MEDLINE Abstracts: Xenotransplantation
MEDLINE Abstracts: Xenotransplantation
What's new concerning xenotransplantation? Find out in this easy-to-navigate collection of recent MEDLINE abstracts compiled by the editors at Medscape.
Moatti JP
Ann N Y Acad Sci 1998 Dec;862:188-201
Worldwide ethical considerations have led to banning markets for human organs and to promoting supply of organs for transplantation strictly on a donor noncommercial basis. In most industrialized countries, including France, there is a shortage of organs available for transplantation. Following on the earlier debate between Titmuss and Arrow over banning the market for blood supply, this presentation first challenges the conventional economic view that the ban is necessarily responsible for these critical shortages. It will argue that it is the obstacles to adequate exhortation (i.e., the efforts to inform and persuade participants in the donor system who cannot be paid for what they supply) rather than the inefficiency per se of appeals to donor altruism that are the cause of a shortage. The paper will then discuss the way a market for non-human organs may be an efficient alternative to a donor system by supplying a substitute good. Data from a survey in a random sample of the French general population (> or = 18 years of age in June 1997; response rate = 62.0%; n = 1,011) show that less than half of the respondents (42.4%) agreed that xenotransplantations should be developed. Support for xenotransplantation was higher (50.6% vs. 38.2% in the rest of the sample, p < 0.001) among respondents who declare that in case of an accidental death of a family member, they would accept the use of his organs for transplantation, among those with the highest level of knowledge about transplantation (48.6% vs. 39.4%, p < 0.005), and among blood donors (45.9% vs. 38.3%, p < 0.02). Supply of non-human organs should remain under the control of the public sector in order to be consonant with current donor systems for human organs. Recommendations for adequate regulation of the R&D process of non-human alternatives for organ transplantations will be made.
Coffman KL, Sher L, Hoffman A, et al.
Psychosomatics 1998 Jul-Aug;39(4):379-383
For centuries, many cultures have described mythical creatures with bodies that combined human and animal features, often the result of violating taboos. This study attempted to investigate the beliefs of transplant patients about xenografting. A survey was given to 100 patients ranging in age from 17 to 74 years old, with 65 men and 35 women, including 72 whites, 18 Hispanics, 5 African Americans, and 4 Asian Americans. The subjects included liver, heart, kidney, lung, and multi-organ transplant patients. The patients were not aware of plans for xenografting at the center under study. Eighty patients agreed with xenografting in an emergency situation. Ten subjects replied, "under no circumstances." Ninety percent believed animal research has advanced medical science. In descending order, the patients preferred human (96%), monkey (44%), mechanical (43%), pig (42%), or dog (34%) organs. Twenty-four patients thought a xenograft would change their appearance, personality, or eating or sexual habits. Twenty patients believed animals have souls. The patients also documented any ethical concerns about xenografting.
Schlitt HJ, Brunkhorst R, Haverich A, et al.
Langenbecks Arch Surg 1999 Aug;384(4):384-391
Background: The prospect of xenotransplantation has stimulated considerable hopes as well as major concerns. The question of whether or not patients accept xenografts is influenced not only by scientific facts but also by psychological factors. It was the aim of this study to analyze the attitudes of patients toward transplantation of xenogeneic organs and evaluate factors influencing these attitudes.
Methods: To this end, attitudes toward xenogeneic compared with allogeneic organ grafts were evaluated by means of detailed questionnaires in 1049 patients in Germany, who either had received transplants (n=722) or were on the waiting list for various organ grafts (n=327). Answers were correlated to demographic data as well as to the physical and mental conditions of the patients.
Results: The survey indicates that 77% of patients would accept xenografts while 7% would refuse them if results of xenotransplantation were comparable with those of allotransplantation. If xenotransplantation were associated with increased risks due to more intensive medication 58% would still basically accept xenografts. Acceptance of xenografts was significantly higher in patients who had received transplants and among males. Age, religion, waiting time, and type of organ were not found to influence acceptance rates. Xenografts were thought to be associated with considerable or severe emotional stress by 23% of patients, versus 3% for allografts. The pig was the preferred donor animal, and gene therapeutic manipulation for improvement of results would be accepted by 84%. Inadequate graft function/increased risk of rejection and risk of disease transmission were the major concerns for 60% and 52% of patients, respectively; emotional concerns were the major concerns for 24% and animal-rights concerns for 15%.
