Myeloid-derived suppressor cells in cancer: Current knowledge and future perspectives

MDSCs (myeloid-derived suppressor cells) are crucial for immune system evasion in cancer. They accumulate in peripheral blood and tumor microenvironment, suppressing immune cells like T-cells, natural killer cells and dendritic cells. They promote tumor angiogenesis and metastasis by secreting cytokines and growth factors and contribute to a tumor-promoting environment. The accumulation of MDSCs in cancer patients has been linked to poor prognosis and resistance to various cancer therapies. Targeting MDSCs and their immunosuppressive mechanisms may improve treatment outcomes and enhance immune surveillance by developing drugs that inhibit MDSC function, by preventing their accumulation and by disrupting the tumor-promoting environment. This review presents a detailed overview of the MDSC research in cancer with regulation of their development and function. The relevance of MDSC as a prognostic and predictive biomarker in different types of cancers, along with recent advancements on the therapeutic approaches to target MDSCs are discussed in detail.

The emerging role of osteoclasts in the treatment of bone metastases: rationale and recent clinical evidence

The occurrence of bone metastasis is a grave medical concern that substantially impacts the quality of life in patients with cancer. The precise mechanisms underlying bone metastasis remain unclear despite extensive research efforts, and efficacious therapeutic interventions are currently lacking. The ability of osteoclasts to degrade the bone matrix makes them a crucial factor in the development of bone metastasis. Osteoclasts are implicated in several aspects of bone metastasis, encompassing the formation of premetastatic microenvironment, suppression of the immune system, and reactivation of quiescent tumor cells. Contemporary clinical interventions targeting osteoclasts have proven effective in mitigating bone-related symptoms in patients with cancer. This review comprehensively analyzes the mechanistic involvement of osteoclasts in bone metastasis, delineates potential therapeutic targets associated with osteoclasts, and explores clinical evidence regarding interventions targeting osteoclasts.

Clinical Relevance of Tumour-Infiltrating Immune Cells in HER2-Negative Breast Cancer Treated with Neoadjuvant Therapy

Currently, therapy response cannot be accurately predicted in HER2-negative breast cancer (BC). Measuring stromal tumour-infiltrating lymphocytes (sTILs) and mediators of the tumour microenvironment and characterizing tumour-infiltrating immune cells (TIICs) may improve treatment response in the neoadjuvant setting. Tumour tissue and peripheral blood samples were retrospectively collected from 118 patients, and sTILs were evaluated. Circulating exosomes and myeloid-derived suppressor cells were determined by flow cytometry. TIICs markers (CD4, CD8, CD20, CD1a, and CD68) were assessed immunohistochemically. High sTILs were significantly associated with pathological complete response (pCR; p = 0.048) and event-free survival (EFS; p = 0.027). High-CD68 cells were significantly associated with pCR in triple-negative (TN, p = 0.027) and high-CD1a cells with EFS in luminal-B (p = 0.012) BC. Cluster analyses of TIICs revealed two groups of tumours (C1 and C2) that had different immune patterns and clinical outcomes. An immunoscore based on clinicopathological variables was developed to identify high risk (C1) or low-risk (C2) patients. Additionally, cluster analyses revealed two groups of tumours for both luminal-B and TNBC. Our findings support the association of sTILs with pCR and show an immunological component in a subset of patients with HER2-negative BC. Our immunoscore may be useful for future escalation or de-escalation treatments.

Study on the mechanism of MDSC-platelets and their role in the breast cancer microenvironment

Myeloid-derived suppressor cells (MDSCs) are key immunosuppressive cells in the tumor microenvironment (TME) that play critical roles in promoting tumor growth and metastasis. Tumor-associated platelets (TAPs) help cancer cells evade the immune system and promote metastasis. In this paper, we describe the interaction between MDSCs and TAPs, including their generation, secretion, activation, and recruitment, as well as the effects of MDSCs and platelets on the generation and changes in the immune, metabolic, and angiogenic breast cancer (BC) microenvironments. In addition, we summarize preclinical and clinical studies, traditional Chinese medicine (TCM) therapeutic approaches, and new technologies related to targeting and preventing MDSCs from interacting with TAPs to modulate the BC TME, discuss the potential mechanisms, and provide perspectives for future development. The therapeutic strategies discussed in this review may have implications in promoting the normalization of the BC TME, reducing primary tumor growth and distant lung metastasis, and improving the efficiency of anti-tumor therapy, thereby improving the overall survival (OS) and progression-free survival (PFS) of patients. However, despite the significant advances in understanding these mechanisms and therapeutic strategies, the complexity and heterogeneity of MDSCs and side effects of antiplatelet agents remain challenging. This requires further investigation in future prospective cohort studies.

The Proportion of Myeloid-derived Suppressor Cells in the Graft as a Potential Predictor of Acute Graft-versus-host Disease in Haploid Allogeneic Hematopoietic Stem Cell Transplantation

Myeloid-derived suppressor cells (MDSC) are powerful immunomodulatory cells that play an important role in infectious and inflammatory disorders, but the correlation between graft MDSC amount and early transplant outcomes remains unknown in allogeneic hematopoietic stem cell transplantation. We collected data from 91 patients with acute leukemia undergoing haploidentical allogeneic hematopoietic stem cell transplantation. The grafts were analyzed in terms of CD34+ cells, CD3+ T cells and subpopulation, and MDSC (HLA-DR -/low CD33 + CD16 - ) by flow cytometry. The cutoff value of the MDSC proportion in the graft on the receiver operating curve was 8.89%, with a sensitivity of 0.833 and specificity of 0.852. Day +100 cumulative incidences of II-IV and III-IV acute graft-versus-host disease (aGVHD) in the low MDSC group were 73.5% and 38.8%, respectively, and that in the high MDSC group were 5.3% and 0%, with a significant difference in incidences of II-IV and III-IV aGVHD ( P <0.001). The overall survival, relapse-free survival, and GVHD-relapse-free survival (GRFS) at 1 year were 66.3% versus 80.5% ( P =0.043), 71.6% versus 71.7% ( P =0.248), and 22.1% versus 62.8% ( P <0.001), respectively. No significant difference in the cumulative incidence of relapse between the 2 groups was observed. Multivariate analysis revealed that higher MDSC proportions were associated with a lower risk of II-IV aGVHD. Graft MDSC proportion exceeding 8.89% was significantly associated with higher overall survival and GRFS. The prophylaxis of antithymocyte globulin+post-transplant cyclophosphamide and higher MDSC proportion in the graft were favorable factors for improving GRFS. In conclusion, graft MDSC proportion may be a significant predictor of aGVHD.

Tumor microenvironment and immune system preservation in early-stage breast cancer: routes for early recurrence after mastectomy and treatment for lobular and ductal forms of disease

BACKGROUND

Intra-ductal cancer (IDC) is the most common type of breast cancer, with intra-lobular cancer (ILC) coming in second. Surgery is the primary treatment for early stage breast cancer. There are now irrefutable data demonstrating that the immune context of breast tumors can influence growth and metastasis. Adjuvant chemotherapy may be administered in patients who are at a high risk of recurrence. Our goal was to identify the processes underlying both types of early local recurrences.

