Myeloid-derived suppressor cells in human peripheral blood: Optimized quantification in healthy donors and patients with metastatic renal cell carcinoma

Neutrophil Diversity (Immature, Aged, and Low-Density Neutrophils) and Functional Plasticity: Possible Impacts of Iron Overload in β-Thalassemia

Neutrophil dysfunction is a form of immune suppression in patients with β-thalassemia (Beta-thal), although data on this are limited. In this study, blood from patients and healthy volunteers was analyzed. Flow cytometry analysis demonstrated an increase in immature neutrophils (CD16- CD62L+) and aged (senescent) neutrophils (CD16+ CD62L-) in Beta-thal patients compared to healthy volunteers. The Beta-thal neutrophils demonstrated less prominent chemotaxis and phagocytosis than healthy neutrophils at the baseline. With phorbol myristate acetate (PMA) or lipopolysaccharide (LPS) stimulations, some of the indicators, including the flow cytometry markers (CD11b, CD62L, CD66b, CD63, apoptosis, and reactive oxygen species) and neutrophil extracellular traps (NETs; detected by anti-citrullinated histone 3 immunofluorescence), were lower than the control. Additionally, low-density neutrophils (LDNs), which are found in the peripheral blood mononuclear cell (PBMC) fraction, were observed in Beta-thal patients but not in the control group. The expression of CD11b, CD66b, CD63, arginase I, and ROS in LDNs was higher than the regular normal-density neutrophils (NDNs). The proliferation rate of CD3+ T cells isolated from the PBMC fraction of healthy volunteers was higher than that of the cells from patients with Beta-thal. The incubation of red blood cell (RBC) lysate plus ferric ions with healthy NDNs transformed the NDNs into the aged neutrophils (decreased CD62L) and LDNs. In conclusion, iron overload induces neutrophil diversity along with some dysfunctions.

Proof of concept nanotechnological approach to in vitro targeting of malignant melanoma for enhanced immune checkpoint inhibition

Immunotherapies, including immune checkpoint inhibitors, have limitations in their effective treatment of malignancies. The immunosuppressive environment associated with the tumor microenvironment may prevent the achievement of optimal outcomes for immune checkpoint inhibitors alone, and nanotechnology-based platforms for delivery of immunotherapeutic agents are increasingly being investigated for their potential to improve the efficacy of immune checkpoint blockade therapy. In this manuscript, nanoparticles were designed with appropriate size and surface characteristics to enhance their retention of payload so that they can transmit their loaded drugs to the tumor. We aimed to enhance immune cell stimulation by a small molecule inhibitor of PD-1/PD-L1 (BMS202) using nanodiamonds (ND). Melanoma cells with different disease stages were exposed to bare NDs, BMS202-NDs or BMS202 alone for 6 h. Following this, melanoma cells were co-cultured with freshly isolated human peripheral blood mononuclear cells (hPBMCs). The effects of this treatment combination on melanoma cells were examined on several biological parameters including cell viability, cell membrane damage, lysosomal mass/pH changes and expression of γHA2X, and caspase 3. Exposing melanoma cells to BMS202-NDs led to a stronger than normal interaction between the hPBMCs and the melanoma cells, with significant anti-proliferative effects. We therefore conclude that melanoma therapy has the potential to be enhanced by non-classical T-cell Immune responses via immune checkpoint inhibitors delivered by nanodiamonds-based nanoparticles.

Reduced Type 2 Innate Lymphocyte Cell Frequencies in Patent Wuchereria bancrofti-Infected Individuals

Approximately 51 million individuals suffer from lymphatic filariasis (LF) caused mainly by the filarial worm Wuchereria bancrofti. Mass drug administration (MDA) programs led to a significant reduction in the number of infected individuals, but the consequences of the treatment and clearance of infection in regard to host immunity remain uncertain. Thus, this study investigates the composition of myeloid-derived suppressor cells (MDSCs), macrophage subsets and innate lymphoid cells (ILCs), in patent (circulating filarial antigen (CFA)+ microfilariae (MF)+) and latent (CFA+MF-) W. bancrofti-infected individuals, previously W. bancrofti-infected (PI) individuals cured of the infection due to MDA, uninfected controls (endemic normal (EN)) and individuals who suffer from lymphoedema (LE) from the Western Region of Ghana. Frequencies of ILC2 were significantly reduced in W. bancrofti-infected individuals, while the frequencies of MDSCs, M2 macrophages, ILC1 and ILC3 were comparable between the cohorts. Importantly, clearance of infection due to MDA restored the ILC2 frequencies, suggesting that ILC2 subsets might migrate to the site of infection within the lymphatic tissue. In general, the immune cell composition in individuals who cured the infection were comparable to the uninfected individuals, showing that filarial-driven changes of the immune responses require an active infection and are not maintained upon the clearance of the infection.

