CpG motifs in bacterial DNA trigger direct B-cell activation

CpG DNA and LPS induce distinct patterns of activation in human monocytes

A specific set of immune functions is switched on in response to DNA containing unmethylated CpG dinucleotides in particular base contexts ('CpG motifs'). Plasmids, viral vectors and antisense oligodeoxynucleotides used for DNA vaccination, gene replacement or gene blockade contain immunostimulatory CpG motifs which may have independent biological activity. Although the immune stimulatory effects of CpG motifs on murine cells are well established, the evaluation of their possible effects on human cells is complicated by the higher LPS sensitivity of human leukocytes compared with those in mice. To address this issue, we analyzed CpG- and LPS-mediated immune activation of human PBMC. The biologic activity of LPS could be detected within 4 h using intracellular TNF staining of monocytes with flow cytometry at concentrations just one-twentieth (0.0014 Eu/ml) of the lower detection limit for the routinely used LAL assay (0.03 EU/ml). In contrast to the rapid LPS response, CpG DNA-stimulated TNF and IL-6 synthesis in human monocytes was not detectable until 18 h. E. coli DNA induced IL-6 synthesis in a concentration-dependent manner (30 micrograms/ml E. coli DNA; 409 pg/ml +/- 75 pg/ml, n = 7, IL-6 ELISA), but calf thymus DNA did not (< 10 pg/ml). Likewise, the CpG oligodeoxynucleotides 1760 (phosphorothioate) and 2059 (unmodified) induced IL-6 synthesis, but the corresponding control oligonucleotides 1908 and 2077 did not CpG DNA and LPS enhanced IL-6 synthesis synergistically. ICAM-1-expression of monocytes was increased 4.6-fold by E. coli DNA, 3.5-fold by 1760 and three-fold by 2059, compared with 3.6-fold by a maximal LPS stimulus and no change with non-CpG DNA. In conclusion, CpG-motifs induce TNF, IL-6 and ICAM-1 expression in human monocytes, but the kinetics of this differ from that induced by LPS, which makes it possible to distinguish immune activation by these agents. These results have important implications for the clinical development of therapeutic DNA in humans.

Effect of immune response on gene transfer to the lung via systemic administration of cationic lipidic vectors

Cationic lipid-mediated intravenous gene delivery shows promise in treating pulmonary diseases including lung tumor metastases, pulmonary hypertension, and acute respiratory distress syndrome. Nevertheless, clinical applications of cationic lipidic vectors via intravenous administration are limited by their transient gene expression. In addition, repeated dosing is not effective at frequent intervals. In an effort to elucidate the mechanism of gene inactivation, we report in this study that cationic lipid-protamine-DNA (LPD) complexes, but not each component alone, can induce a high level of cytokine production, including interferon-gamma and tumor necrosis factor-alpha. Furthermore, we demonstrate that LPD administration triggers apoptosis in the lung, a phenomenon that may be mediated in part by the two cytokines. Treatment of mice with antibodies against the two cytokines prolongs the duration of gene expression and also improves lung transfection on a second administration of LPD. Although the mechanism underlying LPD-induced cytokine production is unclear, methylation of the DNA significantly decreased the level of both interferon-gamma and tumor necrosis factor-alpha, suggesting that unmethylated CpG sequences in plasmid DNA play an important role. These data suggest that decreasing the CpG-mediated immune response while not affecting gene expression may be a useful therapeutic strategy to improve cationic lipid-mediated intravenous gene delivery to the lung.

Conformational variation of the central CG site in d(ATGACGTCAT)2 and d(GAAAACGTTTTC)2. An NMR, molecular modelling and 3D-homology investigation

The determination of the solution structure of two self-complementary oligomers d(ATGACGTCAT)2 (CG10) and d(GAAAACGTTTTC)2 (CG12), both containing the 5'-pur-ACGT-pyr-3' sequence, is reported. The impact of the base context on the conformation of the central CpG site has been examined by a combined approach of: (a) 2D 1H-NMR and 31P-NMR; (b) molecular mechanics under experimental constraints; (c) back-calculations of NOESY spectra and iterative refinements of distances; and (d) 3D-homology search of the central tetrad ACGT within the complete oligonucleotides. A full NMR study of each fragment is achieved by means of standard 2D experiments: NOESY, 2D homonuclear Hartmann-Hahn spectroscopy, double-quantum-filtered COSY and heteronuclear 1H-31P correlation. Sugar phase angle, epsilon-zeta difference angle and NOE-derived distances are input as experimental constraints to generate molecular models by energy minimization with the help of jumna. The morass program is used to iteratively refine the structures obtained. The similarity of the two ACGTs within the whole oligonucleotides is investigated. Both the decamer and the dodecamer adopt a B-like DNA conformation. However, the helical parameters within this conformational type are significantly different in CG12 and CG10. The central CpG step conformation is not locked by its nearest environment (5'A and 3'T) as seen from the structural analysis of ACGT in the two molecules. In CG12, despite the presence of runs of A-T pairs, CpG presents a high twist of 43 degrees and a sugar phase at the guanine of about 180 degrees, previously observed in other ACGT-containing-oligomers. Conversely, ACGT in CG10 exhibits strong inclinations, positive rolls, a flat profile of sugar phase, twist and glycosidic angles, as a result of the nucleotide sequence extending beyond the tetrad. The structural specificity of CG10 and its flexibility (as reflected by its energy) are tentatively related to the process of recognition of the cyclic AMP response element by its cognate protein.

Dose Dependence of CTL Precursor Frequency Induced by a DNA Vaccine and Correlation with Protective Immunity Against Influenza Virus Challenge

Intramuscular injection of BALB/c mice with a DNA plasmid encoding nucleoprotein (NP) from influenza virus A/PR/8/34 (H1N1) provides cross-strain protection against lethal challenge with influenza virus A/HK/68 (H3N2). CTL specific for the H-2Kd-restricted epitope NP147–155 are present in these mice and are thought to play a role in the protection. To assess the effectiveness of NP DNA immunization in comparison with influenza virus infection in the induction of CTL responses, we monitored the frequency of CTL precursors (CTLp) in mice following i.m. injection with NP DNA or intranasal infection with influenza virus and showed that the CTLp frequency in NP DNA-immunized mice can reach levels found in mice that had been infected with influenza virus. We also measured the CTLp frequency, anti-NP Ab titers, and T cell proliferative responses in mice that were injected with titrated dosages of NP DNA and documented a correlation of the CTLp frequency and the Ab titers, but not proliferative responses, with the injection dose. Furthermore, we observed a positive correlation between the frequency of NP147–155 epitope-specific CTLp and the extent of protective immunity against cross-strain influenza challenge induced by NP DNA injection. Collectively, these results and our early observations from adoptive transfer experiments of in vitro activated lymphocytes from NP DNA-immunized mice suggest a protective function of NP-specific CTLp in mice against cross-strain influenza virus challenge.

