Concordant Xenotransplantation Research Articles

The effect of Monocarboxylate Transporter (MCT1) inhibitor, AR-C117977 on accelerated rejection of cardiac grafts in pre-sensitised rats and concordant xenotransplantation

The effect of Monocarboxylate Transporter (MCT1) inhibitor, AR-C117977 on accelerated rejection of cardiac grafts in pre-sensitised rats and concordant xenotransplantation

A New Cardiac Concordant Xenotransplantation Model

Objective A simplified method of heterotopic abdominal cardiac xenotransplantation and its technique problems are described. Methods Hamster-to-rat cardiac xenotransplantation was performed by means of “sleeve and cuff” method. The left common carotid artery of the donor heart was anastomosed to the left renal artery of the recipient with a “sleeve” anastomosis, and the “cuffed” right pulmonary artery was anastamosed to the left renal vein of the rat. The viability of the donor heart was examined daily by palpating the left abdominal wall of the rat. Results Among 105 rats that underwent heterotopic cardiac xenotransplantation, 95 were completed successfully. The xenograft survived for 3 to 4 days after the procedure suffering typical acute vascular rejection. Conclusions A useful, easy model to investigate the mechanisms of concordant xenotransplantation was established.

Physiological aspects of xenotransplantation

Increasing efforts are being directed at providing solutions to the shortage of organs for allotransplantation. The immunological and infectious barriers to the use of xenografts have been extensively studied. However, physiological compatibility cannot be assured. A review of the physiological performance of clinical cases of renal, cardiac, and hepatic concordant xenotransplantation demonstrates some incompatibility between even closely related species. However, evidence from laboratory-based experiments suggests that a significant degree of physiological compatibility can be predicted for the transplantation of organs between discordant species. Preclinical studies involving genetically modified porcine hearts and kidneys transplanted into primate recipients demonstrate life-supporting function but also highlight interspecies differences that must be further studied before xenotransplantation can be a viable alternative to allotransplantation

Matching the Results Obtained in Concordant Primate Xenotransplantation Models

Matching the Results Obtained in Concordant Primate Xenotransplantation Models

Coagulation and thrombotic disorders associated with pig organ and hematopoietic cell transplantation in nonhuman primates.

Efforts to achieve tolerance to transplanted pig organs in nonhuman primates by the induction of a state of mixed hematopoietic chimerism have been associated with disorders of coagulation and thrombosis. Activation of recipient vascular endothelium and platelets by porcine hematopoietic cells and/or activation of donor organ vascular endothelium and/or molecular differences between the species may play roles. Irradiation or drug therapy could possibly potentiate endothelial cell activation and/or injury. We have investigated parameters of coagulation and platelet activation in nonhuman primates after (1) a regimen aimed at inducing mixed hematopoietic chimerism and tolerance (TIR that included total body irradiation, T cell depletion, and splenectomy; (2) pig bone marrow or pig peripheral blood mobilized progenitor cell transplantation (PCTx); and/or (3) pig organ transplantation (POTx). Five experimental groups were studied. Baboons were the recipient subjects in all groups except Group 1. Gp 1 Cynomolgus monkeys (n=6) underwent TIR + allotransplantation of hematopoietic cells and a kidney or heart or TIR + concordant xenotransplantation (using baboons as donors) of cells and a kidney; Gp 2 Baboons (n=4) underwent TIR with or without (+/-) autologous hematopoietic cell infusion; Gp 3 (n=12) PCTx+/-TIR; Gp 4 (n=5) POTx+/-TIR; Gp 5 (n=4) TIR + PCTx + POTx. Platelet counts, with plasma prothrombin time, partial thromboplastin time, fibrinogen levels, fibrin split products and/or D-dimer were measured. In the absence of a discordant (porcine) cellular or organ transplant (Groups 1 and 2), TIR resulted in transient thrombocytopenia only, in keeping with bone marrow depression from irradiation. PCTx alone (Group 3) was associated with the rapid development of a thrombotic thrombocytopenic (TTP)-like microangiopathic state, that persisted longer when PCTx was combined with TIR. POTx (+/-TIR) (Group 4) was associated with a gradual fall (over several days) in platelet counts and fibrinogen with disseminated intravascular coagulation (DIC); after graft excision, the DIC generally resolved. When TIR, PCTx and POTx were combined (Group 5), an initial TTP-like state was superseded by a consumptive picture of DIC within the first week, necessitating graft removal. Both PCTx and POTx lead to profound alterations in hemostasis and coagulation parameters that must be overcome if discordant xenotransplantation of hematopoietic cells and organs is to be fully successful. Disordered thromboregulation could exacerbate vascular damage and potentiate activation of coagulation pathways after exposure to xenogeneic cells or a vascularized xenograft.

