T cell activation death & memory in alloimmune responses

描述(由申请人提供)：该计划的长期目标是使用小鼠移植模型来解决有关耐受性要求和障碍的机械性问题。尽管取得了很大的进步，但在严格的小鼠模型和灵长类动物中，很少有策略能诱导可重复的耐受。因此，在第三个资助期的竞争性更新中，我们的目标是定义耐受机制，并制定策略来克服它们，以便在灵长类动物和最终人类中以严格的模式进行翻译。 为什么在严格的系统(如皮肤、大型动物)中很难做到耐受性？本实验室及其他使用外周(即非骨髓/胸腺)方法诱导耐受的研究表明：(1)仅含初始T细胞的小鼠较容易诱导长期移植存活/耐受；(2)调控细胞的缺失和诱导在此过程中均起关键作用；(3)记忆细胞因特定免疫、异源免疫或由于非特异性T细胞耗尽后的稳态增殖而存在，是一种强大的耐受屏障。基于这些发现，我们的总体理论框架是，耐受的主要障碍是效应器/记忆T细胞对死亡的抵抗，以及调节性T细胞的稳态和/或功能缺陷。我们相信，我们现在已经有了必要的工具和模型来制定和测试这个框架预测的特定假设。目标1将确定为什么体内平衡增殖是耐受性的障碍。我们将验证这样的假设，即这种屏障是在淋巴细胞减少的情况下，原始T细胞、记忆T细胞和调节性T细胞被抗T细胞试剂删除的不同敏感性的结果，以及它们随后通过自身稳定的增殖“恢复”的能力的结果。目的#2将测试记忆CD4T细胞对死亡和调节的敏感性。使用TCR转基因MHC II类同种异体反应性CD4T细胞系统，我们将检验两个独立的假说，即记忆T细胞比它们的幼稚的对应者更能抵抗死亡(假说1)和调节(假说2)。目的#3将确定免疫调节缺陷是否为耐受机制。使用同种异体反应性CD4+TCR转基因小鼠，我们将检验这一假说，即未能获得或维持耐受性是由于缺乏调控，这与产生的调控细胞的抗原特异性、间接同种异体识别的可用性或缺乏、选定组织/器官的固有免疫原性以及供体和受体之间的抗原差异程度有关。这些在明确的临床相关模型中确定耐受机制的研究应该有助于开发新的方法来诱导人类的耐受。

DESCRIPTION (provided by applicant): The long-term goal of this program is to use murine transplantation models to address mechanistic questions about requirements for, and barriers to, tolerance. Despite great advances, very few strategies induce reproducible tolerance in stringent mouse models and in primates. Therefore, in this competing renewal for a third funding period, our goals are to define mechanisms of resistance to tolerance, and to develop strategies to overcome them for translation in stringent model, in primates and ultimately humans. Why is tolerance in stringent systems (e.g., skin, large animals) so hard to achieve? Studies from our lab and others using peripheral (i.e., non-bone marrow/thymic) approaches to induce tolerance, have shown that: (1) It is relatively easy to induce long-term graft survival/tolerance in mice harboring only naive T cells; (2) Both deletion and the induction of regulatory cells play key roles in this process; and (3) Memory cells, existing due to specific immunization, heterologous immunity, or as a result of homeostatic proliferation following non-specific T cell depletion, are a potent barrier to tolerance. Based on these findings, our overall theoretical framework is that primary barriers to tolerance are resistance to death by effector/memory T cells, and defects in the homeostasis and/or function of regulatory T cells. We believe we now have the necessary tools and models in hand to formulate and test specific hypothesis predicted by this framework. Aim #1 will determine why homeostatic proliferation is a barrier to tolerance. We will test the hypotheses that this barrier is the result of the differential susceptibility of naive T cells, memory T cells, and regulatory T cells to undergo deletion by anti-T cell reagents, and their subsequent ability to "recover" via homeostatic proliferation, under conditions of lymphopenia. Aim #2 will test the susceptibility of memory CD4 T cells to death and regulation. Using a TCR transgenic MHC class II alloreactive CD4 T cell system, we will examine two separate hypotheses, namely that memory T cells are more resistant to death (hypothesis 1) and to regulation (hypothesis 2) than their naive counterparts. Aim #3 will determine whether defects in immunoregulation are mechanisms of tolerance resistance. Using alloreactive CD4+ TCR transgenic mice we will test the hypothesis that failure to acquire or maintain tolerance is due to lack of regulation, relating to either the antigen specificity of the regulatory cell generated, the availability, or lack thereof, of indirect allorecognition, the inherent immunogenicity of selected tissues/organs, and the degree of antigenic disparity between donor and recipient. These studies to define mechanisms of resistance to tolerance in defined clinically relevant models should help in developing novel approaches to induce tolerance in humans.