Myeloid-derived Suppressor Cells Subpopulations Research Articles

Myeloid-Derived Suppressor Cells in Bladder Cancer: An Emerging Target

Bladder cancer remains a prevalent and challenging malignancy. Myeloid-derived suppressor cells (MDSCs) have emerged as key contributors to the immunosuppressive tumor microenvironment, facilitating tumor progression, immune evasion, and resistance to therapies. This review explores the role of MDSC in bladder cancer, highlighting their involvement in immune regulation; tumor progression; and resistance to therapies such as bacillus Calmette–Guérin (BCG) therapy, chemotherapy, and immune checkpoint inhibitors (ICIs). We also discuss their potential as biomarkers and therapeutic targets, with current evidence suggesting that targeting MDSCs, either alone or in combination with existing treatments such as BCG and ICIs, may enhance anti-tumor immunity and improve clinical outcomes. However,, challenges remain, particularly regarding the identification and therapeutic modulation of MDSC subpopulations. Further research is warranted to fully elucidate their role in bladder cancer and to optimize MDSC-targeted therapies.

Myeloid-derived suppressor cells in peripheral blood as predictive biomarkers in patients with solid tumors undergoing immune checkpoint therapy: systematic review and meta-analysis

BackgroundImmunotherapeutic approaches, including immune checkpoint inhibitor (ICI) therapy, are increasingly recognized for their potential. Despite notable successes, patient responses to these treatments vary significantly. The absence of reliable predictive and prognostic biomarkers hampers the ability to foresee outcomes. This meta-analysis aims to evaluate the predictive significance of circulating myeloid-derived suppressor cells (MDSC) in patients with solid tumors undergoing ICI therapy, focusing on progression-free survival (PFS) and overall survival (OS).MethodsA comprehensive literature search was performed across PubMed and EMBASE from January 2007 to November 2023, utilizing keywords related to MDSC and ICI. We extracted hazard ratios (HRs) and 95% confidence intervals (CIs) directly from the publications or calculated them based on the reported data. A hazard ratio greater than 1 indicated a beneficial effect of low MDSC levels. We assessed heterogeneity and effect size through subgroup analyses.ResultsOur search yielded 4,023 articles, of which 17 studies involving 1,035 patients were included. The analysis revealed that patients with lower levels of circulating MDSC experienced significantly improved OS (HR=2.13 [95% CI 1.51–2.99]) and PFS (HR=1.87 [95% CI 1.29–2.72]) in response to ICI therapy. Notably, heterogeneity across these outcomes was primarily attributed to differences in polymorphonuclear MDSC (PMN-MDSC) subpopulations and varying cutoff methodologies used in the studies. The monocytic MDSC (M-MDSC) subpopulation emerged as a consistent and significant prognostic marker across various subgroup analyses, including ethnicity, tumor type, ICI target, sample size, and cutoff methodology.ConclusionsOur findings suggest that standardized assessment of MDSC, particularly M-MDSC, should be integral to ICI therapy strategies. These cells hold the promise of identifying patients at risk of poor response to ICI therapy, enabling tailored treatment approaches. Further research focusing on the standardization of markers and validation of cutoff methods is crucial for integrating MDSC into clinical practice.Systematic Review Registrationhttps://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023420095, identifier CRD42023420095.

The post-septic peripheral myeloid compartment reveals unexpected diversity in myeloid-derived suppressor cells.

Sepsis engenders distinct host immunologic changes that include the expansion of myeloid-derived suppressor cells (MDSCs). These cells play a physiologic role in tempering acute inflammatory responses but can persist in patients who develop chronic critical illness. Cellular Indexing of Transcriptomes and Epitopes by Sequencing and transcriptomic analysis are used to describe MDSC subpopulations based on differential gene expression, RNA velocities, and biologic process clustering. We identify a unique lineage and differentiation pathway for MDSCs after sepsis and describe a novel MDSC subpopulation. Additionally, we report that the heterogeneous response of the myeloid compartment of blood to sepsis is dependent on clinical outcome. The origins and lineage of these MDSC subpopulations were previously assumed to be discrete and unidirectional; however, these cells exhibit a dynamic phenotype with considerable plasticity.

Abstract 3636: Myeloid cell rebound associated with GD2-CAR-T cell therapy in solid tumor patients

