Myeloid-derived Suppressor Cells In Bone Marrow Research Articles

Deacetylase sirtuin 2 negatively regulates myeloid-derived suppressor cell functions in allograft rejection

Although myeloid-derived suppressor cells (MDSCs) are critical for allograft survival, their regulatory mechanism remains unclear. Herein, our results showed that metabolism sensor sirtuin 2 (SIRT2) negatively regulates the functions of MDSCs in inducing allogeneic skin graft rejection. Genetic deletion of SIRT2 in myeloid cells (Sirt2Δmye) increased the number of CD11b+Gr1+ MDSCs in bone marrow, spleens, draining lymph nodes, and allografts, inhibited the production of proinflammatory cytokine tumor necrosis factor ɑ, enhanced the production of anti-inflammatory cytokine interleukin 10, and potentiated the suppressive activation of MDSCs in prolonging allograft skin survival. C-X-C motif chemokine receptor 2 is critical for mediating the recruitment and cytokine production of MDSCs induced by SIRT2. Mechanistically, Sirt2Δmye enhanced NAD+ levels, succinate dehydrogenase subunit A (SDHA) activities, and oxidative phosphorylation (OXPHOS) levels in MDSCs after transplantation. Pharmacologically blocking nicotinamide phosphoribosyltransferase effectively reverses the production of cytokines and suppressive activities of MDSC induced by Sirt2Δmye. Blocking OXPHOS with knockdown of SDHA or pharmacological blocking of SDHA significantly restores Sirt2Δmye-mediated stronger MDSC suppressive activity and inflammatory factor productions. Thus, our findings identify a previously unrecognized interplay between NAD+ and SDH-mediated OXPHOS metabolic pathways in regulating MDSC functions induced by the metabolic sensor SIRT2 in allogeneic transplantation.

Jagged1+ Myeloid-Derived Suppressor Cells Are Required for Recovery of the Hematopoietic Bone Marrow Niche after Myelosuppression

Myelosuppressive treatments such as chemotherapy and radiotherapy are widely used to treat a variety of hematopoietic diseases and disorders, however current treatment regiments induce broad cytotoxicity illustrated by off-target tissue damage. In order for timely recovery of vascular and hematopoietic function, bone marrow (BM) endothelial cells must regenerate following myelosuppression. The identity and mechanism by which myelosuppressive-resistant cells that trigger endothelial regeneration in the damaged BM microenvironment are unknown. In the present study, we show that Jagged1 (Jag1) expression was significantly upregulated in various hematopoietic populations, particularly in myeloid-derived suppressor cells (MDSCs), following myelosuppression. By crossing Jag1conditional knockoutmice with Vav1-Cre driver mice, we generated the Jag1f/fVavCre+ strain that specific deletes Jag1 in hematopoietic cells. We demonstrate that loss of hematopoietic Jag1 does not affect numbers and function of hematopoietic stem and progenitor cells (HSPCs) under homeostatic condition, but Jag1f/fVavCre+ mice rapidly succumb to both chemo- and radio-therapeutic stress exhibited by severe pancytopenia, very limited endothelial regeneration, and rapid weight loss and morbidity. Full recovery can be achieved by adoptive transfer of WT bone marrow MDSCs, which we show can efficiently rescue the severe phenotypes of Jag1f/fVavCre+ by improving endothelial cell recovery and hematopoietic niche regeneration. Using reporter models, we show that robust Notch pathway activation in endothelial cells is mediated by Jag1+MDSCs. This leads to hematopoietic recovery due to proliferation and elevated numbers of HSPCs in Jag1f/fVavCre+ mice. Treatment with Jag1-coated nanoparticles similarly rescues viability of the BM endothelial cells. Our findings indicate that hematopoietic Jag1 is essential in accelerating niche regeneration and hematopoietic recovery and is a potential therapeutic target in ameliorating damage from multiple myelosuppressive treatments.

