The requirement of intrathymic mixed chimerism and clonal deletion for a long‐lasting skin allograft tolerance in cyclophosphamide‐induced tolerance

Abstract

Mechanisms of cyclophosphamide (CY)-induced tolerance were studied. When C3H/He Slc (C3H; H-2k, Mls-1b) mice were primed i.v. with 1 x 10(8) viable spleen cells from H-2-identical AKR/J Sea (AKR; H-2k, Mls-1a) mice and treated with 200 mg/kg of CY 2 days later, a long-lasting skin allograft tolerance to AKR was established. When [C57BL/6 Sea (B6; H-2b, Mls-1b) x AKR]F1 (B6AKF1) cells were used as the tolerogen, however, only a moderate, but not long-lasting, skin tolerance to AKR was observed. In the C3H mice treated with AKR cells and CY, the intrathymic clonal deletion of V beta 6+ T cells, which are strongly correlated with reactivity to Mls-1a antigens, was observed in the chimeric thymus on day 35, although neither the clonal deletion of V beta 6-bearing T cells nor the mixed chimerism was observed in the thymus on day 14. In the C3H mice treated with B6AFKF1 cells followed by CY, however, neither the clonal deletion of V beta 6+ T cells nor the mixed chimerism was observed in the thymus throughout the test period. In the lymph nodes of the C3H mice treated with AKR cells and CY, only CD4+ V beta 6+ T cells, bur not CD8+V beta 6+ T cells, had selectively decreased by day 14, and they were hardly detectable on day 35. The selective decrease of CD4+V beta 6+ T cells in the lymph nodes was also observed by day 14 when B6AKF1 cells were used as the tolerogen, although CD4+V beta 6+ T cells gradually increased on day 35, at which time almost all skin grafts from AKR had already been rejected. These results strongly support the necessity of the intrathymic mixed chimerism and clonal deletion of donor-reactive T cells for a long-lasting skin allograft tolerance in CY-induced tolerance.

Promotion of Pancreatic Islet Allograft Survival By Intrathymic Transplantation of Bone Marrow

“…Consequently, the residence of islets in the thymic microenvironment may not measurably affect class 11-restricted in vitro responses. In several models of specific unresponsiveness achieved by allogeneic BMC transplantation, tolerance correlates with the presence of microchimerism in the thymus and peripheral lymphoid organs of the recipients (17)(18)(19). To determine whether a similar chimeric state had developed in our model, the lymphoid organs of WF rats that had received intrathymic Lewis BMC (without subsequent islet grafts) were examined at various times after inoculation by immunohistochemistry with a murine monoclonal antibody (1-1.69) specific for Lewis class I alloantigens (8).…”

Donor CD4+ Foxp3+ regulatory T cells are necessary for posttransplantation cyclophosphamide-mediated protection against GVHD in mice

“…Based on murine data in skin allografting models, 24 the dominant mechanism by which PTCy has been thought to mediate tolerance induction is through clonal deletion of alloreactive T cells stimulated early post-transplant. Indeed, when we utilized a widely used CD8 1 T cell-dependent GVHD model (C3H.SW→B6) 25,26 in which PTCy (200 mg/kg IP) was administered on day 13 post-alloBMT.…”

Neonatally tolerant rats actively eliminate donor‐specific lymphocytes despite persistent chimerism

“…We would argue that penetrating the N K cell system holds the key to organ transplant survival. Increasing evidence indicates that the presence of alloantigen is instrumental in maintaining tolerance and in preventing allograft rejection [35,44,[56][57][58][59]. If donor BM, given at the time of organ transplantation [60], can be made to survive by tolerizing the NK cell system, a practical means is provided to induce and maintain both central and peripheral T cell tolerance.…”