Role of T regulatory suppression in autoimmunity and cancer

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It has recently become clear that a subset of T cells e.g. CD4+CD25+FoxP3+T regulatory (Treg) cells are essential in the maintenance of immune homeostasis and have feedback suppressive effects on immune responses. These Treg cells have been reported to suppress autoimmune responses and consequently, unfortunately, also protect tumors from immune rejection. Our observation suggested that the susceptibility to autoimmunity and cancer in genetically different mouse strains might be determined by the number and suppressive activity of Tregs. We previously showed that the immunosuppressive agent dexamethasone (DEX), which is used to treat autoimmune disease and the lymphoproliferative cytokine Interleukin-2, each upregulated the number of Treg cells in mice. Furthermore, when administered together they had even greater effects in promoting immunosuppressive Treg cell activities. When administered together prior to an antigen (MOG) that induces experimental autoimmune encephalomyelitis (EAE), IL-2 plus DEX reduced the incidence and severity of EAE in susceptible mice. Thus, upregulation of Tregs by cortisone-derivatives can counteract induction of autoimmune disease. Pertussis toxin (PTX) is coadministered as an adjuvant along with an appropriate autoantigen in Complete Freunds adjuvant (CFA) in order to induce EAE in susceptible mouse strains. This was associated with a decrease in the number of functional Treg cells and concomitant activation of TLR4 by PTX. We established that PTX also has the capacity to induce DC to produce high levels of IL-6. This leads, in conjunction with coproduced TGFbeta, to the activation of the TH17 pathway with copious production of IL-17, which has been implicated in promoting a variety of autoimmune diseases. Thus, we plan to investigate the effect of the rather unique multiplicity of adjuvant effects of PTX on overcoming tolerance to tumor by using it in therapeutic anticancer vaccines. In the current fiscal year my group showed that an immunosuppressive drug, Rapamycin, unlike cyclosporine A, also promotes the generation of functional Tregs, while inhibiting differentiation of Th17 cells. It is therefore a good therapy for autoimmune diseases, but may promote tumor growth. Finally, to our surprise our studies of the effects of various cytokines and alarmins on Tregs revealed that TNF also is a potent upregulator of Treg numbers and activity. Although TNF is a well known proinflammatory cytokine, which has initial activating effects on T efferent cells, later during in vitro and in vivo mouse immune responses especially as a costimulant with IL-2, TNF induces the proliferative expansion of functional Treg cells that preferentially express the TNFR2 receptor. Neither IL-1 nor IL-6 had such biphasic effects. Thus, TNF appears to induce a unique delayed down-regulatory effect on immune responses. This is absent in TNFR2 knockout mice and may account for their less severe (lethal) sepsis (LPS) induced inflammatory reactions. We have further investigated the role of TNFR2 on Tregs and the possibility that tumors by producing TNF may be promoting the increase in Tregs infiltrating tumors with consequent down- regulation of tumor immune responses. We have found that TNFR2+ Tregs (CD4+CD25+FOXP3+) are much more suppressive than TNFR2-Tregs. Tumor infiltrating T cells consist largely of super-suppressive Tregs that inhibit host immune responses to the tumor by T effector cells. A number of lung and breast tumors and their infiltrating leukocytes have been shown to produce TNF. Preliminary studies show that inhibition of interaction of TNF-TNFR2 is associated with a notable decrease in tumor growth.It has recently become clear that a subset of T cells e.g. CD4+CD25+FoxP3+T regulatory (Treg) cells are essential in the maintenance of immune homeostasis and have feedback suppressive effects on immune responses. These Treg cells have been reported to suppress autoimmune responses and consequently, unfortunately, also protect tumors from immune rejection. Our observation suggested that the susceptibility to autoimmunity and cancer in genetically different mouse strains might be determined by the number and suppressive activity of Tregs. We previously showed that the immunosuppressive agent dexamethasone (DEX), which is used to treat autoimmune disease and the lymphoproliferative cytokine Interleukin-2, each upregulated the number of Treg cells in mice. Furthermore, when administered together they had even greater effects in promoting immunosuppressive Treg cell activities. When administered together prior to an antigen (MOG) that induces experimental autoimmune encephalomyelitis (EAE), IL-2 plus DEX reduced the incidence and severity of EAE in susceptible mice. Thus, upregulation of Tregs by cortisone-derivatives can counteract induction of autoimmune disease. Pertussis toxin (PTX) is coadministered as an adjuvant along with an appropriate autoantigen in Complete Freunds adjuvant (CFA) in order to induce EAE in susceptible mouse strains. This was associated with a decrease in the number of functional Treg cells and concomitant activation of TLR4 by PTX. We established that PTX also has the capacity to induce DC to produce high levels of IL-6. This leads, in conjunction with coproduced TGFbeta, to the activation of the TH17 pathway with copious production of IL-17, which has been implicated in promoting a variety of autoimmune diseases. Thus, we plan to investigate the effect of the rather unique multiplicity of adjuvant effects of PTX on overcoming tolerance to tumor by using it in therapeutic anticancer vaccines. In the current fiscal year my group showed that an immunosuppressive drug, Rapamycin, unlike cyclosporine A, also promotes the generation of functional Tregs, while inhibiting differentiation of Th17 cells. It is therefore a good therapy for autoimmune diseases, but may promote tumor growth. Finally, to our surprise our studies of the effects of various cytokines and alarmins on Tregs revealed that TNF also is a potent upregulator of Treg numbers and activity. Although TNF is a well known proinflammatory cytokine, which has initial activating effects on T efferent cells, later during in vitro and in vivo mouse immune responses especially as a costimulant with IL-2, TNF induces the proliferative expansion of functional Treg cells that preferentially express the TNFR2 receptor. Neither IL-1 nor IL-6 had such biphasic effects. Thus, TNF appears to induce a unique delayed down-regulatory effect on immune responses. This is absent in TNFR2 knockout mice and may account for their less severe (lethal) sepsis (LPS) induced inflammatory reactions. We have further investigated the role of TNFR2 on Tregs and the possibility that tumors by producing TNF may be promoting the increase in Tregs infiltrating tumors with consequent down- regulation of tumor immune responses. We have found that TNFR2+ Tregs (CD4+CD25+FOXP3+) are much more suppressive than TNFR2-Tregs. Tumor infiltrating T cells consist largely of super-suppressive Tregs that inhibit host immune responses to the tumor by T effector cells. A number of lung and breast tumors and their infiltrating leukocytes have been shown to produce TNF. Prel [summary truncated at 7800 characters]