Oligodeoxynucleotides Enhance Lipopolysaccharide-Stimulated Synthesis of Tumor Necrosis Factor: Dependence on Phosphorothioate Modification and Reversal by Heparin

Antisense oligonucleotides and their applications in rare neurological diseases

Rare diseases affect almost 500 million people globally, predominantly impacting children and often leading to significantly impaired quality of life and high treatment costs. While significant contributions have been made to develop effective treatments for those with rare diseases, more rapid drug discovery strategies are needed. Therapeutic antisense oligonucleotides can modulate target gene expression with high specificity through various mechanisms determined by base sequences and chemical modifications; and have shown efficacy in clinical trials for a few rare neurological conditions. Therefore, this review will focus on the applications of antisense oligonucleotides, in particular splice-switching antisense oligomers as promising therapeutics for rare neurological diseases, with key examples of Duchenne muscular dystrophy and spinal muscular atrophy. Challenges and future perspectives in developing antisense therapeutics for rare conditions including target discovery, antisense chemical modifications, animal models for therapeutic validations, and clinical trial designs will also be briefly discussed.

Sequence- and Structure-Dependent Cytotoxicity of Phosphorothioate and 2'-O-Methyl Modified Single-Stranded Oligonucleotides

Single-stranded oligonucleotides (SSOs) are a rapidly expanding class of therapeutics that comprises antisense oligonucleotides, microRNAs, and aptamers, with ten clinically approved molecules. Chemical modifications such as the phosphorothioate backbone and the 2'-O-methyl ribose can improve the stability and pharmacokinetic properties of therapeutic SSOs, but they can also lead to toxicity in vitro and in vivo through nonspecific interactions with cellular proteins, gene expression changes, disturbed RNA processing, and changes in nuclear structures and protein distribution. In this study, we screened a mini library of 277 phosphorothioate and 2'-O-methyl-modified SSOs, with or without mRNA complementarity, for cytotoxic properties in two cancer cell lines. Using circular dichroism, nucleic magnetic resonance, and molecular dynamics simulations, we show that phosphorothioate- and 2'-O-methyl-modified SSOs that form stable hairpin structures through Watson-Crick base pairing are more likely to be cytotoxic than those that exist in an extended conformation. In addition, moderate and highly cytotoxic SSOs in our dataset have a higher mean purine composition than pyrimidine. Overall, our study demonstrates a structure-cytotoxicity relationship and indicates that the formation of stable hairpins should be a consideration when designing SSOs toward optimal therapeutic profiles.

The Medicinal Chemistry of Artificial Nucleic Acids and Therapeutic Oligonucleotides

Nucleic acids play a central role in human biology, making them suitable and attractive tools for therapeutic applications. While conventional drugs generally target proteins and induce transient therapeutic effects, nucleic acid medicines can achieve long-lasting or curative effects by targeting the genetic bases of diseases. However, native oligonucleotides are characterized by low in vivo stability due to nuclease sensitivity and unfavourable physicochemical properties due to their polyanionic nature, which are obstacles to their therapeutic use. A myriad of synthetic oligonucleotides have been prepared in the last few decades and it has been shown that proper chemical modifications to either the nucleobase, the ribofuranose unit or the phosphate backbone can protect the nucleic acids from degradation, enable efficient cellular uptake and target localization ensuring the efficiency of the oligonucleotide-based therapy. In this review, we present a summary of structure and properties of artificial nucleic acids containing nucleobase, sugar or backbone modifications, and provide an overview of the structure and mechanism of action of approved oligonucleotide drugs including gene silencing agents, aptamers and mRNA vaccines.

Comparison between genetic and pharmaceutical disruption of Ldlr expression for the development of atherosclerosis

Antisense oligonucleotides (ASOs) against Ldl receptor (Ldlr-ASO) represent a promising strategy to promote hypercholesterolemic atherosclerosis in animal models without the need for complex breeding strategies. Here, we sought to characterize and contrast atherosclerosis in mice given Ldlr-ASO with those bearing genetic Ldlr deficiency. To promote atherosclerosis, male and female C57Bl6/J mice were either given weekly injections of Ldlr-ASO (5 mg/kg once per week) or genetically deficient in Ldlr (Ldlr-/-). Mice consumed either standard rodent chow or a diet high in saturated fat and sucrose with 0.15% added cholesterol for 16 weeks. While both models of Ldlr deficiency promoted hypercholesterolemia, Ldlr-/- mice exhibited nearly 2-fold higher cholesterol levels than Ldlr-ASO mice, reflected by increased VLDL and LDL levels. Consistent with this, the en face atherosclerotic lesion area was 3-fold and 3.6-fold greater in male and female mice with genetic Ldlr deficiency, respectively, as compared with the modest atherosclerosis observed following Ldlr-ASO treatment. Aortic sinus lesion sizes, fibrosis, smooth muscle actin, and necrotic core areas were also larger in Ldlr-/- mice, suggesting a more advanced phenotype. Despite a more modest effect on hypercholesterolemia, Ldlr-ASO induced greater hepatic inflammatory gene expression, macrophage accumulation, and histological lobular inflammation than was observed in Ldlr-/- mice. We conclude Ldlr-ASO is a promising tool for the generation of complex rodent models with which to study atherosclerosis but does not promote comparable levels of hypercholesterolemia or atherosclerosis as Ldlr-/- mice and increases hepatic inflammation. Thus, genetic Ldlr deficiency may be a superior model, depending on the proposed use.

Cerebrospinal Fluid and Clinical Profiles in Adult Type 2-3 Spinal Muscular Atrophy Patients Treated with Nusinersen: An 18-Month Single-Centre Experience

BACKGROUND AND OBJECTIVES

Nusinersen was approved as the first disease-modifying therapy in spinal muscular atrophy (SMA). Our aim was to analyse therapy-related changes in cerebrospinal fluid (CSF) and serum parameters of adult type 2-3 SMA and to correlate biochemical data with motor functional status.

METHODS

Nine adult SMA type 2-3 patients and ten control subjects without neurodegenerative diseases were included in our single-centre study. Cross-sectional analysis of CSF routine parameters, CSF neurofilament light chain, CSF Tau, CSF phospho-Tau and serum creatinine was performed between SMA patients at baseline (T0) and control subjects. The above-mentioned fluid parameters were longitudinally analysed in the SMA cohort after loading dose (T1) and after four maintenance doses (T2, T3, T4, T5). Hammersmith Functional Motor Scale Expanded (HFMSE), Revised Upper Limb Module (RULM) and the 6-minute walking test (6MWT) were used to evaluate motor outcomes.