GM-CSF-mediated inducement of bone marrow MDSCs by TSA and effect on survival of graft in mice

ObjectiveThis study analyzed the effect of HDAC inhibitor, trichostatin A (TSA), in inducing granulocyte–macrophage colony-stimulating factor (GM-CSF)-mediated bone marrow (BM) cell differentiation to myeloid-derived suppressor cells (MDSCs) in vitro and in vivo.MethodsBM cell differentiation to CD11b + GR-1 + MDSCs was achieved by in vitro culture with TSA and GM-CSF, and the collected cells were analyzed by mixed lymphocyte culture to identify suppressive actions against effector T cells. RT-PCR and ELISA were conducted to analyze the CCL5 mRNA and protein levels in TSA + GM-CSF + BM, GR-1 + MDSCs and GR-1 + MDSC + CCL5 groups. The survival of cardiac grafts was compared between groups.ResultsTSA was beneficial for the GM-CSF-mediated BM differentiation to CD11b + GR-1 + MDSCs. Adoptive transfer of GR-1 + MDSCs was powerful in suppressing CD4 + CD25-T cell proliferation and the effect was mediated by iNOS and HO-1; it also increased CCL5 gradient concentration between grafts and plasma to recruit Treg to grafts and prolong the survival of the grafts. Survival analysis revealed that the survival of grafts after adoptive transfer of GR-1 + MDSCs could be prolonged.ConclusionThis study helps in further research on the application value of MDSCs in the field of transplant, and may provide a new thought for the cell therapy in inducing immune tolerance in organ transplant.

B7H3 expression and significance in idiopathic pulmonary fibrosis.

The clinical significance of B7H3 (CD276) and its cleavage product soluble B7H3 (sB7H3) in idiopathic pulmonary fibrosis (IPF) is unknown. Mounting evidence suggests the potential utility of peripheral blood myeloid cell enumeration to predict disease outcome and indicate active lung disease. Here we hypothesized that sB7H3 is involved in regulation of circulating myeloid cells in pulmonary fibrosis. In support of this possibility, both plasma sB7H3 and B7H3+ cells were elevated in IPF patient blood samples, which correlated negatively with lung function. To analyze its function, the effects of sB7H3 on naïve or bleomycin-treated mice were examined. The results revealed that sB7H3 injection induced an influx of myeloid-derived suppressor cells (MDSCs) and Ccl2 expression in lung tissue of naïve mice, accompanied by enhanced overall inflammation. Additionally, sB7H3 caused accumulation of MDSCs in bone marrow with increased expression of inflammatory cytokines. Notably, in vitro assays revealed chemotaxis of MDSCs to sB7H3, which was dependent on TLT-2 (TREML2), a putative receptor for sB7H3. Thus, increased circulating sB7H3 and/or B7H3+ cells in IPF patient blood samples correlated with lung function decline and potential immunosuppressive status. The correlation of sB7H3 with deterioration of lung function might be due to its ability to enhance inflammation and recruitment of MDSCs into the lung and their expansion in the bone marrow, and thus potentially contribute to IPF exacerbation. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Receptor Tyrosine Kinase Inhibitor Sunitinib as Novel Immunotherapy to Inhibit Myeloid-Derived Suppressor Cells for Treatment of Endometriosis.

Endometriosis is a common, benign, and hormone-dependent gynaecological disorder that displays altered immunoinflammatory profiles. Myeloid-derived suppressor cells (MDSCs) suppressed immunosurveillance in endometriosis in human and mouse model. Receptor tyrosine kinase inhibitor Sunitinib can induce MDSC apoptosis and suppress the progression of cancer. However, the effects of Sunitinib on MDSCs in endometriosis and the underlying mechanism are not clear. In this study, we employed an animal study of the endometriosis model in mice for treatment of Sunitinib. After syngeneic endometrium transplantation and treatment, endometriotic lesion volume, weight, and histology were compared. Peritoneal fluid, peripheral blood, and bone marrow MDSC subsets and their molecular signaling were monitored by flow cytometry. Peritoneal cytokines were assayed by ELISA. The gene expression profiles of isolated CD11b+Ly6G+Ly6Clo cells were studied by RNA sequencing. We found that Sunitinib significantly decreased the endometriotic lesion size and weight after 1 and 3 weeks, and decreased p-STAT3 activation in MDSCs after 1 week of treatment. In the first week, Sunitinib specifically increased the G-MDSC population in peritoneal fluid but the isolated CD11b+Ly6G+Ly6Clo MDSCs after Sunitinib treatment were presented as mature polynuclear MDSCs, while the control group had immature mononuclear MDSCs. Importantly, we found Sunitinib differentially suppressed gene expressions of immunosuppressive function and differentiation in peritoneal G-MDSCs. Apelin signaling pathway associated genes and inflammation related genes were upregulated, and amino acid metabolism regulator genes were downregulated in bone marrow G-MDSCs. For endometriotic lesions, the PPARG gene governing glucose metabolism and fatty acid storage, which is important for the development of endometriosis was upregulated. In conclusion, Sunitinib inhibited endometriotic lesions, by promoting peritoneal fluid MDSCs maturation and inhibiting the immunosuppressive function. These findings suggest that Sunitinib changed the immune microenvironment and inhibited the development of endometriosis, which has potential therapeutic effects as novel immunotherapy to promote MDSCs maturation, differentiation, and metabolism for the treatment of endometriosis.

