Mechanistic insights into immune suppression in brain tumors: a role for beta-arrestin 2

摘要 位于大脑内的癌症，包括原发脑瘤和转移瘤，都表现出令人沮丧的表现。 预后和对免疫治疗反应不佳，部分原因是显著的全身肿瘤诱导 免疫抑制。全身免疫抑制是IC肿瘤的一个标志，与肿瘤类型无关。 IC肿瘤患者和小鼠的全身性免疫缺陷包括艾滋病水平的淋巴细胞减少、淋巴组织 器官收缩和T细胞在骨髓中的隔离。骨髓T细胞隔离遵循 T细胞鞘氨醇-1-磷酸受体1(S1P1)的丢失，这是一种起“出境签证”作用的表面蛋白 调节T细胞从淋巴器官流出。S1P1的表面水平可以通过敲除(KO)来稳定 β-arrestin 2(βarr2)，负责S1P1内化的蛋白质。出乎意料的是，β被植入了r2KO小鼠 患有IC的肿瘤显示出前所未有的~50%-80%的长期生存益处 额外的干预。这种增强的生存需要CD4+和CD8+T细胞，而T细胞 激活疗法进一步延长了β的存活期。这些数据表明，βArr2KO小鼠安装了 增强βArr2KO小鼠的T细胞抗肿瘤免疫应答，尽管增强T细胞的机制 功能仍不清楚。 T细胞要在体内启动有效的抗肿瘤免疫反应并清除肿瘤，它们必须激活 核因子--活化B细胞轻链增强剂(NF-κ-B)。核因子-κB的功能就像是“主控” βARR2是一种已知的核因子-κB激活的抑制剂。重要的是，这个β是ARR2-NF-κB 轴受交感神经系统(SNS)的调节，特别是通过β-2肾上腺素能受体 (β2AR)。SNs通过β2AR发出信号，增加βARR2水平，从而阻止NF-κB的激活。SNS 其他IC病理中的过度激活与IC相同的全身免疫缺陷有关 肿瘤，我们有证据表明，在IC肿瘤荷瘤小鼠中SNS信号增加。值得注意的是，β是一种肿瘤- 生育小鼠表现出较少的淋巴细胞减少和淋巴器官收缩。此外，SNS封锁废除了 荷瘤野生型(WT)小鼠的骨髓T细胞隔离。综上所述，这些发现表明1) βARR2通过抑制NF-κB在限制抗肿瘤免疫反应中发挥关键作用，2)SNs IC肿瘤引起的过度激活可能导致免疫抑制的βARR2活性增加。 这项提议的长期目标是产生对肿瘤驱动的免疫抑制的机械性见解。 这将为许可和改进免疫疗法的治疗方法提供信息。这项工作的主要目标是 建议确定1.βArr2缺乏对抗肿瘤T细胞功能的影响和2.IC肿瘤- SNS过度激活对βARR2活性和抗肿瘤免疫的影响。

ABSTRACT Cancers located within the brain, including both primary brain tumors and metastases, exhibit dismal prognoses and do not respond well to immunotherapy, in part due to marked systemic tumor-induced immunosuppression. Systemic immune suppression is a hallmark of IC tumors, independent of tumor type. Systemic immune deficiencies in patients and mice with IC tumors include AIDS-level lymphopenia, lymphoid organ contraction, and sequestration of T cells in the bone marrow (BM). BM T cell sequestration follows the loss of T cell sphingosine-1-phosphate receptor 1 (S1P1), a surface protein that functions as an “exit visa” mediating T cell egress from lymphoid organs. Surface levels of S1P1 can be stabilized by knocking out (KO) β-arrestin 2 (βarr2), the protein responsible for S1P1 internalization. Unexpectedly, βarr2KO mice implanted with IC tumors demonstrate an unprecedented ~50-80% long-term survival benefit in the absence of any additional intervention. Both CD4+ and CD8+ T cells are required for this enhanced survival, and T cell activating therapies further extend βarr2KO survival. These data suggest that βarr2KO mice mount an enhanced T cell anti-tumor immune response in βarr2KO mice, although the mechanism of enhanced T cell function remains unclear. For T cells to mount an effective anti-tumor immune response and clear tumors in vivo, they must activate Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-κB). NF-κB functions as a “master regulator” of inflammation, and βarr2 is a known inhibitor of NF-κB activation. Importantly, this βarr2-NF-κB axis is regulated by the sympathetic nervous system (SNS), specifically through the beta-2 adrenergic receptor (β2AR). SNS signaling through the β2AR increases βarr2 levels and thereby prevents NF-κB activation. SNS overactivation in other IC pathologies has been linked to the same systemic immune deficits seen with IC tumors, and we have evidence of increased SNS signaling in IC tumor-bearing mice. Notably, βarr2KO tumor- bearing mice exhibit less lymphopenia and lymphoid organ contraction. Furthermore, SNS blockade abrogates BM T cell sequestration in tumor-bearing wild-type (WT) mice. Taken together, these findings suggest that 1) βarr2 plays a key role in restricting anti-tumor immune responses by inhibiting NF-κB, and 2) SNS overactivation due to IC tumors may drive increased immunosuppressive βarr2 activity. The long-term goal of this proposal is to generate mechanistic insights into tumor-driven immunosuppression that will inform therapeutic approaches to license and improve immunotherapies. The primary objectives of this proposal are to determine the impact of 1. βarr2 deficiency on anti-tumor T cell function and 2. IC tumor- driven SNS overactivation on βarr2 activity and anti-tumor immunity.