Characterization of cytokine-induced myeloid-derived suppressor cells from normal human peripheral blood mononuclear cells

USC-HN2, a new model cell line for recurrent oral cavity squamous cell carcinoma with immunosuppressive characteristics

Head and neck squamous cell carcinomas (HNSCC) are common and aggressive tumors that have not seen an improvement in survival rates in decades. These tumors are believed to evade the immune system through a variety of mechanisms and are therefore highly immune modulatory. In order to elucidate their interaction with the immune system and develop new therapies targeting immune escape, new pre-clinical models are needed. A novel human cell line, USC-HN2, was established from a patient biopsy specimen of invasive, recurrent buccal HNSCC and characterized by morphology, heterotransplantation, cytogenetics, phenotype, gene expression, and immune modulation studies and compared to a similar HNSCC cell line; SCCL-MT1. Characterization studies confirmed the HNSCC origin of USC-HN2 and demonstrated a phenotype similar to the original tumor and typical of aggressive oral cavity HNSCC (EGFR(+)CD44v6(+)FABP5(+)Keratin(+) and HPV(-)). Gene and protein expression studies revealed USC-HN2 to have highly immune-modulatory cytokine production (IL-1β, IL-6, IL-8, GM-CSF, and VEGF) and strong regulatory T and myeloid derived suppressor cell (MDSC) induction capacity in vitro. Of note, both USC-HN2 and SCCL-MT1 were found to have a more robust cytokine profile and MDSC induction capacity when compared to seven previously established HNSCC cell lines. Additionally, microarray gene expression profiling of both cell lines demonstrate up-regulation of antigen presenting genes. Because USC-HN2 is therefore highly immunogenic, it also induces strong immune suppression to evade immunologic destruction. Based upon these results, both cell lines provide an excellent model for the development of new suppressor cell-targeted immunotherapies.

Myelodysplastic syndromes: the role of the immune system in pathogenesis

The myelodysplastic syndromes (MDS) represent a complex spectrum of clonal hematopoietic stem cell disorders manifested by cytopenias, risk of infection, and variable risk of progression to acute myelogenous leukemia. Several theories of MDS pathogenesis exist, with contributions of genetic, epigenetic, apoptotic, differentiation, and cytokine milieu abnormalities. Immune dysregulation has also been implicated in MDS pathogenesis. In some forms of MDS it is evident that immune dysregulation may be a primary pathophysiologic abnormality, while in others the abnormal immune function may represent only a small part of the pathologic puzzle. We review the current literature regarding natural killer (NK) cell, T cell, and myeloid derived suppressor cell abnormalities in the spectrum of MDS.

Functional characterization of human Cd33+ and Cd11b+ myeloid-derived suppressor cell subsets induced from peripheral blood mononuclear cells co-cultured with a diverse set of human tumor cell lines

Background

Tumor immune tolerance can derive from the recruitment of suppressor cell populations, including myeloid-derived suppressor cells (MDSC). In cancer patients, MDSC accumulation correlates with increased tumor burden, but the mechanisms of MDSC induction remain poorly understood.

Methods

This study examined the ability of human tumor cell lines to induce MDSC from healthy donor PBMC using in vitro co-culture methods. These human MDSC were then characterized for morphology, phenotype, gene expression, and function.

Results

Of over 100 tumor cell lines examined, 45 generated canonical CD33⁺HLA-DR^lowLineage^- MDSC, with high frequency of induction by cervical, ovarian, colorectal, renal cell, and head and neck carcinoma cell lines. CD33⁺ MDSC could be induced by cancer cell lines from all tumor types with the notable exception of those derived from breast cancer (0/9, regardless of hormone and HER2 status). Upon further examination, these and others with infrequent CD33⁺ MDSC generation were found to induce a second subset characterized as CD11b⁺CD33^lowHLA-DR^lowLineage^-. Gene and protein expression, antibody neutralization, and cytokine-induction studies determined that the induction of CD33⁺ MDSC depended upon over-expression of IL-1β, IL-6, TNFα, VEGF, and GM-CSF, while CD11b⁺ MDSC induction correlated with over-expression of FLT3L and TGFβ. Morphologically, both CD33⁺ and CD11b⁺ MDSC subsets appeared as immature myeloid cells and had significantly up-regulated expression of iNOS, NADPH oxidase, and arginase-1 genes. Furthermore, increased expression of transcription factors HIF1α, STAT3, and C/EBPβ distinguished MDSC from normal counterparts.

