Injection of mice with antibody to interferon enhances the growth of transplantable murine tumors

Type I interferon and cancer

Type I interferon (IFN) is a class of proinflammatory cytokines with a dual role on malignant transformation, tumor progression, and response to therapy. On the one hand, robust, acute, and resolving type I IFN responses have been shown to mediate prominent anticancer effects, reflecting not only their direct cytostatic/cytotoxic activity on (at least some) malignant cells, but also their pronounced immunostimulatory functions. In line with this notion, type I IFN signaling has been implicated in the antineoplastic effects of various immunogenic therapeutics, including (but not limited to) immunogenic cell death (ICD)-inducing agents and immune checkpoint inhibitors (ICIs). On the other hand, weak, indolent, and non-resolving type I IFN responses have been demonstrated to support tumor progression and resistance to therapy, reflecting the ability of suboptimal type I IFN signaling to mediate cytoprotective activity, promote stemness, favor tolerance to chromosomal instability, and facilitate the establishment of an immunologically exhausted tumor microenvironment. Here, we review fundamental aspects of type I IFN signaling and their context-dependent impact on malignant transformation, tumor progression, and response to therapy.

Radiation and Immune Checkpoint Inhibitors: Combination Therapy for Treatment of Hepatocellular Carcinoma

The liver tumor immune microenvironment has been thought to possess a critical role in the development and progression of hepatocellular carcinoma (HCC). Despite the approval of immune checkpoint inhibitors (ICIs), such as programmed cell death receptor 1 (PD-1)/programmed cell death ligand 1 (PD-L1) and cytotoxic T lymphocyte associated protein 4 (CTLA-4) inhibitors, for several types of cancers, including HCC, liver metastases have shown evidence of resistance or poor response to immunotherapies. Radiation therapy (RT) has displayed evidence of immunosuppressive effects through the upregulation of immune checkpoint molecules post-treatment. However, it was revealed that the limitations of ICIs can be overcome through the use of RT, as it can reshape the liver immune microenvironment. Moreover, ICIs are able to overcome the RT-induced inhibitory signals, effectively restoring anti-tumor activity. Owing to the synergetic effect believed to arise from the combination of ICIs with RT, several clinical trials are currently ongoing to assess the efficacy and safety of this treatment for patients with HCC.

Role of Hypoxia in the Interferon Response

In solid tumors, as the tumor grows and the disease progresses, hypoxic regions are often generated, but in contrast to most normal cells which cannot survive under these conditions, tumour cells adapt to hypoxia by HIF-driven mechanisms. Hypoxia can further promote cancer development by generating an immunosuppressive environment within the tumour mass, which allows tumour cells to escape the immune system recognition. This is achieved by recruiting immunosuppressive cells and by upregulating molecules which block immune cell activation. Hypoxia can also confer resistance to antitumor therapies by inducing the expression of membrane proteins that increase drug efflux or by inhibiting the apoptosis of treated cells. In addition, tumor cells require an active interferon (IFN) signalling pathway for the success of many anticancer therapies, such as radiotherapy or chemotherapy. Therefore, hypoxic effects on this pathway needs to be addressed for a successful treatment.

Antiviral Responses in Cancer: Boosting Antitumor Immunity Through Activation of Interferon Pathway in the Tumor Microenvironment

In recent years, it became apparent that cancers either associated with viral infections or aberrantly expressing endogenous retroviral elements (EREs) are more immunogenic, exhibiting an intense intra-tumor immune cell infiltration characterized by a robust cytolytic apparatus. On the other hand, epigenetic regulation of EREs is crucial to maintain steady-state conditions and cell homeostasis. In line with this, epigenetic disruptions within steady-state cells can lead to cancer development and trigger the release of EREs into the cytoplasmic compartment. As such, detection of viral molecules by intracellular innate immune sensors leads to the production of type I and type III interferons that act to induce an antiviral state, thus restraining viral replication. This knowledge has recently gained momentum due to the possibility of triggering intratumoral activation of interferon responses, which could be used as an adjuvant to elicit strong anti-tumor immune responses that ultimately lead to a cascade of cytokine production. Accordingly, several therapeutic approaches are currently being tested using this rationale to improve responses to cancer immunotherapies. In this review, we discuss the immune mechanisms operating in viral infections, show evidence that exogenous viruses and endogenous retroviruses in cancer may enhance tumor immunogenicity, dissect the epigenetic control of EREs, and point to interferon pathway activation in the tumor milieu as a promising molecular predictive marker and immunotherapy target. Finally, we briefly discuss current strategies to modulate these responses within tumor tissues, including the clinical use of innate immune receptor agonists and DNA demethylating agents.

Type I Interferon Response in Radiation-Induced Anti-Tumor Immunity

The anti-tumor activity of interferons (IFNs) was first appreciated about half a century ago, and IFN-α2 was the first cancer immunotherapy approved by the US Food and Drug Administration. Radiation therapy (RT), one of the pillars of cancer treatment, directly causes DNA damage, which can lead to senescence and cell death in tumor cells. In recent years, however, RT-induced immunomodulatory effects have been recognized to play an indispensable role in achieving the optimum therapeutic effect of RT. Increasing evidence indicates that RT enhances adaptive anti-tumor immunity by augmenting the innate immune sensing of tumors in a type I IFN-dependent matter. This review briefly introduces the role of type I interferon in cancer and the available evidence on the overall effects of RT on tumor immunity mediated via type I IFN. Recent advances in deciphering the molecular mechanisms underlying the induction of type I IFNs triggered by RT, their clinical implications, and therapeutic opportunities will be highlighted.

Type I Interferons as Joint Regulators of Tumor Growth and Obesity

Simple Summary

The escalating global epidemic of overweight and obesity is a major public health and economic problem, as excess body weight represents a significant risk factor for several chronic diseases including cancer. Despite the strong scientific evidence for a link between obesity and cancer, the mechanisms involved in this interplay have not yet been fully understood. The aim of this review is to evaluate the role of type I interferons, a family of antiviral cytokines with key roles in the regulation of both obesity and cancer, highlighting how the dysregulation of the interferon system can differently affect these pathological conditions.

