依赖NKG2D的肿瘤免疫逃避

活化性受体NKG2D(natural-killer group 2,member D)和其配基在NK、γδ+T和CD8+T细胞介导的肿瘤免疫应答中扮演了重要角色.NKG2D识别肿瘤细胞表面的配体激活效应细胞,产生有效的抗肿瘤免疫应答.但是在完全具有免疫能力的机体内,表达NKG2D配基的肿瘤仍能够生长发育,因此,在患肿瘤小鼠和肿瘤病人中一定存在着依赖NKG2D的免疫逃避机制.本文就依赖于NKG2D的免疫逃避作一详细综述,主要包括:干涉NKG2D受体的免疫逃避、干涉NKG2D配基的免疫逃避、细胞因子破坏NKG2D受体和配基的免疫逃避、抑制性细胞参与NKG2D介导的免疫逃避.这些研究为抗肿瘤治疗提供了新的途径.     

NK细胞活化受体NKG2D及sMICA在晚期肺癌免疫监视中的作用

背景与目的 NK细胞活化受体NKG2D及sMICA是近来肿瘤研究领域热点之一.本研究旨在观察晚期肺癌患者外周血中NK细胞受体NKG2D及sMICA表达水平的变化,并探讨它们在晚期肺癌免疫监控中的作用及其临床意义.方法 采用流式细胞术榆测115例肺癌患者外周血NK细胞受体NKG2D、T淋巴细胞哑群及NK细胞百分比,采用酶联免疫吸附反应检测肺癌患者外周血sMICA值,并以50例健康人作为对照.结果 晚期肺癌患者外周血sMICA、CD8+T细胞、NK细胞数量较对照组明显升高,而NK细胞受体NKG2D、CD3+T细胞、CD4+>T细胞、CD4+T/CD8+T值较对照组下降.NK细胞受体NKG2D和sMICA呈负相关(r=-0.319,P<0.05).NK细胞受体NKG2D与CD4+T细胞、CD4+T/CD8+T成正相关(P0.05),与CD8+T细胞成负相关(P<0.05);sMICA与CD4+T细胞、CD4+T/CD8+T成负相关(P<0.05),与CD8+T细胞成正相关(P<0.05);它们与CD3+T、NK细胞均无相关性(P>0.05).结论 外周血sMICA上调介导NK细胞活化受体NKG2D下调机制参与了晚期肺癌以肿瘤为中心抑制免疫网络的形成,它们可作为监视晚期肺癌患者免疫状态的参考指标,也可作为评估肺癌发生、发展的参考依据.     

以NKG2A 为靶点的肿瘤免疫治疗：现状、问题与对策

自然杀伤细胞2 族成员A（NKG2A）为免疫细胞表面重要的免疫检查点,NKG2A 与其配体HLA-E 的结合会抑制NK 细胞和T 细胞的免疫效应功能,甚至使之发生功能耗竭,导致肿瘤细胞免疫逃逸。抗NKG2A 抗体可以通过阻断NKG2A 与其配 体的结合而恢复NK 细胞和T 细胞的功能,从而唤醒强大的抗肿瘤免疫。与其他免疫检查点（如PD-1、CTLA-4 等）相比,NKG2A 阻断性抗体在临床肿瘤治疗中具有其独特的优势,其阻断NKG2A 的识别及其信号通路,能够同时逆转T 细胞和NK 细胞的功能 耗竭,全面唤醒机体的抗肿瘤效应。基于NKG2A 的抗肿瘤免疫疗法正在开展多项临床试验,显示出良好的安全性和有效性。本 文就NKG2A 及其配体的表达与信号转导、NKG2A 介导免疫细胞的功能耗竭,以及目前以NKG2A 为靶点的肿瘤免疫治疗策略和 临床研究进展现状、存在问题和对策进行阐述,为以NKG2A 为靶点的肿瘤免疫治疗策略的开发和临床应用提供参考。     

