Myeloid-derived suppressor cells (MDSCs), characterized by the co-expression of CD11b and Gr1, are a heterogeneous population of immature myeloid cells that exhibit strong suppressive functions against T cell responses. In inflammatory conditions like IBD, there is an increase in MDSCs but this is not sufficient to improve intestinal inflammation in IBD. Herein, we investigated the expansion of MDSCs in TNBS-induced acute colitis and whether the adoptive transfer of in vitro generated MDSCs ameliorated intestinal inflammation. We found that CD11b+Gr1+ MDSCs were significantly increased in experimental colitis. Further, this increase correlated to some extent with the severity of the disease. As per our protocol, MDSCs were generated from bone marrow cells co-cultured with hepatic stellate cells (HSCs), an essential cell type to obtain functional MDSCs in vitro. Adoptive transfer of HSC-induced MDSCs improved body weight loss and significantly downregulated inflammatory cytokines TNF, IFN-γ, and IL-17 in colonic tissue. Our results indicate MDSCs are immunoregulatory players in intestinal inflammation and that the adoptive transfer of in vitro generated MDSCs may provide a novel therapeutic approach for inflammatory bowel disease.

Thesis (Ph.D.)--University of Melbourne, The Walter and Eliza Hall Institute of Medical Research, Division of Cancer and Haematology, Dept. of Medical Biology,Faculty of Medicine,Dentistry and Health Sciences, 2006. / Typescript. Includes bibliographical references (leaves 192-210).

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature suppressor cells that are generated due to aberrant myelopoiesis under pathological conditions. Although MDSCs have been recognized for more than 20 years under the guise of different monikers, these particular populations of myeloid cells gained more attention recently due to their immunosuppressive properties, which halt host immune responses to growing cancers or overwhelming infections. While MDSCs may contribute to immune homeostasis after infection or tissue injury by limiting excessive inflammatory processes, their expansion may be at the expense of pathogen elimination and thus may lead to disease persistence. Therefore, MDSCs may be either damaging or obliging to the host by attenuating, for example, antitumor or anti-infectious immune responses. In this review, we recapitulate the biological and immunological aspects of MDSCs, including their generation, distribution, trafficking and the factors involved in their activation, expansion, suppressive functions, and interplay between MDSCs and regulatory T cells, with a focus on the perspectives of infection and inflammation.