RESULTS

Improvements in HFMSE, RULM and 6MWT were observed only after the loading dose of nusinersen. No significant differences in routine CSF parameters and CSF markers of neurodegeneration were found between SMA patients and control subjects. Serum creatinine levels were significantly lower in SMA patients than in control subjects. CSF/serum albumin ratio (Qalb) significantly increased from T0 to each time point, without any further increase after the maintenance doses. Persistent systemic oligoclonal bands (OCBs) were found in five patients from baseline. Three more patients developed persistent systemic OCBs from T1; one patient showed intrathecal OCBSs from baseline to T5. Markers of neurodegeneration did not change during the follow-up and did not correlate with motor scores at baseline and at each timepoint. Serum creatinine levels significantly correlated with HFMSE and RULM at each time point.

CONCLUSIONS

The increase of the Qalb values and the development of systemic OCBs in some SMA patients could be due to repeated lumbar puncture and to the immunogenic effect of nusinersen. On the other hand, the presence of OCBs in serum and/or CSF at baseline should be further investigated. Furthermore, biomarkers of neurodegeneration did not play a prognostic role in our cohort of adult SMA patients.

Progress in the molecular pathogenesis and nucleic acid therapeutics for Parkinson's disease in the precision medicine era

Parkinson's disease (PD) is one of the most common neurodegenerative disorders that manifest various motor and nonmotor symptoms. Although currently available therapies can alleviate some of the symptoms, the disease continues to progress, leading eventually to severe motor and cognitive decline and reduced life expectancy. The past two decades have witnessed rapid progress in our understanding of the molecular and genetic pathogenesis of the disease, paving the way for the development of new therapeutic approaches to arrest or delay the neurodegenerative process. As a result of these advances, biomarker‐driven subtyping is making it possible to stratify PD patients into more homogeneous subgroups that may better respond to potential genetic‐molecular pathway targeted disease‐modifying therapies. Therapeutic nucleic acid oligomers can bind to target gene sequences with very high specificity in a base‐pairing manner and precisely modulate downstream molecular events. Recently, nucleic acid therapeutics have proven effective in the treatment of a number of severe neurological and neuromuscular disorders, drawing increasing attention to the possibility of developing novel molecular therapies for PD. In this review, we update the molecular pathogenesis of PD and discuss progress in the use of antisense oligonucleotides, small interfering RNAs, short hairpin RNAs, aptamers, and microRNA‐based therapeutics to target critical elements in the pathogenesis of PD that could have the potential to modify disease progression. In addition, recent advances in the delivery of nucleic acid compounds across the blood–brain barrier and challenges facing PD clinical trials are also reviewed.

The Nonclinical Safety Profile of GalNAc-conjugated RNAi Therapeutics in Subacute Studies

Short interfering RNAs (siRNAs) and antisense oligonucleotides (ASOs) are the most clinically advanced oligonucleotide-based platforms. A number of N-acetylgalactosamine (GalNAc)-conjugated siRNAs (GalNAc-siRNAs), also referred to as RNA interference (RNAi) therapeutics, are currently in various stages of development, though none is yet approved. While the safety of ASOs has been the subject of extensive review, the nonclinical safety profiles of GalNAc-siRNAs have not been reported. With the exception of sequence differences that confer target RNA specificity, GalNAc-siRNAs are largely chemically uniform, containing limited number of phosphorothioate linkages, and 2’-O-methyl and 2’-deoxy-2’-fluoro ribose modifications. Here, we present the outcomes of short-term (3–5 week) rat and monkey weekly repeat-dose toxicology studies of six Enhanced Stabilization Chemistry GalNAc-siRNAs currently in clinical development. In nonclinical studies at supratherapeutic doses, these molecules share similar safety signals, with histologic findings in the organ of pharmacodynamic effect (liver), the organ of elimination (kidney), and the reticuloendothelial system (lymph nodes). The majority of these changes are nonadverse, partially to completely reversible, correlate well with pharmacokinetic parameters and tissue distribution, and often reflect drug accumulation. Furthermore, all GalNAc-siRNAs tested to date have been negative in genotoxicity and safety pharmacology studies.

Antisense oligonucleotide therapies: the promise and the challenges from a toxicologic pathologist's perspective

Many antisense oligonucleotides (ASOs) from several classes of molecules are currently in drug development. Despite over 20 years of pharmaceutical research, few ASOs have been marketed due to problems with clinical efficacy or preclinical toxicologic challenges. However, a number of recent developments have renewed interest in this class including the registration of mipomersen, the advent of successful screening strategies to eliminate more toxic molecules, and new understanding of the risks of off-target nucleotide binding and mitigation of potential off-target effects. Recent advances in backbone chemistries, conjugation to other moieties, and new delivery systems have allowed better tissue penetration, enhanced intracellular targeting, and less frequent dosing, resulting in fewer toxicities. While these new developments provide invigorated interest in these platforms, a few lingering challenges and preclinical/clinical toxicity issues remain to be completely resolved, including: (1) proinflammatory effects (vasculitis/inflammatory infiltrates); (2) nephrotoxicity and hepatotoxicity unrelated to lysosomal accumulation; and (3) thrombocytopenia. Recent investigative work by several laboratories have helped elucidate mechanisms for these issues, allowing a better understanding of the clinical relevance and implications of particular toxicities. It is important for toxicologists, pathologists, and regulatory reviewers to be familiar with new developments in the ASO field and their implications, as a greater number of new types of antisense molecules undergo preclinical toxicity testing.

CpG-Induced IFN-α production of plasmacytoid dendritic cells: time and dosage dependence and the effect of structural modifications to the CpG backbone

Plasmacytoid dendritic cells (pDCs) represent a highly specialized immune cell subset and are considered to be the main sentinels against viral infections and play an important role in the development of immune tolerance. pDCs are able to recognize cytosine-phosphate-guanosine (CpG) motifs within microbial DNA, which are unmethylated CG dinucleotides in a certain sequence context and trigger the secretion of interferon (IFN)-α and other proinflammatory cytokines. Here we used the typical class A CpG oligodeoxynucleotide (ODN) 2216, the B-class ODN 2006, and the newly synthesized CpG ODN TM64 to explore the potency and kinetics of IFN-α stimulation of pDC. TM64 CpG ODN has a hexanucleotide sequence TCGTGT that leads to an increased cellular uptake and features a CpG nucleotide within the sequence that leads to a potent specific B-cell stimulation, thus characteristics similar to a class B CpG. Our data reveals that all CpGs act as both dosage- and time-dependent stimuli of IFN-α secretion. The relationship between concentration of the stimulant and the secreted amount of IFN-α is not linear and results in a plateau formation, with saturation kinetics. Alteration to the backbone can change duration and quantity of overall IFN-α secretion.

