MDSC: Markers, development, states, and unaddressed complexity

The role of notch signaling in regulating myeloid-derived suppressor cells: Implications in Cancer and autoimmune diseases

Myeloid-derived suppressor cells (MDSCs) encompass monocytes and granulocytes, which are innate immune cells capable of suppressing T cells and NK cells. MDSCs exert numerous detrimental effects, as they facilitate tumor initiation, promote tumor growth and metastasis, suppress host immune responses, and evade immune surveillance, thereby hindering anticancer responses. Conversely, in autoimmune diseases, MDSCs exhibit dysfunctional immunosuppressive functions and often display pro-inflammatory effects, which can exacerbate immune disorders. We postulate that this discrepancy is attributable to the involvement of the Notch signaling pathway. The Notch signaling pathway is an evolutionarily conserved mechanism that plays a crucial role in maintaining normal mammalian physiological functions. The Notch receptor undergoes three cleavage events before being transported into the nucleus, where it regulates the transcription of target genes. The role of Notch or MDSCs in different diseases has been fully reported, but the regulatory role of Notch signaling pathway on MDSCs in different diseases has been rarely reported.In this review, we characterize the activation, expansion, and immune suppression mechanisms of MDSCs. We then introduce the Notch signaling pathway and finally discuss its role in colorectal cancer, breast cancer, lung cancer, as well as T-cell acute lymphoblastic leukemia, systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis. The Notch signaling pathway regulates MDSCs through distinct mechanisms in these contexts. We hope this review will aid both beginners and experts in systematically understanding the regulation of MDSCs by the Notch signaling pathway in cancer and autoimmune diseases.

CD301b+ monocyte-derived dendritic cells mediate resistance to radiotherapy

Monocytes infiltrating tumors acquire various states that distinctly impact cancer treatment. Here, we show that resistance of tumors to radiotherapy (RT) is controlled by the accumulation of monocyte-derived dendritic cells (moDCs). These moDCs are characterized by the expression of CD301b and have a superior capacity to generate regulatory T cells (Tregs). Accordingly, moDC depletion limits Treg generation and improves the therapeutic outcome of RT. Mechanistically, we demonstrate that granulocyte-macrophage colony-stimulating factor (GM-CSF) derived from radioresistant tumor cells following RT is necessary for the accumulation of moDCs. Our results unravel the immunosuppressive function of moDCs and identify GM-CSF as an immunotherapeutic target during RT.

MYO1F in neutrophils is required for the response to immune checkpoint blockade therapy

Tumor-associated neutrophils (TANs) represent a significant barrier to the effectiveness of immune checkpoint blockade (ICB) therapy. A comprehensive understanding of TANs' regulatory mechanisms is therefore essential for predicting ICB efficacy and improving immunotherapy strategies. Our study reveals that MYO1F is selectively downregulated in neutrophils within both human cancers and murine tumor models, showing a negative correlation with ICB response. Mechanistically, MYO1F normally inhibits neutrophil immunosuppression and proliferation by restraining STAT3 activity. However, during tumorigenesis, tumor-derived TGF-β1 disrupts the binding of SPI1 to intron 8 of Myo1f via DNA methylation, thereby suppressing Myo1f transcription. The resultant decrease in MYO1F reprograms neutrophils into an immunosuppressive state through the STAT3-dependent signaling pathways. This immunosuppressive state further contributes to tumor microenvironment (TME) remodeling by inducing CTL exhaustion. These findings establish MYO1F as a critical regulator within TANs, highlighting its significant role in modulating ICB therapy efficacy.

Immune-based strategies for the treatment of biofilm infections

Biofilms are bacterial communities surrounded by a polymeric matrix that can form on implanted materials and biotic surfaces, resulting in chronic infection that is recalcitrant to immune- and antibiotic-mediated clearance. Therefore, biofilm infections present a substantial clinical challenge, as treatment often involves additional surgical interventions to remove the biofilm nidus, prolonged antimicrobial therapy to clear residual bacteria, and considerable risk of treatment failure or infection recurrence. These factors, combined with progressive increases in antimicrobial resistance, highlight the need for alternative therapeutic strategies to circumvent undue morbidity, mortality, and resource strain on the healthcare system resulting from biofilm infections. One promising option is reprogramming dysfunctional immune responses elicited by biofilm. Here, we review the literature describing immune responses to biofilm infection with a focus on targets or strategies ripe for clinical translation. This represents a complex and dynamic challenge, with context-dependent host-pathogen interactions that differ across infection models, microenvironments, and individuals. Nevertheless, consistencies among these variables exist, which could facilitate the development of immune-based strategies for the future treatment of biofilm infections.

Interleukin-7 enhances recruitment of MDSCs by regulating MCP-1 via JAK1/STAT3 signaling pathway in non-small cell lung cancer

Lung cancer is one of the most commonly diagnosed cancers worldwide and the leading cause of cancer-related deaths worldwide. In recent years, an increasing number of studies have shown that the tumor immune microenvironment (TIME) has a significant impact on the development of lung cancer. Interleukin-7 (IL-7) is an essential cytokine for the adaptive immune system and plays an important immunoregulatory role in different types of tumors. However, the relationship between IL-7 and TIME in non-small cell lung cancer (NSCLC) is not yet known. This study found that the expression of MCP-1 and CD11b was correlated with the expression of IL-7/IL-7R. MCP-1, IL-7R, tumor differentiation and tumor stage were the strongest predictors of survival. In addition, IL-7 upregulates MCP-1 through JAK1/STAT3 pathway to affect the migration of MDSCs and exert tumor immunosuppressive effect. Furthermore, CCR2 inhibitor and depletion of MDSCs suppressed the promoting effect of IL-7 mediated development of lung cancer. These findings provided the important mechanism that IL-7 upregulate MCP-1 through JAK1/STAT3 pathway to recruit MDSCs and put forth blockage of CCR2 inhibitor and MDSCs recruitment as a prospective immunotherapy strategy for the treatment of NSCLC.

Bile acids produced by gut microbiota activate TGR5 to promote colorectal liver metastasis progression by inducing MDSCs infiltration in liver

BACKGROUND

CRLM (Colorectal liver metastasis), a prevalent form of distant metastasis in colorectal cancer, is a leading cause of mortality in affected patients. Despite advancements in immunotherapy for colorectal cancer, clinical benefits in CRLM patients remain limited. The immunosuppressive liver microenvironment plays a pivotal role in facilitating metastatic colonization and disease progression.

METHODS

We performed fecal metabolomics in ABX (antibiotic-treated) mice and single-cell RNA sequencing on hepatic tissues from four cohorts: CRC (colorectal cancer) , CRLM, LCA-fed CRC, and LCA-fed CRLM mice, to delineate intergroup immune heterogeneity. Cellular and molecular profiling across groups was conducted via Luminex multiplex assays, flow cytometry, and immunofluorescence. Integrated multi-omics analyses elucidated LCA-driven pathways modulating metastatic progression RESULTS: We demonstrated that LCA (lithocholic acid), a gut microbiota-derived metabolite, activates TGR5 in hepatic CAFs (cancer-associated fibroblasts) to upregulate CCL3 secretion. Elevated CCL3 levels subsequently recruit MDSCs (myeloid-derived suppressor cells) into metastatic niches. While MDSCs primarily suppress T-cell activation, we identified a paradoxical role of MDSC-derived CCL2 in attenuating immunosuppression via CCR2 signaling, suggesting a compensatory pro-inflammatory axis within the tumor microenvironment CONCLUSIONS: These findings suggest new immunotherapeutic strategies for the treatment of CRLM.

Sex differences in bladder cancer: understanding biological and clinical implications

Bladder cancer (BC) remains a significant global health concern, with substantial sex and racial disparities in incidence, progression, and outcomes. BC is the sixth most common cancer among males and the seventeenth most common among females worldwide. Over 90% of BC cases are urothelial carcinoma (UC) with high degrees of pathological heterogeneity. Molecular subtyping of BC has also revealed distinct luminal, basal, and neuroendocrine subtypes, each with unique genetic and immune signatures. Emerging research uncovers the biasing effects of the sex hormones with androgens increasing BC risk through both tumor cell intrinsic and extrinsic mechanisms. The sex chromosomes, including both the X and Y chromosomes, also contribute to the sex differences in BC. The effect of sex chromosome is both independent from and synergistic with the effects of sex hormones. Loss of the Y chromosome is frequently observed in BC patients, while an extra copy of the X chromosome confers better protection against BC in females than in males. Advent of advanced technologies such as multiomics and artificial intelligence will likely further improve the understanding of sex differences in BC, which may ultimately lead to personalized preventative and treatment strategies depending on the biological sex of patients. This review delves into the impacts of biology of sex on BC, emphasizing the importance of further research into sex-specific biology to improve cancer prevention and care.

