Interrogating the Fgl2-FcγRIIB axis on CD8+ T cells: A novel mechanism mediating apoptosis of tumor-specific memory CD8+ T cells

项目总结： 每50个美国人中就有一个会在一生中被诊断出患有黑色素瘤，而皮肤黑色素瘤是 最致命的皮肤癌。肿瘤免疫治疗是治疗该病的突破性方法，具有细胞毒性。 CD8+T细胞肿瘤的侵袭是免疫治疗成功的关键因素。因此，确定有效的 提高患者肿瘤特异性CD8+T细胞反应的大小和功能的策略 仍然是一个重要的目标。CD8+T细胞上的抑制分子对T细胞信号转导和免疫是必不可少的 动态平衡。然而，这些分子的表达增加与抗肿瘤效应减弱有关。 反应以及较差的患者存活率。FcγRIIB是最近在一个亚群上发现的抑制性Fc受体 CD8+T细胞。FcγRIIB+CD8+T细胞活化标志物表达增加，增殖能力增强 能力，并分泌更多的促炎细胞因子比他们的FcγRIIB-在小鼠和人类， 使它们成为抗肿瘤反应的必需品。最近，我们发现一种免疫抑制剂 细胞因子纤维蛋白原样蛋白2(FGL2)是一种与CD8+T细胞表面的FcγRIIB结合并诱导FcγRIIB- 介导CD8+T细胞的凋亡。本研究的目的是探讨Fgl2的作用机制。 通过以下目的使用同基因小鼠模型调节肿瘤特异性的FcγRIIB+CD8+T细胞。目标1： 确定Fgl2的细胞来源，Fgl2对肿瘤特异性CD8+T细胞起关键调节作用。我们的研究 结果表明，Foxp3+调节性T细胞和CD8+T细胞在小鼠和人的肿瘤中都表达Fgl2。因此， 我们将确定这些细胞类型分泌的Fgl2对于FcγRIIB介导的CD8+是否必要和/或足够 T细胞凋亡，这一发现将为后续针对这一细胞类型的治疗提供动力。 目的2：阐明FcγRIIB的CD8+T细胞亚型诱导白血病细胞凋亡的机制。 Fgl2结合的配体。我们的研究表明，CD8+T细胞表达一种不同的FcγRIIB亚型，这种亚型可以 被Fgl2结合，但Fgl2-FcγRIIB结合后的即时信号事件仍不清楚。我们将确定 与FcγRIIB胞内区相关的蛋白质，特别是在Fgl2与配体结合后。这个项目 是在黑色素瘤的背景下，因为治疗的成功很大程度上受到CD8+T细胞渗透的影响，但 这些发现的影响可能适用于其他免疫“热门”肿瘤，这些肿瘤的免疫疗法 势头正在增强。我们拥有几个鼠标模型和关于FCγRIIB在 CD8+T细胞的反应使我们有资格解决所提出的目标。拟议目标的影响是 尽管它们将识别新的靶点，但当被阻断时，可以挽救CD8+T记忆种群 对肿瘤的免疫反应至关重要的细胞。然后，这些“被拯救”的细胞将释放它们的效应器 改善黑色素瘤患者反应的功能。作为CD8+T细胞抑制分子与免疫抑制 细胞因子对CD8+T细胞的渗透有负面影响，研究这些相互作用具有重要意义 我们进入了癌症免疫治疗的时代--一种依赖于患者CD8+T细胞反应的治疗方法。

PROJECT SUMMARY: One in fifty Americans will be diagnosed with melanoma in their lifetime and skin cutaneous melanoma is the deadliest skin cancer. Cancer immunotherapy is a breakthrough approach to treat this disease and cytotoxic CD8+ T-cell tumor infiltration is a critical factor to immunotherapeutic success. As such, identifying effective strategies to increase the magnitude and functionality of the patient’s tumor-specific CD8+ T-cell response remains an important goal. Inhibitory molecules on CD8+ T cells are imperative to T-cell signaling and immune homeostasis. However, elevated expression of these molecules is correlated with dampened antitumor effector response as well as poorer patient survival. FcγRIIB is an inhibitory Fc receptor recently discovered on a subset of CD8+ T cells. FcγRIIB+ CD8+ T cells exhibit increased expression of activation markers, higher proliferative ability, and secrete more proinflammatory cytokines than their FcγRIIB- counterparts in mice and humans, making them imperative to the antitumor response. Recently, we discovered that an immunosuppressive cytokine, fibrinogen-like protein 2 (Fgl2), is a ligand that binds FcγRIIB on CD8+ T cells and induces FcγRIIB- mediated apoptosis of CD8+ T cells. The goal of this research is to interrogate the mechanism by which Fgl2 regulates tumor-specific FcγRIIB+ CD8+ T cells using syngeneic mouse models via the following aims. AIM 1: Determine the cellular source of Fgl2 that critically regulates tumor-specific CD8+ T cells. Our studies show that both Foxp3+ regulatory T cells and CD8+ T cells express Fgl2 at the tumors of mice and humans. Thus, we will determine if Fgl2 secreted by these cell types is necessary and/or sufficient for FcγRIIB-mediated CD8+ T-cell apoptosis, findings which would provide the impetus for subsequent therapeutic targeting of this cell type. AIM 2: Elucidate the mechanism by which the CD8+ T-cell isoform of FcγRIIB induces apoptosis upon ligand binding by Fgl2. Our studies show that CD8+ T cells express a distinct isoform of FcγRIIB that can be bound by Fgl2, but the immediate signaling events after Fgl2-FcγRIIB binding remain unknown. We will identify proteins associated with the intracellular domain of FcγRIIB, specifically after ligand binding by Fgl2. This project is in the context of melanoma as therapeutic success is heavily influenced by CD8+ T-cell infiltration, but the impact of these findings could be applied to other immunologically “hot” tumors where immunotherapies are gaining momentum. Our possession of several mouse models and unique expertise on the role of FcγRIIB in CD8+ T-cell responses uniquely qualify us to address the proposed aims. The impact of the proposed aims is considerable as they will identify novel targets, that when blocked, could rescue a population of memory CD8+ T cells that are crucial to the immune response to tumor. Then, these “rescued” cells would unleash their effector function to improve melanoma patient response. As CD8+ T-cell inhibitory molecules and immunosuppressive cytokines negatively impact CD8+ T-cell infiltration, studying these interactions are of paramount importance as we enter an era of cancer immunotherapy- a treatment dependent on the patient CD8+ T-cell response.