Absence of Gal epitope prolongs survival of swine lungs in an ex vivo model of hyperacute rejection

Nguyen B‐NH, Azimzadeh AM, Schroeder C, Buddensick T, Zhang T, Laaris A, Cochrane M, Schuurman H‐J, Sachs DH, Allan JS, Pierson RN. Absence of Gal epitope prolongs survival of swine lungs in an ex vivo model of hyperacute rejection. Xenotransplantation 2011; 18: 94–107. © 2011 John Wiley & Sons A/S. Abstract: Background: Galactosyl transferase gene knock‐out (GalTKO) swine offer a unique tool to evaluate the role of the Gal antigen in xenogenic lung hyperacute rejection. Methods: We perfused GalTKO miniature swine lungs with human blood. Results were compared with those from previous studies using wild‐type and human decay‐accelerating factor‐transgenic (hDAF^+/+) pig lungs. Results: GalTKO lungs survived 132 ± 52 min compared to 10 ± 9 min for wild‐type lungs (P = 0.001) and 45 ± 60 min for hDAF^+/+ lungs (P = 0.18). GalTKO lungs displayed stable physiologic flow and pulmonary vascular resistance (PVR) until shortly before graft demise, similar to autologous perfusion, and unlike wild‐type or hDAF^+/+ lungs. Early (15 and 60 min) complement (C3a) and platelet activation and intrapulmonary platelet deposition were significantly diminished in GalTKO lungs relative to wild‐type or hDAF^+/+ lungs. However, GalTKO lungs adsorbed cytotoxic anti‐non‐Gal antibody and elaborated high levels of thrombin; their demise was associated with increased PVR, capillary congestion, intravascular thrombi and strong CD41 deposition not seen at earlier time points. Conclusions: In summary, GalTKO lungs are substantially protected from injury but, in addition to anti‐non‐Gal antibody and complement, platelet adhesion and non‐physiologic intravascular coagulation contribute to Gal‐independent lung injury mechanisms.     

Inhibition of platelet aggregation by the GPIIb/IIIa antagonist Reopro does not significantly prolong xenograft survival in an ex vivo model

Effects on hyperacute rejection were studied in a discordant model with the platelet GPIIb/IIIa antagonist Reopro. Pig kidneys perfused with human blood survived median 118 min in the Reopro group and 103 min in the controls (P = 0.22). Platelet and leukocyte counts decreased, whereas plasma thrombospondin and soluble as well as platelet membrane P-selectin increased significantly in both groups without significant intergroup differences. beta-Thromboglobulin and myeloperoxidase increased significantly more in the control group than in the Reopro group (P = 0.009 and P = 0.02, respectively). The classical complement pathway was substantially and similarly activated in both groups. Light and electron microscopy revealed arterial thrombi and numerous glomerular platelet aggregates in the control group in contrast to the Reopro group. In conclusion, Reopro reduced platelet aggregation, and platelet and leukocyte activation to some extent, but had no effect on complement activation and did not significantly prolong xenograft survival, even though better preservation of morphology was shown.     

转人CRP基因在异种移植中的研究

目的：研究转入补体调节蛋白（CRP）DAF、MCP和CD59基因对抑制人补体激活从而克服超急性排斥反应的作用。方法：利用显微注射建立转人衰变加速因子（hDAF)小鼠和猪的模型和转梁hMCP及hCD59真核表达质粒的猪内皮细胞（EC）,研究小鼠和猪EC表达抑制人补体激活的人补体调节蛋白（CRP）对异种移植超急性排斥反应的抑制作用。结果（1）转人DAF基因小鼠心脏用新鲜人血连续丛外灌注,转基因组心脏搏动时间（174．6min)比对照组（106．5min)明显延延长。（2）转hDAF基因猪心脏异位移植给猕猴、移植心最长存活90h,受者死亡前移植心仍有功能,移植心病理检查未见超急性排斥反应病理改变。（3）转DAF基因基因猪EC死亡率在不同浓度血清时均明显低于对照组,在转hDAF基因猪EC上再分别转染hMCP及hCD59真核表达质粒,转hDAF hMCP或hDAF hCD59在不同血清浓度时EC死亡率较单纯hDAF组明显下降（P＜0．05）。结论,转人DAF及MCP、CD59补体调节蛋白基因能克服人对异种器官或组织的超急性排斥反应。     

Human serum-induced expression of E-selectin on porcine aortic endothelial cells in vitro is totally complement mediated.

