Myeloid-derived Suppressor Cells In Cancer Research Articles

Key role of myeloid-derived suppressor cells in cancer: perspectives and therapeutic opportunities in prostate cancer

Key role of myeloid-derived suppressor cells in cancer: perspectives and therapeutic opportunities in prostate cancer

In vitro osteoclastogenesis assessment using murine myeloid-derived suppressor cells.

The study of myeloid-derived suppressor cells (MDSCs) has been commonly reported in the context of cancer immunology. MDSCs play a key role in cancer growth and progression by inhibiting both innate and adaptive immunity. In addition to the immunosuppressive function of MDSCs in cancer, a novel function of MDSCs as osteoclast precursors has recently been attracting attention. Because monocytic-MDSCs (M-MDSCs) are derived from the same myeloid lineage as macrophages, which are osteoclast progenitors, M-MDSCs can undergo differentiation into osteoclasts, contributing to bone destruction not only in the cancer microenvironment but also in inflammatory conditions including obesity and osteoarthritis. Herein, we present details of the technique to evaluate osteoclasts in vitro, as well as specific techniques to isolate M-MDSCs and identify them. This protocol can be easily adapted to isolate M-MDSCs from most pathologic conditions for easy evaluation.

Fluorescent Detection of Peroxynitrite Produced by Myeloid-Derived Suppressor Cells in Cancer and Inhibition by Dasatinib.

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that expand dramatically in many cancer patients. This expansion contributes to immunosuppression in cancer and reduces the efficacy of immune-based cancer therapies. One mechanism of immunosuppression mediated by MDSCs involves production of the reactive nitrogen species peroxynitrite (PNT), where this strong oxidant inactivates immune effector cells through destructive nitration of tyrosine residues in immune signal transduction pathways. As an alternative to analysis of nitrotyrosines indirectly generated by PNT, we used an endoplasmic reticulum (ER)-targeted fluorescent sensor termed PS3 that allows direct detection of PNT produced by MDSCs. When the MDSC-like cell line MSC2 and primary MDSCs from mice and humans were treated with PS3 and antibody-opsonized TentaGel microspheres, phagocytosis of these beads led to production of PNT and generation of a highly fluorescent product. Using this method, we show that splenocytes from a EMT6 mouse model of cancer, but not normal control mice, produce high levels of PNT due to elevated numbers of granulocytic (PMN) MDSCs. Similarly, peripheral blood mononuclear cells (PBMCs) isolated from blood of human melanoma patients produced substantially higher levels of PNT than healthy human volunteers, coincident with higher peripheral MDSC levels. The kinase inhibitor dasatinib was found to potently block the production of PNT both by inhibiting phagocytosis in vitro and by reducing the number of granulocytic MDSCs in mice in vivo, providing a chemical tool to modulate the production of this reactive nitrogen species (RNS) in the tumor microenvironment.

Modulation of T-cell function by myeloid-derived suppressor cells in hematological malignancies.

Myeloid-derived suppressor cells (MDSCs) are pathologically activated neutrophils and monocytes that negatively regulate the immune response to cancer and chronic infections. Abnormal myelopoiesis and pathological activation of myeloid cells generate this heterogeneous population of myeloid-derived suppressor cells. They are characterized by their distinct transcription, phenotypic, biochemical, and functional features. In the tumor microenvironment (TME), myeloid-derived suppressor cells represent an important class of immunosuppressive cells that correlate with tumor burden, stage, and a poor prognosis. Myeloid-derived suppressor cells exert a strong immunosuppressive effect on T-cells (and a broad range of other immune cells), by blocking lymphocyte homing, increasing production of reactive oxygen and nitrogen species, promoting secretion of various cytokines, chemokines, and immune regulatory molecules, stimulation of other immunosuppressive cells, depletion of various metabolites, and upregulation of immune checkpoint molecules. Additionally, the heterogeneity of myeloid-derived suppressor cells in cancer makes their identification challenging. Overall, they serve as a major obstacle for many cancer immunotherapies and targeting them could be a favorable strategy to improve the effectiveness of immunotherapeutic interventions. However, in hematological malignancies, particularly B-cell malignancies, the clinical outcomes of targeting these myeloid-derived suppressor cells is a field that is still to be explored. This review summarizes the complex biology of myeloid-derived suppressor cells with an emphasis on the immunosuppressive pathways used by myeloid-derived suppressor cells to modulate T-cell function in hematological malignancies. In addition, we describe the challenges, therapeutic strategies, and clinical relevance of targeting myeloid-derived suppressor cells in these diseases.

