Evidence that deoxyspergualin prevents sensitization and first-set cardiac xenograft rejection in rats by suppression of antibody formation.

This study provides evidence of antibodies playing an important role in hamster-to-rat cardiac xenograft rejection and discusses the use of 15-deoxyspergualin (DSG) to suppress this first-set rejection, as well as hyperacute rejection induced by sensitization. The effect of recipient splenectomy (Spx) as an adjuvant to DSG to control first set xenograft rejection was also examined. When hyperimmune serum was taken from control recipients at rejection time and injected i.v. into new recipients of cardiac xenografts, hyperacute graft rejection resulted. Survival depended on the amount of serum injected and ranged from 14.7 +/- 2.5 min with 3 ml of serum to 233.3 +/- 61.1 min with 0.5 ml. Experiments on first-set xenograft rejection revealed that a dose of 2.5 mg/kg/day DSG could prolong xenograft survival from 3.4 +/- 0.5 days in untreated controls to 9.5 +/- 2.6 days (P less than 0.01). A dose of 5 mg/kg/day DSG, though it increased graft survival to 16.4 +/- 5.9 days, proved to be toxic to the recipients. Spx alone prolonged xenograft survival to 5.2 +/- 0.4 days, and, when combined with 2.5 mg/kg/day DSG administration, prolonged graft survival to 22.1 +/- 5.5 days (P less than 0.01 vs. DSG alone). The appearance of cytotoxic antibodies was delayed, and titers decreased from 1:256 in untreated controls to 1:16-1:64 both in the group that underwent Spx only and in the group that received 2.5 mg/kg/day DSG. Combined treatment suppressed antibody response for more than two weeks. Experiments on hyperacute rejection induced by sensitization revealed that 1 ml of hamster whole blood transfused into prospective heart recipients 1 week before grafting resulted in graft loss in 18.2 +/- 6.1 min. Pretransplant transfusion and concomitant daily administration of 5 mg/kg/day DSG until one day after grafting not only prevented hyperacute rejection but prolonged graft survival to 7.0 +/- 0.7 days. This survival was significantly longer than with DSG alone (4.2 +/- 0.8 days, P less than 0.01). We concluded that the marked suppression of antibody formation by DSG plays a major role in preventing first-set xenograft rejection and hyperacute rejection induced by sensitization.

Suppressor cells induced by donor-specific transfusion and deoxyspergualin in rat cardiac xenografts.

The effect of donor-specific blood transfusion (DST), in combination with pretransplant immunosuppression with deoxyspergualin (DSG), on hamster-to-Wistar rat cardiac xenograft survival was assessed. While DST given on day -6 sensitized the recipients, resulting in hyperacute xenograft rejection, the addition of 5 mg/kg/k/day DSG from the day of transfusion to the day of grafting not only prevented hyperacute rejection but resulted in prolongation of graft survival from 3.4 +/- 0.5 days in untreated controls to 7.0 +/- 0.7 days (P less than 0.01). In contrast, DSG alone as pretransplant immunosuppression had no beneficial effect and rejection occurred in 4.0 +/- 0.7 days. This effect appears to be at least donor species-specific, in the sense that ACI cardiac allograft survival was not prolonged when transplanted into xenotransfused and DSG-treated Wistar recipients. DST alone resulted in marked increase in antibody titers, showing the value of 1:512 or more on transplantation day. On the other hand, combined treatment suppressed the titers to 1:1-1:4 on that day. An adoptive cell transfer system was used to analyze the mechanisms underlying this effect. When sublethally irradiated secondary hosts were transferred with 5 x 10(7) lymph node cells (LNCs) harvested on day 0 from xenotransfused and DSG-treated rats, the test heart xenograft survived longer than the irradiated and nontransferred controls, suggesting the presence of suppressor cells. Further in vitro studies demonstrate that LNCs from DST+DSG-treated rats response less in a mixed lymphocyte reaction to hamster LNCs (41% on day 0 [P less than 0.01]), compared with the controls. In coculture experiments, the LNCs from treated recipients suppressed the response of unmodified Wistar LNCs to hamster LNCs by 76% on day 0 compared with the positive controls (P less than 0.01). On the other hand, the transfer of serum taken from treated rats on day 0 did not lead to prolongation of test heart xenografts in syngeneic naive hosts. These findings suggest that the mechanisms underlying the hyporesponsiveness induced by pretreatment with DST and DSG include the induction of suppressor cells, although a degree of clonal deletion can not be ruled out. The generation of serum suppressor factors seems to have no role in this phenomenon.

