水苏糖对模拟异种心脏移植超急性排斥反应的抑制作用

目的观察水苏糖对猪到人异种心脏移植超急性排斥反应的抑制作用。方法以人血液体外灌注猪游离心脏为基础，模拟猪到人异种心脏移植的超急性排斥反应模型。实验分为A、B两组：即分别用人血液灌注及人血液加水苏糖灌注猪离体心脏。观察灌注后两组心脏的跳动时间；体外灌注1h后，对两组灌注心脏进行免疫组织化学（测定IgG及IgM的沉积）及病理学分析。结果A组灌注心脏平均跳动时间为（9．5±2．5）min；B组灌注心脏平均跳动时间为（46．8±8．1）min，其中有1个心脏在灌注的1h内一直跳动；两组心脏跳动时间比较，差异有统计学意义（P〈0．01）。A组心肌间质呈弥漫性出血、水肿，血管扩张，内皮细胞肿胀、坏死；免疫组织化学检查显示心肌血管内皮组织中有IgG及IgM沉积。B组心肌间质未见出、凝血和坏死，血管内皮细胞未见肿胀；免疫组织化学检测未见IgG及IgM沉积。结论水苏糖对异种心脏移植超急性排斥反应具有抑制作用。     

猪到人异种心脏移植超急性排斥反应实验模型的建立：人血体外灌注猪冠状动脉系统

目的建立一种猪到人异种心脏移植超急性排斥反应实验模型。方法 8只广西巴马猪正中切口锯开胸骨进胸,肝素化,完整剪取猪心脏,用4℃生理盐水反复冲洗各心腔及心脏表面,用改良圣托马斯液经主动脉灌注,冲洗冠状动脉系统后,建立人血液体外灌注猪游离心脏冠状动脉系统,记录各模型心脏搏动的持续时间,1h后对灌注心脏进行免疫组织化学（测定IgG及IgM的沉积）及病理学分析。结果 8个人血液体外灌注猪心脏冠状动脉系统实验模型均成功建立,灌注心脏平均搏动时间为（9.25±1.90）min;心肌间质弥漫性出血、水肿,血管扩张,内皮细胞肿胀、坏死;心肌血管内皮细胞有IgG及IgM沉积。结论通过人血液体外灌注猪心脏冠状动脉系统建立的猪到人异种心脏移植实验模型能模拟超急性排斥反应,操作简单,容易复制。     

猪到猕猴异种心脏移植超急性排斥反应的免疫学及病理学变化

目的观察猪到猕猴异种心脏移植超急性排斥反应时的免疫学及病理学变化。方法采用猪到猕猴腹腔内异位心脏移植模型,检测发生超急性排斥反应者的血液中补体、天然抗体及T淋巴细胞亚群的变化,并对移植心脏进行免疫组化(测定C3、C4、C5b9、IgG及IgM的沉积)及病理学分析。结果发生超急性排斥反应时,血清补体C3、C4的含量、总补体活性及抗猪内皮细胞天然抗体均有一定程度的下降;CD4 /CD8 T淋巴细胞的比率也有所下降;移植心脏中均有补体C3、C4、C5b9的沉积,IgG及IgM也均有沉积,但IgG和IgM沉积强度的差异无统计学意义;病理学改变主要为心肌间质弥漫性出血、水肿,毛细血管内普遍淤血。结论补体通过经典途径激活参与猪到猕猴异种心脏移植超急性排斥反应;超急性排斥反应时受者血中天然抗体水平明显下降;CD4 T淋巴细胞可能参与异种移植超急性排斥反应过程并有所消耗;发生超急性排斥反应的移植物突出病理表现为间质出血。     

