Subsets, expansion and activation of myeloid-derived suppressor cells

Recruitment of Polymorphonuclear Myeloid-Derived Suppressor Cells During Cryptococcus neoformans Infection

Cryptococcosis is a disease originating in the lungs, often seen in immunosuppressed patients. In severe cases, it can lead to meningoencephalitis and can be fatal. Biochemical studies have shown that the capsule of Cryptococcus neoformans is predominantly composed of glucuronoxylomannan (GXM), with glucuronoxylomannogalactan (GXMGal) present in smaller amounts. These polysaccharides have different effects on the immune system, with GXM mainly having anti-inflammatory properties, while GXMGal is more pro-inflammatory. Myeloid-derived suppressor cells (MDSCs) are a diverse group of immature myeloid cells, including progenitor cells and precursors of macrophages, granulocytes, and dendritic cells at different stages of development. MDSCs are known to suppress immune responses in various diseases, including bacterial and fungal infections, through mechanisms such as the inhibition of T cell proliferation. In this study, we show that infection with either B3501 or CAP67 strains results in the accumulation of granulocytic MDSC precursors in bronchoalveolar cavities. The MDSCs recruited by the B3501 strain suppress T cell proliferation, while those recruited by the CAP67 strain do not. Furthermore, we observed the expression of PD-L1 on these MDSCs, suggesting a potential mechanism of immunosuppression during infection. These findings reveal how the polysaccharides of C. neoformans might weaken the host's immune defense.

The impact of cytokines and tumour-conditioned medium on the properties of murine in vitro generated myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of immature myeloid cells playing a critical role in immune suppression. In vitro-generated MDSCs are a convenient tool to study the properties of tumour-associated MDSCs. Here, we compared six protocols for in vitro generation of functional mouse MDSCs from bone marrow progenitors. The protocols included granulocyte-macrophage colony-stimulating factor (GM-CSF) alone or in combination with interleukin-6 (IL-6) or granulocyte colony-stimulating factor (G-CSF), with or without a tumour-conditioned medium (TCM) derived from B16-F10 melanoma. Obtained MDSCs were characterized by morphology, phenotype, gene expression of key immunosuppressive factors, and in vitro suppression of T cell proliferation. All tested protocols yielded approximately 25% monocytic and 50% polymorphonuclear MDSCs. Protocols using IL-6 generated MDSCs with reduced maturation and differentiation status, upregulated Arg1 and Nos1 mRNA expression, increased levels of Arg-1 and TGF-β proteins and enhanced ROS production compared to the other protocols. All tested protocols yielded MDSCs that efficiently inhibited T cell proliferation in vitro, with some advantage for the GM-CSF and G-CSF + GM-CSF protocols. Interestingly, a combination of protocols with B16-F10-derived TCM resulted in the generation of MDSCs with reduced immunosuppressive properties. Our results provide valuable insights into the optimal conditions for in vitro generation of MDSCs with specific immunosuppressive properties.

Dual roles of myeloid-derived suppressor cells in various diseases: a review

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that originate from bone marrow stem cells. In pathological conditions, such as autoimmune disorders, allergies, infections, and cancer, normal myelopoiesis is altered to facilitate the formation of MDSCs. MDSCs were first shown to promote cancer initiation and progression by immunosuppression with the assistance of various chemokines and cytokines. Recently, various studies have demonstrated that MDSCs play two distinct roles depending on the physiological and pathological conditions. MDSCs have protective roles in autoimmune disorders (such as uveoretinitis, multiple sclerosis, rheumatoid arthritis, ankylosing spondylitis, type 1 diabetes, autoimmune hepatitis, inflammatory bowel disease, alopecia areata, and systemic lupus erythematosus), allergies, and organ transplantation. However, they play negative roles in infections and various cancers. Several immunosuppressive functions and mechanisms of MDSCs have been determined in different disease conditions. This review comprehensively discusses the associations between MDSCs and various pathological conditions and briefly describes therapeutic approaches.

The diverse effects of cisplatin on tumor microenvironment: Insights and challenges for the delivery of cisplatin by nanoparticles

Cisplatin is a well-known platinum-based chemotherapy medication that is widely utilized for some malignancies. Despite the direct cytotoxic consequences of cisplatin on tumor cells, studies in the recent decade have revealed that cisplatin can also affect different cells and their secretions in the tumor microenvironment (TME). Cisplatin has complex impacts on the TME, which may contribute to its anti-tumor activity or drug resistance mechanisms. These regulatory effects of cisplatin play a paramount function in tumor growth, invasion, and metastasis. This paper aims to review the diverse impacts of cisplatin and nanoparticles loaded with cisplatin on cancer cells and also non-cancerous cells in TME. The impacts of cisplatin on immune cells, tumor stroma, cancer cells, and also hypoxia will be discussed in the current review. Furthermore, we emphasize the challenges and prospects of using cisplatin in combination with other adjuvants and therapeutic modalities that target TME. We also discuss the potential synergistic effects of cisplatin with immune checkpoint inhibitors (ICIs) and other agents with anticancer potentials such as polyphenols and photosensitizers. Furthermore, the potential of nanoparticles for targeting TME and better delivery of cisplatin into tumors will be discussed.

Fully functional monocytic MDSC generation from the murine HoxB8 cell line

Myeloid-derived suppressor cells (MDSC) play a crucial role in controlling T-cell responses, but their development and suppressor mechanisms are not fully understood. To study the molecular functions of MDSC, a large number of standardized cells are required. Traditionally, bone marrow (BM) has been used to generate myeloid cell types, including MDSC. In this study, we demonstrate that a previously described protocol for generating monocytic MDSC (M-MDSC) from murine BM with GM-CSF can be fully transferred to BM cells that are conditionally transformed with HoxB8 gene (HoxB8 cells). HoxB8 cells have an extended lifespan and efficiently differentiate into MDSC that are quantitatively and qualitatively comparable to M-MDSC from BM cells. Flow cytometric analyses of LPS/IFN-γ activated cultures revealed the same iNOS+ and/or Arg1+ PD-L1high M-MDSC subsets in similar frequencies from BM or HoxB8 cells. In vitro suppression of CD4+ and CD8+ T-cell proliferations was also largely comparable in their efficacy and its iNOS- or Arg1-dependent suppressor mechanisms, which was confirmed by the similar amounts of nitric oxide (NO) secretion measured from the suppressor assay. Therefore, our data suggest that murine M-MDSC generation from HoxB8 cells with GM-CSF can be used to substitute BM cultures.

Combining Cryo-Thermal Therapy with Anti-IL-6 Treatment Promoted the Maturation of MDSCs to Induce Long-Term Survival in a Mouse Model of Breast Cancer

Immunosuppression plays a significant role in tumor recurrence and metastasis, ultimately causing poor survival outcomes. Overcoming immunosuppression and stimulating durable antitumor immunity are essential for tumor treatment. In our previous study, a novel cryo-thermal therapy involving liquid nitrogen freezing and radiofrequency heating could reduce the proportion of Myeloid-derived suppressor cells (MDSCs), but the remaining MDSCs produced IL-6 by the NF-κB pathway, resulting in an impaired therapeutic effect. Therefore, here we combined cryo-thermal therapy with anti-IL-6 treatment to target the MDSC-dominant immunosuppressive environment, thereby optimizing the efficacy of cryo-thermal therapy. We found that combinational treatment significantly increased the long-term survival rate of breast cancer-bearing mice. Mechanistic investigation revealed that combination therapy was capable of reducing the proportion of MDSCs in the spleen and blood while promoting their maturation, which resulted in increased Th1-dominant CD4+ T-cell differentiation and enhancement of CD8+ T-mediated tumor killing. In addition, CD4+ Th1 cells promoted mature MDSCs to produce IL-7 through IFN-γ, indirectly contributing to the maintenance of Th1-dominant antitumor immunity in a positive feedback loop. Our work suggests an attractive immunotherapeutic strategy targeting the MDSC-dominant immunosuppressive environment, which would offer exciting opportunities for highly immunosuppressive and unresectable tumors in the clinic.

