Depletion Of Myeloid-derived Suppressor Cells Research Articles

Requirement for Interactions of Natural Killer T Cells and Myeloid-Derived Suppressor Cells for Transplantation Tolerance

The goal of the study was to elucidate the cellular and molecular mechanisms by which a clinically applicable immune tolerance regimen of combined bone marrow and heart transplants in mice results in mixed chimerism and graft acceptance. The conditioning regimen of lymphoid irradiation and anti-T cell antibodies changed the balance of cells in the lymphoid tissues to create a tolerogenic microenvironment favoring the increase of natural killer T (NKT) cells, CD4+ CD25+ regulatory T cells and Gr-1+ CD11b+ myeloid-derived suppressor cells (MDSCs), over conventional T cells (Tcons). The depletion of MDSCs abrogated chimerism and tolerance, and add back of these purified cells was restorative. The conditioning regimen activated the MDSCs as judged by the increased expression of arginase-1, IL-4Rα and programmed death ligand 1, and the activated cells gained the capacity to suppress the proliferation of Tcons to alloantigens in the mixed leukocyte reaction. MDSC activation was dependent on the presence of host invariant NKT cells. The conditioning regimen polarized the host invariant NKT cells toward IL-4 secretion, and MDSC activation was dependent on IL-4. In conclusion, there was a requirement for MDSCs for chimerism and tolerance, and their suppressive function was dependent on their interactions with NKT cells and IL-4.

Lung-residing myeloid-derived suppressors display dual functionality in murine pulmonary tuberculosis.

Myeloid cells encompass distinct populations with unique functions during homeostasis and disease. Recently, a novel subset of innate cells, myeloid-derived suppressor cells (MDSCs), has been described in cancer, which suppresses T-cell responses and fosters disease progression. The role of MDSCs in infection is insufficiently addressed. To examine the presence and function of MDSCs during experimental pulmonary tuberculosis (TB) and further understand the immunologic consequences of direct interactions between MDSCs and lung bacterial pathogens. Using cell-based approaches and experimental mouse models for pulmonary TB we characterized MDSCs as novel myeloid populations directly interacting with Mycobacterium tuberculosis (Mtb). MDSCs readily phagocytosed Mtb, and released proinflammatory (IL-6, IL-1α) and immunomodulatory (IL-10) cytokines while retaining their suppressive capacity. MDSCs were identified at the site of infection in the lung in disease-resistant and -susceptible mice during pulmonary TB. Excessive MDSC accumulation in lungs correlated with elevated surface expression of IL-4Rα and heightened TB lethality, whereas targeted depletion of MDSCs ameliorated disease. Our data reveal that MDSCs provide a niche for pathogen survival and tailor immunity in TB. These findings suggest MDSCs as amenable targets for host-directed therapies and emphasize them as cellular-immune regulators during chronic inflammatory conditions, including chronic infections and microbial complications of neoplastic disorders.

Infiltrating S100A8+ myeloid cells promote metastatic spread of human breast cancer and predict poor clinical outcome.

The mechanisms by which breast cancer (BrC) can successfully metastasize are complex and not yet fully understood. Our goal was to identify tumor-induced stromal changes that influence metastatic cell behavior, and may serve as better targets for therapy. To identify stromal changes in cancer-bearing tissue, dual-species gene expression analysis was performed for three different metastatic BrC xenograft models. Results were confirmed by immunohistochemistry, flow cytometry, and protein knockdown. These results were validated in human clinical samples at the mRNA and protein level by retrospective analysis of cohorts of human BrC specimens. In pre-clinical models of BrC, systemic recruitment of S100A8+ myeloid cells-including myeloid-derived suppressor cells (MDSCs)-was promoted by tumor-derived factors. Recruitment of S100A8+ myeloid cells was diminished by inhibition of tumor-derived factors or depletion of MDSCs, resulting in fewer metastases and smaller primary tumors. Importantly, these MDSCs retain their ability to suppress T cell proliferation upon co-culture. Secretion of macrophage inhibitory factor (MIF) activated the recruitment of S100A8+ myeloid cells systemically. Inhibition of MIF, or depletion of MDSCs resulted in delayed tumor growth and lower metastatic burden. In human BrC specimens, increased mRNA and protein levels of S100A8+ infiltrating cells are highly associated with poor overall survival and shorter metastasis free survival of BrC patients, respectively. Furthermore, analysis of nine different human gene expression datasets confirms the association of increased levels of S100A8 transcripts with an increased risk of death. Recruitment of S100A8+ myeloid cells to primary tumors and secondary sites in xenograft models of BrC enhances cancer progression independent of their suppressive activity on T cells. In clinical samples, infiltrating S100A8+ cells are associated with poor overall survival. Targeting these molecules or associated pathways in cells of the tumor microenvironment may translate into novel therapeutic interventions and benefit patient outcome.

