Plasticity of myeloid-derived suppressor cells in cancer

The interplay between the tumor microenvironment and tumor-derived small extracellular vesicles in cancer development and therapeutic response

The tumor microenvironment (TME) plays an essential role in tumor cell survival by profoundly influencing their proliferation, metastasis, immune evasion, and resistance to treatment. Extracellular vesicles (EVs) are small particles released by all cell types and often reflect the state of their parental cells and modulate other cells' functions through the various cargo they transport. Tumor-derived small EVs (TDSEVs) can transport specific proteins, nucleic acids and lipids tailored to propagate tumor signals and establish a favorable TME. Thus, the TME's biological characteristics can affect TDSEV heterogeneity, and this interplay can amplify tumor growth, dissemination, and resistance to therapy. This review discusses the interplay between TME and TDSEVs based on their biological characteristics and summarizes strategies for targeting cancer cells. Additionally, it reviews the current issues and challenges in this field to offer fresh insights into comprehending tumor development mechanisms and exploring innovative clinical applications.

MDSCs in bone metastasis: Mechanisms and therapeutic potential

Bone metastasis (BM) is a frequent complication associated with advanced cancer that significantly increases patient mortality. Myeloid-derived suppressor cells (MDSCs) play a pivotal role in BM progression by promoting angiogenesis, inhibiting immune responses, and inducing osteoclastogenesis. MDSCs induce immunosuppression through diverse mechanisms, including the generation of reactive oxygen species, nitric oxide, and immunosuppressive cytokines. Within the bone metastasis niche (BMN), MDSCs engage in intricate interactions with tumor, stromal, and bone cells, thereby establishing a complex regulatory network. The biological activities and functions of MDSCs are regulated by the microenvironment within BMN. Conversely, MDSCs actively contribute to microenvironmental regulation, thereby promoting BM development. A comprehensive understanding of the indispensable role played by MDSCs in BM is imperative for the development of novel therapeutic strategies. This review highlights the involvement of MDSCs in BM development, their regulatory mechanisms, and their potential as viable therapeutic targets.

Eosinophils, basophils and myeloid-derived suppressor cells in chronic Loa loa infection and its treatment in an endemic setting

BACKGROUND

Chronic infection by Loa loa remains an unsolved immunological paradox. Despite harboring subcutaneously migrating adult worms and often high densities of microfilariae, most patients experience only relatively mild symptoms, yet microfilaricidal treatment can trigger life-threatening inflammation. Here, we investigated innate cell populations hypothesized to play a role in these two faces of the disease, in an endemic population in Gabon.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed numbers and activation of eosinophils and basophils, as well as myeloid-derived suppressor cell (MDSC) subsets and associated circulating cytokine levels by flow cytometry in sex- and age-matched L. loa-uninfected (LL-), -amicrofilaraemic (MF-) and -microfilaraemic (MF+) individuals (n = 42), as well as microfilaraemic individuals treated with albendazole (n = 26). The percentage of eosinophils was lower in LL- (3.0%) than in the combined L. loa-infected population, but was similar in MF+ (13.1%) and MF- (12.3%). Upon treatment of MF+, eosinophilia increased from day 0 (17.2%) to day 14 (24.8%) and had decreased below baseline at day 168 (6.3%). Expression of the eosinophil activation marker CD123 followed the same pattern as the percentage of eosinophils, while the inverse was observed for CD193 and to some extent CD125. Circulating IL-5 levels after treatment followed the same pattern as eosinophil dynamics. Basophil numbers did not differ between infection states but increased after treatment of MF+. We did not observe differences in MDSC numbers between infection states or upon treatment.

CONCLUSIONS/SIGNIFICANCE

We demonstrate that both chronic infection and treatment of L. loa microfilaraemia are associated with eosinophil circulation and distinct phenotypical activation markers that might contribute to inflammatory pathways in this setting. In this first ever investigation into MDSC in L. loa infection, we found no evidence for their increased presence in chronic loiasis, suggesting that immunomodulation by L. loa is induced through other pathways.

A review concerning the breast cancer-related tumour microenvironment

Breast cancer (BC) is currently the most common malignant tumour in women and one of the leading causes of their death around the world. New and increasingly personalised diagnostic and therapeutic tools have been introduced over the last few decades, along with significant advances regarding the study and knowledge related to BC. The tumour microenvironment (TME) refers to the tumour cell-associated cellular and molecular environment which can influence conditions affecting tumour development and progression. The TME is composed of immune cells, stromal cells, extracellular matrix (ECM) and signalling molecules secreted by these different cell types. Ever deeper understanding of TME composition changes during tumour development and progression will enable new and more innovative therapeutic strategies to become developed for targeting tumours during specific stages of its evolution. This review summarises the role of BC-related TME components and their influence on tumour progression and the development of resistance to therapy. In addition, an account on the modifications in BC-related TME components associated with therapy is given, and the completed or ongoing clinical trials related to this topic are presented.

Enhancement of antitumor response of staphylococcal enterotoxin C2 mutant 2M-118 by promoting cell-mediated antitumor immunity

BACKGROUND

Staphylococcal enterotoxin C2 (SEC2) is used as an immunotherapeutic drug in China. However, SEC2 are limited due to its immunosuppressive and toxic effects. A SEC2 2M-118 (H118A/T20L/G22E) mutant generated by site-directed mutagenesis was studied to elucidate the underlying antitumor mechanism.

METHODS

The effects of 2M-118 on mouse fibrosarcoma (Meth-A) cells and cytokine responses were tested in vitro using a transwell assay and ELISA, respectively. 2M-118 effect on immune function in tumor-bearing mice was tested. Cytokine levels and antitumor responses were measured using ELISA and flow cytometry, respectively. TUNEL staining and immunohistochemistry were employed to detect the tumor apoptosis and CD4+ and CD8+ tumor infiltrating lymphocytes (TILs) in tumor tissue.

RESULTS

2M-118 demonstrated the growth inhibition on tumor cells, increase of cytokines production (IL-2, IFN-γ, and TNF-α) and splenocyte proliferation in vitro. 2M-118 effectively inhibited tumor development and increased lymphocytes and cytokines in a tumor-bearing mouse model. Additionally, 2M-118 regulated the tumormicroenvironment by reducing the number of myeloid-derived suppressor cells (MDSCs), increasing the number of TILs, and inducing tumorcell apoptosis.

CONCLUSION

2M-118 promotes immune function and enhances antitumor response. This indicates that 2M-118 could potentially be developed as a novel anti-tumor drug with-highefficiencyandlowtoxicity.

Natural Killer Cells Reprogram Myeloid-Derived Suppressor Cells to Induce TNF-α Release via NKG2D-Ligand Interaction after Cryo-Thermal Therapy

In our previous studies, a novel cryothermal therapy (CTT) was developed to induce systemic long-term anti-tumor immunity. Natural killer (NK) cells were found to play an important role in CTT-induced long-term immune-mediated tumor control at the late stage after CTT, but the underlying mechanism is unclear. Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that have potent immunosuppressive effects on T cells and weaken the long-term benefits of immunotherapy. Consequently, overcoming MDSC immunosuppression is essential for maintaining the long-term efficacy of immunotherapy. In this study, we revealed that NK cells considerably diminish MDSC accumulation at the late stage after CTT, boost T cell production, increase T cell activation, and promote MDSC maturation, culminating in Th1-dominant CD4+ T cell differentiation and enhancing NK and CD8+ T cell cytotoxicity. Additionally, NK cells activate ERK signaling in MDSCs through NKG2D-ligand interaction to increase the activity of tumor necrosis factor (TNF)-α converting enzyme (TACE)-cleaved membrane TNF-α. Furthermore, Increased TACE activity releases more soluble TNF-α from MDSCs to promote MDSC maturation. In our studies, we propose a novel mechanism by which NK cells can overcome MDSC-induced immunosuppression and maintain CTT-induced persistent anti-tumor immunity, providing a prospective therapeutic option to improve the performance of cancer immunotherapy.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

The Role of Myeloid-Derived Suppressor Cells in Multiple Sclerosis and Its Animal Model

Myeloid-derived suppressor cells (MDSCs), a heterogeneous cell population that consists of mostly immature myeloid cells, are immunoregulatory cells mainly characterized by their suppressive functions. Emerging findings have revealed the involvement of MDSCs in multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). MS is an autoimmune and degenerative disease of the central nervous system characterized by demyelination, axon loss, and inflammation. Studies have reported accumulation of MDSCs in inflamed tissues and lymphoid organs of MS patients and EAE mice, and these cells display dual functions in EAE. However, the contribution of MDSCs to MS/EAE pathogenesis remains unclear. This review aims to summarize our current understanding of MDSC subsets and their possible roles in MS/EAE pathogenesis. We also discuss the potential utility and associated obstacles in employing MDSCs as biomarkers and cell-based therapies for MS.

Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4

The involvement of the prostaglandin E2 (PGE2) system in cancer progression has long been recognized. PGE2 functions as an autocrine and paracrine signaling molecule with pleiotropic effects in the human body. High levels of intratumoral PGE2 and overexpression of the key metabolic enzymes of PGE2 have been observed and suggested to contribute to tumor progression. This has been claimed for different types of solid tumors, including, but not limited to, lung, breast, and colon cancer. PGE2 has direct effects on tumor cells and angiogenesis that are known to promote tumor development. However, one of the main mechanisms behind PGE2 driving cancerogenesis is currently thought to be anchored in suppressed antitumor immunity, thus providing possible therapeutic targets to be used in cancer immunotherapies. EP2 and EP4, two receptors for PGE2, are emerging as being the most relevant for this purpose. This review aims to summarize the known roles of PGE2 in the immune system and its functions within the tumor microenvironment. SIGNIFICANCE STATEMENT: Prostaglandin E2 (PGE2) has long been known to be a signaling molecule in cancer. Its presence in tumors has been repeatedly associated with disease progression. Elucidation of its effects on immunological components of the tumor microenvironment has highlighted the potential of PGE2 receptor antagonists in cancer treatment, particularly in combination with immune checkpoint inhibitor therapeutics. Adjuvant treatment could increase the response rates and the efficacy of immune-based therapies.

Targeting tumorous Circ-E-Cadherinencoded C-E-Cad inhibits the recruitment and function of breast cancer-associated myeloid-derived suppressor cells

We previously demonstrated that the C-E-cad protein encoded by circ-E-cadherin promotes the self-renewal of glioma stem cells. The expression pattern of C-E-cad in breast cancer and its potential function in the tumor microenvironment are unclear. The expression of circ-E-cadherin and C-E-cad was detected in breast cancer specimens. The influence of C-E-cad expression on MDSCs was assessed using FACS and in vivo tumorigenesis experiments. The synergistic effect of anti-C-E-cad and anti-PD-1 antibodies was validated in vivo. circ-E-cadherin and the encoded protein C-E-cad were found to be upregulated in breast cancer vs. normal samples. C-E-cad promotes the recruitment of MDSCs, especially PMN-MDSCs. C-E-cad activates EGFR signaling in tumor cells and promotes the transcription of CXCL8; moreover, C-E-cad binds to MDSCs and maintains glycolysis in PMN-MDSCs. Targeting C-E-cad enhanced anti-PD-1 efficiency. Our data suggested that C-E-cad is markedly overexpressed in breast cancer and promotes MDSC recruitment and survival. Targeting C-E-cad increases the efficacy of immune checkpoint inhibitor therapy.

Key players of immunosuppression in epithelial malignancies: Tumor-infiltrating myeloid cells and γδ T cells

BACKGROUND

The tumor microenvironment of solid tumors governs the differentiation of otherwise non-immunosuppressive macrophages and gamma delta (γδ) T cells into strong immunosuppressors while promoting suppressive abilities of known immunosuppressors such as myeloid-derived suppressor cells (MDSCs) upon infiltration into the tumor beds.

RECENT FINDINGS

In epithelial malignancies, tumor-associated macrophages (TAMs), precursor monocytic MDSCs (M-MDSCs), and gamma delta (γδ) T cells often acquire strong immunosuppressive abilities that dampen spontaneous immune responses by tumor-infiltrating T cells and B lymphocytes against cancer. Both M-MDSCs and γδ T cells have been associated with worse prognosis for multiple epithelial cancers.

CONCLUSION

Here we discuss recent discoveries on how tumor-associated macrophages and precursor M-MDSCs as well as tumor associated-γδ T cells acquire immunosuppressive abilities in the tumor beds, promote cancer metastasis, and perspectives on how possible novel interventions could restore the effective adaptive immune responses in epithelial cancers.

Improved Innate Immune Function in Patients with Chronic Lymphocytic Leukemia Treated with Targeted Therapy in Clinical Trials

PURPOSE

Patients with chronic lymphocytic leukemia (CLL) have increased risk of severe infections. Although adaptive immune dysfunction is well described, clinical tools for identifying patients at risk are lacking, warranting investigation of additional immune components. In contrast to chemotherapy, targeted agents could spare or even improve innate immune function. Therefore, we investigated innate immune phenotypes and function in patients with CLL before and during targeted treatment.

EXPERIMENTAL DESIGN

Baseline and consecutive blood samples were collected from patients with CLL treated with acalabrutinib (n = 17) or ibrutinib+venetoclax (n = 18) in clinical trials. Innate immune function was assessed by TruCulture, a whole-blood ligand-stimulation assay quantifying cytokine release in response to standardized stimuli. Innate immune phenotypes were characterized by flow cytometry. As a proxy for infections, we mapped antimicrobial use before and during treatment.

RESULTS

At baseline, patients with CLL displayed impaired stimulated cytokine responses to the endotoxin lipopolysaccharide (LPS) along with deactivated monocytes, enrichment of myeloid-derived suppressor cells and metamyelocytes, and elevated (unstimulated) proinflammatory cytokines. Two/three cycles of acalabrutinib or ibrutinib normalized LPS-stimulated responses, in parallel with decreased duration of infections. Innate immune profiles and elevated proinflammatory cytokines further normalized during longer-term acalabrutinib or ibrutinib+venetoclax, paralleled by decreased infection frequency.

CONCLUSIONS

Innate immune impairment and infection susceptibility in patients with CLL were restored in parallel during targeted therapy. Thus, targeted treatment may reduce the risk of infections in CLL, as currently under investigation in the PreVent-ACaLL phase 2 trial of acalabrutinib+venetoclax for high-risk CLL (NCT03868722).

Engagement of sialylated glycans with Siglec receptors on suppressive myeloid cells inhibits anticancer immunity via CCL2

The overexpression of sialic acids on glycans, called hypersialylation, is a common alteration found in cancer cells. Sialylated glycans can enhance immune evasion by interacting with sialic acid-binding immunoglobulin-like lectin (Siglec) receptors on tumor-infiltrating immune cells. Here, we investigated the effect of sialylated glycans and their interaction with Siglec receptors on myeloid-derived suppressor cells (MDSCs). We found that MDSCs derived from the blood of lung cancer patients and tumor-bearing mice strongly express inhibitory Siglec receptors and are highly sialylated. In murine cancer models of emergency myelopoiesis, Siglec-E knockout in myeloid cells resulted in prolonged survival and increased tumor infiltration of activated T cells. Targeting suppressive myeloid cells by blocking Siglec receptors or desialylation strongly reduced their suppressive potential. We further identified CCL2 as a mediator involved in T-cell suppression upon interaction between sialoglycans and Siglec receptors on MDSCs. Our results demonstrated that sialylated glycans inhibit anticancer immunity by modulating CCL2 expression.

