Clinical Significance and Functional Studies of Myeloid-Derived Suppressor Cells in Chronic Hepatitis C Patients

MYELOID-DERIVED SUPPRESSOR CELLS TWO YEARS AFTER HEPATITIS C VIRUS ERADICATION USING DIRECTLY ACTING ANTIVIRALS

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) have immature morphology, relatively weak phagocytic activity, as well as some immunosuppressive functions. The capacity of MDSCs to inhibit T-cell-mediated immunological responses is their most notable functional characteristic. Down-regulating antitumor immune surveillance is one way that the expansion and activation of MDSCs contribute significantly to the occurrence and progression of tumors. Increased levels of MDSCs in patients with chronic hepatitis C virus (HCV) infection could suppress T-cell responses, promoting viral escape and hepatitis progression. This may make HCV-infected individuals more vulnerable to severe infections, hepatic and extra-hepatic tumors, and a diminished capacity to react to immunization. It is still unknown if effective HCV eradication with directly acting antivirals (DAAs) can restore immune functions and immune surveillance capacity.

OBJECTIVE

The purpose of this study was to observe the frequency of M-MDSCs (CD33+, CD11b+, and HLA-DR) in patients with a previous history of HCV, 2-3 years after virus eradication using DAA therapy.

METHODS

This study was conducted on 110 subjects: fifty-five subjects without liver cirrhosis who were treated with HCV using DAAs and attained SVR for a period of 2-3 years and 55 age- and gender-matched healthy controls. The study was conducted during the period from January to July 2022. Patients were recruited from the National Viral Hepatitis Treatment Unit, Alexandria University Hepatology outpatient clinic, and the Alexandria University Tropical Medicine outpatient clinic. The frequencies of MDSCs (CD33+CD11b + HLA-DR-) by flow cytometry were assessed.

RESULTS

Even after the virus had been eradicated for longer than two years, MDSC levels in HCV-treated individuals were found to be considerably higher. In the HCV-treated group, the median number of MDSCs was 5, with an interquartile range (IQR) of 3.79-7.69. In contrast, the median for the control group was 3.1, with an IQR of 1.4-3.2 (P˂0.001).

CONCLUSION

Successful DAA therapy leads to slow and partial immunological reconstitution, as demonstrated by the failure to attain normal levels of MDSC's 2 years after successful HCV eradication despite the normalization of laboratory parameters as well as the absence of liver fibrosis. The clinical implications of these findings should be thoroughly studied.

Immunomodulatory actions of myeloid-derived suppressor cells in the context of innate immunity

Myeloid-derived suppressor cells (MDSCs) are notable innate immune cells, which are further divided into two subpopulations, i.e., monocytic and granulocytic. These cells are traditionally considered to mainly suppress the T-cell responses. However, more updated data indicate that their properties are rather immunomodulatory than solely immunosuppressive. Indeed, MDSCs display extensive crosstalk with other either innate or adaptive immune cells, and, according to the situation under which they are triggered, they may enhance or attenuate the immune response. However, their positive role in host's defense mechanisms under specific conditions is rarely discussed in the literature. In this mini-review, the authors briefly summarise the mechanisms of action of MDSCs under distinct conditions, such as infections and malignancies, with a particular emphasis on their role as components of the innate immunity system.

Differential kinetics of splenic CD169+ macrophage death is one underlying cause of virus infection fate regulation

Acute infection and chronic infection are the two most common fates of pathogenic virus infections. While several factors that contribute to these fates are described, the critical control points and the mechanisms that underlie infection fate regulation are incompletely understood. Using the acute and chronic lymphocytic choriomeningitis virus (LCMV) infection model of mice, we find that the early dynamic pattern of the IFN-I response is a differentiating trait between both infection fates. Acute-infected mice generate a 2-wave IFN-I response while chronic-infected mice generate only a 1-wave response. The underlying cause is a temporal difference in CD8 T cell-mediated killing of splenic marginal zone CD169+ macrophages. It occurs later in acute infection and thus enables CD169+ marginal zone macrophages to produce the 2nd IFN-I wave. This is required for subsequent immune events including induction of inflammatory macrophages, generation of effector CD8+ T cells and virus clearance. Importantly, these benefits come at a cost for the host in the form of spleen fibrosis. Due to an earlier marginal zone destruction, these ordered immune events are deregulated in chronic infection. Our findings demonstrate the critical importance of kinetically well-coordinated sequential immune events for acute infection control and highlights that it may come at a cost for the host organism.

Mononuclear myeloid-derived suppressor cells expansion is associated with progression of liver failure in patients with acute decompensation of cirrhosis

Patients with acute decompensation (AD) of cirrhosis have different clinical courses. Immune dysfunction affects disease outcomes. The profile of myeloid-derived suppressor cells (MDSCs), polymorphonuclear- (PMN-MDSCs) and mononuclear- (M-MDSCs) subsets in AD and their associations with different clinical courses are still unclear. This study included 36 healthy controls (HC), 20 patients with compensated cirrhosis (CC) and 107 patients with AD. Based on the condition at enrollment and 90 days of follow-up, the patients with AD were divided into AD-acute-on-chronic liver failure (AD-ACLF), stable decompensated cirrhosis (SDC), unstable decompensated cirrhosis (UDC) and pre-acute-on-chronic liver failure (Pre-ACLF) groups. The percentages of MDSCs, PMN-MDSCs, and M-MDSCs in the peripheral blood of patients with AD were significantly higher than those in HC and CC. Lactate levels, Child-Pugh score, and MDSCs were risk factors for the occurrence of AD. A positive correlation exists between MDSCs and indices of systemic inflammation and liver failure. In the AD cohort, the percentages of M-MDSCs in the Pre-ACLF and AD-ACLF groups were significantly higher than those in the UDC and SDC groups. The percentages of MDSCs and PMN-MDSCs in the AD groups increased; however, the difference was not statistically significant. MDSCs and M-MDSCs positively correlated with the incidence of liver failure. Sex, alcoholic etiology, bacterial infection, and M-MDSCs were independent risk factors for liver failure in patients with AD. Our data indicate that M-MDSCs expansion, rather than PMN-MDSCs expansion, might predict poor prognosis in patients with AD. Reducing the suppressive activity and number of MDSCs and M-MDSCs are promising strategies for immunotherapy in patients with AD.

Effect of Direct Acting Antivirals (DAAs) on Myeloid-Derived Suppressor Cells Population in Egyptian Chronic Hepatitis C Virus Patients: A Potential Immunomodulatory Role of DAAs

Chronic hepatitis C is a major health concern with high morbidity and mortality rates. The introduction of direct acting antivirals (DAAs) as a first-line treatment for hepatitis C virus (HCV) has significantly enhanced HCV eradication. However, DAA therapy is facing rising concerns regarding long-term safety, viral resistance, and reinfection. HCV is associated with different immune alteration mechanisms that can evade immunity and establish persistent infection. One of these suggested mechanisms is the accumulation of myeloid-derived suppressor cells (MDSCs), which is known to accumulate in chronic inflammatory conditions. Moreover, the role of DAA in restoring immunity after successful viral eradication is still unclear and needs further investigations. Thus, we aimed to investigate the role of MDSCs in chronic HCV Egyptian patients and its response to DAA in treated compared with untreated patients. Fifty untreated chronic hepatitis C (CHC) patients, 50 DAA-treated CHC patients, and 30 healthy individuals were recruited. We used flow cytometer analysis to measure MDSCs frequency and enzyme-linked immunosorbent assay analysis to evaluate the serum level of interferon (IFN)-γ. We found a significant elevation in MDSC% among the untreated group (34.5 ± 12.4%) compared with the DAA-treated group (18.3 ± 6.7%), while the control group had a mean of (3.8 ± 1.6%). IFN-γ concentration was higher in treated patients compared with untreated. We also found a significant negative correlation (rs -0.662) (p < 0.001) between MDSC% and IFN-γ concentration among treated HCV patients. Our results revealed important evidence of MDSCs accumulation in CHC patients and partial retrieval of the immune system regulatory function after DAA therapy.

