顺铂对荷瘤小鼠髓源性抑制细胞的下调作用及其机制研究

Myeloid-derived suppressor cells (MDSCs), as an important population of immunosuppressive cells, have been reported to expand and accumulate abnormally in peripheral blood and lymphoid organs in patients with a variety of tumors. They could inhibit the activation, proliferation and function of effector T cells through various mechanisms, thus leading to the failure of anti-tumor immune response. The accumulation of MDSCs in tumor-bearing hosts was attributed to the tumor-derived cytokines (VEGF, IL-6, IL-10)-induced abnormal activation of JAK2/STAT3 signaling pathway, which played pivotal role in the proliferation and differentiation of MDSCs, and the inhibition of JAK2/STAT3 signaling pathway could successfully induce the differentiation of MDSCs to dendritic cells (DCs), the most important antigen-presenting cells (APCs) in the immune system. Our previous work found that pretreatment with cisplatin (DDP) could reduce the percentages of MDSCs and increase the percentages of DCs in peripheral blood, bone marrow and secondary lymphoid tissues from mice bearing B16 melanoma. However, the underlying mechanisms mediating the DDP-induced down-regulation of MDSCs remains unclear. Therefore in this study, the effect of treatment with various doses of DDP exerting on the frequencies, phenotypes and functions of MDSCs in various murine tumor models would be observed to further confirm the down-regulating effect of DDP on MDSCs. Furthermore, the MDSCs-DCs differentiation regulated by the JAK2/STAT3 signaling pathway would also be investigated to elucidate the potential molecular mechanisms mediating DDP-induced down-regulation of MDSCs.

髓源性抑制细胞（Myeloid-derived suppressor cells, MDSCs）在多种肿瘤患者的外周血及淋巴器官中异常积聚，可通过多种途径抑制抗肿瘤免疫应答的发生。研究发现肿瘤细胞可分泌VEGF、IL-6及IL-10等细胞因子活化MDSCs中JAK2/STAT3信号通路，抑制MDSCs的分化，诱导其异常积聚；JAK2/STAT3信号通路的阻遏则可诱导MDSCs向树突状细胞（Dendritic cells, DCs）的分化。我们的前期工作发现顺铂可下调B16黑色素瘤荷瘤小鼠外周血及次级淋巴组织中MDSCs的比例，上调DCs的比例，但介导这一作用的机制尚不清楚。本研究拟在多种动物肿瘤模型中观察不同剂量的顺铂对MDSCs数目、表型及功能的调节作用，以证实顺铂对MDSCs的下调作用，并探讨JAK2/STAT3信号通路调节的MDSCs-DCs分化在顺铂下调MDSCs现象中所起的作用。

髓源性抑制细胞（Myeloid-derived suppressor cells, MDSCs）在多种肿瘤患者的外周血及淋巴器官中异常积聚，可通过多种途径抑制抗肿瘤免疫应答的发生。近年来研究发现一些化疗药物可选择性清除MDSCs，但介导化疗药物选择性下调MDSCs的作用机制尚未阐明。.我们的前期工作发现顺铂（Cisplatin, DDP）可下调B16黑色素瘤模型中小鼠外周血、骨髓、脾脏组织及肿瘤引流淋巴结中MDSCs的比例，以此改善机体免疫内环境，增强后续输注的细胞因子诱导的杀伤细胞（cytokine-induced killer cells, CIK cells）的抗肿瘤作用。在此工作基础上，我们进一步在多种小鼠移植瘤模型中证实了DDP对MDSCs的选择性下调作用，且此种下调作用在MDSCs的数目、表型及功能方面均有体现，且DDP对机体其他免疫细胞如T细胞、B细胞及NK细胞均无影响。通过对多种剂量DDP作用后MDSCs变化的动态观察，确定了最具免疫调节作用的DDP处理剂量及处理时间，为免疫治疗的联合方案的设计提供了实验基础。.随后我们探索了介导DDP下调MDSCs作用的机制。MDSCs在肿瘤宿主体内的积聚被认为与肿瘤源性细胞因子（VEGF、IL-6、IL-10）诱导的MDSCs中JAK2/STAT3信号通路的异常活化相关，通过对JAK2/STAT3信号通路的阻遏可逆转MDSCs的分化受抑，促使其向树突状细胞（Dendritic cells, DCs）的成功分化。.我们发现DDP处理后荷瘤鼠脾脏组织中MDSCs的p-JAK2、p-STAT3水平显著降低，肿瘤组织中IL-6水平亦显著降低，提示DDP可抑制肿瘤细胞分泌IL-6，阻遏脾脏组织中MDSCs的JAK2/STAT3信号通路的活化，进而促进MDSCs向DCs的分化。最后我们进行了验证实验，通过给予JAK2/STAT3信号通路抑制剂JSI-124以及中和性IL-6抗体，分别与DDP处理比较，观察其在DDP下调MDSCs现象中的作用。数据显示JAK2/STAT3信号通路抑制剂JSI-124可发挥与DDP相当的下调作用，而中和性IL-6抗体并未能显著下调MDSCs的数目与功能。提示在DDP下调MDSCs作用中，JAK2/STAT3信号通路的受抑是介导机制，而IL-6的下调并不是DDP免疫调节作用的唯一上游事件。