Myeloid-driven mechanisms as barriers to antitumor CD8+ T cell activity

Exportin 1 governs the immunosuppressive functions of myeloid-derived suppressor cells in tumors through ERK1/2 nuclear export

Myeloid-derived suppressor cells (MDSCs) are a main driver of immunosuppression in tumors. Understanding the mechanisms that determine the development and immunosuppressive function of these cells could provide new therapeutic targets to improve antitumor immunity. Here, using preclinical murine models, we discovered that exportin 1 (XPO1) expression is upregulated in tumor MDSCs and that this upregulation is induced by IL-6-induced STAT3 activation during MDSC differentiation. XPO1 blockade transforms MDSCs into T-cell-activating neutrophil-like cells, enhancing the antitumor immune response and restraining tumor growth. Mechanistically, XPO1 inhibition leads to the nuclear entrapment of ERK1/2, resulting in the prevention of ERK1/2 phosphorylation following the IL-6-mediated activation of the MAPK signaling pathway. Similarly, XPO1 blockade in human MDSCs induces the formation of neutrophil-like cells with immunostimulatory functions. Therefore, our findings revealed a critical role for XPO1 in MDSC differentiation and suppressive functions; exploiting these new discoveries revealed new targets for reprogramming immunosuppressive MDSCs to improve cancer therapeutic responses.

Myeloid-derived suppressor cells-induced exhaustion of CD8 + T-cell participates in rejection after liver transplantation

Liver transplantation (LT) rejection remains the most pervasive problem associated with this procedure, while the mechanism involved is still complicated and undefined. One promising solution may involve the use of myeloid-derived suppressor cells (MDSC). However, the immunological mechanisms underlying the effects of MDSC after LT remain unclear. This study is meant to clarify the role MDSCs play after liver transplantation. In this study, we collected liver tissue and peripheral blood mononuclear cells (PBMC) from LT patients showing varying degrees of rejection, as well as liver and spleen tissue samples from mice LT models. These samples were then analyzed using flow cytometry, immunohistochemistry and multiple immunofluorescence. M-MDSCs and CD8 + T-cells extracted from C57/BL6 mice were enriched and cocultured for in vitro experiments. Results, as obtained in both LT patients and LT mice model, revealed that the proportion and frequency of M-MDSC and PD-1 + T-cells increased significantly under conditions associated with a high degree of LT rejection. Within the LT rejection group, our immunofluorescence results showed that a close spatial contiguity was present between PD-1 + T-cells and M-MDSCs in these liver tissue samples and the proportion of CD84/PD-L1 double-positive M-MDSC was greater than that of G-MDSC. There was a positive correlation between the activity of CD84 and immunosuppressive function of M-MDSCs including PD-L1 expression and reactive oxygen species (ROS) production, as demonstrated in our in vitro model. M-MDSCs treated with CD84 protein were able to induce co-cultured CD8 + T-cells to express high levels of exhaustion markers. We found that CD84 regulated M-MDSC function via expression of PD-L1 through activation of the Akt/Stat3 pathway. These results suggest that the capacity for CD84 to regulate M-MDSC induction of CD8 + T-cell exhaustion may play a key role in LT rejection. Such findings provide important, new insights into the mechanisms of tolerance induction in LT.

Induced electric fields inhibit breast cancer growth and metastasis by modulating the immune tumor microenvironment

Despite tremendous advances in oncology, metastatic triple-negative breast cancer remains difficult to treat and manage with established therapies. Here, we show in mice with orthotopic triple-negative breast tumors that alternating (100 kHz), and low intensity (<1 mV/cm) induced electric fields (iEFs) significantly reduced primary tumor growth and distant lung metastases. Non-contact iEF treatment can be delivered safely and non-invasively in vivo via a hollow, rectangular solenoid coil. We discovered that iEF treatment enhances anti-tumor immune responses at both the primary breast and secondary lung sites. In addition, iEF reduces immunosuppressive TME by reducing effector CD8+ T cell exhaustion and the infiltration of immunosuppressive immune cells. Furthermore, iEF treatment reduced lung metastasis by increasing CD8+ T cells and reducing immunosuppressive Gr1+ neutrophils in the lung microenvironment. We also observed that iEFs reduced the metastatic potential of cancer cells by inhibiting epithelial-to-mesenchymal transition. By introducing a non-invasive and non-toxic electrotherapeutic for inhibiting metastatic outgrowth and enhancing anti-tumor immune response in vivo, treatment with iEF technology could add to a paradigm-shifting strategy for cancer therapy.