BACKGROUND: Whereas complement is a key mediator of hyperacute xenograft rejection, its role in acute vascular rejection (AVR) is a matter of controversy. AVR is associated with de novo synthesis of endothelial cell-derived inflammatory mediators, including the leukocyte-recruiting adhesion molecule E-selectin. Here we investigate the role and mechanism of complement in human serum-induced porcine endothelial cell activation. METHODS: An in vitro xenotransplantation method was designed using porcine aortic endothelial cells stimulated with human serum in microculture wells. E-selectin expression was measured by cell-enzyme immunoassay. Complement inhibitors acting at different levels in the cascade were investigated for their effect on E-selectin expression. RESULTS: E-selectin was strongly induced by normal human serum but not by heat-inactivated serum. Compstatin, a synthetic C3 inhibitor, markedly reduced human serum-induced E-selectin expression. Purified C1-inhibitor suppressed E-selectin induction completely, indicating activation through the classical or lectin pathway. Furthermore, a monoclonal antibody (mAb) that inhibits cleavage of C5 or another mAb that blocks the function of C7, completely inhibited the expression of serum-induced E-selectin, consistent with the terminal C5b-9 complement complex being the mediator of the endothelial cell activation. Inhibition of the alternative pathway using a novel antifactor D mAb did not reduce E-selectin expression. CONCLUSION: Human serum-induced expression of porcine E-selectin is totally complement dependent, induced by a C1-inhibitor regulated pathway and mediated through the terminal complement complex. The data may have implications for therapeutic strategies, particularly of C1-inhibitor and anti-C5 mAb, to protect against endothelial cell activation and subsequent AVR of porcine xenografts.     

供体骨髓间充质干细胞干预非协调性异种肝移植免疫排斥反应的实验研究

目的研究骨髓间充质干细胞(MSCs)对非协调性异种肝移植排斥反应的免疫干预作用。方法密度梯度离心法分离培养豚鼠MSCs,流式细胞仪检测其膜表面CD34、CD45、CD44和CD29的表达,脂肪细胞诱导液培养诱导MSCs向脂肪细胞分化。豚鼠MSCs输注大鼠后检测不同时相免疫球蛋白IgG、IgM、IgA以及补体C3、C4的浓度变化。豚鼠和大鼠各30只随机分为3组,所有大鼠受体经环磷酰胺预处理,A组为MSCs输注组;B组为生理盐水输注组;C组为地塞米松输注组。各组行豚鼠大鼠原位肝脏移植手术,观察受体的存活情况及排斥反应情况。结果MSCs膜表面CD34阴性、CD45阴性、CD44阳性、CD29阳性。脂肪细胞诱导液培养后细胞内出现脂滴沉着。MSCs细胞悬液输注受体后各个时相的免疫球蛋白IgG、IgM和补体C3较输注前有显著降低(P<0.01),而IgA和补体C4与输注前相比无明显变化(P>0.05),输注后的免疫球蛋白IgG、IgM和补体C3各个时相点之间的浓度变化无显著差异(P>0.05)。肝脏移植模型A组受体存活时间为(431±27)min,较B组和C组的存活时间[(148±16)min、(141±22)min]显著延长(P<0.01)。A组受体超急性排斥反应发生较迟,程度轻。结论MSCs的鉴定可根据细胞形态,膜表面标志物和分化能力来确定,MSCs可干预异种肝脏移植的超急性排斥反应的发生。     

Hyperacute rejection in ex vivo-perfused porcine lungs transgenic for human complement regulatory proteins