Managing the immune microenvironment of osteosarcoma: the outlook for osteosarcoma treatment

Osteosarcoma, with poor survival after metastasis, is considered the most common primary bone cancer in adolescents. Notwithstanding the efforts of researchers, its five-year survival rate has only shown limited improvement, suggesting that existing therapeutic strategies are insufficient to meet clinical needs. Notably, immunotherapy has shown certain advantages over traditional tumor treatments in inhibiting metastasis. Therefore, managing the immune microenvironment in osteosarcoma can provide novel and valuable insight into the multifaceted mechanisms underlying the heterogeneity and progression of the disease. Additionally, given the advances in nanomedicine, there exist many advanced nanoplatforms for enhanced osteosarcoma immunotherapy with satisfactory physiochemical characteristics. Here, we review the classification, characteristics, and functions of the key components of the immune microenvironment in osteosarcoma. This review also emphasizes the application, progress, and prospects of osteosarcoma immunotherapy and discusses several nanomedicine-based options to enhance the efficiency of osteosarcoma treatment. Furthermore, we examine the disadvantages of standard treatments and present future perspectives for osteosarcoma immunotherapy.

Peripheral expansion of myeloid-derived suppressor cells is related to disease activity and damage accrual in inflammatory myopathies

OBJECTIVE

To assess the proportion of myeloid-derived suppressor cells (MDSCs), their expression of arginase-1 and programmed cell death ligand 1 (PD-L1) and their relationship with the clinical phenotype of patients with idiopathic inflammatory myopathies (IIMs).

METHODS

We recruited 37 IIM adult patients and 10 healthy donors in Mexico City. We evaluated their clinical features, the proportion of MDSCs and their expression of PD-L1 and arginase-1 by flow cytometry. Polymorphonuclear (PMN)-MDSCs were defined as CD33dim, CD11b+ and CD66b+ while monocytic (M)-MDSCs were CD33+, CD11b+, HLA-DR- and CD14+. Serum cytokines were analysed with a multiplex assay. We compared the quantitative variables with the Kruskal-Wallis and Mann-Whitney U tests and assessed correlations with Spearman's ρ.

RESULTS

Most patients had dermatomyositis [n = 30 (81.0%)]. IIM patients had a peripheral expansion of PMN-MDSCs and M-MDSCs with an enhanced expression of arginase-1 and PD-L1. Patients with active disease had a decreased percentage {median 1.75% [interquartile range (IQR) 0.31-5.50 vs 10.71 [3.16-15.58], P = 0.011} of M-MDSCs and a higher absolute number of PD-L1+ M-MDSCs [median 23.21 cells/mm3 (IQR 11.16-148.9) vs 5.95 (4.66-102.7), P = 0.046] with increased expression of PD-L1 [median 3136 arbitrary units (IQR 2258-4992) vs 1961 (1885-2335), P = 0.038]. PD-L1 expression in PMN-MDSCs correlated with the visual analogue scale of pulmonary disease activity (r = 0.34, P = 0.040) and damage (r = 0.36, P = 0.031), serum IL-5 (r = 0.55, P = 0.003), IL-6 (r = 0.46, P = 0.003), IL-8 (r = 0.53, P = 0.018), IL-10 (r = 0.48, P = 0.005) and GM-CSF (r = 0.48, P = 0.012). M-MDSCs negatively correlated with the skeletal Myositis Intention to Treat Index (r = -0.34, P = 0.038) and positively with IL-6 (r = 0.40, P = 0.045).

CONCLUSION

MDSCs expressing arginase-1 and PD-L1 are expanded in IIM and correlate with disease activity, damage accrual and serum cytokines.

The emerging role of regulatory cell-based therapy in autoimmune disease

Autoimmune disease, caused by unwanted immune responses to self-antigens, affects millions of people each year and poses a great social and economic burden to individuals and communities. In the course of autoimmune disorders, including rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and multiple sclerosis, disturbances in the balance between the immune response against harmful agents and tolerance towards self-antigens lead to an immune response against self-tissues. In recent years, various regulatory immune cells have been identified. Disruptions in the quality, quantity, and function of these cells have been implicated in autoimmune disease development. Therefore, targeting or engineering these cells is a promising therapeutic for different autoimmune diseases. Regulatory T cells, regulatory B cells, regulatory dendritic cells, myeloid suppressor cells, and some subsets of innate lymphoid cells are arising as important players among this class of cells. Here, we review the roles of each suppressive cell type in the immune system during homeostasis and in the development of autoimmunity. Moreover, we discuss the current and future therapeutic potential of each one of these cell types for autoimmune diseases.

Myeloid-derived suppressor cell: A crucial player in autoimmune diseases

Myeloid-derived suppressor cells (MDSCs) are identified as a highly heterogeneous group of immature cells derived from bone marrow and play critical immunosuppressive functions in autoimmune diseases. Accumulating evidence indicates that the pathophysiology of autoimmune diseases was closely related to genetic mutations and epigenetic modifications, with the latter more common. Epigenetic modifications, which involve DNA methylation, covalent histone modification, and non-coding RNA-mediated regulation, refer to inheritable and potentially reversible changes in DNA and chromatin that regulate gene expression without altering the DNA sequence. Recently, numerous reports have shown that epigenetic modifications in MDSCs play important roles in the differentiation and development of MDSCs and their suppressive functions. The molecular mechanisms of differentiation and development of MDSCs and their regulatory roles in the initiation and progression of autoimmune diseases have been extensively studied, but the exact function of MDSCs remains controversial. Therefore, the biological and epigenetic regulation of MDSCs in autoimmune diseases still needs to be further characterized. This review provides a detailed summary of the current research on the regulatory roles of DNA methylation, histone modifications, and non-coding RNAs in the development and immunosuppressive activity of MDSCs, and further summarizes the distinct role of MDSCs in the pathogenesis of autoimmune diseases, in order to provide help for the diagnosis and treatment of diseases from the perspective of epigenetic regulation of MDSCs.

Selective depletion of polymorphonuclear myeloid derived suppressor cells in tumor beds with near infrared photoimmunotherapy enhances host immune response

The immune system is recognized as an important factor in regulating the development, progression, and metastasis of cancer. Myeloid-derived suppressor cells (MDSCs) are a major immune-suppressive cell type by interfering with T cell activation, promoting effector T cell apoptosis, and inducing regulatory T cell expansion. Consequently, reducing or eliminating MDSCs has become a goal of some systemic immunotherapies. However, by systemically reducing MDSCs, unwanted side effects can occur. Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed treatment that selectively kills targeted cells without damaging adjacent normal cells. The aim of this study is to evaluate the antitumor efficacy of MDSC-directed NIR-PIT utilizing anti-Ly6G antibodies to specifically destroy polymorphonuclear (PMN)-MDSCs in the tumor microenvironment (TME) in syngeneic mouse models. PMN-MDSCs were selectively eliminated within tumors by Ly6G-targeted NIR-PIT. There was significant tumor growth suppression and prolonged survival in three treated tumor models. In the early phase after NIR-PIT, dendritic cell maturation/activation and CD8⁺ T cell activation were enhanced in both intratumoral tissues and tumor-draining lymph nodes, and NK cells demonstrated increased expression of cytotoxic molecules. Host immunity remained activated in the TME for at least one week after NIR-PIT. Abscopal effects in bilateral tumor models were observed. Furthermore, the combination of NIR-PIT targeting cancer cells and PMN-MDSCs yielded synergistic effects and demonstrated highly activated host tumor immunity. In conclusion, we demonstrated that selective local PMN-MDSCs depletion by NIR-PIT could be a promising new cancer immunotherapy.