Five-Day Spacing of Two Fractionated Ablative Radiotherapies Enhances Antitumor Immunity

PURPOSE

This study aimed to enhance tumor control and abscopal effects by applying diverse stereotactic ablative radiation therapy (SABR) schedules.

METHODS AND MATERIALS

FSaII, CT-26, and 4T1 cells were used for tumor growth delay and lung metastases analysis after 1- or 5-day intervals radiation therapy (RT) with 40, 20, and 20 Gy, respectively. Immunodeficient BALB/c-nude, immunocompetent C3H, and BALB/c mouse models were used. For immune monitoring, FSaII tumors were analyzed using flow cytometry, immunofluorescence staining, and real-time quantitative reverse transcription polymerase chain reaction. The spleens were used for the ELISpot assay and flow cytometry to determine effector CD8 T cells. For abscopal effect analysis in CT-26 tumors, the volume of the nonirradiated secondary tumors was measured after primary tumors were irradiated with 1-day or 5-day intervals.

RESULTS

Contrary to the high-dose 1-day interval RT, the 5-day interval RT significantly delayed tumor growth in immunocompetent mice, which was not observed in immunodeficient mice. In addition, the 5-day interval RT significantly reduced the number of lung metastases in FSaII and CT-26 tumors. Five-day spacing was more effective than 1-day interval in enhancing the antitumor immunity via increasing the secretion of tumor-specific IFN-γ, activating the CD8 T cells, and suppressing the monocytic myeloid-derived suppressor cells. The 5-day spacing inhibited nonirradiated secondary tumor growth more effectively than did the 1-day interval.

CONCLUSIONS

Compared with the 1-day interval RT, the 5-day interval RT scheme demonstrated enhanced antitumor immunity of CD8 T cells associated with inhibition of myeloid-derived suppressor cells. Enhancing antitumor immunity leads to significant improvements in both primary tumor control and the abscopal effect.

Cancer immune exclusion: breaking the barricade for a successful immunotherapy

Immunotherapy has changed the course of cancer treatment. The initial steps were made through tumor-specific antibodies that guided the setup of an antitumor immune response. A new and successful generation of antibodies are designed to target immune checkpoint molecules aimed to reinvigorate the antitumor immune response. The cellular counterpart is the adoptive cell therapy, where specific immune cells are expanded or engineered to target cancer cells. In all cases, the key for achieving positive clinical resolutions rests upon the access of immune cells to the tumor. In this review, we focus on how the tumor microenvironment architecture, including stromal cells, immunosuppressive cells and extracellular matrix, protects tumor cells from an immune attack leading to immunotherapy resistance, and on the available strategies to tackle immune evasion.

Instigation of the epoch of nanovaccines in cancer immunotherapy

Cancer is an unprecedented proliferation of cells leading to abnormalities in differentiation and maturation. Treatment of primary and metastatic cancer is challenging. In addition to surgery, chemotherapy and radiation therapies have been conventionally used; however, they suffer from severe toxicity and non-specificity. Immunotherapy, the science of programming the body's own defense system against cancer has gained tremendous attention in the last few decades. However, partial immunogenic stimulation, premature degradation and inability to activate dendritic and helper T cells has resulted in limited clinical success. The era of nanomedicine has brought about several breakthroughs in various pharmaceutical and biomedical fields. Hereby, we review and discuss the interplay of tumor microenvironment (TME) and the immunological cascade and how they can be employed to develop nanoparticle-based cancer vaccines and immunotherapies. Nanoparticles composed of lipids, polymers and inorganic materials contain useful properties suitable for vaccine development. Proteinaceous vaccines derived from mammalian viruses, bacteriophages and plant viruses also have unique advantages due to their immunomodulation capabilities. This review accounts for all such considerations. Additionally, we explore how attributes of nanotechnology can be utilized to develop successful nanomedicine-based vaccines for cancer therapy. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Inhibiting the biogenesis of myeloid-derived suppressor cells enhances immunotherapy efficacy against mammary tumor progression

