CXCR2+ MDSCs promote breast cancer progression by inducing EMT and activated T cell exhaustion

Breast Cancer Immune Landscape: Interplay Between Systemic and Local Immunity

Breast cancer (BC) is one of the most common malignancies in women worldwide. Numerous studies in immuno-oncology and successful trials of immunotherapy have demonstrated the causal role of the immune system in cancer pathogenesis. The interaction between the tumor and the immune system is known to have a dual nature. Despite cytotoxic lymphocyte activity against transformed cells, a tumor can escape immune surveillance and leverage chronic inflammation to maintain its own development. Research on antitumor immunity primarily focuses on the role of the tumor microenvironment, whereas the systemic immune response beyond the tumor site is described less thoroughly. Here, a comprehensive review of the formation of the immune profile in breast cancer patients is offered. The interplay between systemic and local immune reactions as self-sustaining mechanism of tumor progression is described and the functional activity of the main cell populations related to innate and adaptive immunity is discussed. Additionally, the interaction between different functional levels of the immune system and their contribution to the development of the pro- or anti-tumor immune response in BC is highlighted. The presented data can potentially inform the development of new immunotherapy strategies in the treatment of patients with BC.

Immune modulation in malignant pleural effusion: from microenvironment to therapeutic implications

Immune microenvironment and immunotherapy have become the focus and frontier of tumor research, and the immune checkpoint inhibitors has provided novel strategies for tumor treatment. Malignant pleural effusion (MPE) is a common end-stage manifestation of lung cancer, malignant pleural mesothelioma and other thoracic malignancies, which is invasive and often accompanied by poor prognosis, affecting the quality of life of affected patients. Currently, clinical therapy for MPE is limited to pleural puncture, pleural fixation, catheter drainage, and other palliative therapies. Immunization is a new direction for rehabilitation and treatment of MPE. The effusion caused by cancer cells establishes its own immune microenvironment during its formation. Immune cells, cytokines, signal pathways of microenvironment affect the MPE progress and prognosis of patients. The interaction between them have been proved. The relevant studies were obtained through a systematic search of PubMed database according to keywords search method. Then through screening and sorting and reading full-text, 300 literatures were screened out. Exclude irrelevant and poor quality articles, 238 literatures were cited in the references. In this study, the mechanism of immune microenvironment affecting malignant pleural effusion was discussed from the perspectives of adaptive immune cells, innate immune cells, cytokines and molecular targets. Meanwhile, this study focused on the clinical value of microenvironmental components in the immunotherapy and prognosis of malignant pleural effusion.

Combination of Anti-Angiogenics and Immunotherapies in Renal Cell Carcinoma Show Their Limits: Targeting Fibrosis to Break through the Glass Ceiling?

This review explores treating metastatic clear cell renal cell carcinoma (ccRCC) through current therapeutic modalities-anti-angiogenic therapies and immunotherapies. While these approaches represent the forefront, their limitations and variable patient responses highlight the need to comprehend underlying resistance mechanisms. We specifically investigate the role of fibrosis, prevalent in chronic kidney disease, influencing tumour growth and treatment resistance. Our focus extends to unravelling the intricate interplay between fibrosis, immunotherapy resistance, and the tumour microenvironment for effective therapy development. The analysis centres on connective tissue growth factor (CTGF), revealing its multifaceted role in ccRCC-promoting fibrosis, angiogenesis, and cancer progression. We discuss the potential of targeting CTGF to address the problem of fibrosis in ccRCC. Emphasising the crucial relationship between fibrosis and the immune system in ccRCC, we propose that targeting CTGF holds promise for overcoming obstacles to cancer treatment. However, we recognise that an in-depth understanding of the mechanisms and potential limitations is imperative and, therefore, advocate for further research. This is an essential prerequisite for the successful integration of CTGF-targeted therapies into the clinical landscape.

Reciprocal relationship between cancer stem cells and myeloid-derived suppressor cells: implications for tumor progression and therapeutic strategies

Recently, there has been an increased focus on cancer stem cells (CSCs) due to their resilience, making them difficult to eradicate. This resilience often leads to tumor recurrence and metastasis. CSCs adeptly manipulate their surroundings to create an environment conducive to their survival. In this environment, myeloid-derived suppressor cells (MDSCs) play a crucial role in promoting epithelial-mesenchymal transition and bolstering CSCs' stemness. In response, CSCs attract MDSCs, enhancing their infiltration, expansion and immunosuppressive capabilities. This interaction between CSCs and MDSCs increases the difficulty of antitumor therapy. In this paper, we discuss the interplay between CSCs and MDSCs based on current research and highlight recent therapeutic strategies targeting either CSCs or MDSCs that show promise in achieving effective antitumor outcomes.

MDSC-targeted liposomal all-trans retinoic acid suppresses mMdscs and improves immunotherapy in HBV infection

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are evolving as a prominent determinant in cancer occurrence and development and are functionally found to suppress T cells in cancer. Not much research is done regarding its involvement in viral infections. This research was designed to investigate the role of MDSCs in hepatitis B virus (HBV) infection and how targeting these cells with our novel all-trans retinoic acid encapsulated liposomal formulation could improve immunotherapy in C57BL/6 mice.

METHODS

Ten micrograms (10 μg) of plasmid adeno-associated virus (pAAV/HBV 1.2, genotype A) was injected hydrodynamically via the tail vein of C57BL/6 mice. An all-trans retinoic acid encapsulated liposomal formulation (L-ATRA) with sustained release properties was used in combination with tenofovir disoproxil fumarate (TDF), a nucleotide analog reverse transcriptase inhibitor (nRTI) to treat the HBV infection. The L-ATRA formulation was given at a dose of 5 mg/kg intravenously (IV) twice a week. The TDF was given orally at 30 mg/kg daily.

RESULTS

Our results revealed that L-ATRA suppresses MDSCs in HBV infected mice and enhanced T-cell proliferation in vitro. In vivo studies showed higher and improved immunotherapeutic effect in mice that received L-ATRA and TDF concurrently in comparison with the groups that received monotherapy. Lower HBV DNA copies, lower concentrations of HBsAg and HBeAg, lower levels of ALT and AST and less liver damage were seen in the mice that received the combination therapy of L-ATRA + TDF.

CONCLUSIONS

In effect, targeting MDSCs with the combination of L-ATRA and TDF effectively reduced mMDSC and improved immunotherapy in the HBV infected mice. Targeting MDSCs could provide a breakthrough in the fight against hepatitis B virus infection.

Regulation of T cells by myeloid-derived suppressor cells: emerging immunosuppressor in lung cancer

Myeloid-derived suppressor cells (MDSCs), major components maintaining the immune suppressive microenvironment in lung cancer, are relevant to the invasion, metastasis, and poor prognosis of lung cancer, through the regulation of epithelial-mesenchymal transition, remodeling of the immune microenvironment, and regulation of angiogenesis. MDSCs regulate T-cell immune functions by maintaining a strong immunosuppressive microenvironment and promoting tumor invasion. This raises the question of whether reversing the immunosuppressive effect of MDSCs on T cells can improve lung cancer treatment. To understand this further, this review explores the interactions and specific mechanisms of different MDSCs subsets, including regulatory T cells, T helper cells, CD8 + T cells, natural killer T cells, and exhausted T cells, as part of the lung cancer immune microenvironment. Second, it focuses on the guiding significance confirmed via clinical liquid biopsy and tissue biopsy that different MDSC subsets improve the prognosis of lung cancer. Finally, we conclude that targeting MDSCs through action targets or signaling pathways can help regulate T-cell immune functions and suppress T-cell exhaustion. In addition, immune checkpoint inhibitors targeting MDSCs may serve as a new approach for enhancing the efficiency of immunotherapy and targeted therapy for lung cancer in the future, providing better comprehensive options for lung cancer treatment.