Phagocytic antigen processing and effects of microbial products on antigen processing and T-cell responses

Processing of exogenous antigens and microbes involves contributions by multiple different endocytic and phagocytic compartments. During the processing of soluble antigens, different endocytic compartments have been demonstrated to use distinct antigen-processing mechanisms and to process distinct sets of antigenic epitopes. Processing of particulate and microbial antigens involves phagocytosis and functions contributed by phagocytic compartments. Recent data from our laboratory demonstrate that phagosomes containing antigen-conjugated latex beads are fully competent class II MHC (MHC-II) antigen-processing organelles, which generate peptide:MHC-II complexes. In addition, phagocytosed antigen enters an alternate class I MHC (MHC-I) processing pathway that results in loading of peptides derived from exogenous antigens onto MHC-I molecules, in contrast to the cytosolic antigen source utilized by the conventional MHC-I antigen-processing pathway. Antigen processing and other immune response mechanisms may be activated or inhibited by microbial components to the benefit of either the host or the pathogen. For example, antigen processing and T-cell responses (e.g. Th1 vs Th2 differentiation) are modulated by multiple distinct microbial components, including lipopolysaccharide, cholera toxin, heat labile enterotoxin of Escherichia coli, DNA containing CpG motifs (found in prokaryotic and invertebrate DNA but not mammalian DNA) and components of Mycobacterium tuberculosis.

Mammalian granulocyte-macrophage colony-stimulating factor and some CpG motifs have an effect on the immunogenicity of DNA and subunit vaccines in fish

A eukaryotic plasmid DNA carrying the AACGTT CpG motif in its ampR gene is a 'danger' signal for mice and caused an increase in the specific antibody titres of fish and mice after immunization with beta-galactosidase (beta-gal). A second pUC-based plasmid, which is inactive in mice and contains the GACGTC CpG motif in its cytomegalovirus (CMV) promoter, had no effect on antibody responses to beta-gal in either fish or mice. A synthetic oligonucleotide, which contains the GACGTT motif, potentiated antibody responses to co-administered beta-gal protein in mice, but not in fish. This is early evidence that lower and higher vertebrates recognize different unmethylated CpG motifs as 'danger' signals. In addition, plasmid DNA expressing mouse granulocyte-macrophage colony-stimulating factor (GM-CSF) had a marked effect on cytotoxic T-cell-like activity in fish by reducing the average number of myofibres that expressed beta-gal, 28 days after co-injection with plasmid DNA expressing beta-gal. Although the mechanism by which the mouse GM-CSF exerted its biological effects in fish is unknown, this finding might have important implications for fish vaccination, particularly when cytotoxic T cells may play a critical role.

Inhibition of translation of hepatitis C virus RNA by 2-modified antisense oligonucleotides

Inhibition of hepatitis C virus (HCV) gene expression by antisense oligonucleotides was investigated using both a rabbit reticulocyte lysate in vitro translation assay and a transformed human hepatocyte cell expression assay. Screening of overlapping oligonucleotides complementary to the HCV 5' noncoding region and the core open reading frame (ORF) identified a region susceptible to translation inhibition between nucleotides 335 and 379. Comparison of 2'-deoxy-, 2'-O-methyl-, 2'-O-methoxyethyl-, 2'-O-propyl-, and 2'-fluoro-modified phosphodiester oligoribonucleotides demonstrated that increased translation inhibition correlated with both increased binding affinity and nuclease stability. In cell culture assays, 2'-O-methoxyethyl-modified oligonucleotides inhibited HCV core protein synthesis with comparable potency to phosphorothioate oligodeoxynucleotides. Inhibition of HCV core protein expression by 2'-modified oligonucleotides occurred by an RNase H-independent translational arrest mechanism.

Decreased bone resorption, osteoclast differentiation, and expression of vacuolar H+-ATPase in antisense DNA-treated mouse metacarpal and calvaria cultures ex vivo

Expression and function of vacuolar H(+)-ATPase, a key enzyme in bone resorption, were monitored in antisense DNA-treated bone organ cultures ex vivo. A novel fluoroimmunoassay was used to quantitate mRNA levels after treatment with various antisense, sense, or random DNA oligonucleotides. Conventional slot blots and in vitro translation experiments were used to monitor the efficiency of the antisense molecules. In cell cultures, the used antisense molecules were transported into osteoclasts and a population of mononuclear cells. A significant decrease in bone resorption and in the expression of the 16 kDa, 31 kDa, 42 kDa, 60 kDa, 70 kDa, and 116 kDa subunits of V-ATPase was seen after antisense treatment. Also, osteoclast differentiation was decreased in antisense-treated mouse metacarpal cultures. These data show that the proper function of V-ATPase in osteoclasts requires expression of the 16 kDa, 31 kDa, 42 kDa, 60 kDa, 70 kDa, and 116 kDa subunits of V-ATPase. Antisense DNA molecules can be used to inhibit osteoclast differentiation and function in tissue cultures, in which the physical and chemical cellular environment resembles that in vivo. However, more studies are needed to learn if antisense DNA molecules can be used for inhibiting bone resorption also in vivo.

CpG-oligodeoxynucleotides co-stimulate primary T cells in the absence of antigen-presenting cells

CpG-containing oligodeoxynucleotides (CpG-ODN) act as powerful adjuvant during in vivo induction of T cell responses. While CpG-ODN directly activate antigen-presenting cells (APC) and thus exert an extrinsic activity on T cells, it is unclear whether they directly affect T cells (intrinsic activity). Here we analyze the effects of CpG-ODN on T cells in an APC-free cell culture. We report that CpG-ODN co-stimulate T cells provided they were triggered via their TCR. CpG-ODN induced IL-2 production, IL-2 receptor expression and thus proliferation. Proliferation was blocked by cyclosporin A or anti-IL-2 monoclonal antibodies (mAb) but not by anti-IL-4 mAb. Moreover, CpG-co-stimulated T cells differentiated into cytolytic T lymphocytes in vitro. Of note, IL-2-driven growth of primed T cells was not affected by CpG-ODN. Co-stimulation was also operative in T cells from CD28-/- mice and in TCR-transgenic T cells stimulated with peptide. CpG-ODN-mediated co-stimulation of T cells in vitro may thus explain part of the potent adjuvant effects of CpG-ODN in vivo.

