Long-term follow-up of patients with osteochondral allografts. A correlation between immunologic responses and clinical outcome.

This article confirms immunologic responses in humans to histocompatibility antigens (Class I and II) presented by frozen osteochondral allografts. These observations include a correlation of immune responses with long-term clinical outcome. As found in animal models, matching of histocompatibility antigens, particularly to Class II, improves clinical and, presumably, biologic success following implantation of massive frozen bone allografts in humans. The presence of sensitization clearly does not preclude a satisfactory outcome, nor have other reconstructive alternatives (e.g., metallic implants) been shown to be superior in their long-term results.     

Immune response to perforated and partially demineralized bone allografts

Immune responses have been shown to be involved in the pathogenesis of clinical complications of cortical bone allografts. In an attempt to reduce the immunogenicity of these allografts, we evaluated cortical bone allografts modified by laser perforation and partial demineralization transplanted orthotopically into sheep tibiae. The recipient animals were divided into three groups, of eight animals each, according to the type of cortical allograft that was transplanted: group 1, no treatment (control); group 2, demineralization only; and group 3, laser perforation and partial demineralization. All animals were tissue-typed by biochemical definition of MHC class I molecules, using unidimensional isoelectric focusing and Western blotting. Mismatches of donors and recipients were assessed by testing samples of each donor and recipient pair in parallel and by comparing their individual bands. Donor-specific alloantibodies were detected by a similar technique, using an enzyme-linked immunosorbent assay (ELISA) format. Negative controls were included in all tests. All grafts were poorly immunogenic, whether they were untreated, processed by partial demineralization, or processed by both laser perforation and partial demineralization. Only two recipient animals showed a transient, antibody-mediated donor-specific immune response. One of these animals had received a control allograft, whereas the other animal had received a laser-perforated and partially demineralized bone allograft. All of the grafts in this study, including control grafts, were stripped of soft tissues and their bone marrow was removed; cellular sources of alloantibody stimulation may have been eliminated by these processes. The results of this study suggest that immune responses to bone allografts may be reduced by removing the bone marrow and adjacent soft tissues. The processing of cortical bone allografts by laser perforation and partial demineralization appeared to have little effect on immune responses.     

Orthotopic bone transplantation in mice. II. Studies of the alloantibody response.

The alloantibody response of mice receiving cortical bone allografts was investigated. Such grafts were highly immunogenic, resulting in antibody responses at least as strong as those to skin allografts in the same combinations. The duration of the response to a single bone allograft was very prolonged (greater than 10 months). The antibody response was shown to be directed against H-2K, H-2D, Ia, and at least two non-H-2 antigens. Although the great majority of the parenchymal cells of the graft were dead, the immunogenicity of the graft required living cells, since bone that had previously been frozen and thawed was nonimmunogenic. By retransplanting bone allografts to a second recipient it was possible to demonstrate that the grafts remained immunogenic for at least 4 weeks after transplantation, indicating that the living immunogenic cells survived in the recipient for at least 4 weeks. Such cells may be certain cells of the cortical bone itself, or else residual bone marrow elements which adhere to the endosteal surface of the bone. The observation that a small subpopulation of living cells can provoke strong immune responses against a wide variety of antigens may have implications for understanding the immunogenicity of other types of allografts.     

Bone graft materials. An overview of the basic science

Autograft, allograft, and synthetic bone graft substitute materials play an important role in reconstructive orthopaedic surgery, and understanding the biologic effects of these materials is necessary for optimum use. Although vascularized and cancellous autograft show optimum skeletal incorporation, host morbidity limits autograft availability. Experimental studies have confirmed an immune response to allograft bone, but the clinical significance of this response in humans still is unclear. Small amounts of cancellous allograft in humans usually are remodeled completely; large allografts become incorporated by limited, surface intramembranous bone formation suggesting that these graft are primarily osteoconductive. Several synthetic skeletal substitute materials also are osteoconductive, and may show remodeling characteristics similar to allograft. Demineralized bone matrix and some isolated or synthetic proteins can induce endochondral bone formation, and therefore are osteoinductive. The extent and distribution of remodeling of bone graft materials are influenced by many factors, including the quality of the host site and the local mechanical environment (strain). Graft materials are likely to become more specialized for use in specific clinical applications, and composite preparations may soon provide bone graft materials with efficacy that equals or exceeds that of autogenous grafts.     