"Open Sesame" to the complexity of pattern recognition receptors of myeloid-derived suppressor cells in cancer.

Pattern recognition receptors are primitive sensors that arouse a preconfigured immune response to broad stimuli, including nonself pathogen-associated and autologous damage-associated molecular pattern molecules. These receptors are mainly expressed by innate myeloid cells, including granulocytes, monocytes, macrophages, and dendritic cells. Recent investigations have revealed new insights into these receptors as key players not only in triggering inflammation processes against pathogen invasion but also in mediating immune suppression in specific pathological states, including cancer. Myeloid-derived suppressor cells are preferentially expanded in many pathological conditions. This heterogeneous cell population includes immunosuppressive myeloid cells that are thought to be associated with poor prognosis and impaired response to immune therapies in various cancers. Identification of pattern recognition receptors and their ligands increases the understanding of immune-activating and immune-suppressive myeloid cell functions and sheds light on myeloid-derived suppressor cell differences from cognate granulocytes and monocytes in healthy conditions. This review summarizes the different expression, ligand recognition, signaling pathways, and cancer relations and identifies Toll-like receptors as potential new targets on myeloid-derived suppressor cells in cancer, which might help us to decipher the instruction codes for reverting suppressive myeloid cells toward an antitumor phenotype.

Myeloid-Derived Suppressor Cells in Cancer and COVID-19 as Associated with Oxidative Stress.

Myeloid-derived suppressor cells MDSCs are a heterogeneous population of cells that expand beyond their physiological regulation during pathologies such as cancer, inflammation, bacterial, and viral infections. Their key feature is their remarkable ability to suppress T cell and natural killer NK cell responses. Certain risk factors for severe COVID-19 disease, such as obesity and diabetes, are associated with oxidative stress. The resulting inflammation and oxidative stress can negatively impact the host. Similarly, cancer cells exhibit a sustained increase in intrinsic ROS generation that maintains the oncogenic phenotype and drives tumor progression. By disrupting endoplasmic reticulum calcium channels, intracellular ROS accumulation can disrupt protein folding and ultimately lead to proteostasis failure. In cancer and COVID-19, MDSCs consist of the same two subtypes (PMN-MSDC and M-MDSC). While the main role of polymorphonuclear MDSCs is to dampen the response of T cells and NK killer cells, they also produce reactive oxygen species ROS and reactive nitrogen species RNS. We here review the origin of MDSCs, their expansion mechanisms, and their suppressive functions in the context of cancer and COVID-19 associated with the presence of superoxide anion •O2- and reactive oxygen species ROS.

P-421 Increased myeloid-derived suppressor cells in women with recurrent miscarriage and recurrent implantation failure

Abstract Study question We sought to explore the levels of myeloid-derived suppressor cells (MDSCs) in women experiencing recurrent miscarriage (RM) or recurrent implantation failure (RIF) Summary answer MDSCs were significantly expanded in RM patients with respect to fertile healthy women (p = 0.03, 8.25 vs 7.00). What is known already RM and RIF are two distinct disorders that can be associated with a baseline pro-inflammatory state. Different surrogate inflammatory biomarkers have been associated with these disorders in a subgroup of patients, including expanded cytotoxic NK cells, increased pro-inflammatory cytokines or reduced regulatory T cells (TReg). MDSCs are a heterogeneous population of leukocytes, known for their capacity to modulate immune responses. The immunosuppressive function of MDSC in cancer has been well established, while a controversial role in autoimmune diseases has been reported. Typically, there are two major groups of MDSCs in humans: granulocytic/polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). Study design, size, duration A cross-sectional study to evaluate the levels of MDSCs in women with RM and RIF consecutively referred to our Reproductive Immunology Unit. 55 patients and 23 healthy women were evaluated from 2021 to 2022. RM was defined as the loss of two or more pregnancies and not necessarily consecutive. RIF was defined as the failure to achieve a clinical pregnancy after transferring at least four good-quality embryos. Participants/materials, setting, methods A full fertility screening was performed for all women and their partners as part of routine care. A group of healthy non-pregnant women up to 45 years old with two or more children (proven fertility) and no spontaneous miscarriage was used as control group. Freshly collected blood samples were analyzed by multiparametric flow cytometry using a BD FACS CANTO II. Peripheral blood M-MDSCs were characterized based on HLA-DR, CD14, CD33 and CD45 expression. Main results and the role of chance In this study, we evaluated 55 women, 35 that fulfilled RM criteria and 20 with RIF. In addition, a group of 23 non-pregnant fertile women was included as a control group. We characterized MDSCs as CD14+CD33+CD45+HLA-DR-/LOW, according to previous reports. We observed a significant expansion of peripheral blood MDSCs in RM group compared to the control group (8.25% [6.62-11.9] vs 7.05% [6-7.8], p = 0.03) and RIF group showed a similar increasing trend compared to controls (8.6% [5.65-12.35] vs 7.05% [6-7.8], p = 0.09). We performed ROC curves analysis to evaluate the predictive power. We established an optimal cut-off level of 8.3% in RM group, with a sensitivity of 50% and a specificity of 86.96%. Moreover, women with more than 8.3% had a higher probability of presenting RM compared to the control group (OR: 6.66; CI: 1.68-26.46). MDSCs are characterized by their ability to exert a potent immunosuppressive function. However, recent investigations have shown that MDSCs could act as pro-inflammatory cells under certain inflammatory conditions, such as autoimmune diseases. In this context, MDSCs could worsen the pro-inflammatory state in women, leading to miscarriage or implantation failure. Limitations, reasons for caution In order to validate these results, we should extend our cohort and control group. Moreover, we need to perform a functional evaluation of this subset so we could elucidate their role in these conditions. Wider implications of the findings MDSCs might be a good predictor for RM and RIF patients and with others (as expanded NK cells) may classify a subgroup of patients with a pro-inflammatory profile that can benefit from personalized therapies. Trial registration number Not aplicable