Cancer stem cell-immune cell crosstalk in the tumor microenvironment for liver cancer progression

Crosstalk between cancer cells and the immune microenvironment is determinant for liver cancer progression. A tumor subpopulation called liver cancer stem cells (CSCs) significantly accounts for the initiation, metastasis, therapeutic resistance, and recurrence of liver cancer. Emerging evidence demonstrates that the interaction between liver CSCs and immune cells plays a crucial role in shaping an immunosuppressive microenvironment and determining immunotherapy responses. This review sheds light on the bidirectional crosstalk between liver CSCs and immune cells for liver cancer progression, as well as the underlying molecular mechanisms after presenting an overview of liver CSCs characteristic and their microenvironment. Finally, we discuss the potential application of liver CSCs-targeted immunotherapy for liver cancer treatment.

IRF8-driven reprogramming of the immune microenvironment enhances anti-tumor adaptive immunity and reduces immunosuppression in murine glioblastoma

Background

Glioblastoma (GBM) has a highly immunosuppressive tumor immune microenvironment (TIME), largely mediated by myeloid-derived suppressor cells (MDSCs). Here, we utilized a retroviral replicating vector (RRV) to deliver Interferon Regulatory Factor 8 (IRF8), a master regulator of type 1 conventional dendritic cell (cDC1) development, in a syngeneic murine GBM model. We hypothesized that RRV-mediated delivery of IRF8 could "reprogram" intratumoral MDSCs into antigen-presenting cells (APCs) and thereby restore T-cell responses.

Methods

Effects of RRV-IRF8 on survival and tumor growth kinetics were examined in the SB28 murine GBM model. Immunophenotype was analyzed by flow cytometry and gene expression assays. We assayed functional immunosuppression and antigen presentation by ex vivo T-cell-myeloid co-culture.

Results

Mice with RRV-IRF8 pre-transduced intracerebral tumors had significantly longer survival and slower tumor growth compared to controls. RRV-IRF8 treated tumors exhibited significant enrichment of cDC1s and CD8+ T-cells. Additionally, myeloid cells derived from RRV-IRF8 tumors showed decreased expression of the immunosuppressive markers Arg1 and IDO1 and demonstrated reduced suppression of naïve T-cell proliferation in ex vivo co-culture, compared to controls. Furthermore, DCs from RRV-IRF8 tumors showed increased antigen presentation compared to those from control tumors. In vivo treatment with azidothymidine (AZT), a viral replication inhibitor, showed that IRF8 transduction in both tumor and non-tumor cells is necessary for survival benefit, associated with a reprogrammed, cDC1- and CD8 T-cell-enriched TIME.

Conclusions

Our results indicate that reprogramming of glioma-infiltrating myeloid cells by in vivo expression of IRF8 may reduce immunosuppression and enhance antigen presentation, achieving improved tumor control.

NLRP6 deficiency suppresses colorectal cancer liver metastasis growth by modulating M-MDSC-induced immunosuppressive microenvironment

Colorectal cancer liver metastasis (CRLM) a profound influence on the prognosis of patients with colorectal cancer (CRC), prompting a comprehensive inquiry into its underlying mechanisms. Amidst the multifaceted tumor microenvironment, myeloid-derived suppressor cells (MDSCs) have emerged as pivotal orchestrators of immune modulation. However, their specific contributions to the CRLM have not been explored. The role of NLRP6, a member of the NOD-like receptor family, is of interest. Employing a liver metastasis model, our investigation revealed a heightened accumulation of monocytic MDSCs (M-MDSCs) within metastatic sites, culminating in an immunosuppressive milieu characterized by depleted CD8+ T cell populations. Remarkably, the absence of NLRP6 disrupts this intricate immunosuppressive network, highlighting its nuanced role in sculpting the trajectory of CRLM. This study elucidates the interplay between NLRP6 and MDSCs, potentially guiding novel therapeutic strategies to recalibrate the immune microenvironment in CRLM and enhance patient outcomes.

Anti-stromal nanotherapeutics for hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most commonly diagnosed primary liver cancer, has become a leading cause of cancer-related death worldwide. Accumulating evidence confirms that the stromal constituents within the tumor microenvironment (TME) exacerbate HCC malignancy and set the barriers to current anti-HCC treatments. Recent developments of nano drug delivery system (NDDS) have facilitated the application of stroma-targeting therapeutics, disrupting the stromal TME in HCC. This review discusses the stromal activities in HCC development and therapy resistance. In addition, it addresses the delivery challenges of NDDS for stroma-targeting therapeutics (termed anti-stromal nanotherapeutics in this review), and provides recent advances in anti-stromal nanotherapeutics for safe, effective, and specific HCC therapy.

Myeloid derived suppressor cells in peripheral blood can be a prognostic factor in canine transitional cell carcinoma

Myeloid-derived suppressor cells (MDSCs) are immature cells with immunosuppressive properties found in the tumor microenvironment. MDSCs are divided into two major subsets: polymorphonuclear MDSCs (PMN-MDSCs) and monocytic MDSCs (M-MDSCs). Both MDSC subsets contribute to the creation of an immunosuppressive environment for tumor progression. In humans, patients with high levels of MDSCs show worse outcomes for several types of cancers. However, the association between MDSCs and clinical features has rarely been investigated in canine studies. In the present study, we measured the proportion of PMN-MDSCs and M-MDSCs in the peripheral blood and tumor tissue of dogs with hepatocellular carcinoma (HCC), prostate cancer (PC), transitional cell carcinoma (TCC), lymphoma, and pulmonary adenocarcinoma. Additionally, we examined immunosuppressive ability of PMN-MDSCs and M-MDSCs in peripheral blood mononuclear cells of TCC case on CD4+, CD8+ and interferon-γ+ cells and investigated the relationships of MDSCs with clinical features and outcomes. PMN-MDSCs increased in HCC, PC, TCC, and lymphoma. In contrast, M-MDSCs increased in the TCC. Both PMN-MDSCs and M-MDSCs exhibited immunosuppressive effects on CD8+, CD4+ and interferon-γ+ cells. In dogs with TCC, lymph node metastasis was associated with high level of PMN-MDSCs but not with M-MDSCs. High levels of both PMN-MDSCs and M-MDSCs were related to advanced tumor stage. Kaplan-Meier analysis revealed that high levels of both PMN-MDSCs and M-MDSCs were significantly associated with shorter overall survival. In addition, the Cox proportional hazard regression model showed that M-MDSCs and the tumor stage were independent prognostic factors for TCC. These results suggest that PMN-MDSCs and M-MDSCs may be involved in tumor progression and could be prognostic factors and promising therapeutic targets in dogs with TCC.

Targeting neutrophils: Mechanism and advances in cancer therapy

BACKGROUND

Cancer is a thorny problem which cannot be conquered by mankind at present and recent researchers have put their focus on tumor microenviroment. Neutrophils, the prominent leukocytes in peripheral blood that accumulate in tumours, serves as frontline cells in response to tumour progression owing to the rapid development of micro biotechnology. Hence, targeted therapy with these neutrophils has made targeting treatment a promising field in cancer therapy.

MAIN BODY

We broadly summarise some studies on the phenotypes and functions of tumour-associated neutrophils as well as the unique web-like products of neutrophils that play a role in cancer progression-neutrophil extracellular traps-and the interactions between neutrophils and the tumour microenvironment. Moreover, several targeted neutrophils therapeutic studies have made some progress and provided potential strategies for the treatment of cancer.

CONCLUSION

This review aims to offer a holistic perspective on therapeutic interventions targeting neutrophils to further inspire more researches on cancer therapies.

Intrinsic and Microenvironmental Drivers of Glioblastoma Invasion

Gliomas are diffusely infiltrating brain tumors whose prognosis is strongly influenced by their extent of invasion into the surrounding brain tissue. While lower-grade gliomas present more circumscribed borders, high-grade gliomas are aggressive tumors with widespread brain infiltration and dissemination. Glioblastoma (GBM) is known for its high invasiveness and association with poor prognosis. Its low survival rate is due to the certainty of its recurrence, caused by microscopic brain infiltration which makes surgical eradication unattainable. New insights into GBM biology at the single-cell level have enabled the identification of mechanisms exploited by glioma cells for brain invasion. In this review, we explore the current understanding of several molecular pathways and mechanisms used by tumor cells to invade normal brain tissue. We address the intrinsic biological drivers of tumor cell invasion, by tackling how tumor cells interact with each other and with the tumor microenvironment (TME). We focus on the recently discovered neuronal niche in the TME, including local as well as distant neurons, contributing to glioma growth and invasion. We then address the mechanisms of invasion promoted by astrocytes and immune cells. Finally, we review the current literature on the therapeutic targeting of the molecular mechanisms of invasion.

