手术切除荷瘤淋巴结后小鼠肺组织内CD45+、CD68+、CD163+和CD11b+免疫细胞表达的变化

目的:探讨手术切除荷瘤淋巴结对小鼠远隔脏器肺组织内免疫细胞表达的影响。方法:将小鼠B16F10黑色素瘤细胞接种至小鼠髂下淋巴结（SiLN）,15天后手术切除荷瘤淋巴结,所有小鼠分为手术切除SiLN组和未切除SiLN组（对照组）。应用HE及Elastic-Masson (EM)胶原纤维染色观察小鼠肺组织的一般形态结构和胶原纤维的变化;免疫组化染色观察肺组织中CD45+、CD68+、CD163+和CD11b+免疫细胞表达变化。结果:与对照组相比,手术切除SiLN组小鼠肺组织炎细胞浸润显著增加;血管周围胶原纤维稀疏;CD45+总免疫细胞、CD68+巨噬细胞、CD163+M2型巨噬细胞和CD11b+髓源性抑制性细胞（myeloid-derived suppressor cells,MDSCs）表达均显著增加（P＜0.05）。结论:手术切除荷瘤淋巴结促进小鼠肺组织内CD163+M2型巨噬细胞、CD11b+ MDSCs的表达增加,可能有利于远隔脏器肺组织内支持肿瘤细胞定植的炎性微环境的形成。     

乳腺癌患者髓系来源抑制性细胞的鉴定与免疫作用研究

目的:探讨乳腺癌患者体内一群髓系来源抑制性细胞(MDSCs)的表型特点及它对淋巴细胞的抑制作用.方法:收集20例乳腺癌患者外周血及肿瘤组织,10例体检正常健康者外周血,通过流式和免疫组织化学染色技术检测MDSCs的表型特点及比例.采用免疫磁珠技术分选乳腺癌患者肿瘤中的MDSCs,通过瑞氏染色观察细胞形态,分别利用MTT法、流式细胞术和ELISA法检测其对自体淋巴细胞增殖、凋亡和细胞因子分泌的影响.结果:流式细胞仪检测结果显示乳腺癌患者肿瘤组织及外周血中有一群具有髓系前体细胞形态的MDSCs,表面标志为CD45+ CD13+CD33+CD14-CD15-.实验结果显示肿瘤组织来源的MDSCs显著抑制自体淋巴细胞增殖,促进其调亡,并显著抑制其分泌IFN-γ,促进TGF-β、IL-10释放.结论:乳腺癌患者肿瘤组织中存在一群具有独特表型特点的MDSCs,不仅抑制自体淋巴细胞增殖和因子分泌,同时促进细胞凋亡.     

髓系来源的抑制性细胞在小鼠H22原位种植性肝癌中的表达及其意义

目的:比较小鼠H22原位种植性肝癌模型中髓系来源的抑制性细胞（MDSCs）和调节性T细胞（Tregs）的表达，确定主要的免疫抑制性细胞。并探讨主要免疫抑制性细胞在小鼠H22原位种植性肝癌模型中的意义。方法:建立小鼠H22原位种植性肝癌模型，用流式细胞术的方法比较外周血、脾脏、肿瘤组织中MDSCs、Tregs的比例。分析MDSCs与CD4+T细胞、CD8+T细胞、NK细胞、NKT细胞的相关性。通过脾脏切除的方法下调MDSCs的表达，观察对肿瘤存活的影响。结果:MDSCs的比例无论在外周血、脾脏还是肿瘤组织中都显著高于Tregs。MDSCs的比例与CD4+T细胞、CD8+T细胞、NK细胞、NKT细胞呈负相关。下调MDSCs的比例可以显著延长小鼠存活期。结论:小鼠H22原位种植性肝癌中主要的免疫抑制性细胞是MDSCs。MDSCs的高表达预示着不良的小鼠存活期。     