NKG2D受体配体系统介导肿瘤免疫逃逸的研究进展

摘 要：NK细胞作为机体固有免疫的重要组成部分，在肿瘤免疫监视机制中起重要作用。NKG2D是NK细胞重要的激活受体，通过识别位于肿瘤细胞表面的NKG2D配体，介导细胞毒效应清除肿瘤细胞。然而存在多种因素可影响NKG2D受体与配体的表达，阻断了NKG2D信号转导，为肿瘤细胞免疫逃逸提供可能。NKG2D受体配体系统还可作为临床诊疗的靶点，为肿瘤患者诊断、治疗以及评估预后提供依据。本文就NKG2D受体配体系统介导的肿瘤细胞免疫逃逸的机制以及目前已有的针对性免疫治疗方法进行综述，为临床应用提供更多思路。     

基于HLA-E功能特点的肿瘤免疫治疗新策略

人类白细胞抗原-E（HLA-E）在多种肿瘤中呈高表达,其与肿瘤患者预后的关系呈现肿瘤类型依赖性。HLA-E主要通过与NK细胞或T细胞上的激活性（NKG2C）或抑制性（NKG2A）受体结合,在调控抗肿瘤免疫应答中发挥重要作用。基于此,靶向 HLA-E/NKG2A 以阻断 HLA-E 与 NKG2A 的相互作用或抑制 HLA-E 表达,有望成为增强抗肿瘤免疫应答的新策略。鉴于HLA-E的功能特点设计增强型或通用型的T/NK细胞过继免疫疗法,有望提高过继免疫细胞疗法的治疗效果,具有良好的研发和临床应用前景。如何将靶向HLA-E或NKG2A的疗法与其他免疫疗法有效联合,实现更精准的免疫治疗以提高临床治疗效果是目前该方面研发和应用需要解决的难题之一。     

CD4^＋T细胞与肿瘤免疫

CD4^＋T细胞不仅辅助激活CD8^＋T细胞,而且对记忆性细胞毒性T淋巴细胞（CTL）应答的产生和维持起重要作用,并具有直接的抗肿瘤功能。另外CD4^＋CD25^＋调节性T细胞（Tregs）具有免疫负调控功能。在肿瘤免疫抑制及免疫逃逸中发挥重要作用,是肿瘤免疫治疗失败的重要原因。近年肿瘤免疫治疗已获得很大进步,相关肿瘤疫苗的研究也备受关注.     

DC—NK的相互作用以一种新的不依赖CD4^＋T辅助细胞的方式诱导抗肿瘤CTL应答

通常认为CTL活化需要CD4^＋T细胞的辅助。但是在某些动物模型上发现，表达NKG2D配体、CD70／CD80或MHCI类分子缺陷的肿瘤细胞可活化NK细胞进而诱导抗肿瘤CTL应答。CD4^＋T细胞在NK诱导CTL中的作用尚无定论。     

NKG2D受体在抗肿瘤免疫中的作用

随着NK细胞活化型受体NKG2D及其配体的发现，人们对免疫效应细胞抗肿瘤作用的分子机制的认识有了显著进展，现综述NKG2D受体一配体的识别机制及其在抗肿瘤免疫中的作用。     

NKG2D受体在抗肿瘤免疫中的作用

随着NK细胞活化型受体NKG2D及其配体的发现,人们对免疫效应细胞抗肿瘤作用的分子机制的认识有了显著进展,现综述NKG2D受体-配体的识别机制及其在抗肿瘤免疫中的作用。     

NKG2D及其配体与肿瘤免疫治疗研究新进展

NKG2D为自然杀伤(NK)细胞表面的C型凝集素样活化性受体,NKG2D与肿瘤细胞表面配体结合,杀伤肿瘤细胞,但在肿瘤患者和患肿瘤小鼠体内存在着依赖NKG2D的免疫逃避机制.近年来利用各种分子生物技术调节受体和配体的表达来避免免疫逃避.     