Conclusions

These studies demonstrate the universal nature of MDSC induction by human solid tumors and characterize two distinct MDSC subsets: CD33⁺HLA-DR^lowHIF1α⁺/STAT3⁺ and CD11b⁺HLA-DR^lowC/EBPβ⁺, which should enable the development of novel diagnostic and therapeutic reagents for cancer immunotherapy.

Elevated myeloid-derived suppressor cells in pancreatic, esophageal and gastric cancer are an independent prognostic factor and are associated with significant elevation of the Th2 cytokine interleukin-13

We undertook a comprehensive analysis of circulating myeloid-derived suppressor cells (MDSCs) and T regulatory cells (Tregs) in pancreatic, esophageal and gastric cancer patients and investigated whether MDSCs are an independent prognostic factor for survival. We evaluated a series of plasma cytokines and in particular re-evaluated the Th2 cytokine interleukin-13 (IL-13). Peripheral blood was collected from 131 cancer patients (46 pancreatic, 60 esophageal and 25 gastric) and 54 healthy controls. PBMC were harvested with subsequent flow cytometric analysis of MDSC (HLADR⁻ Lin1^low/− CD33⁺ CD11b⁺) and Treg (CD4⁺ CD25⁺ CD127^low/− FoxP3⁺) percentages. Plasma IL-2, IL-4, IL-5, IL-6, IL-10, IL-12 (p70), IL-13, IL-17, G-CSF, IFN-γ, TNF-α and VEGF levels were analyzed by the Bio-Plex cytokine assay. Plasma arginase I levels were analyzed by ELISA. MDSCs and Tregs were statistically significantly elevated in pancreatic, esophageal and gastric cancer compared with controls, and MDSC numbers correlated with Treg levels. Increasing MDSC percentage was associated with increased risk of death, and in a multivariate analysis, MDSC level was an independent prognostic factor for survival. A unit increase in MDSC percentage was associated with a 22% increased risk of death (hazard ratio 1.22, 95% confidence interval 1.06–1.41). Arginase I levels were also statistically significantly elevated in upper gastrointestinal cancer patients compared with controls. There was Th2 skewing for cytokine production in all three diseases, and importantly there were significant elevations of the pivotal Th2 cytokine interleukin-13, an increase that correlated with MDSC levels.

Distinct myeloid suppressor cell subsets correlate with plasma IL-6 and IL-10 and reduced interferon-alpha signaling in CD4⁺ T cells from patients with GI malignancy

Interferon-alpha (IFN-α) promotes anti-tumor immunity through its actions on immune cells. We hypothesized that elevated percentages of myeloid-derived suppressor cells (MDSC) and increased pro-inflammatory cytokines in peripheral blood would be associated with impaired response to IFN-α in patients with gastrointestinal (GI) malignancies. This study evaluated relationships between plasma IL-6, IL-10, circulating MDSC subsets, and IFN-α-induced signal transduction in 40 patients with GI malignancies. Plasma IL-6 and IL-10 were significantly higher in patients versus normal donors. CD33(+)HLADR(-)CD11b(+)CD15(+) and CD33(+)HLADR(-/low)CD14(+) MDSC subsets were also elevated in patients versus normal donors (P < 0.0001). Plasma IL-6 was correlated with CD33(+)HLADR(-)CD15(+) MDSC (P = 0.008) and IL-10 with CD33(+)HLADR(-)CD15(-) MDSC (P = 0.002). The percentage of CD15(+) and CD15(-) but not CD14(+) MDSC subsets were inversely correlated with IFN-α-induced STAT1 phosphorylation in CD4(+) T cells, while co-culture with in vitro generated MDSC led to reduced IFN-α responsiveness in both PBMC and the CD4(+) subset of T cells from normal donors. Exploratory multivariable Cox proportional hazards models revealed that an increased percentage of the CD33(+)HLADR(-)CD15(-) MDSC subset was associated with reduced overall survival (P = 0.049), while an increased percentage of the CD33(+)HLADR(-/low)CD14(+) subset was associated with greater overall survival (P = 0.033). These data provide evidence for a unique relationship between specific cytokines, MDSC subsets, and IFN-α responsiveness in patients with GI malignancies.