Abstract 1103: MDSC targeting therapy for uterine cervical cancer displaying TRL

Abstract Objectives: The aim of this study was to investigate the clinical implications and underlying mechanism of tumor-related-leukocytosis (TRL) in cervical cancer. Methods: The clinical data of cervical cancer patients who were treated with definitive radiotherapy were analyzed to investigate the association between TRL and treatment outcome in retrospective and prospective settings. Clinical samples, cervical cancer cell lines, and a mouse model of cervical cancer were employed to examine the mechanisms responsible for TRL in cervical cancer, focusing on the myeloid-derived suppressor cell (MDSC) and tumor-derived granulocyte colony-stimulating factor(G-CSF). Results: TRL was significantly associated with shorter survival. The TRL-positive patients displayed upregulated tumor G-CSF expression and elevated serum G-CSF levels and increased MDSC frequencies in the blood compared with the TRL-negative patients. In vitro and in vivo investigations revealed that tumor-derived G-CSF is involved in the underlying causative mechanism of TRL and that the increase in the number of MDSC induced by tumor-derived G-CSF is responsible for the rapidly progressive nature of TRL-positive cervical cancer. The administration of anti-Gr-1 antibody or the depletion of MDSC by splenectomy significantly inhibited tumor growth in TRL-positive cervical cancer. Conclusion: TRL is an indicator of a poor prognosis in cervical cancer patients treated with definitive radiotherapy. MDSC induced by tumor-derived G-CSF is responsible for the rapidly progressive nature of TRL-positive cervical cancer. MDSC-targeting treatments might have therapeutic potential in TRL-positive cervical cancer. Note: This abstract was not presented at the meeting. Citation Format: Yuri Matsumoto, Mahiru Kawano, Tomoyuki Sasano, Seiji Mabuchi. MDSC targeting therapy for uterine cervical cancer displaying TRL. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1103. doi:10.1158/1538-7445.AM2014-1103

Abstract 150: Role of reactive oxygen species in doxorubicin-induced apoptosis of myeloid-derived suppressor cells

Abstract The expansion of myeloid-derived suppressor cells (MDSC) in the blood, secondary lymphoid organs and tumor beds in animal cancer models and in patients with many types of cancers participates to the immunosuppressive environment associated with the development of tumors. MDSC frequency correlates with the disease stage and prognosis. MDSC can not only impair innate and adaptive antitumor immune responses, but these cell also contribute to enhance tumor angiogenesis and metastatic potential. The therapeutic targeting of MDSC (depletion,functional inactivation or differentiation into pro-inflammatory cells) promotes the efficacy of immunotherapeutic interventions. Conventional anticancer agents such as docetaxel, gemcitabine or sunitinib have been used to eliminate tumor-induced MDSC. We have observed that the anthracycline doxorubicin can deplete MDSC that expanded in the murine mammary tumor models 4T1 and EMT6 and in the EL4 thymoma model. Doxorubicin-mediated elimination of MDSC is associated with increased T and NK cell activity and the combination of this drug with adoptive T lymphocyte transfer impairs tumor development and metastatic spreading. We here present results indicating that doxorubicin-mediated apoptosis of MDSC may depend on an increased production of reactive oxygen species (ROS) by these cells. MDSC from gp91-/- mice (lacking the gp91phox glycosylated subunit of the NADPH oxidase flavocytochrome b558, responsible for the production of superoxide ion O2·-) were less sensitive to doxorubicin-induced cell death than their wild-type counterparts. Consistently, the effects of doxorubicin on MDSC were partially impaired in tumor-bearing gp91-/- animals compared to wild-type mice. Interestingly the level of ROS in CD4+ or CD8+ T and NK cells were low and unchanged by doxorubicin administration. These observations may partly explain the selective effects of this chemotherapeutic agent on immunosuppressive MDSC while effector lymphocytes are spared and the subsequent increased in the effector to suppressor cell ratios, resulting in a mitigated immunosuppressive tumor environment. Citation Format: Darya Alizadeh, Emmanuel Katsanis, Nicolas Larmonier. Role of reactive oxygen species in doxorubicin-induced apoptosis of myeloid-derived suppressor cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 150. doi:10.1158/1538-7445.AM2014-150

γδT cells drive myeloid-derived suppressor cell-mediated CD8+ T cell exhaustion in hepatitis B virus-induced immunotolerance.