Simple therapy for cardiac concordant xenotransplantation: only 1 week of DSG administration with suppression of t-cell reactions

Simple therapy for cardiac concordant xenotransplantation: only 1 week of DSG administration with suppression of t-cell reactions

Effect of FTY720 on immunoregulation in concordant xenotransplantation.

The present study was designed to analyze the immunosuppressive activity of FTY720 in concordant xenotransplantation. When T and B lymphocytes of human peripheral blood were incubated with FTY720, the number of viable cells decreased in a dose-dependent manner at doses higher than 4 x 10(-5) M. DNA fragmentation was observed at doses higher than 1 x 10(-5) M in T cell-rich fractions and at doses higher than 4 x 10(-5) M in B cell-rich fractions. These data demonstrate that FTY720 is cytotoxic to B lymphocytes as well as T lymphocytes and apoptosis may play an important role in this cytotoxicity. Golden Syrian hamsters were the donors and Lewis rats the recipients of skin grafts. The recipients were divided into the following four groups: (1) untreated recipients, (2) FTY720 (5 mg/kg per day) was administered orally for 8 days (days-1-6), (3) FK506 (1 mg/kg per day) was injected i.m. for 7 days (days 0-6), and (4) FK506 (1 mg/kg per day) was injected i.m. for 7 days (days 0-6) and FTY720 (5 mg/kg per day) was administered orally for 8 days (days-1-6). The mean graft survival times in groups 1-4 were 9.7 +/- 0.52 days (n = 6), 12.0 +/- 0.71 days (n = 6), 13.2 +/- 1.6 days (n = 6), and 37.7 +/- 4.3 days (n = 6), respectively. There was a significant difference in the mean survival time between groups one and four. Combined therapy with FTY720 and FK506 is a useful tool for immunoregulation in xenotransplantation.

Effect of FTY720 on immunoregulation in concordant xenotransplantation

Effect of FTY720 on immunoregulation in concordant xenotransplantation

INDUCTION OF SPECIES-SPECIFIC HOST ACCOMMODATION IN THE HAMSTER-TO-LEWIS RAT TRANSPLANTATION MODEL

474 Background: The combination of two immunosuppressants, leflunomide (Lef) and cyclosporine (CsA), completely inhibits immune xenoreactions in the hamster-to-Lewis rat xenotransplantation model. In addition, a transient treatment with Lef and CsA subdues early T-independent xenoreactivity and uncovers a late immune response that can be controlled by CsA alone. We attribute this acquired sensitivity to CsA to a modification in the recipient's humoral response to the xenograft and refer to this change as host accommodation. This study further characterizes the induction of host accomodation in this rodent model of concordant xenotransplantation. Methods: Accommodation was induced in Lewis rats transplanted with hearts from Golden Syrian hamster with the combination of Lef (5 mg/kg/d) and CsA (20 mg/kg/d) for 7-21 days and maintained on CsA (20 mg/kg/d) for the duration of the experiment. The specificity of the accommodated state was defined by transplanting additional hamster or mouse hearts into the accommodated Lewis recipients. The titers of xenoreactive antibodies were determined by flow cytometry. Results: Host accommodation was induced in Lewis rats receiving hamster hearts and the combination of Lef and CsA, but not with either of these agents alone. A ≥7 day treatment of Lef and CsA was able to convert xenoreactivity from one that was resistant to CsA treatment into one that was completely controlled by CsA. The presence of the hamster xenograft was critical for the induction of host accommodation since the immunosuppressive regimen alone, or in combination with donor-specific transfusion with spleen cells, were unable to modify the anti-hamster reactivity in Lewis rats. Finally we report that when accommodation was induced in the presence of hamster hearts, these accommodated Lewis rats were able to acutely reject third-party mouse hearts while under CsA therapy. Conclusions: Induction of host accommodation requires the combination of Lef and CsA as well as the presence of the xenograft, and is associated with a loss in the ability to mount a T-independent xenoantibody response. The ability of the accommodated host to respond with a T-dependent xenoantibody response is retained and is controllable with CsA alone. Finally, the species-specificity of host-accommodation suggests that xenoreactive T-independent humoral responses can be selectively deleted without significant loss of other innate, antigen-specific T-independent humoral responses.

