Nitric oxide-producing myeloid-derived suppressor cells inhibit vascular E-selectin expression in human squamous cell carcinomas

High-Risk Non-Melanoma Skin Cancers: Biological and Therapeutic Advances

Nonmelanoma skin cancers (NMSCs) are the most common cancers, with high-risk NMSCs sharing features such as poor histologic differentiation, invasion into deeper layers, and anatomic location. NMSC includes basal cell carcinoma, cutaneous squamous cell carcinoma, and Merkel cell carcinoma. Herein, the authors describe advances in understanding the genetic mechanisms of malignant transformation and the composition of tumor microenvironment for these cancers. They summarize recent therapeutic advances, including targeted therapy and immunotherapy for NMSCs. Effective skin protection against ultraviolet radiation-induced carcinogenesis remains an urgent unmet need for NMSC prevention. The authors highlight immune-based interventions as novel strategies to address this need.

Immune Checkpoints and Cellular Landscape of the Tumor Microenvironment in Non-Melanoma Skin Cancer (NMSC)

Non-melanoma skin cancer (NMSC) is primarily categorized into basal cell carcinoma (BCC), the most prevalent form of skin cancer, and cutaneous squamous cell carcinoma (cSCC), the second most common type. Both BCC and cSCC represent a significant health burden, particularly in immunocompromised individuals and the elderly. The immune system plays a pivotal role in the development and progression of NMSC, making it a critical focus for therapeutic interventions. This review highlights key immunological targets in BCC and cSCC, with a focus on immune checkpoint molecules such as PD-1/PD-L1 and CTLA-4, which regulate T cell activity and contribute to immune evasion. This review also highlights anti-tumor immune cell subsets within the tumor microenvironment (TME), such as tumor-infiltrating lymphocytes (TILs) and dendritic cells. Additionally, it examines the immunosuppressive elements of the TME, including regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and cancer-associated fibroblasts (CAFs), as well as their roles in NMSC progression and resistance to therapy. Emerging strategies targeting these immune elements, such as monoclonal antibodies, are also discussed for their potential to enhance anti-tumor immune responses and improve clinical outcomes. By elucidating the immunological landscape of BCC and cSCC and drawing comparisons to melanoma, this review highlights the transformative potential of immunotherapy in treating these malignancies.

Exploring the role of the immune microenvironment in hepatocellular carcinoma: Implications for immunotherapy and drug resistance

Hepatocellular carcinoma (HCC), the most common type of liver tumor, is a leading cause of cancer-related deaths, and the incidence of liver cancer is still increasing worldwide. Curative hepatectomy or liver transplantation is only indicated for a small population of patients with early-stage HCC. However, most patients with HCC are not candidates for radical resection due to disease progression, leading to the choice of the conventional tyrosine kinase inhibitor drug sorafenib as first-line treatment. In the past few years, immunotherapy, mainly immune checkpoint inhibitors (ICIs), has revolutionized the clinical strategy for HCC. Combination therapy with ICIs has proven more effective than sorafenib, and clinical trials have been conducted to apply these therapies to patients. Despite significant progress in immunotherapy, the molecular mechanisms behind it remain unclear, and immune resistance is often challenging to overcome. Several studies have pointed out that the complex intercellular communication network in the immune microenvironment of HCC regulates tumor escape and drug resistance to immune response. This underscores the urgent need to analyze the immune microenvironment of HCC. This review describes the immunosuppressive cell populations in the immune microenvironment of HCC, as well as the related clinical trials, aiming to provide insights for the next generation of precision immunotherapy.

Targeting amino acid-metabolizing enzymes for cancer immunotherapy

Despite the immune system's role in the detection and eradication of abnormal cells, cancer cells often evade elimination by exploitation of various immune escape mechanisms. Among these mechanisms is the ability of cancer cells to upregulate amino acid-metabolizing enzymes, or to induce these enzymes in tumor-infiltrating immunosuppressive cells. Amino acids are fundamental cellular nutrients required for a variety of physiological processes, and their inadequacy can severely impact immune cell function. Amino acid-derived metabolites can additionally dampen the anti-tumor immune response by means of their immunosuppressive activities, whilst some can also promote tumor growth directly. Based on their evident role in tumor immune escape, the amino acid-metabolizing enzymes glutaminase 1 (GLS1), arginase 1 (ARG1), inducible nitric oxide synthase (iNOS), indoleamine 2,3-dioxygenase 1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and interleukin 4 induced 1 (IL4I1) each serve as a promising target for immunotherapeutic intervention. This review summarizes and discusses the involvement of these enzymes in cancer, their effect on the anti-tumor immune response and the recent progress made in the preclinical and clinical evaluation of inhibitors targeting these enzymes.

Immunosuppressive regulatory cells in cancer immunotherapy: restrain or modulate?

Immunosuppressive regulatory cells (IRCs) play important roles in negatively regulating immune response, and are mainly divided into myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs). Large numbers of preclinical and clinical studies have shown that inhibition or reduction of IRCs could effectively elevate antitumor immune responses. However, several studies also reported that excessive inhibition of IRCs function is one of the main reasons causing the side effects of cancer immunotherapy. Therefore, the reasonable regulation of IRCs is crucial for improving the safety and efficiency of cancer immunotherapy. In this review, we summarised the recent research advances in the cancer immunotherapy by regulating the proportion of IRCs, and discussed the roles of IRCs in regulating tumour immune evasion and drug resistance to immunotherapies. Furthermore, we also discussed how to balance the potential opportunities and challenges of using IRCs to improve the safety of cancer immunotherapies.

Immune Cell Migration to Cancer

Immune cell migration is required for the development of an effective and robust immune response. This elegant process is regulated by both cellular and environmental factors, with variables such as immune cell state, anatomical location, and disease state that govern differences in migration patterns. In all cases, a major factor is the expression of cell surface receptors and their cognate ligands. Rapid adaptation to environmental conditions partly depends on intrinsic cellular immune factors that affect a cell's ability to adjust to new environment. In this review, we discuss both myeloid and lymphoid cells and outline key determinants that govern immune cell migration, including molecules required for immune cell adhesion, modes of migration, chemotaxis, and specific chemokine signaling. Furthermore, we summarize tumor-specific elements that contribute to immune cell trafficking to cancer, while also exploring microenvironment factors that can alter these cellular dynamics within the tumor in both a pro and antitumor fashion. Specifically, we highlight the importance of the secretome in these later aspects. This review considers a myriad of factors that impact immune cell trajectory in cancer. We aim to highlight the immunotherapeutic targets that can be harnessed to achieve controlled immune trafficking to and within tumors.

