B7家族的新成员-B7-H1、B7-H2、B7-H3、B7-DC

T细胞的活化需要TCR与抗原肽-MHC的第一信号,以及共刺激因子的第二信号系统.B7家族是重要的共刺激分子,属于免疫球蛋白家族.除B7-1和B7-2外,近几年又发现了B7家族的新成员--B7-H1、B7-H2、B7-H3、B7-DC等,与T、B细胞的活化及免疫应答等有关.深入研究B7家族成员的结构和作用机制,有助于T、B细胞活化机制以及免疫耐受、肿瘤免疫研究的深入和发展.     

B7家族的新成员—B7-H1、B7-H2、B7-H3、B7-DC

T细胞的活化需要TCR与抗原肽-MHC的第一信号，以及共刺激因子的第二信号系统。B7家族是重要的共刺激分子，属于免疫球蛋白家族。除B7-1和B7-2外，近几年又发现了B7家族的新成员——B7-H1、B7-H2、B7-H3、B7-DC等，与T、B细胞的活化及免疫应答等有关。深入研究B7家族成员的结构和作用机制，有助于T、B细胞活化机制以及免疫耐受、肿瘤免疫研究的深入和发展。     

B7家族成员的研究新进展

B7分子属免疫球蛋白超家族成员,表达于多种免疫细胞和非免疫细胞上.抗原提呈细胞表面的B7分子与T细胞上的相应受体结合可提供T细胞活化的第二信号,从而调节和控制T细胞的活化、增殖及免疫应答.B7家族成员在感染、肿瘤以及自身免疫性疾病等发病机制中起着关键作用.选择性阻断协同刺激分子有望能成为临床治疗这些疾病的一种新途径.近...     

B7-H3——肿瘤免疫治疗的新热点

B7-H3是新近发现的共刺激分子B7家族的一个新成员,在T细胞介导的免疫反应中起重要的调节作用。B7-H3蛋白质在正常组织、细胞中不表达或极低表达,却高表达于多种肿瘤组织,并与肿瘤的进展、患者的生存及预后密切相关。有研究发现该分子可能是通过与髓样细胞触发受体家族成员TLT-2结合发挥作用,但确切的作用机制尚不完全清楚。目前认为B7-H3在肿瘤免疫中的作用存在争议,一方面它可以发挥共刺激作用,增加IFN-γ及TNF-α等细胞因子的分泌,增强CTL活性,提高机体抗肿瘤免疫反应。另一方面,它还能够抑制CD4+T淋巴细胞活化以及IFN-γ及IL-4等细胞因子的产生,发挥共抑制作用。进一步研究B7-H3的生物学作用将为肿瘤免疫中T细胞介导的免疫应答调控提供新的免疫治疗前景。本文就B7-H3与肿瘤关系及其在肿瘤免疫中的作用作一综述。     

005 可诱导共刺激分子的研究进展

可诱导共刺激分子(Inducible Costimulatory Molecule,ICOS)是新发现的表达于活化T细胞的共刺激分子,属CD28/CTLA-4家族.ICOS的小鼠配体B7RP-1和人类配体B7-H2具有不同的表达形式和条件.人类ICOS通路可被抗原-TCR信号和IL-2激活.该共刺激通路诱导T细胞分化、增殖并分泌IL-4、IL-10、IFN-γ和TNF-γ等细胞因子,对B细胞和CTL细胞免疫应答也有一定的影响.阻断ICOS通路会引起T细胞凋亡.ICOS与CD28通路无功能交叉性,在免疫应答过程中具有重要而且独特的作用.     

树突状细胞表达的PD-L1的研究进展

树突状细胞（DC）是专职的抗原提呈细胞,通过表达多种免疫调节分子在调节T细胞免疫反应中起关键作用。其表达的PD-L1是近年来新发现的B7家族的负性共刺激分子,与其相应受体结合,能够传递负性刺激信号导致T细胞反应无力,抑制细胞因子的分泌,诱导活化T细胞凋亡,最终诱导免疫耐受,介导肿瘤免疫逃逸,并在自身免疫性疾病,病毒,细菌感染等免疫反应中起重要作用。     