Targeted delivery of oligonucleotides into tumor-associated macrophages for cancer immunotherapy

Tumor-associated macrophages (TAMs) have been proven to be a driving force in the initiation, proliferation, metastasis and angiogenesis of various tumors. Specifically, alterations in the functions of TAMs exhibited inhibitory effects on tumor growth. However, there is currently no research being conducted on the targeting delivery of drugs into TAMs for cell-specific tumor immunotherapy. In the present study, we developed a TAMs targeted delivery system that is triggered by the acidic microenvironment in the tumor to release a TAMs-recognizing nano-complex loaded with oligonucleotides. By using this system, we demonstrated a significant anti-tumor effect of an oligonucleotide combination of CpG oligonucleotide, anti-IL-10 and anti-IL-10 receptor oligonucleotides. These nucleic acid drugs delivered by the delivery system accumulated in the TAMs of an allograft hepatoma murine model by intravenous injection, suppressed the pro-tumor functions and stimulated the anti-tumor activities of TAMs. More importantly, the nucleic acid drug-based immune-regulation was restricted to the tumor microenvironment and did not cause an upregulation of serum inflammatory cytokines. Our present study provides an effective therapeutic strategy for regulating cell-specific functions using nucleic acid drugs.

TLR-based immune adjuvants

This work describes the nature and strength of the immune response induced by various Toll-like receptor ligands and their ability to act as vaccine adjuvants. It reviews the various ligands capable of triggering individual TLRs, and then focuses on the efficacy and safety of those agents for which clinical results are available.

CpG DNA as a vaccine adjuvant

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs trigger cells that express Toll-like receptor 9 (including human plasmacytoid dendritic cells and B cells) to mount an innate immune response characterized by the production of Th1 and proinflammatory cytokines. When used as vaccine adjuvants, CpG ODNs improve the function of professional antigen-presenting cells and boost the generation of humoral and cellular vaccine-specific immune responses. These effects are optimized by maintaining ODNs and vaccine in close proximity. The adjuvant properties of CpG ODNs are observed when administered either systemically or mucosally, and persist in immunocompromised hosts. Preclinical studies indicate that CpG ODNs improve the activity of vaccines targeting infectious diseases and cancer. Clinical trials demonstrate that CpG ODNs have a good safety profile and increase the immunogenicity of coadministered vaccines.

CpG oligonucleotides as adjuvants for vaccines targeting infectious diseases

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, accelerating and boosting antigen-specific immune responses. CpG motifs promote the induction of Th1 and pro-inflammatory cytokines and support the maturation/activation of professional antigen presenting cells (particularly plasmacytoid dendritic cells). These effects are optimized by maintaining close physical contact between the CpG ODN and the immunogen. Co-administering CpG ODN with a variety of vaccines has improved the resultant humoral and/or cellular immune responses, culminating in enhanced protective immunity in rodent and primate challenge models. Ongoing clinical studies indicate that CpG ODN are safe and well-tolerated when administered as adjuvants to humans, and that they can support increased vaccine-specific immune responses.

Broad-spectrum drugs against viral agents

Development of antivirals has focused primarily on vaccines and on treatments for specific viral agents. Although effective, these approaches may be limited in situations where the etiologic agent is unknown or when the target virus has undergone mutation, recombination or reassortment. Augmentation of the innate immune response may be an effective alternative for disease amelioration. Nonspecific, broad-spectrum immune responses can be induced by double-stranded (ds)RNAs such as poly (ICLC), or oligonucleotides (ODNs) containing unmethylated deocycytidyl-deoxyguanosinyl (CpG) motifs. These may offer protection against various bacterial and viral pathogens regardless of their genetic makeup, zoonotic origin or drug resistance.

Low molecular weight heparin suppresses tumor necrosis factor expression from deep vein thrombosis

Prior investigations have shown that low molecular weight heparin (LMWH) possesses anti-inflammatory properties in addition to its anticoagulant effects. The physiology of this anti-inflammatory mechanism is poorly understood. Experiments were performed to assess the in vivo anti-inflammatory effects of LMWH in a rat model of deep vein thrombosis (DVT). Sprague-Dawley rats were divided into three groups and underwent laparotomy and inferior vena cava (IVC) ligation directly below the renal veins to induce thrombosis. Twenty-four hours later, intraluminal clot was confirmed at repeat laparotomy using an electromagnetic flowmeter and visual inspection. An intravenous infusion of LMWH or urokinase or no infusion (control) was then performed. Subcutaneous LMWH was given postoperatively to the heparin group. Twenty-four hours after the second operation, the animals were killed, the IVC harvested, the cells from the IVC purified, and cytokine measurements done. The LMWH group showed an overall statistically significant decrease in tumor necrosis factor-alpha (TNF-alpha) levels compared to both the control and urokinase groups by analysis of variance (918 pg/mL vs. 1,345 and 1,623, respectively; P = 0.001). To ensure accuracy, individual pairwise comparisons were performed, which also showed statistically significant TNF-alpha suppression by LMWH compared to control (P = 0.015) and urokinase (P = 0.0009). Treatment of DVT with LMWH causes suppression of TNF-alpha expression. This may, in part, explain its anti-inflammatory effects.

TLR9 and the recognition of self and non-self nucleic acids

Toll-like receptors (TLRs) are involved in the innate recognition of foreign material and their activation leads to both innate and adaptive immune responses directed against invading pathogens. TLR9 is intracellularly expressed in the endo-lysosomal compartments of specialized immune cells. TLR9 is activated in response to DNA, in particular DNA containing unmethylated CpG motifs that are more prevalent in microbial than mammalian DNA. By detecting foreign DNA signatures TLR9 can sense the presence of certain viruses or bacteria inside the cell and mount an immune response. However, under certain conditions, TLR9 can also recognize self-DNA and this may promote immune pathologies with uncontrolled chronic inflammation. The autoimmune disease systemic lupus erythematosis (SLE) is characterized by the presence of immune stimulatory complexes containing autoantibodies against endogenous DNA and DNA- and RNA-associated proteins. Recent evidence indicates that the autoimmune response to these complexes involves TLR9 and the related single-stranded RNA-responsive TLRs 7 and 8, and therefore some breakdown in the normal ability of these TLRs to distinguish self and foreign DNA. Evidence suggests that immune cells use several mechanisms to discriminate between stimulatory and nonstimulatory DNA; however, it appears that TLR9 itself binds rather indiscriminately to a broad range of DNAs. We therefore propose that there is an additional recognition step by which TLR9 senses differences in the structures of bound DNA.

