CCR5-mediated homing of regulatory T cells and monocytic-myeloid derieved suppressor cells to dysfunctional endothelium contributes to early atherosclerosis.

A disbalance between immune regulatory cells and inflammatory cells is known to drive atherosclerosis. However, the exact mechanism is not clear. Here, we investigated the homing of immune regulatory cells, mainly, regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) subsets in asymptomatic coronary artery disease (CAD) risk factor-exposed young individuals (dyslipidemia [DLP] group) and stable CAD patients (CAD group). Compared with healthy controls (HCs), Tregs frequency was reduced in both DLP and CAD groups but expressed high levels of CCR5 in both groups. The frequency of monocytic-myeloid-derived suppressor cells (M-MDSCs) was increased while polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) were decreased in CAD patients only. Interestingly, although unchanged in frequency, M-MDSCs of the DLP group expressed high levels of CCR5. Serum levels of chemokines (CCL5, CX3CL1, CCL26) and inflammatory cytokines (IL-6, IL-1ß, IFN-γ, TNF-α) were higher in the DLP group. Stimulation with inflammatory cytokines augmented CCR5 expression in Tregs and M-MDSCs isolated from HCs. Activated endothelial cells showed elevated levels of CX3CL1 and CCL5 in vitro. Blocking CCR5 with D-Ala-peptide T-amide (DAPTA) increased Treg and M-MDSC frequency in C57Bl6 mice fed a high-fat diet. In accelerated atherosclerosis model, DAPTA treatment led to the formation of smooth muscle-rich plaque with less macrophages. Thus, we show that CCR5-CCL5 axis is instrumental in recruiting Tregs and M-MDSCs to dysfunctional endothelium in the asymptomatic phase of atherosclerosis contributing to atherosclerosis progression. Drugs targeting CCR5 in asymptomatic and CAD risk-factor/s-exposed individuals might be a novel therapeutic regime to diminish atherogenesis.

Silencing of tumoral carbohydrate sulfotransferase 15 reactivates lymph node pancreatic cancer T cells in mice.

Limited intratumoral T-cell infiltration in pancreatic ductal adenocarcinoma (PDAC) is an obstacle to immunotherapy, yet the efficient approach to enhance tumor-infiltrating T cells is not fully established. Here, we show that tumor-specific knockdown of carbohydrate sulfotransferase 15 (CHST15), a tumor stromal proteoglycan-synthetic enzyme, suppresses tumor growth in a T-cell-dependent manner in a murine model of PDAC. Silencing of tumoral CHST15 unexpectedly expanded CD4+ and CD8+ T cells in tumor draining LN (TDLN), leading to accelerated accumulation of EdU+ proliferating CD4+ and CD8+ T cells and granzyme B+ CD8+ T cells in the tumor. RNA expression analysis indicated that tumoral CHST15 knockdown (KD) downregulated matrix remodeling-related genes, while upregulated anti-tumor T-cell activity-related genes in both tumor and TDLN. CHST15 KD significantly diminished intratumoral and TDLN Ly6C/G+ myeloid-derived suppressor cells prior to TDLN T-cell expansion, suggesting that tumoral CHST15 remotely regulated myeloid-derived suppressor cell mediated T-cell suppression in the TDLN. Our findings illustrate a novel immunotherapeutic potential of tumoral CHST15 blockage by reactivating T cells in immune suppressive TDLN of PDAC.

Myeloid-derived suppressor cells alleviate adverse ventricular remodeling after acute myocardial infarction.