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.

Targeted Gene Expression Profiling of Human Myeloid Cells From Blood and Lung Compartments of Patients With Tuberculosis and Other Lung Diseases.

Myeloid-derived suppressor cells (MDSC) have been identified in the peripheral blood and granulomas of patients with active TB disease, but their phenotype-, function-, and immunosuppressive mechanism- spectrum remains unclear. Importantly, the frequency and signaling pathways of MDSC at the site of disease is unknown with no indication how this compares to MDSC identified in peripheral blood or to those of related myeloid counterparts such as alveolar macrophages and monocytes. Most phenotypic and functional markers have been described in oncological studies but have not yet been validated in TB. Using a panel of 43 genes selected from pathways previously shown to contribute to tumor-derived MDSC, we set out to evaluate if the expression of these additional functional markers and properties may also be relevant to TB-derived MDSC. Differential expression was investigated between MDSC, alveolar macrophages and monocytes enriched from bronchoalveolar lavage fluid and peripheral blood of patients with active TB, patients with other lung diseases (OLD). Results demonstrated that anatomical compartments may drive compartment-specific immunological responses and subsequent MDSC immunosuppressive functions, demonstrated by the observation that MDSC and/or monocytes from PB alone can discriminate, via hierarchical clustering, between patients with active TB disease and OLD. Our data show that the gene expression patterns of MDSC in peripheral blood and bronchoalveolar lavage fluid do not cluster according to disease states (TB vs OLD). This suggests that MDSC from TB patients may display similar gene expression profiles to those found for MDSC in cancer, but this needs to be validated in a larger cohort. These are important observations for TB research and may provide direction for future studies aimed at repurposing and validating cancer immunotherapies for use in TB.

Myeloid-derived suppressor-like cells - a potential biomarker for prognosis of colorectal cancer?