A hexanucleotide selected for increased cellular uptake in cis contains a highly active CpG-motif in human B cells and primary peripheral blood mononuclear cells

The relationship between immunostimulation of human B cells by cytosine-phosphate-guanosine (CpG) -containing oligonucleotides and their physical cellular uptake is of mechanistic interest and a prerequisite for rational improvements of the therapeutic potential of CpG-harbouring oligonucleotides. Here, a combinatorial approach was used to identify nucleotide sequence motifs that facilitate increased cellular uptake in mammalian cells. Oligonucleotides harbouring the selected hexanucleotide TCGTGT in cis show increased cellular uptake. This motif contains a CpG dinucleotide within a sequence context that shows a very strong CpG-specific stimulatory activity on human B cells. Here we describe the influence of concentration, length and sequence position of the unmethylated CpG dinucleotide on immunostimulation. A comparison between phosphorothioate-derivatives and unmodified TCGTGT-containing oligonucleotides strongly indicates a great CpG-specificity for the unmodified CpG-harbouring oligonucleotides but not for the phosphorothioate versions. This work describes a link between the physical cellular uptake of naked oligonucleotides harbouring the selected cellular uptake motif TCGTGT, its strong CpG-specific stimulation of human B cells and its relationship with the sequence context of CpG and its cellular uptake.

Adjuvant activity of CpG oligodeoxynucleotides

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs directly stimulate human B cells and plasmacytoid dendritic cells (pDCs), thereby promoting the production of Th1 and proinflammatory cytokines and the maturation/activation of professional antigen-presenting cells. These activities enable CpG ODNs to act as immune adjuvants, accelerating and boosting antigen-specific immune responses by 5- to 500-fold. The CpG motifs present in bacterial DNA plasmids may contribute to the immunogenicity of DNA vaccines. Ongoing clinical studies indicate that CpG ODNs are safe and well tolerated when administered as adjuvants to humans and can improve vaccine-induced immune responses.

Cytokine responses to CpG DNA in human leukocytes

Previous studies have implicated a role of bacterial DNA, containing unmethylated cytosine-phosphate-guanosine (CpG) motifs, in the initiation of systemic inflammation. This is based on the ability of CpG-DNA to act in synergy with lipopolysaccharide (LPS) to trigger tumor necrosis factor alpha (TNFalpha) production in murine monocytes and to enhance LPS toxicity in rodents. In this study we investigated the capacity of CpG-DNA to trigger and modulate cytokine responses in human leukocytes. A human blood assay, as well as isolated cultures of monocytes and neutrophils, was exposed to the synthetic oligodeoxynucleotides (ODNs) CpG ODN (2006) and GpC ODN (2006-GC), alone or in combination with peptidoglycan or LPS. Plasma or supernatants were isolated and analyzed for TNFalpha, interleukin-1 beta (IL-1beta), IL-6 and IL-8 by ELISA. In the blood, 2006 (but not 2006-GC) induced the release of TNFalpha (P < 0.05) and possibly IL-1beta and IL-6. IL-8 was induced in a CpG-independent manner. When co-administered with peptidoglycan, both ODNs enhanced the release of cytokines, but not consistently CpG dependent. When co-administered with LPS, only IL-8 values were enhanced, whereas IL-6 was suppressed at early time points. In monocyte and neutrophil cultures, CpG dependent induction of cytokine release was not observed. However, both ODNs inhibited LPS-induced IL-6. In conclusion, the capacity of CpG DNA to trigger the release of TNFalpha and to enhance LPS-induced release of this cytokine is confirmed in human whole blood, but not in adherent human monocytes. Most effects of the ODNs on cytokine release in human leukocytes were CpG independent.

Locked nucleic acid: a potent nucleic acid analog in therapeutics and biotechnology

Locked nucleic acid (LNA) is a class of nucleic acid analogs possessing very high affinity and excellent specificity toward complementary DNA and RNA, and LNA oligonucleotides have been applied as antisense molecules both in vitro and in vivo. In this review, we briefly describe the basic physiochemical properties of LNA and some of the difficulties that may be encountered when applying LNA technology. The central part of the review focuses on the use of LNA molecules in regulation of gene expression, including delivery to cells, stability, unspecific effects, toxicity, pharmacokinetics, and design of LNA oligonucleotides. The last part evaluates LNA as a diagnostic tool in genotyping.

[Do antisense oligonucleotides improve viral immunopathology?]

BACKGROUND

Tumor necrosis factor (TNF)-alpha as a proinflammatory cytokine is of great importance during the development of herpes simplex virus-1 keratitis (HSK). In this study the local administration of antisense oligonucleotides (ASON) targeting TNF-alpha was examined for its usefulness in ameliorating this disease.

METHODS

Uptake and efficacy of the oligonucleotides were studied in vitro by fluorescence microscopy and flow cytometry. Substance- and sequence-specific influences on the development of HSK were scrutinized in an animal model.

RESULTS

Quick and stable uptake of FITC-labeled ASON by isolated spleen and lymph node cells was proved. The production of TNF-alpha by these cells after stimulation with HSV antigen or concanavalin A (ConA) was clearly downregulated after addition of ASON. In vivo, incidence and development of HSK were ameliorated after subepithelial corneal injection of ASON targeting TNF-alpha. When buffer and control oligonucleotides were given, no significant influence on the disease was found.

CONCLUSION

The ASON effectively reduced TNF-alpha secretion in vitro and suppressed the development of experimental HSK in vivo.

Phase II study of ISIS 3521, an antisense oligodeoxynucleotide to protein kinase C alpha, in patients with previously treated low-grade non-Hodgkin's lymphoma

BACKGROUND

The purpose of this study was to assess the efficacy and safety of ISIS 3521, an antisense phosphorothioate oligonucleotide to protein kinase C alpha in patients with relapsed low-grade non-Hodgkin's lymphoma (NHL).