METHODS

This was a case-control observational study. Within 2 years of receiving adjuvant taxan and anthracycline-based chemotherapy, as well as modified radical mastectomy (MRM), early stage IDC and ILC recurred. Vimentin, α-smooth muscle actin (SMA), platelet-derived growth factor (PDGF), matrix metalloproteinase (MMP1), and clustered differentiation (CD95) were investigated.

RESULTS

Of the samples in the ductal type group, 25 showed local recurrence, and 25 did not. Six individuals in the lobular-type group did not experience recurrence, whereas seven did. Vimentin (p = 0.000 and 0.021), PDGF (p = 0.000 and 0.002), and CD95 (p = 0.000 and 0.045) expressions were significantly different in ductal and lobular carcinoma types, respectively. Measurement of ductal type was the sole significant difference found in MMP1 (p = 0.000) and α-SMA (p = 0.000). α-SMA and CD95 were two variables that helped the recurrence mechanism in the ductal type according to the pathway analysis. In contrast, the CD95 route is a recurrent mechanism for the lobular form.

CONCLUSIONS

While the immune system plays a larger role in ILC, the tumor microenvironment and immune system both influence the recurrence of IDC. According to this study, improving the immune system may be a viable cancer treatment option.

Tumor Microenvironment: A Niche for Cancer Stem Cell Immunotherapy

Tumorigenic Cancer Stem Cells (CSCs), often called tumor-initiating cells (TICs), represent a unique subset of cells within the tumor milieu. They stand apart from the bulk of tumor cells due to their exceptional self-renewal, metastatic, and differentiation capabilities. Despite significant progress in classifying CSCs, these cells remain notably resilient to conventional radiotherapy and chemotherapy, contributing to cancer recurrence. In this review, our objective is to explore novel avenues of research that delve into the distinctive characteristics of CSCs within their surrounding tumor microenvironment (TME). We will start with an overview of the defining features of CSCs and then delve into their intricate interactions with cells from the lymphoid lineage, namely T cells, B cells, and natural killer (NK) cells. Furthermore, we will discuss their dynamic interplay with myeloid lineage cells, including macrophages, neutrophils, and myeloid-derived suppressor cells (MDSCs). Moreover, we will illuminate the crosstalk between CSCs and cells of mesenchymal origin, specifically fibroblasts, adipocytes, and endothelial cells. Subsequently, we will underscore the pivotal role of CSCs within the context of the tumor-associated extracellular matrix (ECM). Finally, we will highlight pre-clinical and clinical studies that target CSCs within the intricate landscape of the TME, including CAR-T therapy, oncolytic viruses, and CSC-vaccines, with the ultimate goal of uncovering novel avenues for CSC-based cancer immunotherapy.

Unveiling the mechanistic role of the Aryl hydrocarbon receptor in environmentally induced Breast cancer

The aryl hydrocarbon receptor (AhR) is a crucial cytosolic evolutionary conserved ligand-activated transcription factor and a pleiotropic signal transducer. The biosensor activity of the AhR is attributed to the promiscuity of its ligand-binding domain. Evidence suggests exposure to environmental toxins such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls and halogenated aromatic hydrocarbons activates the AhR signaling pathway. The constitutive activation of the receptor signaling system leads to multiple health adversities and enhances the risk of several cancers, including breast cancer (BC). This review evaluates several mechanisms that integrate the tumor-inducing property of such environmental contaminants with the AhR pathway assisting in BC tumorigenesis, progress and metastasis. Intriguingly, immune evasion is identified as a prominent hallmark in BC. Several emerging pieces of evidence have identified AhR as a potent immunosuppressive effector in several cancers. Through AhR signaling pathways, some tumors can avoid immune detection. Thus the relevance of AhR in the immunomodulation of breast tumors and its putative mode of action in the breast tumor microenvironment are discussed in this review. Additionally, the work also explores BC stemness and its associated inflammation in response to several environmental cues. The review elucidates the context-dependent ambiguous behavior of AhR either as an oncogene or a tumor suppressor with respect to its ligand. Conclusively, this holistic piece of literature attempts to potentiate AhR as a promising pharmacological target in BC and updates on the therapeutic manipulation of its various exogenous and endogenous ligands.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Exosomal miRNAs and breast cancer: a complex theranostics interlink with clinical significance

Breast cancer (BC) remains the most challenging global health crisis of the current decade, impacting a large population of females annually. In the field of cancer research, the discovery of extracellular vesicles (EVs), specifically exosomes (a subpopulation of EVs), has marked a significant milestone. In general, exosomes are released from all active cells but tumour cell-derived exosomes (TDXs) have a great impact (TDXs miRNAs, proteins, lipid molecules) on cancer development and progression. TDXs regulate multiple events in breast cancer such as tumour microenvironment remodelling, immune cell suppression, angiogenesis, metastasis (EMT-epithelial mesenchymal transition, organ-specific metastasis), and therapeutic resistance. In BC, early detection is the most challenging event, exosome-based BC screening solved the problem. Exosome-based BC treatment is a sign of the transforming era of liquid biopsy, it is also a promising therapeutic tool for breast cancer. Exosome research goes to closer precision oncology via a single exosome profiling approach. Our hope is that this review will serve as motivation for researchers to explore the field of exosomes and develop an efficient, and affordable theranostics approach for breast cancer.

The recent progress of myeloid-derived suppressor cell and its targeted therapies in cancers

Myeloid-derived suppressor cells (MDSCs) are an immature group of myeloid-derived cells generated from myeloid cell precursors in the bone marrow. MDSCs appear almost exclusively in pathological conditions, such as tumor progression and various inflammatory diseases. The leading function of MDSCs is their immunosuppressive ability, which plays a crucial role in tumor progression and metastasis through their immunosuppressive effects. Since MDSCs have specific molecular features, and only a tiny amount exists in physiological conditions, MDSC-targeted therapy has become a promising research direction for tumor treatment with minimal side effects. In this review, we briefly introduce the classification, generation and maturation process, and features of MDSCs, and detail their functions under various circumstances. The present review specifically demonstrates the environmental specificity of MDSCs, highlighting the differences between MDSCs from cancer and healthy individuals, as well as tumor-infiltrating MDSCs and circulating MDSCs. Then, we further describe recent advances in MDSC-targeted therapies. The existing and potential targeted drugs are divided into three categories, monoclonal antibodies, small-molecular inhibitors, and peptides. Their targeting mechanisms and characteristics have been summarized respectively. We believe that a comprehensive in-depth understanding of MDSC-targeted therapy could provide more possibilities for the treatment of cancer.

Enhancement of immune surveillance in breast cancer by targeting hypoxic tumor endothelium: Can it be an immunological switch point?