Proper development and activation of cells of the myeloid lineage are critical for supporting innate immunity. This myelopoiesis is orchestrated by interdependent interactions between cytokine receptors, transcription factors and, as recently described, microRNAs (miRNAs). miRNAs contribute to normal and dysregulated myelopoiesis. Alterations in myelopoiesis underlie myeloid-derived suppressor cell (MDSC) expansion, a poorly understood heterogeneous population of immature and suppressive myeloid cells that expand in nearly all diseases where inflammation exists. MDSCs associated with inflammation often have immunosuppressive properties, but molecular mechanisms responsible for MDSC expansion are unclear. Emerging data implicate miRNAs in MDSC expansion. This review focuses on miRNAs that contribute to myeloid lineage differentiation and maturation under physiological conditions, and introduces the concept that altered miRNA expression my underlie expansion and accumulation of MDSCs. We divide our miRNAs into those with potential to promote MDSC expansion and two with known direct links to MDSC expansion, miR-223 and miR-494.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20253号 / 医博第4212号 / 新制||医||1020(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 河本 宏, 教授 戸井 雅和, 教授 小川 誠司 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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Myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) play an essential role in the immunosuppressive networks that contribute to tumor immune evasion. The mechanisms by which tumors promote the expansion and/or function of these suppressive cells and the cross-regulation between MDSC and Treg remain incompletely defined. The current work evaluates the influence of MDSC, expanded in two mouse cancer models, on immunosuppressive Treg. We demonstrate that tumor-induced MDSC endowed with the potential of suppressing conventional T lymphocytes surprisingly impair TGF-β1-mediated generation of induced Treg (iTreg) from naïve CD4⁺ T lymphocytes. Suppression of iTreg generation by MDSC occurs early in the differentiation process, and is cell contact dependent. This inhibition of FoxP3-expressing T lymphocyte differentiation by MDSC does not depend on arginase 1, cystine/cysteine depletion, iNOS/NO, or PD-1/PD-L1 signaling. These findings therefore indicate that MDSC from tumor-bearing hosts have the heretofore unreported ability to restrict some immunosuppressive Treg subpopulations.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature cells at various stages of differentiation. These cells are broadly characterized by the simultaneous expression of the surface markers CD11b and Gr1 and have been found to accumulate in large numbers in response to many different tumors in both mice and humans, including HER2/neu+ breast cancers. The adoptive immunotherapy of cancers has been a promising field, yet the clinical efficacy of adoptive immunotherapies targeted against human breast cancers and many other cancers has been extremely limited. Given the influx of MDSC in tumor-bearing individuals, we hypothesized that these cells were the reason for the failure of adoptively transferred T cells to effectively reject primary tumors. Using either monoclonal antibodies or the chemotherapeutic drug, gemcitabine, we aimed to eliminate MDSC cells in vivo to determine if adoptively transferred T cells would be more effective in the absence of these cells. We further aimed to characterize the mechanism of T cell suppression by MDSC and the tumor-derived soluble factor(s) responsible for their accumulation. We have found that the elimination of MDSC in vivo does result in significant tumor inhibition when adoptively transferred T cells are administered. Furthermore, the use of gemcitabine in conjunction with adoptively transferred T cells resulted in complete tumor rejection in 100% of mice and was accompanied by large antibody titers against HER2/neu as well as strong recall responses characterized by IFN-g release and subsequent rejection of further tumor challenges. We report herein that suppression by MDSC is contact dependent and affects the proliferation of both CD4+ and CD8+ T cells. The accumulation of MDSC in tumor-bearing mice can be entirely attributed to tumor-derived soluble factors, with GM-CSF specifically causing the generation and maintenance of these cells. Our findings suggest that the adoptive immunotherapy of breast carcinomas in a clinical setting should be combined with the use of gemcitabine, and that the use of GM-CSF as an adjuvant in cancer vaccines should be carefully re-evaluated as this cytokine may result in increased MDSC accumulation in vivo.