Abstract

Type I interferons (IFN-I) are antiviral cytokines endowed with multiple biological actions, including antitumor activity. Studies in mouse models and cancer patients support the concept that endogenous IFN-I play important roles in the control of tumor development and growth as well as in response to several chemotherapy/radiotherapy treatments. While IFN-I signatures in the tumor microenvironment are often considered as biomarkers for a good prognostic response to antitumor therapies, prolonged IFN-I signaling can lead to immune dysfunction, thereby promoting pathogen or tumor persistence, thus revealing the “Janus face” of these cytokines in cancer control, likely depending on timing, tissue microenvironment and cumulative levels of IFN-I signals. Likewise, IFN-I exhibit different and even opposite effects on obesity, a pathologic condition linked to cancer development and growth. As an example, evidence obtained in mouse models shows that localized expression of IFN-I in the adipose tissue results in inhibition of diet–induced obesity, while hyper-production of these cytokines by specialized cells such as plasmacytoid dendritic cells in the same tissue, can induce systemic inflammatory responses leading to obesity. Further studies in mouse models and humans should reveal the mechanisms by which IFN-I can regulate both tumor growth and obesity and to understand the role of factors such as genetic background, diet and microbioma in shaping the production and action of these cytokines under physiological and pathological conditions.

Human Tumor-Infiltrating Dendritic Cells: From in Situ Visualization to High-Dimensional Analyses

The interaction between tumor cells and the immune system is considered to be a dynamic process. Dendritic cells (DCs) play a pivotal role in anti-tumor immunity owing to their outstanding T cell activation ability. Their functions and activities are broad ranged, triggering different mechanisms and responses to the DC subset. Several studies identified in situ human tumor-infiltrating DCs by immunostaining using a limited number of markers. However, considering the heterogeneity of DC subsets, the identification of each subtype present in the immune infiltrate is essential. To achieve this, studies initially relied on flow cytometry analyses to provide a precise characterization of tumor-associated DC subsets based on a combination of multiple markers. The concomitant development of advanced technologies, such as mass cytometry or complete transcriptome sequencing of a cell population or at a single cell level, has provided further details on previously identified populations, has unveiled previously unknown populations, and has finally led to the standardization of the DCs classification across tissues and species. Here, we review the evolution of tumor-associated DC description, from in situ visualization to their characterization with high-dimensional technologies, and the clinical use of these findings specifically focusing on the prognostic impact of DCs in cancers.

Interferon signaling in cancer. Non-canonical pathways and control of intracellular immune checkpoints

The interferons (IFNs) are cytokines with important antineoplastic and immune modulatory effects. These cytokines have been conserved through evolution as important elements of the immune surveillance against cancer. Despite this, defining their precise and specific roles in the generation of antitumor responses remains challenging. Emerging evidence suggests the existence of previously unknown roles for IFNs in the control of the immune response against cancer that may redefine our understanding on how these cytokines function. Beyond the engagement of classical JAK-STAT signaling pathways that promote transcription and expression of gene products, the IFNs engage multiple other signaling cascades to generate products that mediate biological responses and outcomes. There is recent emerging evidence indicating that IFNs control the expression of both traditional immune checkpoints like the PD-L1/PD1 axis, but also less well understood "intracellular" immune checkpoints whose targeting may define new approaches for the treatment of malignancies.

Host-Intrinsic Interferon Status in Infection and Immunity

Most genetic ablations of interferon (IFN) signaling abolish both the experimentally induced IFN response and constitutive IFN, whose effects are well established in autoimmunity but understudied during infection. In host-pathogen interactions, most IFN-mediated responses are attributed to infection-driven IFN. However, IFNs confer their activity by regulating networks of interferon-stimulated genes (ISGs), a process that requires de novo transcription and translation of both IFN and downstream ISGs through feedback of IFN receptor signaling. Due to the temporal requirement for IFN activity, many rapid antimicrobial responses may instead result from pre-established IFN signature stemming from host-intrinsic processes. Addressing the permeating effects of constitutive IFN is therefore needed to accurately describe immunity as host intrinsic or pathogen induced.

Disruption of IFN-I Signaling Promotes HER2/Neu Tumor Progression and Breast Cancer Stem Cells

Type I interferon (IFN-I) is a class of antiviral immunomodulatory cytokines involved in many stages of tumor initiation and progression. IFN-I acts directly on tumor cells to inhibit cell growth and indirectly by activating immune cells to mount antitumor responses. To understand the role of endogenous IFN-I in spontaneous, oncogene-driven carcinogenesis, we characterized tumors arising in HER2/neu transgenic (neuT) mice carrying a nonfunctional mutation in the IFNI receptor (IFNAR1). Such mice are unresponsive to this family of cytokines. Compared with parental neu^+/- mice (neuT mice), IFNAR1^-/- neu^+/- mice (IFNAR-neuT mice) showed earlier onset and increased tumor multiplicity with marked vascularization. IFNAR-neuT tumors exhibited deregulation of genes having adverse prognostic value in breast cancer patients, including the breast cancer stem cell (BCSC) marker aldehyde dehydrogenase-1A1 (ALDH1A1). An increased number of BCSCs were observed in IFNAR-neuT tumors, as assessed by ALDH1A1 enzymatic activity, clonogenic assay, and tumorigenic capacity. In vitro exposure of neuT⁺ mammospheres and cell lines to antibodies to IFN-I resulted in increased frequency of ALDH⁺ cells, suggesting that IFN-I controls stemness in tumor cells. Altogether, these results reveal a role of IFN-I in neuT-driven spontaneous carcinogenesis through intrinsic control of BCSCs. Cancer Immunol Res; 6(6); 658-70. ©2018 AACR.

The added value of type I interferons to cytotoxic treatments of cancer

Type I interferons (IFNs) exert anti-proliferative, antiviral and immunomodulatory activities. They are also involved in cell differentiation and anti-tumor defense processes. A growing body of literature indicates that the success of conventional chemotherapeutics, epigenetic drugs, targeted anticancer agents and radiotherapy (RT) relies, at least in part, on the induction of type I IFN signaling in malignant cells, tumor-infiltrating antigen presenting cells or other immune cells within lymphoid organs or blood. The mechanisms underlying type I IFN induction and the clinical consequences of these observations are only beginning to be elucidated. In the present manuscript, we reviewed the recent advances in the field and provided our personal view on the role of type I IFNs induced in the context of cytotoxic anticancer treatments and on its possible exploitation as a complement in cancer therapy.