MDSCs与肿瘤免疫逃逸

髓源抑制性细胞(myeloidderived suppressor cells, MDSCs)是一群异质性细胞,来源于骨髓祖细胞和未成熟髓细胞(immature myeloid cells, IMCs),是树突状细胞（dendritic cells, DCs）、巨噬细胞和（或）粒细胞的前体。在荷瘤小鼠的血液、脾脏和肿瘤组织及肿瘤患者的外周血和肿瘤组织存在大量MDSCs的扩增。MDSCs可以通过多种途径抑制机体的获得性和天然抗肿瘤免疫,使肿瘤细胞逃避机体的免疫监视和攻击,促进肿瘤发展。MDSCs首先从骨髓募集到外周,并在外周被激活后才能发挥抗肿瘤免疫抑制功能,肿瘤来源的慢性炎症相关的一系列因子在介导MDSCs的募集和活化中起关键作用。当前靶向MDSCs的抗肿瘤治疗取得了一定的进展,但MDSCs从发现到现在仅仅经历了10年左右的时间,该领域中许多的未知尚需要大量的基础和临床研究来阐明。本文主要介绍MDSCs的特征及其亚群、MDSCs的募集和活化、MDSCs介导免疫逃逸的机制及当前靶向MDSCs的抗肿瘤治疗策略,以期为从事该领域的研究工作者提供参考。     

骨髓间充质干细胞预防手术后肿瘤肺转移动物模型研究

背景与目的:近年来研究发现,肿瘤患者术后髓系抑制细胞(myeloid-derived suppressor cells,MDSCs)较术前升高,且其促肿瘤血管生成和肿瘤生长作用增强,骨髓间充质干细胞(bone marrow mesenchymal stem cells,BMSCs)可抑制MDSCs活化与增殖.但围手术期MDSCs的变化与肿瘤术后转移的关系及BMSCs能否通过抑制MDSCs预防手术后肿瘤转移尚不清楚.该研究拟探讨围手术期MDSCs变化与手术后肿瘤转移的相关性及BMSCs对围手术期MDSCs和手术后肿瘤转移的影响.方法:C57BL/6小鼠经尾静脉注射LLC细胞后分为4组:对照组(C组)、麻醉组(A组)、麻醉后开腹组(AL组)及麻醉后开腹并肝叶切除组(ALH组).AL组小鼠手术后分为2组:术后无治疗组(AL1组)和术后给予同系BMSCs治疗组(ALB组).流式细胞术检测小鼠外周血单个核细胞(peripheral blood mononuclear cells,PBMCs)中Gr-1+CD11b+细胞的含量;第14天计数小鼠肺表面转移灶.小鼠骨髓细胞体外诱导MDSCs体系中加入BMSCs共培养的方法探讨BMSCs对MDSCs生成的影响.结果:与C、A组相比,AL和ALH组小鼠肺转移灶显著增多(P<0.01);且ALH组较AL组显著增多(P<0.05).手术后AL和ALH组小鼠PBMCs中Gr-1+CD11b+细胞与C、A组相比显著升高;与AL组比较,ALH组Gr-1+CD11b+细胞显著升高.第14天,AL及ALB组小鼠肺表面转移灶数量分别为38.00±9.57和6.54±1.49,差异有统计学意义(P<0.01).ALB组小鼠PBMCs中Gr-1+CD11b+细胞与AL1组相比明显降低.小鼠骨髓细胞体外诱导MDSCs体系中加入BMSCs可显著抑制MDSCs的活化和增殖.结论:手术应激诱导MDSCs并促肿瘤肺转移形成,BMSCs可以抑制MDSCs的生成进而抑制手术后肺转移形成.     

TGFβ信号通路的阻断导致乳腺癌细胞募集Gr-1+CD11b+髓样免疫抑制细胞促进肿瘤的转移

TGFβ信号通路的异常对于肿瘤的发生发展有着密切的关系。在肿瘤发生早期，TGF6发挥肿瘤抑制因子的作用，TGFβ通路的失活通常会导致肿瘤的发生。然而随着肿瘤的不断发展，TGFβ的作用开始变得复杂化。Gr-1＋CD11b＋髓系来源的髓样细胞又称为髓样免疫抑制细胞（MISCs）或髓系来源的抑制细胞（MDSCs）是近年来免疫学研究的热点之一。在小鼠体内它们同时表达巨噬细胞系的髓样细胞表面标识CD11b和粒细胞表面标识Gr-1，因此得名。目前研究表明，该群细胞发挥着免疫抑制作用，对于肿瘤的免疫逃逸起关键作用。     