Myeloid derived suppressor cells and innate immune system interaction in tumor microenvironment

The tumor microenvironment is a complex domain that not only contains tumor cells but also a plethora of other host immune cells. By nature, the tumor microenvironment is a highly immunosuppressive milieu providing growing conditions for tumor cells. A major immune cell population that contributes most in the development of this immunosuppressive microenvironment is the MDSC, a heterogenous population of immature cells. Although found in small numbers only in the bone marrow of healthy individuals, they readily migrate to the lymph nodes and tumor site during cancer pathogenesis. MDSC mediated disruption of antitumor T cell activity is a major cause of the immunosuppression at the tumor site, but recent findings have shown that MDSC mediated dysfunction of other major immune cells might also play an important role. In this article we will review how crosstalk with MDSC alters the activity of both conventional and unconventional immune cells that inhibits the antitumor immunity and promotes cancer progression.

Differential immune landscapes in appendicular versus axial skeleton

Roughly 400,000 people in the U.S. are living with bone metastases, the vast majority occurring in the spine. Metastases to the spine result in fractures, pain, paralysis, and significant health care costs. This predilection for cancer to metastasize to the bone is seen across most cancer histologies, with the greatest incidence seen in prostate, breast, and lung cancer. The molecular process involved in this predilection for axial versus appendicular skeleton is not fully understood, although it is likely that a combination of tumor and local micro-environmental factors plays a role. Immune cells are an important constituent of the bone marrow microenvironment and many of these cells have been shown to play a significant role in tumor growth and progression in soft tissue and bone disease. With this in mind, we sought to examine the differences in immune landscape between axial and appendicular bones in the normal noncancerous setting in order to obtain an understanding of these landscapes. To accomplish this, we utilized mass cytometry by time-of-flight (CyTOF) to examine differences in the immune cell landscapes between the long bone and vertebral body bone marrow from patient clinical samples and C57BL/6J mice. We demonstrate significant differences between immune populations in both murine and human marrow with a predominance of myeloid progenitor cells in the spine. Additionally, cytokine analysis revealed differences in concentrations favoring a more myeloid enriched population of cells in the vertebral body bone marrow. These differences could have clinical implications with respect to the distribution and permissive growth of bone metastases.

Tumor-Mediated Neutrophil Polarization and Therapeutic Implications

Neutrophils are immune cells with reported phenotypic and functional plasticity. Tumor-associated neutrophils display many roles during cancer progression. Several tumor microenvironment (TME)-derived factors orchestrate neutrophil release from the bone marrow, recruitment and functional polarization, while simultaneously neutrophils are active stimulators of the TME by secreting factors that affect immune interactions and subsequently tumor progression. Successful immunotherapies for many cancer types and stages depend on the targeting of tumor-infiltrating lymphocytes. Neutrophils impact the success of immunotherapies, such as immune checkpoint blockade therapies, by displaying lymphocyte suppressive properties. The identification and characterization of distinct neutrophil subpopulations or polarization states with pro- and antitumor phenotypes and the identification of the major TME-derived factors of neutrophil polarization would allow us to harness the full potential of neutrophils as complementary targets in anticancer precision therapies.

Antibiotics in early life and childhood pre-B-ALL. Reasons to analyze a possible new piece in the puzzle

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer with precursor B-cell ALL (pB-ALL) accounting for ~ 85% of the cases. Childhood pB-ALL development is influenced by genetic susceptibility and host immune responses. The role of the intestinal microbiome in leukemogenesis is gaining increasing attention since Vicente-Dueñas' seminal work demonstrated that the gut microbiome is distinct in mice genetically predisposed to ALL and that the alteration of this microbiome by antibiotics is able to trigger pB-ALL in Pax5 heterozygous mice in the absence of infectious stimuli. In this review we provide an overview on novel insights on the role of the microbiome in normal and preleukemic hematopoiesis, inflammation, the effect of dysbiosis on hematopoietic stem cells and the emerging importance of the innate immune responses in the conversion from preleukemic to leukemic state in childhood ALL. Since antibiotics, which represent one of the most widely used medical interventions, alter the gut microbial composition and can cause a state of dysbiosis, this raises exciting epidemiological questions regarding the implications for antibiotic use in early life, especially in infants with a a preleukemic "first hit". Sheading light through a rigorous study on this piece of the puzzle may have broad implications for clinical practice.

Immunosuppressive effects and mechanisms of three myeloid-derived suppressor cells subsets including monocytic-myeloid-derived suppressor cells, granulocytic-myeloid-derived suppressor cells, and immature-myeloid-derived suppressor cells

Context

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immune cells of myeloid lineage. Recent reports have suggested that human MDSC are divided into three subsets: monocytic MDSC (M-MDSC), granulocytic MDSC (G-MDSC), and immature MDSC (I-MDSC). However, the characteristics of each human MDSC subset still remain unclear.

Materials and Methods

To evaluate the immunosuppressive effects and mechanisms, we first performed a T-cell suppression assay using cells obtained from healthy donor peripheral blood samples. The levels of immune inhibitory molecules in the culture supernatant of each MDSC subset were measured to reveal the T-cell suppressive mechanisms. Then, we compared these results with the results from cells obtained from cancer patient blood samples. Finally, we investigated the difference in the frequency of each MDSC subset between the healthy donors and the cancer patients.

Results

Although M-MDSC and G-MDSC suppressed T-cell activation, I-MDSC had no T-cell suppressive effect. We found that the culture supernatant of M-MDSC and G-MDSC contained high levels of interleukin-1 receptor antagonist (IL-1RA) and arginase, respectively, in both healthy donors and cancer patients. No inhibitory molecules were detected in the culture supernatant of I-MDSC. The population of functional MDSC (M-MDSC and G-MDSC) in the total MDSC was significantly increased in cancer patients compared with that in healthy donors.

Conclusions

Although M-MDSC and G-MDSC, which released IL-1RA and arginase, respectively, suppressed T-cell activation, I-MDSC did not have an immunosuppressive effect. The population of functional MDSC was increased in cancer patients compared with that in healthy donors.

MDSCs interactions with other immune cells and their role in maternal-fetal tolerance

MDSCs (myeloid-derived suppressor cells) are a population of immature and heterogeneous bone marrow cells with immunosuppressive functions, and they are mainly divided into two subgroups: granulocytic MDSCs (G-MDSCs) and monocytic MDSCs (M-MDSCs). Immunosuppression is the main and most important function of MDSCs, and they mainly exert an inhibitory effect through endoplasmic reticulum stress and some enzymes related to inhibitors, as well as some cytokines and other factors. In addition, MDSCs also interact with other immune cells, especially NK cells, DCs and Tregs, to participate in immune regulation. A large number of MDSCs are found during normal pregnancy. Combined with their immunosuppressive effects, these results suggest that MDSCs are likely to be closely related to maternal-fetal immune tolerance. This review mainly shows the interaction of MDSCs with other immune cells and the important role of MDSCs in maternal-fetal tolerance. The current research shows that MDSCs are mainly mediated by STAT3, HLA-G, CXCR2, Arg-1 and HIF1-α in immune regulation during pregnancy. Interpreting maternal-fetal tolerance from the perspective of MDSCs provides a special perspective for research on immune regulation and maternal-fetal tolerance of MDSCs to obtain a more comprehensive understanding of immune regulation and immune tolerance.