Eliminating myeloid-derived suppressor cells alleviates immunosuppression and reduces susceptibility to secondary infections in a two-hit sepsis model

Myeloid-derived suppressor cells (MDSCs) are known for their immunosuppressive effects on both innate and adaptive immunity, particularly targeting T cells, and they undergo continuous expansion during sepsis. However, the pathophysiological significance of MDSCs in sepsis-induced immunosuppression remains to be fully elucidated. In this study, we investigated the dynamic changes in MDSCs during sepsis and their contribution to sepsis-induced immunosuppression using a clinically relevant "two-hit" sepsis model. Our findings revealed that mice surviving cecal ligation and puncture (CLP) exhibited a significant accumulation and enhanced activity of MDSCs, which correlated with sepsis-related immune paralysis, impaired bacterial clearance, and heightened susceptibility to secondary infections. Importantly, administration of the liver X receptor (LXR) agonist GW3965 at the late stage of sepsis significantly restored immune function, decreased susceptibility to secondary infections, enhanced bacterial clearance, and improved prognosis by eliminating MDSCs. These results highlight the pivotal role of MDSCs in the development of sepsis-associated immunosuppression and indicate that targeting MDSCs could be a promising therapeutic approach to mitigate immunosuppression in sepsis.

Contemporary understanding of myeloid-derived suppressor cells in the acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) tumor microenvironment

INTRODUCTION

Myeloid-derived suppressor cells (MDSCs) are a key immunosuppressive component in the tumor microenvironment, contributing to immune evasion and disease progression in acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS).

AREAS COVERED

We searched PubMed for literature that evaluated the effect of MDSCs in myeloid diseases. MDSCs impact outcomes by facilitating leukemic stem cell survival, impairing immune checkpoint efficacy, and modulating the bone marrow niche. While these immunosuppressive properties can mitigate graft-versus-host disease post-transplantation, sustained MDSC-mediated immunosuppression can also increase the risk of leukemia relapse.We review MDSC development and function, including metabolic reprogramming, epigenetic modifications, and cytokine-mediated pathways. Therapeutic strategies targeting MDSCs, such as depletion, functional reprogramming, and inhibition of key metabolic and immune pathways, show promising data in preclinical models. However, clinical translation remains hindered by challenges in MDSC quantification and standardization of functional assays. This review underscores the potential of combining MDSC-targeted therapies with conventional and novel treatments to improve patient outcomes in AML and MDS.

EXPERT OPINION

Future studies should focus on standardizing MDSC assessment, elucidate their dynamic roles in therapy, and optimize combination approaches for clinical application.

Boosting antitumor immunity in breast cancers: Potential of adjuvants, drugs, and nanocarriers

Despite advancements in breast cancer treatment, therapeutic resistance, and tumor recurrence continue to pose formidable challenges. Therefore, a deep knowledge of the intricate interplay between the tumor and the immune system is necessary. In the pursuit of combating breast cancer, the awakening of antitumor immunity has been proposed as a compelling avenue. Tumor stroma in breast cancers contains multiple stromal and immune cells that impact the resistance to therapy and also the expansion of malignant cells. Activating or repressing these stromal and immune cells, as well as their secretions can be proposed for exhausting resistance mechanisms and repressing tumor growth. NK cells and T lymphocytes are the prominent components of breast tumor immunity that can be triggered by adjuvants for eradicating malignant cells. However, stromal cells like endothelial and fibroblast cells, as well as some immune suppressive cells, consisting of premature myeloid cells, and some subsets of macrophages and CD4+ T lymphocytes, can dampen antitumor immunity in favor of breast tumor growth and therapy resistance. This review article aims to research the prospect of harnessing the power of drugs, adjuvants, and nanoparticles in awakening the immune reactions against breast malignant cells. By investigating the immunomodulatory properties of pharmacological agents and the synergistic effects of adjuvants, this review seeks to uncover the mechanisms through which antitumor immunity can be triggered. Moreover, the current review delineates the challenges and opportunities in the translational journey from bench to bedside.

The accumulation of myeloid-derived suppressor cells participates in abdominal infection-induced tumor progression through the PD-L1/PD-1 axis

Gastric cancer (GC) is the third leading cause of cancer-related deaths worldwide, with gastrectomy being the primary treatment option. Sepsis, a systemic inflammatory response to infection, may influence tumor growth by creating an immunosuppressive environment conducive to cancer cell proliferation and metastasis. Here, the effect of abdominal infection on tumor growth and metastasis was investigated through the implementation of a peritoneal metastasis model and a subcutaneous tumor model. In a murine model induced by cecal ligation and puncture (CLP) to simulate the effects of sepsis, we observed significant immune dysregulation, including T-cell exhaustion and the release of myeloid-derived suppressor cells (MDSCs). This immune alteration was associated with increased programmed cell death protein 1 (PD-1) expression on T cells and programmed cell death 1 ligand 1 (PD-L1) expression on MDSCs within the tumor microenvironment, fostering an immune-suppressive environment. Polymorphonuclear MDSCs (PMN-MDSCs) expressing elevated PD-L1 after sepsis demonstrated more substantial suppressive effects on T-cell proliferation than controls. Treatment with anti-PD-1 monoclonal antibodies successfully restored T-cell function, reduced mortality, and decreased metastasis in CLP mice. These findings emphasize the impact of sepsis on tumor progression and suggest targeting the PD-1/PD-L1 axis as a potential therapeutic strategy for managing immune dysfunction in patients with cancer.

From neglect to necessity: the role of innate immunity in cutaneous squamous cell carcinoma therapy

As the second most common non-melanoma skin cancer, cutaneous squamous cell carcinoma (cSCC) has experienced a significant increase in incidence. Although clinical detection is relatively easy, a considerable number of patients are diagnosed at an advanced stage, featuring local tissue infiltration and distant metastasis. Cemiplimab, along with other immune checkpoint inhibitors, enhances T cell activation by blocking the PD-1 pathway, resulting in notable improvements in clinical outcomes. Nonetheless, approximately 50% of the patients with advanced cSCC remain unresponsive to this therapeutic approach. It emphasizes the importance of finding innovative therapeutic targets and strategies to boost the success of immunotherapy across a wider range of patients. Therefore, we focused on frequently neglected functions of innate immune cells. Emerging evidence indicates that innate immune cells exhibit considerable heterogeneity and plasticity, fundamentally contributing to tumor initiation and development. The identification and eradication of cancer cells, along with the modulation of adaptive immune responses, are essential roles of these cells. Consequently, targeting innate immune cells to activate anti-tumor immune responses presents significant potential for enhancing immunotherapeutic strategies in cSCC.

MiR- 150 deletion promotes lung tumor growth by upregulating P-STAT3 and ROS in MDSCs

Lung cancer is the second most common cancer in the world. Myeloid-derived suppressor cells (MDSCs) are important cell populations in the microenvironment of lung cancer, which affects the development and treatment of lung cancer. A large number of studies have shown that miRNA can regulate MDSCs, promoting tumor development. Here we aim to explore the role of miR- 150 on MDSCs in lung tumors. We established lung tumor models by injecting miR- 150 knock-out (miR- 150 KO) mice with LLC subcutaneously. MiR- 150 deletion promoted tumor growth and increased the ratio of MDSCs in tumors. In addition, knockdown of miR- 150 resulted in high serum levels of IL- 6 and G-CSF and promoted the expression of suppressive-associated molecules in MDSCs. In vitro, inhibition of miR- 150 led to increased expression of ROS, IRE1α and P-STAT3 in MDSCs. In vivo administration of STAT3 inhibitor significantly inhibited tumor growth in miR- 150 KO mice and reduced ROS level in tumor MDSCs. Our results indicated that miR- 150 deletion promotes lung tumor growth by upregulating P-STAT3 and ROS in MDSCs, suggesting that STAT3 inhibitors are effective in blocking the production of ROS in MDSCs lacking miR- 150.

