CD40 agonists alter tumor stroma and show efficacy against pancreatic carcinoma in mice and humans

Genetically engineered mouse models of pancreatic cancer

Pancreatic ductal adenocarcinoma is the 10th most common cancer and the fourth leading cause of cancer-related death in the United States. Despite great effort, the prognosis for patients with this disease remains dismal with a 5-year survival rate of just 4% to 6%. Although several important advances have improved our understanding of the underlying biology of pancreatic cancer, this knowledge has not translated into novel therapeutic approaches and effective systemic or targeted therapies. Pancreatic cancer is one of the malignancies most difficult to treat, with remarkable intrinsic resistance to both standard and targeted chemotherapy as well as ionizing radiation. Surgical intervention remains the only potentially curative approach. However, most patients present with inoperable and/or metastatic disease and are therefore excluded from surgery. Accordingly, new therapeutic options are desperately needed. In vivo models to study innovative and alternative treatment approaches are of major importance. A variety of genetically engineered mouse models of pancreatic cancer have been developed over the last decade. However, these models display different characteristics, and not all of them are suited for preclinical studies. In this review, we aim to review the mouse models available, their experimental use, their clinical relevance and limitations, and future directions.

Mechanical disruption of tumors by iron particles and magnetic field application results in increased anti-tumor immune responses

The primary tumor represents a potential source of antigens for priming immune responses for disseminated disease. Current means of debulking tumors involves the use of cytoreductive conditioning that impairs immune cells or removal by surgery. We hypothesized that activation of the immune system could occur through the localized release of tumor antigens and induction of tumor death due to physical disruption of tumor architecture and destruction of the primary tumor in situ. This was accomplished by intratumor injection of magneto-rheological fluid (MRF) consisting of iron microparticles, in Balb/c mice bearing orthotopic 4T1 breast cancer, followed by local application of a magnetic field resulting in immediate coalescence of the particles, tumor cell death, slower growth of primary tumors as well as decreased tumor progression in distant sites and metastatic spread. This treatment was associated with increased activation of DCs in the draining lymph nodes and recruitment of both DCs and CD8(+)T cells to the tumor. The particles remained within the tumor and no toxicities were observed. The immune induction observed was significantly greater compared to cryoablation. Further anti-tumor effects were observed when MRF/magnet therapy was combined with systemic low dose immunotherapy. Thus, mechanical disruption of the primary tumor with MRF/magnetic field application represents a novel means to induce systemic immune activation in cancer.

Harnessing the power of the immune system to target cancer

For many years, immunotherapeutic approaches for cancer held more promise than actual clinical benefit for the majority of patients. However, several recent key advances in tumor immunology have now turned the tide in favor of immunotherapy for the treatment of many different cancer types. In this review, we describe four of the most effective immunotherapeutic approaches currently used in the clinic: cancer vaccines, immunostimulatory agents, adoptive T cell therapy, and immune checkpoint blockade. In addition, we discuss some of the most promising future strategies that aim to utilize multiple immunotherapies or combine them with other approaches to more effectively target cancer.

Desmoplasia in pancreatic cancer. Can we fight it?

The hallmark of pancreatic tumours, the desmoplastic reaction, provides a unique microenvironment that affects pancreatic tumour behaviour, its ability to grow and metastasize as well as resist the effects of chemotherapy. Complex molecular interactions and pathways give rise to the desmoplastic reaction. Breakdown or penetration of the desmoplastic reaction may hold the key to overcoming the limits of delivery of efficacious chemotherapy or the development of new targeted treatments. Herein we discuss such new developments to fight the desmoplastic reaction, including inhibitors of the epidermal growth factor, fibroblast growth factor, the hedgehog pathway, as well as new molecular targets like CD40 agonist and its effects on T cells, extracellular matrix modifying enzymes such as LOXL2 inhibitor and novel tumour penetrating peptides for delivery of drugs.

Targeting of 4-1BB by monoclonal antibody PF-05082566 enhances T-cell function and promotes anti-tumor activity

4-1BB (CD137, TNFRSF9) is a costimulatory receptor expressed on several subsets of activated immune cells. Numerous studies of mouse and human T cells indicate that 4-1BB promotes cellular proliferation, survival, and cytokine production. 4-1BB agonist mAbs have demonstrated efficacy in prophylactic and therapeutic settings in both monotherapy and combination therapy tumor models and have established durable anti-tumor protective T-cell memory responses. PF-05082566 is a fully human IgG2 that binds to the extracellular domain of human 4-1BB with high affinity and specificity. In preclinical studies, this agonist antibody demonstrated its ability to activate NF-κB and induce downstream cytokine production, promote leukocyte proliferation, and inhibit tumor growth in a human PBMC xenograft tumor model. The mechanism of action and robust anti-tumor efficacy of PF-05082566 support its clinical development for the treatment of a broad spectrum of human malignancies.

Dendritic cell-based immunotherapy in mesothelioma

Mesothelioma is a rare thoracic malignancy with a dismal prognosis. Current treatment options are scarce and clinical outcomes are rather disappointing. Due to the immunogenic nature of mesothelioma, several studies have investigated immunotherapeutic strategies to improve the prognosis of patients with mesothelioma. In the last decade, progress in knowledge of the modulation of the immune system to attack the tumor has been remarkable, but the optimal strategy for immunotherapy has yet to be unraveled. Because of their potent antigen-presenting capacity, dendritic cells are acknowledged as a promising agent in immunotherapeutic approaches in a number of malignancies. This review gives an update and provides a future perspective in which immunotherapy may improve the outcome of mesothelioma therapy.