Focus on T cell exhaustion: new advances in traditional Chinese medicine in infection and cancer

In chronic infections and cancers, T lymphocytes (T cells) are exposed to persistent antigen or inflammatory signals. The condition is often associated with a decline in T-cell function: a state called "exhaustion". T cell exhaustion is a state of T cell dysfunction characterized by increased expression of a series of inhibitory receptors (IRs), decreased effector function, and decreased cytokine secretion, accompanied by transcriptional and epigenetic changes and metabolic defects. The rise of immunotherapy, particularly the use of immune checkpoint inhibitors (ICIs), has dramatically changed the clinical treatment paradigm for patients. However, its low response rate, single target and high immunotoxicity limit its clinical application. The multiple immunomodulatory potential of traditional Chinese medicine (TCM) provides a new direction for improving the treatment of T cell exhaustion. Here, we review recent advances that have provided a clearer molecular understanding of T cell exhaustion, revealing the characteristics and causes of T cell exhaustion in persistent infections and cancers. In addition, this paper summarizes recent advances in improving T cell exhaustion in infectious diseases and cancer with the aim of providing a comprehensive and valuable source of information on TCM as an experimental study and their role in collaboration with ICIs therapy.

Involvement in Tumorigenesis and Clinical Significance of CXCL1 in Reproductive Cancers: Breast Cancer, Cervical Cancer, Endometrial Cancer, Ovarian Cancer and Prostate Cancer

C-X-C motif chemokine ligand 1 (CXCL1) is a member of the CXC chemokine subfamily and a ligand for CXCR2. Its main function in the immune system is the chemoattraction of neutrophils. However, there is a lack of comprehensive reviews summarizing the significance of CXCL1 in cancer processes. To fill this gap, this work describes the clinical significance and participation of CXCL1 in cancer processes in the most important reproductive cancers: breast cancer, cervical cancer, endometrial cancer, ovarian cancer, and prostate cancer. The focus is on both clinical aspects and the significance of CXCL1 in molecular cancer processes. We describe the association of CXCL1 with clinical features of tumors, including prognosis, ER, PR and HER2 status, and TNM stage. We present the molecular contribution of CXCL1 to chemoresistance and radioresistance in selected tumors and its influence on the proliferation, migration, and invasion of tumor cells. Additionally, we present the impact of CXCL1 on the microenvironment of reproductive cancers, including its effect on angiogenesis, recruitment, and function of cancer-associated cells (macrophages, neutrophils, MDSC, and T_reg). The article concludes by summarizing the significance of introducing drugs targeting CXCL1. This paper also discusses the significance of ACKR1/DARC in reproductive cancers.

Novel strategies for cancer immunotherapy: counter-immunoediting therapy

The advent of immunotherapy has made an indelible mark on the field of cancer therapy, especially the application of immune checkpoint inhibitors in clinical practice. Although immunotherapy has proven its efficacy and safety in some tumors, many patients still have innate or acquired resistance to immunotherapy. The emergence of this phenomenon is closely related to the highly heterogeneous immune microenvironment formed by tumor cells after undergoing cancer immunoediting. The process of cancer immunoediting refers to the cooperative interaction between tumor cells and the immune system that involves three phases: elimination, equilibrium, and escape. During these phases, conflicting interactions between the immune system and tumor cells result in the formation of a complex immune microenvironment, which contributes to the acquisition of different levels of immunotherapy resistance in tumor cells. In this review, we summarize the characteristics of different phases of cancer immunoediting and the corresponding therapeutic tools, and we propose normalized therapeutic strategies based on immunophenotyping. The process of cancer immunoediting is retrograded through targeted interventions in different phases of cancer immunoediting, making immunotherapy in the context of precision therapy the most promising therapy to cure cancer.

The dynamic tumor-stromal crosstalk: implications of 'stromal-hot' tumors in the process of epithelial-mesenchymal transition in breast cancer

BACKGROUND

Breast cancer metastatic programming involves an intricate process by which the tumor cell coevolves with the surrounding extracellular niche. The supporting cells from the local host stroma get transformed into cancer-associated stromal cells. This complex crosstalk leads to extracellular matrix remodeling, invasion, and eventually distant metastasis.

METHODS

In this review, we examine the protein-miRNA secretome that is crucial for this crosstalk. We also provide evidence from the literature for the pivotal role played by the various stromal cells like fibroblasts, adipocytes, and immune cells in promoting the process of EMT in breast cancer. Through in-silico analysis, we have also attempted to establish that stromal presence is integral to the process of EMT.

RESULTS AND CONCLUSION

The in-silico analysis delineates the persuasive role of the stroma in mediating epithelial-to-mesenchymal transition. This review elucidates the importance of examining the role of the stromal niche that can yield promising diagnostic markers and pave avenues for formulating tailored anti-cancer therapy. Process of EMT as driven by 'stroma-hot' tumors: The process of EMT is driven by the stromal cells. The stromal cells in the form of  fibroblasts, adipocytes, endothelial cells, mesenchymal stromal cells and tissue associated macrophages secrete the miRNA-protein secretome that modulates the stromal niche and the tumor cells to be become 'tumor associated'. This drives tumor progression and invasion. The 'stromal-hot' tumors eventually get the benefit of the surplus nurturing from the stroma that facilitates EMT leading to distant organ seeding and metastasis.

Myeloid cells in the era of cancer immunotherapy: Top 3 unanswered questions

Myeloid cells are increasingly being recognized as central players orchestrating or suppressing antitumor immune responses. With the advent of high-resolution analytical methods such as single-cell technologies, we now appreciate the heterogeneity and complexity of the myeloid compartment in the context of cancer. Because of their highly plastic nature, targeting myeloid cells has shown promising results either as a monotherapy or in combination with immunotherapy in preclinical models and cancer patients. However, the complexity of myeloid cell cellular crosstalk and molecular networks contributes to our poor understanding of the different myeloid cell subsets in tumorigenesis, which makes targeting myeloid cells challenging. Here, we summarize varied myeloid cell subsets and their contribution to tumor progression with a main focus on mononuclear phagocytes. The top three unanswered questions challenging the field of myeloid cells and cancer in the era of cancer immunotherapy are addressed. Through these questions, we discuss how myeloid cell origin and identity influence their function and disease outcomes. Different therapeutic strategies used to target myeloid cells in cancer are also addressed. Finally, the durability of myeloid cell targeting is interrogated by examining the complexity of resultant compensatory cellular and molecular mechanisms.

The role of myeloid derived suppressor cells in musculoskeletal disorders

The immune system is closely linked to bone homeostasis and plays a pivotal role in several pathological and inflammatory conditions. Through various pathways it modulates various bone cells and subsequently sustains the physiological bone metabolism. Myeloid-derived suppressor cells (MDSCs) are a group of heterogeneous immature myeloid-derived cells that can exert an immunosuppressive function through a direct cell-to-cell contact, secretion of anti-inflammatory cytokines or specific exosomes. These cells mediate the innate immune response to chronic stress on the skeletal system. In chronic inflammation, MDSCs act as an inner offset to rebalance overactivation of the immune system. Moreover, they have been found to be involved in processes responsible for bone remodeling in different musculoskeletal disorders, autoimmune diseases, infection, and cancer. These cells can not only cause bone erosion by differentiating into osteoclasts, but also alleviate the immune reaction, subsequently leading to long-lastingly impacted bone remodeling. In this review, we discuss the impact of MDSCs on the bone metabolism under several pathological conditions, the involved modulatory pathways as well as potential therapeutic targets in MDSCs to improve bone health.

