The inflammasome component NLRP3 impairs antitumor vaccine by enhancing the accumulation of tumor-associated myeloid-derived suppressor cells

Transcriptional regulation of myeloid-derived suppressor cells

Myeloid-derived suppressor cells are a heterogeneous group of pathologically activated immature cells that play a major role in the negative regulation of the immune response in cancer, autoimmunity, many chronic infections, and inflammatory conditions, as well as in the regulation of tumor angiogenesis, tumor cell invasion, and metastases. Accumulation of myeloid-derived suppressor cells is governed by a network of transcriptional regulators that could be combined into 2 partially overlapping groups: factors promoting myelopoiesis and preventing differentiation of mature myeloid cells and factors promoting pathologic activation of myeloid-derived suppressor cells. In this review, we discuss the specific nature of these factors and their impact on myeloid-derived suppressor cell development.

Emerging roles of myeloid derived suppressor cells in hepatic inflammation and fibrosis

Myeloid derived suppressor cells (MDSC) are a heterogeneous population of immune cells that are potent suppressors of immune responses. MDSC emerge in various compartments in the body, such as blood, bone marrow or spleen, especially in conditions of cancer, infections or inflammation. MDSC usually express CD11b, CD33, and low levels of human leukocyte antigen-DR in humans or CD11b and Gr1 (Ly6C/G) in mice, and they can be further divided into granulocytic or monocytic MDSC. The liver is an important organ for MDSC induction and accumulation in hepatic as well as extrahepatic diseases. Different hepatic cells, especially hepatic stellate cells, as well as liver-derived soluble factors, including hepatocyte growth factor and acute phase proteins (SAA, KC), can promote the differentiation of MDSC from myeloid cells. Importantly, hepatic myeloid cells like neutrophils, monocytes and macrophages fulfill essential roles in acute and chronic liver diseases. Recent data from patients with liver diseases and animal models linked MDSC to the pathogenesis of hepatic inflammation, fibrosis and hepatocellular carcinoma (HCC). In settings of acute hepatitis, MDSC can limit immunogenic T cell responses and subsequent tissue injury. In patients with chronic hepatitis C, MDSC increase and may favor viral persistence. Animal models of chronic liver injury, however, have not yet conclusively clarified the involvement of MDSC for hepatic fibrosis. In human HCC and mouse models of liver cancer, MDSC are induced in the tumor environment and suppress anti-tumoral immune responses. Thus, the liver is a primary site of MDSC in vivo, and modulating MDSC functionality might represent a promising novel therapeutic target for liver diseases.

Perception of self: distinguishing autoimmunity from autoinflammation

Rheumatic diseases can be divided in two groups, autoinflammatory and autoimmune disorders. The clinical presentation of both types of diseases overlap, but the pathological pathways underlying rheumatic autoinflammation and autoimmunity are distinct and are the subject of ongoing research. There are a number of ways in which these groups of diseases differ in terms of disease mechanisms and therapeutic responses. First, autoinflammatory diseases are driven by endogenous danger signals, metabolic mediators and cytokines, whereas autoimmunity involves the activation of T and B cells, the latter requiring V-(D)-J recombination of receptor-chain gene segments for maturation. Second, the efficacy of biologic agents directed against proinflammatory cytokines (for example IL-1β and TNF) also highlights differences between autoinflammatory and autoimmune processes. Finally, whereas autoinflammatory diseases are mostly driven by inflammasome-induced IL-1β and IL-18 production, autoimmune diseases are associated with type I interferon (IFN) signatures in blood. In this Review, we provide an overview of the monocyte intracellular pathways that drive autoinflammation and autoimmunity. We convey recent findings on how the type I IFN pathway can modulate IL-1β signalling (and vice versa), and discuss why IL-1β-mediated autoinflammatory diseases do not perpetuate into autoimmunity. The origins of intracellular autoantigens in autoimmune disorders are also discussed. Finally, we suggest how new mechanistic knowledge of autoinflammatory and autoimmune diseases might help improve treatment strategies to benefit patient care.

