靶向CD47 抗肿瘤治疗的研究进展

[摘要] CD47 是细胞表面高度糖化的穿膜蛋白，是一种“别吃我”信号，可与信号调节蛋白α（SIRPα）等形成CD47-SIRPα 抑制信号复合体，从固有免疫和适应性免疫两方面同时逃避机体的免疫监视。研究发现，CD47 在血液肿瘤和多种实体瘤中高表达，通过与巨噬细胞上的SIRPα 配体结合，启动一系列抑制性的信号转导而躲避吞噬，其高水平表达既能促进肿瘤细胞的生长又能促进肿瘤细胞的转移。通过抗CD47 抗体阻断CD47-SIRPα 信号通路，达到抑制肿瘤细胞的免疫逃逸，增强巨噬细胞的吞噬作用和适应性免疫应答，是免疫治疗肿瘤的新途径。目前，国内外开展了越来越多靶向CD47-SIRPα 的药物或抗体的基础研究和临床试验，有望从抗体分子设计和重组蛋白等方面解决靶向CD47 抗肿瘤治疗时发生的贫血和输液相关不良反应等问题。本文就CD47 的分子结构与生理功能、CD47-SIRPα 表达调控机制、CD47 抗肿瘤治疗研究现状以及靶向CD47 导致的相关生物安全性问题和解决方案等方面进行综述，为CD47新靶点的基础研究和临床应用提供参考。     

CD47与淋巴瘤免疫治疗相关性的研究进展

CD47属于免疫球蛋白超家族成员,在人体多种细胞和组织上均有表达,但在肿瘤细胞上表达得更多,特别是在各种造血系统肿瘤中高表达。肿瘤细胞上表达的CD47与巨噬细胞上的信号调节蛋白α（SIRPα）结合抑制巨噬细胞对肿瘤的吞噬作用可导致肿瘤免疫逃逸。近年来CD47成为肿瘤研究的新热点,本文就CD47的结构与表达、CD47-SIRPα、靶向CD47抗体药物与淋巴瘤免疫治疗相关性研究作一综述。     

CD47与胰腺癌相关性的研究进展

CD47分子是一种高度糖化的跨膜蛋白,存在于所有组织的多种细胞表面上。近几年的研究表明,CD47分子与多种恶性肿瘤密切相关,在大部分肿瘤细胞中呈现高表达,它与特异性配体结合后,可对免疫细胞吞噬肿瘤细胞产生抑制作用,使其产生免疫逃逸,故可促进肿瘤的发生与发展。胰腺癌是常见的消化系统肿瘤,恶性程度极高,诊断、治疗困难,预后不理想。与其他肿瘤类似,胰腺肿瘤与人体免疫系统之间也存在一定相关性,但CD47与胰腺癌相关性的研究甚少,故本文将从CD47的分子结构、生理功能、表达情况及与胰腺癌的相关性进行综述,并对胰腺癌的免疫治疗进行总结和展望。     

小鼠实体瘤中IFN-γ和TNF依赖的ALV旁观清除

肿瘤细胞表达特异性抗原,被CTL识别并靶向杀伤,但肿瘤仍可通过多种机制逃逸机体免疫系统的杀伤.肿瘤微环境中基质细胞在肿瘤生长过程中并不是旁观者,可调控肿瘤的生长,是肿瘤免疫逃逸的重要机制.因此,靶向基质可治疗肿瘤.肿瘤抗原缺失体(antigen loss variants,ALV)是肿瘤遗传不稳定性形成的抗原缺失肿瘤细胞群体,不能被CTL识别和杀伤.因此,ALV是肿瘤免疫逃逸的重要机制,也是免疫治疗肿瘤的主要障碍.     