建立猪心脏移植至猕猴腹腔内的异位心脏移植模型

目的 评价改进后的猪心脏移植至猕猴腹腔内的异位心脏移植模型的效果。方法 建立21例猪心脏移植至猕猴腹腔内的异位心脏移植模型，其中采用传统手术方法11例，改进方法10例。改进方法为缩短供心缺血时间，调整了手术顺序，先游离受者供吻合的腹主动脉及下腔静脉段后，再行供心切取，并且改进了切取供心的方法。比较2种手术方法的热缺血时间、移植心功能恢复情况及术后并发症。结果 采用传统手术方法时，移植心准备时间为20～30min，热缺血时间为3～5min，总缺血时间为80～90min，再灌注后均未恢复正常的全心搏动，仅见右心收缩，移植后发生并发症较多（包括出血、吻合口血栓形成、肠道并发症及静脉回流不畅等）。改进手术方法后，移植心准备时间为5～10min，热缺血时间〈1min，总缺血时间为35～40min，再灌注后有6例恢复全心搏动，发生并发症较少。结论 改进后的猪心脏移植到猕猴腹腔内的异位心脏移植模型，其手术方法明显优于传统方法。     

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。     

单核细胞、NK细胞和T细胞在猪-猕猴延迟性异种移植排斥反应中的作用

目的观察单核细胞、NK细胞和T细胞在猪-猕猴延迟性异种移植排斥反应(DXR)中的作用。方法建立湖北白猪-云南猕猴的腹腔异位心脏移植模型，实验分为2组：对照组(n=5)，不使用中华眼睛蛇毒因(Y-CVF)；实验组(n=4)应用Y-CVF完全清除受者体内补体。2组受体猴均采用环孢素A(CsA)，环磷酰胺(CTX)和甲基强的松龙(MP)三联免疫抑制治疗。免疫组织化学方法检测移植心组织中细胞间黏附分子(ICAM)-1、肿瘤坏死因子(TNF)-α、单核细胞、NK细胞和T细胞的表达。结果对照组3个移植心在15～60min内发生超急性排斥反应(HAR)，另2个分别存活22h及6d，移植心均未见明显的炎性细胞浸润及ICAM-1和TNF-α的表达。实验组移植心存活时间分别为8、10、13和13d，移植物浸润细胞中可见大量的单核细胞(50％)，少量的NK细胞(8％～10％)，CD4^ T细胞(15％)和C08^ T细胞(25％)。移植物血管内皮细胞表面出现ICAM-1的表达上调，移植物间质中出现TNF-α的表达增加。结论单核细胞、NK细胞和T细胞介导的移植物损伤，在应用Y-CVF处理的猪-猕猴DXR发生中发挥重要作用。     

清除补体避免猪到猕猴异种心脏移植超急性排斥反应的实验研究

目的 观察纯化的眼镜蛇毒因子(CVF)对猪到狱猴异种心脏移植超急性排斥反应的影响。方法 以幼猪为供者，施行猪到狱猴腹腔内异位心脏移植，实验组(n＝4)使用CVF完全清除受者体内补体，对照组(n＝5)不使用CVF，两个组术后均采用环抱素A、甲泼尼龙和环磷酰胺抑制排斥反应，通过检测血清C3、C4水平及总补体活性验证CVF的效果，移植心停跳时切取移植心进行病理检查。结果 在使用CVF后，实验组血清C3降为0，总补体活性CH50值也几乎为0，末发现明显毒副反应，移植猪心存活时间平均为lld，最长达13d，病理学提示均发生了延迟性异种排斥反应；对照组3个移植心在移植后60min内发生超急性排斥反应，另2个分别存活22h及6d。结论 纯化的CVF有良好的清除补体的作用，且末见明显副作用；使用CVF可克服猪到狱猴异种心脏移植超急性排斥反应的发生。     

