Myeloid-Derived Suppressor Cells: Implications in the Resistance of Malignant Tumors to T Cell-Based Immunotherapy

Recent Findings on Therapeutic Cancer Vaccines: An Updated Review

Cancer remains one of the global leading causes of death and various vaccines have been developed over the years against it, including cell-based, nucleic acid-based, and viral-based cancer vaccines. Although many vaccines have been effective in in vivo and clinical studies and some have been FDA-approved, there are major limitations to overcome: (1) developing one universal vaccine for a specific cancer is difficult, as tumors with different antigens are different for different individuals, (2) the tumor antigens may be similar to the body's own antigens, and (3) there is the possibility of cancer recurrence. Therefore, developing personalized cancer vaccines with the ability to distinguish between the tumor and the body's antigens is indispensable. This paper provides a comprehensive review of different types of cancer vaccines and highlights important factors necessary for developing efficient cancer vaccines. Moreover, the application of other technologies in cancer therapy is discussed. Finally, several insights and conclusions are presented, such as the possibility of using cold plasma and cancer stem cells in developing future cancer vaccines, to tackle the major limitations in the cancer vaccine developmental process.

Myeloid-derived suppressor cells in cancer and cancer therapy

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

Current status and future of cancer vaccines: A bibliographic study

Background

Cancer vaccines are an important component of tumour immunotherapy. An increasing number of studies have shown that cancer vaccines have considerable clinical benefits. With the development of tumour precision medicine, cancer vaccines have become important because of their individualised targeting effects. However, few bibliometric studies have conducted comprehensive systematic reviews in this field. This study aimed to assess the scientific output and trends in cancer vaccine research from a global perspective.

Methods

We collected publications on cancer vaccines from the Web of Science Core Collection database, which was limited to articles and reviews in English. Microsoft Excel, VOS Viewer, and CiteSpace V were used for quantitative and visual analyses.

Results

A total of 7807 articles were included. From 1991 to 2022, the number of publications increased annually. The United States had the highest number of articles published in this field (48.28 %), the highest citation frequency (183,964 times), and the highest H-index (182). The National Institutes of Health topped the list with 476 articles. Schlom J had the highest number of published articles (128) and was the main investigator in this field. The journal, Cancer Immunology Immunotherapy, had published the highest number of articles in related fields. In recent years, tumour microenvironment, immune checkpoint inhibitors, particle vaccines, tumour antigens, and dendritic cells have become research hotspots related to cancer vaccines.

Conclusion

Cancer vaccines are a popular research topic in the field of tumour immunotherapy. Related research and publications will enter a boom stage. "Immune checkpoint inhibitors", "tumour microenvironment" and "dendritic cells" may become future research hotspots, while "T-cell suppressor" is a potential puzzle to be solved.

Navigating the Immune Maze: Pioneering Strategies for Unshackling Cancer Immunotherapy Resistance

Cancer immunotherapy has ushered in a transformative era in oncology, offering unprecedented promise and opportunities. Despite its remarkable breakthroughs, the field continues to grapple with the persistent challenge of treatment resistance. This resistance not only undermines the widespread efficacy of these pioneering treatments, but also underscores the pressing need for further research. Our exploration into the intricate realm of cancer immunotherapy resistance reveals various mechanisms at play, from primary and secondary resistance to the significant impact of genetic and epigenetic factors, as well as the crucial role of the tumor microenvironment (TME). Furthermore, we stress the importance of devising innovative strategies to counteract this resistance, such as employing combination therapies, tailoring immune checkpoints, and implementing real-time monitoring. By championing these state-of-the-art methods, we anticipate a paradigm that blends personalized healthcare with improved treatment options and is firmly committed to patient welfare. Through a comprehensive and multifaceted approach, we strive to tackle the challenges of resistance, aspiring to elevate cancer immunotherapy as a beacon of hope for patients around the world.