PATIENTS AND METHODS

Twenty-six patients received ISIS 3521 (2 mg/kg/day) as a continuous infusion over 21 days of each 28-day cycle.

RESULTS

The median age of the patients was 53 years (range 37-77). Histological subtypes were low-grade follicular lymphoma (n = 22) and B-cell small lymphocytic lymphoma (n = 4). Twenty-one (81%) had stage III/IV disease. The median number of previous lines of chemotherapy was two (range one to six). A total of 87 cycles of ISIS 3521 were administered. Twenty-three patients were assessable for response. Three patients achieved a partial response. No complete responses were observed. Ten patients had stable disease. Grade 3-4 toxicity was as follows: neutropenia (3.8%) and thrombocytopenia (26.9%).

CONCLUSIONS

ISIS 3521 has demonstrated anti-tumour activity in patients with relapsed low-grade NHL. There may be a potential role for this agent in combination with conventional chemotherapy for advanced low-grade lymphoma, and further trials are warranted.

Use of CpG oligodeoxynucleotides as immune adjuvants

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs directly stimulate human B cells and plasmacytoid dendritic cells (pDCs), thereby promoting the production of T helper 1 (Th1) and pro-inflammatory cytokines and the maturation/activation of professional antigen-presenting cells. These activities enable CpG ODNs to act as immune adjuvants, accelerating and boosting antigen-specific immune responses by 5-500-fold. These effects are optimized by maintaining close physical contact between the CpG DNA and the immunogen. Animal challenge models establish that protective immunity can be accelerated and magnified by coadministering CpG DNA with vaccines. Ongoing clinical studies indicate that CpG ODNs are safe and well tolerated when administered as adjuvants to humans, and in some cases, they increase vaccine-induced immune responses.

Use of CpG oligodeoxynucleotides as immunoprotective agents

Single-stranded oligodeoxynucleotides (ODNs) synthesised to express unmethylated 'CpG motifs' mimic the ability of bacterial DNA to trigger the innate immune system. CpG ODNs stimulate cells that express Toll-like receptor 9, initiating an immunomodulatory cascade resulting in the activation of B and T lymphocytes, natural killer cells, monocytes, macrophages and dendritic cells. CpG ODNs improve the host's ability to resist infection by accelerating and improving the induction of an innate and then adaptive immune response, characterised by the production of Th1 and pro-inflammatory cytokines, chemokines and polyreactive antibodies. Studies in rodents and non-human primates demonstrate that CpG ODNs can protect the host against bacterial, viral, fungal and parasitic infections. CpG-induced protection develops rapidly but persists for only a few weeks. Preclinical and clinical trials suggest that CpG ODNs can be used safely to activate the human immune system.

Progress in antisense technology

Antisense technology exploits oligonucleotide analogs to bind to target RNAs via Watson-Crick hybridization. Once bound, the antisense agent either disables or induces the degradation of the target RNA. Antisense agents can also alter splicing. During the past decade, much has been learned about the basic mechanisms of antisense, the medicinal chemistry, and the pharmacologic, pharmacokinetic, and toxicologic properties of antisense molecules. Antisense technology has proven valuable in gene functionalization and target validation. With one drug marketed, Vitravenetm, and approximately 20 antisense drugs in clinical development, it appears that antisense drugs may prove important in the treatment of a wide range of diseases.

Identification of a sequence from the genome of porcine circovirus type 2 with an inhibitory effect on IFN-alpha production by porcine PBMCs

Porcine circovirus type 2 (PCV-2) has been identified as the causal agent of postweaning multisystemic wasting syndrome and has been associated with several other disease syndromes in pigs. To date, however, little is known regarding the mechanism(s) underlying the pathogenesis of PCV-2-induced diseases and the interaction of the virus with the host immune system. In the present study, oligodeoxynucleotides (ODNs), with central CpG motifs selected from the genome of PCV-2, were demonstrated to modulate the immune response of porcine PBMCs. Four of the five ODNs tested were demonstrated to act in a stimulatory manner via induction of IFN-alpha production, whereas only one of the five ODNs showed inhibitory activity. Also, this inhibitory ODN was demonstrated to completely inhibit IFN-alpha production induced by the other stimulatory ODNs and showed a variable degree of inhibitory action on other known inducers of IFN-alpha. Although no single common characteristic among resistant or susceptible inducers could be identified, the presence of immune modulatory sequences in the genome of PCV-2 may represent an underlying mechanism of the pathogenesis of PCV-2-associated diseases.

Identification of CpG oligodeoxynucleotide motifs that stimulate nitric oxide and cytokine production in avian macrophage and peripheral blood mononuclear cells

Unmethylated CpG dinucleotides within specific flanking bases (referred to as CpG motif) are relatively abundant in bacterial DNA and are known to stimulate innate immune responses. In this study, synthetic CpG containing oligodeoxydinucleotides (CpG-ODNs) were evaluated for their ability to stimulate nitric oxide (NO), interleukin-1beta (IL-1beta), and interferon-gamma (IFN-gamma) production using an avian macrophage cell line (HD11) and peripheral blood mononuclear cells (PBMC). Results showed ODNs containing the CpG motif can activate the HD11cells and induce NO production. The optimal CpG-ODN motif for NO induction was GTCGTT. Increasing GTCGTT motifs in CpG-ODN significantly enhanced the stimulatory effect. Deviation of flanking bases of the CpG dinucleotide diminished the stimulatory activity. We also found CpG-ODN differentially stimulated expression of cytokine genes. The most active CpG motif for NO induction was also a strong stimulant for the IL-1beta gene expression in the HD11 cells, whereas different CpG motifs were found to induce IFN-gamma gene expression in PBMC.