TLR2 limits development of hepatocellular carcinoma by reducing IL18-mediated immunosuppression

Immune mechanisms underlying hepatocellular carcinoma (HCC) are not well understood. Here, we show that the Toll-like receptor TLR2 inhibits production of the proinflammatory cytokine IL18 and protects mice from DEN-induced liver carcinogenesis. On this protocol, Tlr2(-/-) mice exhibited more aggressive HCC development associated with impaired CD8(+) T-cell function. Furthermore, Ly6C(high)IL18Rα(+) myeloid-derived suppressor cells (MDSC) were increased in number in the livers of Tlr2(-/-) mice before tumor onset. MDSC in this setting exhibited higher iNOS levels that could inhibit IFNγ production and CD8(+) T-cell proliferation in vitro. Notably, Tlr2(-/-) hepatocytes produced more mature IL18 after DEN treatment that was sufficient to drive MDSC accumulation there. IL18 administration was sufficient to induce accumulation of MDSC, whereas hepatocyte-specific silencing of IL18 in Tlr2(-/-) mice decreased the proportion of MDSC, increased the proportion of functional CD8(+) T cells, and alleviated HCC progression. IL18 production was mediated by caspase-8 insofar as the decrease in its silencing was sufficient to attenuate levels of mature IL18 in Tlr2(-/-) mice. Furthermore, the TLR2 agonist Pam3CSK4 inhibited both caspase-8 and IL18 expression, decreasing MDSC, increasing CD8(+) T-cell function, and promoting HCC regression. Overall, our findings show how TLR2 deficiency accelerates IL18-mediated immunosuppression during liver carcinogenesis, providing new insights into immune control that may assist the design of effective immunotherapies to treat HCC.

Adverse immunoregulatory effects of 5FU and CPT11 chemotherapy on myeloid-derived suppressor cells and colorectal cancer outcomes

Colorectal cancer is associated with chronic inflammation and immunosuppression mediated by myeloid-derived suppressor cells (MDSC). Although chemotherapy reduces tumor burden at early stages, it tends to have limited effect on a progressive disease, possibly due to adverse effects on the immune system in dictating disease outcome. Here, we show that patients with advanced colorectal cancer display enhanced MDSC levels and reduced CD247 expression and that some conventional colorectal cancer chemotherapy supports the immunosuppressive tumor microenvironment. A FOLFOX combined therapy reduced immunosuppression, whereas a FOLFIRI combined therapy enhanced immunosuppression. Mechanistic studies in a colorectal cancer mouse model revealed that FOLFIRI-like therapy including the drugs CPT11 and 5-fluorouracil (5FU) damaged host immunocompetence in a manner that limits treatment outcomes. CPT11 blocked MDSC apoptosis and myeloid cell differentiation, increasing MDSC immunosuppressive features and mouse mortality. In contrast, 5FU promoted immune recovery and tumor regression. Thus, CPT11 exhibited detrimental immunoregulatory effects that offset 5FU benefits when administered in combination. Our results highlight the importance of developing therapeutic regimens that can target both the immune system and tumor towards improved personalized treatments for colorectal cancer.

A mutual activation loop between breast cancer cells and myeloid-derived suppressor cells facilitates spontaneous metastasis through IL-6 trans-signaling in a murine model

INTRODUCTION

Tumor cell interactions with the microenvironment, especially those of bone-marrow-derived myeloid cells, are important in various aspects of tumor metastasis. Myeloid-derived suppressor cells (MDSCs) have been suggested to constitute tumor-favoring microenvironments. In this study, we elucidated a novel mechanism by which the MDSCs can mediate spontaneous distant metastasis of breast cancer cells.

METHODS

Murine breast cancer cells, 4T1 and EMT6, were orthotopically grafted into the mammary fat pads of syngeneic BALB/c mice. CD11b(+)Gr-1(+) MDSCs in the spleen, liver, lung and primary tumor mass were analyzed. To evaluate the role of MDSCs in the distant metastasis, MDSCs were depleted or reconstituted in tumor-bearing mice. To evaluate whether MDSCs in the metastasizing tumor microenvironment affect breast cancer cell behavior, MDSCs and cancer cells were co-cultivated. To investigate the role of MDSCs in in vivo metastasis, we blocked the interactions between MDSCs and cancer cells.