Regulation of epithelial-mesenchymal transition by tumor microenvironmental signals and its implication in cancer therapeutics

Epithelial-mesenchymal transition (EMT) has been implicated in various aspects of tumor development, including tumor invasion and metastasis, cancer stemness, and therapy resistance. Diverse stroma cell types along with biochemical and biophysical factors in the tumor microenvironment impinge on the EMT program to impact tumor progression. Here we provide an in-depth review of various tumor microenvironmental signals that regulate EMT in cancer. We discuss the molecular mechanisms underlying the role of EMT in therapy resistance and highlight new therapeutic approaches targeting the tumor microenvironment to impact EMT and tumor progression.

Multifaceted role of chemokines in solid tumors: From biology to therapy

Chemokines are small secretory chemotactic cytokines that control the directed migration of immune cells. Chemokines are involved in both anti-and pro-tumorigenic immune responses. Accumulating evidence suggests that the balance between these responses is influenced by several factors such as the stage of tumorigenesis, immune cell activation, recruitment of immune activating or immunosuppressive cells in the tumor microenvironment (TME), and chemokine receptor expression on effector and regulatory target cells. Cancer cells engage in a complex network with their TME components via several factors including growth factors, cytokines and chemokines that are critical for the growth of primary tumor and metastasis. However, chemokines show a multifaceted role in tumor progression including maintenance of stem-like properties, tumor cell proliferation/survival/senescence, angiogenesis, and metastasis. The heterogeneity of solid tumors in primary and metastatic cancers presents a challenge to the development of successful cancer therapy. Despite extensive research on how solid tumors escape immune cell-mediated anti-tumor response, finding an effective therapy for metastatic cancer still remains a challenge. This review discusses the multifarious roles of chemokines in solid tumors including various chemokine signaling pathways such as CXCL8-CXCR1/2, CXCL9, 10, 11-CXCR3, CXCR4-CXCL12, CCL(X)-CCR(X) in primary and metastatic cancers. We further discuss the novel therapeutic approaches that have been developed by major breakthroughs in chemokine research to treat cancer patients by the strategic blockade/activation of these signaling axes alone or in combination with immunotherapies.

Cancer-associated inflammation: pathophysiology and clinical significance

Purpose

Cancer cells, despite stemming from the own cells of their host, usually elicit an immune response. This response usually enables elimination of cancer at its earliest stages. However, some tumors develop mechanisms of escaping immune destruction and even profiting from tumor-derived inflammation.

Methods

We summarized the roles of different immune cell populations in various processes associated with cancer progression and possible methods of reshaping tumor-associated inflammation to increase the efficacy of cancer therapy.

Results

Changes in various signaling pathways result in attraction of immunosuppressive, pro-tumorigenic cells, such as myeloid-derived suppressor cells, tumor-associated macrophages, and neutrophils, while at the same time suppressing the activity of lymphocytes, which have the potential of destroying cancer cells. These changes promote tumor progression by increasing angiogenesis and growth, accelerating metastasis, and impairing drug delivery to the tumor site.

Conclusion

Due to its multi-faceted role in cancer, tumor-associated inflammation can serve as a valuable therapy target. By increasing it, whether through decreasing overall immunosuppression with immune checkpoint inhibitor therapy or through more specific methods, such as cancer vaccines, oncolytic viruses, or chimeric antigen receptor T cells, cancer-derived immunosuppression can be overcome, resulting in immune system destroying cancer cells. Even changes occurring in the microbiota can influence the shape of antitumor response, which could provide new attractive diagnostic or therapeutic methods. Interestingly, also decreasing the distorted tumor-associated inflammation with non-steroidal anti-inflammatory drugs can lead to positive outcomes.

Tissue-Resident Innate Immune Cell-Based Therapy: A Cornerstone of Immunotherapy Strategies for Cancer Treatment

Cancer immunotherapy has led to impressive advances in cancer treatment. Unfortunately, in a high percentage of patients is difficult to consistently restore immune responses to eradicate established tumors. It is well accepted that adaptive immune cells, such as B lymphocytes, CD4⁺ helper T lymphocytes, and CD8⁺ cytotoxic T-lymphocytes (CTLs), are the most effective cells able to eliminate tumors. However, it has been recently reported that innate immune cells, including natural killer cells (NK), dendritic cells (DC), macrophages, myeloid-derived suppressor cells (MDSCs), and innate lymphoid cells (ILCs), represent important contributors to modulating the tumor microenvironment and shaping the adaptive tumor response. In fact, their role as a bridge to adaptive immunity, make them an attractive therapeutic target for cancer treatment. Here, we provide a comprehensive overview of the pleiotropic role of tissue-resident innate immune cells in different tumor contexts. In addition, we discuss how current and future therapeutic approaches targeting innate immune cells sustain the adaptive immune system in order to improve the efficacy of current tumor immunotherapies.

CCR4+ monocytic myeloid-derived suppressor cells are associated with the increased epithelial-mesenchymal transition in pancreatic adenocarcinoma patients

Among all the cancer-related deaths globally, pancreatic ductal adenocarcinoma (PDAC) accounts for the seventh leading cause of mortality. A dysregulated immune system disrupts anti-tumor immunity by abnormal accumulation of myeloid-derived suppressor cells (MDSCs), but the underlying mechanisms are still inconclusive. To gain new insights into the role of MDSCs in tumor settings, we aimed to determine the mechanism of expansion of various subsets of MDSCs in PDAC patients and their role in promoting invasiveness. We assessed the load of MDSCs, chemokines responsible for the recruitment of MDSCs in PDAC patients by flow cytometry. We investigated the chemokine profile of tumor tissue using qRT-PCR and the status of epithelial-mesenchymal transition (EMT) related markers E-Cadherin, N-Cadherin, Snail, and ZEB1 by qRT-PCR and immunohistochemistry. We found a higher frequency of tumor infiltrated MDSCs in PDAC patients. Chemokine ligands CCL2 and the receptor CCR4 were markedly elevated in the PDAC tumor, while CCR4+ monocytic MDSCs (M-MDSCs) were found significantly elevated in peripheral blood and tumor tissue. In tumor tissue, expression of E-Cadherin was significantly reduced, while N-Cadherin, Snail, and ZEB1 were markedly raised. The frequency of CCR4+ M-MDSCs significantly correlated with the expression of mesenchymal transition markers N-Cadherin, Snail, and ZEB1. Collectively, these results suggest that the CCL2-CCR4 axis plays a crucial role in driving the recruitment of M-MDSCs, which is associated with increased invasiveness in PDAC. This study sheds light on the expansion mechanism of MDSCs, which can serve as a crucial target of future anti-cancer strategies to inhibit tumor cell invasiveness.

Coordinated Regulation of Myeloid-Derived Suppressor Cells by Cytokines and Chemokines

Simple Summary

In this review, we summarize the effects of various cytokines and chemokines as a network to regulate the expansion, recruitment, and immunosuppressive functions of myeloid-derived suppressor cells in cancer metastasis.

Abstract

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that impair immune cell functions and promote tumor progression. Mounting evidence indicates that cytokines and chemokines in the tumor microenvironment alter MDSCs. Various cytokines and chemokines are involved in MDSC production, their infiltration into tumors, and their exertion of suppressive functions. Here, we consider those cytokines, chemokines, and MDSCs as an intricately connected, complex system and we focus on how tumors manipulate the MDSCs through various cytokines and chemokines. We also discuss treatment capitalizing on cytokines/chemokine signaling aimed at combating the potent immunosuppressive activities of MDSCs to improve disease outcomes.