Innate immune signaling and regulation in cancer immunotherapy

A pre-existing T cell-inflamed tumor microenvironment has prognostic utility and also can be predictive for response to contemporary cancer immunotherapies. The generation of a spontaneous T cell response against tumor-associated antigens depends on innate immune activation, which drives type I interferon (IFN) production. Recent work has revealed a major role for the STING pathway of cytosolic DNA sensing in this process. This cascade of events contributes to the activation of Batf3-lineage dendritic cells (DCs), which appear to be central to anti-tumor immunity. Non-T cell-inflamed tumors lack chemokines for Batf3 DC recruitment, have few Batf3 DCs, and lack a type I IFN gene signature, suggesting that failed innate immune activation may be the ultimate cause for lack of spontaneous T cell activation and accumulation. With this information in hand, new strategies for triggering innate immune activation and Batf3 DC recruitment are being developed, including novel STING agonists for de novo immune priming. Ultimately, the successful development of effective innate immune activators should expand the fraction of patients that can respond to immunotherapies, such as with checkpoint blockade antibodies.

Antitumour actions of interferons: implications for cancer therapy

The interferons (IFNs) are a family of cytokines that protect against disease by direct effects on target cells and by activating immune responses. The production and actions of IFNs are finely tuned to achieve maximal protection and avoid the potential toxicity associated with excessive responses. IFNs are back in the spotlight owing to mounting evidence that is reshaping how we can exploit this pathway therapeutically. As IFNs can be produced by, and act on, both tumour cells and immune cells, understanding this reciprocal interaction will enable the development of improved single-agent or combination therapies that exploit IFN pathways and new 'omics'-based biomarkers to indicate responsive patients.

From DNA Damage to Nucleic Acid Sensing: A Strategy to Enhance Radiation Therapy

Local irradiation (IR) is widely used in the treatment of primary and metastatic tumors. However, the impact of IR on the immune response is currently being defined. Local and distant relapse after radiotherapy often occurs. The current rationale for the use of IR is based on direct cytotoxicity to cancer cells; however, recent studies have shown that reduction of tumor burden following ablative (large-dose) IR largely depends on type I IFN signaling and CD8(+) T-cell response. Here, we review recent findings indicating that antitumor effects of radiation are contributed by both innate and adaptive immune responses. We focus on immune mechanisms, including cytosolic DNA sensing pathways that bridge the traditional view of IR-mediated DNA damage to DNA-sensing immune pathways. Also, we discuss how the efficacy of radiotherapy might be enhanced by targeting nucleic acid-sensing pathways. These findings highlight the mechanisms governing tumor escape from the immune response and the therapeutic potential of synergistic strategies to improve the efficacy of radiotherapy via immunotherapeutic intervention.

Myeloid-derived cells in tumors: effects of radiation

The discrepancy between the in vitro and in vivo response to radiation is readily explained by the fact that tumors do not exist independently of the host organism; cancer cells grow in the context of a complex microenvironment composed of stromal cells, vasculature, and elements of the immune system. As the antitumor effect of radiotherapy depends in part on the immune system, and myeloid-derived cells in the tumor microenvironment modulate the immune response to tumors, it follows that understanding the effect of radiation on myeloid cells in the tumor is likely to be essential for comprehending the antitumor effects of radiotherapy. In this review, we describe the phenotype and function of these myeloid-derived cells, and stress the complexity of studying this important cell compartment owing to its intrinsic plasticity. With regard to the response to radiation of myeloid cells in the tumor, evidence has emerged demonstrating that it is both model and dose dependent. Deciphering the effects of myeloid-derived cells in tumors, particularly in irradiated tumors, is key for attempting to pharmacologically modulate their actions in the clinic as part of cancer therapy.

Strict requirement for vector-induced type I interferon in efficacious antitumor responses to virally encoded IL12

Host responses are increasingly considered important for the efficacious response to experimental cancer therapies that employ viral vectors, but little is known about the specific nature of host responses required. In this study, we investigated the role of host type I interferons (IFN-I) in the efficacy of virally delivered therapeutic genes. Specifically, we used a Semliki Forest virus encoding IL12 (SFV-IL12) based on its promise as an RNA viral vector for cancer treatment. Intratumoral injection of SFV-IL12 induced production of IFN-I as detected in serum. IFN-I production was abolished in mice deficient for the IFNβ transcriptional regulator IPS-1 and partially attenuated in mice deficient for the IFNβ signaling protein TRIF. Use of bone marrow chimeric hosts established that both hematopoietic and stromal cells were involved in IFN-I production. Macrophages, plasmacytoid, and conventional dendritic cells were each implicated based on cell depletion experiments. Further, mice deficient in the IFN-I receptor (IFNAR) abolished the therapeutic activity of SFV-IL12, as did a specific antibody-mediated blockade of IFNAR signaling. Reduced efficacy was not caused by an impairment in IL12 expression, because IFNAR-deficient mice expressed the viral IL12 transgene even more strongly than wild-type (WT) hosts. Chimeric host analysis for the IFNAR involvement established a strict requirement in hematopoietic cells. Notably, although tumor-specific CD8 T lymphocytes expanded robustly after intratumoral injection of WT mice with SFV-IL12, this did not occur in mice where IFNAR was inactivated genetically or pharmacologically. Overall, our results argued that the antitumor efficacy of a virally based transgene therapeutic relied strongly on a vector-induced IFN-I response, revealing an unexpected mechanism of action that is relevant to a broad array of current translational products in cancer research.

Mouse, but not human STING, binds and signals in response to the vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid

Vascular disrupting agents such as 5,6-dimethylxanthenone-4-acetic acid (DMXAA) represent a novel approach for cancer treatment. DMXAA has potent antitumor activity in mice and, despite significant preclinical promise, failed human clinical trials. The antitumor activity of DMXAA has been linked to its ability to induce type I IFNs in macrophages, although the molecular mechanisms involved are poorly understood. In this study, we identify stimulator of IFN gene (STING) as a direct receptor for DMXAA leading to TANK-binding kinase 1 and IFN regulatory factor 3 signaling. Remarkably, the ability to sense DMXAA was restricted to murine STING. Human STING failed to bind to or signal in response to DMXAA. Human STING also failed to signal in response to cyclic dinucleotides, conserved bacterial second messengers known to bind and activate murine STING signaling. Collectively, these findings detail an unexpected species-specific role for STING as a receptor for an anticancer drug and uncover important insights that may explain the failure of DMXAA in clinical trials for human cancer.