Mechanisms underlying immunosuppression by regulatory cells

Regulatory cells, such as regulatory T cells (Tregs), regulatory B cells (Bregs), and myeloid-derived suppressor cells (MDSCs), play a crucial role in preserving immune tolerance and controlling immune responses during infections to prevent excessive immune activation. However, pathogens have developed strategies to hijack these regulatory cells to decrease the overall effectiveness of the immune response and persist within the host. Consequently, therapeutic targeting of these immunosuppressive mechanisms during infection can reinvigorate the immune response and improve the infection outcome. The suppressive mechanisms of regulatory cells are not only numerous but also redundant, reflecting the complexity of the regulatory network in modulating the immune responses. The context of the immune response, such as the type of pathogen or tissue involved, further influences the regulatory mechanisms involved. Examples of these immunosuppressive mechanisms include the production of inhibitory cytokines such as interleukin 10 (IL-10) and transforming growth factor beta (TGF-β) that inhibit the production of pro-inflammatory cytokines and dampen the activation and proliferation of effector T cells. In addition, regulatory cells utilize inhibitory receptors like cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) to engage with their respective effector cells, thereby suppressing their function. An alternative approach involves the modulation of metabolic reprogramming in effector immune cells to limit their activation and proliferation. In this review, we provide an overview of the major mechanisms mediating the immunosuppressive effect of the different regulatory cell subsets in the context of infection.

Myeloid-derived suppressor cells in cancer and cancer therapy

Anticancer agents continue to dominate the list of newly approved drugs, approximately half of which are immunotherapies. This trend illustrates the considerable promise of cancer treatments that modulate the immune system. However, the immune system is complex and dynamic, and can have both tumour-suppressive and tumour-promoting effects. Understanding the full range of immune modulation in cancer is crucial to identifying more effective treatment strategies. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid cells that develop in association with chronic inflammation, which is a hallmark of cancer. Indeed, MDSCs accumulate in the tumour microenvironment, where they strongly inhibit anticancer functions of T cells and natural killer cells and exert a variety of other tumour-promoting effects. Emerging evidence indicates that MDSCs also contribute to resistance to cancer treatments, particularly immunotherapies. Conversely, treatment approaches designed to eliminate cancer cells can have important additional effects on MDSC function, which can be either positive or negative. In this Review, we discuss the interplay between MDSCs and various other cell types found in tumours as well as the mechanisms by which MDSCs promote tumour progression. We also discuss the relevance and implications of MDSCs for cancer therapy.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Amino acid metabolism in immune cells: essential regulators of the effector functions, and promising opportunities to enhance cancer immunotherapy

Amino acids are basic nutrients for immune cells during organ development, tissue homeostasis, and the immune response. Regarding metabolic reprogramming in the tumor microenvironment, dysregulation of amino acid consumption in immune cells is an important underlying mechanism leading to impaired anti-tumor immunity. Emerging studies have revealed that altered amino acid metabolism is tightly linked to tumor outgrowth, metastasis, and therapeutic resistance through governing the fate of various immune cells. During these processes, the concentration of free amino acids, their membrane bound transporters, key metabolic enzymes, and sensors such as mTOR and GCN2 play critical roles in controlling immune cell differentiation and function. As such, anti-cancer immune responses could be enhanced by supplement of specific essential amino acids, or targeting the metabolic enzymes or their sensors, thereby developing novel adjuvant immune therapeutic modalities. To further dissect metabolic regulation of anti-tumor immunity, this review summarizes the regulatory mechanisms governing reprogramming of amino acid metabolism and their effects on the phenotypes and functions of tumor-infiltrating immune cells to propose novel approaches that could be exploited to rewire amino acid metabolism and enhance cancer immunotherapy.

Barriers to immune cell infiltration in tumors

Increased immune cell infiltration into tumors is associated with improved patient survival and predicts response to immune therapies. Thus, identification of factors that determine the extent of immune infiltration is crucial, so that methods to intervene on these targets can be developed. T cells enter tumor tissues through the vasculature, and under control of interactions between homing receptors on the T cells and homing receptor ligands (HRLs) expressed by tumor vascular endothelium and tumor cell nests. HRLs are often deficient in tumors, and there also may be active barriers to infiltration. These remain understudied but may be crucial for enhancing immune-mediated cancer control. Multiple intratumoral and systemic therapeutic approaches show promise to enhance T cell infiltration, including both approved therapies and experimental therapies. This review highlights the intracellular and extracellular determinants of immune cell infiltration into tumors, barriers to infiltration, and approaches for intervention to enhance infiltration and response to immune therapies.

Understanding the squamous cell carcinoma immune microenvironment

Primary cutaneous squamous cell carcinoma (cSCC) is the second most common human cancer with a rising incidence of about 1.8 million in the United States annually. Primary cSCC is usually curable by surgery; however, in some cases, cSCC eventuates in nodal metastasis and death from disease specific death. cSCC results in up to 15,000 deaths each year in the United States. Until recently, non-surgical options for treatment of locally advanced or metastatic cSCC were largely ineffective. With the advent of checkpoint inhibitor immunotherapy, including cemiplimab and pembrolizumab, response rates climbed to 50%, representing a vast improvement over chemotherapeutic agents used previously. Herein, we discuss the phenotype and function of SCC associated Langerhans cells, dendritic cells, macrophages, myeloid derived suppressor cells and T cells as well as SCC-associated lymphatics and blood vessels. Possible role(s) of SCC-associated cytokines in progression and invasion are reviewed. We also discuss the SCC immune microenvironment in the context of currently available and pipeline therapeutics.

Exposure of Immunogenic Tumor Antigens in Surrendered Immunity and the Significance of Autologous Tumor Cell-Based Vaccination in Precision Medicine

The mechanisms by which immune systems identify and destroy tumors, known as immunosurveillance, have been discussed for decades. However, several factors that lead to tumor persistence and escape from the attack of immune cells in a normal immune system have been found. In the process known as immunoediting, tumors decrease their immunogenicity and evade immunosurveillance. Furthermore, tumors exploit factors such as regulatory T cells, myeloid-derived suppressive cells, and inhibitory cytokines that avoid cytotoxic T cell (CTL) recognition. Current immunotherapies targeting tumors and their surroundings have been proposed. One such immunotherapy is autologous cancer vaccines (ACVs), which are characterized by enriched tumor antigens that can escalate specific CTL responses. Unfortunately, ACVs usually fail to activate desirable therapeutic effects, and the low immunogenicity of ACVs still needs to be elucidated. This difficulty highlights the significance of immunogenic antigens in antitumor therapies. Previous studies have shown that defective host immunity triggers tumor development by reprogramming tumor antigenic expressions. This phenomenon sheds new light on ACVs and provides a potential cue to improve the effectiveness of ACVs. Furthermore, synergistically with the ACV treatment, combinational therapy, which can reverse the suppressive tumor microenvironments, has also been widely proposed. Thus, in this review, we focus on tumor immunogenicity sculpted by the immune systems and discuss the significance and application of restructuring tumor antigens in precision medicine.