Understanding immune checkpoints and PD-1/PD-L1-mediated immune resistance towards tumour immunotherapy

Immunotherapy has emerged as a transformative approach in the treatment of various cancers, offering new hope for patients previously faced with limited treatment options. A cornerstone of cancer immunotherapy lies in targeting immune checkpoints, particularly the programmed cell death protein-1 (PD-1) and programmed death-ligand 1 (PD-L1) pathway. Immune checkpoints serve as crucial regulators of the immune response, preventing excessive immune activity and maintaining self-tolerance. PD-1, expressed on the surface of T cells, and its ligand PD-L1, expressed on various cell types, including cancer cells and immune cells, play a central role in this regulatory process. Although the success rate associated with these immunotherapies is very promising, most patients still show intrinsic or acquired resistance. Since the mechanisms related to PD-1/PD-L1 resistance are not well understood, an in-depth analysis is necessary to improve the success rate of anti-PD-1/PD-L1 therapy. Hence, here we provide an overview of PD-1, its ligand PD-L1, and the resistance mechanism towards PD-1/PD-L1. Furthermore, we have discussed the plausible solution to increase efficacy and clinical response. For the following research, joint endeavours of clinicians and basic scientists are essential to address the limitation of resistance towards immunotherapy.

Metabolism Shapes Immune Responses to Staphylococcus aureus

BACKGROUND

Staphylococcus aureus (S. aureus) is a common cause of hospital- and community-acquired infections that can result in various clinical manifestations ranging from mild to severe disease. The bacterium utilizes different combinations of virulence factors and biofilm formation to establish a successful infection, and the emergence of methicillin- and vancomycin-resistant strains introduces additional challenges for infection management and treatment.

SUMMARY

Metabolic programming of immune cells regulates the balance of energy requirements for activation and dictates pro- versus anti-inflammatory function. Recent investigations into metabolic adaptations of leukocytes and S. aureus during infection indicate that metabolic crosstalk plays a crucial role in pathogenesis. Furthermore, S. aureus can modify its metabolic profile to fit an array of niches for commensal or invasive growth.

KEY MESSAGES

Here we focus on the current understanding of immunometabolism during S. aureus infection and explore how metabolic crosstalk between the host and S. aureus influences disease outcome. We also discuss how key metabolic pathways influence leukocyte responses to other bacterial pathogens when information for S. aureus is not available. A better understanding of how S. aureus and leukocytes adapt their metabolic profiles in distinct tissue niches may reveal novel therapeutic targets to prevent or control invasive infections.

Stemness genes and miR-1247-3p expression associate with clinicopathological parameters and prognosis in lung adenocarcinoma

Lung cancer makes up one-fourth of all cancer-related mortality with the highest mortality rate among all cancers. Despite recent scientific advancements in cancer therapeutics, the 5-year survival rate of lung adenocarcinoma (LUAD) cancer patients remains below 15 percent. It has been suggested that the high mortality rate of LUAD is linked to the acquisition of progenitor-like cells with stem-like characteristics that assist the whole tumor in regulating immune cell infiltration. To examine this hypothesis further, this study mined several databases to explore the presence of stemness-related genes and miRNAs in LUAD cancers. We examine their association with immune and accessory cell infiltration rates and patient survival. We found 3 stem cell-related genes, ORC1L, KIF20A, and DLGAP5, present in LUAD that also correlate with changes in immune infiltration rates and reduced patient survival rates. Additionally, the modulation in myeloid-derived suppressor cell (MDSC) infiltration and miRNA hsa-mir-1247-3p mediated targeting of tumor suppressor SLC24A4 and oncogenes RAB3B and HJURP appears to primarily regulate LUAD patient survival. Given these findings, hsa-mir-1247-3p and/or its associated gene targets may offer a promising avenue to enhance patient survivability.

Trained immunity: Target for prophylaxis and therapy

Trained immunity is a de facto memory for innate immune responses, leading to long-term functional reprogramming of innate immune cells. In physiological conditions, trained immunity leads to adaptive states that enhance resistance against pathogens and contributes to immunosurveillance. Dysregulated trained immunity can however lead either to defective innate immune responses in severe infections or cancer or to inflammatory and autoimmune diseases if trained immunity is inappropriately activated. Here, we review the immunological and molecular mechanisms that mediate trained immunity induction and propose that trained immunity represents an important target for prophylactic and therapeutic approaches in human diseases. On the one hand, we argue that novel approaches that induce trained immunity may enhance vaccine efficacy. On the other hand, induction of trained immunity in cancer, and inhibition of exaggerated induction of trained immunity in inflammatory disorders, are viable targets amenable for new therapeutic approaches.