Interferon-α as antiviral and antitumor vaccine adjuvants: mechanisms of action and response signature

Interferon-α (IFN-α) are cytokines endowed with multiple biologic effects, including activities on cells of the immune system, which are important for inducing protective antiviral and antitumor responses. Studies in mouse models have been instrumental for understanding the immune adjuvant activity of these cytokines and some of their mechanisms of action. In particular, recent studies conducted on both mouse and human models suggest that IFN-α act as effective immune adjuvants for inducing antiviral and antitumor immunity and that the effects of IFN on the differentiation and activation of dendritic cells (DC) play an important role in the induction of protective responses. In spite of the long record of IFN-α clinical use, a few clinical trials have attempted to evaluate the efficacy of these cytokines used as vaccine adjuvants. Recently, studies on the IFN-α signature in cells from patients treated with IFN-α under different modalities and various clinical settings have provided important insights for understanding the in vivo mechanisms of the IFN immune adjuvant activity in humans and may contribute to the identification of molecular markers with a clinical response. These studies further support the interest of evaluating the clinical efficacy of IFN-α when used as a vaccine adjuvant and also suggest that the DC generated in vitro from monocytes in the presence of this cytokine can exhibit a special advantage for the development of effective therapeutic vaccination strategies in cancer patients.

Host type I IFN signals are required for antitumor CD8+ T cell responses through CD8{alpha}+ dendritic cells

The generation of antitumor CD8⁺ T cell responses requires type I interferon responsiveness in host antigen-presenting cells

Despite lack of tumor control in many models, spontaneous T cell priming occurs frequently in response to a growing tumor. However, the innate immune mechanisms that promote natural antitumor T cell responses are undefined. In human metastatic melanoma, there was a correlation between a type I interferon (IFN) transcriptional profile and T cell markers in metastatic tumor tissue. In mice, IFN-β was produced by CD11c⁺ cells after tumor implantation, and tumor-induced T cell priming was defective in mice lacking IFN-α/βR or Stat1. IFN signaling was required in the hematopoietic compartment at the level of host antigen-presenting cells, and selectively for intratumoral accumulation of CD8α⁺ dendritic cells, which were demonstrated to be essential using Batf3^−/− mice. Thus, host type I IFNs are critical for the innate immune recognition of a growing tumor through signaling on CD8α⁺ DCs.

The efficacy of radiotherapy relies upon induction of type i interferon-dependent innate and adaptive immunity

The most widely held explanation for the efficacy of local radiotherapy (RT) is based on direct cytotoxicity to cancer cells through the induction of lethal DNA damage. Recent studies have shown that local ablative radiation of established tumors can lead to increased T-cell priming and T-cell-dependent tumor regression, but the underlying mechanism remains unclear. Here, we describe an essential role for type I IFN in local RT-mediated tumor control. We show that ablative RT increases intratumoral production of IFN-β and, more surprisingly, the antitumor effect of RT is abolished in type I IFN nonresponsive hosts. Furthermore, the major target of RT-induced type I IFN is the hematopoietic compartment. RT drastically enhances the cross-priming capacity of tumor-infiltrating dendritic cells (TIDC) from wild-type mice but not type I IFN receptor-deficient mice. The enhanced cross-priming ability of TIDCs after RT was dependent on autocrine production of type I IFNs. By using adenoviral-mediated expression of IFN-β, we show that delivery of exogenous IFN-β into the tumor tissue in the absence of RT is also sufficient to selectively expand antigen-specific T cells leading to complete tumor regression. Our study reveals that local high-dose RT can trigger production of type I IFN that initiates a cascading innate and adaptive immune attack on the tumor.

Targeting the effector site with IFN-alphabeta-inducing TLR ligands reactivates tumor-resident CD8 T cell responses to eradicate established solid tumors

Effective antitumor CD8 T cell responses may be activated by directly targeting the innate immune system within tumors. We investigated this response by injecting a range of TLR agonists into established tumors using a mouse model of malignant mesothelioma stably transduced with the hemagglutinin (HA) gene as a marker Ag (AB1-HA). Persistent delivery of the dsRNA mimetic poly(I:C) into established AB1-HA tumors resulted in complete tumor resolution in 40% of mice, with the remaining mice also showing a significant delay in tumor progression. Experiments in athymic nude mice along with CD8 depletion and IFN-alphabeta blocking studies revealed that tumor resolution required both CD8 T cells and type I IFN induction, and was associated with local changes in MHC class I expression. Surprisingly, however, tumor resolution was not associated with systemic dissemination or tumor infiltration of effector CD8 T cells. Instead, the antitumor response was critically dependent on the reactivation of tumor-resident CD8 T cell responses. These studies suggest that, once reactivated, pre-existing local CD8 T cell responses are sufficient to resolve established tumors and that in situ type I IFN is a determining factor.

The antitumor effects of interferon: A personal history

Early experiments showed that administration of mouse interferon preparations inhibited the development of viral-induced or spontaneous viral associated leukemias in mice. Interferon alpha/beta was also shown to inhibit the growth of transplantable tumors of different origins in all strains of mice tested. The finding that interferon alpha/beta inhibited the growth of sublines of tumors selected for resistance to interferon alpha/beta indicated the role of interferon induced host mechanisms in the antitumor effects observed. The different host antitumor mechanisms and especially the interaction of interferon alpha/beta with the immune system have been briefly discussed. Injection of mice with a neutralizing antibody to interferon alpha/beta demonstrated the essential role of endogenous interferon alpha/beta in the defense of the mouse against the development of syngeneic, allogeneic and xenogeneic tumors.