Natural Killer Cell Interactions With Myeloid Derived Suppressor Cells in the Tumor Microenvironment and Implications for Cancer Immunotherapy

The tumor microenvironment (TME) is a complex and heterogeneous environment composed of cancer cells, tumor stroma, a mixture of tissue-resident and infiltrating immune cells, secreted factors, and extracellular matrix proteins. Natural killer (NK) cells play a vital role in fighting tumors, but chronic stimulation and immunosuppression in the TME lead to NK cell exhaustion and limited antitumor functions. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of myeloid cells with potent immunosuppressive activity that gradually accumulate in tumor tissues. MDSCs interact with innate and adaptive immune cells and play a crucial role in negatively regulating the immune response to tumors. This review discusses MDSC-mediated NK cell regulation within the TME, focusing on critical cellular and molecular interactions. We review current strategies that target MDSC-mediated immunosuppression to enhance NK cell cytotoxic antitumor activity. We also speculate on how NK cell-based antitumor immunotherapy could be improved.

Long Noncoding RNA RUNXOR Promotes Myeloid-Derived Suppressor Cell Expansion and Functions via Enhancing Immunosuppressive Molecule Expressions during Latent HIV Infection

RUNX1 overlapping RNA (RUNXOR) is a long noncoding RNA and a key regulator of myeloid-derived suppressor cells (MDSCs) via targeting runt-related transcription factor 1 (RUNX1). We and others have previously reported MDSC expansion and inhibition of host immune responses during viral infections; however, the mechanisms regulating MDSC differentiation and suppressive functions, especially the role of RUNXOR-RUNX1 in the regulation of MDSCs in people living with HIV (PLHIV), remain unknown. In this study, we demonstrate that RUNXOR and RUNX1 expressions are upregulated in MDSCs that expand and accumulate in human PBMCs derived from PLHIV. We found that the upregulation of RUNXOR and RUNX1 is associated with the expressions of several key immunosuppressive molecules, including arginase 1, inducible NO synthase, STAT3, IL-6, and reactive oxygen species. RUNXOR and RUNX1 could positively regulate each other's expression and control the expressions of these suppressive mediators. Specifically, silencing RUNXOR or RUNX1 expression in MDSCs from PLHIV attenuated MDSC expansion and immunosuppressive mediator expressions, whereas overexpressing RUNXOR in CD33+ myeloid precursors from healthy subjects promoted their differentiation into MDSCs and enhanced the expression of these mediators. Moreover, loss of RUNXOR-RUNX1 function in MDSCs improved IFN-γ production from cocultured autologous CD4 T cells derived from PLHIV. These results suggest that the RUNXOR-RUNX1 axis promotes the differentiation and suppressive functions of MDSCs via regulating multiple immunosuppressive signaling molecules and may represent a potential target for immunotherapy in conjunction with antiviral therapy in PLHIV.

Comments on the ambiguity of selected surface markers, signaling pathways and omics profiles hampering the identification of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSC) are important immune-regulatory cells but their identification remains difficult. Here, we provide a critical view on selected surface markers, transcriptional and translational pathways commonly used to identify MDSC by specific, their developmental origin and new possibilities by transcriptional or proteomic profiling. Discrimination of MDSC from their non-suppressive counterparts is a prerequisite for the development of successful therapies. Understanding the switch mechanisms that direct granulocytic and monocytic development into a pro-inflammatory or anti-inflammatory direction will be crucial for therapeutic strategies. Manipulation of these myeloid checkpoints are exploited by tumors and pathogens, such as M. tuberculosis (Mtb), HIV or SARS-CoV-2, that induce MDSC for immune evasion. Thus, specific markers for MDSC identification may reveal also novel molecular candidates for therapeutic intervention at the level of MDSC.

Mechanisms of Immune Evasion in Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) results from a clonal expansion of abnormal lymphoid progenitors of B cell (BCP-ALL) or T cell (T-ALL) origin that invade bone marrow, peripheral blood, and extramedullary sites. Leukemic cells, apart from their oncogene-driven ability to proliferate and avoid differentiation, also change the phenotype and function of innate and adaptive immune cells, leading to escape from the immune surveillance. In this review, we provide an overview of the genetic heterogeneity and treatment of BCP- and T-ALL. We outline the interactions of leukemic cells in the bone marrow microenvironment, mainly with mesenchymal stem cells and immune cells. We describe the mechanisms by which ALL cells escape from immune recognition and elimination by the immune system. We focus on the alterations in ALL cells, such as overexpression of ligands for various inhibitory receptors, including anti-phagocytic receptors on macrophages, NK cell inhibitory receptors, as well as T cell immune checkpoints. In addition, we describe how developing leukemia shapes the bone marrow microenvironment and alters the function of immune cells. Finally, we emphasize that an immunosuppressive microenvironment can reduce the efficacy of chemo- and immunotherapy and provide examples of preclinical studies showing strategies for improving ALL treatment by targeting these immunosuppressive interactions.

Adoptive Transfer of Regulatory Immune Cells in Organ Transplantation

Chronic graft rejection remains a significant barrier to solid organ transplantation as a treatment for end-organ failure. Patients receiving organ transplants typically require systemic immunosuppression in the form of pharmacological immunosuppressants for the duration of their lives, leaving these patients vulnerable to opportunistic infections, malignancies, and other use-restricting side-effects. In recent years, a substantial amount of research has focused on the use of cell-based therapies for the induction of graft tolerance. Inducing or adoptively transferring regulatory cell types, including regulatory T cells, myeloid-derived suppressor cells, and IL-10 secreting B cells, has the potential to produce graft-specific tolerance in transplant recipients. Significant progress has been made in the optimization of these cell-based therapeutic strategies as our understanding of their underlying mechanisms increases and new immunoengineering technologies become more widely available. Still, many questions remain to be answered regarding optimal cell types to use, appropriate dosage and timing, and adjuvant therapies. In this review, we summarize what is known about the cellular mechanisms that underly the current cell-based therapies being developed for the prevention of allograft rejection, the different strategies being explored to optimize these therapies, and all of the completed and ongoing clinical trials involving these therapies.

In Vitro Generation of Murine Myeloid-Derived Suppressor Cells, Analysis of Markers, Developmental Commitment, and Function

Myeloid-derived suppressor cells (MDSC) appear at relatively low frequencies in diseased organs such as tumors or infection sites, but accumulate systemically in the spleen. So far MDSC have been reported in humans and experimental animals such as mice, rats, and nonhuman primates. Therefore, methods to generate MDSC in large amounts in vitro can serve as an additional tool to study their biology. Here, we describe in detail the generation of murine MDSC with GM-CSF from bone marrow (BM). Both subsets of granulocytic (G-MDSC) and monocytic MDSC (M-MDSC) are generated by this cytokine. We provide panels of phenotypic markers to distinguish them from non-suppressive cells and define developmental stages of monocytes developing into M-MDSC by two subsequent steps in vitro.

