Phosphorothioate-modified TLR9 ligands protect cancer cells against TRAIL-induced apoptosis

Tilsotolimod: an investigational synthetic toll-like receptor 9 (TLR9) agonist for the treatment of refractory solid tumors and melanoma

INTRODUCTION

Cancer immunotherapy has seen tremendous strides in the past 15 years, with the introduction of several novel immunotherapeutic agents. Nevertheless, as clinical practice has shown, significant challenges remain with a considerable number of patients responding sub-optimally to available therapeutic options. Research has demonstrated the important immunoregulatory role of the tumor microenvironment (TME), with the potential to either hinder or promote an effective anti-tumor immune response. As such, scientific efforts have focused on investigating novel candidate immunomodulatory agents with the potential to alter the TME toward a more immunopotentiating composition.

AREAS COVERED

Herein, we discuss the novel investigational toll-like receptor 9 agonist tilsotolimod currently undergoing phase II and III clinical trials for advanced refractory cancer, highlighting its mode of action, efficacy, tolerability, and potential future applications in the treatment of cancer. To this effect, we conducted an exhaustive Web of Science and PubMed search to evaluate available research on tilsotolimod as of August 2021.

EXPERT OPINION

With encouraging early clinical results demonstrating extensive TME immunomodulation and abscopal effects on distant tumor lesions, tilsotolimod has emerged as a potential candidate immunomodulatory agent with the possibility to augment currently available immunotherapy and provide novel avenues of treatment for patients with advanced refectory cancer.

Hsp90 Inhibitor SNX-2112 Enhances TRAIL-Induced Apoptosis of Human Cervical Cancer Cells via the ROS-Mediated JNK-p53-Autophagy-DR5 Pathway

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent cancer cell apoptosis-inducing factor that can induce apoptosis in a variety of cancer cells. However, resistance to TRAIL in cancer cells is a huge obstacle in creating effective TRAIL-targeted clinical therapies. Thus, agents that can either enhance the effect of TRAIL or overcome its resistance are needed. In this study, we combined TRAIL with SNX-2112, an Hsp90 inhibitor we previously developed, to explore the effect and mechanism that SNX-2112 enhanced TRAIL-induced apoptosis in cervical cancer cells. Our results showed that SNX-2112 markedly enhanced TRAIL-induced cytotoxicity in HeLa cells, and this combination was found to be synergistic. Additionally, we found that SNX-2112 sensitized TRAIL-mediated apoptosis caspase-dependently in TRAIL-resistant HeLa cells. Mechanismly, SNX-2112 downregulated antiapoptosis proteins, including Bcl-2, Bcl-XL, and FLIP, promoted the accumulation of reactive oxygen species (ROS), and increased the expression levels of p-JNK and p53. ROS scavenger NAC rescued SNX-2112/TRAIL-induced apoptosis and suppressed SNX-2112-induced p-JNK and p53. Moreover, SNX-2112 induced the upregulation of death-receptor DR5 in HeLa cells. The silencing of DR5 by siRNA significantly decreased cell apoptosis by the combined effect of SNX-2112 and TRAIL. In addition, SNX-2112 inhibited the Akt/mTOR signaling pathway and induced autophagy in HeLa cells. The blockage of autophagy by bafilomycin A1 or Atg7 siRNA abolished SNX-2112-induced upregulation of DR5. Meanwhile, ROS scavenger NAC, JNK inhibitor SP600125, and p53 inhibitor PFTα were used to verify that autophagy-mediated upregulation of DR5 was regulated by the SNX-2112-stimulated activation of the ROS-JNK-p53 signaling pathway. Thus, the combination of SNX-2112 and TRAIL may provide a novel strategy for the treatment of human cervical cancer by overcoming cellular mechanisms of apoptosis resistance.