Advances in the development of cancer immunotherapies

Manipulating the immune system in order to induce clinically relevant responses against cancer is a longstanding goal. Interventions to enhance tumor-specific immunity through vaccination, sustaining effector T cell activation, or increasing the numbers of tumor-specific T cells using ex vivo expansion, have all resulted in clinical successes. Here, we examine recent clinical advances and major ongoing studies in the field of cancer immunotherapy. Single agents have so far benefited a limited proportion of patients, and future studies combining different types of immunotherapies and other therapeutic modalities, such as drugs against specific signaling pathways driving cancer cell growth, are needed to pave the way for the development of effective anticancer treatments causing durable responses.

Small molecule-gold nanorod conjugates selectively target and induce macrophage cytotoxicity towards breast cancer cells

Gold nanoparticles are known to activate anti-tumor potential in macrophage immune cells; however, the subsequent effects of these cells on others nearby are poorly understood. A novel gold-nanoparticle conjugate that selectively targets and induces cytotoxic activity of tumor-associated macrophages towards breast cancer cells in co-culture is synthesized. These constructs are promising new tools for studying fundamental biological interactions with nanoscale materials and candidates for emerging macrophage-mediated delivery applications.

Polysaccharide-K (PSK) increases p21(WAF/Cip1) and promotes apoptosis in pancreatic cancer cells

BACKGROUND

Polysaccharide-K (PSK, Krestin(®)) is a natural remedy and one of the most commonly used medicinal mushroom extracts. It has been used as oral adjuvant treatment in cancer therapy in Japan and other Asian countries for more than 40 years. PSK is thought to be an immune modulator, however, its antitumor actions remain undefined. The aim of the present study was to investigate underlying mechanisms by which PSK exerts its antitumor effects on malignant epithelial cells.

METHODS

Antitumor activities of PSK were evaluated on multiple human pancreatic adenocarcinoma cells in vitro. Cell viability, apoptotic pathways, cytokine expression and involvement of TLR2 and TLR4 were monitored by MTT, flow cytometry, Western blotting and protein arrays.

RESULTS

We demonstrate that PSK acts as a growth inhibitor for pancreatic cancer cells, known otherwise to be highly resistant to conventional chemotherapies. Pancreatic cancer cells can be protected against PSK-mediated growth inhibition by neutralizing antibodies against TLR2 and TLR4. The antiproliferative actions were associated with upregulated cell cycle regulatory p21(WAF/Cip1) and pro-apoptotic protein Bax levels, resulting in cell cycle arrest and induction of apoptosis. In addition, a significant growth inhibition and additive effect was observed with PSK and gemcitabine administered as combined treatment.

CONCLUSION

While previous studies have emphasized the potential importance of PSK in immune activation, the present results uncover additional mechanisms on epithelial cells that may contribute to the antitumor effects provided by PSK as suggested by clinical observations.

Monocyte CD40 expression in head and neck squamous cell carcinoma (HNSCC)

CD40, an antigen-presenting cell expressed costimulatory receptor molecule, binds to T cell expressed CD40-ligand (CD40-L). Using a mouse tumor model, we showed previously that lower CD40/CD40-L expression levels promoted tumor growth whereas higher CD40/CD40-L expression levels led to tumor regression indicating duality in CD40 functions. Whether CD40/CD40-L expressions are regulated in cancer patients is unknown. Herein, we show that the CD40 and CD40-L expressions on monocytes and T cells, respectively, decrease as the head and neck squamous cell carcinoma (HNSCC) patients progress from stage-I through stage-IV suggesting a novel CD40/CD40-L expression based staging of HNSCC tumor. The staging is confirmed by TNM and histo-pathological staging. The levels of soluble CD40 (sCD40) and sCD40-L are also modulated in patients' plasma. As CD40 expressing monocytes increase in the post-operative patients, CD40 expression levels are possibly regulated by tumor load. This change is accompanied by increased IL-12 expressing monocytes and decreased IL-10 expression levels. Thus, our findings on CD40/CD40-L expression in HNSCC patients bear significant implications.

Disruption of SIRPα signaling in macrophages eliminates human acute myeloid leukemia stem cells in xenografts

Inhibition of macrophage SIRPα–CD47 interactions mediates phagocytosis and clearance of acute myeloid leukemia stem cells.

Although tumor surveillance by T and B lymphocytes is well studied, the role of innate immune cells, in particular macrophages, is less clear. Moreover, the existence of subclonal genetic and functional diversity in some human cancers such as leukemia underscores the importance of defining tumor surveillance mechanisms that effectively target the disease-sustaining cancer stem cells in addition to bulk cells. In this study, we report that leukemia stem cell function in xenotransplant models of acute myeloid leukemia (AML) depends on SIRPα-mediated inhibition of macrophages through engagement with its ligand CD47. We generated mice expressing SIRPα variants with differential ability to bind human CD47 and demonstrated that macrophage-mediated phagocytosis and clearance of AML stem cells depend on absent SIRPα signaling. We obtained independent confirmation of the genetic restriction observed in our mouse models by using SIRPα-Fc fusion protein to disrupt SIRPα–CD47 engagement. Treatment with SIRPα-Fc enhanced phagocytosis of AML cells by both mouse and human macrophages and impaired leukemic engraftment in mice. Importantly, SIRPα-Fc treatment did not significantly enhance phagocytosis of normal hematopoietic targets. These findings support the development of therapeutics that antagonize SIRPα signaling to enhance macrophage-mediated elimination of AML.

Emerging frontiers in pancreatic cancer research: elaboration of key genes, cells and the extracellular milieu

PURPOSE OF REVIEW

We review recent literature with a view to forge an integrative understanding of the molecular, cellular and extracellular milieu of pancreatic cancer, and discuss them in the context of development of novel, personalized therapeutic options.