Abstract GD2 is a validated cancer immunotherapy target with highly restricted normal tissue expression. Promising activity of GD2-CAR-T cell therapy in diffuse midline glioma and neuroblastoma has promoted interest in this therapy. We initiated three phase 1 clinical trials of escalating doses of intravenously administered autologous GD2-CAR-T cells in patients with advanced GD2-positive solid tumors. Emerging evidence suggests that CAR-T cells may increase circulating myeloid derived suppressor cells (MDSCs) and that this event may be mediated and/or triggered by CAR-T cell-derived cytokines and chemokines. These findings may help to explain the limited persistence of CAR-T cell therapy in solid tumor patients. Hence, we sought evidence of MDSC generation and secretion of relevant cytokines and chemokines in our clinical trial patients. The CARPETS trial (www.anzctr.org.au: ACTRN12620000622909) recently closed to recruitment after enrolling 12 patients (7 melanoma, 4 colorectal cancer, and 1 sarcoma). No significant adverse events were attributable to CAR-T cell therapy. We opened two other GD2-CAR-T cell therapy trials in 2023: LEVI’S-CATCH (ACTRN12622000675729) in patients with diffuse midline glioma at Sydney Children’s Hospital and KARPOS (ACTRN12622001514796) in adult patients with recurrent glioblastoma at Royal Adelaide Hospital. To date, 3 patients have enrolled to LEVI’S-CATCH with the first patient clearing the dose limiting (DLT) evaluation period. Three patients completed enrolment to the first dose cohort of KARPOS without DLTs. In all CARPETS patients, CAR-T cell expansion, which was measured by by DNA quantitative PCR and flow cytometry, peaked during the 6-week post-CAR-T infusion DLT evaluation period. In 6 CARPETS patients for whom peripheral blood samples were available, we found by flow cytometry, newly formed or increased size of pre-existing subpopulations of non-classical monocytes and/or MDSCs of mononuclear and/or polymorphonuclear class, which peaked at or after the time of peak CAR-T cell expansion. Typically, serum levels of inflammatory cytokines and chemokines such as TNF, IL-6, IL-8, CCL2, GM-CSF, and CXCL10, were detected only after the CAR-T cell infusion with variable patterns of the timing and concentration of analyte observed among the 12 patients. At the time of writing, blood samples from the first KARPOS patient showed CAR-T cell expansion and the subsequent increases in circulating myeloid derived suppressor cells and inflammatory cytokines. We expect that full data sets for these parameters will be presented for current and future enrolled patients to both studies. To improve CAR-T cell persistence in solid tumor patients, these data indicate the need for new therapeutic strategies to mitigate effects of CAR-T cell induced myeloid cells with antitumor activity. Citation Format: Michael P. Brown, Tessa Gargett, Nga T. Truong, Orazio Vittorio, David S. Ziegler. Myeloid cell rebound associated with GD2-CAR-T cell therapy in solid tumor patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3636.

Proliferation of MDSCs may indicate a lower CD4+T cell immune response in schistosomiasis japonica.

Schistosoma japonicum (S. japonicum) is the main species of Schistosoma prevalent in China. Myeloid-derived suppressor cells (MDSCs) are important immunoregulatory cells and generally expand in parasite infection, but there is little research relating to MDSCs in Schistosoma infection. Fifty-six S. japonicum-infected patients were included in this study. MDSCs and percentages and absolute cell numbers of lymphocyte subsets, including CD3+ T cells, CD4+ T cells, CD8+ T cells, B cells and natural killer (NK) cells were detected using flow cytometry. The degree of liver fibrosis was determined using color Doppler ultrasound. Patients infected with S. japonicum had a much higher percentage of MDSCs among peripheral blood mononuclear cells (PBMCs) than the healthy control. Regarding subpopulations of MDSCs, the percentage of granulocytic myeloid-derived suppressor cells (G-MDSCs) was clearly increased. Correlation analysis showed that the absolute cell counts of T-cell subsets correlated negatively with the percentages of MDSCs and G-MDSCs among PBMCs. The percentage of G-MDSCs in PBMCs was also significantly higher in patients with liver fibrosis diagnosed by color doppler ultrasound (grade>0), and the percentage of G-MDSCs in PBMCs and liver fibrosis grading based on ultrasound showed a positive correlation. S. japonicum infection contributes to an increase in MDSCs, especially G-MDSCs, whose proliferation may inhibit the number of CD4+ T cells in peripheral blood. Meanwhile, there is a close relationship between proliferation of G-MDSCs and liver fibrosis in S. japonicum-infected patients.

<i>In vitro</i> production of myeloid-derived suppressor cells from peripheral blood monocytes

