A TOLERANCE APPROACH TO XENOTRANSPLANTATION

描述(由申请人提供)：异种移植提供了最好的近期希望，以满足目前身体同种器官严重短缺对移植领域施加的关键限制。我们在本计划项目资助的前一个项目期间的研究取得了相当大的进展，从猪到狒狒的心脏和肾脏异种移植的器官存活率现在以月为单位衡量，而不是以天为单位。提高存活率的一个主要因素是发展了一种新的小型猪基因敲除品系(Galt-KO)，它不在细胞上表达Gal表位，从而避免了以前由天然抗Gal抗体引起的严重排斥反应。我们还表明，使用这些新的捐赠者，器官存活率的最大改善是使用旨在诱导耐受的方案。然而，在这项技术准备好临床应用之前，还需要进一步的改进。这一新的应用汇集了五个项目，这些项目致力于该研究领域最有前途的方法和最紧迫的问题：1)通过带血管胸腺移植诱导耐受；2)通过混合嵌合体诱导耐受；3)利用人类免疫系统建立小鼠耐受模型；4)异种移植中的病毒发病机制；以及5)异种移植的血栓调节障碍。所有这些项目都是高度互动的，并利用了大量的共享资源，其中许多将通过大型动物核心提供。这项工作将在一个独特的环境中进行，提供与同一研究中心从事基础和细胞免疫学以及相关小动物和大动物模型工作的科学家的互动，以及与致力于将新疗法应用于临床的临床医生的互动。 项目1：使用Galt-KO血管胸腺移植诱导浣熊异种耐受(Yamada，K.) 项目1描述(由申请人提供)：项目1的总体目标是通过移植带血管的胸腺移植物来诱导跨越猪到狒狒的异种屏障的持久耐受性。为此，我们将：1)优化我们的免疫抑制药物方案：我们之前已经证明，带血管的胸腺移植物支持胸腺生成，并通过完全不匹配的同种异体屏障诱导移植耐受。在这个异种移植模型中，我们将尝试优化实现持久胸腺植入所需的免疫调节治疗方案；2)确定植入的胸腺是否能诱导对来自与胸腺供者基因相同的近亲交配供体动物的异种肾移植的耐受。如果成功，该策略将扩展到同时进行胸腺和肾脏的异种移植；以及3)利用体外试验，重点研究跨越这一物种屏障的耐受的特异性，阐明供者胸腺诱导耐受的机制。这些研究将与PPG中的其他项目高度互动。因此，如果有必要，最佳治疗方案将根据Sykes和他的同事在项目3中研究的猪到灵长类动物耐受的小鼠模型的结果进行修改。如果最终抗体介导的排斥反应不能通过胸腺移植有效地预防，我们将尝试通过胸腺移植和造血移植相结合的方法来诱导B细胞耐受，这在项目2中正在研究中。我们还将与项目5合作，研究移植后凝血障碍的机制。总之，我们希望这些研究将为胸腺移植在诱导移植耐受中的潜在作用提供新的见解。

DESCRIPTION (provided by applicant): Xenotransplantation offers the best near-term hope for satisfying the critical limitation imposed on the field of transplantation today by the severe shortage of cadaveric allogeneic organs. Our studies in the previous Project period of this Program Project grant have made considerable progress, and organ survivals of both heart and kidney xenotransplants from pigs to baboons are now measured in months rather than days. A major factor in this improved survival has been the development of a new, knock-out strain of miniature swine (GalT-KO), which do not express the Gal epitope on their cells, thus avoiding the severe rejection previously caused by natural anti-Gal antibodies. We have also shown that the greatest improvement in organ survivals using these new donors is observed using protocols designed to induce tolerance. Nevertheless, additional improvements will be required before this technology is ready for clinical application. This renewal application brings together five Projects devoted to the most promising approaches and the most pressing problems in this field of research: 1) tolerance induction through vascularized thymic transplantation; 2) tolerance induction through mixed chimerism; 3) modeling of tolerance in mice with human immune systems; 4) Viral pathogenesis in Xenotransplantation; and 5) thromboregulatory barriers to Xenotransplantation. All of these Projects-are highly interactive, and utilize numerous shared resources, many of which will be made available through the large animal core. The work will be carried out in a unique environment, which provides interactions with scientists working in basic and cellular immunology and working on relevant small and large animal models in the same research center, as well as with clinicians committed to taking new therapies to clinical applications. PROJECT 1: Use of GalT-KO Vascularized Thymic Transplantation for the Induction of Xenogeneic Tolerance in Baboons (Yamada, K.) PROJECT 1 DESCRIPTION (provided by applicant): The overall objective of Project 1 is to induce durable tolerance across a pig-to-baboon xenogeneic barrier through transplantation of vascularized thymic grafts. For this purpose, we will: 1) optimize our immunosuppressive drug regimen: We have demonstrated previously that vascularized thymic grafts support thymopoiesis and induce transplant tolerance across fully mismatched allogeneic barriers. In this xenogeneic model, we will attempt to optimize the immunomodulatory treatment regimen required to achieve durable thymus engraftment; 2) determine whether the engrafted thymus can induce tolerance to a kidney xenograft from an inbred donor animal genetically identical to the thymus donor. If successful, the strategy will be extended to simultaneous thymus plus kidney xenotransplantation; and 3) elucidate the mechanism of donor thymus-induced tolerance, using in vitro assays and focusing on the specificity of tolerance across this species barrier. These studies will be highly interactive with other Projects in this PPG. Thus, the optimal treatment regimen will be modified, if necessary, on the basis of results from a mouse model of pig-to-primate tolerance through thymus transplantation being investigated by Sykes and colleagues in Project 3. If eventual antibody-mediated rejection cannot be effectively prevented through thymic transplantation, we will attempt to induce B-cell tolerance by combining thymic transplantation with hematopoietic transplantation, being studied in Project 2. We will also collaborate with Project 5 on the mechanism of any post-transplant coagulation disorders observed. Together, we hope these studies will provide new insights into the potential role of thymic transplantation in the induction of transplantation tolerance.