气管异种移植的现状

气管异种移植目前还处于动物实验阶段,尚不能应用于临床,主要原因是异种气管移植后的免疫排斥问题未能解决,社会伦理学方面还存有争议。移植气管的保存与再血管化也是当前所面临的主要问题。其中,能否解决移植后宿主对气管的免疫排斥是移植成败的关键。该文通过介绍异种气管移植的概况,了解其研究进展及所面临的挑战。     

C1 inhibitor for prophylaxis of xenograft rejection after pig to cynomolgus monkey kidney transplantation

BACKGROUND: Early rejection of discordant porcine xenografts in primate recipients is initiated by the intragraft binding of either preformed (hyperacute xenograft rejection) or induced (acute vascular rejection) antiporcine recipient antibodies with subsequent complement activation via the classical pathway. We have investigated the efficacy of the supplemental administration of C1-inhibitor (C1-INH), a specific inhibitor of the classical complement activation pathway, for prophylaxis of xenograft rejection in a pig to primate kidney xenotransplantation setting. METHODS: Based on the results of pharmacokinetic studies performed in two nontransplanted monkeys, supplemental C1-INH therapy was administered daily to three Cynomolgus monkeys receiving a life-supporting porcine kidney transplant together with cyclophosphamide-induction/cyclosporine A/mycophenolat-mofetil/steroid immunosuppressive therapy. RESULTS: In the three monkeys receiving porcine kidney xenografts and continuous C1-INH treatment none of the grafts underwent hyperacute rejection; all xenografts showed initial function. Recipient survival was 13, 15, and 5 days. No graft was lost due to acute vascular rejection. All animals died with a functioning graft (latest creatinine 96, 112, and 96 micromol/liter) due to bacterial septicemia. CONCLUSION: We conclude that, in our model, supplemental C1-INH therapy together with a standard immunosuppressive regimen can be helpful for prevention of xenograft rejection in a pig to primate kidney xenotransplantation setting. The optimal dose and duration of C1-INH treatment, however, has yet to be determined.     

Acute cellular xenograft rejection

Abstract: The acute cellular rejection process after xenotransplantation of vascularized organs, i.e. heart, kidney and liver, has so far been difficult to study since the implanted organs are lost in a hyperacute rejection before cellular rejection develops. Primarily non-vascularized xenografts-e.g. pancreatic islets-escape the hyperacute rejection, but succumb to cell-mediated rejection during the first week after transplantation in either mice, rats or cynomolugus monkeys. The present view on the mechanisms orchestrating islet xenograft rejection in these animal models will be summarized and in part generalized to give insight into the process of acute cellular xenograft rejection.     

FTY720在鼠类异种胰岛移植排斥反应中的作用

目的 在小鼠异种胰岛细胞移植模型上，研究FTY720在控制异种胰岛移植排斥反应中的作用。方法 使用胰管内胶原酶注射和不连续密度梯度纯化法获取大鼠胰岛，建立小鼠肾被膜下移植模型。受体小鼠随机分为3组：对照组，末使用任何免疫抑制药物；实验1组，自移植当日起每日单独喂服FTY720(1.0mg／kg)；实验2组，亦于移植当日起每日联合喂服FTY720(1.0mg／kg)和环孢霉素A(CsA，15mg／kg)，均连续喂饲14d。分别于术后第3，5，7，14天切取移植物，观察并分析排斥反应。结果 对照组和实验1组，植入。肾被膜下的胰岛组织多在1周内完全被排斥，术后第7天胰岛轮廓消失，仅见大量淋巴细胞浸润。实验2组于移植后第7天及第14天肾被膜下仍可见大量完整的胰岛细胞，几乎未见或偶尔可见淋巴细咆浸润。结论 FTY720单独作为免疫抑制剂并不能抑制鼠类异种胰岛移植的排斥反应；联合应用FTY720及CsA则可有效地抑制鼠类异种胰岛移植排斥反应的发生。     

Protective Effects of Recombinant Human Antithrombin III in Pig-to-Primate Renal Xenotransplantation