NKG2D ligands in tumor immunity

The activating receptor NKG2D (natural-killer group 2, member D) and its ligands play an important role in the NK, gammadelta(+) and CD8(+) T-cell-mediated immune response to tumors. Ligands for NKG2D are rarely detectable on the surface of healthy cells and tissues, but are frequently expressed by tumor cell lines and in tumor tissues. It is evident that the expression levels of these ligands on target cells have to be tightly regulated to allow immune cell activation against tumors, but at the same time avoid destruction of healthy tissues. Importantly, it was recently discovered that another safeguard mechanism controlling activation via the receptor NKG2D exists. It was shown that NKG2D signaling is coupled to the IL-15 receptor pathway in a cell-specific manner suggesting that priming of NKG2D-mediated activation depends on the cellular microenvironment and the distinct cellular context. This review will provide a broad overview of our up-to-date knowledge of the NKG2D receptor and its ligands in the context of tumor immunology. Strategies to amplify NKG2D-mediated antitumor responses and counteract tumor immune escape mechanisms will be discussed.     

NKG2D ligand expression in pediatric brain tumors

Adult brain tumors establish an immunosuppressive tumor microenvironment as a modality of immune escape, with several immunotherapies designed to overcome this barrier. However, the relationship between tumor cells and immune cells in pediatric brain tumor patients is not as well-defined. In this study, we sought to determine whether the model of immune escape observed in adult brain tumors is reflected in patients with pediatric brain tumors by evaluating NKG2D ligand expression on tissue microarrays created from patients with a variety of childhood brain tumor diagnoses, and infiltration of Natural Killer and myeloid cells. We noted a disparity between mRNA and protein expression for the 8 known NKG2D ligands. Surprisingly, high-grade gliomas did not have increased NKG2D ligand expression compared to normal adjacent brain tissue, nor did they have significant myeloid or NK cell infiltration. These data suggest that pediatric brain tumors have reduced NK cell-mediated immune surveillance, and a less immunosuppressive tumor microenvironment as compared to their adult counterparts. These data indicate that therapies aimed to improve NK cell trafficking and functions in pediatric brain tumors may have a greater impact on anti-tumor immune responses and patient survival, with fewer obstacles to overcome.     

NKG2D signaling in cancer immunosurveillance

The immune system is able to detect and eliminate transformed cells. The activating receptor NKG2D is particularly relevant for cancer immunosurveillance. NKG2D ligand expression renders tumor cells more susceptible to be killed by NK and T cells, and correlates with the clinical outcome of the disease. However, tumors develop mechanisms to overcome the NKG2D‐mediated immune response, which has been associated with poor prognosis and impairment of the clinical benefits of immunotherapy in many human cancers. The highly specific pattern of expression displayed by the NKG2D ligands, mainly confined to tumor cells, together with the strong immune response triggered by this receptor clearly supports the idea that the NKG2D‐mediated pathway may be a powerful target for the treatment of cancer. This review draws together the most recent discoveries concerning the biology of the NKG2D signaling and their therapeutic relevance in the context of cancer.     

Tumor-associated MICA is shed by ADAM proteases

The immunoreceptor NKG2D promotes immunosurveillance of malignant cells and protects the host from tumor initiation by activating natural killer cells and costimulating CD8 T cells. NKG2D-mediated recognition of malignant cells by cytotoxic lymphocytes is enabled through the tumor-associated expression of NKG2D ligands (NKG2DL) resulting from cellular or genotoxic stress. Shedding of NKG2DL is thought to constitute a major countermechanism of tumor cells to subvert NKG2D-mediated immunosurveillance. Here, we report that the prototypical NKG2DL MICA is released by proteolytic cleavage in the stalk of the MICA ectodomain, where deletions, but not alanine substitutions, impede MICA shedding. Small compound-mediated stimulation and inhibition of MICA shedding adduced characteristics that indicated an involvement of members of the "a disintegrin and metalloproteinase" (ADAM) family. Accordingly, MICA shedding by tumor cells was inhibited by silencing of the related ADAM10 and ADAM17 proteases, which are known to promote tumor growth by releasing epidermal growth factor receptor ligands. Collectively, our data show that ADAM10 and ADAM17 are critically involved in the tumor-associated proteolytic release of soluble MICA facilitating tumor immune escape. Hence, therapeutic blockade of ADAM10 and ADAM17 seems promising for cancer treatment by targeting both growth and immune escape of tumors.     

