CD34+ immune suppressive cells in the peripheral blood of patients with head and neck cancer

The role of granulocyte-macrophage colony-stimulating factor in head and neck cancer

OBJECTIVE

To review the molecular mechanisms and biological roles of granulocyte-macrophage colony-stimulating factor (GM-CSF) in head and neck squamous cell carcinoma, highlighting its potential clinical applications.

DESIGN

The search terms "granulocyte-macrophage colony-stimulating factor", "GM-CSF", "CSF2″ and "head and neck squamous cell carcinoma" or "head and neck cancer" were queried in the PubMed/MEDLINE and Scopus databases.

RESULTS

Despite of being a widely expressed cytokine, the number of studies investigating the specific roles of GM-CSF in head and neck cancer was limited. Most of them investigated GM-CSF in conjunction with other cytokines. When studied alone, conflicting findings were observed in head and neck squamous cell carcinoma. GM-CSF has been shown to induce angiogenesis and local tumor invasion. Additionally, it has also been implicated in immune evasion. On the other hand, GM-CSF stimulated the differentiation of dendritic cells, which are responsible for presenting tumor antigens, and for the regulation of T cell function. Even with these paradoxical effects, there are few studies investigating the potential of GM-CSF as adjuvant therapy in head and neck cancer.

CONCLUSION

The effects of GM-CSF in head and neck cancer may be pro- or antitumor. Understanding how one arm and not the other is activated is essential to assess the applicability and the safety of this cytokine as a therapeutic agent.

Induction of M‑MDSCs with IL6/GM‑CSF from adherence monocytes and inhibition by WP1066

Peripheral blood monocytes acquire the phenotype of myeloid-derived suppressor cells (MDSCs) by induction of cytokine or co-culture with cancer cells and are widely used to model MDSCs for in vitro studies. However, the simplest method of plastic adhesive sorting is poorly described as the purity of monocyte resulting from this method is the lowest compared with flow cytometry cell-sorting and magnetic beads sorting. Therefore, the present study aimed at investigating the effect of the plastic adhesive monocyte isolation techniques on the resulting MDSCs phenotype. Monocytes were allowed to adhere for 1 h and cultured with IL6 and granulocyte-macrophage colony-stimulating factors (GM-CSF) for 7 days. Plastic adhesion sorting resulted in early low monocyte yield and purity, but high purity of MDSCs was obtained by refreshing the induction medium. The resulting MDSCs were the major subpopulation of CD33⁺CD11b⁺CD14⁺CD15^-human leukocyte antigen (HLA)^-/low cells and provided the potent capacity to suppress T cell proliferation and cytokine IFN-γ production. Moreover, the induced MDSCs were inhibited by STAT3 inhibitor WP1066, resulting in downregulation of phosphorylated-STAT3 and PD-L1 expression and upregulation of apoptosis respectively. In conclusion, the present study described the generation of monocytic MDSCs from adherence monocytes and the inhibition of STAT3 inhibitor WP1066 on the induced MDSCs. The present study contributed to the development of a new clinical drug, WP1066 targeting MDSC.

Increase in polymorphonuclear myeloid-derived suppressor cells and regulatory T-cells in children with B-cell acute lymphoblastic leukemia

Our study aimed to evaluate the levels of MDSCs and Tregs in pediatric B-cell acute lymphoblastic leukemia (B-ALL), their relation to patients' clinical and laboratory features, and the impact of these cells on the induction response. This study included 31 pediatric B-ALL patients and 27 healthy controls. All patients were treated according to the protocols of the modified St. Jude Children's Research Hospital total therapy study XIIIB for ALL. Levels of MDSCs and Tregs were analyzed using flow cytometry. We observed a reduction in the levels of CD4 + T-cells and an increase in both the polymorphonuclear MDSCs (PMN-MDSCs) and Tregs. The frequencies of PMN-MDSCs and Tregs were directly related to the levels of peripheral and bone marrow blast cells and CD34 + cells. Complete postinduction remission was associated with reduced percentages of PMN-MDSCs and Tregs, with the level of PMN-MDCs in this subpopulation approaching that of healthy controls. PMN-MDSCs and Tregs jointly play a critical role in maintaining an immune-suppressive state suitable for B-ALL tumor progression. Thereby, they could be independent predictors of B-ALL progress, and finely targeting both PMN-MDSCs and Tregs may be a promising approach for the treatment of B-ALL.

