TGF-beta-mediated suppression by CD4+CD25+ T cells is facilitated by CTLA-4 signaling

Induction of oral tolerance to HSP60 or an HSP60-peptide activates T cell regulation and reduces atherosclerosis

OBJECTIVE

HSP60-specific T cells contribute to the development of the immune responses in atherosclerosis. This can be dampened by regulatory T cells activated via oral tolerance induction, and we explored the effect of oral tolerance induction to HSP60 and the peptide HSP60 (253 to 268) on atherosclerosis.

METHODS AND RESULTS

HSP60 and HSP60 (253 to 268) were administered orally to LDLr(-/-) mice before induction of atherosclerosis and resulted in a significant 80% reduction in plaque size in the carotid arteries and in a 27% reduction in plaque size at the aortic root. Reduction in plaque size correlated with an increase in CD4(+)CD25(+)Foxp3(+) regulatory T cells in several organs and in an increased expression of Foxp3, CD25, and CTLA-4 in atherosclerotic lesions of HSP60-treated mice. The production of interleukin (IL)-10 and transforming growth factor (TGF)-beta by lymph node cells in response to HSP60 was observed after tolerance induction.

CONCLUSIONS

Oral tolerance induction to HSP60 and a small HSP60-peptide leads to an increase in the number of CD4(+)CD25(+)Foxp3(+) regulatory T cells, resulting in a decrease in plaque size as a consequence of increased production of IL-10 and TGF-beta. We conclude that these beneficial results of oral tolerance induction to HSP60 and HSP60 (253 to 268) may provide new therapeutic approaches for the treatment of atherosclerosis.

TGF-β1 Variants in Chronic Beryllium Disease and Sarcoidosis

Evidence suggests a genetic predisposition to chronic beryllium disease (CBD) and sarcoidosis, which are clinically and pathologically similar granulomatous lung diseases. TGF-beta1, a cytokine involved in mediating the fibrotic/Th1 response, has several genetic variants which might predispose individuals to these lung diseases. We examined whether certain TGF-beta1 variants and haplotypes are found at higher rates in CBD and sarcoidosis cases compared with controls and are associated with disease severity indicators for both diseases. Using DNA from sarcoidosis cases/controls from A Case Control Etiologic Study of Sarcoidosis Group (ACCESS) and CBD cases/controls, TGF-beta1 variants were analyzed by sequence-specific primer PCR. No significant differences were found between cases and controls for either disease in the TGF-beta1 variants or haplotypes. The -509C and codon 10T were significantly associated with disease severity indicators in both CBD and sarcoidosis. Haplotypes that included the -509C and codon 10T were also associated with more severe disease, whereas one or more copies of the haplotype containing the -509T and codon 10C was protective against severe disease for both sarcoidosis and CBD. These studies suggest that the -509C and codon 10T, implicated in lower levels of TGF-beta1 protein production, are shared susceptibility factors associated with more severe granulomatous disease in sarcoidosis and CBD. This association may be due to lack of down-regulation by TGF-beta1, although future studies will be needed to correlate TGF-beta1 protein levels with known TGF-beta1 genotypes and assess whether there is a shared mechanisms for TGF-beta1 in these two granulomatous diseases.

Tumor necrosis factor alpha inhibits the suppressive effect of regulatory T cells on the hepatitis B virus-specific immune response