肿瘤发生与免疫逃逸相关机制的研究进展

摘 要：肿瘤免疫逃逸是肿瘤细胞逃避宿主免疫系统监视和攻击,促进肿瘤生存和增殖的重要途径。此外,肿瘤细胞内异常表达的PI3K-AKT、MAPK等信号通路增强了其增殖、侵袭、转移、抗凋亡等能力,从而在与宿主免疫系统的抗争中处于有利地位。通过对肿瘤与免疫逃逸相关机制的研究,有利于包括免疫治疗在内的各种肿瘤治疗方法的发展。     

肿瘤干细胞免疫逃逸机制及相关免疫疗法的研究进展

肿瘤干细胞（cancer stem cell,CSC）与正常干细胞生物学特征相似,具有自我更新、无限增殖和抗化学毒物损伤的能力, 与肿瘤的发生、治疗、预后、复发和转移关系极为密切。在肿瘤发生初期,虽然机体的免疫监视系统可以有效地对肿瘤细胞进行识 别和清除,但CSC可通过下调抗原加工和提呈机制成分、分泌免疫抑制因子、高表达免疫检查点分子以及激活免疫耐受信号通路等 机制调控免疫细胞功能,或促进抑制性免疫微环境的建立以逃避免疫系统对其的清除,从而使肿瘤得以进展。目前,靶向CSC与免 疫系统相互作用的多种方法正在被积极研究中,一些靶向CSC的新型免疫疗法正处于临床研发阶段。本文综述了近年来CSC相关 免疫逃逸机制及针对免疫逃逸的可能有效的治疗手段（包括DC疫苗、CAR-T细胞、免疫检查点抑制剂等）的研究进展。     

PD-1/PD-L1通路在乳腺癌治疗中的作用及意义

程序性死亡受体1（programmed death-1,PD-1,CD279）为共刺激受体CD28超家族成员,主要表达在活化T细胞、B细胞、单核细胞以及自然杀伤细胞表面。程序性死亡配体1（programmed death-ligand 1,PD-L1,CD274）为PD-1的一个重要配体,广泛表达于肿瘤细胞以及抗原呈递细胞（APC）表面。以PD-1/PD-L1为靶点的肿瘤免疫治疗为肿瘤治疗开辟了新的道路。PD-1通过与PD-L1和(或)PD-L2结合,抑制T细胞活化,诱导T细胞凋亡,在肿瘤免疫逃逸中起着重要的作用。目前PD-1/PD-L1信号通路成为免疫靶向治疗的新靶点,相关研究在非小细胞肺癌、晚期黑色素瘤等多种恶性肿瘤领域有重大进展,研究发现PD-L1 在多种肿瘤细胞包括乳腺癌中表达上调,提示 PD-1/PD-L1通路可能参与肿瘤的免疫逃逸。本文将针对PD-1/PD-L1通路在乳腺癌治疗中的作用及意义进行综述。     

CD47在淋巴瘤治疗中的研究进展

CD47作为一种跨膜蛋白,广泛分布于多种细胞,通过与巨噬细胞上信号调节蛋白α（SIRPα）结合,释放抑制信号,逃避巨噬细胞的吞噬。淋巴瘤细胞CD47表达上调是诱导免疫逃逸的重要机制之一,也是潜在的治疗靶点。文章就CD47诱导的免疫逃逸、靶向CD47的单克隆抗体和细胞免疫治疗等治疗手段在淋巴瘤治疗中的研究进展进行综述。     

非小细胞肺癌免疫检查点阻断剂治疗进展*

目前大部分肺癌患者就诊时已是晚期,不宜手术切除,主要采用放疗、化疗和靶向治疗等综合治疗,5 年生存率较低。免疫检查点阻断剂通过调整机体的免疫系统功能,打破肿瘤细胞免疫逃逸机制,使T 细胞活化并清除肿瘤细胞,成为一种有效的肿瘤治疗方式。目前免疫检查点阻断剂在非小细胞肺癌（non-small celll ung cancer ,NSCLC ）临床试验中取得一定疗效,很多研究正在开展,这有可能改变NSCLC 的治疗模式。本文将阐述免疫检查点阻断剂在NSCLC 中的治疗作用及联合其他治疗的应用前景。      