Conclusions: These findings show that the potential acceptance rate of xenografts would be quite high, with a more positive attitude in transplanted patients than in waiting-list patients; there was no major difference in acceptance rate for various types of organs. Major concerns about xenotransplantation currently are functional inferiority and transmission of diseases.
Medbury HJ, Hibbins M, Lehnert AM, et al.
Transplantation 1997 Nov 15;64(9):1307-1314
Background: Islet xenografts have clinical potential, may avoid hyperacute rejection, and therefore are a good place to examine the cellular xenograft immune response. The aim of this study was to examine the cellular, humoral, and cytokine response in islet xenograft rejection and to determine the difference in the immune response with a different donor species.
Methods: Two islet xenograft models (DA rat islets to B6AF1 mouse and canine islets to B6AF1 mouse) and a mouse syngeneic control model were examined histologically and by a semiquantitative polymerase chain reaction method.
Results: There was significant up-regulation of all intragraft cytokines tested (interleukin [IL]-2, IL-4, IL-5, IL-10, and interferon-gamma) in both xenograft models compared with the controls. However, the dog islet grafts had higher levels of IL-4 and IL-5 gene expression than the rat islet grafts, which, conversely, had higher levels of interferon-gamma gene expression. These differences correlated with the histological and anti-donor antibody production differences between the two models. The dog to mouse model had an intense eosinophilic infiltrate and an early up-regulation of anti-donor antibody, whereas there was little eosinophilic infiltrate and a delayed anti-donor antibody up-regulation in the rat to mouse model.
Conclusions: The mouse used different mechanisms to reject the rat and canine islets, suggesting that the immune response in islet xenograft rejection may be dependent on the species combination. It may not be possible to characterize the cellular xenograft rejection response in a bipolar manner as has been the case with humoral rejection response. Caution therefore needs to be taken before extrapolating the cellular immune responses seen in animal models to the clinical setting.
King K
EDNTNA ERCA J 1998 Jul-Sep;24(3):25-26
Xenotransplantation research has occurred intermittently without success this century and is also not an area without controversy, which includes the potential health risks that could occur and the use of animals. The tremendous discrepancy between those in need of transplantation and the number of living and cadaveric donors has once again renewed interest in this field. The National Kidney Foundation undertook an opinion survey to facilitate understanding of both transplant recipients' and non-recipients' knowledge of, and attitudes toward, xenotransplantation. The majority of respondents approved of the concept and greater than 70% of both groups would consider a xenotransplant. The main concern of both groups was the ability of the animal organ to function properly.
Obatake M, Kushida M, Kimmel S, et al.
Transplantation 1999 Jun 15;67(11):1480-1484
Background: A new vascularized concordant xenotransplant model using the Chinese hamster as donor and mouse as recipient species is reported. This model takes advantage of the wealth of informative immune reagents and knockout and transgenic backgrounds available for the mouse.
Methods: Heterotopic auxillary cardiac transplantation was performed. The mean survival time was assessed by daily palpation. Xenoreactive antibody production was measured by flow cytometry, and cardiac xenografts were examined by light microscopy.
Results: The tempo of xenograft rejection in this model is consistent with concordant species combination. IgM and IgG3 responses were not critical for the concordant xenograft rejection. Long-term survival (>100 days) of the concordant cardiac xenografts was observed without any immunosuppression in nude mice. Reconstitution of nude mice with CD3+ T cells induced the xenograft rejection in 5.7 days (P<0.01).
Conclusion: This new concordant cardiac xenotransplant model demonstrates that T-dependent xenogeneic immune response is necessary and critical for the xenograft rejection.
Blum MG, Collins BJ, Chang AC, et al.