The fundamental pathophysiological mechanism in the progression of chronic heart failure following acute myocardial infarction (AMI) is ventricular remodeling, in which innate and adaptive immunity both play critical roles. Myeloid-derived suppressor cells (MDSCs) have been demonstrated to function in a range of pathological conditions, such as infections, inflammation, autoimmune diseases, and tumors. However, it is unclear how MDSCs contribute to cardiac remodeling following AMI. This study aimed to identify the function and underlying mechanism of MDSCs in controlling cardiac remodeling following AMI. Following AMI in mice, MDSCs frequencies changed dynamically, considerably increased on day 7 in blood, spleens, lymph nodes and hearts, and decreased afterwards. Consistently, mice with AMI displayed enhanced cardiac function on day 14 post-AMI, reduced infract size and higher survival rates on day 28 post-AMI following the adoptive transfer of MDSCs. Furthermore, MDSCs inhibited the inflammatory response by decreasing pro-inflammatory cytokine (TNF-α, IL-17, Cxcl-1, and Cxcl-2) expression, up-regulating anti-inflammatory cytokine (TGF-ß1, IL-10, IL-4, and IL-13) expression, reducing CD3+ T cell infiltration in the infarcted heart and enhancing M2 macrophage polarization. Mechanistically, MDSCs improved the release of anti-inflammatory factors (TGF-ß1 and IL-10) and decreased the injury of LPS-induced cardiomyocytes in vitro in a manner dependent on cell-cell contact. Importantly, blockade of IL-10 partially abolished the cardioprotective role of MDSCs. This study found that MDSCs contributed to the restoration of cardiac function and alleviation of adverse cardiac remodeling after AMI possibly by inhibiting inflammation.

Comprehensive mapping of immune perturbations associated with aplastic anemia.

BACKGROUND: Aplastic anemia (AA) is an immune-mediated syndrome characterized by bone marrow failure. Therefore, comprehending the cellular profile and cell interactions in affected patients is crucial. METHODS: Human peripheral blood mononuclear cells (PBMCs) were collected from both healthy donors (HDs) and AA patients, and analyzed using multicolor flow cytometry. Utilizing the FlowSOM and t-SNE dimensionality reduction technique, we systematically explored and visualized the major immune cell alterations in AA. This analysis provided a foundation to further investigate the subtypes of cells exhibiting significant changes. RESULTS: Compared to HDs, peripheral blood from patients with AA exhibits a marked reduction in CD56Dim natural killer (NK) cells, which also show diminished functionality. Conversely, an increase in NK-like CD56+ monocytes, which possess compromised functionality. Along with a significant reduction in myeloid-derived suppressor cells (MDSCs), which show recovery post-treatment. Additionally, MDSCs serve as effective clinical markers for distinguishing between acquired aplastic anemia (AAA) and congenital aplastic anemia (CAA). Our comprehensive analysis of correlations among distinct immune cell types revealed significant associations between NKBri cells and CD8+ T cell subsets, as well as between NKDim cells and CD4+ T cells, these results highlight the intricate interactions and correlations within the immune cell network in AA. CONCLUSION: Our study systematically elucidates the pronounced immune dysregulation in patients with AA. The detailed mapping of the immune landscape not only provides crucial insights for basic research but also holds promise for enhancing the accuracy of diagnoses and the effectiveness of timely therapeutic interventions in clinical practice. Consequently, this could potentially reduce the high mortality rate associated with AA.

Optimized CAR-T therapy based on spatiotemporal changes and chemotactic mechanisms of MDSCs induced by hypofractionated radiotherapy.

Poor intratumoral infiltration is the major challenge for chimeric antigen receptor (CAR)-T cell therapy in solid tumors. Hypofractionated radiotherapy (HFRT) has been reported to induce immune cell infiltration and reshape the tumor immune microenvironment. Here, we showed that HFRT (5 × 5 Gy) mediated an early accumulation of intratumoral myeloid-derived suppressor cells (MDSCs) and decreased infiltration of T cells in the tumor microenvironment (TME) of immunocompetent mice bearing triple-negative breast cancer (TNBC) or colon cancer, which was further confirmed in tumors from patients. RNA sequencing (RNA-seq) and cytokine profiling analysis revealed that HFRT induced the activation and proliferation of tumor-infiltrated MDSCs, which was mediated by the interactions of multiple chemokines and chemokine receptors. Further investigation showed that when combined with HFRT, CXCR2 blockade significantly inhibited MDSCs trafficking to tumors and effectively enhanced the intratumoral infiltration and treatment efficacy of CAR-T cells. Our study demonstrates that MDSCs blockade combined with HFRT is promising for CAR-T cell therapy optimization in solid tumors.

Carbon Ion Irradiation Activates Anti-Cancer Immunity.

