TNF Receptor Superfamily Signaling in Immune Tolerance

描述(由申请人提供)：胸腺中的阴性选择和调节性T细胞发育是中枢和外周耐受的关键组成部分。这两个过程都与TCR对自体多肽的亲和力有关：MHC复合体；正选择需要与这种自身抗原的弱相互作用，而自然的Treg发育和负选择通常需要与这种抗原的中等到更高的亲和力相互作用。我们现在有一个关于参与这些过程的多肽配体的亲和力和亲和力的大量尽管不完整的知识库。相反，作为负选择和Treg发育基础的基本信号通路仍然没有得到很好的证实。虽然已经确定了调控负选择和Treg发育的单个信号分子，但我们对这些过程中涉及的更大的通路以及类似的信号通路如何导致截然相反的结果--即通过负选择导致胸腺细胞死亡与通过分化为Treg而存活--缺乏基本的了解。支持这项资助的中心假设是，这些过程由肿瘤坏死受体超家族(TNFRSF)的三个成员-GITR、OX40和TNFR2调节。我们的初步数据表明，这三种TNFRSF受体的表达与TCR信号强度直接相关，是Treg发育所必需的。我们认为，TCR信号的强度表现为特定TNFRSF成员表达的增加，较高的TNFRSF信号导致Tregs的优先发展，从而使Treg TCR谱系倾斜，有利于更高的自我反应能力。更多的初步数据表明，GITR、OX40和TNFR2也影响TCR依赖的负选择。我们认为GITR、OX40和TNFR2通过不同的下游信号通路启动胸腺细胞的负选择和Treg的发育。在我们的模型中，TNFRSF信号启动了CD4+胸腺细胞的细胞死亡和对IL2的反应；那些随后接收IL2信号的细胞优先分化为Tregs，而那些未能分化为Tregs的细胞 启动IL2依赖的信号经历克隆性删除。这项拨款中提议的研究将直接测试这些假设，并定义共刺激受体CD28如何影响这些过程。最后，我们将确定在移植物抗宿主病模型中，特定于Tregs的TNFRSF依赖信号的改变是否会改变它们的功能。因此，这项拨款申请中提出的研究将阐明特定的TNFRSF成员如何将TCR和CD28信号与功能Treg池的建立联系起来，并有助于扩大接受负选择的胸腺细胞的谱系。这些研究还将阐明TNFRSF激动剂和拮抗剂如何在未来用于增强Tregs的治疗潜力。

DESCRIPTION (provided by applicant): Negative selection and regulatory T cell development in the thymus are critical components of central and peripheral tolerance. Both of these processes have been linked to the affinity of the TCR for self-peptide:MHC complexes; positive selection requires weak interactions with such self-antigens while natural Treg development and negative selection typically require moderate to higher affinity interactions with such antigens. We now have a substantial albeit incomplete knowledge base about the affinity and avidity of peptide ligands involved in these processes. In contrast, the basic signaling pathways that underlie negative selection and Treg development still remain poorly established. While individual signaling molecules that regulate negative selection and Treg development have been identified, we lack a basic understanding of the larger pathways involved in these processes and how similar signaling pathways can give rise to diametrically opposed outcomes - namely death of a thymocyte via negative selection versus survival via differentiation into a Treg. The central hypothesis underlying this grant is that these processes are regulated by three members of the tumor necrosis receptor superfamily (TNFRSF) - GITR, OX40 and TNFR2. Our preliminary data document that expression of these three TNFRSF receptors correlates directly with TCR signal strength and is required for Treg development. We propose that TCR signal strength is manifested as increasing expression of specific TNFRSF members and that higher TNFRSF signaling leads to preferential development of Tregs, thereby skewing the Treg TCR repertoire in favor of higher self-reactivity. Additional preliminary data suggest that GITR, OX40 and TNFR2 also influence TCR-dependent negative selection. We propose that signaling via GITR, OX40 and TNFR2 primes developing thymocytes for both negative selection and Treg development via distinct downstream signaling pathways. In our model TNFRSF signaling primes CD4+ thymocytes for cell death as well as cell responsiveness to IL2; those cells that subsequently receive an IL2 signal preferentially differentiate into Tregs while those that fail to initiate IL2-dependent signals undergo clonal deletion. The studies proposed in this grant will directly test these hypotheses as well define how the costimulatory receptor CD28 impinges on these processes. Finally, we will determine whether altering TNFRSF-dependent signals specifically in Tregs alters their function in a model of graft-versus-host disease. Thus, the studies proposed in this grant application will elucidate how specific TNFRSF members link TCR and CD28 signals to the establishment of a functional Treg pool and help broaden the repertoire of thymocytes undergoing negative selection. These studies will also illuminate how TNFRSF agonists and antagonists could be used to augment the therapeutic potential of Tregs in the future.