While immune checkpoint inhibitors (ICIs) have transformed the therapeutic landscape in oncology, they are effective in select subsets of patients. Efficacy may be limited by tumor-driven immune suppression, of which 1 key mechanism is the development of myeloid-derived suppressor cells (MDSCs). A fundamental gap in MDSC therapeutics is the lack of approaches that target MDSC biogenesis. We hypothesized that targeting MDSC biogenesis would mitigate MDSC burden and bolster tumor responses to ICIs. We tested a class of agents, dihydroorotate dehydrogenase (DHODH) inhibitors, that have been previously shown to restore the terminal differentiation of leukemic myeloid progenitors. DHODH inhibitors have demonstrated preclinical safety and are under clinical study for hematologic malignancies. Using mouse models of mammary cancer that elicit robust MDSC responses, we demonstrated that the DHODH inhibitor brequinar (a) suppressed MDSC production from early-stage myeloid progenitors, which was accompanied by enhanced myeloid maturation; (b) augmented the antitumor and antimetastatic activities of programmed cell death 1-based (PD-1-based) ICI therapy in ICI-resistant mammary cancer models; and (c) acted in concert with PD-1 blockade through modulation of MDSC and CD8+ T cell responses. Moreover, brequinar facilitated myeloid maturation and inhibited immune-suppressive features in human bone marrow culture systems. These findings advance the concept of MDSC differentiation therapy in immuno-oncology.

The immunosuppressive microenvironment and immunotherapy in human glioblastoma

Glioblastoma multiforme (GBM) is the most malignant intracranial tumor in adults, characterized by extensive infiltrative growth, high vascularization, and resistance to multiple therapeutic approaches. Among the many factors affecting the therapeutic effect, the immunosuppressive GBM microenvironment that is created by cells and associated molecules via complex mechanisms plays a particularly important role in facilitating evasion of the tumor from the immune response. Accumulating evidence is also revealing a close association of the gut microbiota with the challenges in the treatment of GBM. The gut microbiota establishes a connection with the central nervous system through bidirectional signals of the gut-brain axis, thus affecting the occurrence and development of GBM. In this review, we discuss the key immunosuppressive components in the tumor microenvironment, along with the regulatory mechanism of the gut microbiota involved in immunity and metabolism in the GBM microenvironment. Lastly, we concentrate on the immunotherapeutic strategies currently under investigation, which hold promise to overcome the hurdles of the immunosuppressive tumor microenvironment and improve the therapeutic outcome for patients with GBM.

Madecassic acid alleviates colitis-associated colorectal cancer by blocking the recruitment of myeloid-derived suppressor cells via the inhibition of IL-17 expression in γδT17 cells

INTRODUCTION

Madecassic acid (MA), a triterpene compound isolated from Centella Asiatica herbs, has previously been shown to attenuate colitis induced by DSS in mice. In the present study, we address whether and how MA ameliorates colitis-associated colorectal cancer (CAC), which accounts for a considerable proportion of colorectal cancer.

METHODS

CAC was induced by AOM/DSS in mice, and MA was administered orally once a day. To identify the source cells of IL-17 and the target cells for MA reducing the expression of IL-17 in the colons of CAC mice, single-cell suspensions were prepared from the colons of CAC mice and analyzed by flow cytometry. An adoptive transfer experiment was performed to verify the importance of the decreasing γδT17 cell population in the anti-CAC effect of MA.

RESULTS

Oral administration of MA reduced the burden and incidence of tumors in the CAC mice. MA decreased the number of MDSCs in the colon tissues of CAC mice and ameliorated anti-tumor immune responses. MA could prevent the migration of MDSCs by inhibiting the activation of γδT17 cells and the expression of chemokines. The population of activated-γδT17 cells in the tumor microenvironment of CAC mice positively correlated with the number of MDSCs and tumors as well as tumor load. Moreover, the anti-CAC effect of MA was significantly counteracted by the adoptive transfer of γδT17 cells.

CONCLUSIONS

MA alleviates CAC by blocking the recruitment of MDSCs to increase the population of anti-tumor immune cells in tumor microenvironment via inhibition of the activation of γδT17 cells.