Carbon ion beams have the unique property of higher linear energy transfer, which causes clustered damage of DNA, impacting the cell repair system. This sometimes triggers apoptosis and the release in the cytoplasm of damaged DNA, leading to type I interferon (IFN) secretion via the activation of the cyclic GMP-AMP synthase-stimulator of interferon genes pathway. Dendritic cells phagocytize dead cancer cells and damaged DNA derived from injured cancer cells, which together activate dendritic cells to present cancer-derived antigens to antigen-specific T cells in the lymph nodes. Thus, carbon ion radiation therapy (CIRT) activates anti-cancer immunity. However, cancer is protected by the tumor microenvironment (TME), which consists of pro-cancerous immune cells, such as regulatory T cells, myeloid-derived suppressor cells, and tumor-associated macrophages. The TME is too robust to be destroyed by the CIRT-mediated anti-cancer immunity. Various modalities targeting regulatory T cells, myeloid-derived suppressor cells, and tumor-associated macrophages have been developed. Preclinical studies have shown that CIRT-mediated anti-cancer immunity exerts its effects in the presence of these modalities. In this review article, we provide an overview of CIRT-mediated anti-cancer immunity, with a particular focus on recently identified means of targeting the TME.

Targeting N6-methyladenosine reader YTHDF1 with siRNA boosts antitumor immunity in NASH-HCC by inhibiting EZH2-IL-6 axis.

BACKGROUND & AIMS: RNA N6-methyladenosine (m6A) reader protein YTHDF1 has been implicated in cancer; however, its role in hepatocellular carcinoma (HCC), especially in non-alcoholic steatohepatitis-associated HCC (NASH-HCC), remains unknown. Here, we investigated the functional role of YTHDF1 in NASH-HCC and its interplay with the tumor immune microenvironment. METHODS: Hepatocyte-specific Ythdf1-overexpressing mice were subjected to a NASH-HCC-inducing diet. Tumor-infiltrating immune cells were profiled with single-cell RNA-sequencing, flow cytometry, and immunostaining. The molecular target of YTHDF1 was elucidated with RNA-sequencing, m6A-sequencing, YTHDF1 RNA immunoprecipitation-sequencing, proteomics, and ribosome-profiling. Ythdf1 in NASH-HCC models was targeted by lipid nanoparticle (LNP)-encapsulated small-interfering Ythdf1. RESULTS: YTHDF1 is overexpressed in tumor tissues compared to adjacent peri-tumor tissues from patients with NASH-HCC. Liver-specific Ythdf1 overexpression drives tumorigenesis in dietary models of spontaneous NASH-HCC. Single-cell RNA-sequencing and flow cytometry revealed that Ythdf1 induced accumulation of myeloid-derived suppressor cells (MDSCs) and suppressed cytotoxic CD8+ T-cell function. Mechanistically, Ythdf1 expression in NASH-HCC cells induced the secretion of IL-6, which mediated MDSC recruitment and activation, leading to CD8+ T-cell dysfunction. EZH2 mRNA was identified as a key YTHDF1 target. YTHDF1 binds to m6A-modified EZH2 mRNA and promotes EZH2 translation. EZH2 in turn increased expression and secretion of IL-6. Ythdf1 knockout synergized with anti-PD-1 treatment to suppress tumor growth in NASH-HCC allografts. Furthermore, therapeutic targeting of Ythdf1 using LNP-encapsulated small-interfering RNA significantly increased the efficacy of anti-PD-1 blockade in NASH-HCC allografts. CONCLUSIONS: We identified that YTHDF1 promotes NASH-HCC tumorigenesis via EZH2-IL-6 signaling, which recruits and activates MDSCs to cause cytotoxic CD8+ T-cell dysfunction. YTHDF1 may be a novel therapeutic target to improve responses to anti-PD-1 immunotherapy in NASH-HCC. IMPACT AND IMPLICATIONS: YTHDF1, a N6-methyladenosine reader, is upregulated in patients with non-alcoholic steatohepatitis (NASH)-associated hepatocellular carcinoma (HCC); however, its role in modulating the tumor immune microenvironment in NASH-HCC remains unclear. Here, we show that Ythdf1 mediates immunosuppression in NASH-HCC and that targeting YTHDF1 in combination with immune checkpoint blockade elicits robust antitumor immune responses. Our findings suggest novel therapeutic targets for potentiating the efficacy of immune checkpoint blockade in NASH-HCC and provide the rationale for developing YTHDF1 inhibitors for the treatment of NASH-HCC.

Myeloid-derived suppressor cells cross-talk with B10 cells by BAFF/BAFF-R pathway to promote immunosuppression in cervical cancer.