The Immunoregulatory Role of Myeloid-Derived Suppressor Cells in the Pathogenesis of Rheumatoid Arthritis

Myeloid-derived suppressor cells (MDSCs) are a group of cells that regulate the immune response and exert immunosuppressive effects on various immune cells. Current studies indicate that MDSCs have both anti-inflammatory effects and proinflammatory effects on rheumatoid arthritis (RA) and RA animal models. MDSCs inhibit CD4+ T cells, which secrete proinflammatory factors such as IFN-γ, IL-2, IL-6, IL-17, and TNF-α, by inhibiting iNOS, ROS, and IFN-γ and promoting the production of the anti-inflammatory factor IL-10. MDSCs can suppress dendritic cells by reducing MHC-II and CD86 expression, expand Treg cells in vitro through the action of IL-10, inhibit B cells through NO and PGE2, and promote Th17 cell responses by secreting IL-1β. As a type of osteoclast precursor cell, MDSCs can differentiate into osteoclasts through activation of the NF-κB pathway via IL-1α. Overall, our study reviews the research progress related to MDSCs in RA, focusing on the effects of MDSCs on various types of cells and aiming to provide ideas to help reveal the important role of MDSCs in RA.

Mesenchymal stem cells inhibited the differentiation of MDSCs via COX2/PGE2 in experimental sialadenitis

Background

Mesenchymal stem cells (MSCs) can regulate innate and adaptive immune systems through interacting with immune cells directly and secreting multiple soluble factors. Due to their immunosuppressive properties, MSC transplantation has been applied to treat many clinical and experimental autoimmune diseases. However, the therapeutic effects and mechanisms by which MSCs regulate myeloid cells in Sjögren’s syndrome (SS) still remain elusive.

Methods

The number and immune-suppressive activity of myeloid-derived suppressor cells (MDSCs), polymorphonuclear MDSCs (PMN-MDSCs), and monocytic MDSCs (M-MDSCs) were determined in non-obese diabetic (NOD) mice with sialadenitis and in NOD mice with human umbilical cord-derived MSC (UC-MSC) transplantation. Bone marrow cells were cultured with MSC-conditioned medium (MSC-CM) for 4 days. The number and immune-suppressive gene of MDSCs were detected by flow cytometry or qRT-PCR.

Results

The results showed that the number of MDSCs and PMN-MDSCs was higher and M-MDSCs were lower in NOD mice with sialadenitis. UC-MSCs ameliorated SS-like syndrome by reducing MDSCs, PMN-MDSCs, and M-MDSCs and promoting the suppressive ability of MDSCs significantly in NOD mice. UC-MSCs inhibited the differentiation of MDSCs. In addition, UC-MSCs enhanced the suppressive ability of MDSCs in vitro. Mechanistically, MSCs inhibited the differentiation of MDSCs and PMN-MDSCs via secreting prostaglandin E2 (PGE2) and inhibited the differentiation of M-MDSCs through secreting interferon-β (IFN-β).

Conclusions

Our findings suggested that MSCs alleviated SS-like symptoms by suppressing the aberrant accumulation and improving the suppressive function of MDSCs in NOD mice with sialadenitis.

Recent Advances: The Imbalance of Immune Cells and Cytokines in the Pathogenesis of Hepatocellular Carcinoma

Recent advancement in the immunological understanding of genesis of hepatocellular carcinoma (HCC) has implicated a decline in anti-tumour immunity on the background of chronic inflammatory state of liver parenchyma. The development of HCC involves a network of immunological activity in the tumour microenvironment involving continuous interaction between tumour and stromal cells. The reduction in anti-tumour immunity is secondary to changes in various immune cells and cytokines, and the tumour microenvironment plays a critical role in modulating the process of liver fibrosis, hepatocarcinogenesis, epithelial-mesenchymal transition (EMT), tumor invasion and metastasis. Thus, it is considered as one of primary factor behind the despicable tumour behavior and observed poor survival; along with increased risk of recurrence following treatment in HCC. The primary intent of the present review is to facilitate the understanding of the complex network of immunological interactions of various immune cells, cytokines and tumour cells associated with the development and progression of HCC.

Understanding the Differentiation, Expansion, Recruitment and Suppressive Activities of Myeloid-Derived Suppressor Cells in Cancers

There has been a great interest in myeloid-derived suppressor cells (MDSCs) due to their biological functions in tumor-mediated immune escape by suppressing antitumor immune responses. These cells arise from altered myelopoiesis in response to the tumor-derived factors. The most recognized function of MDSCs is suppressing anti-tumor immune responses by impairing T cell functions, and these cells are the most important players in cancer dissemination and metastasis. Therefore, understanding the factors and the mechanism of MDSC differentiation, expansion, and recruitment into the tumor microenvironment can lead to its control. However, most of the studies only defined MDSCs with no further characterization of granulocytic and monocytic subsets. In this review, we discuss the mechanisms by which specific MDSC subsets contribute to cancers. A better understanding of MDSC subset development and the specific molecular mechanism is needed to identify treatment targets. The understanding of the specific molecular mechanisms responsible for MDSC accumulation would enable more precise therapeutic targeting of these cells.

Targeting the Immune Microenvironment in the Treatment of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a highly aggressive solid tumor, with a 5-year mortality rate of ~50%. The development of immunotherapies has improved the survival of patients with HNSCC, but, the long-term prognosis of patients with recurrent or metastatic HNSCC remains poor. HNSCC is characterized by intratumoral infiltration of regulatory T cells, dysfunctional natural killer cells, an elevated Treg/CD8+ T cell ratio, and increased programmed cell death ligand 1 protein on tumor cells. This leads to an immunocompromised niche in favor of the proliferation and treatment resistance of cancer cells. To achieve an improved treatment response, several potential combination strategies, such as increasing the neoantigens for antigen presentation and therapeutic agents targeting components of the tumor microenvironment, have been explored and have shown promising results in preclinical studies. In addition, large-scale bioinformatic studies have also identified possible predictive biomarkers of HNSCC. As immunotherapy has shown survival benefits in recent HNSCC clinical trials, a comprehensive investigation of immune cells and immune-related factors/cytokines and the immune profiling of tumor cells during the development of HNSCC may provide more insights into the complex immune microenvironment and thus, facilitate the development of novel immunotherapeutic agents.

Interleukin‑33 expression in ovarian cancer and its possible suppression of peritoneal carcinomatosis

Refractory peritoneal carcinomatosis is a common terminal feature of epithelial ovarian cancer (EOC). Previous reports have suggested that immunotherapy is a promising therapeutic strategy for EOC. Interleukin (IL)‑33 is a member of the IL‑1 superfamily of cytokines. The role of IL‑33 in tissue inflammation and promoting type 2 immune responses has been established, and recently, there is accumulating evidence to suggest the involvement of IL‑33 in carcinogenesis. In this study, we focused on the association between the tumor expression of IL‑33 and ovarian peritoneal carcinomatosis. We used an immunosufficient murine model of peritoneal carcinomatosis and human EOC samples. The overexpression of IL‑33 in the ID8 mouse EOC cell line tumors significantly prolonged the survival of immunocompetent mice in the peritoneal carcinomatosis setting, but not in the subcutaneous model. In addition, the silencing of IL‑33 in ID8‑T6 cells (subclone with high dissemination potential) significantly shortened the survival of the tumor‑bearing mice. This was likely due to the intratumoral accumulation of CD8+ and CD4+ T cells, and a decrease in CD11b+Gr1+ cells. Furthermore, IL‑33 induced the intraperitoneal microenvironment favoring tumor elimination through the inhibition of differentiation into CD11b+Gr1+ cells. On the whole, the findings of this study suggest IL‑33 to be a cytokine that reflects antitumor peritoneal conditions. Further investigation of the antitumorigenic role of IL‑33 may aid in the development of more effective therapeutic approaches for the treatment of EOC with peritoneal carcinomatosis.