Role of endogenous interferon and LPS in the immunomodulatory effects of bovine lactoferrin in murine peritoneal macrophages

Lactoferrin (Lf) plays an important role in host defense against infection and excessive inflammation. Although the mechanisms underlying its immunomodulatory properties have not been fully elucidated yet, recent evidence suggests that some of these effects may be related to its capacity to form complexes with LPS. We report that the culture of resting mouse peritoneal macrophages (PM) with bovine Lf (bLf), prior to infection with the vesicular stomatitis virus (VSV), resulted in a significant reduction of virus yield with respect to control cultures. The antiviral activity of bLF was related to its capacity of inducing IFN-alpha/beta expression, which in turn inhibited VSV replication. Indeed, the accumulation of IFN-beta but not of IFNalpha(1-2) transcripts was up-modulated markedly early after bLf addition. Furthermore, bLf did not exert any antiviral activity in the presence of neutralizing antibodies to IFN-alpha/beta in PM from wild-type mice, as well as in PM from mice genetically defective for the response to IFN. The antiviral activity of bLf relied on its intrinsic capacity to bind LPS, as this protein did not induce IFN expression in PM from LPS-hyporesponsive mice. It is interesting that this LPS-binding property was dispensable for the production of TNF-alpha, which also occurred in LPS-hyporesponsive mice. Overall, these results indicate that some of the immunomodulatory effects ascribed to Lf may be related to its capacity to favor Type I IFN expression and argue in favor of an important role of the LPS-binding feature and TLR4 in some of the effects ascribed to this molecule.

Interferons, immunity and cancer immunoediting

A clear picture of the dynamic relationship between the host immune system and cancer is emerging as the cells and molecules that participate in naturally occurring antitumour immune responses are being identified. The interferons (IFNs) - that is, the type I IFNs (IFNalpha and IFNbeta) and type II IFN (IFNgamma) - have emerged as central coordinators of tumour-immune-system interactions. Indeed, the decade-old finding that IFNgamma has a pivotal role in promoting antitumour responses became the focus for a renewed interest in the largely abandoned concept of cancer immunosurveillance. More recently, type I IFNs have been found to have distinct functions in this process. In this Review, we discuss the roles of the IFNs, not only in cancer immunosurveillance but also in the broader process of cancer immunoediting.

Overcoming Resistance to Interferon-Induced Apoptosis of Renal Carcinoma and Melanoma Cells by DNA Demethylation

Epigenetic editing of gene expression by aberrant methylation of DNA may help tumor cells escape attack from the innate and acquired immune systems. Resistance to antiproliferative effects and apoptosis induction by interferons (IFNs) was postulated to result from silencing of IFN response genes by promoter hypermethylation. Treatment of human ACHN renal cell carcinoma (RCC) and A375 melanoma cells with the DNA demethylating nucleoside analog 5-AZA-2′-deoxycytidine (5-AZA-dC) synergistically augmented antiproliferative effects of IFN- alpha (α) 2 and IFN-beta (β). Either 5-AZA-dC or an antisense to DNA methyltransferase 1 (DNMT1) overcame resistance to apoptosis induction by IFNs with up to 85% apoptotic cells resulting from the combinations. No similar potentiation occurred in normal kidney epithelial cells. IFN response genes were augmented more than 10 times in expression by 5-AZA-dC. Demethylation by 5-AZA-dC of the promoter of the prototypic, apoptosis-associated IFN response gene XAF1 was confirmed by methylation-specific polymerase chain reaction. siRNA to XAF1 inhibited IFN-induced apoptosis; conversely, overexpression of XAF1 overcame resistance to apoptosis induction by IFN-β. As occurred with apoptosis-resistant melanoma cells in vitro, tumor growth inhibition in the nude mouse of human A375 melanoma xenografts resulted from treatment with 5-AZA-dC in combination with IFN-β, an effect not resulting from either single agent. The importance of epigenetic remodeling of expression of immune-modifying genes in tumor cells was further suggested by identifying reactivation of the cancer-testis antigens MAGE and RAGE in ACHN cells after DNMT1 depletion. Thus, inhibitors of DNMT1 may have clinical relevance for immune modulation by augmentation of cytokine effects and/or expression of tumor-associated antigens.

Innate Immune Recognition and Suppression of Tumors

In this chapter, we first summarized the strong evidence that now supports the existence of an effective cancer immune surveillance process that prevents cancer development in both mice and humans. We then focused the remainder of the chapter on methods of tumor recognition that contribute to natural host immune suppression of tumors. In particular, NKG2D is a type II transmembrane-anchored glycoprotein expressed as a disulfide-linked homodimer on the surface of all mouse and human natural killer cells (NK cells). Stimulation of NK cell through NKG2D triggers cell-mediated cytotoxicity and in some cases induces production of cytokines. NKG2D binds to family of ligands with structural homology to major histocompatibility complex (MHC) class I, however, NKG2D ligands often display upregulated surface expression on stressed cells and are frequently overexpressed by tumors unlike conventional MHC class I molecules. Evidence clearly implicate that NKG2D recognition plays an important role in tumor immune surveillance.

Cancer Immunosurveillance and Immunoediting: The Roles of Immunity in Suppressing Tumor Development and Shaping Tumor Immunogenicity

Cellular transformation and tumor development result from an accumulation of mutational and epigenetic changes that alter normal cell growth and survival pathways. For the last 100 years, there has been a vigorous debate as to whether the unmanipulated immune system can detect and eliminate such altered host derived cells despite the fact that cancer cells frequently express either abnormal proteins or abnormal levels of normal cellular proteins that function as tumor antigens. In this review, we discuss the current state of this argument and point out some of the recent key experiments demonstrating that immunity not only protects the host from cancer development (i.e., provides a cancer immunosurveillance function) but also can promote tumor growth, sometimes by generating more aggressive tumors. The terminology "cancer immunoediting" has been used to describe this dual host protective and tumor promoting action of immunity, and herein we summarize the ever-increasing experimental and clinical data that support the validity of this concept.

Review: Milstein Award lecture: interferons and cancer: where from here?

Interferons (IFNs) remain the most broadly active cytokines for cancer treatment, yet ones for which the full potential is not reached. IFNs have impacted positively on both quality and quantity of life for hundreds of thousands of cancer patients with chronic leukemia, lymphoma, bladder carcinoma, melanoma, and renal carcinoma. The role of the IFN system in malignant pathogenesis continues to enhance understanding of how the IFN system may be modulated for therapeutic advantage. Reaching the full potential of IFNs as therapeutics for cancer will also result from additional understanding of the genes underlying apoptosis induction, angiogenesis inhibition, and influence on immunologic function. Food and Drug Administration (FDA) approval of IFNs occurred less than 20 years ago; after 40 years, third-generation products of early cytotoxics, such as 5- fluorouracil (5FU), are beginning to reach clinical approval. Thus, substantial potential exists for additional application of IFNs and IFN inducers as anticancer therapeutics, particularly when one considers that their pleiotropic cellular and molecular effects have yet to be fully defined.