Immunomodulatory cytokines as therapeutic agents for melanoma

Melanoma is the most aggressive form of skin cancer whose worldwide incidence is rising faster than any other cancer. Few treatment options are available to patients with metastatic disease, and standard chemotherapeutic agents are generally ineffective. Cytokines such as IFN-α or IL-2 can promote immune recognition of melanoma, occasionally inducing dramatic and durable clinical responses. Here, we discuss several immunomodulatory agents, the safety of which are being evaluated in clinical trials. Challenges include an incomplete understanding of signaling pathways, appropriate clinical dose and route, and systemic immunosuppression in advanced melanoma patients. We consider how targeted cytokine therapy will integrate into the clinical arena, as well as the low likelihood of success of single cytokine therapies. Evidence supports a synergy between cytokine immunotherapy and other therapeutic approaches in melanoma, and strengthening this area of research will improve our understanding of how to use cytokine therapy better.

Dual specificity phosphatase 1 regulates human inducible nitric oxide synthase expression by p38 MAP kinase

The role of dual specificity phosphatase 1 (DUSP1) in inducible nitric oxide synthase (iNOS) expression in A549 human pulmonary epithelial cells, J774 mouse macrophages and primary mouse bone marrow-derived macrophages (BMMs) was investigated. iNOS expression was induced by a cytokine mixture (TNF, IFNγ and IL-1β) in A549 cells and by LPS in J774 cells, and it was inhibited by p38 MAPK inhibitors SB202190 and BIRB 796. Stimulation with cytokine mixture or LPS enhanced also DUSP1 expression. Down-regulation of DUSP1 by siRNA increased p38 MAPK phosphorylation and iNOS expression in A549 and J774 cells. In addition, LPS-induced iNOS expression was enhanced in BMMs from DUSP1^(−/−) mice as compared to that in BMMs from wild-type mice. The results indicate that DUSP1 suppresses iNOS expression by limiting p38 MAPK activity in human and mouse cells. Compounds that enhance DUSP1 expression or modulate its function may be beneficial in diseases complicated with increased iNOS-mediated NO production.

A signature of immune function genes associated with recurrence-free survival in breast cancer patients

The clinical significance of tumor-infiltrating immune cells has been reported in a variety of human carcinomas including breast cancer. However, molecular signature of tumor-infiltrating immune cells and their prognostic value in breast cancer patients remain elusive. We hypothesized that a distinct network of immune function genes at the tumor site can predict a low risk versus high risk of distant relapse in breast cancer patients regardless of the status of ER, PR, or HER-2/neu in their tumors. We conducted retrospective studies in a diverse cohort of breast cancer patients with a 1-5 year tumor relapse versus those with up to 7 years relapse-free survival. The RNAs were extracted from the frozen tumor specimens at the time of diagnosis and subjected to microarray analysis and real-time RT-PCR. Paraffin-embedded tissues were also subjected to immunohistochemistry staining. We determined that a network of immune function genes involved in B cell development, interferon signaling associated with allograft rejection and autoimmune reaction, antigen presentation pathway, and cross talk between adaptive and innate immune responses were exclusively upregulated in patients with relapse-free survival. Among the 299 genes, five genes which included B cell response genes were found to predict with >85% accuracy relapse-free survival. Real-time RT-PCR confirmed the 5-gene prognostic signature that was distinct from an FDA-cleared 70-gene signature of MammaPrint panel and from the Oncotype DX recurrence score assay panel. These data suggest that neoadjuvant immunotherapy in patients with high risk of relapse may reduce tumor recurrence by inducing the immune function genes.

IL-1β regulates a novel myeloid-derived suppressor cell subset that impairs NK cell development and function

Chronic inflammation is associated with promotion of malignancy and tumor progression. Many tumors enhance the accumulation of myeloid-derived suppressor cells (MDSC), which contribute to tumor progression and growth by suppressing anti-tumor immune responses. Tumor-derived IL-1β secreted into the tumor microenvironment has been shown to induce the accumulation of MDSC possessing an enhanced capacity to suppress T cells. In this study, we found that the enhanced suppressive potential of IL-1β-induced MDSC was due to the activity of a novel subset of MDSC lacking Ly6C expression. This subset was present at low frequency in tumor-bearing mice in the absence of IL-1β-induced inflammation; however, under inflammatory conditions, Ly6C(neg) MDSC were predominant. Ly6C(neg) MDSC impaired NK cell development and functions in vitro and in vivo. These results identify a novel IL-1β-induced subset of MDSC with unique functional properties. Ly6C(neg) MDSC mediating NK cell suppression may thus represent useful targets for therapeutic interventions.