Role of myeloid-derived suppressor cells during Trypanosoma cruzi infection

Chagas disease (CD), caused by the protozoan parasite Trypanosoma cruzi, is the third largest parasitic disease burden globally. Currently, more than 6 million people are infected, mainly in Latin America, but international migration has turned CD into an emerging health problem in many nonendemic countries. Despite intense research, a vaccine is still not available. A complex parasite life cycle, together with numerous immune system manipulation strategies, may account for the lack of a prophylactic or therapeutic vaccine. There is substantial experimental evidence supporting that T. cruzi acute infection generates a strong immunosuppression state that involves numerous immune populations with regulatory/suppressive capacity. Myeloid-derived suppressor cells (MDSCs), Foxp3+ regulatory T cells (Tregs), regulatory dendritic cells and B regulatory cells are some of the regulatory populations that have been involved in the acute immune response elicited by the parasite. The fact that, during acute infection, MDSCs increase notably in several organs, such as spleen, liver and heart, together with the observation that depletion of those cells can decrease mouse survival to 0%, strongly suggests that MDSCs play a major role during acute T. cruzi infection. Accumulating evidence gained in different settings supports the capacity of MDSCs to interact with cells from both the effector and the regulatory arms of the immune system, shaping the outcome of the response in a very wide range of scenarios that include pathological and physiological processes. In this sense, the aim of the present review is to describe the main knowledge about MDSCs acquired so far, including several crosstalk with other immune populations, which could be useful to gain insight into their role during T. cruzi infection.

Deciphering the roles of myeloid derived suppressor cells in viral oncogenesis

Myeloid derived suppressor cells (MDSCs) are a heterogenous population of myeloid cells derived from monocyte and granulocyte precursors. They are pathologically expanded in conditions of ongoing inflammation where they function to suppress both innate and adaptive immunity. They are subdivided into three distinct subsets: monocytic (M-) MDSC, polymorphonuclear (or neutrophilic) (PMN-) MDSC and early-stage (e-) MDSC that may exhibit differential function in different pathological scenarios. However, in cancer they are associated with inhibition of the anti-tumour immune response and are universally associated with a poor prognosis. Seven human viruses classified as Group I carcinogenic agents are jointly responsible for nearly one fifth of all human cancers. These viruses represent a large diversity of species, including DNA, RNA and retroviridae. They include the human gammaherpesviruses (Epstein Barr virus (EBV) and Kaposi's Sarcoma-Associated Herpesvirus (KSHV), members of the high-risk human papillomaviruses (HPVs), hepatitis B and C (HBV, HCV), Human T cell leukaemia virus (HTLV-1) and Merkel cell polyomavirus (MCPyV). Each of these viruses encode an array of different oncogenes that perturb numerous cellular pathways that ultimately, over time, lead to cancer. A prerequisite for oncogenesis is therefore establishment of chronic infection whereby the virus persists in the host cells without being eradicated by the antiviral immune response. Although some of the viruses can directly modulate the immune response to enable persistence, a growing body of evidence suggests the immune microenvironment is modulated by expansions of MDSCs, driven by viral persistence and oncogenesis. It is likely these MDSCs play a role in loss of immune recognition and function and it is therefore essential to understand their phenotype and function, particularly given the increasing importance of immunotherapy in the modern arsenal of anti-cancer therapies. This review will discuss the role of MDSCs in viral oncogenesis. In particular we will focus upon the mechanisms thought to drive the MDSC expansions, the subsets expanded and their impact upon the immune microenvironment. Importantly we will explore how MDSCs may modulate current immunotherapies and their impact upon the success of future immune-based therapies.

Low-dose decitabine modulates myeloid-derived suppressor cell fitness via LKB1 in immune thrombocytopenia

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature cells and natural inhibitors of adaptive immunity. Metabolic fitness of MDSCs is fundamental for its suppressive activity toward effector T cells. Our previous studies showed that the number and inhibitory function of MDSCs were impaired in patients with immune thrombocytopenia (ITP) compared with healthy controls. In this study, we analyzed the effects of decitabine on MDSCs from patients with ITP, both in vitro and in vivo. We found that low-dose decitabine promoted the generation of MDSCs and enhanced their aerobic metabolism and immunosuppressive functions. Lower expression of liver kinase 1 (LKB1) was found in MDSCs from patients with ITP, which was corrected by decitabine therapy. LKB1 short hairpin RNA (shRNA) transfection effectively blocked the function of MDSCs and almost offset the enhanced effect of decitabine on impaired MDSCs. Subsequently, anti-CD61 immune-sensitized splenocytes were transferred into severe combined immunodeficient (SCID) mice to induce ITP in murine models. Passive transfer of decitabine-modulated MDSCs significantly raised platelet counts compared with that of phosphate buffered saline-modulated MDSCs. However, when LKB1 shRNA-transfected MDSCs were transferred into SCID mice, the therapeutic effect of decitabine in alleviating thrombocytopenia was quenched. In conclusion, our study suggests that the impaired aerobic metabolism of MDSCs is involved in the pathogenesis of ITP, and the modulatory effect of decitabine on MDSC metabolism contributes to the improvement of its immunosuppressive function. This provides a possible mechanism for sustained remission elicited by low-dose decitabine in patients with ITP.

Decreased Polymorphonuclear Myeloid-Derived Suppressor Cells and ROS Production Correlated Closely with Bronchopulmonary Dysplasia in Preterm Infants

Background. Bronchopulmonary dysplasia (BPD) is one of the most serious complications in premature infants. Myeloid-derived suppressor cells (MDSCs) have been indicated to promote immune tolerance and induce anti-inflammatory responses during the neonatal stage. However, the role of MDSCs in BPD has not been completely expounded. Methods. 130 cases of newborns were collected from six tertiary hospitals in Guangzhou from August 2019 to June 2022. They were divided into BPD group, non-BPD preterm infants group, and term infants group according to gestational age and presence of BPD. The peripheral blood was collected and used to analyze the proportion, phenotypic, and function of MDSCs at 3 to 7 days and 8 to 14 days after birth, respectively. Results. We indicated that the number of both MDSCs in premature infants is reduced, and the number of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in peripheral blood of BPD infants was significantly lower than that of non-BPD infants under 34 weeks of gestational age ( $P<0.05$ ). Furthermore, PMN-MDSCs from peripheral blood of patients presented inhibitory effect on proliferation of CD4+T and CD8+T cells in each group. However, PMN-MDSCs from BPD group had obviously weaker inhibitory effect on proliferation of CD4+T and CD8+T cells than that from non-BPD preterm infants group. In addition, we demonstrated that the expression of NADPH oxidase (Nox2) and reactive oxygen species (ROS) in PMN-MDSCs of BPD children was significantly lower than that in non-BPD preterm infants, suggesting that ROS pathway was affected in BPD in premature infants. Conclusion. This study preliminarily revealed the role of PMN-MDSCs in the pathogenesis of BPD in premature infants. The specific immune regulation mechanism of PMN-MDSCs in BPD will provide new ideas and strategies for clinical prevention and treatment of BPD in premature infants.

B7H3-dependent myeloid-derived suppressor cell recruitment and activation in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease without effective curative therapy. Recent evidence shows increased circulating myeloid-derived suppressor cells (MDSCs) in cancer, inflammation, and fibrosis, with some of these cells expressing B7H3. We sought to investigate the role of MDSCs in IPF and its potential mediation via B7H3. Here we prospectively collected peripheral blood samples from IPF patients to analyze for circulating MDSCs and B7H3 expression to assess their clinical significance and potential impact on co-cultured lung fibroblasts and T-cell activation. In parallel, we assess MDSC recruitment and potential B7H3 dependence in a mouse model of pulmonary fibrosis. Expansion of MDSCs in IPF patients correlated with disease severity. Co-culture of soluble B7H3 (sB7H3)-treated mouse monocytic MDSCs (M-MDSCs), but not granulocytic MDSCs (G-MDSCs), activated lung fibroblasts and myofibroblast differentiation. Additionally, sB7H3 significantly enhanced MDSC suppression of T-cell proliferation. Activated M-MDSCs displayed elevated TGFβ and Arg1 expression relative to that in G-MDSCs. Treatment with anti-B7H3 antibodies inhibited bone marrow-derived MDSC recruitment into the bleomycin-injured lung, accompanied by reduced expression of inflammation and fibrosis markers. Selective telomerase reverse transcriptase (TERT) deficiency in myeloid cells also diminished MDSC recruitment associated with the reduced plasma level of sB7H3, lung recruitment of c-Kit⁺ hematopoietic progenitors, myofibroblast differentiation, and fibrosis. Lung single-cell RNA sequencing (scRNA-seq) revealed fibroblasts as a predominant potential source of sB7H3, and indeed the conditioned medium from activated mouse lung fibroblasts had a chemotactic effect on bone marrow (BM)-MDSC, which was abolished by B7H3 blocking antibody. Thus, in addition to their immunosuppressive activity, TERT and B7H3-dependent MDSC expansion/recruitment from BM could play a paracrine role to activate myofibroblast differentiation during pulmonary fibrosis with potential significance for disease progression mediated by sB7H3.

