Chemoattraction of femoral CD34+ progenitor cells by tumor-derived vascular endothelial cell growth factor

Turning 'Cold' tumors 'Hot': immunotherapies in sarcoma

Immunotherapies have an established role in the management of several advanced malignancies. Their responses are largely dependent on the presence of PD-L1, microsatellite instability (MSI), and high tumor mutation burden. Sarcomas are heterogenous tumors which comprise over 100 subtypes. They are broadly considered immunologically inert or “cold”. Immunotherapy as monotherapy has shown interesting responses in a certain handful of subtypes, such as undifferentiated pleomorphic sarcoma, dedifferentiated and pleomorphic liposarcoma, and alveolar soft part sarcoma. However, the mechanisms of action of immunotherapy agents in several sarcoma subtypes remains unknown. Several sarcoma types such as leiomyosarcoma have been shown to have an immunosuppressive microenvironment. Early clinical studies suggest the emergence of B cell infiltration in sarcoma tumor tissues as well as the role of PD-1 and PD-L1 as biomarkers of response. Immunotherapy combinations with conventional chemotherapies, radiation therapies, tyrosine kinase inhibitors and oncolytic viruses are showing promise in turning these “cold” tumors “hot”. Several novel agents as well as repurposing therapies with the potential to enhance immunotherapy responses are undergoing pre-clinical and clinical studies in other tumor types. Herein we review current clinical studies which have explored the use of immunotherapeutic agents in the management of sarcomas and discuss the challenges and future directions.

Immune Cell Metabolism in Tumor Microenvironment

Tumor microenvironment (TME) is composed of tumor cells, immune cells, cytokines, extracellular matrix, etc. The immune system and the metabolisms of glucose, lipids, amino acids, and nucleotides are integrated in the tumorigenesis and development. Cancer cells and immune cells show metabolic reprogramming in the TME, which intimately links immune cell functions and edits tumor immunology. Recent findings in immune cell metabolism hold the promising possibilities toward clinical therapeutics for treating cancer. This chapter introduces the updated understandings of metabolic reprogramming of immune cells in the TME and suggests new directions in manipulation of immune responses for cancer diagnosis and therapy.

Radiotherapy Both Promotes and Inhibits Myeloid-Derived Suppressor Cell Function: Novel Strategies for Preventing the Tumor-Protective Effects of Radiotherapy

Cancer immunotherapies aimed at neutralizing the programmed death-1 (PD-1) immune suppressive pathway have yielded significant therapeutic efficacy in a subset of cancer patients. However, only a subset of patients responds to antibody therapy with either anti-PD-1 or anti-PD-L1 antibodies. These patients appear to have so-called “hot” tumors containing tumor-reactive T cells. Therefore, checkpoint blockade therapy may be effective in a larger percentage of cancer patients if combined with therapeutics that also activate tumor-reactive T cells. Radiotherapy (RT) is a prime candidate for combination therapy because it facilitates activation of both local antitumor immunity and antitumor immunity at non-radiated, distant sites (abscopal response). However, RT also promotes tumor cell expression of PD-L1 and facilitates the development of myeloid-derived suppressor cells (MDSC), a population of immune suppressive cells that also suppress through PD-L1. This article will review how RT induces MDSC, and then describe two novel therapeutics that are designed to simultaneously activate tumor-reactive T cells and neutralize PD-1-mediated immune suppression. One therapeutic, a CD3xPD-L1 bispecific T cell engager (BiTE), activates and targets cytotoxic T and NKT cells to kill PD-L1⁺ tumor cells, despite the presence of MDSC. The BiTE significantly extends the survival time of humanized NSG mice reconstituted with human PBMC and carrying established metastatic human melanoma tumors. The second therapeutic is a soluble form of the costimulatory molecule CD80 (sCD80). In addition to costimulating through CD28, sCD80 inhibits PD-1 suppression by binding to PD-L1 and sterically blocking PD-L1/PD-1 signaling. sCD80 increases tumor-infiltrating T cells and significantly extends survival time of mice carrying established, syngeneic tumors. sCD80 does not suppress T cell function via CTLA-4. These studies suggest that the CD3xPD-L1 BiTE and sCD80 may be efficacious therapeutics either as monotherapies or in combination with other therapies such as radiation therapy for the treatment of cancer.