Oral administration of PLGA-encapsulated CpG ODN and Campylobacter jejuni lysate reduces cecal colonization by Campylobacter jejuni in chickens

Campylobacter jejuni (C. jejuni) is a major cause of bacterial food-borne illness in humans. It is considered a commensal organism of the chicken gut and infected chickens serve as a reservoir and shed bacteria throughout their lifespan. Contaminated poultry products are considered the major source of infection in humans. Therefore, to reduce the risk of human campylobacteriosis, it is essential to reduce the bacterial load in poultry products. The present study aimed to evaluate the protective effects of soluble and PLGA-encapsulated oligodeoxynucleotides (ODN) containing unmethylated CpG motifs (E-CpG ODN) as well as C. jejuni lysate as a multi-antigen vaccine against colonization with C. jejuni. The results revealed that oral administration of a low (5 µg) or high (50 µg) dose of CpG resulted in a significant reduction in cecal C. jejuni colonization by 1.23 and 1.32 log₁₀ (P < .05) in layer chickens, respectively, whereas E-CpG significantly reduced cecal C. jejuni colonization by 1.89 and 1.46 log₁₀ in layer and broiler chickens at day 22 post-infection (slaughter age in broilers), respectively. Similar patterns were observed for C. jejuni lysate; oral administration of C. jejuni lysate reduced the intestinal burden of C. jejuni in layer and broiler chickens by 2.24 and 2.14 log₁₀ at day 22 post-infection, respectively. Moreover, the combination of E-CpG and C. jejuni lysate reduced bacterial counts in cecal contents by 2.42 log₁₀ at day 22 post-infection in broiler chickens. Anti-C. jejuni IgG antibody (Ab) titers were significantly higher for broiler chickens receiving a low or high dose of E-CpG or a low dose of C. jejuni lysate than for chickens receiving the placebo. Furthermore, a positive correlation was observed between serum IgG Ab titers and cecal counts of C. jejuni in these groups. These findings suggest that PLGA-encapsulated CpG or C. jejuni lysate could be a promising strategy for control of C. jejuni in chickens.

Bacterial flagellin-a potent immunomodulatory agent

Flagellin is a subunit protein of the flagellum, a whip-like appendage that enables bacterial motility. Traditionally, flagellin was viewed as a virulence factor that contributes to the adhesion and invasion of host cells, but now it has emerged as a potent immune activator, shaping both the innate and adaptive arms of immunity during microbial infections. In this review, we summarize our understanding of bacterial flagellin and host immune system interactions and the role flagellin as an adjuvant, anti-tumor and radioprotective agent, and we address important areas of future research interests.

Innate adjuvant receptor Toll-like receptor 3 can promote breast cancer through cell surface

Toll-like receptor 3 has been targeted in different cancers for adjuvant therapy. The ligand-mediated effects of TLR-3 on cancer cells are discordant. In the present work, we have addressed the hypothesis possibility of cell membrane-bound action of TLR-3 in breast cancer to justify its pro-tumor effect. TLR-3 was stimulated by Poly (I:C) on the surface of human breast cancer cells MCF-7 and MDA-MB-231 for up to 72 h. To check the cell survival and growth, thiazol blue tetrazolium bromide (MTT) assay, apoptosis assay, and cell cycle analysis were carried out. For changes in the metastatic properties, in vitro colony formation assay, scratch-wound healing assay and adhesion assay were also done. Using real-time PCR and immunocytochemistry, expression of E-cadherin, was studied. To determine the affect of cytoplasmic stimulation, Poly (I:C) was delivered with lipid transfection reagent. The results of the aforesaid experiments showed that there was a gradual increase of cellular survivability, growth, and metastasis after the cell surface stimulation of TLR-3 with Poly (I:C). Interestingly, E-cadherin expression was increased both at transcriptional and translational level. On the other hand, when Poly (I:C) was delivered in the cytoplasm by lipid transfecting medium, the cells survivability was decreased. For the first time, in the present work, we are convincingly reporting the functional evidence that TLR-3 induces cell survivability and metastasis through cell surface. The present work may help for the proper understanding of the adjuvant therapy of breast cancer.

