Myeloid-derived suppressor cells in human cancer. Cancer J. 2010;16:348-353. [PMID: 20693846 DOI: 10.1097/ppo.0b013e3181eb3358]

Infiltration of alternatively activated macrophages in cancer tissue is associated with MDSC and Th2 polarization in patients with esophageal cancer

Myeloid derived suppressor cells (MDSCs) expand in cancer bearing hosts and contribute to tumor immune evasion. M2 macrophages constitute a major cellular component of cancer-related inflammation. However, the correlation between circulating MDSCs and infiltrating M2 macrophages in tumor tissues from patients with esophageal cancer (ECA), and its potential relationship with the polarization of Th2 cells remain unclear. In the present study, we showed the level of MDSCs in PBMC and Arg1 in plasma were significantly elevated in ECA patients, and the increased ratio of MDSC in PBMC was closely related to the expression of CD163 in cancer tissues. In addition, the ECA patients exhibited remarkable increases in the mRNA levels of IL-4 and GATA3, as well as the protein levels of IL-13 and IL-6, but IFN-γ and IL-12 in peripheral blood were decreased. Our data indicate that the increased Th2 cytokines are associated with MDSCs and M2 macrophages polarization, and foster the infiltration of CD163⁺M2 macrophages in cancer tissues, which promote the formation of immunosuppressive microenvironment in ECA patients.

Identification of myeloid-derived suppressor cells in the synovial fluid of patients with rheumatoid arthritis: a pilot study

Background

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of innate immune cells with a granulocyte-like or monocyte-like phenotype and a unique ability to suppress T-cell responses. MDSCs have been shown to accumulate in cancer patients, but recent studies suggest that these cells are also present in humans and animals suffering from autoimmune diseases. We previously identified MDSCs in the synovial fluid (SF) of mice with experimental autoimmune arthritis. The goal of the present study was to identify MDSCs in the SF of patients with rheumatoid arthritis (RA).

Methods

RA SF cells were studied by flow cytometry using antibodies to MDSC cell surface markers as well as by analysis of cell morphology. The suppressor activity of RA SF cells toward autologous peripheral blood T cells was determined ex vivo. We employed both antigen-nonspecific (anti-CD3/CD28 antibodies) and antigen-specific (allogeneic cells) induction systems to test the effects of RA SF cells on the proliferation of autologous T cells.

Results

SF from RA patients contained MDSC-like cells, the majority of which showed granulocyte (neutrophil)-like phenotype and morphology. RA SF cells significantly suppressed the proliferation of anti-CD3/CD28-stimulated autologous T cells upon co-culture. When compared side by side, RA SF cells had a more profound inhibitory effect on the alloantigen-induced than the anti-CD3/CD28-induced proliferation of autologous T cells.

Conclusion

MDSCs are present among RA SF cells that are commonly regarded as inflammatory neutrophils. Our results suggest that the presence of neutrophil-like MDSCs in the SF is likely beneficial, as these cells have the ability to limit the expansion of joint-infiltrating T cells in RA.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2474-15-281) contains supplementary material, which is available to authorized users.

Role of TGF-β signaling in generation of CD39+CD73+ myeloid cells in tumors

There is growing evidence that generation of adenosine from ATP, which is mediated by the CD39/CD73 enzyme pair, predetermines immunosuppressive and proangiogenic properties of myeloid cells. We have previously shown that the deletion of the TGF-β type II receptor gene (Tgfbr2) expression in myeloid cells is associated with decreased tumor growth, suggesting protumorigenic effect of TGF-β signaling. In this study, we tested the hypothesis that TGF-β drives differentiation of myeloid-derived suppressor cells into protumorigenic terminally differentiated myeloid mononuclear cells (TDMMCs) characterized by high levels of cell-surface CD39/CD73 expression. We found that TDMMCs represent a major cell subpopulation expressing high levels of both CD39 and CD73 in the tumor microenvironment. In tumors isolated from mice with spontaneous tumor formation of mammary gland and conditional deletion of the type II TGF-β receptor in mammary epithelium, an increased level of TGF-β protein was associated with further increase in number of CD39(+)CD73(+) TDMMCs compared with MMTV-PyMT/TGFβRII(WT) control tumors with intact TGF-β signaling. Using genetic and pharmacological approaches, we demonstrated that the TGF-β signaling mediates maturation of myeloid-derived suppressor cells into TDMMCs with high levels of cell surface CD39/CD73 expression and adenosine-generating capacity. Disruption of TGF-β signaling in myeloid cells resulted in decreased accumulation of TDMMCs, expressing CD39 and CD73, and was accompanied by increased infiltration of T lymphocytes, reduced density of blood vessels, and diminished progression of both Lewis lung carcinoma and spontaneous mammary carcinomas. We propose that TGF-β signaling can directly induce the generation of CD39(+)CD73(+) TDMMCs, thus contributing to the immunosuppressive, proangiogenic, and tumor-promoting effects of this pleiotropic effector in the tumor microenvironment.

Mapping the immunosuppressive environment in uterine tumors: implications for immunotherapy

The major hurdle for cancer vaccines to be effective is posed by tumor immune evasion. Several common immune mechanisms and mediators are exploited by tumors to avoid immune destruction. In an attempt to shed more light on the immunosuppressive environment in uterine tumors, we analyzed the presence of PD-L1, PD-L2, B7-H4, indoleamine 2,3-dioxygenase (IDO), galectin-1, galectin-3, arginase-1 activity and myeloid-derived suppressor cell (MDSC) infiltration. IDO, PD-L1, PD-L2 and B7-H4 were analyzed by immunohistochemistry. PD-L2 was mostly expressed at low levels in these tumors. We found high IDO expression in 21 % of endometrial carcinoma samples and in 14 % of uterine sarcoma samples. For PD-L1 and B7-H4, we found high expression in 92 and 90 % of endometrial cancers, respectively, and in 100 and 92 % of the sarcomas. Galectin-1 and 3 were analyzed in tissue lysates by ELISA, but we did not find an increase in both molecules in tumor lysates compared with benign tissues. We detected expression of galectin-3 by fibroblasts, immune cells and tumor cells in single-cell tumor suspensions. In addition, we noted a highly significant increase in arginase-1 activity in endometrial carcinomas compared with normal endometria, which was not the case for uterine sarcomas. Finally, we could demonstrate MDSC infiltration in fresh tumor suspensions from uterine tumors. These results indicate that the PD-1/PD-L1 interaction and B7-H4 could be possible targets for immune intervention in uterine cancer patients as well as mediation of MDSC function. These observations are another step toward the implementation of inhibitors of immunosuppression in the treatment of uterine cancer patients.

Uterine cervical cancer displaying tumor-related leukocytosis: a distinct clinical entity with radioresistant feature

BACKGROUND

Tumor-related leukocytosis (TRL) is occasionally found in patients with nonhematopoietic malignancies. We investigated the clinical implication of TRL and individualized treatment for TRL-positive cervical cancer, as well as the underlying biological mechanism.

METHODS

Clinical data from 258 cervical cancer patients treated with definitive radiotherapy were analyzed to investigate the association between TRL and treatment outcome. Clinical samples, cervical cancer cell lines, and a mouse model of cervical cancer were used to examine the mechanisms responsible for TRL in cervical cancer, focusing on the role of tumor-derived granulocyte colony-stimulating factor (G-CSF) and myeloid-derived suppressor cells (MDSCs). All statistical tests were two-sided.

