Induction of Allograft Nonresponsiveness After Intrathymic Inoculation With Donor Class I Allopeptides

Abstract

We have recently demonstrated that cardiac allograft rejection in the PVG.R8-to-PVG.1U rat strain combination involves the recognition of a isolated class I (RT1.Aa) molecules as peptides in the context of the recipient MHC molecules. Three synthetic peptides (P1, P2, and P3) corresponding to the alpha-helices of the RT1.Aa molecule served as T-cell epitopes for graft rejection. In this study, we demonstrate that two of these peptides (P2 and P3) are sufficient to induce immune nonresponsiveness (median survival time >237 days) to cardiac allografts when presented to the recipient immune system in the thymus 7 days before transplantation. This effect was time dependent, as intrathymic inoculation 60 days before transplantation did not prolong graft survival (median survival time=12 days). Previous studies have demonstrated a critical role for alloantibody responses in mediating graft rejection in this rat strain combination. We, therefore, studied the role alloantibody responses may play in the observed immune nonresponsiveness. The titers of alloantibody in serum samples harvested from graft recipients at different times after transplantation were measured. We used recipient primary aortic endothelial cells genetically manipulated to express the donor RT1.Aa molecule as targets in an enzyme-linked immunosorbent assay. High titers of anti-RT1.Aa IgM antibody were detected in unmanipulated controls at the time of graft rejection. The IgM antibody switched to high IgG titers in intrathymically inoculated rats with accelerated or delayed rejection. Graft rejection in intrathymically manipulated recipients that had achieved a transient state of immunological nonresponsiveness correlated with higher titers of the IgG2b alloantibody. In marked contrast, the long-term graft survivors expressed undetectable or low levels of the IgG2b antibody and moderate to high levels of the IgG1 and IgG2a subclasses. These data suggest that the IgG2b alloantibody may contribute to the rejection reaction, whereas IgG1 and IgG2a may be involved in active enhancement of graft survival.

Prevention of Chronic Rejection with Immunoregulatory Cells Induced by Intrathymic Immune Modulation with Class I Allopeptides

“…Three synthetic RT1.A a peptides corresponding to the regions of disparity in the α1 and α2 domains of the donor and recipient molecules served as efficient CD4 + T‐cell epitopes during graft rejection. Intrathymic inoculation of these peptides under the cover of transient immunosuppression with antilymphocyte serum (ALS) resulted in immune hyporesponsiveness that led to prolonged graft survival (12,13). The state of immune hyporesponsiveness was donor‐specific, dose‐dependent, and effective only when peptides were presented intrathymically, but not systemically (12,14).…”

Induction of Transplant Tolerance with Immunodominant Allopeptide-pulsed Host Lymphoid and Myeloid Dendritic Cells

“…The immunologically privileged position of the thymus in central tolerance to self makes it a potential site for induction and maintenance of specific tolerance to alloantigens (Ag) since MHC-restricted T-cell recognition of foreign MHC Ag is not an inherent property of the developing T cells but is learned during T-cell maturation (5). Recent studies which show that the deliberate introduction of an alloMHC peptide into the adult thymus induces donor-specific tolerance to cardiac and islet allografts (6)(7)(8)(9)(10) suggest that thymic dendritic cells (DCs) play a pivotal role in acquisition of central tolerance by inducing deletion or functional inactivation of self-reactive immature T cells bearing TCR with high affinity for peptide/MHC molecules present on the surface of thymic DCs (4). We reasoned, therefore, that presentation of allopeptides by self DCs to developing T cells in the thymus might induce acquired thymic tolerance.…”

Advances in strategies for inducing central tolerance in organ allograft recipients

“…Subsequently, many studies in rodent models have shown that IT administration of donor alloantigen in various forms, such as spleen cells (28), or MHC allopeptides (29), can induce tolerance to organ allografts.…”