Identification and Validation of an Annexin-Related Prognostic Signature and Therapeutic Targets for Bladder Cancer: Integrative Analysis

Abnormal expression and dysfunction of Annexins (ANXA1-11, 13) have been widely found in several types of cancer. However, the expression pattern and prognostic value of Annexins in bladder cancer (BC) are currently still unknown. In this study, survival analysis by our in-house OSblca web server revealed that high ANXA1/2/3/5/6 expression was significantly associated with poor overall survival (OS) in BC patients, while higher ANXA11 was associated with increased OS. Through Oncomine and GEPIA2 database analysis, we found that ANXA2/3/4/13 were up-regulated, whereas ANXA1/5/6 were down-regulated in BC compared with normal bladder tissues. Further LASSO analysis built an Annexin-Related Prognostic Signature (ARPS, including four members ANXA1/5/6/10) in the TCGA BC cohort and validated it in three independent GEO BC cohorts (GSE31684, GSE32548, GSE48075). Multivariate COX analysis demonstrated that ARPS is an independent prognostic signature for BC. Moreover, GSEA results showed that immune-related pathways, such as epithelial-mesenchymal transition and IL6/JAK/STAT3 signaling were enriched in the high ARPS risk groups, while the low ARPS risk group mainly regulated metabolism-related processes, such as adipogenesis and bile acid metabolism. In conclusion, our study comprehensively analyzed the mRNA expression and prognosis of Annexin family members in BC, constructed an Annexin-related prognostic signature using LASSO and COX regression, and validated it in four independent BC cohorts, which might help to improve clinical outcomes of BC patients, offer insights into the underlying molecular mechanisms of BC development and suggest potential therapeutic targets for BC.

Myeloid-Derived Suppressor Cells: A Multifaceted Accomplice in Tumor Progression

Myeloid-derived suppressor cell (MDSC) is a heterogeneous population of immature myeloid cells, has a pivotal role in negatively regulating immune response, promoting tumor progression, creating pre-metastases niche, and weakening immunotherapy efficacy. The underlying mechanisms are complex and diverse, including immunosuppressive functions (such as inhibition of cytotoxic T cells and recruitment of regulatory T cells) and non-immunological functions (mediating stemness and promoting angiogenesis). Moreover, MDSC may predict therapeutic response as a poor prognosis biomarker among multiple tumors. Accumulating evidence indicates targeting MDSC can reverse immunosuppressive tumor microenvironment, and improve therapeutic response either single or combination with immunotherapy. This review summarizes the phenotype and definite mechanisms of MDSCs in tumor progression, and provide new insights of targeting strategies regarding to their clinical applications.

Suppressing MDSC Recruitment to the Tumor Microenvironment by Antagonizing CXCR2 to Enhance the Efficacy of Immunotherapy

Simple Summary

While the development of immunotherapy has greatly advanced cancer treatment, many patients do not benefit from immunotherapy. Numerous strategies have been developed to improve response to immunotherapy across cancer types, including blocking the activity of immunosuppressive immune cells, cytokines, and signaling pathways that are linked to poor responses. Myeloid-derived suppressor cells (MDSCs) are associated with poor responses to immunotherapy, and the chemokine receptor, CXCR2, is involved in recruiting MDSCs to the tumor. In this review, we present studies that explore the potential of inhibiting MDSCs through blocking CXCR2 as a strategy to enhance response to existing and novel immunotherapies.

Abstract

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of cells derived from immature myeloid cells. These cells are often associated with poor responses to cancer therapy, including immunotherapy, in a variety of tumor types. The C-X-C chemokine receptor 2 (CXCR2) signaling axis plays a key role in the migration of immunosuppressive MDSCs into the tumor microenvironment (TME) and the pre-metastatic niche. MDSCs impede the efficacy of immunotherapy through a variety of mechanisms. Efforts to target MDSCs by blocking CXCR2 is an active area of research as a method for improving existing and novel immunotherapy strategies. As immunotherapies gain approval for a wider array of clinical indications, it will become even more important to understand the efficacy of CXCR2 inhibition in combating immunotherapy resistance at different stages of tumor progression.

Beyond immunosuppressive effects: dual roles of myeloid-derived suppressor cells in bone-related diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells (IMCs) with immunosuppressive functions, whereas IMCs originally differentiate into granulocytes, macrophages, and dendritic cells (DCs) to participate in innate immunity under steady-state conditions. At present, difficulties remain in identifying MDSCs due to lacking of specific biomarkers. To make identification of MDSCs accurately, it also needs to be determined whether having immunosuppressive functions. MDSCs play crucial roles in anti-tumor, angiogenesis, and metastasis. Meanwhile, MDSCs could make close interaction with osteoclasts, osteoblasts, chondrocytes, and other stromal cells within microenvironment of bone and joint, and thereby contributing to poor prognosis of bone-related diseases such as cancer-related bone metastasis, osteosarcoma (OS), rheumatoid arthritis (RA), osteoarthritis (OA), and orthopedic trauma. In addition, MDSCs have been shown to participate in the procedure of bone repair. In this review, we have summarized the function of MDSCs in cancer-related bone metastasis, the interaction with stromal cells within the bone microenvironment as well as joint microenvironment, and the critical role of MDSCs in bone repair. Besides, the promising value of MDSCs in the treatment for bone-related diseases is also well discussed.

Dynamic EMT: a multi-tool for tumor progression

The process of epithelial-mesenchymal transition (EMT) is fundamental for embryonic morphogenesis. Cells undergoing it lose epithelial characteristics and integrity, acquire mesenchymal features, and become motile. In cancer, this program is hijacked to confer essential changes in morphology and motility that fuel invasion. In addition, EMT is increasingly understood to orchestrate a large variety of complementary cancer features, such as tumor cell stemness, tumorigenicity, resistance to therapy and adaptation to changes in the microenvironment. In this review, we summarize recent findings related to these various classical and non-classical functions, and introduce EMT as a true tumorigenic multi-tool, involved in many aspects of cancer. We suggest that therapeutic targeting of the EMT process will-if acknowledging these complexities-be a possibility to concurrently interfere with tumor progression on many levels.

The Emerging Role of T-Cell Immunoglobulin Mucin-3 in Breast Cancer: A Promising Target For Immunotherapy

Cancer treatment through immune checkpoint receptor blockade has made significant advances in the recent years. However, resistance to the current immune checkpoint inhibitors (ICIs) has been observed in many patients, who consequently do not respond to these treatments. T-cell immunoglobulin mucin-3 (Tim-3) is a novel immune checkpoint molecule emerging as a potential therapeutic target for cancer immunotherapy. Epidemiologic findings reveal that genetic polymorphisms in the Tim-3 gene are associated with increased susceptibility to breast cancer. In patients with breast cancer, Tim-3 is expressed both on immune and tumor cells. Accumulating evidence demonstrates that Tim-3 can notably affect breast cancer treatment outcome and prognosis. Therefore, Tim-3 is being regarded as a high-potential target for improving breast cancer therapy. In this review, we summarize the role of Tim-3 in breast cancer and the regulation mechanisms of Tim-3 to furnish evidences for future research and therapy.

The roles of polymorphonuclear myeloid-derived suppressor cells in endometriosis

OBJECTIVES

This study aimed to determine the systemic and local proportions, focal localization, and characteristics of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in endometriosis.

STUDY DESIGN

Peripheral blood and peritoneal fluid were obtained from patients with a benign gynecologic condition (controls) or endometriosis. PMN-MDSCs were defined as CD33⁺HLA-DR^low/-CD14^-CD15⁺ and monocytic (M)-MDSCs were defined as CD33⁺HLA-DR^low/-CD14⁺CD15^-, and were identified using flowcytometry. Ovarian endometriotic tissues were obtained, and the expression of lectin-type oxidized low density lipoprotein receptor-1 (LOX1) as a marker of PMN-MDSCs, arginine 1 (Arg1), and matrix metalloproteinase 9 (MMP9) were detected using immunohistochemistry. Anti-Ly6G antibody was administered to endometriosis model mice, and the number and weight of the lesions were measured, and cell proliferations and apoptosis in the lesions were analyzed using Ki67 immunohistochemistry and TUNEL assay.