Delayed rejection of pig kidney xenografts by primates is associated with vascular injury that may be accompanied by a form of consumptive coagulopathy in recipients. Using a life-supporting pig-to-baboon renal xenotransplantation model, we have tested the hypothesis that treatment with recombinant human antithrombin III would prevent or at least delay the onset of rejection and coagulopathy. Non-immunosuppressed baboons were transplanted with transgenic pig kidneys expressing the human complement regulators CD55 and CD59. Recipients were treated with an intravenous infusion of antithrombin III eight hourly (250 units per kg body weight), with or without low molecular weight heparin. Antithrombin-treated recipients had preservation of normal renal function for 4-5 days, which was twice as long as untreated animals, and developed neither thrombocytopenia nor significant coagulopathy during this period. Thus, recombinant antithrombin III may be a useful therapeutic agent to ameliorate both early graft damage and the development of systemic coagulation disorders in pig-to-human xenotransplantation.     

A review of pig liver xenotransplantation: Current problems and recent progress

Pig liver xenotransplantation appears to be more perplexing when compared to heart or kidney xenotransplantation, even though great progress has been achieved. The relevant molecular mechanisms involved in xenogeneic rejection, including coagulopathy, and particularly thrombocytopenia, are complex, and need to be systematically investigated. The deletion of expression of Gal antigens in the liver graft highlights the injurious impact of nonGal antigens, which continue to induce humoral rejection. Innate immunity, particularly mediated by macrophages and natural killer cells, interplays with inflammation and coagulation disorders. Kupffer cells and liver sinusoidal endothelial cells (LSECs) together mediate leukocyte, erythrocyte, and platelet sequestration and phagocytosis, which can be exacerbated by increased cytokine production, cell desialylation, and interspecies incompatibilities. The coagulation cascade is activated by release of tissue factor which can be dependent or independent of the xenoreactive immune response. Depletion of endothelial anticoagulants and anti‐platelet capacity amplify coagulation activation, and interspecies incompatibilities of coagulation‐regulatory proteins facilitate dysregulation. LSECs involved in platelet phagocytosis and transcytosis, coupled with hepatocyte‐mediated degradation, are responsible for thrombocytopenia. Adaptive immunity could also be problematic in long‐term liver graft survival. Currently, relevant evidence and study results of various genetic modifications to the pig donor need to be fully determined, with the aim of identifying the ideal transgene combination for pig liver xenotransplantation. We believe that clinical trials of pig liver xenotransplantation should initially be considered as a bridge to allotransplantation.     

Pathologic characteristics of transplanted kidney xenografts

For xenotransplantation to become a clinical reality, we need to better understand the mechanisms of graft rejection or acceptance. We examined pathologic changes in α1,3-galactosyltransferase gene-knockout pig kidneys transplanted into baboons that were treated with a protocol designed to induce immunotolerance through thymic transplantation (n=4) or were treated with long-term immunosuppressants (n=3). Hyperacute rejection did not occur in α1,3-galactosyltransferase gene-knockout kidney xenografts. By 34 days, acute humoral rejection led to xenograft loss in all three xenografts in the long-term immunosuppression group. The failing grafts exhibited thrombotic microangiopathic glomerulopathy with multiple platelet-fibrin microthrombi, focal interstitial hemorrhage, and acute cellular xenograft rejection. Damaged glomeruli showed IgM, IgG, C4d, and C5b-9 deposition. They also demonstrated endothelial cell death, diffuse endothelial procoagulant activation with high expression of tissue factor and vWF, and low expression of the ectonucleotidase CD39. In contrast, in the immunotolerance group, two of four grafts had normal graft function and no pathologic findings of acute or chronic rejection at 56 and 83 days. One of the remaining kidneys had mild but transient graft dysfunction with reversible, mild microangiopathic glomerulopathy, probably associated with preformed antibodies. The other kidney in the immunotolerance group developed unstable graft function at 81 days and developed chronic xenograft glomerulopathy. In summary, the success of pig-to-primate xenotransplantation may necessitate immune tolerance to inhibit acute humoral and cellular xenograft rejection.     

Xenotransplantation of the liver]

The development of pigs transgenic for human regulators of complement activation resulted in the nearly total elimination of episodes of hyperacute rejection following discordant solid organ xenotransplantation. Following discordant heart or kidney transplantation, in subhuman primates, graft survival rates of up to several months can be observed. In contrast to these organs, the xenotransplantation of the liver is associated with the inherent problem of the immunological and metabolic compatibility of the large variety of xenoproteins generated. Based on a review of data mainly derived from experimental ex-vivo xenoliver perfusions in patients with hepatic coma, whole organ orthotopic or heterotopic liver xenotransplantation currently is not likely to become a relevant option for the treatment of patients with endstage liver failure. In contrast, clinical studies utilizing different forms of bioartificial liver assist devices are currently underway. Based on preliminary data published, this form of liver support therapy might enter the clinic in the near future.     