Immunological unresponsiveness to hepatic allografts in rats. Immunological reactivities of the recipient to donor antigens.

Wistar (RT1bv1) rats transplanted orthotopically with ACI (RT1a) livers survive indefinitely without any immunosuppression, while heterotopic heart grafts or skin grafts are rejected acutely in this combination. Levels of alkaline phosphatase after liver allografting remain significantly higher than those found in controls receiving syngeneic grafts. We studied changes in immune responsiveness in rats receiving liver grafts. Local graft-versus-host reactivity was present at all times assayed. Delayed type hypersensitivity reactions were already positive 2 weeks after liver transplantation and increased in strength. Liver graft-bearing rats were subsequently grafted with donor or third-party skin. Third-party skin grafts survived significantly longer on liver-grafted rats than on untreated controls when grafted within the first week after grafting. Donor-type skin grafts survived longer than controls when grafted within the first 4 weeks after liver grafting, although the skin grafts were eventually rejected. Donor-type skin grafted more than 8 weeks after liver grafting was rejected acutely. In an adoptive transfer assay, ACI hearts survived significantly longer in Wistar rats given serum from Wistar donors 2-4 weeks after ACI liver grafts than in untreated controls. On the other hand, spleen cells obtained at any period after liver grafting were not capable of prolonging cardiac allograft survival after transfer to syngeneic recipients. Thus cellular responses to ACI antigen are not changed during the life-span of liver-grafted animals. Evidence suggests that a serum "enhancing" factor protects the donor liver from rejection in the initial period after liver transplantation. The long-term acceptance of liver grafts is discussed.

Donor species complement after liver xenotransplantation. The mechanism of protection from hyperacute rejection.

Hamster hearts transplanted into stable rat recipients of hamster livers (OLT rats) were hyperacutely rejected after transfer with unaltered rat antihamster hyperimmune serum (HS). This was followed by immediate liver xenograft rejection in 4 of 5 rats. In contrast, simple heat inactivation of the rat HS resulted in prolonged survival of hamster hearts to 25 days without deterioration effect in the liver xenografts. This effect was species-specific because third-party mouse heart grafts in OLT rats were hyperacutely rejected in minutes if either active or heat inactivated antimouse HS was given. In cytotoxicity experiments, the complement in OLT serum produced weak lysis of hamster lymphocytes, while efficiently doing so with mouse cell targets. Because normal hamster serum caused no lysis at all of hamster target cells, the residual low-grade lysis of OLT serum was possibly being mediated by extrahepatic sources of rat C. In conclusion, the homology of C and target cells represents a mechanism of protection that the liver confers to other organs, and that is mostly easily seen in xenografts but may be allospecifically operational with allografts as well within the limits of MHC restriction.

Abrogation of chronic rejection in a murine model of aortic allotransplantation by prior induction of donor-specific tolerance.

Aortic allotransplantation in mice has been well established as a model of choice to study the evolvement of chronic rejection, the etiopathology of which is believed to be that of immune origin. This has prompted the postulation that prior induction of donor-specific tolerance would attenuate or abrogate the underlying events that culminate in posttransplant arteriosclerosis. To study the effects of donor-specific tolerance on chronic rejection, we performed orthotopic liver transplantation without immunosuppression in mice 30 days before aortic allotransplantation across C57Bl/ 10J (H2b)-->C3H (H2k) strain combinations (group III). Aortic allografting in syngeneic (group I; C3H-->C3H) and allogeneic (group II, C57Bl/10J-->C3H) animals served as controls. No morphological changes were evidenced in the transplanted aortas in group I animals. Contrarily, aortic allografts in group II animals underwent a self-limiting acute cellular rejection, which resolved completely and was succeeded by day 30 after transplantation by histopathological changes pathognomonic of chronic rejection. There was evidence for diffuse myointimal thickening, progressive concentric luminal narrowing, and patchy destruction of internal elastic membranes resulting in massive vascular obliteration by day 120 after transplantation. It was of interest that no arteriosclerotic changes were observed for the duration of follow-up (up to 120 days after transplantation) in transplanted aortas (liver donor-type) harvested from animals in group III. However, vasculopathy was prominent in third-party aortic grafts transplanted into tolerant recipients. Taken together, these data suggest that prior induction of tolerance abrogates the development of chronic rejection; this protection seems to be donor specific.

Biliary interleukin 6 levels as indicators of hepatic allograft rejection in rats.