RECENT FINDINGS

Pancreatic tumorigenesis, examined using genetically engineered mouse models, appears to be driven by local inflammation, in concert with the 'big four' mutations involving oncogenic KRAS, SMAD4, CDKN2A, and TP53, through induction of epithelial-to-mesenchymal transition (EMT) and cancer stem cells, and accompanied by metastasis. High-throughput sequencing of pancreatic ductal adenocarcinoma as well as neuroendocrine tumors and rarer subtypes of cancers of the pancreas has revealed several novel mutations in genes like PALB2, guanine nucleotide-binding protein, alpha stimulating, death-domain-associated protein, α thalassemia/mental retardation syndrome X linked, switch/sucrose nonfermentable pathway related, and in genes in the ubiquitin-dependent pathways such as USP9X. Therapeutic targeting of the tumor-stroma axis by cytokines and immune response modulators and the role of autophagy in pancreatic cancer are some other salient themes explored in the recent publications.

SUMMARY

Recent publications shed new light on the mutational landscape of pancreatic cancer and further delineate the distinctive pancreatic cancer-stroma ecosystem as determined by the dynamic interplay of inflammation, hallmark mutations, EMT, and cancer stem cells.

Overcoming the stromal barrier: technologies to optimize drug delivery in pancreatic cancer

Pancreatic cancer has historically proven resistant to anticancer agents. On the one hand, drugs might be more efficient if higher levels could be achieved at the tumor site rather than the normal tissues. On the other hand, the thick stroma and the relative absence of abundant vessels may account at least partially for the failure of successive clinical trials to demonstrate effective treatments in this type of malignancy. In this context, the development and testing in clinical trials of treatment strategies that aim to optimize drug delivery is an important target in improving the prognosis of patients with pancreatic cancer.

Immunotherapy of cancer in 2012

The immunotherapy of cancer has made significant strides in the past few years due to improved understanding of the underlying principles of tumor biology and immunology. These principles have been critical in the development of immunotherapy in the laboratory and in the implementation of immunotherapy in the clinic. This improved understanding of immunotherapy, enhanced by increased insights into the mechanism of tumor immune response and its evasion by tumors, now permits manipulation of this interaction and elucidates the therapeutic role of immunity in cancer. Also important, this improved understanding of immunotherapy and the mechanisms underlying immunity in cancer has fueled an expanding array of new therapeutic agents for a variety of cancers. Pegylated interferon-α2b as an adjuvant therapy and ipilimumab as therapy for advanced disease, both of which were approved by the United States Food and Drug Administration for melanoma in March 2011, are 2 prime examples of how an increased understanding of the principles of tumor biology and immunology have been translated successfully from the laboratory to the clinical setting. Principles that guide the development and application of immunotherapy include antibodies, cytokines, vaccines, and cellular therapies. The identification and further elucidation of the role of immunotherapy in different tumor types, and the development of strategies for combining immunotherapy with cytotoxic and molecularly targeted agents for future multimodal therapy for cancer will enable even greater progress and ultimately lead to improved outcomes for patients receiving cancer immunotherapy.

Cancer immunoediting by the innate immune system in the absence of adaptive immunity

In the absence of adaptive immunity, NK cells polarize M1 macrophages to facilitate cancer immunoediting.

Cancer immunoediting is the process whereby immune cells protect against cancer formation by sculpting the immunogenicity of developing tumors. Although the full process depends on innate and adaptive immunity, it remains unclear whether innate immunity alone is capable of immunoediting. To determine whether the innate immune system can edit tumor cells in the absence of adaptive immunity, we compared the incidence and immunogenicity of 3′methylcholanthrene-induced sarcomas in syngeneic wild-type, RAG2^−/−, and RAG2^−/−x γc^−/− mice. We found that innate immune cells could manifest cancer immunoediting activity in the absence of adaptive immunity. This activity required natural killer (NK) cells and interferon γ (IFN-γ), which mediated the induction of M1 macrophages. M1 macrophages could be elicited by administration of CD40 agonists, thereby restoring editing activity in RAG2^−/−x γc^−/− mice. Our results suggest that in the absence of adaptive immunity, NK cell production of IFN-γ induces M1 macrophages, which act as important effectors during cancer immunoediting.

Clinical significance of tumor-associated inflammatory cells in metastatic neuroblastoma

PURPOSE

Children diagnosed at age ≥ 18 months with metastatic MYCN-nonamplified neuroblastoma (NBL-NA) are at high risk for disease relapse, whereas those diagnosed at age < 18 months are nearly always cured. In this study, we investigated the hypothesis that expression of genes related to tumor-associated inflammatory cells correlates with the observed differences in survival by age at diagnosis and contributes to a prognostic signature.

METHODS

Tumor-associated macrophages (TAMs) in localized and metastatic neuroblastomas (n = 71) were assessed by immunohistochemistry. Expression of 44 genes representing tumor and inflammatory cells was quantified in 133 metastatic NBL-NAs to assess age-dependent expression and to develop a logistic regression model to provide low- and high-risk scores for predicting progression-free survival (PFS). Tumors from high-risk patients enrolled onto two additional studies (n = 91) served as independent validation cohorts.

RESULTS

Metastatic neuroblastomas had higher infiltration of TAMs than locoregional tumors, and metastatic tumors diagnosed in patients at age ≥ 18 months had higher expression of inflammation-related genes than those in patients diagnosed at age < 18 months. Expression of genes representing TAMs (CD33/CD16/IL6R/IL10/FCGR3) contributed to 25% of the accuracy of a novel 14-gene tumor classification score. PFS at 5 years for children diagnosed at age ≥ 18 months with NBL-NA with a low- versus high-risk score was 47% versus 12%, 57% versus 8%, and 50% versus 20% in three independent clinical trials, respectively.

CONCLUSION

These data suggest that interactions between tumor and inflammatory cells may contribute to the clinical metastatic neuroblastoma phenotype, improve prognostication, and reveal novel therapeutic targets.