Vitamin D deficiency in head and neck cancer patients - prevalence, prognostic value and impact on immune function

Vitamin D deficiency is frequently observed in human cancer patients and a prognostic relevance could be shown for some entities. Additionally, it is known that vitamin D can stimulate the patients' antitumor immunity. However, valid epidemiological data for head and neck squamous cell carcinoma (HNSCC) patients are sparse and functional studies on a possible connection between vitamin D and the patients' immune system are missing. 25-OH vitamin D serum levels were analyzed in 231 HNSCC patients and 232 healthy controls and correlated with clinical data and patient survival. Intra- and peritumoral infiltration with T-cell, NK-cell and macrophage populations was analyzed in 102 HNSCC patients by immunohistochemistry. In 11 HNSCC patients, NK-cells were isolated before and after vitamin D substitution and analyzed for their cytotoxic activity directed against a HNSCC cell line. Vitamin D serum levels were significantly lower in HNSCC patients compared with healthy controls. Low vitamin D levels were associated with lymphatic metastasis and a negative HPV status and were a significant predictor of poor overall survival. HNSCC patients with severe vitamin D deficiency showed significantly altered intra- and peritumoral immune cell infiltrate levels. After vitamin D substitution, the patients' NK cells showed a significant rise in cytotoxic activity. Taken together, we could show that Vitamin D deficiency is highly prevalent in HNSCC patients and is a predictor of poor survival. Vitamin D substitution used as an adjuvant in immune therapies such as cetuximab and nivolumab treatment could support antitumorigenic immune responses, thus contributing to the improvement of the patients' prognosis in the context of a multimodal therapy.

Chemotherapy alters the increased numbers of myeloid-derived suppressor and regulatory T cells in children with acute lymphoblastic leukemia

INTRODUCTION

Acute lymphoblastic leukemia (ALL) is the most common cancer diagnosed in children. The precise mechanism behind the relapse in this disease is not clearly known. One possible mechanism could be the accumulation of immunosuppressive cells, including myeloid-derived suppressor cells (MDSCs) and T regulatory cells (T_regs) which we and others have reported to mediate suppression of anti-tumor immune responses.

AIM

In this study, we aimed to analyze the numbers of these cells in a population of B-ALL pediatric patients.

METHODS

Peripheral blood samples withdrawn from B-ALL pediatric patients (n = 45 before, during and after the induction phase of chemotherapy. Using multi parametric flow cytometric analysis. MDSCs were identified as Lin^-HLA-DR^-CD33⁺CD11b⁺; and T_reg cells were defined as CD4⁺CD25⁺CD127^-/low.

RESULTS

Early diagnosed B-ALL patients showed significant increases in the numbers of MDSCs and T_regs as compared to healthy volunteers. During induction of chemotherapy, however, the patients showed higher and lower numbers of MDSCs and T_reg cells, respectively as compared to early diagnosed patients (i.e., before chemotherapy). After induction of chemotherapy, the numbers of MDSCs and T_reg cells showed higher increases and decreases, respectively as compared to the numbers in patients during chemotherapy.

CONCLUSION

Our results indicate that B-ALL patients harbor high numbers of both MDSCs and T_regs cells. This pilot study opens a new avenue to investigate the mechanism mediating the emergence of these cells on larger number of B-ALL patients at different treatment stages.

Myeloid derived suppressor cells in chronic myeloid leukemia

The suppression of the immune system creates a permissive environment for development and progression of cancer. One population of immunosuppressive cells that have become the focus of intense study is myeloid derived suppressor cells (MDSCs), immature myeloid cells able to induce immune-escape, angiogenesis, and tumor progression. Two different subpopulations have been identified and studied: granulocytic and monocytic MDSCs, with a different immunophenotype and immunosuppressive properties. Recently, an accumulation of both Gr-MDSCs and Mo-MDSCs cells has been found in the peripheral blood of chronic myeloid leukemia (CML) patients. They are part of the tumor clone showing BCR/ABL expression. Imatinib therapy decreases both MDSCs and arginase 1 levels to normal ones. This review will focus on actual knowledge for human MDSCs and their immunosuppressive activity in CML patients, with a critical attention to comparison of Gr-MDSCs and polymorphonuclear cells (PMNs). We will then suggest the monitoring of MDSCs in patients who have discontinued tyrosine kinase inhibitors (TKIs) therapy to evaluate if their increase could correlate with disease relapse.

The immune system and head and neck squamous cell carcinoma: from carcinogenesis to new therapeutic opportunities

Head and neck squamous cell carcinomas (HNSCCs) exhibit complex interactions with the host immune system that may simultaneously explain resistance to various therapeutic modalities and that may also provide opportunities for therapeutic intervention. Discoveries in immunologic research over the last decade have led to an increased understanding of these interactions as well as the development of a multitude of investigational immunotherapies. Here, we describe the interaction between HNSCC and the immune system, including a discussion of immune cells involved with tumor carcinogenesis and the role of immune-modulating factors derived from tumors. We also describe the current immunotherapeutic approaches being investigated for HNSCC, including a discussion of the successes and limitations. With this review, we hope to present HNSCC as a model to guide future research in cancer immunology.