烙铁头血小板活化素延长豚鼠到大鼠的异种移植心脏存活时间

目的 研究烙铁头血小板活化素（TMVA）对大鼠血小板聚集的抑制作用以及对豚鼠到大鼠的异种移植心存活时间的影响。方法 （1）TMVA对血小板聚集率的影响：将Wistar大鼠随机分为3组，每组5只，各组经阴茎背静脉注射不同剂量（20、50或100μg／kg）的TMVA，于注射前以及注射后0．5h和24h时抽血，测定血小板聚集率。（2）TMVA对豚鼠到大鼠的异种移植心存活时间的影响：以豚鼠为供者，Wistar大鼠为受者，制作颈部异位心脏移植模型，实验组于移植心恢复血液循环前0．5h经静脉给予TMVA50μg／kg，另设不使用TMVA的对照组。观察移植心的存活时间，停跳后的移植心组织行病理学检查，并用放射免疫法检测心肌组织内6-酮-前列腺素F1α（6-keto-PGF1α）及血栓素B2（TXB2）的含量。结果（1）静脉给予50或100μg／kg的TMVA后0．5h即能完全抑制血小板聚集。（2）实验组移植心的存活时间为10～135min，中位数为42min；对照组为4～16min，中位数为5min，两组比较，差异有统计学意义（P〈0．01）。两组移植心心肌组织均有明显的间质水肿、出血等超急性排斥反应的表现，但实验组心肌组织中未见血小板微血栓，而对照组可见血小板微血栓。两个组6-keto-PGF1α。与TXB2的差异无统计学意义，但实验组6-keto-PGF1α。与TXB2的比值明显高于对照组（P〈0．05）。结论 TMVA在体内能抑制血小板聚集及异种移植物排斥过程中血小板微血栓形成，能显著延缓豚鼠到大鼠异种心脏移植超急性排斥反应的发生。     

眼镜蛇毒因子清除补体对大鼠异种心脏移植超急性排斥反应的影响

目的　探讨眼睛蛇毒因子 (CVF)对血清总补体活性及对豚鼠到大鼠异种心脏移植超急性排斥反应的影响。方法　 1 5只正常大鼠随机分成 3组 ,按组分别一次性静脉给予 2 0、50、1 0 0 μg/kg的CVF ,检测不同时间点的补体活性 ;在豚鼠到大鼠异位心脏移植前 2 4h静脉给予CVF50 μg/kg,观察CVF对异种心脏移植超急性排斥反应的影响。结果　在给予CVF后 6h ,3个剂量组的血清总补体活性均显著降低 ,3个组用药后均未见明显毒副反应。使用CVF的实验组 ,移植的异种心脏存活时间显著延长 ,平均达 56 .1 3h ,对照组仅为 0 .1 9h(P <0 .0 0 1 ) ,病理检查结果证实实验组均未发生超急性排斥反应 ,仅见延迟性异种排斥反应 (DXR)的病理特征 ,对照组均见超急性排斥反应的病理特征 ,且总补体活性较术前有明显下降。结论　眼镜蛇毒因子有良好的降低大鼠补体活性的作用 ,且副作用不明显 ;使用眼镜蛇毒因子可克服豚鼠到大鼠的异种心脏移植超急性排斥反应的发生。     

建立同种大鼠心脏移植超急性排斥反应动物模型

目的建立大鼠心脏移植超急性排斥反应的实验动物模型。方法以BN大鼠为供者，Lewis大鼠为受者。供、受者间连续进行3次皮肤移植，使受者预致敏。再进行颈部异位心脏移植。采用微量淋巴毒试验监测受者体内抗供者抗体滴度的变化。结果预致敏后的受者体内抗供者抗体滴度明显升高。7只受者心脏移植后有6只移植心在24h内被排斥，病理学证实为超急性排斥反应。结论供、受者间连续3次皮肤移植预致敏后，再行心脏移植可以建立稳定的同种移植超急性排斥反应模型。     

Decay-accelerating factor prevents acute humoral rejection induced by low levels of anti-alphaGal natural antibodies