The mechanisms of liver hepatitis B virus (HBV)-induced systemic immune tolerance are still elusive, and the role of γδT cells has not yet been described. We examined the function of γδT cells in HBV-carrier mice--immunocompetent mice with plasmid-mediated persistent HBV expression in the liver. In this study, we found that γδT cell deficiency led to a break in HBV-induced tolerance and subsequent recovery of hepatic HBV-specific CD8(+) T cells. Of interest, IL-17(-/-) mice phenocopied TCRδ(-/-) mice in terms of losing HBV persistence, and adoptive transfer of γδT cells restored HBV-persistent expression in TCRδ(-/-) mice. We further observed that hepatic CD11b(+)Gr1(+) myeloid-derived suppressor cells (MDSCs) play a major role in this mechanism, as they were significantly reduced in both HBV-carrier TCRδ(-/-) and IL-17(-/-) mice. MDSC numbers also recovered after adoptive transfer of γδT cells, particularly Vγ4(+) T cells. Furthermore, anti-Gr1-mediated MDSC depletion in HBV-carrier mice accelerated HBV elimination from the host, whereas MDSCs transferred to γδT cell-deficient mice restored HBV-induced tolerance. Accordingly, inhibition of MDSCs by the arginase-1 inhibitor norNOHA enhanced the number of HBV-specific CD8(+) T cells and promoted HBV clearance. We also observed enhanced CD8(+) T cell number with a notable decline of MDSCs in TCRδ(-/-) mice compared with wild-type mice during the recombinant adeno-associated virus/HBV1.3 virus infection. Importantly, HBV-carrier TCRδ(-/-) mice not only exhibited increased anti-HBV CD8(+) T cells but also markedly reduced MDSCs. Overall, the current study reveals that γδT cells play a previously unrecognized regulatory role in liver tolerance by mobilizing MDSC infiltration to the liver, leading to MDSC-mediated CD8(+) T cell exhaustion.

Requirement for Interactions of Natural Killer T Cells and Myeloid Derived Suppressor Cells for Transplantation Tolerance.

The goal of the study was to elucidate the cellular and molecular mechanisms by which a clinically applicable immune tolerance regimen of combined bone marrow and heart transplants in mice results in mixed chimerism and graft acceptance. The conditioning regimen of total lymphoid irradiation and anti-T cell antibodies changed the balance of cells in the lymphoid tissues to create a tolerogenic microenvironment favoring the increase of natural killer T (NKT) cells, CD4+CD25+ Tregs, and Gr-1+CD11b+ myeloid derived suppressor cells (MDSCs), over conventional T cells. The depletion of MDSCs abrogated chimerism and tolerance, and add back of these purified cells was restorative. The conditioning regimen activated the MDSCs as judged by the increased expression of arginase-1, IL-4Ra, and PDL1, and the activated cells gained the capacity to suppress the proliferation of conventional T cells to alloantigens in the mixed leukocyte reaction. MDSC activation was dependent on the presence of host invariant NKT cells. The conditioning regimen polarized the host invariant NKT cells toward IL-4 secretion, and MDSC activation was dependent on IL-4. In conclusion, there was a requirement for MDSCs for chimerism and tolerance, and their suppressive function was dependent on their interactions with NKT cells and IL-4.

Uterine cervical cancer displaying tumor-related leukocytosis: a distinct clinical entity with radioresistant feature.

