Comparison of tolerance inducibility to class I or class II antigens between cyclophosphamide (CP)-induced tolerance and transfusion with donor cells: general effectiveness of CP-induced tolerance and difference of skin graft prolongation in each class I antigen-disparate combination

Induction of mixed allogeneic chimerism for leukemia

Hybrid (C56BL/6 x DBA) (BDF1; H-2b/H-2d) mice bearing the P815 leukemia (H-2d) were grafted with a (CBA x C57BL/6)F1 (CBF1; H-2k/H-2b) cell suspension, comprising bone marrow cells (BMC; 25 x 10(6)/mouse) and spleen cells (SC; 55 x 10(6)/mouse) on day-4, then treated with cyclophosphamide (200 mg/kg) on day-2 and finally grafted once more with CBF1 cells (25 x 10(6) BMC + 7 x 10(6) SC) on day 0. Allogeneic cell graftings performed in this way induced durable mixed hematopoietic chimerism and significantly prolonged the survival of recipients, compared with that of leukemia-bearers grafted with syngeneic cells. The results obtained raise the possibility of using allogeneic hematopoietic tissue transplantation in combination with non-lethal cytoreductive therapy to induce a long-lasting graft-vs-leukemia effect.

Permanent and specific transplantation tolerance induced by a nonmyeloablative treatment to a wide variety of allogeneic tissues: I. Induction of tolerance by a short course of total lymphoid irradiation and selective elimination of the donor-specific host lymphocytes

The long-term success of organ transplantation is limited by complications resulting from consistent nonspecific immunosuppression. Induction of stable, donor-specific tolerance remains the main goal of transplantation immunology. In this article, a new, nonmyeloablative method is described for induction of transplantation tolerance to fully mismatched bone marrow cells (BMC), bone marrow stromal precursors, heart muscle, and skin allografts. The method is based on pretransplant conditioning with no postgraft immunosuppression, and consists of a short course (six daily fractions of 200 cGy) of total lymphoid irradiation (sTLI), followed by selective elimination of donor-specific alloreactive cells of the host escaping low-dose sTLI. Donor-specific alloreactive cells were activated by intravenous inoculation with a high dose of donor BMC (3 x 10(7) cells) 1 day after sTLI, and eliminated by a single intraperitoneal dose (200 mg/kg) of cyclophosphamide given 1 day after cell transfer. Infusion of a low number of T cell-depleted BMC (3 x 10(6) cells) after tolerogenic preconditioning converted recipients to stable mixed chimeras free of graft-versus-host disease. The same treatment provided long-lasting acceptance of heterotopically transplanted allografts of the heart muscle and of the stromal precursors to the hematopoietic microenvironment. This treatment also led to acceptance and life-long survival of full-thickness donor skin allografts. However, skin allografts survived only in mice that received donor T cell-depleted BMC after cyclophosphamide and had 20-50% donor cells in the blood. Our results suggest that after sTLI, additional selective clonal deletion of residual host cells induces a state of long-lasting specific tolerance to a wide variety of donor-derived tissues.

The induction of tolerance to alloantigens using MHC class I molecules

The identification of approaches that allow the adult immune system to be manipulated to facilitate the induction of tolerance to alloantigens is important for the development of more specific immunosuppressive therapy for use in transplantation. Novel strategies using genetic manipulation of recipient cells for the induction of tolerance to MHC class I antigens have been tested in experimental systems in the past year. These, together with new insights into the mechanisms responsible for maintaining peripheral tolerance, have advanced our progress in this challenging area of transplantation biology.