Allograft incorporation: a biomechanical evaluation in a rat model

Allogeneic bone from Sprague-Dawley rat femurs was subjected to levels of freezing and/or irradiation that are known to have produced changes in the associated immune responses to these grafts. This bone was transplanted into an experimentally created gap in the femur of Lewis rats. The subsequent healing of the transplants in the Lewis rats was studied at 2, 4, 8, and 16 weeks after transplantation using torsion testing to failure. There was no clear advantageous biologic response in the union of the grafted material accompanying the alterations in immunologic response as measured by biomechanical testing of the proximal osteosynthesis site in torsion. The torsional strength of all of these groups remained lower than that of intact bone. Furthermore, none of the frozen and/or irradiated allografts exceeded the strength of the fresh allograft at a statistically significant level.     

Histopathology of cryopreserved bone allo- and isografts: pretreatment with dimethyl sulfoxide.

Partial graft cell survival and enhanced graft revascularization have suggested fast freezing using the cryoprotective substance dimethyl sulfoxide (DMSO) as a promising means to improve the biologic function and immune tolerance of allograft bone. This study determines the presence of osteoblasts (cola(1)(I) mRNA), osteoclasts (TRAP), and cytotoxic T cells (CTLs; GrA mRNA) within pretreated bone grafts 12 days after transplantation. The grafts were transplanted either as isografts, allografts, or allografts in presensitized recipients. In fresh isografts, serving as control, well-formed blood vessels and the highest numbers of viable osteoblasts and osteoclasts were found. In fresh allografts, blood vessels were observed within the marrow cavity and the bone was partially covered by osteoblasts and osteoclasts accompanied by CTLs. In DMSO-pretreated frozen allografts, blood vessels together with osteoblasts were observed in three of five, but in none of five grafts frozen without DMSO. However, infiltration with CTLs was higher in DMSO-pretreated frozen allografts when compared to grafts frozen without DMSO. In presensitized allograft recipients, independent of the pretreatment, in none of the grafts were either blood vessels or osteoblasts found. Thus, fast cryopreservation of bone using DMSO improves vascularization and expression of cola(1)(I) mRNA (osteoblasts) after allografting when compared to cryopreservation alone, potentially improving graft incorporation. As these grafts were still invaded by CTLs, the long-term effect of DMSO pretreatment needs to be defined.     

Development of transplanted fetal bones: differences between isografts and allografts in mice

Allogeneic bone from bone banks frequently is used when large skeletal defects have to be bridged in orthopaedic surgery. Beside immunologic rejection of the graft, the loss in osteogenic potential caused by bone banking procedures may be a major reason for limited clinical success. Similar problems as described for bone have occurred with cartilage and osteochondral transplants. Improving the properties of allogenic bone so that its biologic activity becomes comparable to autologous bone could be substantially beneficial for the outcome of allograft transplantation. To dissect the steps involved in the integration of a fetal osteochondral graft as it matures to bone, the current study compared the development and biologic function of metatarsals from 18-day-old fetal mice freshly transplanted in three different immunologic settings. Morphologic assessment of (1) isografts and (2) allografts in nonsensitized hosts 12 days after transplantation revealed that the grafts bear an intrinsic potential to develop after transplantation. In allografts in nonsensitized hosts, however, a slight alteration in biologic activity as compared with isografts could be detected already in this early phase after transplantation by in situ hybridization for messenger ribonucleic acids encoding extracellular matrix proteins. (3) In contrast to isografts and allografts in nonsensitized hosts, morphologic features and biologic function of allografts transplanted to presensitized hosts were altered severely.     

Evidence that tolerance to cultured thyroid allografts is an active immunological process. Protection of third-party grafts bearing new antigens when associated with tolerogenic antigens.

We studied the tolerance phenomenon that develops in long-term recipients of cultured thyroid allografts. Allogeneic mouse thyroids were cultured under hyperbaric oxygen or acidic conditions and then transplanted beneath the kidney capsule of C57BL/6 recipients. Donors differed from the recipients in minor antigens alone, major histocompatibility complex antigens alone, or both. At 35-77 weeks after the first cultured graft, recipients received two more cultured grafts under the capsule of the opposite kidney and were immunized with donor spleen cells (SC). At 5 weeks after the second transplantation, we observed that whereas second grafts carrying new antigens alone were rejected, second grafts carrying new antigens in association with antigens in the first graft were significantly protected. In another set of experiments, normal mice became tolerant to cultured allografts after 2 weeks in parabiosis with tolerant individuals. Tolerant mice showed reduced specific in vivo and in vitro cytotoxic T lymphocyte responses. However, the frequency of CTL precursors of tolerant mice was the same as in normal mice. The reduced in vitro CTL responses were restored to normal levels by the addition of a lymphokine rich medium. Also, we observed that the injection of specifically activated immune SC caused the rejection of cultured allografts in normal but not in tolerant recipients. We conclude that the tolerance that develops in recipients of cultured allografts is an active immunological process that affects the activation and effector function of CTL.     