Chronicity of hepatitis B virus (HBV) infection is characterized by a weak immune response to the virus. CD4+CD25+ regulatory T cells (Treg) are present in increased numbers in the peripheral blood of chronic HBV patients, and these Treg are capable of suppressing the HBV-specific immune response. The aim of this study was to abrogate Treg-mediated suppression of the HBV-specific immune response. Therefore, Treg and a Treg-depleted cell fraction were isolated from peripheral blood of chronic HBV patients. Subsequently, the suppressive effect of Treg on the response to HBV core antigen (HBcAg) and tetanus toxin was compared, and the effect of exogenous tumor necrosis factor alpha (TNF-alpha), interleukin-1-beta (IL-1beta), or neutralizing antibodies against interleukin-10 (IL-10) or transforming growth factor beta (TGF-beta) on Treg-mediated suppression was determined. The results show that Treg of chronic HBV patients had a more potent suppressive effect on the response to HBcAg compared with the response to tetanus toxin. Neutralization of IL-10 and TGF-beta or exogenous IL-1beta had no effect on Treg-mediated suppression of the anti-HBcAg response, whereas exogenous TNF-alpha partially abrogated Treg-mediated suppression. Preincubation of Treg with TNF-alpha demonstrated that TNF-alpha had a direct effect on the Treg. No difference was observed in the type II TNF receptor expression by Treg from chronic HBV patients and healthy controls.

CONCLUSION

Treg-mediated suppression of the anti-HBV response can be reduced by exogenous TNF-alpha. Because chronic HBV patients are known to produce less TNF-alpha, these data implicate an important role for TNF-alpha in the impaired antiviral response in chronic HBV.

CD8+ T cell-mediated suppression of autoimmunity in a murine lupus model of peptide-induced immune tolerance depends on Foxp3 expression

Systemic lupus erythematosus is an autoimmune disease caused by autoantibodies, including IgG anti-DNA. New Zealand Black/New Zealand White F(1) female mice, a model of spontaneous polygenic systemic lupus erythematosus, tolerized with an artificial peptide (pConsensus) based on anti-DNA IgG sequences containing MHC class I and class II T cell determinants, develop regulatory CD4+CD25+ T cells and CD8+ inhibitory T cells (CD8+ Ti), both of which suppress autoantibody production. CD8+ Ti inhibit primarily via secretion of TGF-beta. In the present study, we show that the inhibitory function of CD8+ T cells from tolerized mice is sustained for up to 8 wk and at all times depends on expression of Foxp3. Both CD28-positive and CD28-negative CD8+ T cells contain inhibitory cells, but the expression of mRNA for Foxp3 and for TGF-beta is higher and lasts longer in the CD28- subset. In vitro addition of TGF-beta (in the presence of IL-2) induces Foxp3 expression in a dose-response manner. Gene inhibition or blockade with small interfering RNA of Foxp3 abrogates the ability of the CD8+ Ti to inhibit anti-DNA production and the proliferation of CD4+ Th cells. Moreover, a significant correlation between expression of Foxp3 and ability of CD8+ Ti to secrete TGF-beta is observed. Therefore, CD8+ Ti in this system of tolerance are similar to CD4+CD25+ regulatory T cells in their dependence on expression of Foxp3, and there may be a bidirectional Foxp3/TGF-beta autocrine loop that determines the ability of the CD8+ T cells to control autoimmunity.

Cutting edge: regulatory T cells induce CD4+CD25-Foxp3- T cells or are self-induced to become Th17 cells in the absence of exogenous TGF-beta

Recent studies have shown that TGF-beta together with IL-6 induce the differentiation of IL-17-producing T cells (Th17) T cells. We therefore examined whether CD4(+)CD25(+)Foxp3(+) regulatory T cells, i.e., cells previously shown to produce TGF-beta, serve as Th17 inducers. We found that upon activation purified CD25(+) T cells (or sorted GFP(+) T cells obtained from Foxp3-GFP knockin mice) produce high amounts of soluble TGF-beta and when cultured with CD4(+)CD25(-)Foxp3(-) T cells in the presence of IL-6 induce the latter to differentiate into Th17 cells. Perhaps more importantly, upon activation, CD4(+)CD25(+)Foxp3(+)(GFP(+)) T cells themselves differentiate into Th17 cells in the presence of IL-6 (and in the absence of exogenous TGF-beta). These results indicate that CD4(+)CD25(+)Foxp3(+) regulatory T cells can function as inducers of Th17 cells and can differentiate into Th17 cells. They thus have important implications to our understanding of regulatory T cell function and their possible therapeutic use.