Escape mechanisms from antiangiogenic therapy: an immune cell's perspective

Neovascularization, the formation of new blood vessels, has become a well-established hallmark of cancer. Its functional importance for the manifestation and progression of tumors has been validated further by the beneficial therapeutic effects of angiogenesis inhibitors, most notably those targeting vascular endothelial growth factor signaling pathways. However, with the transient and short-lived nature of patient response, it has become evident that tumors have the ability to adapt to the pressures of vascular growth restriction. Observations made both in the clinic and at the bench suggest the existence of several escape mechanisms that either reestablish neovascularization in tumors or change tumor behavior to enable propagation and progression without obligate neovascularization. Some of these bypass mechanisms are regulated by low oxygen conditions (hypoxia) caused by therapy-induced vessel regression. Induction of hypoxia and hypoxia-inducible factors regulate a wide range of tumor-promoting pathways, including those of neovascularization, that can upregulate additional proangiogenic factors and drive the recruitment of various bone marrow-derived cells that have the capacity to express proangiogenic factors or directly contribute to neovasculature.

Immune regulatory activity of vitamin d3 in head and neck cancer

While vitamin D exhibits a multitude of cellular effects that can impact on cancer development and progression, this review focuses on its immune modulatory effects. These immune modulatory effects can be both direct and indirect. Compared to other cancer types, head and neck squamous cell carcinomas (HNSCC) have received less attention, but are a fascination immunologically because of the profound extent to which they inhibit immune defenses. This review describes the mechanisms of some of these immune inhibitory processes and how vitamin D can help overcome aspects of this immune suppression.

Basics of tumor development and importance of human papilloma virus (HPV) for head and neck cancer

Head and Neck Squamous Cell Carcinomas (HNSCC) are the 6(th) most common cancers worldwide. While incidence rates for cancer of the hypopharynx and larynx are decreasing, a significant increase in cancer of the oropharynx (OSCC) is observed. Classical risk factors for HNSCC are smoking and alcohol. It has been shown for 25 to 60% of OSCC to be associated with an infection by oncogenic human papilloma viruses (HPV). The development of "common" cancer of the head and neck is substantially enhanced by an accumulation of genetic changes, which lead to an inactivation of tumor suppressor genes or activation of proto-oncogenes. A more or less uniform sequence of different DNA-damages leads to genetic instability. In this context, an early and frequent event is deletion on the short arm of chromosome 9, which results in inactivation of the p16-gene. In contrast, for HPV-induced carcinogenesis, expression of the viral proteins E6 and E7 is most important, since they lead to inactivation of the cellular tumor-suppressor-proteins p53 and Rb. The natural route of transoral infection is a matter of debate; peroral HPV-infections might be frequent and disappear uneventfully in most cases. Smoking seems to increase the probability for developing an HPV-associated OSCC. The association of HNSCC with HPV can be proven with established methods in clinical diagnostics. In addition to classical prognostic factors, diagnosis of HPV-association may become important for selection of future therapies. Prognostic relevance of HPV probably surmounts many known risk-factors, for example regional metastasis. Until now, no other molecular markers are established in clinical routine. Future therapy concepts may vary for the two subgroups of patients, particularly patients with HPV-associated OSCC may take advantage of less aggressive treatments. Finally, an outlook will be given on possible targeted therapies.

Implication of stem cells in the biology and therapy of head and neck cancer

The progress which has been made in the therapy of patients with head and neck cancer in recent years mainly concern the HPV associated HNSCC and the quality of life. The overall survival of patients carrying non HPV associated HNSCC during the last thirty years has not experienced any significant improvement and must be referred to as static [1], [2]. The problem of the illness remains unchanged in the frequent and poorly controllable relapse situation. The locoregionally originating tumours or lymph node metastases show a considerably poorer response towards current therapies. Likewise for a number of patients a formation of distant metastases seems to develop during the course of the illness. Those distant metastases are also therapeutically rather difficult to control. Therefore the mortality of the non HPV induced head and neck cancer remains unchanged.

The term “stem cell” describes the entity cell, which acts as a reservoir for new cells in order to replace defective or necrotic cells. A fundamental characteristic of stem cells is the constant ability to multiply into different type of cells, which subsequently do not proliferate.

With the insight of new knowledge within the regenerative medicine and the ability of stem cells of self regenerating proliferation and their multipotency in the differentiation, the origin of cancer attains a new distinction. If you look on the tumour as a malignant wound it becomes obvious, that the regeneration or the composition of additional tissue depends on the presence and differentiation of stem cells. The wound healing, which is a regeneration of tissue depends not only on stationary stem cells. In fact stem cells are attracted for “homing” in the defective areas by despatch of various messengers, which then form and replace the vascular tree or other tissue [3], [4].

Next to those stem cells, which functionally help to form tumour tissue, a small entity of “real cancer stem cells” in solid tumours is expected. Those occur in tumours and they have typical stem cell characteristics like self-regeneration and the potential of differentiation and are potentially responsible for tumour growth. With their ability of self-regeneration they would have the ability to form a complete tumour out of every single cell. That tumour would histologically look like the tumour those cells initially originated from. Of particular interest regarding those currently still elusive cancer stem cells is their resistance towards current therapies like radiotherapy or chemotherapy. Those insights now get a completely new meaning in tumour biology: Does a cancer stem cell exist, which is able to initiate and keep up tumour growth despite all possible therapeutic interventions?

