Transient chimerism and allograft tolerance

 描述（由申请人提供）：与大多数造血细胞移植（HCT）准备方案相关的毒性和移植物抗宿主病（GVHD）风险限制了混合嵌合体方法用于同种异体移植耐受的适用性。本提案的总体目标是进一步开发一种新的方案，用于瞬时嵌合和耐受诱导，该方案不依赖于毒性调节并避免GVHD的风险。一些接受这种新方案的小型猪HCT受体出现短暂的外周血嵌合体，在移植后1-3个月内变得无法检测到，类似于在患者中观察到的短暂嵌合体。初步数据表明，暴露于供体外周血细胞使用该协议的结果在稳定的B细胞耐受性与短暂的T细胞耐受性，并发生免疫调节的异基因细胞介导的干细胞移植独立。由于新发育的B细胞在整个生命过程中在骨髓中不断形成，因此发现供体细胞不持续存在并且不存在供体抗原的其他来源使得克隆缺失机制不太可能单独负责该模型中B细胞耐受性的维持。我们假设，一个积极的监管机制参与防止germinal中心形成后，进一步暴露于供体细胞和组织，使用这种新的温和的空调协议保留了这种监管机制。我们还假设对同种异体细胞的免疫调节反应在促进器官移植耐受诱导中起直接作用。我们提出，与目前的教条相反，在暴露于供体细胞时，保留而不是完全消融宿主免疫细胞，包括B-和T-细胞群体，可能有利于诱导稳定的耐受机制。本研究计划的目标是确定通过猪的瞬时嵌合体可靠诱导移植耐受的机制和必要的免疫抑制条件，并将这些发现转化为非人灵长类动物（NHP）。这些目标将通过以下具体目标来实现：1）使用MHC定义的小型猪确定在同种异体细胞输注后诱导稳定的B细胞耐受性和短暂的T细胞无反应性的机制;（二）确定供体细胞来源和受体预处理方案的必要组成部分，从而持续诱导对同种异体细胞的免疫调节反应而不是免疫刺激反应猪;和3）确认这种新方法在猪和NHP中实现稳定的肾移植耐受性的功效，作为临床试验的先决条件。这些研究的结果将指导进一步的临床方案修改，以提高同种异体移植耐受性，同时显着降低移植患者的毒性。

 DESCRIPTION (provided by applicant): Toxicities associated with most preparative regimens for hematopoietic cell transplantation (HCT) and the risk of graft-versus-host-disease (GVHD) limit the applicability of mixed chimerism approaches for allograft tolerance. The overall objective of this proposal is to further develop a novel protocol for transient chimerism and tolerance induction that does not rely on toxic conditioning and avoids the risk of GVHD. Some miniature swine HCT recipients conditioned with this novel protocol develop transient peripheral blood chimerism that becomes undetectable within 1-3 months post transplantation, similar to the transient chimerism observed in patients. Preliminary data demonstrate that exposure to donor peripheral blood cells using this protocol results in stable B-cell tolerance together with transient T-cell tolerance, and that immune modulation mediated by allogeneic cells occurs independently from stem cell engraftment. As newly developing B cells are continuously forming throughout life in the bone marrow, the finding that donor cells do not persist and no other source of donor antigen is present makes it unlikely that clonal deletion mechanisms are solely responsible for maintenance of B-cell tolerance in this model. We hypothesize that an active regulatory mechanism is involved in preventing germinal center formation upon further exposure to donor cells and tissue and that use of this novel mild conditioning protocol preserves this regulatory mechanism. We also hypothesize that the immune modulatory response to allogeneic cells plays a direct role in facilitating organ allograft tolerance induction. We propos that, in contrast to current dogma, preserving rather than completely ablating host immune cells, including B- and T-cell populations, at the time of exposure to donor cells may be beneficial for inducing stable tolerance mechanisms. The goals of this research proposal are to determine the mechanisms and the necessary immunosuppressive conditions which lead to reliable induction of transplantation tolerance through transient chimerism in swine, and to translate these findings to non-human primates (NHP). These goals will be achieved through the following Specific Aims: 1) Determine the mechanisms involved in induction of stable B-cell tolerance and transient T-cell unresponsiveness following allogeneic cell infusion using MHC-defined miniature swine; 2) Determine the donor cell source and the necessary components of the recipient conditioning protocol which lead to consistent induction of immunomodulatory rather than immunostimulatory responses to allogeneic cells in swine; and 3) Confirm the efficacy of this novel approach for achieving stable renal allograft tolerance in both swine and NHP as a prerequisite to clinical trials. Results of these studies will guide further clinical protocol modifications to enhance allograft tolerance while significantly reducing toxicity in transplant patients.