CD47分子在弥漫大B细胞淋巴瘤肿瘤微环境中的研究进展

弥漫大B细胞淋巴瘤（DLBCL）是成年人常见的高度侵袭性恶性血液肿瘤。DLBCL为一种高度异质性淋巴瘤,患者在分子生物学特征、临床表现和预后方面均存在巨大差异。目前越来越多的证据表明,肿瘤微环境对DLBCL的发生、发展发挥着重要的作用。CD47分子是一种整合素相关蛋白,在DLBCL细胞中过度表达,并在淋巴瘤免疫逃逸中起关键作用。本文拟就CD47分子相关信号通路、在DLBCL肿瘤微环境中的作用和DLBCL中靶向CD47分子的治疗策略等方面的研究进展进行综述。     

CD47‐signal regulatory protein α signaling system and its application to cancer immunotherapy

Tumor cells evade immune surveillance through direct or indirect interactions with various types of immune cell, with much recent attention being focused on modifying immune cell responses as the basis for the development of new cancer treatments. Signal regulatory protein α (SIRPα) and CD47 are both transmembrane proteins that interact with each other and constitute a cell‐cell communication system. SIRPα is particularly abundant in myeloid cells such as macrophages and dendritic cells, whereas CD47 is expressed ubiquitously and its expression level is elevated in cancer cells. Recent studies have shown that blockade of CD47‐SIRPα interaction enhances the phagocytic activity of phagocytes such as macrophages toward tumor cells in vitro as well as resulting in the efficient eradication of tumor cells in a variety of xenograft or syngeneic mouse models of cancer. Moreover, CD47 blockade has been shown to promote the stimulation of tumor‐specific cytotoxic T cells by macrophages or dendritic cells. Biological agents, such as Abs and recombinant proteins, that target human CD47 or SIRPα have been developed and are being tested in preclinical models of human cancer or in clinical trials with cancer patients. Preclinical studies have also suggested that CD47 or SIRPα blockade may have a synergistic antitumor effect in combination with immune checkpoint inhibitors that target the adaptive immune system. Targeting of the CD47‐SIRPα signaling system is thus a promising strategy for cancer treatment based on modulation of both innate and acquired immune responses to tumor cells.     

Cytotoxic T lymphocytes: role in immunosurveillance and in immunotherapy

Experiments in mice and recent human clinical studies have clearly shown the contribution of CD8+ T lymphocyte in the control of tumor development. CD8+ T lymphocytes are a constitutive component of the immune response during the development of cancer. In murine models, the efficiency of various cancer vaccines mainly depends on their ability to induce CD8+ T lymphocytes. Clinical responses in immunotherapy treated cancer patients have been associated with the presence of antitumor specific CD8+ T lymphocytes. In spontaneous regressive melanomas, intratumor antigen specific CD8+ cytotoxic T cells were expanded suggesting their involvement in the tumor shrinkage. Administration of antitumor specific cytotoxic T clones in mice resulted in antitumor responses which directly demonstrated the therapeutic efficiency of these cells. However, in most cases during cancer progression, the presence of antitumor CD8 T lymphocyte is not associated with clinical responses. Intrinsic functional abnormalities of these cells or a defect of CD8+ T cell migration to the tumor may in part explain their failure to inhibit tumor development. On the other hand, tumors also develop immune escape mechanisms (down modulation of tumor antigens, secretion of immunosuppressive factors, expression of anti-apoptotic molecules by the tumors, or pro-apoptotic factors inducing T cell death) to resist to the CD8+ T cell attack. To circumvent these tumor escape mechanisms, efficient cancer vaccines will have to recruit CD8+ T cells associated with other immune effectors.     

