Mechanisms of myeloid-derived suppressor cell-mediated immunosuppression in colorectal cancer and related therapies

Severe immunosuppression is a hallmark of colorectal cancer(CRC).Myeloid-derived suppressor cells(MDSCs),one of the most abundant components of the tumor stroma,play an important role in the invasion,metastasis,and immune escape of CRC.MDSCs create an immunosuppressive microenvironment by inhibiting the proliferation and activation of immunoreactive cells,including T and natural killer cells,as well as by inducing the proliferation of immunosuppressive cells,such as regulatory T cells and tumor-associated macrophages,which,in turn,promote the growth of cancer cells.Thus,MDSCs are key contributors to the emergence of an immunosup-pressive microenvironment in CRC and play an important role in the breakdown of antitumor immunity.In this narrative review,we explore the mechanisms through which MDSCs contribute to the immunosuppressive microenvironment,the current therapeutic approaches and technologies targeting MDSCs,and the therapeutic potential of modulating MDSCs in CRC treatment.This study provides ideas and methods to enhance survival rates in patients with CRC.

Circulating myeloid-derived suppressor cells in patients with pancreatic cancer

BACKGROUND： Myeloid-derived suppressor cells （MDSCs） are heterogeneous cell types that suppress T-cell responses in cancer patients and animal models, some MDSC subpopulations are increased in patients with pancreatic cancer. The present study was to investigate a specific subset of MDSCs in patients with pancreatic cancer and the mechanism of MDSCs increase in these patients. METHODS： Myeloid cells from whole blood were collected from 37 patients with pancreatic cancer, 17 with cholangiocarcinoma, and 47 healthy controls. Four pancreatic cancer cell lines were co- cultured with normal peripheral blood mononudear cells （PBMCs） to test the effect of tumor cells on the conversion of PBMCs to MDSCs. Levels of granulocyte-macrophage colony-stimulating factor （GM-CSF） and arginase activity in the plasma of cancer patients were analyzed by enzyme-linked immunosorbent assay. RESULTS： CD14＋/CD11b＋/HLA-DR MDSCs were increased in patients with pancreatic or bile duct cancer compared with those in healthy controls, and this increase was correlated with clinical cancer stage. Pancreatic cancer cell lines induced PBMCs to MDSCs in a dose-dependent manner. GM-CSF and arginase activity levels were significantly increased in the se rum of patients with pancreatic cancer. CONCLUSIONS： MDSCs were tumor related： tumor cells induced PBMCs to MDSCs in a dose-dependent manner and circulating CD14＋/CD11b＋/HLA-DR- MDSCs in pancreatic cancer patients were positively correlated with tumor burden. MDSCs might be useful markers for pancreatic cancer detection and progression.

Role of myeloid-derived suppressor cells in autoimmune disease

Myeloid-derived suppressor cells(MDSCs) represent an important class of immunoregulatory cells that can be activated to suppress T cell functions. These MDSCs can inhibit T cell functions through cell surface interactions and the release of soluble mediators. MDSCs accumulate in the inflamed tissues and lymphoid organs of patients with autoimmune diseases. Much of our knowledge of MDSC function has come from studies involving cancer models, however many recent studies have helped to characterize MDSC involvement in autoimmune diseases. MDSCs are a heterogeneous group of immature myeloid cells with a number of different functions for the suppression of T cell responses. However, we have yet to fully understand their contributions to the development and regulation of autoimmune diseases. A number of studies have described beneficial functions of MDSCs during autoimmune diseases, and thus there appears to be a potential role for MDSCs in the treatment of these diseases. Nevertheless, many questions remain as to the activation, differentiation, and inhibitory functions of MDSCs. This review aims to summarize our current knowledge of MDSC subsets and suppressive functions in tissue-specific autoimmune disorders. We also describe the potential of MDSC-basedcell therapy for the treatment of autoimmune diseases and note some of hurdles facing the implementation of this therapy.