Myeloid-Derived Suppressor Cells: Immune-Suppressive Cells That Impair Antitumor Immunity and Are Sculpted by Their Environment

Myeloid-derived suppressor cells (MDSC) are a diverse population of immature myeloid cells that have potent immune-suppressive activity. Studies in both mice and humans have demonstrated that MDSC accumulate in most individuals with cancer, where they promote tumor progression, inhibit antitumor immunity, and are an obstacle to many cancer immunotherapies. As a result, there has been intense interest in understanding the mechanisms and in situ conditions that regulate and sustain MDSC, and the mechanisms MDSC use to promote tumor progression. This article reviews the characterization of MDSC and how they are distinguished from neutrophils, describes the suppressive mechanisms used by MDSC to mediate their effects, and explains the role of proinflammatory mediators and the tumor microenvironment in driving MDSC accumulation, suppressive potency, and survival.

A history of exploring cancer in context

The concept that progression of cancer is regulated by interactions of cancer cells with their microenvironment was postulated by Stephen Paget over a century ago. Contemporary tumour microenvironment (TME) research focuses on the identification of tumour-interacting microenvironmental constituents, such as resident or infiltrating non-tumour cells, soluble factors and extracellular matrix components, and the large variety of mechanisms by which these constituents regulate and shape the malignant phenotype of tumour cells. In this Timeline article, we review the developmental phases of the TME paradigm since its initial description. While illuminating controversies, we discuss the importance of interactions between various microenvironmental components and tumour cells and provide an overview and assessment of therapeutic opportunities and modalities by which the TME can be targeted.

Increased, but Functionally Impaired, CD14(+) HLA-DR(-/low) Myeloid-Derived Suppressor Cells in Psoriasis: A Mechanism of Dysregulated T Cells

The clinical extent of psoriasis pathology is regulated in part by defects in immune networks, including a defect in the suppressive actions of regulatory T cells. Recently, CD14(+) HLA-DR(-/low) monocytic myeloid-derived suppressor cells (Mo-MDSCs) have been shown to suppress T-cell activation as one of their suppressive mechanisms. However, little is known about the role of Mo-MDSCs and their functional relationship to T-cell suppression in relation to human chronic immune-mediated inflammatory diseases, including psoriasis. Despite psoriasis being a hyperinflammatory condition, Mo-MDSCs were elevated in psoriatic patient peripheral blood mononuclear cells compared to nonpsoriatic healthy controls (2.6% vs. 0.9%, P < 0.002). Freshly isolated psoriatic Mo-MDSCs directly suppressed CD8 T-cell proliferation less efficiently than healthy control Mo-MDSCs. In addition, psoriatic Mo-MDSCs expressed reduced surface expression of programmed cell death protein 1 compared to healthy controls. Additional in vitro assays also demonstrated that psoriatic and control Mo-MDSCs both induce regulatory T-cell conversion from naïve T effector cells, but, importantly, the regulatory T cells induced by psoriatic Mo-MDSCs displayed decreased suppressive functionality. These results suggest that aberrations in psoriatic Mo-MDSCs prevent proper suppression of effector T-cell expansion and hamper the immune system's ability to correctly self-regulate.

Tolerance and immune suppression in the tumor microenvironment

The concept of immunological tolerance has guided and permeated much of modern immunology. Ray Owen's ground-breaking observations in twin cattle provided the first mechanistic explanation for tolerance to self-molecules and established tolerance as a beneficial process that protects the host against autoreactivity. However, his studies also opened the door to understanding that tolerance may be detrimental, such as occurs when cancer cells induce tolerance/immune suppression resulting in inhibition of anti-tumor immunity. This article briefly traces the early history of the field of tumor immunology with respect to tolerance, and then focuses on a relatively recently identified population of cells called myeloid-derived suppressor cells (MDSCs). MDSC are instrumental in causing tolerance/immune suppression in individuals with cancer. They are present in most individuals with cancer and because of their potent immune suppressive activity are a major deterrent to natural anti-tumor immunity and a significant obstacle to immunotherapy.

