Volume 39, Issue 1, 25 July 2013, Pages 1-10
第 39 卷第 1 期,2013 年 7 月 25 日,第 1-10 页
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Oncology Meets Immunology: The Cancer-Immunity Cycle
肿瘤学与免疫学的结合:癌症--免疫循环 rights and content 获取权利和内容
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The genetic and cellular alterations that define cancer provide the immune system with the means to generate T cell responses that recognize and eradicate cancer cells. However, elimination of cancer by T cells is only one step in the Cancer-Immunity Cycle, which manages the delicate balance between the recognition of nonself and the prevention of autoimmunity. Identification of cancer cell T cell inhibitory signals, including PD-L1, has prompted the development of a new class of cancer immunotherapy that specifically hinders immune effector inhibition, reinvigorating and potentially expanding preexisting anticancer immune responses. The presence of suppressive factors in the tumor microenvironment may explain the limited activity observed with previous immune-based therapies and why these therapies may be more effective in combination with agents that target other steps of the cycle. Emerging clinical data suggest that cancer immunotherapy is likely to become a key part of the clinical management of cancer.
癌症的基因和细胞改变为免疫系统提供了产生 T 细胞反应的手段,从而识别并消灭癌细胞。然而,T 细胞消灭癌细胞只是癌症-免疫循环中的一个步骤,该循环在识别非我和预防自身免疫之间保持着微妙的平衡。包括 PD-L1 在内的癌细胞 T 细胞抑制信号的发现,促使人们开发出一种新的癌症免疫疗法,这种疗法能特异性地阻碍免疫效应抑制,重振并有可能扩大原有的抗癌免疫反应。肿瘤微环境中抑制因子的存在可能解释了以往基于免疫的疗法活性有限的原因,也解释了为什么这些疗法与针对周期其他步骤的药物联合使用可能更有效。新出现的临床数据表明,癌症免疫疗法很可能成为癌症临床治疗的关键部分。

Main Text 正文

Introduction 导言

The development of cancer immunotherapy has reached an important inflection point in the history of cancer therapy (reviewed in Mellman et al., 2011). Durable monotherapy responses are consistently being reported for a broad range of human cancers with several different agents (Hamid et al., 2013a, Herbst et al., 2013, Hodi et al., 2010, Topalian et al., 2012b), providing a compelling argument that cancer immunotherapy is active in a range of indications beyond melanoma, a disease often thought to be atypically immunogenic (Jacobs et al., 2012). In addition to encouraging activity, many of the cancer immunotherapy approaches report safety profiles that are milder and more manageable than traditional or targeted (i.e., oncogene-centric) cancer therapies.
癌症免疫疗法的发展已经到了癌症治疗史上的一个重要拐点(Mellman 等人,2011 年综述)。目前不断有报告称,多种不同的药物对多种人类癌症产生了持久的单药治疗反应(Hamid等人,2013a;Herbst等人,2013;Hodi等人,2010;Topalian等人,2012b),为癌症免疫疗法在黑色素瘤以外的一系列适应症中具有活性提供了令人信服的论据,而黑色素瘤通常被认为是一种非典型免疫原性疾病(Jacobs等人,2012)。除了令人鼓舞的活性外,许多癌症免疫疗法的安全性也比传统或靶向(即以癌基因为中心)癌症疗法更温和、更易于管理。

Cancer is characterized by the accumulation of a variable number of genetic alterations and the loss of normal cellular regulatory processes (Tian et al., 2011). These events have long been known to result in the expression of neoantigens, differentiation antigens, or cancer testis antigens, which can lead to presentation of peptides bound to major histocompatibility class I (MHCI) molecules on the surface of cancer cells, distinguishing them from their normal counterparts. Since the work of Boon and colleagues, we have known that these cancer-specific peptide-MHCI complexes can be recognized by CD8+ T cells produced spontaneously in cancer patients (Boon et al., 1994). However, even when T cell responses occurred, they rarely provided protective immunity nor could they be mobilized to provide a basis for therapy.
癌症的特点是积累了数量不等的基因改变和丧失了正常的细胞调控过程(Tian 等人,2011 年)。人们早就知道这些事件会导致新抗原、分化抗原或癌症睾丸抗原的表达,从而导致与癌细胞表面的主要组织相容性 I 类(MHCI)分子结合的肽的呈现,将癌细胞与正常细胞区分开来。自布恩及其同事的研究以来,我们已经知道这些癌症特异性肽-MHCI 复合物可被癌症患者自发产生的 CD8 + T 细胞识别(布恩等人,1994 年)。然而,即使出现了 T 细胞反应,它们也很少能提供保护性免疫力,也不能动员它们为治疗提供依据。

As demonstrated by elegant analyses of cancer in mice, the continued deletion of cancer cells expressing T cell targets (immune editing) may enable cancers to evolve to avoid attack (Dunn et al., 2002). Despite these findings, recent results from human cancer have demonstrated that overcoming negative regulators to T cell responses in lymphoid organs (checkpoints) and in the tumor bed (immunostat function) are likely to explain the failure of immune protection in many patients (Mullard, 2013). Factors in the tumor microenvironment can act to modulate the existing activated antitumor T cell immune response, acting as an immune rheostat or “immunostat.” This class of molecules, including PD-L1:PD-1 (reviewed in Chen et al., 2012, Topalian et al., 2012a), emphasizes that the immune response in cancer reflects a series of carefully regulated events that may be optimally addressed not singly but as a group. The challenge now is to use this new understanding to develop new drugs and implement clinical strategies.
正如对小鼠癌症进行的优雅分析所证明的那样,持续删除表达 T 细胞靶标(免疫编辑)的癌细胞可能使癌症进化以躲避攻击(Dunn 等人,2002 年)。尽管有这些发现,但人类癌症的最新研究结果表明,克服淋巴器官(检查点)和肿瘤床(免疫抑制剂功能)中对 T 细胞反应的负调控因子很可能是许多患者免疫保护失败的原因(Mullard,2013 年)。肿瘤微环境中的因素可以调节现有的活化抗肿瘤 T 细胞免疫反应,起到免疫调节器或 "免疫抑制剂 "的作用。这一类分子,包括 PD-L1:PD-1(综述于 Chen 等人,2012 年;Topalian 等人,2012a),强调了癌症中的免疫反应反映了一系列精心调控的事件,这些事件可能不是单独而是作为一个群体得到最佳处理。现在的挑战是如何利用这一新的认识来开发新药和实施临床策略。

The articles contained in this issue each address key aspects of how the immune response can control or be manipulated to enhance anticancer immunity (Galon et al., 2013, Kalos and June, 2013, Motz and Coukos, 2013, Palucka and Banchereau, 2013, van den Boorn and Hartmann, 2013, Zitvogel et al., 2013). Here, we will integrate this information and consider how it might best be used in clinical development.
本期文章分别探讨了如何控制或操纵免疫反应以增强抗癌免疫力的关键问题(Galon 等人,2013 年;Kalos 和 June,2013 年;Motz 和 Coukos,2013 年;Palucka 和 Banchereau,2013 年;van den Boorn 和 Hartmann,2013 年;Zitvogel 等人,2013 年)。在此,我们将整合这些信息,并考虑如何在临床开发中更好地利用这些信息。