Myeloid-derived suppressor cells (MDSCs) are of interest as key regulators of the immune response for the development and improvement of cellular technologies in biomedicine. Enhancing the suppressive activity of these cells is important for developing therapies for autoimmune diseases and miscarriages, and their suppression may be useful in the treatment of cancer, since MDSCs are known to suppress antitumor immunity. However, there is a problem that prevents the active study of MDSCs, i.e., the difficulty in obtaining sufficient numbers of this cell population. Isolation of MDSCs in cancer patients poses an ethical challenge. Moreover, these MDSC may differ in subpopulation composition and suppressive activity due to individual factors. Researchers who generate human MDSC from bone marrow cells may also face similar problems. Therefore, finding a reliable and affordable source of these cells to facilitate the study of their functions is extremely important. Attempts to obtain human MDSCs in vitro have been ongoing for a long time. GM- CSF, IL-6, IL- 1β, IL-4, PGE2, LPS, M-CSF, IFNγ are described as factors that induce the ex vivo MDSC differentiation. However, despite multiple factors used, not all protocols are clearly reproducible, leading to generation of a sufficient number of cells in the target population. Previously, we had also developed a scheme for MDSC differentiation from CD11b+ cells derived from human peripheral blood, which made it possible to obtain a tangible but still insufficient percentage of cells to study functional activity.
 To increase the number of MDSCs in cultures, we developed a protocol aimed for differentiation of these cells from peripheral blood monocytes (CD14+ cells) previously transformed into PCMO (programmed cells of monocytic origin). The monocytes isolated by immunomagnetic separation were cultured in a de-differentiating medium (complete culture medium supplemented with M-CSF, IL-3 and β-mercaptoethanol) for one week. Later on, the medium was replaced by the addition of GM-CSF, being cultured for three days, followed by addition of LPS and IL-1β in order to induce suppressive activity. We have found that culturing CD14+ cells on a two-week schedule with prior creation of dedifferentiation conditions resulted in a slightly decreased percentage of viable cells in culture. However, there was a trend towards an increased ratio of MDSCs in culture (from an average of 34 to 40%) and an increase in their suppressive activity (arginase and IDO expression). The percentage of Arg+ cells increased by average of 10%, and IDO+ cells, by 16%. Moreover, the percentage of mature M-MDSCs was significantly (several-fold) higher when compared with differentiation protocol using CD11b+ cells. Hence, this method of MDSCs production enables us to increase the number of cells belonging to the conditionally “mature” monocyte subpopulation of MDSCs, as well as the percentage of functional suppressor cells in the population. The described scheme may be used to improve the quality of studies aimed at modulating MDSC functions in order to develop new therapeutic approaches.

Content of myeloid-derived suppressor cells in autoimmune diseases in children

Myeloid-derived suppressor cells (MDSCs) play an important role in regulation of immune response. An increase in their number in adult patients with autoimmune diseases has been reported. G-MDSCs, M-MDSCs, and MDSCs(M-G-) at different stages of autoimmune disease may both activate T cell proliferation, leading to disease progression, or inhibit it, thus promoting Treg differentiation. Arginase-1 (Arg- 1) is an enzyme in MDSCs that reduces the concentration of arginine required for T lymphocyte proliferation. Our aim was to evaluate the content of MDSCs populations and functional activity of MDSCs in children with autoimmune diseases. 75 children with inflammatory bowel diseases (IBD), 60 children with multiple sclerosis (MS), 69 children with psoriasis (PS), 62 healthy age-matched children were included into the study. The content of MDSCs ((CD3, CD19, CD56, HLA-DR)-, CD11b+ and CD33+), subpopulations of MDSCs (M-MDSCs, G-MDSCs expressing CD14 and CD15), assessment of Arg-1 activity were performed by flow cytometry techniques. The content of MDSCs in patients with IBD, MS and PS was significantly higher than in the comparison group and depended on the state of exacerbation/remission. In exacerbation and remission of IBD, MS and PS, a significant increase of MDSCs was revealed when compared with healthy children; the highest values were found in children in exacerbation of MS (Me-3.5 (2.5-5.6) % MNC against Me-1.6 (0.9-2.5) % MNC, p 0.001). In patients with MS, the content of G-MDSC, M-MDSC was significantly higher, and MDSC(M-G-) was lower than in healthy children. An increase in absolute amounts of G-MDSCs was shown in MS exacerbation compared to the disease remission state (p = 0.022). For patients with IBD, a significant increase in percentage of MDSCs and M-MDSCs (p = 0.014 and p = 0.045, respectively) was obtained in exacerbation of the disease relative to remission state. In patients with IBD, MS, and PS, a significant increase in Arg-1 activity in MDSCs was found, with a decreased number of MDSCs in patients in remission compared to exacerbation phase of the disease. In children with autoimmune diseases, an increase in the MDSC populations was found. The activity of arginase-1 in MDSCs is increased in remission, along with a decrease in their numbers.

Role of myeloid-derived suppressor cells in prediction of the effectiveness of biologics in children with psoriasis

Psoriasis is a chronic inflammatory skin disease characterized by increased proliferation of epidermal cells, impaired keratinization, and an inflammatory reaction in the dermis due to activation of T-lymphocytes and synthesis of proinflammatory cytokines. Pathophysiology of psoriasis is associated not only with activation of proinflammatory reactions, but also with decreased anti-inflammatory functions of immunosuppressive cells. It is known that Treg, Breg and MDSCs do not perform their classical homeostatic functions in psoriasis. In recent years, there have been more and more cases of developing resistance to ongoing therapy with genetically engineered biological drugs (GEBD) in childhood, requiring replacement or discontinuation of the drug. The aim of our work was to estimate the content of MDSCs subpopulations and their functional activity in the peripheral blood of children with psoriasis at different effectiveness of biotherapeutic drugs. We examined 110 children with psoriasis vulgaris before the appointment of biologics, at 16 and 52 weeks of therapy with adalimumab, etanercept and ustikinumab, aged 6 to 18 years. Сomparison group consisted of 34 healthy children. The effectiveness of therapy was assessed by the achievement of PASI 75 by one year of therapy. Contents of myeloid-derived suppressor cells (MDSCs) and their subpopulations, and the activity of arginase-1 were assessed by multicolor flow cytometry. An increased content of MDSCs was found in children with psoriasis against the comparison group (p = 0.000). Analysis of the effectiveness of biologics in children with psoriasis, according to PASI, showed a significant reduction in disease severity in the group of patients with good effect, both at week 16 of therapy (p = 0.000) and by one year (p = 0.017). In the group of patients with good effect of biological therapy, percentage of total MDSCs population was higher, both before start of treatment and by 52nd week of therapy (p 0.01). Children with psoriasis showed increased immunosuppressive function of MDSCs by arginase-1 activity versus the comparison group (p = 0.000). The arginase-1 activity in patients with psoriasis at the stage of disease regression (PASI 10) was significantly increased relative to children in progressive stage of psoriasis (PASI10; p = 0.001). Thus, the content of MDSCs and their suppressive activity in children with psoriasis is an informative efficiency predictor of the biological drugs. Fading of biotherapy effect after the induction course is accompanied by decreased number of MDSCs and their functional activity.

