Increased circulating myeloid-derived suppressor cells correlate with clinical cancer stage, metastatic tumor burden, and doxorubicin-cyclophosphamide chemotherapy

The Functional Crosstalk between Myeloid-Derived Suppressor Cells and Regulatory T Cells within the Immunosuppressive Tumor Microenvironment

Simple Summary

Immunotherapy improved the therapeutic landscape for patients with advanced cancer diseases. However, many patients do not benefit from immunotherapy. The bidirectional crosstalk between myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) contributes to immune evasion, limiting the success of immunotherapy by checkpoint inhibitors. This review aims to outline the current knowledge of the role and the immunosuppressive properties of MDSC and Treg within the tumor microenvironment (TME). Furthermore, we will discuss the importance of the functional crosstalk between MDSC and Treg for immunosuppression, issuing particularly the role of cell adhesion molecules. Lastly, we will depict the impact of this interaction for cancer research and discuss several strategies aimed to target these pathways for tumor therapy.

Abstract

Immune checkpoint inhibitors (ICI) have led to profound and durable tumor regression in some patients with metastatic cancer diseases. However, many patients still do not derive benefit from immunotherapy. Here, the accumulation of immunosuppressive cell populations within the tumor microenvironment (TME), such as myeloid-derived suppressor cells (MDSC), tumor-associated macrophages (TAM), and regulatory T cells (Treg), contributes to the development of immune resistance. MDSC and Treg expand systematically in tumor patients and inhibit T cell activation and T effector cell function. Numerous studies have shown that the immunosuppressive mechanisms exerted by those inhibitory cell populations comprise soluble immunomodulatory mediators and receptor interactions. The latter are also required for the crosstalk of MDSC and Treg, raising questions about the relevance of cell–cell contacts for the establishment of their inhibitory properties. This review aims to outline the current knowledge on the crosstalk between these two cell populations, issuing particularly the potential role of cell adhesion molecules. In this regard, we further discuss the relevance of β2 integrins, which are essential for the differentiation and function of leukocytes as well as for MDSC–Treg interaction. Lastly, we aim to describe the impact of such bidirectional crosstalk for basic and applied cancer research and discuss how the targeting of these pathways might pave the way for future approaches in immunotherapy.

Role of myeloid-derived suppressor cells in metastasis

The spread of primary tumor cells to distant organs, termed metastasis, is the principal cause of cancer mortality and is a critical therapeutic target in oncology. Thus, a better understanding of metastatic progression is critical for improved therapeutic approaches requiring insight into the timing of tumor cell dissemination and seeding of distant organs, which can lead to the formation of occult lesions. However, due to limitations in imaging techniques, primary tumors can only be detected when they reach a relatively large size (e.g., > 1 cm³), which, based on our understanding of tumor evolution, is 10 to 20 years (30 doubling times) following tumor initiation. Recent insights into the timing of metastasis are based on the genomic profiling of paired primary tumors and metastases, suggesting that tumor cell seeding of secondary sites occurs early during tumor progression and years prior to diagnosis. Following seeding, tumor cells may remain in a dormant state as single cells or micrometastases before emerging as overt lesions. This timeline and the role of metastatic dormancy are regulated by interactions between the tumor, its microenvironment, and tumor-specific T cell responses. An improved understanding of the mechanisms and interactions responsible for immune evasion and tumor cell release from dormancy would support the development of novel targeted therapeutics. We posit herein that the immunosuppressive mechanisms mediated by myeloid-derived suppressor cells (MDSCs) are a major contributor to tumor progression, and that these mechanisms promote tumor cell escape from dormancy. Thus, while extensive studies have demonstrated a role for MDSCs in the escape from adoptive and innate immune responses (T-, natural killer (NK)-, and B cell responses), facilitating tumor progression and metastasis, few studies have considered their role in dormancy. In this review, we discuss the role of MDSC expansion, driven by tumor burden, and its role in escape from dormancy, resulting in occult metastases, and the potential for MDSC inhibition as an approach to prolong the survival of patients with advanced malignancies.

Immune suppression in gliomas

INTRODUCTION

The overall survival in patients with gliomas has not significantly increased in the modern era, despite advances such as immunotherapy. This is in part due to their notorious ability to suppress local and systemic immune responses, severely restricting treatment efficacy.

METHODS

We have reviewed the preclinical and clinical evidence for immunosuppression seen throughout the disease process in gliomas. This review aims to discuss the various ways that brain tumors, and gliomas in particular, co-opt the body's immune system to evade detection and ensure tumor survival and proliferation.

RESULTS

A multitude of mechanisms are discussed by which neoplastic cells evade detection and destruction by the immune system. These include tumor-induced T-cell and NK cell dysfunction, regulatory T-cell and myeloid-derived suppressor cell expansion, M2 phenotypic transformation in glioma-associated macrophages/microglia, upregulation of immunosuppressive glioma cell surface factors and cytokines, tumor microenvironment hypoxia, and iatrogenic sequelae of immunosuppressive treatments.

CONCLUSIONS

Gliomas create a profoundly immunosuppressive environment, both locally within the tumor and systemically. Future research should aim to address these immunosuppressive mechanisms in the effort to generate treatment options with meaningful survival benefits for this patient population.

Anti-pulmonary metastases from cervical cancer responses induced by a human papillomavirus peptide vaccine adjuvanted with CpG-oligodeoxynucleotides in vivo

Metastasis, particularly hematogenous metastasis, is associated with poor prognosis in patients with cervical cancer. The lungs are the most common site for hematogenous metastasis of cervical cancer. The currently available therapeutic modalities, including surgery, radiotherapy, or chemotherapy do not provide satisfactory clinical outcome for patients with pulmonary metastases. Therefore, it is necessary to investigate an alternative efficacious treatment modality. Therapeutic vaccines may evoke tumor-specific immune responses in patients to attack tumor cells, representing an attractive treatment option for controlling metastatic tumors. Our previous study demonstrated that a single administration of a human papillomavirus 16 E7 peptide vaccine, adjuvanted with unmethylated CpG-oligodeoxynucleotides, induced the clearance of subcutaneous xenograft cervical cancer. In this study, we investigated the anti-metastases responses induced by this vaccine using a murine model of pulmonary metastases from cervical cancer. The results showed that subcutaneous administration of the vaccine inhibited the growth of pulmonary metastases, which may be attributed to the increased infiltration of CD4 + and CD8 + T cells, and decreased number of immunosuppressive cells (including myeloid-derived suppressive cells and tumor-associated macrophages) in the lungs. Meanwhile, the alteration in a panel of cytokines, chemokines, and matrix metalloproteinases induced by the vaccination may contribute to the re-modulation of the local suppressive environment and inhibition of pulmonary metastases. To the best of our knowledge, this is the first report on the efficacy of the vaccine formula against murine pulmonary metastases from cervical cancer.

Myeloid-derived suppressor cells and regulatory T cells share common immunoregulatory pathways-related microRNAs that are dysregulated by acute lymphoblastic leukemia and chemotherapy

BACKGROUND

Relapse remains a critical challenge in children with acute lymphoblastic leukemia (ALL). The emergence of immunoregulatory cells, including myeloid-derived suppressor cells (MDSCs), and T regulatory (T_reg) cells, has been considered one potential mechanism of relapse in children with ALL.

AIM

This study aimed to address the microRNAs (miRNAs) related to MDSCs and T_reg cells and to explore their targeted immunoregulatory pathways.

METHODS

Affymetrix microarray was used for global miRNA profiling in B-ALL pediatric patients before, during, and after induction of chemotherapy. Bioinformatics analysis was performed on MDSCs and T_reg cells-related dysregulated miRNAs, and miR-Pathway analysis was performed to explore their targeted immunoregulatory pathways.

RESULTS

516 miRNAs were dysregulated in ALL patients as compared to the healthy donor. Among them, 13 miRNAs and 8 miRNAs related to MDSCs and T_reg cells, respectively, were common in all patients. Besides, 12 miRNAs were shared between MDSCs and T_reg cells; 4 of them were common in all patients. Four immune-related pathways; TNF, TGF-β, FoxO, and Hippo were found implicated.