A critical function for type I interferons in cancer immunoediting

'Cancer immunoediting' is a process wherein the immune system protects hosts against tumor development and facilitates outgrowth of tumors with reduced immunogenicity. Although interferon-gamma (IFN-gamma) is known to be involved in this process, the involvement of type I interferons (IFN-alpha/beta) has not been elucidated. We now show that, like IFN-gamma, endogenously produced IFN-alpha/beta was required for the prevention of the growth of primary carcinogen-induced and transplantable tumors. Although tumor cells are important IFN-gamma targets, they are not functionally relevant sites of the actions of the type I interferons. Instead, host hematopoietic cells are critical IFN-alpha/beta targets during development of protective antitumor responses. Therefore, type I interferons are important components of the cancer immunoediting process and function in a way that does not completely overlap the functions of IFN-gamma.

Natural mechanisms protecting against cancer

Carcinogenesis is a multistage process. At each step of this process, there are natural mechanisms protecting against development of cancer. The majority of cancers in humans is induced by carcinogenic factors present in our environment including our food. However, some natural substances present in our diet or synthesized in our cells are able to block, trap or decompose reactive oxygen species (ROS) participating in carcinogenesis. Carcinogens can also be removed from our cells. If DNA damage occurs, it is repaired in most of the cases. Unrepaired DNA alterations can be fixed as mutations in proliferating cells only and mutations of very few strategic genes can induce tumor formation, the most relevant are those activating proto-oncogenes and inactivating tumor suppressor genes. A series of mutations and/or epigenetic changes is required to drive transformation of a normal cell into malignant tumor. The apparently unrestricted growth has to be accompanied by a mechanism preserving telomeres which otherwise shorten with succeeding cell divisions leading to growth arrest. Tumor can not develop beyond the size of 1-2mm in diameter without the induction of angiogenesis which is regulated by natural inhibitors. To invade the surrounding tissues epithelial tumor cells have to lose some adhesion molecules keeping them attached to each other and to produce enzymes able to dissolve the elements of the basement membrane. On the other hand, acquisition of other adhesion molecules enables interaction of circulating tumor cells with endothelial cells facilitating extravasation and metastasis. One of the last barriers protecting against cancer is the activity of the immune system. Both innate and adaptive immunity participates in anti-tumor effects including the activity of natural killer (NK) cells, natural killer T cells, macrophages, neutrophils and eosinophils, complement, various cytokines, specific antibodies, and specific T cytotoxic cells. Upon activation neutrophils and macrophages are able to kill tumor cells but they can also release ROS, angiogenic and immunosuppressive substances. Many cytokines belonging to different families display anti-tumor activity but their role in natural anti-tumor defense remains largely to be established.

Regulation of neoplastic angiogenesis

The progressive growth of neoplasms and the production of metastasis depend on the development of adequate vasculature, i.e., angiogenesis. The extent of angiogenesis is determined by the balance between positive- and negative-regulating molecules that are released by tumor and host cells in the microenvironment. The growth of many neoplasms is associated with the absence of the endogenous inhibitor of angiogenesis, interferon beta (IFN beta). A survey of multiple mouse and human tumors shows a lack of IFN beta associated with extensive angiogenesis. Therapy with IFN alpha or beta either by subcutaneous injection of the protein or by introduction of viral vectors that contain the IFN beta gene inhibit angiogenesis and, hence, progressive tumor growth.

CD2+/CD14+ monocytes rapidly differentiate into CD83+ dendritic cells

Since denditric cells (DC) represent the main players linking innate and adaptive immunity, their prompt generation from blood cells would be instrumental for an efficient immune response to infections. Consistent with this, CD2+ monocytes were found to express the DC maturation marker CD83, along with acquisition of high antigen-presenting activity, after a surprisingly short time in culture. This rapid process is associated with expression of IFN-alpha/beta genes and secretion of low levels of pro-inflammatory cytokines. Exposure of monocytes to IFN-alpha, but not to IL-4, induced persistence of CD2+/CD83+ cells, which were fully competent in stimulating primary responses by naive T cells. These results unravel the natural pathway by which infection-induced signals rapidly transform pre-armed monocytes into active DC.

Suppression of lymphoma and epithelial malignancies effected by interferon gamma

The immunosurveillance of transformed cells by the immune system remains one of the most controversial and poorly understood areas of immunity. Gene-targeted mice have greatly aided our understanding of the key effector molecules in tumor immunity. Herein, we describe spontaneous tumor development in gene-targeted mice lacking interferon (IFN)-gamma and/or perforin (pfp), or the immunoregulatory cytokines, interleukin (IL)-12, IL-18, and tumor necrosis factor (TNF). Both IFN-gamma and pfp were critical for suppression of lymphomagenesis, however the level of protection afforded by IFN-gamma was strain specific. Lymphomas arising in IFN-gamma-deficient mice were very nonimmunogenic compared with those derived from pfp-deficient mice, suggesting a comparatively weaker immunoselection pressure by IFN-gamma. Single loss of IL-12, IL-18, or TNF was not sufficient for spontaneous tumor development. A significant incidence of late onset adenocarcinoma observed in both IFN-gamma- and pfp-deficient mice indicated that some epithelial tissues were also subject to immunosurveillance.

Type I IFN as a natural adjuvant for a protective immune response: lessons from the influenza vaccine model

The identification of natural adjuvants capable of selectively promoting an efficient immune response against infectious agents would represent an important advance in immunology, with direct implications for vaccine development, whose progress is generally hampered by the difficulties in defining powerful synthetic adjuvants suitable for clinical use. Here, we demonstrate that endogenous type I IFN is necessary for the Th1 type of immune response induced by typical adjuvants in mice and that IFN itself is an unexpectedly powerful adjuvant when administered with the human influenza vaccine, for inducing IgG2a and IgA production and conferring protection from virus challenge. The finding that these cytokines, currently used in patients, are necessary for full expression of adjuvant activity and are sufficient for the generation of a protective immune response opens new perspectives in understanding the basis of immunity and in vaccine development.