Myeloid-derived suppressor cells depletion may cause pregnancy loss via upregulating the cytotoxicity of decidual natural killer cells

PROBLEM

Maternal immune system tolerance to the semiallogeneic fetus is critical for a successful pregnancy. Studies have shown that myeloid-derived suppressor cells (MDSCs) play an important role in maintaining feto-maternal tolerance. However, the mechanisms remain poorly understood.

METHODS

Flow cytometry was used to evaluate the percentage of MDSCs in an allogeneic-normal-pregnant mouse model during different periods of gestation. We further assessed the percentage of MDSCs and their subtypes (granulocytic MDSCs [GR-MDSCs] and monocytic MDSCs [MO-MDSCs]) in a spontaneous abortion mouse model. The levels of the immunosuppressive molecules ARG-1, iNOS, IL-10, and TGF-β in MDSCs were also evaluated. MDSCs were depleted by anti-Gr-1 injection, and the resorption rate was calculated. The cytotoxicity of decidual natural killer (NK) cells was evaluated, and the percentage of regulatory NK (NKreg) cells and regulatory T lymphocytes (Tregs) were evaluated.

RESULTS

Myeloid-derived suppressor cells was accumulated in a time-dependent manner during pregnancy. However, the percentage of MDSCs was decreased in the spontaneous abortion mice compared with that in the control mice. In addition, the levels of ARG-1, iNOS, IL-10, and TGF-β in MDSCs decreased differentially. Finally, depletion of MDSCs was associated with increased rates of resorption and the proportion of NKreg and Treg cells in uterine tissues; meanwhile, the cytotoxicity of decidual NK cells was upregulated by increasing the level of perforin, granzyme B, and natural killer group protein 2 D-activating NK receptor (NKG2D).

CONCLUSION

Depletion of MDSCs may cause pregnancy loss, while upregulating the cytotoxicity of decidual NK cells and increasing NKreg and Treg cell numbers.

Phenotypic and Functional Diversities of Myeloid-Derived Suppressor Cells in Autoimmune Diseases

Myeloid-derived suppressor cells (MDSCs) are identified as a heterogeneous population of cells with the function to suppress innate as well as adaptive immune responses. The initial studies of MDSCs were primarily focused on the field of animal tumor models or cancer patients. In cancer, MDSCs play the deleterious role to inhibit tumor immunity and to promote tumor development. Over the past few years, an increasing number of studies have investigated the role of MDSCs in autoimmune diseases. The beneficial effects of MDSCs in autoimmunity have been reported by some studies, and thus, immunosuppressive MDSCs may be a novel therapeutic target in autoimmune diseases. There are some controversial findings as well. Many questions such as the activation, differentiation, and suppressive functions of MDSCs and their roles in autoimmune diseases remain unclear. In this review, we have discussed the current understanding of MDSCs in autoimmune diseases.

Myeloid-Derived Suppressor Cells and Their Potential Application in Transplantation

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immunosuppressive cells of the myeloid lineage upregulated by mediators of inflammation, such as IL-2, granulocyte colony-stimulating factor, and S100A8/A9. These cells have been studied extensively by tumor biologists. Because of their robust immunosuppressive potential, MDSCs have stirred recent interest among transplant immunologists as well. MDSCs inhibit T-cell responses through, among other mechanisms, the activity of arginase-1 and inducible nitric oxide synthase, and the expansion of T regulatory cells. In the context of transplantation, MDSCs have been studied in several animal models, and to a lesser degree in humans. Here, we will review the immunosuppressive qualities of this important cell type and discuss the relevant studies of MDSCs in transplantation. It may be possible to exploit the immunosuppressive capacity of MDSCs for the benefit of transplant patients.

Histamine targets myeloid-derived suppressor cells and improves the anti-tumor efficacy of PD-1/PD-L1 checkpoint blockade

Myeloid-derived suppressor cells (MDSCs) are immature monocytes and granulocytes that impede immune-mediated clearance of malignant cells by multiple mechanisms, including the formation of immunosuppressive reactive oxygen species (ROS) via the myeloid cell NADPH oxidase (NOX2). Histamine dihydrochloride (HDC), a NOX2 inhibitor, exerts anti-cancer efficacy in experimental tumor models but the detailed mechanisms are insufficiently understood. To determine effects of HDC on the MDSC compartment we utilized three murine cancer models known to entail accumulation of MDSC, i.e. EL-4 lymphoma, MC-38 colorectal carcinoma, and 4T1 mammary carcinoma. In vivo treatment with HDC delayed EL-4 and 4T1 tumor growth and reduced the ROS formation by intratumoral MDSCs. HDC treatment of EL-4 bearing mice also reduced the accumulation of intratumoral MDSCs and reduced MDSC-induced suppression of T cells ex vivo. Experiments using GR1-depleted and Nox2 knock out mice supported that the anti-tumor efficacy of HDC required presence of NOX2⁺ GR1⁺ cells in vivo. In addition, treatment with HDC enhanced the anti-tumor efficacy of programmed cell death receptor 1 (PD-1) and PD-1 ligand checkpoint blockade in EL-4- and MC-38-bearing mice. Immunomodulatory effects of a HDC-containing regimen on MDSCs were further analyzed in a phase IV trial (Re:Mission Trial, ClinicalTrials.gov; NCT01347996) where patients with acute myeloid leukemia received HDC in conjunction with low-dose IL-2 (HDC/IL-2) for relapse prevention. Peripheral CD14⁺HLA-DR^−/low MDSCs (M-MDSCs) were reduced during cycles of HDC/IL-2 therapy and a pronounced reduction of M-MDSCs during HDC/IL-2 treatment heralded favorable clinical outcome. We propose that anti-tumor properties of HDC may comprise the targeting of MDSCs.

Administration of cytokine-induced myeloid-derived suppressor cells ameliorates renal fibrosis in diabetic mice

Background

Diabetes is a proinflammatory state. Fibrosis of the renal glomerulus is the most common cause of end-stage renal disease. Glomerulosclerosis is caused by the accumulation of extracellular matrix (ECM) proteins in the mesangial interstitial space. Mesangial cells are unique stromal cells in the renal glomerulus that form the vascular pole of the renal corpuscle along with the mesangial matrix. Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that rapidly expand to regulate host immunity during inflammation, infection, and cancer. High concentrations of granulocyte–macrophage colony-stimulating factor (GM-CSF) alone or in combination with other molecules represent the most common ex-vivo protocol for differentiating MDSCs from bone marrow or from peripheral blood mononuclear cells. In this study, we analyzed and characterized the functions of MDSCs under the influence of mouse mesangial cells (MMCs) in a hyperglycemic environment and investigated whether cytokine-induced MDSCs ameliorated renal glomerulosclerosis in diabetic mice.

Methods

Cytokine-induced MDSCs were propagated from bone marrow cells cultured with mouse recombinant GM-CSF, IL-6, and IL-1β. Diabetic mice were induced with streptozotocin (STZ) and maintained at a blood glucose concentration exceeding 350 mg/dl. The ECM of the renal cortex and fibronectin expression of MMCs were analyzed through immunohistochemistry and western blotting. Arginase 1 and inducible NO synthase expressions of MDSCs were evaluated using quantitative reverse-transcriptase PCR. Cytokines released from MMCs were examined using a cytokine array assay.

Results

MDSCs in the diabetic mice were redistributed from the bone marrow into peripheral organs. An increase in fibronectin production was also observed in the renal glomerulus. MMCs in vitro produced more fibronectin and proinflammatory cytokines, such as macrophage inflammatory protein-2, RANTES, and stromal-cell-derived factor-1, under hyperglycemic conditions. The adoptive transfer of cytokine-induced MDSCs into STZ-induced mice normalized the glomerular filtration rate to reduce the kidney to body weight ratio and decrease fibronectin production in the renal glomerulus, ameliorating renal fibrosis. These results demonstrate the anti-inflammatory properties of cytokine-induced MDSCs and offer an alternative immunotherapy protocol for the management of diabetic nephropathy.