Background/Aim. Myeloid-derived suppressor cells (MDSC) represent a heterogeneous group of immature cells of myeloid origin, which have the ability to inhibit both the innate and adaptive immune response. Due to its immunosuppressive effect, MDSC can promote the growth and progression of cancer. Colorectal cancer (CRC) is one of the most common cancers in the general population for whose advanced stages of the disease there is still no good therapy. In addition to contributing to the development and spread of CRC, MDSC could potentially be markers of its prognosis. The aim of the study was to examine the potential prognostic role of peripheral blood MDSC counts in CRC patients. Methods. In a prospective study we analyzed the possibility of using CD16low granulocytes and mononuclear (M-MDSC) like cells as well as neutrophyl to lymphocyte ratio (NLR), lymphocite to monocyte ratio (LMR), CD16hi/CD16low granulocytes ratio and M/MMDSC like cells ratios before starting of the treatment as a biomarker for overall survival (OS) in patients with CRC. Hazards ratios (HRs) with the corresponding 95% confidence intervals (95%CIs) were calculated to evaluate the prognostic role of MDSCs in cancer. Results. The analysis was performed in 47 patients in stage III and IV CRC according to the TNM/AJCC disease classification. Dependable data were obtained in 32 patients. Patients blood samples are taken before the possible start of treatment (surgery, chemotherapy). Increased percentage and absolute values of CD16low granulocytes as well as absolute values of M-MDSC-like cells have been shown to be associated with shorter overall survival (OS) (p < 0.0066, p < 0.0013 and p < 0.0119, respectively). The relationship of CD16hi/CD16low granulocytes ratio and M/M-MDSC like cells ratio with OS indicated the existence of positive correlations between these parameters, which higher value of this relationship indicated longer survival of patients (p < 0.0054 and p < 0.0426, respectively). Relationship between OS and NLR indicators found statistically significant inverse correlation with NLR (p = 0.0349). No statistical significance was found in the relationship between OS and LMR. Conclusion. This study shows that percent and absolute numbers of CD16low granulocytes, as well as absolute number of M-MDSC like cells, CD16hi/CD16low granulocytes ratio, M/M-MDSC like cells and NLR ratio ratio may be reliable indicators of survival in patients with CRC.

Lenvatinib enhances T cell immunity and the efficacy of adoptive chimeric antigen receptor-modified T cells by decreasing myeloid-derived suppressor cells in cancer

BackgroundLenvatinib, a tyrosine kinase inhibitor, has been approved for the treatment of several cancers. However, its regulatory activity and related mechanisms on T cell antitumour immunity need to be further investigated. MethodsThe antitumour activity of lenvatinib in immunocompetent and immunodeficient mice was compared to determine the role of T cell immunity. The antitumour activity of T cells was analysed by cytokine production and adoptive T cell therapy. The immunosuppressive effects of MDSCs on T cells were determined by detecting cytokine production in T cells after being cocultured with MDSCs. The adjuvant immunotherapy effect of lenvatinib was determined by combination therapy with CAR-T cells targeted carbonic anhydrase IX (CAIX) in a murine renal cancer model. ResultsThe antitumour activity of lenvatinib was greater in immunocompetent mice than in immunodeficient mice and was attenuated by CD8+T cell depletion. Lenvatinib increased proliferation, tumour infiltration and antitumour activity of T cells. Importantly, adoptive transfer of lenvatinib-treated T cells showed a long-term antitumour response in vivo. Mechanistically, lenvatinib upregulated T cell-related chemokines (CXCL10 and CCL8) in tumours and decreased the frequency and immunosuppressive activity of MDSCs. Furthermore, lenvatinib enhanced the efficacy of CAR-T cells in a murine renal cancer model. ConclusionOur study revealed novel antitumour mechanisms of lenvatinib by enhancing T cell-mediated antitumour immunity. These findings are of great significance for guiding the clinical use of lenvatinib and provide a good candidate for future combination therapy with T-cell therapies or other immunotherapies.

Innate immune cells in the tumor microenvironment.

The tumor immune microenvironment (TIME) is a complex ecosystem that contains adaptive and innate immune cells that have tumor-promoting and anti-tumor effects. There is still much to learn about the diversity, plasticity, and functions of innate immune cells in the TIME and their roles in determining the response to immunotherapies. Experts discuss recent advances in our understanding of their biology in cancer as well as outstanding questions and potential therapeutic avenues.

Immunosuppressive Effects of Myeloid-Derived Suppressor Cells in Cancer and Immunotherapy.

The primary function of myeloid cells is to protect the host from infections. However, during cancer progression or states of chronic inflammation, these cells develop into myeloid-derived suppressor cells (MDSCs) that play a prominent role in suppressing anti-tumor immunity. Overcoming the suppressive effects of MDSCs is a major hurdle in cancer immunotherapy. Therefore, understanding the mechanisms by which MDSCs promote tumor growth is essential for improving current immunotherapies and developing new ones. This review explores mechanisms by which MDSCs suppress T-cell immunity and how this impacts the efficacy of commonly used immunotherapies.

