鼠伤寒沙门菌(Salmonella typhimurium)，图片来自SCIMAT/SCIENCE PHOTO LIBRARY。
研究人员认为经改造后表达一种细菌鞭毛蛋白(flagellin)的肿瘤细胞可能代表一种新的对抗癌症的免疫接种策略。鞭毛蛋白是一种已知的Toll样受体5(toll-like receptor 5, TLR-5)的配体，也能被Nod样受体(Nod-like receptor, NLR)家族中两个成员NLRC4和NAIP5(neuronal apoptisis inhibitor protein, 神经元凋亡抑制蛋白)识别。美国纽约市大学西奈山医学院Julie Magarian Blander教授领导的一个研究小组证实，一种癌细胞系改造后表达模式抗原卵清蛋白(ovalbumin, OVA)与鞭毛蛋白的融合物，接着将这些改造后的癌细胞注射到小鼠中，然后在小鼠皮下注射活着的亲代肿瘤细胞(parental tumor cell)，结果这些小鼠能够有效地抵抗癌症产生。
重要的是，研究人员证实这种保护效应依赖于鞭毛蛋白同时与TLR5和NLRC4/NAIP5结合：NLR结合对于小鼠产生持续性的T细胞抗癌免疫反应是非常关键的。研究小组就这项研究在Science Translational Medicine期刊上发表一篇题名为“Simultaneous Targeting of Toll- and Nod-Like Receptors Induces Effective Tumor-Specific Immune Responses”的论文。
Blander博士等对一种胸腺瘤细胞系进行改造使得它能够表达由模式抗原卵清蛋白和来自鼠伤寒沙门菌(Salmonella typhimurium)的鞭毛蛋白组成的融合蛋白。初步测试表明将这些改造过的癌细胞注射进实验用小鼠腹腔后会触发小鼠免疫系统招募嗜中性白细胞和巨噬细胞快速清除掉这些癌细胞。这种癌细胞清除反应特异性地依赖于TLR5信号传导，但是进一步分析也显示TLR5和NLRC4/NAIP5信号传导在促使抗肿瘤CD4+ T细胞和CD8+ T细胞做好抗击肿瘤侵入的准备和抑制肿瘤生长中发挥着同样重要的作用。
最为关键的是，当表达OVA-鞭毛蛋白的癌细胞用作疫苗时，这些接受接种免疫的动物当遭受活着的亲代肿瘤细胞攻击时，只要TLR5和NLRC4/NAIP5识别都没受到破坏，就能够成功地阻止肿瘤产生。当只表达鞭毛蛋白的肿瘤细胞用来接种免疫小鼠时，研究人员也能观察到这种保护效应。
相反地，用只表达OVA的癌细胞接种免疫小鼠就不能提供这种保护作用，即便是将它们同一种重组鞭毛蛋白一起注射到小鼠中也是如此。实际上，触发CD4+和CD8+ T细胞免疫反应依赖于树突细胞对鞭毛蛋白和肿瘤抗原的关联性识别从而使得提供给T细胞的抗原呈递最优化以及由此产生的有意义的T细胞反应。论文作者强调，“强化的抗原呈递主要依赖于肿瘤细胞内实际存在的鞭毛蛋白。”
Blander博士领导的研究小组说，他们的发现提示着基于鞭毛蛋白修饰的肿瘤细胞人们可能开发出一种新的抗癌疫苗，甚至不需要整入肿瘤特异性的或外源的抗原。
论文作者作出结论，“我们的发现描绘一种诱导抗癌免疫反应的新策略：将微生物结构与TLR和NLR双重刺激活性引入肿瘤细胞。这就确保在微生物识别的炎症背景下识别肿瘤来演的抗原，从而激活对抗肿瘤的天然免疫防御的胞浆途径(cytosolic pathway)和吞噬途径。” (生物谷：towersimper编译)
doi:10.1126/scitranslmed.3002868
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Simultaneous Targeting of Toll- and Nod-Like Receptors Induces Effective Tumor-Specific Immune Responses
Johan Garaude, Andrew Kent, Nico van Rooijen and J. Magarian Blander
Toll-like receptor (TLR) ligands are increasingly being used as adjuvants in cancer vaccine trials to harness innate immunity and prime effective antitumor immune responses. Despite some success, enhancing tumor antigen presentation, promoting a protective antitumor response, and overcoming the immunosuppressive tumor microenvironment pose considerable challenges that necessitate further improvements in vaccine design. Here, we show that expression of the TLR ligand flagellin within tumor cells constitutes an effective antitumor vaccination strategy that relies on simultaneous engagement of TLR5 and the Nod-like receptors (NLRs) NLRC4/NAIP5 (neuronal apoptosis inhibitory protein 5) by flagellin along with associative recognition of tumor antigen for optimal antigen presentation to T cells. Although TLR5 signaling was critical for mediating rapid macrophage-dependent clearance of flagellin-expressing tumor cells in vivo, TLR5 and NLRC4/NAIP5 were equally important for priming antitumor CD4+ and CD8+ T cells and suppressing tumor growth. Vaccination with irradiated flagellin-expressing tumor cells prevented tumor development, and disrupting flagellin recognition by TLR5 or NLRC4/NAIP5 impaired protective immunization against an existing or subsequent tumor. Our findings delineate a new strategy to induce anticancer immune responses consisting of introducing microbial structures with dual TLR and NLR stimulatory activity into tumor cells. This ensures recognition of tumor-derived antigen within the inflammatory context of microbial recognition and additionally activates both the phagocytic and the cytosolic pathways of innate immune defense against the tumor