Interleukin 6 has recently been noted to be present during the rejection response to grafted organs. In this study, we investigated biliary and serum interleukin 6 levels following liver transplantation in rats. IL-6 levels in bile and serum of naive rats were below 0.6 U/ml and 0.5 +/- 0.2 U/ml (mean +/- SD), respectively. Both biliary and serum IL-6 levels showed high values (greater than 10.0 U/ml and greater than 1.6 U/ml, respectively) on the day after transplantation, which seemed to reflect the inflammatory status caused by the surgical stress. Later samplings showed that the kinetics of serum IL-6 differed among the animals without any definite feature related to graft rejection. In contrast, biliary IL-6 levels correlated well with the severity of the rejection response as determined histologically. Biliary IL-6 levels started to rise at the onset of the rejection response (6.6 +/- 0.6 U/ml), increased further with its progression (19.3 +/- 7.8 U/ml), and then finally fell in the terminal stage (less than 2.0 U/ml). Elevation of biliary IL-6 was observed at an early stage when abnormalities could be detected histologically but not in liver function tests and bile flow. Therefore, biliary IL-6 levels may be of value for the early diagnosis of rejection following liver transplantation.

Tacrolimus pretreatment attenuates preexisting xenospecific immunity and abrogates hyperacute rejection in a presensitized hamster to rat liver transplant model.

In the hamster to rat liver transplant model, we determined the efficacy of tacrolimus in attenuating natural xenospecific humoral immunity and in abrogating the hyperacute liver rejection that is produced by presensitizing the Lewis rat recipient. Hamster livers, transplanted orthotopically into naive rats (controls), were rejected with animal death after 6.4.+/- 0.5 (SD) days. The infusion on (day -6) of 1.5 x 10(7) hamster hepatocytes, or of 1.5 x 10(8) nonparenchymal cells (NPC), resulted in hyperacute rejection and death in < or = 1.9 days. However, when the rats were pretreated with 1 mg/kg/day tacrolimus from days -6 to -1, survival of non-presensitized animals was prolonged to 25 +/- 20 days and that of recipients presensitized with hamster hepatocytes to 36 +/- l6 days or with NPC to 32 +/- 1.7 days. The tacrolimus pretreatment significantly reduced the hamster-specific complement-dependent cytotoxic antibodies response directed to liver NPC but not to lymph node cell targets. These observations suggest that the prolongation of survival by appropriately timed treatment with this T cell directed drug model is caused by the inhibition of humoral as well as cellular xenograft rejection.

Prolonged survival of hamster-to-rat liver xenografts using splenectomy and cyclosporine administration.

The immunosuppressive effect of splenectomy, alone or in combination with cyclosporine (CsA), was examined in hamster-to-rat orthotopic liver xenografts. The mean survival time was 7.3 +/- 0.5 days in untreated controls, 7.6 +/- 0.8 days with 40 mg/kg/day CsA, 7.2 +/- 0.4 days with splenectomy alone, and 17.6 +/- 5.6 days with splenectomy combined with 30 mg/kg/day CsA (P less than 0.01). The longest survival time was 27 days in this group. Marked enlargement of the spleen and high lymphocytotoxic antibody titer were characteristic of the unmodified recipients and those treated with CsA alone. Splenectomy by itself decreased the antibody formation without improvement of graft survival. In animals treated with the combined regimen, the lymphocytotoxic antibody titer was significantly suppressed, and the PMN and round cell infiltration were greatly reduced. Therefore, a synergistic effect was postulated between cyclosporine and splenectomy in this liver xenograft system.

Marked mitigation of transplant vascular sclerosis in FasLgld (CD95L) mutant recipients. The role of alloantibodies in the development of chronic rejection.