RESULTS

Using a murine breast cancer cell model, we showed that murine breast cancer cells with high IL-6 expression recruited more MDSCs and that the metastasizing capacity of cancer cells paralleled MDSC recruitment in tumor-bearing mice. Metastasizing, but not non-metastasizing, tumor-derived factors induced MDSCs to increase IL-6 production and full activation of recruited MDSCs occurred in the primary tumor site and metastatic organ in the vicinity of metastasizing cancer cells, but not in lymphoid organs. In addition, tumor-expanded MDSCs expressed Adam-family proteases, which facilitated shedding of IL-6 receptor, thereby contributing to breast cancer cell invasiveness and distant metastasis through IL-6 trans-signaling. The critical role of IL-6 trans-signaling was confirmed in both the afferent and efferent pathways of metastasis.

CONCLUSION

In this study, we showed that metastasizing cancer cells induced higher MDSCs infiltration and prompted them to secret exaggerated IL-6 as well as soluble IL-6Ra, which, in turn, triggered a persistent increase of pSTAT3 in tumor cells. This potential tumor-MDSC axis involving IL-6 trans-signaling directly affected breast cancer cell aggressiveness, leading to spontaneous metastasis.

Nod-like receptors: key molecular switches in the conundrum of cancer

It is believed the immune system can contribute to oncogenic transformation especially in settings of chronic inflammation, be activated during immunosurveillance to destroy early neoplastic cells before they undergo malignant outgrowth, and finally, can assist growth of established tumors by preventing clearance, remodeling surrounding tissue, and promoting metastatic events. These seemingly opposing roles of the immune system at the different stages of cancer development must all be mediated by innate signaling mechanisms that regulate the overall state of immune activation. Recently, the cytosolic nod-like receptor (NLR) pathway of innate immunity has gained a lot of attention in the tumor immunology field due to its known involvement in promoting inflammation and immunity, and conversely, in regulating tissue repair processes. In this review, we present all the current evidence for NLR involvement in the different stages of neoplasia to understand how a single molecular pathway can contribute to conflicting immunological interactions with cancer.

Cell-death-associated molecular patterns as determinants of cancer immunogenicity

SIGNIFICANCE

Accumulating evidence indicates that the success of some anticancer treatments (select chemotherapies or radiotherapy or trastuzumab) could be related to the stimulation of an anticancer immune response through the induction of an immunogenic tumor cell death (ICD).

RECENT ADVANCES

Preclinical data revealed that dying tumor cells can emit a series of danger signals (so-called "cell-death-associated molecular patterns" (CDAMP)) that will dictate the recruitment and activation of specific inflammatory phagocytes. Hence, tumor cells succumbing to ICD are characterized by specific metabolic and molecular changes that will trigger a hierarchy of polarizing cytokine-producing cells, culminating in the recruitment and reactivation of antitumor interferon-γ-producing effector T cells which contribute to the success of cytotoxic treatments.

CRITICAL ISSUES

In this review, we summarize the molecular and cellular bases of this ICD, underscoring the crucial role of high mobility group box 1 protein (HMGB1) and adenosine tri-phosphate, both of which are released from dying tumor cells during ICD and are implicated in the chemotherapy-elicited anticancer immune response.

FUTURE DIRECTIONS

We discuss here how such CDAMP could serve as predictive biomarkers that could discriminate immunogenic from nonimmunogenic anti-cancer compounds, and, in case of deficiency, could be compensated by surrogate products to ameliorate the success rate of conventional anticancer treatment modalities.

Luteoloside suppresses proliferation and metastasis of hepatocellular carcinoma cells by inhibition of NLRP3 inflammasome

The inflammasome is a multi-protein complex which when activated regulates caspase-1 activation and IL-1β secretion. Inflammasome activation is mediated by NLR proteins that respond to stimuli. Among NLRs, NLRP3 senses the widest array of stimuli. NLRP3 inflammasome plays an important role in the development of many cancer types. However, Whether NLRP3 inflammasome plays an important role in the process of hepatocellular carcinoma (HCC) is still unknown. Here, the anticancer effect of luteoloside, a naturally occurring flavonoid isolated from the medicinal plant Gentiana macrophylla, against HCC cells and the underlying mechanisms were investigated. Luteoloside significantly inhibited the proliferation of HCC cells in vitro and in vivo. Live-cell imaging and transwell assays showed that the migration and invasive capacities of HCC cells, which were treated with luteoloside, were significantly inhibited compared with the control cells. The inhibitory effect of luteoloside on metastasis was also observed in vivo in male BALB/c-nu/nu mouse lung metastasis model. Further studies showed that luteoloside could significantly reduce the intracellular reactive oxygen species (ROS) accumulation. The decreased levels of ROS induced by luteoloside was accompanied by decrease in expression of NLRP3 inflammasome resulting in decrease in proteolytic cleavage of caspase-1. Inactivation of caspase-1 by luteoloside resulted in inhibition of IL-1β. Thus, luteoloside exerts its inhibitory effect on proliferation, invasion and metastasis of HCC cells through inhibition of NLRP3 inflammasome. Our results indicate that luteoloside can be a potential therapeutic agent not only as an adjuvant therapy for HCC, but also, in the control and prevention of metastatic HCC.