Increased levels of circulating granulocytic myeloid‑derived suppressor cells in lumbar disc herniation.

Myeloid-derived suppressor cells (MDSCs) expand when the body undergoes inflammatory diseases and chronic diseases. However, its role in intervertebral disc degeneration remains unclear. The present study aimed to characterize specific subsets of MDSCs as potential indicators of disease progression in patients with lumbar disc herniation (LDH). The Gene Expression Omnibus (GEO) database was used to analyze the changes in granulocyte MDSCs (G-MDSCs). Peripheral blood samples were collected from 40 patients with LDH and 15 healthy controls, and flow cytometry was used to characterize different subsets of MDSCs. All subjects underwent lumbar spine magnetic resonance imaging. Then, t-distributed stochastic neighborhood embedding and FlowSOM were used to analyze the data obtained by CytoFlex. The correlation between circulating MDSCs and the clinicopathological stage of LDH was then further analyzed. The GEO database predicted that G-MDSCs were highly expressed in patients with LDH. The frequency of circulating G-MDSCs increased with Pfirrmann stage III and IV, while the percentage of mononuclear MDSCs (M-MDSCs) only increased. Patient age and sex did not correlate with the frequency of circulating G-MDSCs and M-MDSCs. The results of the computer algorithm analysis were consistent with those of our manual gating. The present study showed that the occurrence of LDH led to changes in the MDSC subpopulation in the circulating peripheral blood of patients, and the frequency of circulating G-MDSCs in patients with clinical stage III and IV LDH increased with the degree of degeneration. The determination of G-MDSCs can be used as an auxiliary examination item for LDH.

Myeloid-derived suppressor cells as biomarkers of the effectiveness of therapy with new biological agents in axial spondyloarthritis

Innate immune cells, including myeloid cells — myeloid derived suppressor cells (MDSCs) — are supposed to play an important role in the pathogenesis of axial spondyloarthritis (AxSp). Myeloid derived suppressor cells represent a heterogeneous population of immature cells capable of suppressing innate and adaptive immune responses with the most pronounced suppressor activity against T cells. Biological disease-modifying antirheumatic drugs (bDMARDs) can reduce the clinical and laboratory disease activity, but their effectiveness varies widely in different patients with AxSp. The present study is aimed at studying MDSCs subpopulations and their suppressive function depending on the response to bDMARD therapy in AxSp. The study included AxSp patients with a disease duration of 16.5 years (median); HLA-B27 (+) status was detected in 79% of cases. All patients received bDMARDs at least the past 12 weeks, including TNF inhibitors (etanercept, certolizumab pegol, adalimumab, or golimumab) or IL-17 inhibitors (secukinumab, ixekizumab, or netakimab). Percentage of granulocytic MDSCs (G-MDSCs, Lin-HLA-DR-CD33+CD66b+), monocytic MDSCs (M-MDSCs, HLA-DRlow/-CD14+), MDSCs of early stage differentiation (E-MDSCs, Lin-HLA-DR- CD33+CD66b-), as well as intracellular expression of arginase-1 was assessed by flow cytometry. Frequency of circulating MDSC subpopulations of patients with a stable response to bDMARDs (responders) did not differ significantly compared to healthy donors. Patients not responding to bDMARDs therapy showed increased relative and absolute number of E-MDSCs compared to healthy donors (pU = 0.01 and pU = 0.02, respectively) and the responders (pU = 0.03 and pU = 0.07, respectively). Increased percentage of E-MDSCs was positively correlated to disease activity — ESR (Rs = 0.821; p = 0.023), CRP (Rs = 0.714; p = 0.07) and ASDASCRP (Rs = 0.829; p = 0.042) in the non-responder group. Responder patients exhibited no correlation between disease activity and circulating MDSCs. The suppressor potential of MDSCs was analyzed by the intracellular expression of arginase-1 molecule which is involved in the inhibition of T cell response. Patients with the stable response were characterized by increased expression of arginase-1 in E-MDSCs compared to donors (pU = 0.02). Non-responders did not demonstrate significant changes in Arg-1 expression, however, the percentage of arginase-1-expressing G-MDSCs was positively correlated to indexes ASDASESR (Rs = 0.857; p = 0.014) and BASDAI (Rs = 0.785; p = 0.036). Thus, E-MDSCs as well as arginase-1 expression in MDSCs may serve as biomarkers of effectiveness bDMARD therapy, and act as potential candidate predictors of response to therapy in AxSp.