可诱导共刺激分子的研究进展

可诱导共刺激分子 (InducibleCostimulatoryMolecule ,ICOS)是新发现的表达于活化T细胞的共刺激分子 ,属CD2 8/CTLA 4家族。ICOS的小鼠配体B7RP 1和人类配体B7 H2具有不同的表达形式和条件。人类ICOS通路可被抗原 TCR信号和IL 2激活。该共刺激通路诱导T细胞分化、增殖并分泌IL 4、IL 10、IFN γ和TNF γ等细胞因子 ,对B细胞和CTL细胞免疫应答也有一定的影响。阻断ICOS通路会引起T细胞凋亡。ICOS与CD2 8通路无功能交叉性 ,在免疫应答过程中具有重要而且独特的作用。     

PD-L1分子与疾病免疫调节

PD-LI(曾命名为B7-H1)是迄今发现的B7家族中较新的共刺激分子,与T细胞上的配体(PD-1)结合后可调节T细胞的活化及分化.它通过激活初始T细胞、抑制活化的效应T细胞及调节细胞因子的分泌等而参与多种免疫过程.以PD-L1为靶点的免疫调节与动物器官移植排斥反应、自身免疫性疾病、慢性病毒感染、肿瘤免疫逃逸等疾病的发生、发展密切相关.本文就PD-LI在上述疾病中发生、发展及治疗中的作用做一综述.     

调节性B细胞与自身免疫性疾病

以往认为,B细胞通过产生特异性抗体提呈抗原产生共刺激分子活化T细胞、并通过细胞因子发挥免疫作用.但是近年来研究发现,B细胞对免疫应答和炎性反应有调节作用,这种B细胞被命名为调节性B细胞(Br).Br通过分泌调节性的细胞因子IL-10和TGF-β影响B细胞和致病性T细胞之间的相互作用而抑制病理性免疫反应.因而了解Br的生物学功能、活化机制以及在自身免疫性疾病中的作用具有重要意义.     

协同刺激分子B7-H3在消化系统疾病中的研究进展

<正>T细胞介导的免疫应答在机体特异性识别和清除内、外源性抗原过程中起重要作用,T细胞的活化增殖分化有赖于双重信号,其中抗原递呈细胞上的MHC-抗原肽复合体与TCR特异性结合传递第一信号,而B7-CD28等共刺激家族传递第二信号,由此决定了T细胞的状态是增强、抑制、弱化或者演变为无反应状态。共刺激分子如B7-CD28家族对T细胞的正负调节作用已成为研究的热点领域。B7家     

B/T淋巴细胞间抑制信号研究进展

B7-CD28家族共刺激信号分子在T淋巴细胞激活、抑制机体耐受及产生理想的T细胞免疫应答等方面起着关键作用。B7-CD28家族共信号分子已经被集中的研究,并且引起免疫调控领域充分的重视。CD80/CD86/CD28/CTLA-4经典途径的新功能的发现以及这一家族包括B7-H1/B7-DC/PD-1,B7-H2/ICOS,B7-H4和BTLA的新途径的确定,都拓宽了我们对T细胞介导的免疫应答和免疫耐受调控的理解。本文就CTLA-4、PD-1和BTLA对T细胞应答的负性调节以及在维持外周耐受中起作用的研究进展作一综述。     

新型共刺激分子B7-H4在肿瘤免疫中的研究进展

B7-H4是共刺激分子B7家族的最新成员,是B7家族相关的第3个T细胞抗原特异性反应的负性调控分子,在CD4^＋、CD8^＋T细胞的分化发育、细胞周期的进展以及细胞因子的产生方面发挥广泛的抑制效应。B7-H4途径在器官特异性自身免疫病、病毒感染、移植耐受和肿瘤免疫逃避等方面可能具有重要的作用,因而对B7-H4在肿瘤免疫逃避中发挥的作用的深人研究可以为肿瘤的生物学诊断及治疗策略提供一个新的方向。     

New checkpoints in cancer immunotherapy

Immune responses must be fine-tuned to allow effective clearance of invading pathogens, while maintain tolerance to self-antigens. T cells are the major effector cells for fighting and killing tumor cells. Immune checkpoints play a pivotal role in T cell activation, and determine the functional outcome of T cell receptor (TCR) signaling. The blockade of immune checkpoints CTLA-4 and PD-1 has already been one of the most successful cancer immunotherapies. In this review, we will focus on three novel inhibitory B7 family checkpoint molecules, B7-H3, B7S1 and VISTA. The aim of this article is to summarize their expressions in tumors as well as their roles in controlling and suppressing T cell immune responses and anti-tumor immunity. These pathways may be explored in future cancer immunotherapy.     