Role of T Regulatory Cells and Myeloid-Derived Suppressor Cells in COVID-19

Coronavirus disease 2019 (COVID-19) has been raised as a pandemic disease since December 2019. Immunosuppressive cells including T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs) are key players in immunological tolerance and immunoregulation; however, they contribute to the pathogenesis of different diseases including infections. Tregs have been shown to impair the protective role of CD8⁺ T lymphocytes against viral infections. In COVID-19 patients, most studies reported reduction, while few other studies found elevation in Treg levels. Moreover, Tregs have a dual role, depending on the different stages of COVID-19 disease. At early stages of COVID-19, Tregs have a critical role in decreasing antiviral immune responses, and consequently reducing the viral clearance. On the other side, during late stages, Tregs reduce inflammation-induced organ damage. Therefore, inhibition of Tregs in early stages and their expansion in late stages have potentials to improve clinical outcomes. In viral infections, MDSC levels are highly increased, and they have the potential to suppress T cell proliferation and reduce viral clearance. Some subsets of MDSCs are expanded in the blood of COVID-19 patients; however, there is a controversy whether this expansion has pathogenic or protective effects in COVID-19 patients. In conclusion, further studies are required to investigate the role and function of immunosuppressive cells and their potentials as prognostic biomarkers and therapeutic targets in COVID-19 patients.

Therapeutic Values of Myeloid-Derived Suppressor Cells in Hepatocellular Carcinoma: Facts and Hopes

Simple Summary

Myeloid-derived suppressor cells restrict the effectiveness of immune-checkpoint inhibitors for a subset of patients mainly through thwarting T cell infiltration into tumor sites. Treatments targeting MDSCs have shown potent inhibitory effects on multiple tumors, including hepatocellular carcinoma. In this review, we summarize the pathological mechanisms of MDSCs and their clinical significance as prognostic and predictive biomarkers for HCC patients, and we provide the latest progress of MDSCs-targeting treatment in HCC.

Abstract

One of the major challenges in hepatocellular carcinoma (HCC) treatment is drug resistance and low responsiveness to systemic therapies, partly due to insufficient T cell infiltration. Myeloid-derived suppressor cells (MDSCs) are immature marrow-derived cell populations with heterogeneity and immunosuppression characteristics and are essential components of the suppressive tumor immune microenvironment (TIME). Increasing evidence has demonstrated that MDSCs are indispensable contributing factors to HCC development in a T cell-dependent or non-dependent manner. Clinically, the frequency of MDSCs is firmly linked to HCC clinical outcomes and the effectiveness of immune checkpoint inhibitors (ICIs) and tyrosine kinase inhibitors (TKIs). Furthermore, MDSCs can also be used as prognostic and predictive biomarkers for patients with HCC. Therefore, treatments reprograming MDSCs may offer potential therapeutic opportunities in HCC. Here, we recapitulated the dynamic relevance of MDSCs in the initiation and development of HCC and paid special attention to the effect of MDSCs on T cells infiltration in HCC. Finally, we pointed out the potential therapeutic effect of targeting MDSCs alone or in combination, hoping to provide new insights into HCC treatment.

Correlation of myeloid-derived suppressor cells with C-reactive protein, ferritin and lactate dehydrogenase levels in patients with severe COVID-19

The novel coronavirus disease 2019 (COVID‐19) remains a global health emergency, and understanding the interactions between the virus and host immune responses is crucial to preventing its lethal effects. The expansion of myeloid‐derived suppressor cells (MDSCs) in COVID‐19, thereby suppressing immune responses, has been described as responsible for the severity of the disease, but the correlation between MDSC subsets and COVID‐19 severity remains elusive. Therefore, we classified patients according to clinical and laboratory findings—aiming to investigate the relationship between MDSC subsets and laboratory findings such as high C‐reactive protein, ferritin and lactate dehydrogenase levels, which indicate the severity of the disease. Forty‐one patients with COVID‐19 (26 mild and 15 severe; mean age of 49.7 ± 15 years) and 26 healthy controls were included in this study. MDSCs were grouped into two major subsets—polymorphonuclear MDSCs (PMN‐MDSCs) and monocytic MDSCs—by flow cytometric immunophenotyping, and PMN‐MDSCs were defined as mature and immature, according to CD16 expressions, for the first time in COVID‐19. Total MDSCs, PMN‐MDSCs, mature PMN‐MDSCs and monocytic MDSCs were significantly higher in patients with COVID‐19 compared with the healthy controls (P < .05). Only PMN‐MDSCs and their immature PMN‐MDSC subsets were higher in the severe subgroup than in the mild subgroup. In addition, a significant correlation was found between C‐reactive protein, ferritin and lactate dehydrogenase levels and MDSCs in patients with COVID‐19. These findings suggest that MDSCs play a role in the pathogenesis of COVID‐19, while PMN‐MDSCs, especially immature PMN‐MDSCs, are associated with the severity of the disease.

A Tale of Two Viruses: Immunological Insights Into HCV/HIV Coinfection

Nearly 2.3 million individuals worldwide are coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV). Odds of HCV infection are six times higher in people living with HIV (PLWH) compared to their HIV-negative counterparts, with the highest prevalence among people who inject drugs (PWID) and men who have sex with men (MSM). HIV coinfection has a detrimental impact on the natural history of HCV, including higher rates of HCV persistence following acute infection, higher viral loads, and accelerated progression of liver fibrosis and development of end-stage liver disease compared to HCV monoinfection. Similarly, it has been reported that HCV coinfection impacts HIV disease progression in PLWH receiving anti-retroviral therapies (ART) where HCV coinfection negatively affects the homeostasis of CD4⁺ T cell counts and facilitates HIV replication and viral reservoir persistence. While ART does not cure HIV, direct acting antivirals (DAA) can now achieve HCV cure in nearly 95% of coinfected individuals. However, little is known about how HCV cure and the subsequent resolution of liver inflammation influence systemic immune activation, immune reconstitution and the latent HIV reservoir. In this review, we will summarize the current knowledge regarding the pathogenesis of HIV/HCV coinfection, the effects of HCV coinfection on HIV disease progression in the context of ART, the impact of HIV on HCV-associated liver morbidity, and the consequences of DAA-mediated HCV cure on immune reconstitution and HIV reservoir persistence in coinfected patients.

Mesenchymal Stem Cells Can Both Enhance and Inhibit the Cellular Response to DNA Immunization by Genes of Nonstructural Proteins of the Hepatitis C Virus

Despite extensive research, there is still no vaccine against the hepatitis C virus (HCV). The aim of this study was to investigate whether MSCs can exhibit adjuvant properties during DNA vaccination against hepatitis C. We used the pcNS3-NS5B plasmid encoding five nonstructural HCV proteins and MSCs derived from mice bone marrow. Five groups of DBA mice were immunized with the plasmid and/or MSCs in a different order. Group 1 was injected with the plasmid twice at intervals of 3 weeks; Group 2 with the plasmid, and after 24 h with MSCs; Group 3 with MSCs followed by the plasmid the next day; Group 4 with only MSCs; and Group 5 with saline. When the MSCs were injected prior to DNA immunization, the cell immune response to HCV proteins assessed by the level of IFN-γ synthesis was markedly increased compared to DNA alone. In contrast, MSCs injected after DNA suppressed the immune response. Apparently, the high level of proinflammatory cytokines detected after DNA injection promotes the conversion of MSCs introduced later into the immunosuppressive MSC2. The low level of cytokines in mice before MSC administration promotes the high immunostimulatory activity of MSC1 in response to a DNA vaccine. Thus, when administered before DNA, MSCs are capable of exhibiting promising adjuvant properties.