Phosphorothioate modification of the TLR9 ligand CpG ODN inhibits poly(I:C)-induced apoptosis of hepatocellular carcinoma by entry blockade

Toll-like receptors (TLRs) play a crucial role in the innate immune response and subsequent induction of adaptive immune responses. Recently, it has been noted that TLRs on tumor cells are involved in tumor development, and several TLR agonists, such as the TLR3 agonist poly(I:C) and the TLR9 agonist CpG ODN, are being developed as vaccine adjuvants and cancer immunotherapeutics. In this study, we investigated whether combining poly(I:C) with a TLR9 agonist CpG ODN would result in a stronger anti-tumor effect on hepatocellular carcinoma cells (HCCs). Surprisingly, we found that simultaneous transfection of poly(I:C) and ODN M362 exhibited a lower pro-apoptotic effect on HCCs than transfection with poly(I:C) alone. Simultaneous co-transfection was accompanied by down-regulation of poly(I:C)-related innate receptors, pro-inflammatory cytokines and apoptotic genes induced by poly(I:C), indicating that ODN M362 blocked the activation of poly(I:C)-triggered intrinsic immune responses and cellular apoptosis. Further studies indicated that these effects were partly due to the phosphorothioate-modification of CpG ODN, which blocked the entry of poly(I:C) into tumor cells. This entry blockade was avoided by administering poly(I:C) after CpG ODN. Moreover, poly(I:C)-mediated pro-apoptotic effects were enhanced in vitro and in vivo by pre-treating HCC cells with CpG ODN. Our findings thus suggest that when combining poly(I:C) and CpG ODN for cancer therapy, these agents should be used in an alternating rather than simultaneous manner to avoid the blocking effect of phosphorothioate-modified TLR9 ligands.

Two death-inducing human TRAIL receptors to target in cancer: similar or distinct regulation and function?

The emergence during evolution of two tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors, receptor-1/DR4 and -2/DR5, able to induce apoptosis has raised the question whether they differ in function and regulation, which is of key importance for selecting either DR4 or DR5 selective pro-apoptotic agents for cancer treatment. In this review we found practically no information regarding possible differences in DR4 and DR5 function based on structural differences. On the other hand, a panel of different DR4 or DR5 selective pro-apoptotic agonists have been developed that were explored for efficacy in different tumour types in a large number of studies. Leukemic cells appear mainly sensitive for DR4-induced apoptosis, contrasting the situation in other tumour types that show heterogeneity in receptor preference and, in some cases, a slight overall preference for DR5. Both receptors were found to mediate intracellular stress-induced apoptosis, although this is most frequently reported for DR5. Interestingly, DR5 was also found to transmit non-apoptotic signalling in resistant tumour cells and recently nuclear localization and a role in microRNA maturation has been described. DR4 expression is most heavily regulated by promoter methylation, intracellular trafficking and post-translational modifications. DR5 expression is predominantly regulated at the transcriptional level, which may reflect its ability to respond to cellular stressors. It will be important to further increase our understanding of the mechanisms determining TRAIL receptor preference in order to select the appropriate TRAIL receptor selective agonists for therapy, and to develop novel strategies to enhance apoptosis activation in tumours.

Non-invasive imaging of Toll-like receptor 5 expression using 131I-labeled mAb in the mice bearing H22 tumors

Toll-like receptor 5 (TLR5) is overexpressed in several cancers and metastases, and presents an enticing target for molecular imaging of primary tumors. In the present study, ¹³¹I-anti-TLR5 monoclonal antibody (mAb) was evaluated for its use as a novel radiotracer for imaging hepatocarcinoma in mice bearing H22 tumors. The expression of TLR5 was analyzed by quantitative polymerase chain reaction and immunohistochemistry. The anti-TLR5 mAb and isotype immunoglobulin G (IgG) were radiolabeled with iodine-131 by the Iodogen method. The in vitro stability of iodinalized probes was determined in serum or saline for a series of times, and then evaluated with radio-thin-layer chromatography. The biodistribution study and autoradiography were performed in H22 tumor-bearing mice. It was found that H22-xenografted tumor tissue exhibited a higher level of TLR5 expression compared with normal liver tissues. ¹³¹I-anti-TLR5 mAb and ¹³¹I-IgG were obtained subsequent to purification, with high radiochemical purity (>95%), and remained stable for 48 h in human serum. The target-to-non-target ratio in the ¹³¹I-anti-TLR5 mAb group was significantly higher compared with the ¹³¹I-IgG group. The biodistribution study and autoradiography demonstrated that ¹³¹I-anti-TLR5 mAb was specifically retained in hepatocarcinoma with a high tumor uptake. Altogether, these results show that ¹³¹I-anti-TLR5 mAb is capable of detecting lesions in a TLR5-expressing tumor, with high target selectivity, and may offer a promising agent for hepatocarcinoma diagnosis and encourage further investigation.