Immune effects of bevacizumab: killing two birds with one stone

Angiogenesis or new vessel formation is essential for tumour growth and progression. Therefore, targeting angiogenesis has been an attractive strategy in the treatment ofcancer. Bevacizumab is a recombinant humanized monoclonal IgG1 antibody thattargets vascular endothelial growth factor-A (VEGF-A) - a key molecular player inangiogenesis. Bevacizumumab has shown clinical efficacy in phase III clinical trials inseveral advanced solid malignancies. The clinical efficacy of bevacizumumab isprimarily due to its antiangiogenic effects; however, there are direct antitumor effectsand immunomodulatory effects. Enhancing the immune system to restore itsantitumour activity has been utilized successfully in clinical setting. In this article we willdiscuss the possible immunomodulatory effects of the most clinically usedantiangiogenic agent; bevacizumumab.

Myeloid derived suppressor cells in physiological and pathological conditions: the good, the bad, and the ugly

Myeloid derived suppressor cells (MDSCs), a heterogeneous population of myeloid progenitors, are recognized as a key element in tumor escape and progression. The importance of MDSCs in human malignancies has been demonstrated in recent years, and new approaches targeting their suppressive/tolerogenic action are currently being tested in both preclinical model and clinical trials. However, emerging evidence suggests that MDSCs may play a prominent role as regulator of the physiologic, the chronic, and the pathologic immune responses. This review will focus on the biology of MDSC in light of these new findings and the possible role of this myeloid population not only in the progression of the tumor but also in its initiation.

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.

Dynamic change and impact of myeloid-derived suppressor cells in allogeneic bone marrow transplantation in mice

Myeloid-derived suppressor cells (MDSCs) are a group of myeloid cells composed of hematopoietic progenitor cells, immature macrophages, dendritic cells, and granulocytes, which accumulate in inflammatory diseases and various cancers. Here, we investigated the dynamic changes and effects of MDSCs in graft-versus-host disease (GVHD) development and/or tumor relapse after syngeneic and allogeneic bone marrow transplantation (BMT). We found that adding functional MDSCs in donor graft alleviated GVHD, whereas removal of MDSCs in vivo exacerbated GVHD. After T cell-deplete BMT, MDSCs transiently accumulated in the blood and spleen of recipients without GVHD. In contrast, after T cell-replete BMT, the levels of blood MDSCs were constantly elevated in recipients with GVHD. MDSC accumulation positively correlated with the severity of GVHD. Additionally, MDSC accumulation was further increased upon tumor relapse. Although MDSCs isolated from both syngeneic and allogeneic BMT recipients inhibited T cell proliferation in response to alloantigen stimulation ex vivo, MDSCs from the recipients with GVHD showed much higher suppressive potency compared with those from recipients without GVHD. These results indicate that MDSCs can regulate the immune response in acute GVHD, and possibly tumor relapse, subsequent to allogeneic BMT.

Protumor activities of the immune response: insights in the mechanisms of immunological shift, oncotraining, and oncopromotion

Experimental and clinical studies indicate that cells of the innate and adaptive immune system have both anti- and pro-tumor activities. This dual role of the immune system has led to a conceptual shift in the role of the immune system's regulation of cancer, in which immune-tumor cell interactions are understood as a dynamic process that comprises at least five phases: immunosurveillance, immunoselection, immunoescape, oncotraining, and oncopromotion. The tumor microenvironment shifts immune cells to perform functions more in tune with the tumor needs (oncotraining); these functions are related to chronic inflammation and tissue remodeling activities. Among them are increased proliferation and survival, increased angiogenesis and vessel permeability, protease secretion, acquisition of migratory mesenchymal characteristics, and self-renewal properties that altogether promote tumor growth and metastasis (oncopromotion). Important populations in all these pro-tumor processes are M2 macrophages, N2 neutrophils, regulatory T cells, and myeloid derived suppressor cells; the main effectors molecules are CSF-1, IL-6, metalloproteases, VEGF, PGE-2, TGF- β , and IL-10. Cancer prognosis correlates with densities and concentrations of protumoral populations and molecules, providing ideal targets for the intelligent design of directed preventive or anticancer 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.