The Cancer-Immunity Cycle

For an anticancer immune response to lead to effective killing of cancer cells, a series of stepwise events must be initiated and allowed to proceed and expand iteratively. We refer to these steps as the Cancer-Immunity Cycle (Figure 1). In the first step, neoantigens created by oncogenesis are released and captured by dendritic cells (DCs) for processing (step 1). In order for this step to yield an anticancer T cell response, it must be accompanied by signals that specify immunity lest peripheral tolerance to the tumor antigens be induced. Such immunogenic signals might include proinflammatory cytokines and factors released by dying tumor cells or by the gut microbiota (Figure 2, Table 1). Next, DCs present the captured antigens on MHCI and MHCII molecules to T cells (step 2), resulting in the priming and activation of effector T cell responses against the cancer-specific antigens (step 3) that are viewed as foreign or against which central tolerance has been incomplete. The nature of the immune response is determined at this stage, with a critical balance representing the ratio of T effector cells versus T regulatory cells being key to the final outcome. Finally, the activated effector T cells traffic to (step 4) and infiltrate the tumor bed (step 5), specifically recognize and bind to cancer cells through the interaction between its T cell receptor (TCR) and its cognate antigen bound to MHCI (step 6), and kill their target cancer cell (step 7). Killing of the cancer cell releases additional tumor-associated antigens (step 1 again) to increase the breadth and depth of the response in subsequent revolutions of the cycle. In cancer patients, the Cancer-Immunity Cycle does not perform optimally. Tumor antigens may not be detected, DCs and T cells may treat antigens as self rather than foreign thereby creating T regulatory cell responses rather than effector responses, T cells may not properly home to tumors, may be inhibited from infiltrating the tumor, or (most importantly) factors in the tumor microenvironment might suppress those effector cells that are produced (reviewed by Motz and Coukos, 2013).
要使抗癌免疫反应能够有效杀死癌细胞,必须启动一系列步骤性事件,并允许其反复进行和扩展。我们将这些步骤称为癌症-免疫循环(图 1)。第一步,肿瘤发生产生的新抗原被释放出来,并被树突状细胞(DC)捕获进行处理(步骤 1)。为了使这一步产生抗癌 T 细胞反应,必须伴有指定免疫的信号,以免诱发外周对肿瘤抗原的耐受。这些免疫信号可能包括垂死肿瘤细胞或肠道微生物群释放的促炎细胞因子和因子(图 2,表 1)。接下来,DC 将捕获的 MHCI 和 MHCII 分子上的抗原呈现给 T 细胞(步骤 2),从而启动和激活效应 T 细胞对癌症特异性抗原的反应(步骤 3),这些抗原被视为外来抗原或中枢耐受不完全的抗原。免疫反应的性质在这一阶段确定,T效应细胞与T调节细胞比例的关键平衡是最终结果的关键。最后,活化的效应 T 细胞向肿瘤床迁移(第 4 步)和浸润(第 5 步),通过其 T 细胞受体(TCR)和与 MHCI 结合的同源抗原之间的相互作用,特异性地识别并结合到癌细胞上(第 6 步),并杀死目标癌细胞(第 7 步)。杀死癌细胞会释放出更多的肿瘤相关抗原(步骤 1),从而在随后的循环中增加反应的广度和深度。在癌症患者中,"癌症-免疫循环 "并不能发挥最佳作用。 肿瘤抗原可能无法被检测到,DC 和 T 细胞可能将抗原视为自身抗原而非外来抗原,从而产生 T 调节细胞反应而非效应细胞反应,T 细胞可能无法正常归巢到肿瘤,可能被抑制浸润肿瘤,或者(最重要的是)肿瘤微环境中的因素可能会抑制效应细胞的产生(Motz 和 Coukos,2013 年综述)。

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Figure 1. The Cancer-Immunity Cycle
图 1.癌症-免疫循环

The generation of immunity to cancer is a cyclic process that can be self propagating, leading to an accumulation of immune-stimulatory factors that in principle should amplify and broaden T cell responses. The cycle is also characterized by inhibitory factors that lead to immune regulatory feedback mechanisms, which can halt the development or limit the immunity. This cycle can be divided into seven major steps, starting with the release of antigens from the cancer cell and ending with the killing of cancer cells. Each step is described above, with the primary cell types involved and the anatomic location of the activity listed. Abbreviations are as follows: APCs, antigen presenting cells; CTLs, cytotoxic T lymphocytes.
癌症免疫力的产生是一个循环过程,可以自我传播,导致免疫刺激因子的积累,原则上应扩大和拓宽 T 细胞反应。这一循环的另一个特点是,抑制因子会导致免疫调节反馈机制,从而阻止或限制免疫力的发展。这个周期可分为七个主要步骤,从癌细胞释放抗原开始,到杀死癌细胞结束。上文介绍了每个步骤,并列出了所涉及的主要细胞类型和活动的解剖位置。缩写如下:APCs,抗原呈递细胞;CTLs,细胞毒性 T 淋巴细胞。

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Figure 2. Stimulatory and Inhibitory Factors in the Cancer-Immunity Cycle
图 2.癌症-免疫循环中的刺激因素和抑制因素

Each step of the Cancer-Immunity Cycle requires the coordination of numerous factors, both stimulatory and inhibitory in nature. Stimulatory factors shown in green promote immunity, whereas inhibitors shown in red help keep the process in check and reduce immune activity and/or prevent autoimmunity. Immune checkpoint proteins, such as CTLA4, can inhibit the development of an active immune response by acting primarily at the level of T cell development and proliferation (step 3). We distinguish these from immune rheostat (“immunostat”) factors, such as PD-L1, can have an inhibitory function that primarily acts to modulate active immune responses in the tumor bed (step 7). Examples of such factors and the primary steps at which they can act are shown. Abbreviations are as follows: IL, interleukin; TNF, tumor necrosis factor; IFN, interferon; CDN, cyclic dinucleotide; ATP, adenosine triphosphate; HMGB1, high-mobility group protein B1; TLR, Toll-like receptor; HVEM, herpes virus entry mediator; GITR, glucocorticoid-induced TNFR family-related gene; CTLA4, cytotoxic T-lympocyte antigen-4; PD-L1, programmed death-ligand 1; CXCL/CCL, chemokine motif ligands; LFA1, lymphocyte function-associated antigen-1; ICAM1, intracellular adhesion molecule 1; VEGF, vascular endothelial growth factor; IDO, indoleamine 2,3-dioxygenase; TGF, transforming growth factor; BTLA, B- and T-lymphocyte attenuator; VISTA, V-domain Ig suppressor of T cell activation; LAG-3, lymphocyte-activation gene 3 protein; MIC, MHC class I polypeptide-related sequence protein; TIM-3, T cell immunoglobulin domain and mucin domain-3. Although not illustrated, it is important to note that intratumoral T regulatory cells, macrophages, and myeloid-derived suppressor cells are key sources of many of these inhibitory factors. See text and Table 1 for details.
癌症-免疫循环的每一步都需要众多因素的协调,其中既有刺激因素,也有抑制因素。绿色显示的刺激因子可促进免疫,而红色显示的抑制因子则有助于控制这一过程,降低免疫活性和/或防止自身免疫。免疫检查点蛋白(如 CTLA4)可主要作用于 T 细胞的发育和增殖水平,从而抑制活跃免疫反应的发展(第 3 步)。我们将其与免疫流变因子("immunostat")(如 PD-L1)区分开来,后者具有抑制功能,主要作用是调节肿瘤床的主动免疫反应(第 7 步)。本文举例说明了此类因子及其作用的主要步骤。缩写如下:IL,白细胞介素;TNF,肿瘤坏死因子;IFN,干扰素;CDN,环状二核苷酸;ATP,三磷酸腺苷;HMGB1,高迁移率基团蛋白 B1;TLR,Toll 样受体;HVEM,疱疹病毒进入介质;GITR,糖皮质激素诱导的 TNFR 家族相关基因;CTLA4,细胞毒性 T 淋巴细胞抗原-4;PD-L1,程序性死亡配体 1;CXCL/CCL,趋化因子基团配体;LFA1,淋巴细胞功能相关抗原-1;ICAM1,细胞内粘附分子 1;VEGF,血管内皮生长因子;IDO,吲哚胺 2,3-二氧化酶;TGF,转化生长因子;BTLA,B 和 T 淋巴细胞衰减因子;VISTA,V-domain Ig suppressor of T cell activation;LAG-3,淋巴细胞活化基因 3 蛋白;MIC,MHC I 类多肽相关序列蛋白;TIM-3,T 细胞免疫球蛋白结构域和粘蛋白结构域-3。 虽然没有图示,但必须指出的是,瘤内 T 调节细胞、巨噬细胞和髓源性抑制细胞是这些抑制因子的主要来源。详见正文和表 1。

Table 1. Cancer-Immunity Cycle: Examples of Positive and Negative Regulators at Each Step
表 1.癌症-免疫循环:每个步骤的正负调节因子示例