RESULTS

TRL was statistically significantly associated with younger age (Wilcoxon rank sum test, P = .03), larger tumor size (Wilcoxon rank sum test, P = .006), advanced clinical stage (χ(2) test, P = .01), and shorter overall survival (Cox proportional hazard modeling and Wald tests, P < .001). Among cervical cancer patients, TRL was associated with upregulated tumor G-CSF expression (χ(2) test, P < .001), elevated serum G-CSF levels (Student t test, P = .03), larger spleens (Student t test, P = .045), and increased MDSC frequencies in the blood (Student t test, P < .001) compared with the TRL-negative patients. In vitro and in vivo experiments revealed that tumor-derived G-CSF was involved in the underlying causative mechanism of TRL and MDSCs induced by tumor-derived G-CSF are responsible for the rapidly progressive and radioresistant nature of TRL-positive cervical cancer. The administration of anti-Gr-1 neutralizing antibody or the depletion of MDSCs by splenectomy (n = 6 per group) inhibited tumor growth and enhanced radiosensitivity in TRL-positive cervical cancer xenografts (Wilcoxon rank sum test, P = .008 and P = .02, respectively).

CONCLUSIONS

TRL is associated with resistance to radiotherapy among cervical cancer patients, and MDSC-targeting treatments may have therapeutic potential in these patients.

Myeloid cell dysfunction and the pathogenesis of the diabetic chronic wound

Diabetes can promote a state of chronic inflammation associated with serious complications that are difficult to treat, including ulceration of the lower extremities and chronic wounds. Chronic wounds are often incurable and contribute to both a reduced quality of life for patients and an enormous burden for healthcare services. In diabetes, the inflammatory response early in wound healing is inappropriately amplified and prolonged, leading to the persistent presence in the wound of vastly elevated numbers of dysfunctional, hyperpolarised macrophages that fail to transition to a pro-healing phenotype. Recent evidence suggests that systemic chronic inflammation induces intrinsic defects in monocytes via chromatin modifications that may pre-programme monocytes to a pro-inflammatory phenotype, while the local wound environment inhibits differentiation to a pro-healing phenotype. Current understanding remains incomplete, and careful dissection of how local and systemic inflammation combine to negatively influence myeloid cell development will be key to developing effective therapies aimed at healing the diabetic wound.

Trial Watch: Adoptive cell transfer for anticancer immunotherapy

The expression "adoptive cell transfer" (ACT) is commonly employed to indicate an immunotherapeutic regimen involving the isolation of autologous blood-borne or tumor-infiltrating lymphocytes, their selection/expansion/activation ex vivo, and their reinfusion into the patient, most often in the context of lymphodepleting pre-conditioning and in combination with immunostimulatory treatments. Optionally, the cellular material for ACT is genetically manipulated before expansion to (1) target specific tumor-associated antigens; (2) endogenously express immunostimulatory molecules; and/or (3) persist for long periods upon reinfusion. Consistent efforts have been dedicated at the amelioration of this immunotherapeutic regimen throughout the past decade, resulting in the establishment of ever more efficient and safer ACT protocols. Accordingly, the number of clinical trials testing ACT in oncological indications does not cease to increase. In this Trial Watch, we summarize recent developments in this exciting area of research, covering both high-impact studies that have been published during the last 12 months and clinical trials that have been launched in the same period to evaluate the safety and therapeutic potential of ACT in cancer patients.

Circulating hematopoietic stem and progenitor cells are myeloid-biased in cancer patients

Cancer is associated with a profound perturbation in myelopoiesis that results in the accumulation of myeloid-derived suppressor cells (MDSCs) to promote disease progression. Recent studies in mice suggest that tumor-derived factors could regulate the differentiation of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow and subsequently contribute to dysregulation of hematopoiesis. However, the nature and role of HPSCs in patients with cancer remain unknown. Here we show, in detailed studies of the peripheral blood from 133 untreated patients with seven different types of tumors, that the composition of circulating HSPCs was significantly altered in patients with solid tumors. The frequencies of circulating granulocyte-monocyte progenitors (GMPs) were increased four to seven fold in all types of tumors examined, and the circulating hematopoietic precursors exhibited myeloid bias with a skew toward granulocytic differentiation in patients with solid tumors. These myeloid precursors are selectively enriched in tumor tissues, and the high levels of circulating GMPs were positively correlated with disease progression. By using cord blood-derived CD34(+) cells, we developed an in vitro short-term culture model to effectively induce the rapid generation of MDSCs. We found that, among the factors produced by various tumors, GM-CSF, granulocyte colony-stimulating factor, and IL-6 could not only promote the myeloid-biased differentiation, but also induce the differentiation of myeloid precursors into functional MDSCs. These findings suggest that the altered circulating HSPCs may serve as an important link between dysregulated bone marrow hematopoiesis and accumulated MDSCs in patients with cancer.

Frequencies of circulating MDSC correlate with clinical outcome of melanoma patients treated with ipilimumab

Metastatic melanoma has a poor prognosis with high resistance to chemotherapy and radiation. Recently, the anti-CTLA-4 antibody ipilimumab has demonstrated clinical efficacy, being the first agent to significantly prolong the overall survival of inoperable stage III/IV melanoma patients. A major aim of patient immune monitoring is the identification of biomarkers that predict clinical outcome. We studied circulating myeloid-derived suppressor cells (MDSC) in ipilimumab-treated patients to detect alterations in the myeloid cell compartment and possible correlations with clinical outcome. Lin(-) CD14(+) HLA-DR(-) monocytic MDSC were enriched in peripheral blood of melanoma patients compared to healthy donors (HD). Tumor resection did not significantly alter MDSC frequencies. During ipilimumab treatment, MDSC frequencies did not change significantly compared to baseline levels. We observed high inter-patient differences. MDSC frequencies in ipilimumab-treated patients were independent of baseline serum lactate dehydrogenase levels but tended to increase in patients with severe metastatic disease (M1c) compared to patients with metastases in skin or lymph nodes only (M1a), who had frequencies comparable to HD. Interestingly, clinical responders to ipilimumab therapy showed significantly less lin(-) CD14(+) HLA-DR(-) cells as compared to non-responders. The data suggest that the frequency of monocytic MDSC may be used as predictive marker of response, as low frequencies identify patients more likely benefitting from ipilimumab treatment. Prospective clinical trials assessing MDSC frequencies as potential biomarkers are warranted to validate these observations.

Primary 4T1 tumor resection provides critical "window of opportunity" for immunotherapy

It is believed that primary tumor resection modulates host-tumor immune interaction, but this has not been characterized in a stringent breast cancer tumor model. This report, using the 4T1 murine mammary tumor model, characterizes for the first time the dynamic longitudinal changes in immunosuppressive and effector components of the immune system after resection of an established orthotopic primary tumor with a defined natural history of developing lung metastases. More specifically, we analyzed changes of absolute numbers and frequencies of MDSC, regulatory T cells (Treg), as well as activated CD4 and CD8 positive T cells in spleens and, in some studies, lungs of 4T1 tumor-bearing mice and mice after primary tumor resection. Importantly, using mathematical analyses we established that primary resection of an orthotopic tumor had created a "window of opportunity" with decreased tumor-associated immune suppression that existed for approximately 10 days. Although tumor resection did slightly prolong survival, it did not affect the ultimate development of metastatic disease since animals with resected tumors or intact primary tumors eventually died by day 47 and 43, respectively. This window of opportunity likely occurs in humans providing a rationale and parameters for integration and testing of immunotherapeutic strategies in this critical "window of opportunity" to combat the development of metastatic disease.