RESULTS

In the peripheral blood, the proportion of PMN-MDSCs was significantly higher in endometriosis (3.20 vs 1.63 %, p < 0.05), but the proportion of M-MDSCs did not differ between the groups. In the peritoneal fluid, the proportion of PMN-MDSCs was significantly higher in endometriosis (7.82 × 10^-1% vs 6.48 × 10^-2%, p < 0.05), whereas the proportion of M-MDSCs did not differ between the groups. PMN-MDSCs were detected in the stromal cell layer of the endometriotic cyst wall. Double staining for LOX1 and Arg1, and LOX1 and MMP9 was confirmed. Administration of Ly6G antibody did not change the number or weight of endometriosis lesions, but significantly decreased Ki67-positive cells and increased TUNEL-positive cells in the lesions.

CONCLUSIONS

PMN-MDSCs may contribute to the pathogenesis of endometriosis via Arg1 and MMP9 expression.

MAPK10 Expression as a Prognostic Marker of the Immunosuppressive Tumor Microenvironment in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) remains a devastating malignancy worldwide due to lack of effective therapy. The immune-rich contexture of HCC tumor microenvironment (TME) makes this tumor an appealing target for immune-based therapies; however, the immunosuppressive TME is still a major challenge for more efficient immunotherapy in HCC. Using bioinformatics analysis based on the TCGA database, here we found that MAPK10 is frequently down-regulated in HCC tumors and significantly correlates with poor survival of HCC patients. HCC patients with low MAPK10 expression have lower expression scores of tumor infiltration lymphocytes (TILs) and stromal cells in the TME and increased scores of tumor cells than those with high MAPK10 expression. Further transcriptomic analyses revealed that the immune activity in the TME of HCC was markedly reduced in the low-MAPK10 group of HCC patients compared to the high-MAPK10 group. Additionally, we identified 495 differentially expressed immune-associated genes (DIGs), with 482 genes down-regulated and 13 genes up-regulated in parallel with the decrease of MAPK10 expression. GO enrichment and KEGG pathway analyses indicated that the biological functions of these DIGs included cell chemotaxis, leukocyte migration and positive regulation of the response to cytokine–cytokine receptor interaction, T cell receptor activation and MAPK signaling pathway. Protein–protein interaction (PPI) analyses of the 495 DIGs revealed five potential downstream hub genes of MAPK10, including SYK, CBL, VAV1, LCK, and CD3G. Several hub genes such as SYK, LCK, and VAV1 could respond to the immunological costimulatory signaling mediated by the transmembrane protein ICAM1, which was identified as a down-regulated DIG associated with low-MAPK10 expression. Moreover, ectopic overexpression or knock-down of MAPK10 could up-regulate or down-regulate ICAM1 expression via phosphorylation of c-jun at Ser63 in HCC cell lines, respectively. Collectively, our results demonstrated that MAPK10 down-regulation likely contributes to the immunosuppressive TME of HCC, and this gene might serve as a potential immunotherapeutic target and a prognostic factor for HCC patients.

Myeloid-Derived Suppressor Cells: Implications in the Resistance of Malignant Tumors to T Cell-Based Immunotherapy

T lymphocytes function as major players in antigen-mediated cytotoxicity and have become powerful tools for exploiting the immune system in tumor elimination. Several types of T cell-based immunotherapies have been prescribed to cancer patients with durable immunological response. Such strategies include immune checkpoint inhibitors, adoptive T cell therapy, cancer vaccines, oncolytic virus, and modulatory cytokines. However, the majority of cancer patients still failed to take the advantage of these kinds of treatments. Currently, extensive attempts are being made to uncover the potential mechanism of immunotherapy resistance, and myeloid-derived suppressor cells (MDSCs) have been identified as one of vital interpretable factors. Here, we discuss the immunosuppressive mechanism of MDSCs and their contributions to failures of T cell-based immunotherapy. Additionally, we summarize combination therapies to ameliorate the efficacy of T cell-based immunotherapy.

The Multifaceted Effects of Breast Cancer on Tumor-Draining Lymph Nodes

Breast cancer (BC) accounts for significant morbidity and mortality among women worldwide. About one in three patients with breast cancer present with lymph node (LN) metastasis and LN status is one of the most important prognostic predictors in patients with BC. In addition to their prognostic value, LNs initiate adaptive immunity against BC. Yet, BC cells often avoid immune-mediated destruction in LNs. This review provides an overview of the ways by which BC cells modulate LN stromal and hematopoietic cells to promote metastasis and immune evasion.

The MNK1/2-eIF4E Axis Supports Immune Suppression and Metastasis in Postpartum Breast Cancer

Breast cancer diagnosed within 10 years following childbirth is defined as postpartum breast cancer (PPBC) and is highly metastatic. Interactions between immune cells and other stromal cells within the involuting mammary gland are fundamental in facilitating an aggressive tumor phenotype. The MNK1/2-eIF4E axis promotes translation of prometastatic mRNAs in tumor cells, but its role in modulating the function of nontumor cells in the PPBC microenvironment has not been explored. Here, we used a combination of in vivo PPBC models and in vitro assays to study the effects of inactivation of the MNK1/2-eIF4E axis on the protumor function of select cells of the tumor microenvironment. PPBC mice deficient for phospho-eIF4E (eIF4E^S209A) were protected against lung metastasis and exhibited differences in the tumor and lung immune microenvironment compared with wild-type mice. Moreover, the expression of fibroblast-derived IL33, an alarmin known to induce invasion, was repressed upon MNK1/2-eIF4E axis inhibition. Imaging mass cytometry on PPBC and non-PPBC patient samples indicated that human PPBC contains phospho-eIF4E high-expressing tumor cells and CD8⁺ T cells displaying markers of an activated dysfunctional phenotype. Finally, inhibition of MNK1/2 combined with anti-PD-1 therapy blocked lung metastasis of PPBC. These findings implicate the involvement of the MNK1/2-eIF4E axis during PPBC metastasis and suggest a promising immunomodulatory route to enhance the efficacy of immunotherapy by blocking phospho-eIF4E. SIGNIFICANCE: This study investigates the MNK1/2-eIF4E signaling axis in tumor and stromal cells in metastatic breast cancer and reveals that MNK1/2 inhibition suppresses metastasis and sensitizes tumors to anti-PD-1 immunotherapy.

Epithelial-mesenchymal transition: When tumor cells meet myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous myeloid cell population characterized by protumoral functions in the tumor immune network. An increasing number of studies have focused on the biological functions of MDSCs in tumor immunity. Epithelial-mesenchymal transition (EMT) is a cellular plasticity process accompanied by a loss of epithelial phenotypes and an acquisition of mesenchymal phenotypes. In general, tumor cells that undergo EMT are more likely to invade and metastasize. Recently, extensive evidence suggests that EMT is closely related to a highly immunosuppressive environment. This review will summarize the immunosuppressive capacities of MDSC subsets and their distinct role in tumor EMT and further discuss immunotherapy for tumor EMT by targeting MDSCs.