Age-related expansion and increased osteoclastogenic potential of myeloid-derived suppressor cells

Aging is associated with excessive bone loss that is not counteracted with the development of new bone. However, the mechanisms underlying age-related bone loss are not completely clear. Myeloid-derived suppressor cells (MDSCs) are a population of heterogenous immature myeloid cells with immunosuppressive functions that are known to stimulate tumor-induced bone lysis. In this study, we investigated the association of MDSCs and age-related bone loss in mice. Our results shown that aging increased the accumulation of MDSCs in the bone marrow and spleen, while in the meantime potentiated the osteoclastogenic activity of the CD11b+Ly6ChiLy6G+ monocytic subpopulation of MDSCs. In addition, CD11b+Ly6ChiLy6G+ MDSCs from old mice exhibited increased expression of c-fms compared to young mice, and were more sensitive to RANKL-induced osteoclast gene expression. On the other hand, old mice showed elevated production of IL-6 and receptor activator of nuclear factor kappa-B ligand (RANKL) in the circulation. Furthermore, IL-6 and RANKL were able to induce the proliferation of CD11b+Ly6ChiLy6G+ MDSCs and up-regulate c-fms expression. Moreover, CD11b+Ly6ChiLy6G+ MDSCs obtained from old mice showed increased antigen-specific T cell suppressive function, pStat3 expression, and cytokine production in response to inflammatory stimulation, compared to those cells obtained from young mice. Our findings suggest that CD11b+Ly6ChiLy6G+ MDSCs are a source of osteoclast precursors that together with the presence of persistent, low-grade inflammation, contribute to age-associated bone loss in mice.

Ex Vivo-Induced Bone Marrow-Derived Myeloid Suppressor Cells Prevent Corneal Allograft Rejection in Mice.

PurposeTo investigate the effects of ex vivo–induced bone marrow myeloid-derived suppressor cells (BM-MDSCs) on allogeneic immune responses in corneal transplantation.MethodsBone marrow cells from C57BL/6J (B6) mice were cultured with IL-6 and GM-CSF for four days. The ex vivo induction of the BM-MDSCs was assessed using flow cytometry, inducible nitric oxide synthase (iNOS) mRNA expression using reverse transcription–quantitative polymerase chain reaction, and nitric oxide (NO) production in allogeneic stimulation. T-cell proliferation and regulatory T-cell (Treg) expansion were investigated on allogeneic stimulation in the presence of ex vivo–induced BM-MDSCs. IFN-γ, IL-2, IL-10, and TGF-β1 protein levels were measured using enzyme-linked immunosorbent assays. After subconjunctival injection of ex vivo–induced BM-MDSCs, the migration of the BM-MDSCs into corneal grafts, allogeneic corneal graft survival, neovascularization, and lymphangiogenesis were assessed using flow cytometry, slit-lamp microscopy, and immunohistochemistry.ResultsThe combination of GM-CSF and IL-6 significantly induced BM-MDSCs with increased iNos mRNA expression. The ex vivo–induced BM-MDSCs promoted NO release in allogeneic stimulation in vitro. The ex vivo–induced BM-MDSCs inhibited T-cell proliferation and promoted Treg expansion. Decreased IFN-γ and increased IL-2, IL-10, and TGF-β1 production was observed in coculture of ex vivo–induced BM-MDSCs. Injected ex vivo–induced BM-MDSCs were confirmed to migrate into the grafts. The injected BM-MDSCs also prolonged corneal graft survival and prevented angiogenesis and lymphangiogenesis.ConclusionsThe ex vivo–induced BM-MDSCs have suppressive effects on allogeneic immune responses and prolong corneal allograft survival via the iNOS pathway, indicating that they may be a potential therapeutic tool for corneal transplantation.