Comparison of Two Methods of Pancreas Islets Immunoisolation

The efficacy of two methods of Langerhans islets immunoisolation was compared. For this purpose the function of islets encapsulated with alginate/polyethylenimine/protamine/heparin (APPH) or with alginate/poly-L-lisine/alginate (APA) membranes was assessed: in vitro according to their survival and response to glucose challenges, and in vivo according to their capability to provide sufficient insulin delivery to maintain normal fasting blood glucose following xenotransplantation to streptozotocin diabetic mice. In vitro insulin secretion and the response to glucose challenge of APPH and APA encapsulated islets were comparable to free islets. In vivo intraperitoneal concordant xenotransplantation of APA encapsulated rat islets reversed the diabetic state of streptozotocin diabetic mice for a longer period, than APPH islet grafts. This study clearly demonstrated the inadequacy of in vitro methods in the prediction of in vivo results of islets transplantation.

In vivo 31P MRS evaluation of the rejection process and differences in anesthetic procedures in a concordant xenotransplantation: Mouse heart to rat modell

In vivo 31P MRS evaluation of the rejection process and differences in anesthetic procedures in a concordant xenotransplantation: Mouse heart to rat modell

The influence of concordant xenografts on the humoral and cell-mediated immune responses to subsequent allografts in primates

The humoral and cell-mediated immune responses to subsequent allografts were determined in primate recipients after concordant xenotransplantation as a bridge to allotransplantation. Heterotopic heart transplants ( n = 4) were performed from cynomolgus monkeys into ABH type–matched olive baboons followed 2 weeks later by allotransplantation from ABH type–matched baboon donors. Allografts were explanted at 8 weeks. All recipients underwent splenectomy at the time of xenotransplantation and received immunosuppression with cyclosporine, azathioprine, and methylprednisolone. Concordant xenotransplantation in these primates did not induce humoral or cell-mediated immune responses that jeopardized subsequent allografts. The degree of xenospecific immune reactivity, as determined by specific cytotoxicity of recipient T-cell lines derived from the xenograft and extent of histologic xenograft rejection, did not predict the severity of subsequent allograft rejection. In two of the four recipients, xenotransplantation induced an alloreactive humoral response against antigens expressed by the B cells of more than 50% of members from a panel of 12 unrelated baboons. In all recipients, priming with xenogeneic splenocytes in vitro induced an accelerated proliferative T-cell response to allogeneic lymphocytes from 16% of this panel. This study affirms the role of concordant xenografts as appropriate biologic bridges to human allotransplantation. However, our results suggest that xenoreactive baboon memory CD4 T cells may recognize major histocompatibility complex class II–like structures shared between the xenogeneic and allogeneic targets. The potential allorecognition induced by a xenograft may affect the process of subsequent allograft donor selection. (J T HORAC C ARDIOVASC S URG 1996;112:1002-9)

Xenogeneic ex vivo hemoperfusion of rhesus monkey livers with human blood.

In order to copy the clinical situation of concordant xenotransplantation, Rhesus Monkey livers were hemoperfused with human blood. Changes of immunological (TNFalpha, IL-1beta, IL-2, IL-2R, IL-6, IFNgamma, TXB2, 6kPGF1alpha, sICAM-1, sELAM-1, sHLA-I-Ag) and pathophysiological (GOT, GPT, LDH, CK) parameters were followed. Our experiment proves that all phenomena start in the first hour of xenogeneic blood circulation. Xenogeneic rejection in our concordant system is surprisingly severe. Preformed natural antibodies only cannot be the reason of such a damage. We think that beside other important immunological mechanisms, humoral mediators play a considerable role at the beginning of a xenogeneic rejection.