Improving cancer immunotherapy by targeting tumor-induced immune suppression

The status of a host's immune response influences both the development and progression of a malignancy such that immune responses can have both pro- and anti-tumorigenic effects. Cancer immunotherapy is a form of treatment that aims to improve the ability of a cancer-bearing individual to reject the tumor immunologically. However, antitumor immunity elicited by the host or by immunotherapeutic strategies, can be actively attenuated by mechanisms that limit the strength and/or duration of immune responses, including the presence of immunoregulatory cell types or the production of immunosuppressive factors. As our knowledge of tumor-induced immune suppression increases, it has become obvious that these mechanisms are probably a major barrier to effective therapy. The identification of multiple mechanisms of tumor-induced immune suppression also provides a range of novel targets for new cancer therapies. Given the vital role that a host's immune response is known to play in cancer progression, therapies that target immune suppressive mechanisms have the potential to enhance anticancer immune responses thus leading to better immune surveillance and the limitation of tumor escape. In this review, mechanisms of tumor-associated immune suppression have been divided into four forms that we have designated as (1) regulatory cells; (2) cytokines/chemokines; (3) T cell tolerance/exhaustion and (4) metabolic. We discuss select mechanisms representing each of these forms of immunosuppression that have been shown to aid tumors in evading host immune surveillance and overview therapeutic strategies that have been recently devised to "suppress these suppressors."

Immunosuppressive functions of hepatic myeloid-derived suppressor cells of normal mice and in a murine model of chronic hepatitis B virus

The immunosuppressive state of tumour-bearing hosts is attributable, at least in part, to myeloid-derived suppressor cells (MDSC). However, the role of MDSC in physiological conditions and diseases other than cancer has not been addressed. As the liver is a tolerogenic organ, the present study attempted to localize and assess functions of hepatic MDSC in a normal liver and in a murine model of chronic hepatitis B virus (HBV) infection. MDSC was identified in the liver of normal mice and HBV transgenic mice (TM) as CD11b(+) Gr1(+) cells by dual-colour flow cytometry. Highly purified populations of MDSC and their subtypes were isolated by fluorescence-activated cell sorting. The functions of MDSC and their subtypes were evaluated in allogenic mixed lymphocyte reaction (MLR) and hepatitis B surface antigen (HBsAg)-specific T cell proliferation assays. Normal mice-derived liver MDSC, but not other myeloid cells (CD11b(+) Gr1(-) ), suppressed T cell proliferation in allogenic MLR in a dose-dependent manner. Alteration of T cell antigens and impaired interferon-γ production seems to be related to MDSC-induced immunosuppression. In HBV TM, the frequencies of liver MDSC were about twice those of normal mice liver (13·6±3·2% versus 6·05±1·21%, n=5, P<0·05). Liver-derived MDSC from HBV TM also suppressed proliferative capacities of allogenic T cells and HBsAg-specific lymphocytes. Liver MDSC may have a critical role in maintaining homeostasis during physiological conditions. As liver MDSC had immunosuppressive functions in HBV TM, they may be a target of immune therapy in chronic HBV infection.

The suppressive tumor microenvironment: a challenge in cancer immunotherapy

In this review, we introduce the changing public perception of vaccines and immunotherapy in cancer treatments. We discuss the roles that different immunosuppressive cells play in the tumor microenvironment. Tumor associated macrophages (TAMs) and M1 and M2 macrophage phenotypes are discussed in depth. Additionally, the role that myeloid derived suppressor cells (MDSC) and T regulatory cells (Tregs) play in the tumor microenvironment is addressed. Highlighted are examples of therapies used against each suppressive cell type, which vary from the hypothetical to the ineffective; the inefficient to the successful. A variety of treatments have been tried to combat this fundamental problem, indeed the cause that allows cancerous mutated cells to survive, multiply and overtake the body. Efficient methods to disable each particular suppressive type of cell have been introduced; this review summarizes the discussion with a table to guide future development. We see gene therapy as the most innovative and flexible method to lead the charge to specifically modifying the tumor microenvironment.

