Effect Of Myeloid-derived Suppressor Cells Research Articles

Microenvironmental oxygen pressure orchestrates an anti- and pro-tumoral γδ T cell equilibrium via tumor-derived exosomes

γδ T cells are a unique lymphocyte population that have been reported to have either anti- or pro-tumoral functions in several cancer types, but the mechanisms are underinvestigated. Exosomes, initially considered to be cellular "garbage dumpsters," are now implicated in mediating interactions with the cellular environment. Hypoxia is a common feature of solid tumors and is believed to alter tumor-derived exosomes (TEXs), which mediate the hypoxic evolution of the tumor microenvironment in return. This study sought to investigate whether TEXs mediate the anti- and pro-tumoral equilibrium of γδ T cells under different oxygen pressures in the tumor microenvironment. We show that TEXs can alter the expansion and cytotoxicity of γδ T cells in an HSP70-dependent but dendritic cell-independent manner. The stimulating effects of normoxic TEXs on γδ T-cell activity were absent from hypoxic TEXs, which enhanced the suppressive effect of myeloid-derived suppressor cells (MDSCs) on γδ T cells through a miR-21/PTEN/PD-L1 regulation axis. Finally, the therapeutic outcome benefited from combined miR-21 and PD-L1 targeting in oral squamous cell carcinoma (OSCC)-bearing immunocompetent mice. We conclude that oxygen pressure in the tumor microenvironment orchestrates an anti- and pro-tumoral γδ T-cell equilibrium by altering TEX content, which subsequently regulates MDSC function in a miR-21/PTEN/PD-L1-axis-dependent manner. Our results should prompt further investigation into integrated exosomal miRNA inhibition and immune checkpoint inhibitor therapeutic modalities for patients with OSCC.

Effect of myeloid-derived suppressor cells on B cell function in mice bearing breast cancer

Effect of myeloid-derived suppressor cells on B cell function in mice bearing breast cancer

Human T cells modulate myeloid-derived suppressor cells through a TNF-α-mediated mechanism

Myeloid-derived suppressor cells (MDSC) represent an innate immune cell subset capable of suppressing T-cell responses in cancer and chronic inflammation. While the effect of MDSC on T cells has been defined thoroughly, the reciprocal impact of T cells on MDSC homeostasis remains poorly understood. Therefore, we comprehensively analyzed the effect of different T-cell subsets on the generation and survival of human MDSC. Using an in vitro MDSC generation assay, we demonstrate that unstimulated CD4+, but not CD8+ T cells, induce polymorphonuclear MDSC (PMN-MDSC) from CD33+ myeloid cells. This effect was dependent on direct cell-cell contact and required TNF-α signaling. Soluble TNF-α was dispensable for PMN-MDSC generation, suggesting that transmembrane TNF-α is involved in that trans-cellular process. Stimulated human CD3+ T cells delayed the apoptosis of PMN-MDSC, which was independent of TNF-α signaling or direct cell-cell contact, but was recapitulated by IL-2. Taken together, our study shows that human T cells modulate MDSC generation and survival through two distinct mechanisms and thereby fine-tune the homeostasis of human MDSC in a regulated manner.

Nitric Oxide Production by Myeloid-Derived Suppressor Cells Plays a Role in Impairing Fc Receptor-Mediated Natural Killer Cell Function.

