Induction and Maintenance of Transplantation Tolerance by Treatment with a Donor Specific Transfusion and Anti-CD154 mAb: a Dissertation

Abstract

A two-element protocol consisting of one donor-specific transfusion (DST) plus a brief course of anti-CD154 mAb greatly prolongs the survival of murine islet, skin, and cardiac allografts. To study the mechanisms involved in the induction of allograft survival, we determined the fate of tracer populations of alloreactive T cell receptor (TcR) transgenic CD8+ T cells circulating in a normal microenvironment. In the first portion of this thesis, we observed that DST plus anti-CD154 mAb prolonged allograft survival and deleted alloreactive TcR transgenic CD8+ T cells. Neither component alone did so. Skin allograft survival was also prolonged in normal recipients treated with anti-CD154 mAb plus a depleting anti-CD8 mAb and in C57BL/6-CD8 knockout mice treated with anti-CD154 mAb monotherapy. We conclude that, in the presence of anti-CD154 mAb, DST leads to an allotolerant state in part by deleting alloreactive CD8+ T cells. Consistent with this conclusion, blockade of CTLA4 and B7-l/2 by CTLA4-Ig, which is known to abrogate the effects of DST and anti-CD154 mAb, prevented the deletion of alloreactive TcR transgenic CD8+ T cells. Also in support of our hypothesis, depletion of CD4+ T cells, which is known to abrogate the effects of DST and anti-CD154 mAb, prevented the deletion of alloreactive TcR transgenic CD8+ T cells. We continued by examining the effects of IFN-γ, IL-10 and IL-4. None of these cytokines had any significant effect on the deletion of alloreactive TcR transgenic CD8+ T cells induced by co-stimulation blockade. The last part of this thesis studied the behavior of alloreactive TcR transgenic CD8+ T cells during the maintenance phase of allograft survival induced by our two-element protocol. Using a hematopoietic TcR transgenic chimera system, our results demonstrated that levels of alloreactive CD8+ T cells remained low throughout the maintenance phase. These results document for the first time that peripheral deletion of alloantigen-specific CD8+ T cells is an important mechanism through which allograft survival can be prolonged by co-stimulatory blockade. We propose a unifying mechanism to explain allograft prolongation by DST and blockade by co-stimulation blockade.