Endogenous type I interferons as a defense against tumors

We have reviewed the experimental results which indicate that endogenous type I interferon (IFN) present either constitutively or possibly induced by the tumor plays an important role in limiting the development of transplantable tumors in mice. Thus, treatment with potent polyclonal neutralizing antibodies to IFN alpha/beta markedly enhanced the subcutaneous growth, invasiveness and metastases of xenogeneic tumor cells (uninfected or infected with RNA or DNA viruses) in athymic nude mice; enhanced the intraperitoneal transplantability of six different syngeneic murine tumors in three strains of immunocompetent mice; and completely abrogated the resistance of allogeneic C57Bl/6 (H-2(b)) or C3H (H-2(k)) mice to the multiplication of Friend erythroleukemia cells (H-2(d)) in the liver and spleen resulting in the death of most mice. The mechanisms by which mice respond to the injection of relatively few tumor cells appear to be multiple, to depend on the site of tumor growth, to occur early and prior to an immunologic response. Endogenous type I IFN appears to constitute an essential component of these defense mechanisms enabling the host to restrict tumor growth.

Enhanced tumor development in mice lacking a functional type I interferon receptor

The aim of this study was to investigate the contribution of endogenous - that is, without the addition of any interferon (IFN) inducer - type I IFN production in the defense against tumor development. To this purpose, the IFN-alpha receptor (IFNAR) knockout (KO)-induced mutation, resulting in the complete absence of IFN-alpha/beta activity, was introduced into a C3H genetic background by 10 backcross generations, followed by brother-sister matings for at least four generations. The resulting mice were inoculated either with syngeneic C3H melanoma K1735 cells, with allogeneic 3LL carcinoma cells, or with allogeneic B16F10 melanoma cells. With all three tumor cell lines, tumor development and ensuing mortality were enhanced in the IFNAR KO animals. This indicates that endogenous IFN-alpha/beta production is a mediator of natural immunity to tumor development.

Interferon-alpha in tumor immunity and immunotherapy

Interferon-alpha (IFN-alpha) is a pleiotropic cytokine belonging to type I IFN, currently used in cancer patients. Early studies in mouse tumor models have shown the importance of host immune mechanisms in the generation of a long-lasting antitumor response to type I IFN. Recent studies have underscored new immunomodulatory effects of IFN-alpha, including activities on T and dendritic cells, which may explain IFN-induced tumor immunity. Reports on new immune correlates in cancer patients responding to IFN-alpha represent additional evidence on the importance of the interactions of IFN-alpha with the immune system for the generation of durable antitumor response. This knowledge, together with results from studies on genetically modified tumor cells expressing IFN-alpha, suggest novel strategies for using these cytokines in cancer immunotherapy and in particular the use of IFN-alpha as an immune adjuvant for the development of cancer vaccines.

Gene therapy of cancer with interferon: lessons from tumor models and perspectives for clinical applications

Cytokine gene transfer is a current approach in studies of gene therapy of cancer IFNs represent valuable cytokines for these studies, since they exert multiple biological effects, including anti-tumor activities. Early studies have been focused on IFN-gamma. Recently, several reports have shown that the transfer of type I IFN (especially IFN-alpha) genes represents a powerful approach for inducing tumor suppression. Recent studies have underscored new IFN-induced activities on immune cells. This knowledge adds a further rationale for the use of IFN-alpha in strategies of gene therapy of cancer and can be exploited for the design of more selective and effective anticancer treatments.

Cyclophosphamide induces type I interferon and augments the number of CD44hi T lymphocytes in mice: implications for strategies of chemoimmunotherapy of cancer

In a previous study, we reported that a single injection of cyclophosphamide (CTX) in tumor-bearing mice resulted in tumor eradication when the animals were subsequently injected with tumor-sensitized lymphocytes. Notably, CTX acted by inducing bystander effects on T cells, and the response to the combined CTX/adoptive immunotherapy regimen was inhibited in mice treated with antibodies to mouse interferon (IFN)–/β. In the present study, we have investigated whether CTX induced the expression of type I IFN, and we have characterized the CTX effects on the phenotype of T cells in normal mice. CTX injection resulted in an accumulation of type I IFN messenger RNA in the spleen of inoculated mice, at 24 to 48 hours, that was associated with IFN detection in the majority of the animals. CTX also enhanced the expression of the Ly-6C on spleen lymphocytes. This enhancement was inhibited in mice treated with anti–type I IFN antibodies. Moreover, CTX induced a long-lasting increase in in vivo lymphocyte proliferation and in the percentage of CD44hiCD4+ and CD44hiCD8+T lymphocytes. These results demonstrate that CTX is an inducer of type I IFN in vivo and enhances the number of T cells exhibiting the CD44hi memory phenotype. Since type I IFN has been recently recognized as the important cytokine for the in vivo expansion and long-term survival of memory T cells, we suggest that induction of this cytokine may explain at least part of the immunomodulatory effects observed after CTX treatment. Finally, these findings provide a new rationale for combined treatments with CTX and adoptive immunotherapy in cancer patients.

Constitutive expression of interferon beta in differentiated epithelial cells exposed to environmental stimuli

The body's first line of defense against external challenge are the epithelial cells that line the skin and the respiratory, digestive, and genitourinary tracts. Inasmuch as interferon-beta (IFN-beta) participates in host defense against viral, bacterial, and parasitic infections and tumors, we hypothesized that this secreted protein is expressed in various murine epithelial cell types that line portals of entry to the body. We used immunohistochemistry and in situ hybridization techniques to measure IFN-beta expression in the various epithelial cell types and in internal murine organs sheltered from environmental stimuli. The epithelial cell types lining the skin, digestive tract, urinary tract, reproductive tract, and upper respiratory tract constitutively expressed IFN-beta. Specifically, all differentiated epithelial cells at risk of environmental exposure expressed IFN-beta (protein and mRNA) with the exception of the ciliated epithelial cells lining the lower respiratory tract. Epithelial cells of internal organs that are not directly exposed to external pathogens did not express IFN-beta.