CONCLUSION

Our pilot study concluded certain miRNAs related to MDSCs and T_reg cells, these miRNAs were linked to immunoregulatory pathways. Our results open avenues for testing those miRNA as molecular biomarkers for the immunosuppressive tumor microenvironment.

Nod1 promotes colorectal carcinogenesis by regulating the immunosuppressive functions of tumor-infiltrating myeloid cells

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 demonstrate the immunosuppressive potential of Nod1, the bacterial sensor of diaminopimelic acid (DAP)-containing MPs. Using a model of self-limiting peritonitis, we show that systemic Nod1 activation promotes an autophagy-dependent reprogramming of macrophages toward an alternative phenotype. Moreover, Nod1 stimulation induces the expansion of myeloid-derived suppressor cells (MDSCs) and maintains their immunosuppressive potential via arginase-1 activity. Supporting the role of MDSCs and tumor-associated macrophages in cancer, we demonstrate that myeloid-intrinsic Nod1 expression sustains 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 activity of myeloid cells and fuel tumor progression in CRC.

In Vitro Generation of Human Neutrophilic Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of cells of myeloid origin. MDSC are functionally defined by their capacity to suppress T, NK, and B cell responses and henceforth altering the disease outcome in various pathological conditions. MDSC are further subdivided into three distinct subsets: monocytic (M-) MDSC, neutrophilic or polymorphonuclear (PMN-) MDSC, and early-stage (e-) MDSC. However, since surface markers utilized to define MDSC are expressed on other myeloid cells too, it is mandatory to functionally assess the suppressive activity for characterizing these cells. Here, we provide a protocol for generation of PMN-MDSC in vitro from freshly isolated human peripheral blood mononuclear cells. These MDSC can be used further to perform functional assays to determine their immunosuppressive potential or test their activities in various biological conditions, for instance in infection and cancer.

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).

Reactive myelopoiesis and the onset of myeloid-mediated immune suppression: Implications for adoptive cell therapy

Adoptive T cell therapy (ACT) in combination with lymphodepleting chemotherapy is an effective strategy to induce the eradication of cancer, providing long-term regressions in patients. However, only a minority of patients that receive ACT with tumor-specific T cells exhibit durable benefit. Thus, there is an urgent need to characterize mechanisms of resistance and define strategies to alleviate immunosuppression in the context of ACT in cancer. This article reviews the importance of lymphodepleting regimens in promoting the optimal engraftment and expansion of T cells in hosts after adoptive transfer. In addition, we discuss the role of concomitant immunosuppression and the accumulation of myeloid derived suppressor cells (MDSCs) during immune recovery after lymphodepleting regimens and mobilization regimens.

Dual roles of myeloid-derived suppressor cells induced by Toll-like receptor signaling in cancer

Myeloid-derived suppressor cells (MDSCs) are one of the major components of the tumor microenvironment (TME), and are the main mediators of tumor-induced immunosuppression. Recent studies have reported that the survival, differentiation and immunosuppressive activity of MDSCs are affected by the Toll-like receptor (TLR) signaling pathway. However, the regulatory effect of TLR signaling on MDSCs remains controversial. TLR-induced MDSC can acquire different immunosuppressive activities to influence the immune response that can be either beneficial or detrimental to cancer immunotherapy. The present review summarizes the effects of TLR signals on the number, phenotype and inhibitory activity of MDSCs, and their role in cancer immunotherapy, which cannot be ignored if effective cancer immunotherapies are to be developed for the immunosuppression of the TME.

Strategies to Improve Chimeric Antigen Receptor Therapies for Neuroblastoma

Chimeric antigen receptors (CARs) are among the curative immunotherapeutic approaches that exploit the antigen specificity and cytotoxicity function of potent immune cells against cancers. Neuroblastomas, the most common extracranial pediatric solid tumors with diverse characteristics, could be a promising candidate for using CAR therapies. Several methods harness CAR-modified cells in neuroblastoma to increase therapeutic efficiency, although the assessment has been less successful. Regarding the improvement of CARs, various trials have been launched to overcome insufficient capacity. However, the reasons behind the inadequate response against neuroblastoma of CAR-modified cells are still not well understood. It is essential to update the present state of comprehension of CARs to improve the efficiency of CAR therapies. This review summarizes the crucial features of CARs and their design for neuroblastoma, discusses challenges that impact the outcomes of the immunotherapeutic competence, and focuses on devising strategies currently being investigated to improve the efficacy of CARs for neuroblastoma immunotherapy.

Defining the emergence of myeloid-derived suppressor cells in breast cancer using single-cell transcriptomics

Myeloid-derived suppressor cells (MDSCs) are innate immune cells that acquire the capacity to suppress adaptive immune responses during cancer. It remains elusive how MDSCs differ from their normal myeloid counterparts, which limits our ability to specifically detect and therapeutically target MDSCs during cancer. Here, we sought to determine the molecular features of breast cancer-associated MDSCs using the widely studied mouse model based on the mouse mammary tumor virus (MMTV) promoter-driven expression of the polyomavirus middle T oncoprotein (MMTV-PyMT). To identify MDSCs in an unbiased manner, we used single-cell RNA sequencing to compare MDSC-containing splenic myeloid cells from breast tumor-bearing mice with wild-type controls. Our computational analysis of 14,646 single-cell transcriptomes revealed that MDSCs emerge through an aberrant neutrophil maturation trajectory in the spleen that confers them an immunosuppressive cell state. We establish the MDSC-specific gene signature and identify CD84 as a surface marker for improved detection and enrichment of MDSCs in breast cancers.

Blood Myeloid-Derived Suppressor Cells Correlate with Neutrophil-to-Lymphocyte Ratio and Overall Survival in Metastatic Urothelial Carcinoma

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) were linked to pathologic stage in bladder urothelial carcinoma (UC). Neutrophil lymphocyte ratio (NLR) is an inflammatory biomarker with a prognostic role in metastatic (m)UC.

OBJECTIVE

We hypothesized that MDSC levels correlate with NLR and overall survival (OS) in mUC.

PATIENTS AND METHODS

MDSCs were measured in blood samples from patients with mUC in fresh unfractionated whole blood (WB) and peripheral blood mononuclear cells (PBMC) by flow cytometry and defined as LinloCD33+/HLADR- (Total MDSC). MDSC subsets were defined as polymorphonuclear (PMN-MDSC: CD15+/CD14-), monocytic (M-MDSC: CD15-/CD14+), and uncommitted (UNC-MDSC: CD15-/CD14-). MDSC populations were presented as a percentage of live nucleated blood cells. Spearman's rank correlation assessed correlations between MDSC and NLR. Kaplan-Meier curves and log-rank test estimated OS from the time of MDSC collection to last follow-up or date of death.

RESULTS

Of the 76 patients, 78% were men and 43% were never smokers with a median age of 69 years (range 31-83); 72% had pure UC and 76% had lower tract UC. Prior therapies included intravesical therapy (22%), neoadjuvant chemotherapy (30%), cystectomy or nephroureterectomy (55%). Median follow-up for all patients was 12 months (0.6-36.5). PMN-MDSC was the predominant subset in WB and PBMC. There was significant correlation between individual MDSC subsets in WB and PBMC (p ≤ 0.001). Both WB UNC-MDSC/PMN-MDSC ratios (rho = - 0.27, p = 0.03) and PBMC UNC-MDSC/PMN-MDSC (rho = - 0.28, p = 0.02) were negatively correlated with NLR. Median OS was 17.7 months (95% CI: 11.0-NE). Overall 1-year and 3-year survival rates were 0.60 (95% CI 0.49-0.73) and 0.15 (95% CI 0.03-0.67), respectively. Higher WB UNC-MDSC levels (HR 3.78, p = 0.0022) and higher NLR (HR 2.6, p = 0.0179) were associated with shorter OS.

CONCLUSIONS

Specific MDSC subsets correlate with NLR. Higher WB UNC-MDSC levels and higher NLR were negative prognostic factors. Given the feasibility of serial blood draws, dynamic assessment of MDSC over time and further validation with longer follow-up are warranted.