Regulation of cancer stem cell activities by tumor-associated macrophages

Recent studies revealed that tumor-associated macrophages play a decisive role in the regulation of tumor progression by manipulating tumor oncogenesis, angiogenesis and immune functions within tumor microenvironments. However, the role of cancer stem cells in the tumorigenic activities of tumor-associated macrophages during the course of transformation and treatment remains largely unknown. Recent studies have clarified the functional aspects of tumor-associated macrophages in the regulation of the tumorigenic activities and anticancer drug responsiveness of cancer stem cells through complex networks formed by distinct sets of cytokines, chemokines and growth factors. In this article we discuss recent advances and future perspectives regarding the molecular interplay between cancer stem cells and tumor-associated macrophages and provide future perspective about the therapeutic implication against treatment-resistant variants of cancer.

The mesenchyme in malignancy: a partner in the initiation, progression and dissemination of cancer

The tumor microenvironment presents an exciting opportunity for innovative prognostic and therapeutic approaches to human cancer. The diverse cellular and extracellular contribution to tumor growth argues that prevention and cure of human cancers will result only from a multifaceted approach to cancer therapy. In this review we provide a foundation for considering the mesenchymal contribution to the tumor microenvironment. We address normal mesenchymal development, physiological interactions between the epithelium and stroma and the cellular hierarchy within these compartments. We focus on cancer-associated fibroblasts in gastrointestinal malignancy but our models have also been informed by other tumor systems. The review provides a framework for characterizing the overall biological contribution of the mesenchyme to human disease. Understanding the biological heterogeneity of specific mesenchymal cells in cancer will provide new opportunities for targeted cancer prevention and therapy.

In vitro generation of monocyte-derived macrophages under serum-free conditions improves their tumor promoting functions

The tumor promoting role of M2 macrophages has been described in in vivo models and the presence of macrophages in certain tumor types has been linked to a poor clinical outcome. In light of burgeoning activities to clinically develop new therapies targeting tumor-associated macrophages (TAMs), reliable in vitro models faithfully mimicking the tumor promoting functions of TAMs are required. Generation and activation of human monocyte-derived macrophages (MDM) in vitro, described as M1 or M2 macrophages attributed with tumoricidal or tumor-promoting functions, respectively, has been widely reported using mainly serum containing culture methods. In this study, we compared the properties of macrophages originating from monocytes cultured either in media containing serum together with M-CSF for M2 and GM-CSF for M1 macrophages or in serum-free media supplemented with M-CSF or GM-CSF and cytokines such as IL-4, IL-10 to induce activated M2 or LPS together with IFN-γ to generate activated M1 phenotype. We observed differences in cell morphology as well as increased surface receptor expression levels in serum-containing culture whereas similar or higher cytokine production levels were detected under serum-free culture conditions. More importantly, MDM differentiated under serum-free conditions displayed enhanced tumoricidal activity for M1 and tumor promoting property for M2 macrophages in contrast to MDM differentiated in the presence of serum. Moreover, evaluation of MDM phagocytic activity in serum free condition resulted in greater phagocytic properties of M2 compared to M1. Our data therefore confirm the tumor promoting properties of M2 macrophages in vitro and encourage the targeting of TAMs for cancer therapy.

A phase 1 study of lucatumumab, a fully human anti-CD40 antagonist monoclonal antibody administered intravenously to patients with relapsed or refractory multiple myeloma

In this open-label, multicentre, phase 1 study a fully human anti-CD40 antagonist monoclonal antibody, lucatumumab, was evaluated in patients with relapsed/refractory multiple myeloma (MM). The primary objective was to determine the maximum tolerated dose (MTD) based on dose-limiting toxicities (DLTs). Secondary objectives included safety, pharmacokinetics, pharmacodynamics and antimyeloma activity. Twenty-eight patients, enrolled using a standard '3 + 3' dose escalation, received one or two (n = 3) cycles of lucatumumab 1·0, 3·0, 4·5 or 6·0 mg/kg once weekly for 4 weeks. Common lucatumumab-related adverse events were reversible, mild-to-moderate infusion reactions. Severe adverse events were anaemia, chills, hypercalcaemia and pyrexia (7% each). DLTs included grade 4 thrombocytopenia, grade 3 increased alanine aminotransferase and grade 4 increased lipase (n = 1 each). The MTD was 4·5 mg/kg. At doses ≥3·0 mg/kg, sustained receptor occupancy (≥87%), observed throughout weekly infusions up to 5 weeks after the last infusion, correlated with an estimated half-life of 4-19 d. Twelve patients (43%) had stable disease, and one patient (4%) maintained a partial response for ≥8 months. These findings indicate that single-agent lucatumumab was well tolerated up to 4·5 mg/kg with modest clinical activity in relapsed/refractory MM, warranting further study as a combination therapy.

Multivalent porous silicon nanoparticles enhance the immune activation potency of agonistic CD40 antibody

One of the fundamental paradigms in the use of nanoparticles to treat disease is to evade or suppress the immune system in order to minimize systemic side effects and deliver sufficient nanoparticle quantities to the intended tissues. However, the immune system is the body's most important and effective defense against diseases. It protects the host by identifying and eliminating foreign pathogens as well as self-malignancies. Here we report a nanoparticle engineered to work with the immune system, enhancing the intended activation of antigen presenting cells (APCs). We show that luminescent porous silicon nanoparticles (LPSiNPs), each containing multiple copies of an agonistic antibody (FGK45) to the APC receptor CD40, greatly enhance activation of B cells. The cellular response to the nanoparticle-based stimulators is equivalent to a 30-40 fold larger concentration of free FGK45. The intrinsic near-infrared photoluminescence of LPSiNPs is used to monitor degradation and track the nanoparticles inside APCs.