Neoadjuvant immune checkpoint therapy: Enabling insights into fundamental human immunology and clinical benefit

While immune checkpoint therapy (ICT) has revolutionized cancer treatment, most patients with advanced disease fail to achieve durable benefit. To address this challenge, it is essential to integrate mechanistic research with clinical studies to: (1) understand response mechanisms, (2) identify patient-specific resistance pathways, (3) develop biomarkers for patient selection, and (4) design novel therapies to overcome resistance. We propose that incorporating "direct-in-patient" studies into clinical trials is crucial for bridging the gap between fundamental science and clinical oncology. In this review, we first highlight recent clinical success of ICT in the neoadjuvant setting, where treatment is given in earlier disease stages to improve outcomes. We then explore how neoadjuvant clinical trials could be utilized to drive mechanistic laboratory-based investigations. Finally, we discuss novel scientific concepts that will potentially aid in overcoming resistance to ICT, which will require future clinical trials to understand their impact on human immune responses.

Cytokine-mediated regulation of immune cell metabolic pathways in the tumor microenvironment

Cancer, an important global health problem, is defined by aberrant cell proliferation and continues to be the main cause of death globally. The tumor microenvironment (TME) plays an essential role in the development of cancer, resistance to therapy, and regulation of the immune response. Some immune cells in the TME, like T cells, B cells, macrophages, dendritic cells, and natural killer cells, can either stop or help tumor growth, depending on how metabolic and cytokine changes happen. Cytokines function as essential signaling molecules that modulate immune cell metabolism, altering their functionality. This review focuses on how cytokine-mediated metabolic reprogramming affects the activity of immune cells inside the TME, which can either make the immune response stronger or weaker. New ways of treating cancer that focus on metabolic pathways and cytokine signaling, such as using IL (Interleukin) - 15, IL- 10, and IL- 4, show promise in boosting immune cell activity and making cancer treatments more effective. Finding these pathways could lead to new ways to treat cancer with immunotherapy that focus on metabolic competition and immune resistance in the TME.

Neural crest-associated gene FOXD1 induces an immunosuppressive microenvironment by regulating myeloid-derived suppressor cells in melanoma

BACKGROUND

Neural crest-associated genes play pivotal roles in tumor initiation, progression, and the intricate dynamics of the tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSC) within the TME are important in dampening T cell activity and contributing to resistance against immunotherapeutic interventions. The neural crest-associated gene Forkhead Box D1 (FOXD1) has been identified as an oncogenic factor that induces melanoma dedifferentiation and progression. However, the underlying mechanisms and the impact of FOXD1 on the antitumor immune response remain unclear.

METHODS

To investigate the impacts of FOXD1 on the melanoma microenvironment, we analyzed publicly available datasets from multiple platforms, including TNMplot, TIMER2.0, etc. In addition, FOXD1 was overexpressed (OE) or knocked down in melanoma cells to identify its biological functions in vitro and in vivo. Flow cytometry and arginase activity assay were used to analyze the phenotype and function of MDSC. Western blot, reverse transcription-PCR, or ELISA assays were employed to analyze the expression of FOXD1 and its downstream effectors. In vivo experiments were conducted to investigate the role of FOXD1 in melanoma progression and the influence on MDSC accumulation within the TME.

RESULTS

We demonstrate that increased FOXD1 levels inversely correlated with melanoma responsiveness to immunotherapy. Ex-vivo analyses unveiled that monocytes, exposed to conditioned medium from FOXD1-OE melanoma cells, effectively suppressed T cell proliferation and upregulated the expression of programmed death-ligand 1 (PD-L1) and other immunosuppressive factors. FOXD1 was identified as a direct regulator of interleukin 6 (IL6) expression, which is pivotal for MDSC induction. Blocking IL6 reversed MDSC-associated immunosuppression. Additionally, miR-581, a potential negative regulator of FOXD1, attenuated the impact of FOXD1 on IL6 expression and MDSC differentiation. In vivo experiments demonstrated that tumors derived from FOXD1 OE melanoma cells contained a significantly higher frequency of PD-L1+ MDSC compared with controls, while FOXD1 knockdown resulted in reduced tumor growth and diminished MDSC accumulation.

CONCLUSION

Our study elucidated a novel function of FOXD1 in melanoma pathogenesis, highlighting its role in orchestrating the immunosuppressive TME by promoting the generation of MDSC via IL6 upregulation.

Targeting DKK3 to remodel tumor immune microenvironment and enhance cancer immunotherapy

Cancer immunotherapy such as immune checkpoint blockade (ICB) therapy has made important breakthroughs in cancer treatment, however, currently only parts of cancer patients benefit from ICB therapy. The suppressive tumor immune microenvironment (TIME) impedes the treatment response of immunotherapy, indicating the necessity to explore new treatment targets. Here, we reported a new potential immunotherapeutic target, Dickkopf-3 (DKK3), for cancer treatment. DKK3 expression is up-regulated in the tumors from multiple cancer types, and high DKK3 expression is associated with worse survival outcome across different cancers. We observed that DKK3 directly inhibits the activation of CD8+ T cells and the Th1 differentiation of CD4+ T cells ex vivo. Also, by establishing four different mouse cancer models, we found that DKK3 blockade triggers effective anti-tumor effects and improve the survival of tumor-bearing mice in vivo. DKK3 blockade also remodels the suppressive TIME of different cancer types, including the increased infiltration of CD8+ T cells, IFN-γ+CD8+ T cells, Th1 cells, and decreased infiltration of M2 macrophages and MDSCs in the TIME. Moreover, we found that combined blockade of DKK3 and PD-1 induces synergistic tumor-control effect in our mouse cancer model. Therefore, our study reveals the impact of DKK3 in the TIME and cancer progression, which suggests that DKK3 is a novel and promising immunotherapeutic target for enhanced cancer immunotherapy.

Single-cell transcriptomic analysis identified resistant MDSCs and a stress-tolerant gene co-expression network as common MDSC features across multiple disease settings

Background

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immunosuppressive myeloid cells. The identification of a molecular signature common to MDSC regardless of tissue source would aid in the classification of cells as MDSCs.

Methods

Single-cell RNA sequencing (scRNA-seq) was performed on GM-CSF+ IL-6-induced human MDSCs to characterize the extent of heterogeneity within monocytic MDSCs (M-MDSCs). Cytokine-treated PBMCs were also cultured in the absence of serum to include an additional element of cell stress. Independent published bulk and single-cell transcriptomic datasets were used for validation.

Findings

A cluster of cells with preserved MDSC features was induced by the combination of inflammatory signals and cell stress in the form of serum starvation (resistant MDSCs, rMDSCs). A gene co-expression module (the yellow module) was identified specific to rMDSCs. The genes upregulated in MDSCs can be further classified into stress-tolerant vs. -sensitive features. This yellow module mostly contained stress-tolerant genes and showed excellent separation for distinguishing M-MDSCs from control cells across a range of in vitro and in vivo conditions (ROC AUC = 0.954), a feature not found in the stress-sensitive genes. Importantly, rMDSCs were identified in scRNA-seq datasets of immune cells from multiple human cancer types. Tumor C1Q macrophages, which have been associated with immunosuppression, highly expressed the yellow module gene signature.

Interpretation

These results demonstrate the importance of the combined roles of inflammation and cellular stress in shaping the features of M-MDSCs and highlight cellular resilience represented by rMDSCs and the role of stress-tolerant features in defining common MDSC features.

B7H3 in Gastrointestinal Tumors: Role in Immune Modulation and Cancer Progression: A Review of the Literature

B7-H3 (CD276), a member of the B7 immune checkpoint family, plays a critical role in modulating immune responses and has emerged as a promising target in cancer therapy. It is highly expressed in various malignancies, where it promotes tumor evasion from T cell surveillance and contributes to cancer progression, metastasis, and therapeutic resistance, showing a correlation with the poor prognosis of patients. Although its receptors were not fully identified, B7-H3 signaling involves key intracellular pathways, including JAK/STAT, NF-κB, PI3K/Akt, and MAPK, driving processes crucial for supporting tumor growth such as cell proliferation, invasion, and apoptosis inhibition. Beyond immune modulation, B7-H3 influences cancer cell metabolism, angiogenesis, and epithelial-to-mesenchymal transition, further exacerbating tumor aggressiveness. The development of B7-H3-targeting therapies, including monoclonal antibodies, antibody-drug conjugates, and CAR-T cells, offers promising avenues for treatment. This review provides an up-to-date summary of the B7H3 mechanisms of action, putative receptors, and ongoing clinical trials evaluating therapies targeting B7H3, focusing on the molecule's role in gastrointestinal tumors.

Single-Cell Transcriptome Analysis Reveals the Effect of MIF on Myeloid-Derived Suppressor Cells in Multiple Myeloma

INTRODUCTION

Multiple myeloma (MM) is a highly lethal hematologic malignancy. Myeloid-derived suppressor cells (MDSCs) exert vital effects on myeloma cells in the bone marrow microenvironment. Macrophage migration inhibitory factor (MIF) is a chemokine-like inflammatory cytokine that can not only prevent the free movement of macrophages but also regulate innate and adaptive immune responses. This study intends to explore the relationship between MIF and MDSCs in the bone marrow microenvironment.