Proteolytic release of soluble UL16-binding protein 2 from tumor cells

The MHC class I-related ligands of the immunoreceptor NKG2D are frequently expressed by tumor cells and stimulate tumor immunity mediated by CD8 T cells and natural killer (NK) cells. In humans, NKG2D ligands (NKG2DL) are encoded by the MHC-encoded MIC and non-MHC-encoded UL16-binding protein (ULBP) families of proteins. Recently, we and others showed that tumor cells release soluble MICA (sMICA), thereby counteracting NKG2D-mediated tumor immunosurveillance. Here, we now report that ULBP2 molecules are likewise released from tumor cells in a processed soluble form, and that soluble ULBP2 (sULBP2) can be detected in sera of some patients with hematopoietic malignancies. Tumor cell-derived sULBP2 as opposed to cell-bound ULBP2 does not down-regulate NKG2D on NK cells. Unexpectedly, the glycosylphosphatidylinositol-anchored ULBP2 molecules are not released by phospholipases but by the action of metalloproteases. Proteolytic shedding of both NKG2D ligands MICA and ULBP2 by tumor cells was strongly enhanced after phorbol 12-myristate 13-acetate treatment and paralleled by a markedly reduced susceptibility to NKG2D-mediated cytotoxicity. Shedding of MICA and ULBP2 can be blocked by the same inhibitors, suggesting the involvement of related metalloproteases. Thus, our data suggest that reducing NKG2DL surface densities is due to a common cleavage process executed by metalloproteases that promotes escape of tumors from NKG2D-mediated immunosurveillance.     

肺癌患者调节性T细胞与NK细胞活化受体NKG2D的相关性及其临床意义

目的 分析肺癌患者外周血中CD+4 CDHi25 CDLo127调节性T细胞及自然杀伤细胞(NK细胞)活化受体NKG2D的表达水平之间的关系,探讨其在肿瘤免疫逃逸机制中的作用及临床意义.方法 选择70例肺癌患者,均经病理确诊.采用流式细胞术(FCM)检测患者外周血中CD+4 CDHi25 CDLo127调节性T细胞、NK细胞及NKG2D表达水平,并以50名健康人为对照.结果 肺癌患者外周血中CD+4 CDHi25 CDLo127调节性T细胞比例较健康对照组明显升高[(8.4±4.1)％与(6.7±1.7)％],差异有统计学意义(t=3.09,P＜0.05);肺癌组NK细胞比例与健康对照组比较[(15.6±8.3)％与(17.2±4.2)％],差异无统计学意义(t=-1.33,P＞0.05);肺癌组NKG2D较健康对照组明显降低[(83.3±4.9)％与(87.4±2.9)％],差异有统计学意义(t=3.16,P＜ 0.05).CD+4 CDHi25 CDLo127调节性T细胞与NKG2D呈负相关性(r=-0.302,P＜0.05).结论 在肺癌患者外周血中调节性T细胞可能通过下调NKG2D,参与肿瘤免疫逃逸机制,二者可作为评估肺癌患者免疫功能状态及预后的参考指标.     

Interferon‐γ down‐regulates NKG2D ligand expression and impairs the NKG2D‐mediated cytolysis of MHC class I‐deficient melanoma by natural killer cells