Steps 步骤(+) Stimulators (+) 刺激器(−) Inhibitors (-) 抑制剂Other Considerations 其他考虑因素Example References 参考示例
1. Release of cancer antigens
Immunogenic or necrotic cell death
Tolergenic or apoptotic cell death
Tumor-associated neoantigens and cancer testis antigens
Ferguson et al., 2011 弗格森等人,2011 年
2. Cancer antigen presentation
• Proinflammatory cytokines (e.g., TNF-α, IL1, IFN-α)
- 促炎细胞因子(如 TNF-α、IL1、IFN-α 等)

• Immune cell factors: CD40L/CD40
- 免疫细胞因子CD40L/CD40

• Endogenous adjuvants released from dying tumors: CDN (STING ligand), ATP, HMGB1
- 垂死肿瘤释放的内源性佐剂:CDN(STING 配体)、ATP、HMGB1

• Gut microbiome products: TLR ligands
- 肠道微生物群产品:TLR 配体
IL-10, IL-4, IL-13 IL-10、IL-4、IL-13Dendritic cell maturity 树突状细胞成熟Lippitz, 2013, Mellman et al., 2011
Lippitz, 2013, Mellman 等人, 2011
3. Priming and activation
CD28:B7.1, CD137 (4-1BB)/CD137L, OX40:OX40L, CD27:CD70, HVEM, GITR, IL-2, IL-12
cd28:b7.1、cd137 (4-1bb)/cd137l、ox40:ox40l、cd27:cd70、hvem、gitr、il-2、il-12
CTLA4:B7.1, PD-L1:PD-1, PD-L1:B7.1, prostaglandins
CTLA4:B7.1, PD-L1:PD-1, PD-L1:B7.1, 前列腺素
Central tolerance, T cell repertoire, T regulatory cells
中枢耐受性、T 细胞群、T 调节细胞
Franciszkiewicz et al., 2012, Lippitz, 2013, Riella et al., 2012, So et al., 2006
Franciszkiewicz 等人,2012 年;Lippitz,2013 年;Riella 等人,2012 年;So 等人,2006 年
4. Trafficking of T cells to tumors
4.T 细胞向肿瘤的迁移
Franciszkiewicz et al., 2012, Peng et al., 2012
Franciszkiewicz 等人,2012 年;Peng 等人,2012 年
5. Infiltration of T cells into tumors
5.T 细胞渗入肿瘤
LFA1:ICAM1, selectins LFA1:ICAM1, 选择素VEGF, endothelin B receptor
血管内皮生长因子、内皮素 B 受体
Franciszkiewicz et al., 2013
Franciszkiewicz 等人,2013 年
6. Recognition of cancer cells by T cells
6.T 细胞识别癌细胞
T cell receptor T 细胞受体Reduced peptide-MHC expression on cancer cells
减少癌细胞上多肽-MHC 的表达
Mellman et al., 2011 梅尔曼等人,2011 年
7. Killing of cancer cells
IFN-γ, T cell granule content
IFN-γ、T 细胞颗粒含量
PD-L1:PD-1, PD-L1:B7.1, TIM-3:phospholipids, BTLA, VISTA, LAG-3, IDO, Arginase, MICA:MICB, B7-H4, TGFβT regulatory cells, myeloid-derived suppressor cells, M2 macrophages, hypoxia
T 调节细胞、髓源抑制细胞、M2 巨噬细胞、缺氧
Chen et al., 2012, Greaves and Gribben, 2013, Mellman et al., 2011, Topalian et al., 2012a
Chen 等人,2012;Greaves 和 Gribben,2013;Mellman 等人,2011;Topalian 等人,2012a

The goal of cancer immunotherapy is to initiate or reinitiate a self-sustaining cycle of cancer immunity, enabling it to amplify and propagate, but not so much as to generate unrestrained autoimmune inflammatory responses. Cancer immunotherapies must therefore be carefully configured to overcome the negative feedback mechanisms. Although checkpoints and inhibitors are built into each step that oppose continued amplification and can dampen or arrest the antitumor immune response, the most effective approaches will involve selectively targeting the rate-limiting step in any given patient. Amplifying the entire cycle may provide anticancer activity but at the potential cost of unwanted damage to normal cells and tissues. Many recent clinical results suggest that a common rate-limiting step is the immunostat function, immunosuppression that occurs in the tumor microenvironment (Predina et al., 2013, Wang et al., 2013).
癌症免疫疗法的目标是启动或重新启动癌症免疫的自我维持循环,使其能够扩大和传播,但又不至于产生无节制的自身免疫炎症反应。因此,癌症免疫疗法必须精心配置,以克服负反馈机制。虽然每个步骤中都有检查点和抑制剂,它们会阻止继续扩大,并能抑制或阻止抗肿瘤免疫反应,但最有效的方法是选择性地针对任何特定患者的限速步骤。放大整个周期可能会提供抗癌活性,但代价可能是对正常细胞和组织造成不必要的损伤。最近的许多临床结果表明,一个常见的限速步骤是免疫抑制剂功能,即肿瘤微环境中出现的免疫抑制(Predina 等人,2013 年;Wang 等人,2013 年)。

Initiating Anticancer Immunity: Antigen Release, Presentation, and T Cell Priming
启动抗癌免疫:抗原释放、呈递和 T 细胞启动

Attempts to activate or introduce cancer antigen-specific T cells, as well as stimulate the proliferation of these cells over the last 20 years, have led to mostly no, minimal or modest appreciable anticancer immune responses. The majority of these efforts involved the use of therapeutic vaccines because vaccines can be easy to deploy and have historically represented an approach that has brought enormous medical benefit (reviewed by Palucka and Banchereau, 2013). Yet, cancer vaccines were limited on two accounts. First, until recently, there was a general lack of understanding of how to immunize human patients to achieve potent cytotoxic T cell responses. This limitation reflects continued uncertainties concerning the identities of antigens to use, their mode of delivery, the types of adjuvants required, and the proximal characteristics of the desired T cell response (Palucka and Banchereau, 2013). Second, the presence of the immunostat in the tumor microenvironment may dampen or disable antitumor immune responses before clinically relevant tumor kill can occur. Thus, as long as these negative signals are in place, the prospects for vaccine-based approaches used alone are likely to be limited.
在过去 20 年中,人们尝试激活或引入癌症抗原特异性 T 细胞,并刺激这些细胞的增殖,但结果大多是没有、极少或适度的抗癌免疫反应。这些研究大多涉及治疗性疫苗的使用,因为疫苗易于使用,而且历来是一种能带来巨大医疗利益的方法(Palucka 和 Banchereau,2013 年综述)。然而,癌症疫苗在两个方面受到限制。首先,直到最近,人们对如何免疫人类患者以获得有效的细胞毒性 T 细胞反应还普遍缺乏了解。这种局限性反映了在使用抗原的特性、传递方式、所需佐剂的类型以及所需的 T 细胞反应的近端特征方面仍然存在不确定性(Palucka 和 Banchereau,2013 年)。其次,肿瘤微环境中免疫抑制剂的存在可能会在临床相关的肿瘤杀伤发生之前抑制或禁用抗肿瘤免疫反应。因此,只要存在这些负面信号,单独使用基于疫苗的方法的前景很可能是有限的。

Although vaccination can accelerate the anticancer immunity in the context of treatments that suppress negative regulators (Palucka and Banchereau, 2013), a number of significant challenges need to be overcome. First is the identification of the appropriate tumor antigens to include in any vaccine. A large, monovalent antigen trial (using the C-T antigen MAGE-A3) is currently under way (Kruit et al., 2013, Vansteenkiste et al., 2013), yet it is not clear that any one candidate will necessarily generate sufficiently robust T cell responses in all patients. Moreover, a single antigenic target, especially one not derived from a protein that is an inherent oncogenic driver, seems more likely to enable resistance by antigenic drift (immune editing) than a multivalent vaccine (Palucka and Banchereau, 2013).
虽然疫苗接种可以在抑制负调控因子的治疗中加速抗癌免疫(Palucka 和 Banchereau,2013 年),但仍有许多重大挑战需要克服。首先是确定疫苗中应包含的适当肿瘤抗原。目前正在进行一项大型单价抗原试验(使用 C-T 抗原 MAGE-A3)(Kruit 等人,2013 年;Vansteenkiste 等人,2013 年),但目前还不清楚任何一种候选抗原是否一定能在所有患者中产生足够强大的 T 细胞应答。此外,与多价疫苗相比,单一抗原靶点,尤其是并非来自固有致癌驱动蛋白的靶点,似乎更有可能通过抗原漂移(免疫编辑)产生抗药性(Palucka 和 Banchereau,2013 年)。