Bone marrow cells are differentiated into MDSCs by BCC-Ex through down-regulating the expression of CXCR4 and activating STAT3 signalling pathway.

Studies showed that the increase of myeloid‐derived suppressor cells (MDSCs) in tumour microenvironment is closely related to the resistant treatment and poor prognosis of metastatic breast cancer. However, the effect of tumour‐derived exosomes on MDSCs and its mechanism are not clear. Here, we reported that breast cancer cells (4T1)‐secreted exosomes (BCC‐Ex) were able to differentiate bone marrow cells into MDSCs and significantly inhibited the proliferation of T lymphocytes to provide an immunosuppressive microenvironment for cancer cells in vivo and in vitro. The number of MDSCs in bone marrow and spleen of 4T1 tumour‐bearing mice and BCC‐Ex infused mice was significantly higher than that of normal mice, whereas the number of T lymphocytes in spleen was significantly decreased. In addition, BCC‐Ex markedly promoted the differentiation of MDSCs from bone marrow cells or bone marrow cells derived macrophages, seen as the increased expressions of MDSCs‐related functional proteins Arginase‐1 (Arg‐1) and inducible nitric oxide synthase (iNOS). Furthermore, BCC‐Ex significantly down‐regulated the expressions of chemokine receptor CXCR4 and markedly up‐regulated the levels of inflammatory cytokines IL‐6 and IL‐10 in bone marrow cells and macrophages and remarkably inhibited the division and proliferation of T cells. Importantly, CXCR4 agonist, CXCL12, could reverse the function of BCC‐Ex, indicating that BCC‐Ex‐induced MDSCs might be dependent on the down‐regulation of CXCR4. Western blot showed that BCC‐Ex significantly promoted the phosphorylation of STAT3 in bone marrow cells, resulting in the inhibitions of the proliferation and apoptosis of bone marrow cells, and the aggravation of the differentiation of bone marrow cells into MDSCs.

Chronic restraint stress promotes the mobilization and recruitment of myeloid-derived suppressor cells through β-adrenergic-activated CXCL5-CXCR2-Erk signaling cascades.

Myeloid-derived suppressor cells (MDSCs) play an important role in tumor immune escape. Recent studies have shown that MDSCs contribute to tumor progression under psychological stress, but the underlying mechanism of MDSCs mobilization and recruitment remains largely unknown. In the present study, a chronic restraint stress paradigm was applied to the H22 hepatocellular carcinoma (HCC) bearing mice to mimic the psychological stress. We observed that chronic restraint stress significantly promoted HCC growth, as well as the mobilization of MDSCs to spleen and tumor sites from bone marrow. Meanwhile, chronic restraint stress enhanced the expression of C-X-C motif chemokine receptor 2 (CXCR2) and pErk1/2 in bone marrow MDSCs, together with elevated chemokine (C-X-C motif) ligand 5 (CXCL5) expression in tumor tissues. In vitro, the treatments of MDSCs with epinephrine (EPI) and norepinephrine (NE) but not corticosterone (CORT)-treated H22 conditioned medium obviously inhibited T-cell proliferation, as well as enhanced CXCR2 expression and extracellular signal-regulated kinase (Erk) phosphorylation. In vivo, β-adrenergic blockade with propranolol almost completely reversed the accelerated tumor growth induced by chronic restraint stress and inactivated CXCL5-CXCR2-Erk signaling pathway. Our findings support the crucial role of β-adrenergic signaling cascade in the mobilization and recruitment of MDSCs under chronic restraint stress.

Runx2 Deficiency in Osteoblasts Promotes Myeloma Progression by Altering the Bone Microenvironment at New Bone Sites.

