A role for th2 cytokines in the suppression of CD8⁺ T cell-mediated graft rejection

A major histocompatibility complex (MHC) class I-specific T cell receptor (TCR)-transgenic mouse was used to study classical-type transplantation tolerance in the adult. Engraftment of MHC class I-incompatible bone marrow and tolerance to donor-type skin grafts were obtained using dimethylmyeleran (DMM) as a myeloabiative agent and a non-depleting anti-CD8 monoclonal antibody (mAb) as the sole immunosuppressant. Surprisingly, bone marrow engraftment was facilitated by host CD4⁺ T cells, a subset normally considered unable to reject class I MHC-incompatible grafts. A combination of mAb to interleukins (IL)-4 and -10 antagonized the 'permissive' effects of host CD4⁺ T cells, indicating a possible role for Th2-type immunoregulation that can act on CD8⁺ T cells in this form of transplantation tolerance. The fate of graft-reactive T cells was monitored using anti-clonotypic antibodies. It was observed that bone marrow engraftment then led to peripheral deletion of mAb-blockaded, clonotype⁺ CD8⁺ T cells.