Myeloid-derived suppressor cells: an emerging target for anticancer immunotherapy

The clinical responses observed following treatment with immune checkpoint inhibitors (ICIs) support immunotherapy as a potential anticancer treatment. However, a large proportion of patients cannot benefit from it due to resistance or relapse, which is most likely attributable to the multiple immunosuppressive cells in the tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSCs), a heterogeneous array of pathologically activated immature cells, are a chief component of immunosuppressive networks. These cells potently suppress T-cell activity and thus contribute to the immune escape of malignant tumors. New findings indicate that targeting MDSCs might be an alternative and promising target for immunotherapy, reshaping the immunosuppressive microenvironment and enhancing the efficacy of cancer immunotherapy. In this review, we focus primarily on the classification and inhibitory function of MDSCs and the crosstalk between MDSCs and other myeloid cells. We also briefly summarize the latest approaches to therapies targeting MDSCs.

Myeloid-derived suppressor cells: an emerging target for anticancer immunotherapy

The clinical responses observed following treatment with immune checkpoint inhibitors (ICIs) support immunotherapy as a potential anticancer treatment. However, a large proportion of patients cannot benefit from it due to resistance or relapse, which is most likely attributable to the multiple immunosuppressive cells in the tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSCs), a heterogeneous array of pathologically activated immature cells, are a chief component of immunosuppressive networks. These cells potently suppress T-cell activity and thus contribute to the immune escape of malignant tumors. New findings indicate that targeting MDSCs might be an alternative and promising target for immunotherapy, reshaping the immunosuppressive microenvironment and enhancing the efficacy of cancer immunotherapy. In this review, we focus primarily on the classification and inhibitory function of MDSCs and the crosstalk between MDSCs and other myeloid cells. We also briefly summarize the latest approaches to therapies targeting MDSCs.

Targeting tumour-reprogrammed myeloid cells: the new battleground in cancer immunotherapy

Tumour microenvironment is a complex ecosystem in which myeloid cells are the most abundant immune elements. This cell compartment is composed by different cell types, including neutrophils, macrophages, dendritic cells, and monocytes but also unexpected cell populations with immunosuppressive and pro-tumour roles. Indeed, the release of tumour-derived factors influences physiological haematopoiesis producing unconventional cells with immunosuppressive and tolerogenic functions such as myeloid-derived suppressor cells. These pro-tumour myeloid cell populations not only support immune escape directly but also assist tumour invasion trough non-immunological activities. It is therefore not surprising that these cell subsets considerably impact in tumour progression and cancer therapy resistance, including immunotherapy, and are being investigated as potential targets for developing a new era of cancer therapy. In this review, we discuss emerging strategies able to modulate the functional activity of these tumour-supporting myeloid cells subverting their accumulation, recruitment, survival, and functions. These innovative approaches will help develop innovative, or improve existing, cancer treatments.

MDSCs and T cells in solid tumors and non-Hodgkin lymphomas: an immunosuppressive speech

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous subset of cells expanded during multiple pathological settings, including cancers. In tumors, MDSCs are dominant drivers of T-cell immunosuppression. To accomplish their job, they exploit multiple mechanisms ultimately leading to the paralysis of anti-tumor immunity. Among the variety of MDSC-ways of working within the tumor microenvironment, the generation of reactive species and the metabolic reprogramming have emerged as pivotal determinants of their immunosuppressive power. In this review we will overview integral mechanisms of MDSC-mediated immunosuppression in solid tumors, with a particular focus on Non-Hodgkin lymphoma.

Granulocyte-Macrophage Colony-Stimulating Factor Modulates Myeloid-Derived Suppressor Cells and Treg Activity in Decompensated Cirrhotic Patients With Sepsis

Background

Decompensated cirrhosis patients are more prone to bacterial infections. Myeloid-derived suppressor cells (MDSCs) expand in sepsis patients and disrupt immune cell functions. Granulocyte-macrophage colony-stimulating factor (GM-CSF) therapy helps in restoring immune cell functions and resolving infections. Its role in MDSC modulation in cirrhosis with sepsis is not well understood.

Methods

A total of 164 decompensated cirrhotic—62 without (w/o), 72 with sepsis, and 30 with sepsis treated with GM-CSF—and 15 healthy were studied. High-dimensional flow cytometry was performed to analyze MDSCs, monocytes, neutrophils, CD4 T cells, and Tregs at admission and on days 3 and day 7. Ex vivo co-cultured MDSCs with T cells were assessed for proliferation and apoptosis of T cells and differentiation to Tregs. Plasma factors and mRNA levels were analyzed by cytokine-bead assay and qRT-PCR.

Results

Frequencies of MDSCs and Tregs were significantly increased (p = 0.011 and p = 0.02) with decreased CD4 T cells (p = 0.01) in sepsis than w/o sepsis and healthy controls (HCs) (p = 0.000, p = 0.07, and p = 0.01) at day 0 and day 7. In sepsis patients, MDSCs had increased IL-10, Arg1, and iNOS mRNA levels (p = 0.016, p = 0.043, and p = 0.045). Ex vivo co-cultured MDSCs with T cells drove T-cell apoptosis (p = 0.03, p = 0.03) with decreased T-cell proliferation and enhanced FOXP3⁺ expression (p = 0.044 and p = 0.043) in sepsis compared to w/o sepsis at day 0. Moreover, blocking the MDSCs with inhibitors suppressed FOXP3 expression. GM-CSF treatment in sepsis patients significantly decreased MDSCs and FOXP3⁺ Tregs but increased CD4 T-cell functionality and improved survival.

Conclusion

MDSCs have an immunosuppressive function by expanding FOXP3⁺ Tregs and inhibiting CD4⁺ T-cell proliferation in sepsis. GM-CSF treatment suppressed MDSCs, improved T-cell functionality, and reduced Tregs in circulation.

Inhibition of NOS1 promotes the interferon response of melanoma cells

Background

NOS1 expression predicts poor prognosis in patients with melanoma. However, the molecular function of NOS1 in the type I IFN response and immune escape of melanoma is still unknown.

