The immunobiology of CD4+ CD25+ T regulatory cells

描述(由申请人提供)：人们对了解T调节(Treg)细胞的基本免疫生物学很感兴趣，因为它们提供了一种方法来抑制在自身免疫性疾病期间或由于造血干细胞移植(HSCT)或组织移植排斥反应而发生的不必要的免疫反应。Treg细胞免疫生物学中一个鲜为人知的重要领域涉及到这些抑制性T细胞在维持外周自身耐受方面的抗原特异性。我们已经开发了体内模型系统，允许直接检查TCR的多样性和特异性，因为它与自身免疫性疾病的控制有关。在一个模型中，Treg细胞过继转移到IL-2RB-/-小鼠体内，由于未能产生有效的Treg细胞，这些小鼠产生了快速致命性的全身自身免疫。这些供体Treg细胞完全防止这种自身免疫，并提供特定的治疗性Treg细胞群来检查有关TCR多样性和特异性的问题。在另一个临床相关的模型中，宿主Treg细胞在HSCT后存活下来，其功能是抑制来自供体的自身反应性T细胞。我们使用这些模型来解决有关高TCR多样性的Treg细胞对自我耐受的重要性的问题。我们的初步工作表明，在免疫耐受严重崩溃的情况下，自身免疫的控制只需一小部分可用的Treg TCR谱系，并伴随着大量的外周重塑。最终，对Treg TCR多样性的过于严格的限制有时会导致自身免疫。后者的发现与TCR谱系偏斜代表潜在的内在Treg细胞缺陷导致自身免疫的假设是一致的。这项提案计划建立在这些数据的基础上，并利用这些模型的独特功能来更准确地定义在控制自身免疫方面对Treg TCR多样性和特异性的要求。一个重要的相关目标是研究对Treg特异性的外周调节的作用机制。为了解决这些问题，我们提出了以下具体目标：1)通过评估具有有限多样性的Treg细胞抑制自身免疫的有效性和持久性，进一步表征TCR多样性与Foxp3+调节性T细胞的相关性；2)测试对动态平衡机制的需求，以驱动Treg TCR谱系的外周重塑；以及3)评估改变TCR对Treg和自身反应性T细胞的选择对外周自我耐受和Treg TCR谱系重塑的影响。这些目标的完成应该会扩大我们对Treg TCR的选择和多样性的了解，因为它直接与这些细胞维持自我耐受的机制有关。这一提议有可能通过提供新的和必要的信息来影响该领域，这些信息可能对于将Treg细胞应用于免疫治疗的众多场景至关重要，其中一个场景是希望抑制不想要的免疫反应。 公共卫生相关性：在免疫治疗中利用Treg细胞被认为是一条很有前途的新途径，可以高度特异且潜在无毒地抑制在衰弱的自身免疫性疾病中发生的不必要的免疫反应。成功的Treg细胞治疗需要关于合适的TCR特异性的信息，以最佳地抑制自身反应性T细胞。建议的研究旨在利用我们的新型小鼠模型来促进对Treg TCR多样性和特异性控制自身反应性T细胞的需求的理解。在感染、造血干细胞移植、免疫抑制药物和肿瘤化疗药物使用后，免疫系统必须不断地重新平衡。事实上，HSCT后Treg细胞的TCR谱系发生了重塑。因此，选择和重塑Treg TCR谱系所涉及的机制是理解免疫耐受和自身免疫易感性的基础，并与广泛使用的临床治疗相关。除了这些问题，一种罕见的系统性自身免疫性疾病与人类IL-2R的遗传缺陷有关。IL-2、IL-2Ra和IL-2Rb基因多态性是多种人类自身免疫性疾病的重要遗传危险因素，包括多发性硬化症、1型糖尿病、类风湿性关节炎和乳糜泻。其中一些研究中使用的IL-2RB缺乏模型也与人类自身免疫有重要联系。了解在IL-2RB缺乏的模型中逆转自身免疫的因素也可能提供关于几种人类自身免疫性疾病普遍存在的病因和潜在治疗方法的新信息。

DESCRIPTION (provided by applicant): There is considerable interest in understanding the basic immunobiology of T regulatory (Treg) cells as they offer a means to inhibit unwanted immune responses that occur during autoimmune disease or as a consequence of hematopoietic stem cell transplantation (HSCT) or tissue transplant rejection reactions. An important area of Treg cell immunobiology that is poorly understood concerns the antigen specificity of these suppressor T cells in maintaining peripheral self-tolerance. We have developed in vivo model systems that permits direct examination of TCR diversity and specificity as it relates to control of autoimmune disease. In one model, Treg cells are adoptively transferred into IL-2Rb-/- mice, which develop rapid lethal systemic autoimmunity due to their failed production of effective Treg cells. These donor Treg cells fully prevent this autoimmunity and provide a defined population of therapeutic Treg cells to examine issues regarding TCR diversity and specificity. In another clinically relevant model, host Treg cells that survive lethal conditioning after HSCT function to suppress autoreactive donor-derived T cells. We have used these models to address questions concerning the importance of high TCR diversity of Treg cells for self-tolerance. Our initial work shows that in settings of rampant breakdown of immune tolerance, control of autoimmunity is achieved by only a fraction of the available Treg TCR repertoire that was accompanied by substantial peripheral reshaping. Ultimately, too severe constraints on Treg TCR diversity sometimes resulted in