Tumor-related leukocytosis (TRL) is occasionally found in patients with nonhematopoietic malignancies. We investigated the clinical implication of TRL and individualized treatment for TRL-positive cervical cancer, as well as the underlying biological mechanism. Clinical data from 258 cervical cancer patients treated with definitive radiotherapy were analyzed to investigate the association between TRL and treatment outcome. Clinical samples, cervical cancer cell lines, and a mouse model of cervical cancer were used to examine the mechanisms responsible for TRL in cervical cancer, focusing on the role of tumor-derived granulocyte colony-stimulating factor (G-CSF) and myeloid-derived suppressor cells (MDSCs). All statistical tests were two-sided. TRL was statistically significantly associated with younger age (Wilcoxon rank sum test, P = .03), larger tumor size (Wilcoxon rank sum test, P = .006), advanced clinical stage (χ(2) test, P = .01), and shorter overall survival (Cox proportional hazard modeling and Wald tests, P < .001). Among cervical cancer patients, TRL was associated with upregulated tumor G-CSF expression (χ(2) test, P < .001), elevated serum G-CSF levels (Student t test, P = .03), larger spleens (Student t test, P = .045), and increased MDSC frequencies in the blood (Student t test, P < .001) compared with the TRL-negative patients. In vitro and in vivo experiments revealed that tumor-derived G-CSF was involved in the underlying causative mechanism of TRL and MDSCs induced by tumor-derived G-CSF are responsible for the rapidly progressive and radioresistant nature of TRL-positive cervical cancer. The administration of anti-Gr-1 neutralizing antibody or the depletion of MDSCs by splenectomy (n = 6 per group) inhibited tumor growth and enhanced radiosensitivity in TRL-positive cervical cancer xenografts (Wilcoxon rank sum test, P = .008 and P = .02, respectively). TRL is associated with resistance to radiotherapy among cervical cancer patients, and MDSC-targeting treatments may have therapeutic potential in these patients.

Agonistic anti-CD137 antibody treatment leads to antitumor response in mice with liver cancer.

Immunotherapy is a promising strategy against hepatocellular carcinoma (HCC). We assessed the therapeutic effects of stimulating CD137, a member of the TNF receptor family, with agonistic monoclonal antibodies (mAb). Agonistic anti-CD137 mAb treatment was tested on two in situ models of HCC in immunocompetent mice. We also studied the mediators involved at different time points. In an orthotopic HCC the treatment consistently leads to complete tumor regression in 40-60% of animals. The protection is long lasting in the animals responding to the treatment, which can reject a second tumor challenge more than 3 months after treatment and eradication of the first malignancy. The main mediators of the effect are T lymphocytes and NK cells, demonstrated through depletion experiments. In addition, adoptive transfer of splenocytes prepared from anti-CD137 mAb-treated and -cured mice to naive mice allowed them to, in turn, reject the tumor. The efficacy of anti-CD137 mAb treatment is associated with early, sustained recruitment of iNOS-positive macrophages within tumor nodules. Moreover, in the absence of treatment, tumor development is accompanied by infiltration by myeloid derived suppressor cells (MDSC) and regulatory T lymphocytes. In mice responding to the anti-CD137 mAb treatment, this infiltration is very limited, and a combination treatment with a depletion of MDSC leads to the recovery of 80% of the mice. These results demonstrate that agonistic anti-CD137 mAb is a promising therapeutic strategy for anti-tumor immunity stimulation against HCC.

Negative impact of myeloid-derived suppressor cells on CD8 effector T cell trafficking within the tumor microenvironment (TUM4P.924)

Abstract The success of immunotherapy and, unexpectedly, chemotherapy and radiation hinges on cytotoxic T cells gaining access to tumor targets. These observations have prompted interest in developing strategies to improve T cell trafficking in tumors. Here, we report that the ability of tumor vessels to respond to IL-6-dependent preconditioning regimens that boost CD8 effector T cell homing is temporally and inversely related to the expansion of myeloid-derived suppressor cells (MDSC) within the tumor microenvironment. Using real-time intravital imaging and immunofluorescence histology, IL-6 therapies were shown to convert vessels from T cell-low to -high recruitment sites in murine tumors with minimal MDSC infiltration (i.e., CT26 colorectal, B16 melanoma, EMT6 mammary tumors). This conversion requires induction of the ICAM-1 trafficking molecule on tumor vessels. Conversely, mammary (4T1, AT-3 and PyMT-MMTV) and pancreatic (Pan02) tumors with high MDSC burdens were refractory to IL-6 therapies, but became responsive after acute MDSC depletion. To further investigate contributions of MDSC to poor trafficking, IL-6-responsive tumors were admixed at a ratio of 2:1 with MDSC from tumor-bearing mice. Sustained elevation of MDSC in admixed tumors resulted in failure to support increased T cell trafficking in response to IL-6-dependent therapy. Taken together, these findings identify a novel role for MDSC in immune evasion by limiting T cell trafficking at tumor vascular loci.