Postallograft lenalidomide induces strong NK cell-mediated antimyeloma activity and risk for T cell-mediated GvHD: Results from a phase I/II dose-finding study

Lenalidomide may prevent relapses after allogeneic stem cell transplantation by promoting the immune-mediated graft-versus-tumor effect. We performed a prospective phase I/II study to define the dose-limiting toxicity and the immunologic effects of lenalidomide given early (day 100-180) after allograft for four cycles in patients with multiple myeloma. According to the Fibonacci design, 24 patients with a median age of 53 years were included. Dose-limiting toxicity was organ toxicity owing to graft-versus-host disease, and the maximum tolerable dose was 5 mg. The incidence of graft-versus-host disease after lenalidomide was 38%, occurring after a median of 22 days, and was beside organ toxicity, a leading cause to discontinue the study in 29% of the patients. Immune monitoring revealed a significant increase in peripheral γ-interferon-secreting CD4(+) and CD8(+) T cells within the first week of lenalidomide treatment followed by a delayed increase in T regulatory cells. Furthermore, natural killer (NK) cells isolated from the peripheral blood of patients evidenced a significantly improved antimyeloma activity after lenalidomide treatment. The immune effect might have contributed to the increased CR rate from 24-42% after lenalidomide treatment because nonresponding patients showed significantly less natural killer and T cell activation. (Study registered under: NCT 00778752.).

Antitumor effects of cytoplasmic delivery of an innate adjuvant receptor ligand, poly(I:C), on human breast cancer

Innate adjuvant receptors are expressed in immune cells and some types of cancers. If antitumor therapies targeting these receptors are established, it is likely that they will be therapeutically beneficial because antitumor effects and immune-cell activation can be induced simultaneously. In this study, we tested this possibility of using an innate adjuvant receptor ligand, polyinosinic-polycytidylic acid [poly(I:C)], to treat human breast cancer cell lines. Three breast cancer cell lines (MCF-7, MDA-MB-231, and BT-549) were used in this study. Poly(I:C) was transfected into these cancer cells to stimulate melanoma differentiation-associated gene (MDA) 5, which is a cytoplasmic adjuvant receptor. Poly(I:C) transfection significantly reduced the viability of all cell lines in a manner partially dependent on MDA5. Flow cytometeric analyses and immunoblot assays revealed that the antitumor effect depended on both caspase-dependent apoptosis and c-Myc- and cyclinD1-dependent growth arrest. Interestingly, poly(I:C) transfection was accompanied by autophagy, which is thought to protect cancer cells from apoptosis after poly(I:C) transfection. In a xenograft mouse model, local transfection of poly(I:C) significantly inhibited the growth of xenografted MDA-MB-231 cells. Our findings indicate that cytoplasmic delivery of poly(I:C) can induce apoptosis and growth arrest of human breast cancer cells, and that therapy-associated autophagy prevents apoptosis. The results of this study suggest that the innate adjuvant receptors are promising targets and that their ligands could serve as antitumor reagents, which have the potential to simultaneously induce antitumor effects and activate immune cells.