Impact of MHC mismatch and freezing on bone graft incorporation: An experimental study in rats

Cortical bone graft failure develops for poorly defined reasons, and the effects of the immune responses on the incorporation of an allograft are less clear. In a rat model of tibial allotransplantation, we have studied biometric and histological changes of the graft and the humoral immune response against it. We have also compared fresh with prefrozen grafts to study putative effects of freezing on the healing of the graft and the immune response against it. Fresh and frozen cortical bone grafts matched or mismatched for major histocompatibility complex antigens (syngeneic and allogeneic grafts) were implanted in an 8‐mm segmental defect in the tibia. The construct was stabilized with intramedullary nailing. Incorporation of the graft was assessed with use of conventional radiography, micro computed tomography (CT(, biomechanical testing and histological examination. The immune response was evaluated by monitoring distribution of leukocytes in the blood and by measuring antibodies in a tailor‐made fluorescence activating cell scanning (FACS( analysis. We found that the fresh syngeneic grafts were well integrated after 8 weeks with intact bone cells. In the fresh allogeneic grafts, all cells were dead with radiological signs of resorption, and mechanical testing indicated failure of incorporation. The frozen grafts showed poorer overall reconstruction than the fresh syngeneic grafts, but the incorporation was better than the fresh allogeneic grafts. A measurable alloantibody response was only detected after fresh allografting. The combined results suggest that freezing of bone allograft impedes the antibody response against major histocompatibility complex (MHC( antigens and improves incorporation, but frozen allografts still perform poorer than do frozen syngeneic grafts. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:925–931, 2008     

The biology of bone graft repair

Cancellous and cortical autografts histologically have three differences: (1) cancellous grafts are revascularized more rapidly and completely than cortical grafts; (2) creeping substitution of cancellous bone initially involves an appositional bone formation phase, followed by a resorptive phase, whereas cortical grafts undergo a reverse creeping substitution process; (3) cancellous grafts tend to repair completely with time, whereas cortical grafts remain as admixtures of necrotic and viable bone. Physiologic skeletal metabolic factors influence the rate, amount, and completeness of bone repair and graft incorporation. The mechanical strengths of cancellous and cortical grafts are correlated with their respective repair processes: cancellous grafts tend to be strengthened first, whereas cortical grafts are weakened. Bone allografts are influenced by the same immunologic factors as other tissue grafts. Fresh bone allografts may be rejected by the host's immune system. The histoincompatibility antigens of bone allografts are presumably the proteins or glycoproteins on cell surfaces. The matrix proteins may or may not elicit graft rejection. The rejection of a bone allograft is considered to be a cellular rather than a humoral response, although the humoral component may play a part. The degree of the host response to an allograft may be related to the antigen concentration and total dose. The rejection of a bone allograft is histologically expressed by the disruption of vessels, an inflammatory process including lymphocytes, fibrous encapsulation, peripheral graft resorption, callus bridging, nonunions, and fatigue fractures.     

Different healing rates of bone autografts, syngeneic grafts, and allografts in an experimental rat model

Matching of donors and recipients for tissue antigens is vitally important for successful transplantation of essentially all organs and tissues, the major exception being bone. The importance of tissue-typing for the healing of bone allografts remains, however, a controversial issue as development of both humoral and cell-mediated immunity against the grafted bone has been observed in some experimental systems. In the present study, we compared the healing patterns of frozen antigen-mismatched allografts, frozen antigen-matched allografts (syngeneic grafts), and fresh cortical bone autografts in an experimental rat model. Histomorphometry of the graft-host interface revealed that new bone formation started significantly earlier in autografts than in allografts or syngeneic grafts. By 2 weeks, the level of new bone formation in the syngeneic grafts had reached that in autografts. Antigen-mismatched allografts, however, continued to exhibit a retarded formation of new bone throughout the union process. These histomorphometric observations were confirmed by molecular biologic analyses for the mRNA levles of type I collagen, which increased earlier and reached a higher level in autografts than in allografts. Use of syngeneic grafts resulted in a longer persistence of type I collagen mRNA expression in the healing tissue than in antigen-mismatched allografts. No apparent differences were seen between allografts and autografts in the expression of type III collagen. No cartilage-specific type JI collagen mRNA was observed, indicating that antigen-mismatching or preservation by freezing did not alter the basic mechanism of the interface healing process, although it did slow down the beginning of the process. The experiments suggest that a major antigen mismatch between donor and recipient affects the temporal gene expression of extracellular bone matrix and delays new bone formation at the graft-host interface of cortical bone allografts.     