Conclusions

The application of cytokine-induced MDSCs provides a promising treatment for renal fibrosis and the prevention of diabetic nephropathy.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0915-0) contains supplementary material, which is available to authorized users.

Clinical Relevance and Suppressive Capacity of Human Myeloid-Derived Suppressor Cell Subsets

Purpose: Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of pathologically expanded myeloid cells with immunosuppressive activity. In human disease, three major MDSC subpopulations can be defined as monocytic (M-MDSC), granulocytic [polymorphonuclear-MDSC (PMN-MDSC)], and early stage (e-MDSC), which lacks myeloid lineage markers of the former two subsets. The purpose of this study was to determine and compare the immunosuppressive capacity and clinical relevance of each of these subsets in patients with solid cancer.Experimental Design: The frequency of MDSC subsets in the peripheral blood was determined by flow cytometry in a cohort of 49 patients with advanced head and neck cancer (HNC) and 22 patients with urological cancers. Sorted and purified MDSC subsets were tested in vitro for their T-cell-suppressive capacity. Frequency of circulating MDSC was correlated with overall survival of patients with HNC.Results: A high frequency of PMN-MDSC most strongly correlated with poor overall survival in HNC. T-cell-suppressive activity was higher in PMN-MDSC compared with M-MDSC and e-MDSC. A subset of CD66b⁺/CD11b⁺/CD16⁺ mature PMN-MDSC displayed high expression and activity of arginase I, and was superior to the other subsets in suppressing proliferation and cytokine production of T cells in both cancer types. High levels of this CD11b⁺/CD16⁺ PMN-MDSC, but not other PMN-MDSC subsets, strongly correlated with adverse outcome in HNC.Conclusions: A subset of mature CD11b⁺/CD16⁺ PMN-MDSC was identified as the MDSC subset with the strongest immunosuppressive activity and the highest clinical relevance. Clin Cancer Res; 24(19); 4834-44. ©2018 AACR.

Role of neutrophils in equine asthma

Neutrophilic bronchiolitis is the primary lesion in asthma-affected horses. Neutrophils are key actors in host defense, migrating toward sites of inflammation and infection, where they act as early responder cells toward external insults. However, neutrophils can also mediate tissue damage in various non-infectious inflammatory processes. Within the airways, these cells likely contribute to bronchoconstriction, mucus hypersecretion, and pulmonary remodeling by releasing pro-inflammatory mediators, including the cytokines interleukin (IL)-8 and IL-17, neutrophil elastase, reactive oxygen species (ROS), and neutrophil extracellular traps (NETs). The mechanisms that regulate neutrophil functions in the tissues are complex and incompletely understood. Therefore, the inflammatory activity of neutrophils must be regulated with exquisite precision and timing, a task achieved through a complex network of mechanisms that regulates neutrophil survival. The discovery and development of compounds that can help regulate ROS, NET formation, cytokine release, and clearance would be highly beneficial in the design of therapies for this disease in horses. In this review, neutrophil functions during inflammation will be discussed followed by a discussion of their contribution to airway tissue injury in equine asthma.

Toll-like receptors in immunity and inflammatory diseases: Past, present, and future

The immune system is a very diverse system of the host that evolved during evolution to cope with various pathogens present in the vicinity of environmental surroundings inhabited by multicellular organisms ranging from achordates to chordates (including humans). For example, cells of immune system express various pattern recognition receptors (PRRs) that detect danger via recognizing specific pathogen-associated molecular patterns (PAMPs) and mount a specific immune response. Toll-like receptors (TLRs) are one of these PRRs expressed by various immune cells. However, they were first discovered in the Drosophila melanogaster (common fruit fly) as genes/proteins important in embryonic development and dorso-ventral body patterning/polarity. Till date, 13 different types of TLRs (TLR1-TLR13) have been discovered and described in mammals since the first discovery of TLR4 in humans in late 1997. This discovery of TLR4 in humans revolutionized the field of innate immunity and thus the immunology and host-pathogen interaction. Since then TLRs are found to be expressed on various immune cells and have been targeted for therapeutic drug development for various infectious and inflammatory diseases including cancer. Even, Single nucleotide polymorphisms (SNPs) among various TLR genes have been identified among the different human population and their association with susceptibility/resistance to certain infections and other inflammatory diseases. Thus, in the present review the current and future importance of TLRs in immunity, their pattern of expression among various immune cells along with TLR based therapeutic approach is reviewed.

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TLRs are first described PRRs that revolutionized the biology of host-pathogen interaction and immune response

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The discovery of different TLRs in humans proved milestone in the field of innate immunity and inflammation

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The pattern of expression of all the TLRs expressed by human immune cells

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An association of various TLR SNPs with different inflammatory diseases

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Currently available drugs or vaccines based on TLRs and their future in drug targeting along with the role in reproduction, and regeneration

A Retroviral Replicating Vector Encoding Cytosine Deaminase and 5-FC Induces Immune Memory in Metastatic Colorectal Cancer Models

Treatment of tumors with Toca 511, a gamma retroviral replicating vector encoding cytosine deaminase, followed by 5-fluorocytosine (5-FC) kills tumors by local production of 5-fluorouracil (5-FU). In brain tumor models, this treatment induces systemic anti-tumor immune responses and long-term immune-mediated survival. Phase 1 Toca 511 and Toca FC (extended-release 5-FC) clinical trials in patients with recurrent high-grade glioma show durable complete responses and promising survival data compared to historic controls. The work described herein served to expand on our earlier findings in two models of metastatic colorectal carcinoma (mCRC). Intravenous (i.v.) delivery of Toca 511 resulted in substantial tumor-selective uptake of vector into metastatic lesions. Subsequent treatment with 5-FC resulted in tumor shrinkage, improved survival, and immune memory against future rechallenge with the same CT26 CRC cell line. Similar results were seen in a brain metastasis model of mCRC. Of note, 5-FC treatment resulted in a significant decrease in myeloid-derived suppressor cells (MDSCs) in mCRC tumors in both the liver and brain. These results support the development of Toca 511 and Toca FC as a novel immunotherapeutic approach for patients with mCRC. A phase 1 study of i.v. Toca 511 and Toca FC in solid tumors, including mCRC, is currently underway (NCT02576665).

Epigenetics in myeloid derived suppressor cells: a sheathed sword towards cancer

Myeloid-derived suppressor cells (MDSCs), a heterogeneous population of cells composed of progenitors and precursors to myeloid cells, are deemed to participate in the development of tumor-favoring immunosuppressive microenvironment. Thus, the regulatory strategies targeting MDSCs' expansion, differentiation, accumulation and function could possibly be effective “weapons” in anti-tumor immunotherapies. Epigenetic mechanisms, which involve DNA modification, covalent histone modification and RNA interference, result in the heritable down-regulation or silencing of gene expression without a change in DNA sequences. Epigenetic modification of MDSC's functional plasticity leads to the remodeling of its characteristics, therefore reframing the microenvironment towards countering tumor growth and metastasis. This review summarized the pertinent findings on the DNA methylation, covalent histone modification, microRNAs and small interfering RNAs targeting MDSC in cancer genesis, progression and metastasis. The potentials as well as possible obstacles in translating into anti-cancer therapeutics were also discussed.

