VEGF as a mediator of tumor-associated immunodeficiency

A novel function for dendritic cell: clearance of VEGF via VEGF receptor-1

It has been reported that the plasma levels of VEGF in tumor patients decreased during dendritic cell (DC)-based immunotherapy, but the underlying mechanism remains unclear. Our current report demonstrates that VEGF levels were significantly decreased in the supernatants of DCs incubated with rhVEGF or tumor conditioned medium (TCM) while the intracellular VEGF in DCs was increased. The increased intracellular VEGF was not due to the de novo VEGF synthesis by DCs because exogenous VEGF inhibited the mRNA expression of VEGF in DCs. More direct evidence was provided to demonstrate that Cy3-labeled VEGF could be internalized by DCs specifically and efficiently. In addition, the activity of DCs to internalize VEGF was abolished by neutralizing antibody against VEGF receptor-1 (Flt-1) and inhibitors of endocytosis such as carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and genistein. This study highlights a novel function of DCs and allows a better understanding of the DC-VEGF interaction.

Current insights on the biology and clinical aspects of VEGF regulation

Vascular endothelial growth factor (VEGF) is a key molecule that orchestrates the formation and function of vascular networks. Impaired regulation of angiogenesis is implicated in a number of pathologic states. For instance, neoplasias exhibit uncontrolled angiogenesis, whereas ischemia and states of vascular insufficiency involve reduced VEGF activity. As the role of VEGF has been elucidated in these disease processes, its therapeutic role has been developed. The Food and Drug Administration has approved several anti-VEGF agents for treating colorectal, lung, and kidney cancer. VEGF-inducing agents have also been used experimentally to induce angiogenesis in patients with critical limb ischemia. As more knowledge is gathered about the biology of VEGF and its receptors, there is greater promise for therapeutic modulation of VEGF expression. The purpose of this review is to describe the various therapeutic and biologic factors that regulate the expression of VEGF.

Divergent effects of hypoxia on dendritic cell functions

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that patrol tissues to sense danger signals and activate specific immune responses. In addition, they also play a role in inflammation and tissue repair. Here, we show that oxygen availability is necessary to promote full monocyte-derived DC differentiation and maturation. Low oxygen tension (hypoxia) inhibits expression of several differentiation and maturation markers (CD1a, CD40, CD80, CD83, CD86, and MHC class II molecules) in response to lipopolysaccharide (LPS), as well as their stimulatory capacity for T-cell functions. These events are paralleled by impaired up-regulation of the chemokine receptor CCR7, an otherwise necessary event for the homing of mature DCs to lymph nodes. In contrast, hypoxia strongly up-regulates production of proinflammatory cytokines, particularly TNFalpha and IL-1beta, as well as the inflammatory chemokine receptor CCR5. Subcutaneous injection of hypoxic DCs into the footpads of mice results in defective DC homing to draining lymph nodes, but enhanced leukocyte recruitment at the site of injection. Thus, hypoxia uncouples the promotion of inflammatory and tissue repair from sentinel functions in DCs, which we suggest is a safeguard mechanism against immune reactivity to damaged tissues.

Co-delivery of cancer-associated antigen and Toll-like receptor 4 ligand in PLGA nanoparticles induces potent CD8+ T cell-mediated anti-tumor immunity

The purpose of this study was to evaluate the efficacy of poly(lactic-co-glycolic acid) (PLGA)-based vaccines in breaking immunotolerance to cancer-associated self-antigens. Vaccination of mice bearing melanoma B16 tumors with PLGA nanoparticles (NP) co-encapsulating the poorly immunogenic melanoma antigen, tyrosinase-related protein 2 (TRP2), along with Toll-like receptor (TLR) ligand (7-acyl lipid A) was examined. Remarkably, this vaccine was able to induce therapeutic anti-tumor effect. Activated TRP2-specific CD8 T cells were capable of interferon (IFN)-gamma secretion at lymph nodes and spleens of the vaccinated mice. More importantly, TRP2/7-acyl lipid A-NP treated group has shown immunostimulatory milieu at the tumor microenvironment, as evidenced by increased level of pro-inflammatory cytokines compared to control group. These results support the potential use of PLGA nanoparticles as competent carriers for future cancer vaccine formulations.

Prognostic role of immunosuppressive acidic protein in patients with esophageal cancer

Immunosuppressive acidic protein (IAP) suppresses several immune responses in vivo and in vitro , and high preoperative IAP levels could predict the impairment of the host's immunity. In this study prognostic significance of preoperative IAP levels was investigated in 68 esophageal cancer patients with curative resection and eight with non-curative resection. The curative group had significantly lower levels than the non-curative group (432 +/- 183 mg/mL vs. 739 +/- 235 mg/mL, P < 0.0001). The IAP levels were associated with T-status (P < 0.0001), lymphatic invasion (P < 0.05), and p-stages (P < 0.0001). When 5-year survival rate of patients with curative resection was compared by setting various cutoff values of IAP between high and low IAP groups, several cutoff points (400-580 mg/mL) were revealed to be significantly associated with survival. Setting cutoff value of IAP to 560 mg/mL resulted in a most significant difference of 5-year survival rate of patients between the high and low IAP groups (13.9% and 61.5%, P < 0.0001). These data indicate that pre-operative IAP level is a useful parameter to predict the prognosis of esophageal cancer patients after curative resection.

Different signaling pathways expressed by chicken naive CD4(+) T cells, CD4(+) lymphocytes activated with staphylococcal enterotoxin B, and those malignantly transformed by Marek's disease virus

Proteomics methods, based on liquid chromatography and tandem mass spectrometry, produce large "shotgun" proteomes that are most appropriately compared not at the level of differentially expressed proteins only but at the more comprehensive level of biological networks and pathways. This is now possible with the emergence of functional annotation databases and tools, databases of canonical pathways and molecular interactions and computational text mining tools. Here, we used shotgun proteomics, and the differential proteomics modeling functionalities available in the Pathwaystudio network modeling program to define the cell physiology of Hodgkin's disease antigen-overexpressing (CD30 (hi)) CD4 (+) T cell lymphomas using the unique Marek's disease (MD) natural animal model. CD30 (hi) lymphoma cells have characteristics of activated T cells but are also fundamentally different from their nontransformed healthy counterparts. We compared the cell physiology of naïve, superantigen-activated and MD-transformed CD4 (+) T cell proteomes. While the superantigen-activated cells had signaling pathways associated with cell activation, inflammation, proliferation and cell death, the MD-transformed cells had growth factor, cytokine, adhesion, and transcription factor signaling responses associated with oncogenicity, cell proliferation, angiogenesis, motility, and metastasis.