天然免疫检查点CD47-SIRPα在恶性肿瘤中的研究进展

针对CTLA-4/B7和PD-1/PD-L1的免疫检查点抑制剂现已广泛应用于临床,其他检查点抑制剂也正在开发中。CD47是广泛表达于正常细胞表面的蛋白质,在肿瘤细胞中呈过表达状态,其受体为髓系抑制性免疫受体SIRPα。阻断CD47与SIRPα之间的相互作用可增强巨噬细胞和中性粒细胞的吞噬作用进而消灭肿瘤细胞。此外,越来越多的证据表明阻断CD47-SIRPα轴还可以增强抗原呈递细胞的功能,从而刺激T细胞介导的抗癌免疫。随着该领域研究的发展,CD47-SIRPα轴的临床应用将会是未来肿瘤免疫治疗的热点之一。     

CD47: a potential immunotherapy target for eliminating cancer cells

The relationship between the immune system and cancer growth and aggravation has been discussed over a century. A number of molecules have been shown to participate in this process. CD47, a normal universally expressed member of the immunoglobulin superfamily, plays multiple functions in immune system. Researches demonstrated that CD47 was also highly expressed on the surface of tumor cells as well as cancer stem cells (CSCs). Whether the highly expressed CD47 was associated with tumor growth, metastasis, recurrence, or drug resistance has become the hotspot. Besides the roles of CD47 in tumor immunoregulation, the monoclonal antibodies targeting CD47 used in acute myelogenous leukemia (AML) and bladder CSCs were reported, which shed new light on tumor treatment. CSCs have been recognized as the root of tumor drug resistance and recurrence. Whether CD47 on CSCs could serve as a potential target for future anti-cancer treatment forms the focus of our review. Here we highlight the potential roles of CD47 in immune system, and discuss the promising therapeutic application of anti-CD47 antibodies for eliminating tumor cells.     

Immune response and cancer

Cellular transformation is initiated by genetic and epigenetic mutations that activate oncogenes and inactivate tumor suppressor pathways. Cancers thus arise when somatic cells escape intrinsic and extrinsic tumor suppressor mechanisms in the context of their cellular microenvironment. Given the well established importance of the immune system at controlling and shaping developing tumors, pointing the different strategies of tumor escape may provide important insights for the development of effective cancer therapies. In respect, a better understanding of the molecular interactions between tumors and the host immune system may thus allow the development of novel integrated approaches based on the simultaneous control of tumor escape pathways and the activation of anti-cancer immune responses. We hereafter review the currently known escape strategies developed by tumors and discuss the very limited success of trials using active immunization with vaccines or adoptive immunotherapy conducted to date, with a focus on potential therapeutic avenues. We believe that the induction of clinically relevant anti-cancer immunity and tumor rejection require an orchestrated set of events that are thus far impossible to activate by a single approach. Therefore, combining immunotherapy with conventional therapies may help in breaking down the existing barriers.     

CD40 ligand immunotherapy in cancer: an efficient approach

Cancer cells do not elicit a clinically sufficient anti-tumor immune response that results in tumor rejection. Recently, many investigators have been trying to enhance anti-tumor immunity and encouraging results have been reported. This review will discuss current anti-cancer immunotherapy; interleukin-2 therapy, tumor vaccine secreting Granulocyte macrophage-colony stimulating factor, dendritic cells fused with tumor cells, and CD40 ligand immunotherapy. Moreover, we introduce our two kinds of CD40 ligand immuno-genetherapy; (1) oral CD40 ligand gene therapy against lymphoma using attenuated Salmonella typhimurium (published in BLOOD 2000), (2) cancer vaccine transfected with CD40 ligand ex vivo for neuroblastoma (unpublished). Both approaches resulted in a high degree of protection against the tumor progression and they are simple and safe in the murine system.     