Follicular lymphoma intratumoral CD4+CD25+GITR+ regulatory T cells potently suppress CD3/CD28-costimulated autologous and allogeneic CD8+CD25- and CD4+CD25- T cells

Regulatory T cells (T(R)) play a critical role in the inhibition of self-reactive immune responses and as such have been implicated in the suppression of tumor-reactive effector T cells. In this study, we demonstrate that follicular lymphoma (FL)-infiltrating CD8+ and CD4+ T cells are hyporesponsive to CD3/CD28 costimulation. We further identify a population of FL-infiltrating CD4+CD25+GITR+ T(R) that are significantly overrepresented within FL nodes (FLN) compared with that seen in normal (nonmalignant, nonlymphoid hyperplastic) or reactive (nonmalignant, lymphoid hyperplastic) nodes. These T(R) actively suppress both the proliferation of autologous nodal CD8+CD25- and CD4+CD25- T cells, as well as cytokine production (IFN-gamma, TNF-alpha and IL-2), after CD3/CD28 costimulation. Removal of these cells in vitro by CD25+ magnetic bead depletion restores both the proliferation and cytokine production of the remaining T cells, demonstrating that FLN T cell hyporesponsiveness is reversible. In addition to suppressing autologous nodal T cells, these T(R) are also capable of suppressing the proliferation of allogeneic CD8+CD25- and CD4+CD25- T cells from normal lymph nodes as well as normal donor PBL, regardless of very robust stimulation of the target cells with plate-bound anti-CD3 and anti-CD28 Abs. The allogeneic suppression is not reciprocal, as equivalent numbers of CD25+FOXP3+ cells derived from either normal lymph nodes or PBL are not capable of suppressing allogeneic CD8+CD25- and CD4+CD25- T cells, suggesting that FLN T(R) are more suppressive than those derived from nonmalignant sources. Lastly, we demonstrate that inhibition of TGF-beta signaling partially restores FLN T cell proliferation suggesting a mechanistic role for TGF-beta in FLN T(R)-mediated suppression.

T-cell costimulation blockade in immunologic diseases: role of CD28 family members

The destruction of many immune-mediated diseases is a result of T-cell responses against usually harmless antigens. Extensive research has been conducted to discover new mechanisms to specifically modulate harmful effector T cells while leaving normal immune responses intact. Since proteins of the CD28 family members are expressed on T cells, blockade of these proteins has become a possible target for potential therapies. The CD28 family contains proteins that have the ability to both enhance and diminish T-cell responses. Therefore, blockade of targets that enhance T-cell signaling may reduce destructive autoimmune responses, while blockade of targets that diminish T-cell signaling may enhance antitumor responses. In this article, the function of these proteins will be reviewed and a sample of clinical trials highlighting the potential efficacy and drawbacks of their use in humans will be described briefly. Finally, inducible costimulator and programmed death-1, two future targets of T-cell therapies, will be highlighted.

Simian immunodeficiency virus (SIV) infection influences the level and function of regulatory T cells in SIV-infected rhesus macaques but not SIV-infected sooty mangabeys

Differences in clinical outcome of simian immunodeficiency virus (SIV) infection in disease-resistant African sooty mangabeys (SM) and disease-susceptible Asian rhesus macaques (RM) prompted us to examine the role of regulatory T cells (Tregs) in these two animal models. Results from a cross-sectional study revealed maintenance of the frequency and absolute number of peripheral Tregs in chronically SIV-infected SM while a significant loss occurred in chronically SIV-infected RM compared to uninfected animals. A longitudinal study of experimentally SIV-infected animals revealed a transient increase in the frequency of Tregs from baseline values following acute infection in RM, but no change in the frequency of Tregs occurred in SM during this period. Further examination revealed a strong correlation between plasma viral load (VL) and the level of Tregs in SIV-infected RM but not SM. A correlation was also noted in SIV-infected RM that control VL spontaneously or in response to antiretroviral chemotherapy. In addition, immunofluorescent cell count assays showed that while Treg-depleted peripheral blood mononuclear cells from RM led to a significant enhancement of CD4+ and CD8+ T-cell responses to select pools of SIV peptides, there was no detectable T-cell response to the same pool of SIV peptides in Treg-depleted cells from SIV-infected SM. Our data collectively suggest that while Tregs do appear to play a role in the control of viremia and the magnitude of the SIV-specific immune response in RM, their role in disease resistance in SM remains unclear.

