Toll-like receptor-7 tolerizes malignant B cells and enhances killing by cytotoxic agents

Molecular Masking of Synthetic Immunomodulator Evokes Antitumor Immunity With Reduced Immune Tolerance and Systemic Toxicity by Temporal Activity Recovery and Sustained Stimulation

Activation of the innate immune system counteracts tumor-induced immunosuppression. Hence, small molecule-based toll-like receptor 7/8 agonists (TLR7/8a), which can modulate immunosuppression in the tumor microenvironment along with the activation of innate immunity, are emerging as essential components of cancer immunotherapy. However, the clinical application of synthetic TLR7/8a therapies is limited by systemic immune-associated toxicity and immune tolerance induced by uncontrolled stimulatory activities and repeated treatments. To address these limitations, a dynamic immunomodulation strategy incorporating masking and temporal recovery of the activity of TLR7/8a through prodrug-like TLR7/8a (pro-TLR7/8a) at the molecular level and a sustained and controlled release of active TLR7/8a from nanoliposome (pro-TLR7/8a) (NL(pro-TLR7/8)) in a macroscale depot are designed. Immunization with cationic NL(pro-TLR7/8) and anionic antigens triggers robust activation of innate immune cells as well as antigen-specific T cell responses, eliciting reprogramming of immunosuppressive cells into tumor-suppressive cells, with decreased systemic adverse effects and immune tolerance. Combination treatment with NL(pro-TLR7/8a) and immune checkpoint inhibitors (anti-CTLA-4 plus anti-PD-L1) or nanoliposomes (Doxorubicin) has synergistic effects on antitumor immunity in various tumor models. The concept of pro-TLR7/8a suggested herein may facilitate the advancement of small-molecule-based immunomodulators for clinical translation and safe and effective cancer immunotherapy.

Small-Molecule Modulators Targeting Toll-like Receptors for Potential Anticancer Therapeutics

Toll-like receptors (TLRs) are key components of the innate immune system and serve as a crucial link between innate and acquired immunity. In addition to immune function, TLRs are involved in other important pathological processes, including tumorigenesis. TLRs have dual regulatory effects on tumor immunity by activating nuclear factor κ-B signaling pathways, which induce tumor immune evasion or enhance the antitumor immune response. Therefore, TLRs have become a popular target for cancer prevention and treatment, and TLR agonists and antagonists offer considerable potential for drug development. The TLR7 agonist imiquimod (1) has been approved by the U.S. Food and Drug Administration as a treatment for malignant skin cancer. Herein, the structure, signaling pathways, and function of the TLR family are summarized, and the structure-activity relationships associated with TLR selective and multitarget modulators and their potential application in tumor therapy are systematically discussed.

Engineering kinetics of TLR7/8 agonist release from bottlebrush prodrugs enables tumor-focused immune stimulation

Imidazoquinolines (IMDs), such as resiquimod (R848), are of great interest as potential cancer immunotherapies because of their ability to activate Toll-like receptor 7 (TLR7) and/or TLR8 on innate immune cells. Nevertheless, intravenous administration of IMDs causes severe immune-related toxicities, and attempts to improve their tissue-selective exposure while minimizing acute systemic inflammation have proven difficult. Here, using a library of R848 "bottlebrush prodrugs" (BPDs) that differ only by their R848 release kinetics, we explore how the timing of R848 exposure affects immune stimulation in vitro and in vivo. These studies led to the discovery of R848-BPDs that exhibit optimal activation kinetics to achieve potent stimulation of myeloid cells in tumors and substantial reductions in tumor growth following systemic administration in mouse syngeneic tumor models without any observable systemic toxicity. These results suggest that release kinetics can be tuned at the molecular level to provide safe yet effective systemically administered immunostimulant prodrugs for next-generation cancer immunotherapies.

Paradoxical activation of chronic lymphocytic leukemia cells by ruxolitinib in vitro and in vivo

Introduction

Chronic lymphocytic leukemia (CLL) is characterized by an aberrant cytokine network that can support tumor growth by triggering janus kinase (JAK)/STAT pathways. Targeting cytokine-signaling should then be a rational therapeutic strategy but the JAK inhibitor ruxolitinib failed to control and seemingly accelerated the disease in clinical trials.

Methods

The effect of ruxolitinib on primary human CLL cells was studied in vitro and in vivo.

Results

Ruxolitinib increased phosphorylation of IRAK4, an important toll-like receptor (TLR)- signaling intermediate, in circulating CLL cells in vitro. It also enhanced p38 and NFKB1 phosphorylation while lowering STAT3 phosphorylation in CLL cells activated with TLR-7/8 agonists and IL-2. Among the cytokines made by activated CLL cells, high levels of IL-10 contributed strongly to STAT3 phosphorylation and inhibited TLR7 activity. Ruxolitinib limited TLR-mediated IL10 transcription and markedly reduced IL-10 production in vitro. It also decreased blood levels of IL-10 while increasing TNFα along with phospho-p38 expression and gene sets associated with TLR-activation in CLL cells in vivo. The bruton's tyrosine kinase inhibitor ibrutinib decreased IL-10 production in vitro but, in contrast to ruxolitinib, blocked initial IL10 transcription induced by TLR-signaling in vitro, decreased TNFα production, and deactivates CLL cells in vivo.

Discussion

These findings suggest the possible benefits of inhibiting growth factors with JAK inhibitors in CLL are outweighed by negative effects on potential tumor suppressors such as IL-10 that allow unrestrained activation of NFκB by drivers such as TLRs. Specific inhibition of growth-promoting cytokines with blocking antibodies or infusing suppressive cytokines like IL-10 might be better strategies to manipulate cytokines in CLL.