Mesenchymal Stem Cells Can Both Enhance and Inhibit the Cellular Response to DNA Immunization by Genes of Nonstructural Proteins of the Hepatitis C Virus

Despite extensive research, there is still no vaccine against the hepatitis C virus (HCV). The aim of this study was to investigate whether MSCs can exhibit adjuvant properties during DNA vaccination against hepatitis C. We used the pcNS3-NS5B plasmid encoding five nonstructural HCV proteins and MSCs derived from mice bone marrow. Five groups of DBA mice were immunized with the plasmid and/or MSCs in a different order. Group 1 was injected with the plasmid twice at intervals of 3 weeks; Group 2 with the plasmid, and after 24 h with MSCs; Group 3 with MSCs followed by the plasmid the next day; Group 4 with only MSCs; and Group 5 with saline. When the MSCs were injected prior to DNA immunization, the cell immune response to HCV proteins assessed by the level of IFN-γ synthesis was markedly increased compared to DNA alone. In contrast, MSCs injected after DNA suppressed the immune response. Apparently, the high level of proinflammatory cytokines detected after DNA injection promotes the conversion of MSCs introduced later into the immunosuppressive MSC2. The low level of cytokines in mice before MSC administration promotes the high immunostimulatory activity of MSC1 in response to a DNA vaccine. Thus, when administered before DNA, MSCs are capable of exhibiting promising adjuvant properties.

Mesenchymal Stem Cells Can Both Enhance and Inhibit the Cellular Response to DNA Immunization by Genes of Nonstructural Proteins of the Hepatitis C Virus

Despite extensive research, there is still no vaccine against the hepatitis C virus (HCV). The aim of this study was to investigate whether MSCs can exhibit adjuvant properties during DNA vaccination against hepatitis C. We used the pcNS3-NS5B plasmid encoding five nonstructural HCV proteins and MSCs derived from mice bone marrow. Five groups of DBA mice were immunized with the plasmid and/or MSCs in a different order. Group 1 was injected with the plasmid twice at intervals of 3 weeks; Group 2 with the plasmid, and after 24 h with MSCs; Group 3 with MSCs followed by the plasmid the next day; Group 4 with only MSCs; and Group 5 with saline. When the MSCs were injected prior to DNA immunization, the cell immune response to HCV proteins assessed by the level of IFN-γ synthesis was markedly increased compared to DNA alone. In contrast, MSCs injected after DNA suppressed the immune response. Apparently, the high level of proinflammatory cytokines detected after DNA injection promotes the conversion of MSCs introduced later into the immunosuppressive MSC2. The low level of cytokines in mice before MSC administration promotes the high immunostimulatory activity of MSC1 in response to a DNA vaccine. Thus, when administered before DNA, MSCs are capable of exhibiting promising adjuvant properties.

HCV-Associated Exosomes Upregulate RUNXOR and RUNX1 Expressions to Promote MDSC Expansion and Suppressive Functions through STAT3-miR124 Axis

RUNX1 overlapping RNA (RUNXOR) is a long non-coding RNA and plays a pivotal role in the differentiation of myeloid cells via targeting runt-related transcription factor 1 (RUNX1). We and others have previously reported that myeloid-derived suppressor cells (MDSCs) expand and inhibit host immune responses during chronic viral infections; however, the mechanisms responsible for MDSC differentiation and suppressive functions, in particular the role of RUNXOR–RUNX1, remain unclear. Here, we demonstrated that RUNXOR and RUNX1 expressions are significantly upregulated and associated with elevated levels of immunosuppressive molecules, such as arginase 1 (Arg1), inducible nitric oxide synthase (iNOS), signal transducer and activator of transcription 3 (STAT3), and reactive oxygen species (ROS) in MDSCs during chronic hepatitis C virus (HCV) infection. Mechanistically, we discovered that HCV-associated exosomes (HCV-Exo) can induce the expressions of RUNXOR and RUNX1, which in turn regulates miR-124 expression via STAT3 signaling, thereby promoting MDSC differentiation and suppressive functions. Importantly, overexpression of RUNXOR in healthy CD33⁺ myeloid cells promoted differentiation and suppressive functions of MDSCs. Conversely, silencing RUNXOR or RUNX1 expression in HCV-derived CD33⁺ myeloid cells significantly inhibited their differentiation and expressions of suppressive molecules and improved the function of co-cultured autologous CD4 T cells. Taken together, these results indicate that the RUNXOR–RUNX1–STAT3–miR124 axis enhances the differentiation and suppressive functions of MDSCs and could be a potential target for immunomodulation in conjunction with antiviral therapy during chronic HCV infection.

LncRNA HOTAIRM1 promotes MDSC expansion and suppressive functions through the HOXA1-miR124 axis during HCV infection

HOXA transcript antisense RNA myeloid-specific 1 (HOTAIRM1) is a long non-coding RNA (lncRNA) that plays a pivotal role in regulating myeloid cell development via targeting HOXA1 gene expression. We and others have previously shown that myeloid-derived suppressor cells (MDSCs), a heterogeneous population of immature myeloid cells, expand during chronic viral (HCV, HIV) infections. However, the role of HOTAIRM1 in the development and suppression of MDSCs during viral infection remains unknown. In this study, we demonstrate that the expressions of HOTAIRM1 and its target HOXA1 are substantially upregulated to promote the expressions of immunosuppressive molecules, including arginase 1, inducible nitric oxide synthase, signal transducer and activator of transcription 3, and reactive oxygen species, in CD33+ myeloid cells derived from hepatitis C virus (HCV)-infected patients. We show that HCV-associated exosomes (HCV-Exo) can modulate HOTAIRM1, HOXA1, and miR124 expressions to regulate MDSC development. Importantly, overexpression of HOTAIRM1 or HOXA1 in healthy CD33+ myeloid cells promoted the MDSC differentiation and suppressive functions; conversely, silencing of HOTAIRM1 or HOXA1 expression in MDSCs from HCV patients significantly reduced the MDSC frequency and their suppressive functions. In essence, these results indicate that the HOTAIRM1-HOXA1-miR124 axis enhances the differentiation and suppressive functions of MDSCs and may be a potential target for immunomodulation in conjunction with antiviral therapy during chronic viral infection.

Control of B Cell Lymphoma by Gammaherpesvirus-Induced Memory CD8 T Cells

Persistent infection with gammaherpesviruses (γHV) can cause lymphomagenesis in immunocompromised patients. Murine γHV-68 (MHV-68) is an important tool for understanding immune factors contributing to γHV control; however, modeling control of γHV-associated lymphomagenesis has been challenging. Current model systems require very long incubation times or severe immune suppression, and tumor penetrance is low. In this report, we describe the generation of a B cell lymphoma on the C57BL/6 background, which is driven by the Myc oncogene and expresses an immunodominant CD8 T cell epitope from MHV-68. We determined MHV-68-specific CD8 T cells in latently infected mice use either IFN-γ or perforin/granzyme to control γHV-associated lymphoma, but perforin/granzyme is a more potent effector mechanism for lymphoma control than IFN-γ. Consistent with previous reports, CD4-depleted mice lost control of virus replication in persistently infected mice. However, control of lymphoma remained intact in the absence of CD4 T cells. Collectively, these data show the mechanisms of T cell control of B cell lymphoma in γHV-infected mice overlap with those necessary for control of virus replication, but there are also important differences. This study establishes a tool for further dissecting immune surveillance against, and optimizing adoptive T cell therapies for, γHV-associated lymphomas.

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.

Effects of Hypertonic Saline and Hydroxyethyl Starch on Myeloid-Derived Suppressor Cells in Hemorrhagic Shock Mice under Secondary Bacterial Attack

Objectives

The primary target is to reveal whether the resuscitation with hypertonic saline (HTS) or hydroxyethyl starch (HES) would have different effects on the myeloid-derived suppressor cell (MDSC) count and monocytic MDSC (M-MDSC)/granulocytic/neutrophilic MDSC (G-MDSC) rate in the peripheral blood, spleen, and bone marrow nucleated cells (BMNC) in a controlled hemorrhagic shock mouse model under secondary Escherichia coli bacterial infection attack, comparing to resuscitation with normal saline (NS) in 72 hours.

Method

After hemorrhagic shock with bacteremia, which is induced by Escherichia coli bacterial infection attack, comparing to resuscitation with normal saline (NS) in 72 hours. Method. After hemorrhagic shock with bacteremia, which is induced by Escherichia coli 35218 injection, the mice were distributed into control, NS, HTS, and HES groups. The peripheral blood nucleated cells (PBNC), spleen single-cell suspension, and bone marrow nucleated cells were collected. The flow cytometry was used to detect the MDSC, M-MDSC, and G-MDSC.

Result

In PBNC, after resuscitation with NS, the MDSC was continuously higher, while the rate of M-MDSC/G-MDSC were continuously lower (P < 0.05). In HTS, the MDSC varied, higher at 24 and 72 hours (P < 0.05). In HTS, the MDSC varied, higher at 24 and 72 hours (P < 0.05). In HTS, the MDSC varied, higher at 24 and 72 hours (P < 0.05). In HTS, the MDSC varied, higher at 24 and 72 hours (P < 0.05). In HTS, the MDSC varied, higher at 24 and 72 hours (P < 0.05), the M-MDSC/G-MDSC were continuously lower (P < 0.05). In the spleen, resuscitation with HTS, the M-MDSC/G-MDSC were continuously lower (P < 0.05). In BMNC, after resuscitation with HES, the M-MDSC/G-MDSC were lower at 24 and 72 hours (P < 0.05).