Multiple myeloma is a plasma cell malignancy that thrives in the bone marrow (BM), with frequent progression to new local and distant bone sites. Our previous studies demonstrated that multiple myeloma cells at primary sites secrete soluble factors and suppress osteoblastogenesis via the inhibition of Runt-related transcription factor 2 (Runx2) in pre- and immature osteoblasts (OB) in new bone sites, prior to the arrival of metastatic tumor cells. However, it is unknown whether OB-Runx2 suppression in new bone sites feeds back to promote multiple myeloma dissemination to and progression in these areas. Hence, we developed a syngeneic mouse model of multiple myeloma in which Runx2 is specifically deleted in the immature OBs of C57BL6/KaLwRij mice (OB-Runx2-/- mice) to study the effect of OB-Runx2 deficiency on multiple myeloma progression in new bone sites. In vivo studies with this model demonstrated that OB-Runx2 deficiency attracts multiple myeloma cells and promotes multiple myeloma tumor growth in bone. Mechanistic studies further revealed that OB-Runx2 deficiency induces an immunosuppressive microenvironment in BM that is marked by an increase in the concentration and activation of myeloid-derived suppressor cells (MDSC) and the suppression and exhaustion of cytotoxic CD8+ T cells. In contrast, MDSC depletion by either gemcitabine or 5-fluorouracil treatment in OB-Runx2-/- mice prevented these effects and inhibited multiple myeloma tumor growth in BM. These novel discoveries demonstrate that OB-Runx2 deficiency in new bone sites promotes multiple myeloma dissemination and progression by increasing metastatic cytokines and MDSCs in BM and inhibiting BM immunity. Importantly, MDSC depletion can block multiple myeloma progression promoted by OB-Runx2 deficiency.Significance: This study demonstrates that Runx2 deficiency in immature osteoblasts at distant bone sites attracts myeloma cells and allows myeloma progression in new bone sites via OB-secreted metastatic cytokines and MDSC-mediated suppression of bone marrow immunity.

The role and mechanism of myeloid-derived suppressor cells in mice with nonalcoholic steatohepatitis

Objective To investigate the effects of myeloid-derived suppressor cells (MDSCs) on nonalcoholic steatohepatitis mice. Methods ⑴ Male C57BL/6 mice aged 6-8 weeks were randomly divided into normal diet group, CDAA group(choline deficient amino acid diet) and CSAA group (choline sufficient amino acid diet). ⑵ After the success of the non-alcoholic steatohepatitis model, serum was collected from some mice to detect biochemical indexes; Liver tissue was retained for microscopic observation by hematoxylin-eosin (HE) staining; The changes of T cell subsets in peripheral blood of mice in each group were detected by flow cytometry. In addition, The proportion and subtype of CD11b+ Gr-1+ MDSCs cells in liver, spleen, blood and bone marrow were also detected by flow cytometry. ⑶ The bone marrow-derived Gr-1highLy-6G+ was purified by magnetic bead sorting technique, and the purified Gr-1highLy-6G+ was transferred into non-alcoholic steatohepatitis (NASH) mice by tail vein injection. The role of MDSCs in NASH was analyzed by detection of serological indexes of liver function and pathological dyeing. Results ⑴ There was no significant difference in body weight and liver index between the groups (P>0.05). Serological indicators: alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood glucose, interleukin (IL)-6 and interferon-γ (INF-γ) in the model group were significantly higher than those in the normal group (P 0.05); the MDSCs of liver in CDAA group is lower than that of normal group (P normal group (P<0.01), CD11b+ Gr-1dimLy-6G-(M-MDSC) showed a downward trend, CDAA group < normal group; ⑶ Serum AST and ALT levels of NASH mice who receiving Gr-1highLy-6G+ MDSCs from normal bone marrow were significantly decreased (P<0.001), and histopathological changes were alleviated. Conclusions ⑴ The NASA mouse model can be successfully established on the CDAA diet. ⑵ The CDAA-induced NASH mice may have immune dysfunction, mainly manifesting in the change of bone marrow MDSCs subpopulations and the increase of CD11b+ Gr-1highLy-6G+ (G-MDSC). ⑶ MDSCs derived from normal mouse bone marrow can alleviate the pathological changes of NASH. Key words: Myeloid-derived suppressor cells; Non-alcoholic steatohepatitis; T-lymphocytes; Interleukin-6; Mice

1α, 25 Dihydroxyvitamin D (1,25(OH)2D) inhibits the T cell suppressive function of myeloid derived suppressor cells (MDSC)