Antisense pharmacodynamics: critical issues in the transport and delivery of antisense oligonucleotides

This review critically examines current understanding of the kinetics and biodistribution of antisense oligonucleotides, both at the cellular level and at the level of the intact organism. The pharmacodynamic relationships between biodistribution and the ultimate biological effects of antisense agents are considered. The problems and advantages inherent in the use of delivery systems are discussed in the light of further enhancing in vivo pharmacological actions of oligonucleotides.

New technologies for making vaccines

Technologies for making active vaccines fall into 3 general groups: live, subunit (killed or inactivated) and genetic. Each of these groups is further divisible into multiple categories, which include recombinant-derived antigens as well as native microorganisms and their components. In addition, there are new enabling technologies such as delivery systems and vectors which can be applied to these approaches. Most disease targets, whether infectious or noninfectious in origin, can be approached by the application of several different vaccine technologies, as can be tested during the discovery phase of research. The criteria for choosing early in a development program which of the vaccine technologies are likely to ultimately be most fruitful for a given application include: knowledge of the pathogenesis of the given infection/disease; technical feasibility; immunobiology and associated mechanisms; preclinical efficacy profile; anticipated clinical safety; regulatory; manufacturing; and marketing. All of these criteria should be considered together in making selections for an R&D program. This paper is reviewing the major vaccine technologies and relevant examples of how these criteria are used to make decisions in vaccine development.

Activation of spleen lymphocytes by plasmid DNA

Plasmid pUC19 DNA was shown to stimulate in vitro proliferation of CBA mouse splenocytes in a dose-dependent manner. Simultaneous treatment of the cells with the plasmid DNA and Con A or LPS produced an additive effect, while PMA acted synergistically with DNA. Monovalent Fab fragments of rabbit anti-mouse Ig (RAMIg) antibodies significantly inhibited plasmid DNA-induced polyclonal lymphocyte activation suggesting the involvement of Ig receptors in this process. Affinity modification of lymphocytes membrane-cytosole proteins with a 32P-labeled alkylating oligonucleotide derivative resulted in labeling of 67-82 and 23 kDa polypeptides corresponding to IgD and IgM heavy and light chains respectively. The immunoglobulin nature of the 82 and 23 kDa oligonucleotide-binding polypeptides was confirmed by immunoprecipitation with RAMIg antibodies.

Activation of target-tissue immune-recognition molecules by double-stranded polynucleotides

Abnormal expression of major histocompatibility complex (MHC) class I and class II in various tissues is associated with autoimmune disease. Autoimmune responses can be triggered by viral infections or tissue injuries. We show that the ability of a virus or a tissue injury to increase MHC gene expression is duplicated by any fragment of double-stranded (ds) DNA or dsRNA introduced into the cytoplasm of nonimmune cells. Activation is sequence-independent, is induced by ds polynucleotides as small as 25 bp in length, and is not duplicated by single-stranded polynucleotides. In addition to causing abnormal MHC expression, the ds nucleic acids increase the expression of genes necessary for antigen processing and presentation: proteasome proteins (e.g., LMP2), transporters of antigen peptides; invariant chain, HLA-DM, and the costimulatory molecule B7.1. The mechanism is different from and additive to that of gamma-interferon (gammaIFN), i.e., ds polynucleotides increase class I much more than class II, whereas gammaIFN increases class II more than class I. The ds nucleic acids also induce or activate Stat1, Stat3, mitogen-activated protein kinase, NF-kappaB, the class II transactivator, RFX5, and the IFN regulatory factor 1 differently from gammaIFN. CpG residues are not responsible for this effect, and the action of the ds polynucleotides could be shown in a variety of cell types in addition to thyrocytes. We suggest that this phenomenon is a plausible mechanism that might explain how viral infection of tissues or tissue injury triggers autoimmune disease; it is potentially relevant to host immune responses induced during gene therapy.

DNA vaccines: technology and application as anti-parasite and anti-microbial agents

DNA vaccines have been termed The Third Generation of Vaccines. The recent successful immunization of experimental animals against a range of infectious agents and several tumour models of disease with plasmid DNA testifies to the powerful nature of this revolutionary approach in vaccinology. Among numerous advantages, a major attraction of DNA vaccines over conventional vaccines is that they are able to induce protective cytotoxic T-cell responses as well as helper T-cell and humoral immunity. Here we review the current state of nucleic acid vaccines and cover a wide range of topics including delivery mechanisms, uptake and expression of plasmid DNA, and the types of immune responses generated. Further, we discuss safety issues, and document the use of nucleic acid vaccines against viral, bacterial and parasitic diseases, and cancer. The early potential promise of DNA vaccination has been fully substantiated with recent, exciting developments including the movement from testing DNA vaccines in laboratory models to non-human primates and initial human clinical trials. These advances and the emerging voluminous literature on DNA vaccines highlight the rapid progress that has been made in the DNA immunization field. It will be of considerable interest to see whether the progress and optimism currently prevailing can be maintained, and whether the approach can indeed fulfil the medical and commerical promise anticipated.

Genetic vaccines

In a few short years, genetic vaccine technology has moved rapidly from a novel concept to an important strategy for the development of human and veterinary vaccines, for numerous indications. This article discusses current areas in which further refinements in technology will influence a variety of infectious disease treatments, including intramuscular and intradermal inoculation, gene gun inoculation, the mechanism of antigen presentation, and the use of genetic adjuvants.

Immunostimulatory CpG motifs trigger a T helper-1 immune response to human immunodeficiency virus type-1 (HIV-1) gp 160 envelope proteins

Bacterial DNA sequences containing unmethylated CpG motifs have recently been proposed to exhibit immunostimulatory effects on B-, T- and NK cells, leading to the induction of humoral and cell-mediated immune responses. In the present study we investigated the immunomodulatory effects of a CpG-containing oligodeoxynucleotide (CpG ODN) to the HIV-1 gp 160 envelope (Env) protein in the BALB/c mouse model. Priming and boosting of mice with gp 160 adsorbed to aluminium hydroxide (Alum) induced a typical T helper-2 (Th2)-dominated immune response with high titers of gp 160-specific immunoglobulin (Ig)G1 isotypes but a weak IgG2a response. Specifically re-stimulated splenocytes from these mice predominantly secreted interleukin (IL)-5 but only minute amounts of interferon-gamma (IFN-gamma) upon specific re-stimulation. In contrast, a boost immunisation of gp 160/Alum primed mice with a gp 160/Alum/CpG combination resulted in a seven times higher production of IgG2a antibodies, without affecting the titers of IgG1 isotypes. Furthermore, approximately 10-fold increased levels of IFN-gamma, but significantly reduced amounts of IL-5, were secreted from gp 160-restimulated splenic cells. A further greater than 30-fold increase in the levels of specific IgG2a responses and a substantially elevated secretion of IFN-gamma were observed when the mice received gp160/Alum/CpG combinations for priming and boost injections. Thus, CpG ODNs are useful as an adjuvant to induce a typical Th0/Th1 response to HIV gp 160 proteins. However, despite the induction of a more Th1-like immune response, gp 16O/Alum/CpG combinations were not sufficient to prime an Env-specific cytotoxic T-cell (CTL) response.