The Role of Myeloid-Derived Suppressor Cells in Tumor Growth and Metastasis

Myeloid-derived suppressor cells (MDSCs) are immature bone marrow-derived suppressive cells that are an important component of the pathological immune response associated with cancer. Expansion of MDSCs has been linked to poor disease outcome and therapeutic resistance in patients with various malignancies, making these cells potential targets for next-generation treatment strategies. MDSCs are classified into monocytic (M-MDSC) and polymorphonuclear/granulocytic (PMN-MDSC) subtypes that undertake distinct and numerous roles in the tumor microenvironment or systemically to drive disease progression. In this chapter, we will discuss how MDSC subsets contribute to the growth of primary tumors and induce metastatic spread by suppressing the antitumor immune response, supporting cancer stem cell (CSC)/epithelial-to-mesenchymal transition (EMT) phenotypes and promoting angiogenesis. We will also summarize the signaling networks involved in the crosstalk between cancer cells and MDSCs that could represent putative immunotherapy targets.

Immunosuppressive effects and mechanisms of three myeloid-derived suppressor cells subsets including monocytic-myeloid-derived suppressor cells, granulocytic-myeloid-derived suppressor cells, and immature-myeloid-derived suppressor cells

Context

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immune cells of myeloid lineage. Recent reports have suggested that human MDSC are divided into three subsets: monocytic MDSC (M-MDSC), granulocytic MDSC (G-MDSC), and immature MDSC (I-MDSC). However, the characteristics of each human MDSC subset still remain unclear.

Materials and Methods

To evaluate the immunosuppressive effects and mechanisms, we first performed a T-cell suppression assay using cells obtained from healthy donor peripheral blood samples. The levels of immune inhibitory molecules in the culture supernatant of each MDSC subset were measured to reveal the T-cell suppressive mechanisms. Then, we compared these results with the results from cells obtained from cancer patient blood samples. Finally, we investigated the difference in the frequency of each MDSC subset between the healthy donors and the cancer patients.

Results

Although M-MDSC and G-MDSC suppressed T-cell activation, I-MDSC had no T-cell suppressive effect. We found that the culture supernatant of M-MDSC and G-MDSC contained high levels of interleukin-1 receptor antagonist (IL-1RA) and arginase, respectively, in both healthy donors and cancer patients. No inhibitory molecules were detected in the culture supernatant of I-MDSC. The population of functional MDSC (M-MDSC and G-MDSC) in the total MDSC was significantly increased in cancer patients compared with that in healthy donors.

Conclusions

Although M-MDSC and G-MDSC, which released IL-1RA and arginase, respectively, suppressed T-cell activation, I-MDSC did not have an immunosuppressive effect. The population of functional MDSC was increased in cancer patients compared with that in healthy donors.

Correlation analysis of the proportion of monocytic myeloid-derived suppressor cells in colorectal cancer patients

Monocytic myeloid-derived suppressor cells (mMDSCs) are a class of immunosuppressive immune cells with prognostic value in many solid tumors. It is reported that the proportion of mMDSCs in the peripheral blood can be a predictive marker for response to cancer immunotherapy. In this study, we performed a correlation analysis of the proportion of mMDSCs in freshly-drawn peripheral blood, levels of plasma proteins, and demographic factors in colorectal cancer (CRC) patients, to find factors that could be used to predict mMDSC proportions. Freshly-drawn mMDSCs were measured using flow cytometry on peripheral blood mononuclear cells (PBMCs) from healthy donors (n = 24) and CRC patients (n = 78). The plasma concentrations of 29 different cytokines, chemokines, growth factors, and enzymes were measured using a multiplex assay or enzyme-linked immunosorbent assay. Correlation analysis to find mMDSC-associated factors was conducted using univariate and multivariate models. In univariate correlation analysis, there were no plasma proteins that were associated with mMDSC proportions in CRC patients. In multivariate analysis, considering all variables including age, sex, and plasma proteins, levels of inducible nitric acid synthase (iNOS) (p = 0.013) and platelet-derived growth factor (PDGF)-BB (p = 0.035) were associated with mMDSC proportion in PBMCs (mMDSC proportion [%] = 0.2929 − 0.2389 * PDGF-BB + 0.3582 * iNOS) (p < 0.005, r = 0.32). Measuring the plasma concentrations of iNOS and PDGF-BB may be useful in predicting the proportion of mMDSCs in CRC patients’ peripheral blood. Further research is required to establish and validate these predictive factors.