Chronic intake of high fish oil diet induces myeloid-derived suppressor cells to promote tumor growth

Omega-3 polyunsaturated fatty acids enriched fish oil exerts beneficial anti-inflammatory effects in animal models with acute and chronic inflammatory diseases. Myeloid-derived suppressor cells (MDSCs), comprised of myeloid progenitors and precursors of myeloid cells, play vital roles in cancer. How fish oil affects the generation of MDSCs and the tumor development remains largely unexplored. Here, we show that dietary intake of high fish oil diet suppresses CD8(+) T cells activation and proliferation in vivo via elevated levels of MDSCs. Mechanistically, high fish oil diet induces the expression of immunosuppressive cytokine IL-10 and promotes myelopoiesis in the spleen as well as other peripheral tissues. The immature myeloid cells in the spleen exhibit morphological and functional characteristics of MDSCs with the capability to downregulate CD8(+) T cells activation. Depletion of MDSCs using anti-Gr-1 antibody decreases the growth of subcutaneously transferred B16 melanoma in mice on high fish oil diet. Interestingly, diet-induced production of MDSCs is not solely dependent of the spleen, as splenectomy has no effect on the tumor progress. Our data show that the liver functions as an alternative extramedullary hematopoiesis organ to support MDSCs differentiation and maintain tumor growth. Taken together, our study provides a novel insight into the physiological effects of fish oil and points to MDSCs as a possible mediator linking dietary fish oil intake and immunosuppression in cancer immunosurveillance.

Targeted depletion of an MDSC subset unmasks pancreatic ductal adenocarcinoma to adaptive immunity

BackgroundPancreatic ductal adenocarcinoma (PDA) is characterised by a robust desmoplasia, including the notable accumulation of immunosuppressive cells that shield neoplastic cells from immune detection. Immune evasion may be further enhanced...

Depletion of myeloid-derived suppressor cells during interleukin-12 immunogene therapy does not confer a survival advantage in experimental malignant glioma

Myeloid-derived suppressor cells (MDSCs) accumulate in the glioma microenvironment during tumor progression and promote immunosuppression. Interleukin-12 (IL-12) immunogene therapy can alter MDSCs toward an antigen-presenting cell phenotype and these mature cells can have a central role in antigen presentation. It remains unclear, however, how MDSC depletion can affect glioma immunotherapy. In this study, we generated a replication-deficient adenoviral vector, Ad.5/3.cRGD-mIL12p70, that transduces the GL261-based murine glioma cell line, resulting in the induction of biologically active, murine IL12p70 expression. Ex vivo, IL-12 expressed by GL261 cells induced interferon-γ synthesis in CD8(+) T cells (P<0.001), CD4(+) T cells (P=0.009) and natural killer cells (P=0.036). When injected 1 week after tumor implantation, Ad.5/3.cRGD-mIL12p70 successfully prolonged the survival of glioma-bearing mice. Sixty percent of animals treated with IL-12 immunotherapy were long-term survivors over 175 days, whereas all the control group animals expired by 40 days after tumor implantation (P=0.026). Mice receiving Ad.5/3.cRGD-mIL12p70 also accumulated 50% less MDSCs in the brain than the control group (P=0.007). Moreover, in the IL-12 group, MDSCs significantly overexpressed CD80 and major histocompatibility complex class II molecules (P=0.041). Depletion of MDSCs with Gr1(+) antibody had no survival benefit induced by IL-12-mediated immunotherapy. Of note, IL-12 therapy increased the presence of myeloid dendritic cells (mDCs) in the glioma microenvironment (P=0.0069). Ultimately, the data show that in the context of IL-12 immunogene therapy, MDSCs are dispensable and mDCs may provide the majority of antigen presentation in the brain.