Advances in adoptive T-cell therapy for metastatic melanoma

Adoptive T cell therapy (ACT) is a fast developing, niche area of immunotherapy (IO), which is revolutionising the therapeutic landscape of solid tumour oncology, especially metastatic melanoma (MM). Identifying tumour antigens (TAs) as potential targets, the ACT response is mediated by either Tumour Infiltrating Lymphocytes (TILs) or genetically modified T cells with specific receptors - T cell receptors (TCRs) or chimeric antigen receptors (CARs) or more prospectively, natural killer (NK) cells. Clinical trials involving ACT in MM from 2006 to present have shown promising results. Yet it is not without its drawbacks which include significant auto-immune toxicity and need for pre-conditioning lymphodepletion. Although immune-modulation is underway using various combination therapies in the hope of enhancing efficacy and reducing toxicity. Our review article explores the role of ACT in MM, including the various modalities - their safety, efficacy, risks and their development in the trial and the real world setting.

Immunosuppressive cells in oncolytic virotherapy for glioma: challenges and solutions

Glioblastoma is a highly aggressive form of brain cancer characterized by the abundance of myeloid lineage cells in the tumor microenvironment. Tumor-associated macrophages and microglia (TAM) and myeloid-derived suppressor cells (MDSCs), play a pivotal role in promoting immune suppression and tumor progression. Oncolytic viruses (OVs) are self-amplifying cytotoxic agents that can stimulate local anti-tumor immune responses and have the potential to suppress immunosuppressive myeloid cells and recruit tumor-infiltrating T lymphocytes (TILs) to the tumor site, leading to an adaptive immune response against tumors. However, the impact of OV therapy on the tumor-resident myeloid population and the subsequent immune responses are not yet fully understood. This review provides an overview of how TAM and MDSC respond to different types of OVs, and combination therapeutics that target the myeloid population to promote anti-tumor immune responses in the glioma microenvironment.

Revising the Landscape of Cytokine-Induced Killer Cell Therapy in Lung Cancer: Focus on Immune Checkpoint Inhibitors

Undeniably, immunotherapy has markedly improved the survival rate of cancer patients. The scenario is no different in lung cancer, where multiple treatment options are now available and the inclusion of immunotherapy yields better clinical benefits than previously used chemotherapeutic strategies. Of interest, cytokine-induced killer (CIK) cell immunotherapy has also taken a central role in clinical trials for the treatment of lung cancer. Herein, we describe the relative success of CIK cell therapy (alone and combined with dendritic cells as DC/CIKs) in lung cancer clinical trials and discuss its combination with known immune checkpoint inhibitors (anti-CTLA-4 and anti-PD-1/PD-L1). Additionally, we provide insights into the findings of several preclinical in vitro/in vivo studies linked to lung cancer. In our opinion, CIK cell therapy, which recently completed 30 years and has been approved in many countries, including Germany, offers tremendous potential for lung cancer. Foremost, when it is optimized on a patient-by-patient basis with special attention to the patient-specific genomic signature.

The Hippo signalling pathway and its implications in human health and diseases

As an evolutionarily conserved signalling network, the Hippo pathway plays a crucial role in the regulation of numerous biological processes. Thus, substantial efforts have been made to understand the upstream signals that influence the activity of the Hippo pathway, as well as its physiological functions, such as cell proliferation and differentiation, organ growth, embryogenesis, and tissue regeneration/wound healing. However, dysregulation of the Hippo pathway can cause a variety of diseases, including cancer, eye diseases, cardiac diseases, pulmonary diseases, renal diseases, hepatic diseases, and immune dysfunction. Therefore, therapeutic strategies that target dysregulated Hippo components might be promising approaches for the treatment of a wide spectrum of diseases. Here, we review the key components and upstream signals of the Hippo pathway, as well as the critical physiological functions controlled by the Hippo pathway. Additionally, diseases associated with alterations in the Hippo pathway and potential therapies targeting Hippo components will be discussed.

