Targeting of IL-2 receptor with a caspase fusion protein disrupts autoimmunity in prediabetic and diabetic NOD mice

Aims/hypothesis Interruption of IL-2 signalling is an attractive therapeutic target in autoimmune disorders. In this study we evaluated the effect of a fusion protein composed of IL-2 and caspase-3 (IL2-cas) on NOD mice, as compared with disease induction by cyclophosphamide. Methods IL2-cas was assessed in NOD mice at various ages and in conjunction with cyclophosphamide administration. The effect of IL2-cas on diabetogenic cells was evaluated in adoptive transfer experiments and in cell suspension in vitro. Results IL2-cas induced apoptosis in T cells expressing the α chain of the IL-2 receptor (cluster of differentiation [CD]25) in vitro, with superior survival of T cells expressing CD4 and forkhead box P3 (FOXP3). The fusion protein decreased mixed lymphocyte reactivity, and pretreatment with IL2-cas decreased the efficacy of adoptive transfer of diabetes into NOD severe combined immunodeficiency mice. Administration of one dose of IL2-cas decreased the incidence of diabetes in NOD mice, showing a superior beneficial effect when administered at young age, and effectively blocked induction of hyperglycaemia by cyclophosphamide, reducing the severity of islet inflammation. Administration of IL2-cas caused an acute increase in CD25⁻FOXP3⁺ T cells in the lymph nodes, pancreas and thymus in NOD mice, with similar effects in wild-type mice. Administration of IL2-cas after onset of hyperglycaemia resulted in superior survival. Conclusions/interpretation Targeted elimination of cells expressing the IL-2 receptor by this fusion protein disrupts the autoimmune pathogenesis in prediabetic and diabetic NOD mice, despite depletion of CD25⁺ regulatory T cells. Furthermore, this particular fusion protein is permissive to the development of FOXP3⁺ T cells that might contribute to protracted protection from the progression of insulitis and overt hyperglycaemia.