Immunosuppression induced by myeloid-derived suppressor cells (MDSCs) is one of the main obstacles to the efficacy of immunotherapy for cervical cancer. Recent studies on the immunosuppressive ability of MDSCs have primarily focused on T cells, but the effect of MDSCs on B cells function is still unclear. In a study of clinical specimens, we found that the accumulation of MDSCs in patients with cervical cancer was accompanied by high expression of B cell activating factor (BAFF) on the surface and high expression of interleukin (IL)-10-producing B cells (B10) in vivo. We found that the absence of BAFF could significantly inhibit tumor growth in a cervical cancer model using BAFF KO mice. Further studies showed that abundant MDSCs in cervical cancer induced B cells to differentiate into B10 cells by regulating BAFF which acted on the BAFF receptor (BAFF-R) of them. In this process, we found that a large amount of IL-10 secreted by B10 cells can activate STAT3 signaling pathway in MDSCs, and then form a positive feedback loop to promote the differentiation of B10 cells. Therefore, this study reveals a new mechanism of BAFF-mediated mutual immune regulation between MDSCs and B cells in the occurrence and development of cervical cancer.

Single-cell sequencing reveals the immune microenvironment landscape related to anti-PD-1 resistance in metastatic colorectal cancer with high microsatellite instability.

BACKGROUND: The objective response rate of microsatellite instability-high (MSI-H) metastatic colorectal cancer (mCRC) patients with first-line anti-programmed cell death protein-1 (PD-1) monotherapy is only 40-45%. Single-cell RNA sequencing (scRNA-seq) enables unbiased analysis of the full variety of cells comprising the tumor microenvironment. Thus, we used scRNA-seq to assess differences among microenvironment components between therapy-resistant and therapy-sensitive groups in MSI-H/mismatch repair-deficient (dMMR) mCRC. Resistance-related cell types and genes identified by this analysis were subsequently verified in clinical samples and mouse models to further reveal the molecular mechanism of anti-PD-1 resistance in MSI-H or dMMR mCRC. METHODS: The response of primary and metastatic lesions to first-line anti-PD-1 monotherapy was evaluated by radiology. Cells from primary lesions of patients with MSI-H/dMMR mCRC were analyzed using scRNA-seq. To identify the marker genes in each cluster, distinct cell clusters were identified and subjected to subcluster analysis. Then, a protein‒protein interaction network was constructed to identify key genes. Immunohistochemistry and immunofluorescence were applied to verify key genes and cell marker molecules in clinical samples. Immunohistochemistry, quantitative real-time PCR, and western blotting were performed to examine the expression of IL-1ß and MMP9. Moreover, quantitative analysis and sorting of myeloid-derived suppressor cells (MDSCs) and CD8+ T cells were performed using flow cytometry. RESULTS: Tumor responses in 23 patients with MSI-H/dMMR mCRC were evaluated by radiology. The objective response rate was 43.48%, and the disease control rate was 69.57%. ScRNA-seq analysis showed that, compared with the treatment-resistant group, the treatment-sensitive group accumulated more CD8+ T cells. Experiments with both clinical samples and mice indicated that infiltration of IL-1ß-driven MDSCs and inactivation of CD8+ T cells contribute to anti-PD-1 resistance in MSI-H/dMMR CRC. CONCLUSIONS: CD8+ T cells and IL-1ß were identified as the cell type and gene, respectively, with the highest correlation with anti-PD-1 resistance. Infiltration of IL-1ß-driven MDSCs was a significant factor in anti-PD-1 resistance in CRC. IL-1ß antagonists are expected to be developed as a new treatment for anti-PD-1 inhibitor resistance.

The PMN-MDSC - A key player in glucocorticoid resistance following combined physical and psychosocial trauma.