Xenotransplantation 1998 Feb;5(1):35-43
Two complement inhibitors, FUT-175 (FUT) and K76-COOH (K76), were studied as single agents in an ex vivo, in situ model of pig lung rejection by human blood. Pulmonary toxicity (primarily increased pulmonary vascular resistance [PVR]) was seen with FUT at a dose which inhibited complement in vitro (0.4 mg/ml); a lower dose (0.1 mg/ml) was therefore used. K76 had little apparent toxicity at a dose which inhibited complement in vitro (6 mg/ml), but activated complement, leading to C3a elaboration. Efficacy was then assessed by 1) deposition of complement pathway components in the lung and 2) lung survival during perfusion with human blood. Neither agent consistently prolonged median lung survival (FUT: 50 min. +/- 28 SEM; K76: 37 +/- 16), blocked thromboxane production, or prevented PVR elevation compared to experiments using unmodified human blood (survival 9 min. +/- 2). At the doses used, both agents prevented deposition of terminal complement complex (TCC) in the lung. This finding demonstrates that the various phenomena associated with hyperacute lung rejection (thromboxane release, PVR elevation, capillary leak, and intraalveolar hemorrhage) can all occur despite abrogation of membrane attack complex formation. We can not exclude a contribution by drug toxicity or complement damage (mediated by C3a or other complement pathway components proximal to TCC) to the observed lung injury. We conclude that, although both FUT and K76 inhibit deposition of TCC in the lung, at the dose tested neither drug is useful as a single agent to prolong survival in a pig-to-human lung xenograft model.
Palmetshofer A, Galili U, Dalmasso AP, et al.
Transplantation 1998 Apr 15;65(7):971-978
Background: Xenoreactive natural antibodies (XNAs) and complement mediate hyperacute rejection of discordant xenografts. Inhibition of complement alone results in some prolongation of graft survival, but delayed xenograft rejection still precludes long-term graft survival. In vitro data provide evidence for the direct proinflammatory activation of endothelial cells (ECs) by XNAs. These antibodies are primarily directed against galactose alpha(1-3)-galactose (alpha-gal), the major xenoantigen in the pig to primate xenotransplant model. Previous studies have shown EC activation by XNAs but failed to address the question of whether alpha-gal-specific ligands can induce EC activation. The aim of this study was to investigate whether agonist binding to the alpha-gal epitope by alpha-gal-specific lectins as compared with XNAs or elicited xenoreactive antibodies can directly elicit type II porcine aortic EC (PAEC) activation (i.e., activation that requires protein synthesis).
Methods and Results: The tetravalent, alpha-gal-binding Bandeiraea simplicifolia lectin I (BS-I), the wholly alpha-gal-specific BS-I isolectin B4, and elicited primate anti-pig xenoreactive antibodies (decomplemented cynomolgus monkey anti-porcine serum) induced E-selectin protein expression in PAECs. This induction was alpha-gal-specific, as preincubation with synthetic alpha-gal carbohydrate or adsorption of lectin or serum to rabbit, but not human, red blood cells removed the activating component. E-selectin expression, induced by BS-I, was inhibited in the presence of genistein, a tyrosine kinase inhibitor, and by mepacrine, an inhibitor of phospholipase A2. Human and primate XNAs lacked this activity when tested at relevant concentrations; however, stimulation of PAECs with affinity-purified human XNA (IgM and IgG) resulted in slightly increased interleukin-8 and P-selectin mRNA levels but had no apparent effects on E-selectin transcription. BS-I strongly induced E-selectin, P-selectin, intercellular adhesion molecule-1, and interleukin-8 mRNA in an NF-kappaB-dependent manner.
Conclusions: Several agonists that specifically bind to alpha-gal can evoke type II EC activation. Hence, anti-Gal antibodies may contribute directly to xenograft rejection in the absence of complement activation.
Lin SS, Weidner BC, Byrne GW, et al.
J Clin Invest 1998 Apr 15;101(8):1745-1756
Long-term success in xenotransplantation is currently hampered by acute vascular rejection. The inciting cause of acute vascular rejection is not yet known; however, a variety of observations suggest that the humoral immune response of the recipient against the donor may be involved in the pathogenesis of this process. Using a pig-to-baboon heterotopic cardiac transplant model, we examined the role of antibodies in the development of acute vascular rejection. After transplantation into baboons, hearts from transgenic pigs expressing human decay-accelerating factor and CD59 underwent acute vascular rejection leading to graft failure within 5 d; the histology was characterized by endothelial injury and fibrin thrombi. Hearts from the transgenic pigs transplanted into baboons whose circulating antibodies were depleted using anti-immunoglobulin columns (Therasorb, Unterschleisshein, Germany) did not undergo acute vascular rejection in five of six cases. Biopsies from the xenotransplants in Ig-depleted baboons revealed little or no IgM or IgG, and no histologic evidence of acute vascular rejection in the five cases. Complement activity in the baboons was within the normal range during the period of xenograft survival. In one case, acute vascular rejection of a xenotransplant occurred in a baboon in which the level of antidonor antibody rose after Ig depletion was discontinued. This study provides evidence that antibodies play a significant role in the pathogenesis of acute vascular rejection, and suggests that acute vascular rejection might be prevented or treated by therapies aimed at the humoral immune response to porcine antigens.