Lewis Y antigen modified CD47 is an independent risk factor for poor prognosis and promotes early ovarian cancer metastasis

CD47 is a membrane receptor that belongs to the immunoglobulin superfamily and plays an important role in the mechanisms of tumor immune escape. CD47 participates in tumor immune escape by combining with SIRPα to reduce the phagocytic activity of macrophages. There are six potential N-glycosylation sites on CD47, and glycosylation is known to be necessary for its membrane localization. However, it is still unknown to what extent glycosylation influences CD47 ligand binding properties and subsequent signaling. By using immunoprecipitation and confocal laser scanning microscopy, we showed that CD47 contains Lewis y antigen. Immunohistochemical analysis demonstrated that both the positive expression and the overexpression of CD47 and Lewis y antigen in cancer tissues and borderline tumors were significantly higher than those in benign ovarian tumors and normal ovarian tissues (P < 0.05). A linear correlation between the expression patterns of CD47 and Lewis y antigen was evident (r = 0.47, P < 0.01). The high expression of CD47 and Lewis y antigen showed significant correlations with the clinical pathological parameters of ovarian cancer [International Federation of Gynecology and Obstetrics (FIGO) standards, lymph node metastasis, and degree of differentiation] (P < 0.05). The Cox model and Kaplan-Meier tests showed that high expression of CD47 was an independent adverse risk factor for the prognosis of ovarian cancer. Cases with both high CD47 and Lewis y antigen expression had poor prognoses. Our study demonstrates that Lewis y antigens of CD47 may play a crucial role in the development of ovarian cancer, and could be new targets for immunotherapy for ovarian cancer.     

Improving antitumor immune responses by circumventing immunoregulatory cells and mechanisms.

Although numerous immunotherapeutic strategies have been studied in patients with cancer, consistent induction of clinical responses remains a formidable challenge. Cancer vaccines are often successful at generating elevated numbers of tumor-specific T lymphocytes in peripheral blood, however, despite this, tumors usually continue to grow unabated. Recent evidence suggests that endogenous regulatory cells, known to play a major role in the induction of immune tolerance to self and prevention of autoimmunity, as well as suppressive myeloid cells invoked in the tumor-bearing state, may be largely responsible for preventing effective antitumor immune responses. This review will focus on the major regulatory cell subtypes, including CD4(+)CD25(+) T-regulatory cells, type 1 regulatory T cells, natural killer T cells, and immature myeloid cells. Studies in humans and in animal models have shown a role for all of these cells in tumor progression, although the mechanisms by which they act to suppress immunity remain largely undefined. Elucidation of the dominant molecular mechanisms mediating immune suppression in vivo will allow more precise targeting of the relevant regulatory cell populations, as well as the development of novel strategies and clinical reagents that will directly block molecules that induce the suppression of antitumor immunity.     

Strategies of antigen-specific T-cell-based immunotherapy for cancer

The critical role of antigen-specific T-cells in the eradication of cancer has been demonstrated in numerous animal models, while significant challenges need to be conquered before antigen-specific T-cell immunotherapy can achieve true success in clinical practice. These challenges include: (1) weak or nonimmunogenicity of spontaneous tumors, (2) negative immune regulation mechanisms of the host immune system, (3) immune inhibition exerted by tumor cells, (4) physical barrier in solid tumor, and (5) escape or resistance to immune attack by tumor cells. Nonetheless, significant success has been achieved in several clinical trials recently, highlighting the possibility of successful manipulation of the immune system for control and elimination of tumor. We focused our study on summarizing the current knowledge and corresponding strategies for improving autologous cytotoxic T-cell (CTL)-based cancer immunotherapy, which include the following aspects: (1) the selection of tumor antigens for stimulation of CTL, (2) strategies of enhancing maturation and antigen presentation activity of dendritic cells (DC), (3) strategies of activation and maintenance of CTL response, and (4) recruitment of suitable immune effector cells to tumor sites. The successful manipulation of the immune system, based on the more and more detailed knowledge of tumor immunology, may finally reach the goal of "immune surveillance of malignancy."