Methods

The CRISPR/Cas9 system was used to generate NOS1-knockout melanoma cells and the biological characteristics of NOS1-knockout cells were evaluated by MTT assay, clonogenic assay, EdU assay, and flow cytometric assay. The effect on tumor growth was tested in BALB/c-nu and C57BL/6 mouse models. The gene expression profiles were detected with Affymetrix microarray and RNA-seq and KEGG (Kyoto Encyclopedia of Genes and Genomes) and CLUE GO analysis was done. The clinical data and transcriptional profiles of melanoma patients from the public database TCGA (The Cancer Genome Atlas) and GEO (Gene Expression Omnibus, GSE32611) were analyzed by Qlucore Omics Explorer.

Results

NOS1 deletion suppressed the proliferation of melanoma A375 cells in culture, blocked cell cycling at the G0/G1 phase, and decreased the tumor growth in lung metastasis nodes in a B16 melanoma xenograft mouse model. Moreover, NOS1 knockout increased the infiltration of CD3+ immune cells in tumors. The transcriptomics analysis identified 2203 differential expression genes (DEGs) after NOS1 deletion. These DEGs indicated that NOS1 deletion downregulated mostly metabolic functions but upregulated immune response pathways. After inhibiting with NOS1 inhibitor N-PLA, melanoma cells significantly increased the response to IFN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upalpha $$\end{document}α by upregulation expression of IFN\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upalpha $$\end{document}α simulation genes (ISGs), especially the components in innate immune signaling, JAK-STAT, and TOLL-LIKE pathway. Furthermore, these NOS1-regulating immune genes (NOS1-ISGs) worked as a signature to predict poor overall survival and lower response to chemotherapy in melanoma patients.

Conclusion

These findings provided a transcriptional evidence of NOS1 promotion on tumor growth, which is correlated with metabolic regulation and immune escape in melanoma cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03403-w.

Infection-Derived Monocytic MDSCs Require TGF-β to Suppress Filarial-Specific IFN-γ But Not IL-13 Release by Filarial-Specific CD4+ T Cells In Vitro

Lymphatic filariasis (LF) remains a major health problem with severe economic repercussions in endemic communities of Sub-saharan Africa, South-East Asia and South America. The rodent-specific nematode Litomosoides sigmodontis (Ls) is used to study the immunomodulatory potential of filariae and research has elucidated pathways involving regulatory T cells (Tregs), IL-10 producing cells and alternatively activated macrophages (AAMs) and that CD4+ T cells play a paramount role during infection. Myeloid-derived suppressor cells (MDSCs) have been identified and characterised in man in cancer and other pathologies. The hallmark of MDSC populations is the suppression of T and B cell responses using various mechanisms, which are mostly specific to the pathology or setting. However, until now, it remains unclear whether they play a role in filarial-specific responses. We report here that monocytic MDSCs (Mo-MDSCs, CD11b+Ly6C+Ly6G-) and polymorphonuclear MDSCs (PMN-MDSCs, CD11b+Ly6Cint/loLy6G+) expanded in the thoracic cavity (TC, the site of infection) and correlated positively with filarial life-stages in Ls-infected BALB/c mice. In vitro, only infection-derived Mo-MDSCs showed a suppressive nature by preventing IL-13 and IFN-γ secretion from filarial-specific CD4+ T cells upon co-culture with soluble worm extract. This suppression was not mediated by IL-10, IL-6 or TNF-α, and did not require cell-contact, nitric oxide (NO), IL-4/IL-5 signalling pathways or CCR2. Interestingly, neutralizing TGF-β significantly rescued IFN-γ but not IL-13 production by filarial-specific CD4+ T cells. In comparison to naive cells, PCR array data showed an overall down-regulation of inflammatory pathways in both infection-derived Mo-MDSCs and PMN-MDSCs. In conclusion, these primary data sets show activity and expansion of MDSCs during Ls infection adding this regulatory cell type to the complex milieu of host responses during chronic helminth infections.

Role of myeloid-derived suppressor cells in viral respiratory infections; Hints for discovering therapeutic targets for COVID-19

The expansion of myeloid-derived suppressor cells (MDSCs), known as heterogeneous population of immature myeloid cells, is enhanced during several pathological conditions such as inflammatory or viral respiratory infections. It seems that the way MDSCs behave in infection depends on the type and the virulence mechanisms of the invader pathogen, the disease stage, and the infection-related pathology. Increasing evidence showing that in correlation with the severity of the disease, MDSCs are accumulated in COVID-19 patients, in particular in those at severe stages of the disease or ICU patients, contributing to pathogenesis of SARS-CoV2 infection. Based on the involved subsets, MDSCs delay the clearance of the virus through inhibiting T-cell proliferation and responses by employing various mechanisms such as inducing the secretion of anti-inflammatory cytokines, inducible nitric oxide synthase (iNOS)-mediated hampering of IFN-γ production, or forcing arginine shortage. While the immunosuppressive characteristic of MDSCs may help to preserve the tissue homeostasis and prevent hyperinflammation at early stages of the infection, hampering of efficient immune responses proved to exert significant pathogenic effects on severe forms of COVID-19, suggesting the targeting of MDSCs as a potential intervention to reactivate T-cell immunity and thereby prevent the infection from developing into severe stages of the disease. This review tried to compile evidence on the roles of different subsets of MDSCs during viral respiratory infections, which is far from being totally understood, and introduce the promising potential of MDSCs for developing novel diagnostic and therapeutic approaches, especially against COVID-19 disease.

Myeloid-derived suppressor cells as immunosuppressive regulators and therapeutic targets in cancer

Myeloid-derived suppressor cells (MDSCs) are a heterogenic population of immature myeloid cells with immunosuppressive effects, which undergo massive expansion during tumor progression. These cells not only support immune escape directly but also promote tumor invasion via various non-immunological activities. Besides, this group of cells are proved to impair the efficiency of current antitumor strategies such as chemotherapy, radiotherapy, and immunotherapy. Therefore, MDSCs are considered as potential therapeutic targets for cancer therapy. Treatment strategies targeting MDSCs have shown promising outcomes in both preclinical studies and clinical trials when administrated alone, or in combination with other anticancer therapies. In this review, we shed new light on recent advances in the biological characteristics and immunosuppressive functions of MDSCs. We also hope to propose an overview of current MDSCs-targeting therapies so as to provide new ideas for cancer treatment.