Activation with CpG-A and CpG-B oligonucleotides reveals two distinct regulatory pathways of type I IFN synthesis in human plasmacytoid dendritic cells

Two different CpG oligonucleotides (ODN) were used to study the regulation of type I IFN in human plasmacytoid dendritic cells (PDC): ODN 2216, a CpG-A ODN, known to induce high amounts of IFN-alpha in PDC, and ODN 2006, a CpG-B ODN, which is potent at stimulating B cells. CpG-A ODN showed higher and prolonged kinetics of type I IFN production compared with that of CpG-B ODN. In contrast, CpG-B ODN was more active than CpG-A ODN in stimulating IL-8 production and increasing costimulatory and Ag-presenting molecules, suggesting that CpG-A and CpG-B trigger distinct regulatory pathways in PDC. Indeed, CpG-A ODN, but not CpG-B ODN, activated the type I IFNR-mediated autocrine feedback loop. PDC were found to express high constitutive levels of IFN regulatory factor (IRF)7. IRF7 and STAT1, but not IRF3, were equally up-regulated by both CpG-A and CpG-B. CD40 ligand synergistically increased CpG-B-induced IFN-alpha independent of the IFNR but did not affect CpG-B-induced IFN-beta. In conclusion, our studies provide evidence for the existence of two distinct regulatory pathways of type I IFN synthesis in human PDC, one dependent on and one independent of the IFNR-mediated feedback loop. The alternate use of these pathways is based on the type of stimulus rather than the quantity of IFN-alphabeta available to trigger the IFNR. Constitutive expression of IRF7 and the ability to produce considerable amounts of IFN-alpha independent of the IFNR seem to represent characteristic features of PDC.

Antitumor effect of G3139 Bcl-2 antisense oligonucleotide is independent of its immune stimulation by CpG motifs in SCID mice

The Bcl-2 antisense oligonucleotide (AS-ODN) G3139 chemosensitizes human malignancies by downregulating the antiapoptotic protein Bcl-2. Because G3139 contains two potential immunostimulatory CpG motifs, we asked if immune stimulation contributes to the antitumor activity observed previously. 5'-Methylation of cytosines in CpG motifs abrogates immune stimulation by oligonucleotides. We, therefore, studied the antitumor and immunostimulatory potential of G3139 vs. an identical oligonucleotide, except for methylation of cytosines in the two CpG motifs (G4232). In a human melanoma SCID mouse xenotransplantation model, G3139 or G4232 was administered by continuous subcutaneous (s.c.) or bolus intraperitoneal (i.p.) infusion. Both G3139 and G4232 significantly reduced tumor growth by about one third relative to the saline-treated group. Furthermore, we noted a similar downregulation of Bcl-2 expression and increase in tumor cell apoptosis caused by G3139 and G4232 compared with saline controls. However, mice treated with G3139 had a pronounced increase in spleen weight and interleukin-12 (IL-12) plasma levels relative to mice treated with either G4232 or saline. Splenomegaly and elevated IL-12 plasma levels suggest that G3139 can be immunostimulatory. However, there is clear evidence that the antitumor effect of G3139 in this model appears to be a Bcl-2 antisense effect that is independent of immune stimulation, as G3139 and its immune-silent counterpart G4232 caused similar tumor suppression and apoptosis induction.

Plasmacytoid dendritic cells: the key to CpG

The vertebrate immune system has established TLR9 to detect microbial DNA based on unmethylated CG dinucleotides within certain sequence contexts (CpG motifs). In humans, the expression of toll-like receptor 9 (TLR9) is restricted to B cells and plasmacytoid dendritic cells (PDC). The PDC is characterized by the ability to rapidly synthesize large amounts of type I IFN (IFN-alpha and IFN-beta) in response to viral infection. In contrast to other dendritic cell subsets which express a broad profile of TLRs, the TLR profile in PDC is restricted to TLR7 and TLR9. So far, CpG DNA is the only defined microbial molecule recognized by PDC. An intriguing feature of PDC is its ability to simultaneously produce the two major Th1-inducing cytokines in humans, IFN-alpha and IL-12, both at high levels. The ratio of IFN-alpha versus IL-12 and the quantity of these cytokines are regulated by T helper cell-mediated costimulation via CD40 ligation. The ratio also depends on the differentiation stage of the PDC at the time of stimulation and the type of CpG ODN used. We propose a model in which the establishment of Th1 responses in vivo is improved by appropriately stimulated PDC that otherwise - in the absence of CpG DNA--support Th2 or Th0 responses and thus have been called DC2.

CpG motifs in bacterial DNA and their immune effects

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs. Oligodeoxynucleotides (ODN) containing CpG motifs activate host defense mechanisms leading to innate and acquired immune responses. The recognition of CpG motifs requires Toll-like receptor (TLR) 9, which triggers alterations in cellular redox balance and the induction of cell signaling pathways including the mitogen activated protein kinases (MAPKs) and NF kappa B. Cells that express TLR-9, which include plasmacytoid dendritic cells (PDCs) and B cells, produce Th1-like proinflammatory cytokines, interferons, and chemokines. Certain CpG motifs (CpG-A) are especially potent at activating NK cells and inducing IFN-alpha production by PDCs, while other motifs (CpG-B) are especially potent B cell activators. CpG-induced activation of innate immunity protects against lethal challenge with a wide variety of pathogens, and has therapeutic activity in murine models of cancer and allergy. CpG ODN also enhance the development of acquired immune responses for prophylactic and therapeutic vaccination.

Sensitization of B-cell chronic lymphocytic leukemia cells to recombinant immunotoxin by immunostimulatory phosphorothioate oligodeoxynucleotides

A recombinant anti-CD25 immunotoxin, LMB-2, has shown clinical efficacy in hairy cell leukemia and T-cell neoplasms. Its activity in B-cell chronic lymphocytic leukemia (B-CLL) is inferior but might be improved if B-CLL cells expressed higher numbers of CD25 binding sites. It was recently reported that DSP30, a phosphorothioate CpG-oligodeoxynucleotide (CpG-ODN) induces immunogenicity of B-CLL cells by up-regulation of CD25 and other antigens. The present study investigated the antitumor activity of LMB-2 in the presence of DSP30. To this end, B-CLL cells from peripheral blood of patients were isolated immunomagnetically to more than 98% purity. Incubation with DSP30 for 48 hours augmented CD25 expression in 14 of 15 B-CLL samples, as assessed by flow cytometry. DSP30 increased LMB-2 cytotoxicity dose dependently whereas a control ODN with no CpG motif did not. LMB-2 displayed no antitumor cell activity in the absence of CpG-ODN as determined colorimetrically with an (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay. In contrast, B-CLL growth was inhibited in 12 of 13 samples with 50% inhibition concentrations (IC50) in the range of LMB-2 plasma levels achieved in clinical studies. Two samples were not evaluable because of spontaneous B-CLL cell death in the presence of DSP30. Control experiments with an immunotoxin that does not recognize hematopoietic cells, and an anti-CD22 immunotoxin, confirmed that sensitization to LMB-2 was specifically due to up-regulation of CD25. LMB-2 was much less toxic to normal B and T lymphocytes compared with B-CLL cells. In summary, immunostimulatory CpG-ODNs efficiently sensitize B-CLL cells to a recombinant immunotoxin by modulation of its target. This new treatment strategy deserves further attention.