The importance of advanced cytometry in defining new immune cell types and functions relevant for the immunopathogenesis of HIV infection

: In the last years, novel, exciting immunological findings of interest for HIV research and treatment were identified thanks to different cytometric approaches. The analysis of the phenotypes and functionality of cells belonging to the immune system could clarify their role in the immunopathogenesis of HIV infection, and to elaborate key concepts, relevant in the treatment of this disease. Important discoveries have been made concerning cells that are important for protective immunity like lymphocytes that display polyfunctionality, resident memory T cells, innate lymphoid cells, to mention a few. The complex phenotype of myeloid-derived suppressor cells has been investigated, and relevant changes have been reported during chronic and primary HIV infection, in correlation with changes in CD4 T-cell number, T-cell activation, and with advanced disease stage. The search for markers of HIV persistence present in latently infected cells, namely those molecules that are important for a functional or sterilizing cure, evidenced the role of follicular helper T cells, and opened a discussion on the meaning and use of different surface molecules not only in identifying such cells, but also in designing new strategies. Finally, advanced technologies based upon the simultaneous detection of HIV-RNA and proteins at the single cell level, as well as those based upon spectral cytometry or mass cytometry are now finding new actors and depicting a new scenario in the immunopathogenesis of the infection, that will allow to better design innovative therapies based upon novel drugs and vaccines.

NOX2-Derived Reactive Oxygen Species in Cancer

The formation of reactive oxygen species (ROS) by the myeloid cell NADPH oxidase NOX2 is critical for the destruction of engulfed microorganisms. However, recent studies imply that ROS, formed by NOX2⁺ myeloid cells in the malignant microenvironment, exert multiple actions of relevance to the growth and spread of neoplastic cells. By generating ROS, tumor-infiltrating myeloid cells and NOX2⁺ leukemic myeloid cells may thus (i) compromise the function and viability of adjacent cytotoxic lymphocytes, including natural killer (NK) cells and T cells, (ii) oxidize DNA to trigger cancer-promoting somatic mutations, and (iii) affect the redox balance in cancer cells to control their proliferation and survival. Here, we discuss the impact of NOX2-derived ROS for tumorigenesis, tumor progression, regulation of antitumor immunity, and metastasis. We propose that NOX2 may be a targetable immune checkpoint in cancer.

IGFLR1 as a Novel Prognostic Biomarker in Clear Cell Renal Cell Cancer Correlating With Immune Infiltrates

Objective

Insulin Growth Factor-Like receptor 1 (IGFLR1) reflects progressive disease and confers a poor prognosis in clear cell renal cell cancer (ccRCC). However, extensive studies highlighting the mechanisms involved in how IGFLR1 triggers the progression of ccRCC remain lacking.

Methods

In the present study, the expression level of IGFLR1 mRNA and correlation between IGFLR1 expression and prognosis of ccRCC were analyzed based on The Cancer Genome Atlas (TCGA) ccRCC cohort. Further, we analyzed methylation and copy number variation to try to explain the difference in IGFLR1 expression. Subsequently, we investigated the correlation between IGFLR1 and tumor-infiltrating immune cells with the aid of TIMER (Tumor Immune Estimation Resource). The potential candidates' genes associated with IGFLR1 were screened by variation analysis, which were used for further enrichment analysis of signaling pathways and immune gene sets to infer the certain function and corresponding mechanisms in which IGFLR1 was involved in ccRCC. Finally, we establish prognostic risk models using multivariate Cox regression analysis and analyzed the possible involvement of IGFLR1 in chemotherapeutic drug resistance.

Results

The results showed that upregulated IGFLR1 was detected in ccRCC compared with para-cancer tissues and significantly affected the prognosis of ccRCC (overall survival: Logrank p < 0.0001; disease free survival: Logrank p = 0.022). Univariate and multivariate analyses indicated that IGFLR1 was an independent prognostic factor for ccRCC (HR = 2.064, p = 0.006) and the risk prognostic model based on age, M, level of platelet and calcium and IGFLR1 expression had satisfying predictive ability. The correlation analysis showed that the expression level of IGFLR1 was positively correlated with the abundance of myeloid derived suppressor cell and their marker genes in ccRCC significantly. IGFLR1 may be related to the regulatory activation, intercellular adhesion of lymphocytes and drug resistance in cancer.

Conclusion

These findings suggested that IGFLR1 was significantly associated with the prognosis in a variety of cancers, particularly ccRCC. IGFLR1 may play an important role in tumor related immune infiltration and showed potential diagnostic, therapeutic and prognostic value in ccRCC.

Polymorphonuclear-MDSCs Facilitate Tumor Regrowth After Radiation by Suppressing CD8+ T Cells

PURPOSE

Radiation therapy (RT) is widely used in the treatment of cancer. Unfortunately, RT alone is insufficient to control the disease in most cases, as regrowth after irradiation still occur. Thus, it would be meaningful to explore the underlying mechanism of tumor regrowth after irradiation. Myeloid-derived suppressor cells (MDSCs) contribute to the immunosuppressive tumor microenvironment and hinder the therapeutic efficacy of RT. However, it is unclear whether MDSCs-mediated immune suppression contributes to local relapse after irradiation. In this article, we tried to figure out how MDSCs sabotage the therapeutic effect of RT, and tried to determine the potential synergistic effect of combination between targeting MDSCs and RT.

METHODS AND MATERIALS

A syngeneic murine model of Lewis lung cancer was used. The abundance of tumor infiltrating MDSCs and tumor growth after irradiation was assessed. The percentage and functional state of CD8⁺ T cells were measured by flow cytometry, with or without polymorphonuclear (PMN)-MDSCs depletion. Arginase 1 (ARG1) expression and activity of MDSCs were examined by hematoxylin and eosin staining and flow cytometry. ARG1 inhibitor and phosphodiesterase 5 inhibitor sildenafil were administered after RT to figure out the underlying mechanism of MDSCs-mediated immunosuppression.

RESULTS

We demonstrated that irradiation recruited MDSCs, especially the polymorphonuclear subset, into the tumor microenvironment. PMN-MDSCs inhibited the CD8⁺ T cell response by elevating ARG1 expression. Selective depletion of PMN-MDSCs or inhibition on ARG1 promoted the infiltration and activation of intratumoral CD8⁺ T cells, and delayed tumor regrowth after irradiation. We showed that sildenafil reduced the accumulation and ARG1 expression of PMN-MDSCs after irradiation, thus abrogating the MDSCs-mediated immunosuppression.

CONCLUSIONS

Our results have suggested that PMN-MDSCs participate in the irradiation-induced immune suppression through ARG1 activation. We have also found that sildenafil has the potential to facilitate antitumor immunity, which provides a new alternative to delay tumor recurrence after RT.

Osteopontin: A Key Regulator of Tumor Progression and Immunomodulation

Simple Summary

Anti-PD-1/PD-L1 and anti-CTLA-4-based immune checkpoint blockade (ICB) immunotherapy have recently emerged as a breakthrough in human cancer treatment. Durable efficacy has been achieved in many types of human cancers. However, not all human cancers respond to current ICB immunotherapy and only a fraction of the responsive cancers exhibit efficacy. Osteopontin (OPN) expression is highly elevated in human cancers and functions as a tumor promoter. Emerging data suggest that OPN may also regulate immune cell function in the tumor microenvironment. This review aims at OPN function in human cancer progression and new findings of OPN as a new immune checkpoint. We propose that OPN compensates PD-L1 function to promote tumor immune evasion, which may underlie human cancer non-response to current ICB immunotherapy.