Association of myeloid-derived suppressor cells with hematopoietic recovery after high-dose chemotherapy in multiple myeloma

Myeloid-derived suppressor cells (MDSCs) play an important role in the immune response regulation in many pathologies, primarily in malignant tumors, but their role in the hematopoietic stem cell engraftment and the hematopoietic recovery after high-dose chemotherapy and autologous stem cell transplantation remains practically unexplored. This study is aimed at studying the correlation between the number of MDSC subpopulations and blood parameters at the stage of hematopoietic recovery after high-dose chemotherapy and autologous hematopoietic stem cell transplantation in patients with multiple myeloma (MM). Circulating MDSCs were assessed at the stage of leukopenia recovery (absolute leukocyte count in peripheral blood (PB) > 1 x 109/L) by flow cytometry. The number of transplanted CD34+CD45+ hematopoietic stem cells was 4.38 x 106/kg (IQR (3.1—5.6) x 106/kg). The duration of recovery from leukopenia varied from 8 to 18 days (Me 12 days). The number of MDSCs at the engraftment was not associated with the number of CD34+ cells/kg in the graft. The relative number of monocytic MDSCs (M-MDSCs, CD14+HLA-DRlow/-) directly correlated with the number of monocytes at the stage of recovery from leukopenia (R = 0.417, p = 0.002). Granulocytic MDSCs (PMN-MDSCs, Lin-HLA-DR-CD33+CD66b+) were characterized by an inverse correlation with the number of monocytes (R = -0.493, p = 0.0003) while the association with the absolute number of neutrophils was weak (R = 0.273, p = 0.048). The number of lymphocytes at the stage of recovery from leukopenia had an inverse correlation with PMN-MDSCs (R = -0.347, p = 0.014) and did not correlate with M-MDSCs. When analyzing the duration of leukopenia, an inverse correlation with this indicator was revealed for the percentage and absolute number of M-MDSCs (R = -0.347, p = 0.018 and R = -0.469, p = 0.0008, respectively). Multiple regression analysis showed dependence of the lymphopenia duration on the proportion of circulating M-MDSCs (p = 0.014) and the number of transplanted CD34+ cells/kg (p = 0.032). According to the data of multivariate analysis of variance, the number of transplanted CD34+ cells/kg and the number of M-MDSCs were significant factors for the duration of leukopenia. At the same time, such clinical parameters as the depth of response and minimal residual disease status before high-dose chemotherapy and hematopoietic stem cell transplantation, as well as the MM stage, did not affect the duration of hematopoietic recovery. Thus, the obtained results indicate the association of a higher number of M-MDSCs with a shorter duration of leukopenia after high-dose chemotherapy with autologous stem cell transplantation and indicate a positive role of M-MDSCs in hematopoietic recovery in the early post-transplant period in patients with MM.

Modified method for differentiation of myeloid-derived suppressor cells in vitro enhances immunosuppressive ability via glutathione metabolism

Myeloid-derived suppressor cells (MDSCs), which accumulate in tumor bearers, are known to suppress anti-tumor immunity and thus promote tumor progression. MDSCs are considered a major cause of resistance against immune checkpoint inhibitors in patients with cancer. Therefore, MDSCs are potential targets in cancer immunotherapy. In this study, we modified an in vitro method of MDSC differentiation. Upon stimulating bone marrow (BM) cells with granulocyte-macrophage colony-stimulating factor in vitro, we obtained both lymphocyte antigen 6G positive (Ly-6G+) and negative (Ly-6G−) MDSCs (collectively, hereafter referred to as conventional MDSCs), which were non-immunosuppressive and immunosuppressive, respectively. We then found that MDSCs differentiated from Ly-6G− BM (hereafter called 6G− BM-MDSC) suppressed T-cell proliferation more strongly than conventional MDSCs, whereas the cells differentiated from Ly-6G+ BM (hereafter called 6G+ BM-MDSC) were non-immunosuppressive. In line with this, conventional MDSCs or 6G− BM-MDSC, but not 6G+ BM-MDSC, promoted tumor progression in tumor-bearing mice. Moreover, we identified that activated glutathione metabolism was responsible for the enhanced immunosuppressive ability of 6G− BM-MDSC. Finally, we showed that Ly-6G+ cells in 6G− BM-MDSC, which exhibited weak immunosuppression, expressed higher levels of Cybb mRNA, an immunosuppressive gene of MDSCs, than 6G+ BM-MDSC. Together, these data suggest that the depletion of Ly-6G+ cells from the BM cells leads to differentiation of immunosuppressive Ly-6G+ MDSCs. In summary, we propose a better method for MDSC differentiation in vitro. Moreover, our findings contribute to the understanding of MDSC subpopulations and provide a basis for further research on MDSCs.

Tristetraprolin limits age-related expansion of myeloid-derived suppressor cells.