Inflammasomes in cancer: a double-edged sword

Chronic inflammatory responses have long been observed to be associated with various types of cancer and play decisive roles at different stages of cancer development. Inflammasomes, which are potent inducers of interleukin (IL)-1β and IL-18 during inflammation, are large protein complexes typically consisting of a Nod-like receptor (NLR), the adapter protein ASC, and Caspase-1. During malignant transformation or cancer therapy, the inflammasomes are postulated to become activated in response to danger signals arising from the tumors or from therapy-induced damage to the tumor or healthy tissue. The activation of inflammasomes plays diverse and sometimes contrasting roles in cancer promotion and therapy depending on the specific context. Here we summarize the role of different inflammasome complexes in cancer progression and therapy. Inflammasome components and pathways may provide novel targets to treat certain types of cancer; however, using such agents should be cautiously evaluated due to the complex roles that inflammasomes and pro-inflammatory cytokines play in immunity.

Licensing Adaptive Immunity by NOD-Like Receptors

The innate immune system is composed of a diverse set of host defense molecules, physical barriers, and specialized leukocytes and is the primary form of immune defense against environmental insults. Another crucial role of innate immunity is to shape the long-lived adaptive immune response mediated by T and B lymphocytes. The activation of pattern recognition receptors (PRRs) from the Toll-like receptor family is now a classic example of innate immune molecules influencing adaptive immunity, resulting in effective antigen presentation to naïve T cells. More recent work suggests that the activation of another family of PRRs, the NOD-like receptors (NLRs), induces a different set of innate immune responses and accordingly, drives different aspects of adaptive immunity. Yet how this unusually diverse family of molecules (some without canonical PRR function) regulates immunity remains incompletely understood. In this review, we discuss the evidence for and against NLR activity orchestrating adaptive immune responses during infectious as well as non-infectious challenges.

Yin and yang of tumor inflammation: how innate immune suppressors shape the tumor microenvironments

Pattern recognition-mediated sensing systems direct host immunity towards either antitumor immunosurveillance or protumorigenic inflammation. These activities imply dual and conflicting roles in the regulation of tumor-associated inflammation. On the one hand, recent evidence has revealed that several signaling components and cell-surface receptors suppress innate immune signals and constitute a negative feedback machinery preventing excess and continuous inflammation within tumor microenvironments. On the other hand, these same components also negatively regulate intrinsic tumorigenic activities by targeting nuclear factor-kappaB (NF-κB)-mediated antiapoptotic and inflammatory signals. Furthermore, the activation status of innate immune suppressors may reflect the functional plasticity of interactions between tumor cells and innate immune cells and determine whether tumor inflammation supports anti- or pro-tumorigenic responses. Thus, innate immune suppressors may provide valuable information about the immunogenic or tumorigenic status of tumor-associated inflammation thereby serving as potential biomarkers that predict tumor progression. Comprehensive analysis for identifying general and unique features of each innate immune suppressor in the regulation of tumor inflammation should explore the development of new biomarkers for improving future therapeutic strategies.

Beneficial and Detrimental Roles of NLRs in Carcinogenesis

Inflammation plays a critical role in tumorigenesis and can contribute to oncogenic mutations, tumor promotion, and angiogenesis. Tumor-promoting inflammation is driven by many factors including the presence of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. One major source of IL-1β and IL-18 secretion is through the activation of inflammasomes. Inflammasomes are multi-protein complexes that upon activation lead to the processing and secretion of IL-1β and IL-18 mediated by the cysteine protease caspase-1. Several inflammasomes, including NLRP3, NLRC4, and NLRP6, have been implicated in tumorigenesis. However, inflammasomes play divergent roles in different types of cancer reflecting the complexity of inflammation during tumorigenesis. Understanding the role of inflammasome activation during specific stages of tumorigenesis and also during cancer immunotherapy will help identify novel therapeutic targets that could improve treatment strategies for cancer patients. Here we will discuss recent advances in understanding the mechanism by which NLRs regulate carcinogenesis.

