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

Abstract

Intrathymic immune modulation with RT1.A a allopeptides in the PVG.R8-to-PVG.1 U rat strain combination leads to long-term survival of cardiac allografts. This regimen, however, does not induce transplantation tolerance, since most long-surviving allografts undergo chronic rejection. We investigated recipients with chronic rejection for donor-specific immune nonresponsiveness and immunoregulatory cells as possible mechanisms responsible for long-term graft survival. There was a significant reduction in the proliferative response of T cells from long-term allograft recipients to donor alloantigens as compared with that of naïve T cells. Adoptive transfer of splenocytes from intrathymically manipulated primary long-term graft survivors into minimally irradiated secondary hosts resulted in indefinite survival of > 80% of allografts, providing evidence for immunoregulatory cells. Secondary recipients had total absence of donor-reactive cellular and humoral responses. Immunoregulation was also transferable from secondary to tertiary graft recipients. More importantly, there was a significant reduction in the incidence of chronic rejection in secondary hosts (> 85%) and complete prevention of acute and chronic rejection in tertiary hosts. This study demonstrates that intrathymic immunomodulation with class I allopeptides results in the generation of immunoregulatory cells that do not block chronic rejection in primary hosts where they develop, but prevent both acute and chronic allograft rejection when adoptively transferred into secondary and tertiary recipients.

Tolerance to Rat Heart Grafts Induced by Intrathymic Immunomodulation Is Mediated by Indirect Recognition Primed CD4+CD25+ Treg Cells

“…These range from clonal deletion/anergy to active suppression, depending on the type of graft and rat/mouse strain combinations used (3,4). A limited number of studies, including a recent report by our laboratory, have implicated immunoregulatory cells as the key component of tolerance mechanisms in this model (5)(6)(7). The phenotype of these cells and their mechanisms of action, however, remain to be elucidated.…”

“…Intra-abdominal heterotopic cardiac grafting of PVG.R8 hearts into PVG.1U recipients was performed 7 days after intrathymic injection as previously described (5). Rats intrathymically injected with PBS and syngeneic PVG.1U heart grafts were used as controls.…”

“…Tolerance can further be transferred from secondary to tertiary graft recipients in a similar manner. Although, in our model, the existence and effects of these regulatory cells were clearly demonstrated, a detailed characterization has not been performed (5).…”

“…We have previously shown that intrathymic inoculation of donor allopeptides or splenocytes combined with a transient immunosuppressive treatment resulted in the prevention of cardiac allograft rejection in a PVG.R8-to-PVG.1U rat model (5,17). This model is unique in that it involves a single MHC class I molecule, RT1.A a , which can only be presented to the recipient CD4 ϩ T cells via indirect recognition in the context of class II MHC molecules.…”

“…This model is unique in that it involves a single MHC class I molecule, RT1.A a , which can only be presented to the recipient CD4 ϩ T cells via indirect recognition in the context of class II MHC molecules. Furthermore, although intrathymic immunomodulation with donor antigens is effective in preventing acute rejection, it fails to abrogate chronic rejection (5). Animals with chronic rejection express high levels of Th2 cytokines and contain a regulatory cell population that is capable of inducing tolerance, as demonstrated by the lack of both acute and chronic rejection, in secondary naïve graft recipients following adoptive transfer.…”