The role of surface ig binding in the activation of human B cells by phosphorothioate oligodeoxynucleotides

Phosphorothioate oligodeoxynucleotides (sODNs) can induce T-cell-independent polyclonal activation of human B cells by a mechanism that depends on both sequence and back-bone structure. Because matrix-bound as well as soluble sODNs are mitogenic, this stimulation may result from the engagement of surface receptor(s). In order to investigate whether surface immunoglobin (Ig) could be a receptor for sODNs, the interaction of sODNs-fluorescein isothiocyanate (FITC) with Ig-coated beads was examined. sODNs specifically bound to human IgM and IgG. Moreover, binding of sODN to human B cells induced temperature-dependent capping of bound receptors and colocalization of FITC-sODN and IgM into aggregated caps on the surface of human B cells. A role of surface Ig was furthermore shown by observations that antibody-mediated capping of B-cell surface IgM or IgD inhibited subsequent binding of sODNs and that the capacity of sODN to stimulate human B cells was blocked by excess IgM or IgG, by nonstimulatory antibodies to sIgM, as well as by a variety of negatively charged molecules. Together, these results indicate that sODNs engage surface Ig by charge-charge interactions that lead to activation of human B cells.

Toll-like receptor expression reveals CpG DNA as a unique microbial stimulus for plasmacytoid dendritic cells which synergizes with CD40 ligand to induce high amounts of IL-12

Human plasmacytoid dendritic cells (DC) (PDC, CD123+) and myeloid DC (MDC, CD11c+) may be able to discriminate between distinct classes of microbial molecules based on a different pattern of Toll-like receptor (TLR) expression. TLR1-TLR9 were examined in purified PDC and MDC. TLR9, which is critically involved in the recognition of CpG motifs in mice, was present in PDC but not in MDC. TLR4, which is required for the response to LPS, was selectively expressed on MDC. Consistent with TLR expression, PDC were susceptible to stimulation by CpG oligodeoxynucleotide (ODN) but not by LPS, while MDC responded to LPS but not to CpG ODN. In PDC, CpG ODN supported survival, activation (CD80, CD86, CD40, MHC class II), chemokine production (IL-8, IP-10) and maturation (CD83). CD40 ligand (CD40L) and CpG ODN synergized to activate PDC and to stimulate the production of IFN-alpha and IL-12 including bioactive IL-12 p70. Previous incubation of PDC with IL-3 decreased the amount of CpG-induced IFN-alpha and shifted the cytokine response in favor of IL-12. CpG ODN-activated PDC showed an increased ability to stimulate proliferation of naive allogeneic CD4 T cells, butTh1 polarization of developing T cells required simultaneous activation of PDC by CD40 ligation and CpG ODN. CpG ODN-stimulated PDC expressed CCR7, which mediates homing to lymph nodes. In conclusion, our studies reveal that IL-12 p70 production by PDC is under strict control of two signals, an adequate exogenous microbial stimulus such as CpG ODN, and CD40L provided endogenously by activated T cells. Thus, CpG ODN acts as an enhancer of T cell help, while T cell-controlled restriction to foreign antigens is maintained.

Antisense therapy in oncology: new hope for an old idea?

There is a potential role for antisense oligonucleotides in the treatment of disease. The principle of antisense technology is the sequence-specific binding of an antisense oligonucleotide to target mRNA, resulting in the prevention of gene translation. The specificity of hybridisation makes antisense treatment an attractive strategy to selectively modulate the expression of genes involved in the pathogenesis of diseases. One antisense drug has been approved for local treatment of cytomegalovirus-induced retinitis, and several antisense oligonucleotides are in clinical trials, including oligonucleotides that target the mRNA of BCL2, protein-kinase-C alpha, and RAF kinase. Antisense oligonucleotides are well tolerated and might have therapeutic activity. Here, we summarise treatment ideas in this field, summarise clinical trials that are being done, discuss the potential contribution of CpG motif-mediated effects, and look at promising molecular targets to treat human cancer with antisense oligonucleotides.

Novel therapies for chronic myelogenous leukemia

The BCR-ABL oncogene is essential to the pathogenesis of chronic myelogenous leukemia, and immune mechanisms play an important role in control of this disease. Understanding of the molecular pathogenesis of chronic myelogenous leukemia has led to the development of several novel therapies, which can be broadly divided into therapies based on 1) inhibition of the BCR-ABL oncogene expression, 2) inhibition of other genes important to the pathogenesis of chronic myelogenous leukemia, 3) inhibition of BCR-ABL protein function, and 4) immunomodulation. We have systematically reviewed each of these novel therapeutic approaches in this article.

Potential roles of antisense technology in cancer chemotherapy

Antisense technology may play a major role in cancer chemotherapy. It is clearly a tool of exceptional value in the functionalization of genes and their validation as potential targets for cancer chemotherapy. Additionally, there is now substantial evidence that antisense drugs are safe, and a growing body of data showing activity in animal models of human disease including cancer, and suggesting efficacy in patients with cancer. In this article, I review the progress in the technology, the anticancer antisense drugs in development and potential roles that antisense technology might play.

Phosphorothioate backbone modification modulates macrophage activation by CpG DNA

Macrophages respond to unmethylated CpG motifs present in nonmammalian DNA. Stabilized phosphorothioate-modified oligodeoxynucleotides (PS-ODN) containing CpG motifs form the basis of immunotherapeutic agents. In this study, we show that PS-ODN do not perfectly mimic native DNA in activation of macrophages. CpG-containing PS-ODN were active at 10- to 100-fold lower concentrations than corresponding phosphodiester ODN in maintenance of cell viability in the absence of CSF-1, in induction of NO production, and in activation of the IL-12 promoter. These enhancing effects are attributable to both increased stability and rate of uptake of the PS-ODN. By contrast, PS-ODN were almost inactive in down-modulation of the CSF-1R from primary macrophages and activation of the HIV-1 LTR. Delayed or poor activation of signaling components may contribute to this, as PS-ODN were slower and less effective at inducing phosphorylation of the extracellular signal-related kinases 1 and 2. In addition, at high concentrations, non-CpG PS-ODN specifically inhibited responses to CpG DNA, whereas nonstimulatory phosphodiester ODN had no such effect. Although nonstimulatory PS-ODN caused some inhibition of ODN uptake, this did not adequately explain the levels of inhibition of activity. The results demonstrate that the phosphorothioate backbone has both enhancing and inhibitory effects on macrophage responses to CpG DNA.

