Induction of unresponsiveness to major transplantable organs in adult mammals: a recapitulation of ontogeny by irradiation and bone marrow replacement

Donor age and gender are the strongest predictors of marrow recovery from cadaveric vertebral bodies

The purpose of this retrospective analysis was to determine whether there were donor factors that were useful for predicting the yield of nucleated cells from marrow derived from cadaveric vertebral bodies. An analysis of 132 donors over a 6-year period was performed. The average number of vertebral bodies procured from each donor was 10.2 +/- 1.6 (range 5-14). The total number of nucleated cells recovered per donor ranged from 24 x 10(9) to 160 x 10(9) with an average recovery of 69 +/- 28 x 10(9) cells. The cell viability of the recovered cells was > 95%. The average age of the donors was 33 +/- 14 years (mean +/- SD; range 12-65) with an average weight of 169 +/- 41 lb (range 82-308 lb). Males comprised 68% of the donor population. The average number of days from admission to death was 1.9 +/- 1.7 with a range of 1-11.4 days and the interval between asystole and procurement averaged 3.1 +/- 2.3 h (range (0.1-14.7 h). The majority of donors died from head trauma due to an intracranial bleed, gunshot wound, or closed head injury. Regression analysis of the data indicated that the total nucleated cell yield tended to decrease with increasing time between hospital admission and death. The data also indicated that in general female donors yielded lower cell numbers independent of age and male donors under 30 years of age yielded the highest number of cells.

History of clinical transplantation

The emergence of transplantation has seen the development of increasingly potent immunosuppressive agents, progressively better methods of tissue and organ preservation, refinements in histocompatibility matching, and numerous innovations in surgical techniques. Such efforts in combination ultimately made it possible to successfully engraft all of the organs and bone marrow cells in humans. At a more fundamental level, however, the transplantation enterprise hinged on two seminal turning points. The first was the recognition by Billingham, Brent, and Medawar in 1953 that it was possible to induce chimerism-associated neonatal tolerance deliberately. This discovery escalated over the next 15 years to the first successful bone marrow transplantations in humans in 1968. The second turning point was the demonstration during the early 1960s that canine and human organ allografts could self-induce tolerance with the aid of immunosuppression. By the end of 1962, however, it had been incorrectly concluded that turning points one and two involved different immune mechanisms. The error was not corrected until well into the 1990s. In this historical account, the vast literature that sprang up during the intervening 30 years has been summarized. Although admirably documenting empiric progress in clinical transplantation, its failure to explain organ allograft acceptance predestined organ recipients to lifetime immunosuppression and precluded fundamental changes in the treatment policies. After it was discovered in 1992 that long-surviving organ transplant recipients had persistent microchimerism, it was possible to see the mechanistic commonality of organ and bone marrow transplantation. A clarifying central principle of immunology could then be synthesized with which to guide efforts to induce tolerance systematically to human tissues and perhaps ultimately to xenografts.

Variable chimerism, graft-versus-host disease, and tolerance after different kinds of cell and whole organ transplantation from Lewis to brown Norway rats

The bidirectional paradigm of tolerance involving reciprocal host vs. graft and graft vs. host reactions was examined after Lewis (LEW)-->Brown Norway (BN) transplantation of different whole organs (liver, intestine, heart, and kidney) or of 2.5 x 10(8) LEW leukocytes obtained from bone marrow, spleen, lymph nodes, and thymus. The experiments were performed without immunosuppression or under 14 daily doses of postoperative tacrolimus, which were continued in weekly doses to 100 days in a "continuous treatment" subgroup, and to 27 days in a short treatment group. Without immunosuppression, all organs and cell suspensions failed to engraft or were acutely rejected. GVHD (usually fatal) was always caused when either the long or short treatment was used for recipients of intestinal grafts and cell suspensions of spleen and lymph nodes. In contrast, both immunosuppressive protocols allowed engraftment of bone marrow cells, liver, heart, and kidney without clinical GVHD, whereas thymus cell suspensions and small doses of whole blood neither engrafted nor caused GVHD. At 100 days, now drug-free for 73 days, the liver, bone marrow, and heart recipients were tolerant in that they accepted all challenge LEW heart and/or liver grafts for 100 more days despite in vitro evidence of donor-specific reactivity (split tolerance). At 200 days, histopathologic studies of the challenge livers were normal no matter what the priming graft. However, the still-beating challenge hearts had a spectrum from normal to severe chronic rejection that defined the tolerogenicity of the original primary grafts: liver best-->bone marrow next-->heart least. Both the GVHD propensity and tolerogenicity in these experiments were closely associated with recipient tissue chimerism 30 and 100 days after the experiments began. The tissue chimerism was invariably multilineage, but the GVHD outcome was associated with T cell over-representation. These observations provide guidelines that should be considered in devising leukocyte augmentation protocols for human whole organ recipients. The results are discussed in relation to the historical tolerance studies of Billingham, Brent, and Medawar; Good; Monaco; and Calne.