Synergistic antitumor effects of CpG oligodeoxynucleotide and STAT3 inhibitory agent JSI-124 in a mouse melanoma tumor model

One of the major limitations for cancer immunotherapy is related to the frequent existence of an intra-tumoral immunosuppressive environment, to which STAT3 (Signal transducer and activator of transcription-3) activation in tumor and dendritic cells (DCs) are believed to contribute. In this study, we tested the hypothesis that the combination of CpG (a DC activator) and JSI-124 (a STAT3 inhibitor) may generate synergistic antitumor effects compared to CpG or JSI-124 alone. B16-F10, a mouse melanoma cell line that has constitutively active STAT3, was grafted in C57BL/6 mice and then tumor-bearing mice treated intra-tumorally with (a) phosphate buffered saline, (b) 10 microg CpG, (c) 1 mg kg(-1) JSI-124 or (d) 10 microg CpG+1 mg kg(-1) JSI-124. The effects of treatments on tumor growth, survival and antitumor immune responses were evaluated. Although significant antitumor effects were detected with the single-agent treatments, the CpG+JSI-124 treatment resulted in synergistic antitumor effects compared to CpG or JSI-124 alone. Correlating with these findings, the combination therapy resulted in significantly higher intra-tumoral levels of several proinflammatory, TH1-related cytokines (including IL-12, IFN-gamma, TNF-alpha and IL-2), increases in intra-tumoral CD8+ and CD4+ T cells expressing activation/memory markers and NK cells and increases in activated DCs in the tumors and regional lymph nodes (LNs). Concomitantly, the combination therapy led to a significantly decreased level of immunosuppression, as evidenced by lower intra-tumoral level of VEGF and TGF-beta, and decreased number of CD4+CD25+Foxp3+ regulatory T cells in the regional LNs. This study has provided the proof-of-principle for combining CpG and JSI-124 to enhance antitumor immune responses.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Ecoimmunity: immune tolerance by symmetric co-evolution

It is widely accepted that immune tolerance toward "self" is established by central and peripheral adaptations of the immune system. Mechanisms that have been demonstrated to play a role in the induction and maintenance of tolerance include thymic deletion of self-reactive T cells, peripheral T cell anergy and apoptosis, as well as thymic and peripheral induction of regulatory T cells. However, a large body of experimental findings cannot be rationalized solely based on adaptations of the immune system to its environment. Here we propose a new model termed Ecoimmunity, where the immune system and the tissue are viewed as two sides of a continuously active and co-evolving predator-prey system. Ecoimmunity views self-tolerance, not as an equilibrium in which autoimmunity is chronically suppressed, but as a symmetrical balanced conflict between the ability of immune cells to destroy tissue cells by numerous mechanisms, and the capacity of adapted tissue cells to avoid predation. This balance evolves during ontogeny, in parallel to immune adaptations, embryonic tissue cells adapt their phenotype to the corresponding immune activity by developing the ability to escape or modulate damaging local immune responses. This phenotypic plasticity of tissue cells is directed by epigenetic selection of gene expression pattern and cellular phenotype amidst an ongoing immune pressure. Thus, whereas some immune cells prey predominantly on pathogens and infected cells, self-reactive cells continuously prey on incompetent tissue cells that fail to express the adapted phenotype and resist predation. This model uses ecological generalization to reconcile current contradictory observations as well as classical enigmas related to both autoimmunity and to tolerance toward foreign tissues. Finally, it provides empirical predictions and alternative strategies toward clinical challenges.

Inflammatory cell infiltration of tumors: Jekyll or Hyde

Inflammatory cell infiltration of tumors contributes either positively or negatively to tumor invasion, growth, metastasis, and patient outcomes, creating a Dr. Jekyll or Mr. Hyde conundrum when examining mechanisms of action. This is due to tumor heterogeneity and the diversity of the inflammatory cell phenotypes that infiltrate primary and metastatic lesions. Tumor infiltration by macrophages is generally associated with neoangiogenesis and negative outcomes, whereas dendritic cell (DC) infiltration is typically associated with a positive clinical outcome in association with their ability to present tumor antigens (Ags) and induce Ag-specific T cell responses. Myeloid-derived suppressor cells (MDSCs) also infiltrate tumors, inhibiting immune responses and facilitating tumor growth and metastasis. In contrast, T cell infiltration of tumors provides a positive prognostic surrogate, although subset analyses suggest that not all infiltrating T cells predict a positive outcome. In general, infiltration by CD8(+) T cells predicts a positive outcome, while CD4(+) cells predict a negative outcome. Therefore, the analysis of cellular phenotypes and potentially spatial distribution of infiltrating cells are critical for an accurate assessment of outcome. Similarly, cellular infiltration of metastatic foci is also a critical parameter for inducing therapeutic responses, as well as establishing tumor dormancy. Current strategies for cellular, gene, and molecular therapies are focused on the manipulation of infiltrating cellular populations. Within this review, we discuss the role of tumor infiltrating, myeloid-monocytic cells, and T lymphocytes, as well as their potential for tumor control, immunosuppression, and facilitation of metastasis.

The effect of anti-VEGF therapy on immature myeloid cell and dendritic cells in cancer patients

Impairment of dendritic cells (DC), the most effective activators of anticancer immune responses, is one mechanism for defective antitumor immunity, but the causes of DC impairment are incompletely understood. We evaluated the association of impaired DC differentiation with angiogenesis-associated molecules D-dimer, vascular endothelial growth factor (VEGF), urokinase plasminogen activator (uPA), and plasminogen activator inhibitor (PAI-1) in peripheral blood from 41 patients with lung, breast, and colorectal carcinoma. Subsequently, we studied the effect of administration of the anti-VEGF antibody (bevacizumab) on DC maturation and function in vivo. Compared with healthy volunteers, cancer patients had a bias toward the immunoregulatory DC2, had deficits in DC maturation after overnight in vitro culture, and had a significant increase in immature myeloid cell progenitors of DC (0.50 +/- 0.31% vs. 0.32 +/- 0.16% of peripheral blood mononuclear cells, respectively, P = 0.011). A positive correlation was found between the percentage of DC2 and PAI-1 (R = 0.50) and between immature myeloid cells and VEGF (R = 0.52). Bevacizumab administration to cancer patients was associated with a decrease in the accumulation of immature progenitor cells (0.39 +/- 0.30% vs. 0.27 +/- 0.24%, P = 0.012) and induced a modest increase in the DC population in peripheral blood (0.47 +/- 0.23% vs. 0.53 +/- 0.30%). Moreover, anti-VEGF antibody treatment enhanced allo-stimulatory capacity of DC and T cell proliferation against recall antigens. These data suggest that DC differentiation is negatively associated with VEGF levels and may be one explanation for impaired anticancer immunity, especially in patients with advanced malignancies.

Dendritic cell subsets in health and disease

The dendritic cell (DC) system of antigen-presenting cells controls immunity and tolerance. DCs initiate and regulate immune responses in a manner that depends on signals they receive from microbes and their cellular environment. They allow the immune system to make qualitatively distinct responses against different microbial infections. DCs are composed of subsets that express different microbial receptors and express different surface molecules and cytokines. Our studies lead us to propose that interstitial (dermal) DCs preferentially activate humoral immunity, whereas Langerhans cells preferentially induce cellular immunity. Alterations of the DC system result in diseases such as autoimmunity, allergy, and cancer. Conversely, DCs can be exploited for vaccination, and novel vaccines that directly target DCs in vivo are being designed.