Co-inhibitory role of T-cell-associated B7-H1 and B7-DC in the T-cell immune response

B7-H1 and B7-DC expressed on antigen-presenting cells inhibit the T-cell response via the PD-1 counter-receptor on T cells, and co-stimulate T-cell immunity under certain conditions via an unidentified co-stimulatory receptor. However, little is known about the functional consequence of T-cell-associated B7-H1 or B7-DC in the T-cell immune response. Therefore, we evaluated the physiological role of B7-H1 and B7-DC expressed on T cells in terms of cell proliferation and cytokine production by alloreactive T cells. We found that PD-1, B7-H1, and B7-DC were up-regulated in alloreactive CD4(+) and CD8(+) T cells in vitro and in vivo. In the alloreactive T-T model, blockade of the B7-H1:PD-1 or B7-DC:PD-1 pathways significantly increased the proliferation, and IFN-gamma and IL-2 production of alloreactive T cells, although it did not affect the production of other cytokines, including IL-4, IL-10, and IL-12. The data indicate that T-cell-associated B7-H1 and B7-DC negatively regulate the T-cell response via the T-T interaction.     

Intact B7-H3 signaling promotes allograft prolongation through preferential suppression of Th1 effector responses

Ligands of the B7 family provide both positive and negative costimulatory signals to the CD28 family of receptors on T lymphocytes, the balance of which determines the immune response. B7-H3 is a member of the B7 family whose function in T-cell activation has been the subject of some controversy: in autoimmunity and tumor immunity, it has been described as both costimulatory and coinhibitory, while in transplantation, B7-H3 signaling is thought to contribute to graft rejection. However, we now demonstrate results to the contrary. Signaling through a putative B7-H3 receptor prolonged allograft survival in a fully MHC-mismatched cardiac model and promoted a shift toward a Th2 milieu; conversely, B7-H3 blockade, achieved by use of a blocking antibody, resulted in accelerated rejection, an effect associated with enhanced IFN-γ production. Finally, graft prolongation achieved by CTLA4 Ig was shortened both by B7-H3 blockade and the absence of recipient B7-H3. These findings suggest a coinhibitory role for B7-H3. However, experience with other CD28/B7 family members suggests that immune redundancy plays a crucial role in determining the functions of various pathways. Given the abundance of conflicting data, it is plausible that, under differing conditions, B7-H3 may have both positive and negative costimulatory functions.     

Targeting the B7 Family of Co-Stimulatory Molecules

As more patient data is cross-referenced with animal models of disease, the primary focus on T_h1 autoreactive effector cell function in autoimmune diseases, such as rheumatoid arthritis and multiple sclerosis, has shifted towards the role of T_h17 autoreactive effector cells and the ability of regulatory T cells (T_reg) to modulate the pro-inflammatory autoimmune response. Therefore, the currently favored hypothesis is that a delicate balance between T_h1/17 effector cells and T_reg cell function is critical in the regulation of inflammatory autoimmune disease. An intensive area of research with regard to the T_h1/17:T_reg cell balance is the utilization of blockade and/or ligation of various co-stimulatory or co-inhibitory molecules, respectively, during ongoing disease to skew the immune response toward a more tolerogenic/regulatory state. Currently, FDA-approved therapies for multiple sclerosis patients are all aimed at the suppression of immune cell function. The other favored method of treatment is a modulation or deletion of autoreactive immune cells via short-term blockade of activating co-stimulatory receptors via treatment with fusion proteins such as CTLA4-Ig and CTLA4-FasL. Based on the initial success of CTLA4-Ig, there are additional fusion proteins that are currently under development. Examples of the more recently identified B7/CD28 family members are PD-L1, PD-L2, inducible co-stimulatory molecule-ligand (ICOS-L), B7-H3, and B7-H4, all of which may emerge as potential fusion protein therapeutics, each with unique, yet often overlapping functions. The expression of both stimulatory and inhibitory B7 molecules seems to play an essential role in modulating immune cell function through a variety of mechanisms, which is supported by findings that suggest each B7 molecule has developed its own indispensable niche in the immune system. As more data are generated, the diagnostic and therapeutic potential of the above B7 family-member-derived fusion proteins becomes ever more apparent. Besides defining the biology of these B7/CD28 family members in vivo, additional difficulty in the development of these therapies lies in maintaining the normal immune functions of recognition and reaction to non-self-antigens following viral or bacterial infection in the patient. Further complicating the clinical translation of these therapies, the mechanism of action identified for a particular reagent may depend upon the method of immune-cell activation and the subset of immune cells targeted in the study.     

