Molecularly self-assembled nucleic acid nanoparticles for targeted in vivo siRNA delivery

Nanoparticles are used for delivering therapeutics into cells. However, size, shape, surface chemistry and the presentation of targeting ligands on the surface of nanoparticles can affect circulation half-life and biodistribution, cell-specific internalization, excretion, toxicity and efficacy. A variety of materials have been explored for delivering small interfering RNAs (siRNAs)--a therapeutic agent that suppresses the expression of targeted genes. However, conventional delivery nanoparticles such as liposomes and polymeric systems are heterogeneous in size, composition and surface chemistry, and this can lead to suboptimal performance, a lack of tissue specificity and potential toxicity. Here, we show that self-assembled DNA tetrahedral nanoparticles with a well-defined size can deliver siRNAs into cells and silence target genes in tumours. Monodisperse nanoparticles are prepared through the self-assembly of complementary DNA strands. Because the DNA strands are easily programmable, the size of the nanoparticles and the spatial orientation and density of cancer-targeting ligands (such as peptides and folate) on the nanoparticle surface can be controlled precisely. We show that at least three folate molecules per nanoparticle are required for optimal delivery of the siRNAs into cells and, gene silencing occurs only when the ligands are in the appropriate spatial orientation. In vivo, these nanoparticles showed a longer blood circulation time (t(1/2) ≈ 24.2 min) than the parent siRNA (t(1/2) ≈ 6 min).

Toll-like receptor 9 signaling mediates the anti-inflammatory effects of probiotics in murine experimental colitis

BACKGROUND & AIMS

We tested whether the attenuation of experimental colitis by live probiotic bacteria is due to their immunostimulatory DNA, whether toll-like receptor (TLR) signaling is required, and whether nonviable probiotics are effective.

METHODS

Methylated and unmethylated genomic DNA isolated from probiotics (VSL-3), DNAse-treated probiotics and Escherichia coli (DH5 alpha) genomic DNA were administered intragastrically (i.g.) or subcutaneously (s.c.) to mice prior to the induction of colitis. Viable or gamma-irradiated probiotics were administered i.g. to wild-type mice and mice deficient in different TLR or in the adaptor protein MyD88, 10 days prior to administration of dextran sodium sulfate (DSS) to their drinking water and for 7 days thereafter.

RESULTS

Intragastric and s.c. administration of probiotic and E. coli DNA ameliorated the severity of DSS-induced colitis, whereas methylated probiotic DNA, calf thymus DNA, and DNase-treated probiotics had no effect. The colitis severity was attenuated to the same extent by i.g. delivery of nonviable gamma-irradiated or viable probiotics. Mice deficient in MyD88 did not respond to gamma-irradiated probiotics. The severity of DSS-induced colitis in TLR2 and TLR4 deficient mice was significantly decreased by i.g. administration of gamma-irradiated probiotics, whereas, in TLR9-deficient mice, gamma-irradiated probiotics had no effect.

CONCLUSIONS

The protective effects of probiotics are mediated by their own DNA rather than by their metabolites or ability to colonize the colon. TLR9 signaling is essential in mediating the anti-inflammatory effect of probiotics, and live microorganisms are not required to attenuate experimental colitis because nonviable probiotics are equally effective.

Injection of the cAMP-responsive element into the nucleus of Aplysia sensory neurons blocks long-term facilitation

In both vertebrates and invertebrates, long-term memory differs from short-term in requiring protein synthesis during training. Studies of the gill and siphon withdrawal reflex in Aplysia indicate that similar requirements can be demonstrated at the level of sensory and motor neurons which may participate in memory storage. A single application of serotonin, a transmitter that mediates sensitization, to individual sensory and motor cells in dissociated cell cultures leads to enhanced transmitter release from the sensory neurons that is independent of new macromolecular synthesis. Five applications of serotonin cause a long-term enhancement, lasting one or more days, which requires translation and transcription. Prolonged application or intracellular injection into the sensory neuron of cyclic AMP, a second messenger for the action of serotonin, also produce long-term increases in synaptic strength, suggesting that some of the gene products important for long-term facilitation are cAMP-inducible. In eukaryotic cells, most cAMP-inducible genes so far studied are activated by the cAMP-dependent protein kinase (A kinase), which phosphorylates transcription factors that bind the cAMP-responsive element TGACGTCA. The cAMP-responsive element (CRE) binds a protein dimer of relative molecular mass 43,000, the CRE-binding protein (CREBP), which has been purified and shown to increase transcription when phosphorylated by the A kinase. Here we show that extracts of the Aplysia central nervous system and extracts of sensory neurons contain a set of proteins, including one with properties similar to mammalian CREBPs, that specifically bind the mammalian CRE sequence. Microinjection of the CRE sequence into the nucleus of a sensory neuron selectively blocks the serotonin-induced long-term increase in synaptic strength, without affecting short-term facilitation. Taken together, these observations suggest that one or more CREB-like transcriptional activators are required for long-term facilitation.