Increased levels of granulocytic myeloid-derived suppressor cells in peripheral blood and tumour tissue of pancreatic cancer patients

Pancreatic cancer (PC) often presents late with poor survival. While role of immunosuppressive cells in preclinical studies provided help to develop immunotherapeutic agents, these cells remain under investigation in PC. The aim of this study was to characterise the different subsets of myeloid-derived suppressor cells (MDSCs) and evaluate their level and function in the circulation and tissue of PC patients. Significant increases in circulating and tumour-infiltrating granulocytic (Lin-HLA-DR-CD33+CD11b+CD15+), but not monocytic (Lin-HLA-DR-CD14+), MDSCs were detected in PC patients when compared with healthy donors and patients with chronic pancreatitis. The circulating MDSCs from PC patients expressed arginase 1, which represents their functional state. Blood levels of MDSCs showed no association with PC stage or preoperative levels of tumour markers. These findings provide a first characterisation of the phenotype of different subsets of peripheral and local MDSCs in PC patients and suggest that the frequency and contribution of these cells are predominantly granulocytic. This information demonstrates that MDSCs play a role in pancreatic cancer and future large validation studies may help in the development of new immunotherapeutic strategies to inhibit or eliminate MDSC function.

Modulating the tumor immune microenvironment as an ovarian cancer treatment strategy

After more than 30 years of iterations of surgical debulking plus chemotherapy, the need for complementary ovarian cancer treatments has become clear. In the ovarian cancer microenvironment, myeloid immunosuppressive leukocytes, lymphocytes, fibroblasts and endothelial cells, as well as their secreted products, surface molecules and paracrine survival factors, all provide opportunities for novel interventions. The potential of targeting microenvironmental elements in ovarian cancer patients is underscored by recently successful anti-angiogenic therapies. The compartmentalized nature of ovarian cancer, its immunogenicity and its accessibility make it an ideal disease for targeting non-tumor host cells. This review discusses the 'state-of-the-art' of the field, with an emphasis on the potential of modulating the activity of abundant microenvironmental immune cells, which govern both angiogenesis and immunosuppression.

Adipose tissue in obesity-related inflammation and insulin resistance: cells, cytokines, and chemokines

Adipose tissue is a complex organ that comprises a wide range of cell types with diverse energy storage, metabolic regulation, and neuroendocrine and immune functions. Because it contains various immune cells, either adaptive (B and T lymphocytes; such as regulatory T cells) or innate (mostly macrophages and, more recently identified, myeloid-derived suppressor cells), the adipose tissue is now considered as a bona fide immune organ, at the cross-road between metabolism and immunity. Adipose tissue disorders, such as those encountered in obesity and lipodystrophy, cause alterations to adipose tissue distribution and function with broad effects on cytokine, chemokine, and hormone expression, on lipid storage, and on the composition of adipose-resident immune cell populations. The resulting changes appear to induce profound consequences for basal systemic inflammation and insulin sensitivity. The purpose of this review is to synthesize the current literature on adipose cell composition remodeling in obesity, which shows how adipose-resident immune cells regulate inflammation and insulin resistance—notably through cytokine and chemokine secretion—and highlights major research questions in the field.

Cellular and molecular mechanisms in cancer immune escape: a comprehensive review

Immune escape is the final phase of cancer immunoediting process wherein cancer modulates our immune system to escape from being destroyed by it. Many cellular and molecular events govern the cancer's evasion of host immune response. The tumor undergoes continuous remodeling at the genetic, epigenetic and metabolic level to acquire resistance to apoptosis. At the same time, it effectively modifies all the components of the host's immunome so as to escape from its antitumor effects. Moreover, it induces accumulation of suppressive cells like Treg and myeloid derived suppressor cells and factors which also enable it to elude the immune system. Recent research in this area helps in defining the role of newer players like miRNAs and exosomes in immune escape. The immunotherapeutic approaches developed to target the escape phase appear quite promising; however, the quest for a perfect therapeutic agent that can achieve maximum cure with minimal toxicity continues.

The dark side of dendritic cells: development and exploitation of tolerogenic activity that favor tumor outgrowth and immune escape

Dendritic cells (DC) play a central role in the regulation of the immune responses by providing the information needed to decide between tolerance, ignorance, or active responses. For this reason different therapies aim at manipulating DC to obtain the desired response, such as enhanced cell-mediated toxicity against tumor and infected cells or the induction of tolerance in autoimmunity and transplantation. In the last decade studies performed in these settings have started to identify (some) molecules/factors involved in the acquisition of a tolerogenic DC phenotype as well as the underlying mechanisms of their regulatory function on different immune cell populations.

Macrophages are more potent immune suppressors ex vivo than immature myeloid-derived suppressor cells induced by metastatic murine mammary carcinomas

Myeloid-derived suppressor cells (MDSCs) are emerging as potential promoters of metastatic tumor growth, and there is interest in targeting immature MDSCs by inducing their differentiation into more mature myeloid cells. We used all-trans retinoic acid (ATRA) to differentiate MDSCs in mice bearing metastatic 4T1 or 4TO7 murine mammary tumors, and assessed the immune-suppressive mechanisms and potencies of different myeloid cell subpopulations. Metastatic mammary tumors induced the accumulation of distinct populations of immature CD11b(+)Gr1(+)F4/80(-)Ly6C(mid)Ly6G(+) MDSCs ("Gr1(+) cells") and mature CD11b(+)Gr1(-)F4/80(+) cells ("F4/80(+) cells") in metastatic target organs. ATRA triggered the differentiation of Gr1(+) cells into F4/80(+) cells in the lungs and, unexpectedly, enhanced pulmonary metastatic tumor growth. We found that F4/80(+)Ly6C(-)Ly6G(-) mature macrophages (Ms) were up to 30-fold more potent immune suppressors than Gr1(+) cells on a per-cell basis, which we postulate may contribute to the increased metastatic growth observed with ATRA treatment. F4/80(+) cells and Gr1(+) cells used different reactive oxygen species (ROS)-mediated mechanisms of immunosuppression ex vivo, with F4/80(+) cells producing higher levels of ROS, which is consistent with their superior immunosuppressive abilities. These data highlight the potent immunosuppressive functions of Ms, reveal that Ms can suppress T cell responses via ROS production, and suggest that ROS inhibitors may be useful in promoting antitumor immune responses. Our findings also caution against using ATRA to modulate myeloid cell differentiation and function to treat breast cancer metastases in the lung, and support the development of therapeutic strategies to enhance antitumor immunity by targeting myeloid cells as a collective group.

Myeloid-derived suppressor cell function is reduced by Withaferin A, a potent and abundant component of Withania somnifera root extract

Myeloid cells play a crucial role in tumor progression. The most common tumor-infiltrating myeloid cells are myeloid-derived suppressor cells (MDSC) and tumor-associated macrophages (TAMs). These cells promote tumor growth by their inherent immune suppressive activity which is enhanced by their cross-talk. The root extract of the plant Withania somnifera (Ashwagandha) (WRE) has been reported to reduce tumor growth. HPLC analysis identified Withaferin A (WA) as the most abundant constituent of WRE and led us to determine whether the anti-tumor effects of WRE and WA involve modulating MDSC and TAM activity. A prominent effect of MDSC is their production of IL-10 which increases upon cross-talk with macrophages, thus polarizing immunity to a pro-tumor type 2 phenotype. In vitro treatment with WA decreased MDSC production of IL-10 and prevented additional MDSC production of IL-10 generated by MDSC-macrophage cross-talk. Macrophage secretion of IL-6 and TNFα, cytokines that increase MDSC accumulation and function, was also reduced by in vitro treatment with WA. Much of the T-cell suppressive activity of MDSC is due to MDSC production of reactive oxygen species (ROS), and WA significantly reduced MDSC production of ROS through a STAT3-dependent mechanism. In vivo treatment of tumor-bearing mice with WA decreased tumor weight, reduced the quantity of granulocytic MDSC, and reduced the ability of MDSC to suppress antigen-driven activation of CD4+ and CD8+ T cells. Thus, adjunctive treatment with WA reduced myeloid cell-mediated immune suppression, polarized immunity toward a tumor-rejecting type 1 phenotype, and may facilitate the development of anti-tumor immunity.