A Proteomic Atlas of Lineage and Cancer-Polarized Expression Modules in Myeloid Cells Modeling Immunosuppressive Tumor-Infiltrating Subsets

Monocytic and granulocytic myeloid-derived suppressor cells together with tumor-infiltrating macrophages constitute the main tumor-infiltrating immunosuppressive myeloid populations. Due to the phenotypic resemblance to conventional myeloid cells, their identification and purification from within the tumors is technically difficult and makes their study a challenge. We differentiated myeloid cells modeling the three main tumor-infiltrating types together with uncommitted macrophages, using ex vivo differentiation methods resembling the tumor microenvironment. The phenotype and proteome of these cells was compared to identify linage-dependent relationships and cancer-specific interactome expression modules. The relationships between monocytic MDSCs and TAMs, monocytic MDSCs and granulocytic MDSCs, and hierarchical relationships of expression networks and transcription factors due to lineage and cancer polarization were mapped. Highly purified immunosuppressive myeloid cell populations that model tumor-infiltrating counterparts were systematically analyzed by quantitative proteomics. Full functional interactome maps have been generated to characterize at high resolution the relationships between the three main myeloid tumor-infiltrating cell types. Our data highlights the biological processes related to each cell type, and uncover novel shared and differential molecular targets. Moreover, the high numbers and fidelity of ex vivo-generated subsets to their natural tumor-shaped counterparts enable their use for validation of new treatments in high-throughput experiments.

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

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

Interaction Between MDSC and NK Cells in Solid and Hematological Malignancies: Impact on HSCT

Myeloid derived suppressor cells (MDSC) are heterogeneous populations that through the release of soluble factors and/or by cell-to-cell interactions suppress both innate and adaptive immune effector cells. In pathological conditions, characterized by the presence of inflammation, a partial block in the differentiation potential of myeloid precursors causes an accumulation of these immunosuppressive cell subsets both in peripheral blood and in tissues. On the contrary, NK cells represent a major player of innate immunity able to counteract tumor growth. The anti-tumor activity of NK cells is primarily related to their cytolytic potential and to the secretion of soluble factors or cytokines that may act on tumors either directly or indirectly upon the recruitment of other cell types. NK cells have been shown to play a fundamental role in haploidentical hemopoietic stem cell transplantation (HSCT), for the therapy of high-risk leukemias. A deeper analysis of MDSC functional effects demonstrated that these cells are capable, through several mechanisms, to reduce the potent GvL activity exerted by NK cells. It is conceivable that, in this transplantation setting, the MDSC-removal or -inactivation may represent a promising strategy to restore the anti-leukemia effect mediated by NK cells. Thus, a better knowledge of the cellular interactions occurring in the tumor microenvironment could promote the development of novel therapeutic strategies for the treatment of solid and hematological malignances.

Tumor Microenvironment and Nitric Oxide: Concepts and Mechanisms

The cancer tissue exists not as a single entity, but as a combination of different cellular phenotypes which, taken together, dramatically contribute to the entirety of their ecosystem, collectively termed as the tumor microenvironment (TME). The TME is composed of both immune and nonimmune cell types, stromal components, and vasculature-all of which cooperate to promote cancer progression. Not all immune cells, however, are immune-suppressive; some of them can promote the immune microenvironment to fight the invading and uncontrollably dividing cell populations at the initial stages of tumor growth. Yet, many of these processes and cellular phenotypes fall short, and the immune ecosystem more often than not ends up stabilizing in favor of the "resistant" resident cells that begin clonal expansion and may progress to metastatic forms. Stromal components, making up the extracellular matrix and basement membrane, are also not the most innocuous: CAFs embedded throughout secrete proteases that allow the onset of one of the most invasive processes-angiogenesis-through destruction of the ECM and the basement membrane. Vasculature formation, because of angiogenesis, is the largest invader of the TME and the reason metastasis happens. Vasculature is so sporadic and omnipresent in the TME that most drug therapies are mainly focused on stopping this uncontrollable process. As the tumor continues to grow, different processes are constantly supplying it with the ingredients favorable for tumor progression and eventual metastasis. For example, angiogenesis promotes blood vessel formation that will allow the bona fide escape of tumor cells to take place. Another process like hypoxia will present itself in several forms throughout the tumor (mild or acute, cycling or permanent), starting mechanisms such as epithelial to mesenchymal transitions (EMT) of resident cells and inadvertently placing the cells in such a stressful condition that production of ROS and DNA damage is unavoidable. DNA damage can induce mutagenicity while allowing resistant cells to survive. This is where drugs and treatments can subsequently suffer in effectiveness. Finally, another molecule has just surfaced as being a very important player in the TME: nitric oxide. Often overlooked and equated with ROS and initially assigned in the category of pathogenic molecules, nitric oxide can definitely do some damage by causing metabolic reprogramming and promotion of immunosuppressive phenotypes at low concentrations. However, its actions seem to be extremely dose-dependent, and this issue has become a hot target of current treatment goals. Shockingly, nitric oxide, although omnipresent in the TME, can have a positive effect on targeting the TME broadly. Thus, while the TME is a myriad of cellular phenotypes and a combination of different tumor-promoting processes, each process is interconnected into one whole: the tumor microenvironment.

Interaction Between MDSC and NK Cells in Solid and Hematological Malignancies: Impact on HSCT

Myeloid derived suppressor cells (MDSC) are heterogeneous populations that through the release of soluble factors and/or by cell-to-cell interactions suppress both innate and adaptive immune effector cells. In pathological conditions, characterized by the presence of inflammation, a partial block in the differentiation potential of myeloid precursors causes an accumulation of these immunosuppressive cell subsets both in peripheral blood and in tissues. On the contrary, NK cells represent a major player of innate immunity able to counteract tumor growth. The anti-tumor activity of NK cells is primarily related to their cytolytic potential and to the secretion of soluble factors or cytokines that may act on tumors either directly or indirectly upon the recruitment of other cell types. NK cells have been shown to play a fundamental role in haploidentical hemopoietic stem cell transplantation (HSCT), for the therapy of high-risk leukemias. A deeper analysis of MDSC functional effects demonstrated that these cells are capable, through several mechanisms, to reduce the potent GvL activity exerted by NK cells. It is conceivable that, in this transplantation setting, the MDSC-removal or -inactivation may represent a promising strategy to restore the anti-leukemia effect mediated by NK cells. Thus, a better knowledge of the cellular interactions occurring in the tumor microenvironment could promote the development of novel therapeutic strategies for the treatment of solid and hematological malignances.

The Role of Nitric Oxide in Cancer: Master Regulator or NOt?