髓源抑制性细胞与恶性肿瘤的研究进展

髓源抑制性细胞(myeloid derived suppressor cells，MDSCs)是一群异质性细胞，包括多种处于不同分化阶段的髓样细胞，如髓系祖细胞、未成熟的巨噬细胞、粒细胞、单核细胞、树突状细胞等。在荷瘤小鼠的血液、脾脏和肿瘤组织及肿瘤患者的外周血和肿瘤组织中存在大量MDSCs的扩增，与肿瘤的进展密切相关。恶性肿瘤来源的多种因子如粒细胞-巨噬细胞集落刺激因子（granulocyte-macrophage colony stimulating factor，GM-CSF）、白细胞介素（interleukin,IL）-6、S100钙结合蛋白A8/A9（S100 calcium binding protein A8/A9，S100A8/A9）等是导致MDSCs扩增的关键因素。MDSCs可通过抑制机体抗肿瘤免疫、上皮-间质转化(epithelial-mesenchymal transition，EMT）、侵袭、血管生成、转移前小生境形成等多种途径导致肿瘤发生发展。本文主要介绍MDSCs的亚群、功能、募集和活化机制，MDSCs作为预后标志物的价值以及当前靶向MDSCs的抗肿瘤治疗策略，以期加深对MDSCs与恶性肿瘤关系的认识。     

肿瘤诱导的髓系来源抑制细胞中IDO表达相关机制研究

目的:建立正常CD33+细胞与肿瘤细胞共培养系统,模拟肿瘤局部髓系来源抑制细胞的诱导过程,观察吲哚胺2,3双加氧酶在MDSCs中表达及其免疫抑制作用,并探讨MDSCs中IDO表达相关机制.方法:免疫磁珠分选健康供者CD33+细胞,体外与乳腺癌细胞系MDA-MB-231共孵育诱导MDSCs,以单独培养CD33+细胞为对照组,培养2天后收获实验组MDSCs及对照组CD33+细胞,流式细胞仪检测细胞表型;实时定量PCR和Western Blotting方法检测IDO和STAT3的表达与活化情况;Annexin V-FITC的方法检测MDSCs对T细胞促凋亡作用,并观察IDO在MDSCs诱导T细胞凋亡中的作用.结果:正常CD33+细胞与MDA-MB-231共孵育2天后,出现一群表型为Lin-CD33+13+CD14-CD15-的MDSCs,体外诱导的MDSCs中IDOmRNA及蛋白表达增加、STAT3蛋白磷酸化增强,经过STAT3磷酸化抑制剂JSI-124预处理后,MDSCs中IDO蛋白表达明显降低并可诱导高百分比T细胞凋亡,经IDO抑制剂1-MT处理后T细胞凋亡显著降低.结论:体外将乳腺癌细胞系与正常CD33+细胞共孵育可以诱导出具有独特表型特征和免疫抑制活性的MDSCs,而STAT3磷酸化导致的IDO表达升高可能是MDSCs抑制T细胞功能的主要机制之一.     

三氧化二砷负向调控MDSC的肿瘤免疫抑制功能

目的:研究三氧化二砷(arsenic trioxide,As2O3)是否通过抑制髓系来源抑制性细胞(myeloid-derived suppressor cells,MDSCs)负向调控MDSCs诱导的肿瘤免疫耐受作用.方法:C57BL/6小鼠皮下注射黑素瘤B16细胞和肝癌H22细胞构建移植瘤模型,As2O3处理,观察移植瘤生长情况,流式细胞术检测荷瘤小鼠脾脏内MDSCs和其他免疫细胞的免疫表型,流式细胞术检测2 μmol/L As2O3对B16模型小鼠来源的MDSCs分化的影响.取B16模型小鼠随机分为As2O3处理及对照组,混合淋巴细胞反应检测MDSCs对T细胞免疫抑制活性的改变,ELISA检测B16模型小鼠血清及MDSCs培养上清中TNF-α、IL-10的水平.结果:As2O3抑制B16和H22模型鼠的肿瘤生长,延长B16模型小鼠的生存期,并可显著下调小鼠脾脏内MDSCs的比例.体外经2 μmol/L As2O3处理5d后,B16模型小鼠来源的MDSCs中成熟DCs(CD11c+ CD40+)的比例较对照组显著升高[(27.38±4.57)％ vs (17.44±4.51)％,P=0.0078];As2O3组来源的MDSCs对T细胞的免疫抑制活性明显低于对照组(P =0.016);As2O3组小鼠血清及MDSCs培养上清中TNF-α(F=5.78,P=0.014)和IL-10(F=17.83,P=0.045)的含量均较对照组显著降低.结论:As2O3可通过诱导MDSCs向成熟表型分化、下调其免疫抑制活性等,负调控MDSCs的肿瘤免疫抑制功能.     