Myeloid derived suppressor cells (MDSC) suppress the ability of cytotoxic T cells to attack and clear tumor cells from the body. The active form of vitamin D, 1,25 dihydroxyvitamin D (1,25(OH)2D), regulates myeloid cell biology and previous research showed that in mouse models 1,25(OH)2D reduced the tumor level of CD34+ cells, an MDSC precursor, and reduced metastasis. We tested whether MDSC are vitamin D target cells by examining granulocytic- (G-MDSC) and monocytic (M-MDSC) MDSC from tumors, spleen, and bone marrow. Vitamin D receptor (VDR) mRNA levels are low in MDSC from bone marrow and spleen but are 20-fold higher in tumor MDSC. At all sites, M-MDSC have 4-fold higher VDR mRNA expression than G-MDSC. Bone marrow MDSC were induced to differentiate in vitro into tumor MDSC-like cells by treating with IFN-γ, IL-13, and GM-CSF for 48 h. This treatment significantly elevated Arg1 and Nos2 levels, activated the T cell-suppressive function of MDSC, increased VDR expression 50-fold, and made the MDSC responsive to 1,25(OH)2D treatment. Importantly, 1,25(OH)2D treatment reduced the T cell suppressive capacity of cytokine-induced total MDSC and M-MDSC by ≥70 % and tumor-derived M-MDSC by 30–50 %. Consistent with this finding, VDR deletion (KO) increased T cell suppressive function of in vitro M-MDSC by 30 % and of tumor-derived M-MDSC by 50 % and G-MDSC by 400 %. VDR KO did not alter Nos2 mRNA levels but significantly increased Arg1 mRNA levels in tumor M-MDSC by 100 %. In contrast, 1,25(OH)2D treatment reduced nitric oxide production in both in vitro derived M- and G- MDSC. The major finding of this study is that 1,25(OH)2D signaling through the VDR decreases the immunosuppressive capability of MDSC. Collectively, our data suggest that activation of vitamin D signaling could be used to suppress MDSC function and release a constraint on T-cell mediated clearance of tumor cells.

LDK378 inhibits the recruitment of myeloid-derived suppressor cells to spleen via the p38-GRK2-CCR2 pathway in mice with sepsis.

Myeloid-derived suppressor cells (MDSCs) are functionally immunosuppressive cells that are persistently increased in abundance and associated with adverse clinical outcomes in sepsis. Here, we investigated the therapeutic potential of an anaplastic lymphoma kinase inhibitor, LDK378, in cecal ligation and puncture (CLP)-induced polymicrobial sepsis and examined its effects on the recruitment of MDSCs. LDK378 significantly improved the survival of CLP-induced polymicrobial septic mice, which was paralleled by reduced organ injury, decreased release of inflammatory cytokines and decreased recruitment of MDSCs to the spleen. Importantly, LDK378 inhibited the migration of MDSCs to the spleen by blocking the CLP-mediated upregulation of CC chemokine receptor 2 (CCR2), a chemokine receptor critical for the recruitment of MDSCs. Mechanistically, LDK378 treatment blocked the CLP-induced CCR2 upregulation of MDSCs via partially inhibiting the phosphorylation of p38 and G-protein-coupled receptor kinase-2 (GRK2) in bone marrow MDSCs of septic mice. Furthermore, invitro experiments also showed that lipopolysaccharide (LPS)-induced migration of MDSCs was similarly owing to the activation of GRK2 and upregulation of CCR2 by LPS, whereas the treatment with LDK378 partially blocked the LPS-induced phosphorylation of p38 and GRK2 and decreased the expression of CCR2 on the cell surface, therefore leading to the suppression of MDSC migration. Together, these findings unravel a novel function of LDK378 in the host response to infection and suggest that LDK378 could be a potential therapeutic agent for sepsis.

Abnormal aggregation of myeloid-derived suppressor cells in a mouse model of cyclophosphamide-induced premature ovarian failure

Oocytes are extremely sensitive to radiation and chemotherapy, and premature ovarian failure (POF) is one of the side effects of anti-tumor therapy. The pathogenesis of POF is very complex and still not fully elucidated. A mouse POF model was established after 14 days of cyclophosphamide injection. POF mice presented ovarian atrophy, destroyed follicular structure, a reduction in the number of primordial and mature follicles, and an decrease in the number of corpora luteal along with increased level of follicle-stimulating hormone (FSH), decreased levels of estradiol (E2), and anti-Mullerian hormone (AMH). Additionally, the proportion of bone marrow myeloid-derived suppressor cells (MDSCs) in peripheral blood, spleen, and ovarian tissue increased. MDSCs were mainly distributed around follicles and corpora luteal. Levels of mTOR and p-mTOR increased in ovarian tissue and inhibition of mTOR with rapamycin reduced the aggregation of MDSCs in peripheral blood, spleen, and ovarian tissue. This investigation sheds new light on the modulatory role of mTOR and demonstrates that an increase in MDSC number may play a key role in the pathological reaction during POF. Inhibition of mTOR and reduction of MDSCs in the ovary may represent a novel strategy for the treatment of POF.