METHODS

Single-cell RNA sequencing (scRNA-seq) analysis was performed based on the GSE124310 dataset (containing the MM and normal samples). Cell types were annotated using the feature genes collected from CellMarker 2.0. Ligand-receptor pairs for communication between MDSC subsets and other cells were inferred using CellChat. Characterizations of relevant cells were determined by flow cytometry.

RESULTS

scRNA-seq analysis showed that 10 cellular subsets were annotated. Based on the differential expression of MIF, MDSCs were divided into two subsets, MIF+MDSCs and MIF-MDSCs. There was a difference in the ratios of MIF+MDSCs and MIF-MDSCs between the MM and Normal groups. Cell communication analysis showed that MIF+MDSCs and Plasma cells had low signal intensity in the RETN-CAP1 pathway, while MIF-MDSCs and Plasma cells had high signal intensity in the RETN-CAP1 pathway. Flow cytometry assay showed that RETN, Arg-1, and iNOS expression in MDSCs was significantly increased in the MM group compared with the normal group, and RETN, Arg-1, and iNOS expression was higher in MIF+MDSCs than that in MIF-MDSCs. CAP1 expression in Plasma cells was significantly elevated in the MM group compared with the Normal group.

CONCLUSION

MIF is high-expressed in MM patients and could be correlated with MDSCs in the bone marrow microenvironment.

Immune profiling of premalignant lesions in patients with Peutz-Jeghers syndrome

BACKGROUND

Peutz-Jeghers syndrome (PJS), is a rare autosomal dominant hereditary disease characterized by an elevated risk of various cancers. Serine/Threonine Kinase 11 (STK11) gene is a major tumor suppressor crucial for immune evasion with and beyond tumorigenic cells. It has garnered increasing attention in the realm of oncology treatment, particularly in the context of immunotherapy development.

OBJECTIVE

This study aimed to assess the suitability of polyps obtained from individuals with PJS, resulting from germline STK11 deficiency, for immunotherapy. Additionally, we seek to identify potential shared mechanisms related to immune evasion between PJS polyps and cancers. To achieve this, we examined PJS polyps alongside familial adenomatous polyposis (FAP) and sporadic polyps.

METHODS

Polyps were compared among themselves and with either the paracancerous tissues or colon cancers. Pathological and gene expression profiling approaches were employed to characterize infiltrating immune cells and assess the expression of immune checkpoint genes.

RESULTS

Our findings revealed that PJS polyps exhibited a closer resemblance to cancer tissues than other polyps in terms of their immune microenvironment. Notably, PJS polyps displayed heightened expression of the immune checkpoint gene CD80 and an accumulation of myeloid cells, particularly myeloid-derived suppressor cells (MDSCs).

CONCLUSION

The findings suggest an immunobiological foundation for the increased cancer susceptibility in PJS patients, paving the way for potential immune therapy applications in this population. Furthermore, utilizing PJS as a model may facilitate the exploration of immune evasion mechanisms, benefiting both PJS and cancer patients.

Myeloid-derived suppressor cells alleviate adverse ventricular remodeling after acute myocardial infarction

The fundamental pathophysiological mechanism in the progression of chronic heart failure following acute myocardial infarction (AMI) is ventricular remodeling, in which innate and adaptive immunity both play critical roles. Myeloid-derived suppressor cells (MDSCs) have been demonstrated to function in a range of pathological conditions, such as infections, inflammation, autoimmune diseases, and tumors. However, it is unclear how MDSCs contribute to cardiac remodeling following AMI. This study aimed to identify the function and underlying mechanism of MDSCs in controlling cardiac remodeling following AMI. Following AMI in mice, MDSCs frequencies changed dynamically, considerably increased on day 7 in blood, spleens, lymph nodes and hearts, and decreased afterwards. Consistently, mice with AMI displayed enhanced cardiac function on day 14 post-AMI, reduced infract size and higher survival rates on day 28 post-AMI following the adoptive transfer of MDSCs. Furthermore, MDSCs inhibited the inflammatory response by decreasing pro-inflammatory cytokine (TNF-α, IL-17, Cxcl-1, and Cxcl-2) expression, up-regulating anti-inflammatory cytokine (TGF-β1, IL-10, IL-4, and IL-13) expression, reducing CD3+ T cell infiltration in the infarcted heart and enhancing M2 macrophage polarization. Mechanistically, MDSCs improved the release of anti-inflammatory factors (TGF-β1 and IL-10) and decreased the injury of LPS-induced cardiomyocytes in vitro in a manner dependent on cell-cell contact. Importantly, blockade of IL-10 partially abolished the cardioprotective role of MDSCs. This study found that MDSCs contributed to the restoration of cardiac function and alleviation of adverse cardiac remodeling after AMI possibly by inhibiting inflammation.

Genetic immune escape in cancer: timing and implications for treatment

Genetic immune escape (GIE) alterations pose a significant challenge in cancer by enabling tumors to evade immune detection. These alterations, which can vary significantly across cancer types, may often arise early in clonal evolution and contribute to malignant transformation. As tumors evolve, GIE alterations are positively selected, allowing immune-resistant clones to proliferate. In addition to genetic changes, the tumor microenvironment (TME) and non-genetic factors such as inflammation, smoking, and environmental exposures play crucial roles in promoting immune evasion. Understanding the timing and mechanisms of GIE, alongside microenvironmental influences, is crucial for improving early detection and developing more effective therapeutic interventions. This review highlights the implications of GIE in cancer development and immunotherapy resistance, and emphasizes the need for integrative approaches.

Hybrid Outer Membrane Vesicles with Genetically Engineering for Treatment of Implant-Associated Infections and Relapse Prevention Through Host Immunomodulation

Implant-associated infections (IAIs) are refractory to elimination, and the local immunosuppressive microenvironment (IME) exacerbates therapeutic difficulties, ultimately causing persistence and relapse. Therefore, exploring immunostrengthening treatments holds great promise for reversing IME and thoroughly eradicating chronic or repetitive infections. Bacterial outer membrane vesicles (OMVs) have emerged as potential immunostimulatory candidates; however, they lack active targeting capabilities and cause non-specific inflammatory side effects. In this study, bone marrow-derived mesenchymal stem cells (BMSCs) are genetically engineered to overexpress CXCR4 and isolated cell membranes (mBMSCCXCR4) for hybridization with OMVs derived from Escherichia coli (E. coli) to produce nanovesicles (mBMSCCXCR4@OMV). The resulting mBMSCCXCR4@OMV nanovesicles demonstrate excellent bone marrow targeting capability and are effectively taken up by bone marrow-derived macrophages, triggering the efficient transition to pro-inflammatory M1 status through TLR/NF-κB pathway. This alteration promotes innate bactericidal capacity and antigen presentation. Subsequent activation of T and B cells and inhibition of myeloid-derived suppressor cells (MDSCs) facilitated in vivo adaptive immunity in mouse models. Additionally, mBMSCCXCR4@OMV boosted memory B cell and bacteria-specific antibody responses. Together, these data highlight the potential of mBMSCCXCR4@OMV to eradicate complicated IAIs and provide whole-stage protection against postsurgical relapse, thus marking a significant immunotherapeutic advancement in the post-antibiotic era.

Overcoming immunotherapy resistance in glioblastoma: challenges and emerging strategies

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults, characterized by rapid proliferation, extensive infiltration, and significant intratumoral heterogeneity. Despite advancements in conventional treatments, including surgery, radiotherapy, and chemotherapy, the prognosis for GBM patients remains poor, with a median survival of approximately 15 months. Immunotherapy has emerged as a promising alternative; however, the unique biological and immunological features, including its immunosuppressive tumor microenvironment (TME) and low mutational burden, render it resistant to many immunotherapeutic strategies. This review explores the key challenges in GBM immunotherapy, focusing on immune evasion mechanisms, the blood-brain barrier (BBB), and the TME. Immune checkpoint inhibitors and CAR-T cells have shown promise in preclinical models but have limited clinical success due to antigen heterogeneity, immune cell exhaustion, and impaired trafficking across the BBB. Emerging strategies, including dual-targeting CAR-T cells, engineered immune cells secreting therapeutic molecules, and advanced delivery systems to overcome the BBB, show potential for enhancing treatment efficacy. Addressing these challenges is crucial for improving GBM immunotherapy outcomes.