Immunotherapeutic approaches in pancreatic cancer

With growing understanding of the regulation of immune responses, multiple new immunotherapeutic targets have evolved. This article gives a survey over the current approaches in pancreatic cancer therapy including peptide vaccinations, unspecific immunotherapy, allogene modified tumor cell vaccines, and vector-based vaccines. Although several trials have shown detectable immune responses, such as delayed-type hypersensitivity reactions and cytokine release in enzyme-linked immunosorbent spot (ELISPOTS) assays, and some have reported prolonged survival for immune responders, immunotherapy remains experimental. However, some approaches have made it into a phase III setting. In addition, the emerging concept of tumor stem cells may lead to a new focus on immunotherapy, since these often highly chemotherapy-resistant cells are thought to be the source of recurrences.

Tumour-released exosomes and their implications in cancer immunity

Tumour cells release vesicular structures, defined as microvesicles or exosomes, carrying a large array of proteins from their originating cell. The expression of antigenic molecules recognized by T cells has originally suggested a role for these organelles as a cell-free antigen source for anticancer vaccines. However, recent evidence shows that tumour exosomes may also exert a broad array of detrimental effects on the immune system, ranging from apoptosis in activated antitumour T cells to impairment of monocyte differentiation into dendritic cells and induction of myeloid suppressive cells. Immunosuppressive exosomes of tumour origin can be found in neoplastic lesions and sera from cancer patients, implying a potential role of this pathway in in vivo tumour progression. Through the expression of molecules involved in angiogenesis promotion, stromal remodelling, delivery of signalling pathways through growth factor/receptor transfer, chemoresistance and genetic intercellular exchange, tumour exosomes could represent a versatile tool for moulding host environment. Hence, their secretion by neoplastic cells may in the future become a novel pathway to target for therapeutic intervention in cancer patients.

Pathways mediating the expansion and immunosuppressive activity of myeloid-derived suppressor cells and their relevance to cancer therapy

Cancer immunotherapy has focused on inducing and expanding CTLs and improving the immune recognition of weak antigenic determinants expressed by tumors. However, few positive clinical outcomes have been reported due, in part, to tumor-associated immunologic tolerance, supporting the need for an emphasis on overcoming immunosuppression. Systemic immunosuppression is associated with abnormal myelopoiesis secondary to tumor growth, myelosuppressive therapy, and growth factor administration and subsequent expansion/mobilization of bone marrow-derived immunosuppressive cells. These myeloid-derived suppressor cells (MDSC) reduce activated T-cell number and inhibit their function by multiple mechanisms, including depletion of l-arginine by arginase-1 (ARG1) production of nitric oxide, reactive oxygen species, and reactive nitrogen oxide species by inducible nitric oxide synthase. Increased numbers of MDSCs are associated with neoplastic, inflammatory, infectious, and graft-versus-host diseases where they restrain exuberant or novel T-cell responses. In this review, we discuss critical components of MDSC-mediated suppression of T-cell function, including cellular expansion and activation-induced secretion of immunosuppressive mediators. Both components of MDSC bioactivity are amenable to pharmacologic intervention as discussed herein. We also focus on the relationship between MDSCs, tumor growth, therapeutic responses, and the mechanisms of cellular expansion, activation, and immunosuppression.

A vascular endothelial growth factor receptor-2 inhibitor enhances antitumor immunity through an immune-based mechanism

PURPOSE

Given the complex tumor microenvironment, targeting multiple cellular components may be the most effective cancer treatment strategy. Therefore, we tested whether antiangiogenic and immune-based therapy might synergize by characterizing the activity of DC101, an antiangiogenic monoclonal antibody specific for vascular endothelial growth factor receptor-2 (VEGF-R2), alone and with HER-2/neu (neu)-targeted vaccination.

EXPERIMENTAL DESIGN

Neu-expressing breast tumors were measured in treated nontolerant FVB mice and immune-tolerant neu transgenic (neu-N) mice. Neu-specific and tumor cell-specific immune responses were assessed by intracellular cytokine staining, ELISPOT, and CTL assays.

RESULTS

DC101 decreased angiogenesis and increased tumor cell apoptosis. Although DC101 increased serum levels of the immunosuppressive cytokine VEGF, no evidence of systemic immune inhibition was detected. Moreover, DC101 did not impede the influx of tumor-infiltrating lymphocytes. In FVB mice, DC101 inhibited tumor growth in part through a T cell-dependent mechanism, resulting in both increased tumor-specific CD8(+) T cells and tumor regression. Combining DC101 with neu-specific vaccination accelerated tumor regression, augmenting the lytic activity of CD8(+) cytotoxic T cells. In tolerant neu-N mice, DC101 only delayed tumor growth without inducing frank tumor regression or antigen-specific T-cell activation. Notably, mitigating immune tolerance by inhibiting regulatory T cell activity with cyclophosphamide revealed DC101-mediated augmentation of antitumor responses in vaccinated neu-N mice.

CONCLUSIONS

This is the first report of DC101-induced antitumor immune responses. It establishes the induction of tumor-specific T-cell responses as one consequence of VEGF-R2 targeting with DC101. These data support the development of multitargeted cancer therapy combining immune-based and antiangiogenic agents for clinical translation.

Signal 3 availability limits the CD8 T cell response to a solid tumor

CD8 T cells need a third signal, along with Ag and costimulation, for effective survival and development of effector functions, and this can be provided by IL-12 or type I IFN. Adoptively transferred OT-I T cells, specific for H-2K(b) and OVA, encounter Ag in the draining lymph nodes of mice with the OVA-expressing E.G7 tumor growing at a s.c. site. The OT-I cells respond by undergoing limited clonal expansion and development of effector functions (granzyme B expression and IFN-gamma production), and they migrate to the tumor where they persist but fail to control tumor growth. In contrast, OT-I T cells deficient for both the IL-12 and type I IFN receptors expand only transiently and rapidly disappear. These results suggested that some signal 3 cytokine is available, but that it is insufficient to support a CTL response that can control tumor growth. Consistent with this, administration of IL-12 at day 10 of tumor growth resulted in a large and sustained expansion of wild-type OT-I cells with enhanced effector functions, and tumor growth was controlled. This did not occur when the OT-I cells lacked the IL-12 and type I IFN receptors, demonstrating that the therapeutic effect of IL-12 results from direct delivery of signal 3 to the CD8 T cells responding to tumor Ag in the signal 3-deficient environment of the tumor.

Tumor exosomes inhibit differentiation of bone marrow dendritic cells

The production of exosomes by tumor cells has been implicated in tumor-associated immune suppression. In this study, we show that, in mice, exosomes produced by TS/A murine mammary tumor cells target CD11b(+) myeloid precursors in the bone marrow (BM) in vivo, and that this is associated with an accumulation of myeloid precursors in the spleen. Moreover, we demonstrate that TS/A exosomes block the differentiation of murine myeloid precursor cells into dendritic cells (DC) in vitro. Addition of tumor exosomes at day 0 led to a significant block of differentiation into DC, whereas addition at later time points was less effective. Similarly, exosomes produced by human breast tumor cells inhibited the differentiation of human monocytes in vitro. The levels of IL-6 and phosphorylated Stat3 were elevated 12 h after the tumor exosome stimulation of murine myeloid precursors, and tumor exosomes were less effective in inhibiting differentiation of BM cells isolated from IL-6 knockout mice. Addition of a rIL-6 to the IL-6 knockout BM cell culture restored the tumor exosome-mediated inhibition of DC differentiation. These data suggest that tumor exosome-mediated induction of IL-6 plays a role in blocking BM DC differentiation.