转染4-1BBL基因的胃癌细胞在小鼠体内的抗肿瘤及免疫调节作用

目的:观察转染4-1BBL基因的小鼠胃癌细胞株MFC的体内致瘤性及其对小鼠免疫功能的影响。方法:通过脂质体介导以重组质粒pMKITneo和pMKITneo/4-1BBL转染小鼠胃癌细胞株MFC。用RT-PCR法检测目的基因的表达。计数法绘制体外培养细胞生长曲线。将转染前后肿瘤细胞,分别接种于615小鼠背部皮下观察其致瘤性。流式细胞仪测定荷瘤小鼠外周血NK、CD4 T和CD8 T细胞数,并测定荷瘤小鼠肿瘤结节内细胞凋亡率。结果:MFC/4-1BBL细胞中可检测到4-1BBLmRNA表达。转染前后肿瘤细胞的体外生长速度无明显变化。MFC/4-1BBL细胞在小鼠体内的致瘤性较MFC/pMKITneo细胞和野生型MFC细胞明显降低。接种MFC/4-1BBL细胞的小鼠外周血NK细胞及CD8 T细胞数明显增多;其肿瘤结节内细胞凋亡率亦明显增高。结论:转染4-1BBL基因后并未影响MFC细胞的体外生长,但其在小鼠体内的致瘤性明显降低。MFC/4-1BBL细胞可诱导荷瘤小鼠体内CD8 T和NK细胞增殖,而且能促进肿瘤细胞的凋亡。     

A mutual activation loop between breast cancer cells and myeloid-derived suppressor cells facilitates spontaneous metastasis through IL-6 trans-signaling in a murine model

Introduction

Tumor cell interactions with the microenvironment, especially those of bone-marrow-derived myeloid cells, are important in various aspects of tumor metastasis. Myeloid-derived suppressor cells (MDSCs) have been suggested to constitute tumor-favoring microenvironments. In this study, we elucidated a novel mechanism by which the MDSCs can mediate spontaneous distant metastasis of breast cancer cells.

Methods

Murine breast cancer cells, 4T1 and EMT6, were orthotopically grafted into the mammary fat pads of syngeneic BALB/c mice. CD11b⁺Gr-1⁺ MDSCs in the spleen, liver, lung and primary tumor mass were analyzed. To evaluate the role of MDSCs in the distant metastasis, MDSCs were depleted or reconstituted in tumor-bearing mice. To evaluate whether MDSCs in the metastasizing tumor microenvironment affect breast cancer cell behavior, MDSCs and cancer cells were co-cultivated. To investigate the role of MDSCs in in vivo metastasis, we blocked the interactions between MDSCs and cancer cells.

Results

Using a murine breast cancer cell model, we showed that murine breast cancer cells with high IL-6 expression recruited more MDSCs and that the metastasizing capacity of cancer cells paralleled MDSC recruitment in tumor-bearing mice. Metastasizing, but not non-metastasizing, tumor-derived factors induced MDSCs to increase IL-6 production and full activation of recruited MDSCs occurred in the primary tumor site and metastatic organ in the vicinity of metastasizing cancer cells, but not in lymphoid organs. In addition, tumor-expanded MDSCs expressed Adam-family proteases, which facilitated shedding of IL-6 receptor, thereby contributing to breast cancer cell invasiveness and distant metastasis through IL-6 trans-signaling. The critical role of IL-6 trans-signaling was confirmed in both the afferent and efferent pathways of metastasis.