Type1 IFN signaling on Tregs modulates the migration of Myeloid Derived Suppressor Cells

Abstract Multiple sclerosis is an autoimmune disorder whose severity is reduced with immune suppressive drugs. Therapeutic intervention with interferon-beta reduces disease exacerbations and delays relapses. The receptor for type 1 interferon, IFNAR, is present on virtually all cell types making it difficult to dissect the mechanisms involved. To address this issue, we induced experimental autoimmune encephalomyelitis (EAE) in mice with a conditional deletion (cKO) of IFNAR in T regulatory (Treg) cells (IFNARfl/flxFoxp3YFP-Cre). cKO mice developed severe EAE with an earlier onset than control mice. Although Treg cells from cKO mice appeared to be more activated, the activation status of and effector cytokine production by CD4+T cells in the draining lymph nodes (dLN) was similar in WT and cKO mice during the priming phase, but higher in cKO CD4+T cells in the effector phase. Interestingly, we noted a substantial reduction of myeloid derived suppressor cells (MDSCs) in the dLN of cKO mice, while generation of MDSCs in bone marrow and recruitment to spleen of WT and cKO mice were comparable. Surprisingly, we noted a decrease in the production of monocyte and granulocyte cell recruiting chemokine ligands by CD4+ and CD8+ T cells, B cells and endothelial cells in the dLN during the priming phase in the cKO mice. While modulation of Treg cell number and function by MDSCs has been documented, this study is one of the first to demonstrate that Treg cells modify the lymph node microenvironment by modulating MDSC homing and raises the possibility of a novel role for Treg cells in regulating the kinetics of MDSC recruitment during inflammatory conditions. This research was supported by the Intramural Research Program of NIAID, NIH.

Tumor derived EDIL3 modulates the expansion and osteoclastogenesis of myeloid derived suppressor cells in murine breast cancer model

Epidermal growth factor-like repeats and discoidin I like domain 3 (EDIL3) is an integrin ligand which is implicated in bone metabolism and bone marrow myelopoiesis. Recently, myeloid derived suppressor cells (MDSCs) as osteoclast progenitor have been demonstrated in several kinds of cancers including breast cancer. In this paper we explored the association between tumor derived EDIL3 and MDSCs in a murine breast cancer model. Knockdown of EDIL3 in MDA-MB-231 breast cancer cells inhibited the expansion of tumor induced MDSCs in bone marrow. However, generation of bone marrow derived MDSCs in vitro was not affected by recombinant EDIL3. Osteoclastogenesis of MDSCs was dose-dependently inhibited by recombinant EDIL3 in vitro via binding to Mac-1 but not LFA-1. Moreover, in accordance with previous studies, our data showed that tumor derived EDIL3 was involved in tumor associated bone loss. The convoluted effects of EDIL3 on MDSCs compose a potential mechanism hired by tumor cells for perpetration approximately.

Estrogen promotes multiple myeloma through enhancing the immunosuppressive activity of MDSC

Although the role of estrogen in solid cancers has been widely investigated, its effect in hematologic malignancies including multiple myeloma (MM) is not known. Here, we utilized a syngeneic mouse model of MM to address this question. In this model, treatment with 17β-estradiol significantly promoted progression of the disease. This effect has not been attributed to the direct effect of estrogen on MM cells but rather was mediated through estrogen-induced alterations in tumor microenvironment. In MM bone marrow, myeloid-derived suppressor cells (MDSCs) represent one of the major cellular populations. 17β-estradiol did not promote expansion and accumulation of MDSCs. However, it significantly increased their ability to suppress T cells proliferation. Thus, these data demonstrated that estrogen promotes progression of MM by enhancing an immunosuppressive function of the bone marrow MDSCs.