Data registration

Patient data were registered in an anonymization system at Tsukuba Clinical Research & Development Organization (T-CReDO).

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.

Clinical significance of peripheral blood CD11b+/CD33+/HLA-DR- myeloid cells in infants and children with infectious diseases and increased CRP

Background: At early ages, recurrent or persistent infections are associated with increased serum C-reactive protein (CRP). Inflammatory mediators release inhibitory cells named myeloid-derived suppressor cell (MDSC) into circulating and tumor tissues. In the present study, we assayed the percentage and count of whole blood CD11b+/CD33+/HLA-DR- MDSCs or myeloid cells at early ages with infectious diseases and increased CRP. Methods: In this study, the clinical significance of CD11b+/CD33+/HLA-DR- MDSCs or myeloid cells was evaluated in whole blood samples from 40 patients with infectious disease and 20 healthy controls by flow cytometry analysis. Subsequently, the Pearson correlation between the percentage and absolute count of MDSCs with clinical parameters were obtained by SPSS analysis. A p value of < 0.05 was considered statistically significant. Results: We found a significantly higher level of MDSCs in infants and children with infectious diseases and increased CRP as compared to healthy controls (P=0.003). However, the results of analysis showed no correlation between MDSC percentage and count with grouped age and sex in patient groups. Conclusion: Our findings showed a significant correlation between the high level of serum CRP and peripheral blood CD11b+/CD33+/HLA-DR- MDSCs at early ages. This study could be a roadmap for future studies to use increased CRP as a potential prognostic biomarker to target MDSCs in children with recurrent or persistent infections.

Myeloid Cells in Circulation and Tumor Microenvironment of Colorectal Cancer Patients with Early and Advanced Disease Stages

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of cells that have been implicated in the development of an immunosuppressive environment, which promotes tumorigenesis and tumor progression. Numerous studies have reported expansion of MDSCs in circulation and the tumor microenvironment (TME) of cancer patients. However, due to the heterogenic nature of MDSCs and the different approaches for their identification, their detailed characterization and impact on disease progression in cancer patients are warranted. In this study, we investigated the levels of different myeloid cell subsets and antigen-presenting cells (APCs) using flow cytometry in unfractionated whole blood (WB), peripheral blood mononuclear cells (PBMCs), tumor tissue (TT), and adjacent normal tissue (NT) of colorectal cancer (CRC) patients. We found high levels of granulocytic myeloid cells (GMCs) in whole blood, but their levels were significantly lower in PBMCs. Importantly, we found significantly higher levels of GMCs in the TME compared to NT. In addition, monocytic myeloid cells (MMCs) showed significantly higher levels in PBMCs of CRC patients, compared to healthy donors (HDs). Notably, patients with advanced disease stages showed significantly higher levels of GMCs compared to early stages in whole blood, but PBMCs and tumor-infiltrating myeloid cells did not show any significant differences. Lastly, we found that levels of GMCs decreased, while IMCs increased in the TME with tumor budding. Our results highlight the importance of investigating the levels of different myeloid cell subsets in PBMCs versus whole blood of cancer patients and improve current knowledge on the potential prognostic significance of myeloid cells in CRC patients.