CD33+ HLA-DR- Myeloid-Derived Suppressor Cells Are Increased in Frequency in the Peripheral Blood of Type1 Diabetes Patients with Predominance of CD14+ Subset

INTRODUCTION:

Type 1 Diabetes Mellitus (T1D) is an autoimmune disease that results from the destruction of insulin-producing beta cells of the pancreas by autoreactive T cells. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that can potently suppress T cell responses.

AIM:

To detect the presence of MDSCs in T1D and compare their percentage in T1D versus healthy individuals.

METHOD:

Thirty T1D patients were included in the study. Diabetic patients with nephropathy (n = 18) and diabetic patients without nephropathy (n = 12). A control group of healthy individuals (n = 30) were also included. CD33⁺ and HLA-DR– markers were used to identify MDSCs by flow cytometry. CD14 positive and negative MDSCs subsets were also identified.

RESULTS:

MDSCs was significantly increased in T1D than the control group and diabetic patient with nephropathy compared to diabetic patients without nephropathy. M-MDSCs (CD14⁺ CD33⁺ HLA–DR⁻) were the most abundant MDSCs subpopulation in all groups, however their percentage decrease in T1D than the control group.

CONCLUSION:

MDSCs are increased in the peripheral blood of T1D with a predominance of the CD14⁺ MDSCs subset. Future studies are needed to test the immune suppression function of MDSCs in T1D.

A functional characteristic of cysteine-rich protein 61: Modulation of myeloid-derived suppressor cells in liver inflammation

There is increasing awareness of the immunologic roles of liver mononuclear populations, including myeloid-derived suppressor cells (MDSCs). We took advantage of a large well-defined cohort of 148 patients with liver inflammation and 45 healthy controls to focus on the qualitative and quantitative characteristics of MDSCs. We investigated the frequency, phenotype, and functional capacities of MDSCs by using peripheral blood MDSCs in a cohort of 55 patients with primary biliary cholangitis (PBC), 40 with autoimmune hepatitis, 39 with chronic hepatitis B, 14 with nonalcoholic fatty liver disease, and 45 healthy controls. This was followed by a liver-targeted determination in 27 patients with PBC, 27 with autoimmune hepatitis, 20 with chronic hepatitis B, 14 with nonalcoholic fatty liver disease, and 6 controls. We then focused on mechanisms of this expansion with PBC as an example, using both ursodeoxycholic acid-naive and treated patients. HLA-DR^-/low CD33⁺ CD11b⁺ CD14⁺ CD15^- monocytic MDSCs were elevated in diseases characterized by liver inflammation compared to healthy controls. Using PBC as a focus, there was a significant correlation between levels of circulating MDSCs and disease-related biochemical markers (alkaline phosphatase, total bilirubin). We found higher amounts of MDSCs in patients with PBC who were responsive to ursodeoxycholic acid. MDSCs from PBC were found to manifest a potent immunosuppressive function. There was a significant correlation in the accumulation of hepatic MDSCs in the inflamed lesions of PBC with histologic changes, such as fibrosis. We also found that cysteine-rich protein 61 (CCN1), a highly expressed protein in impaired cholangiocytes and hepatocytes, contributes to MDSC expansion and MDSC inducible nitric oxide synthase-associated immune suppression.

CONCLUSION

CCN1 modulates expansion and a suppressive function of MDSCs. Our data highlight the potential functions of CCN1 on MDSCs and suggest therapeutic implications in inflammatory liver diseases. (Hepatology HEPATOLOGY 2018;67:232-246).

Inhibition of IL-18-mediated myeloid derived suppressor cell accumulation enhances anti-PD1 efficacy against osteosarcoma cancer

Myeloid derived suppressor cells (MDSC) are very important in tumor immune evasion and they dramatically increased in peripheral blood of patients with osteosarcoma cancer. The association between MDSC and various cytokines has been studied in the peripheral blood. However, little is known about the mechanism drawing MDSC into tumor parenchyma. This study was to analyze the correlation between MDSC subsets and interleukin 18 (IL-18) level in osteosarcoma tumor model and its effect on the immunotherapy. MDSC were isolated from the blood and parenchyma and analyzed in the osteosarcoma tumor model. IL-18 levels were detected by enzyme-linked immunosorbent assay (ELISA) assay, real-time PCR, western blot and flow cytometry. Moreover, combination treatment with IL-18 inhibition and anti-PD1 was conducted to assess the therapeutic effects of IL-18 blockade. Results showed MDSC levels had a positive correlation with IL-18, suggesting IL-18 may attract MDSC into the parenchyma. IL-18 gene and protein expression significantly increased in blood and tumor lysates of tumor-bearing mice. Anti-IL-18 treatment significantly decreased G-MDSC and M-MDSC in the peripheral blood and tumor. Furthermore, combination therapy decreased the tumor burden and increased CD4⁺ and CD8⁺ T cell infiltration, as well as the production of interferon gamma (IFNγ) and granzyme B. Our study revealed a possible correlation between MDSC subsets and IL-18 inducing MDSC migration into the tumor tissue, in addition to provide the potential target to enhance the efficacy of immunotherapy in patients with osteosarcoma.

Phenotype and Function of Myeloid-Derived Suppressor Cells Induced by Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a major etiologic agent of periodontitis, has been reported to induce the expansion of myeloid-derived suppressor cells (MDSC); however, little is known regarding the subpopulations of MDSC expanded by P. gingivalis infection. Flow cytometry was used to evaluate bone marrow and spleen cells from mice infected with P. gingivalis and controls for surface expression of CD11b, Ly6G, and Ly6C. To characterize the phenotype of MDSC subpopulations induced by infection, cells were sorted based on the differential expression of Ly6G and Ly6C. Moreover, since MDSC are suppressors of T cell immune activity, we determined the effect of the induced subpopulations of MDSC on the proliferative response of OVA-specific CD4⁺ T cells. Lastly, the plasticity of MDSC to differentiate into osteoclasts was assessed by staining for tartrate-resistant acid phosphatase activity. P. gingivalis infection induced the expansion of three subpopulations of MDSC (Ly6G⁺⁺ Ly6C⁺, Ly6G⁺ Ly6C⁺⁺, and Ly6G⁺ Ly6C⁺); however, only CD11b⁺ Ly6G⁺ Ly6C⁺⁺-expressing cells exerted a significant suppressive effect on T cell proliferation. Inhibition of proliferative responses required T cell-MDSC contact and was mediated by inducible nitric oxide synthase and cationic amino acid transporter 2 via gamma interferon. Furthermore, only the CD11b⁺ Ly6G⁺ Ly6C⁺⁺ subpopulation of MDSC induced by P. gingivalis infection was able to differentiate into osteoclasts. Thus, the inflammatory response induced by P. gingivalis infection promotes the expansion of immune-suppressive cells and consequently the development of regulatory inhibitors that curtail the host response. Moreover, monocytic MDSC have the plasticity to differentiate into OC, thus perhaps contributing to the OC pool in states of periodontal disease.

Myeloid-derived suppressor cells modulate B-cell responses

Myeloid-derived suppressor cells (MDSCs) are key regulators of adaptive immunity by suppressing T-cell functions. However, their potential action on or interaction with B cells remained poorly understood. Here we demonstrate that human polymorphonuclear MDSCs differentially modulate B-cell function by suppressing B-cell proliferation and antibody production. We further demonstrate that this MDSC-mediated effect is cell contact dependent and involves established mediators such as arginase-1, nitric oxide (NO), reactive oxygen species (ROS) as well as B-cell death. Collectively, our studies provide novel evidence that human MDSCs modulate B cells, which could have future implications for immunotherapy approaches.