CD28／CTLA4：B7在T细胞激活和效应过程中的共刺激作用

抗原特异性Ｔ细胞的激活需要ＴＣＲ－ＣＤ３复合体接受抗原提呈细胞提呈的抗原信息，同时还需多种辅助分子提供的共刺激信号。ＣＤ２８／ＣＴＡＬ４：Ｂ７介导的共刺激信号在ＣＤ４ Ｔ细胞激活、ＣＤ８Ｔ细胞杀伤活性的诱导和效应过程中起重要作用。本文综述了ＣＤ２８／ＣＴＬＡ：Ｂ７的分子特性，在Ｔ细胞激活、效应过程中的共刺激作用，ＣＤ２８介导的信号传导途径及在肿瘤免疫、移植免疫研究中的意义。     

CD28共刺激信号的传导途径

目前大量实验已证实ＣＤ２８和ＣＴＬＡ４与其配体Ｂ７家族分子结合后所产生的共刺激信号在Ｔ细胞活化过程中起重要作用。关于ＣＤ２８和ＣＴＬＡ－４信号传导的分子机制的研究正受到重视。由于ＣＴＬＡ－４的功能尚待进一步确定，信号传导方面的资料又较少，本文仅就ＣＤ２８信号的启动、信号传导中涉及的分子作一综述，并将ＣＤ２８共刺激途径与ＴＣＲ途径进行了简略比较。     

CD28／CTLA4：B7在T细胞激活和效应过程中的共刺激作用

抗原特异性Ｔ细胞的激活需要ＴＣＲ－ＣＤ３复合体接受抗原提呈细胞提呈的抗原信息，同时还需多种辅助分子提供的共刺激信号。ＣＤ２８／ＣＴＡＬ４：Ｂ７介导的共刺激信号在ＣＤ４Ｔ细胞激活、ＣＤ８Ｔ细胞杀伤活性的诱导和效应过程中起重要作用。本文综述了ＣＤ２８／ＣＴＬＡ：Ｂ７的分子特性，在Ｔ细胞激活、效应过程中的共刺激作用，ＣＤ２８介导的信号传导途径及在肿瘤免疫、移植免疫研究中的意义。     

类风湿关节炎患者外周血及滑膜液X型胶原反应性

目的：探讨类风湿关节炎（ＲＡ）患者体内是否存在抗Ｘ型胶原Ｂ细胞反应。方法：以ＥＬ－４ ＯＵ^rＢＵ^r／ｒＩＬ－２／ＰＭＡ作为刺激系统,通过酶联斑点技术检测抗Ｘ型胶原免疫球蛋白分泌Ｂ细胞（ａｎｔｉ－ＨＣＸ ＩＳＣ）频率。结果：２８例ＲＡ患者滑漠中１１例出现ａｎｔｉ－ＨＣＸ ＩＳＣ,而对照组骨性关节炎（ＯＡ）患者滑膜液中则未检测到ａｎｔｉ－ＨＣＸ ＩＳＣ。ＲＡ患者外周血主滑漠液ＣＤ１９^ 及ＣＤ２０^ 细胞     

类风湿关节炎患者外周血及滑膜液Ⅹ型胶原反应性B细胞检测及其特异性分析

目的：探讨类风湿关节炎（ＲＡ）患者体内是否存在抗Ⅹ型胶原Ｂ细胞反应。方法：以ＥＬ４ＯＵｒＢＵｒ／ｒＩＬ２／ＰＭＡ作为刺激系统,通过酶联斑点技术检测抗Ⅹ型胶原免疫球蛋白分泌Ｂ细胞（ａｎｔｉＨＣⅩＩＳＣ）频率。结果：２８例ＲＡ患者滑膜中１１例出现ａｎｔｉＨＣⅩＩＳＣ,而对照组骨性关节炎（ＯＡ）患者滑膜液中则未检测到ａｎｔｉＨＣⅩＩＳＣ。ＲＡ患者外周血及滑膜液ＣＤ１９＋及ＣＤ２０＋细胞百分率于刺激前后无明显变化,但ＣＤ５＋Ｂ细胞百分率却明显增加,外周血刺激前后分别为１７．０±６．０,２７．０±９．０,滑膜液分别为８．０±３．２,１６．０±６．０。结论：（１）ＲＡ患者体内存在抗Ⅹ型胶原Ｂ细胞反应,（２）ＣＤ４＋ＥＬ４ＯＵｒＢＵｒ／ｒＩＬ２／ＰＭＡ是激活ＣＤ５＋自身抗体产生Ｂ细胞的有效方法。     