Zaidi A, Schmoeckel M, Bhatti F, et al.
Transplantation 1998 Jun 27;65(12):1584-1590
Background: In order to circumvent the complement-mediated hyperacute rejection of discordant xenografts, a colony of pigs transgenic for the human regulator of complement activity, human decay-accelerating factor (hDAF), has been produced.
Methods: Seven kidneys from hDAF transgenic pigs and six kidneys from nontransgenic control pigs were transplanted into cynomolgus monkeys; both native kidneys were removed during the same operation. The recipient animals were immunosuppressed with cyclosporine, steroids, and cyclophosphamide.
Results: In the transgenic group, the median survival time was 13 days (range, 6-35 days); the median survival time in the control group was 6.5 days (range, 0.3-30 days). There were no cases of hyperacute rejection in the transgenic group, and the two longest-surviving kidneys in this group showed no evidence of rejection on histological examination. In contrast, all control kidneys underwent antibody-mediated rejection, one demonstrating hyperacute rejection and the others acute vascular rejection.
Conclusion: This study demonstrates that (i) a kidney from an hDAF transgenic pig can support the life of a primate for up to 35 days (and also shows the basic physiological compatibility between the pig and nonhuman primate); (ii) nontransgenic kidneys are not routinely hyperacutely rejected; and (iii) the presence of hDAF on the kidney confers some protection against acute vascular rejection. Improved immunosuppression and immunological monitoring may enable extended survival.
Friedman T, Smith RN, Colvin RB, et al.
Diabetes 1999 Dec;48(12):2340-2348
T-cell-mediated rejection is likely to present a significant barrier to porcine islet xenotransplantation. Little is known, however, about human anti-porcine islet rejection because no suitable model exists to study this process. To address this problem, we have developed an immunodeficient mouse model to study rejection of fetal porcine islet cell clusters (ICCs) by human lymphocytes. Transplantation of porcine ICCs into hyperglycemic recombinase activating gene-deficient (R-) mice restores normal blood glucose levels within 5 weeks. Adoptive transfer of in vitro-stimulated human peripheral blood mononuclear cells into R- mice before islet cell transplantation leads to acute cellular rejection of porcine ICCs. The first human cells observed to infiltrate rejecting grafts are CD4+ T-cells. Although CD8+ T-cells are observed within the grafts at later time points, CD4+ T-cells predominate until the graft is destroyed. Adoptive transfer of purified human CD4+ T-cells before ICC transplantation is sufficient to cause acute cellular rejection. These data demonstrate that human CD4+ T-cells play a critical role in porcine ICC xenograft rejection.
Bellucci S, Bondolfi A, Husing B, Ruegsegger A
Ann N Y Acad Sci 1998 Dec 30;862:155-165
The Swiss Technology Assessment (TA) project on xenotransplantation is intended to study the opportunities and risks of this technique, recognizing the input of those involved in and those affected by it. This also implies taking into account the clinicoscientific, social, ethical, economic, and legal aspects. The situation in Switzerland is analyzed in depth, with reference to the acceptance, ethics, and existing federal legislation pertinent to xenotransplantation. Apart from consultation with experts from various specialized areas, a written questionnaire was sent to more than 100 organizations, institutions, companies, and individuals. The resulting assessments range from clear approval to complete rejection of the notion of xenotransplantation. Even acceptance was granted only on condition that criteria such as security (minimum risk of infection) and respect for human dignity and animal protection issues are respected. Such criteria are generally accepted, but if concrete conclusions must be drawn, we must recognize that opinions vary in today's discussions on ethics in Switzerland. It is commonly agreed that animals are not objects, but their precise status is not clear. Moreover, there are no patented ethical "recipes" for handling risks.
MEDLINE Abstracts: Xenotransplantation
What's new concerning xenotransplantation? Find out in this easy-to-navigate collection of recent MEDLINE abstracts compiled by the editors at Medscape.