MDSC in autoimmunity

Myeloid derived suppressor cells (MDSC) were first described nearly two decades ago. Until recently, however, descriptions of MDSC populations were found almost exclusively in animal models of cancer or in cancer patients. Over the last few years, an increasing number of reports have been published describing populations of myeloid cells with MDSC-like properties in murine models of autoimmune disease. In contrast to the proposed deleterious role of MDSC in cancer--where these cells likely inhibit tumor immunity--in the context of autoimmunity, MDSC have the potential to suppress the autoimmune response, thereby limiting tissue injury. A logical corollary of this hypothesis is that a failure of endogenous MDSC to appropriately control autoimmune T cell responses in vivo may actually contribute to the pathogenesis of autoimmune disease.

LPS-induced CD11b+Gr1(int)F4/80+ regulatory myeloid cells suppress allergen-induced airway inflammation

In humans, the bacterial product lipopolysaccharide (LPS) has been associated with protection from allergic diseases such us asthma. However, in mouse models of allergic asthma, differential effects of LPS have been noted based on the dose. A low dose of LPS promotes Th2 responses and allergic disease but a high dose has been associated with suppression of allergic airway inflammation. Our recent work has described the ability of LPS to increase the frequency of CD11b+Gr1(int)F4/80+(abbreviated as Gr1(int) cells) cells in the lung tissue of mice in a dose-dependent fashion that is dependent on TLR4 and the TLR adaptor protein, MyD88. Both phenotypically and morphologically, the cells were found to have similarities with mycloid-derived suppressor cells. Adoptive transfer of LPS-induced Gr1(int) cells suppressed allergen-induced airway inflammation suggesting regulatory functions of the cells in allergic asthma. Although the Gr1(int) cells are detectable in the lung tissue of LPS-treated mice, they are barely detectable in the lung-draining lymph nodes (Lns) or in the airway lumen. This causes selective enrichment of these cells over dendritic cells (Dcs) in the tissue which upon LPS stimulation migrate to lung-draining LNs. The Gr1(int) cells were found to blunt the ability of the lung DCs to upregulate GATA-3 or to promote STAT5 activation in primed Th2 cells, both transcription factors having critical roles in TH2 effector function. Thus, a complete understanding of the generation and regulation of the Gr1(int) cells would provide new avenues to either promote or delete these cells for disease-specific immunoregulation.

A new mechanism for blocking myeloid-derived suppressor cells by CpG

In this issue of Clinical Cancer Research, Zoglmeier and colleagues show that CpG, via the induction of IFN-α, matures myeloid-derived suppressor cells to abrogate immune suppression in 2 murine solid tumor models.

Extracellular hepatitis C virus core protein activates STAT3 in human monocytes/macrophages/dendritic cells via an IL-6 autocrine pathway

Hepatitis C virus (HCV) infection is highly efficient in the establishment of persistent infection, which leads to the development of chronic liver disease and hepatocellular carcinoma. Impaired T cell responses with reduced IFN-γ production have been reported to be associated with persistent HCV infection. Extracellular HCV core is a viral factor known to cause HCV-induced T cell impairment via its suppressive effect on the activation and induction of pro-inflammatory responses by antigen-presenting cells (APCs). The activation of STAT proteins has been reported to regulate the inflammatory responses and differentiation of APCs. To further characterize the molecular basis for the regulation of APC function by extracellular HCV core, we examined the ability of extracellular HCV core to activate STAT family members (STAT1, -2, -3, -5, and -6). In this study, we report the activation of STAT3 on human monocytes, macrophages, and dendritic cells following treatment with extracellular HCV core as well as treatment with a gC1qR agonistic monoclonal antibody. Importantly, HCV core-induced STAT3 activation is dependent on the activation of the PI3K/Akt pathway. In addition, the production of multifunctional cytokine IL-6 is essential for HCV core-induced STAT3 activation. These results suggest that HCV core-induced STAT3 activation plays a critical role in the alteration of inflammatory responses by APCs, leading to impaired anti-viral T cell responses during HCV infection.