DNA polymerase associated with human hepatitis B antigen

DNA polymerase activity was detected in each of eight preparations of concentrated human hepatitis B antigen (HBAg) rich in Dane particles prepared by high-speed centrifugation of antigen-positive human plasma and in none of seven control preparations prepared in the same way from HBAg-negative plasma. The incorporation of (3)H-thymidine-methyl-5'-triphosphate into DNA was dependent on four deoxyribonucleoside triphosphates and MgCl(2). Treatment of the concentrated HBAg preparations with the nonionic detergent Nonidet P-40 (NP40) more than doubled the enzyme activity. Fractionation of the concentrated HBAg preparation in sucrose density gradients after treatment with NP40 revealed that the enzyme activity appeared within the density range of Dane core antigen but at a slightly higher density than the average for core antigen. The only particles observed by electron microscopy in this region of the gradient were typical 28-nm cores, suggesting that the DNA polymerase activity was associated with a subpopulation of cores. No DNA polymerase activity was found in purified 20-nm HBAg particles. The DNA product of the reaction remained associated with the 110S core and was not susceptible to DNase digestion when associated with the core. Inhibition of the reaction by actinomycin D and daunomycin suggested that the reaction was dependent on a DNA template associated with the core.

Activation of NF-kappaB protects hippocampal neurons against oxidative stress-induced apoptosis: evidence for induction of manganese superoxide dismutase and suppression of peroxynitrite production and protein tyrosine nitration

The transcription factor NF-kappaB is expressed in neurons wherein it is activated in response to a variety of stress- and injury-related stimuli including exposure to cytokines such as tumor necrosis factor-alpha (TNFalpha), and excitotoxic and oxidative insults. NF-kappaB may play a role in the anti-death actions of TNFalpha in cultured hippocampal neurons exposed to metabolic and oxidative insults. We now report that pretreatment of hippocampal cell cultures with agents that activate NF-kappaB (TNFalpha and C2-ceramide) confers resistance of neurons to apoptosis induced by the oxidative insults FeSO4 and amyloid beta-peptide (Abeta25-35). The neuroprotective actions of TNFalpha and ceramide were abolished in cultures cotreated with kappaB decoy DNA demonstrating a requirement for NF-kappaB activation for prevention of cell death. Levels of manganese superoxide dismutase (Mn-SOD) in neurons were increased following exposure of cultures to TNFalpha and ceramide in control cultures, but not in cultures cotreated with kappaB decoy DNA. FeSO4 and Abeta25-35 induced accumulation of mitochondrial peroxynitrite, and membrane lipid peroxidation, in neurons. Peroxynitrite accumulation and lipid peroxidation were largely prevented in neurons pretreated with TNFalpha and ceramide prior to exposure to FeSO4 and Abeta25-35, an effect blocked by kappaB decoy DNA. Immunoreactivity of neurons with an anti-nitrotyrosine antibody was increased following exposure to FeSO4 and Abeta25-35; TNFalpha and C2-ceramide suppressed protein tyrosine nitration, and kappaB decoy DNA blocked the effects of TNFalpha and C2-ceramide. Finally, the peroxynitrite scavenger uric acid protected neurons against apoptosis induced by FeSO4 and Abeta, and suppressed peroxynitrite accumulation. We conclude that, by inducing production of Mn-SOD and suppressing peroxynitrite formation and membrane lipid peroxidation, NF-kappaB plays an anti-apoptotic role in neurodegenerative conditions that involve oxidative stress. The data further suggest important roles for peroxynitrite and NF-kappaB in the pathogenesis of neuronal degeneration in Alzheimer's disease.