Cyclooxygenase-2 Blockade Inhibits Accumulation and Function of Myeloid-derived Suppressor Cells and Restores T Cell Response after Traumatic Stress

Myeloid-derived suppressor cells （MDSCs） play a crucial role in T cell dysfunction, which is related to poor outcome in patients with severe trauma. Cyclooxygenase-2 （Cox-2） contributes to immune disorder in trauma and infection via production of prostaglandin E2. However, the role of Cox-2 in the accumulation and function of MDSCs after traumatic stress has not been fully elucidated. In the present study, we treated murine trauma model with NS398, a selective Cox-2 inhibitor. Then the percentages of CD1 lb＋/Gr-l＋ cells, proliferation and apoptosis of CD4＋ T cells were determined. Ar- ginase activity and arginase-1 （Arg-1） protein expression of splenic CDllb＋/Gr-I＋ cells, and de- layed-type hypersensitivity （DTH） response were analyzed. The results showed that Cox-2 blockade significantly decreased the percentages of CD1 lb＋/Gr-l＋ cells in the spleen and bone marrow 48 and 72 h after traumatic stress. NS398 inhibited arginase activity and down-regulated the Arg-1 expression of splenic CD1 lb＋/Gr-l＋ ceils. Moreover, NS398 could promote proliferation and inhibit apoptosis of CD4＋ T cells. It also restored DTH response of traumatic mice. Taken together, our data revealed that Cox-2 might play a pivotal role in the accumulation and function of MDSC after traumatic stress.

Correlation between circulating myeloid-derived suppressor cells and Th17 cells in esophageal cancer

AIM: To perform a comprehensive investigation into the potential correlation between circulating myeloidderived suppressor cells (MDSCs) and Th17 cells in esophageal cancer (ECA). METHODS: A total of 31 patients newly diagnosed with ECA and 26 healthy subjects were included in the current study. The frequencies of MDSCs and Th17 cells in peripheral blood were determined by flow cytometry. The mRNA expression of cytokines, arginase 1 (Arg1) and inducible NO synthase (iNOS) in peripheral blood mononuclear cells (PBMCs) and plasma Arg1 were assessed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. RESULTS: There was an increased prevalence of MDSCs in the peripheral blood from ECA patients (15.21% ± 2.25%) when compared with healthy control (HC) (1.10% ± 0.12%, P < 0.0001). The plasma levels of Arg1 in ECA patients were significantly higher than those in HC (28.28 ± 4.10 ng/mL vs 9.57 ± 1.51 ng/ mL, P=0.0003). iNOS mRNA levels in the peripheral blood of ECA patients also showed a threefold increase compared with HC (P=0.0162). The frequencies of Th17 cells (CD4 + IL-17A + ) were significantly elevated in ECA patients versus HC (3.50% ± 0.33% vs 1.82% ± 0.19%, P=0.0001). Increased mRNA expression of IL-17 and ROR-γt was also observed in ECA patients compared with HC (P=0.0041 and P=0.0004, respectively), while the mRNA expression of IL-6 and tumor necrosis factor-α (TNF-α) showed significant decreases (P=0.0049 and P < 0.0001, respectively). No obvious correlations were found between the frequencies of MDSCs and Th17 cells in the peripheral blood from ECA patients(r=-0.1725, P=0.3534). Arg1 mRNA levels were positively correlated with levels of IL-6 (r=0.6404, P=0.0031) and TNF-α (r=0.7646, P=0.0001). Similarly, iNOS mRNA levels were also positively correlated with levels of IL-6 (r=0.6782, P=0.0007) and TNF-α (r=0.7633, P < 0.0001). CONCLUSION: This study reveals the relationship between circulating MDSCs and Th17 cells, which may lead to new immunotherapy approaches for ECA based on the associated metabolites and cytokines.

Changes in the frequency of myeloid-derived suppressor cells after transarterial chemoembolization with gelatin sponge microparticles for hepatocellular carcinoma

