A ROLE OF CD8+ T-CELLS IN THE INDUCTION OF ALLOGRAFT TOLERANCE BY DONOR-SPECIFIC BLOOD TRANSFUSION

Abstract

501 Tolerance to heart allografts in adult rats can be induced by donor-specific blood transfusion (DST). Using recombinant Lewis rat strains which share similar genetic background except for their class I and class II MHC molecules, we have previously shown in this LEW.1W-to-LEW.1A heart allograft model, that a dominant CD8+ T-cell clone with a Vβ18-Dβ1-Jβ2.7 TCR-β chain rearrangement was infiltrating the tolerated grafts. This clone, specific for the MHC RT1u haplotype, is induced during the transfusion time course and infiltrates the tolerated grafts as early as day one. In order to assess for a functional role of this clone, we have treated the recipients with the OX8 monoclonal antibody (anti-CD8α) to deplete the CD8+ population. Recipients recieved 1 ml of OX8 supernatant either at day -3 and -1 before transplantation or at day -16, -9, -3 and -1 combined with DST at day -14 an-7 before grafting. As analysed by FACs analysis, no CD8+ cells were circulating in the blood of recipients on the day of the transfusion or transplantation. Results and conclusions: CD8-depleted recipients (n=7) rejected their grafts with a similar kinetic as for untreated recipients(n=10). OX8-DST-treated recipients rejected their grafts (n=5) whereas all controls 3G8-DST-treated recipients (n=4) accepted them indefinitely (more than 100 days). Interestingly, when OX8 treatment was performedafter the first transfusion (DST -14 and -7, OX8 -3 and -1) only 2 of 6 animals rejected. When Vβ repertoire was analysed within these grafts, we still detected the Vβ18-Dβ1-Jβ2.7 clone as strongly as in non-depleted DST-treated recipients. Our results suggest a role for the CD8+ T-cells in the induction of heart allograft tolerance in this model. Moreover we hypothesize that CD8+ T-cells activated by the transfusion (such as the Vβ18-Dβ1-Jβ2.7 clone) are more resistant to the lysis mediated through the OX8 monoclonal antibody, maybe by downregulating their co-receptor as it has been shown for the CD4+ activated T-cells. We are currently assessing whether an adoptive transfer of purified CD8+ cells from a DST-treated rat can induce tolerance in an irradiated untransfused recipient.