Variable chimerism, graft-versus-host disease, and tolerance after different kinds of cell and whole organ transplantation from Lewis to brown Norway rats

The bidirectional paradigm of tolerance involving reciprocal host vs. graft and graft vs. host reactions was examined after Lewis (LEW)-->Brown Norway (BN) transplantation of different whole organs (liver, intestine, heart, and kidney) or of 2.5 x 10(8) LEW leukocytes obtained from bone marrow, spleen, lymph nodes, and thymus. The experiments were performed without immunosuppression or under 14 daily doses of postoperative tacrolimus, which were continued in weekly doses to 100 days in a "continuous treatment" subgroup, and to 27 days in a short treatment group. Without immunosuppression, all organs and cell suspensions failed to engraft or were acutely rejected. GVHD (usually fatal) was always caused when either the long or short treatment was used for recipients of intestinal grafts and cell suspensions of spleen and lymph nodes. In contrast, both immunosuppressive protocols allowed engraftment of bone marrow cells, liver, heart, and kidney without clinical GVHD, whereas thymus cell suspensions and small doses of whole blood neither engrafted nor caused GVHD. At 100 days, now drug-free for 73 days, the liver, bone marrow, and heart recipients were tolerant in that they accepted all challenge LEW heart and/or liver grafts for 100 more days despite in vitro evidence of donor-specific reactivity (split tolerance). At 200 days, histopathologic studies of the challenge livers were normal no matter what the priming graft. However, the still-beating challenge hearts had a spectrum from normal to severe chronic rejection that defined the tolerogenicity of the original primary grafts: liver best-->bone marrow next-->heart least. Both the GVHD propensity and tolerogenicity in these experiments were closely associated with recipient tissue chimerism 30 and 100 days after the experiments began. The tissue chimerism was invariably multilineage, but the GVHD outcome was associated with T cell over-representation. These observations provide guidelines that should be considered in devising leukocyte augmentation protocols for human whole organ recipients. The results are discussed in relation to the historical tolerance studies of Billingham, Brent, and Medawar; Good; Monaco; and Calne.

The current status of hepatic transplantation at the University of Pittsburgh

Tacrolimus is a more potent and satisfactory immunosuppressant than CyA for combination therapy with prednisone. In randomized trials comparing the 2 drugs, the ability of tacrolimus to rescue intractably rejecting grafts on the competing CyA arm allowed equalization of patient and graft survival on both arms when the intent-to-treat analytic methodology was applied. The ability of tacrolimus to systematically rescue the treatment failures of CyA suggested, as a matter of common sense, that it is the preferred baseline drug for hepatic transplantation. This conclusion was supported by analysis of secondary end points, including the ability to prevent rejection. Hepatic-intestinal, multivisceral and isolated intestinal transplantation became feasible on a practical basis only after the advent of tacrolimus. Nevertheless, better management strategies must be devised before intestinal transplantation, alone or with other abdominal viscera, will meet its potential. One such strategy is based on the discovery of the presence of previously unsuspected, low-level donor leukocyte chimerism in long-surviving allograft recipients. We believe that this chimerism is the essential explanation for the feasibility of organ transplantation and a link to the acquired neonatal tolerance demonstrated by Billingham, Brent and Medawar (32). The hematolymphopoietic chimerism in organ recipients explains why weaning to a drug-free state in selected long-term survivors is frequently feasible and particularly if the allograft is a liver. Weaning should never be attempted without a stepwise protocol and careful monitoring of graft function. Recognition of the natural chimerism that develops after whole organ transplantation has led to efforts to augment it with perioperative donor BM infusion. This procedure has been shown to be free of significant complications (including GVHD) in all kinds of whole organ recipients, including those given intestine. The prospects of clinical xenotransplantation must be evaluated in the same context of chimerism as that delineated for allotransplantation with the discovery of spontaneous chimerism. Before addressing chimerism-related questions in xenotransplantation, the additional barrier of the complement activation syndromes that cause hyperacute rejection will have to be surmounted. Although measures to effectively transplant xenografts have so far eluded us, the availability of the more potent drug, tacrolimus, and recognition of the seminal basis of allograft (or xenograft) acceptance via chimerism has inserted an element of reality into the largely wishful thinking that has been evident in discussions about the future of xenotransplantation.

