葡聚糖修饰的CpG作为瘤苗佐剂调节肿瘤微环境中MDSCs亚型并增强T细胞应答的作用及机制

CTL and Th1 are two main effector cells in anti-tumor immune response. Gr-1lowCD11b+MDSCs strongly suppress T cell function. CpG is often used as a tumor vaccine adjuvant to stimulate both CTL and Th1 responses. However, CpG also promotes Gr-1lowCD11b+MDSCs in tumor microenvironment, which is an major reason for the poor therapeutic effects of CpG adjuvant. Here, we developed a new adjuvant (D-CpG) by modifying the CpG with dextran. In murine pulmonary melanoma metastasis model, tumor vaccines with D-CpG adjuvant exhibited significantly better therapeutic effects than that of tumor vaccines with unmodified CpG adjuvant. Further study showed that tumor vaccines with D-CpG adjuvant significantly enhanced CTL and Th1 responses, and significantly decreased the percentage of Gr-1lowCD11b+MDSCs in tumor microenvironment. However, whether the CpG adjuvant can be used in the therapy of other types of tumors or not, and the mechanisms of the enhancement of T-cell response and regulation of Gr-1low CD11b+ MDSCs in tumor microenvironment by this adjuvant are not clear. In this study, we will use murine melanoma and lymphoma model to test the anti-tumor effects of D-CpG adjuvant. Then, we will further study the possible mechanisms of the adjuvant on enhancing T-cell response, and its role in the differentiation, migration and proliferation of MDSCs. This study will provide reliable data for the further application of D-CpG adjuvant.

CTL和Th1是抗肿瘤免疫应答中的主要效应细胞，Gr-1lowCD11b+MDSCs强力抑制T细胞功能。CpG是活化CTL和Th1的常用佐剂，但也促进了肿瘤微环境中的Gr-1lowCD11b+MDSCs，这是其临床治疗效果差的重要原因。我们用葡聚糖对CpG修饰得到了新型佐剂D-CpG。小鼠黑色素瘤肺转移模型中，D-CpG佐剂瘤苗治疗效果明显强于未修饰的CpG；并能显著增强CTL和Th1应答、抑制肿瘤微环境中Gr-1lowCD11b+MDSCs。然而，D-CpG佐剂是否适用于其它肿瘤的免疫治疗、其活化T细胞应答的机制及其调节肿瘤微环境中MDSCs亚型的机制，均不清楚。本研究拟利用小鼠黑色素瘤及淋巴瘤模型，通过体内、外实验明确D-CpG佐剂的肿瘤治疗效应。在此基础上对其增强T细胞应答的机制，在MDSCs亚型的分化、迁移及增殖中的作用及机制进行精细研究。为D-CpG的进一步应用提供可靠数据。

TLRs激动剂因其可激活固有免疫并进一步活化适应性免疫应答的特性，在疫苗佐剂方面有很好的应用前景。在众多TLRs中，TLR9可感知非甲基化的CpG，进而诱导IFN等细胞因子的表达并促进T细胞（尤其是Th1和CTL）扩增。因此，TLR9的激动剂CpG被认为具有激活Th1和CTL应答的潜力，这使得其很适合作为肿瘤疫苗佐剂。尽管临床上研究表明，作为肿瘤疫苗佐剂的CpG可提高T细胞应答。然而，进一步提高CpG的免疫治疗效果依然是临床上的诉求。.本项目中我们通过不同的化学修饰，得到了一系列CpG佐剂衍生物。其中，以葡聚糖（dextran）修饰的CpG——D-CpG，在小鼠黑色素瘤模型中展示了优于CpG的免疫治疗效果。在小鼠原位肿瘤模型中，D-CpG显著降低肿瘤的生长速度；D-CpG显著提高荷瘤小鼠脾脏中CTL和Th1的比例。D-CpG组小鼠脾脏和肿瘤微环境中Gr-1lowCD11b+MDSCs的比例相比于CpG组也显著降低，而Gr-1highCD11b+MDSCs的比例无明显变化。体外功能试验表明，Gr-1lowCD11b+MDSCs显著抑制T细胞增殖，而Gr-1highCD11b+MDSCs对T细胞增殖的无明显抑制效应。在小鼠黑色素瘤肺转移模型中，我们观察到D-CpG有类似于原位模型的免疫学效应。本研究表明D-CpG通过增强Th1和CTL应答、降低肿瘤和脾脏中Gr-1highCD11b+MDSCs的比例，增强了抗肿瘤免疫应答，其有望成为肿瘤疫苗的免疫佐剂。