The role of stroma in pancreatic cancer: diagnostic and therapeutic implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies worldwide and survival has not improved substantially in the past 30 years. Desmoplasia (abundant fibrotic stroma) is a typical feature of PDAC in humans, and stromal activation commonly starts around precancerous lesions. It is becoming clear that this stromal tissue is not a bystander in disease progression. Cancer-stroma interactions effect tumorigenesis, angiogenesis, therapy resistance and possibly the metastatic spread of tumour cells. Therefore, targeting the tumour stroma, in combination with chemotherapy, is a promising new option for the treatment of PDAC. In this Review, we focus on four issues. First, how can stromal activity be used to detect early steps of pancreatic carcinogenesis? Second, what is the effect of perpetual pancreatic stellate cell activity on angiogenesis and tissue perfusion? Third, what are the (experimental) antifibrotic therapy options in PDAC? Fourth, what lessons can be learned from Langton's Ant (a simple mathematical model) regarding the unpredictability of genetically engineered mouse models?

New biomarkers and targets in pancreatic cancer and their application to treatment

Late diagnosis of pancreatic ductal adenocarcinoma (pancreatic cancer) and the limited response to current treatments results in an exceptionally poor prognosis. Advances in our understanding of the molecular events underpinning pancreatic cancer development and metastasis offer the hope of tangible benefits for patients. In-depth mutational analyses have shed light on the genetic abnormalities in pancreatic cancer, providing potential treatment targets. New biological studies in patients and in mouse models have advanced our knowledge of the timing of metastasis of pancreatic cancer, highlighting new directions for the way in which patients are treated. Furthermore, our increasing understanding of the molecular events in tumorigenesis is leading to the identification of biomarkers that enable us to predict response to treatment. A major drawback, however, is the general lack of an adequate systematic approach to advancing the use of biomarkers in cancer drug development, highlighted in a Cancer Biomarkers Collaborative consensus report. In this Review, we summarize the latest insights into the biology of pancreatic cancer, and their repercussions for treatment. We provide an overview of current treatments and, finally, we discuss novel therapeutic approaches, including the role of biomarkers in therapy for pancreatic cancer.

The role of stroma in pancreatic cancer: diagnostic and therapeutic implications

Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies worldwide and survival has not improved substantially in the past 30 years. Desmoplasia (abundant fibrotic stroma) is a typical feature of PDAC in humans, and stromal activation commonly starts around precancerous lesions. It is becoming clear that this stromal tissue is not a bystander in disease progression. Cancer-stroma interactions effect tumorigenesis, angiogenesis, therapy resistance and possibly the metastatic spread of tumour cells. Therefore, targeting the tumour stroma, in combination with chemotherapy, is a promising new option for the treatment of PDAC. In this Review, we focus on four issues. First, how can stromal activity be used to detect early steps of pancreatic carcinogenesis? Second, what is the effect of perpetual pancreatic stellate cell activity on angiogenesis and tissue perfusion? Third, what are the (experimental) antifibrotic therapy options in PDAC? Fourth, what lessons can be learned from Langton's Ant (a simple mathematical model) regarding the unpredictability of genetically engineered mouse models?

Whole cell vaccines--past progress and future strategies

Cancer vaccines have shown success in curing tumors in preclinical models. Accumulating evidence also supports their ability to induce immune responses in patients. In many cases, these responses correlate with improved clinical outcomes. However, cancer vaccines have not yet demonstrated their true potential in clinical trials. This is likely due to the difficulty in mounting a significant anti-tumor response in patients with advanced disease because of pre-existing tolerance mechanisms that are actively turning off immune recognition in cancer patients. This review will examine the recent progress being made in the design and implementation of whole cell cancer vaccines, one vaccine approach that simultaneously targets multiple tumor antigens to activate the immune response. These vaccines have been shown to induce antigen-specific T-cell responses. Preclinical studies evaluating these vaccines given in sequence with other agents and cancer treatment modalities support the use of immunomodulating doses of chemotherapy and radiation, as well as immune-modulating pathway-targeted monoclonal antibodies, to enhance the efficacy of cancer vaccines. Based on emerging preclinical data, clinical trials are currently exploring the use of combinatorial immune-based therapies for the treatment of cancer.

Deciphering the message broadcast by tumor-infiltrating dendritic cells

Human dendritic cells (DCs) infiltrate solid tumors, but this infiltration occurs in favorable and unfavorable disease prognoses. The statistical inference is that tumor-infiltrating DCs (TIDCs) play no conclusive role in predicting disease progression. This is remarkable because DCs are highly specialized antigen-presenting cells linking innate and adaptive immunity. DCs either boost the immune system (enhancing immunity) or dampen it (leading to tolerance). This dual effect explains the dual outcomes of cancer progression. The reverse functional characteristics of DCs depend on their maturation status. This review elaborates on the markers used to detect DCs in tumors. In many cases, the identification of DCs in human cancers relies on staining for S-100 and CD1a. These two markers are mainly expressed by Langerhans cells, which are one of several functionally different DC subsets. The activation status of DCs is based on the expression of CD83, DC-SIGN, and DC-LAMP, which are nonspecific markers of DC maturation. The detection of TIDCs has not kept pace with the increased knowledge about the identification of DC subsets and their maturation status. Therefore, it is difficult to draw a conclusion about the performance of DCs in tumors. We suggest a novel selection of markers to distinguish human DC subsets and maturation states. The use of these biomarkers will be of pivotal importance to scrutinize the prognostic significance of TIDCs.

The role of inflammatory cells in fostering pancreatic cancer cell growth and invasion

The pancreatic ductal adenocarcinoma (PDAC) microenvironment accommodates a variety of cell types and a plethora of complex interactions between tumor cells, host cells and extracellular matrix (ECM) components. Here we review the role of inflammatory cells, in particular mast cells, myeloid-derived suppressor cells, macrophages, T regulatory cells, T helper cells and neutrophils. The picture that emerges is that of a tumor microenvironment, in which the immune response is actively suppressed, and inflammatory cells contribute in a variety of ways to tumor progression.