BACKGROUND: Hyperacute and delayed vascular rejection due to natural antibodies (NAb) present major obstacles in pig-to-primate xenotransplantation. Although "supraphysiologic" expression of human complement regulatory proteins (CRPs) can prevent hyperacute rejection in discordant xenogenic recipients, their physiologic role in the homologous setting is undefined. We have evaluated the effect of the absence of decay-accelerating factor (DAF) on cardiac allograft rejection in the presence of different levels of antidonor antibodies (Ab). METHODS: DAF1-deficient (DAF KO; B6129F2 H-2) mice were used as heart graft donors to alpha1,3-galactosyltransferase deficient (GalT KO; B6, H-2) recipients. Heterotopic heart grafting was performed with or without presensitization. Graft survival, histology, and anti-alphaGal Ab levels were monitored. RESULTS: DAF knockout (KO) but not wild-type (WT) grafts showed hyperacute or acute humoral rejection in nonsensitized GalT KO mice with low levels of anti-alphaGal IgM NAb. However, humoral rejection of both DAF KO and DAF WT donor grafts occurred in presensitized GalT KO recipients. CONCLUSIONS: The expression of DAF prevents hyperacute rejection in mice with low titers of anti-alphaGal antibody. These studies demonstrate the physiologic role of DAF in preventing humoral rejection in the presence of low levels of NAb and have implications for transplantation of discordant vascularized xenografts.     

Induction of anti-Forssman antibodies in the hamster-to-rat xenotransplantation model

BACKGROUND: In the hamster-to-rat heart xenotransplantation model, the serum response of the host contributes to determine whether the xenograft is accommodated or rejected. METHODS: To further characterize the serum response in this model, we compared anti-hamster antibodies found in naive LEW-1A rats, or in LEW-1A rats rejecting or accommodating a hamster heart, using a combination of cobra venom factor (CVF) and cyclosporin A (CsA) given for 10 days, and then CsA alone. RESULTS: Hamster hearts grafted into rat recipients contained IgG and IgA deposits to the same extent whether the xenograft was rejected or accommodated. Only immunoglobulins of the IgM isotype were found to be more abundant in recipients rejecting their graft. A significant part of this IgM response was directed toward the Forssman antigen, a sphingolipid present in the hamster but not in the rat. However, although anti-Forssman antibodies bind in situ to hamster tissues, this binding was not able to induce hyperacute rejection after antibody transfer. Furthermore, depletion of anti-Forssman antibodies from a rejecting serum did not modify its rejection properties. CONCLUSION: Unlike the pig-to-primate discordant xenotransplantation model, in which preexisting anti-carbohydrate antibodies are directly responsible for hyperacute rejection, in the concordant hamster-to-rat situation, the evoked IgM anti-Forssman carbohydrate antibodies do not appear to be the main cause of the vascular rejection.     

蛇毒因子、全身照射、胸腺修饰预处理受者对异种小动物心脏移植的作用

目的　利用眼镜蛇蛇毒因子 (CVF)、全身照射 (WBI)、异基因胸腺修饰等途径预处理受者 ,探讨这些处理对非协调性异种心脏移植物存活期及免疫排斥反应的影响。方法　供者为三色豚鼠 ,受者为SD大鼠 ,随机配对分成空白组 (O组 ) ;单用CVF的对照组 (A组 ) ;CVF +全身照射组 (B组 ) ;CVF +全身照射 +胸腺注射组 (C组 )。各组分别行大鼠腹腔内异位异种心脏移植术。观察各组供心存活时间及排斥后的光镜及电镜表现。结果　 (1)存活时间 :B组、C组和A组均较O组明显延长 (P <0 .0 1) ;B组和C组又较A组明显延长 (P <0 .0 5 ) ;但C组与B组比较 ,差异无显著性 (P >0 .0 5 )。 (2 )病理表现 :O组呈超急性排斥反应 ,另三组均呈延迟性异种排斥改变。结论　在本模型中 ,使用CVF可克服超急性排斥反应 ,联用全身照射可进一步延长供心存活时间 ;但在此基础上加用异基因胸腺修饰对延长供心存活时间无显著意义。     

Life supporting function for over one month of a transgenic porcine heart in a baboon.