Gr-1+ CD11b+ myeloid-derived suppressor cells suppress inflammation and promote insulin sensitivity in obesity

Activation of immune cells, including macrophages and CD8(+) T cells, contributes significantly to the advancement of obesity and its associated medical complications, such as atherosclerosis, insulin resistance, and type 2 diabetes. However, how the activation of these immune cells is regulated in vivo remains largely unexplored. Here we show that a group of immature myeloid cells with cell surface markers of Gr-1(+) CD11b(+) are highly enriched in peripheral tissues (i.e. liver and adipose tissues) during obesity. Down-regulation of these cells in obese animals significantly increases inflammation and impairs insulin sensitivity and glucose tolerance, whereas elevation of these cells via adoptive transfer has the opposite effects. Mechanistically, we show that under obese conditions, the Gr-1(+) cells suppress proliferation and induce apoptosis of CD8(+) T cells and are capable of skewing differentiation of macrophages into insulin-sensitizing, alternatively activated M2 macrophages. Taken together, our study demonstrates that immature myeloid cells provide a checks-and-balances platform to counter proinflammatory immune cells in the liver and adipose tissue during obesity to prevent overt immune responses.

Myeloid-derived suppressor cells in mammary tumor progression in FVB Neu transgenic mice

Female mice transgenic for the rat proto-oncogene c-erb-B2, under control of the mouse mammary tumor virus (MMTV) promoter (neuN), spontaneously develop metastatic mammary carcinomas. The development of these mammary tumors is associated with increased number of GR-1(+)CD11b(+) myeloid derived suppressor cells (MDSCs) in the peripheral blood (PB), spleen and tumor. We report a complex relationship between tumor growth, MDSCs and immune regulatory molecules in non-mutated neu transgenic mice on a FVB background (FVB-neuN). The first and second tumors in FVB-neuN mice develop at a median of 265 (147-579) and 329 (161-523) days, respectively, resulting in a median survival time (MST) of 432 (201 to >500) days. During tumor growth, significantly increased number of MDSCs is observed in the PB and spleen, as well as, in infiltrating the mammary tumors. Our results demonstrate a direct correlation between tumor size and the number of MDSCs infiltrating the tumor and an inverse relationship between the frequency of CD4(+) T-cells and MDSCs in the spleen. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assessment of enzyme and cytokine transcript levels in the spleen, tumor, tumor-infiltrating non-parenchymal cells (NPCs) and mammary glands revealed a significant increase in transcript levels from grossly normal mammary glands and tumor-infiltrating NPCs during tumor progression. Tumor NPCs, as compared to spleen cells from wild-type (w/t) mice, expressed significantly higher levels of arginase-1 (ARG-1), nitric oxide synthase (NOS-2), vascular endothelial growth factor (VEGF-A) and significantly lower levels of interferon (IFN)-gamma, interleukin (IL)-2 and fms-like tyrosine kinase-3 ligand (Flt3L) transcript levels. Transcript levels in the spleens of tumor-bearing (TB) mice also differed from normal mice, although to a lesser extent than transcript levels from tumor-infiltrating NPCs. Furthermore, both spleen cells and NPCs from TB mice, but not control mice, suppressed alloantigen responses by syngeneic control spleen cells. Correlative studies revealed that the number of MDSCs in the spleen was directly associated with granulocyte colony stimulating factor (G-CSF) transcript levels in the spleen; while the number of MDSCs in the tumors was directly correlated with splenic granulocyte macrophage stimulating factor (GM-CSF) transcript levels, tumor volume and tumor cell number. Together our results support a role for MDSCs in tumor initiation and progressive, T-cell depression and loss of function provide evidence which support multiple mechanisms of MDSC expansion in a site-dependent manner.

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.

VEGF-targeted therapy: mechanisms of anti-tumour activity

Several vascular endothelial growth factor (VEGF)-targeted agents, administered either as single agents or in combination with chemotherapy, have been shown to benefit patients with advanced-stage malignancies. VEGF-targeted therapies were initially developed with the notion that they would inhibit new blood vessel growth and thus starve tumours of necessary oxygen and nutrients. It has become increasingly apparent, however, that the therapeutic benefit associated with VEGF-targeted therapy is complex, and probably involves multiple mechanisms. A better understanding of these mechanisms will lead to future advances in the use of these agents in the clinic.