Researcher-Driven Versus Policy-Driven Economic Appraisal. The Case of Xenotransplantation
Moatti JP
Ann N Y Acad Sci 1998 Dec;862:188-201
Worldwide ethical considerations have led to banning markets for human organs and to promoting supply of organs for transplantation strictly on a donor noncommercial basis. In most industrialized countries, including France, there is a shortage of organs available for transplantation. Following on the earlier debate between Titmuss and Arrow over banning the market for blood supply, this presentation first challenges the conventional economic view that the ban is necessarily responsible for these critical shortages. It will argue that it is the obstacles to adequate exhortation (i.e., the efforts to inform and persuade participants in the donor system who cannot be paid for what they supply) rather than the inefficiency per se of appeals to donor altruism that are the cause of a shortage. The paper will then discuss the way a market for non-human organs may be an efficient alternative to a donor system by supplying a substitute good. Data from a survey in a random sample of the French general population (> or = 18 years of age in June 1997; response rate = 62.0%; n = 1,011) show that less than half of the respondents (42.4%) agreed that xenotransplantations should be developed. Support for xenotransplantation was higher (50.6% vs. 38.2% in the rest of the sample, p < 0.001) among respondents who declare that in case of an accidental death of a family member, they would accept the use of his organs for transplantation, among those with the highest level of knowledge about transplantation (48.6% vs. 39.4%, p < 0.005), and among blood donors (45.9% vs. 38.3%, p < 0.02). Supply of non-human organs should remain under the control of the public sector in order to be consonant with current donor systems for human organs. Recommendations for adequate regulation of the R&D process of non-human alternatives for organ transplantations will be made.
Survey Results of Transplant Patients' Attitudes on Xenografting
Coffman KL, Sher L, Hoffman A, et al.
Psychosomatics 1998 Jul-Aug;39(4):379-383
For centuries, many cultures have described mythical creatures with bodies that combined human and animal features, often the result of violating taboos. This study attempted to investigate the beliefs of transplant patients about xenografting. A survey was given to 100 patients ranging in age from 17 to 74 years old, with 65 men and 35 women, including 72 whites, 18 Hispanics, 5 African Americans, and 4 Asian Americans. The subjects included liver, heart, kidney, lung, and multi-organ transplant patients. The patients were not aware of plans for xenografting at the center under study. Eighty patients agreed with xenografting in an emergency situation. Ten subjects replied, "under no circumstances." Ninety percent believed animal research has advanced medical science. In descending order, the patients preferred human (96%), monkey (44%), mechanical (43%), pig (42%), or dog (34%) organs. Twenty-four patients thought a xenograft would change their appearance, personality, or eating or sexual habits. Twenty patients believed animals have souls. The patients also documented any ethical concerns about xenografting.
Attitude of Patients Toward Transplantation of Xenogeneic Organs
Schlitt HJ, Brunkhorst R, Haverich A, et al.
Langenbecks Arch Surg 1999 Aug;384(4):384-391
Background: The prospect of xenotransplantation has stimulated considerable hopes as well as major concerns. The question of whether or not patients accept xenografts is influenced not only by scientific facts but also by psychological factors. It was the aim of this study to analyze the attitudes of patients toward transplantation of xenogeneic organs and evaluate factors influencing these attitudes.
Methods: To this end, attitudes toward xenogeneic compared with allogeneic organ grafts were evaluated by means of detailed questionnaires in 1049 patients in Germany, who either had received transplants (n=722) or were on the waiting list for various organ grafts (n=327). Answers were correlated to demographic data as well as to the physical and mental conditions of the patients.
Results: The survey indicates that 77% of patients would accept xenografts while 7% would refuse them if results of xenotransplantation were comparable with those of allotransplantation. If xenotransplantation were associated with increased risks due to more intensive medication 58% would still basically accept xenografts. Acceptance of xenografts was significantly higher in patients who had received transplants and among males. Age, religion, waiting time, and type of organ were not found to influence acceptance rates. Xenografts were thought to be associated with considerable or severe emotional stress by 23% of patients, versus 3% for allografts. The pig was the preferred donor animal, and gene therapeutic manipulation for improvement of results would be accepted by 84%. Inadequate graft function/increased risk of rejection and risk of disease transmission were the major concerns for 60% and 52% of patients, respectively; emotional concerns were the major concerns for 24% and animal-rights concerns for 15%.
Conclusions: These findings show that the potential acceptance rate of xenografts would be quite high, with a more positive attitude in transplanted patients than in waiting-list patients; there was no major difference in acceptance rate for various types of organs. Major concerns about xenotransplantation currently are functional inferiority and transmission of diseases.
The Cytokine and Histological Response in Islet Xenograft Rejection is Dependent Upon Species Combination
Medbury HJ, Hibbins M, Lehnert AM, et al.