BACKGROUND: Inhibition of hyperacute rejection (HAR) and sustained graft survival have been demonstrated in a pig-to-primate model of heterotopic cardiac xenotransplantation using pigs transgenic for human Decay Accelerating Factor (hDAF). Building on this work, an orthotopic model has been developed. This case records 39-day cardiac xenograft function in a life-supporting capacity with clinically applicable immunosuppression. METHODS: Using a heart from an hDAF transgenic pig, an orthotopic cardiac transplant was performed on an adult baboon. The immunosuppressive regimen consisted of induction with a short course of cyclophosphamide, followed by maintenance therapy with cyclosporine A, mycophenolate mofetil and a tapering course of corticosteroids. Post-operative monitoring included daily anti-pig hemolytic antibody titer surveillance and endomyocardial biopsy. RESULTS: The animal survived 39 days and was active and energetic throughout its postoperative course, remaining free of signs of cardiopulmonary failure. Endomyocardial biopsy performed on post-operative Day 36 revealed only patches of sub-endocardial fibrosis with no signs of active rejection. The baboon succumbed to an acute cardiopulmonary decompensation immediately following administration of medication via oral gavage. Post-mortem histopathology demonstrated well-preserved myocardial architecture with small foci of mild humoral rejection. CONCLUSIONS: This case documents the longest survival recorded to date of a discordant orthotopic cardiac xenograft and illustrates that the hDAF transgene combined with a clinically acceptable maintenance immunosuppressive regimen enables sustained, life-supporting function of porcine cardiac xenografts in non-human primates. The inhibition of hyperacute rejection and the subsequent control of humoral and cellular rejection for over 1 month demonstrated in this experiment represent significant progress in the development of a viable strategy for clinical xenotransplantation.     

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.     

Prevention of hyperacute rejection in a model of orthotopic liver xenotransplantation from pig to baboon using polytransgenic pig livers (CD55, CD59, and H-transferase)

INTRODUCTION: The search for alternative sources for transplant organs leads us to the search for animals as an inexhaustible source of organs. The objective of this study was to analyze whether livers from polytransgenic pigs expressing the human complement regulatory proteins CD55 (hDAF), CD59, and alfa alpha1,2-fucosyltransferase (H-transferase), protected against hyperacute rejection after orthotopic liver xenotransplantation to a baboon and also to study pig liver function in a nonhuman primate. MATERIALS AND METHODS: Nine liver transplants from pig to baboon were divided into two groups: a control group (n = 4) of genetically unmodified pigs and an experimental group (n = 5) of pigs transgenic for CD55, CD59, and H-transferase as donors. All the donating piglets obtained through hysterectomy were maintained in specific pathogen-free conditions. The selection of transgenic pig donors followed demonstration of transgene expression using monoclonal antibodies (antiCD55, antiCD59) and immunohistological studies on liver biopsies. RESULTS: All animals in the control group developed hyperacute rejection with survival rates less than 16 hours without function of transplanted livers. In the experimental group none of the animals suffered hyperacute rejection. Survival in this group was between 13 and 24 hours. The livers were functional, producing bile and maintaining above 35% prothrombin activity. Only in one case was there primary dysfunction of the xenograft. CONCLUSION: Polytransgenic livers for complement regulatory proteins prevent hyperacute rejection when xenotransplanted into a baboon.     

Pig to canine auxiliary hepatic xenotransplantation model: prevention of hyperacute rejection via Kupffer cell blockade and complement regulation

Objectives

Large animal experiment models are a critical prerequisite to preclinical trials. However, the pig-to-primate model is expensive and proper experimental conditions are difficult to establish. Several pig-to-canine lung xenotransplantation experiments have shown hyperacute rejection. Therefore, we designed a pig-to-canine liver xenotransplantation model to study the diverse immunologic and hemodynamic consequences after xenotransplantation and hyperacute rejection.