Stress-associated somatic and psychiatric disorders are often linked to non-resolving low-grade inflammation, which is promoted at least in part by glucocorticoid (GC) resistance of distinct immune cell subpopulations. While the monocyte/macrophage compartment was in the focus of many clinical and preclinical studies, the role of myeloid-derived suppressor cells (MDSCs) in stress-associated pathologies and GC resistance is less understood. As GC resistance is a clear risk factor for posttraumatic complications in patients on intensive care, the exact interplay of physical and psychosocial traumatization in the development of GC resistance needs to be further clarified. In the current study we employ the chronic subordinate colony housing (CSC) paradigm, a well-characterized mouse model of chronic psychosocial stress, to study the role of myeloid cells, in particular of MDSCs, in innate immune activation and GC resistance following combined psychosocial and physical (e.g., bite wounds) trauma. Our findings support the hypothesis that stress-induced neutrophils, polymorphonuclear (PMN)-MDSCs and monocytes/monocyte-like (MO)-MDSCs get primed and activated locally in the bone marrow as determined by toll-like receptor (TLR)2 upregulation and increased basal and lipopolysaccharide (LPS)-induced in vitro cell viability. These primed and activated myeloid cells emigrate into the peripheral circulation and subsequently, if CSC is accompanied by significant bite wounding, accumulate in the spleen. Here, PMN-MDSCs and monocytes/MO-MDSCs upregulate TLR4 expression, which exclusively in PMN-MDSCs promotes NF-κB hyperactivation upon LPS-stimulation, thereby exceeding the anti-inflammatory capacities of GCs and resulting in GC resistance.

Exosomes derived from myeloid-derived suppressor cells facilitate castration-resistant prostate cancer progression via S100A9/circMID1/miR-506-3p/MID1.

BACKGROUND: Castration-resistant prostate cancer (CRPC) is a major cause of recurrence and mortality among prostate cancer (PCa) patients. Myeloid-derived suppressor cells (MDSCs) regulate castration resistance in PCa. Previously, it was shown that intercellular communication was efficiently mediated by exosomes (Exos), but the role and the mechanism of MDSC-derived Exos in CRPC progression was unclear. METHODS: In this study, the circRNA expression profiles in PC3 cells treated with MDSC-Exo and control cells were investigated using a circRNA microarray. RESULTS: The data showed that circMID1 (hsa_circ_0007718) expression was elevated in PC3 cells treated with MDSC-Exo. Moreover, high circMID1 expression was found in PCa compared with benign prostatic hyperplasia (BPH) tissues and in CRPC patients compared with hormone sensitive prostate cancer (HSPC) patients. Further studies showed that MDSC-Exo accelerated PCa cell proliferation, migration, and invasion, while circMID1 deficiency inhibited MDSC-Exo-regulated CRPC progression in vitro and in vivo. Mechanistically, MDSC-derived exosomal S100A9 increased circMID1 expression to sponge miR-506-3p, leading to increased MID1 expression and accelerated tumor progression. CONCLUSION: Together, our results showed that a S100A9/circMID1/miR-506-3p/MID1 axis existed in MDSC-Exo-regulated CRPC progression, which provided novel insights into MDSC-Exo regulatory mechanisms in CRPC progression.

Adipose Tissue-Derived CCL5 Enhances Local Pro-Inflammatory Monocytic MDSCs Accumulation and Inflammation via CCR5 Receptor in High-Fat Diet-Fed Mice.

The C-C chemokine motif ligand 5 (CCL5) and its receptors have recently been thought to be substantially involved in the development of obesity-associated adipose tissue inflammation and insulin resistance. However, the respective contributions of tissue-derived and myeloid-derived CCL5 to the etiology of obesity-induced adipose tissue inflammation and insulin resistance, and the involvement of monocytic myeloid-derived suppressor cells (MDSCs), remain unclear. This study used CCL5-knockout mice combined with bone marrow transplantation (BMT) and mice with local injections of shCCL5/shCCR5 or CCL5/CCR5 lentivirus into bilateral epididymal white adipose tissue (eWAT). CCL5 gene deletion significantly ameliorated HFD-induced inflammatory reactions in eWAT and protected against the development of obesity and insulin resistance. In addition, tissue (non-hematopoietic) deletion of CCL5 using the BMT method not only ameliorated adipose tissue inflammation by suppressing pro-inflammatory M-MDSC (CD11b+Ly6G-Ly6Chi) accumulation and skewing local M1 macrophage polarization, but also recruited reparative M-MDSCs (CD11b+Ly6G-Ly6Clow) and M2 macrophages to the eWAT of HFD-induced obese mice, as shown by flow cytometry. Furthermore, modulation of tissue-derived CCL5/CCR5 expression by local injection of shCCL5/shCCR5 or CCL5/CCR5 lentivirus substantially impacted the distribution of pro-inflammatory and reparative M-MDSCs as well as macrophage polarization in bilateral eWAT. These findings suggest that an obesity-induced increase in adipose tissue CCL5-mediated signaling is crucial in the recruitment of tissue M-MDSCs and their trans-differentiation to tissue pro-inflammatory macrophages, resulting in adipose tissue inflammation and insulin resistance.