Therapeutic efficacy of proton transport inhibitors alone or in combination with cisplatin in triple negative and hormone sensitive breast cancer models

Triple negative breast cancers (TNBCs) are very aggressive and have a poor prognosis due to lack of efficacious therapies. The only effective treatment is chemotherapy that however is frequently hindered by the occurrence of drug resistance. We approached this problem in vitro and in vivo on a triple negative and a hormone sensitive breast cancer cell lines: 4T1 and TS/A. A main defense mechanism of tumors is the extrusion of intracellular protons derived from the metabolic shift to glycolysis, and necessary to maintain an intracellular pH compatible with life. The resulting acidic extracellular milieu bursts the malignant behavior of tumors and impairs chemotherapy. Therefore, we investigated the efficacy of combined therapies that associate cisplatin (Cis) with proton exchanger inhibitors, such as esomeprazole (ESO) and 5-(N-ethyl-N-isopropyl)amiloride (EIPA). Our results demonstrate that in the 4T1 triple negative model the combined therapy Cis plus EIPA is significantly more effective than the other treatments. Instead, in the TS/A tumor the best therapeutic result is obtained with ESO alone. Remarkably, in both 4T1 and TS/A tumors these treatments correlate with increase of CD8+  T lymphocytes and dendritic cells, and a dramatic reduction of M2 macrophages and other suppressor myeloid cells (MDSC) in the tumor infiltrates.

Breast cancer-derived GM-CSF regulates arginase 1 in myeloid cells to promote an immunosuppressive microenvironment

Tumor-infiltrating myeloid cells contribute to the development of the immunosuppressive tumor microenvironment. Myeloid cell expression of arginase 1 (ARG1) promotes a protumor phenotype by inhibiting T cell function and depleting extracellular l-arginine, but the mechanism underlying this expression, especially in breast cancer, is poorly understood. In breast cancer clinical samples and in our mouse models, we identified tumor-derived GM-CSF as the primary regulator of myeloid cell ARG1 expression and local immune suppression through a gene-KO screen of breast tumor cell-produced factors. The induction of myeloid cell ARG1 required GM-CSF and a low pH environment. GM-CSF signaling through STAT3 and p38 MAPK and acid signaling through cAMP were required to activate myeloid cell ARG1 expression in a STAT6-independent manner. Importantly, breast tumor cell-derived GM-CSF promoted tumor progression by inhibiting host antitumor immunity, driving a significant accumulation of ARG1-expressing myeloid cells compared with lung and melanoma tumors with minimal GM-CSF expression. Blockade of tumoral GM-CSF enhanced the efficacy of tumor-specific adoptive T cell therapy and immune checkpoint blockade. Taken together, we show that breast tumor cell-derived GM-CSF contributes to the development of the immunosuppressive breast cancer microenvironment by regulating myeloid cell ARG1 expression and can be targeted to enhance breast cancer immunotherapy.

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.

Not Only Immune Escape-The Confusing Role of the TRP Metabolic Pathway in Carcinogenesis

BACKGROUND

The recently discovered phenomenon that cancer cells can avoid immune response has gained scientists' interest. One of the pathways involved in this process is tryptophan (TRP) metabolism through the kynurenine pathway (KP). Individual components involved in TRP conversion seem to contribute to cancerogenesis both through a direct impact on cancer cells and the modulation of immune cell functionality. Due to this fact, this pathway may serve as a target for immunotherapy and attempts are being made to create novel compounds effective in cancer treatment. However, the results obtained from clinical trials are not satisfactory, which raises questions about the exact role of KP elements in tumorigenesis. An increasing number of experiments reveal that TRP metabolites may either be tumor promoters and suppressors and this is why further research in this field is highly needed. The aim of this study is to present KP as a modulator of cancer development through multiple mechanisms and to point to its ambiguity, which may be a reason for failures in treatment based on the inhibition of tryptophan metabolism.

Altered Metabolism in Glioblastoma: Myeloid-Derived Suppressor Cell (MDSC) Fitness and Tumor-Infiltrating Lymphocyte (TIL) Dysfunction

The metabolism of glioblastoma (GBM), the most aggressive and lethal primary brain tumor, is flexible and adaptable to different adverse conditions, such as nutrient deprivation. Beyond glycolysis, altered lipid metabolism is implicated in GBM progression. Indeed, metabolic subtypes were recently identified based on divergent glucose and lipid metabolism. GBM is also characterized by an immunosuppressive microenvironment in which myeloid-derived suppressor cells (MDSCs) are a powerful ally of tumor cells. Increasing evidence supports the interconnection between GBM and MDSC metabolic pathways. GBM cells exert a crucial contribution to MDSC recruitment and maturation within the tumor microenvironment, where the needs of tumor-infiltrating lymphocytes (TILs) with antitumor function are completely neglected. In this review, we will discuss the unique or alternative source of energy exploited by GBM and MDSCs, exploring how deprivation of specific nutrients and accumulation of toxic byproducts can induce T-cell dysfunction. Understanding the metabolic programs of these cell components and how they impact fitness or dysfunction will be useful to improve treatment modalities, including immunotherapeutic strategies.