Aging results in enhanced myelopoiesis, which is associated with an increased prevalence of myeloid leukemias and the production of myeloid-derived suppressor cells (MDSCs). Tristetraprolin (TTP) is an RNA binding protein that regulates immune-related cytokines and chemokines by destabilizing target mRNAs. As TTP expression is known to decrease with age in myeloid cells, we used TTP-deficient (TTPKO) mice to model aged mice to study TTP regulation in age-related myelopoiesis. Both TTPKO and myeloid-specific TTPKO (cTTPKO) mice had significant increases in both MDSC subpopulations M-MDSCs (CD11b+Ly6ChiLy6G-) and PMN-MDSCs (CD11b+Ly6CloLy6G+), as well as macrophages (CD11b+F4/80+) in the spleen and mesenteric lymph nodes; however, no quantitative changes in MDSCs were observed in the bone marrow. In contrast, gain-of-function TTP knock-in (TTPKI) mice had no change in MDSCs compared with control mice. Within the bone marrow, total granulocyte-monocyte progenitors (GMPs) and monocyte progenitors (MPs), direct antecedents of M-MDSCs, were significantly increased in both cTTPKO and TTPKO mice, but granulocyte progenitors (GPs) were significantly increased only in TTPKO mice. Transcriptomic analysis of the bone marrow myeloid cell populations revealed that the expression of CC chemokine receptor 2 (CCR2), which plays a key role in monocyte mobilization to inflammatory sites, was dramatically increased in both cTTPKO and TTPKO mice. Concurrently, the concentration of CC chemokine ligand 2 (CCL2), a major ligand of CCR2, was high in the serum of cTTPKO and TTPKO mice, suggesting that TTP impacts the mobilization of M-MDSCs from the bone marrow to inflammatory sites during aging via regulation of the CCR2-CCL2 axis. Collectively, these studies demonstrate a previously unrecognized role for TTP in regulating age-associated myelopoiesis through the expansion of specific myeloid progenitors and M-MDSCs and their recruitment to sites of injury, inflammation, or other pathologic perturbations.

Systemic Immune Modulation Alters Local Bone Regeneration in a Delayed Treatment Composite Model of Non-Union Extremity Trauma.

Bone non-unions resulting from severe traumatic injuries pose significant clinical challenges, and the biological factors that drive progression towards and healing from these injuries are still not well understood. Recently, a dysregulated systemic immune response following musculoskeletal trauma has been identified as a contributing factor for poor outcomes and complications such as infections. In particular, myeloid-derived suppressor cells (MDSCs), immunosuppressive myeloid-lineage cells that expand in response to traumatic injury, have been highlighted as a potential therapeutic target to restore systemic immune homeostasis and ultimately improve functional bone regeneration. Previously, we have developed a novel immunomodulatory therapeutic strategy to deplete MDSCs using Janus gold nanoparticles that mimic the structure and function of antibodies. Here, in a preclinical delayed treatment composite injury model of bone and muscle trauma, we investigate the effects of these nanoparticles on circulating MDSCs, systemic immune profiles, and functional bone regeneration. Unexpectedly, treatment with the nanoparticles resulted in depletion of the high side scatter subset of MDSCs and an increase in the low side scatter subset of MDSCs, resulting in an overall increase in total MDSCs. This overall increase correlated with a decrease in bone volume (P = 0.057) at 6 weeks post-treatment and a significant decrease in mechanical strength at 12 weeks post-treatment compared to untreated rats. Furthermore, MDSCs correlated negatively with endpoint bone healing at multiple timepoints. Single cell RNA sequencing of circulating immune cells revealed differing gene expression of the SNAb target molecule S100A8/A9 in MDSC sub-populations, highlighting a potential need for more targeted approaches to MDSC immunomodulatory treatment following trauma. These results provide further insights on the role of systemic immune dysregulation for severe trauma outcomes in the case of non-unions and composite injuries and suggest the need for additional studies on targeted immunomodulatory interventions to enhance healing.

Myeloid-derived suppressor cells in cancer

Numerous recent studies have shown that myeloid-derived suppressor cells (MDSCs), a strongly heterogeneous population of immunosuppressive cells, are dysregulated in the presence of many cancers. MDSCs present different phenotypes and play prominent roles in the tumor microenvironment. To date, gene therapies targeting MDSCs are the most innovative and flexible methods to specifically modify the tumor microenvironment. Here, we summarize current studies related to the phenotypes, functions, and mechanisms of MDSCs and explore the therapeutic landscape of chemokines that affect the balance between subpopulations of MDSCs.