Purpose: mAbs are used to treat solid and hematologic malignancies and work in part through Fc receptors (FcRs) on natural killer cells (NK). However, FcR-mediated functions of NK cells from patients with cancer are significantly impaired. Identifying the mechanisms of this dysfunction and impaired response to mAb therapy could lead to combination therapies and enhance mAb therapy.Experimental Design: Cocultures of autologous NK cells and MDSC from patients with cancer were used to study the effect of myeloid-derived suppressor cells (MDSCs) on NK-cell FcR-mediated functions including antibody-dependent cellular cytotoxicity, cytokine production, and signal transduction in vitro Mouse breast cancer models were utilized to study the effect of MDSCs on antibody therapy in vivo and test the efficacy of combination therapies including a mAb and an MDSC-targeting agent.Results: MDSCs from patients with cancer were found to significantly inhibit NK-cell FcR-mediated functions including antibody-dependent cellular cytotoxicity, cytokine production, and signal transduction in a contact-independent manner. In addition, adoptive transfer of MDSCs abolished the efficacy of mAb therapy in a mouse model of pancreatic cancer. Inhibition of iNOS restored NK-cell functions and signal transduction. Finally, nonspecific elimination of MDSCs or inhibition of iNOS in vivo significantly improved the efficacy of mAb therapy in a mouse model of breast cancer.Conclusions: MDSCs antagonize NK-cell FcR-mediated function and signal transduction leading to impaired response to mAb therapy in part through nitric oxide production. Thus, elimination of MDSCs or inhibition of nitric oxide production offers a strategy to improve mAb therapy. Clin Cancer Res; 24(8); 1891-904. ©2018 AACR.

The Effects Of Myeloid-Derived Suppressor Cells On Cancer And Cancer Treatments

The Effects Of Myeloid-Derived Suppressor Cells On Cancer And Cancer Treatments

Cardioprotective Role of Myeloid-Derived Suppressor Cells in Heart Failure.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that expand in cancer, inflammation, and infection and negatively regulate inflammation and the immune response. Heart failure (HF) is a complex clinical syndrome wherein inflammation induction and incomplete resolution can potentially contribute to HF development and progression. However, the role of MDSCs in HF remains unclear. The percentage of MDSCs in patients with HF and in mice with pressure overload-induced HF using isoproterenol infusion or transverse aortic constriction (TAC) was detected by flow cytometry. The effects of MDSCs on isoproterenol- or TAC-induced HF were observed on depleting MDSCs with 5-fluorouracil (50 mg/kg) or gemcitabine (120 mg/kg), transferring purified MDSCs, or enhancing endogenous MDSCs with rapamycin (2 mg·kg-1·d-1). Hypertrophic markers and inflammatory factors were detected by ELISA, real-time polymerase chain reaction, or Western blot. Cardiac functions were determined by echocardiography and hemodynamic analysis. The percentage of human leukocyte antigen-D-related (HLA-DR)-CD33+CD11b+ MDSCs in the blood of patients with HF was significantly increased and positively correlated with disease severity and increased plasma levels of cytokines, including interleukin-6, interleukin-10, and transforming growth factor-β. Furthermore, MDSCs derived from patients with HF inhibited T-cell proliferation and interferon-γ secretion. Similar results were observed in TAC- and isoproterenol-induced HF in mice. Pharmaceutical depletion of MDSCs significantly exacerbated isoproterenol- and TAC-induced pathological cardiac remodeling and inflammation, whereas adoptive transfer of MDSCs prominently rescued isoproterenol- and TAC-induced HF. Consistently, administration of rapamycin significantly increased endogenous MDSCs by suppressing their differentiation and improved isoproterenol- and TAC-induced HF, but MDSC depletion mostly blocked beneficial rapamycin-mediated effects. Mechanistically, MDSC-secreted molecules suppressed isoproterenol-induced hypertrophy and proinflammatory gene expression in cardiomyocytes in a coculture system. Neutralization of interleukin-10 blunted both monocytic MDSC- and granulocytic MDSC-mediated anti-inflammatory and antihypertrophic effects, but treatment with a nitric oxide inhibitor only partially blocked the antihypertrophic effect of monocytic MDSCs. Our findings revealed a cardioprotective role of MDSCs in HF by their antihypertrophic effects on cardiomyocytes and anti-inflammatory effects through interleukin-10 and nitric oxide. Pharmacological targeting of MDSCs by rapamycin constitutes a promising therapeutic strategy for HF.