Empirical Study on the Therapeutic Effect of Astragalus Polysaccharides in a Mouse Model of Ulcerative Colitis

This study was performed to study the effects of astragalus polysaccharides (APS) in the treatment of ulcerative colitis (UC), and to explore whether myeloid-derived suppressor cells (MDSC) involve in this process. UC model was established by dextran sulfate sodium salt (DSS) inducement in mouse. Then the effects of APS on UC was evaluate at the levels of cytology and molecular biology: exploring the influence of APS on MDSC by analyzing the levels of MDSC before and after the treatments of APS; evaluating the therapeutic effects of APS on UC by pathologic histology. Data showed that the levels of MDSC in bone marrow, spleen, peripheral blood of UC mice were significantly decreased after intervention with APS, indicating APS inhibited the level of MDSC significantly. After depletion bone marrow cells in mice, we further found that the therapeutic effects of APS in MDSC- group was significantly reduced compared with MDSC+ group. It was discovered through pathological analysis that, compared with UC model group, APS intervention group mainly manifested as reduced infiltrating acute and chronic inflammatory cells, necrotic epithelial cells and epithelial ulceration. Therefore, APS could reduce the inflammatory cell infiltration in colonic tissues of UC model mice, repair the damaged colonic mucosa, and promote ulcer healing. In conclusion, APS has a potential application in the treatment of ulcerative colitis, and is dependent or partially dependent on MDSC to achieve this effects.

Analysis of the Expression and Regulation of PD-1 Protein on the Surface of Myeloid-Derived Suppressor Cells (MDSCs).

Myeloid-derived suppressor cells (MDSCs) that are able to suppress T cell function are a heterogeneous cell population frequently observed in cancer, infection, and autoimmune disease. Immune checkpoint molecules, such as programmed death 1 (PD-1) expressed on T cells and its ligand (PD-L1) expressed on tumor cells or antigen-presenting cells, have received extensive attention in the past decade due to the dramatic effects of their inhibitors in patients with various types of cancer. In the present study, we investigated the expression of PD-1 on MDSCs in bone marrow, spleen, and tumor tissue derived from breast tumor-bearing mice. Our studies demonstrate that PD-1 expression is markedly increased in tumor-infiltrating MDSCs compared to expression in bone marrow and spleens and that it can be induced by LPS that is able to mediate NF-κB signaling. Moreover, expression of PD-L1 and CD80 on PD-1+ MDSCs was higher than on PD-1− MDSCs and proliferation of MDSCs in a tumor microenvironment was more strongly induced in PD-1+ MDSCs than in PD-1− MDSCs. Although we could not characterize the inducer of PD-1 expression derived from cancer cells, our findings indicate that the study on the mechanism of PD-1 induction in MDSCs is important and necessary for the control of MDSC activity; our results suggest that PD-1+ MDSCs in a tumor microenvironment may induce tumor development and relapse through the modulation of their proliferation and suppressive molecules.

Immunosuppressive effects of hypoxia-induced glioma exosomes through myeloid-derived suppressor cells via the miR-10a/Rora and miR-21/Pten Pathways.

While immunosuppressive environments mediated by myeloid-derived suppressor cells (MDSCs) have been well documented in glioma patients, the mechanisms of MDSC development and activation have not been clearly defined. Here, we elucidated a role for glioma-derived exosomes (GDEs) in potentiating an MDSC pathway. We isolated normoxia-stimulated and hypoxia-stimulated GDEs and studied their MDSC induction abilities in vivo and in vitro. Analyses of spleen and bone marrow MDSC proportions (flow cytometry) and reactive oxygen species (ROS), arginase activity, nitric oxide (NO), T-cell proliferation and immunosuppressive cytokine (IL-10 and TGF-β, ELISA) levels were used to assess MDSC expansion and functional capacity. We also performed microRNA (miRNA) sequencing analysis of two types of GDEs to find miRNAs that potentially mediate the development and activation of MDSCs. GDE miRNA intracellular signaling in MDSCs was also studied. Hypoxia promoted the secretion of GDEs, and mouse MDSCs could uptake GDEs. Hypoxia-stimulated GDEs had a stronger ability to induce MDSCs than N-GDEs. The hypoxia-inducible expression of miR-10a and miR-21 in GDEs mediated GDE-induced MDSC expansion and activation by targeting RAR-related orphan receptor alpha (RORA) and phosphatase and tensin homolog (PTEN). Mice inoculated with miR-10a or miR-21 knockout glioma cells generated fewer MDSCs than those inoculated with normal glioma cells. These data elucidated a mechanism by which glioma cells influence the differentiation and activation of MDSCs via exosomes and demonstrated how local glioma hypoxia affects the entirety of tumor immune environments.