A phase II study of ABT-510 (thrombospondin-1 analog) for the treatment of metastatic melanoma

OBJECTIVES

Thrombospondins are natural inhibitors of angiogenesis, tumor metastases, and tumor growth (melanoma). ABT-510 is a synthetic analog of thrombospondin-1, well tolerated in phase I studies. We conducted a phase II trial evaluating the clinical efficacy of ABT-510 and its effects on biomarkers of angiogenesis and immunity in patients with metastatic melanoma (MM).

PATIENTS AND METHODS

A 2-stage phase II clinical trial was conducted to assess the clinical efficacy, safety, and pharmacodynamic effects (angiogenesis and immunity) of ABT-510 in patients with stage IV melanoma. The primary endpoint was 18-week treatment failure rate. Patients self-administered 100 mg of ABT-510 subcutaneously twice daily. Blood samples were collected at baseline and every 3 weeks while on therapy. Eligible patients demonstrated measurable disease, good performance status and no evidence of intracranial metastases. Correlative laboratory studies evaluated biomarkers of angiogenesis and immunity.

RESULTS

Twenty-one patients were enrolled. Most patients were stage M1c (71%) and all had prior therapy for MM. Only 3 of the first 20 patients enrolled were progression free and on treatment at 18 weeks resulting in early termination of the study. Decreases in peripheral blood VEGF-A levels and VEGF-C levels, and CD146 and CD34/133 counts relative to pretreatment were detected. Limited changes in antitumor T cell immunity were observed.

CONCLUSIONS

ABT-510 therapy administered at 100 mg twice/day in patients with MM did not demonstrate definite clinical efficacy. Further dose escalation or combination with cytotoxic therapy may be more effective therapeutically.

Vascular endothelial growth factor inhibits the function of human mature dendritic cells mediated by VEGF receptor-2

Dendritic cells (DCs) are the most potent antigen-presenting cells and play a central role in the host-antitumor immunity. Since it has been reported that vascular endothelial growth factor (VEGF) inhibits the functional maturation of immature-DCs and impairs DC differentiation, it is important to elucidate the mechanisms of VEGF-induced DC-dysfunction. To investigate the effects of VEGF against human mature DCs, we investigated how VEGF affects mature DCs with regards to phenotype, induction of apoptosis, IL-12(p70) production and the antigen-presenting function evaluated by allogeneic mixed leukocyte reaction (allo-MLR). We generated monocyte-derived DCs matured with lipopolysaccharide, OK-432 or pro-inflammatory cytokine cocktails. As a result, VEGF treatment did not alter the mature DCs with regard to phenotype, IL-12(p70) production and induction of apoptosis. As a novel and important finding, VEGF inhibited the ability of mature DCs to stimulate allogeneic T cells. Furthermore, this VEGF-induced DC dysfunction was mainly mediated by VEGF receptor-2 (VEGF R2). These observations were confirmed by the findings that the VEGF-induced DC dysfunction was recovered by anti-human VEGF neutralizing mAb or anti-human VEGF R2 blocking mAb, and that placenta growth factor (PlGF), VEGF R1-specific ligand, did not have any effect against mature DCs. Some modalities aiming at reversing mature-DC dysfunction induced by VEGF will be needed in order to induce the effective antitumor immunity.

Possible molecular mechanisms involved in the toxicity of angiogenesis inhibition

Contrary to initial expectations, angiogenesis inhibitors can cause toxicities in patients with cancer. The toxicity profiles of these inhibitors reflect the disturbance of growth factor signalling pathways that are important for maintaining homeostasis. Experiences with angiogenesis inhibitors in clinical trials indicate that short-term toxicities are mostly manageable. However, these agents will also be given in prolonged treatment strategies, so we need to anticipate possible long-term toxicities. In addition, understanding the molecular mechanisms involved in the toxicity of angiogenesis inhibition should allow more specific and more potent inhibitors to be developed.

Tumor suppressive efficacy through augmentation of tumor-infiltrating immune cells by intratumoral injection of chemokine-expressing adenoviral vector

Our goal in the present study was to evaluate antitumor effects and frequency of tumor-infiltrating immune cells upon intratumoral injection of RGD fiber-mutant adenoviral vector (AdRGD) encoding the chemokines CCL17, CCL19, CCL20, CCL21, CCL22, CCL27, XCL1, and CX3CL1. Among eight kinds of chemokine-expressing AdRGDs, AdRGD-CCL19 injection most efficiently induced infiltration of T cells into established B16BL6 tumor parenchyma, whereas most of these T cells were perforin-negative in immunohistochemical analysis. Additionally, the growth of AdRGD-CCL19-injected tumors decreased only slightly as well as that of other tumors treated with each chemokine-expressing AdRGD, which indicated that accumulation of naive T cells in tumor tissue does not effectively damage the tumor cells. Tumor-bearing mice, in which B16BL6-specific T cells were elicited by dendritic cell-based immunization, demonstrated that intratumoral injection of AdRGD-CCL17, -CCL22, or -CCL27 could considerably suppress tumor growth and attract activated T cells. On the other hand, AdRGD-CCL19-injection in the immunized mice showed slight increase of tumor-infiltrating T cells compared to treatment using control vector. Collectively, although AdRGD-mediated chemokine gene transduction into established tumors would be very useful for augmentation of tumor-infiltrating immune cells, a combinational treatment that can systemically induce tumor-specific effector T cells is necessary for satisfactory antitumor efficacy.

Prostate cancer immunotherapy

PURPOSE OF REVIEW

Basic immunology research over several decades has led to an improved understanding of tumor recognition by components of the immune system and mechanisms of tumor evasion from immune detection. These findings have ultimately led to four phase III trials, currently underway, evaluating antitumor active immunotherapies in patients with prostate cancer. This article reviews recent published findings in the area of prostate cancer immunotherapies, focusing on both passive and active immunotherapy approaches that have entered clinical trials.

RECENT FINDINGS

Clinical trials with immune active agents reported in the last year have demonstrated efficacy in the treatment of prostate cancer. These agents include immune modulators such as granulocyte-macrophage colony stimulating factor and anticytotoxic T-lymphocyte-associated antigen 4 monoclonal antibodies, antibody therapies targeting prostate-specific membrane antigen, and vaccines such as those targeting prostatic acid phosphatase, prostate-specific antigen, and cellular vaccines expressing granulocyte-macrophage colony stimulating factor.

SUMMARY

Results from several recent clinical trials have suggested that immune-based therapies have clinical benefit in patients with prostate cancer with potentially less toxicity than traditional systemic treatments. We review recent reports of immunotherapies being evaluated in patients with prostate cancer, and highlight the direction for these therapies in combination with other immunotherapies and other traditional therapies.