Abstract 4633: Crosstalk between MDSCs and Th17

Abstract Expansion of myeloid-derived suppressor cells (MDSCs) within the tumor is a known barrier to successful cancer immunotherapy. MDSCs are heterogeneous population of immature myeloid cells with potent immunosuppressive activity. Emerging evidences in the recent years define the role of immunosuppressive activity of MDSCs on different subsets of CD4+ T cells, however the exact effect of MDSCs on inflammatory Th17 cells during tumor progression is not clear. Here we demonstrate the immunosuppressive effect of MDSCs on Th17 cells. We further show that the interaction between MDSCs and Th17 is not unilateral and reveal that Th17 cells can promote the immunosuppressive effect of MDSCs. MDSCs, either isolated from tumor bearing mice or generated in vitro from bone marrow (BM-derived MDSCs), can both suppress IL-17A expression. Our data also demonstrate that IFNg, produced by Th17 cells is essential for the immunosuppressive activity of BM-derived MDSCs on IL-17A expression and further that the IFNgR1-driven signaling is important for Nos2-mediated immunosuppressive effect of BM-derived MDSCs on IL-17A expression. Understanding the molecular mechanism of the interplay between MDSCs and Th17 cells may help to develop more specific targeted therapy for cancer immunotherapy and improve therapeutic efficacy of the existing therapies against cancer. Note: This abstract was not presented at the meeting. Citation Format: Brijendra Singh. Crosstalk between MDSCs and Th17 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4633. doi:10.1158/1538-7445.AM2017-4633

Myeloid-Derived Suppressor Cells Induce the Expansion of Regulatory B Cells and Ameliorate Autoimmunity in the Sanroque Mouse Model of Systemic Lupus Erythematosus.

This study was undertaken to assess the effect of myeloid-derived suppressor cells (MDSCs) on various B cell subsets, including regulatory B cells, as well as to assess the potential therapeutic effects of MDSC infusion in an animal model of systemic lupus erythematosus (SLE). Splenocytes were cultured with MDSCs, and the populations of various B cells and effector T cell subsets were analyzed by flow cytometry. Lupus mice (roquinsan/san mice) were treated intravenously with MDSCs obtained from C57BL/6 mice, and the levels of serum autoantibodies, degree of proteinuria, histologic changes in the kidney, and populations of various B cell and T cell subsets in the spleen were analyzed. Coculture of MDSCs with splenocytes from C57BL/6 mice resulted in an expansion of the population of interleukin-10-producing B cells. The expansion of regulatory B cells was completely blocked by the addition of NG -monomethyl-l-arginine, an inhibitor of inducible nitric oxide synthase (iNOS). Infusion of MDSCs resulted in a reduction of serum anti-double-stranded DNA antibody levels and degree of proteinuria and an improvement in renal pathology in the roquinsan/san mice. MDSC coculture also resulted in a decrease in the population of effector B cells, such as germinal center B cells and plasma cells. Moreover, infusion of MDSCs resulted in an expansion of the regulatory B cell population as well as a decrease in follicular helper T cells, Th1 cells, and Th17 cells in the spleens of roquinsan/san mice. Our results indicate the MDSCs induce expansion of regulatory B cells via iNOS and ameliorate autoimmunity in a murine model of SLE. These findings indicate that MDSCs may be a promising therapeutic strategy for targeting B cell-mediated autoimmune diseases.

MDSCs enhance Th17 differentiation and disease progression through arginase-1 production in patients with systemic lupus erythematosus

Abstract Expansion of myeloid-derived suppressor cells (MDSCs) has been documented in some murine models and patients with autoimmune diseases, but the exact role of MDSCs in this process remains largely unknown. Although MDSCs are supposed to be immunosuppressive, previous studies have shown that these cells may also enhance Th17 responses via an IL-1-dependent mechanism in murine autoimmune models, such as experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA). However, the role of MDSCs in the development of autoimmune responses in human remains largely unknown. Current study investigates this question in patients with systemic lupus erythematosus (SLE). We found that patients with active SLE (n=32) had a significant increase in HLA-DR−CD11b+CD33+ MDSCs, in the peripheral blood compared to healthy controls (HCs; n=25). The frequency of MDSCs was positively correlated with the level of serum arginase-1 (Arg-1) activity, Th17 responses and disease severity in SLE patients. Consistently, in comparison with MDSCs from HCs, MDSCs from SLE patients exhibited significantly elevated Arg-1 production, and increased potential to promote Th17 differentiation in vitro in an Arg-1-dependent manner that is likely mediated by multiple mechanisms involving RORgt, RORa and mTOR. Moreover, in a humanized SLE model, MDSCs were essential for the induction of Th17 responses and the associated renal injuries and the effect of MDSCs was Arg-1-dependent. Our data provide direct evidence demonstrating a pathogenic role for MDSCs in human SLE, and suggests that targeting MDSCs or Arg-1 may offer novel therapeutic strategies for the treatment of SLE and other Th17 cell-mediated autoimmune diseases.

