LONG-TERM SURVIVAL OF DONOR-SPECIFIC PANCREATIC ISLET XENOGRAFTS IN FULLY XENOGENEIC CHIMERAS ( WF RAT → B 10 MOUSE )

We recently reported that reconstitution of lethally irradiated B1O mouse recipients with 40×106 untreated WF rat bone marrow cells resulted in stable fully xenogeneic chimerism (WF rat → B10 mouse). In these animals, the tolerance induced for skin xenografts was highly MHC specific in that donor-specific WF rat skin grafts were significantly prolonged while MHC-disparate third-party xenografts were rapidly rejected (median survival time [MST] = 9 days). We have now examined whether islet cell xenografts placed under the renal capsule of chimeras rendered diabetic with streptozotocin would be accepted and remain functional to maintain euglycemia. Animals were prepared, typed for chimerism at 6 weeks, and diabetes induced with streptozotocin. Donor-specific WF (Rt1Au) islet cell xenografts were significantly prolonged (MST >180 days) in WF → B10 chimeras, while MHC-disparate third-party F344 rat (Rt1Al) grafts were rejected with a time course similar to unmanipulated B10 mice (MST=8 days). The transplanted donor-specific islet cells were functional to maintain euglycemia, since removal of the grafts at from 100 to 180 days in selected individual chimeras uniformly resulted in return of the diabetic state. These data suggest that donorspecific islet cell xenografts are accepted and remain functional in mice rendered tolerant to rat xenoantigens following bone marrow transplantation. Great advances in the field of transplantation have occurred in the last two decades. The availability of nonspecific immunosuppressive agents has allowed pancreatic transplantation to become an accepted clinical modality for treatment of diabetes. The demand for grafts already exceeds the supply: as of December 1990, 477 patients were awaiting a pancreatic graft (1). However, a number of technical limitations are associated with transplantation of the whole pancreas, resulting in side effects including abscess formation, anastomotic leaks, and rejection. In recent years, the development of procedures to isolate large numbers of purified human pancreatic islets has made it possible to initiate a new phase of clinical trails in pancreatic islet cell transplantation (2–7). Transplantation of pancreatic islet cells is now the most specific replacement therapy for treatment of type 1 insulin-dependent diabetes. Because only 1% of total pancreatic tissue is required to cure diabetes (the islet cells), transplantation 1Presented at the 17th Annual Meeting of the American Society of Transplant Surgeons, May 29-31, 1991, Chicago, IL. 2This work was supported in part by the American Cancer Society IN-58-29, the American College of Surgeons Fellowship Award (1990–1992), NIH ROI AI 30615-01A1. Copyright © 1992 by Williams & Wilkins 3 Address correspondence and reprint requests to Dr. Suzanne T. Ildstad, Division of Transplantation, Department of Surgery, Biomedical Science Tower W1556, Pittsburgh, P A 15213. *Abbreviation: MST, median survival time. NIH Public Access Author Manuscript Transplantation. Author manuscript; available in PMC 2010 October 26. Published in final edited form as: Transplantation. 1992 February ; 53(2): 277–283. N IH PA Athor M anscript N IH PA Athor M anscript N IH PA Athor M anscript of purified, pancreatic islet cells overcomes the associated limitations encountered with transplantation of the whole pancreas. It is well recognized that both the whole pancreas and pancreatic islet cells are highly antigenic (2–14). Although nonspecific immunosuppressive agents have been instrumental in control of alloreactivity to transplanted islet cells, rejection often still occurs (8–10). Attempts to decrease antigenicity of islet cell grafts using in vitro pretreatment of grafts with monoclonal antibodies (11–14), in vitro culture protocols (5,15–17), ultraviolet irradiation (18–20), microencapsulation (21–24), and isolation of hand-picked pure islet cells (25,26) have resulted in some improvement in graft survival but have not reliably prevented rejection. Two limitations therefore exist: the supply of grafts does not meet the demand, and rejection remains a problem. The induction of donor-specific transplantation across a species barrier, using bone marrow stem cells to produce chimerism, has been suggested as a potential approach to prevent rejection of transplanted pancreatic islet xenografts and overcome the shortage of solid organ grafts available for transplantation. The association between bone marrow chimerism and donorspecific transplantation tolerance has been recognized for forty years (27–42). The first association between bone marrow chimerism and tolerance was reported by Billingham, Brent, and Medawar in 1953 when they demonstrated the induction of permanent donor-specific transplantation tolerance for skin grafts by transplantation of bone marrow cells into newborn mouse recipients (27). Subsequently, numerous methods to induce similar tolerance in adult recipients using bone marrow transplantation have been reported (28–38). Monaco et al. demonstrated prolongation of skin allograft survival in mice treated with antilymphocyte serum followed by a critically timed transfusion of donor bone marrow stem cells (30,31). Similar tolerance for alloantigens has now been achieved in a number of other species, including the dog (37) and monkey (38). Recently, Ildstad et al. developed and characterized a model to induce similar donor-specific transplantation tolerance across a species barrier through preparation of fully xenogeneic chimeras (rat → mouse) (43,44). Engraftment of rat bone marrow stem cells in mouse recipients was stable, as evidenced by the presence of rat-derived lymphocytes, myeloid cells, platelets, and red blood cells up to 12 months after reconstitution with untreated rat bone marrow cells. Survival was excellent (>80% at 180 days), and there was no evidence for graft-versus-host disease. Fully xenogeneic chimeras specifically accepted donor-strain rat skin grafts but were competent to reject MHC-disparate third-party mouse and rat skin grafts (43,44). The aim of the present studies was to determine whether long-term acceptance and function of pancreatic islet cell xenografts could be achieved in fully xenogeneic chimeras without requirement for chronic nonspecific immunosuppressive agents. We now report the long-term survival and function of donor-specific xenogeneic pancreatic islet cells in fully xenogeneic chimeras. MATERIALS AND METHODS