靶向MDSC干扰肿瘤微环境在神经母细胞瘤免疫治疗中的作用和机制

The tumor immunosupressive microenvironment is the choke point in immunotherapy of neuroblastoma. Disialoganglioside, highly expressed in cellular surface of neuroblastoma, can activate the recruitment of myeloid-derived suppressor cells and initiate tumor immunosupression. Likewise, chemotactic factor CXC12 with its recepter CXCR4, the dominant factor for relapse and metastasis of neuroblastoma, can also induce myeloid-derived suppressor cells gathering in tumor microenvironment. Although myeloid-derived suppressor cell has been known the major factor for tumor immunosupression, its role and mechanism remain unclear in neuroblastoma. In the previous study, we found that previous administration of low-dose specific chemotherapy drug can effectively interfere with tumor microenvironment in order to get rid of immunosupression and improve immunotherapy effect. So, in present study, as a new target spot, myeloid-derived suppressor cells will be firstly seperated and cultured in vitro and its effect on proliferation and killing activity of effector cells will be explored. Thereafter, the neuroblastoma-bearing animal models will be built in C57BL/6j mice to understand the state of tumor microenvironment in vivo of neuroblastoma, the expressive variation of CXCL12 with its recepter CXCR4 and the mechanism of immunotherapy effect improvement after inhibition of myeloid-derived suppressor cells from different angles. With the tests in vivo and in vitro, we are plan to elucidate the role of myeloid-derived suppressor cell in regulation of tumor immunosupressive microenvironment of neuroblastoma and the effect on relapse, metastasis and immunotherapy of neuroblastoma with targeted inhibition of myeloid-derived suppressor cells, further provide the theoretical basis for a novel immunotherapy of neuroblastoma.

神经母细胞瘤(neuroblastoma, NB)免疫疗效差的瓶颈是肿瘤免疫抑制微环境问题。其细胞高表达的双唾液酸神经节苷脂可诱导髓系抑制性细胞(myeloid-derived suppressor cell, MDSC)在微环境中集聚而启动肿瘤免疫抑制；引致NB复发转移的趋化因子CXCL12及其受体CXCR4也可诱导MDSC的集聚。而MDSC是造成肿瘤免疫抑制的主要因素，但在NB中作用机制不清楚。前期研究发现利用特定低剂量化疗药物预处理可干扰肿瘤微环境，消除免疫抑制，提高疗效。本研究中我们拟以MDSC为新靶点，建立C57BL/6j荷瘤小鼠模型，探讨MDSC对效应细胞增殖及杀伤NB细胞活性影响，了解靶向抑制MDSC后 NB微环境状态、CXCL12与CXCR4表达及免疫疗效改善情况，以阐释MDSC调控NB微环境机制，抑制MDSC对NB复发转移和免疫疗效作用，为探索NB免疫新疗法提供理论依据。

神经母细胞瘤（neuroblastoma, NB）免疫疗效差的瓶颈是肿瘤免疫抑制微环境问题。其细胞高表达的双唾液酸神经节苷脂（disialoganglioside，GD2）可诱导髓系抑制性细胞（myeloid-derived suppressor cell, MDSC）在微环境中集聚而启动肿瘤免疫抑制；引致NB复发转移的趋化因子CXCL12及其受体CXCR4也可诱导MDSC的集聚。而MDSC是造成肿瘤免疫抑制的主要因素，但在NB中作用机制不清楚。本研究以MDSC为新靶点，建立BALB/c荷瘤小鼠模型，体内、外实验探讨MDSC对效应细胞增殖及杀伤NB细胞活性影响，靶向MDSC干扰免疫抑制微环境的可行性及机制、CXCL12与CXCR4表达变化及免疫疗效改善情况。研究发现：MDSC可有效抑制抗原特异性CTL体外杀伤NB细胞，其机制是MDSC可降低CD62L表达来抑制CTL体外增殖、活化和运动而产生免疫耐受，这种抑制作用可通过多柔比星（doxorubicin，DOX）应用而消除；以不同方式（多巴胺或小剂量DOX）靶向抑制MDSC可对肿瘤免疫抑制微环境进行有效调控，影响瘤体中CXCL12及CXCR4表达，抑制肿瘤生长，控制其复发和转移。其机制与促进T细胞增殖、抑制TAM由M1型向M2型极化、降低Treg水平、减弱GD2抗原合成以及调控Jak/STAT信号通路中蛋白表达密切相关；靶向MDSC干扰免疫微环境可提高抗-GD2抗体注射或抗原特异性CTL过继回输治疗NB免疫疗效，其机制与肿瘤HLA-I类抗原和CD8分子表达提高、瘤体中CD8+CTL浸润水平升高、Thl/Th2类细胞因子水平及穿孔素、颗粒酶等杀伤介质分泌增加有关。该研究结果提出了以MDSC为靶点干扰肿瘤微环境增加NB免疫疗效的新方法和新机制，并为探索免疫治疗新药或生物制剂提供了重要理论依据，具有重要科学意义和转化应用前景。