Cellular immunostimulation by CpG-sequence-coated DNA origami structures

To investigate the potential of DNA origami constructs as programmable and noncytotoxic immunostimulants, we tested the immune responses induced by hollow 30-helix DNA origami tubes covered with up to 62 cytosine-phosphate-guanine (CpG) sequences in freshly isolated spleen cells. Unmethylated CpG sequences that are highly specific for bacterial DNA are recognized by a specialized receptor of the innate immune system localized in the endosome, the Toll-like receptor 9 (TLR9). When incubated with oligonucleotides containing CpGs, immune cells are stimulated through TLR9 to produce and secrete cytokine mediators such as interleukin-6 (IL-6) and interleukin-12p70 (IL-12p70), a process associated with the initiation of an immune response. In our studies, the DNA origami tube built from an 8634 nt long variant of the commonly used single-stranded DNA origami scaffold M13mp18 and 227 staple oligonucleotides decorated with 62 CpG-containing oligonucleotides triggered a strong immune response, characterized by cytokine production and immune cell activation, which was entirely dependent on TLR9 stimulation. Such decorated origami tubes also triggered higher immunostimulation than equal amounts of CpG oligonucleotides associated with a standard carrier system such as Lipofectamine. In the absence of CpG oligonucleotides, cytokine production induced by the origami tubes was low and was not related to TLR9 recognition. Fluorescent microscopy revealed localization of CpG-containing DNA origami structures in the endosome. The DNA constructs showed in contrast to Lipofectamine no detectable toxicity and did not affect the viability of splenocytes. We thus demonstrate that DNA origami constructs represent a delivery system for CpG oligonucleotides that is both efficient and nontoxic.

Sulfated polyanion inhibition of scrapie-associated PrP accumulation in cultured cells

The accumulation of an abnormal, protease-resistant form of the protein PrP (PrP-res) in hosts with scrapie and related transmissible spongiform encephalopathies appears to be important in disease pathogenesis. To gain insight into the mechanism of PrP-res accumulation and the in vivo antiscrapie activity of certain polyanions, we have studied effects of sulfated glycans on PrP metabolism in scrapie-infected neuroblastoma cells. Pentosan polysulfate, like the amyloid-binding dye Congo red, potently inhibited the accumulation of PrP-res in these cells without apparent effects on the metabolism of the normal isoform. The inhibition was due primarily to prevention of new PrP-res accumulation rather than destabilization of preexisting PrP-res. PrP-res accumulation remained depressed in the cultures after removal of the inhibitors. The activities of other sulfated glycans, nonsulfated polyanions, dextran, and DEAE-dextran were compared with those of pentosan polysulfate and Congo red. This comparison provided evidence that the density of sulfation and molecular size are factors influencing anti-PrP-res activity of sulfated glycans. The relative potencies of these compounds corresponded well with their previously determined antiscrapie activities in vivo, suggesting that the prophylactic effects of sulfated polyanions may be due to inhibition of PrP-res accumulation. Since PrP-res amyloid is known to contain sulfated glycosaminoglycans, we reason that these inhibitors may competitively block an interaction between PrP and endogenous glycosaminoglycans that is essential for its accumulation in a protease-resistant, potentially amyloidogenic state.

Transfection of a DNA locus that mediates the conversion of 10T1/2 fibroblasts to myoblasts

Stable myoblast cell lines were isolated after a brief exposure of mouse fibroblasts (10T1/2 cells) to 5-azacytidine. We show that transfection of 10T1/2 cells with DNA from these azacytidine-induced myoblasts (or from mouse C2C12 myoblasts) results in myogenic conversion of approximately 1 in 15,000 transfected colonies. In contrast, transfection of 10T1/2 cells with DNA from nonmyogenic cells (parental 10T1/2 cell DNA) does not give rise to myoblast colonies. These results indicate that an azacytidine-induced structural modification (presumably demethylation) in the DNA of a single locus is sufficient to convert 10T1/2 cells into determined myoblasts.