The immunosuppressive role of MDSCs in HCC: mechanisms and therapeutic opportunities

Hepatocellular carcinoma (HCC) is a prevalent malignancy with a significant global burden. Despite substantial advancements in HCC treatment in recent years, therapeutic efficacy remains constrained by immune evasion mechanisms within the tumor microenvironment (TME). Myeloid-derived suppressor cells (MDSCs), as critical immunosuppressive elements of the TME, have garnered increasing attention for their role in tumor progression. Recent studies emphasize their central involvement in promoting immune evasion, tolerance, and immunosuppression in HCC. This review examines the contributions of MDSCs to HCC pathogenesis, elucidates their underlying mechanisms, and discusses ongoing clinical trials, emphasizing their potential as therapeutic targets for improving clinical outcomes.

Harnessing myeloid cells in cancer

Cancer-associated myeloid cells due to their plasticity play dual roles in both promoting and inhibiting tumor progression. Myeloid cells with immunosuppressive properties play a critical role in anti-cancer immune regulation. Cells of different origin, such as tumor associated macrophages (TAMs), tumor associated neutrophils (TANs), myeloid derived suppressor cells (also called MDSCs) and eosinophils are often expanded in cancer patients and significantly influence their survival, but also the outcome of anti-cancer therapies. For this reason, the variety of preclinical and clinical studies to modulate the activity of these cells have been conducted, however without successful outcome to date. In this review, pro-tumor activity of myeloid cells, myeloid cell-specific therapeutic targets, in vivo studies on myeloid cell re-polarization and the impact of myeloid cells on immunotherapies/genetic engineering are addressed. This paper also summarizes ongoing clinical trials and the concept of chimeric antigen receptor macrophage (CAR-M) therapies, and suggests future research perspectives, offering new opportunities in the development of novel clinical treatment strategies.

Lactobacillus rhamnosus GG ameliorates atherosclerosis via suppression of oxidative stress and inflammation by reshaping the gut microbiota

OBJECTIVE

With growing awareness of probiotics' benefits, more studies are exploring their efficacy and mechanisms in reducing atherosclerosis (AS). This study aimed to investigate the potential therapeutic effects of Lactobacillus rhamnosus GG (LGG) on atherosclerotic mice and underlying mechanisms.

DESIGN

ApoE-/- mice were gavaged with a dose of 2 × 109 CFU LGG per mouse once daily, while both ApoE-/- and C57BL/6J mice received normal saline as controls. After 15 weeks, en face Oil Red O staining and aortic sinus morphometry were used to assess the effects of LGG intervention on AS. The expression of the Nrf2/HO-1 pathway, along with oxidative stress and inflammation, was measured in the aortic sinus, aortas, or plasma. Immune cells were analyzed by flow cytometry. 16S rRNA gene sequencing analysis evaluated structural changes in the intestinal microbiota.

RESULTS

LGG-treated ApoE-/- mice showed a significant reduction of AS progression by suppressing oxidative stress and inflammation. Mechanistically, LGG intervention significantly increased the levels of Nrf2/HO-1 in the aortic sinus of ApoE-/- mice. Moreover, decreased aortic macrophages and elevated blood regulatory T cells (Tregs) were found with LGG intervention in the murine AS model. Moreover, compared to C57BL/6J mice, ApoE-/- mice exhibited disrupted intestinal flora. Nonetheless, LGG intervention restored their intestinal flora to a composition resembling that of C57BL/6J mice, thereby increasing the abundance of beneficial bacteria.

CONCLUSION

LGG significantly attenuates AS by reducing oxidative stress and inflammation probably via activating the Nrf2/HO-1 pathway. Remarkably, LGG modulates gut microbiota, further enhancing its protective efficacy against AS.

Tumor-derived extracellular vesicles: key drivers of immunomodulation in breast cancer

Breast cancer (BC) remains a significant global health challenge characterized by its heterogeneity and treatment complexities. Extracellular vesicles (EVs) are small membranous particles released by cells, facilitating intercellular communication by transporting bioactive molecules such as proteins, lipids, and nucleic acids. Tumor-derived EVs have emerged as pivotal regulators in the tumor microenvironment (TME) and drivers of BC progression. These EVs carry diverse cargoes of bioactive molecules, influencing critical processes such as immune modulation, angiogenesis, and metastasis. By altering the behaviors of immune cells including macrophages, dendritic cells, and T cells, tumor-derived EVs contribute to immune evasion and tumor growth. Furthermore, Tumor-derived EVs play a role in mediating drug resistance, impacting the effectiveness of therapeutic interventions. Understanding the multifaceted roles of BC tumor-derived EVs is essential for the development of innovative therapeutic strategies. Targeting pathways mediated by EVs holds promise for enhancing the efficacy of cancer treatments and improving patient outcomes. This comprehensive review provides insights into the intricate interactions of tumor-derived EVs in immune modulation and BC progression, highlighting potential therapeutic targets and avenues for novel cancer therapies.

Erythroid progenitor cell-mediated spleen-tumor interaction deteriorates cancer immunity

Understanding both local and systemic immunity is essential to optimizing the effectiveness of immunotherapy. However, the dynamic alterations in systemic immunity during tumor development are yet to be clearly defined. Here, we identified a previously unrecognized connection that bridges the interaction between the spleen and tumor through erythroid progenitor cells (EPCs), which suppress tumor immunity and promote tumor progression. We performed the single-cell RNA-seq and RNA-seq to demonstrate the presence of EPCs and identify the characteristic and an immunomodulatory role of EPCs during tumor progression. These tumor-hijacked EPCs proliferate in situ in spleens and impaired systemic and local antitumor response through the interaction between tumor and spleen. Specifically, the splenic CD45- EPCs secreted heparin-binding growth factor to regulate PD-L1-mediated immunosuppression of splenic CD45+ EPCs. Educated CD45+ EPCs from the spleen then migrated to the tumors via the CCL5/CCR5 axis, thereby weakening local antitumor immunity. Consequently, targeting EPCs not only revitalized antitumor immunity but also improved the anti-PD-L1 effect by promoting intratumoral T cell infiltration. Importantly, CD45+ EPCs are associated with immunosuppression and reduced survival in patients with head and neck squamous cell carcinoma. Collectively, these findings reveal the role of EPCs in orchestrating the interaction between the spleen and tumor, which could have significant implications for the development of more effective cancer immunotherapy.

Blocking WNT7A Enhances MHC-I Antigen Presentation and Enhances the Effectiveness of Immune Checkpoint Blockade Therapy

The limited infiltration of CD8+ T cells in tumors hampers the effectiveness of T cell-based immunotherapy, yet the mechanisms that limit tumor infiltration by CD8+ T cells remain unclear. Through bulk RNA sequencing of human tumors, we identified a strong correlation between WNT7A expression and reduced CD8+ T-cell infiltration. Further investigation demonstrated that inhibiting WNT7A substantially enhanced MHC-I expression on tumor cells. Mechanistically, WNT7A inhibition inactivated the Wnt/β-catenin signaling pathway and thus resulted in reduced physical interaction between β-catenin and p65 in the cytoplasm, which increased the nuclear translocation of p65 and activated the NF-κB pathway, ultimately promoting the transcription of genes encoding MHC-I molecules. We found that our lead compound, 1365-0109, disrupted the protein-protein interaction between WNT7A and its receptor FZD5, resulting in the upregulation of MHC-I expression. In murine tumor models, both genetic and pharmaceutical suppression of WNT7A led to increased MHC-I levels on tumor cells, and consequently enhanced the infiltration and functionality of CD8+ T cells, which bolstered antitumor immunity and improved the effectiveness of immune checkpoint blockade therapy. These findings have elucidated the intrinsic mechanisms of WNT7A-induced immune suppression, suggesting that therapeutic interventions targeting WNT7A hold promise for enhancing the efficacy of immunotherapy.

CD271high cancer stem cells regulate macrophage polarization in head and neck squamous cell carcinoma

PURPOSE

Cancer stem cells (CSCs) are considered key drivers of progression in head and neck squamous cell carcinoma (HNSCC). Our single-cell RNA sequencing (scRNA-seq) analysis revealed predominant expression of CD271 in CSCs, however, its role as a CSC marker in HNSCC requires further elucidation. We investigated the stemness characteristics of CD271high HNSCC cells and their interactions with the tumor immune microenvironment.