Diapedesis of leukocytes: antisense oligonucleotides for rescue

Ischemia-reperfusion injury is an acute inflammatory process during which leukocytes are intimately involved. In this review, we summarize the current data on the leukocyte cell adhesion cascade in ischemia-reperfusion injury, focus upon studies which have demonstrated specific cell adhesion molecule interactions which mediate the leukocyte involvement in ischemia-reperfusion injury, and suggest future avenues of therapeutic interventions. The increased adhesion between activated vascular endothelium and peripheral blood leukocytes is central to the structural and the functional impairment in ischemia-reperfusion injury. Several families of adhesion molecules, namely the selectins, the intercellular adhesion molecules (ICAMs), and the integrins expressed either on the endothelium or on the leukocytes, are involved the cascade of events. Sequential and overlapping cellular interactions between the members of the three gene families of adhesion receptors result in adhesion of the leukocytes to the endothelium and extravasation at the site of ischemia. The functional importance of ICAM-1 and its beta2 integrin ligands in ischemia-reperfusion of the kidney has been demonstrated by monoclonal antibody blockade studies, in knockout mice and by treatment with antisense oligodeoxynulceotides (ODN). We have shown that antisense ODN for ICAM-1 protected the kidney against ischemic renal failure. In addition, in transplanted kidneys, ICAM-1 inhibition by antisense ODN ameliorates ischemia-reperfusion injury and prevents delayed graft function. Recent developments in antisense ODN technology make this a promising therapeutic approach, and antisense ODN treatment of donors or donor organs for ICAM-1 may be useful for the prevention of reperfusion injury in human renal transplantation and could influence acute and chronic graft function.

DNA immunization with Plasmodium falciparum serine repeat antigen: regulation of humoral immune response by coinoculation of cytokine expression plasmid

We immunized mice with plasmid expressing the 47-kDa amino-terminal domain of the Plasmodium falciparum serine repeat antigen (SERA) using gene gun and investigated humoral immune response to SERA antigen. Significant SERA-specific IgG was observed in BALB/c mice after immunization three times with SERA expression plasmid. Furthermore, these levels were increased by the coinoculation of cytokine (IFN-gamma, IL-4, GM-CSF, or IL-12) expression plasmid. In respect to the SERA-specific Ig subclasses, coinoculation of IFN-gamma, GM-CSF, or IL-12 expression plasmid increased the levels of SERA-specific IgG2a, and these were much higher than that in mice immunized with SERA expression plasmid alone. In contrast to the SERA-specific IgG2a, coinoculation of any cytokine expression plasmid did not change the levels of SERA-specific IgG1. These results indicate that cytokine expression plasmid enhances and regulates humoral immune response elicited by SERA DNA immunization.

Chlamydia infections and heart disease linked through antigenic mimicry

Chlamydia infections are epidemiologically linked to human heart disease. A peptide from the murine heart muscle-specific alpha myosin heavy chain that has sequence homology to the 60-kilodalton cysteine-rich outer membrane proteins of Chlamydia pneumoniae, C. psittaci, and C. trachomatis was shown to induce autoimmune inflammatory heart disease in mice. Injection of the homologous Chlamydia peptides into mice also induced perivascular inflammation, fibrotic changes, and blood vessel occlusion in the heart, as well as triggering T and B cell reactivity to the homologous endogenous heart muscle-specific peptide. Chlamydia DNA functioned as an adjuvant in the triggering of peptide-induced inflammatory heart disease. Infection with C. trachomatis led to the production of autoantibodies to heart muscle-specific epitopes. Thus, Chlamydia-mediated heart disease is induced by antigenic mimicry of a heart muscle-specific protein.

Immunostimulatory CpG-Oligodeoxynucleotides Cause Extramedullary Murine Hemopoiesis

Bacterial DNA and the synthetic CpG-oligodeoxynucleotides (ODNs) derived thereof have attracted attention because they activate cells of the adaptive immune system (lymphocytes) and the innate immune system (APCs) in a sequence-dependent manner. Here, we addressed whether CpG-ODNs affect hemopoiesis. Challenging mice with immunostimulatory CpG-ODN sequences led to transient splenomegaly, with a maximum increase of spleen weight at day 6. The induction of splenomegaly by CpG-ODNs was sequence-specific, dose-dependent, and associated with an increase in splenic cell count, in numbers of granulocyte-macrophage CFUs (GM-CFUs), and early erythroid progenitors (burst-forming units-erythroid). The transfer of spleen cells from CpG-ODN-pretreated animals into lethally irradiated syngeneic mice yielded an increase of spleen CFUs. Furthermore, the challenge of sublethally irradiated mice with CpG-ODNs caused radioprotective effects, in that recovery of GM-CFUs and cytotoxic T cell function was enhanced. The increase in GM-CFU and CTL function correlated with an enhanced resistance to Listeria infection in irradiated mice. We conclude from these data that CpG-ODNs trigger extramedullary hemopoiesis, and that this finding could be of therapeutic relevance in myelosuppression.

Bacterial DNA Containing CpG Motifs Stimulates Lymphocyte-Dependent Protection of Mice Against Lethal Infection with Intracellular Bacteria

Bacterial DNA containing unmethylated CpG motifs activates mammalian lymphocytes and macrophages to produce cytokines and polyclonal Ig. These include IFN-γ, IL-12, TNF-α, and IL-6, which are important in the control of intracellular bacterial infection. Here, we show that bacterial DNA, as well as synthetic oligonucleotides containing CpG motifs, induce protection against large lethal doses of Francisella tularensis live vaccine strain (LVS) and Listeria monocytogenes. Methylation of DNA at CpG dinucleotides or inversion of the motif abolished this protection. Surprisingly, DNA-mediated protection was highly dependent on lymphocytes, particularly B cells, as well as the production of IFN-γ. Optimal protection was elicited 2–3 days after inoculation with DNA and persisted for up to 2 wk. Further, animals surviving lethal challenge developed pathogen-specific secondary immunity. These findings indicate that host innate immune responses to bacterial DNA may contribute to the induction of protective immunity to bacteria and the subsequent development of memory.