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

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

The role of ROS in tumor infiltrating immune cells and cancer immunotherapy

Reactive oxygen species (ROS) are a group of short-lived highly reactive molecules formed intracellularly from molecular oxygen. ROS can alter biochemical, transcriptional, and epigenetic programs and have an indispensable role in cellular function. In immune cells, ROS are mediators of specialized functions such as phagocytosis, antigen presentation, activation, cytolysis, and differentiation. ROS have a fundamental role in the tumor microenvironment (TME) where they are produced by immune cell-intrinsic and -extrinsic mechanisms. ROS can act as a double-edged sword with short exposures leading to activation in various innate and adaptative immune cells, and prolonged exposures, unopposed by redox balancing antioxidants leading to exhaustion, immunosuppression, and unresponsiveness to cancer immunotherapy. Due to its plasticity and impact on the anti-tumor function of immune cells, attempts are currently in process to harness ROS biology with the purpose to improve contemporary strategies of cancer immunotherapy. Here, we provide a short overview how ROS and various antioxidant systems impact on the function of innate and adaptive immune system cells with emphasis on the TME and immune-based therapies for cancer.

Exosomal miRNA-166-5p derived from G-MDSCs promotes proliferation by targeting ITM3E in colorectal cancer

BACKGROUND

The immune milieu of colorectal cancer is a complex phenomenon. It is imperative to investigate the crucial immune factors that promote the progression of colorectal cancer. Immune suppressor cells are granulocytic myeloid-derived suppressor cells (G-MDSCs). However, they also increased cancer growth in other ways that need to be investigated further.

METHODS

Using flow cytometry, we isolated G-MDSCs from colorectal cancer tissues. Ultracentrifugation was used to separate exosomes from the supernatant of G-MDSCs, and western blotting, transmission electron microscopy (TEM), and flow cytometry were used to confirm their presence. RNA sequencing was used to identify unique miRNAs and transcripts, which were subsequently confirmed by RT-qPCR (real-time quantitative real-time PCR). The CCK-8 test was used to determine the rate of proliferation. Lentiviral vectors were employed to manipulate the expression of miRNAs and genes in order to investigate their role in the development of colorectal cancer.

RESULTS

Colorectal cancer tissues have been found to contain granulocyte-myeloid-derived suppressor cells (G-MDSCs) that secrete exosomes. These exosomes have been shown to accelerate cancer progression by promoting cell proliferation. Further research has identified microRNA-166-5p as a target from G-MDSC-derived exosomes. This downregulation leads to the inhibition of integral membrane protein 2B (ITM3E) transcription, which in turn activates the PI3K/Akt signaling pathway. This pathway promotes cell proliferation and can be inhibited using deguelin. The accelerated development of colorectal cancer has been further confirmed in mice models.

CONCLUSION

The primary results of this work show that exosomes produced from G-MDSCs and the miR-166-5p/ITM3E axis have therapeutic and diagnostic promise in colorectal cancer.

The roles of epigallocatechin gallate in the tumor microenvironment, metabolic reprogramming, and immunotherapy

Cancer, a disease that modern medicine has not fully understood and conquered, with its high incidence and mortality, deprives countless patients of health and even life. According to global cancer statistics, there were an estimated 19.3 million new cancer cases and nearly 10 million cancer deaths in 2020, with the age-standardized incidence and mortality rates of 201.0 and 100.7 per 100,000, respectively. Although remarkable advancements have been made in therapeutic strategies recently, the overall prognosis of cancer patients remains not optimistic. Consequently, there are still many severe challenges to be faced and difficult problems to be solved in cancer therapy today. Epigallocatechin gallate (EGCG), a natural polyphenol extracted from tea leaves, has received much attention for its antitumor effects. Accumulating investigations have confirmed that EGCG can inhibit tumorigenesis and progression by triggering apoptosis, suppressing proliferation, invasion, and migration, altering tumor epigenetic modification, and overcoming chemotherapy resistance. Nevertheless, its regulatory roles and biomolecular mechanisms in the immune microenvironment, metabolic microenvironment, and immunotherapy remain obscure. In this article, we summarized the most recent updates about the effects of EGCG on tumor microenvironment (TME), metabolic reprogramming, and anti-cancer immunotherapy. The results demonstrated EGCG can promote the anti-cancer immune response of cytotoxic lymphocytes and dendritic cells (DCs), attenuate the immunosuppression of myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs), and inhibit the tumor-promoting functions of tumor-associated macrophages (TAMs), tumor-associated neutrophils (TANs), and various stromal cells including cancer-associated fibroblasts (CAFs), endothelial cells (ECs), stellate cells, and mesenchymal stem/stromal cells (MSCs). Additionally, EGCG can suppress multiple metabolic reprogramming pathways, including glucose uptake, aerobic glycolysis, glutamine metabolism, fatty acid anabolism, and nucleotide synthesis. Finally, EGCG, as an immunomodulator and immune checkpoint blockade, can enhance immunotherapeutic efficacy and may be a promising candidate for antitumor immunotherapy. In conclusion, EGCG plays versatile regulatory roles in TME and metabolic reprogramming, which provides novel insights and combined therapeutic strategies for cancer immunotherapy.

VISTA promotes the metabolism and differentiation of myeloid-derived suppressor cells by STAT3 and polyamine-dependent mechanisms

Myeloid-derived suppressor cells (MDSCs) impair antitumor immune responses. Identifying regulatory circuits during MDSC development may bring new opportunities for therapeutic interventions. We report that the V-domain suppressor of T cell activation (VISTA) functions as a key enabler of MDSC differentiation. VISTA deficiency reduced STAT3 activation and STAT3-dependent production of polyamines, which causally impaired mitochondrial respiration and MDSC expansion. In both mixed bone marrow (BM) chimera mice and myeloid-specific VISTA conditional knockout mice, VISTA deficiency significantly reduced tumor-associated MDSCs but expanded monocyte-derived dendritic cells (DCs) and enhanced T cell-mediated tumor control. Correlated expression of VISTA and arginase-1 (ARG1), a key enzyme supporting polyamine biosynthesis, was observed in multiple human cancer types. In human endometrial cancer, co-expression of VISTA and ARG1 on tumor-associated myeloid cells is associated with poor survival. Taken together, these findings unveil the VISTA/polyamine axis as a central regulator of MDSC differentiation and warrant therapeutically targeting this axis for cancer immunotherapy.

A telomere-targeting drug depletes cancer initiating cells and promotes anti-tumor immunity in small cell lung cancer

There are few effective treatments for small cell lung cancer (SCLC) underscoring the need for innovative therapeutic approaches. This study focuses on exploiting telomerase, a critical SCLC dependency as a therapeutic target. A prominent characteristic of SCLC is their reliance on telomerase activity, a key enzyme essential for their continuous proliferation. Here we utilize a nucleoside analog, 6-Thio-2'-deoxyguanosine (6TdG) currently in phase II clinical trials, that is preferentially incorporated by telomerase into telomeres leading to telomere dysfunction. Using preclinical mouse and human derived models we find low intermittent doses of 6TdG inhibit tumor growth and reduce metastatic burden. Anti-tumor efficacy correlates with a reduction in a subpopulation of cancer initiating like cells (CICs) identified by their expression of L1CAM/CD133 and highest telomerase activity. 6TdG treatment also leads to activation of innate and adaptive anti-tumor responses. Mechanistically, 6TdG depletes CICs and induces type-I interferon signaling leading to tumor immune visibility by activating tumor cell STING signaling. We also observe increased sensitivity to irradiation after 6TdG treatment in both syngeneic and humanized SCLC xenograft models both of which are dependent on the presence of host immune cells. This study underscores the immune-enhancing and metastasis-reducing effects of 6TdG, employing a range of complementary in vitro and in vivo SCLC preclinical models providing a potential therapeutic approach to SCLC.