Converting antigen-specific diabetogenic CD4 and CD8 T cells to TGF-beta producing non-pathogenic regulatory cells following FoxP3 transduction

Immuno-regulatory defects, including a reduction in the number and function of regulatory T cells, play an important role in the development of autoimmune diabetes in both humans and non-obese diabetic (NOD) mice. In this study we tested the effect of introduction of FoxP3 into antigen non-specific polyclonal and antigen-specific monoclonal T cells on diabetes development in NOD mice. Transduction of FoxP3 into antigen-specific monoclonal (insulin or BDC2.5 mimotope specific) or antigen non-specific polyclonal T cells using retroviral transduction delayed or prevented diabetes development. However, transduced antigen-specific monoclonal T cells were considerably more effective than polyclonal T cells. Regulatory activity was not limited to CD4 T cells as potent diabetogenic CD8 T cells specific for insulin, were also reduced in pathogenicity by FoxP3 induction. The disease suppressive effect, in both CD4 and CD8 cells, was more evident in spontaneously diabetes-prone NOD hosts (non-lymphopenic) than in lymphopenic NOD.scid hosts. We suggest that this strategy of transducing antigen-specific CD4 or CD8 T cells may be a useful therapeutic approach in the prevention of autoimmune diabetes.

Transforming Growth Factor-β: Taking Control of T Cells' Life and Death

To determine how transforming growth factor-beta (TGF-beta) controls T cell function, Marie et al. (2006) and Li et al. (2006a) created mice with T cells lacking TGF-beta signaling receptors. Both report that TGF-beta signaling by T cells is absolutely essential for tolerance and homeostasis.

Oral tolerance

Multiple mechanisms of tolerance are induced by oral antigen. Low doses favor active suppression, whereas higher doses favor clonal anergy/deletion. Oral antigen induces T-helper 2 [interleukin (IL)-4/IL-10] and Th3 [transforming growth factor (TGF)-beta] T cells plus CD4+CD25+ regulatory cells and latency-associated peptide+ T cells. Induction of oral tolerance is enhanced by IL-4, IL-10, anti-IL-12, TGF-beta, cholera toxin B subunit, Flt-3 ligand, and anti-CD40 ligand. Oral (and nasal) antigen administration suppresses animal models of autoimmune diseases including experimental autoimmune encephalitis, uveitis, thyroiditis, myasthenia, arthritis, and diabetes in the non-obese diabetic (NOD) mouse, plus non-autoimmune diseases such as asthma, atherosclerosis, graft rejection, allergy, colitis, stroke, and models of Alzheimer's disease. Oral tolerance has been tested in human autoimmune diseases including multiple sclerosis (MS), arthritis, uveitis, and diabetes and in allergy, contact sensitivity to dinitrochlorobenzene (DNCB), and nickel allergy. Although positive results have been observed in phase II trials, no effect was observed in phase III trials of CII in rheumatoid arthritis or oral myelin and glatiramer acetate (GA) in MS. Large placebo effects were observed, and new trials of oral GA are underway. Oral insulin has recently been shown to delay onset of diabetes in at-risk populations, and confirmatory trials of oral insulin are being planned. Mucosal tolerance is an attractive approach for treatment of autoimmune and inflammatory diseases because of lack of toxicity, ease of administration over time, and antigen-specific mechanisms of action. The successful application of oral tolerance for the treatment of human diseases will depend on dose, developing immune markers to assess immunologic effects, route (nasal versus oral), formulation, mucosal adjuvants, combination therapy, and early therapy.