Mycoplasma hyorhinis activates the NLRP3 inflammasome and promotes migration and invasion of gastric cancer cells

BACKGROUND

Mycoplasma hyorhinis (M.hyorhinis, M.hy) is associated with development of gastric and prostate cancers. The NLRP3 inflammasome, a protein complex controlling maturation of important pro-inflammatory cytokines interleukin (IL)-1β and IL-18, is also involved in tumorigenesis and metastasis of various cancers.

METHODOLOGY/PRINCIPAL FINDINGS

To clarify whether M.hy promoted tumor development via inflammasome activation, we analyzed monocytes for IL-1β and IL-18 production upon M.hy challenge. When exposed to M.hy, human monocytes exhibited rapid and robust IL-1β and IL-18 secretion. We further identified that lipid-associated membrane protein (LAMP) from M.hy was responsible for IL-1β induction. Applying competitive inhibitors, gene specific shRNA and gene targeted mice, we verified that M.hy induced IL-1β secretion was NLRP3-dependent in vitro and in vivo. Cathepsin B activity, K(+) efflux, Ca(2+) influx and ROS production were all required for the NLRP3 inflammasome activation by M.hy. Importantly, it is IL-1β but not IL-18 produced from macrophages challenged with M.hy promoted gastric cancer cell migration and invasion.

CONCLUSIONS

Our data suggest that activation of the NLRP3 inflammasome by M.hy may be associated with its promotion of gastric cancer metastasis, and anti-M.hy therapy or limiting NLRP3 signaling could be effective approach for control of gastric cancer progress.

Impaired innate mucosal immunity in aged mice permits prolonged Streptococcus pneumoniae colonization

Streptococcus pneumoniae is a frequent asymptomatic colonizer of the nasopharyngeal niche and only occasionally progresses toward infection. The burden of pneumococcal disease is particularly high in the elderly, and the mechanisms behind this increased susceptibility are poorly understood. Here we used a mouse model of pneumococcal carriage to study immunosenescence in the upper respiratory tract (URT). Nasal mucosa-associated lymphoid tissue (NALT) showed increased expression of Toll-like receptor 1, interleukin-1β, NLRp3 inflammasome, and CCL2 in naive elderly compared to young animals. This suggests an increased proinflammatory expression profile in the NALT of aged mice at baseline. Simultaneously, we observed a more tolerogenic profile in respiratory epithelia of naive elderly compared to young adult mice with upregulation of the NF-κβ pathway inhibitor peroxisome proliferator-activated receptor gamma (PPARγ). After nasal instillation of pneumococci, pneumococcal colonization was prolonged in elderly mice compared to in young adults. The delay in clearance was associated with absent or delayed upregulation of a proinflammatory mediator(s) in the NALT, diminished influx of macrophages into the URT niche, and absent downregulation of PPARγ in respiratory epithelium, accompanied by diminished expression of cathelicidin (CRAMP) at the site of colonization. These findings suggest that unresponsiveness to pneumococcal challenge due to altered mucosal immune regulation is the key to increased susceptibility to disease in the elderly.

Circulating fibrocytes prepare the lung for cancer metastasis by recruiting Ly-6C+ monocytes via CCL2