Induction of Human T-Cell Tolerance to Pig Xenoantigens via Thymus Transplantation in Mice with an Established Human Immune System

Thymus xenotransplantation has been shown to induce tolerance to porcine xenografts in mice and to permit survival of α1,3Gal-transferase knockout porcine kidney xenografts for months in nonhuman primates. We evaluated the ability of porcine thymus xenotransplantation to induce human T-cell tolerance using a humanized mouse (hu-mouse) model, where a human immune system is preestablished by implantation of fetal human thymus tissue under the kidney capsule and intravenous injection of CD34⁺ hematopoietic stem/progenitor cells. Human T-cell depletion with an anti-CD2 mAb following surgical removal of human thymic grafts prevented the initial rejection of porcine thymic xenografts in hu-mice. In these hu-mice, porcine thymic grafts were capable of supporting human thymopoiesis and T-cell development, and inducing human T-cell tolerance to porcine xenoantigens. Human T cells from these mice responded strongly to third-party pig, but not to the thymic donor swine leukocyte antigen (SLA)-matched pig stimulators in a mixed lymphocyte reaction (MLR) assay. Anti-pig xenoreactive antibodies declined in these hu-mice, whereas antibody levels increased in nontolerant animals that rejected porcine thymus grafts. These data show that porcine thymic xenotransplantation can induce donor-specific tolerance in immunocompetent hu-mice, supporting this approach for tolerance induction in clinical xenotransplantation .     

异种移植排斥反应及其对策研究进展

同种异体组织和器官移植的供体来源有限,使异种移植再度成为研究热点.然而异种移植将面临比同种异体移植复杂得多的排斥反应.本文就异种移植排斥反应及其对策的研究近况作一综述.     

异种移植的研究进展

目的总结异种移植的研究现状与进展。方法复习国内外关于异种移植研究的相关文献并进行综述。结果超急性异种排斥反应是异种移植面临的巨大问题,器官或组织的供体经过基因修饰后,在一定程度上可以减轻超急性异种排斥反应。由于不同的器官具有不同的特性,目前异种器官移植移植物的存活时间存在较大差异。结论通过对相关异种移植实验研究的分析,可以全面地了解异种移植的研究背景,为异种移植提供合适的研究方向。将经基因修饰的动物作为异种器官或组织的供体,有望使移植物避免或减轻超急性异种排斥反应。     

Potential pathological role of pro‐inflammatory cytokines (IL‐6, TNF‐α, and IL‐17) in xenotransplantation

The major limitation of organ transplantation is the shortage of available organs from deceased human donors which leads to the deaths of thousands of patients each year. Xenotransplantation is considered to be an effective way to resolve the problem. Immune rejection and coagulation dysfunction are two major hurdles for the successful survival of pig xenografts in primate recipients. Pro‐inflammatory cytokines, such as IL‐6, TNF‐α, and IL‐17, play important roles in many diseases and in allotransplantation. However, the pathological roles of these pro‐inflammatory cytokines in xenotransplantation remain unclear. Here, we briefly review the signaling transduction and expression regulation of IL‐6, TNF‐α, and IL‐17 and evaluate their potential pathological roles in in vitro and in vivo models of xenotransplantation. We found that IL‐6, TNF‐α, and IL‐17 were induced in most in vitro or in vivo xenotransplantation model. Blockade of these cytokines using gene modification, antibody, or inhibitor had different effects in xenotransplantation. Inhibition of IL‐6 signaling with tocilizumab decreased CRP but did not increase xenograft survival. The one possible reason is that tocilizumab can not suppress IL‐6 signaling in porcine cells or organs. Other drugs which inhibit IL‐6 signaling need to be investigated in xenotransplantation model. Inhibition of TNF‐α was beneficial for the survival of xenografts in pig‐to‐mouse, rat, or NHP models. Blockade of IL‐17 using a neutralizing antibody also increased xenograft survival in several animal models. However, the role of IL‐17 in the pig‐to‐NHP xenotransplantation model remains unclear and needs to be further investigated. Moreover, blockade of TNF‐α and IL‐6 together has got a better effect in pig‐to‐baboon kidney xenotransplantation. Blockade two or even more cytokines together might get better effect in suppressing xenograft rejection. Better understanding the role of these cytokines in xenotransplantation will be beneficial for choosing better immunosuppressive strategy or producing genetic modification pig.     