This presentation will outline the current views regarding cancer stem cells in non HPV associated HNSCC and it will highlight problems, which are currently researched on. The objective must be to understand the biology of those cells in a way that make an extended range of therapeutics possible. A therapy, which specifically targets cancer stem cells, could improve the chances of recovery.

Regulation of suppressive function of myeloid-derived suppressor cells by CD4+ T cells

Myeloid derived suppressor cells play a critical role in T cell suppression in cancer. Here, we discuss the mechanisms of how MDSC suppress CD4(+) or CD8(+) T cells in an antigen dependent or non-dependent manner.

Immunotherapy for head and neck cancer: advances and deficiencies

The concept of immunotherapy as a treatment for cancer patients has been in existence for decades. However, more recent immune therapeutic approaches have involved targeting of tumor-specific antigens. Although improvements have been made in using such immune stimulatory treatment strategies for a variety of solid cancers, the use of these strategies for patients with head and neck squamous cell carcinoma (HNSCC) is lagging behind. Immunotherapeutic approaches for HNSCC are particularly complicated by the profound immune suppression that is induced by HNSCC, which potentially decreases the effectiveness of immune stimulatory efforts. Trials involving patients with various solid cancers have shown the enhanced effectiveness of combining various immunotherapeutic approaches or combining immunotherapy with chemotherapy or radiation therapy. Treatment of HNSCC with such combination approaches has not been extensively investigated and has the added challenge of the need to overcome the HNSCC-induced immune suppression. This study focuses on clinical trials that have tested immunotherapeutic approaches for HNSCC patients and the challenges associated with such approaches. In addition, it will call attention to immunotherapeutic strategies that have been shown to be successful in the treatment of other solid cancers to identify potential strategies that may apply to the treatment of HNSCC.

Clinical outcome of patients with various advanced cancer types vaccinated with an optimized cryptic human telomerase reverse transcriptase (TERT) peptide: results of an expanded phase II study

BACKGROUND

TERT (telomerase reverse transcriptase) plays a critical role in tumor cell growth and survival. In an expanded phase II study, we evaluated the immunological and clinical responses to the TERT-targeting Vx-001 vaccine in patients with advanced solid tumors.

METHODS

HLA-A*0201-positive patients received two subcutaneous injections of the optimized TERT(572Y) peptide followed by four injections of the native TERT(572) peptide, every 3 weeks. Peptide-specific immune responses were evaluated by enzyme-linked immunosorbent spot at baseline, and after the second and the sixth vaccinations.

RESULTS

Fifty-five patients were enrolled and 34 (62%) completed the six vaccinations. A TERT-specific T-cell immune response was observed in 55% and 70% of patients after the second and the sixth vaccinations, respectively. The disease control rate (DCR) was 36% [95% confidence interval (CI) 24% to 49%], including one complete and one partial response. Immunologically responding patients had a better clinical outcome than nonresponders [DCR: 44% versus 14% (P = 0.047); progression-free survival (PFS): 5.2 versus 2.2 months (P = 0.0001) and overall survival: 20 versus 10 months (P = 0.041)]. Multivariate analysis revealed that the immunological response was an independent variable associated with increased PFS (hazard ratio = 3.35; 95% CI 1.7-6.7).

CONCLUSION

Vx-001 vaccine was well tolerated and induced a TERT-specific immunological response, which was significantly correlated with improved clinical outcome.

Myeloid-derived suppressor cells in human cancer

Myeloid-derived suppressor cells are one of the major factors responsible for immune suppression in cancer. They also contribute to limited efficacy of current vaccination strategies. Here, we give an overview of the myeloid-derived suppressor cells field focusing primarily on the studies in cancer patients and current and future therapeutic options targeting these cells.

Use of alpha,25-dihydroxyvitamin D3 treatment to stimulate immune infiltration into head and neck squamous cell carcinoma

Prior studies have shown that treatment of head and neck squamous cell carcinoma (HNSCC) patients with 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] reduced intratumoral levels of immune inhibitory CD34(+) progenitor cells while increasing levels of mature progeny dendritic cells. This finding was extended to a pilot study to determine whether 1,25(OH)(2)D(3) treatment concurrently increases levels of intratumoral CD4(+) and CD8(+) T cells, increases intratumoral levels of immune cells expressing the early activation marker CD69, and prolongs time to HNSCC recurrence. The clinical trial comprised 16 patients with newly diagnosed HNSCC being untreated and 16 patients being treated with 1,25(OH)(2)D(3) during the 3-week interval between cancer diagnosis and surgical treatment. Immunologic effects of treatment were monitored by immunohistochemical analyses of surgically removed HNSCC. Clinical effectiveness of 1,25(OH)(2)D(3) treatment in this study was measured by the time to HNSCC recurrence. HNSCC tissues of patients who received treatment with 1,25(OH)(2)D(3) contained increased levels of CD4(+) cells and, more significantly, CD8(+) T cells. Also prominent was an increase in cells expressing the lymphoid activation marker CD69. Results of this pilot study suggest that patients treated with 1,25(OH)(2)D(3) had a lengthier time to tumor recurrence compared with patients who were not treated before surgery.