Enhanced IFN Sensing by Aggressive Chronic Lymphocytic Leukemia Cells

Type I IFN is made by cells in response to stress. Cancer cells exist in a state of stress, but their IFN response is complex and not completely understood. This study investigated the role of autocrine IFN in human chronic lymphocytic leukemia (CLL) cells. CLL cells were found to make low amounts of IFN via TANK-binding kinase 1 pathways, but p-STAT1 and -STAT2 proteins along with IFN-stimulated genes that reflect IFN activation were variably downregulated in cultured CLL cells by the neutralizing IFNAR1 Ab anifrolumab. Patients with CLL were segregated into two groups based on the response of their leukemia cells to anifrolumab. Samples associated with more aggressive clinical behavior indicated by unmutated IGHV genes along with high CD38 and p-Bruton’s tyrosine kinase expression exhibited responses to low amounts of IFN that were blocked by anifrolumab. Samples with more indolent behavior were unaffected by anifrolumab. Hypersensitivity to IFN was associated with higher expression of IFNAR1, MX1, STAT1, and STAT2 proteins and lower activity of negative regulatory tyrosine phosphatases. Autocrine IFN protected responsive CLL cells from stressful tissue culture environments and therapeutic drugs such as ibrutinib and venetoclax in vitro, in part by upregulating Mcl-1 expression. These findings suggest hypersensitivity to IFN may promote aggressive clinical behavior. Specific blockade of IFN signaling may improve outcomes for patients with CLL with higher-risk disease.

Evolution of Toll-like receptor 7/8 agonist therapeutics and their delivery approaches: From antiviral formulations to vaccine adjuvants

Imidazoquinoline derivatives (IMDs) and related compounds function as synthetic agonists of Toll-like receptors 7 and 8 (TLR7/8) and one is FDA approved for topical antiviral and skin cancer treatments. Nevertheless, these innate immune system-activating drugs have potentially much broader therapeutic utility; they have been pursued as antitumor immunomodulatory agents and more recently as candidate vaccine adjuvants for cancer and infectious disease. The broad expression profiles of TLR7/8, poor pharmacokinetic properties of IMDs, and toxicities associated with systemic administration, however, are formidable barriers to successful clinical translation. Herein, we review IMD formulations that have advanced to the clinic and discuss issues related to biodistribution and toxicity that have hampered the further development of these compounds. Recent strategies aimed at enhancing safety and efficacy, particularly through the use of bioconjugates and nanoparticle formulations that alter pharmacokinetics, biodistribution, and cellular targeting, are described. Finally, key aspects of the biology of TLR7 signaling, such as TLR7 tolerance, that may need to be considered in the development of new IMD therapeutics are discussed.

Agonist and antagonist ligands of toll-like receptors 7 and 8: Ingenious tools for therapeutic purposes

The discovery of the TLRs family and more precisely its functions opened a variety of gates to modulate immunological host responses. TLRs 7/8 are located in the endosomal compartment and activate a specific signaling pathway in a MyD88-dependant manner. According to their involvement into various autoimmune, inflammatory and malignant diseases, researchers have designed diverse TLRs 7/8 ligands able to boost or block the inherent signal transduction. These modulators are often small synthetic compounds and most act as agonists and to a much lesser extent as antagonists. Some of them have reached preclinical and clinical trials, and only one has been approved by the FDA and EMA, imiquimod. The key to the success of these modulators probably lies in their combination with other therapies as recently demonstrated. We gather in this review more than 360 scientific publications, reviews and patents, relating the extensive work carried out by researchers on the design of TLRs 7/8 modulators, which are classified firstly by their biological activities (agonist or antagonist) and then by their chemical structures, which total syntheses are not discussed here. This review also reports about 90 clinical cases, thereby showing the biological interest of these modulators in multiple pathologies.

Clinico-Biological Implications of Modified Levels of Cytokines in Chronic Lymphocytic Leukemia: A Possible Therapeutic Role

B-cell chronic lymphocytic leukemia (B-CLL) is the main cause of mortality among hematologic diseases in Western nations. B-CLL is correlated with an intense alteration of the immune system. The altered functions of innate immune elements and adaptive immune factors are interconnected in B-CLL and are decisive for its onset, evolution, and therapeutic response. Modifications in the cytokine balance could support the growth of the leukemic clone via a modulation of cellular proliferation and apoptosis, as some cytokines have been reported to be able to affect the life of B-CLL cells in vivo. In this review, we will examine the role played by cytokines in the cellular dynamics of B-CLL patients, interpret the contradictions sometimes present in the literature regarding their action, and evaluate the possibility of manipulating their production in order to intervene in the natural history of the disease.

Association of blood IgG with tumor necrosis factor-alpha and clinical course of chronic lymphocytic leukemia

The intrinsic humoral immunodeficiency of chronic lymphocytic leukemia (CLL) is often managed with immunoglobulin replacement therapy (IgRT) to maintain IgG levels in the low-normal range (6–8 g/L) but optimal targets for IgG and timing to commence IgRT are unclear. IgG levels fell near 6 g/L at rates of −0.85±0.14 g/L/year in 51 patients who required treatment for CLL within 4.5±0.4 years from initial diagnosis and − 0.27±0.04 g/L/year in 40 patients with progressive disease who remained untreated after 8.5±0.5 years. In contrast, endogenous IgG levels remained above 8 g/L in patients with highly indolent disease (n = 25) and TNFα and beta-2-microglobulin (β2M) in blood decreased when IgRT was used to increase IgG levels over 9 g/L. At 15 g/L but not 5 g/L, the IgRT product Hizentra® inhibited B cell receptor (BCR)-activation, TNFα production, and survival in vitro, particularly of CLL cells that spontaneously made little TNFα. These findings suggest deterioration of the humoral immune system is associated with progressive CLL and altering the dosing of IgRT to achieve higher than conventional IgG target levels may have therapeutic activity.

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Immunoglobulin levels decline at rates that reflect the clinical course of CLL.

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IgG levels over 10 g/L achieved with replacement therapy are associated with evidence of disease control in vivo and inhibition of BCR-mediated activation of CLL cells in vitro.

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Monitoring rates of decline of Ig levels in CLL patients gives biological information on disease severity.