Immunomodulatory and anti-tumor activities of native and heat denatured Abrus agglutinin

Abrus agglutinin (AAG), a hetero tetrameric gal beta (1-3) NAc gal specific lectin, is isolated from seeds of Abrus precatorius. In our previous studies we found that the protein could act as an immunomodulator and immunoadjuvant in native (NA) and heat denatured (HDA) conditions. An anticancer effect of the lectin is reported, but its mode of action is not clearly known. In the present study, the anti-tumor activity of AAG (NA, HDA) has been evaluated in a murine Dalton's lymphoma (DL) ascites tumorogenic model. We found that treatment with both NA and HDA were able to decrease the tumor cell number in vivo and significantly increased median survival time. In vitro studies showed that AAG (NA, HDA) treatment of Dalton's lymphoma ascites cells (DLAC) resulted in growth inhibition at the concentration of 1 microg/ml and above. Whereas, AAG (NA, HDA) at much lower concentrations (approximately 1 ng/ml) can stimulate peritoneal macrophage and spleen derived NK cells in vitro demonstrating cytotoxicity against DLAC. Cell cycle analysis showed an increased number of cells in Sub-G0/G1 phase for in vitro and in vivo treatments. In summary, AAG (NA, HDA) at non-toxic concentration was able to elicit anti-tumor effects in DL bearing mice by stimulating the innate immune system and Th1 type immunomodulation.

Vascular endothelial growth factor and immunosuppression in cancer: current knowledge and potential for new therapy

Two decades of research into the role of immunosuppression and angiogenesis in tumor biology have revealed multiple links between the two. Vascular endothelial growth factor, originally thought to be solely involved in vascular growth and permeability, has emerged as a significant agent of immune tolerance in the tumor microenvironment. This review examines two major elements of this field: the research behind the role of vascular endothelial growth factor in immunosuppression, especially as pertains to dendritic cell function; and the subsequent research into the potential for using antiangiogenic therapy to both starve tumors by hypoxia and enhance the response of tumors to immunotherapy. Several strategies tested so far have yielded incomplete, yet promising, results.

Vascular endothelial growth factor blockade reduces intratumoral regulatory T cells and enhances the efficacy of a GM-CSF-secreting cancer immunotherapy

PURPOSE

The purpose of the present study was to evaluate granulocyte macrophage colony-stimulating factor (GM-CSF)-secreting tumor cell immunotherapy in combination with vascular endothelial growth factor (VEGF) blockage in preclinical models.

EXPERIMENTAL DESIGN

Survival and immune response were monitored in the B16 melanoma and the CT26 colon carcinoma models. VEGF blockade was achieved by using a recombinant adeno-associated virus vector expressing a soluble VEGF receptor consisting of selected domains of the VEGF receptors 1 and 2 (termed sVEGFR1/R2). Dendritic cell and tumor infiltrating lymphocyte activation status and numbers were evaluated by fluorescence-activated cell sorting analysis. Regulatory T cells were quantified by their CD4+CD25hi and CD4+FoxP3+ phenotype.

RESULTS

The present study established that GM-CSF-secreting tumor cell immunotherapy with VEGF blockade significantly prolonged the survival of tumor-bearing mice. Enhanced anti-tumor protection correlated with an increased number of activated CD4+ and CD8+ tumor-infiltrating T cells and a pronounced decrease in the number of suppressive regulatory T cells residing in the tumor. Conversely, overexpression of VEGF from tumors resulted in elevated numbers of regulatory T cells in the tumor, suggesting a novel mechanism of VEGF-mediated immune suppression at the tumor site.

CONCLUSION

GM-CSF-secreting cancer immunotherapy and VEGF blockade increases the i.t. ratio of effector to regulatory T cells to provide enhanced antitumor responses. This therapeutic combination may prove to be an effective strategy for the treatment of patients with cancer.

Prophylactic naked DNA vaccination with the human vascular endothelial growth factor induces an anti-tumor response in C57Bl/6 mice

Passive immunotherapy against soluble pro-angiogenic factors and/or their receptors in endothelial cells has become a promising approach in cancer therapeutics. There is also experimental evidence indicating that an active immunotherapy strategy directed towards these target molecules could also be effective. In this paper we show that it is possible to reduce tumor growth or increase the survival of tumor-bearing C57Bl/6 mice when animals are vaccinated with the human vascular endothelial growth factor (VEGF) isoform 121 gene (hVEGF(121)), and later challenged with melanoma or lung carcinoma tumor cells. Immunization was done with 10 microg DNA doses of the hVEGF121 gene, which is highly homologous to its mouse counterpart, administered on a weekly basis using a plasmid bearing 5 CpG bacterial motifs. Histopathology analyses of tumors of hVEGF(121) immunized animals showed a decrease in tumor cell density around vessels and in mitotic figures, as well as an increase in apoptotic tumor cells. A statistically significant cell cytotoxic response was found when spleen cells of immunized mice were co-cultured in vitro with mouse tumor VEGF-producing cells. Vaccination with an hVEGF121 gene mutated to make it deficient for VEGF receptor binding, produced similar in vitro and in vivo results, and significantly reduced the number of spontaneous metastases produced by the mouse Lewis lung carcinoma. Our results indicate that human VEGF DNA can be employed for anti-angiogenic active immunotherapy in mice, and that direct cell cytotoxicity is a contributor mechanism to the overall anti-tumor effects seen in immunized animals.

VEGF-specific Short Hairpin RNA–expressing Oncolytic Adenovirus Elicits Potent Inhibition of Angiogenesis and Tumor Growth

RNA interference is being developed to treat cancer. Although highly target specific, its use has been limited by its short duration of expression. To overcome this shortcoming, we constructed an oncolytic adenovirus (Ad)-based short hairpin RNA (shRNA) expression system (Ad-DeltaB7-shVEGF) against vascular endothelial growth factor (VEGF), a key mediator in angiogenesis. To demonstrate the VEGF-specific nature of this Ad-based shRNA, replication-incompetent Ad expressing VEGF-specific shRNA (Ad-DeltaE1-shVEGF) was also generated. Ad-DeltaE1-shVEGF was highly effective in reducing VEGF expression, and elicited an antiangiogenic effect in vitro and in vivo. Similarly, Ad-DeltaB7-shVEGF exhibited potent antiangiogenic effects in the matrigel plug assay. Moreover, Ad-DeltaB7-shVEGF demonstrated a greater antitumor effect and enhanced survival compared to the cognate control oncolytic Ad, Ad-DeltaB7. Ad-DeltaB7-shVEGF induced significant reduction in tumor vasculature, verifying the antiangiogenic mechanism. Furthermore, both the duration and magnitude of gene silencing by Ad-DeltaB7-shVEGF was greater than Ad-DeltaE1-shVEGF. These results suggest that the combined effects of oncolytic viral therapy and cancer cell-specific expression of VEGF-targeted shRNA elicits greater antitumor effect than an oncolytic Ad alone.

