-STAT3 expression in Treg. Neutralizing Abs specific for TGF-β1 and/or IL-10 significantly inhibited TMV ability to expand Treg.Conclusions/SignificanceThis study suggests that TMV have immunoregulatory properties. They induce Treg, promote Treg expansion, up-regulate Treg suppressor function and enhance Treg resistance to apoptosis. Interactions of TMV with Treg represent a newly-defined mechanism that might be involved in regulating peripheral tolerance by tumors and in supporting immune evasion of human cancers.

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Summary

Purpose Regulatory CD4+CD25highFoxp3+ T cells (Treg) control peripheral immune tolerance. Patients with cancer, including those with hematologic malignancies, have elevated numbers of Treg in the peripheral circulation and in tumor tissues. However, mechanisms of suppression and clinical significance of Treg, especially in patients with acute myelogenous leukemia (AML), has not been well defined. Experimental Design We prospectively evaluated the phenotype, function, and mechanisms of suppression used by Treg in newly diagnosed untreated AML patients. The relationship between the frequency of circulating Treg and the disease status as well as treatment outcome was also evaluated. Results The percentage of circulating Treg was higher (P < 0.0001) and their phenotype was distinct in AML patients relative to normal controls. Suppression mediated by Treg coincubated with proliferating autologous responder cells was also higher (P < 0.001) in AML than that mediated by control Treg. Using Transwell inserts, we showed that interleukin-10 and transforming growth factor-β1 production as well as cell-to-cell contact were necessary for Treg-mediated suppression. Also, the pretreatment Treg frequency predicted response to chemotherapy. Unexpectedly, patients who achieved complete remission still had elevated frequency of Treg, which mediated high levels of suppressor activity. Conclusions Treg accumulating in the peripheral circulation of AML patients mediate vigorous suppression via contact-dependent and contact-independent mechanisms. Patients with lower Treg frequency at diagnosis have a better response to induction chemotherapy. During the post-induction period, the Treg frequency and suppressive activity remain elevated in complete remission, suggesting that Treg are resistant to conventional chemotherapy.

Toll-like receptors (TLRs) expressed on immune cells trigger inflammatory responses. TLRs are also expressed on ovarian cancer (OvCa) cells, but the consequences of signaling via the TLR4/MyD88 pathway in these cells are unclear. Here, TLR4 and MyD88 expression in OvCa tissues (n=20) and cell lines (OVCAR3, SKOV3, AD10, A2780 and CP70) was evaluated by RT-PCR, Western blots and immunohistochemistry. Cell growth, apoptosis, NF-κB translocation, IRAK4 and TRIF expression and cJun phosphorylation were measured following tumor cell exposure to the TLR4 ligands, lipopolysacharide (LPS) or Paclitaxel (PTX). Culture supernatants were tested for cytokine levels. TLR4 was expressed in all tumors, tumor cell lines and normal epithelium. MyD88 was detectable in tumor tissues and in 3/5 OvCa lines but not in normal cells. In MyD88+ SCOV3 cells, LPS or PTX binding to TLR4 induced IRAK4 activation and cJun phosphorylation, activated the NF-κB pathway and promoted IL-8, IL-6, VEGF and MCP-1 production and resistance to drug-induced apoptosis. Silencing of TLR4 in SCOV3 cells with siRNA resulted in p-cJun downregulation and a loss of PTX resistance. In PTX sensitive, MyD88neg A2780 cells, TLR4 stimulation upregulated TRIF, and TLR4 silencing eliminated this effect. Thus, TLR4/MyD88 signaling supports OvCa progression and chemoresistance, promoting immune escape.

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Purpose: Regulatory T cell (Treg) frequency and activity are increased in cancer patients and play a major role in tumor escape. Although disease progression is favored by the presence of Treg, mechanisms used by Treg to suppress antitumor immunity are unknown. The ectonucleotidases CD39 and CD73 are expressed in Treg and convert ATP into immunosuppressive adenosine. In this study, the involvement of the adenosinergic pathway in Treg-mediated suppression in head and neck squamous cell carcinoma (HNSCC) patients was evaluated. Experimental Design: HNSCC patients with an active disease (n = 19) and patients with no evident disease after therapy (n = 14) were studied. Ectonucleotidase expression on CD4 + T cells and CD4 + CD25high Treg was evaluated by flow cytometry and compared with normal controls. Ectonucleotidase activity was also compared within these three groups. The data were analyzed for associations of ectonucleotidase expression/function with disease stage. Results: The percentages and expression levels of CD39 and CD73 in CD4 + T cells and Treg were greater in HNSCC than in normal controls and highest in patients with no evident disease. Patients' Treg hydrolyzed ATP at higher rates and produced higher levels of adenosine than normal controls' Treg. The increased frequency and enzymatic activity of CD4 + CD39 + cells corresponded to increased adenosine-mediated suppression of effector T cells, which was partly inhibited by ARL67156, an ectonucleotidase inhibitor, and by ZM241385, a selective A 2a /A 2b receptor antagonist. Conclusions: CD39+ Treg frequency and adenosine-mediated suppression are significantly increased in HNSCC patients. The adenosinergic pathway is involved in Treg-mediated immunosuppression in cancer and its attenuation could be a promising immunotherapeutic strategy for patients with HNSCC. ( Head and neck squamous cell carcinoma (HNSCC), arising from the mucosal epithelium, is the fifth most common type of cancer worldwide and the sixth most common cause of cancerrelated mortality (1, 2). Although advances in surgical methods, chemotherapy, and radiation have improved patients' treatment and quality of life, the overall outcome and survival rate among patients with this disease have not notably improved (3). Therefore, novel therapeutic strategies are necessary for the treatment of HNSCC. Recent studies have focused on the dynamic interplay and coevolution of antitumor immune responses and tumor progression in HNSCC (4, 5). These studies have shown that T lymphocytes play a major albeit contradictory role in local tumor expansion, metastasis, and neoangiogenesis. In most human cancers, regulatory T cells (Treg), a small subset of CD4 + T cells, are significantly increased in the peripheral blood as well as in the tumor microenvironment (6-8). Treg are phenotypically defined as CD4 + CD25high FOXP3 + and modulate immune responses by suppressing functions of other T cells. To date, at least two types of Treg are known to exist in man: (a) naturally occurring Treg, which devel...

Human regulatory T cells (Treg) have been variously defined as CD4+CD25+, CD4+CD25high or CD4+CD25highFOXP3+ cells which are responsible for maintaining peripheral tolerance. Their isolation from human peripheral blood or tissues depends on the expression level of CD25(IL-2Rα) - a surface marker which is also expressed on activated effector helper T cells. CD39, a cell surface associated ectonucleotidase, can be used to purify Treg with strong suppressor functions. The CD4+CD39+ T cells catalyze cleavage of adenosine triphosphate (ATP) to adenosine monophosphate (AMP), which is then further cleaved to adenosine. CD4+CD39+ T cells largely overlap with CD4+CD25highFOXP3+ but not CD4+CD25+ T-cell subset, and mediate equally potent immune suppression. Thus, CD39 surface marker can be successfully used for routine isolation of functionally-active human Treg from the peripheral blood of healthy donors or patients with cancer for studies of their role in health and disease.