Nanoparticles decorated with granulocyte-colony stimulating factor for targeting myeloid cells

Dysregulated myeloid cell activity underlies a variety of pathologies, including immunosuppression in malignant cancers. Current treatments to alter myeloid cell behavior also alter other immune cell subpopulations and nonimmune cell types with deleterious side effects. Therefore, improved selectivity of myeloid treatment is an urgent need. To meet this need, we demonstrate a novel, targeted nanoparticle system that achieves superior myeloid selectivity both in vitro and in vivo. This system comprises: (1) granulocyte-colony stimulating factor (G-CSF) as a targeting ligand to promote accumulation in myeloid cells, including immunosuppressive myeloid-derived suppressor cells (MDSCs); (2) albumin nanoparticles 100-120 nm in diameter that maintain morphology and drug payload in simulated physiological conditions; and (3) a fluorophore that enables nanoparticle tracking and models a therapeutic molecule. Here, we show that this strategy achieves high myeloid uptake in mixed primary immune cells and that nanoparticles successfully infiltrate the 4T1 triple-negative breast tumor murine microenvironment, where they preferentially accumulate in myeloid cells in a mouse model. Further development will realize diagnostic myeloid cell tracking applications and therapeutic delivery of myeloid-reprogramming drugs.

Characterization of myeloid-derived suppressor cells and cytokines GM-CSF, IL-10 and MCP-1 in dogs with malignant melanoma receiving a GD3-based immunotherapy

Melanoma in humans and canines is an aggressive and highly metastatic cancer. The mucosal forms in both species share genetic and histopathologic features, making dogs a valuable spontaneous disease animal model. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells of myeloid origin with immunosuppressive capabilities, which are increased in many human cancers and contribute to tumor immune evasion. They are a possible target to improve immunotherapy outcomes. Current information regarding MDSCs in canines is minimal, limiting their use as translational model for the study of MDSCs. The objective of this study was to characterize major MDSCs subsets (monocytic and polymorphonuclear) and the cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 10 (IL-10) and monocyte chemoattractant protein-1 (MCP-1) in canines with malignant melanoma and to evaluate changes in MDSCs and the cytokines over time in response to a GD3-based active immunotherapy. Whole blood and serum collected from 30 healthy controls and 33 patients enrolled in the University of Florida melanoma vaccine trial were analyzed by flow cytometry with canine specific CD11b, MHCII and anti-human CD14 antibodies to assess ostensibly polymorphonuclear-MDSC (CD11b⁺ MHCII^- CD14^-) and monocytic-MDSC (CD11b⁺ MHCII^- CD14⁺) subsets. IL-10, MCP-1 and both MDSCs subsets were significantly elevated in melanoma dogs versus controls. Both MDSCs subsets decreased significantly following GD3-based immunotherapy administration but no significant changes in cytokines were seen over time. To our knowledge, this is the first report documenting increased monocytic-MDSCs in canine melanoma. This is consistent with human malignant melanoma data, supporting dogs as a valuable model for therapeutic intervention studies.

Human T cells modulate myeloid-derived suppressor cells through a TNF-α-mediated mechanism

Myeloid-derived suppressor cells (MDSC) represent an innate immune cell subset capable of suppressing T-cell responses in cancer and chronic inflammation. While the effect of MDSC on T cells has been defined thoroughly, the reciprocal impact of T cells on MDSC homeostasis remains poorly understood. Therefore, we comprehensively analyzed the effect of different T-cell subsets on the generation and survival of human MDSC. Using an in vitro MDSC generation assay, we demonstrate that unstimulated CD4⁺, but not CD8⁺ T cells, induce polymorphonuclear MDSC (PMN-MDSC) from CD33⁺ myeloid cells. This effect was dependent on direct cell-cell contact and required TNF-α signaling. Soluble TNF-α was dispensable for PMN-MDSC generation, suggesting that transmembrane TNF-α is involved in that trans-cellular process. Stimulated human CD3⁺ T cells delayed the apoptosis of PMN-MDSC, which was independent of TNF-α signaling or direct cell-cell contact, but was recapitulated by IL-2. Taken together, our study shows that human T cells modulate MDSC generation and survival through two distinct mechanisms and thereby fine-tune the homeostasis of human MDSC in a regulated manner.

Blood-based analyses of cancer: Circulating myeloid-derived suppressor cells - is a new era coming?