Abstract P015: Characterization and prognostic impact of DC-HIL in advanced colorectal cancer

Abstract Introduction: DC-HIL is the T cell-inhibitory receptor that is expressed by exponentially expanding CD14+HLA-DRno/low myeloid-derived suppressor cells (MDSC) and critically mediates the immunosuppressive function. We previously reported that this DC-HIL expression is associated with colorectal cancer (CRC) progression. The purpose of this investigation was to determine the correlation of DC-HIL-expressing MDSC subpopulation in blood with clinical outcomes in advanced CRC. Methods: Patients with metastatic CRC (n = 63) were analyzed by flow cytometry for DC-HIL or PDL1 expression on blood CD14+HLA-DRno/low MDSC. A retrospective chart review was performed to obtain data on demographics, tumor, and clinical characteristics including tumor laterality, histology, mutational and microsatellite stability status, stage, metastatic sites, CEA level, and white blood cell count, and differential and treatment outcomes including response to therapy and survival. Baseline characteristics were compared using the two-tailed Student's t-test, ANOVA test, or Pearson correlation test as appropriate. Survival analysis was estimated using the Kaplan-Meier method and Cox regression model, and groups were compared using the log-rank test. Results: Median age at diagnosis was 56 years (range 30-78) and patients were predominantly male (59%) and white (76%). Forty pts had left-sided tumors (63%), the majority had moderately differentiated adenocarcinoma (66%) and stage IV colorectal cancer at diagnosis (68%). At the time of DC-HIL collection, 95% of pts had stage IV disease. Most (95%) pts had microsatellite stable disease, 24% of pts had a KRAS mutation and 22% had a BRAF mutation, 69% of patients underwent surgical resection of the primary malignancy or metastatic site or both. Median CEA level was 40 ng/ml, median white blood cell (WBC) count was 5.9 × 109, median absolute monocyte count (AMC) was 0.64 × 109, median absolute neutrophil count (ANC) was 3.6 × 109, median monocyte to lymphocyte ratio (M/L) was 0.53 and median neutrophil to lymphocyte ratio (N/L) was 2.7. Most pts (90%) received FOLFOX chemotherapy as first-line and 84% of pts received an anti-VEGF agent throughout the course of their treatment. Median CD14+/PBMC for pts was 14.4, median %MDSC/PBMC was 7.0, median %DC-HIL+/MDSC was 66, median %DC-HIL+/MDSC/PBMC was 4.1 and median sDC-HIL was 20.0 ng/ml. Our results showed that there was a statically significant correlation between % MDSC/PBMC, %DCHIL+MDSC/PBMC, and the monocyte/lymphocyte (M/L) ratio with p=0.047 and p=0.03 respectively. There was no statistically significant correlation between DCHIL+/MDSC levels and response to therapy, time-to-next therapy (p=0.11), or overall survival (p=0.67). Conclusion: DC-HIL+ MDSC is positively correlated with M/L ratio, a possible prognostic marker in CRC patients. DC-HIL correlates poorly with other clinical outcomes; chemotherapy response, time-to-next therapy, or overall survival. Citation Format: Jude Khatib, Jin-Sung Chung, Sarah Reddy, Nivan Chowattukunnel, Allante Milsap, Yasin Goksu, Kiyoshi Ariizumi, Syed Kazmi. Characterization and prognostic impact of DC-HIL in advanced colorectal cancer [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P015.

Graft-Versus-Host Disease Prevention by In Vitro-Generated Myeloid-Derived Suppressor Cells Is Exclusively Mediated by the CD11b+CD11c+ MDSC Subpopulation.

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid progenitor cells that dampen overwhelming adaptive immune responses through multiple mechanisms and are recognized as an attractive novel immune intervention therapy for counteracting the destructive effects of graft- versus -host disease (GVHD) developing after allogeneic bone marrow transplantation (BMT). MDSCs can be produced in great numbers for cellular therapy, but they present a mixture of subsets whose functions in GVHD prevention are undefined. Here, we generated MDSCs in vitro from murine BM cells in the presence of GM-CSF and defined the integrin CD11c as a marker to subdivide MDSCs into two functional subgroups: CD11b+CD11c+ and CD11b+CD11c− MDSCs. Isolated CD11b+CD11c+ and CD11b+CD11c− MDSCs both inhibited alloantigen-stimulated T-cell proliferation in vitro, although CD11b+CD11c+ MDSCs were more efficient and expressed higher levels of different immunosuppressive molecules. Likewise, expression of surface markers such as MHC class II, CD80, CD86, or PD-L1 further delineated both subsets. Most importantly, only the adoptive transfer of CD11b+CD11c+ MDSCs into a single MHC class I-disparate allogeneic BMT model prevented GVHD development and strongly decreased disease-induced mortality, while CD11b+CD11c− MDSCs were totally ineffective. Surprisingly, allogeneic T-cell homing and expansion in lymphatic and GVHD target organs were not affected by cotransplanted CD11b+CD11c+ MDSCs indicating a clear contradiction between in vitro and in vivo functions of MDSCs. However, CD11b+CD11c+ MDSCs shifted immune responses towards type 2 immunity reflected by increased Th2-specific cytokine expression of allogeneic T cells. Induction of type 2 immunity was mandatory for GVHD prevention, since CD11b+CD11c+ MDSCs were ineffective if recipients were reconstituted with STAT6-deficient T cells unable to differentiate into Th2 cells. Most importantly, the beneficial graft- versus -tumor (GVT) effect was maintained in the presence of CD11b+CD11c+ MDSCs since syngeneic tumor cells were efficiently eradicated. Strong differences in the transcriptomic landscape of both subpopulations underlined their functional differences. Defining CD11b+CD11c+ MDSCs as the subset of in vitro-generated MDSCs able to inhibit GVHD development might help to increase efficiency of MDSC therapy and to further delineate relevant target molecules and signaling pathways responsible for GVHD prevention.