Fibrocytes are circulating, hematopoietic cells that express CD45 and Col1a1. They contribute to wound healing and several fibrosing disorders by mechanisms that are poorly understood. In this report, we demonstrate that fibrocytes predispose the lung to B16-F10 metastasis by recruiting Ly-6C(+) monocytes. To do so, we isolated fibrocytes expressing CD45, CD11b, CD13, and Col1a1 from the lungs of wild type (WT) and Ccr5(-/-) mice. WT but not Ccr5(-/-) fibrocytes increased the number of metastatic foci when injected into Ccr5(-/-) mice (73 ± 2 versus 32 ± 5; p < 0.001). This process was MMP9 dependent. Injection of WT enhanced GFP(+) fibrocytes also increased the number of Gr-1(Int), CD11b(+), and enhanced GFP(-) monocytes. Like premetastatic-niche monocytes, these recruited cells expressed Ly-6C, CD117, and CD45. The transfer of these cells into Ccr5(-/-) mice enhanced metastasis (90 ± 8 foci) compared with B cells (27 ± 2), immature dendritic cells (31 ± 6), or alveolar macrophages (28 ± 3; p < 0.05). WT and Ccl2(-/-) fibrocytes also stimulated Ccl2 expression in the lung by 2.07 ± 0.05- and 2.78 ± 0.36-fold compared with Ccr5(-/-) fibrocytes (1.0 ± 0.06; p < 0.05). Furthermore, WT fibrocytes did not increase Ly-6C(+) monocytes in Ccr2(-/-) mice and did not promote metastasis in either Ccr2(-/-) or Ccl2(-/-) mice. These data support our hypothesis that fibrocytes contribute to premetastatic conditioning by recruiting Ly-6C(+) monocytes in a chemokine-dependent process. This work links metastatic risk to conditions that mobilize fibrocytes, such as inflammation and wound repair.

Blockade of Myd88 signaling induces antitumor effects by skewing the immunosuppressive function of myeloid-derived suppressor cells

Myd88 is an important adaptor molecule for the activation of NADPH oxidase and arginase-1, which are responsible for the suppressive function of myeloid-derived suppressor cells (MDSCs). When wild-type and Myd88(-/-) mice were subcutaneously injected with CT26 colon cancer cells expressing human Her-2/neu, tumor growth was retarded in Myd88(-/-) mice than in wild-type mice. Although the generation of CD11b(+) Gr-1(+) MDSCs was less in Myd88(-/-) mice than in wild-type mice, Myd88(-/-) mice having tumor masses still had significant quantities of MDSCs, suggesting that MDSC generation might be independent of Myd88 signaling. However, MDSCs obtained from tumor-bearing Myd88(-/-) mice failed to suppress antigen-specific proliferation of CD8(+) T cells and CD4(+) T cells, whereas MDSCs from wild-type mice significantly suppressed both types of T cells. Consistent with this, we found that the levels of costimulatory molecules and MHC class II were significantly increased in MDSCs obtained from Myd88(-/-) mice compared with wild-type mice after tumor challenge. Furthermore, CD4(+) T cells residing in tumor-draining lymph nodes of Myd88(-/-) mice secreted more TNF-α than those of wild-type mice. Finally, the blockade of Myd88 signaling by treatment with Myd88 inhibitory peptide, during later tumor stages, significantly inhibited the growth of immunogenic tumors. Overall, these data suggest that signaling through the Myd88 adaptor molecule is critical for the direct suppressive function of MDSCs and approaches to block Myd88-mediated signaling in MDSCs might be effective to inhibit the immunosuppressive function of MDSCs.

Chemotherapy-triggered cathepsin B release in myeloid-derived suppressor cells activates the Nlrp3 inflammasome and promotes tumor growth

Chemotherapeutic agents are widely used for cancer treatment. In addition to their direct cytotoxic effects, these agents harness the host's immune system, which contributes to their antitumor activity. Here we show that two clinically used chemotherapeutic agents, gemcitabine (Gem) and 5-fluorouracil (5FU), activate the NOD-like receptor family, pyrin domain containing-3 protein (Nlrp3)-dependent caspase-1 activation complex (termed the inflammasome) in myeloid-derived suppressor cells (MDSCs), leading to production of interleukin-1β (IL-1β), which curtails anticancer immunity. Chemotherapy-triggered IL-1β secretion relied on lysosomal permeabilization and the release of cathepsin B, which bound to Nlrp3 and drove caspase-1 activation. MDSC-derived IL-1β induced secretion of IL-17 by CD4(+) T cells, which blunted the anticancer efficacy of the chemotherapy. Accordingly, Gem and 5FU exerted higher antitumor effects when tumors were established in Nlrp3(-/-) or Casp1(-/-) mice or wild-type mice treated with interleukin-1 receptor antagonist (IL-1Ra). Altogether, these results identify how activation of the Nlrp3 inflammasome in MDSCs by 5FU and Gem limits the antitumor efficacy of these chemotherapeutic agents.