Breast cancer ranks second among the causes of cancer-related deaths in women. In spite of the recent advances achieved in the diagnosis and treatment of breast cancer, further study is required to overcome the risk of cancer resistance to treatment and thereby improve the prognosis of individuals with advanced-stage breast cancer. The existence of a hypoxic microenvironment is a well-known event in the development of mutagenesis and rapid proliferation of cancer cells. Tumor cells, purposefully cause local hypoxia in order to induce angiogenesis and growth factors that promote tumor growth and metastatic characteristics, while healthy tissue surrounding the tumor suffers damage or mutate. It has been found that these settings with low oxygen levels cause immunosuppression and a lack of immune surveillance by reducing the activation and recruitment of tumor infiltrating leukocytes (TILs). The immune system is further suppressed by hypoxic tumor endothelium through a variety of ways, which creates an immunosuppressive milieu in the tumor microenvironment. Non responsiveness of tumor endothelium to inflammatory signals or endothelial anergy exclude effector T cells from the tumor milieu. Expression of endothelial specific antigens and immunoinhibitory molecules like Programmed death ligand 1,2 (PDL-1, 2) and T cell immunoglobulin and mucin-domain containing-3 (TIM-3) by tumor endothelium adds fuel to the fire by inhibiting T lymphocytes while promoting regulatory T cells. The hypoxic microenvironment in turn recruits Myeloid Derived Suppressor Cells (MDSCs), Tumor Associated Macrophages (TAMs) and T regulatory cells (Treg). The structure and function of newly generated blood vessels within tumors, on the other hand, are aberrant, lacking the specific organization of normal tissue vasculature. Vascular normalisation may work for a variety of tumour types and show to be an advantageous complement to immunotherapy for improving tumour access. By enhancing immune response in the hypoxic tumor microenvironment, via immune-herbal therapeutic and immune-nutraceuticals based approaches that leverage immunological evasion of tumor, will be briefly reviewed in this article. Whether these tactics may be the game changer for emerging immunological switch point to attenuate the breast cancer growth and prevent metastatic cell division, is the key concern of the current study.

Defining the Emergence of New Immunotherapy Approaches in Breast Cancer: Role of Myeloid-Derived Suppressor Cells

Breast cancer (BC) continues to be the most diagnosed tumor in women and a very heterogeneous disease both inter- and intratumoral, mainly given by the variety of molecular profiles with different biological and clinical characteristics. Despite the advancements in early detection and therapeutic strategies, the survival rate is low in patients who develop metastatic disease. Therefore, it is mandatory to explore new approaches to achieve better responses. In this regard, immunotherapy arose as a promising alternative to conventional treatments due to its ability to modulate the immune system, which may play a dual role in this disease since the relationship between the immune system and BC cells depends on several factors: the tumor histology and size, as well as the involvement of lymph nodes, immune cells, and molecules that are part of the tumor microenvironment. Particularly, myeloid-derived suppressor cell (MDSC) expansion is one of the major immunosuppressive mechanisms used by breast tumors since it has been associated with worse clinical stage, metastatic burden, and poor efficacy of immunotherapies. This review focuses on the new immunotherapies in BC in the last five years. Additionally, the role of MDSC as a therapeutic target in breast cancer will be described.

The Role of Different Immunocompetent Cell Populations in the Pathogenesis of Head and Neck Cancer-Regulatory Mechanisms of Pro- and Anti-Cancer Activity and Their Impact on Immunotherapy

Head and neck squamous cell carcinoma (HNSCC) is one of the most aggressive and heterogeneous groups of human neoplasms. HNSCC is characterized by high morbidity, accounting for 3% of all cancers, and high mortality with ~1.5% of all cancer deaths. It was the most common cancer worldwide in 2020, according to the latest GLOBOCAN data, representing the seventh most prevalent human malignancy. Despite great advances in surgical techniques and the application of modern combinations and cytotoxic therapies, HNSCC remains a leading cause of death worldwide with a low overall survival rate not exceeding 40-60% of the patient population. The most common causes of death in patients are its frequent nodal metastases and local neoplastic recurrences, as well as the relatively low response to treatment and severe drug resistance. Much evidence suggests that the tumour microenvironment (TME), tumour infiltrating lymphocytes (TILs) and circulating various subpopulations of immunocompetent cells, such regulatory T cells (CD4+CD25+Foxp3+Tregs), cytotoxic CD3+CD8+ T cells (CTLs) and CD3+CD4+ T helper type 1/2/9/17 (Th1/Th2/Th9/Th17) lymphocytes, T follicular helper cells (Tfh) and CD56dim/CD16bright activated natural killer cells (NK), carcinoma-associated fibroblasts (CAFs), myeloid-derived suppressor cells (MDSCs), tumour-associated neutrophils (N1/N2 TANs), as well as tumour-associated macrophages (M1/M2 phenotype TAMs) can affect initiation, progression and spread of HNSCC and determine the response to immunotherapy. Rapid advances in the field of immuno-oncology and the constantly growing knowledge of the immunosuppressive mechanisms and effects of tumour cancer have allowed for the use of effective and personalized immunotherapy as a first-line therapeutic procedure or an essential component of a combination therapy for primary, relapsed and metastatic HNSCC. This review presents the latest reports and molecular studies regarding the anti-tumour role of selected subpopulations of immunocompetent cells in the pathogenesis of HNSCC, including HPV+ve (HPV+) and HPV-ve (HPV-) tumours. The article focuses on the crucial regulatory mechanisms of pro- and anti-tumour activity, key genetic or epigenetic changes that favour tumour immune escape, and the strategies that the tumour employs to avoid recognition by immunocompetent cells, as well as resistance mechanisms to T and NK cell-based immunotherapy in HNSCC. The present review also provides an overview of the pre- and clinical early trials (I/II phase) and phase-III clinical trials published in this arena, which highlight the unprecedented effectiveness and limitations of immunotherapy in HNSCC, and the emerging issues facing the field of HNSCC immuno-oncology.

Myeloid-derived suppressor cells: A new emerging player in endometriosis

Endometriosis is a common gynecological disorder defined by the presence of endometrial tissue outside the uterus. This is commonly associated with chronic pelvic pain, infertility, and dysmenorrhea, which occurs in approximately 10% of women of reproductive age. Although the exact mechanism remains uncertain, it has been widely accepted to be an estrogen-dependent and inflammatory disease. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of immune cells with immunosuppressive capacity and non-immunological functions. They have been found to be aggressively involved in the pathologies of various disorders. In regards to tumors, the functions of MDSCs have been profoundly shown to inhibit tumor immune response and to promote angiogenesis, tumor metastasis, fibrosis, and epithelial-mesenchymal transition (EMT). In recent years, the elevation of MDSCs in endometriosis was reported by several studies that provoke the assumption that MDSCs might exert similar roles to promote the development of endometriosis. Such that, precision treatments targeting MDSCs might be a promising direction for future study. Herein, we will review the research progress of MDSCs in endometriosis and its potential relevance to the pathogenesis, progression, and therapeutics strategy of endometriosis.

Environmental exposure and the role of AhR in the tumor microenvironment of breast cancer

Activation of the aryl hydrocarbon receptor (AhR) through environmental exposure to chemicals including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins (PCDDs) can lead to severe adverse health effects and increase the risk of breast cancer. This review considers several mechanisms which link the tumor promoting effects of environmental pollutants with the AhR signaling pathway, contributing to the development and progression of breast cancer. We explore AhR's function in shaping the tumor microenvironment, modifying immune tolerance, and regulating cancer stemness, driving breast cancer chemoresistance and metastasis. The complexity of AhR, with evidence for both oncogenic and tumor suppressor roles is discussed. We propose that AhR functions as a "molecular bridge", linking disproportionate toxin exposure and policies which underlie environmental injustice with tumor cell behaviors which drive poor patient outcomes.

