NKG2D blockade facilitates diabetes prevention by antigen-specific Tregs in a virus-induced model of diabetes

It is thought that viral infections might jeopardize regulatory T cell therapy in type 1 diabetes. Viral infections can lead to surface expression of ligands for the activating NKG2D receptor, such as retinoic acid early transcript 1 (Rae-1), whose expression on beta-cells recruits NKG2D(+) autoreactive CD8(+) T cells. Both in men and mice, autoreactive cytotoxic T cells express NKG2D. We showed that NKG2D expression increased on CD4(+) and CD8(+) T cells during virus-induced diabetes development in the rat insulin promotor (RIP) Lymphocytic Choriomeningitis Virus (LCMV) model. Combination treatment with anti-NKG2D and antigen-specific regulatory T cells (Treg), at doses inefficacious in mono-treatment, synergized to prevent diabetes in 75% of the virus-infected RIP-LCMV mice. Nevertheless, NKG2D blockade alone failed to reverse recent-onset diabetes in non-obese diabetic (NOD) mice, despite downregulation of NKG2D on NK cells in the blood and CD8(+) T cells in the spleen and pancreatic lymph nodes. Our data suggest that blocking the interaction of NKG2D with it ligands is insufficient to protect against diabetes when a strong inflammatory process actively drives NKG2D upregulation, but should be considered to help maintaining Treg functionality during ongoing pancreatic inflammation. (C) 2012 Elsevier Ltd. All rights reserved.