Transplantation 1997 Nov 15;64(9):1307-1314
Background: Islet xenografts have clinical potential, may avoid hyperacute rejection, and therefore are a good place to examine the cellular xenograft immune response. The aim of this study was to examine the cellular, humoral, and cytokine response in islet xenograft rejection and to determine the difference in the immune response with a different donor species.
Methods: Two islet xenograft models (DA rat islets to B6AF1 mouse and canine islets to B6AF1 mouse) and a mouse syngeneic control model were examined histologically and by a semiquantitative polymerase chain reaction method.
Results: There was significant up-regulation of all intragraft cytokines tested (interleukin [IL]-2, IL-4, IL-5, IL-10, and interferon-gamma) in both xenograft models compared with the controls. However, the dog islet grafts had higher levels of IL-4 and IL-5 gene expression than the rat islet grafts, which, conversely, had higher levels of interferon-gamma gene expression. These differences correlated with the histological and anti-donor antibody production differences between the two models. The dog to mouse model had an intense eosinophilic infiltrate and an early up-regulation of anti-donor antibody, whereas there was little eosinophilic infiltrate and a delayed anti-donor antibody up-regulation in the rat to mouse model.
Conclusions: The mouse used different mechanisms to reject the rat and canine islets, suggesting that the immune response in islet xenograft rejection may be dependent on the species combination. It may not be possible to characterize the cellular xenograft rejection response in a bipolar manner as has been the case with humoral rejection response. Caution therefore needs to be taken before extrapolating the cellular immune responses seen in animal models to the clinical setting.
Recipient and Non-recipient Attitudes Regarding Xenotransplantation
King K
EDNTNA ERCA J 1998 Jul-Sep;24(3):25-26
Xenotransplantation research has occurred intermittently without success this century and is also not an area without controversy, which includes the potential health risks that could occur and the use of animals. The tremendous discrepancy between those in need of transplantation and the number of living and cadaveric donors has once again renewed interest in this field. The National Kidney Foundation undertook an opinion survey to facilitate understanding of both transplant recipients' and non-recipients' knowledge of, and attitudes toward, xenotransplantation. The majority of respondents approved of the concept and greater than 70% of both groups would consider a xenotransplant. The main concern of both groups was the ability of the animal organ to function properly.
T cells Are Necessary and Critical for Xenograft Rejection in New Concordant Cardiac Xenotransplant Model
Obatake M, Kushida M, Kimmel S, et al.
Transplantation 1999 Jun 15;67(11):1480-1484
Background: A new vascularized concordant xenotransplant model using the Chinese hamster as donor and mouse as recipient species is reported. This model takes advantage of the wealth of informative immune reagents and knockout and transgenic backgrounds available for the mouse.
Methods: Heterotopic auxillary cardiac transplantation was performed. The mean survival time was assessed by daily palpation. Xenoreactive antibody production was measured by flow cytometry, and cardiac xenografts were examined by light microscopy.
Results: The tempo of xenograft rejection in this model is consistent with concordant species combination. IgM and IgG3 responses were not critical for the concordant xenograft rejection. Long-term survival (>100 days) of the concordant cardiac xenografts was observed without any immunosuppression in nude mice. Reconstitution of nude mice with CD3+ T cells induced the xenograft rejection in 5.7 days (P<0.01).
Conclusion: This new concordant cardiac xenotransplant model demonstrates that T-dependent xenogeneic immune response is necessary and critical for the xenograft rejection.
Complement Inhibition by FUT-175 and K76-COOH in a Pig-to-Human Lung Xenotransplant Model
Blum MG, Collins BJ, Chang AC, et al.