Innate immunity and cardiac allograft rejection

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of heart transplantation as a therapy for end-stage heart failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained clinical significance as mounting evidence now indicates that innate immune responses have important roles in the acute and chronic rejection of cardiac allografts including cardiac allograft vasculopathy (CAV). Whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and in the development of CAV. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection. Finally, new data indicate that activation of complement is linked to acute rejection and CAV. In summary, the conventional wisdom that the innate immune system is of little importance in whole-organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, and complement will be necessary to prevent CAV completely and to eventually achieve long-term tolerance to cardiac allografts.     

Lipid extraction decreases the specific immunologic response to bone allografts in rabbits

The immunologic response against frozen bank bone is generally considered to have no clinical importance. In a previous study, the bone formation rate in frozen allografts was measured at standardized conditions in the Bone Harvest Chamber. By defatting frozen allografts, the bone formation rate increased. In the present study, the effect of defatting was further investigated, as the specific immunologic influence was excluded by using autografts. Pairs of grafts were frozen and one graft in each pair was defatted with chloroform/methanol. With these autografts there was no difference in bone formation rate between defatted and non-defatted implants, measured with ^99mTc-MDP. Combined with the previous experiments, the results indicate that the increased bone formation rate in defatted allografts is caused by the removal of specific cell surface antigens. Thus, the immunologic reaction to bank bone can be diminished by defatting.     

Donor marrow-derived cells as immunogens and targets for the immune response to bone and skin allografts

The relative importance of donor marrow-derived cells in the immunogenicity of bone and skin allografts was compared. Radiation chimeras were created to have marrow-derived cells (MDCs) of a different genotype from their nonmarrow-derived cells (NMDCs). Such animals were used as donors of bone or skin for recipients chosen so that either the MDCs or the NMDCs of the graft would be incompatible. Immunogenicity was determined by measuring the recipient antibody response. The effect of the immune response on the bone graft (rejection) was determined by impaired bone healing. When MDCs alone were H-2 disparate with the recipient, bone grafts were immunogenic, and the bone graft healing was impaired. In contrast, skin grafts in the same combinations were immunogenic but were not rejected if the differences were only expressed on the MDCs of the graft. The role of NMDCs in all of these experiments was more difficult to interpret, but the results suggested that NMDCs are relatively unimportant for healing of bone grafts, although critical for rejection of skin grafts. We conclude that, unlike the situation with skin grafts, the major inducers and targets of the immune response to bone allografts are marrow derived.     

Natural history of autografts and allografts

The clinical outcome of bone grafting procedures depends on many factors, including type and fixation of the bone graft as well as the site and status of the host bed. Bone grafts serve one or both of two main functions, as a source of osteogenetic cells and as a mechanical support. Autografts, both cancellous and cortical, are usually implanted fresh and are often osteogenetic, whether by providing a source of osteoprogenitor cells or by being osteoinductive. The latter is a process whereby the transplanted tissue induces mesenchymal cells of the recipient to differentiate into osteoblastic cells. Cortical grafts, whether autogeneic or allogeneic, at least initially act as weight-bearing space fillers or struts. All bone grafts are initially resorbed, but cancellous grafts are completely replaced in time by creeping substitution, while cortical grafts remain an admixture of necrotic and viable bone for a prolonged period of time. The three-dimensional framework, which supports invasion of the bone grafts by capillaries and osteoprogenitor cells, termed "osteoconduction", is another important function of both autografts and allografts. Fresh allografts are more slowly and less completely replaced by host bones because they invoke both local and systemic immune responses that diminish or destroy the osteoinductive and conductive processes. Although freezing or freeze-drying of allografts improves acceptance, their failure rate is still too high. These processes are also influenced by the vascularity and composition of the host bed. Thus, the interaction of the host and the bone graft determines the success of these procedures, which ultimately is to provide a mechanically efficient support structure.     