autoimmunity. This latter finding is consistent with the hypothesis that TCR repertoire skewing represents a potential intrinsic Treg cell deficit that causes autoimmunity. This proposal plans to build on these data and to exploit the unique features of these models to more precisely define the requirements for Treg TCR diversity and specificity in control of autoimmunity. An important related objective is to investigate mechanisms operative that contribute to peripheral modulation of Treg specificities. To address these issues we propose the following specific aims:1) To further characterize the relevance of TCR diversity in Foxp3+ regulatory T cells by evaluating the efficacy and durability of Treg cells with limited diversity to suppress autoimmunity; 2) to test the requirement for homeostatic mechanisms to drive peripheral reshaping of the Treg TCR repertoire; and 3) to evaluate the effect of altering TCR selection of Treg and autoreactive T cells on peripheral self-tolerance and Treg TCR repertoire reshaping. Completion of these aims should expand our knowledge concerning the selection and diversity of the Treg TCR as it directly relates to the mechanisms by which these cells maintain self-tolerance. This proposal has the potential to impact the field by providing new and essential information that is likely critical for application of Treg cells in immunotherapy to the multitude of scenarios where one wish to inhibit unwanted immune responses. PUBLIC HEALTH RELEVANCE: The utilization of Treg cells in immunotherapy is considered a promising new avenue for highly specific and potentially non-toxic suppression of unwanted immune responses that occur during debilitating autoimmune diseases. Successful therapy with Treg cells requires information concerning the proper TCR specificities that optimally suppress autoreactive T cells. The proposed studies are designed to exploit our novel mouse models to advance understanding concerning the requirement for Treg TCR diversity and specificity in control of autoreactive T cells. The immune system must be continually rebalanced after infections, HSCT, or the use of drugs for immunosuppression and tumor chemotherapy. Indeed, TCR repertoire reshaping occurs for Treg cells after HSCT. Thus, the mechanisms involved in selection and reshaping of the Treg TCR repertoire are fundamental to understand the basis of immune tolerance and susceptibility to autoimmunity and relevant to a widely used clinical therapy. Besides these issues, a rare form of systemic autoimmune disease has been linked to genetic defects in the human IL-2R. Polymorphism in IL-2, IL-2Ra and IL-2Rb are prominent genetic risk factors for a variety of human autoimmune diseases, including multiple sclerosis, type 1 diabetes, rheumatoid arthritis and celiac disease. The IL-2Rb-deficient model used in some of these studies also has an important link to human autoimmunity. Understanding the factors that reverse autoimmunity in the IL-2Rb- deficient model may also provide new information concerning the etiology and potential therapy that may be generally common to several human autoimmune diseases.