Costimulation Blockade-Induced Cardiac Allografl Tolerance: Inhibition of T Cell Expansion and Accumulation of Intragraft cD4+Foxp3+ T Cells

Background. Previous studies have demonstrated that anti-CD40L or anti-B7 requires the presence of CD4+CD25+ regulatory T cells (Treg) to induce antigen specific hyporesponsiveness. Other tolerance strategies involving Treg have shown a dependency on interleukin (IL)-10. The objective of this study was to investigate the role of CD4+CD25+ Treg and IL-10 when treating transplant recipients with cytotoxic T lymphocyte-associated antigen (CTLA)-4 immunoglobulin (Ig), anti-CD40L, and anti-lymphocyte function-associated antigen (LFA)-1. Methods. Recombinase activating gene-deficient (Rag1-/-) mice were transplanted with BALB/c hearts and adoptively transferred with IL-10-/- CD4+ T cells, CD4+CD25- T cells or CD4+CD25-CD103- T cells and treated with costimulation blockade. Intragraft T cells from C57BL/6 recipients were analyzed for the expression of the Foxp3 protein after tolerance induction. Results. Mice reconstituted with IL-10-/- CD4+ T cells, CD4+CD25- T cells or CD4+CD25- CD103- T cells and treated with costimulation blockade accepted allografts permanently. Analysis of cells from recipient mice adoptively transferred with CD4+CD25- T cells contained a population of CD4lowCD25+ T cells 100 days after transplantation. Costimulation blockade partially prevented the homeostatic proliferation of CD4+CD25-CD103- T cells in Rag-1-/- recipients. Accepted allografts contained an elevated number of CD4+Foxp3+ T cells. Conclusions. These results indicate that T-cell derived IL-10 is not essential for induction of graft acceptance in mice treated with costimulation blockade, but that treatment limits T-cell expansion in the recipients. The results further indicate that tolerance is maintained by intragraft CD4+Foxp3+ T cells.