Extracellular histones increase plasma thrombin generation by impairing thrombomodulin-dependent protein C activation

BACKGROUND

Histones are basic proteins that contribute to cell injury and tissue damage when released into the extracellular space. They have been attributed a prothrombotic activity, because their injection into mice induces diffuse microvascular thrombosis. The protein C-thrombomodulin (TM) system is a fundamental regulator of coagulation, particularly in the microvasculature, and its activity can be differentially influenced by interaction with several cationic proteins.

OBJECTIVE

To evaluate the effect of histones on the protein C-TM system in a plasma thrombin generation assay and in purified systems.

METHODS

The effect of histones on plasma thrombin generation in the presence or absence of TM was analyzed by calibrated automated thrombinography. Protein C activation in purified systems was evaluated by chromogenic substrate cleavage. The binding of TM and protein C to histones was evaluated by solid-phase binding assay.

RESULTS

Histones dose-dependently increased plasma thrombin generation in the presence of TM, independently of its chondroitin sulfate moiety. This effect was not caused by inhibition of activated protein C activity, but by the impairment of TM-mediated protein C activation. Histones were able to bind to both protein C and TM, but the carboxyglutamic acid domain of protein C was required for their effect. Histones H4 and H3 displayed the highest activity. Importantly, unlike heparin, DNA did not inhibit the potentiating effect of histones on thrombin generation.

CONCLUSIONS

Histones enhance plasma thrombin generation by reducing TM-dependent protein C activation. This mechanism might contribute to microvascular thrombosis induced by histones in vivo at sites of organ failure or severe inflammation.

Type I interferon-mediated stimulation of T cells by CpG DNA

Immunostimulatory DNA and oligodeoxynucleotides containing unmethylated CpG motifs (CpG DNA) are strongly stimulatory for B cells and antigen-presenting cells (APCs). We report here that, as manifested by CD69 and B7-2 upregulation, CpG DNA also induces partial activation of T cells, including naive-phenotype T cells, both in vivo and in vitro. Under in vitro conditions, CpG DNA caused activation of T cells in spleen cell suspensions but failed to stimulate highly purified T cells unless these cells were supplemented with APCs. Three lines of evidence suggested that APC-dependent stimulation of T cells by CpG DNA was mediated by type I interferons (IFN-I). First, T cell activation by CpG DNA was undetectable in IFN-IR-/- mice. Second, in contrast to normal T cells, the failure of purified IFN-IR-/- T cells to respond to CpG DNA could not be overcome by adding normal IFN-IR+ APCs. Third, IFN-I (but not IFN-gamma) caused the same pattern of partial T cell activation as CpG DNA. Significantly, T cell activation by IFN-I was APC independent. Thus, CpG DNA appeared to stimulate T cells by inducing APCs to synthesize IFN-I, which then acted directly on T cells via IFN-IR. Functional studies suggested that activation of T cells by IFN-I was inhibitory. Thus, exposing normal (but not IFN-IR-/-) T cells to CpG DNA in vivo led to reduced T proliferative responses after TCR ligation in vitro.

Immunostimulatory DNA ameliorates experimental and spontaneous murine colitis

BACKGROUND & AIMS

Impaired mucosal barrier, cytokine imbalance, and dysregulated CD4(+) T cells play important roles in the pathogenesis of experimental colitis and human inflammatory bowel disease. Immunostimulatory DNA sequences (ISS-DNA) and their synthetic oligonucleotide analogs (ISS-ODNs) are derived from bacterial DNA, are potent activators of innate immunity at systemic and mucosal sites, and can rescue cells from death inflicted by different agents. We hypothesized that these combined effects of ISS-DNA could inhibit the damage to the colonic mucosa in chemically induced colitis and thereby limit subsequent intestinal inflammation.

METHODS

The protective and the anti-inflammatory effect of ISS-ODN administration were assessed in dextran sodium sulfate-induced colitis and in 2 models of hapten-induced colitis in Balb/c mice. Similarly, these effects of ISS-ODN were assessed in spontaneous colitis occurring in IL-10 knockout mice.