Dendritic cell recovery post-lymphodepletion: a potential mechanism for anti-cancer adoptive T cell therapy and vaccination

Adoptive transfer of autologous tumor-reactive T cells holds promise as a cancer immunotherapy. In this approach, T cells are harvested from a tumor-bearing host, expanded in vitro and infused back to the same host. Conditioning of the recipient host with a lymphodepletion regimen of chemotherapy or radiotherapy before adoptive T cell transfer has been shown to substantially improve survival and anti-tumor responses of the transferred cells. These effects are further enhanced when the adoptive T cell transfer is followed by vaccination with tumor antigens in combination with a potent immune adjuvant. Although significant progress has been made toward an understanding of the reasons underlying the beneficial effects of lymphodepletion to T cell adoptive therapy, the precise mechanisms remain poorly understood. Recent studies, including ours, would indicate a more central role for antigen presenting cells, in particular dendritic cells. Unraveling the exact role of these important cells in mediation of the beneficial effects of lymphodepletion could provide novel pathways toward the rational design of more effective anti-cancer immunotherapy. This article focuses on how the frequency, phenotype, and functions of dendritic cells are altered during the lymphopenic and recovery phases post-induction of lymphodepletion, and how they affect the anti-tumor responses of adoptively transferred T cells.

Myeloid-derived suppressor cells: linking inflammation and cancer

Many cancer immunotherapies developed in experimental animals have been tested in clinical trials. Although some have shown modest clinical effects, most have not been effective. Recent studies have identified myeloid-origin cells that are potent suppressors of tumor immunity and therefore a significant impediment to cancer immunotherapy. "Myeloid-derived suppressor cells" (MDSC) accumulate in the blood, lymph nodes, and bone marrow and at tumor sites in most patients and experimental animals with cancer and inhibit both adaptive and innate immunity. MDSC are induced by tumor-secreted and host-secreted factors, many of which are proinflammatory molecules. The induction of MDSC by proinflammatory mediators led to the hypothesis that inflammation promotes the accumulation of MDSC that down-regulate immune surveillance and antitumor immunity, thereby facilitating tumor growth. This article reviews the characterization and suppressive mechanisms used by MDSC to block tumor immunity and describes the mechanisms by which inflammation promotes tumor progression through the induction of MDSC.

1alpha,25-Dihydroxyvitamin D(3) to skew intratumoral levels of immune inhibitory CD34(+) progenitor cells into dendritic cells

OBJECTIVES

Prior studies showed that immune inhibitory CD34(+) progenitor cells, whose numbers are increased in head and neck squamous cell carcinoma (HNSCC) patients, can be differentiated into immune stimulatory dendritic cells by culture with 1alpha,25-dihydroxyvitamin D(3) (1,25[OH](2)D(3)). This was extended to a pilot study to diminish intratumoral levels of CD34(+) progenitor cells by inducing their maturation into dendritic cells with 1,25(OH)(2)D(3).

STUDY DESIGN

Newly diagnosed HNSCC patients were untreated for 3 weeks or received 3 weeks of 1,25(OH)(2)D(3) treatment befoer surgical treatment.

SUBJECTS AND METHODS

HNSCC tissue was collected by biopsy from six patients who had no prior 1,25(OH)(2)D(3) treatment and at the time of surgical treatment from six untreated patients and 11 patients who completed 1,25(OH)(2)D(3) treatment. Tissues were analyzed by immunohistochemistry for levels of CD34(+) cells and dendritic cells.

RESULTS

After 1,25(OH)(2)D(3) treatment, intratumoral levels of CD34(+) cells and levels of immature dendritic cells declined. However, levels of intratumoral mature dendritic cells increased. Clinical effects of 1,25(OH)(2)D(3) treatment are premature to analyze.

CONCLUSIONS

Treatment of HNSCC patients with 1,25(OH)(2)D(3) reduced levels of immune inhibitory CD34(+) cells while increasing maturation of dendritic cells. This supports added studies to determine the effect of 1,25(OH)(2)D(3) on intratumoral immune competence.

Increased circulating myeloid-derived suppressor cells correlate with clinical cancer stage, metastatic tumor burden, and doxorubicin-cyclophosphamide chemotherapy

Abnormal accumulation of myeloid-derived suppressor cells (MDSC) is an important mechanism of tumor immune evasion. Cyclophosphamide (CTX) has also been shown in non-tumor bearing animals to cause transient surges in MDSC. Knowledge of MDSC is primarily based on preclinical work, and to date only few published studies have involved cancer patients. The goal of this study was to test the hypothesis that circulating MDSC levels correlate with clinical cancer stage, CTX-based chemotherapy, and metastatic tumor burden. Whole blood was collected from 106 newly diagnosed solid tumor patients (stages I-IV). Percentages of circulating MDSC (Lin(-/Lo), HLA DR-, CD33(+)CD11b(+)) were determined prior to initiation of systemic therapy. In 17 early stage breast cancer patients receiving doxorubicin-cyclophosphamide chemotherapy every 14 days (ddAC) blood was collected on day 1 of each cycle. Circulating MDSC were significantly increased in cancer patients of all stages relative to healthy volunteers. A significant correlation between circulating MDSC and clinical cancer stage was also observed. Moreover, among stage IV patients, those with extensive metastatic tumor burden had the highest percent and absolute number of MDSC. Significant increases in circulating MDSC were observed with ddAC when compared with pretreatment levels. Circulating MDSC levels correlate with clinical cancer stage, ddAC, and metastatic tumor burden. This information must be incorporated into the design of future trials exploring immune-based therapeutic strategies. Pharmacologic modulation of MDSC should also be tested in future clinical trials.