Xenotransplantation 1998 Feb;5(1):35-43
Two complement inhibitors, FUT-175 (FUT) and K76-COOH (K76), were studied as single agents in an ex vivo, in situ model of pig lung rejection by human blood. Pulmonary toxicity (primarily increased pulmonary vascular resistance [PVR]) was seen with FUT at a dose which inhibited complement in vitro (0.4 mg/ml); a lower dose (0.1 mg/ml) was therefore used. K76 had little apparent toxicity at a dose which inhibited complement in vitro (6 mg/ml), but activated complement, leading to C3a elaboration. Efficacy was then assessed by 1) deposition of complement pathway components in the lung and 2) lung survival during perfusion with human blood. Neither agent consistently prolonged median lung survival (FUT: 50 min. +/- 28 SEM; K76: 37 +/- 16), blocked thromboxane production, or prevented PVR elevation compared to experiments using unmodified human blood (survival 9 min. +/- 2). At the doses used, both agents prevented deposition of terminal complement complex (TCC) in the lung. This finding demonstrates that the various phenomena associated with hyperacute lung rejection (thromboxane release, PVR elevation, capillary leak, and intraalveolar hemorrhage) can all occur despite abrogation of membrane attack complex formation. We can not exclude a contribution by drug toxicity or complement damage (mediated by C3a or other complement pathway components proximal to TCC) to the observed lung injury. We conclude that, although both FUT and K76 inhibit deposition of TCC in the lung, at the dose tested neither drug is useful as a single agent to prolong survival in a pig-to-human lung xenograft model.
Alpha-galactosyl Epitope-Mediated Activation of Porcine Aortic Endothelial Cells: Type II Activation
Palmetshofer A, Galili U, Dalmasso AP, et al.
Transplantation 1998 Apr 15;65(7):971-978
Background: Xenoreactive natural antibodies (XNAs) and complement mediate hyperacute rejection of discordant xenografts. Inhibition of complement alone results in some prolongation of graft survival, but delayed xenograft rejection still precludes long-term graft survival. In vitro data provide evidence for the direct proinflammatory activation of endothelial cells (ECs) by XNAs. These antibodies are primarily directed against galactose alpha(1-3)-galactose (alpha-gal), the major xenoantigen in the pig to primate xenotransplant model. Previous studies have shown EC activation by XNAs but failed to address the question of whether alpha-gal-specific ligands can induce EC activation. The aim of this study was to investigate whether agonist binding to the alpha-gal epitope by alpha-gal-specific lectins as compared with XNAs or elicited xenoreactive antibodies can directly elicit type II porcine aortic EC (PAEC) activation (i.e., activation that requires protein synthesis).
Methods and Results: The tetravalent, alpha-gal-binding Bandeiraea simplicifolia lectin I (BS-I), the wholly alpha-gal-specific BS-I isolectin B4, and elicited primate anti-pig xenoreactive antibodies (decomplemented cynomolgus monkey anti-porcine serum) induced E-selectin protein expression in PAECs. This induction was alpha-gal-specific, as preincubation with synthetic alpha-gal carbohydrate or adsorption of lectin or serum to rabbit, but not human, red blood cells removed the activating component. E-selectin expression, induced by BS-I, was inhibited in the presence of genistein, a tyrosine kinase inhibitor, and by mepacrine, an inhibitor of phospholipase A2. Human and primate XNAs lacked this activity when tested at relevant concentrations; however, stimulation of PAECs with affinity-purified human XNA (IgM and IgG) resulted in slightly increased interleukin-8 and P-selectin mRNA levels but had no apparent effects on E-selectin transcription. BS-I strongly induced E-selectin, P-selectin, intercellular adhesion molecule-1, and interleukin-8 mRNA in an NF-kappaB-dependent manner.
Conclusions: Several agonists that specifically bind to alpha-gal can evoke type II EC activation. Hence, anti-Gal antibodies may contribute directly to xenograft rejection in the absence of complement activation.
The Role of Antibodies in Acute Vascular Rejection of Pig-to-Baboon Cardiac Transplants
Lin SS, Weidner BC, Byrne GW, et al.
J Clin Invest 1998 Apr 15;101(8):1745-1756
Long-term success in xenotransplantation is currently hampered by acute vascular rejection. The inciting cause of acute vascular rejection is not yet known; however, a variety of observations suggest that the humoral immune response of the recipient against the donor may be involved in the pathogenesis of this process. Using a pig-to-baboon heterotopic cardiac transplant model, we examined the role of antibodies in the development of acute vascular rejection. After transplantation into baboons, hearts from transgenic pigs expressing human decay-accelerating factor and CD59 underwent acute vascular rejection leading to graft failure within 5 d; the histology was characterized by endothelial injury and fibrin thrombi. Hearts from the transgenic pigs transplanted into baboons whose circulating antibodies were depleted using anti-immunoglobulin columns (Therasorb, Unterschleisshein, Germany) did not undergo acute vascular rejection in five of six cases. Biopsies from the xenotransplants in Ig-depleted baboons revealed little or no IgM or IgG, and no histologic evidence of acute vascular rejection in the five cases. Complement activity in the baboons was within the normal range during the period of xenograft survival. In one case, acute vascular rejection of a xenotransplant occurred in a baboon in which the level of antidonor antibody rose after Ig depletion was discontinued. This study provides evidence that antibodies play a significant role in the pathogenesis of acute vascular rejection, and suggests that acute vascular rejection might be prevented or treated by therapies aimed at the humoral immune response to porcine antigens.