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Appropriate IgG target levels for immunoglobulin replacement therapy in CLL may be much higher than for patients with other immunodeficiencies.

Janus and PI3-kinases mediate glucocorticoid resistance in activated chronic leukemia cells

Glucorticoids (GCs) such as dexamethasone (DEX) remain important treatments for Chronic Lymphocytic Leukemia (CLL) but the mechanisms are poorly understood and resistance is inevitable. Proliferation centers (PC) in lymph nodes and bone marrow offer protection against many cytotoxic drugs and circulating CLL cells were found to acquire resistance to DEX-mediated killing in conditions encountered in PCs including stimulation by toll-like receptor agonists and interactions with stromal cells. The resistant state was associated with impaired glucocorticoid receptor-mediated gene expression, autocrine activation of STAT3 through Janus Kinases (JAKs), and increased glycolysis. The JAK1/2 inhibitor ruxolitinib blocked STAT3-phosphorylation and partially improved DEX-mediated killing of stimulated CLL cells in vitro but not in CLL patients in vivo. An automated microscopy-based screen of a kinase inhibitor library implicated an additional protective role for the PI3K/AKT/FOXO pathway. Blocking this pathway with the glycolysis inhibitor 2-deoxyglucose (2-DG) or the PI3K-inhibitors idelalisib and buparlisib increased DEX-mediated killing but did not block STAT3-phosphorylation. Combining idelalisib or buparlisib with ruxolitinib greatly increased killing by DEX. These observations suggest that glucocorticoid resistance in CLL cells may be overcome by combining JAK and PI3K inhibitors.

PPAR-delta modulates membrane cholesterol and cytokine signaling in malignant B cells

A deeper understanding of the mechanisms that underlie aberrant signal transduction in B-cell cancers such as chronic lymphocytic leukemia (CLL) may reveal new treatment strategies. The lipid-activated nuclear receptor peroxisome proliferator-activated receptor delta (PPARδ) accounts for a number of properties of aggressive cancers and was found to enhance Janus kinase (JAK)-mediated phosphorylation of signal transducer and activator of transcription (STAT) proteins in B lymphoma cell lines and primary CLL cells. Autocrine production of cytokines such as IL10 and interferon-beta was not increased by PPARδ but signaling responses to these cytokines were amplified and associated with increased cholesterol biosynthesis and plasma membrane levels. Plasmalemmal cholesterol and STAT phosphorylation from type 1 interferons (IFNs) were increased by PPARδ agonists, transgenes and exogenous cholesterol, and decreased by cyclodextrin, PPARD deletion and chemical PPARδ inhibitors. Functional consequences of PPARδ-mediated perturbation of IFN signaling included impaired upregulation of co-stimulatory molecules. These observations suggest PPARδ modulates signaling processes in malignant B cells in part by altering cholesterol metabolism and changes the outcomes of signaling from cytokines such as IFNs. PPARδ antagonists may have therapeutic activity as anti-leukemic signal transduction modulators.

RNA-seq Profiles of Immune Related Genes in the Spleen of Necrotic Enteritis-afflicted Chicken Lines

The study aimed to compare the necrotic enteritis (NE)-induced transcriptome differences between the spleens of Marek’s disease resistant chicken line 6.3 and susceptible line 7.2 co-infected with Eimeria maxima/Clostridium perfringens using RNA-Seq. Total RNA from the spleens of two chicken lines were used to make libraries, generating 42,736,296 and 42,617,720 usable reads, which were assembled into groups of 29,897 and 29,833 mRNA genes, respectively. The transcriptome changes were investigated using the differentially expressed genes (DEGs) package, which indicated 3,255, 2,468 and 2,234 DEGs of line 6.3, line 7.2, and comparison between two lines, respectively (fold change ≥2, p<0.01). The transcription levels of 14 genes identified were further examined using qRT-PCR. The results of qRT-PCR were consistent with the RNA-seq data. All of the DEGs were analysed using gene ontology terms, the Kyoto Encyclopedia of Genes and Genomes (KEGG) database and the DEGs in each term were found to be more highly expressed in line 6.3 than in line 7.2. RNA-seq analysis indicated 139 immune related genes, 44 CD molecular genes and 150 cytokines genes which were differentially expressed among chicken lines 6.3 and 7.2 (fold change ≥2, p<0.01). Novel mRNA analysis indicated 15,518 novel genes, for which the expression was shown to be higher in line 6.3 than in line 7.2 including some immune-related targets. These findings will help to understand host-pathogen interaction in the spleen and elucidate the mechanism of host genetic control of NE, and provide basis for future studies that can lead to the development of marker-based selection of highly disease-resistant chickens.

Modes of action of TLR7 agonists in cancer therapy

From the numerous Toll-like receptor agonists, only TLR7 agonists have been approved for cancer treatment, although they are current restricted to topical application. The main target cells of TLR7 agonists are plasmacytoid dendritic cells, producing IFN-α and thus acting on other immune cells. Thereby dendritic cells acquire enhanced costimulatory and antigen-presenting capacity, priming an adaptive immune response. Besides NK cells, antigen-specific T cells are the main terminal effectors of TLR7 agonists in tumor therapy. This qualifies TLR7 agonists as vaccine adjuvants, which is currently being tested in clinical trials. However, the systemic application of TLR7 agonists shows insufficient efficacy, most likely owing to toxicity-limited dosing. The use of TLR7 agonists in combinational therapy holds the promise of synergistic activity and lower required doses.