Tissue adhesive indocyanine green-locking granular gel-mediated photothermal therapy combined with checkpoint inhibitor for preventing postsurgical recurrence and metastasis of colorectal cancer

Developing effective therapy to inhibit postoperative recurrence and metastasis of colorectal cancer (CRC) is challenging and significant to reduce mortality and morbidity. Here, a granular hydrogel, assembled from gelatin microgels by dialdehyde starch and interpenetrated with in situ polymerized poly(sulfobetaine methacrylate-co-N-isopropylacrylamide) (P(SBMA-co-NIPAM)), is prepared to load and lock Food and Drug Administration (FDA)-approved indocyanine green (ICG) with definite photothermal function and biosafety for photothermal therapy (PTT) combining with checkpoint inhibitor. The presence of P(SBMA-co-NIPAM) endows granular hydrogel with high retention to water-soluble ICG, preventing easy diffusion and rapid scavenging of ICG. The ICG-locking granular hydrogel can be spread and adhered onto the surgery site at wet state in vivo, exerting a persistent and stable PTT effect. Combined with αPD-L1 treatment, ICG-locking granular hydrogel-mediated PTT can eradicate postsurgery residual and metastatic tumors, and prevent long-term tumor recurrence. Further mechanistic studies indicate that combination treatment effectively promotes dendritic cells maturation in lymph nodes, enhances the number and infiltration of CD8+ T and CD4+ T cells in tumor tissue, and improves memory T cell number in spleen, thus activating the antitumor immune response. Overall, ICG-locking gel-mediated PTT is expected to exhibit broad clinical applications in postoperative treatment of cancers, like CRC.

Tumor microenvironment diversity and plasticity in cancer multidrug resistance

Multidrug resistance (MDR) poses a significant obstacle to effective cancer treatment, and the tumor microenvironment (TME) is crucial for MDR development and reversal. The TME plays an active role in promoting MDR through several pathways. However, a promising therapeutic approach for battling MDR involves targeting specific elements within the TME. Therefore, this comprehensive review elaborates on the research developments regarding the dual role of the TME in promoting and reversing MDR in cancer. Understanding the complex role of the TME in promoting and reversing MDR is essential to developing effective cancer therapies. Utilizing the adaptability of the TME by targeting novel TME-specific factors, utilizing combination therapies, and employing innovative treatment strategies can potentially combat MDR and achieve personalized treatment outcomes for patients with cancer.

Clinicopathological and prognostic values of MET expression in pancreatic adenocarcinoma based on bioinformatics analysis

Pancreatic adenocarcinoma (PAAD) is regarded as one of the most lethiferous cancers worldwide because treatment of pancreatic cancer remains challenging and mostly palliative. Little progress had been made to select certain reliable biomarkers as clinical prognosis. In this context, GSE28735 and GSE16515 were obtained from the Gene Expression Omnibus (GEO). GEO2R tool was used to recognize differentially expressed genes (DEGs). 351 DEGs were screened which included 230 up-regulated genes and 121 down-regulated genes. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to analyze the DEGs and associated signal pathways in the DAVID database. A protein-protein interaction (PPI) network was then constructed to screen 10 hub genes by STRING database and Cityscape software. Analyses of 10 hub genes were performed on GEPIA database and GSCA database, which revealed that MET was high expressed and significantly associated with survival of PAAD patients. Immunohistochemical staining showed that MET was higher expressed in PAAD tissues than adjacent tissues in 20 samples. The clinicopathological analysis revealed that high expression of MET was associated with the degree of differentiation, lymph node metastasis, vascular cancer thrombus and nerve invasion in PAAD tissues (P < .05). Furthermore, the Tumor Immune Estimation Resource (TIMER) database analyzed the correlation between the MET expression level and immune infiltration levels, which elucidated that MET expression was appreciably positively correlated with the infiltration levels of myeloid-derived suppressor cells (MDSCs). Here, these results strongly indicate MET is an unique prognostic biomarker. Its expression level is correlated with certain clinicopathological features and immune cell infiltration.

Radiotherapy remodels the tumor microenvironment for enhancing immunotherapeutic sensitivity

Cancer immunotherapy has transformed traditional treatments, with immune checkpoint blockade being particularly prominent. However, immunotherapy has minimal benefit for patients in most types of cancer and is largely ineffective in some cancers (such as pancreatic cancer and glioma). A synergistic anti-tumor response may be produced through the combined application with traditional tumor treatment methods. Radiotherapy (RT) not only kills tumor cells but also triggers the pro-inflammatory molecules' release and immune cell infiltration, which remodel the tumor microenvironment (TME). Therefore, the combination of RT and immunotherapy is expected to achieve improved efficacy. In this review, we summarize the effects of RT on cellular components of the TME, including T cell receptor repertoires, different T cell subsets, metabolism, tumor-associated macrophages and other myeloid cells (dendritic cells, myeloid-derived suppressor cells, neutrophils and eosinophils). Meanwhile, non-cellular components such as lactate and extracellular vesicles are also elaborated. In addition, we discuss the impact of different RT modalities on tumor immunity and issues related to the clinical practice of combination therapy.

Cholesterol Efflux Drives the Generation of Immunosuppressive Macrophages to Promote the Progression of Human Hepatocellular Carcinoma

Cholesterol is often enriched in tumor microenvironment (TME); however, its impact on disease progression varies in different tissues and cells. Monocytes/macrophages (Mφ) are major components and regulators of the TME and play pivotal roles in tumor progression and therapeutic responses. We aimed to investigate the profile, effects, and regulatory mechanisms of Mφ cholesterol metabolism in the context of human hepatocellular carcinoma (HCC). Here, we found that patients with high serum levels of cholesterol had shorter survival times and lower response rates to anti-PD-1 treatment. However, the cholesterol content in tumor-infiltrating monocytes/Mφ was significantly lower than that in their counterparts in paired nontumor tissues. The expression of the cholesterol efflux transporter, ABCA1, was upregulated in tumor monocytes/Mφ, and ABCA1 upregulation positively associated with decreased cellular cholesterol content and increased serum cholesterol levels. Mechanistically, autocrine cytokines from tumor-treated monocytes increased LXRα and ABCA1 expression, which led to the generation of immature and immunosuppressive Mφ. Although exogenous cholesterol alone had little direct effect on Mφ, it did act synergistically with tumor-derived factors to promote ABCA1 expression in Mφ with more immunosuppressive features. Moreover, high numbers of ABCA1+ Mφ in HCC tumors associated with reduced CD8+ T-cell infiltration and predicted poor clinical outcome for patients. Our results revealed that dysregulated cholesterol homeostasis, due to the collaborative effects of tumors and exogenous cholesterol, drives the generation of immunosuppressive Mφ. The selective modulation of cholesterol metabolism in Mφ may represent a novel strategy for cancer treatment.

Targeting M-MDSCs enhances the therapeutic effect of BNCT in the 4-NQO-induced murine head and neck squamous cell carcinoma model

Purpose

Malignant head and neck squamous cell carcinoma (HNSCC) is characterized by a poor prognosis and resistance to conventional radiotherapy. Infiltrating myeloid-derived suppressive cells (MDSCs) is prominent in HNSCC and is linked to immune suppression and tumor aggressiveness. This study aimed to investigate the impact of boron neutron capture therapy (BNCT) on the MDSCs in the tumor microenvironment and peripheral blood and to explore the potential for MDSCs depletion combined with BNCT to reactivate antitumor immunity.

Methods and materials

Carcinogen, 4-NQO, -induced oral tumors were irradiated with a total physical dose of 2 Gy BNCT in Tsing Hua Open Reactor (THOR). Flow cytometry and immunohistochemistry accessed the dynamics of peripheral MDSCs and infiltrated MDSCs within the tumor microenvironment. Mice were injected with an inhibitor of CSF-1 receptor (CSF-1R), PLX3397, to determine whether modulating M-MDSCs could affect mice survival after BNCT.