Purpose: A series of clinical studies have established the safety and efficacy of transcatheter arterial chemoembolization(TACE) with gelatin sponge microparticles(GSMs) in treating hepatocellular carcinoma(HCC). HCC can lead to obvious necrosis inside tumors, especially larger ones, although it is unclear whether such necrotic tumor tissue can induce favorable immune reactions against the tumor. Myeloid-derived suppressor cells(MDSCs)have immunosuppressive functions and are currently considered a very important cell type affecting tumor immunity. This study observed changes in MDSC frequency in peripheral blood before and after GSM–TACE to evaluate the effect on the immune function of HCC patients.Methods: Eight patients diagnosed with HCC underwent GSM–TACE treatment in the Hepatobiliary Interventional Department of Beijing Tsinghua Chang Gung Hospital, Beijing, China;we followed up with the patients over a period of 30 days post-surgery. We used flow cytometry(FCM) to quantify the frequency of MDSCs in peripheral blood before TACE, 10 days after surgery and 30 days after surgery.Results: MDSC frequency after GSM–TACE had a significant downward trend. Pre-TACE, it was 30.73% ? 11.93%,decreasing to 18.60% ? 11.37% at 10 days after operation. This decrease was not statistically significant(P > 0.05). MDSC frequency was even lower 30 days after TACE(7.63% ? 7.32%) than at 10 days after TACE(P < 0.05), and there was a significant difference compared with pre-TACE(P < 0.001). We evaluated tumor response at 30 days after GSM–TACE according to the Modified Response Evaluation Criteria in Solid Tumors(mRECIST), and all eight patients showed partial response(PR).Conclusion: Our results confirmed that GSM–TACE was beneficial for improving anti-tumor immunity in the treatment of HCC.

Amplification of Functional Myeloid-derived Suppressor Cells during Stem Cell Mobilization Induced by Granulocyte Colony-stimulation-factor

The effects of granulocyte colony-stimulation-factor （G-CSF） on stem cell mobilization and its impact on the amplification of myeloid-derived suppressor cells （MDSCs） of donor mice were ex- amined. A mouse model of stem cell mobilization was established by consecutive subcutaneous injec- tion of 100 μg/kg G-CSF for 5 days. The blood from the donor mice was routinely examined during mobilization. Stem cells and MDSCs were analyzed by flow cytometry. The immunosuppressive mole- cules derived from MDSCs in serum and spleen, including hydrogen dioxide （H202） and nitric oxide （NO）, and the activity of nitric oxide synthase （NOS） were determined during the mobilization. Apop- tosis of T lymphocytes was assessed by using Annexin-V/PI. During stem cell mobilization, the number of lymphocytes and white blood cells in the peripheral blood was increased, and peaked on the 4th day. The number of stem cells in G-CSF-treated mice was significantly greater than that in controls （P〈0.01）. The expansions of MSDCs were also observed after G-CSF mobilization, with a more notable rate of growth in the peripheral blood than in the spleen. The activity of NOS and the production of NO were increased in the donor mice, and the serum H202 levels were approximately 4-fold greater than the con- trois. Consequently, apoptosis of T lymphocytes was increased and showed a positive correlation with the elevated percentage of MDSCs. It was concluded that G-CSF could provide sufficient peripheral blood stem cells for transplantation. Exogenous administration of G-CSF caused the accumulation of MDSCs in the peripheral blood and the spleen, which could lead to apoptosis ofT lymphocytes and may offer a new strategy for the prevention and treatment of graft versus host disease.

Myeloid-derived Suppressor Cells Activate Liver Natural Killer Cells in a Murine Model in Uveal Melanoma

Objective Elevated myeloid-derived suppressor cells(MDSCs)in many malignancies are associated with the increased risk for metastases and poor prognosis.Therefore,a mouse model of intraocular melanoma was established to explore how MDSCs influence liver metastases.Methods In this study,murine B16LS melanoma cells were transplanted into the posterior compartment(PC)of the eye of C57BL/6 mice.Leucocytes from the liver of naive mice and mice bearing melanoma liver metastasis were isolated using isotonic Percoll centrifugation,examined by flow cytometry for their expression of Gr1,CD11b,F4/80,RAE-1,and Mult-1,and further isolated for MDSCs and natural killer(NK)cells.The effects of MDSCs on NK cells were tested by coculturing and assessing the ability of NK cells to produce interferon-gamma(IFN-γ)by ELISA and NK cell cytotoxicity by 3H-thymidine incorporation assay.The impact of IFN-γon liver metastases was examined via selectively depleting IFN-γin vivo.Results The results showed that mice with liver metastases had increased levels of CD11b+Gr1+F4/80+as well as CD11b+Gr1+F4/80−MDSCs.MDSCs significantly enhanced the generation of IFN-γtogether with the cytotoxicity of the NK cells.Furthermore,these effects were cell-cell contact-dependent.Although IFN-γwas not of a toxic nature to the melanoma cells,it profoundly inhibited B16LS cell proliferation.Depleting IFN-γin vivo led to increased liver metastases.Conclusion All these findings first revealed that MDSCs accumulated in liver metastasis of intraocular melanoma could activate the NK cells to produce an effective anti-tumor immune response.Thus,the MDSCs’performance in different tumor models would need more investigation to boost current immunotherapy modalities.