Bone marrow cells are differentiated into MDSCs by BCC-Ex through down-regulating the expression of CXCR4 and activating STAT3 signalling pathway

Studies showed that the increase of myeloid‐derived suppressor cells (MDSCs) in tumour microenvironment is closely related to the resistant treatment and poor prognosis of metastatic breast cancer. However, the effect of tumour‐derived exosomes on MDSCs and its mechanism are not clear. Here, we reported that breast cancer cells (4T1)‐secreted exosomes (BCC‐Ex) were able to differentiate bone marrow cells into MDSCs and significantly inhibited the proliferation of T lymphocytes to provide an immunosuppressive microenvironment for cancer cells in vivo and in vitro. The number of MDSCs in bone marrow and spleen of 4T1 tumour‐bearing mice and BCC‐Ex infused mice was significantly higher than that of normal mice, whereas the number of T lymphocytes in spleen was significantly decreased. In addition, BCC‐Ex markedly promoted the differentiation of MDSCs from bone marrow cells or bone marrow cells derived macrophages, seen as the increased expressions of MDSCs‐related functional proteins Arginase‐1 (Arg‐1) and inducible nitric oxide synthase (iNOS). Furthermore, BCC‐Ex significantly down‐regulated the expressions of chemokine receptor CXCR4 and markedly up‐regulated the levels of inflammatory cytokines IL‐6 and IL‐10 in bone marrow cells and macrophages and remarkably inhibited the division and proliferation of T cells. Importantly, CXCR4 agonist, CXCL12, could reverse the function of BCC‐Ex, indicating that BCC‐Ex‐induced MDSCs might be dependent on the down‐regulation of CXCR4. Western blot showed that BCC‐Ex significantly promoted the phosphorylation of STAT3 in bone marrow cells, resulting in the inhibitions of the proliferation and apoptosis of bone marrow cells, and the aggravation of the differentiation of bone marrow cells into MDSCs.

The diverse roles of myeloid derived suppressor cells in mucosal immunity

The mucosal immune system plays a vital role in protecting the host from the external environment. Its major challenge is to balance immune responses against harmful and harmless agents and serve as a 'homeostatic gate keeper'. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of undifferentiated cells that are characterized by an immunoregulatory and immunosuppressive phenotype. Herein we postulate that MDSCs may be involved in shaping immune responses related to mucosal immunity, due to their immunomodulatory and tissue remodeling functions. Until recently, MDSCs were investigated mainly in cancerous diseases, where they induce and contribute to an immunosuppressive and inflammatory environment that favors tumor development. However, it is now becoming clear that MDSCs participate in non-cancerous conditions such as chronic infections, autoimmune diseases, pregnancy, aging processes and immune tolerance to commensal microbiota at mucosal sites. Since MDSCs are found in the periphery only in small numbers under normal conditions, their role is highlighted during pathologies characterized by acute or chronic inflammation, when they accumulate and become activated. In this review, we describe several aspects of the current knowledge characterizing MDSCs and their involvement in the regulation of the mucosal epithelial barrier, their crosstalk with commensal microbiota and pathogenic microorganisms, and their complex interactions with a variety of surrounding regulatory and effector immune cells. Finally, we discuss the beneficial and harmful outcomes of the MDSC regulatory functions in diseases affecting mucosal tissues. We wish to illuminate the pivotal role of MDSCs in mucosal immunity, the limitations in our understanding of all the players and the intricate challenges stemming from the complex interactions of MDSCs with their environment.

The Role of Myeloid-Derived Suppressor Cells (MDSCs) in the Development and/or Progression of Endometriosis-State of the Art

Endometriosis (EMS) is a common gynecological disease characterized by the presence of endometrial tissue outside the uterus. Approximately 10% of women around the world suffer from this disease. Recent studies suggest that endometriosis has potential to transform into endometriosis-associated ovarian cancer (EAOC). Endometriosis is connected with chronic inflammation and changes in the phenotype, activity, and function of immune cells. The underlying mechanisms include quantitative and functional disturbances of neutrophils, monocytes/macrophages (MO/MA), natural killer cells (NK), and T cells. A few reports have shown that immunosuppressive cells such as regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) may promote the progression of endometriosis. MDSCs are a heterogeneous population of immature myeloid cells (dendritic cells, granulocytes, and MO/MA precursors), which play an important role in the development of immunological diseases such as chronic inflammation and cancer. The presence of MDSCs in pathological conditions correlates with immunosuppression, angiogenesis, or release of growth factors and cytokines, which promote progression of these diseases. In this paper, we review the impact of MDSCs on different populations of immune cells, focusing on their immunosuppressive role in the immune system, which may be related with the pathogenesis and/or progression of endometriosis and its transformation into ovarian cancer.

Targeting the MDSCs of Tumors In Situ With Inhibitors of the MAPK Signaling Pathway to Promote Tumor Regression

Myeloid-derived suppressor cells (MDSCs) are one of the major components of the tumor microenvironment. Evidence has shown differences in the functions and fates of MDSCs in the tumor tissue and the periphery. However, the exact mechanism that regulates MDSC function has not been completely clarified. In this study, we performed RNA sequencing of MDSCs derived from the spleen and tumor. Based on the results of our RNA-seq analysis, mitogen-activated protein kinases (MAPK) were significantly increased in tumor polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). Subsequently, 3 major MAPK pathways, including extracellular signal-regulated protein kinases (ERK), p38 and c-Jun NH2-terminal kinases (JNK), were studied to analyze the role of MAPKs in MDSCs. The ERK 1/2 inhibitor SCH772984 and the JNK inhibitor SP600125 significantly increased the apoptosis of both PMN-MDSCs and M-MDSCs in vitro. In addition, SCH772984 exerted a strong effect on inhibiting tumor growth. The flow cytometry analysis showed significant increases in the ratio of M1:M2 tumor-associated macrophages, meanwhile the number of CD4⁺, CD8⁺, CD4⁺CD69⁺ and CD8⁺CD69⁺ lymphocytes were increased after SCH772984 treatment. Our findings established the effect of MAPKs on the tumor microenvironment via MDSCs and may facilitate the development of new antitumor strategies.

Progress and Challenges of Predictive Biomarkers for Immune Checkpoint Blockade

Over the past decade, immune checkpoint blockade (ICB) therapy has revolutionized the outlook for oncology with significant and sustained improvement in the overall patient survival. Unlike traditional cancer therapies, which target the cancer cells directly, ICB acts on the immune system to enhance anti-tumoral immunity. However, the response rate is still far from satisfactory and most patients are refractory to such treatment. Unfortunately, the mechanisms underlying such heterogeneous responses between patients to ICB therapy remain unclear. In addition, escalating costs of cancer care and unnecessary immune-related adverse events also are pertinent considerations with applications of ICB. Given these issues, identifying explicit predictive biomarkers for patient selection is an urgent unmet need to increase the efficacy of ICB therapy. The markers can be classified as tumor related and non-tumor-related biomarkers. Although substantial efforts have been put into investigating various biomarkers, none of them has been found to be sufficient for effectively stratifying patients who may benefit from immunotherapy. The present write up is an attempt to review the various emerging clinically relevant biomarkers affecting the efficacy of immune checkpoint inhibitors, as well as the limitations associated with their clinical application.

Immunotherapy Targeting Myeloid-Derived Suppressor Cells (MDSCs) in Tumor Microenvironment

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that accumulate in tumor-bearing hosts to reduce T cells activity and promote tumor immune escape in the tumor microenvironment (TME). The immune system in the TME can be stimulated to elicit an anti-tumor immune response through immunotherapy. The main theory of immunotherapy resides on the plasticity of the immune system and its capacity to be re-educated into a potent anti-tumor response. Thus, MDSCs within the TME became one of the major targets to improve the efficacy of tumor immunotherapy, and therapeutic strategies for tumor MDSCs were developed in the last few years. In the article, we analyzed the function of tumor MDSCs and the regulatory mechanisms of agents targeting MDSCs in tumor immunotherapy, and reviewed their therapeutic effects in MDSCs within the TME. Those data focused on discussing how to promote the differentiation and maturation of MDSCs, reduce the accumulation and expansion of MDSCs, and inhibit the function, migration and recruitment of MDSCs, further preventing the growth, invasion and metastasis of tumor. Those investigations may provide new directions for cancer therapy.