Methods

Animals were divided into two groups of 3 each: a cobra venom factor plus gadolinium trichloride (GdCl₃) treatment group (CVF+Gd group) and a control group. Whole livers from 15-kg donor pigs were harvested and perfused with histidine-tryptophan-ketoglutarate solution. Seventy percent of the left lobe of the livers of 17-kg recipient dogs was resected. The harvested pig whole liver was transplanted using the canine left hepatic vein, left portal vein, and common hepatic artery. After graft reperfusion, blood samples and aliquots of liver, lung, and kidney tissues were obtained at 1 hour after reperfusion.

Results

We successfully completed 6 pig-to-canine auxiliary hepatic xenotransplantations. In the control group, the grafts showed a patchy hypoperfused liver surface that was rubbery solid compared with the CVF+Gd group. Serum total protein, albumin, fibrinogen, and platelet counts decreased abruptly; however, there were no significant differences between the two groups. There were no identifiable changes in blood urea nitrogen and creatinine concentrations. Serum prothrombin time, partial thromboplastin time, and further degradation product were increased in both groups; however, in the CVF+Gd group, the slope was more obtuse than in the control group. At microscopy, the graft at 20, 40, and 60 minutes after reperfusion, no intravascular pathologic changes were noted. Only scant intravascular fibrin deposition was observed. Hepatocellular vacuolization and sinusoidal dilatation were seen. There was patch necrosis without a zonal distribution, and intrasinusoidal neutrophil sequestration and interstitial hemorrhage. These findings were milder in the CVF+Gd group.

Conclusion

A pig-to-canine partial auxiliary liver xenotransplantation model is feasible. In the CVF+Gd treatment group, pathologic findings of patch hepatocyte necrosis were less severe. Inasmuch there was no corresponding vascular pathologic finding, these abnormalities are not a direct effect of CVF+Gd treatment. Other factors such as ischemia-reperfusion injury should be considered.     

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.     

Hyperacute rejection in the guinea pig-to-rat model without formation of the membrane attack complex

The guinea pig (GP)-to-rat transplantation model has been widely used to study hyperacute rejection (HAR) of xenografts. In this model heart graft survival beyond 8 days has never been reported. In contrast, survival times of kidney and heart grafts up to 62 days have been reported in the discordant pig-to-primate model. It is not clear why it is so much more difficult to obtain long-term graft survival in the GP-to-rat model as compared to the pig-to-primate model. We hypothesized that mechanisms other than activation of complement may be involved in the rejection of guinea pig grafts by rat recipients. Therefore, we have studied in detail the rejection of GP aortic grafts by rat recipients, either PVG/c+ (complement competent, group 1), or PVG/c- (complement C6 deficient, group 2). PVG/c- rats are not able to form the membrane attack complex (MAC) of complement. Forty-four GP-to-rat aortic transplantations were performed successfully. Recipient rats were sacrificed at various intervals after transplantation (4, 24 and 48 h, and 7 and 28 days, three to six animals per time point per group). Twenty-four hours after transplantation the number of cells in the media was significantly decreased from 11.1 +/- 0.9 cells/mm2 to 3.1 +/- 2.8 cells/mm2 in group 1, whereas the number of medial cells in group 2 remained the same. The number of medial cells was significantly decreased in both groups at 48 h post-transplantation (group 1: 1.8 +/- 2.2 cells/mm2; group 2: 5.5 +/- 3.0 cells/mm2). At that time no infiltrating cells were apparent in the grafts of either two groups. Seven days after transplantation, the number of medial cells remained low in group 1 (1.8 +/- 2.9 cells/mm2) but was increased in group 2 (10.7 +/- 2.6 cells/mm2) as a consequence of infiltrating immune cells. These infiltrating cells consisted mainly of macrophages, but also T cells and NK cells. At 28 days after transplantation the grafts in both groups were completely reorganized and no distinction could be made between media and adventitia. These results show that rejection of GP grafts by rat recipients can occur in the absence of both MAC of complement and immune competent cells. This MAC and immune cells independent type of rejection has not been described before and may explain the difficulty in obtaining long-term graft survival in the GP-to-rat xenotransplantation model.