Results

Peripheral CD11b+Ly6ChighLy6G- monocytic-MDSCs (M-MDSCs), but not CD11b+Ly6CloLy6Ghigh polymorphonuclear-MDSCs (PMN-MDSCs), increased as tumor progression. After BNCT treatment, there were temporarily decreased and persistent increases of M-MDSCs thereafter, either in peripheral blood or in tumors. The administration of PLX-3397 hindered BNCT-caused M-MDSCs infiltration, prolonged mice survival, and activated tumor immunity by decreasing tumor-associated macrophages (TAMs) and increasing CD8+ T cells.

Conclusion

M-MDSCs were recruited into 4-NQO-induced tumors after BNCT, and their number was also increased in peripheral blood. Assessment of M-MDSCs levels in peripheral blood could be an index to determine the optimal intervention window. Their temporal alteration suggests an association with tumor recurrence after BNCT, making M-MDSCs a potential intervention target. Our preliminary results showed that PLX-3397 had strong M-MDSCs, TAMs, and TIL (tumor-infiltrating lymphocyte) modulating effects that could synergize tumor control when combined with BNCT.

The crosstalk between autophagy and myeloid-derived suppressor cell responses in cancer

The development of cancers is aided by the accumulation of myeloid-derived suppressor cells (MDSCs) within tumors, which are highly effective at suppressing anti-tumor immune responses. Direct cell-to-cell interaction and the production of immunosuppressive mediators have both been proposed as pathways for MDSC-mediated suppression of anti-tumor immune responses. The majority of current cancer treatments focus on altering the development and activity of MDSCs so that they have more of an immunogenic character. Autophagy is a catabolic system that contributes to the breakdown of damaged intracellular material and the recycling of metabolites. However, depending on the stage of tumor growth, autophagy can play both a prophylactic and a therapeutic function in carcinogenesis. However, several indirect lines of research have indicated that autophagy is a significant regulator of MDSC activity. The purpose of this work was to outline the interactions between MDSC and autophagy in cancer.

Progress in research on the role played by myeloid-derived suppressor cells in liver diseases

Myeloid-derived suppressor cells (MDSCs) refer to a group of immature myeloid cells with potent immunosuppressive capacity upon activation by pathological conditions. Because of their potent immunosuppressive ability, MDSCs have garnered extensive attention in the past few years in the fields of oncology, infection, chronic inflammation and autoimmune diseases. Research on MDSCs in liver diseases has gradually increased, and their potential therapeutic roles will be further explored. This review presents a summary of the involvement and the role played by MDSCs in liver diseases, thus identifying their potential targets for the treatment of liver diseases and providing new directions for liver disease-related research.

Small Molecule Targeting Immune Cells: A Novel Approach for Cancer Treatment

Conventional and cancer immunotherapies encompass diverse strategies to address various cancer types and stages. However, combining these approaches often encounters limitations such as non-specific targeting, resistance development, and high toxicity, leading to suboptimal outcomes in many cancers. The tumor microenvironment (TME) is orchestrated by intricate interactions between immune and non-immune cells dictating tumor progression. An innovative avenue in cancer therapy involves leveraging small molecules to influence a spectrum of resistant cell populations within the TME. Recent discoveries have unveiled a phenotypically diverse cohort of innate-like T (ILT) cells and tumor hybrid cells (HCs) exhibiting novel characteristics, including augmented proliferation, migration, resistance to exhaustion, evasion of immunosurveillance, reduced apoptosis, drug resistance, and heightened metastasis frequency. Leveraging small-molecule immunomodulators to target these immune players presents an exciting frontier in developing novel tumor immunotherapies. Moreover, combining small molecule modulators with immunotherapy can synergistically enhance the inhibitory impact on tumor progression by empowering the immune system to meticulously fine-tune responses within the TME, bolstering its capacity to recognize and eliminate cancer cells. This review outlines strategies involving small molecules that modify immune cells within the TME, potentially revolutionizing therapeutic interventions and enhancing the anti-tumor response.

The Tian-Men-Dong decoction suppresses the tumour-infiltrating G-MDSCs via IL-1β-mediated signalling in lung cancer

ETHNOPHARMACOLOGICAL RELEVANCE

The traditional Chinese medicine (TCM) Tian-Men-Dong decoction (TD) has been able to effectively treat lung cancer in China for thousands of years. TD improves the quality of life in lung cancer patients by promoting nourishment of yin and reducing dryness, clearing the lung and removing toxins. Pharmacological studies show that TD contains active antitumour ingredients, but its underlying mechanism remains unknown.

AIM OF THE STUDY

This study aims at exploring potential mechanisms of TD in the treatment of lung cancer by regulating granulocytic-myeloid-derived suppressor cells (G-MDSCs).

MATERIALS AND METHODS

An orthotopic lung cancer mouse model was generated by intrapulmonary injection with LLC-luciferase cells in immunocompetent C57BL/6 mice or immunodeficient nude mice. TD/saline was orally administered once to the model mice daily for 4 weeks. Live imaging was conducted to monitor tumour growth. Immune profiles were detected by flow cytometry. H&E and ELISA were applied to test the cytotoxicity of the TD treatment. RT-qPCR and western blotting were performed to detect apoptosis-related proteins in G-MDSCs. A neutralizing antibody (anti-Ly6G) was utilized to exhaust the G-MDSCs via intraperitoneal injection. G-MDSCs were adoptively transferred from wild-type tumour-bearing mice. Immunofluorescence, TUNEL and Annexin V/PI staining were conducted to analyse apoptosis-related markers. A coculture assay of purified MDSCs and T cells labelled with CFSE was performed to test the immunosuppressive activity of MDSCs. The presence of TD/IL-1β/TD + IL-1β in purified G-MDSCs cocultured with the LLC system was used for ex vivo experiments to detect IL-1β-mediated apoptosis of G-MDSCs.

RESULTS

TD prolonged the survival of immune competent C57BL/6 mice in an orthotopic lung cancer model, but did not have the same effect in immunodeficient nude mice, indicating that its antitumour properties of TD are exerted by regulating immunity. TD induced G-MDSC apoptosis via the IL-1β-mediated NF-κB signalling cascade leading to effectively weaken the immunosuppressive activity of G-MDSCs and promote CD8⁺ T-cell infiltration, which was supported by both the depletion and adoptive transfer of G-MDSCs assays. In addition, TD also showed minimal cytotoxicity both in vivo and in vitro.

CONCLUSION

This study reveals for the first time that TD, a classic TCM prescription, is able to regulate G-MDSC activity and trigger its apoptosis via the IL-1β-mediated NF-κB signalling pathway, reshaping the tumour microenvironment and demonstrating antitumour effects. These findings provide a scientific foundation the clinical treatment of lung cancer with TD.

Hypoxia signaling in hepatocellular carcinoma: Challenges and therapeutic opportunities

Hepatocellular carcinoma (HCC) is one of the most common cancers with a relatively high cancer-related mortality. The uncontrolled proliferation of HCC consumes a significant amount of oxygen, causing the development of a hypoxic tumor microenvironment (TME). Hypoxia-inducible factors (HIFs), crucial regulators in the TME, activate several cancer hallmarks leading to the hepatocarcinogenesis of HCC and resistance to current therapeutics. As such, HIFs and their signaling pathways have been explored as potential therapeutic targets for the future management of HCC. This review discusses the current understanding of the structure and function of HIFs and their complex relationship with the various cancer hallmarks. To address tumor hypoxia, this review provides an insight into the various potential novel therapeutic agents for managing HCC, such as hypoxia-activated prodrugs, HIF inhibitors, nanomaterials, antisense oligonucleotides, and natural compounds, that target HIFs/hypoxic signaling pathways in HCC. Because of HCC's relatively high incidence and mortality rates in the past decades, greater efforts should be put in place to explore novel therapeutic approaches to improve the outcome for HCC patients.