DNA-antiviral vaccines: new developments and approaches--a review

Current vaccines can be divided into "live," "recombinant" and "killed" vaccines. Live vaccines are traditionally composed of attenuated viruses or bacteria, selected for their reduced pathogenicity. Recombinant vaccines, driven by a viral or bacterial vector express foreign antigens, or only recombinant proteins injected as antigen. Killed vaccines consist of inactivated whole pathogens. But all these traditional vaccines have some disadvantages: Attenuated live vaccine are able to undergo mutation and as mutated viruses or bacteria can now provoke the diseases against which the vaccine should protect the organism. A further disadvantage of live vaccines is the possibility of shedding which is a real problem especially in veterinary medicine. Clearly, there is a need for better vaccines to protect against diseases without the disadvantages associated with vaccines presently in use. Modern vaccines might be characterized as safe, no risk of reversion to pathogenicity, and they should be stable without the necessity of a "cold chain." Production should be simple, standardized and inexpensive. Vaccine development has now been improved by the ability to use direct inoculations of plasmid DNA encoding viral or bacterial proteins. One of the major benefits of DNA-vaccines, variously termed "DNA-, genetic- or nucleic acid-immunization," is the endogenous synthesis of the encoded protein. Therefore DNA vaccines mimic natural infection and provoke both strong humoral and cellular immune response. This review summarizes new developments and approaches of DNA vaccination and explains the construction of expression plasmids as well as possible mechanisms of immune responses.

Immunostimulatory properties of genomic DNA from different bacterial species

Bacterial DNA has potent immunological properties because of its content of immunostimulatory sequences centering on CpG motifs. To investigate whether DNA from various bacterial species differ in these properties, the activity of a panel of DNA was assessed in in vitro cultures of murine spleen cells. This panel varied in base composition and included DNA from Clostridium perfringens (CP), Escherichia coli (EC), Micrococcus lysodeikticus (MC), Staphylococcus aureus (SA), and, as a mammalian DNA control, calf thymus (CT) DNA. In assays of IL-12 and IFN-gamma production as well as B cell mitogenesis, these DNA showed marked differences in their immunostimulatory activity. For both cytokine and B cell responses, EC DNA demonstrated the highest activity while CP DNA had the lowest activity among the bacterial DNA. To determine whether differences in stimulatory capacity resulted from differences in cell uptake, the activity of DNA complexed with lipofectin was tested. While the addition of lipofectin to DNA increased stimulation by all DNA, it did not change the relative potency of the DNA tested. These results indicate that bacterial DNA differ in their immunostimulatory capacity, most likely reflecting their content of CpG motifs. These differences could affect the induction of innate immunity as well as the consequences of infection.

Main features of DNA-based immunization vectors

DNA-based immunization has initiated a new era of vaccine research. One of the main goals of gene vaccine development is the control of the levels of expression in vivo for efficient immunization. Modifying the vector to modulate expression or immunogenicity is of critical importance for the improvement of DNA vaccines. The most frequently used vectors for genetic immunization are plasmids. In this article, we review some of the main elements relevant to their design such as strong promoter/enhancer region, introns, genes encoding antigens of interest from the pathogen (how to choose and modify them), polyadenylation termination sequence, origin of replication for plasmid production in Escherichia coli, antibiotic resistance gene as selectable marker, convenient cloning sites, and the presence of immunostimulatory sequences (ISS) that can be added to the plasmid to enhance adjuvanticity and to activate the immune system. In this review, the specific modifications that can increase overall expression as well as the potential of DNA-based vaccination are also discussed.

Macrophage inflammatory protein-1alpha (MIP-1alpha) expression plasmid enhances DNA vaccine-induced immune response against HIV-1

CD8+ cell-secreted CC-chemokines, MIP-1alpha, and MIP-beta have recently been identified as factors which suppress HIV. In this study we co-inoculated MIP-1alpha expression plasmid with a DNA vaccine constructed from HIV-1 pCMV160IIIB and pcREV, and evaluated the effect of the adjuvant on HIV-specific immune responses following intramuscular and intranasal immunization. The levels of both cytotoxic T lymphocyte (CTL) activity and DTH showed that HIV-specific cell-mediated immunity (CMI) was significantly enhanced by co-inoculation of the MIP-1alpha expression plasmid with the DNA vaccine compared with inoculation of the DNA vaccine alone. The HIV-specific serum IgG1/IgG2a ratio was significantly lowered when the plasmid was co-inoculated in both intramuscular and intranasal routes, suggesting a strong elicitation of the T helper (Th) 1-type response. When the MIP-1alpha expression plasmid was inoculated intramuscularly with the DNA vaccine, an infiltration of mononuclear cells was observed at the injection site. After intranasal administration, the level of mucosal secretory IgA antibody was markedly enhanced. These findings demonstrate that MIP-1alpha expression plasmid inoculated together with DNA vaccine acts as a strong adjuvant for eliciting Th1-derived immunity.

Characterization of immune responses following intramuscular DNA immunization with the MOMP gene of Chlamydia trachomatis mouse pneumonitis strain

Studies were carried out to characterize the cellular and humoral immune responses evoked by intramuscular DNA vaccination with the major outer membrane protein (MOMP) gene of Chlamydia trachomatis mouse pneumonitis strain. The data demonstrate that DNA vaccinated mice develop antigen-specific delayed-type hypersensitivity, lymphocyte proliferation and interferon-gamma (IFN-gamma) production. Serum antibody responses (mainly immunoglobulin G2a; IgG2a) were evoked in two-thirds of the mice. We conclude that intramuscular DNA immunization with the MOMP gene evokes cellular and humoral immune responses suggestive of a T helper 1 (Th1) bias.

Non-coding plasmid DNA induces IFN-gamma in vivo and suppresses autoimmune encephalomyelitis

Regulatory sequences used in plasmids for naked DNA vaccination can modulate cytokine production in vivo. We demonstrate here that injection of plasmid DNA can suppress the prototypic T cell-mediated autoimmune disease, experimental autoimmune encephalomyelitis, by inducing IFN-gamma.

Bacterial DNA and CpG-containing oligodeoxynucleotides activate cutaneous dendritic cells and induce IL-12 production: implications for the augmentation of Th1 responses

BACKGROUND

Unmethylated CpG sequences in bacterial DNA act as adjuvants selectively inducing Th1 predominant immune responses during genetic vaccination or when used in conjunction with protein Ag. The precise mechanism of this adjuvant effect is unknown. Because dendritic cells (DC) are thought to be crucially involved in T cell priming and Th1/Th2 education during vaccination via skin, we characterized the effects of bacterial DNA and CpG-containing oligodeoxynucleotides (CpG ODN) on cutaneous DC.