Suppression of vaccine immunity by inflammatory monocytes

Vaccine adjuvant-induced inflammation augments vaccine immunity in part by recruiting APCs to vaccine draining lymph nodes (LNs). However, the role of one APC subtype, inflammatory monocytes, in regulating vaccine immunity in healthy animals has not been fully examined in detail. Therefore, vaccine-mediated monocyte recruitment and subsequent immune responses were investigated using murine vaccination models and in vitro assays. Recruitment of inflammatory monocytes to vaccine draining LNs was rapid and mediated primarily by local production of MCP-1, as revealed by studies in MCP-1(-/-) mice. Interrupting monocyte recruitment to LNs by either transient monocyte depletion or monocyte migration blockade led to marked amplification of both cellular and humoral immune responses to vaccination. These results were most consistent with the idea that rapidly mobilized inflammatory monocytes were actually suppressing vaccine responses. The suppressive nature of vaccine-elicited monocytes was confirmed using in vitro cocultures of murine monocytes and T cells. Furthermore, it was determined that inflammatory monocytes suppressed T cell responses by sequestering cysteine, as cysteine supplementation in vitro and in vivo appreciably augmented vaccine responses. These findings indicated, therefore, that vaccination-elicited inflammation, although necessary for effective immunity, also generated potent counter-regulatory immune responses that were mediated primarily by inflammatory monocytes. Therefore, interrupting monocyte-mediated vaccine counterregulatory responses may serve as an effective new strategy for broadly amplifying vaccine immunity.

NLRP3 suppresses NK cell-mediated responses to carcinogen-induced tumors and metastases

The NLRP3 inflammasome acts as a danger signal sensor that triggers and coordinates the inflammatory response upon infectious insults or tissue injury and damage. However, the role of the NLRP3 inflammasome in natural killer (NK) cell-mediated control of tumor immunity is poorly understood. Here, we show in a model of chemical-induced carcinogenesis and a series of experimental and spontaneous metastases models that mice lacking NLRP3 display significantly reduced tumor burden than control wild-type (WT) mice. The suppression of spontaneous and experimental tumor metastases and methylcholanthrene (MCA)-induced sarcomas in mice deficient for NLRP3 was NK cell and IFN-γ-dependent. Focusing on the amenable B16F10 experimental lung metastases model, we determined that expression of NLRP3 in bone marrow-derived cells was necessary for optimal tumor metastasis. Tumor-driven expansion of CD11b(+)Gr-1(intermediate) (Gr-1(int)) myeloid cells within the lung tumor microenvironment of NLRP3(-/-) mice was coincident with increased lung infiltrating activated NK cells and an enhanced antimetastatic response. The CD11b(+)Gr-1(int) myeloid cells displayed a unique cell surface phenotype and were characterized by their elevated production of CCL5 and CXCL9 chemokines. Adoptive transfer of this population into WT mice enhanced NK cell numbers in, and suppression of, B16F10 lung metastases. Together, these data suggested that NLRP3 is an important suppressor of NK cell-mediated control of carcinogenesis and metastases and identify CD11b(+)Gr-1(int) myeloid cells that promote NK cell antimetastatic function.

Inflammasome polymorphisms confer susceptibility to sporadic malignant melanoma

Genetic variants of NLRP3 and NLRP1 are known to modulate levels of pro-inflammatory cytokine interleukin (IL)-1β. The purpose of this study was to investigate the association of NLRP3/NLRP1 polymorphisms with susceptibility and clinical features of malignant melanoma in a Swedish case-control study. Common variants in NLRP3/NLRP1 were investigated in sporadic malignant melanoma patients and healthy controls followed by analysis using logistic regression. NLRP3 variant (rs35829419) was significantly more common in male patients than in controls (OR, 2.22; CI, 1.27-3.86). Upon stratification, significant association with nodular melanoma was observed (OR, 2.89; CI, 1.33-6.30), which intensified in male patients (OR 4.03, CI 1.40-11.59). The NLRP1 variant (rs12150220) was significantly more common in fair-skinned female patients (OR, 1.85; CI, 1.04-3.33) and showed strong associations with nodular melanoma (OR, 6.03; CI, 1.33-25). Our data suggest that NLRP3/NLRP1 polymorphisms are associated with melanoma susceptibility; these findings warrant validation in other independent populations.