CTLA41Ig对丝裂原诱导的淋巴细胞反应的影响

本研究证明ＣＴＬＡ４Ｉｇ一Ｂ７分子结合后，可以阻断Ｂ７与ＣＤ２８的结合。ＣＴＬＡ４Ｉｇ可以掏丝黎明原所解发淋巴细胞的增殖反应，同时抑制细胞因子ＩＬ－２，ＩＬ－４的产生以及ＩＬ－２Ｒ的表达。表明ＣＴＬＡ４Ｉｇ可以通过不同的途径影响Ｔ淋巴细胞的活化。     

系统性红斑狼疮患者CD28表达及其意义

ＣＤ２８是Ｔ细胞激活中重要的共刺激分子。为了解Ｂ７－Ｃ礤刺激途径在系统性红斑狼疮（ＳＬＥ）中的作用，我们对３０例期ＳＬＥ２外周血Ｔ细胞ＣＤ２８的表达进行了检测，并分析了其激活后凋亡情况。结果表明，ＳＬＥ组的ＣＤ２８Ｔ细胞低于正常对照组，在抗ＣＤ３单抗刺激后ＣＤ２８细胞凋亡率增加。这提示ＳＬＥ中Ｂ７－ＣＤ２８共刺激途径介导的ＡＩＣＤ可能导致ＳＬＥ中的Ｔ细胞淋巴细胞贫血症。     

癫痫患者血液和脑脊液免疫异常在其发病机制中的作用

对７２例癫痫患者血液中的ＩｇＧ，ＩｇＡ，ＩｇＭ，Ｃ３，ＣＩＣ，白蛋白，ＣＤ４＾＋细胞，ＣＤ８＾＋细胞和脑脊液中的ＩｇＧ进行检测，并计算ＣＤ４＾＋／ＣＤ８＾＋比值，ＣＳＦ－ＩｇＧ／Ｓ－ＩｇＧ比率，ＣＳＦ－ＡＬＢ／Ｓ－ＡＬＢ比率和ＩｇＧ指数。结果表明癫痫组血液中的５项参数对比照组低，尤其是原发性和末治疗亚组。而ＣＳＦ呈现病理性的免疫增强反应，表现为原发性亚组ＩｇＧ合成，而继发性亚组患者存在血脑屏障功能     

B7／CD28和ICAM—1／LFA—1共刺激信号对T及B细胞功？…

目的 研究共刺激途径Ｂ７／ＣＤ２８和ＩＣＡＭ－１／ＬＦＡ－１对Ｔ细胞活化以及Ｂ细胞效应的作用。方法 在体外建立ＡＰＣ：Ｔ：Ｂ细胞反应系统,用Ｂ７－１单抗和ＩＣＡＭ－１单抗分别阻断Ｂ７／ＣＤ２８和ＩＣＡＭ－１／ＬＦＡ－１共刺激途径,利用＾３Ｈ－ＴｄＲ法检测Ｔ细胞增殖,ＥＬＩＳＡ法测定Ｂ细胞分泌的杭体,用ＲＴ－ＰＣＲ法检测细胞因子基因的表达。结果 Ｂ７－１单抗和ＩＣＡＭ－１单坑均可抑制Ｔ细胞增殖及ＩＬ     