BACKGROUND: In the acute rejection of allografts, the interaction between Fas (CD95) and its ligand (FasL; CD95L) has been shown to be involved in mediating apoptotic cell death. The role, however, of these molecules in the pathogenesis of transplant vascular sclerosis is as yet undetermined. The present study was therefore designed to address this issue. MATERIAL: C3H/HEJ FasLgld (FasL-; H2k) spontaneously mutant mice were used either as donors or recipients of aortic allografts; wild-type C57B1/6 (B6; H2b) were used as corresponding recipients or donors (n=6/group), respectively. Controls included aortas transplanted across appropriate allogeneic and syngeneic strain combinations. For histopathological evaluations, the grafts were harvested at day 40 after transplantation, at which time, splenocytes and sera were also obtained for mixed leukocyte reaction and complement-mediated microcytotoxicity assays, respectively. RESULTS: Similar to aortas obtained from allogeneic controls, allografts harvested from FasL- -->B6 recipients had morphological evidence of chronic rejection characterized by circumferential intimal thickening with partial disruption of the elastic membranes. Correspondingly, heightened antidonor cellular reactivity was also witnessed in these recipients. On the contrary, B6 allografts harvested from the majority of C3H-->FasL- recipients exhibited marked preservation of aortic morphology. Although these recipients had diminished antidonor cellular proliferation, the titers of alloantibodies were markedly elevated. CONCLUSION: The presence of FasL-expressing functional cytotoxic T cells is required for the pathogenesis of transplant vascular sclerosis. The significant reduction and/or absence of chronic rejection with the concomitant retention of antidonor humoral response in C3H FasL- recipients of B6 aortas prompt us to suggest that perhaps posttransplantation vasculopathy is initiated by cell-mediated cytotoxicity with its perpetuation facilitated by alloantibodies.

Prevention of chronic rejection in mouse aortic allografts by combined treatment with CTLA4-Ig and anti-CD40 ligand monoclonal antibody.

BACKGROUND: In this study, using a murine model of aortic allotransplantation, the role of blockade of signaling through CD28/B7 and CD40/CD40 ligand costimulatory pathways in the evolvement of posttransplant vasculopathy was examined. METHODS: Aortic allografts were transplanted across C57BL/1OJ (H2b)-->C3H (H2k) strain combinations. Transient or more stable blockade of second signaling was achieved by either a single injection or multiple injections of CTLA4-Ig fusion protein (200 microg/dose i.p.) and/or anti-CD40 ligand (CD40L) monoclonal antibody (250 microg i.m.). At day 30 after transplantation, the grafts were harvested for histopathological and immunohistochemical examination. RESULTS: Similar to allografts of untreated animals, aortic allografts obtained from recipients treated with either CTLA4-Ig or anti-CD40L monoclonal antibody alone exhibited marked narrowing of the lumen primarily due to concentric intimal thickening caused by proliferation of alpha-smooth muscle actin-positive cells. Contemporaneous treatment, however, with either a single injection or multiple injections of CTLA4-Ig and anti-CD40L monoclonal antibody resulted in marked diminution of intimal thickening. Interestingly, concurrent prolonged inhibition of CD28/B7 and CD40/CD40L pathways resulted in complete abrogation of the development of posttransplant arteriopathy. CONCLUSION: These data suggest that a more stable disruption of signaling through costimulatory pathways may be required to obviate the development of posttransplant vasculopathy.

Effects of immunotherapy on experimental immunodeficiency-related lymphoproliferative disease.

BACKGROUND: Human lymphokine-activated cells (LAK cells) and interferon alpha (IFN-alpha) have been used clinically in the therapy of posttransplant lymphoproliferative disease (PTLD). However, the efficacy of such therapy has not been extensively tested under controlled experimental conditions. METHODS: A B-cell line, derived from PTLD tissue and clonally related to the parent lesion, was tested for its response to IFN-alpha in vitro. The effects of LAK cells and IFN-alpha therapy were examined in a severe combined immunodeficiency disease (SCID) mouse model in vivo. RESULTS: The PTLD cell line studied showed a 30% decrease in the rate of growth upon incubation with 500 U/ml of IFN-alpha. This in vitro response was also reproduced in vivo, in tumor therapy studies conducted in SCID mice. The magnitude of this inhibitory effect in vivo was a function of tumor burden and dose of IFN-alpha. In parallel experiments, LAK cells reduced the tumorigenicity of a lymphoblastoid cell line derived from the peripheral blood of a patient with PTLD, and prolonged the survival of SCID-beige mice with established lymphoproliferative disease. In contrast with two prior studies, in which the use of autologous cytotoxic T cells was found to be necessary, we found the administration of third-party non-HLA-matched LAK cells also to be effective in reducing tumor burden. CONCLUSIONS: These observations demonstrate the efficacy of immunotherapy for lymphoproliferative disease under controlled experimental conditions, and validate currently ongoing efforts exploring the utility of such therapy in the clinical setting.

Permanent acceptance of liver allografts by intraportal injection of donor spleen cells in rats.