Pembrolizumab in combination with gemcitabine for patients with HER2-negative advanced breast cancer: GEICAM/2015-04 (PANGEA-Breast) study

BACKGROUND

We evaluated a new chemoimmunotherapy combination based on the anti-PD1 monoclonal antibody pembrolizumab and the pyrimidine antimetabolite gemcitabine in HER2- advanced breast cancer (ABC) patients previously treated in the advanced setting, in order to explore a potential synergism that could eventually obtain long term benefit in these patients.

METHODS

HER2-negative ABC patients received 21-day cycles of pembrolizumab 200 mg (day 1) and gemcitabine (days 1 and 8). A run-in-phase (6 + 6 design) was planned with two dose levels (DL) of gemcitabine (1,250 mg/m² [DL0]; 1,000 mg/m² [DL1]) to determine the recommended phase II dose (RP2D). The primary objective was objective response rate (ORR). Tumor infiltrating lymphocytes (TILs) density and PD-L1 expression in tumors and myeloid-derived suppressor cells (MDSCs) levels in peripheral blood were analyzed.

RESULTS

Fourteen patients were treated with DL0, resulting in RP2D. Thirty-six patients were evaluated during the first stage of Simon's design. Recruitment was stopped as statistical assumptions were not met. The median age was 52; 21 (58%) patients had triple-negative disease, 28 (78%) visceral involvement, and 27 (75%) ≥ 2 metastatic locations. Progression disease was observed in 29 patients. ORR was 15% (95% CI, 5-32). Eight patients were treated ≥ 6 months before progression. Fourteen patients reported grade ≥ 3 treatment-related adverse events. Due to the small sample size, we did not find any clear association between immune tumor biomarkers and treatment efficacy that could identify a subgroup with higher probability of response or better survival. However, patients that experienced a clinical benefit showed decreased MDSCs levels in peripheral blood along the treatment.

CONCLUSION

Pembrolizumab 200 mg and gemcitabine 1,250 mg/m² were considered as RP2D. The objective of ORR was not met; however, 22% patients were on treatment for ≥ 6 months. ABC patients that could benefit of chemoimmunotherapy strategies must be carefully selected by robust and validated biomarkers. In our heavily pretreated population, TILs, PD-L1 expression and MDSCs levels could not identify a subgroup of patients for whom the combination of gemcitabine and pembrolizumab would induce long term benefit.

TRIAL REGISTRATION

ClinicalTrials.gov and EudraCT (NCT03025880 and 2016-001,779-54, respectively). Registration dates: 20/01/2017 and 18/11/2016, respectively.

Replenishment of myeloid-derived suppressor cells (MDSCs) overrides CR-mediated protection against tumor growth in a murine model of triple-negative breast cancer

Caloric restriction (CR) is the leading non-pharmacological intervention to delay induced and spontaneous tumors in pre-clinical models. These effects of CR are largely attributed to canonical inhibition of pro-growth pathways. However, our recent data suggest that CR impairs primary tumor growth and cancer progression in the murine 4T1 model of triple negative breast cancer (TNBC), at least in part, through reduced frequency of the myeloid-derived suppressor cells (MDSC). In the present study, we sought to determine whether injection of excess MDSCs could block regression in 4T1 tumor growth and metastatic spread in BALB/cJ female mice undergoing daily CR. Our findings show that MDSC injection impeded CR-mediated protection against tumor growth without increasing lung metastatic burden. Overall, these results reveal that CR can slow cancer progression by affecting immune suppressive cells.Impact statement: Inoculation of MDSCs from donor mice effectively impedes the ability of calorie restriction to protect against primary tumor growth without impacting lung metastatic burden in recipient animals.

Leveraging the Dynamic Immune Environment Triad in Patients with Breast Cancer: Tumour, Lymph Node, and Peripheral Blood

During the anti-tumour response to breast cancer, the primary tumour, the peripheral blood, and the lymph nodes each play unique roles. Immunological features at each site reveal evidence of continuous immune cross-talk between them before, during and after treatment. As such, immune responses to breast cancer are found to be highly dynamic and truly systemic, integrating three distinct immune sites, complex cell-migration highways, as well as the temporal dimension of disease progression and treatment. In this review, we provide a connective summary of the dynamic immune environment triad of breast cancer. It is critical that future studies seek to establish dynamic immune profiles, constituting multiple sites, that capture the systemic immune response to breast cancer and define patient-selection parameters resulting in more significant overall responses and survival rates for breast cancer patients.

The modulatory role of dendritic cell-T cell cross-talk in breast cancer: Challenges and prospects

Antigen recognition and presentation are highlighted as the first steps in developing specialized antigen responses. Dendritic cells (DCs) are outstanding professional antigen-presenting cells (APCs) responsible for priming cellular immunity in pathological states, including cancer. However, the diminished or repressed function of DCs is thought to be a substantial mechanism through which tumors escape from the immune system. In this regard, DCs obtained from breast cancer (BC) patients represent a notably weakened potency to encourage specific T-cell responses. Additionally, impaired DC-T-cell cross-talk in BC facilitates the immune evade of cancer cells and is connected with tumor advancement, immune tolerance, and adverse prognosis for patients. In this review we aim to highlight the available knowledge on DC-T-cell interactions in BC aggressiveness and show its therapeutic potential in BC treatment.

Circulating myeloid-derived suppressors cells correlate with clinicopathological characteristics and outcomes undergoing neoadjuvant chemoimmunotherapy in non-small cell lung cancer

PURPOSE

Myeloid-derived suppressors cells (MDSCs) are heterogeneous immunosuppressive cells, closely related to the development, efficacy and prognosis in various tumors. The relationship between clinicopathological characteristics, efficacy of neoadjuvant chemoimmunotherapy (NCIO) and circulating MDSCs in patients with non-small cell lung cancer (NSCLC) was investigated in this study.

METHODS

This study analyzed the clinical data of patients diagnosed at Department of Thoracic Surgery, Beijing Chest Hospital from November 2020 to August 2021. MDSCs and T cells subgroups were measured in fresh peripheral blood mononuclear cells(PBMCs) at baseline. Flow cytometry was used to detect MDSCs and T cells subgroups.

RESULTS

A total of 78 patients with NSCLC and 20 patients with benign nodule underwent direct surgery. 23 patients with NSCLC scheduled to accept NCIO before surgery. NSCLC had elevated levels of total MDSCs, PMN-MDSCs and M-MDSCs compared to patients with benign nodule. MDSCs subgroups were correlated to the pTNM stage in NSCLC patients. The frequency of total MDSCs were moderately positively correlated with regulatory T cells (Tregs)(r = 0.3597, P < 0.01) and negatively correlated with CD4 + T cells(r = 0.2714, P < 0.05). The baseline levels of total MDSCs, PMN-MDSCs and Tregs in pCR patients were significantly decreased than those of non-pCR patients (P < 0.05).

CONCLUSION

Circulating MDSCs were increased in NSCLC patients. MDSC subgroups were related to pTNM stage in NSCLC patients. Total MDSCs were positively correlated with Tregs levels and negatively correlated with CD4 + T cells in peripheral blood. The level of MDSCs and Tregs in peripheral blood may have potential value in predicting pathological response in NSCLC.

