Bi-functional fusion proteins to regulate autoimmunity

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Current therapies are for autoimmune diseases are inadequate as they treat symptoms, not the underlying cause, and are often associated with severe sides effects, especially upon prolonged use. Regulatory T cells (Tregs) represent a major mechanism to actively suppress self-reactive T cells, which are present in all individuals. A breakdown in Tregs leads to activation of self-reactive T cells that contribute to the development of autoimmunity. Correspondingly, an attractive therapeutic approach is to re-regulate the immune system to boost the numbers and/or function of Tregs to limit autoreactive T cells. Extensive work from my lab has established that IL-2 is essential for Treg development and peripheral homeostasis. Furthermore, we showed that key IL-2R-dependent activities were readily supported by low IL-2R signaling in Treg but not T effector (Teff) cells. These findings provide mechanistic support for the notion to use low-dose recombinant IL-2 (rIL-2) as a Treg-selective therapy for autoimmunity. Recent clinical trials across several autoimmune diseases show that low-dose rIL-2 selectively boost Tregs that is often accompanied by clinical improvement. Nevertheless, rIL-2 has poor pharmacokinetics and pharmacodynamics that necessitate frequent administration. Furthermore, autoimmune-related symptoms were not completely resolved, and upon cessation of low-dose rIL-2, the autoimmune-attack usually resumed. New molecularly engineered IL-2-based biologics have been developed that have improved properties when compared to recombinant IL-2 (rIL-2). In this regard, we developed an IL-2-based protein, where IL-2 is linked to CD25. The IL-2/CD25 fusion protein shows selectively toward Tregs and is much more effective than rIL-2 in expanding Tregs and limiting diabetes in NOD mice. However, even with this improved IL-2-based biologic to deliver IL-2 activity, diabetes development was sometimes only delayed. Based on these findings, we have hypothesized that combination strategies will be necessary to enhance the efficacy of low-dose IL-2. One approach that we wish to investigate is to increase Tregs through IL-2 while enhancing immunosuppress by simultaneously applying an immune regulating activity. To accomplish this goal, we have developed a bifunctional fusion protein to deliver these two activities. Thus, the main objective of this proposal is to optimize and evaluate the activities of this fusion protein in vivo through the following specific aims. 1) To assess whether this bifunctional fusion protein is more effective than mIL-2/CD25 to limit autoimmunity in pre-clinical mouse models of colitis and diabetes. 2) To determine the cellular mechanism of action of this bifunctional fusion protein. These studies test the extent this novel fusion protein directly limits Teff cells and affects other immune cells in the tissue site(s) of autoimmune attack. 3) To evaluate the contribution of the bifunctional fusion protein on autoreactive T cells.