Differences in dendritic cell activation and distribution after intravenous, intraperitoneal, and subcutaneous injection of lymphoma cells in mice

Dendritic cells (DCs) are key antigen-presenting cells (APCs) for initiating immune responses. However, in recent years, several groups have shown the defective function of DCs in tumor-bearing mice and in cancer patients. Our aim was to study the effects of lymphoma on DC differentiation and maturation and to assess the input of the tumor microenvironment and intravasation of tumor cells on DC precursors. EL-4 lymphoma cells were administrated via different routes (intraperitoneal, subcutaneous, and intravenous) and DC phenotype was investigated. Bone marrow-derived DCs and APCs obtained from the spleen were examined by flow cytometry, and immunohistochemical analysis of lymphoma, lungs, livers, and spleens was also performed. Intravenous administration of lymphoma cells induced suppression of DC differentiation and maturation assessed as a significant decrease of the IAb, CD80, CD86, CD11b, and CD11c expression on DCs and IAb on splenic APCs. Upregulation of APC differentiation was observed in animals after subcutaneous and intraperitoneal administration of lymphoma cells determined as increased expression of CD40 and CD86 in spleen APCs. These data suggest that the development of antitumor immune response might differ in the host receiving tumor vaccines via different injection routes.

Comparison of the cytotoxic effects of receptor tyrosine kinase inhibitors on macrophage functions; possible side effects in the immune defense

Certain receptor tyrosine kinase (RTK) inhibitors reduced the phagocytic capacity of rat macrophages, without influencing the binding of bacteria to macrophage surface. The NO production of elicited rat macrophages was also decreased due to the inhibition of the expression of NOS II. The most potent inhibitory compound was PD166326 (6-(2,6-dichloro-phenyl)-2-(4-hydroxy-phenylamino)-8-methyl-8H-pyrido[2,3-d]pyrimidin-7-one) belonging to a family of RTK inhibitors of broad spectra. These impairing effects could be explained by the apoptosis inducing property of the inhibitor, evidenced by the destroyed mitochondrial membrane potential. The MTT cell viability test indicated a slight, but significant injury of macrophages. In addition to this compound, two other tested RTK inhibitors caused less marked impairment of macrophage functions, while four compounds were not efficient on macrophages at all. Nevertheless, these damaging effects of the inhibitors did not reduce the anti-tumor effect of the RTK inhibitors on COS 7 cells as evidenced by MTT test and apoptosis study. However, these side effects may be important when RTK inhibitors are selected against tumor growth, indicating that certain inhibitors may impair the immune defense during therapeutical application.

Dendritic cells and tumor microenvironment: a dangerous liaison

The fact that the immune response to cancer is compromised has been convincingly demonstrated in murine tumor models as well as in cancer patients. The unresponsiveness of the host immune system is one of the major mechanisms of tumor escape as well as an important factor that limits the success of cancer immunotherapy. Inadequate function of professional antigen presenting cells dendritic cells (DC) in cancer is one of the major elements of compromised anti-tumor immune response. Despite substantial progress in recent years, the mechanism of inadequate DC function in cancer still remains unclear. The tumor microenvironment has emerged as an important component contributing to DC malfunction. In this review we will discuss the potential role of tumor microenvironment in DC dysfunction.

Immune resistance orchestrated by the tumor microenvironment

It is now little disputed that most if not all cancer cells express antigens that can be recognized by specific CD8(+) T lymphocytes. However, a central question in the field of anti-tumor immunity is why such antigen-expressing tumors are not spontaneously eliminated by the immune system. While in some cases, this lack of rejection may be due to immunologic ignorance, induction of anti-tumor T-cell responses in many patients has been detected in the peripheral blood, either spontaneously or in response to vaccination, without accompanying tumor rejection. These observations argue for the importance of barriers downstream from initial T-cell priming that need to be addressed to translate immune responses into clinical tumor regression. Recent data suggest that the proper trafficking of effector T cells into the tumor microenvironment may not always occur. T cells that do effectively home to tumor metastases are often found to be dysfunctional, pointing toward immunosuppressive mechanisms in the tumor microenvironment. T-cell anergy due to insufficient B7 costimulation, extrinsic suppression by regulatory cell populations, inhibition by ligands such as programmed death ligand-1, metabolic dysregulation by enzymes such as indoleamine-2,3-dioxygenase, and the action of soluble inhibitory factors such as transforming growth factor-beta have all been clearly implicated in generating this suppressive microenvironment. Identification of these downstream processes points to new therapeutic targets that should be manipulated to facilitate the effector phase of anti-tumor immune responses in concert with vaccination or T-cell adoptive transfer.

Association of VEGF genetic polymorphisms with prostate carcinoma risk and clinical outcome

OBJECTIVES

Vascular endothelial growth factor (VEGF) is a potent stimulus of angiogenesis that has an important role in many human malignancies including prostate carcinoma (PCa). We evaluated the role of the functional VEGF polymorphisms as genetic markers for PCa susceptibility and prognosis.

METHODS

The study included 101 patients with PCa and [corrected] 100 age-matched healthy men. The VEGF genotypes -1154G>A were identified by allele-specific polymerase chain reaction (AS-PCR) and the genotypes -634G>C and 936C>T were identified by restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR).

RESULTS

A negative association was found between VEGF -1154AA genotype and PCa risk (OR=0.27; P=0.009). Furthermore, the presence of the VEGF -1154A allele appeared to be associated with a decreased [corrected] risk of higher tumor grade (OR=0.37; P=0.01). A significant increased risk of prostate cancer was associated with the VEGF -634 (GC+CC) combined genotype (OR=1.95; P=0.02). The VEGF -634C allele was associated with the aggressive phenotype of prostate cancer as defined by the high histological grade (OR=3.48; P=0.007). The VEGF -1154A/-634G haplotype was negatively associated with PCa risk (OR=0.48; P=0.005) and high tumor grade compared to low grade (OR=0.37; P=0.02).

CONCLUSIONS

Genetic variations in the VEGF may predict not only PCa risk but also tumor aggressiveness.

Bisphosphonate-induced avascular osteonecrosis of the jaws: a clinical report of 11 cases

Bisphosphonates are compounds used in the treatment of various metabolic and malignant bone diseases. In the last 2 years there has been a significant increase in referrals to the Department of Oral and Maxillofacial Surgery of patients with exposed necrotic jaw bone, diagnosed elsewhere as chronic refractory osteomyelitis of jaws, mostly after several teeth extractions. The only clinical feature in common for all the patients was the use of bisphosphonates in the treatment of bone diseases. A retrospective study was performed of 11 patients with necrotic bone lesions of the jaws of various extents referred to this Department from July 2003 to November 2004. The management of the patients included cessation of bisphosphonate therapy for 2-8 months and various surgical restorative procedures thereafter. Four patients (36%) presented with maxillary bone involvement, 6 (55%) had mandibular bone necrosis and 1 (9%) presented with necrosis at 3 quadrants. All patients had received bisphosphonate therapy for 6 months to 5 years. Biopsies from the necrotic lesions revealed no metastatic disease. One patient who was removed from bisphosphonate therapy for 8 months recovered completely, one other who was not removed from bisphosphonate therapy relapsed and for all the others, with cessation of bisphosphonate therapy for 2-6 months, the results were inconsistent. A new complication of bisphosphonate therapy administration, i.e. osteonecrosis of jaws, seems to be developing. The improved results after cessation of the medication should make clinicians reconsider the merits of the rampant use of bisphosphonates, while further investigation is needed to completely elucidate this complication.

