Endocrine Abstracts

Transfer of hematopoetic stem cells from mice transgenically overexpressing the islet autoantigen insulin could prevent type I diabetes in NOD mice. We tested if such an approach of tolerance induction could be employed by means of retroviral gene transfer of autoantigens into syngeneic hematopoetic stem cells (HSCs). We used glutamic acid decarboxylase 65 (GAD) as the autoantigen as T cell responses against GAD are more easily detected in NOD mice and as it has been previously difficult to establish tolerance against this antigen. We generated retroviruses expressing GAD modified for optimal presentation by antigen presenting cells followed by eGFP. Retroviruses expressing just eGFP served a control. We developed a protocol for efficient in vitro transduction of NOD-HSCs. Mice reconstituted with GAD transduced bone marrow exhibited a long-lasting, multi-lineage hematopoetic chimerism as shown by eGFP. Percentage of eGFP positivity of HSCs correlated with eGPF expression in thymic and in peripheral dendritic cells. Mice receiving eGFP transduced HSCs showed a strong T cell response against GAD and its peptide epitopes while animals getting GAD transduced HSCs were completely tolerant. Chimerism of just 5% with GAD transduced HSCs was still sufficient to induce complete GAD-specific tolerance. Recipients of secondary bone marrow transplants were also tolerant against GAD thereby proving that tolerance was due to transduction of HSCs rather than of committed progenitors. Despite complete tolerance against GAD mice still developed type I diabetes with unchanged kinetics and incidence as compared to mice receiving eGFP transduced HSCs, thereby proving that GAD65 is not an essential autoantigen in the NOD mouse. We prove for the first time that retroviral transduction of HSCs with autoantigens can lead to complete T cell tolerance. Similar approaches with other autoantigens could have a huge potential in the therapy of type I diabetes. Meanwhile the model will be suitable for testing the importance of potential antigens without the need of creating transgenic animals.