Deciding how to configure multivalent vaccines is itself a daunting challenge. It may be insufficient to rely entirely on sequencing the expressed tumor genome looking for point mutations, translocation fusions, or C-T antigens. Not only might this vary from patient to patient or even from cell to cell within a single patient’s tumor, expression at the messenger RNA or protein level does not assure that predicted antigenic peptides will be generated and expressed as peptide-MHCI complexes, especially in the face of the allelic complexity in the MHC. Several groups are actively approaching this problem by using a combination of informatics and mass spectroscopy of peptides eluted from MHCI molecules on both cell lines and primary tumors (Kasuga, 2013, Rammensee et al., 2002, Segal et al., 2008). In principle, this information can be used to guide the formulation of multivalent vaccines, although it does not necessarily address the problem of how to identify MHC class II epitopes that may be required to provide CD4 T cell help that might be needed to produce protective CD8 responses. The use of intact proteins as an immunogen may help mitigate this issue. Moreover, it has thus far proved difficult to identify MHCI-bound peptides that harbor point mutations that could selectively target T cell responses to cancer cells, which is unfortunate given that targeting somatic mutations should reduce the chances of generating autoimmunity or the need to overcome central tolerance (Mellman et al., 2011). Even assuming the correct antigens are in hand, how best to deliver them to patients remains a critical unknown. Peptides in emulsified vehicles represent a common and accessible approach, but in the absence of compelling positive controls for any vaccine, it is impossible to know whether it is an effective approach. Other strategies include direct targeting to DCs, adoptive transfer of antigen-loaded DCs or tumor cells, recombinant viral vectors, and bacterial vectors (especially Listeria; reviewed in Kalos and June, 2013, Palucka and Banchereau, 2013). Work must continue evaluating each of these looking for pharmacodynamic read-outs of CD8 T cell responses. With the clinical success of anti-PD-L1 and anti-PD-1 antibodies, it should now be possible to evaluate different vaccines, adjuvants, and delivery approaches in combination and therefore under conditions that should enhance the ability to judge their relative efficacies with common clinical read-outs, such as partial or complete responses in established tumors.
决定如何配置多价疫苗本身就是一项艰巨的挑战。完全依靠对表达的肿瘤基因组进行测序来寻找点突变、易位融合或 C-T 抗原可能是不够的。不仅如此,在信使 RNA 或蛋白质水平上的表达并不能保证预测的抗原肽会以肽-MHCI 复合物的形式产生和表达,尤其是面对 MHC 中等位基因的复杂性。一些研究小组正在积极解决这一问题,他们将信息学与质谱相结合,对细胞系和原发性肿瘤上的 MHCI 分子洗脱出的肽进行研究(Kasuga,2013 年;Rammensee 等人,2002 年;Segal 等人,2008 年)。原则上,这些信息可用于指导多价疫苗的配制,尽管它并不一定能解决如何识别 MHC II 类表位的问题,而这些表位可能是产生保护性 CD8 反应所需的 CD4 T 细胞帮助所必需的。使用完整蛋白质作为免疫原可能有助于缓解这一问题。此外,迄今为止还很难鉴定出携带点突变的 MHCI 结合肽,这些点突变可选择性地靶向 T 细胞对癌细胞的反应,鉴于靶向体细胞突变应减少产生自身免疫的机会或克服中枢耐受性的需要(Mellman 等人,2011 年),这是令人遗憾的。即使假定已经掌握了正确的抗原,如何以最佳方式将其提供给患者仍是一个关键的未知数。 乳化载体中的多肽是一种常见且容易获得的方法,但由于缺乏任何疫苗的令人信服的阳性对照,因此无法知道这是否是一种有效的方法。其他策略包括直接靶向直流电细胞、载抗原直流电细胞或肿瘤细胞的采纳性转移、重组病毒载体和细菌载体(尤其是李斯特菌;Kalos 和 June,2013 年;Palucka 和 Banchereau,2013 年)。必须继续对这些载体进行评估,寻找 CD8 T 细胞反应的药效学读数。随着抗-PD-L1 和抗-PD-1 抗体在临床上取得成功,现在应该可以对不同的疫苗、佐剂和给药方法进行组合评估,因此评估条件应能提高通过常见的临床读数(如已确诊肿瘤的部分或完全反应)判断其相对疗效的能力。

Work on vaccines should continue in a systematic fashion with human studies, because animal models are unlikely to validate the best path forward (Davis, 2012). It is also unlikely that the best vaccine approaches will differentiate themselves any time soon, given the lack of direct comparisons in clinical studies. This represents a substantial logistical challenge to incorporating vaccination as part of a drug development plan. Not only are such trials long and expensive, but they also represent only one of many potential combinations that are competing to be evaluated in conjunction with other immunotherapies (Vanneman and Dranoff, 2012).
疫苗研究工作应继续以系统的方式进行人体研究,因为动物模型不太可能验证最佳的前进道路(Davis,2012 年)。此外,由于缺乏临床研究的直接比较,最好的疫苗方法也不太可能在短期内脱颖而出。这对将疫苗接种作为药物开发计划的一部分提出了巨大的后勤挑战。此类试验不仅耗时长、费用高,而且只是众多潜在组合中的一种,这些组合将与其他免疫疗法一起进行竞争性评估(Vanneman 和 Dranoff,2012 年)。

Therapeutic vaccination is not the only approach to accelerating and expanding the production of T cell immunity. Because anticancer T cells can be produced spontaneously, there is a growing appreciation that the tumor itself represents a type of endogenous vaccine. Accessing the naturally occurring source of cancer-associated antigens avoids problems associated with selection and delivery (Heo et al., 2013, van den Boorn and Hartmann, 2013). This approach is also convenient, but achieving it requires detailed knowledge around whether standard of care chemotherapy or targeted therapies are compatible with immunotherapies. Some therapies are thought to cause tumor cell death in a fashion that promotes immunity (reviewed in Zitvogel et al., 2013). However, it is unclear whether this effect can be accurately predicted and will, in any event, require empirical study. Chemotherapy, radiation therapy, and targeted therapies must also be evaluated for their effects on the immune system. Although it is assumed that many might be antagonistic, there are some reports that others might promote T cell activity (Demaria et al., 2005, Duraiswamy et al., 2013, Hiniker et al., 2012, Ott et al., 2013, Postow et al., 2012, Stagg et al., 2011, Zitvogel et al., 2013).
治疗性疫苗接种并不是加速和扩大 T 细胞免疫的唯一方法。由于抗癌 T 细胞可以自发产生,人们越来越认识到肿瘤本身就是一种内源性疫苗。利用癌症相关抗原的天然来源可避免与选择和传递相关的问题(Heo 等人,2013 年;van den Boorn 和 Hartmann,2013 年)。这种方法也很方便,但要做到这一点,需要详细了解标准化疗或靶向疗法是否与免疫疗法兼容。有些疗法被认为能以促进免疫的方式导致肿瘤细胞死亡(Zitvogel 等人的综述,2013 年)。不过,目前还不清楚这种效应能否准确预测,无论如何都需要进行实证研究。化疗、放疗和靶向疗法对免疫系统的影响也必须进行评估。虽然许多疗法被认为具有拮抗作用,但也有一些报道称其他疗法可能会促进 T 细胞的活性(Demaria 等人,2005 年;Duraiswamy 等人,2013 年;Hiniker 等人,2012 年;Ott 等人,2013 年;Postow 等人,2012 年;Stagg 等人,2011 年;Zitvogel 等人,2013 年)。

