Abstract 3340: Baboon CD4+ CD25+ T Regulatory Cells Inhibit Anti Porcine Xenogeneic Response
Background: Current strategies to prolong pig to primate cardiac xenograft survival requires heavy immunosuppression that leads to lethal infections and recipient mortality before the transplanted heart is rejected. There is therefore a strong need to create strategies to develop sub lethal ways to prolong graft survival. CD4+CD25+ T regulatory cells (T regs) have been shown to possess a unique potential to induce donor specific unresponsiveness in allografts. In the following study we explored the potential of baboon T regs in suppressing anti pig xenogeneic responses.
Methods: Freshly harvested splenocytes, lymph node cells and peripheral blood lymphocytes were sorted into CD4+CD25− and CD4+CD25+ populations by FACS. Proliferation/suppression assays were set up using irradiated pig PBMC as stimulators and the following groups as responders: A) Purified CD4+CD25− baboon T cells, B) Purified CD4+CD25+ baboon T cells and C) Purified CD4+CD25− plus CD4+CD25+ T cells in 1:1 or 2:1 ratio. The suppression of baboon T cell proliferation in response to pig antigen was compared to prior experiments using human T cells as responders. As the number of Tregs in a sort is usually very low, we also tried to determine whether baboon Tregs can be expanded in vitro.
Results: The purity of enriched CD4+ T cells was >94%, out of which approximately 1.5% CD4+ T cells were also CD25+. A robust proliferative response was observed in group A. Cells in group B were hypo-responsive to porcine antigens. A significant inhibition of response (85% reduction) as compared to group A was observed in group C. This pattern of inhibition was analogous to that reported for human Treg-mediated suppression of the human anti-pig response. Over a 500% expansion of sorted Tregs was observed after stimulation with a high amount of IL-2 and irradiated pig PBMC.
Conclusion: We have demonstrated that baboon Tregs can efficiently suppress in vitro anti pig xenogenic T cell responses and they can be expanded in vitro. Therefore, Treg-based immunotherapy may be an avenue to prevent rejection and induce tolerance in pig to baboon xenotransplantation. The use of Treg-based immunotherapy also has potential to replace or decrease the use of lethal immunosuppression currently required for the long term xenograft survival.