类风湿关节炎患者外周血与滑膜液Ⅰ,Ⅱ,Ⅸ,Ⅹ,Ⅺ …

目的 探讨抗不同类型胶原Ｂ细胞瓜在类风湿关节炎（ＲＡ）出现的意义。方法 以ＥＬ－４ＯＵｒＢＵｒ／ｒＩＬ－２／ＰＭＡ作为刺激系统,应用酶联斑点技术,检测抗Ⅰ、Ⅱ、Ⅸ、Ⅹ、Ⅺ型胶原免疫球蛋白分泌细胞（ａｎｔｉ－ＨＣⅡ ＩＳＣ）。结果 ２８例ＰＡ患者外周血及滑膜液中２１例出现ａｎｔｉ－ＨＣⅡＩＳＣ,Ⅰ、Ⅸ、Ⅹ、Ⅺ型胶原反应性Ｂ细胞阳性者分别为５、６、１１及９例。虽然对某种胶原的反应水平与抗其它型胶原反应     

Anti-ICAM-1 antibody and CTLA-4Ig synergistically enhance immature dendritic cells to induce donor-specific immune tolerance in vivo

Immature dendritic cells (DC) have been demonstrated to induce T-cell hyporesponsiveness in vitro and immune tolerance in vivo. However, immature DC (iDC) may become mature once infused in vivo, thus limiting the prolongation of the allograft survival. Considering that mature DC express high level of B7, intercellular adhesion molecule-1 (ICAM-1), and T-cell activation needs costimulation signals provided by DC, we selected anti-ICAM-1 mAb and cytotoxic T lymphocyte antigen-4Ig fusion protein (CTLA-4Ig) for in vivo administration to block costimulation pathways in order to further improve the efficacy of iDC to induce immune tolerance. Seven days before allogeneic cardiac transplantations, the recipients were intravenously (i.v.) pretreated of donor-derived iDC with or without simultaneous injections of anti-ICAM-1 mAb and CTLA-4Ig. CTLA-4Ig or anti-ICAM-1 mAb administration alone resulted in significant prolongation of cardiac allograft survival induced by iDC. When used simultaneously, CTLA-4Ig and anti-ICAM-1 mAb induced permanent allografts acceptance even in 90% recipients. The recipients could keep the skin alive for a longer time in the donor-specific second transplantation, but no effect was observed on the skin from C3H third-party mice. The efficient induction of donor-specific tolerance observed above may be related to the more potent inhibition of donor-specific T-cell responses including cytotoxicity activity, Th1 cytokines production, and alloantibody production by the combined use of anti-ICAM-1 mAb and CTLA-4Ig. Our data suggest that anti-ICAM-1 antibody and CTLA-4Ig can synergistically enhance iDC to induce donor-specific immune tolerance in vivo.     

Effect of CTLA-4 chimeric protein on rat autoimmune anti-glomerular basement membrane glomerulonephritis

The interaction of the T cell receptor with the antigen/major histocompatibility class II complex is insufficient to induce optimal T cell activation. Co-stimulatory signals, including those provided by CD28/CTLA-4 on T cells and B7 molecules (B7-1, ?2 and ?3) on antigen-presenting cells, are also required. CD28-B7 interactions can be blocked by a soluble human CTLA-4 chimeric protein (CTLA4Ig). We tested the effect of administration of CTLA4Ig on experimental anti-glomerular basement membrane (GBM) autoimmune glomerulonephritis in Wistar-Kyoto rats induced by immunization with bovine GBM. The disease is characterized by development of antibody to the α3 chain of type IV collagen (Goodpasture's antigen), deposition of rat IgG in GBM, infiltration of the kidney by T cells and macrophages, severe crescent formation and renal failure leading to death in 5–6 weeks. Animals injected with human CTLA4Ig from day 0 to day 14 or to day 35 had reduced disease severity. Beneficial effects were observed even when injections were begun after the onset of glomerulonephritis on day 14. However, the rats developed antibody to the human CTLA4Ig, associated with reduction in levels of circulating CTLA4Ig. The results provide evidence for CD28/CTLA-4 signaling in rat autoimmune glomerulonephritis, and suggest that more effective inhibition of B7-dependent T cell activation, such as might be achieved with homologous CTLA4Ig, could be useful in the treatment of autoimmune diseases.     

