B Cell Tolerance to Transplantation Antigens

 描述（由申请人提供）：急性和慢性抗体介导的排斥反应是移植受体的主要问题，因为目前的免疫抑制方案不足以控制针对移植物的体液免疫。我们在临床前猪模型中的初步数据不仅证明了供体造血细胞输注后诱导稳定的B细胞耐受，而且消除了致敏受体中的供体反应性抗体产生。该建议旨在确定诱导对移植抗原稳定的B细胞耐受的机制基础，以促进临床相关方法的发展，以克服对移植物的体液免疫。该项目是基于这样的发现，即供体细胞可以诱导稳定的B细胞耐受，独立于T细胞耐受，当静脉输注在MHC不匹配的猪受体。在部分T细胞耗竭、非常低剂量的全身照射和短疗程的环孢菌素单药治疗后暴露于供体细胞，导致猪受体不能产生供体特异性同种抗体应答，即使在用供体细胞多次免疫后也是如此。在这些动物中，产生对疫苗和蛋白抗原的抗体应答的能力保持完整。在上述温和条件下输注供体细胞后，不再检测到预先存在的抗供体抗体，并且尽管明显缺乏T细胞耐受性，但不能诱导同种抗体。这些初步的数据表明，它可能是有可能的，以具体消除抗供体抗体的生产在预致敏的患者在器官移植前。 我们假设，预先存在的同种异体反应性宿主B细胞在免疫抑制条件下暴露于供体细胞后耐受，该条件足以降低T细胞同种异体反应性，但保留免疫功能。我们还假设，B细胞耐受性是通过一种积极的调节机制来维持的，这种机制防止了在没有免疫抑制的情况下重复暴露于供体细胞时形成生发中心。这些假设将通过以下目标来解决：1）确定诱导和维持B细胞对供体细胞耐受的机制基础; 2）检查可靠地消除高度致敏受体中抗供体抗体产生的条件。了解在临床相关的大型动物模型中诱导和维持B细胞耐受性的机制将有助于设计 适当的临床调节方案，增强或至少不会无意中破坏这些机制。虽然小鼠模型对于理解移植生物学至关重要，但大型动物模型对于促进该领域新发现的临床转化至关重要。在猪中开发的协议有可能直接翻译为 到目前为止，所有这些都可以移植到非人类灵长类动物和/或患者身上。由于致敏患者的治疗仍然是移植领域一个重要的、未满足的需求，这些研究的结果可能会在改善移植结局方面取得突破，特别是在高度致敏患者中。

 DESCRIPTION (provided by applicant): Acute and chronic antibody-mediated rejection are major problems for transplant recipients because current immunosuppressive regimens are insufficient to control humoral immunity against the graft. Our preliminary data in the pre-clinica swine model not only demonstrate induction of stable B-cell tolerance following donor hematopoietic cell infusion but the elimination of donor-reactive antibody production in sensitized recipients. This proposal is designed to determine the mechanistic basis for induction of stable B-cell tolerance to transplantation antigens in order to facilitate development of clinically relevant approaches to overcome humoral immunity to transplants. This project is based on findings that donor cells can induce stable B-cell tolerance, independent of T-cell tolerance, when infused intravenously in MHC-mismatched swine recipients. Exposure to donor cells following partial T-cell depletion, very low-dose total body irradiation, and a short course f cyclosporine mono-therapy, results in inability of swine recipients to generate donor specific alloantibody responses, even after multiple immunizations with donor cells. The ability to generate antibody responses to vaccine and protein antigens remains intact in these animals. Pre-existing anti-donor antibody could no longer be detected following donor cell infusion under the mild conditioning described above and alloantibody could not be induced, despite clear lack of T-cell tolerance. These preliminary data demonstrate that it may be possible to specifically eliminate anti-donor antibody production in pre-sensitized patients prior to organ transplantation. We hypothesize that pre-existing alloreactive host B cells are tolerized following exposure to donor cells under immunosuppressive conditions that sufficiently reduce T-cell alloreactivity, yet preserve immune function. We also hypothesize that B-cell tolerance is maintained by an active regulatory mechanism preventing germinal center formation in response to repeated exposures to donor cells without immunosuppression. These hypotheses will be addressed through the following aims: 1) Determine the mechanistic basis for induction and maintenance of B- cell tolerance to donor cells; and 2) Examine conditions which reliably eliminate anti-donor antibody production in highly sensitized recipients. Understanding the mechanisms involved in inducing and maintaining B-cell tolerance in a clinically relevant large animal model will facilitate design of appropriate clinical conditioning protocols that enhance or at least do not inadvertently destroy these mechanisms. Although murine models have been critical to understanding transplantation biology, large animal models are essential in facilitating clinical translation of novel findings in this field. Protocols developed in swine have potential for direct translation to the clinic, and to date, all have been translatable to non-human primates and/or patients. Since treatment of the sensitized patient remains an important, unmet need in the field of transplantation, results of these studies could lead to a breakthrough in improving transplant outcomes, particularly in highly sensitized patients.