During hematopoiesis, multilineage progenitor cells and the precursors are committed to individual hematopoietic lineages. In normal myelopoiesis, the immature myeloid cells (IMCs) differentiate into macrophages, neutrophils or dendritic cells. However, under tumor burden, these IMCs differentiate into myeloid derived suppressor cells (MDSCs) result in an up-regulation of immune suppressive factors and pro-tumor effect. The development of normal or malignant is tightly controlled by endogenous signals such as transcription factors and epigenetic regulations. HDAC11 is the newest identified members of the histone deacetylase (HDAC) family. Previous study in our group had identified HDAC11 as a negative regulator of interleukin 10 (IL-10) production in antigen-presenting cells (APCs). However, the mechanisms of HDAC11 in regulating myeloid cells differentiation and function remained unclear. We have uncovered for the first time that in the absence of HDAC11, upon LPS stimulation, neutrophils isolated form mice displays an over-production of pro-inflammatory cytokines such as TNF-alpha and IL-6. Strikingly, these HDAC11KO neutrophils showed a significantly higher migratory and phagocytosis activity, resulting from an overexpression of the migratory receptor and cytokine CXCR/L2. We have performed Chromatin Immunoprecipitation (ChIP) analysis on the neutrophils and discovered that HDAC11 was recruited to the promoter regulatory region of these genes we have identified. This part of data will be discussed mainly in chapter 2. Not only does HDAC11 plays a crucial role in the neutrophil function, our group have also found out that lacking of HDAC11 result in an increased suppressive activity of the Myeloid-derived Suppressor Cells (MDSCs). The previous publication of our group had shown that the tumor bearing mice experienced a much more aggressive growth pattern in the HDAC11 KO mice compare with C57BL/6 wild type control. MDSCs isolated from mice lacking HDAC11 appeared to gain increased capability to suppress the function of antigen-specific CD8+ T cells in vitro. Followed by this initial study, in chapter 3, we observed an up-regulation of both expression and enzymatic activity of arginase 1 and Nos2, two enzymes that are crucial in regulating MDSCs suppressive function. The aberrant enzymatic activity of Arg1 and Nos2 in HDAC11KO MDSCs is possibly result from an over-expression of the lineage-specific transcription factor C/EBPβ, which is previously proved to be essential for the differentiation of functional MDSCs. Furthermore, our ChIP data confirmed that HDAC11 may play as an negative regulator of C/EBPβ. Recently, our lab had demonstrated that T cells lacking HDAC11 gained a hyperactive phenotype and anti-tumor effect, indicating that HDAC11 may play a dual role in the host immune system. We further performed an adoptive transfer therapy to C57BL/6 tumor bearing mice. Our data showed that the additional administration of HDAC11KO MDSCs could eliminate, at least partially, the anti-tumor effect by adoptive transfer of HDAC11KO T cells. Taken together, we have uncovered a previously unknown role for HDAC11 as a transcriptional regulator in the myeloid cells differentiation and function. Based on our data and previous work from our lab, we propose a dual role of HDAC11 played in the host immune system. In the absence of HDAC11, host defenders such as neutrophils and T cells are functionally more aggressive against intruders such as pathogen and cancer. However, the immune suppressors such as MDSCs became more suppressive. The contradictory role HDAC11 played in the immune system may provide some insights for the assessment of the pharmacological value of HDAC11 and contribute to the development of novel immunotherapeutic strategies.

Chronic myeloid leukemia (CML) is characterized by the Philadelphia chromosome, a minute chromosome that leads to the creation of the fusion gene BCR/ABL and the transcription of the fusion protein BCR/ABL in transformed cells. The constitutively active tyrosine kinase BCR/ABL confers enhanced proliferation and survival on leukemic cells. CML has in only a few decades gone from being a disease with very bad prognosis to being a disease that can be effectively treated with oral tyrosine kinase inhibitors (TKIs). TKIs are drugs inhibiting BCR/ABL as well as other tyrosine kinases. In this thesis, the focus has been on the immune system of CML patients, on immune escape mechanisms present in untreated patients and on how these are affected by TKI therapy. We have found that newly diagnosed, untreated CML patients exert different kinds of immune escape mechanisms. Patients belonging to the Sokal high-risk group had higher levels of myeloid-derived suppressor cells (MDSCs) as well as high levels of the programmed death receptor 1 (PD-1)-expressing cytotoxic T cells compared to control subjects. Moreover, CML patients had higher levels of myeloid cells expressing the ligand for PD-1, PD-L1. CML patients as well as patients with B cell malignacies had high levels of soluble CD25 in blood plasma. In B cell malignacies, sCD25 was found to be released from T regulatory cells (Tregs). Treatment with the TKIs imatinib or dasatinib decreased the levels of MDSCs in peripheral blood. Tregs on the other hand increased during TKI therapy. The immunostimulatory molecule CD40 as well as NK cells increased during therapy, indicating an immunostimulatory effect of TKIs. When evaluating immune responses, multiplex techniques for quantification of proteins such as cytokines and chemokines are becoming increasingly popular. With these techniques a lot of information can be gained from a small sample volume and complex networks can be more easily studied than when using for example the singleplex ELISA. When comparing different multiplex platforms we found that the absolute protein concentration measured by one platform rarely correlated with the absolute concentration measured by another platform. However, relative quantification was better correlated.