SECTM1 produced by tumor cells attracts human monocytes via CD7-mediated activation of the PI3K pathway

Tumor-associated macrophages (TAMs) play essential roles in tumor progression and metastasis. Tumor cells recruit myeloid progenitors and monocytes to the tumor site, where they differentiate into TAMs; however, this process is not well studied in humans. Here we show that human CD7, a T cell and NK cell receptor, is highly expressed by monocytes and macrophages. Expression of CD7 decreases in M-CSF differentiated macrophages and in Melanoma-conditioned Medium Induced Macrophages (MCMI/Mϕ) in comparison to monocytes. A ligand for CD7, SECTM1 (Secreted and transmembrane protein 1), is highly expressed in many tumors, including melanoma cells. We show that SECTM1 binds to CD7 and significantly increases monocyte migration by activation of the PI3K pathway. In human melanoma tissues, tumor-infiltrating macrophages expressing CD7 are present. These melanomas, with CD7-positive inflammatory cell infiltrations, frequently highly express SECTM1, including an N-terminal, soluble form, which can be detected in the sera of metastatic melanoma patients but not in normal sera. Taken together, our data demonstrate that CD7 is present on monocytes and tumor macrophages, and that its ligand, SECTM1, is frequently expressed in corresponding melanoma tissues, possibly acting as a chemoattractant for monocytes to modulate the melanoma microenvironment.

Expression of the B-cell receptor component CD79a on immature myeloid cells contributes to their tumor promoting effects

The role of myeloid derived suppressor cells (MDSCs) in promoting tumorigenesis is well-established, and significant effort is being made to further characterize surface markers on MDSCs both for better diagnosis and as potential targets for therapy. Here we show that the B cell receptor adaptor molecule CD79a is unexpectedly expressed on immature bone marrow myeloid cells, and is upregulated on MDSCs generated in multiple different mouse models of metastatic but not non-metastatic cancer. CD79a on MDSCs is upregulated and activated in response to soluble factors secreted by tumor cells. Activation of CD79a on mouse MDSCs, by crosslinking with a specific antibody, maintained their immature phenotype (CD11b+Gr1+), enhanced their migration, increased their suppressive effect on T cell proliferation, and increased secretion of pro-tumorigenic cytokines such as IL-6 and CCL22. Furthermore, crosslinking CD79a on myeloid cells activated signaling through Syk, BLNK, ERK and STAT3 phosphorylation. In vivo, CD79+ myeloid cells showed enhanced ability to promote primary tumor growth and metastasis. Finally we demonstrate that CD79a is upregulated on circulating myeloid cells from lung cancer patients, and that CD79a+ myeloid cells infiltrate human breast tumors. We propose that CD79a plays a functional role in the tumor promoting effects of myeloid cells, and may represent a novel target for cancer therapy.

Metabolic targets for cancer therapy

Malignant cells exhibit metabolic changes, when compared to their normal counterparts, owing to both genetic and epigenetic alterations. Although such a metabolic rewiring has recently been indicated as yet another general hallmark of cancer, accumulating evidence suggests that the metabolic alterations of each neoplasm represent a molecular signature that intimately accompanies and allows for different facets of malignant transformation. During the past decade, targeting cancer metabolism has emerged as a promising strategy for the development of selective antineoplastic agents. Here, we discuss the intimate relationship between metabolism and malignancy, focusing on strategies through which this central aspect of tumour biology might be turned into cancer's Achilles heel.

History of myeloid-derived suppressor cells

Tumour-induced granulocytic hyperplasia is associated with tumour vasculogenesis and escape from immunity via T cell suppression. Initially, these myeloid cells were identified as granulocytes or monocytes; however, recent studies have revealed that this hyperplasia is associated with populations of multipotent progenitor cells that have been identified as myeloid-derived suppressor cells (MDSCs). The study of MDSCs has provided a wealth of information regarding tumour pathobiology, has extended our understanding of neoplastic progression and has modified our approaches to immune adjuvant therapy. In this Timeline article, we discuss the history of MDSCs, their influence on tumour progression and metastasis, and the crosstalk between tumour cells, MDSCs and the host macroenvironment.

Myeloid-derived suppressor cells in the inflammatory bowel diseases

BACKGROUND

Myeloid cells are the most abundant and heterogeneous population of leukocytes. They are rapidly recruited from the blood to areas of inflammation and perform a number of important biological functions. Chronic inflammatory conditions contribute to generation of myeloid-derived suppressor cells (MDSCs). These pathologically activated cells are increasingly recognized as important players in cancer, transplantation, and autoimmunity for their abilities to modulate innate and adaptive immune responses.

METHODS

Since clinical data on MDSC accumulation in human patients affected with inflammatory bowel diseases (IBD) are relatively scarce, most of the information described in this review came from studies using experimental mouse models of IBD.

RESULTS

In this review, we discuss possible roles of these cells in chronic immune-mediated disorders focusing on studies conducted in IBD. We will review the available evidence on how MDSCs are involved in modulating T cell responses and look into the complex relationship between Th1, Th17 cells, and myeloid cells. Finally, we will review some recent successes and failures resulted from therapies aimed at manipulating myeloid cell numbers and/or their function.

CONCLUSIONS

Although MDSCs have been described in animal models of experimental colitis and in patients with IBD, their exact role in IBD pathogenesis is unclear and needs to be studied further. Information obtained from these studies will be useful to better understand the cross talk between myeloid cells in T cells during chronic inflammation and may identify novel pathways to be targeted therapeutically.

Ways to enhance lymphocyte trafficking into tumors and fitness of tumor infiltrating lymphocytes

The tumor is a hostile microenvironment for T lymphocytes. Indeed, irregular blood flow, and endothelial cell (EC) anergy that characterize most solid tumors hamper leukocyte adhesion, extravasation, and infiltration. In addition, hypoxia and reprograming of energy metabolism within cancer cells transform the tumor mass in a harsh environment that limits survival and effector functions of T cells, regardless of being induced in vivo by vaccination or adoptively transferred. In this review, we will summarize on recent advances in our understanding of the characteristics of tumor-associated neo-angiogenic vessels as well as of the tumor metabolism that may impact on T cell trafficking and fitness of tumor infiltrating lymphocytes. In particular, we will focus on how advances in knowledge of the characteristics of tumor ECs have enabled identifying strategies to normalize the tumor-vasculature and/or overcome EC anergy, thus increasing leukocyte-vessel wall interactions and lymphocyte infiltration in tumors. We will also focus on drugs acting on cells and their released molecules to transiently render the tumor microenvironment more suitable for tumor infiltrating T lymphocytes, thus increasing the therapeutic effectiveness of both active and adoptive immunotherapies.