Myeloid‐derived suppressor cells are key players in the resolution of inflammation during a model of acute infection

Myeloid-derived suppressor cells (MDSCs) are key players in the immune suppressive network. During acute infection with the causative agent of Chagas disease, Trypanosoma cruzi, BALB/c mice show less inflammation and better survival than C57BL/6 (B6) mice. In this comparative study, we found a higher number of MDSCs in the spleens and livers of infected BALB/c mice compared with infected B6 mice. An analysis of the two major MDSCs subsets revealed a greater number of granulocytic cells in the spleens and livers of BALB/c mice when compared with that in B6 mice. Moreover, splenic MDSCs purified from infected BALB/c mice inhibited ConA-induced splenocyte proliferation. Mechanistic studies demonstrated that ROS and nitric oxide were involved in the suppressive activity of MDSCs, with a higher number of infected CD8(+) T cells suffering surface-nitration compared to uninfected controls. An upregulation of NADPH oxidase p47 phox subunit and p-STAT3 occurred in MDSCs and infected IL-6 KO mice showed less recruitment of MDSCs and impaired survival. Remarkably, in vivo depletion of MDSCs led to increased production of IL-6, IFN-γ, and a Th17 response with very high parasitemia and mortality. These findings demonstrate a new facet of MDSCs as crucial regulators of inflammation during T. cruzi infection.

The proportion and function of peripheral myeloid-derived suppressor cells do not correlate with systemic inflammation in chronic obstructive pulmonary disease

Myeloid-derived suppressor cells (MDSC) have been implicated in the regulation of chronic inflammation. Chronic obstructive pulmonary disease (COPD) involves persistent inflammation, but the role of MDSC has not been explored. Here, proportions of MDSC (CD14−HLA-DR−CD33+CD11b+ cells) were quantified in peripheral blood mononuclear cells (PBMC) isolated from patients with ‘stable’ COPD (n=12), smokers with no evidence of COPD (n=11) and healthy non-smokers (n=11). The proportions of MDSC were similar in all groups. MDSC function was assessed by comparing T-cell and cytokine responses of whole and MDSC-depleted PBMC stimulated with Staphylococcus enterotoxin-B (SEB). Depletion of MDSC did not enhance CD4+ or CD8+ T-cell activation and proliferation, or alter IFNγ and IL-17 production in response to SEB. However production of TGFβ decreased after depletion of MDSC, so MDSC may be a source of this cytokine. In conclusion, COPD was not associated with perturbations in the proportion or function of MDSC in peripheral blood.

Downregulation of Hematopoietic MUC1 during Experimental Colitis Increases Tumor-Promoting Myeloid-Derived Suppressor Cells

MUC1 is a tumor-associated antigen that is aberrantly expressed in cancer and inflammatory bowel disease (IBD). Even though immune cells express low MUC1 levels, their modulations of MUC1 are important in tumor progression. Consistent with previous clinical data that show increased myeloid-derived suppressor cells (MDSCs) in IBD, we now show that downregulation of MUC1 on hematopoietic cells increases MDSCs in IBD, similar to our data in tumor-bearing mice. We hypothesize that MDSC expansion in IBD is critical for tumor progression. To mechanistically confirm the linkage between Muc1 downregulation and MDSC expansion, we generated chimeric mice that did not express Muc1 in the hematopoietic compartment (KO→WT). These mice were used in two models of colitis and colitis-associated cancer (CAC) and their responses were compared with wild-type (WT) chimeras (WT→WT). KO→WT mice show increased levels of MDSCs during colitis and increased protumorigenic signaling in the colon during CAC, resulting in larger colon tumors. RNA and protein analysis show increased upregulation of metalloproteinases, collagenases, defensins, complements, growth factors, cytokines, and chemokines in KO→WT mice as compared with WT→WT mice. Antibody-mediated depletion of MDSCs in mice during colitis reduced colon tumor formation during CAC. Development of CAC is a serious complication of colitis and our data highlight MDSCs as a targetable link between inflammation and cancer. In addition, the lack of MUC1 expression on MDSCs can be a novel marker for MDSCs, given that MDSCs are still not well characterized in human cancers.

Resistance to Streptozotocin-Induced Autoimmune Diabetes in Absence of Complement C3: Myeloid-Derived Suppressor Cells Play a Role

The contribution of complement to the development of autoimmune diabetes has been proposed recently. The underlying mechanisms, however, remain poorly understood. We hypothesize that myeloid-derived suppressor cells (MDSC), which act as regulators in autoimmunity, play a role in resistance to diabetes in absence of complement C3. Indeed, MDSC number was increased significantly in STZ-treated C3−/− mice. These cells highly expressed arginase I and inducible nitric oxide synthase (iNOS). Importantly, depletion of MDSC led to the occurrence of overt diabetes in C3−/− mice after STZ. Furthermore, C3−/− MDSC actively suppressed diabetogenic T cell proliferation and prevented/delayed the development of diabetes in arginase and/or iNOS-dependent manner. Both Tregs and transforming growth factor-β (TGF-β) are crucial for MDSC induction in STZ-treated C3−/− mice as depletion of Tregs or blocking TGF-β bioactivity dramatically decreased MDSC number. These findings indicate that MDSC are implicated in resistance to STZ-induced diabetes in the absence of complement C3, which may be helpful for understanding of mechanisms underlying preventive effects of complement deficiency on autoimmune diseases.