Antisense therapeutics: is it as simple as complementary base recognition?

Antisense oligonucleotides provide a simple and efficient approach for developing target-selective drugs because they can modulate gene expression sequence-specifically. Antisense oligonucleotides have also become efficient molecular biological tools to investigate the function of any protein in the cell. As the application of antisense oligonucleotides has expanded, multiple mechanisms of oligonucleotides have been characterized that impede their routine use. Here, we discuss different mechanisms of action of oligonucleotides and the possible ways of minimizing non-antisense-related [corrected] effects to improve their specificity.

Mechanism and function of a newly identified CpG DNA motif in human primary B cells

The vertebrate immune system recognizes bacterial DNA based on the presence of unmethylated CpG-dinucleotides in particular base contexts ("CpG motifs"). In contrast to mice, knowledge about CpG-mediated effects on human B cells is poor. In the present study we identify and determine an optimal human CpG motif. A phosphodiester oligonucleotide containing this motif strongly stimulated CD86, CD40, CD54, and MHC class II expression, IL-6 synthesis, and proliferation of primary human B cells. These effects required internalization of the oligonucleotide and endosomal maturation. The molecular mechanism of action of this CpG motif was associated with the sustained induction of the NF-kappaB p50/p65 heterodimer and of the transcription-factor complex AP-1. Transcription-factor activation by CpG DNA was preceded by increased phosphorylation of the stress kinases c-Jun N-terminal kinase and p38, and of activating transcription factor-2. In contrast to CpG, signaling through the B cell receptor led to activation of extracellular receptor kinase and to phosphorylation of a different isoform of c-Jun N-terminal kinase. These studies define the structure of a highly active human CpG motif and characterize its molecular mechanism of action in primary human B cells.

Influence of backbone chemistry on immune activation by synthetic oligonucleotides

Depending on base sequence, DNA displays immunological activities relevant to the design of novel therapeutic agents. To determine the influence of backbone structure on these activities, we tested a series of synthetic phosphodiester and phosphorothioate oligonucleotides in in vitro cultures of murine spleen cells. These compounds were 30 bases long and consisted of either a single base or an immunostimulatory sequence (AACGTT) flanked on 5' and 3' ends by 12 nucleotides of each base. Cell activation was assessed by both thymidine incorporation and expression of cell surface CD69; production of interleukin-6 and interleukin-12 was used as a measure of cytokine stimulation. In these assays, phosphorothioate oligonucleotides induced much higher levels of proliferation, CD69 expression, and cytokine production than the comparable phosphodiester compounds and had activity at lower concentrations. The sequence for optimal stimulation by phosphorothioates varied among responses, however. For example, whereas compounds containing an immunostimulatory sequence all induced similar levels of proliferation and CD69 expression, cytokine production was greatest with compounds with dA and dT flanks. Furthermore, while single base dG oligonucleotides stimulated proliferation as both phosphodiesters and phosphorothioates, they failed to stimulate cytokine production. Together, these findings indicate that base sequence as well as backbone chemistry influence immune activation by synthetic oligonucleotides, with the effects varying among responses. While suggesting differences in the structure-function relationships of nucleic acids in their immune activities, these findings also raise the possibility of the design of agents with specific patterns of immune modulation.

Antiproliferative activity of G-rich oligonucleotides correlates with protein binding

Oligonucleotides have been extensively studied as antisense or antigene agents that can potentially modulate the expression of specific genes. These strategies rely on sequence-specific hybridization of the oligonucleotide to mRNA or genomic DNA. Recently, it has become clear that oligonucleotides often have biological activities that cannot be attributed to their sequence-specific interactions with nucleic acids. Here we describe a series of guanosine-rich phosphodiester oligodeoxynucleotides that strongly inhibit proliferation in a number of human tumor cell lines. The presence of G-quartets in the active oligonucleotides is demonstrated using an UV melting technique. We show that G-rich oligonucleotides bind to a specific cellular protein and that the biological activity of the oligonucleotides correlates with binding to this protein. The G-rich oligonucleotide-binding protein was detected in both nuclear and cytoplasmic extracts and in proteins derived from the plasma membrane of cells. We present strong evidence that this protein is nucleolin, a multifunctional phosphoprotein whose levels are related to the rate of cell proliferation. Our results indicate that binding of G-rich oligonucleotides to nucleolin may be responsible for their non-sequence-specific effects. Furthermore, these oligonucleotides represent a new class of potentially therapeutic agents with a novel mechanism of action.

CpG DNA: a potent signal for growth, activation, and maturation of human dendritic cells

DNA molecules containing unmethylated CpG-dinucleotides in particular base contexts ("CpG motifs") are excellent adjuvants in rodents, but their effects on human cells have been less clear. Dendritic cells (DCs) form the link between the innate and the acquired immune system and may influence the balance between T helper 1 (Th1) and Th2 immune responses. We evaluated the effects of CpG oligodeoxynucleotides alone or in combination with granulocyte-macrophage colony-stimulating factor (GMCSF) on different classes of purified human DCs. For primary dendritic precursor cells isolated from human blood, CpG oligonucleotides alone were superior to GMCSF in promoting survival and maturation (CD83 expression) as well as expression of class II MHC and the costimulatory molecules CD40, CD54, and CD86 of DCs. Both CD4-positive and CD4-negative peripheral blood dendritic precursor cells responded to CpG DNA which synergized with GMCSF but these DCs showed little response to lipopolysaccharide (LPS). In contrast, monocyte-derived DCs did not respond to CpG, but they were highly sensitive to LPS, suggesting an inverse correlation between CpG and LPS sensitivity in different subsets of DCs. Compared with GMCSF, CpG-treated peripheral blood DCs showed enhanced functional activity in the mixed lymphocyte reaction and induced T cells to secrete increased levels of Th1 cytokines. These findings demonstrate the ability of specific CpG motifs to strongly activate certain subsets of human DCs to promote Th1-like immune responses, and support the use of CpG DNA-based trials for immunotherapy against cancer, allergy, and infectious diseases.