Abstract

OPN is a multifunctional phosphoglycoprotein expressed in a wide range of cells, including osteoclasts, osteoblasts, neurons, epithelial cells, T, B, NK, NK T, myeloid, and innate lymphoid cells. OPN plays an important role in diverse biological processes and is implicated in multiple diseases such as cardiovascular, diabetes, kidney, proinflammatory, fibrosis, nephrolithiasis, wound healing, and cancer. In cancer patients, overexpressed OPN is often detected in the tumor microenvironment and elevated serum OPN level is correlated with poor prognosis. Initially identified in activated T cells and termed as early T cell activation gene, OPN links innate cells to adaptive cells in immune response to infection and cancer. Recent single cell RNA sequencing revealed that OPN is primarily expressed in tumor cells and tumor-infiltrating myeloid cells in human cancer patients. Emerging experimental data reveal a key role of OPN is tumor immune evasion through regulating macrophage polarization, recruitment, and inhibition of T cell activation in the tumor microenvironment. Therefore, in addition to its well-established direct tumor cell promotion function, OPN also acts as an immune checkpoint to negatively regulate T cell activation. The OPN protein level is highly elevated in peripheral blood of human cancer patients. OPN blockade immunotherapy with OPN neutralization monoclonal antibodies (mAbs) thus represents an attractive approach in human cancer immunotherapy.

Role of Myeloid-Derived Suppressor Cells in High-Dose-Irradiated TRAMP-C1 Tumors: A Therapeutic Target and an Index for Assessing Tumor Microenvironment

PURPOSE

To investigate the temporal and spatial infiltration of TRAMP-C1 tumors by myeloid-derived suppressor cells (MDSCs) after high-dose radiation therapy (RT), and to explore their effect on tumor growth.

METHODS AND MATERIALS

TRAMP-C1 intramuscularly tumors were irradiated with a single dose of 8 Gy or 25 Gy. The dynamics of infiltrated MDSCs and their intratumoral spatial distribution were assessed by immunohistochemistry and flow cytometry. Cytokine levels in the blood and tumor were analyzed by multiplex immunoassay. Mice were injected with anti-Gr-1 antibody to determine whether MDSCs affect tumor growth after RT.

RESULTS

CD11b⁺Gr-1⁺ MDSCs infiltrated TRAMP-C1 tumors irradiated with 25 Gy, but not 8 Gy, within 4 hours and recruitment persisted for at least 2 weeks. Both CD11b⁺Ly6G⁺Ly6C⁺ polymorphonuclear-MDSCs (PMN-MDSCs) and CD11b⁺Ly6G^-Ly6C^hi monocytic-MDSCs (M-MDSCs) were involved. Tumor RT also increased the representation of both MDSC subpopulations in the spleen and peripheral blood. Levels of multiple cytokines were increased in the tumors at 2 weeks, including GM-CSF, G-CSF, CCL-3, CCL-5, CXCL-5, IL-6, IL-17α, and VEGF-a; while G-CSF, IL-6, and TNF-α levels increased in the blood. PMN-MDSCs aggregated in the central necrotic region of the irradiated tumors over time, where they were associated with avascular hypoxia (CD31^-PIMO⁺). MDSCs expressed the proangiogenic factor, matrix metalloproteinase-9, and, within the necrotic area, high levels of arginase-1 and indoleamine 2,3-dioxygenase. Depletion of PMN-MDSCs by Gr-1 antibody increased the efficacy of high-dose RT.

CONCLUSIONS

PMN-MDSCs infiltrate TRAMP-C1 tumors after high-dose RT. Their spatial distribution suggests they are involved in the evolution of an intratumoral state of necrosis associated with avascular hypoxia, and their phenotype is consistent with them being immunosuppressive. They appear to promote tumor growth after RT, making them a prime therapeutic target for therapeutic intervention. Assessment of MDSCs and cytokine levels in blood could be an index of the need for such an intervention.

Targeted Deletion of CXCR2 in Myeloid Cells Alters the Tumor Immune Environment to Improve Antitumor Immunity

Recruitment of myeloid-derived suppressor cells (MDSC) into the tumor microenvironment (TME) contributes to cancer immune evasion. MDSCs express the chemokine receptor CXCR2, and inhibiting CXCR2 suppresses the recruitment of MDSCs into the tumor and the premetastatic niche. Here, we compared the growth and metastasis of melanoma and breast cancer xenografts in mice exhibiting or not exhibiting targeted deletion of Cxcr2 in myeloid cells (CXCR2^myeΔ/Δ vs. CXCR2^myeWT). Detailed analysis of leukocyte populations in peripheral blood and in tumors from CXCR2^myeΔ/Δ mice revealed that loss of CXCR2 signaling in myeloid cells resulted in reduced intratumoral MDSCs and increased intratumoral CXCL11. The increase in intratumoral CXCL11 was derived in part from tumor-infiltrating B1b cells. The reduction in intratumoral MDSCs coupled with an increase in intratumoral B1b cells expressing CXCL11 resulted in enhanced infiltration and activation of effector CD8⁺ T cells in the TME of CXCR2^myeΔ/Δ mice, accompanied by inhibition of tumor growth in CXCR2^myeΔ/Δ mice compared with CXCR2^myeWT littermates. Treatment of tumor-bearing mice with a CXCR2 antagonist (SX-682) also inhibited tumor growth, reduced intratumoral MDSCs, and increased intratumoral B1b cells expressing CXCL11, leading to an increase in activated CD8⁺ T cells in the tumor. Depletion of B220⁺ cells or depletion of CD8⁺ T cells reversed the tumor-inhibitory properties in CXCR2^myeΔ/Δ mice. These data revealed a mechanism by which loss of CXCR2 signaling in myeloid cells modulates antitumor immunity through decreasing MDSCs and enriching CXCL11-producing B1b cells in the TME, which in turn increases CD8⁺ T-cell recruitment and activation in tumors.

HOX Genes Family and Cancer: A Novel Role for Homeobox B9 in the Resistance to Anti-Angiogenic Therapies

Simple Summary

The inhibition of angiogenesis, relying on the use of drugs targeting the VEGF signaling pathway, has become one of the main strategies for cancer treatment. However, the intrinsic and acquired resistance to this type of therapy limit its efficacy. Thus, the identification of novel therapeutic targets is urgently needed. The resistance to anti-angiogenic treatment often occurs through the activation of alternative VEGF independent signaling pathways and recruitment of bone marrow-derived pro-angiogenic cells in the tumor microenvironment. HOX genes are key regulators of embryonic development, also involved in angiogenesis and in cancer progression. HOXB9 upregulation occurs in many types of cancer and it has been identified as a critical transcription factor involved in tumour resistance to anti-angiogenic drugs. Indeed, HOXB9 modulates the expression of alternative pro-angiogenic secreted factors in the tumour microenvironment leading tumor escape from the anti-angiogenic treatments. Hence, HOXB9 could serves as a novel therapeutic target to overcome the resistance to anti-angiogenic therapies.

Abstract

Angiogenesis is one of the hallmarks of cancer, and the inhibition of pro-angiogenic factors and or their receptors has become a primary strategy for cancer therapy. However, despite promising results in preclinical studies, the majority of patients either do not respond to these treatments or, after an initial period of response, they develop resistance to anti-angiogenic agents. Thus, the identification of a novel therapeutic target is urgently needed. Multiple mechanisms of resistance to anti-angiogenic therapy have been identified, including the upregulation of alternative angiogenic pathways and the recruitment of pro-angiogenic myeloid cells in the tumor microenvironment. Homeobox containing (HOX) genes are master regulators of embryonic development playing a pivotal role during both embryonic vasculogenesis and pathological angiogenesis in adults. The importance of HOX genes during cancer progression has been reported in many studies. In this review we will give a brief description of the HOX genes and their involvement in angiogenesis and cancer, with particular emphasis on HOXB9 as a possible novel target for anti-angiogenic therapy. HOXB9 upregulation has been reported in many types of cancers and it has been identified as a critical transcription factor involved in resistance to anti-angiogenic drugs.

Reactive oxygen species in immune cells: A new antitumor target

Immune cells have the potential to control the growth of tumor. However, this effect could be offset by immunosuppression associated with an increased production of reactive oxygen species. Multiple studies indicate that the antitumor effect of immune cells is correlated with their antioxidant capacity. This review discusses the role of reactive oxygen species in the tumor microenvironment by describing their distinct effects on different immune cells, including myeloid-derived suppressor cells, regulatory T cells, tumor-associated macrophages, cytotoxic T lymphocytes, natural killer cells, and dendritic cells. In the end, we conclude with the prospect of treatment for cancer by targeting antioxidant defense in immune cells.