Pam2 lipopeptides enhance the immunosuppressive activity of monocytic myeloid-derived suppressor cells by STAT3 signal in chronic inflammation.

Chronic inflammation develops when the immune system is unable to clear a persistent insult. Unresolved chronic inflammation leads to immunosuppression to maintain the internal homeostatic conditions, which is mediated primarily by myeloid-derived suppressor cells (MDSCs). Toll-like receptors 2 (TLR2) has an important role in chronic inflammation and can be activated by a vast number and diversity of TLR2 ligands, for example Pam2CSK4. However, the regulatory effect of TLR2 signaling on MDSCs in chronic inflammation remains controversial. This study demonstrated that heat-killed Mycobacterium bovis BCG-induced pathology-free chronic inflammation triggered suppressive monocytic MDSCs (M-MDSCs) that expressed TLR2. Activation of TLR2 signaling by Pam2CSK4 treatment enhanced immunosuppression of M-MDSCs by upregulating inducible nitric oxide synthase (iNOS) activity and nitric oxide (NO) production partly through signal transducer and activator of transcription 3 (STAT3) activation. Thus, TLR2 has a fundamental role in promoting the MDSC-mediated immunosuppressive environment during chronic inflammation and might represent a potentially therapeutic target in chronic inflammation disease.

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

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

Targeting immunosuppressor cells with nanoparticles in autoimmunity: How far have we come to?

Autoimmunity is the assault of immune response towards self-antigens, resulting to inflammation and tissue injury. It is staged into three phases and caused by malfunction of immune tolerance. In our body, immune tolerance is synchronized by several immunosuppressor cells such as regulatory T cells and B cells as well as myeloid-derived suppressor cells, which are prominently dysregulated in autoimmunity. Hence, targeting these cell populations serve as a significant potential in the therapy of autoimmunity. Nanotechnology with its advantageous properties is shown to be a remarkable tool as drug delivery system in this field. This review focused on the development of therapeutics in autoimmune diseases utilizing various nanoparticles formulation based on two targeting approaches in autoimmunity, passive and active targeting. Lastly, this review outlined the approved present nanomedicines as well as in clinical evaluations and issues regarding the lack of translation of these nanomedicines into the market, despite the abundant of positive experimental observations.

Effects of vitamin D on macrophages and myeloid-derived suppressor cells (MDSCs) hyperinflammatory response in the lungs of COVID-19 patients.

Vitamin D regulates homeostasis, anti-microbial response, and inflammation. The vitamin D receptors are expressed in the macrophages and other immune cells, regulating the transcription of many different genes, including those coding the anti-microbial peptides. One of the most severe complications of the SARS-CoV-2 infection is the acute respiratory distress syndrome (ARDS) caused by the hyperinflammatory response (commonly called cytokine storm) of the lung macrophages. Studies showed that Vitamin D deficiency increases the severity of the ARDS in COVID-19 infection. We discuss here how the vitamin D supplementation may influence macrophage and myeloid-derived suppressor cells (MDSCs) inflammatory response, subdue the hyperinflammatory response, and lessen the ARDS in COVID-19 patients.

Pseudoneutrophil Cytokine Sponges Disrupt Myeloid Expansion and Tumor Trafficking to Improve Cancer Immunotherapy.

Myeloid-derived suppressor cells (MDSCs) promote tumor immune escape through multiple mechanisms including suppressing antitumor activities of T lymphocytes. However, therapeutic abrogation of MDSCs often causes severe adverse effects, compensatory recruitment of alternative cell populations, and the multiplicity and complexity of relevant cytokines/receptors. Alternatively, suppressing the expansion and tumor trafficking of MDSCs may be a proficient and safe way for cancer treatment. Here we report that pseudoneutrophil cytokine sponges (pCSs) can disrupt expansion and tumor trafficking of MDSCs and reverse immune tolerance. Coated with plasma membranes of neutrophils phenotypically and morphologically similar to polymorphonuclear MDSCs (PMN-MDSCs), the nanosized pCSs inherited most membrane receptors from the "parental" neutrophils, enabling the neutralization of MDSC-related cytokines. Upon pCSs administration, the expansion of MDSCs and their enrichment in peripheral lymphoid organs and tumors were reduced without the compensatory influx of alternative myeloid subsets. In murine breast cancer and melanoma syngeneic models, pCSs treatment dramatically increased the number of tumor-infiltrating T lymphocytes and restored their antitumor functions. In addition, when pCSs were combined with the programmed cell death protein 1 (PD-1), the immune checkpoint blockade synergistically suppressed tumor progression and prolonged animal survival. Overall, the pseudocell nanoplatform opens up new paths toward effective cancer immunotherapy.