Inhibition of complement activation via human membrane-associated complement regulators is known to prevent hyperacute rejection in heart and kidney pig-to-primate transplantation. The protective effect of such strategies in pulmonary xenografts, however, seems to be insufficient. In an ex vivo perfusion, model lungs from donor pigs transgenic for human CD55 (n = 6) or human CD59 (n = 5) were perfused with fresh human blood and compared with nontransgenic organs (n = 6). In addition, a soluble complement component 1 esterase inhibitor (C1-Inh) was applied in h-CD55 transgenic lungs (n = 3). In the h-CD55 transgenic group, survival was prolonged (P < 0.05), quality and maximal time of oxygenation significantly improved and pulmonary vascular resistance reduced compared with the control group. There was a decreased sequestration of platelets, less parenchymal injury and reduced deposition of C(5b-9) in the h-CD55 transgenic group. Additional soluble complement inhibition (C1-Inh) did not prolong survival of h-CD55 transgenic lungs. Survival and pulmonary function in lungs expressing h-CD59 was not significantly different from parameters observed in nontransgenic lungs. In this ex vivo model of pig-to-primate lung transplantation, membrane-based complement inhibition resulted in significantly improved pulmonary function. However, minor histopathological injuries observed in these transgenic xenografts suggested only partial protection from pulmonary dysfunction by complement inhibition alone.     

Acute vascular rejection is associated with systemic complement activation in a pig-to-primate kidney xenograft model

The introduction of h-DAF transgenic porcine organs into pre-clinical pig-to-primate discordant xenotransplantation has led to complete and reliable abrogation of hyperacute xenograft rejection (HAR). Despite additional heavy immunosuppression however, most xenografts are still lost due to acute vascular rejection (AVR), with current treatment protocols being of only limited value. In a life-supporting model of pig-to-primate kidney transplantation, unmodified (n=8) or h-DAF-transgenic (n=9) porcine kidneys were transplanted into cynomolgus monkeys under cyclophosphamide (CyP), cyclosporine and low-dose steroid immunosuppression. Longest recipient survival was 11 days in the control group and 68 days in the h-DAF transgenic group. Stable initial graft function with recipient survival >4 days was generated in eight animals (two controls and six transgenics). In these animals, plasma complement levels were analyzed during ongoing AVR. Compared with baseline levels, a two-fold increase in C3a levels and a four-fold increase in sC5b-9 levels were measured. In parallel to systemic complement activation, increased deposition of C3 and C5b-9 along with massive staining for recipient IgM immunoglobulins was detected in the xenografts on immunohistochemistry. We conclude that acute vascular xenograft rejection of porcine kidneys in cynomolgus monkeys is associated with classical pathway complement activation following binding of induced recipient anti-porcine antibodies. This complement activation can be observed despite membrane bound expression of human complement regulators in the porcine xenografts. Therefore, additional short-term fluid phase complement inhibition seems necessary for the future development of protocols designed for treatment of AVR in the pig-to-primate combination.     

A soluble chimeric inhibitor of C3 and C5 convertases, complement activation blocker-2, prolongs graft survival in pig-to-rhesus monkey heart transplantation

Complement plays a critical role in many pathologic processes and in xenograft rejection. Therefore, effective complement inhibitors are of great interest. In pig-to-primate organ transplantation, hyperacute rejection results from antibody deposition and complement activation. Complement activation blocker-2 (CAB-2), a recombinant soluble chimeric protein derived from human decay accelerating factor (DAF) and membrane cofactor protein, inhibits C3 and C5 convertases of both classical and alternative pathways. CAB-2 reduces complement-mediated tissue injury of a pig heart perfused ex vivo with human blood. Therefore, we studied the efficacy of CAB-2 when a pig heart is transplanted heterotopically into rhesus monkeys receiving no immunosuppression. Graft survival in three control monkeys was 1.26 ± 0.2 h; it was markedly prolonged in eight monkeys that received CAB-2. Of the six monkeys that received a single dose of CAB-2 (15 mg/kg i.v.), four had graft survivals of 21, 95, 96, and 108 h, and two died at 7 to11 h post-transplant with a beating graft, as a result of technical complications. The two monkeys given multiple doses of CAB-2 had graft survivals of 95 and 96 h. CAB-2 markedly inhibited complement activation, as shown by a strong reduction in generation of C3a and SC5b-9. At graft rejection, tissue deposition of iC3b, C4 and C9 was similar or slightly reduced from controls, and deposition of IgG, IgM, C1q and fibrin did not change. Thus, complement inhibition with CAB-2 abrogates hyperacute rejection of pig hearts transplanted into rhesus monkeys, but does not prevent delayed/acute vascular rejection. These studies demonstrate that the beneficial effects of complement inhibition on survival of a pig heart xenograft in rhesus monkeys are similar to those in other primate species and that CAB-2 may be useful in xenotransplantation and other complement-mediated conditions.     