Interferons Alpha, Beta, and Omega

Interferon alpha (IFN-α) is a mixture of closely related proteins, termed “subtypes,” expressed from distinct chromosomal genes. Interferon β (IFN-β) is a single protein species and is molecularly related to IFN-α subtypes, although it is antigenically distinct from them. IFN omega (IFN-ω) is antigenically distinct from IFN-α and IFN-β but is molecularly related to both. The genes of three IFN subtypes are tandemly arranged on the short arm of chromosome 9. They are transiently expressed following induction by various exogenous stimuli, including viruses. They are synthesized from their respective mRNAs for relatively short periods following gene activation and are secreted to act, via specific cell surface receptors, on other cells. IFN-α subtypes are secreted proteins and as such are transcribed from mRNAs as precursor proteins, pre-IFN-α, containing N-terminal signal polypeptides of 23 hydrophobic amino acids (aa) mainly. Pre-IFN-β contains 187 aa, of which 21 comprise the N-terminal signal polypeptide and 166 comprise the mature IFN-β protein. IFN-ω contains 195 aa—the N-terminal 23 comprising the signal sequence and the remaining 172, the mature IFN-ω protein. At the C-terminus, the aa sequence of IFN-ω is six residues longer than that of IFN-α or IFN-β proteins. IFN-α, as a mixture of subtypes, and IFN-ω may be produced together following viral infection of null lymphocytes or monocytes/macrophages. The biological activities of IFNs are mostly dependent upon protein synthesis with selective subsets of proteins mediating individual activities. IFNs can also stimulate indirect antiviral and antitumor mechanisms, depending upon cellular differentiation and the induction of cytotoxic activity.

A physiological role of interferon (IFN)-beta derived from tumor: tumor growth of a mouse bladder carcinoma line MBT-2 is partially suppressed by autocrine IFN-beta

Although some tumor cells endogenously produce a wide variety of cytokines, their physiological roles remain to be fully understood. In this study, we found that mouse subcutaneous tumor induced by inoculation of bladder tumor MBT-2 cells into syngeneic mice secreted a significant amount of interferon (IFN), whereas the cells exhibited no IFN production in in vitro cell culture. Typing experiment using IFN-specific neutralizing antibodies showed that the tumor-derived IFN was exclusively beta type. Since the MBT-2 tumor tissues were homogenous and not infiltrated by immune cells, MBT-2 cells themselves were considered to be IFN-beta producers. By intraperitoneal injection of neutralizing anti-IFN-beta antibodies into MBT-2 cell-inoculated mice, the tumor growth was substantially precipitated and survival days of the tumor-bearing mice were shortened. As the in vitro cell growth of MBT-2 cells was dose-dependently inhibited by IFN-beta, it was suggested that apparent immunogenicity of MBT-2 tumor is partially mediated by tumor suppression by autocrine IFN-beta.

The essential role of endogenous IFN alpha/beta in the anti-metastatic action of sensitized T lymphocytes in mice injected with Friend erythroleukemia cells

Adoptive transfer of splenic T lymphocytes from DBA/2 mice immunized against Friend erythroleukemia cells (FLC) inhibited the development of visceral metastases and increased the survival time of DBA/2 mice challenged i.v. with parental FLC 24 hr to 2 months later. Immune spleen cells were ineffective in mice pre-treated with potent neutralizing antibody to mouse IFN alpha/beta (but not to IFN gamma), demonstrating the essential participation of endogenous IFN alpha/beta in the inhibitory action of immune T lymphocytes against FLC metastases. These findings suggest that the reported inability of immune T lymphocytes to exert an anti-FLC effect in immunodeficient DBA/2 mutant beige (bg/bg) mice (unless these mice had also been treated with IFN alpha/beta), may have been due to lower levels of endogenous IFN alpha/beta in DBA/2 bg/bg mice than in normal DBA/2+/bg mice. Experimental results in support of this hypothesis are presented.

Interferon-gamma reduces tumor-induced Ia- macrophage-mediated suppression: role of prostaglandin E2, Ia, and tumor necrosis factor-alpha

Tumor growth enhances macrophage (M phi) suppressor activity by causing M phi to increase synthesis of inhibitory molecules such as prostaglandin E2 (PGE2) or decreasing their expression of up-regulatory molecules such as the class II MHC protein Ia. Although these tumor-induced changes are correlated, it is unknown whether tumor-bearing host (TBH) Ia- M phi become more suppressive by increasing their PGE2 synthesis. To assess the role of PGE2 in tumor-induced Ia- M phi-mediated suppression of CD4+ T-cell alloreactivity, unseparated (Ia(+)-enriched) or Ia(+)-depleted (Ia-) populations of murine normal host (NH) or TBH splenic M phi were added to mixed lymphocyte reaction (MLR) cultures. NH or TBH Ia- M phi were significantly more suppressive than their respective unseparated populations, and TBH Ia- M phi were more suppressive than their NH counterparts. When PGE2 production was blocked with indomethacin, TBH Ia- M phi-mediated suppression was reduced more than suppression mediated by all other M phi populations. A PGE2-specific ELISA showed more PGE2 in Ia- M phi-containing cultures than in those with whole M phi and more in cultures containing TBH Ia- M phi than in their NH counterparts. Because interferon-gamma (IFN-gamma) is a potent M phi activation molecule that regulates both Ia expression and PGE2 production, the effects of IFN-gamma on tumor-induced Ia- M phi-mediated suppression were investigated. Exogenous IFN-gamma reduced suppression mediated by all M phi populations except NH unseparated M phi. IFN-gamma suppressed alloreactivity without M phi or with NH unseparated M phi. Suppression mediated by NH or TBH Ia-, and TBH unseparated M phi was also reduced when M phi were pre-incubated with IFN-gamma before their addition to MLR cultures. IFN-gamma addition did not block Ia- M phi-mediated suppression by decreasing M phi PGE2 production. In fact, IFN-gamma addition increased PGE2 production two-fold in MLR cultures. However, IFN-gamma partly reduced suppression mediated by exogenous PGE2 added to M phi-depleted cultures. Cytofluorometric analysis showed that IFN-gamma increased the percentage of Ia+ M phi in NH and TBH Ia- M phi populations. Blocking TNF-alpha activity with anti-TNF-alpha antibodies caused IFN-gamma to suppress alloreactivity in all M phi-added cultures. Collectively, these data show that tumor-induced suppression mediated by Ia- M phi is caused by increased PGE2 synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)