Determinants of T Cell Fate in Transplantation Tolerance

移植是治愈终末期器官衰竭的方法，但对于 许多移植受者由于免疫排斥反应。小鼠、NHP模型及患者的研究 人们一直认为记忆中的CD8+T细胞在 抗免疫抑制的同种异体移植排斥反应。因此，分子机制的识别 调节记忆CD8+T细胞反应仍是临床免疫治疗的重要目标 移植。Fc受体，以前已知只在B细胞和先天性免疫细胞上表达，可以 基于激活和抑制Fc受体信号的平衡来微调免疫细胞的激活，许多 比如T细胞共刺激和共抑制分子。在上一个资金周期中，我们发现 抑制性受体Fc CD8RIIb也表达于多种功能效应/记忆γ+T细胞亚群。 并表明FcγRIIb在功能上调节细胞内的CD8+T细胞免疫- 在小鼠和人类临床试验中都是自主的。然而，发生这种情况的机制 目前仍不清楚。首先，FcγRIIB连接导致T细胞死亡的信号尚不清楚。我们 发现CD8+T细胞上的FcγRIIB信号不是由抗体连接控制的，而是由一种新的 免疫抑制细胞因子纤维蛋白原样蛋白2(Fgl2)。此外，我们额外的初步数据表明， FcγRIIBSHIP1依赖的机制导致细胞凋亡的诱导。因此，在目标1中，我们将 确定Fgl2的细胞来源，它对FcγRIIB介导的CD8+T细胞凋亡至关重要 将使用蛋白质组学的方法来阐明近端的细胞内信号分子与 FcγRIIB促进Caspase3/7活性。第二，我们对FcγRIIB+CD8+T细胞进行了新的观察 表现出神经节苷脂代谢酶Gm2a的表达增加，并增加了 CD8+T细胞中Gm2a mRNA与人类队列中对最小免疫抑制的稳定性相关 肾移植受者。这些初步数据构成了在目标2中检验假设的前提： Gm2a是一种新的调节途径，调节移植接受，可能在FcγRIIB中- 依附时尚。最后，在目标3中，我们建议直接测量FcγRIIb、Fgl2和Gm2a在 从人类肾移植受者的验证队列中分离出CD8+T细胞，并确定 CD8+T细胞Fc、γ、RIIb和Gm2a表达与同种异体免疫低下和/或急性 拒绝。这些数据将使我们能够确定表达FcγRIIb/Gm2a的T细胞用作 预测移植后排斥反应风险的生物标志物。总而言之，通过这些机械性 和翻译研究，我们将阐明FcγRIIB的基本分子和细胞通路- 介导的CD8+T细胞反应抑制及其对记忆性CD8+T细胞的治疗作用 临床移植中的反应和改善结果。

Transplantation is a cure for end stage organ failure, yet achieving “one transplant for life” remains elusive for many transplant recipients due to immunologic rejection. Studies in mouse and NHP models and patient populations have consistently implicated memory CD8+ T cells as playing a causal role in mediating immunosuppression-resistant allograft rejection. Thus, the identification of the molecular mechanisms that regulate memory CD8+ T cells responses remains an important goal for immunotherapy in clinical transplantation. Fc receptors, previously known only to be expressed on B cells and innate immune cells, can fine-tune immune cell activation based on the balance of activating and inhibitory Fc receptor signaling, much like T cell costimulatory and coinhibitory molecules. During the last funding cycle we identified that the inhibitory receptor FcγRIIB is also expressed on a subset of multi-functional effector/ memory CD8+ T cells in mice and in humans, and showed that FcγRIIB functionally regulates CD8+ T cell immunity in a cell- autonomous manner in both mice and in a human clinical trial. However, the mechanisms by which this occurs are still not clear. First, the signals via which FcγRIIB ligation leads to T cell death are not known. We discovered that FcγRIIB signaling on CD8+ T cells is not controlled by antibody ligation, but instead by a novel immunosuppressive cytokine fibrinogen-like 2 (Fgl2). Moreover, our additional preliminary data suggest a FcγRIIB SHIP1-dependent mechanism that leads to the induction of apoptosis. Thus, in Aim 1, we will determine the cellular source of Fgl2 that is critical for FcγRIIB-mediated CD8+ T cell apoptosis, and will use a proteomics approach to elucidate the proximal intracellular signaling molecules that associate with FcγRIIB to promote caspase 3/7 activity. Second, we made the novel observation that FcγRIIB+ CD8+ T cells exhibit increased expression of the ganglioside metabolic enzyme Gm2a, and that increased expression of Gm2a mRNA in CD8+ T cells is associated with stability on minimal immunosuppression in a cohort of human renal transplant recipients. These preliminary data form the premise for the hypothesis to be tested in Aim 2: that Gm2a is a novel regulatory pathway that regulates transplant acceptance, potentially in an FcγRIIB- dependent fashion. Finally, in Aim 3 we propose to directly measure FcγRIIB, Fgl2, and Gm2a expression in CD8+ T cells isolated from a validation cohort of human renal transplant recipients, and to determine the association between CD8+ T cell FcγRIIB and Gm2a expression and reduced alloimmunity and/or acute rejection. These data will allow us to determine the ability of FcγRIIB/Gm2a-expressing T cells to be used as a predictive biomarker to stratify the risk of rejection following transplantation. In sum, through these mechanistic and translational studies, we will elucidate the fundamental molecular and cellular pathways of FcγRIIB- mediated inhibition of CD8+ T cell responses, and their therapeutic potential to attenuate memory CD8+ T cell responses and improve outcomes in clinical transplantation.