Subsets of myeloid-derived suppressor cells in tumor-bearing mice

Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of cells that play a critical role in tumor associated immune suppression. In an attempt to identify a specific subset of MDSC primarily responsible for immunosuppressive features of these cells, 10 different tumor models were investigated. All models showed variable but significant increase in the population of MDSC. Variability of MDSC expansion in vivo matched closely the effect of tumor cell condition medium in vitro. MDSC consists of two major subsets of Ly6G(+)Ly6C(low) granulocytic and Ly6G(-)Ly6C(high) monocytic cells. Granulocytic MDSC have increased level of reactive oxygen species and undetectable level of NO whereas monocytic MDSC had increased level of NO but undetectable levels of reactive oxygen species. However, their suppressive activity per cell basis was comparable. Almost all tumor models demonstrated a preferential expansion of granulocytic subset of MDSC. We performed a phenotypical and functional analysis of several surface molecules previously suggested to be involved in MDSC-mediated suppression of T cells: CD115, CD124, CD80, PD-L1, and PD-L2. Although substantial proportion of MDSC expressed those molecules no differences in the level of their expression or the proportion, positive cells were found between MDSC and cells from tumor-free mice that lack immune suppressive activity. The level of MDSC-mediated T cell suppression did not depend on the expression of these molecules. These data indicate that suppressive features of MDSC is caused not by expansion of a specific subset but more likely represent a functional state of these cells.

Cross-talk between myeloid-derived suppressor cells and macrophages subverts tumor immunity toward a type 2 response

Although the immune system has the potential to protect against malignancies, many individuals with cancer are immunosuppressed. Myeloid-derived suppressor cells (MDSC) are elevated in many patients and animals with tumors, and contribute to immune suppression by blocking CD4(+) and CD8(+) T cell activation. Using the spontaneously metastatic 4T1 mouse mammary carcinoma, we now demonstrate that cross-talk between MDSC and macrophages further subverts tumor immunity by increasing MDSC production of IL-10, and by decreasing macrophage production of IL-12. Cross-talk between MDSC and macrophages requires cell-cell contact, and the IL-12 decrease is dependent on MDSC production of IL-10. Treatment with the chemotherapeutic drug gemcitabine, which reduces MDSC, promotes rejection of established metastatic disease in IL-4Ralpha(-/-) mice that produce M1 macrophages by allowing T cell activation, by maintaining macrophage production of IL-12, and by preventing increased production of IL-10. Therefore, MDSC impair tumor immunity by suppressing T cell activation and by interacting with macrophages to increase IL-10 and decrease IL-12 production, thereby promoting a tumor-promoting type 2 response, a process that can be partially reversed by gemcitabine.

Altered recognition of antigen is a mechanism of CD8+ T cell tolerance in cancer

Antigen-specific CD8+ T-cell tolerance, induced by myeloid-derived suppressor cells (MDSCs), is one of the main mechanisms of tumor escape. Using in vivo models, we show here that MDSCs directly disrupt the binding of specific peptide-major histocompatibility complex (pMHC) dimers to CD8-expressing T cells through nitration of tyrosines in a T-cell receptor (TCR)-CD8 complex. This process makes CD8-expressing T cells unable to bind pMHC and to respond to the specific peptide, although they retain their ability to respond to nonspecific stimulation. Nitration of TCR-CD8 is induced by MDSCs through hyperproduction of reactive oxygen species and peroxynitrite during direct cell-cell contact. Molecular modeling suggests specific sites of nitration that might affect the conformational flexibility of TCR-CD8 and its interaction with pMHC. These data identify a previously unknown mechanism of T-cell tolerance in cancer that is also pertinent to many pathological conditions associated with accumulation of MDSCs.

Myeloid-Derived Suppressor Cells

The development of tumor-specific T cell tolerance is largely responsible for tumor escape. Accumulation of myeloid-derived suppressor cells (MDSCs) in animal tumor models as well as in cancer patients is involved in tumor-associated T cell tolerance. In recent years, it has become increasingly evident that MDSCs bring about antigen-specific T cell tolerance by various mechanisms, which is the focus of this chapter.