Nitric oxide (NO) is a key player in both the development and suppression of tumourigenesis depending on the source and concentration of NO. In this review, we discuss the mechanisms by which NO induces DNA damage, influences the DNA damage repair response, and subsequently modulates cell cycle arrest. In some circumstances, NO induces cell cycle arrest and apoptosis protecting against tumourigenesis. NO in other scenarios can cause a delay in cell cycle progression, allowing for aberrant DNA repair that promotes the accumulation of mutations and tumour heterogeneity. Within the tumour microenvironment, low to moderate levels of NO derived from tumour and endothelial cells can activate angiogenesis and epithelial-to-mesenchymal transition, promoting an aggressive phenotype. In contrast, high levels of NO derived from inducible nitric oxide synthase (iNOS) expressing M1 and Th1 polarised macrophages and lymphocytes may exert an anti-tumour effect protecting against cancer. It is important to note that the existing evidence on immunomodulation is mainly based on murine iNOS studies which produce higher fluxes of NO than human iNOS. Finally, we discuss different strategies to target NO related pathways therapeutically. Collectively, we present a picture of NO as a master regulator of cancer development and progression.

Amino Acids and Their Transporters in T Cell Immunity and Cancer Therapy

Metabolism reprogramming is critical for both cancer progression and effective immune responses in the tumor microenvironment. Amino acid metabolism in different cells and their cross-talk shape tumor immunity and therapy efficacy in patients with cancer. In this review, we focus on multiple amino acids and their transporters, solute carrier (SLC) members. We discuss their involvement in regulation of immune responses in the tumor microenvironment and assess their associations with cancer immunotherapy, chemotherapy, and radiation therapy, and we review their potential as targets for cancer therapy. We stress the necessity to understand individual amino acids and their transporters in different cell subsets, the molecular intersection between amino acid metabolism, and effective T cell immunity and its relevance in cancer therapies.

MicroRNAs and lncRNAs-A New Layer of Myeloid-Derived Suppressor Cells Regulation

Myeloid-derived suppressor cells (MDSCs) constitute an important component in regulating immune responses in several abnormal physiological conditions such as cancer. Recently, novel regulatory tumor MDSC biology modulating mechanisms, including differentiation, expansion and function, were defined. There is growing evidence that miRNAs and long non-coding RNAs (lncRNA) are involved in modulating transcriptional factors to become complex regulatory networks that regulate the MDSCs in the tumor microenvironment. It is possible that aberrant expression of miRNAs and lncRNA contributes to MDSC biological characteristics under pathophysiological conditions. This review provides an overview on miRNAs and lncRNAs epiregulation of MDSCs development and immunosuppressive functions in cancer.

Anti-angiogenic Agents in Combination With Immune Checkpoint Inhibitors: A Promising Strategy for Cancer Treatment

Advances in cancer immunity have promoted a major breakthrough in the field of cancer therapy. This is mainly associated with the successful development of immune checkpoint inhibitors (ICIs) for multiple types of human tumors. Blockade with different ICIs, including programmed cell death 1 (PD-1), programmed cell death-ligand 1 (PD-L1), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors, may activate the immune system of the host against malignant cells. However, only a subgroup of patients with cancer would benefit from immune checkpoint blockade. Some patients experience primary resistance to initial immunotherapy, and a majority eventually develop acquired resistance to ICIs. However, the mechanisms involved in the development of drug resistance to immune checkpoint blockade remain unclear. Recent studies supported that combination of ICIs and anti-angiogenic agents could be a promising therapeutic strategy for overcoming the low efficacy of ICIs. Moreover, through their direct anti-cancer effect by inhibiting tumor growth and metastasis, anti-angiogenic drugs reprogram the tumor milieu from an immunosuppressive to an immune permissive microenvironment. Activated immunity by immune checkpoint blockade also facilitates anti-angiogenesis by downregulating the expression of vascular endothelial growth factor and alleviating hypoxia condition. Many clinical trials showed an improved anti-cancer efficacy and prolonged survival following the addition of anti-angiogenic agents to ICIs. This review summarizes the current understanding and clinical development of combination therapy with immune checkpoint blockade and anti-angiogenic strategy.

Myeloid-Derived Suppressor Cells in Tumors: From Mechanisms to Antigen Specificity and Microenvironmental Regulation

Among the various immunological and non-immunological tumor-promoting activities of myeloid-derived suppressor cells (MDSCs), their immunosuppressive capacity remains a key hallmark. Effort in the past decade has provided us with a clearer view of the suppressive nature of MDSCs. More suppressive pathways have been identified, and their recognized targets have been expanded from T cells and natural killer (NK) cells to other immune cells. These novel mechanisms and targets afford MDSCs versatility in suppressing both innate and adaptive immunity. On the other hand, a better understanding of the regulation of their development and function has been unveiled. This intricate regulatory network, consisting of tumor cells, stromal cells, soluble mediators, and hostile physical conditions, reveals bi-directional crosstalk between MDSCs and the tumor microenvironment. In this article, we will review available information on how MDSCs exert their immunosuppressive function and how they are regulated in the tumor milieu. As MDSCs are a well-established obstacle to anti-tumor immunity, new insights in the potential synergistic combination of MDSC-targeted therapy and immunotherapy will be discussed.

Overcoming Drug Resistance to BRAF Inhibitor

One of the most frequently found mutations in human melanomas is in the B-raf gene, making its protein BRAF a key target for therapy. However, in patients treated with BRAF inhibitor (BRAFi), although the response is very good at first, relapse occurs within 6 months, on the average. In order to overcome this drug resistance to BRAFi, various combinations of BRAFi with other drugs have been explored, and some are being applied clinically, such as a combination of BRAF and MEK inhibitors. Experimental data for melanoma in mice show that under continuous treatment with BRAFi, the pro-cancer MDSCs and chemokine CCL2 initially decrease but eventually increase to above their original level, while the anticancer T cells continuously decrease. In this paper, we develop a mathematical model that explains these experimental results. The model is used to explore the efficacy of combinations of BRAFi with anti-CCL2, anti-PD-1 and anti-CTLA-4, with the aim of eliminating or reducing drug resistance to BRAFi.