Myeloid-derived suppressor cells in gastrointestinal cancers:A systemic review

Gastrointestinal(GI)cancers are one of the most common malignancies worldwide,with high rates of morbidity and mortality.Myeloid-derived suppressor cells(MDSCs)are major components of the tumor microenvironment(TME).MDSCs facilitate the transformation of premalignant cells and play roles in tumor growth and metastasis.Moreover,in patients with GI malignancies,MDSCs can lead to the suppression of T cells and natural killer cells.Accordingly,a better understanding of the role and mechanism of action of MDSCs in the TME will aid in the development of novel immune-targeted therapies.

GM3-containing nanoparticles in immunosuppressed hosts:Effect on myeloid-derived suppressor cells

Cancer vaccines to date have not broadly achieved a significant impact on the overall survival of patients. The negative effect on the immune system of the tu-mor itself and conventional anti-tumor treatments such as chemotherapy is, undoubtedly, a key reason for these disappointing results. Myeloid-derived suppres-sor cells （MDSCs） are considered a central node of the immunosuppressive network associated with tumors. These cells inhibit the effector function of natural killer and CD8＋ T cells, expand regulatory T cells and can differentiate into tumor-associated macrophages within the tumor microenvironment. Thus, overcoming the suppressive effects of MDSCs is likely to be criti-cal for cancer immunotherapy to generate effective anti-tumor immune responses. However, the capacity of cancer vaccines and particularly their adjuvants to overcome this inhibitory population has not been well characterized. Very small size proteoliposomes （VSSP） is a nanoparticulated adjuvant specifcally designed to be formulated with vaccines used in the treatment of immunocompromised patients. This adjuvant contains immunostimulatory bacterial signals together with GM3 ganglioside. VSSP promotes dendritic cell maturation, antigen cross-presentation to CD8＋ T cells, Th1 polar-ization, and enhances CD8＋ T cell response in tumor-free mice. Currently, four cancer vaccines using VSSP as the adjuvant are in Phase？Ⅰ？and Ⅱ clinical trials. In this review, we summarize our work characterizing the unique ability of VSSP to stimulate antigen-specifc CD8＋ T cell responses in two immunocompromised sce-narios; in tumor-bearing mice and during chemother-apy-induced leukopenia. Particular emphasis has been placed on the interaction of these nanoparticles with MDSCs, as well as comparison with other cancer vac-cine adjuvants currently in preclinical or clinical studies.

Increased frequency and clinical significance of myeloidderived suppressor cells in human colorectal carcinoma

AIM： To investigate the frequency and clinical signifi- cance of the myeloid-derived suppressor cells （MDSC） in human colorectal carcinoma （CRC）. METHODS： Samples of peripheral blood and tumor tis- sue from 49 CRC patients were analyzed. Mononuclear cells were isolated by FicolI-Hypaque density gradient centrifugation and were subjected to a flow cytometry- based immunophenotypic analysis. RESULTS： A considerable increase in the percentage of CD33＋HLA-DR MDSCs was observed in the periph- eral blood （1.89% ：1= 0.75%） and tumor tissues （2.99%±1.29%） of CRC patients as compared with that in theperipheral blood of healthy controls （0.54%±0.35%）. This expanded CD33＋HLA-DR subset exhibited imma- ture myeloid cell markers, but not lineage markers, and showed up-regulation of CD18/CD11b expression as compared with the MDSCs from healthy donors. Fur- ther studies showed that the MDSC proportion in CRC peripheral blood was correlated with nodal metastasis （P = 0.023）, whereas that in tumor tissues was cor- related with nodal/distant metastasis （P = 0.016/P = 0.047） and tumor stage （P = 0.028）, suggesting the involvement of MDSCs in CRC tumor development. CONCLUSION： Characterization of MDSCs in CRC sug- gests the clinical significance of circulating and tumor- infiltrating MDSCs and may provide new insights into the CRC immunotherapy targeting MDSCs.