Prolonged survival of orthotopically transplanted heart xenograft in infant baboons

Orthotopic concordant xenotransplantation in a juvenile primate model was examined. Eighteen donor rhesus monkeys weighing 2.4 to 3.8 kg (mean 2.9 kg) were matched with juvenile baboons, aged 9 to 19 months (mean 12.7 months) and weighing 3.2 to 4.8 kg (mean 3.9 kg), using ABH blood type and mixed lymphocyte culture. Rhesus monkey hearts were orthotopically transplanted without immunosuppression into six control baboons (group I). In five baboons (group II), 4 mg/kg per day of antilymphocyte globulin was administered for 3 days before the operation and 5 days after the operation. Splenectomy was also performed, and 18 mg/kg per day of FK 506 was administered orally. Intravenous methotrexate, methylprednisolone, or both were used as rescue therapy. Seven baboons (group III) received the same immunosuppression as those in group II, but an intravenous dose of methotrexate (0.1 to 5 mg) was given twice weekly to suppress the proliferative response as monitored by in vitro immunologic assays. Baboons in group I had a mean survival of 8 days; all died as a result of classic cellular rejection. Baboons in group II had a mean survival of 48.4 days (p < 0.05 versus group I). Two died during rescue therapy for rejection, and three died of cytomegalovirus infection. Two group II baboons showed mild rejection at autopsy. Baboons in group III had a mean survival of 127 days, and one baboon was still alive after 286 days. Two died of cytomegalovirus infection, one of toxoplasmosis, one of Klebsiella pneumoniae, one of massive micropulmonary embolism, one of renal failure aggravated by ganciclovir. Only two of the baboons that died showed rejection (estimated as mild) at autopsy. The baboon still alive at 286 days had no rejection on myocardial biopsy on the two hundred forty-fourth postoperative day. FK 506 coupled with low-dose maintenance methotrexate and splenectomy has produced prolonged host survival in this xenotransplantation model. Results suggest that concordant xenotransplantation would be a suitable biologic bridge to allotransplantation.

Sequential, morphological, and antidonor antibody analysis in a hamster-to-rat heart transplantation model.

The pathogenesis and the mechanism of accelerated graft rejection in concordant xenotransplantation are unclear. The histopathological features and kinetics neither fulfill the criteria of classic hyperacute rejection nor resemble an accelerated type of first-set allograft reaction. The aim of this study was to investigate the mechanism of concordant xenograft rejection in relation to the early morphological changes in hamster hearts transplanted to unmodified rat recipients by sequential, immunohistological analysis of grafts, regional lymph nodes, and spleens and to correlate these results to the production of antidonor antibodies, as determined by a flow cytometric assay. Histopathological features were characterized by a gradually increasing myocytolysis with fragmentation and loss of myofilaments. The first slight signs were observed a few hours after transplantation. Later, vascular changes developed, evolving into a leukocytoclastic type of vasculitis, eventually with thrombosis. No significant interstitial lymphocyte infiltration was present, but neutrophilic granulocytes and macrophages appeared. In addition, a distinct increase in B cells in spleens and lymph nodes was noted. Low levels of preformed antidonor antibodies did not increase during the first 48 h; however, significant amounts of species-, but not donor-, specific antibodies were demonstrated at the time of rejection. These data, together with the morphological observations, indicate a primarily humoral xenograft rejection in this model. Minor damage to graft myocytes a few hours after transplantation, progressing to vascular changes within 24-48 h, further suggests that preformed antidonor antibodies directed against endothelial or myocyte determinants may play an initiating role in the pathogenesis of unmodified, concordant xenograft rejection.

Sequential, morphological, and antidonor antibody analysis in a hamster-to-rat heart transplantation model

Abstract. The pathogenesis and the mechanism of accelerated graft rejection in concordant xenotransplantation are unclear. The histopathological features and kinetics neither fulfill the criteria of classic hyperacute rejection nor resemble an accelerated type of first-set allograft reaction. The aim of this study was to investigate the mechanism of concordant xenograft rejection in relation to the early morphological changes in hamster hearts transplanted to unmodified rat recipients by sequential, immunohistological analysis of grafts, regional lymph nodes, and spleens and to correlate these results to the production of antidonor antibodies, as determined by a flow cytometric assay. Histopathological features were characterized by a gradually increasing myocytolysis with fragmentation and loss of myofilaments. The first slight signs were observed a few hours after transplantation. Later, vascular changes developed, evolving into a leuko-cytoclastic type of vasculitis, eventually with thrombosis. No significant interstitial lymphocyte infiltration was present, but neutrophilic granulocytes and macrophages appeared. In addition, a distinct increase in B cells in spleens and lymph nodes was noted. Low levels of preformed antidonor antibodies did not increase during the first 48 h; however, significant amounts of species-, but not donor-, specific antibodies were demonstrated at the time of rejection. These data, together with the morphological observations, indicate a primarily humoral xenograft rejection in this model. Minor damage to graft myocytes a few hours after transplantation, progressing to vascular changes within 24–48 h, further suggests that preformed antidonor antibodies directed against endothelial or myocyte determinants may play an initiating role in the pathogenesis of unmodified, concordant xenograft rejection.