Cell death via DR5, but not DR4, is regulated by p53 in myeloma cells

Myeloma cells are sensitive to TRAIL through the two death receptors DR4 and DR5. Because p53 directly modulates expression of death receptors, we investigated here whether p53 can modulate myeloma sensitivity to TRAIL. We found that p53 affects the sensitivity of myeloma cells to the DR5 agonistic human antibody lexatumumab but not the DR4 antibody mapatumumab. TP53 wild-type myeloma cells overexpressed DR5 in correlation with sensitivity to lexatumumab. Both nongenotoxic (nutlin-3a) and genotoxic (melphalan) p53-inducing stresses increased DR5 expression only in TP53 wild-type cells and synergistically increased lexatumumab efficiency yet did not increase DR4 expression, nor sensitivity to mapatumumab. Silencing of p53 strongly decreased DR5 expression and induced resistance to nutlin-3a and lexatumumab but did not modulate DR4 expression or sensitivity to mapatumumab. Increase of lexatumumab efficiency induced by nutlin-3a was related to a p53-dependent increase of DR5 expression. In primary myeloma cells, nutlin-3a increased DR5 expression and lexatumumab efficiency but did not increase mapatumumab efficiency. Taken together, our findings indicate that p53 controls the sensitivity of myeloma through DR5 but not DR4 and suggest that a subset of patients with multiple myeloma may benefit from DR5 therapy.

Survey of the 2009 commercial optical biosensor literature

We took a different approach to reviewing the commercial biosensor literature this year by inviting 22 biosensor users to serve as a review committee. They set the criteria for what to expect in a publication and ultimately decided to use a pass/fail system for selecting which papers to include in this year's reference list. Of the 1514 publications in 2009 that reported using commercially available optical biosensor technology, only 20% passed their cutoff. The most common criticism the reviewers had with the literature was that "the biosensor experiments could have been done better." They selected 10 papers to highlight good experimental technique, data presentation, and unique applications of the technology. This communal review process was educational for everyone involved and one we will not soon forget.

TLR9 ligand induces the generation of CD20+ plasmablasts and plasma cells from CD27+ memory B-cells

Plasma cells (PCs) have a heterogeneous phenotype in humans. While bone marrow PCs are CD20-CD138+, tonsil PCs are CD20+CD138+/- and peripheral plasmablasts (PBs) are CD20-CD138-. In vitro, PCs are mainly generated by the activation of CD27+ memory B-cells through transient stimulation of CD40, and their phenotype appears similar to that of bone marrow PCs. While CD20 expression is lost at the plasmablastic stage, CD138 expression appears only at the PC stage. Thus, the CD20+CD138± phenotype of tonsil PCs does not represent an intermediate stage in the differentiation of memory B-cells into PCs. Because it has been previously shown that TLR9 activation was more able than CD40 stimulation to induce the differentiation of IgM+ CD27+ B-cells, we wondered whether TLR9 or CD40 stimulation would induce the same phenotype of PCs. Thus, we compared the differentiation of CD27+ B-cells isolated from either the tonsils or peripheral blood and stimulated with either CD40L-expressing fibroblasts or a TLR9 ligand, CpG oligodeoxynucleotide (CpG ODN). We observed that CpG ODN mainly induced CD27+ B-cell differentiation into CD20+CD38+CD138- PBs and CD20+CD38+CD138± PCs, which appear similar to tonsil PCs. Removal of CpG ODN during differentiation induced a decrease in the CD20+ plasmablastic population, and, conversely, stimulation of CD40L-induced pre-plasmablasts with CpG ODN increased the population of CD20+CD38+ PBs. Analysis of Ig secretion showed that CpG ODN induced increased IgM secretion compared to CD40L. PCs from patients with multiple myeloma, the malignant counterpart of bone marrow PCs, rarely express CD20. We show that CpG ODN did not induce or increase CD20 in nine IgG or IgA myeloma cell lines. These data strongly suggest that CpG ODN mainly targets CD27+ IgM+ B-cells.

Toll-like receptor 9 is a novel biomarker for esophageal squamous cell dysplasia and squamous cell carcinoma progression

BACKGROUND

Stimulation of Toll-like receptor 9 (TLR9) has been linked to invasion in various cancer cells in vitro. We investigated TLR9 expression in normal, dysplastic and malignant esophageal squamous epithelium.

METHODS

TLR9 expression was analyzed by immunohistochemistry in 46 cases of esophageal squamous cell carcinoma, including 12 cases with adjacent squamous dysplasia and 24 cases with normal esophageal epithelium. TLR9 expression was compared with tumor grade, stage, proliferation, apoptosis and vascular density.