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

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

Sustained Drug Release From Liposomes for the Remodeling of Systemic Immune Homeostasis and the Tumor Microenvironment

Myeloid Derived Suppressor Cells (MDSCs) play important roles in constituting the immune suppressive environment promoting cancer development and progression. They are consisted of a heterogeneous population of immature myeloid cells including polymorphonuclear MDSC (PMN-MDSC) and monocytes MDSC (M-MDSC) that are found in both the systemic circulation and in the tumor microenvironment (TME). While previous studies had shown that all-trans retinoic acid (ATRA) could induce MDSC differentiation and maturation, the very poor solubility and fast metabolism of the drug limited its applications as an immune-modulator for cancer immunotherapy. We aimed in this study to develop a drug encapsulated liposome formulation L-ATRA with sustained release properties and examined the immuno-modulation effects. We showed that the actively loaded L-ATRA achieved stable encapsulation and enabled controlled drug release and accumulation in the tumor tissues. In vivo administration of L-ATRA promoted the remodeling of the systemic immune homeostasis as well as the tumor microenvironment. They were found to promote MDSCs maturation into DCs and facilitate immune responses against cancer cells. When used as a single agent treatment, L-ATRA deterred tumor growth, but only in immune-competent mice. In mice with impaired immune functions, L-ATRA at the same dose was not effective. When combined with checkpoint inhibitory agents, L-ATRA resulted in greater anti-cancer activities. Thus, L-ATRA may present a new IO strategy targeting the MDSCs that needs be further explored for improving the immunotherapy efficacy in cancer.

Roles of the Exosomes Derived From Myeloid-Derived Suppressor Cells in Tumor Immunity and Cancer Progression

Tumor immunity is involved in malignant tumor progression. Myeloid-derived suppressor cells (MDSCs) play an irreplaceable role in tumor immunity. MDSCs are composed of immature myeloid cells and exhibit obvious immunomodulatory functions. Exosomes released by MDSCs (MDSCs-Exos) have similar effects to parental MDSCs in regulating tumor immunity. In this review, we provided a comprehensive description of the characteristics, functions and mechanisms of exosomes. We analyzed the immunosuppressive, angiogenesis and metastatic effects of MDSCs-Exos in different tumors through multiple perspectives. Immunotherapy targeting MDSCs-Exos has demonstrated great potential in cancers and non-cancerous diseases.

PMN-MDSCs accumulation induced by CXCL1 promotes CD8+ T cells exhaustion in gastric cancer

Myeloid-derived suppressor cells (MDSCs) accumulation in multiple tumor is associated with immune checkpoint inhibitors (ICIs) resistance. However, mechanisms of MDSCs in ICIs resistance of gastric cancer (GC) have not been thoroughly explored. In this study, we found that the PMN-MDSCs frequency rather than the M-MDSCs frequency was correlated with the survival of GC patients and CXCL1 induced PMN-MDSCs accumulation in GC. S100A8/A9 heterodimer, a hallmark of MDSCs, upregulated the CXCL1 expression in GC cells through the TLR4/p38 MAPK/NF-κB pathway. Notably, PMN-MDSCs exerted immunosuppressive effect through S100A8/A9. Mechanically, S100A8/A9 led to CD8⁺ T cells exhaustion including inhibiting CD8⁺ T cells glycolysis, proliferation and TNF-α and IFN-γ production, which was dependent on TLR4/AKT/mTOR pathway. In tumor-bearing mice, the CXCR2 antagonist SB225002 decreased PMN-MDSCs accumulation, increased CD8⁺ T cells infiltration in GC and further enhanced anti-tumor efficacy of anti-PD-1. Taken together, our study identified that CXCL1 induced PMN-MDSCs accumulation in GC, and unveiled how PMN-MDSCs promoted CD8⁺ T cells exhaustion, which may provide a potential therapeutic strategy for GC.

Myeloid-Derived Suppressor Cells in Solid Tumors

Myeloid-derived suppressor cells (MDSCs) are one of the main suppressive cell population of the immune system. They play a pivotal role in the establishment of the tumor microenvironment (TME). In the context of cancers or other pathological conditions, MDSCs can differentiate, expand, and migrate in large quantities during circulation, inhibiting the cytotoxic functions of T cells and NK cells. This process is regulated by ROS, iNOS/NO, arginase-1, and multiple soluble cytokines. The definition of MDSCs and their phenotypes in humans are not as well represented as in other organisms such as mice, owing to the absence of the cognate molecule. However, a comprehensive understanding of the differences between different species and subsets will be beneficial for clarifying the immunosuppressive properties and potential clinical values of these cells during tumor progression. Recently, experimental evidence and clinical investigations have demonstrated that MDSCs have a close relationship with poor prognosis and drug resistance, which is considered to be a leading marker for practical applications and therapeutic methods. In this review, we summarize the remarkable position of MDSCs in solid tumors, explain their classifications in different models, and introduce new treatment approaches to target MDSCs to better understand the advancement of new approaches to cancer treatment.

Chronic stress promotes breast carcinoma metastasis by accumulating myeloid-derived suppressor cells through activating β-adrenergic signaling

Numerous studies have found that chronic stress could promote tumor progression and this may be related to inhibtion of immune system. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells with immunosuppressive activity. MDSCs may represent a key link between chronic stress and tumor progression. However, the role of stress-induced MDSCs in breast cancer progression is unclear. The present study showed that pre-exposure of chronic stress could lead to MDSCs elevation and facilitated breast cancer metastasis in tumor-bearing mice. Adoptive transfer of MDSCs could significantly increase lung metastatic foci. In contrast, lung metastasis could be alleviated by depleting endogenous MDSCs with Gr-1 antibody. The concentration of norepinephrine in serum and the expression of tyrosine hydroxylase in bone marrow could be significantly elevated by chronic stress. Moreover, propranolol, an inhibitor of β-adrenergic signaling, could inhibit breast carcinoma metastasis and prevent the expansion of chronic stress-induced MDSCs. Further study revealed that the expressions of IL-6 and JAK/STAT3 signaling pathways were upregulated by chronic stress in mice, and this upregulation could be inhibited by propranolol. Blocking the IL-6 signal or inhibiting the activation of the JAK/STAT3 signaling pathway could reduce tumor growth and metastasis by attenuating the accumulation of MDSCs in vivo. Besides, propranolol inhibited the expression of IL-6 in supernatant of 4T1 cells induced by isoproterenol and reduced the proportion of inducible MDSCs in vitro. Taken together, these data indicated that chronic stress may accumulate MDSCs via activation of β-adrenergic signaling and IL-6/STAT3 pathway, thereby promoting breast carcinoma metastasis.

3D Cancer Models: Depicting Cellular Crosstalk within the Tumour Microenvironment

The tumour microenvironment plays a critical role in tumour progression and drug resistance processes. Non-malignant cell players, such as fibroblasts, endothelial cells, immune cells and others, interact with each other and with the tumour cells, shaping the disease. Though the role of each cell type and cell communication mechanisms have been progressively studied, the complexity of this cellular network and its role in disease mechanism and therapeutic response are still being unveiled. Animal models have been mainly used, as they can represent systemic interactions and conditions, though they face recognized limitations in translational potential due to interspecies differences. In vitro 3D cancer models can surpass these limitations, by incorporating human cells, including patient-derived ones, and allowing a range of experimental designs with precise control of each tumour microenvironment element. We summarize the role of each tumour microenvironment component and review studies proposing 3D co-culture strategies of tumour cells and non-malignant cell components. Moreover, we discuss the potential of these modelling approaches to uncover potential therapeutic targets in the tumour microenvironment and assess therapeutic efficacy, current bottlenecks and perspectives.