Progress in cancer treatment made by the beginning of the 21st century has shifted the paradigm from one-size-fits-all to tailor-made treatment. The popular vision, to study solid tumors through the relatively noninvasive sampling of blood, is one of the most thrilling and rapidly advancing fields in global cancer diagnostics. From this perspective, immune-cell analysis in cancer could play a pivotal role in oncology practice. This approach is driven both by rapid technological developments, including the analysis of circulating myeloid-derived suppressor cells (cMDSCs), and by the increasing application of (immune) therapies, the success or failure of which may depend on effective and timely measurements of relevant biomarkers. Although the implementation of these powerful noninvasive diagnostic capabilities in guiding precision cancer treatment is poised to change the ways in which we select and monitor cancer therapy, challenges remain. Here, we discuss the challenges associated with the analysis and clinical aspects of cMDSCs and assess whether the problems in implementing tumor-evolution monitoring as a global tool in personalized oncology can be overcome.

Concepts Collide: Genomic, Immune, and Microbial Influences on the Tumor Microenvironment and Response to Cancer Therapy

Cancer research has seen unprecedented advances over the past several years, with tremendous insights gained into mechanisms of response and resistance to cancer therapy. Central to this has been our understanding of crosstalk between the tumor and the microenvironment, with the recognition that complex interactions exist between tumor cells, stromal cells, overall host immunity, and the environment surrounding the host. This is perhaps best exemplified in cancer immunotherapy, where numerous studies across cancer types have illuminated our understanding of the genomic and immune factors that shape responses to therapy. In addition to their individual contributions, it is now clear that there is a complex interplay between genomic/epigenomic alterations and tumor immune responses that impact cellular plasticity and therapeutic responses. In addition to this, it is also now apparent that significant heterogeneity exists within tumors-both at the level of genomic mutations as well as tumor immune responses-thus contributing to heterogeneous clinical responses. Beyond the tumor microenvironment, overall host immunity plays a major role in mediating clinical responses. The gut microbiome plays a central role, with recent evidence revealing that the gut microbiome influences the overall immune set-point, through diverse effects on local and systemic inflammatory processes. Indeed, quantifiable differences in the gut microbiome have been associated with disease and treatment outcomes in patients and pre-clinical models, though precise mechanisms of microbiome-immune interactions are yet to be elucidated. Complexities are discussed herein, with a discussion of each of these variables as they relate to treatment response.

Therapeutic reduction of cell-mediated immunosuppression in mycosis fungoides and Sézary syndrome

Tumor progression is associated with progressive immunosuppression mediated in part by T regulatory cell(s) (Treg) and/or myeloid-derived suppressor cell(s) (MDSC). Development of strategies to reduce populations of immune cells with suppressive function in cancer patients may enable the induction or recovery of immunity against tumor cells, which may limit or reverse disease progression. With a goal of developing Treg and MDSC neutralizing strategies to treat mycosis fungoides (MF) and Sézary syndrome (SzS), we determined the association between disease stage and suppressor cell populations in patients with MF/SzS, including those responding to therapy. We found elevations in Treg populations, across Treg subtypes, in patients with SzS, and these Treg markedly suppressed proliferation of autologous CD4+CD25- responder T cells. Interestingly, while MDSC numbers were not increased in MF/SzS patients, MDSC from patients with stage IB and above produced significantly more reactive oxygen species than those from stage IA MF patients and control cohorts. Therapy with the CD25-targeting agent denileukin diftitox or IFN-α2b was associated with a reduction in Treg numbers or MDSC function, respectively. These studies identify potential mechanisms of action for these therapies and support the development of coordinated strategies targeting both Treg and MDSC activities in patients with MF/SzS.

Circulating CD14+ HLA-DR-/low myeloid-derived suppressor cells predicted early recurrence of hepatocellular carcinoma after surgery

AIM

Myeloid-derived suppressor cells (MDSCs) play an important role in tumor progression. The aim of the present study was to investigate the prognostic value of MDSCs for early recurrence of hepatocellular carcinoma (HCC) in patients undergoing curative resection.

METHODS

Myeloid-derived suppressor cells were measured by flow cytometry. The correlation between MDSCs and tumor recurrence was analyzed using a cohort of 183 patients who underwent curative resection between February 2014 and July 2015. Prognostic significance was further assessed using Kaplan-Meier survival estimates and log-rank tests.