Contribution of myeloid-derived suppressor cells to tumor-induced immune suppression,angiogenesis,invasion and metastasis

Growing evidence suggests that myeloid-derived suppressor cells （MDSCs）,which have been named ＂immature myeloid cells＂ or ＂myeloid suppressor cells＂ （MSCs）,play a critical role during the progression of cancer in tumor-bearing mice and cancer patients.As their name implies,these cells are derived from bone marrow and have a tremendous potential to suppress immune responses.Recent studies indicated that these cells also have a crucial role in tumor progression.MDSCs can directly incorporate into tumor endothelium.They secret many pro-angiogenic factors as well.In addition,they play an essential role in cancer invasion and metastasis through inducing the production of matrix metalloproteinases （MMPs）,chemoattractants and creating a pre-metastatic environment.Increasing evidence supports the idea that cancer stem cells （CSCs） are responsible for tumorigenesis,resistance to therapies,invasion and metastasis.Here,we hypothesize that CSCs may ＂hijack＂ MDSCs for use as alternative niche cells,leading to the maintenance of stemness and enhanced chemo-and radio-therapy resistance.The countermeasure that directly targets to MDSCs may be useful for against angiogenesis and preventing cancer from invasion and metastasis.Therefore,the study of MDSCs is important to understand tumor progression and to enhance the therapeutic efficacy against cancer.

Hypertonic saline resuscitation contributes to early accumulation of circulating myeloid-derived suppressor cells in a rat model of hemorrhagic shock

Background Hemorrhagic shock is usually associated with complicated immune and inflammatory responses, which are sometimes crucial for the prognosis. As regulators of the immune and inflammatory system; proliferation, migration, distribution and activation of myeloid-derived suppressor cells （MDSCs） are intimately linked to the inflammation cascade. Methods In a model of severe hemorrhagic shock, thirty-five rats were randomly divided into control, sham, normal saline resuscitation （NS）, hypertonic saline resuscitation （HTS）, and hydroxyethyl starch resuscitation （HES）, with seven in each group. MDSCs were analyzed by flow cytometric staining of CD11b/c＊Gra~ in peripheral blood mononuclear cells （PBMC）, spleen cell suspensions, and bone marrow nucleated cells （BMNC）. Simultaneously, the expressions of arginase-1 （ARG-1） and inducible nitric oxide synthase （iNOS） mRNA in MDSCs were evaluated by quantitative reverse transcription-polymerase chain reaction （qRT-PCR）. Results In the early stage after hemorrhagic shock, fluid resuscitation and emergency treatment, the MDSCs in the PBMC of NS, HTS and HES groups markedly increased, and MDSCs in BMNC of these groups decreased accordingly, significantly different to the control group. In hemorrhagic shock rats infused with HTS at the early resuscitation stage, MDSCs in PBMC increased about 2 and 4 folds, and MDSCs in BMNC decreased about 1.3 and 1.6 folds, as compared to the sham group respectively, with statistically significant difference. Furthermore, compared to the NS and HES groups, the MDSCs in PBMC of HTS group increased 1.6 and 1.8 folds with statistically significant differences; the MDSCs decrease in BMNC was not significant. However, there was no statistically significant difference in MDSCs of spleen among the five groups. In addition, compared to the control, sham, NS and HES groups, the ARG-1 and iNOS mRNA of MDSCs in PBMC, spleen and BMNC in the HTS group had the highest level of expression, but no statistically significant differences were noted. Conclusions In this model of rat with severe and controlled hemorrhagic shock, small volume resuscitation with HTS contributes to dramatically early migration and redistribution of MDSCs from bone marrow to peripheral circulation, compared to resuscitation with NS or HES.

Glucocorticoid receptor modulates myeloid-derived suppressor cell function via mitochondrial metabolism in immune thrombocytopenia