RESULTS

In normal esophageal squamous epithelium, TLR9 staining intensity decreased linearly from the basal layers to the superficial layers (p < 0.001). Strong TLR9 expression was detected across full thickness of high-grade dysplasia, the intensity clearly differing from the normal squamous epithelium and squamous cell carcinoma (p < 0.001). All squamous cell carcinomas exhibited TLR9 expression that was positively associated with a high grade (p < 0.05), the presence of lymph node metastases (p < 0.05) and previously undetected distant metastases (p < 0.05).

CONCLUSIONS

Expression of TLR9 in the basal parts of normal esophageal epithelium suggests a role related to cell proliferation and differentation. TLR9 upregulation detected in dysplastic epithelium and in disseminated carcinomas indicates that this protein may serve as a novel marker for esophageal squamous dysplasia and carcinoma with metastatic potential.

Activation of Toll-like receptor 5 on breast cancer cells by flagellin suppresses cell proliferation and tumor growth

Increasing evidence showed that Toll-like receptors (TLR), key receptors in innate immunity, play a role in cancer progression and development but activation of different TLRs might exhibit the exact opposite outcome, antitumor or protumor effects. TLR function has been extensively studied in innate immune cells, so we investigated the role of TLR signaling in breast cancer epithelial cells. We found that TLR5 was highly expressed in breast carcinomas and that TLR5 signaling pathway is overly responsive in breast cancer cells. Interestingly, flagellin/TLR5 signaling in breast cancer cells inhibits cell proliferation and an anchorage-independent growth, a hallmark of tumorigenic transformation. In addition, the secretion of soluble factors induced by flagellin contributed to the growth-inhibitory activity in an autocrine fashion. The inhibitory activity was further confirmed in mouse xenografts of human breast cancer cells. These findings indicate that TLR5 activation by flagellin mediates innate immune response to elicit potent antitumor activity in breast cancer cells themselves, which may serve as a novel therapeutic target for human breast cancer therapy.

Toll-like receptor 9 agonists as cancer therapeutics

INTRODUCTION

Toll-like receptor 9 (TLR9) agonists, commonly referred to as CpG oligodeoxynucleotides (ODN), have been added to the arsenal of anti-cancer drugs as monotherapy or in combination with chemotherapy, radiotherapy and other immunotherapeutic approaches as they increase antigen presentation and boost anti-tumor T- and B-cell responses. Several synthetic TLR9 agonists have been developed for clinical grade use and displayed substantial efficacy in the preclinical and clinical models.

AREAS COVERED

This review summarizes TLR9 signaling and the impact of TLR9 agonists on the immune response. The most recent experimental and clinical data are analyzed as well as the development of new TLR9 agonists in current clinical trials.

EXPERT OPINION

Application of TLR9 agonists, in particular, combination strategies with chemo- or radiotherapy seem a promising and efficient immunotherapeutic approach in cancer patients even with refractory disease. Simultaneous application of TLR9 agonists aims at supporting the patient's immune response and overcoming specific immunosuppressant strategies developed by tumors. Combinatory approaches of the future might also seek for synergism of TLR9 agonists with other immunomodulatory strategies such as B-cell activation using the CD40-CD40L system.

A potential mechanism of rituximab-induced inhibition of tumor growth through its sensitization to tumor necrosis factor-related apoptosis-inducing ligand-expressing host cytotoxic cells

Rituximab (anti-CD20 mAb) mediates antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis in B-NHL cells. The contribution of other host-mediated cytotoxic effects has not been examined. The expression of death-inducing ligands (e.g. TRAIL) by host effector cells may contribute to the mechanism of tumor cell destruction in vivo by rituximab-mediated sensitization of resistant B-cell non-Hodgkin lymphoma (B-NHL) cells. We have examined the sensitizing activity of rituximab on B-NHL cell lines resistant to TRAIL (as model) and natural killer (NK)-induced apoptosis. Treatment of TRAIL-resistant B-NHL cell lines with rituximab sensitized the cells to TRAIL apoptosis and synergy was achieved via activation of the type II mitochondrial pathway for apoptosis. Further, rituximab (Fab')(2)-treated tumor cells were killed by purified peripheral blood-derived NK cells via TRAIL. Treatment of B-NHL cells with rituximab inhibited both YY1 DNA-binding activity and expression. Rituximab-mediated sensitization to TRAIL apoptosis was due, in large part, to rituximab-mediated inhibition of the transcription factor Yin Yang 1 (YY1). The direct role of YY1 in TRAIL sensitization by rituximab was shown in cells transfected with YY1 siRNA, and such cells mimicked rituximab and became sensitive to TRAIL-induced apoptosis. These data suggest that, in vivo, host effector cells expressing TRAIL may contribute to rituximab-mediated depletion of B-NHL cells.