The immune contexture and Immunoscore in cancer prognosis and therapeutic efficacy

The international American Joint Committee on Cancer/Union for International Cancer Control (AJCC/UICC) tumour-node-metastasis (TNM) staging system provides the current guidelines for the classification of cancer. However, among patients within the same stage, the clinical outcome can be very different. More recently, a novel definition of cancer has emerged, implicating at all stages a complex and dynamic interaction between tumour cells and the immune system. This has enabled the definition of the immune contexture, representing the pre-existing immune parameters associated with patient survival. Even so, the role of distinct immune cell types in modulating cancer progression is increasingly emerging. An immune-based assay named the 'Immunoscore' was defined to quantify the in situ T cell infiltrate and was demonstrated to be superior to the AJCC/UICC TNM classification for patients with colorectal cancer. This Review provides a broad overview of the main immune parameters positively or negatively shaping cancer development, including the Immunoscore, and their prognostic and predictive value. The importance of the immune system in cancer control is demonstrated by the requirement for a pre-existing intratumour adaptive immune response for effective immunotherapies, such as checkpoint inhibitors. Finally, we discuss how the combination of multiple immune parameters, rather than individual ones, might increase prognostic and/or predictive power.

TGF-β Enhances the Anti-inflammatory Effect of Tumor- Infiltrating CD33+11b+HLA-DR Myeloid-Derived Suppressor Cells in Gastric Cancer: A Possible Relation to MicroRNA-494

BACKGROUND

Accumulation of myeloid-derived suppressor cells (MDSCs) constitutes a key mechanism of tumor immune evasion in gastric cancer (GC). Therefore, searching for more accurate prognostic factors affecting their immunosuppressive role has become a growing interest in cancer immunotherapy research. Increased expression of microRNA-494 was noticed in MDSCs from tumor-bearing mice, suggesting another new therapeutic objective for cancer treatment. It was also discovered that tumor-derived transforming growth factor beta (TGF-β) is responsible for the up-regulation of microRNA-494 in MDSCs. The purpose of this study was to address the effect of recombinant (rTGF-β) on the anti-inflammatory activity of MDSCs in GC and its possible association with micro-RNA-494 expression in tumor tissue.

METHODS

Freshly obtained GC tumor tissue samples and peripheral blood were used for isolation of CD33+11b+HLADR- MDSCs cells from 40 GC patients and 31 corresponding controls using flow cytometry. MDSCs were co-cultured with isolated autologous T cells to assess proliferation and cytokine production in the presence and absence of rTGF-β. Real-time PCR and Enzyme linked immunosorbent assay were used to evaluate tumor expression of miRNA-494 and TGF-β respectively.

RESULTS

Results showed that rTGF-β markedly increased the suppressive ability of tumor MDSCs on proliferation of autologous T cells and interferon gamma production. However, no inhibitory effect was observed for MDSCs from circulation. In addition, infiltration of MDSCs in tumors is associated with the prognosis of GC. MiRNA-494 was also extensively expressed in tumor samples with a significant correlation to MDSCs.

CONCLUSION

These results indicate that tumor-derived MDSCs but not circulatory MDSCs have an immunosuppressive effect on T cells, potentially involving TGF-β mediated stimulation.  Results also suggest a role for miRNA-494 in GC progression. Therefore, control of TGF-β and miRNA-494 may be used as a treatment strategy to downregulate the immunosuppressive effect of MDSCs.
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Combination of preoperative fibrinogen concentration and neutrophil-to-lymphocyte ratio for prediction of the prognosis of patients with resectable breast cancer

Previous studies have demonstrated that the combination of high preoperative fibrinogen levels and high neutrophil-to-lymphocyte ratio (NLR) is associated with poor outcomes in various types of cancer. The present study assessed the prognostic value of a scoring system based on the combination of fibrinogen concentration and neutrophil-to-lymphocyte ratio (F-NLR) in untreated patients with resectable breast cancer (BC). The present study retrospectively analyzed 906 patients who received surgery for resectable BC. Univariate and multivariate analyses were performed to explore the association between the F-NLR score and survival status. The cut-off values for fibrinogen and NLR determined via receiver operating characteristic curve analysis were 3.21 g/l and 2.20, respectively. On the basis of these cut-off values, the whole cohort was divided into three groups according to their F-NLR score: Score 2, fibrinogen ≥3.21 g/l and NLR ≥2.20; score 1, fibrinogen ≥3.21 g/l or NLR ≥2.20; and score 0, fibrinogen <3.21 g/l and NLR <2.20. The F-NLR score was significantly associated with age (≤50 years vs. >50 years; P<0.001), tumor size (≤2 cm vs. >2 cm; P=0.001), lymph node status (P=0.029), TNM stage (I vs. II vs. III; P=0.002) and lymphovascular invasion (P<0.001). The 5-year disease-free survival (DFS) rates in the patients with F-NLR scores of 0, 1 and 2 were 95.7, 87.5 and 74.0%, respectively (P<0.001), and the 5-year overall survival (OS) rates were 97.8, 90.9 and 79.9%, respectively (P<0.001). Furthermore, multivariate analysis demonstrated that the F-NLR score independently predicted DFS [hazard ratio (HR), 2.279; 95% CI, 1.758-2.954; P<0.001] and OS (HR, 2.414; 95% CI, 1.738-3.353; P<0.001). In conclusion, the preoperative F-NLR score was an independent prognostic indicator for untreated patients with resectable BC.

Clinical implications of neutrophil-to-lymphocyte ratio and MDSC kinetics in gastric cancer patients treated with ramucirumab plus paclitaxel

Objective

We aimed to investigate the prognostic value of neutrophil-to-lymphocyte ratio (NLR) and myeloid-derived suppressor cells (MDSCs) in gastric cancer patients treated with second-line ramucirumab plus paclitaxel.

Methods

A total of 116 patients with advanced or metastatic gastric cancer who receive ramucirumab plus paclitaxel were prospectively enrolled. Fresh blood samples were collected before and after treatment, and flow cytometry was performed to assess the proportions of monocytic (mMDSCs) and granulocytic MDSCs (gMDSCs).

Results

Median age was 58 years and 71 (61.2%) patients were male. A baseline NLR≥2.94 was associated with significantly poorer progression-free survival (PFS) and overall survival (OS) vs. an NLR<2.94 (P=0.011 and P=0.002, respectively). In multivariate analysis, an NLR≥2.94 was independently associated with poorer PFS [hazard ratio (HR)=1.58; 95% confidence interval (95% CI): 1.01-2.49, P=0.046] and OS (HR=1.77; 95% CI: 1.04-3.04, P=0.036). While mMDSC counts did not significantly change following two cycles of therapy (P=0.530), gMDSC counts decreased significantly after two treatment cycles (P=0.025) but tended to increase in patients with progressive disease after two treatment cycles (P=0.098). A progressive increase in gMDSC counts (≥44%) was associated with a significantly shorter PFS and OSvs. a gMDSC count increase <44% (P=0.001 and P=0.003, respectively).

Conclusions

The baseline NLR may help guide clinical decisions during ramucirumab plus paclitaxel therapy for gastric cancer. Our gMDSC kinetics data warrant further clinical validation and mechanistic investigation.