RESULTS

In all models of experimental and spontaneous colitis examined, ISS-ODN administration ameliorated clinical, biochemical, and histologic scores of colonic inflammation. ISS-ODN administration inhibited the induction of colonic proinflammatory cytokines and chemokines and suppressed the induction of colonic matrix metalloproteinases in both dextran sodium sulfate- and hapten-induced colitis.

CONCLUSIONS

As the colon is continuously exposed to bacterial DNA, these findings suggest a physiologic, anti-inflammatory role for immunostimulatory DNA in the GI tract. Immunostimulatory DNA deserves further evaluation for the treatment of human inflammatory bowel disease.

DNA from bacteria, but not from vertebrates, induces interferons, activates natural killer cells and inhibits tumor growth

The nucleic acid fraction from cells of 6 species of bacterium and 2 kinds of vertebrate, calf and salmon, was extracted and purified by the same procedures as described previously. When the spleen cells from BALB/c mice were incubated with the nucleic acid fraction from either of the bacteria, natural killer (NK) activity of the cells was remarkably elevated and the cells produced factors to activate macrophages and to inhibit viral growth. It was shown that the factor to activate macrophages was interferon (IFN)-gamma and that to inhibit viral growth was IFN-alpha/beta. On the other hand, the nucleic acid fraction from either of the vertebrate cells did not show such activities. Pretreatment of the bacterial nucleic acid fraction with DNase, but not with RNase, abrogated completely the biological activities. The activities of the bacterial nucleic acid were not influenced by the presence of polymyxin B, an inhibitor of lipopolysaccharide (LPS), and the spleen cells from not only BALB/c mice but also LPS-insensitive C3H/HeJ mice were activated, indicating that the activities of the fraction were not ascribed to LPS contaminated possibly into the fraction, but to DNA itself. Intralesional injection with the bacterial DNA fraction caused regression of mouse IMC tumors, but the injection with the vertebrate DNA fraction did not. These findings prompted us to examine the biological activities of DNA samples from a variety of animals and plants, which were provided from other laboratories or purchased from manufacturers. All of the DNA samples from cells of 5 kinds of bacterium, 2 of virus and 4 of invertebrate augmented NK activity and induced IFN, more or less, in mouse spleen calls, while the DNA from 10 kinds of vertebrate, including 3 of fish and 5 of mammal, showed no such activities. The DNA from 2 species of plants, were also inactive. Possible mechanisms to explain the different biological activities of DNA from different cell sources were discussed based on our previous finding that the particular palindromic sequences with a G-C motif(s) are required for induction of IFNs and activation of NK cells with synthetic 30-mer oligonucleotides.

Spin-trapping and direct electron spin resonance investigations of the redox metabolism of quinone anticancer drugs

The superoxide free radical has been spin trapped in microsomal incubations containing adriamycin, daunorubicin, and mitomycin C. The time sequence of the appearance of the spin-trapped superoxide and the semiquinone radical metabolite of these quinone-containing anticancer drugs indicates that air oxidation of the semiquinone is responsible for the superoxide formation. Superoxide dismutase prevents the formation of the superoxide spin adducts. Microsomal incubations containing anthracyclines intercalated in DNA produce much less superoxide than incubations free of DNA. The first unambiguous ESR evidence for the semiquinone metabolite of mitomycin C in a biological system is also presented.

TLR9 and the NLRP3 inflammasome link acinar cell death with inflammation in acute pancreatitis

BACKGROUND & AIMS

Acute pancreatitis is characterized by early activation of intracellular proteases followed by acinar cell death and inflammation. Activation of damage-associated molecular pattern (DAMP) receptors and a cytosolic complex termed the inflammasome initiate forms of inflammation. In this study, we examined whether DAMP-receptors and the inflammasome provide the link between cell death and the initiation of inflammation in pancreatitis.

METHODS

Acute pancreatitis was induced by caerulein stimulation in wild-type mice and mice deficient in components of the inflammasome (apoptosis-associated speck-like protein containing a caspase recruitment domain [ASC], NLRP3, caspase-1), Toll-like receptor 9 (TLR9), or the purinergic receptor P2X(7). Resident and infiltrating immune cell populations and pro-interleukin-1β expression were characterized in control and caerulein-treated adult murine pancreas. TLR9 expression was quantified in pancreatic cell populations. Additionally, wild-type mice were pretreated with a TLR9 antagonist before induction of acute pancreatitis by caerulein or retrograde bile duct infusion of taurolithocholic acid 3-sulfate.

