MerTK and the Innate Immune Response to Melanoma

受体酪氨酸激酶的家族(Tyro3、Ax1和MerTK)是最后的家族之一 已经确定，也是最后进化的物种之一。它们在多细胞生物体中的主要作用似乎是检测 磷脂酰丝氨酸(PtdSer)通过连接蛋白配体(例如Gas6或Pros)与和结合 激活MerTK和细胞内信号。PtdSer暴露在聚集的血小板表面， 外体，最显著的是在每天经历细胞凋亡的数十亿细胞的外表面。这个 对该家族的稳态功能研究最多的是MerTK在巨噬细胞对细胞凋亡的反应中所起的作用 PtdSer通过触发摄取(泡沫化)并发出这是“自我物质”的信号。此信号可防止 炎性巨噬细胞反应(例如IL-12)并将巨噬细胞极化为类M2(例如IL-10， TGFb)，伤口愈合，交替激活表型。此MerTK操作对于防止 自身免疫有效地摄取死亡细胞和清除自身抗原；这种MerTK作用是有害的和 肿瘤微环境中的免疫抑制作用及其天然免疫渗透。TME MerTK单独或与Ax1和Tyro 3信号通路联合刺激免疫抑制活性 先天免疫细胞库。例如，我们的新数据显示，所有三个RTK都出现在 髓系来源的抑制细胞和每个(MerTK、Ax1和Tyro 3)都增强了MDSC的抑制作用。 MerTK的激活也是抑制耐受树突状细胞交叉提呈的关键，其中 MerTK大幅上调。 在转移性黑色素瘤中，免疫检查点疗法产生了显著的反应，其中一些是 经久耐用。然而，没有M1、Th1免疫渗透的患者受益的可能性较小。我们的整体 假说认为，MerTK、Ax1和Tyro 3在一定程度上是产生反作用、免疫抑制的原因 免疫渗入黑色素瘤(和其他肿瘤类型)，通过其先天免疫细胞的作用。这个RTK 免疫抑制作用可能存在于大多数以缺氧为特征的TME中， 细胞凋亡，存在分泌旁分泌和自分泌的配体(Gas6和Pros)。我们的 目的：研究骨髓间充质干细胞、巨噬细胞单核细胞和巨噬细胞中MerTK(和Ax1、Tyro 3)信号的特征。 树突状细胞耐受、其下游机制及其对适应性T-reg和T-ff细胞的影响 回应。我们将使用野生型和基因敲除小鼠以及临床前同基因和基因工程小鼠 老鼠黑色素瘤作为我们的模型。我们已经合成了UNC合成的小分子MerTK(以及更新的UNC RTK)抑制剂以及基因方法来确定MerTK和其他受体的抑制是否可以 产生一种免疫调节的肿瘤反应。我们还将测试免疫的组合是否 检查点抗体(抗CTLA4和抗PD-1)和RTK抑制剂将提高疗效。

The TAM family (Tyro3, Axl and MerTK) of receptor tyrosine kinases (RTKs) was one of the last families identified and one of the last to evolve. Their principal role in multicellular organisms appears to be detection of phosphatidyl serine (PtdSer) through a linking protein ligand (e.g. Gas6 or ProS) that together bind to and activate MerTK and intracellular signaling. PtdSer is exposed on the surface of aggregating platelets, exosomes and most prominently on the external surface of billions of cells that daily undergo apoptosis. The best studied homeostatic function of the family is the macrophage role of MerTK as it responds to apoptotic PtdSer by triggering ingestion (effercytosis) and signaling that this is “self-material”. This signal prevents an inflammatory macrophage response (e.g. IL-12) and polarizes the macrophage to an M2-like (e.g. IL-10, TGFb), wound healing, alternatively activated phenotype. This MerTK action is crucial for preventing autoimmunity efficiently ingesting dying cells and clearing self-antigens; this MerTK action is deleterious and immunosuppressive in tumor microenvironment (TME) and its innate immune infiltrate. TME immunosuppressive activities are stimulated by MerTK alone or in combination with Axl and Tyro 3 signaling in the innate immune cell repertoire. For example, our new data shows that all three TAM RTKs are present in Myeloid Derived Suppressor Cells and each (MerTK, Axl and Tyro 3) enhances MDSC suppressive action. MerTK activation also is key in the suppression of cross presentation by the tolerizing dendritic cell in which MerTK is substantially upregulated. In metastatic melanoma, immune checkpoint therapy has produced remarkable responses, some of which are durable. However, patients without an M1, Th1 immune infiltrate are less likely to benefit. Our overall hypothesis is that MerTK, Axl and Tyro 3 are in part responsible for the counterproductive, immunosuppressive immune infiltrate in melanoma (and other tumor types) through their innate immune cell action. This TAM RTK immunosuppressive action is probably present in most TMEs which are characterized by hypoxia, abundant apoptotic cells, and presence of secreted paracrine and autocrine TAM ligands (Gas6 and ProS). Our objective is to characterize the MerTK (and Axl, Tyro 3) signals in MDSCs, macrophages monocytes and tolerizing DCs, their downstream mechanisms and their consequences for the adaptive T reg and T eff cell responses. We will use wild type and knockout mice with preclinical syngeneic and genetically-engineered mouse melanomas as our models. We have UNC synthesized small molecule MerTK (and newer UNC TAM RTK) inhibitors as well as genetic methods to determine if inhibition of MerTK and other TAM receptors can produce an immune-modulatory tumor response. We will also test whether the combinations of immune checkpoint antibodies (anti-CTLA4 and anti-PD-1) and TAM RTK inhibitors will increase therapeutic efficacy.