Conclusion

In this study, we showed that metastasizing cancer cells induced higher MDSCs infiltration and prompted them to secret exaggerated IL-6 as well as soluble IL-6Rα, which, in turn, triggered a persistent increase of pSTAT3 in tumor cells. This potential tumor-MDSC axis involving IL-6 trans-signaling directly affected breast cancer cell aggressiveness, leading to spontaneous metastasis.     

miR-223 suppresses differentiation of tumor-induced CD11b⁺ Gr1⁺ myeloid-derived suppressor cells from bone marrow cells

Tumor-associated factors are related to increased accumulation of CD11b(+) Gr1(+) myeloid-derived suppressor cells (MDSCs). However, the exact mechanism of how genetic factors control the expansion of MDSCs in tumor-bearing hosts remains elusive. Herein, we found that tumor-associated MDSCs and their subsets, mononuclear MDSCs and polymorphonuclear MDSCs, have decreased expression of miR-223 when compared to CD11b(+) Gr1(+) cells from the spleen of disease-free mice. With the differentiation of CD11b(+) Gr1(+) MDSCs from bone marrow cells (BMCs) upon exposure to tumor-associated factors, the expression of both pri-miR-223 and mature miR-223 was downregulated, indicating that the expression of miR-223 could be regulated by tumor-associated factors. Interestingly, miR-223 remarkably inhibits differentiation of BMCs into CD11b(+) Gr1(+) MDSCs in the presence of tumor-associated factors by targeting myocyte enhancer factor 2C (MEF2C). Using reconstituted s.c. tumor models, miR-223 also suppresses accumulation of CD11b(+) Gr1(+) MDSCs, whereas its targeting molecule MEF2C increases the number of MDSCs. Tumor growth is slower in mice infused by miR223-engineered BMCs than in mice infused with control transfected BMCs. As miR-223 and its target molecule MEF2C are highly conserved between mice and humans, the modulation of miR-223 in tumor-induced CD11b(+) Gr1(+) MDSCs may exert an important role in controlling the increased accumulation of CD11b(+) Gr1(+) MDSCs in patients with tumor.     

AZD1480 delays tumor growth in a melanoma model while enhancing the suppressive activity of myeloid-derived suppressor cells

AZD1480 is a potent, competitive small-molecule inhibitor of JAK1/2 kinase which inhibits STAT3 phosphorylation and tumor growth. Here we investigated the effects of AZD1480 on the function of different immune cell populations in a melanoma model. When MO4 tumor-bearing mice were treated with AZD1480 we observed a strong inhibition of tumor growth as well as a prolonged survival. Moreover, a significant decrease in the percentage of myeloid-derived suppressor cells (MDSCs) was observed after treatment with AZD1480. However, AZD1480 enhanced the suppressive capacity of murine MDSCs while at the same time impairing the proliferative as well as the IFN-γ secretion capacity of murine T cells. The addition of AZD1480 to co-cultures of human MDSCs and T cells does not affect the suppressive activity of MDSCs but it does reduce the IFN-γ secretion and the proliferative capacity of T cells. We showed that although AZD1480 has the ability to delay the tumor growth of MO4 tumor-bearing mice, this drug has detrimental effects on several aspects of the immune system. These data indicate that systemic targeting of the JAK/STAT pathway by JAK1/2 inhibition can have divergent effects on tumor growth and anti-tumor immune responses.     

膀胱癌来源的外泌体通过促进髓系抑制性细胞的扩增介导毒性T细胞的免疫抑制

目的:探究膀胱癌细胞系MB49来源的外泌体(MB49-Exo)对髓系来源的抑制性细胞(MDSCs)的影响及后者对MB49抗原特异性细胞毒性T淋巴细胞(CTL)免疫功能的调控.方法:试剂盒分离MB49-Exo,并应用透射电子显微镜(TEM)观察外泌体形态,纳米粒径颗粒跟踪分析仪(NTA)和Western blot进行鉴定...     