Myeloid-derived suppressor cells: Important communicators in systemic lupus erythematosus pathogenesis and its potential therapeutic significance

Systemic lupus erythematosus (SLE) is a recognized chronic condition associated with immune system disorders that affect women nine times more commonly than men. SLE is characterized by over-secretion and release of autoantibodies in response to different cellular compartments and self-tolerance breaks to its own antigens. The detailed immunological dysregulation as an associated event that elicits the onset of clinical manifestations of SLE has not been clarified yet. Though, research using several animal models in the last two decades has indicated the role of the immune system in the pathogenesis of this disease. Myeloid-derived suppressor cells (MDSCs) as heterogeneous myeloid cells, are responsible for severe pathological conditions, including infection, autoimmunity, and cancer, by exerting considerable immunosuppressive effects on T-cells responses. It has been reported that these cells are involved in the regulation process of the immune response in several autoimmune diseases, particularly SLE. The function of MDSC is deleterious in infection and cancer diseases, though their role is more complicated in autoimmune diseases. In this review, we summarized the role and function of MDSCs in the pathogenesis and progression of SLE and its possible therapeutic approach.

Mechanisms Underlying the Role of Myeloid-Derived Suppressor Cells in Clinical Diseases: Good or Bad

Myeloid-derived suppressor cells (MDSCs) have strong immunosuppressive activity and are morphologically similar to conventional monocytes and granulocytes. The development and classification of these cells have, however, been controversial. The activation network of MDSCs is relatively complex, and their mechanism of action is poorly understood, creating an avenue for further research. In recent years, MDSCs have been found to play an important role in immune regulation and in effectively inhibiting the activity of effector lymphocytes. Under certain conditions, particularly in the case of tissue damage or inflammation, MDSCs play a leading role in the immune response of the central nervous system. In cancer, however, this can lead to tumor immune evasion and the development of related diseases. Under cancerous conditions, tumors often alter bone marrow formation, thus affecting progenitor cell differentiation, and ultimately, MDSC accumulation. MDSCs are important contributors to tumor progression and play a key role in promoting tumor growth and metastasis, and even reduce the efficacy of immunotherapy. Currently, a number of studies have demonstrated that MDSCs play a key regulatory role in many clinical diseases. In light of these studies, this review discusses the origin of MDSCs, the mechanisms underlying their activation, their role in a variety of clinical diseases, and their function in immune response regulation.

Resistance to Immune Checkpoint Inhibitors Secondary to Myeloid-Derived Suppressor Cells: A New Therapeutic Targeting of Haematological Malignancies

Myeloid-derived suppressor cells (MDSCs) are a set of immature myeloid lineage cells that include macrophages, granulocytes, and dendritic cell precursors. This subpopulation has been described in relation to the tumour processes at different levels, including resistance to immunotherapy, such as immune checkpoint inhibitors (ICIs). Currently, multiple studies at the preclinical and clinical levels seek to use this cell population for the treatment of different haematological neoplasms, together with ICIs. This review addresses the different points in ongoing studies of MDSCs and ICIs in haematological malignancies and their future significance in routine clinical practice.

Role of immune regulatory cells in breast cancer: Foe or friend?

Breast cancer (BC) is the most common cancer among women between the ages of 20 and 50, affecting more than 2.1 million people and causing the annual death of more than 627,000 women worldwide. Based on the available knowledge, the immune system and its components are involved in the pathogenesis of several malignancies, including BC. Cancer immunobiology suggests that immune cells can play a dual role and induce anti-tumor or immunosuppressive responses, depending on the tumor microenvironment (TME) signals. The most important effector immune cells with anti-tumor properties are natural killer (NK) cells, B, and T lymphocytes. On the other hand, immune and non-immune cells with regulatory/inhibitory phenotype, including regulatory T cells (Tregs), regulatory B cells (Bregs), tolerogenic dendritic cells (tDCs), tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), myeloid-derived suppressor cells (MDSCs), mesenchymal stem cells (MSCs), and regulatory natural killer cells (NKregs), can promote the growth and development of tumor cells by inhibiting anti-tumor responses, inducing angiogenesis and metastasis, as well as the expression of inhibitory molecules and suppressor mediators of the immune system. However, due to the complexity of the interaction and the modification in the immune cells' phenotype and the networking of the immune responses, the exact mechanism of action of the immunosuppressive and regulatory cells is not yet fully understood. This review article reviews the immune responses involved in BC as well as the role of regulatory and inhibitory cells in the pathogenesis of the disease. Finally, therapeutic approaches based on inhibition of immunosuppressive responses derived from regulatory cells are discussed.

Role of Epigenetic Regulation in Plasticity of Tumor Immune Microenvironment

The tumor immune microenvironment (TIME), an immunosuppressive niche, plays a pivotal role in contributing to the development, progression, and immune escape of various types of cancer. Compelling evidence highlights the feasibility of cancer therapy targeting the plasticity of TIME as a strategy to retrain the immunosuppressive immune cells, including innate immune cells and T cells. Epigenetic alterations, such as DNA methylation, histone post-translational modifications, and noncoding RNA-mediated regulation, regulate the expression of many human genes and have been reported to be accurate in the reprogramming of TIME according to vast majority of published results. Recently, mounting evidence has shown that the gut microbiome can also influence the colorectal cancer and even extraintestinal tumors via metabolites or microbiota-derived molecules. A tumor is a kind of heterogeneous disease with specificity in time and space, which is not only dependent on genetic regulation, but also regulated by epigenetics. This review summarizes the reprogramming of immune cells by epigenetic modifications in TIME and surveys the recent progress in epigenetic-based cancer clinical therapeutic approaches. We also discuss the ongoing studies and future areas of research that benefits to cancer eradication.

The Peripheral Immune Landscape of Breast Cancer: Clinical Findings and In Vitro Models for Biomarker Discovery

Breast cancer is the deadliest female malignancy worldwide and, while much is known about phenotype and function of infiltrating immune cells, the same attention has not been paid to the peripheral immune compartment of breast cancer patients. To obtain faster, cheaper, and more precise monitoring of patients' status, it is crucial to define and analyze circulating immune profiles. This review compiles and summarizes the disperse knowledge on the peripheral immune profile of breast cancer patients, how it departs from healthy individuals and how it changes with disease progression. We propose this data to be used as a starting point for validation of clinically relevant biomarkers of disease progression and therapy response, which warrants more thorough investigation in patient cohorts of specific breast cancer subtypes. Relevant clinical findings may also be explored experimentally using advanced 3D cellular models of human cancer-immune system interactions, which are under intensive development. We review the latest findings and discuss the strengths and limitations of such models, as well as the future perspectives. Together, the scientific advancement of peripheral biomarker discovery and cancer-immune crosstalk in breast cancer will be instrumental to uncover molecular mechanisms and putative biomarkers and drug targets in an all-human setting.

