THROMBOREGULATORY BARRIERS TO XENOTRANSPLANTATION

一旦我们更充分地了解排斥反应的机制，异种移植可能成为临床现实，并能持续获得异种移植物的生存而无全身毒性。虽然超急性排斥反应现在可以消除，但血管化异种移植物仍然会发生急性血管排斥反应，或者称为延迟性异种移植物排斥反应。后一种排斥模式与基于血管的炎症、血小板减少症和可能演变为弥散性血管内凝血（DIC）的凝血因子消耗相关。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相关。这些情况下DIC和血栓性微血管病的潜在机制尚不清楚。这些情况下DIC和血栓性微血管病的潜在机制尚不清楚。在血管化异种移植物内，或在异种细胞输注后可能在受体血管系统内，低水平的炎症介质可促进血管血栓形成。灵长类凝血因子如凝血酶与天然抗凝剂如异种白细胞和内皮细胞上的血栓调节蛋白之间也可显示分子不相容性。我们计划鉴定并进一步表征灵长类中凝血障碍和血栓形成反应发展的潜在机制，其与血管化异种移植物的移植和/或来自猪的异种细胞的输注在时间上相关。最初，在不存在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定义，然后在体内研究。我们还将证明异种细胞如何引起血小板聚集体的形成。随后将深入研究与过度凝血酶生成、血小板与猪内皮下基质相关的血管性血友病因子的相互作用增强以及调节纤维蛋白溶解的潜在失败相关的分子屏障。我们的数据应表明适当的药理学措施和基因治疗方式控制血栓并发症与器官和细胞异种移植。这种方法应该确定不一致物种之间的凝血调节紊乱是否会成为异种移植物存活的另一个障碍。控制血管炎症和血栓形成还应促进混合异种嵌合体的建立;以促进对血管化异种移植物的免疫耐受机制的严格测试。如果从我们未来的实验观察中开发出新的临床相关的药理学和遗传学抗血栓策略，则这些研究将被判定为成功。

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.