Tolerance Induction in a GalT-KO Pig-to-Baboon Model Through Mixed Chimerism

由于混合嵌合体已在小鼠和人源化小鼠模型（项目3）中显示， 不仅能够诱导中枢T细胞耐受，而且能够阻止新的抗体反应， 尽管存在抗体应答，但异种混合嵌合体的建立仍然是一种有吸引力的手段 以获得异种移植耐受性。在GalT-KO微型猪可用之前， 实现跨越猪与灵长类动物屏障的混合嵌合体归因于高水平的灵长类动物天然 Gal抗原的抗体。然而，尽管GalT-KO的细胞表面上不存在Gal抗原， 造血细胞（HSC），我们已经发现这些细胞被迅速从血液循环中清除， 狒狒输注后不久，逃避建立混合嵌合体。我们的数据显示， 在这种清除中起作用的最重要的因素是：1）非Gal决定簇的天然抗体， 在不同的狒狒中不同程度地存在; 2）缺乏物种特异性细胞膜 CD 47是一种蛋白质，它是抑制先天免疫系统快速清除细胞所必需的。 流通本提案的目标是克服这两个障碍，以建立混合 狒狒中GalT-KO HSC的异种嵌合体。具体来说，我们将：1）优化异种骨 通过避免天然的和诱导的抗非Gal抗体的骨髓移植; 2）测试人 CD 47对猪骨髓在狒狒中的植入的影响，使用用GalT-KO转导的猪骨髓 人CD 47表达载体;和3）测试GalT-KO猪HSC植入狒狒的效果， 单独或与血管化猪胸腺移植联合， GalT-KO肾脏异种移植物的耐受性。目标3将应用目标1和2的结论以及战略 本计划项目1中开发的混合嵌合体方法用于诱导移植 在这种临床前、不一致的种属组合中对器官异种移植物的耐受性。此外，实验 计划将提供关于异种干细胞移植和免疫学的基本信息。 负责灵长类动物异种排斥和耐受诱导的途径。因此，这些研究 这对异种移植的最终应用具有理论和实践意义， 临床模式。

Since mixed chimerism has been shown in mouse and humanized mouse models (Project 3) to have the ability not only to induce central T cell tolerance, but also to prevent new antibody responses and turn off existing antibody responses, the establishment of xenogeneic mixed chimerism remains an attractive means for achieving xenograft tolerance. Before GalT-KO miniature swine were available, the failure of attempts to achieve mixed chimerism across the pig-to-primate barrier was attributed to high levels of primate natural antibodies to the Gal antigen. However, despite the absence of the Gal antigen on the cell surface of GalT-KO hematopoeitic cells (HSC), we have found that these cells are rapidly cleared from the circulation of baboons shortly after infusion, eluding the establishment of mixed chimerism. Our data indicate that two of the most important factors playing a role in this clearance are: 1) natural antibodies to non-Gal determinants, which are variably present in different baboons; and 2) absence of the species-specific cell-membrane protein, CD47, which is required to inhibit the innate immune system from rapidly clearing cells from the circulation. The goal of this proposal is to overcome these two barriers in order to establish mixed xenogeneic chimerism of GalT-KO HSC in baboons. Specifically, we will: 1) Optimize xenogeneic bone marrow engraftment by avoiding natural and induced anti-non-Gal antibodies; 2) Test effect of human CD47 on engraftment of porcine marrow in baboons using GalT-KO pig bone marrow transduced with a human CD47 expression vector; and 3) Test the effect of GalT-KO pig HSC engraftment in baboons, either alone or in combination with vascularized porcine thymus transplantation, on the induction of tolerance of GalT-KO renal xenografts. Aim 3 will apply the findings of Aims 1 and 2, as well as strategies developed in Project 1 of this Program Project, to the mixed chimerism approach for inducing transplantation tolerance to organ xenografts in this preclinical, discordant species combination. In addition, the experiments planned will provide basic information on xenogeneic stem cell engrafment and on the immunologic pathways responsible for xenogeneic rejection and tolerance induction in primates. As such, these studies should have both theoretical and practical implications for the eventual application of xenotransplantation as a clinical modality.