Defining the ability of cyclophosphamide preconditioning to enhance the antigen-specific CD8+ T-cell response to peptide vaccination: creation of a beneficial host microenvironment involving type I IFNs and myeloid cells

Although cyclophosphamide (CTX) has been clearly shown to enhance active specific and adoptive immunotherapies, the mechanism(s) underlying these beneficial effects have not been clearly defined. To define the impact of CTX preconditioning on the antigen-specific CD8 T-cell response to peptide vaccination, we used an adoptive transfer model based on the OT-1 T-cell receptor transgenic mouse. CTX preconditioning dramatically enhanced the antigen-specific CD8 T-cell response to peptide vaccination. Specifically, CTX significantly enhanced the expansion and function of responding CD8 T cells as demonstrated by flow cytometry and cytokine production. In parallel experiments, we attempted to define the mechanism(s) underlying these beneficial effects of CTX therapy. CTX therapy increased the relative number and activation status of myeloid dendritic cells, and was associated with the induction of significant levels of the inflammatory cytokines interferon-alpha, monocyte chemoattractant protein-1, and IL-6. Adoptive transfer experiments into type I IFNR-/- and CR3-/- mice confirmed that the beneficial effects of CTX were at least partially dependent on type I interferons and myeloid cells. Adoptive transfer of up to 150x10(6) naive spleen cells at the time of antigen-specific CD8 T-cell transfer did not abrogate the effects of CTX therapy, suggesting that the creation of a niche in the immune system may not be required. CTX decreased the absolute, but not relative number of CD4+CD25+ Treg cells, consistent with the possibility that regulatory T cells may be targeted by CTX therapy. Of note, combination therapy with CTX and a synthetic TLR3 agonist further enhanced the antigen-specific CD8+ T-cell response. Taken together, our data suggest that CTX modulates specific components of the innate immune system resulting in a beneficial host microenvironment. Specific targeting of these components may enhance the effectiveness of CTX preconditioning for adoptive immunotherapy.

All-trans-retinoic acid improves differentiation of myeloid cells and immune response in cancer patients

Abnormal dendritic cell differentiation and accumulation of immature myeloid suppressor cells (ImC) is one of the major mechanisms of tumor escape. We tested the possibility of pharmacologic regulation of myeloid cell differentiation using all-trans-retinoic acid (ATRA). Eighteen patients with metastatic renal cell carcinoma were treated with ATRA followed by s.c. interleukin 2 (IL-2). Eight healthy individuals comprised a control group. As expected, the cancer patients had substantially elevated levels of ImC. We observed that ATRA dramatically reduced the number of ImC. This effect was observed only in patients with high plasma concentration of ATRA (>150 ng/mL), but not in patients with lower ATRA concentrations (<135 ng/mL). Effects of ATRA on the proportions of different dendritic cell populations were minor. However, ATRA significantly improved myeloid/lymphoid dendritic cell ratio and the ability of patients' mononuclear cells to stimulate allogeneic T cells. This effect was associated with significant improvement of tetanus-toxoid-specific T-cell response. During the IL-2 treatment, the ATRA effect was completely eliminated. To assess the role of IL-2, specimens from 15 patients with metastatic renal cell carcinoma who had been treated with i.v. IL-2 alone were analyzed. In this group also, IL-2 significantly reduced the number and function of dendritic cells as well as T-cell function. These data indicate that ATRA at effective concentrations eliminated ImC, improved myeloid/lymphoid dendritic cell ratio, dendritic cell function, and antigen-specific T-cell response. ATRA treatment did not result in significant toxicity and it could be tested in therapeutic combination with cancer vaccines.

Protective mechanisms of head and neck squamous cell carcinomas from immune assault

Head and neck squamous cell carcinoma (HNSCC) is an aggressive malignancy that is the sixth most common neoplasm in the world. Despite advances in treatments involving surgery, radiation, and chemotherapy, the 5-year survival has remained at less than 50% for the past 30 years, primarily because of local recurrences. Thus, the possibility of immunotherapeutic approaches for patients with HNSCC has gained interest. Unfortunately, patients with HNSCC have profound immune defects that are associated with increased recurrence. This review aims to provide an overview of both the defensive and immune subversive mechanisms by which patients with HNSCC can protect themselves from immune antitumor assault.

Combination docetaxel plus vitamin D(3) as an immune therapy in animals bearing squamous cell carcinomas

OBJECTIVE

Background tumor growth results in the mobilization of immune inhibitory CD34(+) progenitor cells. However, vitamin D(3) can differentiate the CD34(+) cells into immune stimulatory dendritic cells. This study determined if docetaxel treatment could increase the impact of the vitamin D(3) to generate dendritic cells.

METHODS

The murine squamous cell carcinoma model, SCC VII/SF, which is often used as a head and neck cancer model, was used to determine the immunological effects of two cycles of docetaxel plus vitamin D(3).

RESULTS

Vitamin D(3) with or without docetaxel was similarly effective in reducing CD34(+) cell levels within the spleen, lymph nodes, and tumor. Dendritic cell levels were similarly enhanced in the lymph nodes by vitamin D(3) alone or combined with docetaxel. However, the combination treatment caused a prominent increase in intratumoral levels of active T cells, which was not observed by the individual treatments.

CONCLUSION

Incorporating docetaxel treatment with vitamin D(3) differentiation-inducing treatment enhances intratumoral immune responsiveness.