The role of antigen-specific and non-specific immunotherapy in the treatment of cancer

Immunotherapy in the treatment of cancer is increasing, particularly with the recent FDA approval of sipuleucel-T and ipilimumab. The efficacy of anti-tumor immunotherapies has been modest compared to their theoretical and pre-clinical promise. This review evaluates the promise and pitfalls of immunotherapy and highlight some of the obstacles to improving anti-tumor immunotherapy: the need for technical refinement of therapies, the need for an increased understanding of how best to combine therapies with traditional cytotoxic therapies, the inability of patients to mount an effective immune response either due to disease burden or tumor induced immune suppression, the significant toxicities associated with many immunotherapies, and the lack of strongly immunogenic antigens required by many therapies. Further, antigen-non-specific immunotherapies, including cytokines such as interleukins and interferons, immuno-stimulatory agents such as CpG oligonucleotides, or BCG, antibodies targeted against receptors such as the agonistic CD40 or inhibitory CTLA-4 antibodies, and enzyme inhibitors such as those targeting cyclo-oxygenase or indolamine-2,3-dioxygenase are discussed. In addition, potential mechanisms of these therapies such as direct anti-tumor effects, reversal of immune suppression, activation of innate immunity, and antigen-non-specific T-cell activation are reviewed. We also appraise the potential of these antigen-non-specific therapies to overcome some of the previously described pitfalls of immunotherapy. Lastly, we discuss a recent series of studies from our laboratory demonstrating the importance of antigen-non-specific 'bystander activation' of memory T-lymphocytes by immunomodulatory therapies such as interleukin-2 and the antigen-non-specific anti-tumor effects of these cells.

New roads open up for implementing immunotherapy in mesothelioma

Treatment options for malignant mesothelioma are limited, and the results with conventional therapies have been rather disappointing to this date. Chemotherapy is the only evidence-based treatment for mesothelioma patients in good clinical condition, with an increase in median survival of only 2 months. Therefore, there is urgent need for a different approach to battle this malignancy. As chronic inflammation precedes mesothelioma, the immune system plays a key role in the initiation of this type of tumour. Also, many immunological cell types can be found within the tumour at different stages of the disease. However, mesothelioma cells can evade the surveillance capacity of the immune system. They build a protective tumour microenvironment to harness themselves against the immune system's attacks, in which they even abuse immune cells to act against the antitumour immune response. In our opinion, modulating the immune system simultaneously with the targeting of mesothelioma tumour cells might prove to be a superior treatment. However, this strategy is challenging since the tumour microenvironment possesses numerous forms of defence strategies. In this paper, we will discuss the interplay between immunological cells that can either inhibit or stimulate tumour growth and the challenges associated with immunotherapy. We will provide possible strategies and discuss opportunities to overcome these problems.

The tumor immunosuppressive microenvironment impairs the therapy of anti-HER2/neu antibody

It has been well established that immune surveillance plays critical roles in preventing the occurrence and progression of tumor. More and more evidence in recent years showed the host anti-tumor immune responses also play important roles in the chemotherapy and radiotherapy of cancers. Our previous study found that tumor- targeting therapy of anti-HER2/neu mAb is mediated by CD8(+) T cell responses. However, we found here that enhancement of CD8(+) T cell responses by combination therapy with IL-15R/IL-15 fusion protein or anti-CD40, which are strong stimultors for T cell responses, failed to promote the tumor therapeutic effects of anti-HER2/neu mAb. Analysis of tumor microenviornment showed that tumor tissues were heavily infiltrated with the immunosuppressive macrophages and most tumor infiltrating T cells, especially CD8(+) T cells, expressed high level of inhibitory co-signaling receptor PD-1. These data suggest that tumor microenvironment is dominated by the immunosuppressive strategies, which thwart anti-tumor immune responses. Therefore, the successful tumor therapy should be the removal of inhibitory signals in the tumor microenvironment in combination with other therapeutic strategies.

Tumor-derived granulocyte-macrophage colony-stimulating factor regulates myeloid inflammation and T cell immunity in pancreatic cancer

Cancer-associated inflammation is thought to be a barrier to immune surveillance, particularly in pancreatic ductal adenocarcinoma (PDA). Gr-1(+) CD11b(+) cells are a key feature of cancer inflammation in PDA, but remain poorly understood. Using a genetically engineered mouse model of PDA, we show that tumor-derived granulocyte-macrophage colony-stimulating factor (GM-CSF) is necessary and sufficient to drive the development of Gr-1(+) CD11b(+) cells that suppressed antigen-specific T cells. In vivo, abrogation of tumor-derived GM-CSF inhibited the recruitment of Gr-1(+) CD11b(+) cells to the tumor microenvironment and blocked tumor development-a finding that was dependent on CD8(+) T cells. In humans, PDA tumor cells prominently expressed GM-CSF in vivo. Thus, tumor-derived GM-CSF is an important regulator of inflammation and immune suppression within the tumor microenvironment.

Immunocombination therapy for high-risk neuroblastoma

Neuroblastoma (NBL) is an aggressive malignancy of the sympathetic nervous system. Advanced-stage NBLs prove fatal in approximately 50% of patients within 5 years. Therefore, new treatment modalities are urgently needed. Immunotherapy is a treatment modality that can be combined with established forms of treatment. Administration of monoclonal antibodies or dendritic cell-based therapies alone can lead to favorable clinical outcomes in individual cancer patients; for example patients with melanoma, lymphoma and NBL. However, clinical benefit is still limited to a minority of patients, and further improvements are clearly needed. In this article, we review the most commonly used approaches to treat patients with NBL and highlight the prerequisites and opportunities of cell-based immunotherapy, involving both innate and adaptive immune-effector cells. Furthermore, we discuss the potential of the combined application of immunotherapy and novel tumor-targeted therapies for the treatment of both cancer in general and NBL in particular.

