OBJECTIVE: Exposure of beta-cells to inflammatory cytokines leads to apoptotic cell death through the activation of gene networks under the control of specific transcription factors, such as interferon-gamma-induced signal transducer and activator of transcription (STAT)-1. We previously demonstrated that beta-cells lacking STAT-1 are resistant to cytokine-induced cell death in vitro. The aim of this study was to investigate the effect of STAT-1 elimination on immune-mediated beta-cell destruction in vivo. RESEARCH DESIGN AND METHODS: Multiple low-dose streptozotocin (STZ) was given to C57BL/6 mice after syngeneic STAT-1(-/-) or wild-type islet transplantation. STAT-1(-/-) and wild-type islets were also transplanted in alloxan-diabetic BALB/c and spontaneously diabetic nonobese diabetic (NOD) mice. Additionally, mice were treated with interleukin (IL)-1 blockade (IL-1 receptor antagonist [IL-1ra]) and low-dose T-cell suppression (cyclosporine A [CsA]). RESULTS: When exposed to multiple low-dose STZ in an immune-competent host, STAT-1(-/-) islets were more resistant to destruction than wild-type islets (28 vs. 100% diabetes incidence, P < or = 0.05). STAT-1 deletion also protected allogeneic islet grafts against primary nonfunction in autoimmune NOD mice (0 vs. 17% using wild-type islets). However, no difference in survival time was observed. Additionally, treating recipients with IL-1ra and CsA prolonged graft survival in chemically diabetic BALB/c mice, whereas no difference was seen between STAT-1(-/-) and C57BL/6 grafts. CONCLUSIONS: These data indicate that STAT-1 is a key player in immune-mediated early beta-cell dysfunction and death. When considering the many effector mechanisms contributing to beta-cell death following islet transplantation, multiple combined interventions will be needed for prolongation of beta-cell survival in the autoimmune context of type 1 diabetes.