Use of carcinogen-induced premalignant oral lesions in a dendritic cell-based vaccine to stimulate immune reactivity against both premalignant oral lesions and oral cancer

Select groups of premalignant oral lesions carry a high risk of development of secondary premalignant lesions and oral squamous cell carcinoma (OSCC). The goal of the present study was to determine the feasibility of using premalignant lesion-pulsed dendritic cells as a treatment option to prevent development of secondary lesions and development of OSCC. Mice that were treated with the carcinogen 4-nitroquinoline-1-oxide (4NQO) developed premalignant oral lesions and, subsequently, OSCC. Immunohistochemical analyses showed that these 4NQO-induced lesions and OSCC both overexpressed the tumor antigens epidermal growth factor receptor, RAGE and, to a lesser extent, MUC1. Because there was shared overexpression of tumor antigens on premalignant oral lesions and OSCC, dendritic cells pulsed with lysates of 4NQO-induced premalignant lesion cells were tested in vitro and in vivo for their capacity to stimulate T-cell reactivity to premalignant lesion cells and to OSCC. Spleen cells that were sensitized during coculture or in vivo with premalignant lesion-pulsed dendritic cells were cytolytic toward both premalignant lesion cells and OSCC, and secreted increased levels of interferon -gamma in response to challenge with premalignant lesion cells or OSCC as compared with spleen cells that were sensitized with keratinocyte-pulsed dendritic cells. Levels of CD8+ Tcells and interferon-gamma release were also increased in lesions of mice that were vaccinated with premalignant lesion-pulsed dendritic cells. The mice that were vaccinated against premalignant lesions were also more resistant to OSCC challenge. These studies show the feasibility of using premalignant oral lesions to stimulate immune reactivity against both premalignant oral lesions and

Identification and clinical significance of mobilized endothelial progenitor cells in tumor vasculogenesis of hepatocellular carcinoma

PURPOSE

To investigate the distribution, frequency, and clinical significance of mobilized endothelial progenitor cells (EPC) in hepatocellular carcinoma (HCC).

EXPERIMENTAL DESIGN

In healthy controls and patients with HCC, the frequency of circulating EPCs was determined by colony-forming assays, fluorescence-activated cell sorting, and real-time PCR. One hundred sixty-five--amino acid form of vascular endothelial growth factor and platelet-derived growth factor-BB in plasma and tissue were quantified by ELISA. The distribution and frequency of EPCs were evaluated by immunofluorescence, immunohistochemistry, and real-time PCR in normal liver (n = 8), and tumor tissue (TT), adjacent nonmalignant liver tissue (AT), and tumor-free tissue 5 cm from the tumor edge (TF) from 64 patients with HCC. Clinicopathologic data for these patients were evaluated.

RESULTS

Compared with values for healthy controls, colony-forming unit scores were higher in the peripheral blood of patients with HCC. Plasma 165-amino acid form of vascular endothelial growth factor and platelet-derived growth factor-BB correlated with the expression level of the AC133 gene, which was also higher in the peripheral blood of patients with HCC. Immunohistochemical analysis showed that EPCs were incorporated into the microvessels in cirrhotic and tumor tissue. Compared with normal liver (9.00), increased AC133(+) microvessel density (microvessels/0.74 mm(2)) was found in TT (53.56), AT (84.76), and TF (48.33). The levels of AC133 gene expression and AC133-microvessel density in AT, which were the highest among four groups, correlated with clinicopathologic variables (the absence of tumor capsule, venous invasion, proliferating cell nuclear antigen intensity, and early recurrence).

CONCLUSIONS

Mobilized EPCs participate in tumor vasculogenesis of HCC. AC133 gene or antigen in peripheral blood and liver tissue could be used as a biomarker for predicting the progression of HCC.