Microenvironmental interleukin-6 suppresses toll-like receptor signaling in human leukemia cells through miR-17/19A

The regulation of toll-like receptor (TLR) signaling in a tumor microenvironment is poorly understood despite its importance in cancer biology. To address this problem, TLR7-responses of chronic lymphocytic leukemia (CLL) cells were studied in the presence and absence of a human stromal cell-line derived from a leukemic spleen. CLL cells alone produced high levels of tumor necrosis factor (TNF)-α and proliferated in response to TLR7-agonists. A signal transducer and activator of transcription 3 -activating stromal factor, identified as interleukin (IL)-6, was found to upregulate microRNA (miR)-17 and miR-19a, target TLR7 and TNFA messenger RNA, and induce a state of tolerance to TLR7-agonists in CLL cells. Overexpression of the miR-17-92 cluster tolerized CLL cells directly and miR-17 and miR-19a antagomiRs restored TLR7-signaling. Inhibition of IL-6 signaling with antibodies or small-molecule Janus kinase inhibitors reversed tolerization and increased TLR7-stimulated CLL cell numbers in vitro and in NOD-SCIDγc (null) mice. These results suggest IL-6 can act as tumor suppressor in CLL by inhibiting TLR-signaling.

Heterodimer-specific TLR2 stimulation results in divergent functional outcomes in B-cell precursor acute lymphoblastic leukemia

Reports of spontaneous acute lymphoblastic leukemia (ALL) remissions following severe bacterial infections suggest that bacterial components may trigger elimination of ALL. To date, TLR2, which recognizes a broad range of bacterial pathogens through TLR1 or TLR6 heterodimerization, has not been fully evaluated for direct effects on ALL. Studies investigating TLR2 signaling in other tumor cell types utilizing single ligands have yielded contradictory results, and comparative, heterodimer-specific analyses of TLR2 stimulation are lacking. In this study, we report that two well-characterized heterodimer-specific TLR2 ligands, Pam3 CSK4 (TLR2/1), and Pam2 CSK4 (TLR2/6), induce ALL cell lines and primary ALL samples to upregulate CD40 expression. However, only Pam3 CSK4 triggers Caspase-8-mediated apoptosis and sensitizes cells to vincristine-mediated cytotoxicity. Consistent with this result, stimulation of ALL cells through TLR2/1 or TLR2/6 activates Mal, p38 and the NF-κB and PI3K signaling pathways with divergent kinetics that may underlie their distinct downstream effects. Our results reveal a novel branching in downstream responses to heterodimer-specific TLR2 stimulation in ALL cells and emphasize the need for comparative studies to determine differential biological effects observed in specific tumor cells. Based on our results, TLR2/1 ligand Pam3 CSK4 possesses potential for generating anti-ALL activity through its direct effects on leukemic blasts.

Toll-like receptors and B cells: functions and mechanisms

Numerous reports have described Toll-like receptor (TLR) functions in myeloid cells such as dendritic cells (DCs) and macrophages, but relatively fewer studies have examined TLR responses in B lymphocytes. B cells express a wide variety of TLRs and are highly activated after TLR ligation, leading to enhancements in B cell survival, surface molecule expression, cytokine and antibody production, and antigen presentation. During an immune response, B cells can receive signals through TLRs as well as the B cell antigen receptor (BCR) and/or CD40. TLR ligation synergizes with signals through these receptors and augments both innate and adaptive immune functions of B lymphocytes. Additionally, targeting B cell TLRs may provide new therapies against certain types of cancer as well as autoimmune diseases. Here, we summarize TLR expression and contributions to both normal and pathogenic functions in mouse and human B cells.

Toll-like receptors in the pathogenesis of human B cell malignancies

Toll-like receptors (TLRs) are important players in B-cell activation, maturation and memory and may be involved in the pathogenesis of B-cell lymphomas. Accumulating studies show differential expression in this heterogeneous group of cancers. Stimulation with TLR specific ligands, or agonists of their ligands, leads to aberrant responses in the malignant B-cells. According to current data, TLRs can be implicated in malignant transformation, tumor progression and immune evasion processes. Most of the studies focused on multiple myeloma and chronic lymphocytic leukemia, but in the last decade the putative role of TLRs in other types of B-cell lymphomas has gained much interest. The aim of this review is to discuss recent findings on the role of TLRs in normal B cell functioning and their role in the pathogenesis of B-cell malignancies.

Radiation as immunomodulator: implications for dendritic cell-based immunotherapy

The last decade has witnessed significant progress in the field of cancer immunotherapy. This has, in part, been driven by a growing recognition that elements of the innate immune response can be harnessed to induce robust immunity against tumor-associated targets. Nonetheless, as clinically effective immunotherapy for the majority of cancers remains a distant goal, attention has shifted toward multimodality approaches to cancer therapy, sometimes combining novel immunotherapeutics and conventional therapeutics. The traditional view of radiation therapy as immunosuppressive has been challenged, prompting a re-evaluation of its potential as an adjunct to, or even a component of immunotherapy. Radiation therapy may enhance expression of tumor-associated antigens, induce targeting of tumor stroma, diminish regulatory T-cell activity and activate effectors of innate immunity such as dendritic cells through Toll-like receptor (TLR)-dependent mechanisms. Here, we review recent progress in the field of dendritic cell-based immunotherapy, evidence for radiation-induced antitumor immunity and TLR signaling and the results of efforts to rationally integrate radiation into dendritic cell-based immunotherapy strategies.

The activation of TLR7 regulates the expression of VEGF, TIMP1, MMP2, IL-6, and IL-15 in Hela cells

Toll-like receptors (TLRs) play important roles in activation of immunoreaction and tumor development. Toll-like receptor 7 (TLR7), one of the TLRs binding with single-stranded RNA, activates intracellular pathways and stimulates the release of proinflammatory cytokines, chemokines. In this study, we investigated the impact of the TLR7-signaling pathway on the expression of vascular endothelial growth factor (VEGF), matrix metalloproteinase 2 (MMP2), tissue inhibitor of metalloproteinase 1 (TIMP1), interleukin 6 (IL-6), and interleukin 15 (IL-15), which have been testified to refer to the immunomodulating and tumor progression. We confirmed that the TLR7 was expressed by Hela cells, despite the abundance was weak. Gardiquimod, one of the TLR7 ligands, can promote these five genes expression in varying degrees. After stimulating with gardiquimod, the expression of the IL-15V1, 3 increased about 4.5 times on RNA level, the other expression was only up-regulated about 2 times. We also discovered that gardiquimod could activate the MAPK/ERK- and PI3K/AKT-signaling pathways, and the specific inhibitors studies indicate that, the effect of gardiquimod on these genes expression is mainly or partially dependent on the activation of these two signaling pathways. To sum up, the activation of TLR7 signaling pathway may modulate some genes expression in Hela cells and may contribute to the pathogenesis of the cervical cancer.