A heptamethine cyanine dye serves as a potential marker for myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with inhibitory effects on T cell-mediated immune response. MDSCs accumulate under many pathological conditions, including cancers, to avoid anticancer immunity. Unlike mouse MDSCs, common specific surface markers for human MDSCs are not clearly defined, mainly due to the complexity of MDSC subsets. In this study, we investigate specific responses of the infrared dye MHI-148 to MDSCs. Mice bearing 4T1 breast cancer cells were established, and splenocytes were isolated. Flow cytometric analyses demonstrated that MHI-148 was reactive to over 80% of MDSC-specific cells manifesting CD11b⁺/Gr-1⁺ acquired from both tumor-bearing mice and naive mice. Cells sorted positive for either CD11b/Gr-1 or MHI-148 were also identical to their counterparts (99.7% and 97.7%, respectively). MHI-148, however, was not reactive to lymphocyte or monocyte populations. To determine whether MHI-148-reactive cells exert inhibitory effects on T cell proliferation, an EdU-based T cell assay was performed. MHI-148 reactive cells significantly reduced T cell proliferation with increased arginase activity and nitrite production. In an attempt to test MHI-148 as a marker for human MDSCs, MHI-148 was specifically reactive to CD11b⁺/CD33⁺/CD14^- granulocytic MDSCs acquired from selected cancer patients. This study demonstrates that the near-infrared dye MHI-148 specifically reacts to mouse splenocytes with known MDSC-specific markers that have T cell suppressive functions. The dye also selectively binds to a subpopulation of immature myeloid cells acquired from cancer patients. While it is not clear how MHI-148 specifically stains MDSCs, this dye can be a novel tool to detect MDSCs and to predict the prognosis of human cancer patients.     

S-1 eliminates MDSCs and enhances the efficacy of PD-1 blockade via regulation of tumor-derived Bv8 and S100A8 in thoracic tumor

Myeloid-derived suppressor cells (MDSCs) have been known to play a pivotal role in the induction of immune tolerance, which limits the benefits of immune checkpoint inhibitors (ICIs). Recent studies revealed that several chemotherapeutic agents decreased tumor-infiltrating MDSCs. Therefore, combination therapy with cytotoxic chemotherapeutic agents and ICIs was approved for first-line treatment for lung cancer. However, the impact of chemotherapeutic agents on MDSCs and an optimal partner of ICIs has not been fully investigated in thoracic tumors, including lung cancer and malignant pleural mesothelioma. In the present study, we found that treatment with 5-FU and its oral formulation, S-1, suppressed tumor progression and inhibited the accumulation of MDSCs in thoracic tumor-bearing mice. Tumor-infiltrating T cells and dendritic cells were significantly expanded in S-1-treated mice. 5-FU suppressed the ability of tumor cells to recruit MDSCs, while it did not suppress the survival and differentiation of mouse MDSCs in vitro. We also revealed that 5-FU or S-1 significantly downregulated the expression of tumor-derived Bv8 and S100A8. The knockdown of Bv8 or S100A8 in tumor cells suppressed tumor growth and MDSC recruitment in vivo. Furthermore, in comparison with pemetrexed, administration of S-1 improved the synergistic therapeutic efficacy of anti-PD-1 antibodies with or without carboplatin. Our findings revealed a novel mechanism wherein S-1 primed a favorable tumor microenvironment to provide the rationale for combination therapy with S-1 and ICIs as the optimal therapy for thoracic cancer.     

TGF-β Enhances the Anti-inflammatory Effect of Tumor- Infiltrating CD33+11b+HLA-DR Myeloid-Derived Suppressor Cells in Gastric Cancer: A Possible Relation to MicroRNA-494

Background: Accumulation of myeloid-derived suppressor cells (MDSCs) constitutes a key mechanism of tumor immune evasion in gastric cancer (GC). Therefore, searching for more accurate prognostic factors affecting their immunosuppressive role has become a growing interest in cancer immunotherapy research. Increased expression of microRNA-494 was noticed in MDSCs from tumor-bearing mice, suggesting another new therapeutic objective for cancer treatment. It was also discovered that tumor-derived transforming growth factor beta (TGF-β) is responsible for the up-regulation of microRNA-494 in MDSCs. The purpose of this study was to address the effect of recombinant (rTGF-β) on the anti-inflammatory activity of MDSCs in GC and its possible association with micro-RNA-494 expression in tumor tissue. Methods: Freshly obtained GC tumor tissue samples and peripheral blood were used for isolation of CD33+11b+HLADR- MDSCs cells from 40 GC patients and 31 corresponding controls using flow cytometry. MDSCs were co-cultured with isolated autologous T cells to assess proliferation and cytokine production in the presence and absence of rTGF-β. Real-time PCR and Enzyme linked immunosorbent assay were used to evaluate tumor expression of miRNA-494 and TGF-β respectively. Results: Results showed that rTGF-β markedly increased the suppressive ability of tumor MDSCs on proliferation of autologous T cells and interferon gamma production. However, no inhibitory effect was observed for MDSCs from circulation. In addition, infiltration of MDSCs in tumors is associated with the prognosis of GC. MiRNA-494 was also extensively expressed in tumor samples with a significant correlation to MDSCs. Conclusion: These results indicate that tumor-derived MDSCs but not circulatory MDSCs have an immunosuppressive effect on T cells, potentially involving TGF-β mediated stimulation.  Results also suggest a role for miRNA-494 in GC progression. Therefore, control of TGF-β and miRNA-494 may be used as a treatment strategy to downregulate the immunosuppressive effect of MDSCs.     