RESULTS

In vivo, CD14⁺ HLA-DR^-/low MDSCs inhibit T cell proliferation and secretion. The frequency of CD14⁺ HLA-DR^-/low MDSCs was significantly higher in HCC patients (3.7 ± 5.3%, n = 183) than in chronic hepatitis patients (1.4 ± 0.6%, n = 25) and healthy controls (1.1 ± 0.5%, n = 50). High frequency of MDSCs was significantly correlated with recurrence (time to recurrence) (P < 0.001) and overall survival (P = 0.034). Patients with HCC in the high MDSC group were prone to more vascular invasion (P = 0.018) and high systemic immune-inflammation index (SII) (P = 0.009) than those in the low MDSC group. Scatter-plot analyses revealed a significant positive correlation between the SII level and the frequency of MDSCs (r = 0.188, P = 0.011). Patients with HCC with a high MDSC frequency and high SII level had significantly shorter time to recurrence (P < 0.001) and overall survival (P = 0.028) than those with a low MDSC frequency and low SII.

CONCLUSIONS

An increased frequency of MDSCs was correlated with early recurrence and predicted the prognosis of patients with HCC undergoing curative resection. The HCC patients with high frequency of MDSCs should be provided more advanced management and frequent monitoring.

Myeloid cells in circulation and tumor microenvironment of breast cancer patients

Pathological conditions including cancers lead to accumulation of a morphological mixture of highly immunosuppressive cells termed as myeloid-derived suppressor cells (MDSC). The lack of conclusive markers to identify human MDSC, due to their heterogeneous nature and close phenotypical and functional proximity with other cell subsets, made it challenging to identify these cells. Nevertheless, expansion of MDSC has been reported in periphery and tumor microenvironment of various cancers. The majority of studies on breast cancers were performed on murine models and hence limited literature is available on the relation of MDSC accumulation with clinical settings in breast cancer patients. The aim of this study was to investigate levels and phenotypes of myeloid cells in peripheral blood (n = 23) and tumor microenvironment of primary breast cancer patients (n = 7), compared with blood from healthy donors (n = 21) and paired non-tumor normal breast tissues from the same patients (n = 7). Using multicolor flow cytometric assays, we found that breast cancer patients had significantly higher levels of tumor-infiltrating myeloid cells, which comprised of granulocytes (P = 0.022) and immature cells that lack the expression of markers for fully differentiated monocytes or granulocytes (P = 0.016). Importantly, this expansion was not reflected in the peripheral blood. The immunosuppressive potential of these cells was confirmed by expression of Arginase 1 (ARG1), which is pivotal for T-cell suppression. These findings are important for developing therapeutic modalities to target mechanisms employed by immunosuppressive cells that generate an immune-permissive environment for the progression of cancer.

Increased Levels of Circulating and Tumor-Infiltrating Granulocytic Myeloid Cells in Colorectal Cancer Patients

Increased levels of myeloid cells, especially myeloid-derived suppressor cells (MDSCs), have been reported to correlate with bad prognosis and reduced survival in cancer patients. However, limited data are available on their conclusive phenotypes and their correlation with clinical settings. The aim of this study was to investigate levels and phenotype of myeloid cells in peripheral blood and tumor microenvironment (TME) of colorectal cancer (CRC) patients, compared to blood from healthy donors (HDs) and paired, adjacent non-tumor colon tissue. Flow cytometric analysis was performed to examine the expression of different myeloid markers in fresh peripheral blood samples from CRC patients and HDs, and tissue-infiltrating immune cells from CRC patients. We found significantly higher levels of cells expressing myeloid markers and lacking the expression of major histocompatibility complex class II molecule HLA-DR in blood and tumor of CRC patients. Further analysis revealed that these cells were granulocytic and expressed Arginase 1 indicative of their suppressive phenotype. These expanded cells could be neutrophils or granulocytic MDSCs, and we refer to them as granulocytic myeloid cells (GMCs) due to the phenotypical and functional overlap between these cell subsets. Interestingly, the expansion of peripheral GMCs correlated with higher stage and histological grade of cancer, thereby suggesting their role in cancer progression. Furthermore, an increase in CD33+CD11b+HLA-DR-CD14-CD15- immature myeloid cells was also observed in CRC tumor tissue. Our work shows that GMCs are expanded in circulation and TME of CRC patients, which provides further insights for developing immunotherapeutic approaches targeting these cell subsets to enhance antitumor immune and clinical responses.