URRENT CONCEPT OF THE STRUCTURAL AND FUNCTIONAL PROPERTIES OF ALFA-FETOPROTEIN AND THE POSSIBILITIES OF ITS CLINICAL APPLICATION

This paper was aimed to review the literature data from native and foreign sources accumulated for 40-years period of research of the features of the molecular structure, functions, production and application of human alpha-fetoprotein (AFP), which is known as one of the most studied and increasingly demanded proteins. Results of fundamental studies performed with the use of modern methods, including various types of electrophoresis, chromatography, electron microscopy and immunoassay, in order to characterize the principal physicochemical capacities and localization of free and bound forms of AFP, as well as polypeptide structure, heterogeneity and topography of AFP receptors are highlighted here. The data on the mechanisms of AFP synthesis, its conformational features, binding sites and intracellular metabolism are also presented. The concepts of physiological functions and mechanisms of AFP transport in an organism are presented. Data on AFP isolation from the natural primary products and its production by means of recombinant and synthetic methods are shown. This review also summarizes information on the current possibilities of clinical application of AFP and the prospects for its usage in anticancer therapy for targeted delivery of chemotherapy drugs, with emphasis on the description of the recent progress in this field.

The Combinatorial Effect of Cisplatin and Moxibustion on Tumor Growth Inhibition with Special Reference to Modulation of the Immune Microenvironment in Lewis Lung Cancer Mice

Objective

As a first-line treatment for non-small cell lung cancer (NSCLC), the efficacy of chemotherapy is still unsatisfactory. Moxibustion has been shown to improve the side effects of radiotherapy and chemotherapy and regulate immune function. This study aimed to explore the antitumor effects and potential mechanisms of combinatorial cisplatin and moxibustion treatment for NSCLC by targeting the tumor microenvironment.

Methods

Lewis lung cancer (LLC)-bearing mice were induced and treated with cisplatin or/and moxibustion at ST36 (Zusanli), and the growth, weight, and area of the tumor were evaluated. The numbers of various T cell subsets and myeloid cells in the tumor were assessed by flow cytometry, and the gene expression of related markers and cytokines was detected with real-time quantitative polymerase chain reaction (RT-qPCR). In addition, the tumor vascular structure was investigated using CD31 and α-smooth muscle actin (α-SMA) immunofluorescence staining. The expression of the vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) was detected by immunohistochemical staining.

Results

Both cisplatin and moxibustion inhibited LLC tumor growth and reduced both the tumor area and weight, with the combinatorial therapy showing superior outcomes. Moxibustion upregulated the infiltration of CD4⁺ T cells and Th1 cells in the tumor, and the combinatorial therapy increased the proportion of CD8⁺ cytotoxic T cells (CTLs), CD4⁺T cells, Th1, Th9 cells, and M1 macrophages, as well as the expression of Cd69, Ifng, and Cd86 mRNA. The combinatorial therapy improved vascular normalization by increasing both the microvessel density (MVD) and pericyte coverage (α-SMA area density) and inhibiting the expression of the VEGF.

Conclusions

Combinatorial cisplatin and moxibustion treatment inhibited the LLC tumor growth by mechanisms related to the improvement of the tumor immune microenvironment and vascular normalization, providing an effective combinatorial therapy beneficial for patients with NSCLC.

Cargo-free immunomodulatory nanoparticles combined with anti-PD-1 antibody for treating metastatic breast cancer

The presence of immunosuppressive innate immune cells such as myeloid derived suppressor cells (MDSCs), Ly6C-high monocytes, and tumor-associated macrophages (TAMs) at a tumor can inhibit effector T cell and NK cell function. Immune checkpoint blockade using anti-PD-1 antibody aims to overcome the immune suppressive environment, yet only a fraction of patients responds. Herein, we test the hypothesis that cargo-free PLG nanoparticles administered intravenously can divert circulating immune cells from the tumor microenvironment to enhance the efficacy of anti-PD-1 immunotherapy in the 4T1 mouse model of metastatic triple-negative breast cancer. In vitro studies demonstrate that these nanoparticles decrease the expression of MCP-1 by 5-fold and increase the expression of TNF-α by more than 2-fold upon uptake by innate immune cells. Intravenous administration of particles results in internalization by MDSCs and monocytes, with particles detected in the liver, lung, spleen, and primary tumor. Nanoparticle delivery decreased the abundance of MDSCs in circulation and in the lung, the latter being the primary metastatic site. Combined with anti-PD-1 antibody, nanoparticles significantly slowed tumor growth and resulted in a survival benefit. Gene expression analysis by GSEA indicated inflammatory myeloid cell pathways were downregulated in the lung and upregulated in the spleen and tumor. Upregulation of extrinsic apoptotic pathways was also observed in the primary tumor. Collectively, these results demonstrate that cargo-free PLG nanoparticles can reprogram immune cell responses and alter the tumor microenvironment in vivo to overcome the local immune suppression attributed to myeloid cells and enhance the efficacy of anti-PD-1 therapy.