Myeloid-derived suppressor cells and vaccination against pathogens

It is widely accepted that the immune system includes molecular and cellular components that play a role in regulating and suppressing the effector immune response in almost any process in which the immune system is involved. Myeloid-derived suppressor cells (MDSCs) are described as a heterogeneous population of myeloid origin, immature state, with a strong capacity to suppress T cells and other immune populations. Although the initial characterization of these cells was strongly associated with pathological conditions such as cancer and then with chronic and acute infections, extensive evidence supports that MDSCs are also involved in physiological/non-pathological settings, including pregnancy, neonatal period, aging, and vaccination. Vaccination is one of the greatest public health achievements and has reduced mortality and morbidity caused by many pathogens. The primary goal of prophylactic vaccination is to induce protection against a potential pathogen by mimicking, at least in a part, the events that take place during its natural interaction with the host. This strategy allows the immune system to prepare humoral and cellular effector components to cope with the real infection. This approach has been successful in developing vaccines against many pathogens. However, when the infectious agents can evade and subvert the host immune system, inducing cells with regulatory/suppressive capacity, the development of vaccines may not be straightforward. Notably, there is a long list of complex pathogens that can expand MDSCs, for which a vaccine is still not available. Moreover, vaccination against numerous bacteria, viruses, parasites, and fungi has also been shown to cause MDSC expansion. Increases are not due to a particular adjuvant or immunization route; indeed, numerous adjuvants and immunization routes have been reported to cause an accumulation of this immunosuppressive population. Most of the reports describe that, according to their suppressive nature, MDSCs may limit vaccine efficacy. Taking into account the accumulated evidence supporting the involvement of MDSCs in vaccination, this review aims to compile the studies that highlight the role of MDSCs during the assessment of vaccines against pathogens.

Bojungikki-Tang Enhances the Effect of PD-1 Blockade in a Syngeneic Murine Model of Lung Carcinoma

Although immunotherapy has become the standard of treatment for non-small cell lung cancer (NSCLC), only a limited number of patients benefit from it clinically because of the resistance to immunotherapeutic agents. Of late, the usefulness of herbal medicines in combination with immunotherapy has been investigated. Bojungikki-Tang (BJIKT) is a widely used traditional herbal medicine. It synergistically enhances the antitumor effects of chemotherapy and regulates the immune responses in cancer, but its antitumor effect with immunotherapy in NSCLC is unclear. In this study, we investigated the combined effects of BJIKT and an anti-PD-1 antibody in a KLN205-DBA/2 syngeneic lung cancer model. Immunohistochemistry and flow cytometry analyses were performed to analyze the changes in immune cells in the tumor microenvironment. BJIKT plus an anti-PD-1 antibody treatment significantly inhibited tumor growth, unlike the respective monotherapies. Compared to monotherapy, the combination treatment resulted in a higher population of CD8+ cytotoxic T cells and a lower number of Ki67+ cells in the tumor tissues. Furthermore, the combination treatment decreased the proportion of myeloid-derived suppressor cells but increased the proportion of M1-like macrophages compared to that observed with monotherapy. Cytokine analysis showed that the combination treatment increased the levels of T helper type 1-related cytokines. Network pharmacology analysis revealed that BJIKT might regulate multiple signaling pathways related to immune function and tumor progression in NSCLC. These findings indicate that the combination treatment with BJIKT and an anti-PD-1 antibody effectively suppresses tumor growth by regulating immune function and may be an alternative therapeutic option for the treatment of NSCLC.

Entinostat Decreases Immune Suppression to Promote Antitumor Responses in a HER2+ Breast Tumor Microenvironment

