An islet-homing NOD CD8 + cytotoxic T cell clone recognizes GAD 65 and causes insulitis Nicoline Videbæk a,b , Silvia Harach b , Jenny Phillips b , Patricia Hutchings b , Patricia Ozegbe b , Birgitte K. Michelsen a , Anne Cooke b,* a Hagedorn Research Institute, Niels Steensensvej 6, DK 2820, Gentofte, Denmark b Department of Pathology, University of Cambridge, Cambridge, UK Abstract T cells play a central role in the development of diabetes both in man and in the non-obese diabetic (NOD) mouse. Both the CD4 + and CD8 + subsets of T cells are required for the normal development of IDDM in NOD mice. Islet reactive CD4 + T cells play a clear pathogenic role as evidenced from the isolation of diabetogenic CD4 + T cell clones. CD8 + T cells seem to be involved in the initiation of diabetes as lack of these cells leads to protection from diabetes. We have isolated a GAD 65 reactive, cytotoxic CD8 + T cell clone R1 that produces large quantities of IFN and accelerates the onset of insulitis. This clone proliferates and produces IFN in response to GAD 65 presenting APCs and kills GAD 65 presenting targets. Furthermore, it expresses TNF, CD25, CD28, CD44, CD45 and LFA1, but not CD95L This is the first example of a GAD 65 specific CD8 + T cell clone that accelerates the onset of the insulitis, although it does not appear to accelerate the onset of diabetes.  2003 Elsevier Science Ltd. All rights reserved. Keywords: Diabetes; T cells; Insulitis 1. Introduction T cells play a central role in the development of diabetes both in man and in the non-obese diabetic (NOD) mouse. Most experimental observations support the view that CD4 + as well as CD8 + T cells are required for the normal development of IDDM in NOD mice [1–4]. Both subsets of T cells have been shown to be necessary for the transfer of diabetes from diabetic donors to non-diabetic recipient mice [5–7]. However, the relative role of these two subsets in the development of diabetes remains unclear. Transfer studies as well as transgenic studies have shown that both subsets of islet reactive T cells can be diabetogenic on their own as well as require the help of each other [8–12]. Several lines of evidence indicate the requirement for CD8 + T cells at all stages of the diabetogenic process. One of these establishes the role of CD8 + T cells as the final effector cells in the destruction of the pancreatic  cells [13,14]. However, evidence is accumulating for an earlier role of CD8 + T cells. Thus, NOD-b 2 m null mice which cannot express MHC class I and thereby are unable to develop CD8 + T cells, do not develop either insulitis or diabetes [15–18]. Fur- thermore, administration of CD8 mAb at an early age prevents insulitis in NOD mice [19], and a CD8 + T cell clone generated from acutely diabetic NOD mouse islets can only transfer diabetes to young NOD mice less than 10 days old [20]. -cell cytotoxic CD8 + T cells have been isolated from the insulitic lesions of NOD mice [21]. Interestingly, CD8 + T cells isolated from prediabetic NOD mice predominantly recognise K d binding motifs, and cells from young prediabetic NOD donors can transfer IDDM to recipients having MHC class I-positive, but not class I-negative pancreatic  cells [4,22]. Thus, there is good evidence to support the view that CD8 + T cells indeed play a part in initiating insulin-dependent diabetes mellitus. * Corresponding author. Tel.: +44-1223-333907; fax: +44-1223- 333914. E-mail address: ac@mole.bio.cam.ac.uk (A. Cooke). Journal of Autoimmunity 20 (2003) 97–109 www.elsevier.com/locate/issn/08968411 0896-8411/03/$ - see front matter  2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0896-8411(03)00003-9