Regulation of Tumor Immunogenicity in Glioblastoma

项目摘要 胶质母细胞瘤（GBM）是成人中最常见的原发性恶性脑肿瘤，具有普遍致命性 尽管多模式治疗。因此，迫切需要新的治疗方法。免疫疗法，如 检查点阻断，迄今未能证明临床疗效。GBM具有高的内在抗性， 在其它因素中，由于MHC-I的低表达和缺乏T细胞浸润而导致抗肿瘤免疫。 需要促进GBM的免疫原性以使肿瘤对检查点疗法敏感的策略。蛋白 磷酸酶2A（PP 2A）是一种普遍存在的丝氨酸/苏氨酸磷酸酶，由催化（C）、调节（B） 和骨架（A）亚基。我们以前曾报道过，PP 2Ac的药理学抑制可以增强 抗PD 1阻断剂在多种临床前模型（包括GBM）中的疗效。然而，机制或 负责增强的抗肿瘤免疫应答的细胞类型还没有被很好地理解。最近，我们发现 在神经胶质瘤细胞中，通过基因修饰，PP 2Ac的缺乏导致干扰素信号的增强， 是引发抗肿瘤免疫应答的关键。胶质瘤细胞中PP 2A缺陷增强MHC-I表达， 肿瘤T细胞浸润和对体内检查点阻断的敏感性。我们还证明了PP 2Ac 缺陷导致细胞质双链DNA（dsDNA）的产生增加，已知dsDNA激活 cGAS-STING信号传导，干扰素产生的有效模拟物。此外，从所有的无偏筛选 在已知的调节B亚基中，我们鉴定了PPP 2 R2 C，PP 2A的特异性B亚基，具有与 PP 2Ac促进MHC-I表达。在这个项目中，我们将首先阐明PP 2Ac缺乏对 神经胶质瘤细胞对肿瘤微环境的免疫景观，并将识别免疫细胞 负责PP 2Ac调节的抗肿瘤免疫的类型。然后我们将剖析 将PP 2A缺陷与胶质瘤中cGAS-STING激活和干扰素信号传导的促进联系起来 微环境我们还将确定特定的调节B亚基PPP 2 R2 C在调节细胞凋亡中的作用。 dsDNA产生和cGAS-STING信号传导。最后，我们将研究PP 2Ac缺乏的能力， 提高放射治疗的治疗效果，这是当前护理标准的主要组成部分， 已知的cGAS-STING信号传导刺激剂。该项目的直接目标是确定 PP 2A调节GBM的免疫原性，长期目标是开发精确的PP 2A靶向 提高GBM免疫治疗有效性的策略。我们相信这项研究符合NINDS的使命 寻求神经系统的基础知识，并利用这些知识来减轻 神经系统疾病，如脑肿瘤。

PROJECT SUMMARY Glioblastoma (GBM) is the most common primary malignant brain tumor in adults that is universally fatal despite multimodal treatment. Novel therapies are therefore critically needed. Immunotherapy, such as checkpoint blockade, has thus far failed to demonstrate clinical efficacy. GBM has high intrinsic resistance to antitumor immunity due to, among other factors, low expression of MHC-I and lack of T-cell infiltration. Strategies to promote immunogenicity of GBM to sensitize tumor to checkpoint therapy is needed. Protein phosphatase 2A (PP2A) is a ubiquitous serine/threonine phosphatase comprised of a catalytic (C), regulatory (B) and scaffolding (A) subunit. We have previously reported that pharmacological inhibition of PP2Ac can enhance the efficacy of anti-PD1 blockade in multiple preclinical models, including GBM. However, the mechanism(s) or cell type(s) responsible for the enhanced antitumor immune response is not well understood. Recently, we found that deficiency of PP2Ac, by genetic modification, in glioma cells resulted in enhanced interferon signaling, which is essential to eliciting antitumor immune response. PP2A deficiency in glioma cells enhanced MHC-I expression, tumor T-cell infiltration and sensitivity to checkpoint blockade in vivo. We also demonstrated that PP2Ac deficiency led to enhanced production of cytoplasmic double-stranded DNA (dsDNA), which is known to activate cGAS-STING signaling, a potent simulator of interferon production. Moreover, from unbiased screening of all known regulatory B subunits, we identified PPP2R2C, a specific B subunit of PP2A, to have a similar role as PP2Ac in promoting MHC-I expression. In this project, we will first elucidate the effect of PP2Ac deficiency in glioma cells on the immunological landscape of the tumor microenvironment and will identify the immune cell types responsible for PP2Ac modulated antitumor immunity. We will then dissect the molecular mechanisms that link PP2A deficiency to cGAS-STING activation and promotion of interferon signaling in the glioma microenvironment. We will also identify the role of the specific regulatory B subunit, PPP2R2C, in modulating dsDNA production and cGAS-STING signaling. Finally, we will investigate the ability of PP2Ac deficiency to enhance the therapeutic efficacy of radiation therapy, a major component of current standard-of-care and a known stimulator of cGAS-STING signaling. The immediate goal of this project is to identify the mechanisms of PP2A modulated immunogenicity in GBM, with the long-term goal of developing precise PP2A targeting strategies to increase effectiveness of immunotherapies for GBM. We believe this study fits the mission of NINDS to seek fundamental knowledge of the nervous system and to use that knowledge to reduce the burden of neurological disease such as brain tumor.