Treatment with total lymphoid irradiation, cyclosporin A and a monoclonal anti-T-cell antibody in a hamster-to-rat heart transplantation model: Graft survival and morphological analysis

Treatment with preoperative total lymphoid irradiation and post-transplant cyclosporin A has been shown to have a synergistic effect on graft survival in allo- and xenotransplantation. Specific monoclonal antibodies against T cells and T cell subpopulations could offer new ways of preventing graft rejection in xenotransplantation. Graft survival and histology were examined after total lymphoid irradiation plus cyclosporin A treatment versus cyclosporin A plus a monoclonal antibody in a concordant, heterotopic, hamster-to-rat heart transplantation model. Preoperative total lymphoid irradiation was given at a dose of 1.25 Gy, 12 times over a period of 3 weeks. Cyclosporin A at a dose of 12.5 mg/kg per day was administered perorally and OX-19, a pan T cell monoclonal antibody, was given as intraperitoneal injections at doses of 100 micrograms or 500 micrograms/kg per day from day 0 until graft rejection. While total lymphoid irradiation alone prolonged graft survival to 9.4 days, total lymphoid irradiation plus cyclosporin A extended graft survival to a mean of 22 days. Cyclosporin alone or combined with the monoclonal antibody could not increase graft survival significantly when compared to untreated animals, which rejected their grafts within 3.7 days. Vascular rejection was the characteristic morphological finding, even after some weeks of excellent graft function. In conclusion, total lymphoid irradiation and cyclosporin A had a synergistic effect on graft survival in this concordant xenotransplantation model, although recent impressive results from other groups could not be reproduced. Total lymphoid irradiation combined with cyclosporin A appears to delay a primary humoral graft rejection, while the mechanism of rejection, judged by histology, stays the same.

Treatment with total lymphoid irradiation, cyclosporin A and a monoclonal anti-T-cell antibody in a hamster-to-rat heart transplantation model: Graft survival and morphological analysis

Abstract. Treatment with preoperative total lymphoid irradiation and post-transplant cyclosporin A has been shown to have a synergistic effect on graft survival in alio-and xenotransplantation. Specific monoclonal antibodies against T cells and T cell subpopulations could offer new ways of preventing graft rejection in xenotransplantation. Graft survival and histology were examined after total lymphoid irradiation plus cyclosporin A treatment versus cyclosporin A plus a monoclonal antibody in a concordant, heterotopic, hamster-to-rat heart transplantation model. Preoperative total lymphoid irradiation was given at a dose of 1. 25 Gy, 12 times over a period of 3 weeks. Cyclosporin A at a dose of 12. 5 mg/kg per day was administered perorally and OX-19, a pan T cell monoclonal antibody, was given as intraperitoneal injections at doses of 100 μg or 500 μg/kg per day from day 0 until graft rejection. While total lymphoid irradiation alone prolonged graft survival to 9. 4 days, total lymphoid irradiation plus cyclosporin A extended graft survival to a mean of 22 days. Cyclosporin alone or combined with the monoclonal antibody could not increase graft survival significantly when compared to untreated animals, which rejected their grafts within 3. 7 days. Vascular rejection was the characteristic morphological finding, even after some weeks of excellent graft function. In conclusion, total lymphoid irradiation and cyclosporin A had a synergistic effect on graft survival in this concordant xenotransplantation model, although recent impressive results from other groups could not be reproduced. Total lymphoid irradiation combined with cyclosporin A appears to delay a primary humoral graft rejection, while the mechanism of rejection, judged by histology, stays the same.