Inhibitory effect of ginsenoside Rg3 on cancer stemness and mesenchymal transition in breast cancer via regulation of myeloid-derived suppressor cells

Ginsenoside Rg3 (Rg3) has been studied in several cancer models and is suggested to act through various pharmacological effects. We investigated the anticancer properties of Rg3 through myeloid-derived suppressor cell (MDSC) modulation in FM3A mouse mammary carcinoma cells. The effects of Rg3 on MDSCs and consequent changes in cancer stem-like cells (CSCs) and epithelial-mesenchymal transition (EMT) were evaluated by diverse methods. MDSCs promoted cancer by enhancing breast cancer stemness and promoting EMT. Rg3 at a dose without obvious cytotoxicity downregulated MDSCs and repressed MDSC-induced cancer stemness and EMT. Mechanistic investigations suggested that these inhibitory effects of Rg3 on MDSCs and corresponding cancer progression depend upon suppression of the STAT3-dependent pathway, tumor-derived cytokines, and the NOTCH signaling pathway. In a mouse model, MDSCs accelerated tumor progression, and Rg3 delayed tumor growth, which is consistent with the results of in vitro experiments. These results indicated that Rg3 could effectively inhibit the progression of breast cancer. The anticancer effect of Rg3 might be partially due to its downregulation of MDSCs and consequent repression of cancer stemness and EMT in breast cancer. Hence, we suggest the regulation of MDSCs through Rg3 treatment as an effective therapeutic strategy for breast cancer patients.

Implications of metabolism-driven myeloid dysfunctions in cancer therapy

Immune homeostasis is maintained by an adequate balance of myeloid and lymphoid responses. In chronic inflammatory states, including cancer, this balance is lost due to dramatic expansion of myeloid progenitors that fail to mature to functional inflammatory neutrophils, macrophages, and dendritic cells (DCs), thus giving rise to a decline in the antitumor effector lymphoid response. Cancer-related inflammation orchestrates the production of hematopoietic growth factors and cytokines that perpetuate recruitment and activation of myeloid precursors, resulting in unresolved and chronic inflammation. This pathologic inflammation creates profound alterations in the intrinsic cellular metabolism of the myeloid progenitor pool, which is amplified by competition for essential nutrients and by hypoxia-induced metabolic rewiring at the tumor site. Therefore, persistent myelopoiesis and metabolic dysfunctions contribute to the development of cancer, as well as to the severity of a broad range of diseases, including metabolic syndrome and autoimmune and infectious diseases. The aims of this review are to (1) define the metabolic networks implicated in aberrant myelopoiesis observed in cancer patients, (2) discuss the mechanisms underlying these clinical manifestations and the impact of metabolic perturbations on clinical outcomes, and (3) explore new biomarkers and therapeutic strategies to restore immunometabolism and differentiation of myeloid cells towards an effector phenotype to increase host antitumor immunity. We propose that the profound metabolic alterations and associated transcriptional changes triggered by chronic and overactivated immune responses in myeloid cells represent critical factors influencing the balance between therapeutic efficacy and immune-related adverse effects (irAEs) for current therapeutic strategies, including immune checkpoint inhibitor (ICI) therapy.

The Immune Microenvironment in Pancreatic Cancer

The biology of solid tumors is strongly determined by the interactions of cancer cells with their surrounding microenvironment. In this regard, pancreatic cancer (pancreatic ductal adenocarcinoma, PDAC) represents a paradigmatic example for the multitude of possible tumor-stroma interactions. PDAC has proven particularly refractory to novel immunotherapies, which is a fact that is mediated by a unique assemblage of various immune cells creating a strongly immunosuppressive environment in which this cancer type thrives. In this review, we outline currently available knowledge on the cross-talk between tumor cells and the cellular immune microenvironment, highlighting the physiological and pathological cellular interactions, as well as the resulting therapeutic approaches derived thereof. Hopefully a better understanding of the complex tumor-stroma interactions will one day lead to a significant advancement in patient care.

A Perspective on Therapeutic Pan-Resistance in Metastatic Cancer

Metastatic spread represents the leading cause of disease-related mortality among cancer patients. Many cancer patients suffer from metastatic relapse years or even decades after radical surgery for the primary tumor. This clinical phenomenon is explained by the early dissemination of cancer cells followed by a long period of dormancy. Although dormancy could be viewed as a window of opportunity for therapeutic interventions, dormant disseminated cancer cells and micrometastases, as well as emergent outgrowing macrometastases, exhibit a generalized, innate resistance to chemotherapy and even immunotherapy. This therapeutic pan-resistance, on top of other adaptive responses to targeted agents such as acquired mutations and lineage plasticity, underpins the current difficulties in eradicating cancer. In the present review, we attempt to provide a framework to understand the underlying biology of this major issue.

The tumour immune landscape and its implications in cutaneous melanoma

The field of tumour immunology has rapidly advanced in the last decade, leading to the advent of effective immunotherapies for patients with advanced cancers. This highlights the critical role of the immune system in determining tumour development and outcome. The tumour immune microenvironment (TIME) is highly heterogeneous, and the interactions between tumours and the immune system are vastly complex. Studying immune cell function in the TIME will provide an improved understanding of the mechanisms underpinning these interactions. This review examines the role of immune cell populations in the TIME based on their phenotype, function and localisation, as well as contextualising their position in the dynamic relationship between tumours and the immune system. We discuss the function of immune cell populations, examine their impact on patient outcome and highlight gaps in current understanding of their roles in the TIME, both in cancers in general and specifically in melanoma. Studying the TIME by evaluating both pro-tumour and anti-tumour effects may elucidate the conditions which lead to tumour growth and metastasis or immune-mediated tumour regression. Moreover, an in-depth understanding of these conditions could contribute to improved prognostication, more effective use of current immunotherapies and guide the development of novel treatment strategies and therapies.

Microenvironmental Determinants of Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) belongs to the most lethal solid tumors in humans. A histological hallmark feature of PDAC is the pronounced tumor microenvironment (TME) that dynamically evolves during tumor progression. The TME consists of different non-neoplastic cells such as cancer-associated fibroblasts, immune cells, endothelial cells, and neurons. Furthermore, abundant extracellular matrix components such as collagen and hyaluronic acid as well as matricellular proteins create a highly dynamic and hypovascular TME with multiple biochemical and physical interactions among the various cellular and acellular components that promote tumor progression and therapeutic resistance. In recent years, intensive research efforts have resulted in a significantly improved understanding of the biology and pathophysiology of the TME in PDAC, and novel stroma-targeted approaches are emerging that may help to improve the devastating prognosis of PDAC patients. However, none of anti-stromal therapies has been approved in patients so far, and there is still a large discrepancy between multiple successful preclinical results and subsequent failure in clinical trials. Furthermore, recent findings suggest that parts of the TME may also possess tumor-restraining properties rendering tailored therapies even more challenging.

Mechanisms of immune suppression by myeloid-derived suppressor cells: the role of interleukin-10 as a key immunoregulatory cytokine

Chronic immune activation and inflammation are unwanted consequences of many pathological conditions, since they could lead to tissue damage and immune exhaustion, both of which can worsen the pathological condition status. In fact, the immune system is naturally equipped with immunoregulatory cells that can limit immune activation and inflammation. However, chronic activation of downregulatory immune responses is also associated with unwanted consequences that, in turn, could lead to disease progression as seen in the case of cancer and chronic infections. Myeloid-derived suppressor cells (MDSCs) are now considered to play a pivotal role in the pathogenesis of different inflammatory pathological conditions, including different types of cancer and chronic infections. As a potent immunosuppressor cell population, MDSCs can inhibit specific and non-specific immune responses via different mechanisms that, in turn, lead to disease persistence. One such mechanism by which MDSCs can activate their immunosuppressive effects is accomplished by secreting copious amounts of immunosuppressant molecules such as interleukin-10 (IL-10). In this article, we will focus on the pathological role of MDSC expansion in chronic inflammatory conditions including cancer, sepsis/infection, autoimmunity, asthma and ageing, as well as some of the mechanisms by which MDSCs/IL-10 contribute to the disease progression in such conditions.

High M-MDSC Percentage as a Negative Prognostic Factor in Chronic Lymphocytic Leukaemia

Simple Summary

Chronic lymphocytic leukaemia (CLL) is a malignancy of mature B cells. Tumour microenvironment is important for survival and proliferation of malignant cells. In the current study, we investigated the potential role of circulating monocytic myeloid-derived suppressor cells (M-MDSC) in CLL. We have observed an increased percentage of M-MDSC cells in CLL patients. Moreover, we have observed a close association with unfavourable prognostic markers, which suggests a potential role of M-MDSC as a prognostic factor in CLL. We have established an association between a high M-MDSC percentage on the one side and shorter time-to-treatment and overall survival on the other. Therefore, we strongly suggest to use M-MDSC percentage as another prognostic factor.