The role of antibodies in dysfunction of pig-to-baboon pulmonary transplants

OBJECTIVE: Pulmonary transplantation has become the preferred treatment for end-stage lung disease, but application of the procedure is limited because of a paucity of donors. One way to solve donor limitations is to use animal organs as a donor source or xenotransplantation. The current barrier to pulmonary xenotransplantation is the rapid failure of the pulmonary xenograft. Although antibodies are known to play a role in heart and kidney xenograft rejection, their involvement in lung dysfunction is less defined. This project was designed to define the role of antibodies in pulmonary graft rejection in a pig-to-baboon model. METHODS: Orthotopic transgenic swine left lung transplants were performed in baboons depleted of antibodies by one of three techniques before transplantation: (1) ex vivo swine kidney perfusion, (2) total immunoglobulin-depleting column perfusion, and (3) ex vivo swine lung perfusion. Results were compared with those of transgenic swine lung transplants in unmodified baboons. RESULTS: All three techniques of antibody removal resulted in depletion of xenoreactive antibodies. Only pretransplantation lung perfusion improved pulmonary xenograft function compared with lung transplantation in unmodified baboons. CONCLUSIONS: The pathogenesis of pulmonary injury in a swine-to-primate transplant model is different from that in renal and cardiac xenografts. Depletion of antibodies alone does not have a beneficial effect and may actually be detrimental.     

Xenotransplantation of the kidney: a pediatric perspective

The major factor limiting the application of allotransplantation for the treatment of renal failure is a severe shortage of donor organs. One approach to overcoming this limitation is the use of kidneys from animals for clinical transplantation, that is xenotransplantation. Although of interest for many years, the application of xenotransplantation has been prevented because of the devastating immune responses of the recipient against the graft. Research conducted in recent years has elucidated the immune mechanisms underlying the rejection of xenografts and has led to the development of incisive therapeutic strategies, including the genetic engineering of donor animals. Success in dealing with the xenogeneic immune response has encouraged the view that xenotransplantation might be feasible in the near future. It also raises consideration of two additional hurdles, the potential limitations of xenogeneic kidneys as physiological replacement for human kidneys and the possibility that the animal organ might transfer infectious organisms to the recipient and to the wider population. This paper reviews recent progress in the field of xenotransplantation of the kidney and offers a perspective on the hurdles to clinical application that remain. Received: 8 December 1998 / Revised: 4 February 1999 / Accepted: 8 February 1999     

异种移植免疫排斥的研究进展

异种移植是解决人体器官严重短缺的重要思路.随着对异种移植排斥和人畜共患感染性疾病的深入研究,以及α-1,3-半乳糖苷转移酶基因敲除猪的成功构建,以猪为供体的异种移植与临床应用之间的距离正在逐渐缩短.阻碍异种移植发展的主要障碍仍是免疫排斥反应.本文试就目前异种免疫排斥的研究进展进行综述,希望对未来的临床异种移植研究提供参...     

