Exploiting T cell co-inhibition to delay autoimmune disease recurrence

Abstract

Abstract Type 1 diabetes (T1D) results from T cell-mediated destruction of insulin-producing pancreatic β cells. Individuals with long-term disease are at risk of developing life-threatening complications. β cell replacement is a therapy for T1D but is limited by recurrent autoreactive T cell targeted β cell death. Thus, β cells better equipped to inhibit local T cell responses may survive longer in autoimmune recipients. Programmed-death 1 (PD-1) signaling through its ligand PD-L1 inhibits T cells, and may serve as a prominent defense in T1D. Using flow cytometric analysis, in the absence of T cells in NOD.RAG−/− mice we do not detect β cell PD-L1 expression. However, with T cells, we observed an increased proportion of β cells expressing PD-L1 in female non-obese diabetic (NOD) mice which had not developed diabetes. In addition, the majority of remaining live β cells at diabetes onset in NOD mice continue to express high levels of PD-L1. These three situations suggest that islet β cells may increase PD-L1 expression as a last line of defense to limit infiltrating T cell mediated destruction. To manipulate β cell PD-L1 expression prior to transplantation, we screened a panel of diabetes-related cytokines and found that IFN-γ enhances β cell PD-L1 expression. Unfortunately, islet transplant survival was not prolonged, which we hypothesized was due to enhanced MHC class I expression, facilitating CD8+ T cell-mediated killing. We therefore de-coupled PD-L1 from enhanced MHC I expression. Using this approach, enforced β cell PD-L1 expression delays disease recurrence. These data support our hypothesis that β cells expressing T cell co-inhibitory molecules, like PD-L1, can locally inhibit autoreactive T cells which may prevent transplant destruction.