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免疫反应调节Immune Response Modulation) S. O% |$ i, G$ `3 S) o8 }8 _: Q9 M
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多数肿瘤表达的抗原可能引起免疫反应,这是因为它们表达了引起特异性表位的变异蛋白。 然而在绝大多数的肿瘤病例中,可以通过有效地抑制肿瘤微环境中的免疫反应而避免被排斥(Muller and Scherle, 2006; Zou, 2005)。 虽然不是一个压力表型,这是一个能用于逆转这个标志的NOA的例子。多个机制可以保护肿瘤细胞逃避免疫监督。肿瘤细胞可以下调主要组织相容性复合物(MHC)分子的表达来减少抗原递呈(Garrido and Algarra, 2001)。" {- x8 u; D" ^ ]4 U
肿瘤细胞也可以合成和释放如炎症趋化因子之类的免疫调节因子(如CCL2),细胞因子(如 IL6和 IL10), 和前列腺素(如PGE2)以抑制细胞毒性T细胞的活性(Sharma et al., 2005)。 而且,肿瘤微环境中的关键性代谢产物的耗损,如葡萄糖,也会抑制细胞毒性T细胞的伸展(Muller and Scherle, 2006) .+ `: z- g! k; z" V! |5 @ _- I; i
肿瘤对“免疫抑制”NOA基因的依赖可以开发以得到治疗获益。例如环氧化酶2(COX2)抑制剂塞来考昔,以阻滞PGE2合成,已经表明它可以在荷瘤鼠中增强免疫反应(Stolina et al., 2000)。表达在肿瘤细胞中的MHC基因再激活使MHC下调,可能是通过抑制组蛋白脱乙酰基酶(HDAC)或转录抑制物,也是另外一个增强肿瘤免疫监督的方式。 在应用抗CTLA-4抗体干扰抑制性T细胞的研究中显示可以明显增强针对肿瘤抗原的主动免疫,这提供了另一个NOA样治疗的例子(Peggs et al., 2008)。重建抗肿瘤免疫的最大吸引力是它可以在多种肿瘤类型中以一种系统的方式应用,并且使免疫系统能在相对早期检测与消灭肿瘤。
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" Z N9 w' S4 h: ]- [+ MImmune Response Modulation
8 [/ A% \, o2 S Most tumors express antigens that could potentially elicit an immune response due to the expression of a mutant protein that gives rise to a novel epitope. However, in the vast majority of cases tumors are able to prevent rejection by effectively suppressing an immune response in the tumor microenvironment (Muller and Scherle, 2006; Zou, 2005). Although not a 9 H* z4 v! F+ i: }( `- e6 }1 y# r
stress phenotype, there are examples of NOA that can be used to reverse this hallmark. Several mechanisms protect tumor cells from immune surveillance. Tumor cells can down regulate the expression of major istocompatibility complex (MHC) molecules to reduce antigen presentation (Garrido and Algarra, 2001). Tumor cells also synthesize and release a num-
1 U0 t3 |2 J+ ]7 D7 C* xber of immunomodulatory factors such as chemokines (e.g., CCL2), cytokines (e.g., IL6 and IL10), and prostaglandins (e.g., PGE2) to suppress the activation of cytotoxic T cells (Sharma et al., 2005). Furthermore, the depletion of key metabolites in the tumor microenvironment, such as glucose, also inhibits cytotoxic T cell expansion (Muller and Scherle, 2006) .
1 R# X N6 T% S P5 gThe tumor’s addiction to “immunosuppressive” NOA genes could be exploited for therapeutic gains. For example, the cycloxygenase-2 (COX2) inhibitor celecoxib, which blocks PGE2 synthesis, has been shown to enhance immune response to tumors in mice (Stolina et al., 2000). Reactivating MHC gene expression in tumor cells that have downregulated MHC, perhaps by inhibiting a histone deacetylase (HDAC) or a transcriptional repressor, is yet another potential means to enhance tumor immune surveillance. Active immunization against tumor antigens has been shown to be greatly enhanced by interfering with inhibitory T cells through the use of anti-CTLA-4 anti-bodies, providing another example of NOA-like therapy (Peggs et al., 2008). A major attraction of re-establishing the antitumor immune response is that one could potentially apply it in a systematic manner toward many tumor types and allow the immune system to detect and eradicate tumors at a relatively early stage.3 l* c2 I0 x6 B3 ^ |! Q
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