Pegylated Liposomal Alendronate Biodistribution, Immune Modulation, and Tumor Growth Inhibition in a Murine Melanoma Model

While tumor-associated macrophages (TAM) have pro-tumoral activity, the ablation of macrophages in cancer may be undesirable since they also have anti-tumoral functions, including T cell priming and activation against tumor antigens. Alendronate is a potent amino-bisphosphonate that modulates the function of macrophages in vitro, with potential as an immunotherapy if its low systemic bioavailability can be addressed. We repurposed alendronate in a non-leaky and long-circulating liposomal carrier similar to that of the clinically approved pegylated liposomal doxorubicin to facilitate rapid clinical translation. Here, we tested liposomal alendronate (PLA) as an immunotherapeutic agent for cancer in comparison with a standard of care immunotherapy, a PD-1 immune checkpoint inhibitor. We showed that the PLA induced bone marrow-derived murine non-activated macrophages and M2-macrophages to polarize towards an M1-functionality, as evidenced by gene expression, cytokine secretion, and lipidomic profiles. Free alendronate had negligible effects, indicating that liposome encapsulation is necessary for the modulation of macrophage activity. In vivo, the PLA showed significant accumulation in tumor and tumor-draining lymph nodes, sites of tumor immunosuppression that are targets of immunotherapy. The PLA remodeled the tumor microenvironment towards a less immunosuppressive milieu, as indicated by a decrease in TAM and helper T cells, and inhibited the growth of established tumors in the B16-OVA melanoma model. The improved bioavailability and the beneficial effects of PLA on macrophages suggest its potential application as immunotherapy that could synergize with T-cell-targeted therapies and chemotherapies to induce immunogenic cell death. PLA warrants further clinical development, and these clinical trials should incorporate tumor and blood biomarkers or immunophenotyping studies to verify the anti-immunosuppressive effect of PLA in humans.

Mechanisms of tumor-associated macrophages affecting the progression of hepatocellular carcinoma

Tumor-associated macrophages (TAMs) are essential components of the immune cell stroma of hepatocellular carcinoma. TAMs originate from monocytic myeloid-derived suppressor cells, peripheral blood monocytes, and kupffer cells. The recruitment of monocytes to the HCC tumor microenvironment is facilitated by various factors, leading to their differentiation into TAMs with unique phenotypes. TAMs can directly activate or inhibit the nuclear factor-κB, interleukin-6/signal transducer and signal transducer and activator of transcription 3, Wnt/β-catenin, transforming growth factor-β1/bone morphogenetic protein, and extracellular signal-regulated kinase 1/2 signaling pathways in tumor cells and interact with other immune cells via producing cytokines and extracellular vesicles, thus affecting carcinoma cell proliferation, invasive and migratory, angiogenesis, liver fibrosis progression, and other processes to participate in different stages of tumor progression. In recent years, TAMs have received much attention as a prospective treatment target for HCC. This review describes the origin and characteristics of TAMs and their mechanism of action in the occurrence and development of HCC to offer a theoretical foundation for further clinical research of TAMs.

M1/M2 macrophages and their overlaps - myth or reality?

Macrophages represent heterogeneous cell population with important roles in defence mechanisms and in homoeostasis. Tissue macrophages from diverse anatomical locations adopt distinct activation states. M1 and M2 macrophages are two polarized forms of mononuclear phagocyte in vitro differentiation with distinct phenotypic patterns and functional properties, but in vivo, there is a wide range of different macrophage phenotypes in between depending on the microenvironment and natural signals they receive. In human infections, pathogens use different strategies to combat macrophages and these strategies include shaping the macrophage polarization towards one or another phenotype. Macrophages infiltrating the tumours can affect the patient's prognosis. M2 macrophages have been shown to promote tumour growth, while M1 macrophages provide both tumour-promoting and anti-tumour properties. In autoimmune diseases, both prolonged M1 activation, as well as altered M2 function can contribute to their onset and activity. In human atherosclerotic lesions, macrophages expressing both M1 and M2 profiles have been detected as one of the potential factors affecting occurrence of cardiovascular diseases. In allergic inflammation, T2 cytokines drive macrophage polarization towards M2 profiles, which promote airway inflammation and remodelling. M1 macrophages in transplantations seem to contribute to acute rejection, while M2 macrophages promote the fibrosis of the graft. The view of pro-inflammatory M1 macrophages and M2 macrophages suppressing inflammation seems to be an oversimplification because these cells exploit very high level of plasticity and represent a large scale of different immunophenotypes with overlapping properties. In this respect, it would be more precise to describe macrophages as M1-like and M2-like.

Regulatory role of exosomes in colorectal cancer progression and potential as biomarkers

Colorectal cancer (CRC) remains an enormous challenge to human health worldwide. Unfortunately, the mechanism underlying CRC progression is not well understood. Mounting evidence has confirmed that exosomes play a vital role in CRC progression, which has attracted extensive attention among researchers. In addition to acting as messengers between CRC cells, exosomes also participate in the CRC immunomodulatory process and reshape immune function. As stable message carriers and liquid biopsy option under development, exosomes are promising biomarkers in the diagnosis or treatment of CRC. In this review we have described and analyzed the biogenesis and release of exosomes and current research on the role of exosomes in immune regulation and metastasis of CRC. Moreover, we have discussed candidate exosomal molecules as potential biomarkers to diagnose CRC, predict CRC progression, or determine CRC chemoresistance, and described the significance of exosomes in the immunotherapy of CRC. This review provides insight to further understand the role of exosomes in CRC progression and identify valuable biomarkers that facilitate the clinical management of CRC patients.

MDSCs in breast cancer: an important enabler of tumor progression and an emerging therapeutic target

Women worldwide are more likely to develop breast cancer (BC) than any other type of cancer. The treatment of BC depends on the subtype and stage of the cancer, such as surgery, radiotherapy, chemotherapy, and immunotherapy. Although significant progress has been made in recent years, advanced or metastatic BC presents a poor prognosis, due to drug resistance and recurrences. During embryonic development, myeloid-derived suppressor cells (MDSCs) develop that suppress the immune system. By inhibiting anti-immune effects and promoting non-immune mechanisms such as tumor cell stemness, epithelial-mesenchymal transformation (EMT) and angiogenesis, MDSCs effectively promote tumor growth and metastasis. In various BC models, peripheral tissues, and tumor microenvironments (TME), MDSCs have been found to amplification. Clinical progression or poor prognosis are strongly associated with increased MDSCs. In this review, we describe the activation, recruitment, and differentiation of MDSCs production in BC, the involvement of MDSCs in BC progression, and the clinical characteristics of MDSCs as a potential BC therapy target.

Mechanisms of Altered Immune Response in Skin Melanoma

Melanoma, a deadly form of skin cancer, poses significant challenges to the host immune system, allowing tumor cells to evade immune surveillance and persist. This complex interplay between melanoma and the immune system involves a multitude of mechanisms that impair immune recognition and promote tumor progression. This review summarizes the intricate strategies employed by melanoma cells to evade the immune response, including defective immune recognition, immune checkpoint activation, and the role of regulatory T-cells, myeloid-derived suppressor cells, and exosomes in suppressing anti-tumor immunity. Additionally, we discuss potential therapeutic targets aimed at reversing immune evasion in melanoma, highlighting the importance of understanding these mechanisms for developing more effective immunotherapies. Improved insights into the interactions between melanoma and the immune system will aid in the development of novel treatment strategies to enhance anti-tumor immune responses and improve patient outcomes.