METHODS AND RESULTS

Stimulation with CpG ODN 1826 (6 micrograms/ml) induced activation of immature Langerhans cell (LC)-like DC as determined by an increased expression of MHC class II and costimulatory molecules, loss of E-cadherin-mediated adhesion and increased ability to stimulate allogeneic T cells. Composition-matched control ODN 1911 lacking CpG sequences at equal concentrations was without effect. In comparison to LPS and ODN 1911, CpG ODN 1826 selectively stimulated DC to release large amounts of IL-12 (p40) and little IL-6 or TNF-alpha within 18 h and detectable levels of IL-12 p70 within 72 h. Stimulation with Escherichia coli DNA, but not calf thymus DNA, similarly induced DC maturation and IL-12 p40 production. Injection of CpG ODN into murine dermis induced enhanced expression of MHC class II and CD86 by LC in the overlying epidermis and intracytoplasmic IL-12 p40 accumulation in a subpopulation of activated LC.

CONCLUSION

Bacterial DNA and CpG ODN stimulate DC in vitro and in vivo and may preferentially elicit Th1-predominant immune responses because they can activate and mobilize DC, inducing them to produce IL-12.

CpG Oligodeoxynucleotides Can Circumvent the Th2 Polarization of Neonatal Responses to Vaccines But May Fail to Fully Redirect Th2 Responses Established by Neonatal Priming

Neonatal murine responses to a panel of conventional vaccines differ qualitatively from adult responses by a particular polarization toward a Th2 pattern and a frequent limitation of the Th1 and CTL responses required for protection against intracellular microorganisms. In contrast, DNA vaccines induce adult-like Th1/CTL neonatal responses against the same vaccine Ags. In this report, we show that this can be related to their content in unmethylated CpG motifs. Oligodeoxynucleotides (ODN) containing CpG motifs activate neonatal APCs to produce IL-12 in vitro and induce adult-like Th1 responses to tetanus toxoid and measles Ags in vivo, with production of IgG2a-specific Abs and adult-like secretion of IFN-γ and IL-5 by Ag-specific T cells. However, in spite of their capacity to trigger neonatal B cell proliferation in vitro, CpG-ODN only partially enhanced early life Ab responses. Finally, using Th1-driving CpG-ODN with the boosting dose of a protein vaccine was sufficient to redirect adult but not neonatally primed Th2 responses. These observations could be important for the development of novel vaccines that will have to be effective early in life.

Contribution of plasmid DNA to inflammation in the lung after administration of cationic lipid:pDNA complexes

Cationic lipid-mediated gene transfer to the mouse lung induces a dose-dependent inflammatory response that is characterized by an influx of leukocytes and elevated levels of the cytokines interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), and interferon gamma (IFN-gamma). We have examined the contribution of plasmid DNA (pDNA) to this observed toxicity, specifically the role of unmethylated CpG dinucleotides, which have been previously shown to be immunostimulatory. We report here that complexes of cationic lipid GL-67 and unmethylated pDNA (pCF1-CAT) instilled into the lungs of BALB/c mice induced highly elevated levels of the cytokines TNF-alpha, IFN-gamma, IL-6, and IL-12 in the bronchoalveolar lavage fluids (BALF). In contrast, BALF of animals administered either GL-67 alone or GL-67 complexed with SssI-methylated pDNA contained low levels of these cytokines. Similar results were observed using a plasmid (pCF1-null) that does not express a transgene, demonstrating that expression of chloramphenicol acetyltransferase (CAT) was not responsible for the observed inflammation. The response observed was dose dependent, with animals receiving increasingly higher amounts of unmethylated pDNA exhibiting progressively higher levels of the cytokines. Concomitant with this increase in cytokine levels were also elevated numbers of neutrophils in the BALF, suggesting a possible cause- and-effect relationship between neutrophil influx and generation of cytokines. Consistent with this proposal is the observation that reduction of neutrophils in the lung by administration of antibodies against Mac-1alpha and LFA-1 also diminished cytokine levels. This reduction in cytokine levels in the BALF was accompanied by an increase in transgene expression. In an attempt to abate the inflammatory response, sequences in the pDNA encoding the motif RRCGYY, shown to be most immunostimulatory, were selectively mutagenized. However, instillation of a plasmid in which 14 of the 17 CpG sites were altered into BALF/c mice did not reduce the levels of cytokines in the BALF compared with the unmodified vector. This suggests that other unmethylated motifs, in addition to RRCGYY, may also contribute to the inflammatory response. Together, these findings indicate that unmethylated CpG residues in pDNA are a major contributor to the induction of specific proinflammatory cytokines associated with instillation of cationic lipid:pDNA complexes into the lung. Strategies to abate this response are warranted to improve the efficacy of this nonviral gene delivery vector system for the treatment of chronic diseases.

DNA vaccination: transfection and activation of dendritic cells as key events for immunity

The mechanisms underlying initiation and maintenance of CD4 T cell responses after DNA vaccination were studied using a construct coding for nonsecreted fifth component of complement (C5) protein, thus restricting the availability of antigen. The only cell types to express C5 were keratinocytes at the site of DNA application and a small number of dendritic cells present in the draining lymph nodes. Antigen expression persisted for up to 12 wk in keratinocytes, but dendritic cells did not express C5 beyond 2 wk after vaccination. Cross-priming of dendritic cells by C5 expressed in keratinocytes did not occur unless keratinocyte death was induced by irradiation in vitro. CD4 T cells were activated in the draining lymph nodes only and subsequently migrated to the spleen, where memory T cells persisted for longer than 40 wk despite the absence of a source of persistent antigen. While DNA vaccination resulted in transfection of a small proportion of dendritic cells only, it led to general activation of all dendritic cells, thus providing optimal conditions for effective T cell activation and maintenance of memory.

CpG motifs as immune adjuvants

Bacterial DNA contains immunostimulatory motifs that trigger an innate immune response characterized by the production of predominantly Th1-type cytokines. These motifs consist of an unmethylated CpG dinucleotide flanked by two 5' purines and two 3' pyrimidines. We examined whether synthetic oligodeoxynucleotides (oligos) expressing these motifs would act as adjuvants to boost the immune response to DNA- and protein-based immunogens. In vivo experiments demonstrate that CpG-containing oligos augment antigen-specific serum antibody levels by up to tenfold, and IFNgamma production by up to sixfold. These effects were optimized by physically linking the CpG-containing motifs to the immunogen.