CpG oligodeoxynucleotides as TLR9 agonists: therapeutic application in allergy and asthma

Unmethylated cytosine-phosphate-guanine (CpG) dinucleotides in microbial DNA sequences activate Toll-like receptor (TLR) 9, and previous studies have shown that oligodeoxynucleotides (ODNs) containing CpG in specific base sequence motifs (CpG ODNs) can reiterate the majority of the immunomodulatory effects produced by bacterial DNA. Many of the manifestations in allergic diseases are primarily due to T helper (T(h))-2 cell-type responses. CpG ODNs can induce T(h)1 and T-regulatory (T(reg)) cell-type cytokines that can suppress the T(h)2 response. The therapeutic application of TLR9 has been explored extensively in recent years, and many studies are being conducted to assess the safety and efficacy of TLR9 agonists in various diseases, including atopic and infectious diseases, and cancer. Studies in murine models have shown that the development of atopic airway disease can be prevented by treatment with CpG ODNs. Various clinical trials are currently ongoing to determine the efficacy of CpG ODNs as a therapeutic tool for atopic diseases. In this review, we discuss the therapeutic application of CpG ODNs in allergy and asthma. CpG ODNs may be used alone or as an adjuvant to immunotherapy to treat these disorders.

CpG-oligodeoxynucleotide inhibits Smad-dependent bone morphogenetic protein signaling: effects on myeloma cell apoptosis and in vitro osteoblastogenesis

The TLR9 agonist CpG-oligodeoxynucleotide (CpG-ODN) with a phosphorothioate backbone (PTO-CpG-ODN) is evaluated in clinical trials as a vaccine adjuvant or as treatment of cancers. Bone morphogenetic proteins (BMPs) regulate growth and differentiation of several cell types, and also induce apoptosis of cancer cells. Cross-talk between BMP- and TLR-signaling has been reported, and we aimed to investigate whether CpG-ODN influenced BMP-induced osteoblast differentiation or BMP-induced apoptosis of malignant plasma cells. We found that PTO-CpG-ODN inhibited BMP-2-induced osteoblast differentiation from human mesenchymal stem cells. Further, PTO-CpG-ODN counteracted BMP-2- and BMP-6-induced apoptosis of the human myeloma cell lines IH-1 and INA-6, respectively. In contrast, PTO-CpG-ODN did not antagonize the antiproliferative effect of BMP-2 on hMSCs or IH-1 cells. Inhibition of Smad-signaling and p38 MAPK-signaling indicated that apoptosis of IH-1 cells is dependent on Smad-signaling downstream of BMP, whereas the antiproliferative effect of BMP-2 on IH-1 cells also involves p38 MAPK-signaling. Together, the data suggested a specific inhibition by PTO-CpG-ODN on BMP-Smad-signaling. Supporting this we found that PTO-CpG-ODN inhibited BMP-induced phosphorylation of receptor-Smads in human mesenchymal stem cells and myeloma cell lines. This effect appeared to be independent of TLR9 because GpC-ODN and other ODNs with the ability to form multimeric structures inhibited Smad-signaling as efficiently as PTO-CpG-ODNs, and because knockdown of TLR9 by small interfering RNA in INA-6 cells did not blunt the effect of PTO-CpG-ODN. In conclusion, our results demonstrate that PTO-CpG-ODN inhibits BMP-signaling, and thus might provoke unwanted TLR9-independent side effects in patients.