Therapeutic combinations to alter immunosuppressive, solid tumor microenvironments (TME), such as in breast cancer, are essential to improve responses to immune checkpoint inhibitors (ICI). Entinostat, an oral histone deacetylase inhibitor, has been shown to improve responses to ICIs in various tumor models with immunosuppressive TMEs. The precise and comprehensive alterations to the TME induced by entinostat remain unknown. Here, we employed single-cell RNA sequencing on HER2-overexpressing breast tumors from mice treated with entinostat and ICIs to fully characterize changes across multiple cell types within the TME. This analysis demonstrates that treatment with entinostat induced a shift from a protumor to an antitumor TME signature, characterized predominantly by changes in myeloid cells. We confirmed myeloid-derived suppressor cells (MDSC) within entinostat-treated tumors associated with a less suppressive granulocytic (G)-MDSC phenotype and exhibited altered suppressive signaling that involved the NFκB and STAT3 pathways. In addition to MDSCs, tumor-associated macrophages were epigenetically reprogrammed from a protumor M2-like phenotype toward an antitumor M1-like phenotype, which may be contributing to a more sensitized TME. Overall, our in-depth analysis suggests that entinostat-induced changes on multiple myeloid cell types reduce immunosuppression and increase antitumor responses, which, in turn, improve sensitivity to ICIs. Sensitization of the TME by entinostat could ultimately broaden the population of patients with breast cancer who could benefit from ICIs.

Fibronectin-Coated Metal-Phenolic Networks for Cooperative Tumor Chemo-/Chemodynamic/Immune Therapy via Enhanced Ferroptosis-Mediated Immunogenic Cell Death

The development of nanomedicine formulations to overcome the disadvantages of traditional chemotherapeutic drugs and integrate cooperative theranostic modes still remains challenging. Herein, we report the facile construction of a multifunctional theranostic nanoplatform based on doxorubicin (DOX)-loaded tannic acid (TA)-iron (Fe) networks (for short, TAF) coated with fibronectin (FN) for combination tumor chemo-/chemodynamic/immune therapy under the guidance of magnetic resonance (MR) imaging. We show that the DOX-TAF@FN nanocomplexes created through in situ coordination of TA and Fe(III) and physical coating with FN have a mean particle size of 45.0 nm, are stable, and can release both DOX and Fe in a pH-dependent manner. Due to the coexistence of the TAF network and DOX, significant immunogenic cell death can be caused through enhanced ferroptosis of cancer cells via cooperative Fe-based chemodynamic therapy and DOX chemotherapy. Through further treatment with programmed cell death ligand 1 antibody for an immune checkpoint blockade, the tumor treatment efficacy and the associated immune response can be further enhanced. Meanwhile, with FN-mediated targeting, the DOX-TAF@FN platform can specifically target tumor cells with high expression of α_vβ₃ integrin. Finally, the TAF network also enables the DOX-TAF@FN to have an r₁ relaxivity of 6.1 mM^-1 s^-1 for T₁-weighted MR imaging of tumors. The developed DOX-TAF@FN nanocomplexes may represent an updated multifunctional nanosystem with simple compositions for cooperative MR imaging-guided targeted chemo-/chemodynamic/immune therapy of tumors.

Targeting myeloid-derived suppressor cells to attenuate vasculogenic mimicry and synergistically enhance the anti-tumor effect of PD-1 inhibitor

Myeloid-derived suppressor cells (MDSCs) enhance the proliferation of endothelial cells to stimulate angiogenesis. However, many aggressive malignant tumors do not have endothelial cell-dependent blood vessels in the early stage and instead generate microcirculation by forming vasculogenic mimicry (VM). To date, the relationship between MDSCs and tumor cells remains the focus of ongoing studies. In this work, MDSCs were co-cultured with mouse melanoma cells and can enhance proliferation and VM formation of melanoma cells. For MDSCs targeting, doxycycline (DOX) was found to selectively suppress PMN-MDSCs but has no influence on T cells. In addition, DOX pretreatment substantially reduced the promoting ability of MDSCs for the VM formation of B16-F10 cells. DOX also inhibited tumor growth and enhanced the antitumor activity of PD-1 inhibitors in C57BL6 and BALB/c mice subcutaneously inoculated with B16-F10 and 4T1 cells, respectively. In conclusion, the combination of DOX and PD-1 inhibitor could be an anticancer strategy.

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MDSCs accumulated in the B16-F10 tumor-bearing mice

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MDSCs promote the formation of vasculogenic mimicry

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Doxycycline selectively suppressed PMN-MDSCs

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Doxycycline combined with PD-1 inhibitor significantly inhibited tumor growth