Antisense oligonucleotides to the epidermal growth factor receptor

Overexpression of the epidermal growth factor receptor (EGFR) has been observed in human breast tumors and is associated with poor prognosis in breast cancer patients. This would suggest that blocking the activity of the EGFR is a logical approach in the treatment of breast cancer. Three 20-mer phosphorothioate oligodeoxynucleotides were designed to target different regions of the human epidermal growth factor receptor (EGFR) mRNA. Several analogs of these oligodeoxynucleotides (the 2'-fluoro analog, the 2'-propoxy analog, and/or the 5-methyl cytosine analog) were also evaluated. We added these compounds to a human ovarian carcinoma cell line (SKOV3) and a human lung carcinoma line (A549), both of which overexpress the EGFR. All of these antisense oligonucleotides inhibited expression of the 10 kb EGFR mRNA (range: 22-97% inhibition) compared to a scrambled control oligonucleotide or an untreated control. Expression of the less prominent 5.6 kb EGFR mRNA band was also inhibited by all but two of the parent oligonucleotides. No inhibition of this 5.6 kb band was found with the control oligonucleotide. The reduction in the expression of EGFR mRNA by the three most potent antisense compounds was accompanied by a significant reduction of EGFR protein (90-98%) and in vitro growth inhibition of SKOV3 cells as compared to the control oligonucleotide.

Immune responses after immunization with plasmid DNA encoding Bet v 1, the major allergen of birch pollen

BACKGROUND

Immunization with plasmid DNA encoding various antigens is a promising method in vaccine research. Recent studies also indicate that DNA-based immunization might represent a potential approach in allergen-specific immunotherapy.

OBJECTIVE

In this study we have characterized the immune responses induced by recombinant Bet v 1a and plasmid DNA encoding for Bet v 1a, the major allergen of birch pollen in a mouse system.

METHODS

Balb/c mice were injected intraperitoneally with recombinant Bet v 1a and intradermally with plasmid DNA encoding for the gene of Bet v 1a (pCMV-Bet). In addition, the effect of immunostimulatory DNA sequences was investigated by appending CpG motifs to the gene of Bet v 1a, coinjecting CpG-oligodeoxynucleotides together with the pCMV-Bet construct, or both. IgE and IgG antibody responses, as well as IgG subclasses, were measured by ELISA in sera after each immunization. IFN-gamma and IL-4 levels were also measured by ELISA in sera and supernatants of allergen-stimulated spleen cells.

RESULTS

The primary humoral response to a single treatment with pCMV-Bet was very weak, but the reaction could be boosted to higher levels by 2 additional injections. On the other hand, proliferation assays of spleen cells and measurements of cytokine levels already indicated a cellular response after the first injection of plasmid DNA. After 2 immunizations with pCMV-Bet, the ratio of IgG1 to IgG2a pointed to a TH1 subclass profile. IgE was not detectable in any group at any time during the immune reaction. Accordingly, IL-4 levels were markedly reduced in the serum, as well as in the supernatants, of stimulated spleen cells. Animals immunized with pCMV-Bet containing appended CpG motifs at the 3' end of the Bet v 1a gene and/or with the CpG-ODN GCTAGACGTTAGCGT plus pCMV-Bet displayed reduced humoral responses against Bet v 1a when compared with animals injected with pCMV-Bet alone. The levels of IFN-gamma measured after allergen stimulation of isolated spleen cells were significantly higher in animals immunized with pCMV-Bet plus CpG motifs than with pCMV-Bet alone. Immunization with recombinant Bet v 1a protein elicited a strong TH2 -type response, including IgE production, a high titer of IgG1, and IL-4 production in both serum and supernatants of proliferation cultures.

CONCLUSION

In contrast to immunization with protein, DNA immunization induces a strong TH1 -type response against a relevant inhalant allergen. Our data support the concept of developing a novel type of allergen immunotherapy based on plasmid DNA immunization.

Correlation of toxicity and pharmacokinetic properties of a phosphorothioate oligonucleotide designed to inhibit ICAM-1

ISIS 2302 is a phosphorothioate oligodeoxynucleotide with a sequence complementary to the mRNA of human intercellular adhesion molecule 1 (ICAM-1). Hybridization of ISIS 2302 to the mRNA inhibits expression of the ICAM-1 protein in response to inflammatory stimuli. A murine active antisense oligonucleotide, ISIS 3082, has been used for in vivo pharmacology studies and has anti-inflammatory activity in models of organ transplant rejection, ulcerative colitis, and collagen-induced arthritis at doses ranging from 0.03 to 5 mg/kg. The safety assessment for ISIS 2302 includes general toxicity studies up to 6 mo in duration in mice and monkeys, genetic toxicity studies, and reproductive/fertility studies. ISIS 3082 was examined in parallel with ISIS 2302 in mouse toxicity and reproductive studies. The toxicities observed following systemic administration of ISIS 2302 and ISIS 3082 were similar and consistent with those observed for other compounds in this chemical class and, therefore, are independent of the suppression of ICAM-1 expression. Toxicokinetic evaluation demonstrated that toxicities occurred in organs containing the highest concentrations of ISIS 2302. Evidence of immune stimulation. including dose-dependent splenomegaly, lymphoid hyperplasia, and multiorgan mixed mononuclear cell infiltrates, was the most common finding in rodent studies. Monkeys were much less sensitive than mice to immune stimulation. Kidney contained the highest concentrations of ISIS 2302. Morphologic changes observed in kidney included atrophic and regenerative changes in proximal tubular epithelium; however, there was no evidence of functional abnormalities. Additional histologic changes noted in proximal tubular epithelium included basophilic granules, which were reflective of oligonucleotide distribution and uptake in these cells. Liver also contained high concentrations of oligonucleotide, which were associated with Kupffer cell hypertrophy in mice. Changes in serum transaminases, cholesterol, and triglycerides were reflective of hepatic alterations. In monkeys, high concentrations of oligonucleotide caused a transient increase in clotting times and activation of the alternative complement pathway. All toxicities associated with ISIS 2302 were reversible and occurred at doses well above those required for pharmacologic activity or currently used in clinical trials. In addition, there has been no evidence of genetic toxicity associated with ISIS 2302, and no changes in reproductive performance, fertility, or fetal development have been noted in animals treated with ISIS 2302 or ISIS 3082.