Conclusion

In mouse hemorrhagic shock model with bacterial infection, the resuscitation with NS, HTS, or HES induced difference changes in MDSC and M-MDSC/G-MDSC, which were time-dependent and organ-specific. Resuscitation with crystalloid, like NS or HTS, showed longer effects on the MDSC and M-MDSC/G-MDSC in peripheral blood; while HTS has a longer effect on M-MDSC/G-MDSC in the spleen, HES has a stronger impact on the differentiation regulation of MDSC to G-MDSC in the bone marrow.

Genetically Modified Mouse Mesenchymal Stem Cells Expressing Non-Structural Proteins of Hepatitis C Virus Induce Effective Immune Response

Hepatitis C virus (HCV) is one of the major causes of chronic liver disease and leads to cirrhosis and hepatocarcinoma. Despite extensive research, there is still no vaccine against HCV. In order to induce an immune response in DBA/2J mice against HCV, we obtained modified mouse mesenchymal stem cells (mMSCs) simultaneously expressing five nonstructural HCV proteins (NS3-NS5B). The innate immune response to mMSCs was higher than to DNA immunization, with plasmid encoding the same proteins, and to naïve unmodified MSCs. mMSCs triggered strong phagocytic activity, enhanced lymphocyte proliferation, and production of type I and II interferons. The adaptive immune response to mMSCs was also more pronounced than in the case of DNA immunization, as exemplified by a fourfold stronger stimulation of lymphocyte proliferation in response to HCV, a 2.6-fold higher rate of biosynthesis, and a 30-fold higher rate of secretion of IFN-γ, as well as by a 40-fold stronger production of IgG2a antibodies to viral proteins. The immunostimulatory effect of mMSCs was associated with pronounced IL-6 secretion and reduction in the population of myeloid derived suppressor cells (MDSCs). Thus, this is the first example that suggests the feasibility of using mMSCs for the development of an effective anti-HCV vaccine.

The clinical significance of myeloid-derived suppressor cells in dengue fever patients

Background

Myeloid-derived suppressor cells (MDSCs) play immunosuppressive roles in cancers and some infectious diseases; however, their role in dengue fever (DF) remains unknown. This study evaluated the clinical significance of MDSCs in DF patients.

Methods

This study comprised 178 non-severe DF patients, 20 non-dengue fever (NDF) controls, and 30 healthy donors. The DF patients were divided into the following five groups based on the fever duration from its onset to the day of sample collection: fever duration of 1–2, 3–4, 5–6, 7–8, and > 9 days. Among these DF patients, 14 were monitored for eight days, and their peripheral blood samples were collected every two days. The mononuclear cells were isolated and analyzed using flow cytometry. The correlation between the MDSCs and clinical and immunological indicators of the DF patients was evaluated using Spearman analysis.

Results

The count of the peripheral blood MDSCs, especially monocytic MDSCs, of the 178 DF patients were dramatically higher than those of the NDF and healthy controls, and remarkably decreased with the fever duration. Moreover, the MDSC count correlated with some indicators, including the dengue viral load (rho = 0.367, p < .001), body temperature (rho = 0.263, p = .005), prothrombin time (rho = 0.475, p < .001), CD4⁺ T cell number (rho = − 0.317, p < .001), CD8⁺ T cell number (rho = − 0.361, p < .001), “programmed cell death protein 1” (PD-1) (rho = − 0.347, p < .001), “T cell immunoglobulin domain and mucin domain-3” (Tim3) (rho = − 0.258, p = .001), interferon-α (IFN-α) (rho = 0.43, p < .001), and “regulated upon activation normal T-cell expressed and secreted” (RANTES) (rho = 0.278, p = .019). Furthermore, the level of arginase-1, but not nitric oxide, was higher in the DF patients than in the healthy controls and was closely related to the number of MDSCs (rho = 0.265, p = .024).

Conclusions

Our study reveals a significant correlation between MDSCs and DF clinical indicators, posing MDSCs as potential target cells for DF treatment.

Tpl2 Protects Against Fulminant Hepatitis Through Mobilization of Myeloid-Derived Suppressor Cells

Myeloid derived suppressor cells (MDSC) in the liver microenvironment protects against the inflammation-induced liver injury in fulminant hepatitis (FH). However, the molecular mechanism through which MDSC is recruited into the inflamed liver remain elusive. Here we identified a protein kinase Tpl2 as a critical mediator of MDSC recruitment into liver during the pathogenesis of Propionibacterium acnes/LPS-induced FH. Loss of Tpl2 dramatically suppressed MDSC mobilization into liver, leading to exaggerated local inflammation and increased FH-induced mortality. Mechanistically, although the protective effect of Tpl2 for FH-induced mortality was dependent on the presence of MDSC, Tpl2 neither directly targeted myeloid cells nor T cells to regulate FH pathogenesis, but functioned in hepatocytes to mediate the induction of MDSC-attracting chemokine CXCL1 and CXCL2 through modulating IL-25 (also known as IL-17E) signaling. As a consequence, increased MDSC in the inflamed liver specifically restrained the local proliferation of infiltrated pathogenic CD4⁺ T cells, and thus protected against the inflammation-induced acute liver failure. Together, our findings established Tpl2 as a critical mediator of MDSC recruitment and highlighted the therapeutic potential of Tpl2 for the treatment of FH.

In Chronic Hepatitis C Infection, Myeloid-Derived Suppressor Cell Accumulation and T Cell Dysfunctions Revert Partially and Late After Successful Direct-Acting Antiviral Treatment

Chronic HCV infection is characterized by several immunological alterations, such as the accumulation of suppressor cells and of hyperactivated T lymphocytes. However, it is unclear whether direct-acting antiviral (DAA)-mediated HCV clearance restores immune dysfunctions. We performed a phenotypic characterization by flow cytometry of different immune cell subsets, including monocytic myeloid-derived suppressor cells (M-MDSCs) and T lymphocytes in 168 patients with persistent HCV infection not treated, under DAA therapies and sustained virological responders. Chronic HCV infection prompted the accumulation of M-MDSCs independently of patient and clinical characteristics, and altered their metabolic properties. HCV RNA was undetectable in the majority of patients just after few weeks of DAA therapy, whereas M-MDSC levels normalized only 6 months after therapy. In addition, HCV infection deeply perturbed the T cell compartment since a re-distribution of memory CD4⁺ and CD8⁺ T cells was observed at the expenses of naïve cells, and memory T lymphocytes displayed increased activation. Notably, these features were only partially restored by DAA therapies in the CD4, but not in the CD8, compartment as high immune activation levels persisted in the terminally differentiated memory CD8⁺ T cells even more than 1 year after sustained virological response. Together, these results suggest that successful DAA therapies do not lead to full immunological reconstitution as fast as viral clearance.

Systems analysis reveals complex biological processes during virus infection fate decisions

The processes and mechanisms of virus infection fate decisions that are the result of a dynamic virus-immune system interaction with either an efficient effector response and virus elimination or an alleviated immune response and chronic infection are poorly understood. Here, we characterized the host response to acute and chronic lymphocytic choriomeningitis virus (LCMV) infections by gene coexpression network analysis of time-resolved splenic transcriptomes. First, we found an early attenuation of inflammatory monocyte/macrophage prior to the onset of T cell exhaustion, and second, a critical role of the XCL1-XCR1 communication axis during the functional adaptation of the T cell response to the chronic infection state. These findings not only reveal an important feedback mechanism that couples T cell exhaustion with the maintenance of a lower level of effector T cell response but also suggest therapy options to better control virus levels during the chronic infection phase.