细胞毒性T淋巴细胞相关抗原4的研究进展

细胞毒性T淋巴细胞相关抗原4（CTLA-4）属于B7／CD28家族成员，具有下调免疫应答为主的多种免疫学效应。CTLA-4有多个位点基因多态性，其基因多态性可影响CTLA-4分子的表达和功能，同某些免疫因素相关性疾病有关。CTLA-4可表达于免疫细胞为主的多种细胞，有膜结合和可溶性等两种形式。CTLA-4Ig和抗单抗是CTLA-4用于防治自身免疫性疾病、移植排斥及肿瘤的两种分子，其效能在动物试验及临床应用中已得到证实.     

CD28/CTLA-4/B7 and CD40/CD40L costimulation and activation of regulatory T cells

Costimulatory signals are crucial for T cell activation. Attempts to block costimulatory pathways have been effective in preventing unwanted immune reactions. In particular, blocking the CD28/cytotoxic T lymphocyte antigen(CTLA)-4/B7 interaction(using CTLA-4Ig) and the CD40/CD40 L interaction(using anti-CD40 L antibodies) prevents T cell mediated autoimmune diseases, transplant rejection and graft vs host disease in experimental models. Moreover, CTLA-4Ig is in clinical use to treat rheumatoid arthritis(abatacept) and to prevent rejection of renal transplants(belatacept). Under certain experimental conditions, this treatment can even result in tolerance. Surprisingly, the underlying mechanisms of immune modulation are still not completely understood. We here discuss the evidence that costimulation blockade differentially affects effector T cells(Teff) and regulatory T cells(Treg). The latter are required to control inappropriate and unwanted immune responses, and their activity often contributes to tolerance induction and maintenance. Unfortunately, our knowledge on the costimulatory requirements of Treg cells is very limited. We therefore summarize the current understanding ofthe costimulatory requirements of Treg cells, and elaborate on the effect of anti-CD40 L antibody and CTLA-4Ig treatment on Treg cell activity. In this context, we point out that the outcome of a treatment aiming at blocking the CD28/CTLA-4/B7 costimulatory interaction can vary with dosing, timing and underlying immunopathology.     

The clinical utility of inhibiting CD28-mediated costimulation

Summary:  This volume covers many topics in the field of T-cell costimulation. The need for such a volume is testament to the growth of the field. From its beginning as a concept in the 1980s, we have now progressed to the point where many molecules now have functionally defined roles in T-cell costimulation. In addition, the field has progressed 'from bench to bedside'. Abatacept [cytotoxic T-lymphocyte antigen-4 (CTLA-4)-immunoglobulin (Ig) (CTLA-4-Ig)], an inhibitor of CD28-mediated T-cell costimulation, was approved for the treatment of moderate-to-severe rheumatoid arthritis in 2006 by the Food and Drug Administration and in 2007 by the European Medicines Agency. This chapter first presents a personal historical perspective on the early basic studies on the elucidation of the CD28/B7 T-cell costimulatory pathway and the discovery of CTLA-4-Ig. We next present an overview of studies of CTLA-4-Ig in preclinical animal studies. The material discussed in these first two sections is selective rather than exhaustive; their purpose is to provide context for the final section, a summary of human clinical studies performed with abatacept.     

共刺激分子CTLA-4的研究进展及在风湿病治疗中的应用

细胞毒T淋巴细胞抗原-4(CTLA-4)是免疫应答反应起始阶段T细胞活化的重要共同活化分子,它与T细胞表面的配体结合后可以抑制T细胞功能,使T细胞不能被激活,从而抑制免疫反应的发生。在多种风湿病中都发现有CTLA-4等位基因异常和蛋白表达异常。CTLA-4免疫球蛋白(CTLA-4 Ig)是针对CTLA-4的融合蛋白,能选择性地抑制免疫反应,改善患者的临床症状,达到控制疾病进展的目的。但目前的临床研究尚仅限于类风湿关节炎。临床研究的初步结果表明CTLA-4 Ig治疗类风湿关节炎是有效而安全的,但由于其临床应用时间短,在风湿病治疗中的作用还有待进一步的长期临床观察来证实。     