Bypassing Vaccination by Adoptive T Cell Therapy
采用 T 细胞疗法绕过疫苗接种

Another exciting development is that the initial demonstrations that genetically modified autologous T cells could be reinfused into patients to yield substantial clinical benefit, at least in certain B cell malignancies (Grupp et al., 2013; reviewed in Kalos and June, 2013). The most well developed of these is the use of “CARs,” or chimeric antigen receptors, in which a patient’s T cells are transfected with a construct encoding an antibody against a tumor surface antigen (typically CD19) fused to T cell signaling domains (Kochenderfer and Rosenberg, 2013). Similar approaches are under investigation with recombinant T cell receptors (reviewed in Kalos and June, 2013). The procedure avoids the need for immunization and may even overcome mechanisms of immune suppression by overwhelming the system through infusion of large quantities of the modified T cells. This can force the revolution of the Cancer-Immunity Cycle, enhancing the accumulation of stimulatory immune factors, and potentially promotes eventual self-propagation of the cycle. The potential limitations here, which are yet to be fully determined, include whether the approach can be extended to cancers beyond hematologic malignancies, whether the delivery of large numbers of monospecific T cells will cause resistance due to antigenic drift, and whether the toxicity issues already identified can be safely managed.
另一个令人兴奋的进展是,至少在某些B细胞恶性肿瘤中,转基因自体T细胞可再输注到患者体内并产生实质性临床疗效的初步证明(Grupp等人,2013年;Kalos和June,2013年综述)。其中最成熟的是使用 "CARs "或嵌合抗原受体,即用一种编码肿瘤表面抗原抗体(通常为 CD19)的构建体转染患者的 T 细胞,并与 T 细胞信号结构域融合(Kochenderfer 和 Rosenberg,2013 年)。重组 T 细胞受体的类似方法也在研究之中(见 Kalos 和 June,2013 年综述)。这种方法避免了免疫接种,甚至可以通过输注大量改良 T 细胞来压制免疫系统,从而克服免疫抑制机制。这将迫使癌症-免疫循环发生变化,增强刺激性免疫因子的积累,并有可能促进循环的最终自我繁殖。这种方法的潜在局限性尚有待全面确定,其中包括:这种方法是否可以扩展到血液系统恶性肿瘤以外的癌症;输送大量单特异性 T 细胞是否会因抗原漂移而产生抗药性;已经发现的毒性问题是否可以得到安全控制。

T Cell Priming and Activation
T 细胞的启动和激活

Whether tumor antigens are delivered exogenously or are captured and presented by DCs endogenously, another strategy for intervening in the Cancer-Immunity Cycle involves the control of T cell activation. This is the presumed primary mechanism of action of anti-CTLA4 antibodies, such as ipilimumab, which blocks the interaction of the major negative regulator of T cells (CTLA4) with its ligands B7.1 and B7.2 (CD80 and CD86; Qureshi et al., 2011). Thus, during antigen presentation in lymphoid organs (or in the periphery), the expansion of T cell responses is disinhibited, thereby promoting the production of autoreactive T cells, including tumor-specific T cells. The lack of selectivity in T cell expansion combined with the fundamental importance of CTLA4 as a checkpoint may underlie the significant immune-related toxicities seen in patients treated with ipilimumab (Hodi et al., 2010).
无论肿瘤抗原是由外源递送还是由内源性直流电捕获和呈现,干预癌症-免疫循环的另一种策略都涉及对T细胞活化的控制。这是抗 CTLA4 抗体(如伊匹单抗)的主要作用机制,伊匹单抗可阻断 T 细胞主要负调控因子 CTLA4 与其配体 B7.1 和 B7.2(CD80 和 CD86;Qureshi 等人,2011 年)的相互作用。因此,在淋巴器官(或外周)进行抗原呈递时,T 细胞反应的扩展会被抑制,从而促进自反应性 T 细胞(包括肿瘤特异性 T 细胞)的产生。T细胞扩增缺乏选择性,加上CTLA4作为检查点的根本重要性,可能是接受伊匹单抗治疗的患者出现严重免疫相关毒性的原因(Hodi等人,2010年)。

Nevertheless, the ability of this “lever” to create durable clinical responses in some patients has triggered a great deal of effort to seek other immune modulators; modulators that can achieve what ipilimumab can, but in a more selective and controllable fashion that will provide the potential for greater efficacy and frequency of response, with less autoimmune-related toxicity. In addition, the combination of ipilimumab with agents that modulate complimentary steps on the Cancer-Immunity Cycle are already underway (Karan and Van Veldhuizen, 2012, Madan et al., 2012), and preliminary results from combinations that inhibit tumor immunosuppression appear very promising in enhancing both antitumor immune responses and autoimmune toxicity (see below).
然而,这种 "杠杆 "能够在一些患者身上产生持久的临床反应,这引发了人们寻找其他免疫调节剂的大量努力;这些调节剂能够实现伊匹单抗所能实现的目标,但以一种更具选择性和可控性的方式,提供更高的疗效和反应频率,同时减少与自身免疫相关的毒性。此外,ipilimumab与调节癌症-免疫循环中互补步骤的药物的联合用药已经在进行中(Karan和Van Veldhuizen,2012年;Madan等人,2012年),抑制肿瘤免疫抑制的联合用药在增强抗肿瘤免疫反应和自身免疫毒性方面的初步结果似乎很有希望(见下文)。

Immunostat Blockade: PD-L1 and PD-1
免疫抑制剂阻断:PD-L1 和 PD-1

The identification of PD-L1 as a distal immune modulator expressed in 20%–50% of human cancer (Herbst et al., 2013) has led to the development of a number of cancer immunotherapies that target the interactions between PD-L1:PD-1, PD-L1:B7.1, and PD-L2:PD-1 (Table 2; reviewed in Chen et al., 2012, Topalian et al., 2012a). Anti-PD-L1 and anti-PD-1 monotherapy response rates have been presented for over 750 patients (ranging from 13% to 38%) treated across a broad range of human cancer types. Agents tested as monotherapy include MPDL3280A (anti-PDL1; Genentech/Roche; Cho et al., 2013, Hamid et al., 2013b, Herbst et al., 2013, Powderly et al., 2013, Spigel et al., 2013, Tabernero et al., 2013), nivolumab (anti-PD-1; Bristol Myers Squibb; Brahmer et al., 2013, Drake et al., 2013, Sznol et al., 2013, Topalian et al., 2013), and lambrolizumab (anti-PD-1; Merck; Hamid et al., 2013a). Antitumor activity of the PD-L1- and PD-1-targeted therapies that utilize an engineered immunoglobulin G1 (IgG1) (MPDL3280A; modified to eliminate ADCC by altering FcγR binding; Herbst et al., 2013) or IgG4 antibody (nivolumab and lambrolizumab; expected to reduce ADCC; Isaacs et al., 1996) backbone have resulted in particularly rapid antitumor activity, with some responses observed within days of starting treatment. These data suggest that, for many human cancers, the Cancer-Immunity Cycle is intact up to the point of tumor cell killing by T cells, which can be potently restrained by PD-L1. Once the PD-L1:PD-1 interaction is blocked, preexisting anticancer T cells can have their effector function rapidly restored. This is consistent with the proposed mechanism of action of this negative regulator, where PD-L1 (expressed either on tumor cells or on tumor-infiltrating immune cells) binding to PD-1 on activated effector T cells causes the recruitment of the phosphatase SHP-2 and subsequent inactivation of the PI3 kinase-signaling cascade (Chemnitz et al., 2004, Parry et al., 2005). These events block the secretion or production of cytotoxic mediators required for killing. However, this block appears to be rapidly reversible once the inhibition is lifted.
PD-L1是一种远端免疫调节剂,在20%-50%的人类癌症中都有表达(Herbst等人,2013年),因此开发了许多针对PD-L1:PD-1、PD-L1:B7.1和PD-L2:PD-1之间相互作用的癌症免疫疗法(表2;综述见Chen等人,2012年;Topalian等人,2012年a)。抗 PD-L1 和抗 PD-1 单药治疗的反应率已超过 750 例(从 13% 到 38% 不等),这些患者接受了多种人类癌症类型的治疗。作为单一疗法进行测试的药物包括 MPDL3280A(抗 PDL1;基因泰克/罗氏;Cho 等人,2013 年;Hamid 等人,2013b;Herbst 等人,2013 年;Powderly 等人,2013 年;Spigel 等人,2013 年;Tabernero 等人,2013 年)、nivolumab(抗 PDL1;基因泰克/罗氏;Cho 等人,2013 年;Hamid 等人,2013b;Herbst 等人,2013 年;Powderly 等人,2013 年;Spigel 等人,2013 年;Tabernero 等人,2013 年)、2013)、nivolumab(抗-PD-1;Bristol Myers Squibb;Brahmer 等人,2013;Drake 等人,2013;Sznol 等人,2013;Topalian 等人,2013)和 lambrolizumab(抗-PD-1;默克;Hamid 等人,2013a)。利用工程免疫球蛋白 G1 (IgG1)(MPDL3280A;通过改变 FcγR 结合而消除 ADCC;Herbst 等人,2013 年)或 IgG4 抗体(nivolumab 和 lambrolizumab;预计会减少 ADCC;Isaacs 等人,1996 年)骨架的 PD-L1 和 PD-1 靶向疗法的抗肿瘤活性特别快,在开始治疗的几天内就能观察到一些反应。这些数据表明,对于许多人类癌症来说,在 T 细胞杀死肿瘤细胞之前,癌症-免疫循环是完整的,而 PD-L1 可以有效地抑制这种循环。一旦 PD-L1:PD-1 相互作用被阻断,原有的抗癌 T 细胞就能迅速恢复其效应功能。 PD-L1 (表达于肿瘤细胞或肿瘤浸润免疫细胞)与活化效应 T 细胞上的 PD-1 结合,导致磷酸酶 SHP-2 的招募,随后 PI3 激酶-信号级联失活(Chemnitz 等人,2004 年;Parry 等人,2005 年)。这些事件阻止了杀伤所需的细胞毒性介质的分泌或产生。然而,一旦抑制解除,这种阻滞似乎可以迅速逆转。