RESULTS

Caspase-1, ASC, and NLRP3 were required for inflammation in acute pancreatitis. Genetic deletion of Tlr9 reduced pancreatic edema, inflammation, and pro-IL-1β expression in pancreatitis. TLR9 was expressed in resident immune cells of the pancreas, which are predominantly macrophages. Pretreatment with the TLR9 antagonist IRS954 reduced pancreatic edema, inflammatory infiltrate, and apoptosis. Pretreatment with IRS954 reduced pancreatic necrosis and lung inflammation in taurolithocholic acid 3-sulfate-induced acute pancreatitis.

CONCLUSIONS

Components of the inflammasome, ASC, caspase-1, and NLRP3, are required for the development of inflammation in acute pancreatitis. TLR9 and P2X(7) are important DAMP receptors upstream of inflammasome activation, and their antagonism could provide a new therapeutic strategy for treating acute pancreatitis.

Activation of human B cells by phosphorothioate oligodeoxynucleotides

To investigate the potential of DNA to elicit immune responses in man, we examined the capacity of a variety of oligodeoxynucleotides (ODNs) to stimulate highly purified T cell-depleted human peripheral blood B cells. Among 47 ODNs of various sequences tested, 12 phosphorothioate oligodeoxynucleotides (sODNs) induced marked B cell proliferation and Ig production. IL-2 augmented both proliferation and production of IgM, IgG, and IgA, as well as IgM anti-DNA antibodies, but was not necessary for B cell stimulation. Similarly, T cells enhanced stimulation, but were not necessary for B cell activation. After stimulation with the active sODNs, more than 95% of B cells expressed CD25 and CD86. In addition, B cells stimulated with sODNs expressed all six of the major immunoglobulin VH gene families. These results indicate that the human B cell response to sODN is polyclonal. Active sODN coupled to Sepharose beads stimulated B cells as effectively as the free sODN, suggesting that stimulation resulted from engagement of surface receptors. These data indicate that sODNs can directly induce polyclonal activation of human B cells in a T cell-independent manner by engaging as yet unknown B cell surface receptors.

An oligomer complementary to c-myb-encoded mRNA inhibits proliferation of human myeloid leukemia cell lines

To study the role of the protooncogene c-myb in regulating myeloid leukemia cell proliferation and differentiation, we exposed cells of the human leukemia lines HL-60, ML-3, KG-1, and KG-1a to an oligodeoxynucleotide complementary to an 18-base-pair (bp) sequence of c-myb-encoded mRNA. This treatment resulted in a significant decrease in cell proliferation in all of the lines, which was most marked in HL-60 cells. After 5 days in culture, in several separate experiments with different oligomer preparations, 75% growth inhibition was observed in c-myb antisense treated cells in comparison to untreated HL-60 cells. Two c-myb antisense oligomers of identical length with either 2- or 4-bp mismatches had no effect on cell growth nor did an 18-bp c-myb sense or myeloperoxidase antisense oligomer. The effect of a c-myc antisense oligomer (18 bp) on the growth of HL-60, KG-1, and KG-1a cells was also studied. This oligomer had much less inhibitory effect on cell proliferation than did the c-myb antisense sequence. Interestingly, although c-myc antisense treatment induced maturation of HL-60 cells while it inhibited cell proliferation, such an effect was not noted in c-myb antisense treated cells. These studies indicate that the nuclear protein encoded by the c-myb protooncogene is required for maintenance of proliferation in certain leukemia cell lines. In compared to c-myc protein suggest that, at least in HL-60 cells, c-myc amplification or N-ras activation may not be sufficient to maintain the leukemic growth in the absence of c-myb protein. These findings support the hypothesis that development and maintenance of a malignant phenotype requires a multiplicity of interrelated genetic events.

