It has recently become clear that a subset of T cells e.g. T regulatory (Treg) cells have feedback suppressive effects on immune responses. These Treg cells have been reported to suppress autoimmune responses and consequently, unfortunately, also are reported to protect tumors from immune rejection. 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 and function 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 reactions. 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. During the current fiscal year 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. 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 in 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 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 more severe (lethal) septic (LPS) induced inflammatory reactions. We are further investigating the role of TNFR2 on Tregs and the possibility that tumors by producing TNF may be promoting the increase in infiltrating Tregs detected in tumors with consequent down regulation of tumor immune responses.