Exploring the Potential of Breast Microbiota as Biomarker for Breast Cancer and Therapeutic Response

Breast cancer tissue contains its own unique microbiota. Emerging preclinical data indicates that breast microbiota dysbiosis contributes to breast cancer initiation and progression. Furthermore, the breast microbiota may be a promising biomarker for treatment selection and prognosis. Differences in breast microbiota composition have been found between breast cancer subtypes and disease severities that may contribute to immunosuppression, enabling tumor cells to evade immune destruction. Interactions between breast microbiota, gut microbiota, and immune system are proposed, all forming potential targets to increase therapeutic efficacy. In addition, because the gut microbiota affects the host immune system and systemic availability of estrogen and bile acids known to influence tumor biology, gut microbiota modulation could be used to manipulate breast microbiota composition. Identifying breast and gut microbial compositions that respond positively to certain anticancer therapeutics could significantly reduce cancer burden. Additional research is needed to unravel the complexity of breast microbiota functioning and its interactions with the gut and the immune system. In this review, developments in the understanding of breast microbiota and its interaction with the immune system and the gut microbiota are discussed. Furthermore, the biomarker potential of breast microbiota is evaluated in conjunction with possible strategies to target microbiota in order to improve breast cancer treatment.

The role of tumor heterogeneity in immune-tumor interactions

The development of cancer stems from genetic instability and changes in genomic sequences, and hence, the heterogeneity exhibited by tumors is integral to the nature of cancer itself. Tumor heterogeneity can be further altered by factors that are not cancer cell intrinsic, i.e., by the microenvironment, including the patient's immune responses to tumors and administered therapies (immunotherapies, chemotherapies, and/or radiation therapies). The focus of this review is the impact of tumor heterogeneity on the interactions between immune cells and the tumor, taking into account that heterogeneity can exist at several levels. These levels include heterogeneity within an individual tumor, within an individual patient (particularly between the primary tumor and metastatic lesions), among the subtypes of a specific type of cancer, or within cancers that originate from different tissues. Because of the potential for immunity (either the natural immune system or via immunotherapeutics) to halt the progression of cancer, major clinical significance exists in understanding the impact of tumor heterogeneity on the associations between immune cells and tumor cells. Increased knowledge of why, whether, and how immune-tumor interactions occur provides the means to guide these interactions and improve outcomes for patients.

Electroacupuncture regulates inflammatory cytokines by activating the vagus nerve to enhance antitumor immunity in mice with breast tumors

AIMS

The aim of this study was to explore the potential effect of electroacupuncture (EA) at ST36 on mice bearing breast tumors by regulating inflammatory cytokines to enhance antitumor immunity via vagus nerve.

MATERIALS AND METHODS

Female BALB/c mice were implanted with 4T1-luc2 breast tumor cells to establish a murine mammary cancer model. Tumor growth was evaluated by tumor volume, weight and bioluminescence imaging. Inflammatory conditions in serum and tumor tissue were assessed by cytokines (IL-1β, TNF-α and IL-10) and HE staining. Proportions and functions of CD8⁺ T cells, NK cells and MDSCs were identified by flow cytometry and western blot. Involvement of vagal efferent components was confirmed by ChAT and c-Fos double labeling immunohistochemistry in dorsal motor nucleus of vagus (DMV). Subdiaphragmatic vagotomy was employed to determine if the effect of EA was mediated by vagus nerve.

KEY FINDINGS

EA at ST36 reduced the volume and weight of tumors within 22 days after implantation. Proinflammatory cytokines IL-1β and TNF-α in serum, tumor and local inflammatory infiltration were obviously attenuated after EA. Meanwhile, EA intervention significantly augmented the proportion and cytolytic function of CD8⁺ T cells and NK cells, along with a decline in the accumulation and immunosuppressive activities of MDSCs. Finally, c-Fos expression in ChAT⁺ neurons in DMV increased following EA, and the ameliorating effect of EA was obviously blocked by subdiaphragmatic vagotomy.

SIGNIFICANCE

EA intervention relieved tumor progression in breast tumor-bearing mice by alleviating inflammation and enhancing antitumor immunity, which was mediated by eliciting efferent vagus nerve activity.

STAT3 Silencing and TLR7/8 Pathway Activation Repolarize and Suppress Myeloid-Derived Suppressor Cells From Breast Cancer Patients

Cancer cells escape immune destruction. From this perspective, myeloid-derived suppressor cells (MDSCs), which are immunosuppressive in various cancers including breast cancer (BC), are significant. However, the precise mechanisms are unknown. We isolated HLA-DR^-CD33⁺ MDSCs and CD3⁺ T cells from BC patients’ peripheral blood and healthy donors through MACS and immunophenotyped by flow cytometry. Transfection of short-interfering RNAs and treatment with a TLR7/8 agonist altered pathway activities in vitro. Gene expression was analyzed using qRT-PCR, western blotting, and immunohistochemistry. Our findings showed an association between the progression of BC and increased levels of circulating HLA-DR^-CD33⁺ MDSCs. These cells strongly suppress both autologous and analogous CD3⁺ T cell proliferation and enter the tumor microenvironment. We also identified increased STAT3 signaling and increased IDO and IL-10 expression in BC-derived MDSCs as immunosuppression mechanisms. Further, STAT3 inhibition and TLR7/8 pathway stimulation reduce the immunosuppressive activity of patient-derived MDSCs on T cells by inducing MDSC repolarization and differentiation into mature myeloid cells. This also alters the expression of critical cytokines and transcription factors in CD3⁺ T cells and, importantly, reduces breast cancer cells’ proliferation. Finally, while chemotherapy is able to significantly reduce circulating MDSCs’ level in patients with breast cancer, these MDSCs remained highly T cell-suppressive. We identified a novel molecular mechanism of MDSC-mediated immunosuppression. STAT3 inhibition and TLR7/8 pathway stimulation in MDSCs repolarize and suppress MDSCs from breast cancer patients. This offers new opportunities for BC immunotherapy.

Critical immunosuppressive effect of MDSC‑derived exosomes in the tumor microenvironment

Myeloid-derived suppressor cells (MDSCs) are an indispensable component of the tumor microenvironment (TME). Along with the role of MDSC immunosuppression and antitumor immunity, MDSCs facilitate tumor growth, differentiation, and metastasis in several ways that are yet to be explored. Like any other cell type, MDSCs also release a tremendous number of exosomes, or nanovesicles of endosomal origin, that participate in intercellular communications by dispatching biological macromolecules. There have been no investigational studies conducted to characterize the role of MDSC-derived exosomes (MDSC exo) in modulating the TME. In this study, we isolated MDSC exo and demonstrated that they carry a significant level of proteins that play an indispensable role in tumor growth, invasion, angiogenesis, and immunomodulation. We observed a higher yield and more substantial immunosuppressive potential of exosomes isolated from MDSCs in the primary tumor area than those in the spleen or bone marrow. Our in vitro data suggest that MDSC exo are capable of hyper-activating or exhausting CD8 T-cells and induce reactive oxygen species production that elicits activation-induced cell death. We confirmed the depletion of CD8 T-cells in vivo by treating mice with MDSC exo. We also observed a reduction in pro-inflammatory M1-macrophages in the spleen of those animals. Our results indicate that the immunosuppressive and tumor-promoting functions of MDSCs are also implemented by MDSC-derived exosomes which would open up a new avenue of MDSC research and MDSC-targeted therapy.