Spotlight on ROS and β3-Adrenoreceptors Fighting in Cancer Cells

The role of ROS and RNS is a long-standing debate in cancer. Increasing the concentration of ROS reaching the toxic threshold can be an effective strategy for the reduction of tumor cell viability. On the other hand, cancer cells, by maintaining intracellular ROS concentration at an intermediate level called “mild oxidative stress,” promote the activation of signaling that favors tumor progression by increasing cell viability and dangerous tumor phenotype. Many chemotherapeutic treatments induce cell death by rising intracellular ROS concentration. The persistent drug stimulation leads tumor cells to simulate a process called hormesis by which cancer cells exhibit a biphasic response to exposure to drugs used. After a first strong response to a low dose of chemotherapeutic agent, cancer cells start to decrease the response even if high doses of drugs were used. In this framework, β3-adrenoreceptors (β3-ARs) fit with an emerging antioxidant role in cancer. β3-ARs are involved in tumor proliferation, angiogenesis, metastasis, and immune tolerance. Its inhibition, by the selective β3-ARs antagonist (SR59230A), leads cancer cells to increase ROS concentration thus inducing cell death and to decrease NO levels thus inhibiting angiogenesis. In this review, we report an overview on reactive oxygen biology in cancer cells focusing on β3-ARs as new players in the antioxidant pathway.

Immunomodulatory roles of nitric oxide in cancer: tumor microenvironment says "NO" to antitumor immune response

In recent years, an increasing number of studies have shown that there is an important connection between nitric oxide (NO) and the pathology of malignant diseases, but we are far from a complete comprehension of how this simple diatomic molecule contributes to tumorigenesis. The emerging identification of immune-mediated mechanisms regulated by NO may help to unravel the intricate and complex relationships between NO and cancer. Therefore, this review provides a summary of recent advances in our understanding of the immunomodulatory role of NO in cancer, and in particular the role of this pleiotropic signaling molecule as an immunosuppressive mediator in the tumor microenvironment. We will discuss the participation of NO in the different strategies used by tumors to escape from immune system-mediated recognition, including the acquisition of stem cell like capacities by tumor cells and the metabolic reprogramming of tumor infiltrating immune cells. Finally, we will also discuss different therapeutic strategies directed against NO for abating the immunosuppressive tumor microenvironment and to increase the efficacy of immunotherapy in cancer.

Targeted transcriptional profiling of the tumor microenvironment reveals lymphocyte exclusion and vascular dysfunction in metastatic osteosarcoma

Osteosarcoma (OS) is the most common bone tumor in pediatric and adolescent/young adult patients yet little is known about the microenvironment that supports this aggressive disease. We have used targeted gene expression profiling and immunohistochemistry to characterize the microenvironment of metastatic and non-metastatic OS specimens from pediatric patients exhibiting poor histologic response to chemotherapy. Our results indicate that metastatic specimens exhibit lymphocyte exclusion as T cells are confined to the periphery of the pulmonary lesions. Furthermore, our data provides evidence of vascular dysfunction in metastatic OS indicated by increased expression of VEGFA, an increased ANGPT2:ANGPT1 gene expression ratio, and decreased expression of SELE, the gene encoding the adhesion molecule E-selectin. Moreover, correlation analyses show an inverse relationship between lymphocyte abundance and markers of vascular dysfunction exclusively in the metastatic specimens. Together, our data shows that the non-metastatic OS specimens demonstrate increased expression of various immunotherapeutic targets in comparison metastatic specimens and identifies vascular dysfunction and lymphocyte exclusion as important processes for therapeutic intervention in metastatic disease.

Carnosic acid enhances the anti-lung cancer effect of cisplatin by inhibiting myeloid-derived suppressor cells

Cisplatin and other platinum-based drugs are used frequently for treatment of lung cancer. However, their clinical performance are usually limited by drug resistance or toxic effects. Carnosic acid, a polyphenolic diterpene isolated from Rosemary (Rosemarinus officinalis), has been reported to have several pharmacological and biological activities. In the present study, the combination effect of cisplatin plus carnosic acid on mouse LLC (Lewis lung cancer) xenografts and possible underlying mechanism of action were examined. LLC-bearing mice were treated with intraperitoneal injection with cisplatin, oral gavage with carnosic acid, or combination with cisplatin and carnosic acid, respectively. Combination of carnosic acid and cisplatin yielded significantly better anti-growth and pro-apoptotic effects on LLC xenografts than drugs alone. Mechanistic study showed that carnosic acid treatment boosted the function of CD8⁺ T cells as evidenced by higher IFN-γ secretion and higher expression of FasL, perforin as well as granzyme B. In the meantime, the proportion of MDSC (myeloid-derived suppressor cells) in tumor tissues were reduced by carnosic acid treatment and the mRNA levels of iNOS2, Arg-1, and MMP9, which are the functional markers for MDSC, were reduced. In conclusion, our study proved that the functional suppression of MDSC by carnosic acid promoted the lethality of CD8⁺ T cells, which contributed to the enhancement of anti-lung cancer effect of cisplatin.

Vascular Targeting to Increase the Efficiency of Immune Checkpoint Blockade in Cancer

Boosting natural immunity against malignant cells has had a major breakthrough in clinical cancer therapy. This is mainly due to the successful development of immune checkpoint blocking antibodies, which release a break on cytolytic anti-tumor-directed T-lymphocytes. However, immune checkpoint blockade is only effective for a proportion of cancer patients, and a major challenge in the field is to understand and overcome treatment resistance. Immune checkpoint blockade relies on successful trafficking of tumor-targeted T-lymphocytes from the secondary lymphoid organs, through the blood stream and into the tumor tissue. Resistance to therapy is often associated with a low density of T-lymphocytes residing within the tumor tissue prior to treatment. The recruitment of leukocytes to the tumor tissue relies on up-regulation of adhesion molecules and chemokines by the tumor vasculature, which is denoted as endothelial activation. Tumor vessels are often poorly activated due to constitutive pro-angiogenic signaling in the tumor microenvironment, and therefore constitute barriers to efficient leukocyte recruitment. An emerging possibility to enhance the efficiency of cancer immunotherapy is to combine pro-inflammatory drugs with anti-angiogenic therapy, which can enable tumor-targeted T-lymphocytes to access the tumor tissue by relieving endothelial anergy and increasing adhesion molecule expression. This would pave the way for efficient immune checkpoint blockade. Here, we review the current understanding of the biological basis of endothelial anergy within the tumor microenvironment, and discuss the challenges and opportunities of combining vascular targeting with immunotherapeutic drugs as suggested by data from key pre-clinical and clinical studies.