Effect of complement fragment 1 esterase inhibition on survival of human Decay-Accelerating factor pig lungs perfused with human blood

BACKGROUND: The role of complement in hyperacute lung xenograft rejection has not been fully elucidated. The present study evaluates the effect of complement (C) 1 esterase inhibition on hyperacute rejection of human decay-accelerating factor (hDAF)-positive pig lung by human blood. METHODS: Using a modification of an established ex vivo model, right and left lungs from individual animals were surgically isolated and separately perfused. Pigs homozygous for hDAF were perfused with fresh human blood that was either untreated or treated with complement 1 esterase inhibitor (C1-Inh) at doses of 1 U/ml (n = 5), 5 U/ml (n = 3) or 10 U/ml plasma (n = 5). RESULTS: Only C1-Inh at 10 U/ml prolonged survival time (230 +/- 48.3 minutes) as compared with controls (65.6 +/- 26.5 minutes, p < 0.05) and diminished complement activation (C3a and C5a, p < 0.05). Interestingly, a low concentration of C1-Inh increased the pulmonary vascular resistance (PVR; 1 U/ml: 0.54 +/- 0.3; 10 U/ml: 0.19 +/- 0.08). Sequestration of neutrophils (92 +/- 3%) and platelets (64 +/- 13%) was not prevented by any concentration of C1-Inh. Tissue deposition of C3b and C5b-9 were diminished by hDAF expression, and further blunted by treatment, with 10 U/ml C1-Inh. CONCLUSIONS: Complement plays a critical role in early events of lung hyperacute rejection (HAR). However, even potent inhibition of C1 esterase and C3/C5 convertase, using serum C1-Inh in pig lungs homozygous for hDAF expression, does not prevent rapid lung injury. Our findings implicate innate immune pathways resistant to efficient complement regulation, and suggest a role for neutrophils and platelets in the lung's particular vulnerability.     

Immunohistological studies of complement activation after xenogeneic perfusion of a working heart model

Transplantation of organs from one species to another leads to immediate hyperacute rejection. Activation of complement is one important factor involved in this process. Whether complement activation is induced by preformed natural antibodies (PNAbs) via the classical pathway or by an activator surface via the alternative pathway is unclear. In order to simulate the relevant clinical situation of animal donor/human recipient, we perfused working porcine hearts ex vivo with human blood. This also offered the possibility to study the process of complement activation in a precisely defined system with human complement proteins. PNAb titer and complement lytic activity of the plasma were measured. Immunohistological stainings for IgG, IgM, C1q, C4, C3d, C5-9, factor B, and properdin were performed on tissue sections of the left ventricle. PNAb titer almost totally disappeared within the first 5 min of perfusion. Complementlytic activity of the classical pathway decreased similarly within the first 3 h of xenogeneic and autologous perfusion from 70% to 40%. More detailed immunohistological studies revealed positive staining for C3d on endothelium and myocardium of ex vivo perfused xenogeneic hearts. Complement-induced cytotoxicity was proven by the presence of C5-9 (membrane attack complex). However, hardly and C1q and C4 could be found in the ex vivo xenogeneic perfused hearts. Staining for factor B was positive and proved activation via the alternative pathway. Beyond that, the presence of properdin binding even indicated an upregulation of the alternative pathway C3 convertase. In contrast to the prevaling opinion, we found that the alternative pathway plays the dominant role in complement activation in hyperacute xenograft rejection, as shown ex vivo using pig hearts perfused with human blood.