CpG blocks immunosuppression by myeloid-derived suppressor cells in tumor-bearing mice

PURPOSE

The Toll-like receptor (TLR) 9 ligand CpG has been used successfully for the immunotherapy of cancer. Chronic CpG application in tumor-free hosts leads, however, to the expansion of myeloid-derived suppressor cells (MDSC), which can cause T-cell suppression and may thus hamper the development of an effective immune response. Here, we investigated the effect of TLR9 activation on the function of MDSC in tumor-bearing mice.

EXPERIMENTAL DESIGN

We investigated the effect of CpG treatment on the number, phenotype, and function of MDSC in mice bearing subcutaneous C26 tumors and in CEA424-TAg mice bearing autochthonous gastric tumors.

RESULTS

CpG treatment blocks the suppressive activity of MDSC on T-cell proliferation in both tumor models. Inhibition of MDSC function by CpG was particularly pronounced for a highly suppressive Ly6G(hi) polymorphonuclear subset of MDSC. We further show that TLR9 activation by CpG promotes maturation and differentiation of MDSC and strongly decreases the proportion of Ly6G(hi) MDSC in both tumor-bearing and tumor-free mice. We demonstrate that IFN-α produced by plasmacytoid dendritic cells upon CpG stimulation is a key effector for the induction of MDSC maturation in vitro and show that treatment of mice with recombinant IFN-α is sufficient to block MDSC suppressivity.

CONCLUSIONS

We show here for the first time that TLR9 activation inhibits the regulatory function of MDSC in tumor-bearing mice and define a role for the antitumoral cytokine IFN-α in this process.

DNA is an antimicrobial component of neutrophil extracellular traps

Neutrophil extracellular traps (NETs) comprise an ejected lattice of chromatin enmeshed with granular and nuclear proteins that are capable of capturing and killing microbial invaders. Although widely employed to combat infection, the antimicrobial mechanism of NETs remains enigmatic. Efforts to elucidate the bactericidal component of NETs have focused on the role of NET-bound proteins including histones, calprotectin and cathepsin G protease; however, exogenous and microbial derived deoxyribonuclease (DNase) remains the most potent inhibitor of NET function. DNA possesses a rapid bactericidal activity due to its ability to sequester surface bound cations, disrupt membrane integrity and lyse bacterial cells. Here we demonstrate that direct contact and the phosphodiester backbone are required for the cation chelating, antimicrobial property of DNA. By treating NETs with excess cations or phosphatase enzyme, the antimicrobial activity of NETs is neutralized, but NET structure, including the localization and function of NET-bound proteins, is maintained. Using intravital microscopy, we visualized NET-like structures in the skin of a mouse during infection with Pseudomonas aeruginosa. Relative to other bacteria, P. aeruginosa is a weak inducer of NETosis and is more resistant to NETs. During NET exposure, we demonstrate that P. aeruginosa responds by inducing the expression of surface modifications to defend against DNA-induced membrane destabilization and NET-mediated killing. Further, we show induction of this bacterial response to NETs is largely due to the bacterial detection of DNA. Therefore, we conclude that the DNA backbone contributes both to the antibacterial nature of NETs and as a signal perceived by microbes to elicit host-resistance strategies.

Comprising the first line of the innate immune response, neutrophils combat infectious microorganisms through the release of toxic molecules, phagocytosis of invaders and the production of the recently characterized neutrophil extracellular traps (NETs). The antimicrobial activity of NETs has been attributed to proteins bound to the DNA backbone. Our results demonstrate that the DNA lattice of each NET is potently antibacterial and elicits upregulation of protective surface modifications by the opportunistic bacterial pathogen Pseudomonas aeruginosa. These modifications, previously shown to protect bacteria from antimicrobial peptides, confer greater bacterial tolerance to DNA and NET-mediated antibacterial activity. Treatments that quench the cation chelating capacity of DNA restore bacterial viability and suppress the expression of surface modifications even in the presence of intact NETs. These observations highlight the dual function of DNA as an antibacterial component of NETs, but also a signal perceived by bacteria to induce broad host resistance strategies. Therefore, the ability of P. aeruginosa to sense and defend against the antibacterial activity of neutrophil extracellular traps may contribute to long-term survival in chronic infection sites including the Cystic Fibrosis lung.