Deficiency of Kruppel-like factor KLF4 in mammary tumor cells inhibits tumor growth and pulmonary metastasis and is accompanied by compromised recruitment of myeloid-derived suppressor cells

Increasing evidence indicates that myeloid-derived suppressor cells (MDSCs) negatively regulate immune responses during tumor progression, inflammation and infection. However, the underlying molecular mechanisms of their development and mobilization remain to be fully delineated. Kruppel-like factor KLF4 is a transcription factor that has an oncogenic function in breast cancer development, but its function in tumor microenvironment, a critical component for tumorigenesis, has not been examined. By using a spontaneously metastatic 4T1 breast cancer mouse model and an immunodeficient NOD/SCID mouse model, we demonstrated that KLF4 knockdown delayed tumor development and inhibited pulmonary metastasis, which accompanied by decreased accumulation of MDSCs in bone marrow, spleens and primary tumors. Mechanistically, we found that KLF4 knockdown resulted in a significant decrease of circulating GM-CSF, an important cytokine for MDSC biology. Consistently, recombinant GM-CSF restored the frequency of MDSCs in purified bone marrow cells incubated with conditioned medium from KLF4 deficient cells. In addition, we identified CXCL5 as a critical mediator to enhance the expression and function of GM-CSF. Reduced CXCL5 expression by KLF4 knockdown in primary tumors and breast cancer cells was correlated with a decreased GM-CSF expression in our mouse models. Finally, we found that CXCL5/CXCR2 axis facilitated MDSC migration and that anti-GM-CSF antibodies neutralized CXCL5-induced accumulation of MDSCs. Taken together, our data suggest that KLF4 modulates maintenance of MDSCs in bone marrow by inducing GM-CSF production via CXCL5 and regulates recruitment of MDSCs into the primary tumors through the CXCL5/CXCR2 axis, both of which contribute to KLF4-mediated mammary tumor development.

Therapeutic PD-1 pathway blockade augments with other modalities of immunotherapy T-cell function to prevent immune decline in ovarian cancer

The tumor microenvironment mediates induction of the immunosuppressive programmed cell death-1 (PD-1) pathway, and targeted interventions against this pathway can help restore antitumor immunity. To gain insight into these responses, we studied the interaction between PD-1 expressed on T cells and its ligands (PD-1:PD-L1, PD-1:PD-L2, and PD-L1:B7.1), expressed on other cells in the tumor microenvironment, using a syngeneic orthotopic mouse model of epithelial ovarian cancer (ID8). Exhaustion of tumor-infiltrating lymphocytes (TIL) correlated with expression of PD-1 ligands by tumor cells and tumor-derived myeloid cells, including tumor-associated macrophages (TAM), dendritic cells, and myeloid-derived suppressor cells (MDSC). When combined with GVAX or FVAX vaccination (consisting of irradiated ID8 cells expressing granulocyte macrophage colony-stimulating factor or FLT3 ligand) and costimulation by agonistic α-4-1BB or TLR 9 ligand, antibody-mediated blockade of PD-1 or PD-L1 triggered rejection of ID8 tumors in 75% of tumor-bearing mice. This therapeutic effect was associated with increased proliferation and function of tumor antigen-specific effector CD8(+) T cells, inhibition of suppressive regulatory T cells (Treg) and MDSC, upregulation of effector T-cell signaling molecules, and generation of T memory precursor cells. Overall, PD-1/PD-L1 blockade enhanced the amplitude of tumor immunity by reprogramming suppressive and stimulatory signals that yielded more powerful cancer control.

Immune modulation of T-cell and NK (natural killer) cell activities by TEXs (tumour-derived exosomes)

Body fluids of cancer patients contain TEXs (tumour-derived exosomes). Tumours release large quantities of TEXs, and the protein content of exosome or MV (microvesicle) fractions isolated from patients' sera is high. TEXs down-regulate functions of immune cells, thus promoting tumour progression. We isolated TEXs from tumour cell supernatants and sera of patients with solid tumours or AML (acute myelogenous leukaemia). The molecular profile of TEXs was distinct from that of circulating exosomes derived from normal cells. TEXs were co-incubated with activated T-cells, conventional CD4(+) CD25(neg) T-cells or CD56(+) CD16(+) NK (natural killer) cells respectively. TEXs down-regulated CD3ζ and JAK3 (Janus kinase 3) expression in primary activated T-cells and mediated Fas/FasL (Fas ligand)-driven apoptosis of CD8(+) T-cells. TEXs promoted CD4(+) CD25(neg) T-cell proliferation and their conversion into CD4(+) CD25(hi)FOXP3+ (FOXP3 is forkhead box P3) Treg cells (regulatory T-cells), which also expressed IL-10 (interleukin 10), TGFβ1 (transforming growth factor β1), CTLA-4 (cytotoxic T-lymphocyte antigen 4), GrB (granzyme B)/perforin and effectively mediated suppression. Neutralizing antibodies specific for TGFβ1 and/or IL-10 inhibited the ability of TEXs to expand Treg cells. TEXs obtained at diagnosis from AML patients' sera were positive for blast-associated markers CD33, CD34, CD117 and TGFβ1, and they decreased cytotoxic activity of NK cells isolated from NC (normal control) donors, induced Smad phosphorylation and down-regulated NKG2D receptor expression. Correlations between the TEX molecular profile or TEX protein levels and clinical data in cancer patients suggest that TEX-mediated effects on immune cells are prognostically important. In contrast with exosomes released by normal cells, TEXs have immunosuppressive properties and are involved in regulating peripheral tolerance in patients with cancer.

Biomarkers in Exhaled Breath Condensate and Serum of Chronic Obstructive Pulmonary Disease and Non-Small-Cell Lung Cancer

Chronic obstructive pulmonary disease (COPD) and lung cancer are leading causes of deaths worldwide which are associated with chronic inflammation and oxidative stress. Lung cancer, in particular, has a very high mortality rate due to the characteristically late diagnosis. As such, identification of novel biomarkers which allow for early diagnosis of these diseases could improve outcome and survival rate. Markers of oxidative stress in exhaled breath condensate (EBC) are examples of potential diagnostic markers for both COPD and non-small-cell lung cancer (NSCLC). They may even be useful in monitoring treatment response. In the serum, S100A8, S100A9, and S100A12 of the S100 proteins are proinflammatory markers. They have been indicated in several inflammatory diseases and cancers including secondary metastasis into the lung. It is highly likely that they not only have the potential to be diagnostic biomarkers for NSCLC but also prognostic indicators and therapeutic targets.

The role and potential therapeutic application of myeloid-derived suppressor cells in TNBS-induced colitis

MDSCs, a heterogeneous population of cells that expand during many pathogenic conditions, have remarkable abilities to suppress T cell responses. Their role in murine colitis, induced by TNBS and therapeutic application, remains unclear. Murine colitis was induced through intrarectally administrating TNBS, twice. MDSCs in spleen and colonic LPMCs were identified using flow cytometric analysis. In adoptive transfer, MDSCs were isolated from spleen after TNBS challenges by using microbeads or generated in vitro by coculturing bone marrow cells with HSCs and then transferred into naïve mice. Two hours later, mice were then challenged with TNBS, once/week for 2 weeks. The mice were killed four days after the second TNBS delivery, and intestinal inflammation and cytokine levels and MDSC percentages were evaluated. The percentages of CD11b+Gr-1+MDSCs and subsets (CD11b+Ly6C+ and CD11b+Ly6G+MDSCs) were increased in spleen and/or colonic LPMCs in colitis mice and also correlated with the severity of intestinal inflammation. MDSCs isolated from colitis mice suppressed the proliferation of splenocytes in vitro. Adoptive transfer of MDSCs, isolated from colitis mice or generated in vitro, decreased intestinal inflammation, levels of IFN-γ, IL-17, and TNF, and percentages of spleen MDSCs when compared with controls. MDSCs that have inhibitory function in vitro and in vivo are increased and correlated with intestinal inflammation, suggesting that they may be used as a biomarker of disease activity and a cell-based biotherapy in IBD.