Towards curative cancer immunotherapy: overcoming posttherapy tumor escape

The past decade has witnessed the evolvement of cancer immunotherapy as an increasingly effective therapeutic modality, evidenced by the approval of two immune-based products by the FDA, that is, the cancer vaccine Provenge (sipuleucel-T) for prostate cancer and the antagonist antibody against cytotoxic T-lymphocyte antigen-4 (CTLA-4) ipilimumab for advanced melanoma. In addition, the clinical evaluations of a variety of promising immunotherapy drugs are well under way. Benefiting from more efficacious immunotherapeutic agents and treatment strategies, a number of recent clinical studies have achieved unprecedented therapeutic outcomes in some patients with certain types of cancers. Despite these advances, however, the efficacy of most cancer immunotherapies currently under clinical development has been modest. A recurring scenario is that therapeutic maneuvers initially led to measurable antitumor immune responses in cancer patients but ultimately failed to improve patient outcomes. It is increasingly recognized that tumor cells can antagonize therapy-induced immune attacks through a variety of counterregulation mechanisms, which represent a fundamental barrier to the success of cancer immunotherapy. Herein we summarize the findings from some recent preclinical and clinical studies, focusing on how tumor cells advance their survival and expansion by hijacking therapy-induced immune effector mechanisms that would otherwise mediate their destruction.

Workshop on immunotherapy combinations. Society for Immunotherapy of Cancer annual meeting Bethesda, November 3, 2011

Although recent FDA approvals on ipilimumab and sipuleucel-T represent major milestones, the ultimate success of immunotherapy approaches will likely benefit from appropriate combinations with other immunotherapeutic and/or non-immunotherapeutic approaches. However, implementation of ideal combinations in the clinic may still face formidable challenges in regulatory, drug-availability and intellectual property aspects. The 2011 SITC annual meeting hosted a workshop on combination immunotherapy to discuss: 1) the most promising combinations found in the laboratory; 2) early success of combination immunotherapy in clinical trials; 3) industry perspectives on combination approaches, and 4) relevant regulatory issues. The integrated theme was how to accelerate the implementation of efficacious combined immunotherapies for cancer patients. Rodent animal models are providing many examples of synergistic combinations that typically include more than two agents. However, mouse and human immunology differ in a significant number of mechanisms and hence we might be missing opportunities peculiar to humans. Nonetheless, incisive animal experimentation with deep mechanistic insight remains the best compass that we can use to guide our paths in combinatorial immunotherapy. Combination immunotherapy clinical trials are already in progress and preliminary results are extremely promising. As a key to translate promising combinations into clinic, real and “perceived” business and regulatory hurdles were debated. A formidable step forward would be to be able to test combinations of investigational agents prior to individual approval. Taking together the FDA and the industrial perspective on combinatorial immunotherapy, the audience was left with the clear message that this is by no means an impossible task. The general perception is that the road ahead of us is full of combination clinical trials which hopefully will bring clinical benefit to our cancer patients at a fast pace.

The multi-faceted roles of prostaglandin E2 in cancer-infiltrating mononuclear phagocyte biology

Extensive research in the last two decades implemented that the inflammatory cell infiltrate, especially in solid tumors, is a major determinant for patient prognosis. Mononuclear phagocytes, i.e. monocytes/macrophages, dendritic cells and myeloid-derived suppressor cells, constitute the majority of tumor-associated immune cells. Instead of inducing anti-tumor immunity, mononuclear phagocytes are functionally subverted by tumor microenvironmental factors to support each stage of oncogenesis. Although mechanisms how tumors program their inflammatory infiltrate to support tumor development are ill-defined, few master regulators are beginning to emerge. One of them is the inflammatory eicosanoid prostaglandin E(2) (PGE(2)), produced by tumor cells or the infiltrating immune cells. In this review we summarize the impact of PGE(2) on mononuclear phagocytes in inflammation and cancer and discuss potential implications for cancer therapy.

CD40 stimulates a "feed-forward" NF-κB-driven molecular pathway that regulates IFN-β expression in carcinoma cells

IFN-β and the CD40L (CD154) share important roles in the antiviral and antitumor immune responses. In this study, we show that CD40 receptor occupancy results in IFN-β upregulation through an unconventional "feed-forward" mechanism, which is orchestrated by canonical NF-κB and involves the sequential de novo synthesis of IFN regulatory factor (IRF)1 and Viperin (RSAD2), an IRF1 target. RelA (p65) NF-κB, IRF1, and Viperin-dependent IRF7 binding to the IFN-β promoter largely controls its activity. However, full activation of IFN-β also requires the parallel engagement of noncanonical NF-κB2 signaling leading to p52 recruitment to the IFN-β promoter. These data define a novel link between CD40 signaling and IFN-β expression and provide a telling example of how signal propagation can be exploited to ensure efficient regulation of gene expression.

Stroma and pancreatic ductal adenocarcinoma: an interaction loop

Pancreatic ductal adenocarcinoma (PDA) has two exceptional features. First, it is a highly lethal disease, with a median survival of less than 6 months and a 5-year survival rate less than 5%. Second, PDA tumor cells are surrounded by an extensive stroma, which accounts for up to 90% of the tumor volume. It is well recognized that stromal microenvironment can accelerate malignant transformation, tumor growth and progression. More importantly, the interaction loop between PDA and its stroma greatly contributes to tumor growth and progression. We propose that the extensive stroma of PDA is closely linked to its poor prognosis. An improved understanding of the mechanisms that contribute to pancreatic tumor growth and progression is therefore urgently needed. Targeting the stroma may thus provide novel prevention, earlier detection and therapeutic options to this deadly malignancy. Accordingly, in this review, we will summarize the mechanism of PDA stroma formation, the role of the stroma in tumor progression and therapy resistance and the potential of stroma-targeted therapeutics strategies.