γδ T Cells and Tumor Microenvironment: From Immunosurveillance to Tumor Evasion

γδ T cells possess cytotoxic antitumor activity mediated by production of proinflammatory cytokines, direct cytotoxic activity, and regulation of the biological functions of other cell types. Hence, these features have prompted the development of therapeutic strategies in which γδ T cells agonists or ex vivo-expanded γδ T cells are administered to tumor patients. Several studies have shown that γδ T cells are an important component of tumor-infiltrating lymphocytes in patients affected by different types of cancer and a recent analysis of ~18,000 transcriptomes from 39 human tumors identified tumor-infiltrating γδ T cells as the most significant favorable cancer-wide prognostic signature. However, the complex and intricate interactions between tumor cells, tumor microenvironment (TME), and tumor-infiltrating immune cells results in a balance between tumor-promoting and tumor-controlling effects, and γδ T cells functions are often diverted or impaired by immunosuppressive signals originating from the TME. This review focuses on the dangerous liason between γδ T cells and tumoral microenvironment and raises the possibility that strategies capable to reduce the immunosuppressive environment and increase the cytotoxic ability of γδ T cells may be the key factor to improve their utilization in tumor immunotherapy.

Renal cell carcinoma alters endothelial receptor expression responsible for leukocyte adhesion

Renal cell carcinoma (RCC) escapes immune recognition. To elaborate the escape strategy the influence of RCC cells on endothelial receptor expression and endothelial leukocyte adhesion was evaluated. Human umbilical vein endothelial cells (HUVEC) were co-cultured with the RCC cell line, Caki-1, with and without tumor necrosis factor (TNF)-alpha. Intercellular cell adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), endothelial (E)-selectin, standard and variants (V) of CD44 were then analysed in HUVEC, using flow cytometry and Western blot analysis. To determine which components are responsible for HUVEC-Caki-1 interaction causing receptor alteration, Caki-1 membrane fragments versus cell culture supernatant were applied to HUVECS. Adhesion of peripheral blood lymphocytes (PBL) and polymorphonuclear neutrophils (PMN) to endothelium was evaluated by co-culture adhesion assays. Relevance of endothelial receptor expression for adhesion to endothelium was determined by receptor blockage. Co-culture of RCC and HUVECs resulted in a significant increase in endothelial ICAM-1, VCAM-1, E-selectin, CD44 V3 and V7 expression. Previous stimulation of HUVECs with TNF-alpha and co-cultivation with Caki-1 resulted in further elevation of endothelial CD44 V3 and V7 expression, whereas ICAM-1, VCAM-1 and E-selectin expression were significantly diminished. Since Caki-1 membrane fragments also caused these alterations, but cell culture supernatant did not, cell-cell contact may be responsible for this process. Blocking ICAM-1, VCAM-1, E-selectin or CD44 with respective antibodies led to a significant decrease in PBL and PMN adhesion to endothelium. Thus, exposing HUVEC to Caki-1 results in significant alteration of endothelial receptor expression and subsequent endothelial attachment of PBL and PMN.

Myeloid-Derived Suppressor Cells in the Tumor Microenvironment: Current Knowledge and Future Perspectives

The current knowledge on tumor-infiltrating myeloid-derived suppressor cells (MDSCs) is based mainly on the extensive work performed in murine models. Data obtained for human counterparts are generated on the basis of tumor analysis from patient samples. Both sources of information led to determination of the main suppressive mechanisms used by these cell subsets in tumor-bearing hosts. As a result of the identification of protein targets responsible for MDSCs suppressive activity, different therapeutics agents have been used to eliminate/reduce their adverse effect. In the present work, we review the current knowledge on suppressive mechanisms of MDSCs and therapeutic treatments that interfere with their differentiation, expansion or activity. Based on the accumulation of new evidences supporting their importance for tumor progression and metastasis, the interest in these cell types is increasing. We revise the methods of MDSC generation/differentiation ex vivo that may help in overcoming problems associated with limited numbers of cells available from animals and patients for their study.

Rationale for immune-based therapies in Merkel polyomavirus-positive and -negative Merkel cell carcinomas

Merkel cell carcinoma (MCC) is a rare but often deadly skin cancer that is typically caused by the Merkel cell polyomavirus (MCPyV). Polyomavirus T-antigen oncoproteins are persistently expressed in virus-positive MCCs (˜80% of cases), while remarkably high numbers of tumor-associated neoantigens are detected in virus-negative MCCs, suggesting that both MCC subsets may be immunogenic. Here we review mechanisms by which these immunogenic tumors evade multiple levels of host immunity. Additionally, we summarize the exciting potential of diverse immune-based approaches to treat MCC. In particular, agents blocking the PD-1 axis have yielded strikingly high response rates in MCC as compared with other solid tumors, highlighting the potential for immune-mediated treatment of this disease.

Immunomodulatory effects of myeloid-derived suppressor cells in diseases: Role in cancer and infections

Myeloid-derived suppressor cells (MDSCs) are heterogeneous cells capable of abrogating T and B cells responses and have been identified in numerous cancers. As with other regulatory cell populations, they aim to maintain balance between host-defence-associated inflammation and ensuing tissue pathology. MDSC accumulation and/or activation involve several growth factors and cytokines including Granulocyte Macrophage-Colony Stimulating Factor (GM-CSF) and Interleukin (IL)-6 and suppression has been linked to receptors such as IL-4Rα. Other immune pathways, such as Toll-like receptors (TLRs) have also been shown to interfere in MDSC activity adding to the complexity in clarifying their pathways. Monocytic- (Mo-MDSCs) and polymorphonuclear- (PMN-MDSCs) cells are two subsets of MDSCs that have been well characterized and have been shown to function through different mechanisms although both appear to require nitric oxide. In human and murine model settings, MDSCs have been shown to have inhibitory effects on T cell responses during bacterial, parasitic and viral pathologies and an increase of MDSC numbers has been associated with pathological conditions. Interestingly, the environment impacts on MDSC activity and regulatory T cells (Tregs), mast cells and a few cells that may help MDSC in order to regulate immune responses. Since the majority of pioneering data on MDSCs has stemmed from research on malignancies, this review will summarize MDSC biology and function in cancer and highlight current knowledge about these cells during infectious pathologies as well.

Interleukin-22 and Cyclosporine in Aggressive Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinomas (SCCs) account for up to 10,000 deaths annually in the United States. Most of the more than 700,000 SCCs diagnosed are cured by excision with clear margins; however, metastasis can occur despite seemingly adequate treatment in some cases. Immune-suppressed organ transplant recipients are 60 to 100 times more likely to develop SCC than immune-competent individuals. Transplant-associated SCCs occur more frequently and behave more aggressively, showing higher risk of recurrence and metastasis. This article identifies a potential role for interleukin-22 in driving SCC proliferation, particularly in solid organ transplant recipients taking cyclosporine.