Immune suppressive activity of myeloid-derived suppressor cells in cancer requires inactivation of the type I interferon pathway

Myeloid-derived suppressor cells (MDSC) are pathologically activated neutrophils and monocytes with potent immune suppressive activity. These cells play an important role in accelerating tumor progression and undermining the efficacy of anti-cancer therapies. The natural mechanisms limiting MDSC activity are not well understood. Here, we present evidence that type I interferons (IFN1) receptor signaling serves as a universal mechanism that restricts acquisition of suppressive activity by these cells. Downregulation of the IFNAR1 chain of this receptor is found in MDSC from cancer patients and mouse tumor models. The decrease in IFNAR1 depends on the activation of the p38 protein kinase and is required for activation of the immune suppressive phenotype. Whereas deletion of IFNAR1 is not sufficient to convert neutrophils and monocytes to MDSC, genetic stabilization of IFNAR1 in tumor bearing mice undermines suppressive activity of MDSC and has potent antitumor effect. Stabilizing IFNAR1 using inhibitor of p38 combined with the interferon induction therapy elicits a robust anti-tumor effect. Thus, negative regulatory mechanisms of MDSC function can be exploited therapeutically.

Tumor-related stress regulates functional plasticity of MDSCs

Myeloid-derived suppressor cells (MDSCs) impair protective anti-tumor immunity and remain major obstacles that stymie the effectiveness of promising cancer therapies. Diverse tumor-derived stressors galvanize the differentiation, intra-tumoral expansion, and immunomodulatory function of MDSCs. These tumor-associated ‘axes of stress’ underwrite the immunosuppressive programming of MDSCs in cancer and contribute to the phenotypic/functional heterogeneity that characterize tumor-MDSCs. This review discusses various tumor-associated axes of stress that direct MDSC development, accumulation, and immunosuppressive function, as well as current strategies aimed at overcoming the detrimental impact of MDSCs in cancer. To better understand the constellation of signals directing MDSC biology, we herein summarize the pivotal roles, signaling mediators, and effects of reactive oxygen/nitrogen species-related stress, chronic inflammatory stress, hypoxia-linked stress, endoplasmic reticulum stress, metabolic stress, and therapy-associated stress on MDSCs. Although therapeutic targeting of these processes remains mostly pre-clinical, intercepting signaling through the axes of stress could overcome MDSC-related immune suppression in tumor-bearing hosts.

Lenvatinib Enhances T Cell Immunity and the Efficacy of Adoptive Chimeric Antigen Receptor-Modified T Cells by Decreasing Myeloid-Derived Suppressor Cells in Cancer

Background: Lenvatinib, a tyrosine kinase inhibitor, has been approved for the treatment of several cancers. However, its regulatory activity and related mechanisms on T cell antitumour immunity need to be further investigated. Methods: The antitumour activity of lenvatinib in immunocompetent and immunodeficient mice was compared to determine the role of T cell immunity. The antitumour activity of T cells was analysed by cytokine production and adoptive T cell therapy. The immunosuppressive effects of MDSCs on T cells were determined by detecting cytokine production in T cells after being cocultured with MDSCs. The adjuvant immunotherapy effect of lenvatinib was determined by combination therapy with CAR-T cells in a murine renal cancer model. Findings: The antitumour activity of lenvatinib was greater in immunocompetent mice than in immunodeficient mice and was attenuated by CD8+ T cell depletion. Lenvatinib increased proliferation, tumour infiltration and antitumour activity of T cells. Importantly, adoptive transfer of lenvatinib-treated T cells showed a long-term antitumour response in vivo. Mechanistically, lenvatinib upregulated T cell-related chemokines (CXCL10 and CCL8) in tumours and decreased the frequency and immunosuppressive activity of MDSCs. Furthermore, lenvatinib enhanced the efficacy of CAR-T cells in a murine renal cancer model. Interpretation: Our study revealed novel antitumour mechanisms of lenvatinib by enhancing T cell-mediated antitumour immunity. These findings are of great significance for guiding the clinical use of lenvatinib and provide a good candidate for future combination therapy with T-cell therapies or other immunotherapies. Funding: National Science Foundation of China (81773253), Jiangsu Province Social Development Projects (SBE2018740637, BE2020641), Youth Technology Innovation Team of Xuzhou Medical University (TD202003), Jiangsu Provincial Key Medical Discipline (ZDXKA2016014). Declaration of Interest: None to declare. Ethical Approval: All animal procedures were approved and manipulated in strict accordance with the Institutional Ethical Care and Use Committee.