Antigen pretreatment through the oral or intraportal route has been reported to suppress antibody formation or delayed-type hypersensitivity (DTH) response to the same antigens. However, this effect on allografted organs has not been well studied. In this study we evaluated the efficacy for suppression of antibody formation and DTH response to the allogeneic antigens and tried to prolong liver allograft survival in rats. Male ACI (RT1a) rats were used as donors and male BUF (RT1b) rats as recipients. Intraportal or intravenous injection of spleen cells (SPCs) (5 x 10(7)) was performed through the mesenteric vein or the tail vein, respectively. The anti-ACI DTH response was tested by ear challenge of ACI SPCs. Cytotoxic antibody was assessed by complement-dependent cytotoxicity assay. ACI rat liver was transplanted orthotopically to BUF rat by the cuff technique 10 days after SPC injection. Cytotoxic antibody titer rose to X2(6) to X2(8) at 7 to 10 days after intravenous injection of SPCs. However, intraportal injection of the cells rarely caused a rise in antibody titer and even strongly suppressed subsequent antibody formation induced by intravenous injection when given 10 days before. The DTH response was also suppressed by intraportal injection of SPCs, with a mean value of 0.18 +/- 0.13 mm versus 0.67 +/- 0.19 mm for controls or 0.46 +/- 0.04 mm with intravenous injection. Liver-allografted rats died between 9 and 11 days, averaging 10.1 +/- 0.7 days in the control group. All seven transplants injected intraportally with donor SPCs survived more than 100 days, whereas six of eight rats injected intravenously with donor SPCs died of bleeding from the surface of the liver grafts within 12 hours after grafting, with signs similar to those of hyperacute rejection. Four of five rats injected intraportally with F344 (third-party) SPCs died of acute rejection in the same way the control rats died. The liver allograft-bearing rats had permanently accepted ACI skin grafts when tested 60 days after liver transplantation but rejected F344 skin grafts in the normal fashion. Intraportal injection of donor SPCs markedly suppressed the antibody formation, as well as the DTH response, and completely blocked liver allograft rejection. Moreover, the liver allograft-bearing rats proved to be fully tolerant of the donor antigen. This method might be a promising modality for inducing donor-specific tolerance in liver transplantation.

A crucial effect of splenectomy on prolonging cardiac xenograft survival in combination with cyclosporine.

In this study we investigated the effect of splenectomy in combination with cyclosporine (CsA) on survival of heterotopic cardiac xenografts from hamster to rat. A 12-fold prolongation of mean cardiac xenograft survival, to 41 days, was accomplished with the combined therapy. In both untreated controls and CsA-treated recipients rejection occurred in 3 days. Splenectomy by itself prolonged xenograft function to 5 days. Evidence of humoral-mediated rejection in this cross-species combination was given for the extensive thrombosis and hemorrhage in the subepicardial area, the appearance of lymphocytotoxic titers just before graft function ceased, and the presence of IgM deposits in subepicardial vessels of the xenograft. CsA by itself could not modify this pattern of rejection. Splenectomy decreased antibody formation significantly and rejection became more cellular in nature. The regimen of splenectomy in association with CsA suppressed antibody titers and produced a CsA dose-dependent prolongation of xenograft survival. Thus, a complementary or synergistic effect is the result of the immunosuppressive regimen of splenectomy and CsA in hamster-to-rat cardiac xenografts. In this study the effect of splenectomy in controlling the humoral response in concordant xenografts and its role in future clinical xenografting is emphasized.

Functional cooperation of xenoproteins after hamster-to-rat liver transplantation: With particular reference to hamster C3 and secretory component for rat IgA.

Long-term survival after hamster-to-rat liver xenotransplantation has provided the opportunity to study the posttransplantation source of major serum proteins and the functional consequences of several different receptor-ligand interactions, where one or the other is a xenogeneic protein. We report here that serum albumin, α-1-antitrypsin, complement component 3, and other acute phase reactants switch from recipient to donor origin during the first week after transplantation while serum immunoglobulins remain largely that of recipient. Despite the disparate source of complement (hamster) and immunoglobulins (rat), these two proteins were able to cooperate effectively to produce lysis of sheep red blood cells. Moreover, rat IgA was successfully processed by hamster hepatocytes and biliary epithelial cells, being present in the bile of successful liver xenograft recipients within one day after transplantation. The ability of these liver xenograft recipients to survive long-term in conventional and viral-free animal facilities without grossly obvious morbidity or unusual susceptibility to stress, suggests that xenogeneic proteins are able to successfully interact with several different physiologic systems in the hamster-to-rat combination.