Myeloid-derived suppressor cells(MDSCs)are a heterogeneous population of immature cells and natural inhibitors of adaptive immunity.Intracellular metabolic changes in MDSCs exert a direct immunological influence on their suppressive activity.Our previous study demonstrated that high-dose dexamethasone(HD-DXM)corrected the functional impairment of MDSCs in immune thrombocytopenia(ITP);however,the MDSC population was not restored in nonresponders,and the mechanism remained unclear.In this study,altered mitochondrial physiology and reduced mitochondrial gene transcription were detected in MDSCs from HD-DXM nonresponders,accompanied by decreased levels of carnitine palmitoyltransferase-1(CPT-1),a rate-limiting enzyme in fatty acid oxidation(FAO).Blockade of FAO with a CPT-1 inhibitor abolished the immunosuppressive function of MDSCs in HD-DXM responders.We also report that MDSCs from ITP patients had lower expression of the glucocorticoid receptor(GR),which can translocate into mitochondria to regulate the transcription of mitochondrial DNA(mtDNA)as well as the level of oxidative phosphorylation.It was confirmed that the expression of CPT-1 and mtDNA-encoded genes was downregulated in GR-siRNA-treated murine MDSCs.Finally,by establishing murine models of active and passive ITP via adoptive transfer of DXM-modulated MDSCs,we confirmed that GR-silenced MDSCs failed to alleviate thrombocytopenia in mice with ITP.In conclusion,our study indicated that impaired aerobic metabolism in MDSCs participates in the pathogenesis of glucocorticoid resistance in ITP and that intact control of MDSC metabolism by GR contributes to the homeostatic regulation of immunosuppressive cell function.

Increased circulating of myeloid-derived suppressor cells in myelodysplastic syndrome

Myelodysplastic syndrome （MDS） is a group of clonal .hematopoietic stem cell disorders, characterizedby varying degrees ot peripheral cytopema caused by ineffective dysplasia of the myeloid lineages. MDS also has a high risk of progression to acute myeloid leukemia. But the role of immune abnormalities in the pathogenesis of MDS is still not clear. Myeloid-derived suppressor cells （MDSCs） constitute a heterogeneous population of immature cells derived from the bone marrow. In the recent years, MDSCs were reported to play an important role in suppressing lymphocytes in tumor-bearing animal models and cancer patients. This could be one of the mechanisms on tumor immune evasion, which aggravates the development and growth of tumors. In a mice model, MDSCs are characterized by co- expression of GR1 and CDllb. In humans, the phenotype of MDSCs was accepted as Lin- HLA-DR- CD33＋.l In the present study, we investigated the level of circulating MDSCs （Lin- HLA-DR- CD33＋） in patients with MDS and evaluated the association between MDSCs and malignancy in MDS. METHODS Patients Thirty-five patients with MDS （24 men and 11 women, median age 59 years （age range 21-83）, including refractory anemia （n=3）; refractory anemia with ringed sideroblasts （n=3）; refractory cytopenia with multilineage dysplasia （n=9）; refractory anemia with excess blast-I （n=4）; refractory anemia with excess blast-II （n=16））, and without other systemic diseases, were enrolled in the present study. All the patients underwent diagnosis in the Department of Hematology, General Hospital of Tianjin Medical University from March 2011 to April 2012, according to the diagnostic criteria of MDS proposed between 2007 and 2008. After treatment for three months, 14 MDS patients were investigated again for their MDSCs changes. Twenty normal healthy individuals were selected as controls （9 men and 11 women, median age 34 years （age range 26-82））. The study was approved by the Ethics Committee of Tianjin Medical University. Informed written consent was obtained from all the patients and normalindividuals in accordance with the Declaration of Helsinki Flow cytometric analysis Peripheral blood samples were collected in EDTA- anticoagulant tubes from the patients and normal individuals. The number of circulating MDSCs was measured by using flow cytometry （FCM） assay. The markers used in the assay were anti-CD33-APC, anti-LIN- FITC （CD3, CD14, CD16, CD19, CD20, CD56） and anti- HLA-DR-PE antibodies （BD Biosciences, USA）. The number of stem cells from the bone marrow, which was collected in heparin-anticoagulant tubes, was measured by FCM using anti-CD34-PerCP antibodies （BD Biosciences）. Data acquisition and analysis were carried out by using FACS-Calibur flow cytometer （BD Biosciences）, with the Cell Quest software （Becton Dickinson, version 3.1）.