Table 2. Inhibitors of PD-L1 or PD-1 Currently Being Developed in Oncology
表 2.目前在肿瘤学领域开发的 PD-L1 或 PD-1 抑制剂

Therapeutic 治疗Lead Company 牵头公司Antibody Type 抗体类型Affinity/Kd 亲和力/K d Interaction Inhibited 交互作用受抑制Development 发展
Anti-PD-L1 抗 PD-L1
MPDL3280A Herbst et al., 2013.
MPDL3280A Herbst 等人,2013 年。
Genentech/Roche 基因泰克/罗氏Engineered IgG1 (no ADCC)
工程 IgG1(无 ADCC)
0.4 nM 0.4 毫微米PD-L1:PD-1 PD-L1:B7.1Broad (lung pivotal) 广义(肺枢纽)
MEDI-4736 Stewart et al., 2011.
MEDI-4736 Stewart 等人,2011 年。
AstraZeneca 阿斯利康Modified IgG1 (no ADCC) 改良 IgG1(无 ADCC)Not available 不详PD-L1:PD-1 PD-L1:B7.1Phase I 第一阶段
Anti-PD-1 抗 PD-1
Nivolumab Brahmer et al., 2010.
Nivolumab Brahmer 等人,2010 年。
Bristol-Myers Squibb 百时美施贵宝IgG42.6 nM 2.6 毫微米PD-L1:PD-1 PD-L2:PD-1Broad (lung, melanoma, RCC pivotal)
广泛(肺癌、黑色素瘤、RCC 中枢疗法)
Lambrolizumab Patnaik et al., 2012.
Lambrolizumab Patnaik 等人,2012 年。
Merck & Co 默克公司IgG4 (humanized) IgG4(人源化)29 pMPD-L1:PD-1 PD-L2:PD-1Broad (melanoma pivotal) 广义(黑色素瘤中枢疗法)
Pidilizumab Rotem-Yehudar et al., 2009; Westin et al., 2012.
Pidilizumab Rotem-Yehudar 等人,2009 年;Westin 等人,2012 年。
CureTechIgG1 (humanized) IgG1(人源化)Not available 不详Broad 广泛
AMP-224 Smothers et al., 2013.
AMP-224 Smothers 等人,2013 年。
GlaxoSmithKline 葛兰素史克PD-L2 IgG1 Fc fusion PD-L2 IgG1 Fc 融合体Not available 不详PD-L1:PD-1 PD-L2:PD-1Phase I 第一阶段

Most importantly, the PD-L1 and PD-1 antagonists have exhibited significant response rates, and largely unprecedented durable responses. In melanoma, the anti-PD-1 antibody nivolumab has reported an overall response rate (ORR) of 31% (33/107) and a duration of response of 18.4 to 117.0+ weeks (Sznol et al., 2013), whereas lambrolizumab reported an ORR of 38% and duration of response of 1.9 to 10.8 months (Hamid et al., 2013a). Across a broad range of human cancers, which included lung, colon, head and neck, and gastric cancers in addition to melanoma and renal cell carcinoma, the anti-PD-L1 antibody MPDL3280A had an ORR of 21% (29% in melanoma, 22% in lung cancer) with 26 of 29 responses ongoing at the time of the report (time from starting treatment ranged from 3 to 15+ months) (Herbst et al., 2013, Hamid et al., 2013b, Spigel et al., 2013). Additionally, the safety profile of these agents suggests that while many cancer types express PD-L1 to inhibit anticancer immune responses, most patients do not have underlying autoimmunity inhibited only by PD-L1 expression (Francisco et al., 2010). Grade 3-4 treatment-related adverse events were noted to occur in 13% to 21% of patients treated (Hamid et al., 2013a, Herbst et al., 2013, Sznol et al., 2013). The majority of reported cases have been readily manageable with supportive care or by immune suppression with steroid administration. This is in stark contrast to the safety profiles of most therapies that target more proximal steps in the Cancer-Immunity Cycle (e.g., anti-CTLA4; Hodi et al., 2010) and might hint at the benefits of specifically targeting the properties of cancer that inhibit the immune response rather than nonspecific activation of the immune system. Although it is still relatively early in the development of these inhibitors (phase II/III trials are underway), the fact that three different antibodies have yielded such results greatly increases the confidence in a positive outcome.
最重要的是,PD-L1 和 PD-1 拮抗剂显示了显著的应答率,而且基本上是前所未有的持久应答。在黑色素瘤中,抗 PD-1 抗体 nivolumab 的总反应率(ORR)为 31%(33/107),反应持续时间为 18.4 至 117.0+ 周(Sznol 等人,2013 年),而 lambrolizumab 的总反应率为 38%,反应持续时间为 1.9 至 10.8 个月(Hamid 等人,2013a)。抗PD-L1抗体MPDL3280A的ORR为21%(黑色素瘤为29%,肺癌为22%),29例应答中有26例在报告时仍在进行中(从开始治疗起的时间为3至15个月)(Herbst等人,2013年;Hamid等人,2013年b;Spigel等人,2013年)。此外,这些药物的安全性表明,虽然许多癌症类型都表达 PD-L1 以抑制抗癌免疫反应,但大多数患者并没有仅受 PD-L1 表达抑制的潜在自身免疫(Francisco 等人,2010 年)。据悉,在接受治疗的患者中,有 13% 至 21% 会出现 3-4 级治疗相关不良事件(Hamid 等,2013a;Herbst 等,2013;Sznol 等,2013)。大多数报告的病例都可以通过支持性护理或类固醇免疫抑制得到控制。这与针对癌症-免疫循环中更近端步骤的大多数疗法(如抗 CTLA4;Hodi 等人,2010 年)的安全性形成鲜明对比,并可能暗示了专门针对抑制免疫反应的癌症特性而非非特异性激活免疫系统的益处。 虽然这些抑制剂的开发还处于相对早期(二期/三期试验正在进行中),但三种不同的抗体都取得了这样的结果,这大大增加了人们对积极结果的信心。