Changes in peripheral immune cells after intraoperative radiation therapy in low-risk breast cancer

A detailed understanding of the interactions and the best dose-fractionation scheme of radiation to maximize antitumor immunity have not been fully established. In this study, the effect on the host immune system of a single dose of 20 Gy through intraoperative radiation therapy (IORT) on the surgical bed in low-risk breast cancer patients undergoing conserving breast cancer has been assessed. Peripheral blood samples from 13 patients were collected preoperatively and at 48 h and 3 and 10 weeks after the administration of radiation. We performed a flow cytometry analysis for lymphocyte subpopulations, natural killer cells (NK), regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSCs). We observed that the subpopulation of NK CD56+high CD16+ increased significantly at 3 weeks after IORT (0.30-0.42%, P < 0.001), while no changes were found in immunosuppressive profile, CD4+CD25+Foxp3+Helios+ Treg cells, granulocytic MDSCs (G-MDSCs) and monocytic MDSCs (Mo-MDSCs). A single dose of IORT may be an effective approach to improve antitumor immunity based on the increase in NK cells and the non-stimulation of immunosuppressive cells involved in immune escape. These findings support future combinations of IORT with immunotherapy, if they are confirmed in a large cohort of breast cancer patients.

Prognostic significance of S100A8-positive immune cells in relation to other immune cell infiltration in pre-invasive and invasive breast cancers

Myeloid-derived suppressor cells (MDSCs) play an important role in tumor progression through both immunologic and non-immunologic mechanisms. This study was conducted to evaluate the expression of S100A8, a well-known MDSC marker, and the significance of its expression in pre-invasive and invasive breast cancers. S100A8 expression in tumor cells (TCs) and immune cells (ICs) was assessed by immunohistochemistry, and its association with clinicopathologic features and infiltration of other IC subsets including CD4+, CD8+, and FOXP3+ tumor-infiltrating lymphocytes (TILs) and PD-L1+ ICs was evaluated. S100A8 expression in TCs and ICs showed a positive correlation in pre-invasive carcinoma and invasive carcinoma. S100A8+ ICs, but not S100A8+ TCs, were significantly higher in number in invasive carcinoma than in pre-invasive carcinoma. Infiltration of S100A8+ ICs was revealed as a poor prognostic indicator in pre-invasive and invasive carcinomas, especially in hormone receptor-positive subgroup. Infiltration of CD4+, CD8+, and FOXP3+ TIL subsets and PD-L1+ ICs was significantly higher in S100A8+ IC (+) group than in S100A8+ IC (−) group. Combined analyses of IC subset infiltration revealed that infiltration of S100A8+ ICs was associated with poor clinical outcome in the PD-L1+ IC (−), CD8+ TIL-low, and FOXP3+ TIL-low subgroups. In conclusion, S100A8+ ICs seem to undergo a dynamic change during breast cancer progression in association with other IC subset infiltration. The prognostic impact of S100A8+ IC infiltration was greater in less immunogenic tumors.

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.

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

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

A Clinician's Guide to Cancer-Derived Exosomes: Immune Interactions and Therapeutic Implications

Understanding of the role of immunity in the regulation of cancer growth continues to rapidly increase. This is fuelled by the impressive results yielded in recent years by immune checkpoint inhibitors, which block regulatory pathways to increase immune-mediated cancer destruction. Exosomes are cell-secreted membranous nanoscale vesicles that play important roles in regulating physiological and pathophysiological processes. Cancer-derived exosomes (CDEXs) and their biologically-active cargos have been proven to have varied effects in malignant progression, including the promotion of angiogenesis, metastasis, and favorable microenvironment modification. More recently, there is an increasing appreciation of their role in immune evasion. In addition to CDEXs, there are immune-derived exosomes that facilitate communication between immune cells in the non-malignant setting. Investigation of cancer-mediated mechanisms behind interruption or modification of these normal exosomal pathways may provide further understanding of how malignant immune evasion is accomplished. Accumulating evidence indicates that immune-active CDEXs also have the potential to impact clinical oncological management. Whilst immune checkpoint inhibitors have well-established pharmacologically-targeted pathways involving the immune system, other widely used treatments such as radiation and cytotoxic chemotherapies do not. Thus, investigating exosomes in immunotherapy is important for the development of next-generation combination therapies. In this article, we review the ways in which CDEXs impact individual immune cell types and how this contributes to the development of immune evasion. We discuss the relevance of lymphocytes and myeloid-lineage cells in the control of malignancy. In addition, we highlight the ways that CDEXs and their immune effects can impact current cancer therapies and the resulting clinical implications.

The potentials of immune checkpoints for the treatment of blood malignancies

Immune checkpoints are the regulators of the immune system, which include stimulatory and inhibitory receptors. They play substantial roles in the maintenance of immune system homeostasis and the prevention of autoimmunity and cancer. In the current review, immune checkpoints roles are surveyed in the initiation, progression, and treatment of blood malignancies. The significant roles of immune checkpoints are discussed as clinical markers in the diagnosis and prognosis of a plethora of blood malignancies and also as potential targets for the treatment of these malignancies. It could be concluded that the regulation of immune checkpoints in various blood cancers can be employed as a novel strategy to obtain effective results in leukemia treatment and introduce immune checkpoint inhibitors as sufficient weapons against blood cancers in the future.

Oral Capecitabine-Vinorelbine is Associated with Longer Overall Survival When Compared to Single-Agent Capecitabine in Patients with Hormone Receptor-Positive Advanced Breast Cancer

Background: Single-agent capecitabine (C) is a moderately effective chemotherapeutic compound in the treatment of patients with HER2-negative metastatic breast cancer (mBC). The capecitabine-vinorelbine (CV) combination is also used due to a good tolerability profile, but no studies have demonstrated its superiority over single-agent C. Methods: We conducted a retrospective analysis to compare overall response rate (ORR), progression-free survival (PFS), overall survival (OS) and incidence of adverse events (AEs) in patients with HER2-negative mBC treated with CV vs. single-agent C. Results: Out of 290 patients included in this study, 127 (43.8%) received single-agent C, while 163 (56.2%) patients were treated with CV. Median PFS was similar in patients treated with single-agent C or CV, while CV was associated with significantly longer OS in patients with hormone receptor-positive (HR+) BC. This OS advantage was confirmed at multivariable analysis also after propensity score-based matching of patients according to relevant clinical or tumor characteristics. When compared with single-agent C, CV was associated with higher incidence of G3/G4 and any-grade nausea/vomiting, diarrhea and increased transaminases. Conclusions: While prospective studies are needed to confirm our findings, the potential OS advantage of CV over single-agent C in HR+ mBC patients must be weighed against a significantly higher incidence of AEs.

Peptide-based targeting of immunosuppressive cells in cancer

Cancer progression is marked by the infiltration of immunosuppressive cells, such as tumor-associated macrophages (TAMs), regulatory T lymphocytes (Tregs), and myeloid-derived suppressor cells (MDSCs). These cells play a key role in abrogating the cytotoxic T lymphocyte-mediated (CTL) immune response, allowing tumor growth to proceed unabated. Furthermore, targeting these immunosuppressive cells through the use of peptides and peptide-based nanomedicine has shown promising results. Here we review the origins and functions of immunosuppressive cells in cancer progression, peptide-based systems used in their targeting, and explore future avenues of research regarding cancer immunotherapy. The success of these studies demonstrates the importance of the tumor immune microenvironment in the propagation of cancer and the potential of peptide-based nanomaterials as immunomodulatory agents.

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.