Targeted inhibition of myeloid-derived suppressor cells in the tumor microenvironment by low-dose doxorubicin to improve immune efficacy in murine neuroblastoma

Background:High agglomeration of myeloid-derived suppressor cells(MDSCs)in neuroblastoma(NB)impeded therapeutic effects.This study aimed to investigate the role and mechanism of targeted inhibition of MDSCs by low-dose doxorubicin(DOX)to enhance immune efficacy in NB.Methods:Bagg albino(BALB/c)mice were used as tumor-bearing mouse models by injecting Neuro-2a cells,and MDSCs were eliminated by DOX or dopamine(DA)administration.Tumor-bearing mice were randomly divided into 2.5 mg/kg DOX,5.0 mg/kg DOX,50.0 mg/kg DA,and control groups(n=20).The optimal drug and its concentration for MDSC inhibition were selected according to tumor inhibition.NB antigen-specific cytotoxic T cells(CTLs)were prepared.Tumor-bearing mice were randomly divided into DOX,CTL,anti-ganglioside(GD2),DOX+CTL,DOX+anti-GD2,and control groups.Following low-dose DOX administration,immunotherapy was applied.The levels of human leukocyte antigen(HLA)-I,CD8,interleukin(IL)-2 and interferon(IFN)-γin peripheral blood,CTLs,T-helper 1(Th1)/Th2 cytokines,perforin,granzyme and tumor growth were compared among the groups.The Wilcoxon two-sample test and repeated-measures analysis of variance were used to analyze results.Results:The slowest tumor growth(F=6.095,P=0.018)and strongest MDSC inhibition(F=14.632,P=0.001)were observed in 2.5 mg/kg DOX group.Proliferation of T cells was increased(F=448.721,P<0.001)and then decreased(F=2.047,P=0.186).After low-dose DOX administration,HLA-I(F=222.489),CD8(F=271.686),Th1/Th2 cytokines,CD4^(+)and CD8^(+)lymphocytes,granzyme(F=2376.475)and perforin(F=488.531)in tumor,IL-2(F=62.951)and IFN-γ(F=240.709)in peripheral blood of each immunotherapy group were all higher compared with the control group(all ofP values<0.05).The most significant increases in the aforementioned indexes and the most notable tumor growth inhibition were observed in DOX+anti-GD2 and DOX+CTL groups.Conclusions:Low-dose DOX can be used as a potent immunomodulatory agent that selectively impairs MDSC-induced immunosuppression,thereby fostering immune efficacy in NB.

Continuous activation of polymorphonuclear myeloid-derived suppressor cells during pregnancy is critical for fetal development

The maternal immune system is vital in maintaining immunotolerance to the semiallogeneic fetus for a successful pregnancy.Although studies have shown that myeloid-derived suppressor cells(MDSCs)play an important role in maintaining feto-maternal tolerance,little is known about the role of MDSCs in pregnancies with intrauterine growth retardation(IUGR).Here,we reported that the activation of polymorphonuclear myeloid-derived suppressor cells(PMN-MDSCs)during pregnancy was closely associated with fetal growth.In humans,class E scavenger receptor 1(SR-E1),a distinct marker for human PMN-MDSCs,was used to investigate PMN-MDSC function during pregnancy.Continuous activation of SR-E1+PMN-MDSCs was observed in all stages of pregnancy,accompanied by high cellular levels of ROS and arginase-1 activity,mediated through STAT6 signaling.However,SR-E1+PMN-MDSCs in pregnancies with IUGR showed significantly lower suppressive activity,lower arginase-1 activity and ROS levels,and decreased STAT6 phosphorylation level,which were accompanied by an increase in inflammatory factors,compared with those in normal pregnancies.Moreover,the population of SR-E1+PMN-MDSCs was negatively correlated with the adverse outcomes of newborns from pregnancies with IUGR.In mice,decreases in cell population,suppressive activity,target expression levels,and STAT6 phosphorylation levels were also observed in the pregnancies with IUGR compared with the normal pregnancies,which were rescued by the adoptive transfer of PMN-MDSCs from pregnant mice.Interestingly,the growth-promoting factors(GPFs)secreted by placental PMN-MDSCs in both humans and mice play a vital role in fetal development.These findings collectively support that PMN-MDSCs have another new role in pregnancy,which can improve adverse neonatal outcomes.