Decreased melanoma CSF-1 secretion by Cannabigerol treatment reprograms regulatory myeloid cells and reduces tumor progression

During solid tumor progression, the tumor microenvironment (TME) evolves into a highly immunosuppressive milieu. Key players in the immunosuppressive environment are regulatory myeloid cells, including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs), which are recruited and activated via tumor-secreted cytokines such as colony-stimulating factor 1 (CSF-1). Therefore, the depletion of tumor-secreted cytokines is a leading anticancer strategy. Here, we found that CSF-1 secretion by melanoma cells is decreased following treatment with Cannabis extracts. Cannabigerol (CBG) was identified as the bioactive cannabinoid responsible for the effects. Conditioned media from cells treated with pure CBG or the high-CBG extract reduced the expansion and macrophage transition of the monocytic-MDSC subpopulation. Treated MO-MDSCs also expressed lower levels of iNOS, leading to restored CD8+ T-cell activation. Tumor-bearing mice treated with CBG presented reduced tumor progression, lower TAM frequencies and reduced TAM/M1 ratio. A combination of CBG and αPD-L1 was more effective in reducing tumor progression, enhancing survival and increasing the infiltration of activated cytotoxic T-cells than each treatment separately. We show a novel mechanism for CBG in modulating the TME and enhancing immune checkpoint blockade therapy, underlining its promising therapeutic potential for the treatment of a variety of tumors with elevated CSF-1 expression.

The role of myeloid-derived suppressor cells in liver cancer

MDSCs are immature myeloid immune cells, which accumulate in models of liver cancer to reduce effector immune cell activity, contribute to immune escape and treatment resistance. The accumulation of MDSCs suppresses the role of CTL and the killing effects of NK cells, induces the accumulation of Treg cells, and blocks the antigen presentation of DCs, thus promoting the progression of liver cancer. Recently, immunotherapy has emerged a valuable approach following chemoradiotherapy in the therapy of advanced liver cancer. A considerable increasing of researches had proved that targeting MDSCs has become one of the therapeutic targets to enhance tumor immunity. In preclinical study models, targeting MDSCs have shown encouraging results in both alone and in combination administration. In this paper, we elaborated immune microenvironment of the liver, function and regulatory mechanisms of MDSCs, and therapeutic approaches to target MDSCs. We also expect these strategies to supply new views for future immunotherapy for the treatment of liver cancer.

Cancer immune exclusion: breaking the barricade for a successful immunotherapy

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

A Reconstructed Human Melanoma-in-Skin Model to Study Immune Modulatory and Angiogenic Mechanisms Facilitating Initial Melanoma Growth and Invasion

Invasion, immune modulation, and angiogenesis are crucial in melanoma progression. Studies based on animals or two-dimensional cultures poorly recapitulate the tumor-microenvironmental cross-talk found in humans. This highlights a need for more physiological human models to better study melanoma features. Here, six melanoma cell lines (A375, COLO829, G361, MeWo, RPMI-7951, and SK-MEL-28) were used to generate an in vitro three-dimensional human melanoma-in-skin (Mel-RhS) model and were compared in terms of dermal invasion and immune modulatory and pro-angiogenic capabilities. A375 displayed the most invasive phenotype by clearly expanding into the dermal compartment, whereas COLO829, G361, MeWo, and SK-MEL-28 recapitulated to different extent the initial stages of melanoma invasion. No nest formation was observed for RPMI-7951. Notably, the integration of A375 and SK-MEL-28 cells into the model resulted in an increased secretion of immune modulatory factors (e.g., M-CSF, IL-10, and TGFβ) and pro-angiogenic factors (e.g., Flt-1 and VEGF). Mel-RhS-derived supernatants induced endothelial cell sprouting in vitro. In addition, observed A375-RhS tissue contraction was correlated to increased TGFβ release and α-SMA expression, all indicative of differentiation of fibroblasts into cancer-associated fibroblast-like cells and reminiscent of epithelial-to-mesenchymal transition, consistent with A375's most prominent invasive behavior. In conclusion, we successfully generated several Mel-RhS models mimicking different stages of melanoma progression, which can be further tailored for future studies to investigate individual aspects of the disease and serve as three-dimensional models to assess efficacy of therapeutic strategies.

Spatial distribution of tumor-infiltrating T cells indicated immune response status under chemoradiotherapy plus PD-1 blockade in esophageal cancer

Background

The spatial distribution of tumor-infiltrating T cells and its dynamics during chemoradiotherapy combined with PD-1 blockade is little known in esophageal squamous cell carcinoma (ESCC).

Methods

We applied the multiplex immunofluorescence method to identify T cells (CD4⁺, CD8⁺ T cells, and their PD-1^- or PD-1⁺ subsets) and myeloid-derived cells (CD11c⁺ dendritic cells, CD68⁺ macrophages, and their PD-L1⁺ subpopulations) in paired tumor biopsies (n = 36) collected at baseline and during combination (40 Gy of radiation) from a phase Ib trial (NCT03671265) of ESCC patients treated with first-line chemoradiotherapy plus anti-PD-1 antibody camrelizumab. We used the FoundationOne CDx assay to evaluate tumor mutational burden (TMB) in baseline tumor biopsies (n = 14). We dynamically assessed the nearest distance and proximity of T-cell subsets to tumor cells under combination and estimated the association between T-cell spatial distribution and combination outcome, myeloid-derived subsets, TMB, and patient baseline characteristics.

Findings

We found that the tumor compartment had lower T-cell subsets than the stromal compartment but maintained a comparable level under combination. Both before and under combination, PD-1^- T cells were located closer than PD-1⁺ T cells to tumor cells; T cells, dendritic cells, and macrophages showed the highest accumulation in the 5-10-μm distance. Higher CD4⁺ T cells in the tumor compartment and a shorter nearest distance of T-cell subsets at baseline predicted poor OS. Higher baseline CD4⁺ T cells, dendritic cells, and macrophages were associated with worse OS in less than 10-μm distance to tumor cells, but related with better OS in the farther distance. Higher on-treatment PD-1-positive-expressed CD4⁺ and CD8⁺ T cells within the 100-μm distance to tumor cells predicted longer OS. T cells, dendritic cells, and macrophages showed a positive spatial correlation. Both high TMB and smoking history were associated with a closer location of T cells to tumor cells at baseline.

Conclusions

We firstly illustrated the T-cell spatial distribution in ESCC. Combining chemoradiotherapy with PD-1 blockade could improve the antitumor immune microenvironment, which benefits the treatment outcome. Further understanding the precision spatiality of tumor-infiltrating T cells would provide new evidence for the tumor immune microenvironment and for the combination treatment with immunotherapy.

Immunometabolic reprogramming, another cancer hallmark

Molecular carcinogenesis is a multistep process that involves acquired abnormalities in key biological processes. The complexity of cancer pathogenesis is best illustrated in the six hallmarks of the cancer: (1) the development of self-sufficient growth signals, (2) the emergence of clones that are resistant to apoptosis, (3) resistance to the antigrowth signals, (4) neo-angiogenesis, (5) the invasion of normal tissue or spread to the distant organs, and (6) limitless replicative potential. It also appears that non-resolving inflammation leads to the dysregulation of immune cell metabolism and subsequent cancer progression. The present article delineates immunometabolic reprogramming as a critical hallmark of cancer by linking chronic inflammation and immunosuppression to cancer growth and metastasis. We propose that targeting tumor immunometabolic reprogramming will lead to the design of novel immunotherapeutic approaches to cancer.

Current insights into the hepatic microenvironment and advances in immunotherapy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and shows high global incidence and mortality rates. The liver is an immune-tolerated organ with a specific immune microenvironment that causes traditional therapeutic approaches to HCC, such as chemotherapy, radiotherapy, and molecular targeted therapy, to have limited efficacy. The dramatic advances in immuno-oncology in the past few decades have modified the paradigm of cancer therapy, ushering in the era of immunotherapy. Currently, despite the rapid integration of cancer immunotherapy into clinical practice, some patients still show no response to treatment. Therefore, a rational approach is to target the tumor microenvironment when developing the next generation of immunotherapy. This review aims to provide insights into the hepatic immune microenvironment in HCC and summarize the mechanisms of action and clinical usage of immunotherapeutic options for HCC, including immune checkpoint blockade, adoptive therapy, cytokine therapy, vaccine therapy, and oncolytic virus-based therapy.