Abstract

In the current study, we analysed the role and prognostic value of myeloid-derived suppressor cells (MDSC) in chronic lymphocytic leukaemia (CLL). The frequency of circulating monocytic MDSC (M-MDSC; defined as CD14⁺CD11b⁺CD15^-HLA-DR^-/low cells) was assessed in correlation with clinical and laboratory parameters characterising the disease activity and patient immune status. Samples of peripheral blood from untreated CLL patients and healthy volunteers were stained with monoclonal antibodies for flow cytometry analysis. CLL patients with M-MDSC percentages above 9.35% (according to the receiver operating characteristic (ROC) analysis) had a shorter time-to-treatment and shorter survival time than the group with a lower percentage of M-MDSC. The M-MDSC percentage was higher in patients with adverse prognostic factors (i.e., 17p and 11q deletion and CD38 and ZAP-70 expression). A high M-MDSC percentage was linked to significantly lower expression of the CD3ζ in T cells. Furthermore, an analysis of immune regulatory molecules (arginase 1 (ARG1), nitric oxide synthase (NOS2), indoleamine 2,3-dioxygenase (IDO), transforming growth factor beta (TGF-β), and interleukin (IL)-10) was performed. By the means of flow cytometry and RT-qPCR, we showed an overexpression of three of them in M-MDSC of CLL patients. M-MDSC cells seem to be an important factor in the immunosuppressive microenvironment of CLL and seem to be a good and novel prognostic factor

Sympathetic nervous tone limits the development of myeloid-derived suppressor cells

Sympathetic nerves that innervate lymphoid organs regulate immune development and function by releasing norepinephrine that is sensed by immune cells via their expression of adrenergic receptors. Here, we demonstrate that ablation of sympathetic nervous system (SNS) signaling suppresses tumor immunity, and we dissect the mechanism of such immune suppression. We report that disruption of the SNS in mice removes a critical α-adrenergic signal required for maturation of myeloid cells in normal and tumor-bearing mice. In tumor-bearing mice, disruption of the α-adrenergic signal leads to the accumulation of immature myeloid-derived suppressor cells (MDSCs) that suppress tumor immunity and promote tumor growth. Furthermore, we show that these SNS-responsive MDSCs drive expansion of regulatory T cells via secretion of the alarmin heterodimer S100A8/A9, thereby compounding their immunosuppressive activity. Our results describe a regulatory framework in which sympathetic tone controls the development of innate and adaptive immune cells and influences their activity in health and disease.

Activated neutrophils exert myeloid-derived suppressor cell activity damaging T cells beyond repair

Myeloid-derived suppressor cells (MDSCs) have the capacity to suppress T-cell-mediated immune responses and impact the clinical outcome of cancer, infections, and transplantation settings. Although MDSCs were initially described as bone marrow-derived immature myeloid cells (either monocytic or granulocytic MDSCs), mature neutrophils have been shown to exert MDSC activity toward T cells in ways that remain unclear. In this study, we demonstrated that human neutrophils from both healthy donors and cancer patients do not exert MDSC activity unless they are activated. By using neutrophils with genetically well-defined defects, we found that reactive oxygen species (ROS) and granule-derived constituents are required for MDSC activity after direct CD11b-dependent interactions between neutrophils and T cells. In addition to these cellular interactions, neutrophils are engaged in the uptake of pieces of T-cell membrane, a process called trogocytosis. Together, these interactions led to changes in T-cell morphology, mitochondrial dysfunction, and adenosine triphosphate depletion, as indicated by electron microscopy, mass spectrometry, and metabolic parameters. Our studies characterize the different steps by which activated mature neutrophils induce functional T-cell nonresponsiveness and irreparable cell damage.

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.

Granulocytic Myeloid-Derived Suppressor Cells as Negative Regulators of Anticancer Immunity

The immune system plays a critical role in cancer progression and response to therapy. However, the immune system can be compromised during the neoplastic process. Notably, the myeloid lineage, which gives rise to granulocytic cells, including neutrophils, is a well-recognized target of tumor-mediated immune suppression. Ordinarily, granulocytic cells are integral for host defense, but in neoplasia the normal process of granulocyte differentiation (i.e., granulopoiesis) can be impaired leading instead to the formation of granulocytic (or PMN)-myeloid-derived suppressor cells (MDSCs). Such cells comprise various stages of myeloid differentiation and are defined functionally by their highly pro-tumorigenic and immune suppressive activities. Thus, considerable interest has been devoted to impeding the negative contributions of PMN-MDSCs to the antitumor response. Understanding their biology has the potential to unveil novel therapeutic opportunities to hamper PMN-MDSC production in the bone marrow, their mobilization, or their effector functions within the tumor microenvironment and, therefore, bolster anticancer therapies that require a competent myeloid compartment. In this review, we will highlight mechanisms by which the neoplastic process skews granulopoiesis to produce PMN-MDSCs, summarize mechanisms by which they execute their pro-tumorigenic activities and, lastly, underscore strategies to obstruct their role as negative regulators of antitumor immunity.

Combination of thermally ablative focused ultrasound with gemcitabine controls breast cancer via adaptive immunity

Background

Triple-negative breast cancer (TNBC) remains recalcitrant to most targeted therapy approaches. However, recent clinical studies suggest that inducing tumor damage can render TNBC responsive to immunotherapy. We therefore tested a strategy for immune sensitization of murine TNBC (4T1 tumors) through combination of focused ultrasound (FUS) thermal ablation and a chemotherapy, gemcitabine (GEM), known to attenuate myeloid-derived suppressor cells (MDSCs).

Methods

We applied a sparse-scan thermally ablative FUS regimen at the tumor site in combination with systemically administered GEM. We used flow cytometry analysis to investigate the roles of monotherapy and combinatorial therapy in mediating local and systemic immunity. We also tested this combination in Rag1^−/− mice or T cell-depleted wild-type mice to determine the essentiality of adaptive immunity. Further, we layered Programmed cell death protein 1 (PD-1) blockade onto this combination to evaluate its impact on tumor outgrowth and survival.

Results

The immune-modulatory effect of FUS monotherapy was insufficient to promote a robust T cell response against 4T1, consistent with the dominant MDSC-driven immunosuppression evident in this model. The combination of FUS+GEM significantly constrained primary TNBC tumor outgrowth and extended overall survival of mice. Tumor control correlated with increased circulating antigen-experienced T cells and was entirely dependent on T cell-mediated immunity. The ability of FUS+GEM to control primary tumor outgrowth was moderately enhanced by either neoadjuvant or adjuvant treatment with anti-PD-1.

Conclusion

Thermally ablative FUS in combination with GEM restricts primary tumor outgrowth, improves survival and enhances immunogenicity in a murine metastatic TNBC model. This treatment strategy promises a novel option for potentiating the role of FUS in immunotherapy of metastatic TNBC and is worthy of future clinical evaluation.

Trial registration numbers

NCT03237572 and NCT04116320.

Multidirectional Strategies for Targeted Delivery of Oncolytic Viruses by Tumor Infiltrating Immune Cells

Oncolytic virus (OV) immunotherapy has demonstrated to be a promising approach in cancer treatment due to tumor-specific oncolysis. However, their clinical use so far has been largely limited due to the lack of suitable delivery strategies with high efficacy. Direct 'intratumoral' injection is the way to cross the hurdles of systemic toxicity, while providing local effects. Progress in this field has enabled the development of alternative way using 'systemic' oncolytic virotherapy for producing better results. One major potential roadblock to systemic OV delivery is the low virus persistence in the face of hostile immune system. The delivery challenge is even greater when attempting to target the oncolytic viruses into the entire tumor mass, where not all tumor cells are equally exposed to exactly the same microenvironment. The microenvironment of many tumors is known to be massively infiltrated with various types of leucocytes in both primary and metastatic sites. Interestingly, this intratumoral immune cell heterogeneity exhibits a degree of organized distribution inside the tumor bed as evidenced, for example, by the hypoxic tumor microenviroment where predominantly recruits tumor-associated macrophages. Although in vivo OV delivery seems complicated and challenging, recent results are encouraging for decreasing the limitations of systemically administered oncolytic viruses and an improved efficiency of oncolytic viral therapy in targeting cancerous tissues in vitro. Here, we review the latest developments of carrier cell-based oncolytic virus delivery using tumor-infiltrating immune cells with a focus on the main features of each cellular vehicle.