NKG2D operates as an activating receptor on natural killer (NK) cells and costimulates the effector function of αβ CD8⁺ T cells. Ligands of NKG2D, the MHC class I chain‐related (MIC) and UL16 binding protein (ULBP) molecules, are expressed on a variety of human tumors, including melanoma. Recent studies in mice demonstrated that NKG2D mediates tumor immune surveillance, suggesting that antitumor immunity in humans could be enhanced by therapeutic manipulation of NKG2D ligand (NKG2DL) expression. However, signals and mechanisms regulating NKG2DL expression still need to be elucidated. Here, we asked whether the proinflammatory cytokine Interferon‐γ (IFN‐γ) affects NKG2DL expression in melanoma. Cell lines, established from MHC class I‐negative and ‐positive melanoma metastases, predominantly expressed MICA and ULBP2 molecules on their surface. Upon IFN‐γ treatment, expression of MICA, in some cases, also of ULBP2 decreased. Besides melanoma, this observation was made also for glioma cells. Down‐regulation of NKG2DL surface expression was dependent on the cytokine dose and the duration of treatment, but was neither due to an intracellular retention of the molecules nor to an increased shedding of ligands from the tumor cell surface. Instead, quantitative RT‐PCR revealed a decrease of MICA‐specific mRNA levels upon IFN‐γ treatment and siRNA experiments pointed to an involvement of STAT‐1 in this process. Importantly, IFN‐γ‐treated MHC class I‐negative melanoma cells were less susceptible to NKG2D‐mediated NK cell cytotoxicity. Our study suggests that IFN‐γ, by down‐regulating ligand expression, might facilitate escape of MHC class I‐negative melanoma cells from NKG2D‐mediated killing by NK cells. © 2008 Wiley‐Liss, Inc.     

NKG2D-mediated antitumor activity by tumor-infiltrating lymphocytes and antigen-specific T-cell clones isolated from melanoma patients.

PURPOSE: The role of NKG2D receptor in antitumor immunosurveillance has not been completely clarified. We addressed this issue by investigating the involvement of this receptor in tumor-specific immunologic response in melanoma patients. EXPERIMENTAL DESIGN: We determined the presence of NKG2D+ T cells among tumor-infiltrating lymphocytes (TIL) of 10 (one primary and 9 metastatic) melanoma samples and the expression of NKG2D ligands (NKG2DL) by these tumor cells. Moreover, the expression of NKG2D was assessed in a panel of antigen-specific T lymphocytes isolated from melanoma patients and the engagement of NKG2D in antitumor activity mediated by these T cells was determined. RESULTS: TILs located either in the periphery or within the tumor mass of melanoma samples expressed NKG2D and the expression of this receptor by T cells was retained after in vitro culture. However, NKG2DLs were weakly expressed, or not expressed, by most metastatic lesions with only the primary tumor being positive for all these molecules. In contrast, these ligands were expressed, although heterogeneously, by all in vitro established melanoma lines. Moreover, the engagement of NKG2D occurred in antitumor activity by both freshly isolated and in vitro cultured TILs. However, this receptor was involved to a different extent in the antitumor activity of antigen-specific T-cell clones. CONCLUSIONS: These findings indicate that NKG2D+ T cells have a role in the immunologic response against tumor. Thus, new immunotherapeutic treatments for melanoma patients should be designed aimed at augmenting the NKG2D+ T lymphocyte-mediated immune response.     

MicroRNA-mediated down-regulation of NKG2D ligands contributes to glioma immune escape

Malignant gliomas are intrinsic brain tumors with a dismal prognosis. They are well-adapted to hypoxic conditions and poorly immunogenic. NKG2D is one of the major activating receptors of natural killer (NK) cells and binds to several ligands (NKG2DL).Here we evaluated the impact of miRNA on the expression of NKG2DL in glioma cells including stem-like glioma cells. Three of the candidate miRNA predicted to target NKG2DL were expressed in various glioma cell lines as well as in glioblastomas in vivo: miR-20a, miR-93 and miR-106b. LNA inhibitor-mediated miRNA silencing up-regulated cell surface NKG2DL expression, which translated into increased susceptibility to NK cell-mediated lysis. This effect was reversed by neutralizing NKG2D antibodies, confirming that enhanced lysis upon miRNA silencing was mediated through the NKG2D system. Hypoxia, a hallmark of glioblastomas in vivo, down-regulated the expression of NKG2DL on glioma cells, associated with reduced susceptibility to NK cell-mediated lysis. This process, however, was not mediated through any of the examined miRNA. Accordingly, both hypoxia and the expression of miRNA targeting NKG2DL may contribute to the immune evasion of glioma cells at the level of the NKG2D recognition pathway. Targeting miRNA may therefore represent a novel approach to increase the immunogenicity of glioblastoma.