Aryl hydrocarbon receptor activation drives polymorphonuclear myeloid-derived suppressor cell response and efficiently attenuates experimental Sjögren’s syndrome

Myeloid-derived suppressor cells(MDSCs)comprise heterogeneous myeloid cell populations with immunosuppressive capacity that contribute to immune regulation and tolerance induction.We previously reported impaired MDSC function in patients with primary Sjögren’s syndrome(pSS)and mice with experimental SS(ESS).However,the molecular mechanisms underlying MDSC dysfunction remain largely unclear.In this study,we first found that aryl hydrocarbon receptor(AhR)was highly expressed by human and murine polymorphonuclear MDSCs(PMN-MDSCs).Indole-3-propionic acid(IPA),a natural AhR ligand produced from dietary tryptophan,significantly promoted PMN-MDSC differentiation and suppressive function on CD4^(+)T cells.In contrast,feeding a tryptophan-free diet resulted in a decreased PMN-MDSC response,a phenotype that could be reversed by IPA supplementation.The functional importance of PMN-MDSCs was demonstrated in ESS mice by using a cell-depletion approach.Notably,AhR expression was reduced in PMN-MDSCs during ESS development,while AhR antagonism resulted in exacerbated ESS pathology and dysregulated T effector cells,which could be phenocopied by a tryptophan-free diet.Interferon regulatory factor 4(IRF4),a repressive transcription factor,was upregulated in PMN-MDSCs during ESS progression.Chromatin immunoprecipitation analysis revealed that IRF4 could bind to the promoter region of AhR,while IRF4 deficiency markedly enhanced AhR-mediated PMN-MDSC responses.Furthermore,dietary supplementation with IPA markedly ameliorated salivary glandular pathology in ESS mice with restored MDSC immunosuppressive function.Together,our results identify a novel function of AhR in modulating the PMN-MDSC response and demonstrate the therapeutic potential of targeting AhR for the treatment of pSS.

Intermittent fasting boosts antitumor immunity by restricting CD11b^(+)Ly6C^(low)Ly6G^(low) cell viability through glucose metabolism in murine breast tumor model

Intermittent fasting can benefit breast cancer patients undergoing chemotherapy or immunotherapy.However,it is still uncertain how to select immunotherapy drugs to combine with intermittent fasting.Herein we observed that two cycles of fasting treatment significantly inhibited breast tumor growth and lung tissue metastasis,as well as prolonged overall survival in mice bearing 4T1 and 4T07 breast cancer.During this process,both the immunosuppressive monocytic-(M-)and granulocytic-(G-)myeloid-derived suppressor cell(MDSC)decreased,accompanied by an increase in interleukin(IL)7R^(+)and granzyme B^(+)T cells in the tumor microenvironment.Interestingly,we observed that Ly6G^(low)G-MDSC sharply decreased after fasting treatment,and the cell surface markers and protein mass spectrometry data showed potential therapeutic targets.Mechanistic investigation revealed that glucose metabolism restriction suppressed the splenic granulocytemonocyte progenitor and the generation of colony-stimulating factors and IL-6,which both contributed to the accumulation of G-MDSC.On the other hand,glucose metabolism restriction can directly induce the apoptosis of Ly6G^(low)G-MDSC,but not Ly6G^(high)subsets.In summary,these results suggest that glucose metabolism restriction induced by fasting treatment attenuates the immune-suppressive milieu and enhances the activation of CD3^(+)T cells,providing potential solutions for enhancing immune-based cancer interventions.

The role of myeloid-derived suppressor cells in gastrointestinal cancer

Gastrointestinal(GI)cancer encompasses a range ofmalignancies that originate in the digestive system,which together represent the most common form of cancer diagnosed worldwide.However,despite numerous advances in both diagnostics and treatment,the incidence and mortality rate of GI cancer are on the rise.Myeloid-derived suppressor cells(MDSCs)are a heterogeneous population of immature myeloid cells that increase in number under certain pathological conditions,such as infection and inflammation,and this expansion is of particular relevance to cancer.MDSCs are heavily involved in the regulation of the immune system and act to dampen its response to tumors,favoring the escape of tumor cells from immunosurveillance and increasing both metastasis and recurrence.Several recent studies have supported the use of MDSCs as a prognostic and predictive biomarker in patientswith cancer,and potentially as a novel treatment target.In the present review,the mechanisms underlying the immunosuppressive functions of MDSCs are described,and recent researches concerning the involvement of MDSCs in the progression,prognosis,and therapies of GI cancer are reviewed.The aim of this work was to present the development of novel treatments targeting MDSCs in GI cancer in the hope of improving outcomes for patients with this condition.