Life-Supporting Pig-to-Primate Renal Xenotransplantation Using Genetically Modified Donors
Zaidi A, Schmoeckel M, Bhatti F, et al.
Transplantation 1998 Jun 27;65(12):1584-1590
Background: In order to circumvent the complement-mediated hyperacute rejection of discordant xenografts, a colony of pigs transgenic for the human regulator of complement activity, human decay-accelerating factor (hDAF), has been produced.
Methods: Seven kidneys from hDAF transgenic pigs and six kidneys from nontransgenic control pigs were transplanted into cynomolgus monkeys; both native kidneys were removed during the same operation. The recipient animals were immunosuppressed with cyclosporine, steroids, and cyclophosphamide.
Results: In the transgenic group, the median survival time was 13 days (range, 6-35 days); the median survival time in the control group was 6.5 days (range, 0.3-30 days). There were no cases of hyperacute rejection in the transgenic group, and the two longest-surviving kidneys in this group showed no evidence of rejection on histological examination. In contrast, all control kidneys underwent antibody-mediated rejection, one demonstrating hyperacute rejection and the others acute vascular rejection.
Conclusion: This study demonstrates that (i) a kidney from an hDAF transgenic pig can support the life of a primate for up to 35 days (and also shows the basic physiological compatibility between the pig and nonhuman primate); (ii) nontransgenic kidneys are not routinely hyperacutely rejected; and (iii) the presence of hDAF on the kidney confers some protection against acute vascular rejection. Improved immunosuppression and immunological monitoring may enable extended survival.
A Critical Role for Human CD4+ T-cells in Rejection of Porcine Islet Cell Xenografts
Friedman T, Smith RN, Colvin RB, et al.
Diabetes 1999 Dec;48(12):2340-2348
T-cell-mediated rejection is likely to present a significant barrier to porcine islet xenotransplantation. Little is known, however, about human anti-porcine islet rejection because no suitable model exists to study this process. To address this problem, we have developed an immunodeficient mouse model to study rejection of fetal porcine islet cell clusters (ICCs) by human lymphocytes. Transplantation of porcine ICCs into hyperglycemic recombinase activating gene-deficient (R-) mice restores normal blood glucose levels within 5 weeks. Adoptive transfer of in vitro-stimulated human peripheral blood mononuclear cells into R- mice before islet cell transplantation leads to acute cellular rejection of porcine ICCs. The first human cells observed to infiltrate rejecting grafts are CD4+ T-cells. Although CD8+ T-cells are observed within the grafts at later time points, CD4+ T-cells predominate until the graft is destroyed. Adoptive transfer of purified human CD4+ T-cells before ICC transplantation is sufficient to cause acute cellular rejection. These data demonstrate that human CD4+ T-cells play a critical role in porcine ICC xenograft rejection.
The Swiss Technology Assessment Project on Xenotransplantation
Bellucci S, Bondolfi A, Husing B, Ruegsegger A
Ann N Y Acad Sci 1998 Dec 30;862:155-165
The Swiss Technology Assessment (TA) project on xenotransplantation is intended to study the opportunities and risks of this technique, recognizing the input of those involved in and those affected by it. This also implies taking into account the clinicoscientific, social, ethical, economic, and legal aspects. The situation in Switzerland is analyzed in depth, with reference to the acceptance, ethics, and existing federal legislation pertinent to xenotransplantation. Apart from consultation with experts from various specialized areas, a written questionnaire was sent to more than 100 organizations, institutions, companies, and individuals. The resulting assessments range from clear approval to complete rejection of the notion of xenotransplantation. Even acceptance was granted only on condition that criteria such as security (minimum risk of infection) and respect for human dignity and animal protection issues are respected. Such criteria are generally accepted, but if concrete conclusions must be drawn, we must recognize that opinions vary in today's discussions on ethics in Switzerland. It is commonly agreed that animals are not objects, but their precise status is not clear. Moreover, there are no patented ethical "recipes" for handling risks.