Role of immature myeloid cells in mechanisms of immune evasion in cancer

Tumor affects myelopoiesis by inhibiting the process of differentiation/maturation of antigen-presenting cells from their myeloid precursors and by stimulating an accumulation of immature myeloid cells in cancer patients and tumor-bearing mice. These immature myeloid cells can contribute greatly to tumor progression and promote tumor evasion from immune attack: i) by inhibiting development of adaptive immune responses against tumor in lymphoid organs; ii) by migrating into tumor site and differentiating there into highly immune suppressive tumor-associated macrophages. Immature myeloid cells and tumor-associated macrophages utilize different JAK/STAT signaling pathways and different mechanisms to control T cell responses, which include increased production of TGF-beta, reactive oxygen species, peroxynitrites, as well as enhanced L-arginine metabolism. Understanding of precise mechanisms, which tumors use to affect differentiation of APC from myeloid cell precursors and inhibit T cell responses, could help to develop new approaches for cancer therapy and substantially improve efficiency of existing cancer vaccination strategies.

Tumor skewing of CD34+ progenitor cell differentiation into endothelial cells

Tumor production of granulocyte-macrophage colony-stimulating factor (GM-CSF) results in the mobilization of CD34(+) progenitor cells into the peripheral blood and tumor tissue. Using the Lewis lung carcinoma (LLC) model, in vitro studies showed that LLC cells could chemoattract CD34(+) cells predominantly through tumor production of VEGF. Addition of LLC-conditioned medium to CD34(+) cells that were cultured under conditions that support myeloid lineage cells skewed the differentiation of these precursor cells toward endothelial cells expressing CD31 and CD144. This differentiation of CD34(+) cells toward endothelial cells was attributed predominantly to angiopoietin-1 in the tumor-conditioned medium. The CD34(+) cells expressed the angiopoietin receptor Tie-2 and their differentiation into endothelial cells was blocked with neutralizing angiopoietin-1 antibodies. In vivo studies showed that infusion of lacZ(+) CD34(+) cells from the bone marrow of transgenic mice into wild-type mice bearing LLC tumors resulted in the accumulation of lacZ(+) cells within the tumor mass, particularly at the tumor's periphery. That these infused CD34(+) progenitor cells could develop into endothelial cells of the tumor vasculature was supported by their acquisition of the endothelial cell markers CD31 or CD144 within the tumor tissue. These studies demonstrate the capacity of tumor to attract CD34(+) cells to the tumor site and to direct the differentiation of these CD34(+) cells into endothelial cells that can become a component of the tumor vasculature.

Phase IB study of 25-hydroxyvitamin D(3) treatment to diminish suppressor cells in head and neck cancer patients

Patients with head and neck squamous cell carcinoma (HNSCC) have profound immune defects. These defects are associated with a poor prognosis and are mediated, in part, by an increased number of immune inhibitory CD34(+) progenitor cells in their peripheral blood and tumor. The CD34(+) cells suppress autologous T-cell functions. Our prior work had shown that the differentiation inducer 1alpha,25-dihydroxyvitamin D(3) could drive the differentiation of CD34(+) cells isolated from HNSCC patients into dendritic cells. A phase IB clinical trial was initiated with HNSCC patients to determine if 25-hydroxyvitamin D(3) treatment could diminish CD34(+) cell levels and improve immune function. Six patients per treatment group were orally administered 20 or 40 microg/day 25-hydroxyvitamin D(3) for six weeks. Peripheral blood was collected at 0, 1, 2, 4, 6, and 8 weeks, and assessed for markers of immune activity. Although no clinical responses were observed, results of these pilot studies showed that 25-hydroxyvitamin D(3) reduced the presence of immune suppressive CD34(+) cells and improved immune competence of HNSCC patients.

Increased levels of immune inhibitory CD34+ progenitor cells in the peripheral blood of patients with node positive head and neck squamous cell carcinomas and the ability of these CD34+ cells to differentiate into immune stimulatory dendritic cells

OBJECTIVES

This study determined whether mobilization of immune inhibitory CD34+ cells by head and neck squamous cell carcinomas (HNSCC) is most prominent in patients who are node positive and whether these CD34+ cells could differentiate into immune stimulatory dendritic cells.

STUDY DESIGN AND SETTING

Peripheral blood from patients with head and neck cancer was used to measure the frequency of CD34+ cells and their capacity to differentiate into immune stimulatory dendritic cells.

RESULTS

This study demonstrated that increased CD34+ cell levels were most prominent in patients who were node positive and patients with recurrent disease. These CD34+ cells differentiated into dendritic cells that were able to present tetanus toxoid to autologous T-cells.

CONCLUSIONS

Immune suppressive CD34+ cells that are prominent in patients with HNSCC who are node positive are able to develop into immune stimulatory dendritic cells.

SIGNIFICANCE

Differentiation of tumor-mobilized CD34+ cells into dendritic cells may be an immunotherapeutic approach to stimulate antitumor reactivity.