ISWI is an ATP-dependent nucleosome remodeling factor

The ATPase ISWI is a subunit of several distinct nucleosome remodeling complexes that increase the accessibility of DNA in chromatin. We found that the isolated ISWI protein itself was able to carry out nucleosome remodeling, nucleosome rearrangement, and chromatin assembly reactions. The ATPase activity of ISWI was stimulated by nucleosomes but not by free DNA or free histones, indicating that ISWI recognizes a specific structural feature of nucleosomes. Nucleosome remodeling, therefore, does not require a functional interaction between ISWI and the other subunits of ISWI complexes. The role of proteins associated with ISWI may be to regulate the activity of the remodeling engine or to define the physiological context within which a nucleosome remodeling reaction occurs.

Genomic DNA released by dying cells induces the maturation of APCs

Mature APCs play a key role in the induction of Ag-specific immunity. This work examines whether genomic DNA released by dying cells provides a stimulus for APC maturation. Double-stranded but not single-stranded genomic DNA triggered APC to up-regulate expression of MHC class I/II and various costimulatory molecules. Functionally, dsDNA enhanced APC function in vitro and improved primary cellular and humoral immune responses in vivo. These effects were dependent on the length and concentration of the dsDNA but were independent of nucleotide sequence. The maturation of APC induced by dsDNA may promote host survival by improving immune surveillance at sites of tissue injury/infection.

Inhibition of human immunodeficiency virus in early infected and chronically infected cells by antisense oligodeoxynucleotides and their phosphorothioate analogues

Antisense oligodeoxynucleotides, both the phosphorothioate analogues and unmodified oligomers of the same sequence, inhibit replication and expression of human immunodeficiency virus already growing in tissue cultures of MOLT-3 cells with much greater efficacy than do mismatched ("random") oligomers and homooligomers of the same length and with the same internucleotide modification. This preferential inhibitory effect is elicited in as short a time as 4-24 hr postinfection. Likewise, antisense oligomers exhibit greater inhibitory effects on human immunodeficiency virus in chronically infected cells than do mismatched oligomers and homooligomers. Phosphorothioate antisene oligomers are up to 100 times more potent than unmodified oligomers of the same sequence in these inhibitory assays. These results, in major respects, confirm and extend those recently published by Matsukura et al. [Matsukura, M., Zon, G., Shinozuka, K., Robert-Guroff, M., Shimada, T., Stein, C. A., Mitsuza, H., Wong-Staal, F., Cohen, J. S. & Broder, S. (1989) Proc. Natl. Acad. Sci. USA 86, 4244-4248]. They also point out the importance of computer analysis of sequences though to be random but that in reality contain significant areas of likely hybridization, either to the viral genome or to the complementary DNA strand synthesized from it. They thus reinforce the concept that specific base pairing is a crucial feature of oligonucleotide inhibition of human immunodeficiency virus.

The molecular basis for the lack of immunostimulatory activity of vertebrate DNA

Macrophages and B cells are activated by unmethylated CpG-containing sequences in bacterial DNA. The lack of activity of self DNA has generally been attributed to CpG suppression and methylation, although the role of methylation is in doubt. The frequency of CpG in the mouse genome is 12.5% of Escherichia coli, with unmethylated CpG occurring at approximately 3% the frequency of E. coli. This suppression of CpG alone is insufficient to explain the inactivity of self DNA; vertebrate DNA was inactive at 100 micro g/ml, 3000 times the concentration at which E. coli DNA activity was observed. We sought to resolve why self DNA does not activate macrophages. Known active CpG motifs occurred in the mouse genome at 18% of random occurrence, similar to general CpG suppression. To examine the contribution of methylation, genomic DNAs were PCR amplified. Removal of methylation from the mouse genome revealed activity that was 23-fold lower than E. coli DNA, although there is only a 7-fold lower frequency of known active CpG motifs in the mouse genome. This discrepancy may be explained by G-rich sequences such as GGAGGGG, which potently inhibited activation and are found in greater frequency in the mouse than the E. coli genome. In summary, general CpG suppression, CpG methylation, inhibitory motifs, and saturable DNA uptake combined to explain the inactivity of self DNA. The immunostimulatory activity of DNA is determined by the frequency of unmethylated stimulatory sequences within an individual DNA strand and the ratio of stimulatory to inhibitory sequences.