T CELL DIVERSITY AND FUNCTIONAL BIOLOGY

K. Lee¹, G. Miao¹, V. Nguyen¹, H. Scholz², T.V. Brennan¹, S. Kang¹, Q. Tang^1
1Surgery, University of California, San Francisco, San Francisco/UNITED STATES OF AMERICA, ²Institute For Surgical Research, Oslo University Hospital, Oslo/NORWAY

Body: Introduction: Islet transplantation is a minimally invasive strategy to restore normal glucose homeostasis in patients with chronic type 1 diabetes. However, islet transplantation requires non-specific immunosuppression, which is not reliably effective in controlling both alloimmune and recurrent autoimmune destruction of the grafts and can cause significant morbidity to the recipient. These are further compounded by the exquisite sensitivities of isolated islets to the toxicities of commonly used immunosuppressive drugs. Alternative approaches to immunosuppression or tolerance induction will therefore be critical to advancing this field. Regulatory T cells (Tregs) are the immune system’s main mechanism for self-tolerance. Adoptive transfer of Tregs can prevent and reverse autoimmune diabetes in mouse models. In the transplant setting, however, the exceptionally vigorous anti-graft immune response cannot be controlled by Treg cell therapy alone. We hypothesize that efficient and selective reduction of alloreactive T cells may create a therapeutic window for Tregs to induce islet allograft tolerance without additional immunosuppression. Method and results: To selectively delete alloreactive T cells, C57BL/6 mice were injected with 20x10⁶ BALB/c splenocytes (donor-specific transfusion; DST) followed by cyclophosphamide (Cy) treatment 48 hours later. To determine the efficacy of deleting BALB/c-specific T cells, traceable CD4 T cells that directly recognize BALB/c alloantigen expressed on BALB/c cells (from 4C TCR transgenic mice) and those that indirectly recognize processed BALB/c antigen presented by B6 antigen presenting cells (from TEa TCR transgenic mice) were injected one day before DST treatment. This preconditioning regimen reduced direct 4C T cells by 91% and indirect TEa T cells by 97%. Analyses of frequencies of endogenous BALB/c-reactive T cells revealed greater than 80% deletion using the DST + Cy protocol. Despite the high efficacy in deleting donor-specific T cells, this treatment was only able to prolong allogeneic islet grafts by two weeks (Figure 1). Additional infusion of BALB/c antigen-specific Tregs isolated from 4C mice and expanded in vitro led to long-term acceptance of BALB/c islet grafts in 83% of the C57BL/6 recipients (Figure 1). Tolerance induced with this regimen was donor-specific because third-party islets from C3H donors were rejected without delay. Similar protective results were observed in C3H to NOD strain combination when the NOD recipients were treated with C3H DST + Cy and islet antigen-specific Tregs isolated and expanded from BDC2.5 TCR transgenic mice. Conclusion: Combining Treg cell therapy with donor-specific T cell reduction can be an effective approach to induce long-term fully mismatched islet allograft acceptance without additional immunosuppression. These results demonstrate a new concept and a clinically applicable approach to induce allograft tolerance.

Disclosure: All authors have declared no conflicts of interest.