METHODS

scRNA-seq data from hypopharyngeal squamous cell carcinoma (HPSCC) tissues were analyzed to identify expression profile of CSCs. Overall survival was compared between CD271high and CD271low patients based on immunostaining of HPSCC samples. The stemness of CD271high HNSCC cells was evaluated via an in vivo limiting dilution assay. In a C57BL/6 mice model, the percentage of immune cells and macrophage subtypes were analyzed by flow cytometry. The role of CD271 in macrophage polarization was further examined by in vitro coculture of CD271high cells with CD14+ monocytes. Gene expressions were analyzed by qPCR.

RESULTS

CD271 is predominantly expressed in CSCs identified by scRNA-seq analysis. CD271 enhances HNSCC cell proliferation and is negatively correlated with patient prognosis in HPSCC. CD271 knockdown suppressed HNSCC tumor growth and regulated macrophage polarization within the TME. CD271high cells exhibited stemness features and enhanced tumor growth in vivo.

CONCLUSIONS

CD271high HNSCC cells exhibit CSC characteristics and regulate macrophage polarization. Targeting CD271 may improve the immunosuppressive TME to inhibit tumor growth. Combining CD271-targeting agents with other therapies presents a promising strategy that may enhance therapeutic efficacy and prognosis in HNSCC.

Causal relationships between immune cells, inflammatory factors, and preeclampsia: A two-step, two-sample mendelian randomization study

BACKGROUND

Preeclampsia (PE) is a complex hypertensive disorder that occurs during pregnancy, with the immune system playing a key role. Although immune modulation is implicated in PE progression, the roles of specific immune cells and inflammatory mediators remain unclear.

METHODS

We conducted a two-sample, two-step Mendelian randomization (MR) analysis, primarily using the inverse-variance weighted method, to investigate the causal effect of immune cell traits on PE. Additionally, we assessed the potential mediation effects of inflammatory factors.

RESULTS

The MR analyses revealed that 22 immune cell traits exert protective effects against PE, whereas 19 are associated with an increased risk. Additionally, four inflammatory factors were suggested to be linked to PE. Mediation analysis identified the absolute count (AC) of CD33 + HLA DR+ cells, including the CD14 - subset, as causally related to PE. Both the total effect of the CD33 + HLA DR+ AC (odds ratio [OR] = 0.977, 95 % confidence interval [CI], 0.960-0.994; P = 0.010) and the effect of CD33 + HLA DR+ CD14 - cells (OR = 0.977, 95 % CI, 0.963-0.991; P = 0.001) were significant. These effects were partially mediated by STAM-binding protein levels, contributing 16.7 % and 15.0 % to the total effects of the CD33 + HLA DR+ AC and CD33 + HLA DR+ CD14 - AC, respectively.

CONCLUSION

This study establishes a causal relationship between specific immune cells and PE, potentially mediated by inflammatory factors, highlighting the importance of these traits in PE pathogenesis. Further research is needed to validate these findings based on larger, more diverse cohorts.

Involvement of the ubiquitin-proteasome system in the regulation of the tumor microenvironment and progression

The tumor microenvironment is a complex environment comprising tumor cells, non-tumor cells, and other critical non-cellular components. Some studies about tumor microenvironment have recently achieved remarkable progress in tumor treatment. As a substantial part of post-translational protein modification, ubiquitination is a crucial player in maintaining protein stability in cell signaling, cell growth, and a series of cellular life activities, which are also essential for regulating tumor cells or other non-tumor cells in the tumor microenvironment. This review focuses on the role and function of ubiquitination and deubiquitination modification in the tumor microenvironment while discussing the prospect of developing inhibitors targeting ubiquity-related enzymes, thereby providing ideas for future research in cancer therapy.

Myeloid-derived suppressor cells in metabolic and cardiovascular disorders

Dysregulation of immune homeostasis can precipitate chronic inflammation, thus significantly contributing to the onset and progression of metabolic and cardiovascular diseases. Myeloid-derived suppressor cells (MDSCs) constitute a heterogeneous population of immature myeloid cells that are mobilized in response to biological stressors such as tissue damage and inflammation. Although MDSCs have been extensively characterized in the contexts of cancer and infectious diseases, emerging evidence highlights their pivotal roles in the pathophysiology of metabolic and cardiovascular disorders. We discuss growing evidence for the involvement of MDSCs in the progression of metabolic and cardiovascular diseases, with the aim of deepening our understanding of MDSCs in cardiometabolic physiology and identifying the necessary steps for the development of innovative MDSC-targeted therapeutic strategies.

Metabolic reprogramming of neutrophils in the tumor microenvironment: Emerging therapeutic targets

Neutrophils are pivotal in the immune system and have been recognized as significant contributors to cancer development and progression. These cells undergo metabolic reprogramming in response to various stimulus, including infections, diseases, and the tumor microenvironment (TME). Under normal conditions, neutrophils primarily rely on aerobic glucose metabolism for energy production. However, within the TME featured by hypoxic and nutrient-deprived conditions, they shift to altered anaerobic glycolysis, lipid metabolism, mitochondrial metabolism and amino acid metabolism to perform their immunosuppressive functions and facilitate tumor progression. Targeting neutrophils within the TME is a promising therapeutic approach. Yet, focusing on their metabolic pathways presents a novel strategy to enhance cancer immunotherapy. This review synthesizes the current understanding of neutrophil metabolic reprogramming in the TME, with an emphasis on the underlying molecular mechanisms and signaling pathways. Studying neutrophil metabolism in the TME poses challenges, such as their short lifespan and the metabolic complexity of the environment, necessitating the development of advanced research methodologies. This review also discusses emerging solutions to these challenges. In conclusion, given their integral role in the TME, targeting the metabolic pathways of neutrophils could offer a promising avenue for cancer therapy.

Endothelial YAP/TEAD1-CXCL17 signaling recruits myeloid-derived suppressor cells against liver ischemia-reperfusion injury

BACKGROUND AND AIMS

Liver ischemia-reperfusion injury (IRI) is a common complication of liver transplantation and hepatectomy and causes acute liver dysfunction and even organ failure. Myeloid-derived suppressor cells (MDSCs) accumulate and play immunosuppressive function in cancers and inflammation. However, the role of MDSCs in liver IRI has not been defined.

APPROACH AND RESULTS

We enrolled recipients receiving OLT and obtained the pre-OLT/post-OLT blood and liver samples. The proportions of MDSCs were significantly elevated after OLT and negatively associated with liver damage. In single-cell RNA-sequencing analysis of liver samples during OLT, 2 cell clusters with MDSC-like phenotypes were identified and showed maturation and infiltration in post-OLT livers. In the mouse model, liver IRI mobilized MDSCs and promoted their infiltration in the damaged liver, and intrahepatic MDSCs were possessed with enhanced immunosuppressive function by upregulation of STAT3 signaling. Under treatment with αGr-1 antibody or adoptive transfer MDSCs to change the proportion of MDSCs in vivo, we found that intrahepatic MDSCs alleviated liver IRI-induced inflammation and damage by inhibiting M1 macrophage polarization. Mechanistically, bulk RNA-sequencing analysis and in vivo experiments verified that C-X-C motif chemokine ligand 17 (CXCL17) was upregulated by YAP/TEAD1 signaling and subsequently recruited MDSCs through binding with GPR35 during liver IRI. Moreover, hepatic endothelial cells were the major cells responsible for CXCL17 expression in injured livers, among which hypoxia-reoxygenation stimulation activated the YAP/TEAD1 complex to promote CXCL17 transcription.

CONCLUSIONS

Endothelial YAP/TEAD1-CXCL17 signaling recruited MDSCs to attenuate liver IRI, providing evidence of therapeutic potential for managing IRI in liver surgery.

The role of myeloid-derived suppressor cells in children

Myeloid-derived suppressor cells (MDSC) were first recognized over twenty years ago as a key immunomodulatory cell population. Since their initial identification, a growing body of literature points to the importance of MDSC as a heterogeneous, immunosuppressive cell population and as a therapeutic target in adults with cancer. MDSC are potent suppressors of T cells and Natural Killer (NK) cells and can be helpful or harmful to the host depending on the pathophysiology. For example, MDSC are beneficial in pregnancy and prevent spontaneous abortion by promoting maternal-fetal tolerance. Increased MDSC are also associated with improved outcomes in patients with graft vs. host disease by decreasing T cell-driven inflammation. However, MDSC can also be harmful and are known to be pathologic in adults with cancer and chronic infections by promoting tumor escape and impairing pathogen clearance, respectively. Despite the widespread recognition of the importance of MDSC and their immune suppression effects in adults, much less is known regarding the role of MDSC in children. Research investigating MDSC in children lags significantly behind adult studies. In fact, while over 5,000 publications on PubMed discuss MDSC in immune regulation, fewer than 50 of these publications focus specifically on their role in children. This review aims to summarize the existing literature on the role of MDSC in children and identify important directions for future research, including targeting these cells in the pediatric population to improve clinical outcomes.