Gardiquimod inhibits the expression of calcium-induced differentiation markers in HaCaT cells

Toll-like receptor 7 (TLR7) is an important member in pattern recognition receptors families. TLR7 signal pathway is involved in the physiological process in many type cells, but the impact of TRL7 on differentiation in the human keratinocytes is still unknown. In this study, we investigated the expression of TLR7 in keratinocytes, and the effect of TLR7 agonist gardiquimod on the expression of calcium (Ca(2+))-induced keratinocytes differentiation markers in HaCaT cells. Immunohistochemistry and western-blotting analysis showed that TLR7 is expressed in basal keratinocytes of normal skin and in the human keratinocyte cell line HaCaT, but not expressed in the keratinocytes of psoriasis lesions. Pretreatment with gardiquimod could down-regulate Ca(2+)-induced differentiation marker expression and activate Raf-MEK-ERK and PI3K-AKT signal pathways in HaCaT cells. However, specific inhibitors studies showed that the down-regulation of the differentiation markers expression by gardiquimod was not dependent on the activation of these two pathways. TLR7 may play an important role in the pathogenesis of psoriasis through regulating the differentiation of the keratinocytes, and will give a new insight into the psoriasis.

B cell receptor and antigens in CLL

Nowadays, chronic lymphocytic leukemia (CLL) is considered as a prototypic antigen-driven lymphoma, with antigenic stimuli from the microenvironment promoting tumor outgrowth. Antigen recognition is a function of both the clonotypic B cell receptor immunoglobulin (BcR IG) and various other immune sensors, e.g., the Toll-like receptors. The critical role of BcR IG-mediated signaling in CLL development and evolution is underscored by the following: the disease-biased IG gene repertoire; the subdivision of CLL based on the somatic hypermutation load of the BcR IG into two broad categories with vastly different prognosis and eventual outcome; the existence of subsets of cases with distinct, quasi-identical (stereotyped) BcR IGs; and the clinical efficacy of novel therapeutics inhibiting BcR signaling. Here, we trace the immunogenetic evidence for antigen selection in CLL and also consider the types of implicated antigens as well as the immune signaling pathways relevant for CLL ontogeny and clonal progression.

Distinct innate immunity pathways to activation and tolerance in subgroups of chronic lymphocytic leukemia with distinct immunoglobulin receptors

Subgroups of patients with chronic lymphocytic leukemia (CLL) have distinct expression profiles of Toll-like receptor (TLR) pathway-associated genes. To test the hypothesis that signaling through innate immunity receptors may influence the behavior of the malignant clone, we investigated the functional response triggered by the stimulation of TLRs and NOD2 in 67 CLL cases assigned to different subgroups on the basis of immunoglobulin heavy variable (IGHV ) gene usage, IGHV gene mutational status or B-cell receptor (BcR) stereotypy. Differences in the induction of costimulatory molecules and/or apoptosis were observed in mutated versus unmutated CLL. Different responses were also identified in subsets with stereotyped BcRs, underscoring the idea that "subset-biased" innate immunity responses may occur independently of mutational status. Additionally, differential modulation of kinase activities was induced by TLR stimulation of different CLL subgroups, revealing a TLR7-tolerant state for cases belonging to stereotyped subset #4. The distinct patterns of TLR/NOD2 functional activity in cells from CLL subgroups defined by the molecular features of the clonotypic BcRs might prove relevant for elucidating the immune mechanisms underlying CLL natural history and for defining subgroups of patients who might benefit from treatment with specific TLR ligands.

Differential oncogene-related gene expressions in myeloma cells resistant to prednisone and vincristine

Multidrug resistance in cancer may arise due to alterations in gene expression. In this study, sublines of drug-resistant multiple myeloma (MM) cells, namely RPMI-8226 and U-266, were examined for their differential oncogene-related gene expression levels and the relations to drug resistance were analyzed. Drug resistance was induced by application of the prednisone or vincristine using stepwise dose increments. XTT cytotoxicity assay was used for determination of resistance levels. Microarray analysis was carried out and the genes up- or downregulated more than two-folds were considered as significantly changed. Different types of oncogenes were altered in different drug-resistant RPMI-8226 and U-266 multiple myeloma sublines. The oncogenes which belong to Ras superfamily, especially Rho family of GTPases, were upregulated in prednisone-resistant MM cell lines whereas they were either downregulated or not changed in vincristine resistance. ETS and NF-κB2 are among transcription factors which were downregulated in prednisone-resistant cells. Transforming growth factor beta receptor (TGFß) was downregulated in prednisone-resistant MM cell lines while it was upregulated in vincristine-resistant cell lines. Different types of interleukin gene expressions were seen to be altered in resistant MM sublines whereas suppressors of cytokine signalling genes such as SOCS2, SOCS4 and WSB2 were all downregulated. In conclusion, it is seen that different drugs can induce totally different pathways leading to resistance in the same cancer cell lines. Every drug resistance should be evaluated separately. These facts must be considered in cancer chemotherapy and reversal of drug resistance.