Chemoimmunotherapy provides protective immunity of murine pancreatic cancer model (P2070)

Abstract Pancreatic cancer is an aggressive disease with grim prognosis. Immunotherapy is less effective in treating tumors partly due to Myeloid Derived Suppressor Cells (MDSC). In this study we evaluated tumor regression due to MDSC depletion with dendritic cell (DC) vaccination of pancreatic tumor bearing (TB) mice. Flow cytometry results showed a significant increase in the percentage of MDSC in tumors and spleens of TB mice compared to naïve mice. MDSC isolated from TB mice significantly suppressed antigen-specific T cell responses compared to naive mice. Gemcitabine (GM) is a chemotherapeutic drug for cancer therapy. Flow cytometry results showed a significant decrease in the percentage of MDSC in splenocytes from GM-treated TB and naïve mice. To study effects of DC vaccination combined with MDSC depletion on tumor rejection, mice were vaccinated with PANC02 lysate-pulsed DC or PBS, three times at seven-day intervals. One week after final vaccination, mice were challenged with PANC02 tumor cells. Mice in the vaccinated and control groups either received PBS or GM therapy. In vivo depletion of MDSC was performed three days prior to tumor challenge, continued until the end of the experiment and was confirmed using flow cytometry. A significant survival benefit was seen in mice receiving both DC vaccination and MDSC depletion. Results from this study strongly suggest that the depletion of MDSC significantly enhances protective immunity in a murine pancreatic cancer model.

Mast cell-MDSC interactions promote chemokine secretion and parasite expulsion. (P6022)

Abstract Mast cells and myeloid-derived suppressor cells (MDSC) are both increased at sites of growing tumors and parasitic infection. We have tested the effects of mast cell-MDSC interactions in vitro and in vivo. Surprisingly, co-culture of these cells resulted in a significant increase in pro-inflammatory chemokine production, which was attributed to Ly6C+ MDSC. MDSC depletion via gemcitabine treatment in mice infected with Nippostrongylus brasiliensis or Trichenlla spiralis drastically increased parasite burden, reminiscent of mast cell-deficient mice. Gemcitabine also decreased mast cell-dependent antigen-induced airway hyperresponsiveness (AHR) and inflammation, while MDSC injection worsened AHR. These data suggest that the evolutionary purpose of MDSC may be to potentiate Th2-induced, mast cell-dependent inflammatory responses.

Therapeutic regulation of myeloid-derived suppressor cells and immune response to cancer vaccine in patients with extensive stage small cell lung cancer

Myeloid-derived suppressor cells (MDSC) are one of the major factors limiting the efficacy of immune therapy. In a clinical trial of patients with extensive stage small cell lung cancer (SCLC), we tested the possibility that targeting MDSC can improve the induction of immune responses by a cancer vaccine. Forty-one patients with extensive stage SCLC were randomized into three arms: arm A--control, arm B--vaccination with dendritic cells transduced with wild-type p53, and arm C--vaccination in combination with MDSC targeted therapy with all-trans-retinoic acid (ATRA). Interim results of the ongoing clinical trial are presented. Pre-treatment levels of MDSC populations in patients from all three arms were similar. Vaccine alone did not affect the proportion of MDSC, whereas in patients treated with ATRA, the MDSC decreased more than twofold (p = 0.02). Before the start of treatment, no patients had detectable p53-specific responses in IFN-γ ELISPOT. Sequential measurements did not show positive p53 responses in any of the 14 patients from arm A. After immunization, only 3 out of 15 patients (20 %) from arm B developed a p53-specific response (p = 0.22). In contrast, in arm C, 5 out of 12 patients (41.7 %) had detectable p53 responses (p = 0.012). The proportion of granzyme B-positive CD8(+) T cells was increased only in patients from arm C but not in arm B. Depletion of MDSC substantially improved the immune response to vaccination, suggesting that this approach can be used to enhance the effect of immune interventions in cancer.