The irradiated tumor microenvironment: role of tumor-associated macrophages in vascular recovery

Radiotherapy is an important modality used in the treatment of more than 50% of cancer patients in the US. However, despite sophisticated techniques for radiation delivery as well as the combination of radiation with chemotherapy, tumors can recur. Thus, any method of improving the local control of the primary tumor by radiotherapy would produce a major improvement in the curability of cancer patients. One of the challenges in the field is to understand how the tumor vasculature can regrow after radiation in order to support tumor recurrence, as it is unlikely that any of the endothelial cells within the tumor could survive the doses given in a typical radiotherapy regimen. There is now considerable evidence from both preclinical and clinical studies that the tumor vasculature can be restored following radiotherapy from an influx of circulating cells consisting primarily of bone marrow derived monocytes and macrophages. The radiation-induced influx of bone marrow derived cells (BMDCs) into tumors can be prevented through the blockade of various cytokine pathways and such strategies can inhibit tumor recurrence. However, the post-radiation interactions between surviving tumor cells, recruited immune cells, and the remaining stroma remain poorly defined. While prior studies have described the monocyte/macrophage inflammatory response within normal tissues and in the tumor microenvironment, less is known about this response with respect to a tumor after radiation therapy. The goal of this review is to summarize existing research studies to provide an understanding of how the myelomonocytic lineage may influence vascular recovery within the irradiated tumor microenvironment.

Induction and stability of human Th17 cells require endogenous NOS2 and cGMP-dependent NO signaling

Nitric oxide (NO) is a ubiquitous mediator of inflammation and immunity, involved in the pathogenesis and control of infectious diseases, autoimmunity, and cancer. We observed that the expression of nitric oxide synthase-2 (NOS2/iNOS) positively correlates with Th17 responses in patients with ovarian cancer (OvCa). Although high concentrations of exogenous NO indiscriminately suppress the proliferation and differentiation of Th1, Th2, and Th17 cells, the physiological NO concentrations produced by patients’ myeloid-derived suppressor cells (MDSCs) support the development of RORγt(Rorc)+IL-23R⁺IL-17⁺ Th17 cells. Moreover, the development of Th17 cells from naive-, memory-, or tumor-infiltrating CD4+ T cells, driven by IL-1β/IL-6/IL-23/NO-producing MDSCs or by recombinant cytokines (IL-1β/IL-6/IL-23), is associated with the induction of endogenous NOS2 and NO production, and critically depends on NOS2 activity and the canonical cyclic guanosine monophosphate (cGMP)–cGMP-dependent protein kinase (cGK) pathway of NO signaling within CD4⁺ T cells. Inhibition of NOS2 or cGMP–cGK signaling abolishes the de novo induction of Th17 cells and selectively suppresses IL-17 production by established Th17 cells isolated from OvCa patients. Our data indicate that, apart from its previously recognized role as an effector mediator of Th17-associated inflammation, NO is also critically required for the induction and stability of human Th17 responses, providing new targets to manipulate Th17 responses in cancer, autoimmunity, and inflammatory diseases.

Myeloid-derived suppressor cells in cancer: recent progress and prospects

Immunosuppressive cells, mainly myeloid-derived suppressor cells (MDSCs) and T regulatory cells, downregulate antitumour immunity and cancer immunotherapy. MDSCs are a heterogeneous group of immature myeloid cells that negatively regulate the immune responses during tumour progression, inflammation and infection. Whilst there have been extensive laboratory investigations aimed at characterising the MDSC subsets in cancer, there remains a significant gap in our understanding of their phenotypical and functional heterogeneity. In this article, we review data concerning the phenotypical and functional role of MDSCs in cancers. Importantly, we analyse the value of MDSCs as a prognostic factor in various clinical settings and the possible therapeutic approaches towards elimination of their immunosuppressive activity and enhancement of beneficial antitumour immune responses. MDSCs promote tumour immune evasion by inhibiting T-cell responses, as well as by supporting tumour progression. Accumulation of MDSCs is associated with the progression of human cancers, and their elimination was shown to improve anti-tumour immune responses. Phenotypical characterisation of MDSCs has been poorly investigated in many human cancers and lacks comprehensive clinicopathological correlation data. Although the need for effective therapeutic agents to eliminate the MDSC suppressive effect is immense, their role has been examined only in a few clinical settings.

Update on the challenges and recent advances in cancer immunotherapy

This overview provides an analysis of some of the immunotherapies currently in use and under investigation, with a special focus on the tumor microenvironment, which we believe is a major factor responsible for the general failure of immunotherapy to date. It is our expectation that combining immunotherapy with methods of altering the tumor microenvironment and targeting regulatory T cells and myeloid cells will yield favorable results.

New insights into the role of the immune microenvironment in breast carcinoma

Recently, immune edition has been recognized as a new hallmark of cancer. In this respect, some clinical trials in breast cancer have reported imppressive outcomes related to laboratory immune findings, especially in the neoadjuvant and metastatic setting. Infiltration by tumor infiltrating lymphocytes (TIL) and their subtypes, tumor-associated macrophages (TAM) and myeloid-derived suppressive cells (MDSC) seem bona fide prognostic and even predictive biomarkers, that will eventually be incorporated into diagnostic and therapeutic algorithms of breast cancer. In addition, the complex interaction of costimulatory and coinhibitory molecules on the immune synapse and the different signals that they may exert represent another exciting field to explore. In this review we try to summarize and elucidate these new concepts and knowledge from a translational perspective focusing on breast cancer, paying special attention to those aspects that might have more significance in clinical practice and could be useful to design successful therapeutic strategies in the future.

Dendritic cell-based vaccines: barriers and opportunities

Dendritic cells (DCs) have several characteristics that make them an ideal vehicle for tumor vaccines, and with the first US FDA-approved DC-based vaccine in use for the treatment of prostate cancer, this technology has become a promising new therapeutic option. However, DC-based vaccines face several barriers that have limited their effectiveness in clinical trials. A major barrier includes the activation state of the DC. Both DC lineage and maturation signals must be selected to optimize the antitumor response and overcome immunosuppressive effects of the tumor microenvironment. Another barrier to successful vaccination is the selection of target antigens that will activate both CD8(+) and CD4(+) T cells in a potent, immune-specific manner. Finally, tumor progression and immune dysfunction limit vaccine efficacy in advanced stages, which may make DC-based vaccines more efficacious in treating early-stage disease. This review underscores the scientific basis and advances in the development of DC-based vaccines, focuses on current barriers to success and highlights new research opportunities to address these obstacles.

Trial Watch: Adoptive cell transfer for anticancer immunotherapy

Adoptive cell transfer (ACT) represents a prominent form of immunotherapy against malignant diseases. ACT is conceptually distinct from dendritic cell-based approaches (which de facto constitute cellular vaccines) and allogeneic transplantation (which can be employed for the therapy of hematopoietic tumors) as it involves the isolation of autologous lymphocytes exhibiting antitumor activity, their expansion/activation ex vivo and their reintroduction into the patient. Re-infusion is most often performed in the context of lymphodepleting regimens (to minimize immunosuppression by host cells) and combined with immunostimulatory interventions, such as the administration of Toll-like receptor agonists. Autologous cells that are suitable for ACT protocols can be isolated from tumor-infiltrating lymphocytes or generated by engineering their circulating counterparts for the expression of transgenic tumor-specific T-cell receptors. Importantly, lymphocytes can be genetically modified prior to re-infusion for increasing their persistence in vivo, boosting antitumor responses and minimizing side effects. Moreover, recent data indicate that exhausted antitumor T lymphocytes may be rejuvenated in vitro by exposing them to specific cytokine cocktails, a strategy that might considerably improve the clinical success of ACT. Following up the Trial Watch that we published on this topic in the third issue of OncoImmunology (May 2012), here we summarize the latest developments in ACT-related research, covering both high-impact studies that have been published during the last 13 months and clinical trials that have been initiated in the same period to assess the antineoplastic profile of this form of cellular immunotherapy.