Circulating CD14(+) HLA-DR(-/low) myeloid-derived suppressor cells in leukemia patients with allogeneic hematopoietic stem cell transplantation: novel clinical potential strategiesfor the prevention and cellular therapy of graft-versus-host disease.

Myeloid‐derived suppressor cells (MDSCs) are a heterogeneous cell population that includes immature myeloid cells and the progenitor cells of macrophages, dendritic cells (DCs), monocytes, and neutrophils. The expansion and functional importance of MDSCs in patients with cancer and noncancer pathogenic conditions has been recognized. As a result, there has been growing interest in understanding their roles in acute graft‐versus‐host disease (aGVHD) after allogenetic hematopoietic stem cell transplantation (allo‐HSCT). In order to evaluate possible effects of MDSCs on aGVHD development and clinical outcomes, this study systematically detected the dynamic changes of MDSCs accumulation in patients during the first 100 days after allo‐HSCT, and investigated the levels of other cell types and relative cytokines during MDSCs accumulation. Results showed that accumulation of MDSCs in the graft and in peripheral blood when engraftment might contribute to patients' overall immune suppression and result in the successful control of severe aGVHD and long‐term survival without influence on risk of recurrence after allo‐HSCT. But MDSCs levels in the graft had more favorable predictive abilities. Furthermore, MDSCs proportion significantly increased in patients developing aGVHD after allo‐HSCT. It might be caused by secondary inflammatory response, especially related to high concentrations of IL‐6 and TNF‐α. But this accumulation would not be able to counterbalance the aggravation of aGVHD and would not have influence on clinical outcomes and risk of relapse. Overall, MDSCs might be considered as potential new therapeutic option for aGVHD and achieve long‐term immunological tolerance and survival.

Arginase-1-dependent promotion of TH17 differentiation and disease progression by MDSCs in systemic lupus erythematosus.

Expansion of myeloid-derived suppressor cells (MDSCs) has been documented in some murine models and patients with autoimmune diseases, but the exact role of MDSCs in this process remains largely unknown. The current study investigates this question in patients with systemic lupus erythematosus (SLE). Patients with active SLE showed a significant increase in HLA-DR(-)CD11b(+)CD33(+)MDSCs, including both CD14(+)CD66b(-)monocytic and CD14(-)CD66b(+)granulocytic MDSCs, in the peripheral blood compared to healthy controls (HCs). The frequency of MDSCs was positively correlated with the levels of serum arginase-1 (Arg-1) activity, T helper 17 (TH17) responses, and disease severity in SLE patients. Consistently, in comparison with MDSCs from HCs, MDSCs from SLE patients exhibited significantly elevated Arg-1 production and increased potential to promote TH17 differentiation in vitro in an Arg-1-dependent manner. Moreover, in a humanized SLE model, MDSCs were essential for the induction of TH17 responses and the associated renal injuries, and the effect of MDSCs was Arg-1-dependent. Our data provide direct evidence demonstrating a pathogenic role for MDSCs in human SLE. This study also provides a molecular mechanism of the pathogenesis of SLE by demonstrating an Arg-1-dependent effect of MDSCs in the development of TH17 cell-associated autoimmunity, and suggests that targeting MDSCs or Arg-1 may offer potential therapeutic strategies for the treatment of SLE and other TH17 cell-mediated autoimmune diseases.