Branched α-(1,4) glucans from Lentinula edodes (L10) in combination with radiation enhance cytotoxic effect on human lung adenocarcinoma through the Toll-like receptor 4 mediated induction of THP-1 differentiation/activation

This work investigated the role of structure in the binding of polysaccharides from 10 regionally different strains of Lentinula edodes to Toll-like receptor 4 (TLR-4) on monocytes (THP-1) and the potential effect of this interaction on tumor cell viability. Principal component analysis and multiple linear regression identified arabinose, glucose 1 → 4 linkage, and molecular weights about 2700 and 534 kDa as the significant determinant factors associated with TLR-4 binding activity. The branched α-(1,4)-glucan (L10) had the strongest ability to bind to TLR-4 and induce THP-1 cell differentiation. L10 induction of the THP-1 cell differentiation, superoxide production, and cytokine production followed the TLR-4/MyD88/IKK/NFκB pathway. Coculture of irradiated human lung adenocarcinoma A549 cells with L10-activated THP-1 cells resulted in significantly decreased percentage of viable A549 cells from 66 to 37% (p = 0.018), increased levels of superoxide, interleukin-8, and RANTES, and decreased levels of angiogenin and vascular endothelial growth factor. The results indicate that L10-activated monocytes have the potential to boost the antitumor immune response and antitumor activity of radiotherapy.

Toll-like receptor signaling pathway in chronic lymphocytic leukemia: distinct gene expression profiles of potential pathogenic significance in specific subsets of patients

BACKGROUND

Signaling through the B-cell receptor appears to be a major contributor to the pathogenesis of chronic lymphocytic leukemia. Toll-like receptors bridge the innate and adaptive immune responses by acting as co-stimulatory signals for B cells. The available data on the expression of Toll-like receptors in chronic lymphocytic leukemia are limited and derive from small series of patients.

DESIGN AND METHODS

We profiled the expression of genes associated with Toll-like receptor signaling pathways in 192 cases of chronic lymphocytic leukemia and explored potential associations with molecular features of the clonotypic B-cell receptors.

RESULTS

Chronic lymphocytic leukemia cells express all Toll-like receptors expressed by normal activated B cells, with high expression of TLR7 and CD180, intermediate expression of TLR1, TLR6, TLR10 and low expression of TLR2 and TLR9. The vast majority of adaptors, effectors and members of the NFKB, JNK/p38, NF/IL6 and IRF pathways are intermediately-to-highly expressed, while inhibitors of Toll-like receptor activity are generally low-to-undetectable, indicating that the Toll-like receptor-signaling framework is competent in chronic lymphocytic leukemia. Significant differences were identified for selected genes between cases carrying mutated or unmutated IGHV genes or assigned to different subsets with stereotyped B-cell receptors. The differentially expressed molecules include receptors, NFκB/MAPK signaling molecules and final targets of the cascade.

CONCLUSIONS

The observed variations are suggestive of distinctive activation patterns of the Toll-like receptor signaling pathway in subgroups of cases of chronic lymphocytic leukemia defined by the molecular features of B-cell receptors. Additionally, they indicate that different or concomitant signals acting through receptors other than the B-cell receptor can affect the behavior of the malignant clone.

Aberrant interferon-signaling is associated with aggressive chronic lymphocytic leukemia

The type I interferons (IFNs) normally suppress tumor growth by phosphorylating and activating the signal transducer and activator of transcription 1 (STAT1), but also briefly activate STAT3, which promotes cell growth. In chronic lymphocytic leukemia (CLL) cells, the duration of IFN-mediated STAT3 phosphorylation was found to exhibit significant interpatient variability and was prolonged in cells with high risk features, such as 11q- and 17p-deletions involving ataxia telangiectasia mutated (ATM) and p53. This aberrant signaling pattern was associated with a paradoxical increase in cell size and number in response to IFN and similar alterations in IFN-signaling and responses were seen in cell lines that developed in the absence of p53 or ATM. However, direct inhibition of p53 or ATM failed to cause these changes, and CLL cells with aggressive clinical features were found to also express high levels of reactive oxygen species (ROS), which decrease tyrosine phosphatase activity. Prolonged IFN-mediated STAT3 phosphorylation and lowered phosphatase activity could be reversed by antioxidants. These findings suggest that increased ROS levels may corrupt IFN-signaling processes in aggressive CLL cells, causing IFN to be used as a growth factor rather than a tumor suppressor. Antioxidants or STAT3 kinase inhibitors might improve the outcome of IFN therapy in CLL by restoring normal signaling.

Aberrant O-GlcNAcylation characterizes chronic lymphocytic leukemia

O-linked N-Acetylglucosamine (O-GlcNAc) post-translational modifications originate from the activity of the hexosamine pathway, and are known to affect intracellular signaling processes. As aberrant responses to microenvironmental signals are a feature of chronic lymphocytic leukemia (CLL), O-GlcNAcylated protein levels were measured in primary CLL cells. In contrast to normal circulating and tonsillar B cells, CLL cells expressed high levels of O-GlcNAcylated proteins, including p53, c-myc and Akt. O-GlcNAcylation in CLL cells increased following activation with cytokines and through toll-like receptors (TLRs), or after loading with hexosamine pathway substrates. However, high baseline O-GlcNAc levels were associated with impaired signaling responses to TLR agonists, chemotherapeutic agents, B cell receptor crosslinking and mitogens. Indolent and aggressive clinical behavior of CLL cells were found to correlate with higher and lower O-GlcNAc levels, respectively. These findings suggest that intracellular O-GlcNAcylation is associated with the pathogenesis of CLL, which could potentially have therapeutic implications.

Important aspects of Toll-like receptors, ligands and their signaling pathways

Due to the rapid increase of new information on the multiple roles of Toll-like receptors (TLRs), this paper reviews several main properties of TLRs and their ligands and signaling pathways. The investigation of pathogen infections in knockout mice suggests that specific TLRs play a key role in the activation of immune responses. Although the investigation of TLR biology is just beginning, a number of important findings are emerging. This review focuses on the following seven aspects of this emerging field: (a) a history of TLR and ligand studies; (b) the molecular basis of recognition by TLRs: TLR structures, pathogen-associated molecular pattern binding sites, TLR locations and functional responses; (c) cell types in TLR expression; (d) an overview of TLRs and their ligands: expression and ligands of cell-surface TLRs and of intracellular TLRs; (e) TLR-signaling pathways; (f) discussion: TLRs control of innate and adaptive systems; the trafficking of intracellular TLRs to endolysosomes; investigation of TLRs in regulating microRNA; investigation of crystal structure of TLRs with ligand binding; incidence of infectious diseases associated with single nucleotide polymorphisms (SNPs) in TLR genes; risk of cancer related to SNPs in TLR genes; TLR-ligand mediated anti-cancer effects; and TLR-ligand induced chronic inflammation and tumorigenesis; and (g) conclusions.