Functional roles of immature dendritic cells in impaired immunity of solid tumour and their targeted strategies for provoking tumour immunity

Dendritic cells play a crucial role in initiating tumour immunity as well as in the immune response for invading foreign pathogens such as bacteria and viruses. For bacterial and viral infections, the immature dendritic cells (iDCs) residing in peripheral tissues are efficiently activated and matured by pathogen signals for performing the immune response. In contrast, for self-antigens, the naive T cells are not activated by iDCs but proceed to anergy/deletion, and the generation of regulatory T cells for immune tolerance. The induction of immune response and tolerance is regulated strictly by iDCs as the sensor for homeostasis of immune response in the host. Despite the identification of some tumour antigens, tumour immunity is not provoked successfully. Even though there are some critical obstacles to inhibit effective tumour immunity, tumour cells are able to exploit the functional roles of iDCs for tumour progression, which are induced by tumour-derived soluble factors such as vascular endothelial growth factor (VEGF) and functionally modulated in the microenvironment. The iDCs still remain as the critical target for provoking tumour immunity. In this review, the functional roles of tumour-associated iDCs and the strategy for targeting iDCs in effective tumour immunity for the cancer patient are discussed.

Production of VEGF165 by Ewing's sarcoma cells induces vasculogenesis and the incorporation of CD34+ stem cells into the expanding tumor vasculature

The Ewing's sarcoma cell line TC71 overexpresses vascular endothelial growth factor isoform 165 (VEGF165), a potent proangiogenic molecule that induces endothelial cell proliferation, migration, and chemotaxis. CD34+ bone marrow stem cells can differentiate into endothelial and hematopoietic cells. We used a transplant model to determine whether CD34+ cells migrate from the bone marrow to Ewing's sarcoma tumors and participate in the neovascularization process that supports tumor growth. We also examined the role of VEGF165 in CD34+ cell migration. Human umbilical cord CD34+ cells were transplanted into sublethally irradiated severe combined immunodeficient mice. Seven days later, the mice were injected subcutaneously with TC71 tumor cells. Tumors were excised 2 weeks later and analyzed by immunohistochemistry. The tumor sections expressed both human VE-cadherin and mouse CD31, indicating involvement of donor-derived human cells in the tumor vessels. To determine the role of VEGF165 in the chemoattraction of CD34+ cells, we generated two VEGF165-deficient TC71 clones, a stable anti-sense VEGF165 cell line (Clone 17) and a VEGF165 siRNA-inhibited clone (TC/siVEGF(7-1)). The resulting VEGF165-deficient tumor cells had normal growth rates in vitro, but had delayed growth when implanted into mice. Immunohistochemical analysis revealed decreased infiltration of CD34+ cells into both VEGF165-deficient tumors. These data show that bone marrow stem cells contribute to the growing tumor vasculature in Ewing's sarcoma and that VEGF165 is critical for the migration of CD34+ cells from the bone marrow into the tumor.

Tumor skewing of CD34+ cell differentiation from a dendritic cell pathway into endothelial cells

Patients and animals bearing tumors have increased levels of CD34(+) progenitor cells, which are capable of developing into dendritic cells. However, addition of medium conditioned by murine Lewis lung carcinoma cells increases the cellularity of the CD34(+) cell cultures and redirects their differentiation into endothelial cells. The resulting cells resemble endothelial cells phenotypically as well as functionally by their capacity to reorganize into cord structures. Mechanisms by which tumors induced the increased cellularity and skewing toward endothelial cells were examined. Tumor-derived VEGF contributed to the increase in cellularity, but not to the redirection of differentiation. Differentiation into endothelial cells was blocked with sTie-2, suggesting tumor-derived angiopoietins in skewing differentiation. These studies show the capacity of tumors to skew progenitor cell development toward endothelial cells and define the mediators that contribute to endothelial cell development.