Lipid Metabolism and Cancer Immunotherapy: Immunosuppressive Myeloid Cells at the Crossroad

Cancer progression generates a chronic inflammatory state that dramatically influences hematopoiesis, originating different subsets of immune cells that can exert pro- or anti-tumor roles. Commitment towards one of these opposing phenotypes is driven by inflammatory and metabolic stimuli derived from the tumor-microenvironment (TME). Current immunotherapy protocols are based on the reprogramming of both specific and innate immune responses, in order to boost the intrinsic anti-tumoral activity of both compartments. Growing pre-clinical and clinical evidence highlights the key role of metabolism as a major influence on both immune and clinical responses of cancer patients. Indeed, nutrient competition (i.e., amino acids, glucose, fatty acids) between proliferating cancer cells and immune cells, together with inflammatory mediators, drastically affect the functionality of innate and adaptive immune cells, as well as their functional cross-talk. This review discusses new advances on the complex interplay between cancer-related inflammation, myeloid cell differentiation and lipid metabolism, highlighting the therapeutic potential of metabolic interventions as modulators of anticancer immune responses and catalysts of anticancer immunotherapy.

The Great Debate at 'Immunotherapy Bridge', Naples, December 5, 2019

As part of the 2019 Immunotherapy Bridge congress (December 4-5, Naples, Italy), the Great Debate session featured counterpoint views from leading experts on six topical issues in immunotherapy today. These were the use of chimeric antigen receptor T cell therapy in solid tumors, whether the Immunoscore should be more widely used in clinical practice, whether antibody-dependent cellular cytotoxicity is important in the mode of action of anticytotoxic T-lymphocyte-associated protein 4 antibodies, whether the brain is immunologically unique or just another organ, the role of microbiome versus nutrition in affecting responses to immunotherapy, and whether chemotherapy is immunostimulatory or immunosuppressive. Discussion of these important topics are summarized in this report.

The New Era of Cancer Immunotherapy: Targeting Myeloid-Derived Suppressor Cells to Overcome Immune Evasion

Suppression of antitumor immune responses is one of the main mechanisms by which tumor cells escape from destruction by the immune system. Myeloid-derived suppressor cells (MDSCs) represent the main immunosuppressive cells present in the tumor microenvironment (TME) that sustain cancer progression. MDSCs are a heterogeneous group of immature myeloid cells with a potent activity against T-cell. Studies in mice have demonstrated that MDSCs accumulate in several types of cancer where they promote invasion, angiogenesis, and metastasis formation and inhibit antitumor immunity. In addition, different clinical studies have shown that MDSCs levels in the peripheral blood of cancer patients correlates with tumor burden, stage and with poor prognosis in multiple malignancies. Thus, MDSCs are the major obstacle to many cancer immunotherapies and their targeting may be a beneficial strategy for improvement the efficiency of immunotherapeutic interventions. However, the great heterogeneity of these cells makes their identification in human cancer very challenging. Since both the phenotype and mechanisms of action of MDSCs appear to be tumor-dependent, it is important to accurately characterized the precise MDSC subsets that have clinical relevance in each tumor environment to more efficiently target them. In this review we summarize the phenotype and the suppressive mechanisms of MDSCs populations expanded within different tumor contexts. Further, we discuss about their clinical relevance for cancer diagnosis and therapy.

The immunology of renal cell carcinoma

Renal cell carcinoma (RCC) is the most common type of kidney cancer and comprises several subtypes with unique characteristics. The most common subtype (~70% of cases) is clear-cell RCC. RCC is considered to be an immunogenic tumour but is known to mediate immune dysfunction in large part by eliciting the infiltration of immune-inhibitory cells, such as regulatory T cells and myeloid-derived suppressor cells, into the tumour microenvironment. Several possible mechanisms have been proposed to explain how these multiple tumour-infiltrating cell types block the development of an effective anti-tumour immune response, including inhibition of the activity of effector T cells and of antigen presenting cells via upregulation of suppressive factors such as checkpoint molecules. Targeting immune suppression using checkpoint inhibition has resulted in clinical responses in some patients with RCC and combinatorial approaches involving checkpoint blockade are now standard of care in patients with advanced RCC. However, a substantial proportion of patients do not benefit from checkpoint blockade. The identification of reliable biomarkers of response to checkpoint blockade is crucial to facilitate improvements in the clinical efficacy of these therapies. In addition, there is a need for the development of other immune-based strategies that address the shortcomings of checkpoint blockade, such as adoptive cell therapies.

Role of Tumor-Associated Myeloid Cells in Breast Cancer

Stromal immune cells constitute the tumor microenvironment. These immune cell subsets include myeloid cells, the so-called tumor-associated myeloid cells (TAMCs), which are of two types: tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs). Breast tumors, particularly those in human epidermal growth factor receptor 2 (HER-2)-positive breast cancer and triple-negative breast cancer, are solid tumors containing immune cell stroma. TAMCs drive breast cancer progression via immune mediated, nonimmune-mediated, and metabolic interactions, thus serving as a potential therapeutic target for breast cancer. TAMC-associated breast cancer treatment approaches potentially involve the inhibition of TAM recruitment, modulation of TAM polarization/differentiation, reduction of TAM products, elimination of MDSCs, and reduction of MDSC products. Furthermore, TAMCs can enhance or restore immune responses during cancer immunotherapy. This review describes the role of TAMs and MDSCs in breast cancer and elucidates the clinical implications of TAMs and MDSCs as potential targets for breast cancer treatment.

Combinatorial drug therapy in cancer - New insights

Cancer can arise due to mutations in numerous pathways present in our body and thus has many alternatives for getting aggravated. Due to this attribute, it gets difficult to treat cancer patients with monotherapy alone and has a risk of not being eliminated to the full extent. This necessitates the introduction of combinatorial therapy as it employs cancer treatment using more than one method and shows a greater success rate. Combinatorial therapy involves a complementary combination of two different therapies like a combination of radio and immunotherapy or a combination of drugs that can target more than one pathway of cancer formation like combining CDK targeting drugs with Growth factors targeting drugs. In this review, we discuss the various aspects of cancer which include, its causes; four regulatory mechanisms namely: apoptosis, cyclin-dependent kinases, tumor suppressor genes, and growth factors; some of the pathways involved; treatment: monotherapy and combinatorial therapy and combinatorial drug formulation in chemotherapy. The present review gives a holistic account of the different mechanisms of therapies and also drug combinations that may serve to not only complement the monotherapy but can also surpass the resistance against monotherapy agents.

Cross-talk between myeloid-derived suppressor cells and Mucin1 in breast cancer vaccination: On the verge of a breakthrough

Although breast cancer is one of the leading troublesome cancers, the available therapeutic options have not fulfilled the desired outcomes. Immune-based therapy has gained special attention for breast cancer treatment. Although this approach is highly tolerable, its low response rate has rendered it as an undesirable approach. This review aims to describe the essential oncogenic pathways involved in breast cancer, elucidate the immunosuppression and oncogenic effect of Mucin1, and introduce myeloid-derived suppressor cells, which are the main culprits of anti-tumoral immune response attenuation. The various auto-inductive loops between Mucin1 and myeloid-derived suppressor cells are focal in the suppression of anti-tumoral immune responses in patients with breast cancer. These cross-talks between the Mucin1 and myeloid-derived suppressor cells can be the underlying causes of immunotherapy's impotence for patients with breast cancer. This approach can pave the road for the development of a potent vaccine for patients with breast cancer and is translated into clinical settings.