Cardiac xenotransplantation: progress toward the clinic

BACKGROUND: Animal organs could satisfy the demand for solid organ transplants, which currently exceeds the limited human donor supply. Hyperacute rejection, the initial immune barrier to successful xenotransplantation, has been overcome with pig donors transgenic for human complement regulatory proteins. Delayed xenograft rejection, thought to be mediated by anti-pig antibodies predominantly to Gal antigens, is currently regarded as the major barrier to successful xenotransplantation. A median graft survival of 90 days in the life-supporting position is considered a reasonable initial standard for consideration of entry to the clinic. METHODS: A series of 10 heterotopic heart transplants from CD46 transgenic pigs to baboons was completed. Immunosuppression consisted of splenectomy, Rituximab (Anti-CD20), tacrolimus, sirolimus, corticosteroids, and TPC. Thymoglobulin (Rabbit Anti-Thymocyte Globulin) was used to treat putative rejection episodes. RESULTS: Median graft survival was 76 days (range 56-113 days, n = 9). Only three grafts were lost to rejection. The remaining grafts lost were due to recipient mortality with baboon cytomegalovirus (BCMV) being the major cause (n = 4). No cellular infiltrates were present as a manifestation of rejection. Three hearts showed chronic graft vasculopathy. CONCLUSIONS: The median survival of 76 days in this group of heterotopic porcine-to-baboon cardiac xenografts represents a major advance over the median 27-day survival reported in the literature. Cellular rejection may not constitute a direct major barrier to xenotransplantation. A median survival of 90 days may be achievable with better control of BCMV infection. If further studies in the orthotopic position replicate these outcomes, criteria considered appropriate for clinical application of cardiac xenotransplantation would be approached.     

Influence of cold ischemia time, pretransplant anti-porcine antibodies, and donor/recipient size matching on hyperacute graft rejection after discordant porcine to cynomolgus kidney transplantation

Organs transplanted between phylogenetically disparate species, such as from the pig into the primate, are subject to hyperacute rejection (HAR). This form of xenograft rejection is mediated by preformed natural antibodies and is believed to occur invariably in discordant xenografts thus leading to rapid destruction and complete thrombosis of the graft. Recent data, however, have shown that in the porcine to cynomolgus monkey setting, HAR is not inevitably seen after porcine kidney transplantation. The influence of preoperative antiporcine antibody levels in the recipient, cold ischemia time, and donor organ weight on the onset of HAR was investigated by using unmodified large white pigs (aged 3-12 weeks) as organ donors and adult cynomolgus monkeys (aged 1.5-3.5 years) as recipients. Porcine kidney xenotransplantation was performed in either a non-life-supporting model (n=7) or in a life-supporting model (n=8). In both models, no correlation was found between cold ischemia time and HAR. When preoperative anti-porcine antibody levels were investigated, a significant increase in incidence of HAR was observed in animals with elevated anti-porcine IgM (P<0.05) but not IgG levels (P=NS). Interestingly, although 5 of 12 grafts with an organ weight of less than 50 g underwent HAR, none of three grafts with a donor organ weight of more than 70 g showed signs of HAR. In addition, all three larger grafts showed intraoperative and postoperative urine production, although only in 1 (48 g) of the 12 grafts weighing less than 50 g primary graft function was observed. In one animal, a second porcine kidney (23 g) was successfully transplanted (without HAR) immediately after HAR and subsequent removal of a first porcine kidney (20 g). These results indicate that in the porcine to cynomolgus monkey setting anti-porcine IgM rather than IgG anti-porcine antibody levels seem to be of predominant importance for the induction of HAR. By increasing the donor organ size and weight the frequency of the onset of HAR can be at least reduced. This is most likely due to immunoabsorption of the recipients preformed antibodies in the porcine kidney without lethal damage for the graft.     

Xenotransplantation of pancreatic and kidney primordia-where do we stand?

Lack of donor availability limits the number of human donor organs. The need for host immunosuppression complicates transplantation procedures. It is possible to 'grow' new pancreatic tissue or kidneys in situ via xenotransplantation of organ primordia from animal embryos (organogenesis of the endocrine pancreas or kidney). The developing organ attracts its blood supply from the host, enabling the transplantation of pancreas or kidney in 'cellular' form obviating humoral rejection. In the case of pancreas, selective development of endocrine tissue takes place in post-transplantation. In the case of kidney, an anatomically-correct functional organ differentiates in situ. Glucose intolerance can be corrected in formerly diabetic rats and ameliorated in rhesus macaques on the basis of porcine insulin secreted in a glucose-dependent manner by beta cells originating from transplants. Primordia engraft and function after being stored in vitro prior to implantation. If obtained within a 'window' early during embryonic pancreas development, pig pancreatic primordia engraft in non immune suppressed diabetic rats or rhesus macaques. Engraftment of pig renal primordia transplanted directly into rats requires host immune suppression. However, embryonic rat kidneys into which human mesenchymal cells are incorporated into nephronic elements can be transplanted into non-immune suppressed rat hosts. Here we review recent findings germane to xenotransplantation of pancreatic or renal primordia as a novel organ replacement strategy.