The role of toll-like receptors in chronic B-cell malignancies

Toll-like receptors (TLR) are key players in host defence from infection. They recognize a specific set of molecular patterns of microbial origin, immediately trigger an innate immune response, and bridge innate and adaptive immunity. TLR have also been shown to play a role in tumor development. In this context, chronic B-cell malignancies are an interesting example as clonal B lymphocytes remain responsive to and dependent on stimuli originating from the microenvironment which then become crucial for maintaining and propagating the disease. Emerging evidences suggest that, among other microenvironmental elements, TLR ligands may play a role in the pathogenesis of chronic B-cell lymphoid malignancies. Conceivably, their manipulation may find a place in specific settings of treatment of these tumors.

Pathogen recognition receptors, cancer and inflammation in the gut

The pathogen recognition receptors (PRRs) initiate immediate responses against infection and tissue damage to protect the host from microbial invasion. In response to mucosal damage, intestinal PRR signaling initiates damage repair processes. Recent advances appear to link PRR abnormalities and inflammatory as well as neoplastic intestinal disorders. Emerging evidence suggests a dual role of PRRs, in which they may simultaneously induce tumorigenesis and antitumor immunity. PRR may induce tumor cell proliferation by activating cell survival signaling mainly via NF-kappaB, but this signal can activate dendritic cells to promote antitumor immunity. TLR signaling within the tumor cells may result in evasion of immune surveillance, propagation of metastatic growth, or rather, induction of tumor cell apoptosis depending on ligands. Epithelial cells induce endogenous PRR ligands when damaged or during neoplastic transformation. Targeted manipulation of PRR signaling may provide emerging opportunities for the development of new therapeutic strategies for many gastrointestinal diseases.

Topical resiquimod promotes priming of CTL to parenteral antigens

We explored the topical use of resiquimod (R-848), a Toll-like receptor (TLR) 7/8 agonist, in gel formulation, to enhance cross-priming to subcutaneously administered protein antigen in a murine model. Resiquimod application at the time of subcutaneous administration of ovalbumin generated robust antigen-specific CTL as detected by tetramers, IFN-gamma ELISPOT assays and standard cytotoxicity assays. Induced CTL were capable of mediating antigen-specific killing in vivo as measured by in vivo cytotoxicity assays and an ability to protect against B16-OVA tumor challenge. Multiple serial applications of topical resiquimod increased the frequency of antigen-specific CTL when compared to single application. This enhanced frequency was noted despite a marked inhibition of adjuvant mediated pro-inflammatory cytokine release following repeated administration. Topical resiquimod is a potent adjuvant for locally administered subcutaneous vaccines, inducing clinically relevant CTL responses following single application at the time of subcutaneous vaccination.

Antigen receptor signals rescue B cells from TLR tolerance

Interactions between innate and adaptive immune receptors are critical for an optimal immune response, but the role played by Ag receptors in modulating innate receptor functions is less clear. TLRs are a family of pattern recognition receptors that play crucial roles in detecting microbial pathogens and subsequent development of immune responses. However, chronic stimulation through TLRs renders immune cells hyporesponsive to subsequent stimulation with TLR ligands, a phenomenon known as TLR tolerance, well characterized in myeloid cells. However, it has not been studied in detail in B lymphocytes. In addition to the BCR, B cells express almost all known TLRs and respond robustly to many TLR ligands. Thus, B cells may receive signals through both TLRs and BCR during an infection and may respond differently to TLR stimulation than myeloid cells. We tested this possibility by stimulating repeatedly through either TLR alone or both TLR and BCR. Prestimulation through TLR7 resulted in reduced B cell proliferation, cytokine production, and IgM secretion upon subsequent TLR7 restimulation. The hyporesponsiveness to TLR7 restimulation was associated with reduced NF-kappaB and MAPK activation and defective c-Jun phosphorylation. However, simultaneous BCR signaling prevented or reversed TLR7 tolerance in both mouse and human B cells. Importantly, BCR signaling also rescued B cells from TLR7-mediated TLR9 tolerance. Additionally, the reversal of TLR7-mediated JNK activation was dependent on PI3K activation. Together these results present a novel mechanism to prevent and reverse TLR tolerance in B cells.

Prevention of autoimmune disease by induction of tolerance to Toll-like receptor 7

Activation of Toll-like receptors (TLR) contributes to the initiation and maintenance of chronic inflammation in autoimmune diseases, yet repeated exposure to a TLR agonist can induce hyporesponsiveness to subsequent TLR stimulation. Here, we used a synthetic TLR7 agonist, 9-benzyl-8-hydroxy-2-(2-methoxyethoxy) adenine (SM360320, 1V136) to study TLR7 induced attenuation of inflammatory responses and its application to autoimmune diseases. Repeated low dose administration of this TLR7 agonist induced hyporesponsiveness or tolerance to TLR2, -7, and -9 activators and limited the course of neural inflammation in an experimental allergic encephalomyelitis model. The hyporesponsiveness did not depend on T or B lymphocytes, but did require bone marrow derived cells. In addition, TLR7 tolerance reduced inflammation in a passive antibody mediated arthritis model. TLR7 tolerance did not cause global immunosuppression, because susceptibility to Listeria monocytogenes infection was not altered. The mechanism of TLR7 tolerance involved the up-regulation of 2 inhibitors of TLR signaling: Interleukin 1 Receptor Associated Kinase (IRAK) M, and Src homology 2 domain-containing inositol polyphosphate phosphatase (SHIP)-1. These findings suggest that induction of TLR7 tolerance might be a new therapeutic approach to subdue inflammation in autoimmune diseases.