L-arginine and docetaxel synergistically enhance anti-tumor immunity by modifying the immune status of tumor-bearing mice

l-arginine (l-Arg) supplementation has been reported to enhance the function of immune cells, including dendritic cells (DCs) and T lymphocytes, in cancer models thereby countering the suppressive effects of myeloid-derived suppressor cells (MDSCs). The balance of the active immune cells is one factor that determines the progression of cancers in vivo. Docetaxel (DTX), an immunomodulatory chemotherapeutic agent, is now widely used in several types of malignancies including breast cancer. We hypothesized that the combination of DTX and l-Arg would elicit a more robust antitumor response than either molecule alone. To test this hypothesis we utilized BALB/c mice inoculated with 4T1 mammary carcinoma cells. DTX and l-Arg synergistically limited tumor growth in vivo and moderately increased the life span of tumor bearing mice. The anti-tumor effects were associated with the proliferation of splenic CD8+ CTL and CD4+ Th1 effector cells, as well as increased serum levels of interferon gamma. More importantly, DTX+l-Arg effectively increased anti-tumor immunity within the tumor microenvironment. Furthermore, the combined therapy increased the number of myeloid (mDCs) and plasmacytoid (pDCs) dendritic cells, potent activators of the T cell response, and enhanced expression of the maturation markers CD86 and MHC II (required for antigen presentation). The combination therapy also reduced the proliferation of MDSCs. These data suggest that DTX+l-Arg may be a novel therapeutic strategy for breast cancer patients.

Dynamic Change and Impact of Circulating Myeloid-Derived Suppressor Cells in Patients Following Allogeneic Hematopoietic Stem Cell Transplantation

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population involved in tumor-associated immunosuppression and played immune regulatory roles in malignancies, infectious disease, autoimmune disease, trauma and inflammatory disease. Based on the significant suppressive functions, MDSCs raises great interests in the field of allogenetic hematopoietic stem cell transplantation (allo-HSCT) and graft-versus-host disease (GVHD). In recent years, studies described the immunosuppressive functions of CD14+HLA-DR-/low MDSCs, one of the few well-characterized MDSC subsets in human. However, the studies in patients with allo-HSCT are still scanty. This study identified the phenotype of CD14+HLA-DR-/low MDSCs and systematically monitored the dynamic changes of MDSCs accumulation in patients during the first 100 days after allo-HSCT in order to evaluate possible effects of MDSCs on aGVHD development and clinical outcomes. We also detected the frequencies of other cell types and concentrations of relative cytokines during MDSCs accumulation. Results showed that accumulation of MDSCs in the graft and in peripheral blood when engraftment might contribute to patients' overall immune suppression and result in the successful control of severe aGVHD and long-term survival without influence on risk of recurrence after allo-HSCT. However, the level of MDSCs in the graft had more favorable predictive abilities compared with that in PBMCs when engraftment. Furthermore, MDSCs frequencies were significantly increased in patients developing aGVHD after allo-HSCT.In the patients with mild aGVHD (0-2), MDSCs accumulated at the time of engraftment after allo-HSCT and decreased to basal levels at about 4 weeks. MDSCs frequencies would keep in stable levels with slight fluctuations in the following weeks. But, in patients with severe aGVHD (3-4), MDSCs elevated slightly when engraftment. When aGVHD occurred, MDSCs frequencies would significantly increase. And a synchronized reduction of the levels of MDSCs was observed after effective management of aGVHD with immunosuppressive therapy. Besides, the levels of IL-10, IL-6, TNF-α, Arg-1, iNOS and HO-1 increased greatly both in patients with aGVHD and in high MDSCs group. It is speculated that MDSC accumulation at the onset of aGVHD might be caused by secondary inflammatory response, especially related to high concentrations of IL-6 and TNF-α. But the accumulation would not be able to counterbalance the aggravation of aGVHD and would not have influence on clinical outcomes and risk of relapse in future. Overall, we suggested that MDSCs might be considered as a potential new approaches to regulate transplant rejection and achieve the recipient host long-term acceptance and survival. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Tumor-Promoting Effects of Myeloid-Derived Suppressor Cells Are Potentiated by Hypoxia-Induced Expression of miR-210.