From a drug development and clinical care perspective, the activity observed with anti-PD-L1 or anti-PD-1 is clear. Robust single-agent activity was observed rapidly and for extended durations without identified off-target toxicity (Topalian et al., 2013). This situation is distinct from the majority of other agents under investigation (or approved) in oncology, except for a select group of small-molecule inhibitors that target driver oncogenic translocations or mutations (e.g., imatinib for BCR-Abl [Lin et al., 2013], crizotinib for ALK translocations [Rothschild and Gautschi, 2013], vemurafenib [Huang et al., 2013], and dabrafenib [Huang et al., 2013] for the V600E BRAF mutation and erlotinib for mutant EGF receptor [Bulgaru et al., 2003]). Therefore, extended trials looking for incremental effects or complex combination approaches should not be necessary. Furthermore, the potential for biomarker-driven patient selection to optimize treatment benefit appears promising and might distinguish patients most likely to have strong benefit from the inhibition of PD-L1:PD-1 as monotherapy opposed to those that may most likely require a different or combinatorial approach (Powderly et al., 2013, Topalian et al., 2013). These results also emphasize the likely importance of immunosuppression in the natural history of cancer. Unfortunately, as the clinical trial data to date confirm, the majority of patients will not respond or will respond only incompletely to PD-L1 or PD-1 inhibitors. Because multiple other mechanisms of immunosuppression are known that may work together or in parallel with PD-L1:PD-1-mediated inhibition, there is a need to pursue other potential agents that exhibit the same profile of rapid, substantial responses. For example, many tumors are characterized by significant infiltration by T regulatory cells, and targeting these may prove to be a fruitful approach (Jacobs et al., 2012). It is possible that even ipilimumab works, at least in part, by causing T regulatory cell (Treg) depletion.
从药物开发和临床治疗的角度来看,抗-PD-L1 或抗-PD-1 的活性是显而易见的。在没有发现脱靶毒性的情况下,迅速观察到了持续时间较长的强大单药活性(Topalian 等人,2013 年)。这种情况有别于肿瘤学领域正在研究(或已获批准)的大多数其他药物,除了一些针对驱动性致癌基因易位或突变的小分子抑制剂(如针对 BCR-Abl 的伊马替尼 [Lin et al、2013]、针对 ALK 易位的克唑替尼[Rothschild 和 Gautschi,2013]、针对 V600E BRAF 突变的维莫非尼[Huang 等人,2013]和达拉非尼[Huang 等人,2013]以及针对突变 EGF 受体的厄洛替尼[Bulgaru 等人,2003])。因此,没有必要扩大试验范围,寻找增量效应或复杂的联合方法。此外,生物标志物驱动的患者选择似乎很有希望优化治疗效果,并可能将最有可能从抑制 PD-L1:PD-1 单药治疗中获益的患者与最有可能需要采用不同或组合方法的患者区分开来(Powderly 等人,2013 年;Topalian 等人,2013 年)。这些结果还强调了免疫抑制在癌症自然病史中的重要性。不幸的是,正如迄今为止的临床试验数据所证实的,大多数患者对 PD-L1 或 PD-1 抑制剂没有反应或反应不完全。由于已知的其他多种免疫抑制机制可能与 PD-L1:PD-1 介导的抑制同时或并行发挥作用,因此有必要寻找其他潜在的药物,以获得与 PD-L1:PD-1 抑制剂相同的快速、实质性反应。 例如,许多肿瘤的特征是T调节细胞的大量浸润,针对这些细胞的治疗可能是一种富有成效的方法(Jacobs等人,2012年)。即使是伊匹单抗,也有可能至少在一定程度上通过导致T调节细胞(Treg)耗竭而发挥作用。

Combination Immune Therapies

It is reasonable to suspect that immunotherapy approaches, from vaccines to CARs, would be more effective when given in combination with a PD-L1 or PD-1 inhibitor (Goding et al., 2013, West et al., 2013). By disabling the immune inhibition in the tumor microenvironment, approaches that target earlier steps in the Cancer-Immunity Cycle (steps 1–6) are more likely to lead to cancer cell killing. Conversely, PD-L1 or PD-1 inhibition may not be sufficient for optimal antitumor activity in some patients, particularly those that do not demonstrate evidence of tumor immune cell infiltration (Gajewski et al., 2011, Gajewski et al., 2013, Gajewski, 2012). PD-L1- and PD-1-targeted therapies suggest that in patients whose tumors express PD-L1, the proximal steps of the Cancer-Immunity Cycle are intact and may not require further enhancement. These patients are most commonly the patients who exhibit rapid and durable response to PD-L1 or PD-1 inhibition. However, although some PD-L1-negative tumors still respond to PD-L1 or PD-1 monotherapy, the majority of tumors do not (Powderly et al., 2013, Grosso et al., 2013). This outcome can be indicative of patients who have a defect in steps 1 to 6 of the Cancer-Immunity Cycle and may be most commonly a defect in cancer antigen-specific T cell activation or infiltration of T cells into tumors (Powderly et al., 2013). However, more data from human tumors are likely to be necessary to further elucidate what critical breaks in the cycle are most prominent in different human cancers.
我们有理由相信,从疫苗到 CARs 等免疫疗法在与 PD-L1 或 PD-1 抑制剂联合使用时会更加有效(Goding 等人,2013 年;West 等人,2013 年)。通过使肿瘤微环境中的免疫抑制失效,针对癌症-免疫循环早期步骤(步骤 1-6)的方法更有可能杀死癌细胞。相反,PD-L1 或 PD-1 抑制在某些患者中可能不足以达到最佳抗肿瘤活性,尤其是那些没有证据显示肿瘤免疫细胞浸润的患者(Gajewski 等人,2011 年;Gajewski 等人,2013 年;Gajewski,2012 年)。PD-L1和PD-1靶向疗法表明,在肿瘤表达PD-L1的患者中,癌症-免疫循环的近端步骤是完整的,可能不需要进一步加强。这些患者通常对 PD-L1 或 PD-1 抑制剂表现出快速而持久的反应。然而,尽管一些 PD-L1 阴性肿瘤仍对 PD-L1 或 PD-1 单药治疗有反应,但大多数肿瘤却没有反应(Powderly 等人,2013 年;Grosso 等人,2013 年)。这种结果可能表明患者在癌症-免疫循环的第1至第6步中存在缺陷,最常见的可能是癌症抗原特异性T细胞活化或T细胞浸润到肿瘤中的缺陷(Powderly等人,2013年)。然而,要进一步阐明在不同的人类癌症中周期的哪些关键环节最为突出,可能还需要更多来自人类肿瘤的数据。

One approach, combining a CTLA4 targeted therapy (ipilimumab) with a PD-1-targeted inhibitor (nivolumab), appears to enhance the immune activity in patients over either therapy alone in an early phase study (Wolchok et al., 2013). Anti-CTLA4 can lead to enhanced priming and activation of antigen-specific T cells and potentially clearance of regulatory T cells from the tumor microenvironment (Table 1). The blocking of PD-L1 or PD-1 can remove the inhibition of cancer cell killing by T cells (Figure 3). By inhibiting two targets that affect two steps in the Cancer-Immunity Cycle, rapid and deep responses (by modified WHO criteria) were observed in patients with melanoma (ORR: 40% [21/52]; CR: 10% [5/52]). Immune-related toxicities were also enhanced in their magnitude, frequency, and onset (53% Grade 3-4 treatment-related toxicities). Although many of these were serious and required treatment, therapy discontinuation, or hospitalization, the durable partial and complete responses in melanoma may warrant this approach in some patients. In particular, combination therapy appeared to most dramatically benefit patients who were less likely to benefit from PD-L1 or PD-1 inhibition alone, because their tumors were PD-L1-negative (6/13 PD-L1-positive and 9/22 PD-L1-negative patients responded to combination therapy; Wolchok et al., 2013). The addition of a CTLA4-targeted therapy may be completing the defect in the Cancer-Immunity Cycle for patients who are PD-L1-negative. Further studies of preipilimumab and on ipilimumab treatment tumor samples are warranted to better understand this effect.
一种方法是将 CTLA4 靶向疗法(ipilimumab)与 PD-1 靶向抑制剂(nivolumab)相结合,在一项早期研究中,这种方法似乎比单独使用其中一种疗法更能增强患者的免疫活性(Wolchok 等人,2013 年)。抗CTLA4可增强抗原特异性T细胞的启动和激活,并有可能清除肿瘤微环境中的调节性T细胞(表1)。阻断 PD-L1 或 PD-1 可以消除 T 细胞对癌细胞杀伤的抑制(图 3)。通过抑制影响 "癌症-免疫循环 "中两个步骤的两个靶点,黑色素瘤患者观察到了快速而深入的反应(按修改后的世卫组织标准)(ORR:40% [21/52];CR:10% [5/52])。免疫相关毒性的程度、频率和发病率也有所提高(3-4 级治疗相关毒性占 53%)。虽然其中许多毒性反应很严重,需要治疗、中断治疗或住院治疗,但黑色素瘤持久的部分和完全缓解可能会使一些患者有必要采用这种方法。特别是,联合疗法似乎最能使那些不太可能单独从 PD-L1 或 PD-1 抑制中获益的患者受益,因为他们的肿瘤是 PD-L1 阴性的(6/13 名 PD-L1 阳性患者和 9/22 名 PD-L1 阴性患者对联合疗法有反应;Wolchok 等人,2013 年)。对于PD-L1阴性的患者来说,增加CTLA4靶向疗法可能会弥补癌症-免疫循环中的缺陷。为了更好地了解这种效应,有必要对ipilimumab治疗前和ipilimumab治疗后的肿瘤样本进行进一步研究。