The multi-faceted immune modulatory role of S100A4 in cancer and chronic inflammatory disease

S100A4 is a Ca2+-binding protein involved in multiple chronic inflammatory and neoplastic conditions. This review focuses on recent advances in the understanding of S100A4 function in immune cells, comparing and contrasting S100A4 regulation of immune responses in cancer and chronic inflammatory diseases. We provide evidence that S100A4 regulation of immune cell function has a profound role in promoting the pathogenesis of cancer and pro-inflammatory conditions. Finally, we discuss relevant future directions to target S100A4 therapeutically in different disease states.

Interferon-gamma receptor signaling regulates innate immunity during Staphylococcus aureus craniotomy infection

A craniotomy is a neurosurgical procedure performed to access the intracranial space. In 3-5% of cases, infections can develop, most caused by Staphylococcus aureus biofilm formation on the skull surface. Medical management of this infection is difficult, as biofilm properties confer immune and antimicrobial recalcitrance to the infection and necessitate additional surgical procedures. Furthermore, treatment failure rates can be appreciably high. These factors, compounded with rapidly expanding rates of antimicrobial resistance, highlight the need to develop alternative treatment strategies to target and reverse the immune dysfunction that occurs during biofilm infection. Our recent work has identified CD4+ Th1 and Th17 cells as potent regulators of innate immune cell activation during craniotomy infection. Here, we report the role of IFN-γ, versus other Th1- and Th17-derived cytokines, in programing the immune response to biofilm infection using both global and cell type-specific IFN-γR1-deficient (Ifngr1-/-) mice. Bacterial burdens were significantly higher in Ifngr1-/- relative to WT animals despite few changes in immune cell abundance. Single-cell transcriptomics identified candidate explanations for this phenotype as alterations in cell death pathways, innate immune cell activation, MHC-II expression, and T cell responses were significantly reduced in Ifngr1-/- mice. While caspase-1 activation in PMNs and macrophage/microglial MHC-II expression were regulated by IFN-γ signaling, no phenotypes were observed with either granulocyte- or macrophage/microglia Ifngr1-/- conditional knockout mice, suggestive of redundancy. Instead, a decreased Th1/Th17 ratio was identified in Ifngr1-/- animals that was corroborated by elevated IL-17 levels and correlated with dysfunctional T cell-innate immune communication. Further, Th17 cells were less effective than Th1 cells in promoting S. aureus bactericidal activity in microglia and macrophages. Collectively, this work identifies a key protective role for IFN-γ during craniotomy infection by enhancing macrophage and microglial antibacterial activity. Therefore, controlled programming of IFN-γ responses may represent a novel therapeutic strategy for chronic craniotomy infections.

A pathogenic subpopulation of human glioma associated macrophages linked to glioma progression

Malignant gliomas follow two distinct natural histories: de novo high grade tumors such as glioblastoma, or lower grade tumors with a propensity to transform into high grade disease. Despite differences in tumor genotype, both entities converge on a common histologically aggressive phenotype, and the basis for this progression is unknown. Glioma associated macrophages (GAM) have been implicated in this process, however GAMs are ontologically and transcriptionally diverse, rendering isolation of pathogenic subpopulations challenging. Since macrophage contextual gene programs are orchestrated by transcription factors acting on cis -acting promoters and enhancers in gene regulatory networks (GRN), we hypothesized that functional populations of GAMs can be resolved through GRN inference. Here we show via parallel single cell RNA and ATAC sequencing that a subpopulation of human GAMs can be defined by a GRN centered around the Activator Protein-1 transcription factor FOSL2 preferentially enriched in high grade tumors. Using this GRN we nominate ANXA1 and HMOX1 as surrogate cell surface markers for activation, thus permitting prospective isolation and functional validation in human GAMs. These cells, termed malignancy associated GAMs (mGAMs) are pro-invasive, pro-angiogenic, pro-proliferative, possess intact antigen presentation but skew T-cells towards a CD4+FOXP3+ phenotype under hypoxia. Ontologically, mGAMs share somatic mitochondrial mutations with peripheral blood monocytes, and their presence correlates with high grade disease irrespective of underlying tumor mutation status. Furthermore, spatio-temporally mGAMs occupy distinct metabolic niches; mGAMs directly induce proliferation and mesenchymal transition of low grade glioma cells and accelerate tumor growth in vivo upon co-culture. Finally mGAMs are preferentially enriched in patients with newly transformed regions in human gliomas, supporting the view that mGAMs play a pivotal role in glioma progression and may represent a plausible therapeutic target in human high-grade glioma.

The TMBIM1-YBX1 axis orchestrates MDSC recruitment and immunosuppressive microenvironment in pancreatic cancer

Background: Pancreatic ductal adenocarcinoma (PDAC) is notorious for its profoundly immunosuppressive nature. The complex crosstalk between diverse immune cell types and heterogeneous tumor cell populations shapes this challenging tumor immune microenvironment (TIME). In this study, the role of transmembrane BAX inhibitor motif-containing 1 (TMBIM1) in modulating the TIME and its potential as a therapeutic target in PDAC were investigated. Methods: RNA sequencing was used to assess differential gene expression between PANC-1 cells with TMBIM1 knockdown and control cells. Single-cell RNA sequencing further validated the role of TMBIM1 in modulating the expression of CCL2 and PD-L1. Mechanistic insights were gained through chromatin immunoprecipitation, ELISA, real-time quantitative PCR, and flow cytometry experiments. To evaluate the impact of TMBIM1 on immune cell dynamics, we employed an in vitro chemotaxis assay and an in vivo C57BL/6J mouse xenograft model to examine CD8+ T-cell activation and myeloid-derived suppressor cell (MDSC) infiltration. Additionally, the therapeutic potential of TMBIM1 knockdown combined with anti-PD-1 antibody treatment was investigated in PDAC animal models. Results: TMBIM1 was significantly upregulated in pancreatic cancer tissues and cell lines, driving pancreatic cancer cell proliferation, growth, and migration both in vitro and in vivo. Elevated TMBIM1 expression induced high infiltration of MDSCs and fostered an immunosuppressive tumor microenvironment. Mechanistically, TMBIM1 binds to the transcription factor Y box binding protein 1 (YBX1), which in turn increases the affinity of YBX1 for the PD-L1 and CCL2 gene promoters. This interaction results in their upregulation, leading to increased MDSC infiltration, thereby facilitating the immunosuppressive TIME in PDAC. Notably, the combination of TMBIM1 knockdown with anti-PD-1 therapy had a more potent antitumor effect than anti-PD-1 therapy alone. Conclusions: Our study reveals that the TMBIM1/YBX1 axis is a key driver of immune evasion in PDAC and shapes the immunosuppressive TIME through the upregulation of CCL2 and PD-L1 expression. These findings highlight TMBIM1 as a potential therapeutic target to sensitize PDAC to immunotherapy.

Effect of External Beam Radiation Therapy and Brachytherapy on Circulating Myeloid-Derived Suppressor Cell Populations in Patients Treated Definitively for Cervical Cancer

Purpose

The immunosuppressive function of myeloid-derived suppressor cells (MDSCs) has been implicated in the regulation of immune responses against cancer and is associated with poor prognosis. Radiation treatment is known to alter immune cell populations within the tumor; however, whether this results in the recruitment of immunosuppressive MDSC populations is not well understood. Here we evaluate the response of circulating MDSC populations in patients treated per standard-of-care cisplatin chemoradiation therapy (CRT) for locally invasive cervical cancer.

Methods and Materials

Newly diagnosed, treatment-naïve patients with locally advanced cervical cancer were enrolled. Blood samples were collected from patients prior to starting CRT (T0), after external beam radiation therapy (T1), and after high-dose-rate brachytherapy (T2). Samples from each time point were processed, and the prevalence of MDSC subsets was determined using flow cytometry. MDSC populations were identified using Live/Dead-CD11b+CD33+HLA-DR- staining. MDSC subsets were further subdivided into granulocytic (g-, CD15+CD14-), monocytic (m-, CD15-CD14+), or early-MDSCs (e-, CD15-CD14-).

Results

Most patients in our study were Caucasian nonsmokers with human papillomavirus-associated squamous cell carcinoma of the cervix. We saw a trend for increased MDSC frequency in patients with more advanced-stage disease at the time of initiating treatment. MDSCs increase in response to CRT and peak after brachytherapy (T2). In particular, the g-MDSC subset increases by 6.44 times relative to the baseline. There was no correlation between MDSC expansion and response to therapy.