Myeloid-Derived Suppressor Cells: Not Only in Tumor Immunity

Since the realization that immature myeloid cells are powerful modulators of the immune response, many studies on “myeloid-derived suppressor cells” (MDSCs) have documented their ability to promote tumor progression in melanoma and other cancers. Whether MDSCs are induced solely pathologically in tumorigenesis, or whether they also represent physiological immune control mechanisms, is not well-understood, but is particularly important in the light of ongoing attempts to block their activities in order to enhance anti-tumor immunity. Here, we briefly review studies which explore (1) how best to identify MDSCs in the context of cancer and how this compares to other conditions in humans; (2) what the suppressive mechanisms of MDSCs are and how to target them pharmacologically; (3) whether levels of MDSCs with various phenotypes are informative for clinical outcome not only in cancer but also other diseases, and (4) whether MDSCs are only found under pathological conditions or whether they also represent a physiological regulatory mechanism for the feedback control of immunity. Studies unequivocally document that MDSCs strongly influence cancer outcomes, but are less informative regarding their relevance to infection, autoimmunity, transplantation and aging, especially in humans. So far, the results of clinical interventions to reverse their negative effects in cancer have been disappointing; thus, developing differential approaches to modulate MSDCs in cancer and other diseases without unduly comprising any normal physiological function requires further exploration.

MDSCs in infectious diseases: regulation, roles, and readjustment

Many pathogens, ranging from viruses to multicellular parasites, promote expansion of MDSCs, which are myeloid cells that exhibit immunosuppressive features. The roles of MDSCs in infection depend on the class and virulence mechanisms of the pathogen, the stage of the disease, and the pathology associated with the infection. This work compiles evidence supported by functional assays on the roles of different subsets of MDSCs in acute and chronic infections, including pathogen-associated malignancies, and discusses strategies to modulate MDSC dynamics to benefit the host.

Frequency and Implications of myeloid-derived suppressor cells and lymphocyte subsets in Egyptian patients with hepatitis C virus-related hepatocellular carcinoma

BACKGROUND AND AIM

Myeloid-derived suppressor cells (MDSCs) play a pivotal role in tumor immunity and induction of immune tolerance to a variety of antitumor effectors, including T lymphocytes. Herein, we tried to evaluate the frequency and clinical significance of MDSCs and different lymphocyte subsets in hepatitis C virus (HCV)-related hepatocellular carcinoma (HCC).

METHODS

Four groups were enrolled; chronic HCV (CHC; n = 40), HCV-related liver cirrhosis (n = 40), HCV-related HCC (HCV-HCC; n = 75), and healthy control group (n = 20). The percentage of peripheral lymphocytes subsets and total MDSCs with their main two subsets; monocytic (M-MDSCs) and granulocytic (G-MDSCs) was evaluated by flow cytometry.

RESULTS

The frequency of total MSDCs and M-MDSCs was significantly elevated in HCV-HCC especially patients with advanced stage HCC compared with those with early-stage HCC. The frequency of total MSDCs and M-MDSCs was positively correlated with ALT, AFP, and HCV viral load and negatively correlated with CD8⁺ T-cell frequency. CD4 ⁺ T cells were significantly decreased in HCV-HCC patients. The frequency of CD4 ⁺ T cells and CD8 ⁺ T cells was negatively correlated with AFP and AST, but not with albumin or HCV viral load.

CONCLUSION

Taken together, our data suggest that MDSCs, M-MDSCs, and lymphocyte subsets are associated with the development and progression of HCV-related HCC.

Polarization of granulocytic myeloid-derived suppressor cells by hepatitis C core protein is mediated via IL-10/STAT3 signalling

Myeloid-derived suppressor cells (MDSCs) have been described as suppressors of T-cell function in many malignancies. Impaired T-cell responses have been observed in patients with chronic hepatitis C virus infection (CHC), which is reportedly associated with the establishment of persistent HCV infection. Therefore, we hypothesized that MDSCs also play a role in chronic HCV infection. MDSCs in the peripheral blood of 206 patients with CHC and 20 healthy donors were analyzed by flow cytometry. Peripheral blood mononuclear cells (PBMCs) of healthy donors cultured with hepatitis C virus core protein (HCVc) were stimulated with or without interleukin 10 (IL-10). Compared to healthy donors and certain CHC patients with sustained viral response (SVR), CHC patients without SVR presented with a dramatic elevation of G-MDSCs with the HLA-DR^-/low CD33⁺ CD14^- CD11b⁺ phenotype in peripheral blood. The frequency of G-MDSCs in CHC patients was positively correlated with serum HCVc, and G-MDSCs were induced from healthy PBMCs by adding exogenous HCVc. Furthermore, we revealed a potential mechanism by which HCVc mediates G-MDSC polarization; activation of ERK1/2 resulting in IL-10 production and IL-10-activated STAT3 signalling. Finally, we confirmed that HCVc-induced G-MDSCs suppress the proliferation and production of IFN-γ in autologous T-cells. We also found that the frequency of G-MDSCs in serum was associated with CHC prognosis. HCVc maintains immunosuppression by promoting IL-10/STAT3-dependent differentiation of G-MDSCs from PBMCs, resulting in the impaired functioning of T-cells. G-MDSCs may thus be a promising biomarker for predicting prognosis of CHC patients.

Granulocytic myeloid-derived suppressor cell population increases with the severity of alcoholic liver disease

Alcoholic liver disease (ALD) is a progressive liver disease that can cause a series of complications, including cirrhosis, liver failure and hepatocellular carcinoma. Granulocytic myeloid‐derived suppressor cell (gMDSC) populations have been observed to expand in various liver diseases and to inhibit innate and adaptive immunity in patients with liver disease. However, the characteristics of gMDSCs in patients with ALD have not been studied. We studied 24 healthy controls (HCs) and 107 patients with ALD and found an accumulation of gMDSCs in the peripheral blood of patients with alcoholic liver cirrhosis (ALC). Furthermore, ALC patients with a poor prognosis displayed a significant increase in peripheral gMDSCs and showed an increased capacity for arginase I production compared to HCs. In contrast, plasma arginase I levels in ALC patients were negatively correlated with total bilirubin and international normalized ratio, two key parameters of liver damage. Importantly, gMDSCs accumulated in the livers of ALC patients, and the frequency of liver gMDSCs significantly correlated with that of peripheral gMDSCs. In addition, gMDSC enrichment in vitro significantly inhibited the function of natural killer (NK) cells, perhaps preventing the NK‐induced apoptosis of hepatic stellate cells. In summary, increased peripheral and intrahepatic gMDSC populations are present in patients with ALC and may contribute to enhancing the severity of liver cirrhosis.

The effects of direct-acting antiviral agents on the frequency of myeloid-derived suppressor cells and natural killer cells in patients with chronic hepatitis C

Currently, hepatitis C antiviral therapy is entering a new era with the use of direct-acting antiviral (DAA) agents. However, the precise immunological influences of DAA therapy in patients with chronic hepatitis C (CHC) are insufficiently understood. This study aimed to investigate the effects of DAA therapy on the frequency of myeloid-derived suppressor cells (MDSCs), T lymphocytes, and natural killer (NK) cells in patients with CHC. Thirty-two treatment-naive CHC patients were treated with DAA therapy, and the frequency of immune cells was analyzed by flow cytometry at various time points during and after therapy. Sixteen healthy donors were recruited for comparison. DAA therapy decreased the frequency of MDSCs and monocytic MDSCs in patients with CHC to a normal level. DAA therapy also increased the CD8⁺ T and NK cell levels in patients with CHC. In addition, activation (NKp30 and NKp46) and inhibitory (NKG2A) receptors on NK cells were downregulated to yield an NK cell phenotype resembling that observed in the healthy controls. This study provides insight into the normalization of immune cell levels under DAA therapy and indicates that restoration of the immune system in patients with CHC strongly supports long-term curative hepatitis C virus eradication.

Myeloid-derived suppressor cells in non-neoplastic inflamed organs

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are a highly heterogeneous population of immature myeloid cells with immunosuppressive function. Although their function in tumor-bearing conditions is well studied, less is known about the role of MDSCs in various organs under non-neoplastic inflammatory conditions.

MAIN BODY

MDSCs are divided into two subpopulations, G-MDSCs and M-MDSCs, and their distribution varies between organs. MDSCs negatively control inflammation in inflamed organs such as the lungs, joints, liver, kidneys, intestines, central nervous system (CNS), and eyes by suppressing T cells and myeloid cells. MDSCs also regulate fibrosis in the lungs, liver, and kidneys and help repair CNS injuries. MDSCs in organs are plastic and can differentiate into osteoclasts and tolerogenic dendritic cells according to the microenvironment under non-neoplastic inflammatory conditions.

CONCLUSION

This article summarizes recent findings about MDSCs under inflammatory conditions, especially with respect to their function and differentiation in specific organs.