Celecoxib enhances the efficacy of 15-hydroxyprostaglandin dehydrogenase gene therapy in treating murine breast cancer

PURPOSE

The overexpression of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) has been proved to inhibit tumor growth and metastasis through degradation of prostaglandin E2 (PGE2), which is often overexpressed in various cancers and accelerates tumor progression. Cyclooxygenase-2 (COX-2), a synthase of PGE2, actively produces much PGE2 to counteract the 15-PGDH-induced antitumor efficacy. Here, we investigated the combinational effect by using pcDNA3.1(+) encoding mouse 15-PGDH gene therapy and celecoxib, a COX-2 inhibitor, in mouse breast cancers.

METHODS

Mice bearing 4T1 were treated with short-term administration of the COX-2 inhibitor celecoxib (40 mg/kg/day) plus liposome-encapsulated mouse 15-PGDH in order to determine their synergistic antitumor activity in vivo. And the possible mechanisms were investigated.

RESULTS

We observed that the combination treatment of 15-PGDH and celecoxib significantly inhibited tumor growth and lung metastases than monotherapy or controls. Moreover, the effect of combination treatment was associated with significant reduction of PGE2 in serum, which resulted from increased 15-PDGH and decreased COX-2 in tumor tissues. The tumor tissues in combination treatment presented more apoptotic cells and less microvessel density. Notably, the number of myeloid-derived suppressor cells in the spleen was also significantly decreased in the combination treatment than others.

CONCLUSIONS

Our findings suggested that celecoxib increased the antitumor activity of 15-PGDH by synergistically blocking PGE2 pathway, which might be a new feasible way for cancer therapy.

Peripherally administered nanoparticles target monocytic myeloid cells, secondary lymphoid organs and tumors in mice

Nanoparticles have been extensively developed for therapeutic and diagnostic applications. While the focus of nanoparticle trafficking in vivo has traditionally been on drug delivery and organ-level biodistribution and clearance, recent work in cancer biology and infectious disease suggests that targeting different cells within a given organ can substantially affect the quality of the immunological response. Here, we examine the cell-level biodistribution kinetics after administering ultrasmall Pluronic-stabilized poly(propylene sulfide) nanoparticles in the mouse. These nanoparticles depend on lymphatic drainage to reach the lymph nodes and blood, and then enter the spleen rather than the liver, where they interact with monocytes, macrophages and myeloid dendritic cells. They were more readily taken up into lymphatics after intradermal (i.d.) compared to intramuscular administration, leading to ∼50% increased bioavailability in blood. When administered i.d., their distribution favored antigen-presenting cells, with especially strong targeting to myeloid cells. In tumor-bearing mice, the monocytic and the polymorphonuclear myeloid-derived suppressor cell compartments were efficiently and preferentially targeted, rendering this nanoparticulate formulation potentially useful for reversing the highly suppressive activity of these cells in the tumor stroma.

Dendritic cell immunotherapy combined with gemcitabine chemotherapy enhances survival in a murine model of pancreatic carcinoma

Pancreatic cancer is an extremely aggressive malignancy with a dismal prognosis. Cancer patients and tumor-bearing mice have multiple immunoregulatory subsets including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSC) that may limit the effectiveness of anti-tumor immunotherapies for pancreatic cancer. It is possible that modulating these subsets will enhance anti-tumor immunity. The goal of this study was to explore depletion of immunoregulatory cells to enhance dendritic cell (DC)-based cancer immunotherapy in a murine model of pancreatic cancer. Flow cytometry results showed an increase in both Tregs and MDSC in untreated pancreatic cancer-bearing mice compared with control. Elimination of Tregs alone or in combination with DC-based vaccination had no effect on pancreatic tumor growth or survival. Gemcitabine (Gem) is a chemotherapeutic drug routinely used for the treatment for pancreatic cancer patients. Treatment with Gem led to a significant decrease in MDSC percentages in the spleens of tumor-bearing mice, but did not enhance overall survival. However, combination therapy with DC vaccination followed by Gem treatment led to a significant delay in tumor growth and improved survival in pancreatic cancer-bearing mice. Increased MDSC were measured in the peripheral blood of patients with pancreatic cancer. Treatment with Gem also led to a decrease of this population in pancreatic cancer patients, suggesting that combination therapy with DC-based cancer vaccination and Gem may lead to improved treatments for patients with pancreatic cancer.

Therapeutic regulation of myeloid-derived suppressor cells and immune response to cancer vaccine in patients with extensive stage small cell lung cancer

Myeloid-derived suppressor cells (MDSC) are one of the major factors limiting the efficacy of immune therapy. In a clinical trial of patients with extensive stage small cell lung cancer (SCLC), we tested the possibility that targeting MDSC can improve the induction of immune responses by a cancer vaccine. Forty-one patients with extensive stage SCLC were randomized into three arms: arm A--control, arm B--vaccination with dendritic cells transduced with wild-type p53, and arm C--vaccination in combination with MDSC targeted therapy with all-trans-retinoic acid (ATRA). Interim results of the ongoing clinical trial are presented. Pre-treatment levels of MDSC populations in patients from all three arms were similar. Vaccine alone did not affect the proportion of MDSC, whereas in patients treated with ATRA, the MDSC decreased more than twofold (p = 0.02). Before the start of treatment, no patients had detectable p53-specific responses in IFN-γ ELISPOT. Sequential measurements did not show positive p53 responses in any of the 14 patients from arm A. After immunization, only 3 out of 15 patients (20 %) from arm B developed a p53-specific response (p = 0.22). In contrast, in arm C, 5 out of 12 patients (41.7 %) had detectable p53 responses (p = 0.012). The proportion of granzyme B-positive CD8(+) T cells was increased only in patients from arm C but not in arm B. Depletion of MDSC substantially improved the immune response to vaccination, suggesting that this approach can be used to enhance the effect of immune interventions in cancer.

Myeloid-derived suppressor cells regulate growth of multiple myeloma by inhibiting T cells in bone marrow

Myeloid-derived suppressor cells (MDSC) are one of the major factors limiting the immune response in cancer. However, their role in bone marrow (BM), the site of primary localization of multiple myeloma (MM), is poorly understood. In this study, we found a significant accumulation of CD11b(+)CD14(-)CD33(+) immunosuppressive MDSC in BM of patients with newly diagnosed MM. To assess the possible role of MDSC in MM, we used immunocompetent mouse models. Immunosuppressive MDSC accumulated in BM of mice as early as 1 wk after tumor inoculation. S100A9 knockout (KO) mice, which are deficient in their ability to accumulate MDSC in tumor-bearing hosts, demonstrated reduced MDSC accumulation in BM after injection of MM cells compared with wild-type mice. Growth of the immunogenic MM cells was significantly reduced in S100A9KO mice. This effect was associated with the accumulation of Ag-specific CD8(+) T cells in BM and spleens of S100A9KO mice, but not wild-type mice, and was abrogated by the administration of anti-CD8 Ab or adoptive transfer of MDSC. Thus, the accumulation of MDSC at early stages of MM plays a critical role in MM progression and suggests that MDSC can be considered a possible therapeutic target in this disease.