B7-H1 and B7-H4 expression in colorectal carcinoma: Correlation with tumor FOXP3 regulatory T-cell infiltration

B7-H1 and B7-H4 are newly discovered members of the B7-CD28 family. They can inhibit T cell activation and proliferation and regulate T cell immune response negatively. Both B7-H1 and B7-H4 are expressed in many tumors and are classified as co-inhibitors of cell-mediated immunity. FOXP3⁺ regulatory T cells (Tregs) play an important role in the maintenance of tumor immunity tolerance. However, the implication of B7-H1 and B7-H4 expression and their interaction with Tregs infiltration in colorectal cancer are unknown. The present study aimed to determine the expression of B7-H1 and B7-H4 as well as Tregs infiltration in colorectal cancer and to explore the clinical and pathological implication of suppressor immune cells and molecules. Frozen sections and immunohistochemical assay were undertaken to assess B7-H1, B7-H4 expression and Tregs infiltration in fresh specimens collected from 56 patients with colorectal carcinoma. The results showed that expression of B7-H1 and B7-H4 in colorectal carcinoma tissues was significantly higher than in adjacent normal mucosa (P < 0.001). B7-H1 expression was positively correlated to the infiltration depth, lymph node metastasis and advanced Duke's stage (P < 0.05, P < 0.05 and P < 0.05, respectively), whereas B7-H4 expression was positively related to the infiltration depth and lymph node metastasis (P < 0.01 and P < 0.05, respectively). Furthermore, Tregs infiltration was more frequent in tumor tissue than in adjacent normal mucosa and was associated with poor differentiation and positive lymph node metastasis (P < 0.01, and P < 0.01, respectively). The statistical analysis indicated a significant correlation between Tregs infiltration and B7-H1 or B7-H4 expression respectively. These results suggest that over-expression of B7-H1 and B7-H4 has stronger prognostic significance and promote tumor tolerance, and they might contribute to Tregs development in the colorectal carcinoma tolerogenic milieu.     

B7-H1/PD-1共刺激途径与病毒感染

B7-H1及其受体PD-1是共刺激分子B7-CD28家族的重要成员.B7-H1在淋巴组织及外周非淋巴组织广泛诱导性表达,PD-1则主要表达在活化的T细胞、B细胞及髓系细胞表面.B7-H1/PD-1共刺激途径主要作用是负性调节T、B细胞的免疫反应,参与维持外周组织的免疫耐受.病毒感染可以上调B7-H1及PD-1的表达,抑制病毒特异性T细胞的免疫功能,B7-H1/PD-1途径是病毒逃避免疫监视,引发慢性感染的重要通路,因而阻断B7-H1/PD-1共刺激途径能够恢复病毒特异性T细胞的功能,清除病毒感染,这对于病毒感染的免疫治疗,尤其是病毒慢性感染的免疫治疗具有重要意义.     

Soluble B7-H1: differences in production between dendritic cells and T cells

Tumor cells aberrantly express several T cell inhibitory molecules including members of the B7-H co-regulatory family. Presumably tumor-expressed B7-H1 and B7-H3 confer resistance to elimination by the immune system. In addition, elevated levels of soluble B7-H1 (sB7-H1) has been identified in the sera of cancer patients, including renal carcinoma patients and is associated with increased cancer related death. Here we report that sB7-H1 is produced and released by activated mature dendritic cells (mDC). Immature DC, macrophages, monocytes, or T cells are refractory to releasing sB7-H1. Exposure of CD4+ and CD8+ T cells to mDC-derived sB7-H1 molecules induced apoptosis. These data suggest that the immunobiology of B7-H1 is perhaps more complex than previously thought. sB7-H1 molecules may represent an unanticipated contributing factor to immune homeostasis. That both immune and tumor cells can be sources of sB7-H1 suggests that optimization of co-regulatory blockade immunotherapy for solid malignancies of necessity will require impact of targeting tumor and immune-derived B7-H1 molecules.