CD4⁺CD25^highFOXP3⁺ regulatory T cells (Tregs) are involved in graft‐specific tolerance after solid organ transplantation. However, adoptive transfer of polyspecific Tregs alone is insufficient to prevent graft rejection even in rodent models, indicating that graft‐specific Tregs are required. We developed a highly specific chimeric antigen receptor that recognizes the HLA molecule A*02 (referred to as A2‐CAR). Transduction into natural regulatory T cells (nTregs) changes the specificity of the nTregs without alteration of their regulatory phenotype and epigenetic stability. Activation of nTregs via the A2‐CAR induced proliferation and enhanced the suppressor function of modified nTregs. Compared with nTregs, A2‐CAR Tregs exhibited superior control of strong allospecific immune responses in vitro and in humanized mouse models. A2‐CAR Tregs completely prevented rejection of allogeneic target cells and tissues in immune reconstituted humanized mice in the absence of any immunosuppression. Therefore, these modified cells have great potential for incorporation into clinical trials of Treg‐supported weaning after allogeneic transplantation.

Adoptive immunotherapy with ex vivo expanded, polyspecific regulatory T cells (Tregs) is a promising treatment for graft-versus-host disease. Animal transplantation models used by us and others have demonstrated that the adoptive transfer of allospecific Tregs offers greater protection from graft rejection than that of polyclonal Tregs. This finding is in contrast to those of autoimmune models, where adoptive transfer of polyspecific Tregs had very limited effects, while antigen-specific Tregs were promising. However, antigen-specific Tregs in autoimmunity cannot be isolated in sufficient numbers. Chimeric antigen receptors (CARs) can modify T cells and redirect their specificity toward needed antigens and are currently clinically used in leukemia patients. A major benefit of CAR technology is its "off-the-shelf" usability in a translational setting in contrast to major histocompatibility complex (MHC)-restricted T cell receptors. We used CAR technology to redirect T cell specificity toward insulin and redirect T effector cells (Teffs) to Tregs by Foxp3 transduction. Our data demonstrate that our converted, insulin-specific CAR Tregs (cTregs) were functional stable, suppressive and long-lived in vivo. This is a proof of concept for both redirection of T cell specificity and conversion of Teffs to cTregs.

Background and aims: Inappropriate immune responses contribute to the continuous stimulation of the intestinal immune system in chronic inflammatory bowel disease (IBD). Among several pathogenic factors, a numerical deficiency of regulatory T (Treg) cells has been suggested to lead to an insufficient compensation of chronically activated T lymphocytes. This study was conducted to investigate whether increased apoptosis contributes to Treg cell deficiency in IBD and whether successful treatment with antitumour necrosis factor α (TNFα) is achieved by reducing of Treg cell apoptosis. Methods: Apoptosis of CD4⁺Foxp3⁺ Treg cells in tissue sections of patients with active IBD was analysed by immunohistochemistry and TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labelling) staining. Apoptosis of peripheral blood CD4⁺CD25⁺Foxp3⁺ Treg cells was investigated by flow cytometry and annexin-V staining. In addition, caspase activity and apoptosis were measured in sera of patients with IBD treated with anti-TNFα by a luminometric caspase enzyme assay. Results: It is demonstrated that patients with active IBD revealed increased apoptosis of local CD4⁺Foxp3⁺ Treg cells in the inflamed mucosa compared with non-inflamed control colon tissue. Moreover, in peripheral blood a reduced frequency and increased apoptosis of Treg cells were found and accompanied by elevated caspase activity in the serum. During anti-TNFα treatment, Treg cell apoptosis declined in close correlation with elevated peripheral Treg cell numbers and a decrease of caspase activation and disease activity. Conclusions: These data suggest that increased apoptosis of Treg cells plays a potentially important role in the pathogenesis of IBD and can be reversed by anti-TNFα treatment. Measurement of Treg cell apoptosis and serum caspase activity might therefore represent promising tools for monitoring disease activity and treatment response in patients with IBD.

Autoimmune hepatitis (AIH) is defined as a chronic liver disease with loss of tolerance against liver tissue eventually leading to cirrhosis if left untreated. 80%-90% of patients can be treated with a life-long immunosuppression. Unfortunately, there are strong drug-related side effects and steroid-refractory patients. Therefore, there is a need for a model system to investigate the complex immunopathogenesis of this chronic disease and subsequently to develop new therapeutic interventions. We developed a new model of experimental murine AIH (emAIH) by a self-limited adenoviral infection with the hepatic autoantigen formiminotransferase cyclodeaminase (FTCD). After an initial transient hepatitis there was a chronic evolving AIH, finally leading to portal and lobular fibrosis. We could show that the genetic predisposition provided by the NOD background was essential for creating a fertile field for the development of liver-specific autoimmunity. However, a strong environmental trigger was additionally necessary to initiate the disease. Besides the break of humoral tolerance, T-cell tolerance against hepatic self-antigens was also broken and CD4+ T cells were identified as essential drivers of the disease. As the disease was successfully treated with prednisolone and budesonide, the model will be helpful to develop and test new therapeutic interventions. Conclusion : We developed a new murine AIH model closely resembling AIH in patients that explains the mechanisms of AIH pathophysiology. In addition, emAIH provides options to test therapeutic alternatives for patients not achieving remission, with reduced side effects of chronic nonspecific immunosuppression. (Hepatology 2013;58:718–728)