Negative regulation of myeloid-derived suppressor cells in cancer

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells with suppressive function on immune response. In this review, we discuss recent studies about mechanisms of expansion and suppressive function of MDSCs during inflammation, infection and autoimmune diseases, as well as pro-angiogenic and pro-metastatic functions of these cells in tumor development. Further, we focus on novel studies of MDSCs and therapeutic approaches to eliminate these cells in cancer.

Microenvironment generated during EGFR targeted killing of pancreatic tumor cells by ATC inhibits myeloid-derived suppressor cells through COX2 and PGE2 dependent pathway

Background

Myeloid-derived suppressor cells (MDSCs) are one of the major components of the immune-suppressive network, play key roles in tumor progression and limit therapeutic responses. Recently, we reported that tumor spheres formed by breast cancer cell lines were visibly smaller in a Th₁ enriched microenvironment with significantly reduced differentiation of MDSC populations in 3D culture. In this study, we investigated the mechanism(s) of bispecific antibody armed ATC mediated inhibition of MDSC in the presence or absence of Th₁ microenvironment.

Methods

We used 3D co-culture model of peripheral blood mononuclear cells (PBMC) with pancreatic cancer cells MiaPaCa-2 [MiaE] and gemcitabine resistant MiaPaCa-GR [MiaM] cells to generate MDSC in the presence or absence of Th₁ cytokines and EGFRBi armed ATC (aATC).

Results

We show significantly decreased differentiation of MDSC (MiaE, p<0.005; MiaM, p<0.05) in the presence of aATC with or without Th₁ cytokines. MDSC recovered from control cultures (without aATC) showed potent ability to suppress T cell functions compared to those recovered from aATC containing co-cultures. Reduced accumulation of MDSC was accompanied by significantly lower levels of COX2 (p<0.0048), PGE₂ (p<0.03), and their downstream effector molecule Arginase-1 (p<0.01), and significantly higher levels of TNF-α, IL-12 and chemokines CCL3, CCL4, CCL5, CXCL9 and CXCL10 under aATC induced Th₁ cytokine enriched microenvironment.

Conclusions

These data suggest aATC can suppress MDSC differentiation and attenuation of their suppressive activity through down regulation of COX2, PGE₂ and ARG1 pathway that is potentiated in presence of Th₁ cytokines, suggesting that Th₁ enriching immunotherapy may be beneficial in pancreatic cancer treatment.

Epigenetic silencing of retinoblastoma gene regulates pathologic differentiation of myeloid cells in cancer

Two major populations of myeloid-derived suppressor cells (MDSC), monocytic MDSC (M-MDSC) and polymorphonuclear MDSC (PMN-MDSC) regulate immune responses in cancer and other pathologic conditions. Under physiologic conditions, Ly6C^hiLy6G⁻ inflammatory monocytes, which are the normal counterpart of M-MDSC, differentiate into macrophages and dendritic cells (DCs). PMN-MDSC is the predominant group of MDSC that accumulates in cancer. Here we show that a large proportion of M-MDSC in tumor-bearing mice acquired phenotypic, morphological and functional features of PMN-MDSC. Acquisition of this phenotype, but not the functional attributes of PMN-MDSC, was mediated by transcriptional silencing of the retinoblastoma (Rb) gene through epigenetic modifications mediated by histone deacetylase 2 (HDAC-2). These data demonstrate novel mechanism regulation of myeloid cells in cancer.

Tumor-promoting immune-suppressive myeloid-derived suppressor cells in the multiple myeloma microenvironment in humans

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous, immature myeloid cell population with the ability to suppress immune responses. MDSCs have been characterized in infections, inflammatory diseases, and solid tumors; however, their presence and role in the tumor-promoting, immune-suppressive microenvironment in hematologic malignancies remains unclear. We assessed the presence, frequency, and functional characteristics of MDSCs in patients with newly diagnosed, relapsed, and relapsed/refractory multiple myeloma (MM) compared with healthy donors. Additionally, we evaluated the immunomodulatory effects of lenalidomide and bortezomib on MDSCs in MM. CD11b(+)CD14(-)HLA-DR(-/low)CD33(+)CD15(+) MDSCs were significantly increased in both the peripheral blood and the bone marrow of patients with active MM compared with healthy donors. Furthermore, MDSCs induced MM growth while suppressing T-cell-mediated immune responses. Conversely, MM cells induced the development of MDSCs from healthy donor peripheral blood mononuclear cells, confirming a bidirectional interaction between MDSCs and MM cells and immune effector cells. Our results further suggest that MDSCs may be associated with the activity of disease in MM. Importantly, our studies suggest that inhibition of the tumor-promoting and immune-suppressive functions of MDSCs in MM may represent a promising novel immune-based therapeutic strategy.

Myeloid-derived suppressor cells function as novel osteoclast progenitors enhancing bone loss in breast cancer

Enhanced bone destruction is a hallmark of various carcinomas such as breast cancer, where osteolytic bone metastasis is associated with increased morbidity and mortality. Immune cells contribute to osteolysis in cancer growth, but the factors contributing to aggressive bone destruction are not well understood. In this study, we show the importance of myeloid-derived suppressor cells (MDSC) in this process at bone metastatic sites. Because MDSC originate from the same myeloid lineage as macrophages, which are osteoclast precursors, we hypothesized that MDSC may undergo osteoclast differentiation and contribute to enhanced bone destruction and tumor growth. Using an immunocompetent mouse model of breast cancer bone metastasis, we confirmed that MDSC isolated from the tumor-bone microenvironment differentiated into functional osteoclasts both in vitro and in vivo. Mechanistic investigations revealed that nitric oxide signaling was critical for differentiation of MDSC into osteoclasts. Remarkably, osteoclast differentiation did not occur in MDSC isolated from control or tumor-bearing mice that lacked bone metastasis, signifying the essential cross-talk between tumor cells and myeloid progenitors in the bone microenvironment as a requirement for osteoclast differentiation of MDSC. Overall, our results identify a wholly new facet to the multifunctionality of MDSC in driving tumor progression, in this case as a novel osteoclast progenitor that specifically drives bone metastasis during cancer progression.

Monocyte-derived cells of the brain and malignant gliomas: the double face of Janus

OBJECTIVE

Monocyte-derived cells of the brain (MDCB) are a diverse group of functional immune cells that are also highly abundant in gliomas. There is growing evidence that MDCB play essential roles in the pathogenesis of gliomas. The aim of this review was to collate and systematize contemporary knowledge about these cells as they relate to glioma progression and antiglioblastoma therapeutic modalities with a view toward improved effectiveness of therapy.

METHODS

We reviewed relevant studies to construct a summary of different MDCB subpopulations in steady state and in malignant gliomas and discuss their role in the development of malignant gliomas and potential future therapies.

RESULTS

Current studies suggest that MDCB subsets display different phenotypes and differentiation potentials depending on their milieu in the brain and exposure to tumoral influences. MDCB possess specific and unique functions, including those that are protumoral and those that are antitumoral.

CONCLUSIONS

Elucidating the role of mononuclear-derived cells associated with gliomas is crucial in designing novel immunotherapy strategies. Much progress is needed to characterize markers to identify cell subsets and their specific regulatory roles. Investigation of MDCB can be clinically relevant. Specific MDCB populations potentially can be used for glioma therapy as a target or as cell vehicles that might deliver cytotoxic substances or processes to the glioma microenvironment.