Gene immunotherapy of chronic lymphocytic leukemia: a phase I study of intranodally injected adenovirus expressing a chimeric CD154 molecule

New therapies for chronic lymphocytic leukemia (CLL) are needed, particularly those that can eradicate residual disease and elicit anti-CLL immune responses. CD40 ligation on CLL cells, which can be achieved using adenovirus encoding chimeric CD154 (Ad-ISF35), enhances their ability to function as antigen-presenting cells and increases their sensitivity to clearance by immune-effector mechanisms. In this study, we report the results of a first-in-man phase I trial of intranodal direct injection (IDI) of Ad-ISF35 in patients with CLL to evaluate toxicity, safety, and tolerability. Fifteen patients received a single IDI of 1 × 10(10) to 33 × 10(10) Ad-ISF35 viral particles (vp), with a defined maximum tolerated dose as 1 × 10(11) vp. Although the most common adverse events were transient grade 1 to 2 pain at the injection site and flu-like symptoms following IDI, some patients receiving the highest dose had transient, asymptomatic grade 3 to 4 hypophosphatemia, neutropenia, or transaminitis. Increased expression of death receptor, immune costimulatory molecules, and Ad-ISF35 vector DNA was detected in circulating CLL cells. Notably, we also observed preliminary clinical responses, including reductions in leukemia cell counts, lymphadenopathy, and splenomegaly. Six patients did not require additional therapy for more than 6 months, and three achieved a partial remission. In conclusion, Ad-ISF35 IDI was safely delivered in patients with CLLs and induced systemic biologic and clinical responses. These results provide the rationale for phase II studies in CLLs, lymphomas, and CD40-expressing solid tumors.

Toward integrative cancer immunotherapy: targeting the tumor microenvironment

The development of cancer has historically been attributed to genomic alterations of normal host cells. Accordingly, the aim of most traditional cancer therapies has been to destroy the transformed cells themselves. There is now widespread appreciation that the progressive growth and metastatic spread of cancer cells requires the cooperation of normal host cells (endothelial cells, fibroblasts, other mesenchymal cells, and immune cells), both local to, and at sites distant from, the site at which malignant transformation occurs. It is the balance of these cellular interactions that both determines the natural history of the cancer, and influences its response to therapy. This active tumor-host dynamic has stimulated interest in the tumor microenvironment as a key target for both cancer diagnosis and therapy. Recent data has demonstrated both that the presence of CD8⁺ T cells within a tumor is associated with a good prognosis, and that the eradication of all malignantly transformed cells within a tumor requires that the intra-tumoral concentration of cytolytically active CD8⁺ effector T cells remain above a critical concentration until every tumor cell has been killed. These findings have stimulated two initiatives in the field of cancer immunotherapy that focus on the tumor microenvironment. The first is the development of the immune score as part of the routine diagnostic and prognostic evaluation of human cancers, and the second is the development of combinatorial immune-based therapies that reduce tumor-associated immune suppression to unleash pre-existing or therapeutically-induced tumor immunity. In support of these efforts, the Society for the Immunotherapy of Cancer (SITC) is sponsoring a workshop entitled "Focus on the Target: The Tumor Microenvironment" to be held October 24-25, 2012 in Bethesda, Maryland. This meeting should support development of the immune score, and result in a position paper highlighting opportunities for the development of integrative cancer immunotherapies that sculpt the tumor microenvironment to promote definitive tumor rejection.

The biology of personalized cancer medicine: facing individual complexities underlying hallmark capabilities

It is a time of great promise and expectation for the applications of knowledge about mechanisms of cancer toward more effective and enduring therapies for human disease. Conceptualizations such as the hallmarks of cancer are providing an organizing principle with which to distill and rationalize the abject complexities of cancer phenotypes and genotypes across the spectrum of the human disease. A countervailing reality, however, involves the variable and often transitory responses to most mechanism-based targeted therapies, returning full circle to the complexity, arguing that the unique biology and genetics of a patient's tumor will in the future necessarily need to be incorporated into the decisions about optimal treatment strategies, the frontier of personalized cancer medicine. This perspective highlights considerations, metrics, and methods that may prove instrumental in charting the landscape of evaluating individual tumors so to better inform diagnosis, prognosis, and therapy. Integral to the consideration is remarkable heterogeneity and variability, evidently embedded in cancer cells, but likely also in the cell types composing the supportive and interactive stroma of the tumor microenvironment (e.g., leukocytes and fibroblasts), whose diversity in form, regulation, function, and abundance may prove to rival that of the cancer cells themselves. By comprehensively interrogating both parenchyma and stroma of patients' cancers with a suite of parametric tools, the promise of mechanism-based therapy may truly be realized.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Beyond cancer vaccines: a reason for future optimism with immunomodulatory therapy

Despite significant scientific knowledge in the field of cancer immunology, therapeutic strategies using cancer vaccines to generate anti-tumor immunity have historically resulted in only modest clinical benefit. Disappointing results from prior cancer vaccine trials are likely due to multifactorial causes. Perhaps the most important is the role of inherent tumor-induced immune suppression and enhanced immunologic tolerance. Current research directed toward understanding the mechanisms of immunologic tolerance has led to the development of promising therapeutic immune regulatory antibodies that inhibit immunologic checkpoints and subsequently enhance immunologic anti-tumor activity. This review discusses the prior challenges associated with cancer vaccines and describes how, by breaking immune inhibition and facilitating immune stimulation, immune regulatory antibodies show great promise in the treatment of a variety of tumors.