HCV-associated exosomes promote myeloid-derived suppressor cell expansion via inhibiting miR-124 to regulate T follicular cell differentiation and function

Virus-infected cells can regulate non-permissive bystander cells, but the precise mechanisms remain incompletely understood. Here we report that this process can be mediated by transfer of viral RNA-loaded exosomes shed from infected cells to myeloid-derived suppressor cells (MDSCs), which in turn regulate the differentiation and function of T cells during viral infection. Specifically, we demonstrated that patients with chronic hepatitis C virus (HCV) infection exhibited significant increases in T follicular regulatory (TFR) cells and decreases in T follicular helper (TFH) cells. These MDSC-mediated T-cell dysregulations resulted in an increased ratio of TFR/TFH and IL-10 production in peripheral blood. Specifically, co-culture of MDSCs derived from HCV patients with healthy peripheral blood mononuclear cells (PBMCs) induced expansion of TFR, whereas depletion of MDSCs from PBMCs of HCV patients reduced the increases in TFR frequency and IL-10 production, and promoted the differentiation of IFN-γ-producing TFH cells. Importantly, we found that exosomes isolated from the plasma of HCV patients and supernatant of HCV-infected hepatocytes could drive monocytic myeloid cell differentiation into MDSCs. These exosomes were enriched in tetraspanins, such as CD63 and CD81, and contained HCV RNA, but exosomes isolated from patients with antiviral treatment contained no HCV RNA and could not induce MDSC differentiation. Notably, these HCV RNA-containing exosomes (HCV-Exo) were sufficient to induce MDSCs. Furthermore, incubation of healthy myeloid cells with these HCV-Exo inhibited the expression of miR-124, whereas reconstitution of PBMCs with miR-124 abolished the effects of HCV-Exo on MDSC induction. Taken together, these results indicate that HCV-associated exosomes can transfer immunomodulatory viral RNA from infected cells to neighboring immune cells and trigger MDSC expansion, which subsequently promotes TFR differentiation and inhibits TFH function. This study reveals a previously unrecognized path that represents a novel mechanism of immune dysregulation during chronic viral infection.

Ex Vivo Generated Human Cord Blood Myeloid-Derived Suppressor Cells Attenuate Murine Chronic Graft-versus-Host Diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells with anti-inflammatory activity, and expanded murine MDSCs are capable of attenuating preclinical acute graft-versus-host disease (aGVHD) severity. Two murine cGVHD models were used to evaluate the effectiveness of ex vivo cultured human cord blood (hCB) MDSCs in chronic GVHD (cGVHD). First, GVHD recipients surviving in a classic C57BL/6 into MHC-mismatched BALB/c aGVHD model developed cGVHD. Second, donor pretreatment with granulocyte colony-stimulating factor (G-CSF) induced cGVHD. hCB-MDSCs (1 × 10⁶) were intravenously injected to determine their preventive effects (on days 5, 7, 10, and 21) or therapeutic effects (on days 21, 28, and 35). In the first model the onset of clinical cutaneous cGVHD was significantly delayed in preventive hCB-MDSCs-treated allogeneic recipients. Pathologic scoring of target organs confirmed these clinical results. Importantly, thymic tissues of GVHD mice treated with hCB-MDSCs were less severely damaged, showing higher numbers of double (CD4 and CD8) positive T cells with reduced expansion of donor-type CD4 and CD8 T cells. Moreover, late infusion of hCB-MDSCs controlled the severity of established cGVHD that had occurred in control recipients. In the second model, cGVHD induced by G-CSF-mobilized stem cell graft was associated with promotion of Th 17 and Th 2 differentiation. hCB-MDSCs attenuated clinical and pathologic cGVHD severity. Increased production of IL-17 and more infiltration of T cells and macrophages in cGVHD mice were markedly reduced after hCB-MDSCs treatment. Importantly, Foxp3⁺ regulatory T cells and IFN-γ-producing T cells were expanded, whereas IL-17- and IL-4-producing T cells were decreased in allogeneic recipients of hCB-MDSCs. Taken together, these results showed that hCB-MDSCs have preclinical capability of attenuating cGVHD by preserving thymus function and regulating Th 17 signaling, suggesting a possible therapeutic strategy for clinical application.

Gr1-/low CD11b-/low MHCII+ myeloid cells boost T cell anti-tumor efficacy

Conventional APCs that express MHC class II (MHCII) and co-stimulatory molecules include dendritic cells (DCs) and macrophages. Beyond these conventional APCs, immune stimulatory cells have been more recently shown to extend to a class of atypical APCs, composed of mast cells, basophils, and eosinophils. Here, we describe a unique type of APC, Gr1^-/low CD11b^-/low cells with a granularity and size characteristic of myeloid cells and with the ability to present Ag for crosspresentation. These cells constitutively express MHCII and the costimulatory molecules, CD80, CD86, and CD40. They do not express pan markers of myeloid DCs (CD11c), plasmacytoid DCs (Ly6C), or macrophages (F4/80), and their frequency is inversely correlated with myeloid-derived suppressor cells (MDSCs) in tumor-bearing mice. Among splenocytes, they are more abundant than DCs and macrophages, and they exhibit antitumor immune stimulatory function at a steady state without further activation, ex vivo. They are also found within the tumor bed where they retain their immune stimulatory function. Our findings suggest the use of these novel APCs in additional preclinical studies to further investigate their utility in APC-based cancer immunotherapies.

Myeloid-derived suppressor cells coming of age

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells generated during a large array of pathologic conditions ranging from cancer to obesity. These cells represent a pathologic state of activation of monocytes and relatively immature neutrophils. MDSCs are characterized by a distinct set of genomic and biochemical features, and can, on the basis of recent findings, be distinguished by specific surface molecules. The salient feature of these cells is their ability to inhibit T cell function and thus contribute to the pathogenesis of various diseases. In this Review, we discuss the origin and nature of these cells; their distinctive features; and their biological roles in cancer, infectious diseases, autoimmunity, obesity and pregnancy.

Contradictory intrahepatic immune responses activated in high-load hepatitis C virus livers compared with low-load livers

We found a HLA class II histocompatibility antigen gene, DQ alpha 1 chain (HLA-DQA1), that was expressed more than 9-fold higher in high-load hepatitis C virus (HCV) livers than low-load HCV livers using transcriptomics of chronic HCV-infected livers. To further investigate this finding, we examined which cells were positive for HLA-DQA1 and what liver immune responses were different between HCV-high and -low livers. HLA-DQA1-positive cells were significantly increased in the HCV-high group, and most positive cells were identified as non-parenchymal sinusoid cells and lymphocytic infiltrates in the portal area. Parenchymal hepatocytes were negative for HLA-DQA1. HLA-DQA1-positive cells in the liver sinusoid were positive for CD68 (macrophages or Kupffer cells); those in the lymphocytic infiltrates were positive for CD20 (B cells) or CD3 (T cells). mRNA levels of antigen-presenting cell (APC) markers such as CD68 and CD11c were significantly upregulated in the HCV-high group and were correlated with HLA-DQA mRNA levels. CD8B mRNA (CD8⁺ T cells) was upregulated in both HCV-positive livers compared with HCV-negative livers, whereas CD154 mRNA (CD4⁺ T helper cell) was upregulated in the HCV-high group compared with the HCV-low group. The immune regulatory molecules FOXP3 mRNA (regulatory T cell, T reg) and programmed cell death ligand-1 (PD-L1) mRNA were significantly increased in the HCV-high group. HCV-high livers had two molecular immune responses: increased APC numbers and adaptive immunity and the induction of immune tolerance. The local hepatic imbalance of contradictory immune responses might be responsible for high HCV loads.

Matrix Metalloproteinase-9 in Monocytic Myeloid-Derived Suppressor Cells Correlate with Early Infections and Clinical Outcomes in Allogeneic Hematopoietic Stem Cell Transplantation

The recovery of myeloid-derived suppressor cells (MDSCs) and its relevance in clinical acute graft-versus-host disease (GVHD) and post-hematopoietic stem cell transplantation (HSCT) infections remain to be fully characterized. We examined the expansion of circulating monocytic (M-) MDSCs and granulocytic (G-) MDSCs at the time of engraftment in 130 patients undergoing allogeneic HSCT (allo-HSCT). Compared with the G-MDSC group, the high M-MDSC group had a higher infection rate within 100 days, along with worse 1-year cumulative incidence of treatment-related mortality (TRM) and 2-year probability of event-free survival (EFS). The frequency of M-MDSCs was associated with preceding severe mucositis. Transcriptome profiling analysis of 2 isolated MDSC subtype showed significantly greater matrix metalloproteinase-9 (MMP-9) expression in M-MDSCs than in G-MDSCs. M-MDSCs produced abundantly more MMP-9. Importantly, compared with G-MDSCs, M-MDSCs isolated from patients post-HSCT had a greater capacity to suppress T cell responses, and MMP-9 blockade more forcefully inhibited their immunosuppressive effect. MMP-9 levels also were associated with the occurrence of infections and with transplantation outcomes. Based on these findings, we identify M-MDSCs as a major contributor to infections early after allo-HSCT and worse clinical outcomes via MMP-9.