Conclusion

Our study confirms other reports that circulating MDSCs in patients with cervical cancer increase in response to CRT and are associated with more advanced stages. Additionally, we show that MDSC expansion is driven by the g-MDSC subset. We did not see any correlation between MDSC expansion and treatment response, though this may be because of the limited sample size for this study.

The Recruitment and Immune Suppression Mechanisms of Myeloid-Derived Suppressor Cells and Their Impact on Bone Metastatic Cancer

BACKGROUND

MDSCs are immature neutrophils and monocytes with immunosuppressive potentials, involving mononuclear MDSCs (M-MDSCs) and polymorphonuclear MDSCs (PMN-MDSCs).

RECENT FINDINGS

They are significant components of the tumor microenvironment (TME). Besides, recent studies also verified that MDSCs also facilitated the progression of bone metastasis by regulating the network of cytokines and the function of immune cells.

CONCLUSION

It is necessary to summarize the mechanisms of MDSC recruitment and immunosuppression, and their impact on bone metastasis.

CXCL16/CXCR6/TGF-β Feedback Loop Between M-MDSCs and Treg Inhibits Anti-Bacterial Immunity During Biofilm Infection

Staphylococcus aureus (S. aureus) is a leading cause of Periprosthetic  joint  infection (PJI), a severe complication after joint arthroplasty. Immunosuppression is a major factor contributing to the infection chronicity of S. aureus PJI, posing significant treatment challenges. This study investigates the relationship between the immunosuppressive biofilm milieu and S. aureus PJI outcomes in both discovery and validation cohorts. This scRNA-seq analysis of synovium from PJI patients reveals an expansion and heightened activity of monocyte-related myeloid-derived suppressor cells (M-MDSCs) and regulatory T cells (Treg). Importantly, CXCL16 is significantly upregulated in M-MDSCs, with its corresponding CXCR6 receptor also elevated on Treg. M-MDSCs recruit Treg and enhance its activity via CXCL16-CXCR6 interactions, while Treg secretes TGF-β, inducing M-MDSCs proliferation and immunosuppressive activity. Interfering with this cross-talk in vivo using Treg-specific CXCR6 knockout PJI mouse model reduces M-MDSCs/Treg-mediated immunosuppression and alleviates bacterial burden. Immunohistochemistry and recurrence analysis show that PJI patients with CXCR6high synovium have poor prognosis. This findings highlight the critical role of CXCR6 in Treg in orchestrating an immunosuppressive microenvironment and biofilm persistence during PJI, offering potential targets for therapeutic intervention.

Rbfox3 Promotes Transformation of MDSC-Like Tumor Cells to Shape Immunosuppressive Microenvironment

Myeloid-derived suppressor cells (MDSCs) within the tumor microenvironment (TME) contribute to the malignant progression of tumors by exerting immunosuppressive effects. Bacterial lipopolysaccharides (LPS) have been widely demonstrated in various types of solid tumors. LPS can promote the malignant progression of tumors, which mechanism has not yet been fully elucidated. In this study, a type of MDSC-like tumor cells (MLTCs) is found in tumor tissues induced by low-dose and long-term LPS stimulation. MLTCs can simultaneously express tumor cell and MDSCs markers. Similar to MDSCs, MLTCs can produce arginine, nitric oxide, and reactive oxygen species and inhibit the activity of NK and T cells to promote the formation of an immunosuppressive microenvironment. MLTCs can also promote tumor cell proliferation and vasculogenic mimicry formation. CRISPR-Cas9 activity screening studies identified RNA-binding Fox-1 homolog 3 (Rbfox3) as a critical protein for MLTCs formation after LPS treatment. Rbfox3 can transcriptionally regulate the expression of Ass1 in the form of phase-separated particles. Crocin can inhibit the generation of MLTCs by disrupting phase-separated particles of Rbfox3 and enhance the anti-tumor effects of immune checkpoint inhibitors (ICIs).

HDAC1-3 inhibition triggers NEDD4-mediated CCR2 downregulation and attenuates immunosuppression in myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) play a critical role in cancer progression and resistance, thus representing promising targets for immunotherapy. Despite the established role of histone deacetylases (HDACs) in epigenetic regulation of cell fate and function, their specific impact on MDSCs remains elusive. We sought to investigate the effects and underlying mechanisms of HDAC on MDSCs using various HDAC inhibitors. Our results indicate that HDAC1-3 inhibitors reduce CCR2 expression, a chemokine receptor that mediates the migration of monocytic (M-)MDSCs to tumors and attenuated the immunosuppressive activity of MDSCs. In an orthotropic hepatocellular carcinoma (HCC) murine model, HDAC1-3 inhibitors reduced the infiltration of M-MDSCs, increased the number of natural killer cells in tumors, and suppressed tumor growth. Our results also suggest that HDAC1-3 inhibitors potentiate the antitumor effects of anti-programmed cell death protein 1 antibodies. ATAC-seq and RNA-seq analyses revealed 115 genes epigenetically upregulated by HDAC1-3 inhibitors, primarily linked to transcriptional regulation and ubiquitination. We further elucidated that HDAC1-3 inhibitors facilitate CCR2 protein degradation through ubiquitination-mediated by NEDD4 E3 ligase. Our findings reveal a novel mechanism of action of HDAC1-3 inhibitors in MDSCs and suggest a potential synergistic immunotherapy strategy for clinical benefit in HCC.

Hybrid Cell Membrane-Engineered Nanocarrier for Triple-Action Strategy to Address Pseudomonas aeruginosa Infection

Bacterial infections resistant to antimicrobial treatments, particularly those caused by Pseudomonas aeruginosa (P. aeruginosa), frequently lead to elevated mortality rates. Tackling this resistance using therapeutic combinations with varied mechanisms has shown considerable promise. In this study, a bioinspired nanocarrier is successfully designed and engineered for targeted antibiotic delivery and toxin/bacteria clearance. This is achieved by encapsulating antibiotic-loaded framework nucleic acids with hybrid cell membranes acquired from neutrophils and platelets. By coating the hybrid membrane outside the shell, nanocarriers are endowed with the function of neutrophil-like chemotaxis and platelet-like bacteria adhesion to achieve the first stage of inflammation targeting. Based on the specific binding of bacteria toxin to the hybrid membrane, the release of antibiotic-loaded framework nucleic acids is triggered by toxin-mediated membrane lysis to fulfill the second stage of toxin neutralization and bacteria killing. Meanwhile, the immunomodulation potential of framework nucleic acids enables nanocarriers to accomplish the third stage of reversing the immunosuppressive microenvironment. In mouse models of acute and chronic P. aeruginosa pneumonia, the nanocarriers can reduce bacterial burden at a low dosage and decrease mortality with negligible toxicity. In sum, these findings have illustrated the remarkable capability of nanocarriers in treating recalcitrant bacterial infections.

Caerin 1.1/1.9-mediated antitumor immunity depends on IFNAR-Stat1 signalling of tumour infiltrating macrophage by autocrine IFNα and is enhanced by CD47 blockade

Previously, we demonstrated that natural host-defence peptide caerin 1.1/caerin 1.9 (F1/F3) increases the efficacy of anti-PD-1 and therapeutic vaccine, in a HPV16 + TC-1 tumour model, but the anti-tumor mechanism of F1/F3 is still unclear. In this study, we explored the impact of F1/F3 on the tumor microenvironment in a transplanted B16 melanoma model, and further investigated the mechanism of action of F1/F3 using monoclonal antibodies to deplete relevant cells, gene knockout mice and flow cytometry. We show that F1/F3 is able to inhibit the growth of melanoma B16 tumour cells both in vitro and in vivo. Depletion of macrophages, blockade of IFNα receptor, and Stat1 inhibition each abolishes F1/F3-mediated antitumor responses. Subsequent analysis reveals that F1/F3 increases the tumour infiltration of inflammatory macrophages, upregulates the level of IFNα receptor, and promotes the secretion of IFNα by macrophages. Interestingly, F1/F3 upregulates CD47 level on tumour cells; and blocking CD47 increases F1/F3-mediated antitumor responses. Furthermore, F1/F3 intratumor injection, CD47 blockade, and therapeutic vaccination significantly increases the survival time of B16 tumour-bearing mice. These results indicate that F1/F3 may be effective to improve the efficacy of ICB and therapeutic vaccine-based immunotherapy for human epithelial cancers and warrants consideration for clinical trials.