Impact of Circulating Myeloid Cell Clusters on Anti-Tumor Immunity

接受免疫检查点抑制剂（ICI）或过继性治疗的实体癌患者亚组的持久结局 细胞转移（ACT）免疫疗法已经引起了人们对更好地了解耐药性的兴趣， 可以识别新的药物靶点的机制。骨髓来源的抑制细胞（MDSC）具有 基于它们抑制先天性和适应性免疫的能力，它们成为一种这样的屏障。当血液浓度升高时 MDSC被认为是肿瘤患者预后不良的指标，它被广泛认为是肿瘤的主要效应因子。 MDSC的位点在肿瘤微环境（TME）内。这与有据可查的接触是一致的 依赖性机制涉及短寿命的中间体，这些中间体是T细胞活化的已知机制的基础。 被MDSC压制。我们发表的和初步的研究扩大了这一观点，表明MDSC也 通过前所未有的血管内免疫抑制机制在TME外发挥作用。的 这项研究建立在我们发现循环MDSC启动接触依赖性的L- 靶T细胞上的选择素归巢受体，其显著减少细胞毒性T细胞的抗原驱动的扩增 在淋巴结中。我们进一步发现，L-选择素的损失与稳定的MDSC簇的形成相一致， 小鼠肿瘤模型和晚期癌症患者的血液。我们称这些新结构为循环髓样 细胞（CMC）簇。这些观察结果使我们假设CMC簇是一种未被认识到的功能性蛋白。 癌症中的系统性免疫抑制的利基。为了验证这一假设，我们将首先确定是否血液传播 MDSC不仅靶向幼稚T细胞，而且更广泛地攻击干细胞记忆和中央记忆T细胞， 自然杀伤细胞，每一种都需要L-选择素来发挥其抗肿瘤活性。其次，我们将确定CMC是否 簇是L-选择素切割的活性位点，通过使用多管齐下的遗传方法来检测L-选择素 在体内破坏MDSC-T细胞缀合物形成后的命运。这些机理研究集中在β2 整合素由MDSC高度表达，但在正常情况下对快速流动血液中的白细胞无活性， 非病理状态。第三，我们将研究在ICI或 在临床前模型中进行ACT治疗，其中血液是MDSC的主要效应部位，因为它们被排除在外 从TME（通过阻断趋化因子导向的运输）和脾脏（通过脾切除术）。我们会耗尽 使用抗体或临床相关的肝X受体激动剂在该模型中的循环MDSC， MDSC-内在凋亡，以确定血液传播的MDSC是否有助于治疗抗性。互补 研究将检验将循环MDSC与CMC簇和/或T细胞的分析结合的假设， L-选择素将形成一种免疫抑制信号，预测转移性肝癌患者对一线治疗的反应。 癌症患者。拟议的研究将为前所未有的循环功能提供新的见解 骨髓细胞，并可能导致考虑CMC集群作为一个功能性生物标志物的分化 或预选在癌症免疫治疗期间将受益于MDSC消耗方案的患者。

Durable outcomes in subsets of solid cancer patients treated with immune checkpoint inhibitors (ICI) or adoptive cell transfer (ACT) immunotherapy has driven interest in gaining a better understanding of resistance mechanisms that could identify novel druggable targets. Myeloid-derived suppressor cells (MDSC) have emerged as one such barrier based on their ability to inhibit innate and adaptive immunity. While elevated blood MDSC are recognized as a poor prognostic indicator in cancer patients, it is widely thought that the main effector site for MDSC is within the tumor microenvironment (TME). This is in line with the well-documented contact- dependent mechanisms involving short-lived intermediates that underlie known mechanisms of T cell suppression by MDSC. Our published and preliminary studies enlarge on this view, showing that MDSC also function outside the TME through an unprecedented mechanism of intravascular immune suppression. The proposed study builds on our discovery that circulating MDSC initiate contact-dependent cleavage of the L- selectin homing receptor on target T cells that substantially reduces antigen-driven expansion of cytotoxic T cells in lymph nodes. We further found that L-selectin loss coincides with the formation of stable MDSC clusters in the blood of murine tumor models and advanced cancer patients. We term these new structures circulating myeloid cell (CMC) clusters. These observations led us to hypothesize that CMC clusters are an unrecognized functional niche for systemic immune suppression in cancer. To test this hypothesis, we will first determine if blood-borne MDSC target not only naïve T cells, but more broadly attack stem cell memory and central memory T cells and natural killer cells that each require L-selectin for their antitumor activity. Secondly, we will determine if CMC clusters are the active site of L-selectin cleavage by using a multipronged genetic approach to examine L-selectin fate following disruption of MDSC-T cell conjugate formation in vivo. These mechanistic studies center on β2 integrins that are highly expressed by MDSC but are normally inactive on leukocytes in fast-flowing blood under non-pathological conditions. Thirdly, we will examine the translational relevance of CMC clusters during ICI or ACT therapy in a preclinical model in which blood is the primary effector site for MDSC due to their exclusion from the TME (by blocking chemokine-directed trafficking) and spleen (by splenectomy). We will deplete circulating MDSC in this model using antibodies or a clinically relevant liver-X-receptor agonist that induces MDSC-intrinsic apoptosis to establish if blood-borne MDSC contribute to therapeutic resistance. Complementary studies will test the hypothesis that combining the analysis of circulating MDSC with CMC clusters and/or T cell L-selectin will formulate an immunosuppressive signature that predicts response to first-line therapy in metastatic cancer patients. The proposed studies will provide new insights into an unprecedented function of circulating myeloid cells and could lead to the consideration of CMC clusters as a functional biomarker for prognostication or preselection of patients that would benefit from MDSC-depleting regimens during cancer immunotherapy.