CD137 signals in DV during Ag-priming induces tolerance

描述（由申请人提供）：cd137 (4-1BB)，一种激活诱导型T细胞共刺激受体和TNFR超家族成员，在活化的T细胞和NK细胞上表达。我们已经证明，脾脏和骨髓来源的DC中的未成熟树突状细胞群体组成性地表达CD137。在体内，抗cd137介导的共刺激显著增强CD8 T细胞增殖、效应功能、T细胞存活和记忆发育。然而，抗cd137单抗可以抑制T依赖性体液免疫并诱导T辅助能。该应用程序旨在定义导致T细胞激活与T细胞能量的条件，并了解驱动这些反应的机制。我们选择C57BL/6小鼠的急性LCMV病毒感染作为实验模型，因为它允许在单个实验系统中同时研究T细胞和B细胞免疫反应。本文所述的初步数据表明，只要在感染后36小时内给予抗体，抗cd137单抗可以抑制抗lcmv免疫的各个方面的发展。在这些条件下，lcmv感染的小鼠发生病毒血症，无法产生病毒特异性CTL，持续感染，并产生针对病毒的t依赖性抗体水平降低。然而，尽管Gp33-41或Np396-404特异性的四聚体阳性CD8 T细胞无功能，但在感染后100天的耐受小鼠中检测到的频率远高于背景。表达牛痘病毒和流感病毒的VSV表位获得了类似的结果（数据未显示）。因此，CD8 T细胞反应和CD4 T细胞反应一样可以被抗cd137单抗抑制，但单抗给药的时机至关重要。这些观察结果对疫苗开发和APC具有重要意义，因为它们准备抗原原质T细胞。对这一数据的重要解释是，在CD137缺陷小鼠中，当野生型T细胞过继转移时，不会发生诱导抑制。此外，LCMV感染小鼠的T细胞上CD137的表达直到感染后72小时才通过实时PCR或FACS表型分析显示出来。在T细胞启动完成后注射抗cd137的小鼠往往会产生增强的抗病毒免疫。我们在此提供的证据表明，抗CD137单抗仅在T细胞抗原启动时发挥免疫抑制作用，并且抗CD137单抗的主要细胞靶标不是T细胞，而更可能是CD137 DC。在这个提议中，我们希望：(1)确定抗cd137诱导的外周T细胞抑制后未成熟树突状细胞的死亡命运和功能。(2)评估DC中抗cd137介导的信号传导是否直接中止T细胞的免疫应答，诱导产生细胞毒性DC、Treg或CTL。(3)机制确定抗原特异性CD8 T细胞在LCMV感染、抗cd137治疗的小鼠中发生缺失的机制。(4)确定树突状细胞上cd137的表达是否作为抑制正在进行的免疫反应的分子开关。该建议的中心假设是cd137介导的免疫系统内信号传导可导致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细胞活化还是抑制的决定可以由CD137信号传递的时机和这些信号的细胞靶标决定。因此，树突状细胞中cd137介导的信号传导抑制T细胞介导的免疫，并且在LCMV感染中导致T细胞耐受。相反，传递给T细胞的CD137信号可以放大或延长T细胞的免疫应答，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.