Granulocytic myeloid-derived suppressor cells suppress virus-specific CD8+ T cell responses during acute Friend retrovirus infection

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) can suppress T cell responses in several different diseases. Previously these suppressive cells were observed to expand in HIV patients and in a mouse retrovirus model, yet their suppressive effect on virus-specific CD8+ T cells in vitro and in vivo has not been characterized thus far.

RESULTS

We used the Friend retrovirus (FV) model to demonstrate that MDSCs expand and become activated during the late phase of acute FV infection. Only the subpopulation of granulocytic MDSCs (gMDSCs) but not monocytic MDSC suppressed virus-specific CD8+ T cell proliferation and function in vitro. gMDSCs expressed arginase 1, high levels of the inhibitory ligand PD-L1 and the ATP dephosphorylating enzyme CD39 on the cell surface upon infection. All three molecules were involved in the suppressive effect of the gMDSCs in vitro. MDSC depletion experiments in FV-infected mice revealed that they restrict virus-specific CD8+ T cell responses and thus affect the immune control of chronic retroviruses in vivo.

CONCLUSIONS

Our study demonstrates that MDSCs become activated and expand during the acute phase of retrovirus infection. Their suppressive activity on virus-specific CD8+ T cells may contribute to T cell dysfunction and the development of chronic infection.

IFN-α-based treatment of patients with chronic HCV show increased levels of cells with myeloid-derived suppressor cell phenotype and of IDO and NOS

INTRODUCTION

Hepatitis C virus (HCV) infection causes chronic hepatitis, which is often associated with suppressed anti-HCV immune responses. We have recently reported accumulation of myeloid-derived suppressor cells (MDSCs) and suppressed immunity in cancer patients.

AIM

The main aim of this study was to determine whether chronic HCV patients harbor high of MDSCs in general and in nonresponders to IFN-based therapy in particular as well as to analyze the immune suppressive molecules.

METHODS

Peripheral blood samples withdrawn from 154 patients with chronic HCV infection and were categorized into responders and nonresponders based on viral titer upon IFN-α treatment.

RESULTS

The relative and absolute numbers of MDSCs defined as Lin^-/HLA-DR^-/CD33⁺/CD11b⁺ increased in all HCV patients, where they were higher in nonresponders than in responders. Additionally, the levels of MDSCs after 4-6 months of treatment in responders were lower than during the course of treatment. The responders also showed higher levels of IL-2 coincided with increased numbers of dendritic cells (DCs), CD4⁺ and CD8⁺ T cells. The levels of total NOS and IDO were also higher in nonresponders as compared to responders and healthy controls, while the expression levels of CD3ζ was lower in responders as compared to nonresponders and healthy volunteers.

CONCLUSION

Chronic HCV patients harbor high numbers of MDSCs, which are higher in nonresponders than in responders. The higher numbers of MDSCs associated with increases in the suppressing factors.

Paradoxical myeloid-derived suppressor cell reduction in the bone marrow of SIV chronically infected macaques

Myeloid derived suppressor cells (MDSCs), which suppress anti-tumor or anti-viral immune responses, are expanded in the peripheral blood and tissues of patients/animals with cancer or viral infectious diseases. We here show that in chronic SIV infection of Indian rhesus macaques, the frequency of MDSCs in the bone marrow (BM) was paradoxically and unexpectedly decreased, but increased in peripheral blood. Reduction of BM MDSCs was found in both CD14⁺MDSC and Lin^-CD15⁺MDSC subsets. The reduction of MDSCs correlated with high plasma viral loads and low CD4⁺ T cell counts, suggesting that depletion of BM MDSCs was associated with SIV/AIDS disease progression. Of note, in SHIV_SF162P4-infected macaques, which naturally control viral replication within a few months of infection, the frequency of MDSCs in the bone marrow was unchanged. To investigate the mechanisms by which BM MDSCs were reduced during chronic SIV infection, we tested several hypotheses: depletion due to viral infection, alterations in MDSC trafficking, and/or poor MDSC replenishment. We found that the possible mobilization of MDSCs from BM to peripheral tissues and the slow self-replenishment of MDSCs in the BM, along with the viral infection-induced depletion, all contribute to the observed BM MDSC reduction. We first demonstrate MDSC SIV infection in vivo. Correlation between BM CD14⁺MDSC reduction and CD8⁺ T cell activation in tissues is consistent with decreased immune suppression by MDSCs. Thus, depletion of BM MDSCs may contribute to the pathologic immune activation during chronic SIV infection and by extension HIV infection.

Both cancer and infectious diseases including HIV/AIDS lead to the accumulation of myeloid-derived suppressor cells (MDSCs), which can effectively suppress anti-tumor and anti-viral T cell responses to dampen protective immunity. Using a macaque model, we found unexpectedly that the MDSCs in bone marrow (BM) decreased after chronic simian immunodeficiency virus (SIV) infection compared with healthy controls. This was in sharp contrast to the general increase of MDSCs observed in BM during cancer and other infectious/inflammatory diseases, and also contrary to the MDSC expansion in HIV/SIV-infected PBMCs. We further demonstrated that the loss of MDSCs in the bone marrow was associated with the progression to AIDS disease. Investigating the mechanisms by which the MDSCs were decreased in the SIV-infected bone marrow, we found that the possible mobilization of MDSCs from bone marrow to peripheral tissues and the slow self-replenishment of MDSCs in the bone marrow, along with the viral infection-induced depletion, all contribute to the observed bone marrow MDSC reduction. Indeed, this is the first demonstration to our knowledge of SIV infection of MDSCs in vivo. Because of the suppressive nature of the MDSCs, the CD8⁺ T cells might not be effective in killing the virally infected MDSCs. It is tempting to speculate that MDSCs may constitute latent reservoirs. Overall, our data showed that MDSCs act as a double-edged sword in HIV/SIV-infection, and the decrease of MDSCs in bone marrow after SIV infection could serve as an indicator of immune regulatory exhaustion and also contribute to the observed immune hyperactivation seen in HIV/AIDS.

The Role of Myeloid-Derived Suppressor Cells in Viral Infection

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that are well described as potent immune regulatory cells during human cancer and murine tumor models. Reports of MDSCs during viral infections remain limited, and their association with immunomodulation of viral diseases is still being defined. Here, we provide an overview of MDSCs or MDSC-like cells identified during viral infections, including murine viral models and human viral diseases. Understanding the similarities and/or differences of virally induced versus tumor-derived MDSCs will be important for designing future immunotherapeutic approaches.

Decline of miR-124 in myeloid cells promotes regulatory T-cell development in hepatitis C virus infection

Myeloid-derived suppressor cells (MDSCs) and microRNAs (miRNAs) contribute to attenuating immune responses during chronic viral infection; however, the precise mechanisms underlying their suppressive activities remain incompletely understood. We have recently shown marked expansion of MDSCs that promote regulatory T (Treg) cell development in patients with chronic hepatitis C virus (HCV) infection. Here we further investigated whether the HCV-induced expansion of MDSCs and Treg cells is regulated by an miRNA-mediated mechanism. The RNA array analysis revealed that six miRNAs were up-regulated and six miRNAs were down-regulated significantly in myeloid cells during HCV infection. Real-time RT-PCR confirmed the down-regulation of miR-124 in MDSCs from HCV patients. Bioinformatic analysis suggested that miR-124 may be involved in the regulation of signal transducer and activator of transcription 3 (STAT-3), which was overexpressed in MDSCs from HCV patients. Notably, silencing of STAT-3 significantly increased the miR-124 expression, whereas reconstituting miR-124 decreased the levels of STAT-3, as well as interleukin-10 and transforming growth factor-β, which were overexpressed in MDCSs, and reduced the frequencies of Foxp3⁺ Treg cells that were developed during chronic HCV infection. These results suggest that reciprocal regulation of miR-124 and STAT-3 in MDSCs promotes Treg cell development, thus uncovering a novel mechanism for the expansion of MDSC and Treg cells during HCV infection.