Distinct Populations of Immune-Suppressive Macrophages Differentiate from Monocytic Myeloid-Derived Suppressor Cells in Cancer

SUMMARYHere, we report that functional heterogeneity of macrophages in cancer could be determined by the nature of their precursors: monocytes (Mons) and monocytic myeloid-derived suppressor cells (M-MDSCs). Macrophages that are differentiated from M-MDSCs, but not from Mons, are immune suppressive, with a genomic profile matching that of M-MDSCs. Immune-suppressive activity of M-MDSC-derived macrophages is dependent on the persistent expression of S100A9 protein in these cells. S100A9 also promotes M2 polarization of macrophages. Tissue-resident- and Mon-derived macrophages lack expression of this protein. S100A9-dependent immune-suppressive activity of macrophages involves transcription factor C/EBPβ. The presence of S100A9-positive macrophages in tumor tissues is associated with shorter survival in patients with head and neck cancer and poor response to PD-1 antibody treatment in patients with metastatic melanoma. Thus, this study reveals the pathway of the development of immune-suppressive macrophages and suggests an approach to their selective targeting.

Recent advances in myeloid-derived suppressor cell biology.

In recent years, studying the role of myeloid-derived suppressor cells (MDSCs) in many pathological inflammatory conditions has become a very active research area. Although the role of MDSCs in cancer is relatively well established, their role in non-cancerous pathological conditions remains in its infancy resulting in much confusion. Our objectives in this review are to address some recent advances in MDSC research in order to minimize such confusion and to provide an insight into their function in the context of other diseases. The following topics will be specifically focused upon: (1) definition and characterization of MDSCs; (2) whether all MDSC populations consist of immature cells; (3) technical issues in MDSC isolation, estimation and characterization; (4) the origin of MDSCs and their anatomical distribution in health and disease; (5) mediators of MDSC expansion and accumulation; (6) factors that determine the expansion of one MDSC population over the other; (7) the Yin and Yang roles of MDSCs. Moreover, the functions of MDSCs will be addressed throughout the text.

Nod1 Promotes Colorectal Carcinogenesis by Regulating the Immunosuppressive Functions of Tumor-Infiltrating Myeloid Cells

Summary Pioneering studies from the early 1980s suggested that bacterial peptidoglycan-derived muramyl peptides (MPs) could exert either stimulatory or immunosuppressive functions depending, in part, on chronicity of exposure. However, this Janus-faced property of MPs remains largely unexplored. Here, we investigated the immunosuppressive potential of Nod1, the bacterial sensor of diaminopimelic acid (DAP)-containing MPs. Using first a model of self-limiting peritonitis, we show that systemic Nod1 activation promoted an autophagy-dependent reprogramming of macrophages towards an alternative phenotype. Moreover, Nod1 stimulation induced the expansion of myeloid-derived suppressor cells (MDSCs) and maintained their immunosuppressive potential via Arginase-1 activity. Supporting the role of MDSCs in cancer, we demonstrate that myeloid-intrinsic Nod1 expression sustained intra-tumoral Arginase-1 levels to foster an immunosuppressive and tumor-permissive microenvironment during colorectal cancer (CRC) development. Our findings support the notion that bacterial products, via Nod1 detection, modulate the immunosuppressive potential of myeloid cells, which ultimately and inadvertently fuels tumor progression in CRC.

Quantification of Early-Stage Myeloid-Derived Suppressor Cells in Cancer Requires Excluding Basophils.

Myeloid derived suppressor cells (MDSC) are a heterogeneous group of immature cells that accumulate in the peripheral blood and tumor microenvironment and are barriers to cancer therapy. MDSCs serve as prognostic biomarkers and are targets for therapy. On the basis of surface markers, three subsets of MDSCs have been defined in humans: granulocytic, monocytic, and early stage (e-MDSC). The markers attributed to e-MDSCs overlap with those of basophils, which are rare circulating myeloid cells with unrecognized roles in cancer. Thus, we asked whether e-MDSCs in circulation and the tumor microenvironment include basophils. On average, 58% of cells with e-MDSC surface markers in blood and 36% in ascites from patients with ovarian cancer were basophils based on CD123high expression and cytology, whereas cells with immature features were rare. Circulating and ascites basophils did not suppress proliferation of stimulated T cells, a key feature of MDSCs. Increased accumulation of basophils and basogranulin, a marker of basophil degranulation, were observed in ascites compared to serum in patients with newly diagnosed ovarian cancer. Basophils recruited to the tumor microenvironment may exacerbate fluid accumulation by their release of proinflammatory granular constituents that promote vascular leakage. No significant correlation was observed between peripheral basophil counts and survival in patients with ovarian cancer. Our results suggest that studies in which e-MDSCs were defined solely by surface markers should be reevaluated to exclude basophils. Both immaturity and suppression are criteria to define e-MDSCs in future studies.