Signals Affecting Homestasis and Tolerance in Memory T Cells

描述(申请人提供)：虽然在啮齿动物模型中诱导长期耐受相对容易，但将这些方案翻译到高等脊椎动物和临床医学一直是困难的。与老鼠不同，人类经常暴露在病毒病原体中，这些病原体会导致一过性淋巴细胞减少和免疫记忆的产生。人类移植的一个已知障碍是大量的同种异体反应性记忆T细胞，即使在那些以前没有接触过同种异体抗原的人中也是如此。在没有同种异体抗原的情况下产生同种异体记忆T细胞的机制包括在急性或慢性病毒感染后的交叉反应，这一过程被称为异种免疫，以及通过对淋巴细胞减少反应的稳态扩张。了解允许同种异体反应性T细胞长期存活的信号可能会为临床耐受提供新的策略。记忆T细胞的动态平衡是通过单个细胞的长期存活和细胞周转的组合来调节的。这两个过程是通过克隆型T细胞受体(TCR)和细胞因子受体识别的细胞外信号来控制的。TCR信号和细胞因子受体产生的信号的相对贡献可能会因免疫原的性质而有所不同，但体内稳态所需的特定细胞内信号通路尚未很好地定义。这一建议的压倒一切的假设是，T细胞受体介导的记忆T细胞稳态和异源免疫的信号要求不同，取决于记忆细胞是由急性病毒感染、慢性病毒感染还是抗原非依赖性事件产生的。为了解决这一假设，我们开发了一种新的体内小鼠模型，该模型允许记忆T细胞中TCR信号下游的关键近端信号分子SH2结构域包含76千道尔顿的白细胞磷酸蛋白(SLP-76)的时间受控的基因缺失。SLP-76条件性缺陷T细胞为研究记忆性T细胞提供了一个独特的模型，这些T细胞是由完整的TCR信号装置产生的，但缺乏转导抗原特异性或紧张性TCR信号的能力。我们的初步数据显示，与未操纵的记忆表型T细胞相比，SLP-76缺陷的记忆表型T细胞不能在完整的宿主中进行动态平衡分裂。我们建议通过结合病毒感染模型和条件性基因缺失以及对移植耐受的研究来定义和剖析感染对记忆T细胞和移植的动态平衡的影响。

DESCRIPTION (provided by applicant): While it is relatively easy to induce long-term tolerance in rodent models, translation of these protocols to higher vertebrates and clinical medicine has been difficult. Unlike mice, humans are constantly exposed to viral pathogens which induce transient lymphopenia and the generation of immune memory. A known barrier to transplant in humans is a large number of alloreactive memory T cells, even in those individuals without previous exposure to alloantigen. Proposed mechanisms for the generation of alloreactive memory T cells in the absence of alloantigen include cross-reactivity following acute or chronic viral infection in a process termed heterologous immunity and through homeostatic expansion in response to lymphopenia. Understanding the signals that allow alloreactive memory T cells to persist long-term may suggest new strategies for clinical tolerance. Homeostasis of memory T cells is mediated through a combination of long-term survival of individual cells and cell turnover. These two processes are controlled via extracellular signals recognized by the clonotypic T cell receptor (TCR) and cytokine receptors. The relative contribution of TCR signals and cytokine receptor generated signals may vary depending on the nature of the immunogen, however the specific intracellular signaling pathways required for homeostasis have not been well defined. The overriding hypothesis of this proposal is that the T cell receptor mediated signaling requirements for memory T cell homeostasis and for heterologous immunity differ depending on whether a memory cell is generated by acute viral infection, by chronic viral infection, or antigen-independent events. To address this hypotheses, we have developed a novel in vivo murine model which allows temporally controlled genetic deletion in memory T cells of a key proximal signaling molecule downstream of TCR signaling, the SH2 domain containing leukocyte phosphoprotein of 76 kilodaltons (SLP-76). SLP-76 conditionally deficient T cells offer a unique model for studying memory T cells that were generated with an intact TCR signaling apparatus but lack the ability to transduce either antigen-specific or tonic TCR signals. Our preliminary data show that in contrast to non-manipulated memory phenotype T cells, SLP-76 deficient memory phenotype T cells fail to undergo homeostatic division in an intact host. We propose to define and dissect the effect of infection on homeostasis of memory T cells and transplantation by combining viral infection models with conditional gene deletion and studies on transplantation tolerance.