Spontaneous elicitation of potent antitumor immunity and eradication of established tumors by administration of DNA encoding soluble transforming growth factor-beta II receptor without active antigen-sensitization

Since immunity is generally suppressed by immunoregulatory factors, such as transforming growth factor-beta (TGF-beta), interleukin (IL)-10, and vascular endothelial growth factor (VEGF), produced by tumor cells or stromal cells surrounding tumor cells, various kinds of cancer immunotherapy mostly fail to elicit potent antitumor immunity. Herein, we tested whether neutralization of TGF-beta can elicit strong antitumor immune responses and tumor regression in tumor-bearing mice. A plasmid DNA, pcDNA-sTGFbetaR/huIg, encoding a fusion protein consisting of the extracellular domain of TGF-beta type II receptor (TGFbetaRII) and the Fc portion of human IgG heavy chain, was injected through different routes into B6 mice carrying established tumors of E.G7 cells, which consist of the poorly immunogenic tumor cells EL4, transfected with the ovalbumin (OVA) gene. The frequency of OVA-specific cytotoxic T lymphocytes (CTL), in the treated mice. increased resulting in the tumor eradication and relapse-free survival in around 70% of the E.G7-bearing mice. In contrast, administration of mock DNA into E.G7-bearing mice did not elicit tumor-specific immune responses. Therefore, administration of DNA encoding TGFbetaRII allowed tumor-bearing hosts to elicit sufficiently potent antitumor immune responses without requirement of further active antigen-immunization. This strategy seems to be applicable to clinical therapy against cancer, because it is low-cost, safe, and easy to manipulate.

Enhanced antitumor effect of dendritic cell based immunotherapy after intratumoral injection of radionuclide Ho-166 against B16 melanoma

Internal radiotherapy with the intratumoral injection of the beta-emitting radionuclide, Holmium (Ho)-166, into B16 melanoma resulted in a reduction in size and growth rate; however, complete remission was not always achieved. Therefore, additional dendritic cell (DC) therapy was investigated to determine whether it could improve therapeutic results. Malignant melanoma was induced in mice by inoculating B16F10 cell line subcutaneously. Fifty-four mice were divided into four groups: (1) non-treated (group I, n = 11), (2) treated with Ho-166 (group II, n = 16), (3) treated with immature DCs (group III, n = 8), and (4) treated with immature DCs after Ho-166 injection (group IV, n = 19). Changes in tumor size, survival rates, and immunologic profiles were observed. Nineteen days after Ho-166 or PBS injection, mean tumor sizes in the four groups were 6044 +/- 1046, 1658 +/- 523, 3871 +/- 921, and 444 +/- 167 mm(3), respectively. We observed a significant decrease in tumor size (P < 0.05) and an increase in survival in group IV. When the B16F10 cell line was reinjected into the contralateral backs of survivors, much slower growth was observed in group IV (P < 0.05). Both tumor-specific CTL and natural killer cell activities and the infiltration of inflammatory cells into tumor tissues were found to be elevated in group IV. In addition, strong immune responses as determined by in vitro T cell proliferation, ELISA and ELISPOT assay were induced in group IV. Our results suggest that a combination of internal radiotherapy using Ho-166 and immature DCs could be used either to treat unresectable melanoma or as an adjuvant therapy after surgery.

Cycloxygenase-2 inhibition augments the efficacy of a cancer vaccine

Tumor-derived cyclooxygenase-2 (COX-2) and its product, prostaglandin E2, exert strong immunoinhibitory effects that block dendritic cell function and CD4+ and CD8+ T-cell proliferation and function. We have shown previously that the addition of an oral COX-2 inhibitor to immunogene therapy using IFN-beta markedly augmented therapeutic efficacy in murine tumor models. In this study, we hypothesized that COX-2 inhibition might also augment an antitumor vaccination strategy. Mice bearing tumors derived from TC1 cells, a tumor line that expresses the human papillomavirus (HPV) E7 protein, were thus vaccinated with an adenoviral vector expressing HPV E7 protein (Ad.E7). This vaccine approach effectively generated E7-specific CD8+ cells and slowed the growth of small tumors but had little effect on large tumors. However, feeding mice with the COX-2 inhibitor, rofecoxib, restored the effectiveness of the vaccine against large tumors and prolonged survival. This effect was accompanied by a larger percentage of E7-specific CD8+ cells in the regional draining lymph nodes and a markedly increased number of tumor-infiltrating E7-specific CD8+ cells (as determined by flow cytometry) and total CD8+ T cells (as determined by immunohistochemical staining). Increased immunocyte trafficking was likely mediated by the generation of a Th1-type tumor microenvironment because COX-2 inhibition increased expression levels of mRNA for IFN-gamma, interleukin-12, IP-10, and MIG while lowering the expression of vascular endothelial growth factor within tumors. This study shows that the effectiveness of a cancer vaccine can be significantly improved by adding COX-2 inhibition.

An oligonucleotide decoy for Stat3 activates the immune response of macrophages to breast cancer

Tumor-associated macrophages (TAMs) have the potential to induce both immune activation and immune tolerance. Recent studies have indicated that in breast cancers the pro-tumor role of TAMs is dominant. We induced rat peritoneal macrophages with rat breast cancer cell-conditioned medium and analyzed signal transducer and activators of transcription 3 (Stat3) activities of the cells. Then these cells were transfected with Stat3 decoy oligonucleotides (ODNs) and were stimulated by lipopolysaccharide (LPS). The results demonstrate that induced macrophages displayed a reduction of cytotoxicity and antigen-presenting function in comparison with control but transfection with Stat3 decoy ODNs enhanced cytotoxicity and antigen-presenting function of the macrophages. Furthermore, injection of induced macrophages promoted tumor growth accompanied by immunosuppression in the rat tumor models, but injection of induced macrophages transfected with Stat3 decoy ODNs led to retarded tumor growth accompanied by immune activation. The data suggest that immunosuppressive activities of TAMs correlate with over-activated Stat3 signaling of the cells and disruption of Stat3 activity of TAMs can enhance rat immune response to breast cancer.