Inflammasomes in carcinogenesis and anticancer immune responses

In the complex interplay between malignant cells and their microenvironment, caspase-1 activation complexes (inflammasomes) have contrasting roles. Inflammasomes may operate at the cell-autonomous level to eliminate malignant precursors through programmed cell death or, conversely, may stimulate the production of trophic factors for cancer cells and their stroma. In inflammatory cells, caspase-1 activation can fuel a cycle that leads to sterile inflammation and carcinogenesis, whereas in antigen-presenting cells, inflammasomes can stimulate anticancer immune responses. The inhibition of inflammasomes or neutralization of their products, mainly interleukin 1β (IL-1β) and IL-18, has profound effects on carcinogenesis and tumor progression. Thus, inflammasomes are promising therapeutic targets in cancer-related clinical conditions. Here we discuss present and future indications for the clinical use of inflammasome inhibitors.

Inflammation and immune surveillance in cancer

Chronic inflammation is a risk factor for tumor development. However, understanding the effect of the immune system on tumor development has only been significantly advanced over the past two decades. We now appreciate that the immune system, in addition to tumor-suppressive function by eliminating nascent transformed tumor cells, can also exert selection pressure on tumor cells and facilitate tumor growth by providing a favorable tumor microenvironment. Yet, the distinctions between tumor-promoting inflammation and tumor-suppressive immunity are still not clear due to the dual role of some cytokines and other molecules in the immune system. The danger signal hypothesis has shaped our view of the role of immunity in cancer development, but still little is known about the exact role of danger signal receptors in cancer progression. In this review, we introduce the processes of cancer immunoediting and inflammation-induced cancer and discuss what is currently known about the role of danger signal receptors in cancer development and progression.

Monocytes link atherosclerosis and cancer

From many perspectives, cardiovascular diseases and cancers are fundamentally different. On the one hand, atherosclerosis is a disease of lipid accumulation driven by diet and lifestyle, whereas cancer is an attack "from within" driven by mutations. Nevertheless, studies over the past 20 years have forced us to re-evaluate such a view. We are learning that, among other factors, the immune system is indispensable for the development and progression of both diseases. Its components are not only reactive but can also orchestrate both tumor and atherosclerotic lesion growth. In this Viewpoint, we explore how monocytes, which are key constituents of the immune system, forge links between cardiovascular diseases and cancers.

Berkeleyones and related meroterpenes from a deep water acid mine waste fungus that inhibit the production of interleukin 1-β from induced inflammasomes

The Berkeley Pit, an acid mine waste lake, is a source of extremophilic microorganisms that produce interesting bioactive compounds. We have previously reported the isolation of berkeleydione (1), berkeleytrione (2), the berkeleyacetals, and the berkeleyamides from the Pit Lake fungus Penicillium rubrum. In this paper we report the isolation and characterization of berkeleyones A-C (4, 5, and 7) as well as previously described preaustinoid A (3) and A1(6) from this same fungus. These compounds were evaluated as inhibitors of the signaling enzyme caspase-1 and as potential inhibitors of interleukin 1-β production by inflammasomes in induced THP-1 cell line assays.

Green tea polyphenol epigallocatechin-3-gallate suppresses melanoma growth by inhibiting inflammasome and IL-1β secretion

Epigallocatechin-3-gallate (EGCG), the major polyphenolic component of green tea, has been demonstrated to possess anti-inflammatory, antioxidant, anti-mutagenic and anti-carcinogenic properties. The anti-melanoma effect of EGCG has been previously suggested, but no clear mechanism of action has been established. In this study, we demonstrated that EGCG inhibits melanoma cell growth at physiological doses (0.1-1 μM). In the search for mechanisms of EGCG-mediated melanoma cell suppression, we found that NF-κB was inhibited, and that reduced NF-κB activity was associated with decreased IL-1β secretion from melanoma cells. Since inflammasomes are involved in IL-1β secretion, we investigated whether IL-1β suppression was mediated by inflammasomes, and found that EGCG treatment led to downregulation of the inflammasome component, NLRP1, and reduced caspase-1 activation. Furthermore, silencing the expression of NLRP1 abolished EGCG-induced inhibition of tumor cell proliferation both in vitro and in vivo, suggesting a key role of inflammasomes in EGCG efficacy. This paper provides a novel mechanism for EGCG-induced melanoma inhibition: inflammasome downregulation→decreased IL-1β secretion→decreased NF-κB activities→decreased cell growth. In addition, it suggests inflammasomes and IL-1β could be potential targets for future melanoma therapeutics.