The role of myeloid-derived suppressor cells in hematologic malignancies

PURPOSE OF REVIEW

This article focuses on the immunosuppressive impact of myeloid-derived suppressor cells (MDSCs) and the potential clinical implications in hematological malignancies.

RECENT FINDINGS

MDSCs play a critical role in the regulation of the immune response in cancer. They inhibit activation of adaptive immune response and as a result foster the growth of the malignancy. Recent studies have shown that MDSCs serve as prognostic biomarkers and as targets for cancer immunotherapy. Preclinical and clinical studies have identified new approaches to deplete MDSC populations and inhibit MDSC function with combination immunomodulatory therapies including chemotherapeutic agents with immune checkpoint-directed treatment.

SUMMARY

A broad spectrum of publications indicate that direct targeting of MDSCs may abrogate their protumorigenic impact within the tumor microenvironment through activation of the adaptive immune response.

Developmental pathways of myeloid-derived suppressor cells in neoplasia

Immunotherapy has become a major weapon against the war on cancer. This has culminated from decades of seminal work that led to the discovery of innovative approaches to drive adaptive immunity. Notably, was the discovery of immune checkpoint inhibitory receptors on T cells, and the subsequent development of monoclonal antibodies that target those receptors, known as immune checkpoint inhibitors (ICIs). Blocking those receptors using ICIs leads to sustained effector function, which has translated to enhanced antitumor responses across multiple human cancer types. However, these treatments are effective in subsets of patients, implicating significant barriers limiting therapeutic potential. While numerous mechanisms may hinder immunotherapy potency, one prominent mechanism is the production of myeloid-derived suppressor cells (MDSCs). MDSCs comprise monocytic and granulocytic cell types and mediate pro-tumorigenic and immune suppressive activities. Here, we summarize several pathways by which MDSCs arise in cancer, providing a conceptual framework for identifying unique combination therapeutic interventions.

Circulating CD14+ HLA-DRlo/- monocytic cells as a biomarker for epithelial ovarian cancer progression

PROBLEM

Previous studies identified circulating CD14⁺ HLA-DR^lo/- monocytic cells as an immune suppressive subset in solid malignancies, such as prostate, renal cell carcinoma, and pancreatic cancer. Such monocytic cells have been implicated not only in tumour progression but also as a potential barrier for immunotherapy. This study examined the relationship between the frequency of circulating monocytic cells and epithelial ovarian cancer (EOC) progression pre- and post-frontline chemotherapy, defined by disease stage, which is a leading prognostic factor for this malignancy.

METHOD OF STUDY

Incident cases of 236 women with EOC were recruited and comprehensive flow cytometry was utilized to assess the frequency of peripheral blood CD33⁺ CD11b⁺ HLA-DR^-/low CD14⁺ CD15^- monocytic cells, henceforth termed CD14⁺ HLA-DR^lo/- monocytic cells, prior to and after completion of frontline chemotherapy. Multivariable odds ratios (OR) were used to estimate the association between CD14⁺ HLA-DR^lo/- monocytic cell percentages and disease stage. Wilcoxon signed-rank tests evaluated changes in these monocytic cell levels pre- and post-chemotherapy in a patient subset (n = 70).

RESULTS

Patients with elevated frequencies of circulating CD14⁺ HLA-DR^lo/- monocytic cells at diagnosis were at 3.33-fold greater odds of having advanced stage (III/IV) EOC (CI: 1.04-10.64), with a significant trend in increasing CD14⁺ HLA-DR^lo/- monocytic cell levels (P = .04). There was a 2.02% median decrease of these monocytic cells post-chemotherapy among a subset of patients with advanced stage disease (P < .0001).