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Figure 3. Therapies that Might Affect the Cancer-Immunity Cycle
图 3.可能影响癌症-免疫循环的疗法

The numerous factors that come into play in the Cancer-Immunity Cycle provide a wide range of potential therapeutic targets. This figure highlights examples of some of the therapies currently under preclinical or clinical evaluation. Key highlights include that vaccines can primarily promote cycle step 2, anti-CTLA4 can primarily promote cycle step 3, and anti-PD-L1 or anti-PD-1 antibodies can primarily promote cycle step 7. Although not developed as immunotherapies, chemotherapy, radiation therapy, and targeted therapies can primarily promote cycle step 1, and inhibitors of VEGF can potentially promote T cell infiltration into tumors—cycle step 5. Abbreviations are as follows: GM-CSF, granulocyte macrophage colony-stimulating factor; CARs, chimeric antigen receptors.
在癌症-免疫循环中发挥作用的众多因素提供了广泛的潜在治疗靶点。本图重点举例说明了目前正在进行临床前或临床评估的一些疗法。主要亮点包括:疫苗可主要促进循环步骤 2,抗 CTLA4 可主要促进循环步骤 3,而抗 PD-L1 或抗 PD-1 抗体可主要促进循环步骤 7。化疗、放疗和靶向疗法虽然不是作为免疫疗法开发的,但可主要促进周期步骤 1,而血管内皮生长因子抑制剂有可能促进 T 细胞浸润肿瘤--周期步骤 5。缩写如下:GM-CSF,粒细胞巨噬细胞集落刺激因子;CAR,嵌合抗原受体。

Other combinations that merit serious consideration include anti-PD-L1 or anti-PD-1 with vaccination, especially if it becomes possible to monitor a patient’s T cell profile to distinguish individuals who have generated suboptimal T cell responses to their cancers (Duraiswamy et al., 2013, Ge et al., 2013). In addition, combinations with agents that will enhance T cell trafficking and infiltration into the tumor bed should be explored vigorously, because the entry step may be important in some patients. In this class, inhibition of VEGF by the anti-VEGF antibody bevacizumab appears to be a promising candidate based on hints from the preclinical and clinical literature (Motz and Coukos, 2013, Hodi et al., 2010). Similarly, B-Raf inhibitors (vemurafenib) may also enhance T cell infiltration into tumors (Liu et al., 2013). Of course, with increased activity due to combinations comes the increased chance for additive or synergistic toxicity. This further highlights the importance of selecting therapeutic targets that are specific to the ability of a tumor to escape immune eradication over targets that may also play an important role in mediating immune homeostasis and preventing autoimmunity.
其他值得认真考虑的组合包括抗-PD-L1或抗-PD-1与疫苗接种,特别是如果有可能监测患者的T细胞谱,以区分对其癌症产生次优T细胞反应的个体(Duraiswamy等人,2013年;Ge等人,2013年)。此外,还应积极探索与能增强 T 细胞迁移和浸润肿瘤床的药物组合,因为对某些患者来说,进入肿瘤床的步骤可能很重要。在这一类药物中,根据临床前和临床文献(Motz 和 Coukos,2013 年;Hodi 等人,2010 年)的提示,抗血管内皮生长因子抗体贝伐珠单抗抑制血管内皮生长因子似乎是一种很有希望的候选药物。同样,B-Raf抑制剂(vemurafenib)也可增强T细胞对肿瘤的浸润(Liu等人,2013年)。当然,在联合用药增加活性的同时,也增加了相加或协同毒性的机会。这进一步凸显了选择治疗靶点的重要性,这些靶点对肿瘤逃避免疫清除的能力具有特异性,而不是对调解免疫平衡和预防自身免疫也可能发挥重要作用的靶点。

Concluding Remarks 结束语

The objective of understanding the inherent immune biology related to cancer is to better define strategies to harness the human immune response against cancer to achieve durable responses and/or complete eradication of cancer in patients safely. Multiple approaches to cancer therapy exist, and few are as complicated as immune-based therapy. Multiple numbers of systemic factors can effect or contribute to the success or failure of immune therapy and lends to this complexity. Results may be confounded by many currently unmeasured variables, including any given patient’s gut microbiome, their diet, and whether they contract an underlying infection (Brestoff and Artis, 2013, James et al., 2012, Rothman and Paterson, 2013, Xu et al., 2012). Yet, as complicated and incompletely understood human immunology may be, the immune response to cancer may be less complicated and less protean than the biology of cancer cells themselves.
了解与癌症有关的固有免疫生物学的目的是为了更好地确定利用人类免疫反应对抗癌症的策略,使患者安全地获得持久的反应和/或完全根除癌症。癌症治疗有多种方法,但很少有像免疫疗法这样复杂的。多种系统性因素会影响或导致免疫疗法的成败,这也增加了免疫疗法的复杂性。许多目前尚未测量的变量,包括任何特定患者的肠道微生物群、饮食以及是否感染了潜在的感染,都可能对治疗结果产生影响(Brestoff 和 Artis,2013 年;James 等人,2012 年;Rothman 和 Paterson,2013 年;Xu 等人,2012 年)。然而,尽管人类免疫学可能很复杂,人们对它的理解也不全面,但对癌症的免疫反应可能没有癌细胞本身的生物学那么复杂,也没有那么无穷无尽。

The early data from clinical studies of immune-based therapies suggest durable activity that few cancer therapies can approximate. The immune response can be rapid, durable, and adaptable. Once activated, it has the potential to be self-propagating (for example, see Hamid et al., 2013a). These characteristics may preempt the development of secondary resistance seen with most cancer therapies. In fact, with each revolution of the cycle, not only can an accumulation of immune stimulatory factors occur (Powderly et al., 2013), reinforcing the ongoing antitumor immune response, but it can also stimulate the generation of new antitumor immune responses by promoting antigen spreading (for example, see Corbière et al., 2011). As much as immune responses can completely and safely eradicate viral infections, the goal of cancer immunotherapy should remain the complete and safe eradication of cancer from individual patients. Meeting this objective may require only monotherapy approaches in some patients, whereas others may require combined therapies. By understanding the biology present in specific patients, immune-related biomarkers may allow us to map out the Cancer-Immunity Cycle for individual patients and enable tailoring of specific immune therapies or combinations of immune therapies.
基于免疫疗法的临床研究的早期数据表明,这种疗法具有持久的活性,很少有癌症疗法可以与之媲美。免疫反应可以是快速、持久和适应性强的。免疫反应一旦被激活,就有可能自我繁殖(例如,见 Hamid 等人,2013a)。这些特点可能会避免大多数癌症疗法产生二次抗药性。事实上,随着周期的每一次变化,不仅会出现免疫刺激因子的积累(Powderly 等人,2013 年),加强正在进行的抗肿瘤免疫反应,而且还能通过促进抗原扩散来刺激新的抗肿瘤免疫反应的产生(例如,见 Corbière 等人,2011 年)。就像免疫反应可以完全、安全地根除病毒感染一样,癌症免疫疗法的目标仍应是完全、安全地根除患者体内的癌症。要实现这一目标,有些患者可能只需要单一疗法,而有些患者则可能需要联合疗法。通过了解特定患者体内存在的生物学特性,免疫相关生物标记物可能会让我们绘制出个体患者的癌症-免疫循环图,从而量身定制特定的免疫疗法或免疫疗法组合。

References 参考资料