CD137 signals in DV during Ag-priming induces tolerance

描述(申请人提供)：CD137(4-1BB)是一种活化的可诱导T细胞共刺激受体，是TNFR超家族的成员，表达于活化的T细胞和NK细胞上。我们已经证明，在脾和骨髓来源的DC中有一群未成熟的树突状细胞结构性地表达CD137。在体内，抗CD137介导的共刺激显著增强CD8T细胞的增殖、效应功能、T细胞存活和记忆发育。但抗CD137单抗可抑制T细胞依赖的体液免疫，诱导T辅助细胞无能。该应用程序旨在定义导致T细胞激活与T细胞无能的条件，并了解驱动这些反应的机制。我们选择C57BL/6小鼠急性LCMV病毒感染作为实验模型，因为它允许在一个实验系统中同时研究T细胞和B细胞免疫反应。初步数据显示，抗CD137单抗可以抑制抗LCMV免疫的所有方面的发展，只要抗体在感染后36小时内给予。在这些条件下，LCMV感染的小鼠出现病毒血症，不能产生病毒特异性CTL，仍然持续感染，并产生对病毒的T依赖抗体水平降低。然而，对Gp33-41或Np396-404特异的四聚体阳性CD8 T细胞虽然没有功能，但在耐受小鼠感染100天后，仍可检测到远高于本底的频率。表达痘苗病毒和流感病毒的VSV表位也得到了类似的结果(数据未显示)。因此，CD8T细胞反应与CD4T细胞反应一样，可被抗CD137单抗抑制，但给予单抗的时机很关键。这些观察结果对于疫苗开发和APC准备抗原性T细胞具有重要意义。对这一数据的重要解释是，在CD137缺陷小鼠中，野生型T细胞过继转移到其中时，不会发生抑制诱导。此外，LCMV感染小鼠的T细胞上CD137的表达直到感染后72小时才能通过实时荧光聚合酶链式反应或流式细胞仪进行表型检测。在T细胞启动后注射抗CD137的小鼠通常会获得增强的抗病毒免疫力。我们在此提供的证据表明，抗CD137单抗仅在T细胞的抗原启动过程中发挥其影响免疫抑制的作用，并且抗CD137单抗的主要细胞靶点不是T细胞，而更有可能是CD137 DC。在这项建议中，我们希望：(1)确定未成熟树突状细胞在抗CD137诱导的外周T细胞抑制后的命运和功能。(2)评估DC中抗CD137信号是否直接阻断T细胞的免疫应答，诱导产生细胞毒性DC、Treg或CTL。(3)从机制上确定在LCMV感染、抗CD137治疗的小鼠中，抗原特异性CD8T细胞如何发生缺失。(4)确定树突状细胞上CD137的表达是否作为抑制持续免疫反应的分子开关。这一建议的中心假设是，CD137介导的免疫系统内的信号可以导致T细胞免疫增强和T细胞记忆的建立，或抗原特异性T细胞抑制。诱导T细胞激活还是抑制T细胞的决定取决于CD137信号传递的时机和这些信号的细胞靶点。因此，CD137介导的信号在树突状细胞中抑制T细胞介导的免疫，在LCMV感染中导致T细胞耐受。相反，CD137信号传递给T细胞可以增强或延长T细胞的免疫反应，并提高CD8 T细胞的存活率。

DESCRIPTION (provided by applicant): CD 137 (4-1BB), an activation inducible T cell costimulatory receptor and member of the TNFR superfamily is expressed on activated T cells and NK cells. We have shown that a population of immature dendritic cells in the spleen, and bone marrow derived DC constitutively express CD137. In vivo, anti-CD 137-mediated costimulation markedly enhances CD8 T cell proliferation, effector function, T cell survival, and memory development. However, anti-CD 137 mAbs can suppress T-dependent humoral immunity and induce T helper anergy. This application is designed to define the conditions that lead to T cell activation versus T cell anergy, and to understand the mechanisms that drive these responses. We chose acute LCMV viral infection in C57BL/6 mice as an experimental model because it allowed the concomitant study of T cell and B cell immune responses in a single experimental system. Preliminary data described herein show that anti-CD 137 mAbs can suppress the development of all aspects of anti-LCMV immunity providing the antibody is given within 36 hours of infection. Under these conditions LCMV-infected mice developed viremia, failed to generate virus specific CTL, remained persistently infected, and produced diminished levels of T-dependent antibodies to the virus. Nevertheless, tetramer positive CD8 T cells specific for Gp33-41 or Np396-404 although nonfunctional, were detectable at frequencies well above background in the tolerant mice 100 days post-infection. Similar results were obtained with a VSV epitope expressing vaccinia virus and influenza virus (data not shown). Thus, CD8 T cell responses like CD4 T cell responses can be suppressed by anti-CD 137 mAbs but the timing of mAb administration is critical. These observations have important implications with respect to vaccine development and APC as they prepare to antigen prime T cells. Important to the interpretation of this data is the fact that induction of suppression does not occur in CD137 deficient mice into which wild type T cells are adoptively transferred. Furthermore, CD137 expression on T cells from LCMV infected mice is not apparent by real time PCR or FACS phenotyping until 72 hours post-infection. Mice injected with anti-CD137 after T cell priming has been completed more often than not develop enhanced anti-viral immunity. We provide evidence herein that anti-CD 137 mAbs exert their affect immunosuppressive effect only during antigen priming of T cells, and that the primary cellular target of anti-CD137 mAbs are not T cells, but more likely, CD137 DC. In this proposal, we wish to: (1) Determine die fate and function of immature dendritic cells following anti-CD 137-induced peripheral T cell suppression. (2) Assess whether anti-CD 137-mediated signaling in DC directly aborts immune responses by T cells, induces the generation of cytotoxic DC, Treg, or CTL. (3) Mechanistically determine how antigen-specific CD8 T cells undergo deletion in LCMV infected, anti-CD 137 treated mice. (4) Determine whether CD 137 expression on dendritic cells serves as a molecular switch for suppressing ongoing immune responses. The central hypothesis of this proposal is that CD 137 mediated signaling within the immune system can lead to enhanced T cell immunity and the establishment of T cell memory, or antigen specific T cell suppression. The decision to induce T cell activation versus suppression can be determined by the timing of CD137 signal conveyance, and the cellular target of these signals. Thus, CD 137-mediated signaling in dendritic cells suppresses T cell-mediated immunity and in LCMV infection leads T cell tolerance. In contrast, CD137 signals delivered to T cells amplifies or prolongs T cell immune responses and enhances CD8 T cell survival.