Toll-like receptors and their role in carcinogenesis and anti-tumor treatment

Toll-like receptors (TLRs) have been described as major components of the innate immune system, recognizing the conserved molecular structures found in the large groups of pathogens called pathogen-associated molecular patterns (PAMPs). TLR expression is ubiquitous, from epithelial to immunocompetent cells. TLR ligation triggers several adapter proteins and downstream kinases, leading to the induction of key pro-inflammatory mediators but also anti-inflammatory and anti-tumor cytokines. The result of this activation goes beyond innate immunity to shape the adaptive responses against pathogens and tumor cells, and maintains host homeostasis via cell debris utilization. TLRs have already become potent targets in infectious disease treatment and vaccine therapy and in neoplastic disease treatment, due to their ability to enhance antigen presentation. However, some studies show the dual effect of TLR stimulation on malignant cells: they can be proapoptotic or promote survival under different conditions. It is therefore crucial to design further studies assessing the biology of these receptors in normal and transformed cells. The established role of TLRs in human disease therapy is based on TLR7 and TLR4 agonists, respectively for the novel treatment of some types of skin cancer and for the anti-hepatitis B virus vaccine. Some clinical trials involving TLR agonists as potent enhancers of the anti-tumor response in solid tumors have begun.

Expression and function of toll like receptors in chronic lymphocytic leukaemia cells

Mature B-cells can recognize microbial antigens via B-cell-receptor (BCR) in a specific way and via Toll-like receptors (TLR) in a costimulatory manner. A wealth of information is gathering on the possible role of antigenic stimulation in the natural history of Chronic Lymphocytic Leukaemia (CLL). However little is known regarding the repertoire and function of TLR in CLL cells. The TLR family includes 10 different transmembrane proteins devoted to recognize specific pathogen-associated molecular patterns and to alarm immunocompetent cells to trigger an immune response. Here, we studied fresh leukaemic cells for the expression pattern of TLR1 to TLR10, NOD1, NOD2 and SIGIRR (also known as TIR8). CLL cells were found to express several pattern recognition receptors including TLR1, TLR2, TLR6, TLR10, NOD1 and NOD2. The specific TLR expressed by CLL cells were functional. Leukaemic cells, upon stimulation with TLR1/2/6 ligands, such as bacterial lipopeptides, activated the nuclear factor-kappaB signalling pathway, expressed CD86 and CD25 activation molecules, and were protected from spontaneous apoptosis. These findings further support the hypothesis that CLL cells resemble antigen-activated B-cells and suggest a potential role of TLR in modulating CLL cell response in the context of specific antigen recognition.

Toll-like receptors: lessons to learn from normal and malignant human B cells

The humoral immune system senses microbes via recognition of specific microbial molecular motifs by Toll-like receptors (TLRs). These encounters promote plasma cell differentiation and antibody production. Recent studies have demonstrated the importance of the TLR system in enhancing antibody-mediated defense against infections and maintaining memory B cells. These results have led the way to the design of vaccines that target B cells by engaging TLRs. In hematologic malignancies, cells often retain B cell-specific receptors and associated functions. Among these, TLRs are currently exploited to target different subclasses of B-cell leukemia, and TLR agonists are currently being evaluated in clinical trials. However, accumulating evidence suggests that endogenous TLR ligands or chronic infections promote tumor growth, thus providing a need for further investigations to decipher the exact function of TLRs in the B-cell lineage and in neoplastic B cells. The aim of this review is to present and discuss the latest advances with regard to the expression and function of TLRs in both healthy and malignant B cells. Special attention will be focused on the growth-promoting effects of TLR ligands on leukemic B cells and their potential clinical impact.

Radiation therapy and Toll-like receptor signaling: implications for the treatment of cancer

The identification of pathogen-associated molecular patterns, conserved microbial structures that act on Toll-like receptors, has led to a novel avenue of investigation aimed at developing a new generation of cancer immunotherapies. Ligation of Toll-like receptors results in the induction of robust immune responses that may be directed against tumor-associated antigens. Recent data suggest that such strategies may result in enhanced antitumor immunity. Nonetheless, as clinically effective immunotherapy for cancer remains a somewhat distant goal, attention has shifted toward multimodality approaches to cancer therapy, sometimes combining novel immune interventions and conventional treatments. The traditional view of radiation therapy as immunosuppressive has now been challenged, prompting a re-evaluation of its potential as an adjunct to immunotherapy. Radiation therapy can enhance the expression of tumor-associated antigens, induce immune-mediated targeting of tumor stroma, and diminish regulatory T cell activity. Recent evidence suggests that radiation therapy may also activate effectors of innate immunity through TLR-dependent mechanisms, thereby augmenting the adaptive immune response to cancer. In this paper, we will review evidence for enhanced tumor-directed immunity resulting from radiation exposure and early promising data suggesting synergistic effects of radiation and TLR-targeted immunotherapies.

Toll-like receptors: key activators of leucocytes and regulator of haematopoiesis

Toll-like receptors (TLRs) play a critical role in the induction of the immune response to invading pathogens. The detection of pathogens by TLRs initiates a signalling cascade that results in the activation of transcription factors such as nuclear factor (NF)-kappaB and interferon regulatory factors leading to the production of pro-inflammatory cytokines and type 1 interferons. Five cytoplasmic adaptors, MyD88, Mal, Trif, TRAM and SARM, are utilized by the TLRs to activate these signalling pathways. Through the years the main focus of research has been on the activation and function of TLRs in monocytic cells. This review discusses several additional roles of TLRs. TLR activation plays a role in influencing the differentiation of haematopoietic stem cells. Their activation also prevents apoptosis in neutrophils following pathogen invasion. B cells and T cells proliferation and differentiation is influenced by TLR activation and the possible therapeutic benefits of using TLR ligands for the treatment of chronic lymphocytic leukaemia will also be discussed.