Myeloid-derived suppressor cells (MDSC) contribute significantly to the malignant characters conferred by hypoxic tumor microenvironments. However, selective biomarkers of MDSC function in this critical setting have not been defined. Here, we report that miR-210 expression is elevated by hypoxia-inducible factor-1α (HIF1α) in MDSC localized to tumors, compared with splenic MDSC from tumor-bearing mice. In tumor MDSC, we determined that HIF1α was bound directly to a transcriptionally active hypoxia-response element in the miR-210 proximal promoter. miR-210 overexpression was sufficient to enhance MDSC-mediated T-cell suppression under normoxic conditions, while targeting hypoxia-induced miR-210 was sufficient to decrease MDSC function against T cells. Mechanistic investigations revealed that miR-210 modulated MDSC function by increasing arginase activity and nitric oxide production, without affecting reactive oxygen species, IL6, or IL10 production or expression of PD-L1. In splenic MDSC, miR-210 regulated Arg1, Cxcl12, and IL16 at the levels of both mRNA and protein, the reversal of which under normoxic conditions decreased T-cell-suppressive effects and IFNγ production. Interestingly, miR-210 overexpression or targeting IL16 or CXCL12 enhanced the immunosuppressive activity of MDSC in vivo, resulting in increased tumor growth. Taken together, these results provide a preclinical rationale to explore miR-210 inhibitory oligonucleotides as adjuvants to boost immunotherapeutic responses in cancer patients.

Study on the immunosuppressive activities of myeloid derived suppressor cells in patients suffering from recurrent spontaneous abortion

Objective To investigate the roles of myeloid derived suppressor cells (MDSCs) in the maintenance of maternal immune tolerance and to analyze their associations with recurrent spontaneous abortion (RSA). Methods Peripheral blood samples were collected from sixty subjects including non-pregnant healthy subjects, normal pregnant women and women with recurrent spontaneous abortion aged 25 to 35 years (n=20). Flow cytometry analysis was performed to monitor the changes of MDSCs at the 12th, 24th and 36th weeks of gestational age in three normal pregnant women. The differences with the numbers of MDSCs during the same stage of pregnancy in peripheral blood samples were compared among the three groups by flow cytometry analysis. RT-PCR analysis was used for detection of Arg-1 in women with normal pregnancy and RSA. CD8+ T cells were separated from non-pregnant healthy subjects by using magnetic beads. The immunosuppressive effects of MDSCs, isolated from women with normal pregnancy and RSA, on CD8+ T cells were evaluated by using the 3H thymidine incorporation assay. Results The number of MDSCs increased during normal pregnancy and the differences among different weeks were significant (12th week vs 24th week: P=0.0442, 24th week vs 36th week: P=0.0233, 12th week vs 36th week: P=0.0017). The percentages of MDSCs in peripheral blood of the healthy non-pregnant women were the lowest [(0.937±0.127)%], followed by those in women with RSA [(2.151±0.185)%] and normal pregnant women [(3.777±0.427)%]. There was significant difference with the percentage of MDSCs between women with normal pregnancy and RSA (P=0.0250). Compared with women with normal pregnancy, those with RSA showed significantly decreased levels of Arg-1 (P=0.0474) and suppressed activities of MDSCs against CD8+ T cell proliferation (P=0.0230). Conclusion The MDSCs might play an important role in the maintenance of maternal immune tolerance. Decreased number and inhibited function of MDSCs in the peripheral blood of women with RSA might be responsible for the development of RSA. Key words: Myeloid derived suppressor cell; Maternal immune tolerance; Recurrent spontaneous abortion

Antigen-specific T cells conditioned with MDSC display a surprising increased anti-tumor activity after adoptive T cell-based immunotherapy