Efficient expansion of regulatory T cells in vitro and in vivo with a CD28 superagonist

CD4(+)CD25(+) T cells play a central role in the suppression of autoimmunity and inflammation, making their in vivo expansion a highly attractive therapeutic target. By phenotyping with a novel rat CTL antigen-4 (CTLA-4)-specific monoclonal antibody (mAb) and functional in vitro assays, we here first establish that rat CD4(+)CD25(+) T cells correspond to the regulatory T cells (Treg cells) described in mice and humans: they constitutively express CTLA-4, produce IL-10 but not IL-2, and are able to suppress the proliferation of costimulated CD25-negative indicator cells. Furthermore, we show that rat Treg cells respond less well than CD25(-) T cells to conventional costimulation, but are readily expanded in vitro with "superagonistic" CD28-specific mAb which are potent mitogens for all T cells without the need for TCR engagement. In vivo, functional Treg cells are preferentially expanded by CD28 stimulation over other T cell subsets, leading to a 20-fold increase within 3 days in response to a single antibody dose. These data suggest that CD28-driven activation of Treg cells may be highly effective in the treatment of inflammatory and autoimmune diseases.     

Quantitative analysis predicts the relative therapeutic efficacy of different forms of CTLA4Ig

Modulating the activities of costimulatory molecules controlling immune responses holds considerable promise for immunotherapy. CTLA4Ig (abatacept), a soluble version of the T cell-expressed membrane receptor CTLA-4, is approved for the treatment of rheumatoid arthritis. Like natural CTLA-4 molecules, CTLA4Ig ligates B7-1 and B7-2 on antigen presenting cells, preventing CD28-mediated costimulation of T cells. However, CTLA4Ig can also prevent ligation of CTLA-4, potentially blocking vital inhibitory signals, thereby augmenting immunity. There have been no quantitative analyses of the likely effects of CTLA4Ig on costimulatory interactions at the immunological synapse. We present a mathematical model, based on rigorous biophysical and expression data, for simulating the effects of abatacept and a mutated derivative, LEA29Y, on the synaptic interactions of CD28 and CTLA-4. The simulations reveal an unexpectedly large window within which CD28, but not CTLA-4, ligation is blocked by CTLA4Ig, perhaps explaining the efficacy of abatacept at the recommended therapeutic dose (10 mg/kg) and its relative safety. However, the simulations suggest that the present dosing regimen is close to the maximum theoretically safe dose. The simulations also show that, within the therapeutic window, LEA29Y enhances the interaction of CTLA-4 with the more potent of its two native ligands, B7-1. They also suggest that CTLA-4 ligation by B7-1 could, in principle, be enhanced by further decreasing the off-rate of CTLA4Ig for binding to B7-2. Our findings therefore offer molecular explanations for why LEA29Y might prove to be more effective than abatacept in a clinical setting, and suggest ways in which its therapeutic efficacy could be further optimised.     

Cytotoxic T lymphocyte-associated antigen-4 inhibits integrin-mediated stimulation

The negative role exerted by cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) in the regulation of T-cell activity, as induced by T-cell receptor (TCR)/CD3 and CD28 costimulation, has been widely described. In the present work we investigated the role of CTLA-4 in the control of cell activation, as induced by costimulation of the adhesion molecule lymphocyte function-associated antigen-1 (LFA-1) in murine CD4+ T cells. Results show that CTLA-4 engagement inhibits interleukin-2 (IL-2) production, not only when induced by CD3/CD28 costimulation, but also when CD4+ T cells are costimulated by anti-CD3 and anti-LFA-1 monoclonal antibodies (mAbs). LFA-1 has been described to induce Ca2+ mobilization also in the absence of TCR engagement. Moreover, we found that CTLA-4 engagement negatively affects Ca2+ mobilization and NF-AT activation, as induced by LFA-1 engagement alone. PLCgamma1 phosphorylation was also dampened within minutes after CTLA-4 engagement. Altogether these data indicate that through the control of signals induced by different receptors, CTLA-4 could be a global attenuator of T-cell activation.