Selection of bone grafts for revision total hip arthroplasty

The selection of bone grafts to reconstruct deficient bone for revision hip replacement requires an understanding of specific bone graft functions and the critical steps of the biologic incorporation of the graft into the host. Bone grafts provide functions of osteogenesis, either graft derived or by osteoinduction, osteoconduction, or both, and mechanical support. Autologous cancellous bone provides excellent osteogenesis and osteoconduction without structural support. Nonvascularized cortical autografts provide mechanical support and are somewhat osteogenic. Allogeneic cancellous bone is osteoconductive and minimally osteoinductive, whereas cortical allografts provide structural support, if not freeze-dried, and are somewhat osteoconductive. Allogeneic demineralization bone matrix is highly osteoinductive. The selection of the appropriate bone graft depends on the classification of the bone deficiency. Cavitary (contained) defects can be reconstructed with cancellous morselized autograft, frozen or freeze-dried allograft, or allogeneic demineralized bone matrix. Segmental defects require bulk corticocancellous and/or cortical autografts or allografts. The ultimate incorporation of the bone graft depends on the interaction of the graft and the host's mechanical and biologic environment, and host-bone graft contact and stability. Optimum bone graft selection will enhance the clinical outcomes in revision total hip arthroplasty.     

Absence of donor MHC antigen expression ameliorates chronic kidney allograft rejection

BACKGROUND: In previous studies, we have demonstrated that a subset of mouse kidney allografts has prolonged survival without any immunosuppressive treatment. Chronic rejection (CR) develops in these long surviving grafts. The pathologic features of CR in this model are similar to CR in human kidney grafts. METHODS: To explore the role of donor major histocompatibility complex (MHC) antigens in the development of CR, we performed vascularized kidney transplants using kidneys from donor mice that lack expression of both MHC class I and II antigens (MHC-/-). RESULTS: Survival was significantly improved in recipients of MHC-/- allografts. This enhanced survival was associated with higher glomerular filtration rate (GFR) in MHC-/- allografts (4.92 +/- 0.54 cc/min/kg) compared to controls (2.19 +/- 0.63 cc/min/kg; P = 0.004). The typical histologic features of CR were markedly reduced in MHC-/- allografts. Semiquantitative histopathological scores for MHC-/- grafts (13.3 +/- 2.1) were significantly lower than in control allografts (19.0 +/- 1.0; P = 0.04). Along with this improvement in structural abnormalities, significantly fewer CD4+ T (38.3 cells/mm(2) vs. 75.0 cells/mm(2); P = 0.008), CD8+ T cells (38.7 vs. 96 cells/mm(2), respectively; P = 0.008) and macrophages (60 vs. 134 cells/mm(2), respectively; P = 0.04) infiltrated MHC-/- allografts compared to controls. The levels of intragraft cytokine mRNA expression also were reduced in MHC-/- allografts compared to control allografts. Finally, serum alloantibodies were virtually undetectable in recipients of MHC-/- kidney allografts. CONCLUSIONS: Cell surface expression of donor MHC antigens promotes the development of CR. Donor antigen expression promotes the accumulation of infiltrating cells in the graft and the development of donor specific alloantibodies. Abrogation of these responses is associated with improved graft survival and reduced CR in MHC-/- grafts.     

Cryopreservation of osteochondral allografts: dimethyl sulfoxide promotes angiogenesis and immune tolerance in mice

