THROMBOREGULATORY BARRIERS TO XENOTRANSPLANTATION

一旦我们更充分地了解排斥反应的发生机制，并且能够持续地获得无全身毒性的异种移植存活，异种移植可能成为临床现实。尽管超急性排斥反应现在可以被废除，但带血管的异种移植仍然受到急性血管排斥反应的影响，或者称为延迟性异种移植排斥反应。后一种排斥反应模式与血管炎症、血小板减少和凝血因子消耗有关，后者可能演变为弥散性血管内凝血(DIC)。此外，通过混合嵌合体诱导耐受的细胞异种移植程序与广泛的血栓性血管损伤有关。在这些情况下，DIC和血栓性微血管病变的机制尚不清楚。在这些情况下，DIC和血栓性微血管病变的机制尚不清楚。低水平的炎性介质在血管化的异种移植物内，或在异种细胞输注后可能在受体血管系统内，可能会促进血管血栓形成。灵长类凝血因子如凝血酶与天然抗凝血剂如对异种白细胞和血管内皮细胞的血栓调节蛋白之间也显示出分子不相容。我们计划识别并进一步描述灵长类动物凝血功能紊乱和血栓形成反应的发生机制，这些机制与移植带血管的异种移植物和/或输注异种猪细胞有关。首先，在没有补体的情况下，异种反应性抗体介导的促凝血反应将在体外确定，然后在体内进行研究。我们还将演示异种细胞是如何引起血小板聚集的。与过度凝血酶生成有关的分子屏障，与猪血管内皮下基质相关的增强的血小板相互作用相关的von Willebrand因子，潜在的调控纤溶的失败将被深入调查。我们的数据应该为控制与器官和细胞异种移植相关的血栓并发症提供合适的药理学措施和基因治疗方式。这种方法应该确定不协调物种之间凝血调节的紊乱是否会对异种移植物的存活构成另一个障碍。控制血管炎症和血栓形成还应促进建立混合异种嵌合体；促进对血管化异种移植物免疫耐受机制的严格测试。如果从我们未来的实验观察中发展出新的和临床相关的药理和遗传抗血栓策略，这些研究将被判断为成功。

Xenotransplantation may become a clinical reality once we more fully understand the mechanisms of rejection and can consistently obtain xenograft survival without systemic toxicity. Although hyperacute rejection can now be abrogated, vascularized xenografts are still subject to acute vascular rejection, alternatively referred to as delayed xenograft rejection. This latter mode of rejection is associated with vascular-based inflammation, thrombocytopenia and the consumption of coagulation factors that may evolve to disseminated intravascular coagulation (DIC). In addition, cellular xenotransplantation procedures to induce tolerance by mixed chimerism are associated with widespread thrombotic vascular injury. The mechanisms underlying DIC and thrombotic microangiopathy in these settings are unclear. The mechanisms underlying DIC and thrombotic microangiopathy in these settings are unclear. Low levels of inflammatory mediators within vascularized xenografts, or potentially within the recipient vasculature after the infusion of xenogeneic cells, could promote vascular thrombosis. Molecular incompatibilities can also be shown between primate coagulation factors e.g. thrombin, and natural anti-coagulants e.g. thrombomodulin on xenogeneic leukocytes and endothelium We plan to identify and further characterize mechanisms underlying the development of coagulation disturbances and thrombotic responses in primates, temporally related to the transplantation of vascularized xenografts and/or infusion of xenogeneic cells from swine. Initially, xenoreactive antibody mediated pro-coagulant responses in the absence of complement will be defined in vitro and then studied in vivo. We will also demonstrate how xenogeneic cells cause platelet-aggregate formation. Molecular barriers relating to excessive thrombin generation, heightened platelet interactions with porcine sub-endothelial matrix associated von Willebrand factor the potential failure to regulate fibrinolysis will be then investigated in depth. Our data should indicate suitable pharmacological measures and gene therapeutic modalities for the control of thrombotic complications associated with organ and cellular xenotransplantation. This approach should establish whether disordered regulation of coagulation between discordant species will present yet another barrier to xenograft survival. Control of vascular inflammation and thrombosis should also promote establishment of mixed xenogeneic chimerism; to facilitate rigorous testing of mechanisms of immunological tolerance to vascularized xenografts. These studies will be judged successful if novel and clinically relevant pharmacological and genetic anti-thrombotic strategies develop from our future experimental observations.