The success of adoptive T cell-based immunotherapy (ACT) in cancer is limited in part by the accumulation of myeloid-derived suppressor cells (MDSC), which block several T cell functions, including proliferation and expression of effector mediators. Paradoxically, inhibition of CD8+ T cell differentiation during the pre-ACT phase also showed to increase anti-tumor efficacy. Thus, we aimed to determine the effect of MDSC on T cell differentiation and on ACT efficacy after in vitro conditioning of CD8+ T cells. Results indicate that MDSC block the differentiation of CD8+ T cells into effector cells, without altering their activation status, production of IL-2, or signaling through the T cell receptor. Moreover, culturing of CD8+ T cells in the presence of MDSC resulted in an increased ACT anti-tumor activity and elevated frequency and IFNγ production after transfer onto tumor-bearing mice. Additional findings confirmed that undifferentiated CD62L+ T cells mediated the enhanced anti-tumor activity triggered by MDSC-exposed T cells. Mechanistic studies showed that MDSC restricted de novo protein synthesis and activity of mechanistic target of rapamycin (mTOR) in T cells. Silencing of the negative mTOR regulator tuberous sclerosis complex 2 restored mTOR activity in T cells co-cultured with MDSC, but resulted in T cell apoptosis. Thus, our results indicate that culturing of CD8+ T cells in the presence of MDSC improves their anti-tumor efficacy, frequency, and function after ACT possibly through inhibition of mTOR signaling. Continuation of this research will enable the development of novel strategies to enhance the efficacy of ACT in cancer.

Targeted TLR9-activation/STAT3-blocking abrogates immunosuppressive functions of myeloid-derived suppressor cells from late-stage prostate cancer patients

Recent clinical advances underscored that elimination of tumor-induced immunosuppression is prerequisite for successful therapy of advanced human cancers. The myeloid-derived suppressor cells (MDSCs) are one of the major populations limiting T cell-mediated antitumor immune responses in late-stage solid tumors, such as castration-resistant prostate cancers (CRPCs). Targeting MDSCs proved challenging due to their heterogeneity and phenotypic similarities with other myeloid cell lineages. Here, we identify a population of granulocytic MDSCs, which accumulate in patients' blood during progression of prostate cancer from localized to metastatic disease. The CRPC-associated MDSCs potently inhibit proliferation, IFN-γ and Granzyme-B production in autologous CD8+ T cells. Importantly, the MDSCs in blood and in lymph nodes of CRPC patients show high levels of activated STAT3 transcription factor, which is a crucial immune checkpoint regulator. We previously generated an original method to silence genes specifically in TLR9+ myeloid cells using CpG-siRNA conjugates [1,2]. Now, we demonstrate that the CpG-STAT3siRNA is also effectively internalized by human MDSCs and induces STAT3 silencing without the need for transfection reagents. Our further studies demonstrated that two-pronged TLR9-activation/STAT3-blocking by CpG-STAT3siRNA inhibits immunosuppressive effects of CRPC-MDSCs on CD8+ T cells, while both TLR9 triggering or STAT3 inhibition alone have only minimal effects. The reversal of MDSC immunosuppression by CpG-STAT3 siRNA results from reduced expression and enzymatic activity of Arginase I, a downstream STAT3 target gene. Overall, our study demonstrates the feasibility of overcoming immunosuppression in CRPC patients using CpG-STAT3siRNA strategy to alleviate effects of MDSCs. We anticipate that our strategy to reverse MDSC-mediated immunosuppression without depleting myeloid cell populations will generate safer and more effective immunotherapy for late-stage, metastatic prostate cancers and potentially other solid tumors. This project described was supported by the National Cancer Institute of the National Institutes of Health under award number R01CA155367 and by the Department of Defense Prostate Cancer Research Program under award number W81XWH-12-1-0132 to M.K.

Activation of STAT3 promoting immunosuppressive effect on T cells in MDSCs of breast cancer

