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.

The lymphatic vasculature is composed of lymphatic endothelial cells (LECs) that coalesce into a branched hierarchy of small capillaries and larger collecting vessels that regulate interstitial fluids, lipid uptake and immunity. Few studies have focused on pulmonary lymphatic system. To fill these critical knowledge gaps, we interrogated the fetal maturation program of lymphatic endothelium, and we provide evidence that CSF1R-lineage progenitors contribute to LECs in the lung during a temporally defined period in early postnatal life. The pulmonary lymphatic system is required for fluid clearance and air breathing at birth, suggesting a prenatal maturation program. To interrogate this, we developed a cell sorting strategy to enrich pulmonary LECs by their unique cell surface immunophenotype (CD45-, EPCAM-, CD31+, VEGFR3+, PDPN+, LYVE1+) for transcriptional profiling. These experiments highlighted the coordinate down-regulation of genes involved in “cell cycle”, and “mRNA processing” along with coordinate upregulation of “complement/coagulation cascade”, “lipid metabolism”, and “angiogenesis” genes from embryonic day E16.5 to E18.5. The most significantly enriched gene set corresponded to the “interferon-alpha/beta signaling” pathway which was confirmed with qRT-PCR and in-situ hybridization. These data provide the first description of the transcriptional landscape of fetal pulmonary LEC maturation. During development, all LECs are thought to originate from embryonic veins, however multiple studies have suggested a myeloid origin for a subset of LECs. A relationship between myeloid cells and the pulmonary LECs has not been elucidated. Here, we used myeloid-specific inducible CSF1R-CreERtdTomato lineage tracing mice and identified rare, single cells that co-expressed CSF1R- CreERtdTomato and Prox1, the master lymphatic regulator, in the postnatal day 3 lung. This process was temporally restricted to the early postnatal period. Lineage tracing with additional myeloid-Cre mice (CSF1R-iCre and CX3CR1-Cre) also showed contribution to postnatal LECs. To determine the biological significance of CSF1R-derived LECs to postnatal lung biology, we performed conditional Prox1 loss of function experiments. CSF1R-CreER mediated deletion of Prox1 resulted in lymphatic hypoplasia, edematous foci and clotting. These findings suggest that early postnatal CSF1R+ progenitors contribute to the pulmonary lymphatic endothelium and that vascular clotting may result from lymphatic malformation/dysfunction. / 2021-06-14T00:00:00Z

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18127号 / 医博第3847号 / 新制||医||1001(附属図書館) / 30985 / 京都大学大学院医学研究科医学専攻 / (主査)教授 千葉 勉, 教授 松田 道行, 教授 野田 亮 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20229号 / 医博第4188号 / 新制||医||1019(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 武藤 学, 教授 原田 浩, 教授 山田 泰広 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

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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The presence of AML1-ETO (RUNX1-CBF2T1), a fusion oncoprotein resulting from a t(8;21) chromosomal translocation, is a necessary but insufficient event in the development of a subset of acute myeloid leukemias (AML). Although AML1-ETO is able to block differentiation and immortalize hematopoietic stem cells, other contributory events are required for cell proliferation and leukemogenesis, suggesting that specific tumor suppressor genes may counteract the leukemic potential of AML1-ETO. In studying del(9q), one of the most common concomitant chromosomal abnormalities with t(8;21), we identified the loss of TLE4 as a key cooperating event in the development of AML1-ETO AML, leading to increased cell proliferation, blocked apoptosis and differentiation, as well as cytarabine resistance in leukemic cells. This suggested TLE4 functions as a tumor suppressor gene in AML.We found these effects are mediated by the loss of TLE4 regulation of a COX-Wnt inflammatory axis. These effects were consequently reversible by Wnt signaling and cyclooxygenase inhibition, pointing towards anti-inflammatory agents as potentially new therapeutic and adjuvant strategies for AML. While studies in Drosophila implicate TLE/Groucho as a key mediator of various signaling pathways, including receptor tyrosine kinase/Ras/MAPK, Notch, Myc, and Wnt pathways, there is surprisingly little known about the role of TLE in mammalian development. Using a Tle4 knockout (T4KO) mouse, we identified previously unknown roles for Tle4 in regulating vertebrate mammalian hematopoietic and bone development. T4KO mice manifest leukocytopenia and defective hematopoietic stem cell populations. Using serial transplantation and stromal co-culture, we find that these hematopoietic deficiencies arise due to both intrinsic dysfunction of hematopoietic stem cells as well as defective extrinsic regulation of hematopoiesis by the stem cell niche. Additionally, T4KO mice are severely runted and exhibit markedly decreased bone mineralization concomitant with defective osteoblast function and decreased mineral apposition rates. Many of the pathways regulated by TLE are aberrant in cancer, which has led to increasing studies connecting TLE with various malignancies, including synovial cell sarcoma and glioblastoma. Our findings have great implications for current understanding of TLE function in not only cancer, but also bone and hematopoietic development.