IDO1 and Immunotolerance in Glioblastoma

摘要 多形性胶质母细胞瘤（GBM）是成人中最常见且最具侵袭性的脑肿瘤。中位数 GBM 患者的生存期为诊断后 14.6 个月。 GBM 的一个一致特征是瘤内 免疫抑制性调节性 T 细胞 (Treg) 的存在会损害患者的抗 GBM 免疫反应， 与吲哚胺 2,3 双加氧酶 1 (IDO1) 的表达一致，IDO1 是一种限速酶，可将 色氨酸 (Trp) 转变为犬尿氨酸 (Kyn)。利用原位同基因和免疫活性 GL261-C57BL6 移植模型中，我之前证明了 shRNA 介导的小鼠 IDO1 表达抑制 GBM 细胞显着减少瘤内 Treg 积累，同时发生溶细胞 T 细胞反应 导致肿瘤完全消退。这一观察结果促使人们对药物抑制进行研究 IDO1 作为治疗性诱导抗 GBM 免疫的手段。然而令人惊讶的是，政府 IDO1 抑制剂对瘤内 Treg 积聚和动物受试者的存活均没有影响。一个假设是 为这一悖论提供了解释，解决了基因抑制（而不是药理抑制）如何 IDO1 影响肿瘤内 Treg 积累和效应 T 细胞对 GBM 的反应，形成 这个建议。最近，我的实验室发现肿瘤微环境中的细胞，而不是 GBM 细胞， 负责 GL261-C57BL6 模型中几乎所有 IDO1 介导的 Trp 到 Kyn 分解代谢。这一观察， 然而，提出了一个关于肿瘤细胞相关 IDO1 的作用的问题，其基因抑制 促进针对肿瘤的高效 T 细胞反应。这个问题的潜在答案已经出现在 与我们发现 IDO1 定位于 GBM 细胞的细胞核相关。根据这些观察，我们 建议：1) 在人 GBM 中原位建立 IDO1 细胞类型表达和分解代谢，2) 研究 IDO1 人 GBM 细胞中的表达和功能，并 3) 确定 GBM 细胞中核 IDO1 的功能。的 拟议的研究旨在调查旨在逆转的临床相关问题和方法 胶质瘤的免疫抑制，这是为患者合理设计有效免疫疗法的第一步 患有无法治愈的脑癌。

ABSTRACT Glioblastoma multiforme (GBM) is the most common and aggressive form of brain tumor in adults. Median survival for GBM patients is 14.6 months post-diagnosis. A consistent feature of GBM is the intratumoral presence of immunosuppressive regulatory T cells (Treg) that impair patient anti-GBM immune response, coincident with the expression of indoleamine 2,3 dioxygenase 1 (IDO1), a rate-limiting enzyme that converts tryptophan (Trp) to kynurenine (Kyn). Utilizing the orthotopic syngeneic and immunocompetent GL261-C57BL6 engraftment model, I previously demonstrated that shRNA-mediated suppression of IDO1 expression in murine GBM cells significantly decreases intratumoral Treg accumulation coincident with a cytolytic T cell response leading to complete tumor regression. This observation prompted the investigation into pharmacologic inhibition of IDO1 as a means to therapeutically induce anti-GBM immunity. Surprisingly, however, the administration of IDO1 inhibitor had no effect on intratumoral Treg accumulation nor on animal subject survival. A hypothesis that provides an explanation for this paradox, addressing how genetic suppression-, but not pharmacologic inhibition- of IDO1, affects intratumoral Treg accumulation and effector T cell response against GBM, forms the basis of this proposal. Recently, my lab discovered that cells in the tumor microenvironment, but not GBM cells, are responsible for nearly all IDO1-mediated Trp to Kyn catabolism in the GL261-C57BL6 model. This observation, however, raises a question regarding the role of tumor cell-associated IDO1, whose genetic suppression promotes productive T cell response against tumor. A potential answer to this question has emerged in association with our discovery that IDO1 localizes to the nucleus in GBM cells. Based on these observations we propose to: 1) establish IDO1 cell type expression and catabolism in human GBM in situ, 2) investigate IDO1 expression and function in human GBM cells and to 3) determine the function of nuclear IDO1 in GBM cells. The proposed studies aim to investigate clinically-relevant questions and approaches that aim to reverse immunosuppression in glioma, which is the first step to the rational design of effective immunotherapy for patients with incurable brain cancer.