Immunotherapy for lung cancers

Lung cancer is the leading cause of cancer-related deaths worldwide. Although treatment methods in surgery, irradiation, and chemotherapy have improved, prognosis remains unsatisfactory and developing new therapeutic strategies is still an urgent demand. Immunotherapy is a novel therapeutic approach wherein activated immune cells can specifically kill tumor cells by recognition of tumor-associated antigens without damage to normal cells. Several lung cancer vaccines have demonstrated prolonged survival time in phase II and phase III trials, and several clinical trials are under investigation. However, many clinical trials involving cancer vaccination with defined tumor antigens work in only a small number of patients. Cancer immunotherapy is not completely effective in eradicating tumor cells because tumor cells escape from host immune scrutiny. Understanding of the mechanism of immune evasion regulated by tumor cells is required for the development of more effective immunotherapeutic approaches against lung cancer. This paper discusses the identification of tumor antigens in lung cancer, tumor immune escape mechanisms, and clinical vaccine trials in lung cancer.

The biology of myeloid-derived suppressor cells: the blessing and the curse of morphological and functional heterogeneity

Myeloid-derived suppressor cells (MDSC) play an important role in the cellular network regulating immune responses in cancer, chronic infectious diseases, autoimmunity, and in other pathological conditions. Morphological, phenotypic and functional heterogeneity is a hallmark of MDSC. This heterogeneity demonstrates the plasticity of this immune suppressive myeloid compartment, and shows how various tumors and infectious agents can have similar biological effects on myeloid cells despite the differences in the factors that they produce to influence the immune system; however, such a heterogeneity creates ambiguity in the definition of MDSC as well as confusion regarding the origin and fate of these cells. In this review, we will discuss recent findings that help to better clarify these issues and to determine the place of MDSC within the myeloid cell lineage.

The inflammasome component NLRP3 impairs antitumor vaccine by enhancing the accumulation of tumor-associated myeloid-derived suppressor cells

The inflammasome is a proteolysis complex that generates the active forms of the proinflammatory cytokines interleukin (IL)-1β and IL-18. Inflammasome activation is mediated by NLR proteins that respond to microbial and nonmicrobial stimuli. Among NLRs, NLRP3 senses the widest array of stimuli and enhances adaptive immunity. However, its role in antitumor immunity is unknown. Therefore, we evaluated the function of the NLRP3 inflammasome in the immune response using dendritic cell vaccination against the poorly immunogenic melanoma cell line B16-F10. Vaccination of Nlrp3(-/-) mice led to a relative 4-fold improvement in survival relative to control animals. Immunity depended on CD8(+) T cells and exhibited immune specificity and memory. Increased vaccine efficacy in Nlrp3(-/-) hosts did not reflect differences in dendritic cells but rather differences in myeloid-derived suppressor cells (MDSC). Although Nlrp3 was expressed in MDSCs, the absence of Nlrp3 did not alter either their functional capacity to inhibit T cells or their presence in peripheral lymphoid tissues. Instead, the absence of Nlrp3 caused a 5-fold reduction in the number of tumor-associated MDSCs found in host mice. Adoptive transfer experiments also showed that Nlrp3(-/-) MDSCs were less efficient in reaching the tumor site. Depleting MDSCs with an anti-Gr-1 antibody increased the survival of tumor-bearing wild-type mice but not Nlrp3(-/-) mice. We concluded that Nlrp3 was critical for accumulation of MDSCs in tumors and for inhibition of antitumor T-cell immunity after dendritic cell vaccination. Our findings establish an unexpected role for Nlrp3 in impeding antitumor immune responses, suggesting novel approaches to improve the response to antitumor vaccines by limiting Nlrp3 signaling.

Molecular mechanisms regulating myeloid-derived suppressor cell differentiation and function

Myeloid-derived suppressor cells (MDSCs) are one of the main cell populations responsible for regulating immune responses. MDSCs accumulate during tumor progression, autoimmunity, chronic infection and other pathological conditions, and can potently suppress T cell function. Recent studies have demonstrated the ability of MDSCs to modulate the activity of NK and myeloid cells and have implicated MDSCs in the induction of regulatory T cells. Here, we discuss recent findings that describe the molecular mechanisms that regulate the expansion and function of MDSCs, as well as recent attempts to use MDSCs in cell therapy for different pathologic conditions.