Altered Metabolism in Glioblastoma: Myeloid-Derived Suppressor Cell (MDSC) Fitness and Tumor-Infiltrating Lymphocyte (TIL) Dysfunction.

The metabolism of glioblastoma (GBM), the most aggressive and lethal primary brain tumor, is flexible and adaptable to different adverse conditions, such as nutrient deprivation. Beyond glycolysis, altered lipid metabolism is implicated in GBM progression. Indeed, metabolic subtypes were recently identified based on divergent glucose and lipid metabolism. GBM is also characterized by an immunosuppressive microenvironment in which myeloid-derived suppressor cells (MDSCs) are a powerful ally of tumor cells. Increasing evidence supports the interconnection between GBM and MDSC metabolic pathways. GBM cells exert a crucial contribution to MDSC recruitment and maturation within the tumor microenvironment, where the needs of tumor-infiltrating lymphocytes (TILs) with antitumor function are completely neglected. In this review, we will discuss the unique or alternative source of energy exploited by GBM and MDSCs, exploring how deprivation of specific nutrients and accumulation of toxic byproducts can induce T-cell dysfunction. Understanding the metabolic programs of these cell components and how they impact fitness or dysfunction will be useful to improve treatment modalities, including immunotherapeutic strategies.

Metformin induces CD11b+-cell-mediated growth inhibition of an osteosarcoma: implications for metabolic reprogramming of myeloid cells and anti-tumor effects.

CD11b+ myeloid subpopulations, including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs), play crucial roles in the suppression of T-cell-mediated anti-tumor immunity. Regulation of these cell types is a primary goal for achieving efficient cancer immunotherapy. We found that metformin (Met) induces CD11b+-cell-mediated growth inhibition of a K7M2neo osteosarcoma independent of T cells, as growth inhibition of K7M2neo was still observed in wild-type (WT) mice depleted of T cells by antibodies and in SCID; this contrasted with the effect of Met on Meth A fibrosarcoma, which was entirely T-cell-dependent. Moreover, the inhibitory effect seen in SCID was abrogated by anti-CD11b antibody injection. PMN-MDSCs were significantly reduced in both spleens and tumors following Met treatment. In TAMs, production of IL-12 and TNF-α, but not IL-10, became apparent, and elevation of MHC class II with reduction of CD206 was observed, indicating a shift from an M2- to M1-like phenotype via Met administration. Metabolically, Met treatment decreased basal respiration and the oxygen consumption rate (OCR)/extracellular acidification rate (ECAR) ratio of CD11b+ cells in tumors, but not in the spleen. In addition, decreased reactive oxygen species (ROS) production and proton leakage in MDSCs and TAMs were consistently observed in tumors. Uptake of both 2-deoxy-2-d-glucose (2-NBDG) and BODIPY® decreased in MDSCs, but only BODIPY® incorporation was decreased in TAMs. Overall, our results suggest that Met redirects the metabolism of CD11b+ cells to lower oxidative phosphorylation (OXPHOS) while elevating glycolysis, thereby pushing the microenvironment to a state that inhibits the growth of certain tumors.

Myeloid-derived suppressor cells exert immunosuppressive function on the T helper 2 in mice infected with Echinococcus granulosus.

Cystic echinococcosis (CE) is a worldwide hazardous zoonotic parasitosis caused by Echinococcus granulosus. CE development involves complex immunological mechanisms, including participation of multiple immune cells and effector molecules. Myeloid-derived suppressor cells (MDSCs) are known to be involved in chronic and acute inflammatory conditions. In this study, we aimed to characterize the immune function of MDSCs in CE to improve the understanding, prevention and treatment of CE. Our results indicated that MDSCs overexpressing Ly6C and Ly6G inhibit the formation and activity of T helper 2 cells in a NO-dependent manner during E. granulosus infection.