Myeloid-Derived Suppressor Cells Are a Major Source of Wnt5A in the Melanoma Microenvironment and Depend on Wnt5A for Full Suppressive Activity

Metastatic dissemination remains a significant barrier to successful therapy for melanoma. Wnt5A is a potent driver of invasion in melanoma and is believed to be secreted from the tumor microenvironment (TME). Our data suggest that myeloid-derived suppressor cells (MDSC) in the TME are a major source of Wnt5A and are reliant upon Wnt5A for multiple actions. Knockdown of Wnt5A specifically in the myeloid cells demonstrated a clear decrease in Wnt5A expression within the TME in vivo as well as a decrease in intratumoral MDSC and regulatory T cell (Treg). Wnt5A knockdown also decreased the immunosuppressive nature of MDSC and decreased expression of TGFβ1 and arginase 1. In the presence of Wnt5A-depleted MDSC, tumor-infiltrating lymphocytes expressed decreased PD-1 and LAG3, suggesting a less exhausted phenotype. Myeloid-specific Wnt5A knockdown also led to decreased lung metastasis. Tumor-infiltrating MDSC from control animals showed a strong positive correlation with Treg, which was completely ablated in animals with Wnt5A-negative MDSC. Overall, our data suggest that while MDSC contribute to an immunosuppressive and less immunogenic environment, they exhibit an additional function as the major source of Wnt5A in the TME. SIGNIFICANCE: These findings demonstrate that myeloid cells provide a major source of Wnt5A to facilitate metastatic potential in melanoma cells and rely on Wnt5A for their immunosuppressive function.

Immunosuppressive Myeloid Cells Induce Nitric Oxide-Dependent DNA Damage and p53 Pathway Activation in CD8+ T Cells

Tumor-infiltrating myeloid-derived suppressor cells (MDSC) are associated with poor survival outcomes in many human cancers. MDSCs inhibit T cell-mediated tumor immunity in part because they strongly inhibit T-cell function. However, whether MDSCs inhibit early or later steps of T-cell activation is not well established. Here we show that MDSCs inhibited proliferation and induced apoptosis of CD8⁺ T cells even in the presence of dendritic cells (DC) presenting a high-affinity cognate peptide. This inhibitory effect was also observed with delayed addition of MDSCs to cocultures, consistent with functional data showing that T cells expressed multiple early activation markers even in the presence of MDSCs. Single-cell RNA-sequencing analysis of CD8⁺ T cells demonstrated a p53 transcriptional signature in CD8⁺ T cells cocultured with MDSCs and DCs. Confocal microscopy showed induction of DNA damage and nuclear accumulation of activated p53 protein in a substantial fraction of these T cells. DNA damage in T cells was dependent on the iNOS enzyme and subsequent nitric oxide release by MDSCs. Small molecule-mediated inhibition of iNOS or inactivation of the Nos2 gene in MDSCs markedly diminished DNA damage in CD8⁺ T cells. DNA damage in CD8⁺ T cells was also observed in KPC pancreatic tumors but was reduced in tumors implanted into Nos2-deficient mice compared with wild-type mice. These data demonstrate that MDSCs do not block early steps of T-cell activation but rather induce DNA damage and p53 pathway activation in CD8⁺ T cells through an iNOS-dependent pathway.

Crosstalk between Tumor Cells and Immune System Leads to Epithelial-Mesenchymal Transition Induction and Breast Cancer Progression

Herein, we review the current findings of how a variety of accessory cells could participate in shaping the tumor microenvironment and supporting the mechanisms by which cancer cells undertake the epithelial-mesenchymal transition (EMT). EMT, a complex of phenotypic changes, promotes cancer cell invasion and creates resistance to chemotherapies. Among the accessory cells present in the EMT, immune cells (both native and adaptive) can reciprocally influence the tumor cells features, promote EMT and negatively regulate the anticancer immune response. In this review, we look over the role of EMT in crosstalk between tumor cells and the immune system, with specific emphasis on breast tumors. Finally, we suggest that understanding the role of immune cells in cancer progression could create new opportunities for diagnostic and therapeutic interventions in cancer combination therapy.

Dormancy in the Tumor Microenvironment

Tumor cells frequently disseminate to distant organ sites, where they encounter permissive or restrictive environments that enable them to grow and colonize or enter a dormant state. Tumor dormancy is not strictly defined, but generally describes a tumor cell that is non-proliferative or in a state of balanced equilibrium, in which the proliferation rate of the tumor cell or cells is equal to its rate of cell death. The mechanisms that regulate tumor cell entry into and exit from dormancy are poorly understood, but microenvironmental features as well as tumor cell intrinsic factors play an important role in mediating this transition. Upon homing to distant metastatic sites, tumor cells may disseminate into various niches, most frequently the perivascular, hematopoietic stem cell, or endosteal/osteogenic niche. Tumor cells sense the cytokines, growth factors, and chemo-attractants from each of these niches, and tumor cell expression of cognate ligands and receptors can determine whether a tumor cell enters or exits dormancy. In addition to the secreted factors and cell-cell interactions that regulate dormancy, the cellular milieu also impacts upon disseminated tumor cells to promote or restrain their growth in distant metastatic sites. In this chapter we will discuss the role of the osteogenic and perivascular niche on dormant tumor cells, as well as the impact of hypoxia (low oxygen tensions) and the immune system on the restriction and outgrowth of dormant, disseminated tumor cells.

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.

Immune microenvironment in different molecular subtypes of ductal breast carcinoma

PURPOSE

Ductal breast carcinoma as a heterogeneous disease has different molecular subtypes associated with clinical prognosis and patients' survival. The role of immune system as a consistent part of the tumor microenvironment (TME) has been documented in progression of ductal breast carcinoma. Here, we aimed to describe the important immune cells and the immune system-associated molecules in Ductal Carcinoma In situ (DCIS) and Invasive Ductal Carcinoma (IDC) with special emphasis on their associations with different molecular subtypes and patients' prognosis.

RESULTS

The immune cells have a dual role in breast cancer (BC) microenvironment depending on the molecular subtype or tumor grade. These cells with different frequencies are present in the TME of DCIS and IDC. The presence of regulatory cells including Tregs, MDSC, Th2, Th17, M2 macrophages, HLADR^- T cells, and Tγδ cells is related to more immunosuppressive microenvironment, especially in ER^- and TN subtypes. In contrast, NK cells, CTL, Th, and Tfh cells are associated to the anti-tumor activity. These cells are higher in ER⁺ BC, although in other subtypes such as TN or HER2⁺ are associated with a favorable prognosis.

CONCLUSION

Determining the specific immune response in each subtype could be helpful in estimating the possible behavior of the tumor cells in TME. It is important to realize that different frequencies of immune cells in BC environment likely determine the patients' prognosis and their survival in each subtype. Therefore, elucidation of the distinct immune players in TME would be helpful toward developing targeted therapies in each subtype.

Nitroxoline inhibits bladder cancer progression by reversing EMT process and enhancing anti-tumor immunity

Nitroxoline is considered to be an effective treatment for the urinary tract infections. Recently, it has been found to be effective against several cancers. However, few studies have examined the anti-tumor activity of nitroxoline in bladder cancer. The purpose of the study was to reveal the possible mechanisms how nitroxoline inhibited bladder cancer progression. In vitro assay, we demonstrated that nitroxoline inhibited bladder cancer cell growth and migration in a concentration-related manner. Western blot analysis demonstrated that nitroxoline downregulated the expressions of epithelial mesenchymal transition (EMT)-related proteins. Furthermore, treatment with nitroxoline in the C3H/He mice bladder cancer subcutaneous model resulted in significant inhibition of tumor growth. Moreover, the percentage of myeloid-derived suppressor cells (MDSC) in peripheral blood cells significantly decreased after treatment of nitroxoline. Taken together, our results suggested that nitroxoline may be used as a potential drug for bladder cancer.