CONCLUSION

These findings support the potential clinical relevance of CD14⁺ HLA-DR^lo/- monocytic cells in EOC for prognosis and may indicate a non-invasive biomarker to measure disease progression.

The role of myeloid-derived suppressor cells in hematologic malignancies

PURPOSE OF REVIEW

This article focuses on the immunosuppressive impact of myeloid-derived suppressor cells (MDSCs) and the potential clinical implications in hematological malignancies.

RECENT FINDINGS

MDSCs play a critical role in the regulation of the immune response in cancer. They inhibit activation of adaptive immune response and as a result foster the growth of the malignancy. Recent studies have shown that MDSCs serve as prognostic biomarkers and as targets for cancer immunotherapy. Preclinical and clinical studies have identified new approaches to deplete MDSC populations and inhibit MDSC function with combination immunomodulatory therapies including chemotherapeutic agents with immune checkpoint-directed treatment.

SUMMARY

A broad spectrum of publications indicate that direct targeting of MDSCs may abrogate their protumorigenic impact within the tumor microenvironment through activation of the adaptive immune response.

C5aR1 is a master regulator in Colorectal Tumorigenesis via Immune modulation

Numerous factors have been claimed to play important roles in colorectal cancer (CRC) tumorigenesis, including myeloid-derived suppressor cells (MDSCs) and other immune cells, cytokines, and chemokines; however, the precise mechanisms of colorectal tumorigenesis remain elusive, and there is a lack of effective preventive treatments. Here, we investigated the role of complement system, a key regulator of immune surveillance and homeostasis, in colorectal tumorigenesis.

Methods: The prototypical CRC model was induced by combined administration of azoxymethane (AOM)/ dextran sulfate sodium (DSS) in Wild-type (WT), C3-, C5-, C5ar1-, and C5ar2-deficient mice. Using flow cytometry, immunohistochemical staining and multiplex bead assay, we profiled the immune cells, cytokines and chemokines. Bone marrow transplantation was employed to determine the contribution of immune cells in colorectal tumorigenesis. Further, we used C5aR1 antagonist PMX205 to investigate the protective role in colorectal tumorigenesis.

Results: Complement was extensively activated in inflamed tissues of AOM/DSS-induced murine CRC model, leading to multifaceted consequences. The deficiency of complement C5 or especially C5ar1, but not C3 almost completely prevented CRC tumorigenesis. C5a/C5aR1 signaling recruited MDSCs into the inflamed colorectum to impair CD8⁺ T cells, and modulated the production of critical cytokines and chemokines, thus initiating CRC. Moreover, the C5aR1 antagonist PMX205 strongly impeded colorectal tumorigenesis. Bone marrow transplantation further revealed that C5aR1 expression by immune cells was critical for colorectal tumorigenesis.

Conclusion: Our study identifies C5a/C5aR1 signaling as a vital immunomodulatory program in CRC tumorigenesis and suggests a feasible preventive strategy.

Clinical relevance of tumor microenvironment: immune cells, vessels, and mouse models

The tumor microenvironment (TME) plays a crucial role in tumor progression, therapeutic response, and patient outcomes. TME includes immune cells, blood and lymphatic vessels, and so on. There are anti-cancer and pro-cancer immune cells. In general, infiltration of anti-cancer immune cells, such as cytotoxic T cells (CTLs), is associated with a favorable patient prognosis. In contrast, infiltration of pro-cancer immune cells, such as regulatory T cells (Tregs), tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs), is associated with a worse prognosis. However, some immune cells, which play an ambivalent role in cancer immunity, have demonstrated contradictory impacts on patient prognosis. Blood and lymphatic vessels play crucial roles in TME not only as delivery and draining systems of fluid and molecules, but also allowing cancer cells access to systematic circulation to metastasize. Angiogenesis promotes cancer aggressiveness and is associated with a worse prognosis. Its targeted therapy shows a benefit in some cancers, however, because the target can vary by caner type, a benefit of anti-angiogenesis therapy is limited in the current standard of care. Lymphangiogenesis plays a role in lymph node metastasis, thus, it is associated with a poor prognosis in some cancers. To study TME, the mouse model is one of the most commonly used tools. The choice of appropriate mouse model depends on the hypothesis being tested and the scientific question being asked. Here, we review recent studies that investigated the clinical relevance of TME components and introduce mouse models to study TME.