Implication of Ia-positive bone marrow interstitial stem cells in the induction of unresponsiveness to canine renal allografts

The removal from stored autologous host bone marrow of a monocytoid cell population by exposure to methylprednisolone is associated with successful introduction of unresponsiveness to renal allografts in irradiated recipients reconstituted with such treated marrow. The eliminated cells are a prominent component of the canine long bone marrow interstitium and share a number of important properties with dendritic cells (DC), including size and shape; poor or nonadherence to plastic or glass surfaces; negative staining for neutral esterase, acid phosphatase, or peroxidase; nonphagocytic; Ia positive, but negative for IgG or IgM; ability to act as accessory cells in augmenting the intensity of allogeneic mixed-lymphocyte reactions. Both cell types are of bone marrow origin and are susceptible to steroids in vitro. The results suggest that the bone marrow interstitial cells identified in the course of this study may be enriched with populations of canine dendritic cell precursors and dendritic cells at various stages of differentiation. The detection of a receptor site for Helix promatia on the surface of such cells may be of usefulness in their further characterization and in the analysis of their precise role in the modulation of allogeneic unresponsiveness.

Long-term study of vascularized free-draining intraperitoneal pancreatic segmental allografts in beagle dogs

The purpose of the present study was to evaluate the significance of immunogenetic factors on the survival of pancreatic allografts in beagle dogs. Donors and recipients were leukocyte antigen (DLA)-typed and mixed lymphocyte culture (MLC)-tested. Recipients were made diabetic by total pancreatectomy and immediately implanted intraperitoneally with a vascularized, free-draining (duct unligated) pancreatic segmental (FDPS) allograft. Two groups of dogs were studied. In group I consisting of donor-recipient littermates, recipients were immunosuppressed with prednisone and azathioprine (n = 16 dogs), or not immunosuppressed (n = 4). In group II, recipients were made specifically unresponsive by total body radiation, autologous marrow implantation, and kidney transplantation from DLA-MLC identical donors, 1 yr before FDPS transplantation from the corresponding original kidney donors. Survival of the FDPS grafts in group I was inversely related to pretransplant MLC reactivity, irrespective of DLA genotyped match between donor and recipient. Thus, immunosuppressed high MLC reactors (n = 8) rejected FDPS grafts between 7 and 14 d, whereas immunosuppressed low MLC reactors (n = 8) accepted grafts for 25 to 260+ days, and nonimmunosuppressed low MLC reactors (n = 4) accepted grafts for 9-55 d. Rejection (hyperglycemia) of FDPS grafts was sudden, permanent, and unpredictable despite weekly intravenous glucose tolerance tests with measurements of glucose disappearance rates and serum insulin responses. Nevertheless, serial in vitro cell-mediated lymphocytotoxicity (CML) assays revealed increases in CML before graft rejection in low MLC reactors, and decreases in both CML and MLC responses before graft rejection in high MLC reactors. FDPS graft survival was indefinite (>6 mo) in group II dogs, despite low-grade MLC reactivity (2:4 dogs) and CML responses (4:4 dogs). Biopsies of FDPS grafts at 6 mo in normoglycemic dogs showed disappearance of exocrine tissue and coalescence of islets in both groups I and II, but with less fibrosis in group I (immunosuppressed). These results indicate that (a) pancreatic islets in vascularized grafts (FDPS) may survive indefinitely in the presence of a good tissue match best predicted by MLC testing, (b) tissue specific histocompatibility factors appear to be common enough between kidney and pancreas to allow for long-term survival of both organs transplanted from the same donor, at least in appropriate recipients (group II), and (c) immunosuppression is associated with less fibrosis in FDPS allografts.