Tumor promoting capacity of polymorphonuclear myeloid-derived suppressor cells and their neutralization.

Myeloid-derived suppressor cells (MDSC) represent a highly immunosuppressive population that expands in tumor bearing hosts and inhibits both T and NK cell antitumor effector functions. Among MDSC subpopulations, the polymorphonuclear (PMN) one is gaining increasing interest since it is a predominant MDSC subset in most cancer entities and inherits unique properties to facilitate metastatic spread. In addition, further improvement in distinguishing PMN-MDSC from neutrophils has contributed to the design of novel therapeutic approaches. In this review, we summarize the current view on the origin of PMN-MDSC and their relation to classical neutrophils. Furthermore, we outline the metastasis promoting features of these cells and promising strategies of their targeting to improve the efficacy of cancer immunotherapy.

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

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

Myeloid-Derived Suppressor Cells in Immune-Related Bone Marrow Failure: Novel Therapeutic Implication

Immune-related bone marrow failure (IBMF) is characterized by pancytopenia and bone marrow (BM) hypoplasia. Abnormally activated CD8+ T cells are important in its pathogenesis and majority of the patients having this abnormity are diagnosed as aplastic anemia (AA). The exploration of intra-BM immune network will help to conduct novel treatments to this disease.BM mesenchymal stromal cells (MSCs), regulatory T cells (Tregs), natural killer (NK) cells, myeloid-derived suppressor cells (MDSCs) are all immune-regulators within BM microenvironment. Among them, lymphocytes including CD8+ T cells, Tregs, NKs were indicated relating to IBMF pathogenesis with either stimulating or suppressive function. However, the relationship within BM between activated CD8+ T cells and other immune-regulating component remains largely unknown. In this study, we investigated MDSCs' characterization in IBMF models and AA patients to look into the intra-BM immune response during IBMF occurrence and progression.IBMF mice models were produced by lymphocyte infusion as previously described (Chen J, et al. Blood. 2004). To determine the major T cell population responsible for attacking BM environment, we injected H2 b/b -CD3+CD4+ T cells or H2 b/b -CD3+CD8+ T cells in sublethally irradiated hybrid F1 recipients of H2 b/b and H2 d/d mice. The recipients infused with CD3+CD8+ T cells were manifested BMF as pancytopenia, promoted BM-MSC adipogenesis and shorter life span. To further clarify why BM is the major targeted organ of CD8+ T cell in IBMF models, we detected homing receptors and proliferative potential of CD8+ T cells in BM, spleen and lymph nodes. CXCR4, CXCR6, CD49d, TRAIL as well as CD25, EDU were increasingly expressed on intra-BM CD8+ T cells, suggesting that CD8+ T cells reside more sufficiently in BM than in other lymph organs.MDSCs, subgrouped as mMDSCs and gMDSCs by a panel of surface markers, are a heterogeneous population of immature myeloid cells with immunoregulatory function (Gabrilovich DI, et al. Nat Rev Immunol. 2009). The numbers of either circulating MDSCs (CD11b+CD33+HLA-DR-/low) in AA patients or intra-BM MDSCs (CD11b+Gr1+) in IBMF models were decreased compared to normal controls (p=0.0016 and 0.03, respectively), indicating that MDSCs are impacted in the presence of over-activated CD8+ T cells. In vitro co-cultivation of MDSC subpopulation with T cells showed that it was not gMDSCs (CD11b+Ly6G+Ly6Clow, p=0.112) but mMDSCs (CD11b+Ly6G-/lowLy6Chi, p=0.017) capable of reducing anti-CD3/CD28-stimulated T cell proliferation. A nitric oxide synthase (NOS) inhibitor, L-NG-Nitroarginine Methyl Ester (L-NAME), significantly reversed mMDSC-induced T cell hypoproliferation (38.7%±17.5% vs 72.3%±3.5%, p=0.031), suggesting that inducible NOS pathway is an important modulator in the interaction of mMDSC and activated CD8+ T cells.To further investigate whether mMDSCs exert immune regulating function in vivo, freshly sorted H2 b/b -mMDSCs were transfused in sublethally irradiated H2 b/d with CD3+ T cells or lately in IBMF models every three days. The earlier mMDSCs transfusion was able to reduce the severity of pancytopenia and intra-BM infiltration of CD8+ T cells. The overall survival (OS) of repeatedly transfusion group was significantly longer than that of non-mMDSCs transfusion controls (26 days vs 17days, p=0.025).Taking these together, mMDSCs serve as an important regulator with other immune suppressive parts on one side of the teeter-totter, the other side of which the overactivated CD8+ T cells are the major counterpart attacking hematopoietic components in IBMF. In BM microenvironment, immune balance together with orderly multi-differentiation of MSCs and hematopoietic stem cells are all essential to orchestrate normal hematopoiesis. DisclosuresNo relevant conflicts of interest to declare.