Identification and Validation of Stage-Associated PBMC Biomarkers in Breast Cancer Using MS-Based Proteomics

Background: It is well-described that the transcriptome of peripheral blood mononuclear cells (PBMCs) can be altered in the context of many malignancies to allow them avoid the effective immune response, which leads to cancer invasiveness. Here, we used an MS-based strategy to discover biomarkers in the PBMCs of breast cancer (BC) patients and validated them at different stages of BC. Methods: PBMCs were isolated from the breast cancer patients and were cultured alone or co-cultured with breast cancer cell lines. The role of PBMC in the invasion property of breast cancer cells was explored. NF-kB activity was also measured in the co-cultured breast cancer cells. Identification of protein profiles in the secretome and proteome of the co-cultured PBMCs was performed using SWATH mass spectrometry. Pathway enrichment and gene ontology analyses were carried out to look for the molecular pathways correlated with the protein expression profile of PBMCs in the breast cancer patients. Quantitative real-time polymerase chain reaction (qPCR) was performed to validate the candidate genes in the PBMC fraction of the breast cancer patients at the primary and metastatic stages. In silico survival analysis was performed to assess the potential clinical biomarkers in these PBMC subtypes. Results: PBMCs could significantly increase the invasion property of the BC cells concomitant with a decrease in E-cadherin and an increase in both Vimentin and N-cadherin expression. The NF-kB activity in the BC cells significantly increased following co-culturing implying the role of PBMCs in EMT induction. Enrichment analysis showed that the differentially expressed proteins in PBMCs are mainly associated with IL-17, PI3K-Akt, and HIF-1 signaling pathway, in which a set of seven proteins including TMSB4X, HSPA4, S100A9, SRSF6, THBS1, CUL4A, and CANX were frequently expressed. Finally, in silico analysis confirmed that a gene set consisting of S100A9, SRSF6, THBS1, CUL4A, and CANX were found to provide an insight for the identification of metastasis in breast cancer patients. Conclusion: In conclusion, our study revealed that the protein expression profile in PBMCs is a reflection of the proteins expressed in the BC tissue itself; however, the abundance level is different due to the stage of cancer.

Activation of STING by cGAMP Regulates MDSCs to Suppress Tumor Metastasis via Reversing Epithelial-Mesenchymal Transition

The role of cGAMP stimulating cGAS-cGAMP-STING-IRF3 pathway to inhibit tumor growth was well-established. Herein, the efficiency and pharmacological mechanism of cGAMP on regulating tumor metastasis was investigated. The effects of cGAMP regulating CD8⁺ T cells and myeloid-derived suppressor cells (MDSCs) in tumor microenvironment was explored. In this study, we found that cGAMP boosted STING signaling pathway to activate the production of IFN-γ from CD8⁺ T cells, and decreased the population of MDSCs in vivo. The metastasis in CT26 tumor bearing mice was inhibited by cGAMP via regulating EMT process. cGAMP played an important role in suppressing the production of reactive oxygen species (ROS) and nitric oxide (NO) from MDSCs, abolished the suppressive function of MDSCs to the T cells. All in all, the results indicated that the STING agonist cGAMP activated the production of IFN-γ from CD8⁺ T cells to suppress MDSCs in vivo.

Beyond Cell Motility: The Expanding Roles of Chemokines and Their Receptors in Malignancy

The anti-tumor activities of some members of the chemokine family are often overcome by the functions of many chemokines that are strongly and causatively linked with increased tumor progression. Being key leukocyte attractants, chemokines promote the presence of inflammatory pro-tumor myeloid cells and immune-suppressive cells in tumors and metastases. In parallel, chemokines elevate additional pro-cancerous processes that depend on cell motility: endothelial cell migration (angiogenesis), recruitment of mesenchymal stem cells (MSCs) and site-specific metastasis. However, the array of chemokine activities in cancer expands beyond such “typical” migration-related processes and includes chemokine-induced/mediated atypical functions that do not activate directly motility processes; these non-conventional chemokine functions provide the tumor cells with new sets of detrimental tools. Within this scope, this review article addresses the roles of chemokines and their receptors at atypical levels that are exerted on the cancer cell themselves: promoting tumor cell proliferation and survival; controlling tumor cell senescence; enriching tumors with cancer stem cells; inducing metastasis-related functions such as epithelial-to-mesenchymal transition (EMT) and elevated expression of matrix metalloproteinases (MMPs); and promoting resistance to chemotherapy and to endocrine therapy. The review also describes atypical effects of chemokines at the tumor microenvironment: their ability to up-regulate/stabilize the expression of inhibitory immune checkpoints and to reduce the efficacy of their blockade; to induce bone remodeling and elevate osteoclastogenesis/bone resorption; and to mediate tumor-stromal interactions that promote cancer progression. To illustrate this expanding array of atypical chemokine activities at the cancer setting, the review focuses on major metastasis-promoting inflammatory chemokines—including CXCL8 (IL-8), CCL2 (MCP-1), and CCL5 (RANTES)—and their receptors. In addition, non-conventional activities of CXCL12 which is a key regulator of tumor progression, and its CXCR4 receptor are described, alongside with the other CXCL12-binding receptor CXCR7 (RDC1). CXCR7, a member of the subgroup of atypical chemokine receptors (ACKRs) known also as ACKR3, opens the gate for discussion of atypical activities of additional ACKRs in cancer: ACKR1 (DARC, Duffy), ACKR2 (D6), and ACKR4 (CCRL1). The mechanisms involved in chemokine activities and the signals delivered by their receptors are described, and the clinical implications of these findings are discussed.

Reciprocal Signaling between Myeloid Derived Suppressor and Tumor Cells Enhances Cellular Motility and is Mediated by Structural Cues in the Microenvironment

Myeloid derived suppressor cells (MDSCs) have gained significant attention for their immunosuppressive role in cancer and their ability to contribute to tumor progression and metastasis. Understanding the role of MDSCs in driving cancer cell migration, a process fundamental to metastasis, is essential to fully comprehend and target MDSC-tumor cell interactions. This study employs microfabricated platforms, which simulate the structural cues present in the tumor microenvironment (TME) to elucidate the effects of MDSCs on the migratory phenotype of cancer cells at the single cell level. The results indicate that the presence of MDSCs enhances the motility of cancer-epithelial cells when directional cues (either topographical or spatial) are present. This behavior appears to be independent of cell-cell contact and driven by soluble byproducts from heterotypic interactions between MDSCs and cancer cells. Moreover, MDSC cell-motility is also impacted by the presence of cancer cells and the cancer cell secretome in the presence of directional cues. Epithelial dedifferentiation is the likely mechanism for changes in cancer cell motility in response to MDSCs. These results highlight the biochemical and biostructural conditions under which MDSCs can support cancer cell migration, and could therefore provide new avenues of research and therapy aimed at stemming cancer progression.

Myeloid-derived suppressor cells in obstetrical and gynecological diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of myeloid-origin cells which have immunosuppressive activities in several conditions, such as cancer and inflammation. Recent research has also associated MDSCs with numerous obstetrical and gynecological diseases. During pregnancy, MDSCs accumulate to ensure maternal-fetal immune tolerance, whereas they are decreased in patients who suffer from early miscarriage or pre-eclampsia. While the etiology of endometriosis is still unknown, abnormal accumulation of MDSCs in the peripheral blood and peritoneal fluid, alongside an increased level of reactive oxygen species (ROS), has been observed in these patients, which is central to the cellular immune regulations by MDSCs. Additionally, the regulation of MDSCs observed in tumours is also applicable to gynecologic neoplasms, including ovarian cancer and cervical cancer. More recently, emerging evidence has shown that there are high levels of MDSCs in premature ovarian failure (POF) and in vitro fertilization (IVF), but the underlying mechanisms are unknown. In this review, the generation and mechanisms of MDSCs are summarized. In particular, the modulation of these cells in immune-related obstetrical and gynecological diseases is discussed, including potential treatment options targeting MDSCs.