Objective: To explore the status of STAT3 phosphorylation in myeloid-derived suppressor cells (MDSCs) of breast cancer and its function in the immunosuppressive effect of MDSCs on proliferation and cytokine secretion of T cells. Methods: CCD33 cells were isolated from healthy umbilical cord, blood-derived, peripheral blood mononuclear cells and were co-cultured with breast cancer cell line MDA-MB-231 in vitro using Transwell plates to induce MDSCs. The untreated CD33 cells were used as controls. Idoxuridine (IDO) suppressor expression and STAT3 phosphorylation were examined using Western blot assay. The proliferation and cytokine secretion of T cells, which were co-cultured with MDSCs, were determined by methyl thiazol tetrazolium assay and enzyme-linked immunosorbent assay. 1-MT and JSI-124 were used to investigate the function of IDO and pSTAT3 in MDSC-mediated T cell immunosuppression. Results: The protein levels of IDO and pSTAT3 in MDSCs were significantly upregulated. MDSCs obviously suppressed T-cell proliferation, which was reversed by 1-MT or JSI-124 (P<0.05). MDSCs could promote TGF-β and IL-10 secretions, but could also remarkably inhibit IFN-γ secretion (P<0.05). After incubation with 1-MT or JSI-124, the increase in TGF-β and IL-10, as well as the decrease in IFN-γ, was significantly reversed. Conclusion: The upregulated pSTAT3 induced the IDO increase in MDSCs. JSI-124 can block MDSC-mediated immunosuppressive effect on T cells in breast cancer.

Effects of anti-tumor drugs on myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) play an important immunosuppressive role during the tumor development process.And the progression of many tumors are always accompanied with abnormal accumulation of MDSCs.Moreover,both the accumulation and functions of MDSCs could be affected by complicated factors.Therefore,how to effectively reduce the immunosuppressive effects of MDSCs in oncotherapy has become the focus of scholars.Recent studies show that anti-tumor drugs can affect many biological behaviors of MDSCs. Key words: Myeloid cells; Antineoplastic agents; Immunosuppressive agents; Myeloied derived suppressor cells

Targeting myeloid-derived suppressor cells and the PD-1/PD-L1 axis to enhance immunotherapy with anti-CEA designer T cells for the treatment of colorectal liver metastases.

3079 Background: Immunotherapy for colorectal cancer liver metastases (CRCLM) is limited by the intrahepatic immunosuppressive environment mediated in part by myeloid derived suppressor cells (MDSC), which expand in response to tumor. T cell suppression can be mediated by programmed death ligand-1 (PD-L1, CD274) on MDSC binding to programmed death-1 (PD-1, CD279) on T cells. We hypothesize blocking PD-L1 will improve adoptive cellular therapy efficacy for CRCLM through inhibition of MDSC-mediated T cell suppression. Methods: “Designer” T cells (dTc) were produced from activated murine splenocytes transduced with chimeric antigen receptor (CAR) specific for CEA. C57BL/6 mice were injected with CEA+ MC38 tumor cells via spleen, and liver MDSC (CD11b+Gr1+) were purified with immunomagnetic beads after two weeks. MDSC were co-cultured with stimulated dTc with or without in vitro PD-L1 blockade. Results: MDSC expanded 2.4-fold in response to CRCLM, and expressed high levels of PD-L1 (63.8% PD-L1+). PD-L1 was equally expressed on both monocytic (CD11b+Ly6G-Ly6C+) and granulocytic (CD11b+Ly6G+) MDSC subsets (43.6% PD-L1+ and 27.9% PD-L1+, respectively). Expression of related ligand, PD-L2 was found to be negligible in both subsets. The cognate inhibitory receptor, PD-1, was expressed on dTc (23.8% PD-1+) and native T cells (37.3% PD-1+). Increasing endogenous T cell expression of PD-1 significantly correlated with MDSC expansion (r=0.9774, p&lt;0.0001) in response to CRCLM. Co-culture of dTc with MDSC demonstrated the suppressive effect of MDSC on dTc proliferation which was abrogated with in vitro targeting of PD-L1. The percentage of dTc proliferating in the presence of CEA+ tumor decreased from 72.2% to 29.3% (p&lt;0.001) with the addition of MDSC, and immunosuppression was reversed with blockade of PD-L1, which resulted in a 1.6-fold increase in dTc proliferation (p=0.01 ). Conclusions: Liver MDSC expand in the presence of CRCLM and mediate suppression of anti-CEA dTc via PD-L1. Our results indicate that blockade of PD-L1:PD-1 engagement is a viable strategy for enhancing the efficacy of adoptive cell therapy for liver metastases.