The inflammasome component NLRP3 impairs antitumor vaccine by enhancing the accumulation of tumor-associated myeloid-derived suppressor cells

The inflammasome is a proteolysis complex that generates the active forms of the proinflammatory cytokines interleukin (IL)-1β and IL-18. Inflammasome activation is mediated by NLR proteins that respond to microbial and nonmicrobial stimuli. Among NLRs, NLRP3 senses the widest array of stimuli and enhances adaptive immunity. However, its role in antitumor immunity is unknown. Therefore, we evaluated the function of the NLRP3 inflammasome in the immune response using dendritic cell vaccination against the poorly immunogenic melanoma cell line B16-F10. Vaccination of Nlrp3(-/-) mice led to a relative 4-fold improvement in survival relative to control animals. Immunity depended on CD8(+) T cells and exhibited immune specificity and memory. Increased vaccine efficacy in Nlrp3(-/-) hosts did not reflect differences in dendritic cells but rather differences in myeloid-derived suppressor cells (MDSC). Although Nlrp3 was expressed in MDSCs, the absence of Nlrp3 did not alter either their functional capacity to inhibit T cells or their presence in peripheral lymphoid tissues. Instead, the absence of Nlrp3 caused a 5-fold reduction in the number of tumor-associated MDSCs found in host mice. Adoptive transfer experiments also showed that Nlrp3(-/-) MDSCs were less efficient in reaching the tumor site. Depleting MDSCs with an anti-Gr-1 antibody increased the survival of tumor-bearing wild-type mice but not Nlrp3(-/-) mice. We concluded that Nlrp3 was critical for accumulation of MDSCs in tumors and for inhibition of antitumor T-cell immunity after dendritic cell vaccination. Our findings establish an unexpected role for Nlrp3 in impeding antitumor immune responses, suggesting novel approaches to improve the response to antitumor vaccines by limiting Nlrp3 signaling.     

Inhibition of iNOS activity enhances the anti-tumor effects of alpha-galactosylceramide in established murine cancer model

Alpha-garactosylceramide (GalCer) has been shown to have anti-tumor effect in the basic research and clinical studies. However, anti-tumor effect of GalCer is limited. The administration of GalCer increases the production of IFN-γ which is involved in the suppression of tumor growth. On the other hand, the enhancement of IFN-γ production increases immunosuppressive factors such as nitric oxide. This suppressive action might impair the anti-tumor effect of GalCer. In the present study, we evaluated the anti-tumor effect of GalCer in the absence of inducible nitric oxide synthase (iNOS). In lung metastatic model, the number of tumor nodules in the lung of iNOS-KO mice treated with GalCer was significantly reduced compared with that of WT mice treated with GalCer. Moreover, L-NAME, which is the inhibitor for iNOS, enhanced the anti-tumor effect of GalCer in lung metastatic model. The frequency of CD8+ cells in bronchoalveolar lavage fluid increased in iNOS-KO mice treated with GalCer. The administration of GalCer increased the frequency of myeloid-derived suppressor cells (MDSCs) in the lung from tumor-bearing WT mice, but the increase of MDSCs in the lung was not induced in iNOS-KO mice. The subcutaneous tumor experiments revealed that the administration of GalCer in the absence of iNOS expression significantly enhanced the induction of tumor antigen-specific response. Finally, our results indicated that the inhibition of iNOS expression could enhance the therapeutic efficacy of GalCer via the increase of tumor antigen-specific immune response and the suppression of MDSCs.