Monoclonal antibody therapy of ovarian cancer

Despite advances in understanding and treatment, ovarian cancer remains a major cause of cancer mortality worldwide. Debulking surgery and paclitaxel/carboplatin chemotherapy induce good initial responses in most patients, although most cases of advanced disease are not controlled. Monoclonal antibodies hold promise as a potential incremental advance for the treatment of the disease. Antibodies can be used to stimulate the immune response, target tumor-specific receptors to induce antibody-dependent cellular cytotoxicity or interfere with biologic pathways. They can also be used to deliver therapeutic radioisotopes to malignant cells. Oregovomab is in Phase III clinical trials as a consolidation treatment post front-line therapy to trigger tumor-specific cellular immunity. Bevacizumab, which blocks vascular endothelial growth factor, will be entering Phase III as an adjuvant to front-line chemotherapy with a direct effect on angiogenesis. Additional immunostimulating, immune counter-regulatory and receptor-targeting approaches are also reviewed. The family of epidermal growth factor receptors including epidermal growth factor receptor 1 (HER-1) and 2 (HER-2) are both expressed in ovarian cancer and are the subject of ongoing research and development. The recent disappointing results with 90-yttrium-labeled anti-HMFG by single intraperitoneal administration have left the radiopharmaceutical field without a Phase III candidate. Identification of novel targets may advance this therapeutic area in the future. The rapid advances in the fields of immunoregulation and tumor biology should permit an accelerated introduction of antibodies for the treatment of ovarian cancer. These antibodies could complement novel small molecules that are also in development.

Combined antiangiogenic and immune therapy of prostate cancer

Experimental studies of antiangiogenic or immune therapy of cancer have generated a great deal of optimism. However, the results of clinical testing of these therapies are below expectations. We hypothesized that the antitumor efficacy can be increased when immune destruction of tumor cell is combined with destruction of tumor vasculature by antiangiogenic drugs. In the present study the therapeutic efficacy of combined antiangiogenic and immune therapy has been tested against the highly aggressive, MHC class I negative murine RM1 prostate tumor. SU6668 was used as the antiangiogenic drug and recombinant murine B7.2-IgG fusion protein was used to stimulate T cell-mediated immune destruction of tumor cells. SU6668 is an inhibitor of the tyrosine kinase activity of three angiogenic receptors VEGFR2 (Flk-1/KDR), PDGFRbeta and FGFR1 that play a crucial role in tumor-induced vascularization. Our studies show that B7.2-IgG treatment of mice with established RM1 prostate tumors resulted in a significant inhibition of tumor growth. Both CD4+ and CD8+ T cells were responsible for this effect. SU6668 therapy substantially inhibited tumor vascularization and tumor growth. When tumor-bearing mice were treated with SU6668 in combination with B7.2-IgG, the antitumor effects were substantially higher than in mice treated separately with SU6668 or B7.2-IgG. Prolonged treatment of mice with SU6668 did not inhibit the immunoreactivity of T lymphocytes. On the contrary, T cells from mice treated with a combination of SU6668 and B7.2-IgG showed higher proliferative responses and cytokine production following anti-CD3 stimulation than T cells of mice treated separately with these modalities. These results indicate that antiangiogenic and immune therapies using SU6668 and B7.2-IgG are compatible and manifest complementary antitumor effects. Combined antiangiogenic and immune therapy might represent a new strategy for cancer treatment.

Genes to vaccines for immunotherapy: how the molecular biology revolution has influenced cancer immunology

Recent advances in our understanding of the complex signaling pathways involved in immune system regulation, along with analyses of genetic differences between tumors and their normal cellular counterparts, have accelerated development of immune-based strategies for cancer treatment and prevention. More clinically relevant animal models have shown that successful immune-based strategies will require the integration of interventions that target specific tumor antigens with regulators of the antitumor immune response. Immunotherapy for cancer is at a critical crossroad, as therapeutics designed to target cancer-associated antigens and regulatory signaling molecules enter clinical trials. We outline here a paradigm for early-stage clinical development of immunotherapy combinations that use vaccines to drive tumor antigen-specific responses while simultaneously targeting immune regulatory pathways.

Combined radiation therapy and dendritic cell vaccine for treating solid tumors with liver micro-metastasis

BACKGROUND

Tumor metastasis and relapse are major obstacles in combating human malignant diseases. Neither radiotherapy alone nor injection of dendritic cells (DCs) can successfully overcome this problem. Radiation induces tumor cell apoptosis and necrosis, resulting in the release of tumor antigen and danger signals, which are favorable for DC capturing antigens and maturation. Hence, the strategy of combined irradiation and DC vaccine may be a novel approach for treating human malignancies and early metastasis.

METHODS

To develop an effective combined therapeutic approach, we established a novel concomitant local tumor and liver metastases model through subcutaneous (s.c.) and intravenous (i.v.) injection. We selected the optimal time for DC injection after irradiation and investigated the antitumor effect of combining irradiation with DC intratumoral injection and the related mechanism.

RESULTS

Combined treatment with radiotherapy and DC vaccine could induce a potent antitumor immune response, resulting in a significant decrease in the rate of local tumor relapse and the numbers of liver metastases. The related mechanisms for this strong antitumor immunity of this combined therapy might be associated with the production of apoptotic and necrotic tumor antigens and heat shock proteins after irradiation, phagocytosis, migration and maturation of DCs, and induction of more efficient tumor-specific cytotoxic T lymphocyte activity through a cross-presentation pathway.

CONCLUSIONS

Co-administration of local irradiation and intratumoral DC injection may be a promising strategy for treating radiosensitive tumors and eliminating metastasis in the clinic.

Vascular endothelial growth factor impairs the functional ability of dendritic cells through Id pathways

Vascular endothelial growth factor (VEGF) is an angiogenic cytokine that plays an important role in tumor growth and progression. Recent evidence suggests an alternate, albeit indirect, role of VEGF on host immune response to tumors. VEGF appears to diminish host immunity by altering the function of major antigen-presenting cells such as dendritic cells (DCs) [D.I. Gabrilovich, T. Ishida, S. Nadaf, J.E. Ohm, D.P. Carbone, Antibodies to vascular endothelial growth factor enhance the efficacy of cancer immunotherapy by improving endogenous dendritic cell function, Clin. Cancer Res. 5 (1999) 2963-2970, D. Gabrilovich, T. Ishida, T. Oyama, S. Ran, V. Kravtsov, S. Nadaf, D.P. Carbone, Vascular endothelial growth factor inhibits the development of dendritic cells and dramatically affects the differentiation of multiple hematopoietic lineages in vivo, Blood 92 (1998) 4150-4166, T. Oyama, S. Ran, T. Ishida, S. Nadaf, L. Kerr, D.P. Carbone, D.I. Gabrilovich, Vascular endothelial growth factor affects dendritic cell maturation through the inhibition of nuclear factor-kappa B activation in hemopoietic progenitor cells, J. Immunol. 160 (1998) 1224-1232.]. DCs are prime initiators of host immunity as they are known to activate both primary as well as secondary immune responses [J. Banchereau, F. Briere, C. Caux, J. Davoust, S. Lebecque, Y.J. Liu, B. Pulendran, K. Palucka, Immunobiology of dendritic cells, Ann. Rev. Immunol. 18 (2000) 767-811.]. However, the exact nature of how VEGF suppresses DC function is not fully clear. In this report, we show that DCs cultured in the presence of VEGF are less potent in stimulating antigen-specific T-cells. Furthermore, by using DCs derived from Id1(-/-) mice that are defective in Flt-1 signaling, we demonstrated that the inhibitory function of VEGF on DC function is most likely mediated by Flt-1. Thus, the role of VEGF in downregulating host immunity may highlight a unique role of VEGF in the pathogenesis of cancer.