BACKGROUND: Although transplantation of cryopreserved bone allografts has become a routine procedure in orthopaedic surgery, biological and immunological impairment remains an unsolved problem that causes clinical failures. Experimental and clinical evidence has indicated that bone grafts that are revascularized early remain viable and contribute to union at the recipient site. Unprotected cryopreservation, used in most bone banks to reduce graft antigenicity, is associated with complete loss of graft viability, potentially contributing to graft failure. The differences in the survival of various cell types during cryopreservation with use of dimethyl sulfoxide, particularly the increased sensitivity of leukocytes to fast freezing, has resulted in a new approach to modulate immunogenicity. On the basis of this concept, it was proposed that a reduction in the immune response and enhanced revascularization of osteochondral allografts could be achieved by rapid cryopreservation with dimethyl sulfoxide. To test this hypothesis, angiogenesis and immune tolerance were quantified in a murine model with use of intravital microscopy. METHODS: Fresh osteochondral tissue and osteochondral tissue that had been cryopreserved with and without dimethyl sulfoxide was transplanted into dorsal skinfold chambers as isografts and as allografts in presensitized and nonsensitized recipient mice. To quantify angiogenesis, the onset of hemorrhages in the vicinity of the grafts and the revascularization of the grafts were determined by means of intravital fluorescence microscopy. To determine the recipient's intravascular immune response to the grafts, the leukocyte-endothelium interaction was assessed on the twelfth day after transplantation. RESULTS: Nine of nine fresh isografts were revascularized at a mean (and standard deviation) of 57 +/- 33 hours, eight of nine isografts that had been cryopreserved with dimethyl sulfoxide were revascularized at 98 +/- 50 hours, and zero of nine isografts that had been cryopreserved without dimethyl sulfoxide were revascularized. Seven of seven fresh allografts were revascularized at 53 +/- 6 hours, and ten of ten allografts that had been cryopreserved with dimethyl sulfoxide were revascularized at 82 +/- 29 hours. However, signs of revascularization faded in four of the seven fresh allografts whereas reperfusion was maintained in the majority (seven) of the ten grafts frozen in the presence of dimethyl sulfoxide. Similar to the findings associated with unprotected frozen isografts, zero of ten unprotected frozen allografts were revascularized. None of the allografts that had been transplanted into presensitized recipients were revascularized, regardless of whether they had been implanted fresh (nine grafts) or had been implanted after protected (eight grafts) or unprotected (nine grafts) freezing. Quantification of the leukocyte-endothelium interaction revealed a reduction in the intravascular immune response to frozen allografts (both protected and unprotected) compared with fresh allografts. CONCLUSION: Osteochondral allografts that had been pretreated by cryopreservation with dimethyl sulfoxide demonstrated improved angiogenesis induction and enhanced immune tolerance compared with unprotected frozen grafts. A selective reduction in donor passenger leukocytes is the proposed mechanism underlying this phenomenon. Clinical Relevance: In the absence of presensitization, cryopreservation with dimethyl sulfoxide appears to reduce the immune response to allografts and to enhance their revascularization; in the presence of presensitization, alternatives to allograft transplantation should be considered since the allografts will be exposed to a deleterious immune response.     

Revisiting liver transplant immunology: from the concept of immune engagement to the dualistic pathway paradigm.

Ever since the demonstration that allografts are rejected through immune reactions of the host, clinical therapies for organ allografts have relied on immune suppression to prevent these destructive events. A growing body of clinical and experimental data suggests that allografts elicit multiple, interactive immune responses. The result is not inevitably graft rejection, and "spontaneous" acceptance of fully allogeneic liver grafts occurs in rodents without immunosuppression. A spectrum of results range from spontaneous acceptance without immunosuppression to rejection with immunosuppression. The "dualistic pathway paradigm" aims to reconcile apparently conflicting observations in liver transplantation and proposes that: (1) immune engagement between the host and the allograft is instrumental in both rejection and acceptance; (2) there exist in all mammalian species congruent interactive pathways of immune activation whereby the fate of the allograft is determined by the quantitative results of these interactions; (3) the dualistic effect of immunosuppressive drugs on pathways of immune activation, conferring the capacity for favorable or unfavorable graft outcome should be investigated in experimental models in which organ allografts are spontaneously accepted. In conclusion the design of clinical strategies based on this research may contribute to protocols resulting in allograft acceptance without chronic immunosuppression.     

Studies on the antigenicity of bone. II. Donor-specific anti-HLA antibodies in human recipients of freeze-dried allografts

Freeze-dried bone allografts from donors of known tissue type evoked donor-specific anti-HLA antibodies in nine of forty-three patients (forty-four procedures). Eight of the nine sensitized patients were followed roentgenographically for an average of twenty-three months and were known to have had a satisfactory resolution of the benign process for which the graft was employed. The ninth patient was doing well when lost to follow-up four months after receiving a bone allograft. Clinical Relevance: The questions of whether immune responses to bone allografts occur in humans and, if so, adversely influence the incorporation of the graft can be answered at this time only by demonstrating the presence and frequency of such responses and how they correlate with clinical events. A large variety of techniques can be used to demonstrate immune responses. The technique that we used revealed that a small group of patients became sensitized to HLA antigens that were known to be present in the allograft donor but none of the recipients had evidence of adverse effects caused by the graft, as judged non-invasively.