Vascular progenitor cells: origin and mechanisms of mobilization, differentiation, integration, and vasculogenesis

The recent discovery of progenitor cells in peripheral blood that can differentiate into endothelial or vascular smooth muscle cells has led to the re-evaluation of many traditionally held beliefs about vascular biology. Most notably, concepts of vascular regeneration and repair, previously considered limited to the proliferation of existing differentiated cells within vascular tissue, have been expanded to include the potential for postnatal vasculogenesis. These cells have since been identified in the bone marrow, heart, skeletal muscle, and other peripheral tissues, including the vasculature itself. The significance of these cells lies not only in developing our understanding of normal vascular biology, but also in the insights they may provide into vascular diseases such as atherosclerosis. In addition, a potential role in therapeutics has already been explored in early clinical trials in humans. The mechanisms underlying the mobilization, target tissue integration, differentiation, and the observed therapeutic benefits of these cells are now being elucidated. It is these mechanisms, and the current understanding of the lineage of these cells, that constitutes the focus of this review.

Characterization of Lewis lung clonal variants in a model of syngeneic pulmonary murine metastases

Lung cancer is the leading cause of cancer-related mortality world-wide. Since the majority of cancer deaths result from metastatic complications, understanding cellular alterations contributing to organ specific metastases is a continuing cancer research goal. Desirable models involve easy, efficient methodologies for development of pulmonary metastases utilizing genetically related syngeneic tumor cell lines varying in clonogenic frequency and growth rate for comparative studies. This work focused on development and characterization of primary and metastatic Lewis lung subclones (LLCC3, LLC1, LLCab) in a histocompatible C57B1/6 model. Surgical resection of primary tumors utilizing these cell lines resulted in reliable development of pulmonary metastases (> 90% of injected mice), while tail-vein injection proved sporadic (20% of injected mice). The preliminary analysis of selected cell-surface molecules indicates potential genetic differences that may underlie phenotypic variations. The combination of subcutaneous resection methodology and variant cell lines results in robust metastatic lung cancer for testing potential therapeutic interventions.

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.

Myeloid cell expansion elicited by the progression of spontaneous mammary carcinomas in c-erbB-2 transgenic BALB/c mice suppresses immune reactivity

Transgenic female mice expressing the transforming rat oncogene c-erbB-2 (HER-2/neu) under the mouse mammary tumor virus (MMTV) promoter (BALB-neuT) spontaneously develop mammary carcinomas with a progression resembling that of human breast cancer. In these mice, activating antitumor immunotherapy fails to induce T cell-mediated cytotoxicity, suggesting a suppression of the immune response. We found a direct correlation between tumor multiplicity and an increased proportion of Gr-1+ (Ly6G)/Mac-1+(CD11b)/ER-MP12+(CD31) immature myeloid cells in the peripheral blood (PB) and spleen, suggesting that tumor load profoundly affects overall BALB-neuT hematopoiesis. In fact, myeloid colony formation was increased in bone marrow (BM) and spleen. The immature myeloid cells displayed suppressive activity on host T lymphocytes, which progressively failed to respond to alloantigens and CD3 triggering, while maintaining the ability to proliferate in response to nonspecific mitogens. Transplantation of normal BM into BALB-neuT mice readily resulted in hypertrophic hematopoiesis with myeloid cell expansion. This persistent influence of the tumor was mediated through the release of vascular endothelial growth factor (VEGF) but not granulocyte-macrophage colony-stimulating factor (GM-CSF), and was down-modulated when tumor load was reduced but not when BM was transplanted. Together, the data obtained in the BALB-neuT model of naturally occurring carcinogenesis show that tumor-associated immune suppression is secondary to a more general alteration of host hematopoiesis, conditioned by tumor-secreted soluble factors.

Principals of neovascularization for tissue engineering

The goals in tissue engineering include the replacement of damaged, injured or missing body tissues with biological compatible substitutes such as bioengineered tissues. However, due to an initial mass loss after implantation, improved vascularization of the regenerated tissue is essential. Recent advances in understanding the process of blood vessel growth has offered significant tools for therapeutic neovascularization. Several angiogenic growth factors including vascular endothelial cell growth factor (VEGF) and basic fibroblast growth factor (bFGF) were used for vascularization of ischemic tissues. Three approaches have been used for vascularization of bioengineered tissue: incorporation of angiogenic factors in the bioengineered tissue, seeding endothelial cells with other cell types and prevascularization of matrices prior to cell seeding. This paper reviews the process of blood vessel growth and tissue vascularization, and discuss strategies for efficient vascularization of engineered tissues.