Enzymatic and genetic bases on assimilation, depolymerization, and transport of heteropolysaccharides in bacteria

When microorganisms utilize macromolecules for their growth, they commonly produce extracellular depolymerization enzymes and then incorporate the depolymerized low-molecular-weight products. Assimilation of heteropolysaccharides (gellan and xanthan) by Bacillus sp. GL1 depends on this generally accepted mechanism. On the other hand, Sphingomonas sp. A1 represents an unexplored specific and interesting system for macromolecule assimilation. In the presence of heteropolysaccharide (alginate), the bacterium forms a mouthlike pit on its cell surface and directly incorporates the macromolecule using a novel ATP-binding cassette transporter (ABC transporter). In this review, we discuss enzymatic and genetic bases on the depolymerization and assimilation routes of heteropolysaccharides in bacteria, with particular emphasis on the novel incorporation system for macromolecules, characteristic post-translational modification processes of polysaccharide lyases and on the mouthlike pit structure on the bacterial cell surface.

DNA vaccines for viral diseases

DNA vaccines, with which the antigen is synthesized in vivo after direct introduction of its encoding sequences, offer a unique method of immunization that may overcome many of the deficits of traditional antigen-based vaccines. By virtue of the sustained in vivo antigen synthesis and the comprised stimulatory CpG motifs, plasmid DNA vaccines appear to induce strong and long-lasting humoral (antibodies) and cell-mediated (T-help, other cytokine functions and cytotoxic T cells) immune responses without the risk of infection and without boost. Other advantages over traditional antigen-containing vaccines are their low cost, the relative ease with which they are manufactured, their heat stability, the possibility of obtaining multivalent vaccines and the rapid development of new vaccines in response to new strains of pathogens. The antigen-encoding DNA may be in different forms and formulations, and may be introduced into cells of the body by numerous methods. To date, animal models have shown the possibility of producing effective prophylactic DNA vaccines against numerous viruses as well as other infectious pathogens. The strong cellular responses also open up the possibility of effective therapeutic DNA vaccines to treat chronic viral infections.

The role of superantigens in vasculitis

Multiple risk factors are involved in susceptibility to vasculitis. Inherited determinants may increase the risk but are insufficient to induce the disease. Environmental factors, such as infections, are important modulators and probably trigger the disease in most cases. One of the possible triggers may be a bacterial superantigen (SAg). SAgs may activate autoreactive T cells that mediate autoimmune vessel wall destruction. Furthermore, SAgs may activate autoreactive B cells to produce autoantibodies that are involved in the pathophysiology of vasculitis, such as antineutrophil cytoplasmic autoantibodies or anti-endothelial cell antibodies. In patients with Kawasaki disease, Wegener's granulomatosis, and infection-related forms of vasculitis, SAg-producing microorganisms have regularly been found. Activation of circulating T cells and skewing of the T-cell repertoire have been reported in most forms of vasculitis. In the past year, for the first time, patients were described in which T-cell receptor V beta expansions were documented simultaneously with the typing of the microbial SAgs, providing evidence that the observed changes in the T-cell repertoire could be caused by these bacterial SAgs. In the future, elucidation of the immunologic mechanisms by which SAgs may play a role in the pathophysiology of vasculitis will provide more effective methods for the treatment of vasculitis.

CpG DNA can induce strong Th1 humoral and cell-mediated immune responses against hepatitis B surface antigen in young mice

Successful neonatal immunization of humans has proven difficult. We have evaluated CpG-containing oligonucleotides as an adjuvant for immunization of young mice (1-14 days old) against hepatitis B virus surface antigen. The protein-alum-CpG formulation, like the DNA vaccine, produced seroconversion of the majority of mice immunized at 3 or 7 days of age, compared with 0-10% with the protein-alum or protein-CpG formulations. All animals, from neonates to adults, immunized with the protein-alum vaccine exhibited strong T helper (Th)2-like responses [predominantly IgG1, weak or absent cytotoxic T lymphocytes (CTL)]. Th2-type responses also were induced in young mice with protein-CpG (in 1-, 3-, and 7-day-old mice) and protein-alum-CpG (in 1- and 3-day-old mice) but immunization carried out at older ages gave mixed Th1/Th2 (Th0) responses. DNA vaccines gave Th0-like responses when administered at 1 and 7 days of age and Th1-like (predominantly IgG2a and CTL) responses with 14-day-old or adult mice. Surprisingly, the protein-alum-CpG formulation was better than the DNA vaccine for percentage of seroconversion, speed of appearance, and peak titer of the antibody response, as well as prevalence and strength of CTL. These findings may have important implications for immunization of human infants.

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 Sequences Inhibit IL-5, Eosinophilic Inflammation, and Airway Hyperresponsiveness in Mice

We have used a mouse model of allergen-induced airway hyperresponsiveness to demonstrate that immunostimulatory DNA sequences (ISS) containing a CpG DNA motif significantly inhibit airway eosinophilia and reduce responsiveness to inhaled methacholine. ISS not only inhibited eosinophilia of the airway (by 93%) and lung parenchyma (91%), but also significantly inhibited blood eosinophilia (86%), suggesting that ISS was exerting a significant effect on the bone marrow production of eosinophils. The inhibition of the bone marrow production of eosinophils by 58% was associated with a significant inhibition of T cell-derived cytokine generation (IL-5, granulocyte-macrophage CSF, and IL-3). ISS exerted this inhibitory effect on T cell cytokine production indirectly by stimulating monocytes/macrophages and NK cells to generate IL-12 and IFNs. The onset of the ISS effect on reducing the number of tissue eosinophils was both immediate (within 1 day of administration) and sustained (lasted 6 days), and was not due to ISS directly inducing eosinophil apoptosis. ISS was effective in inhibiting eosinophilic airway inflammation when administered either systemically (i.p.), or mucosally (i.e., intranasally or intratracheally). Interestingly, a single dose of ISS inhibited airway eosinophilia as effectively as daily injections of corticosteroids for 7 days. Moreover, while both ISS and corticosteroids inhibited IL-5 generation, only ISS was able to induce allergen-specific IFN-γ production and redirect the immune system toward a Th1 response. Thus, systemic or mucosal administration of ISS before allergen exposure could provide a novel form of active immunotherapy in allergic diseases.

Cellular distribution of phosphorothioate oligonucleotide following intravenous administration in mice

Oligonucleotides are promising therapeutic agents for the prevention or treatment of a variety of diseases. The therapeutic potential of oligonucleotide therapy depends greatly on the bioavailability of oligonucleotides to their target cells and organs. We previously reported the pharmacokinetics and distribution of phosphorothioate oligonucleotide in mice using [35S]-labeled oligonucleotide ([35S]-oligo). To extend this study, we administered 30 mg/kg of fluorescent-labeled oligonucleotide (FITC-oligo) to mice and examined oligonucleotide distribution by measuring the fluorescence intensity in various cells and tissues using flow cytometry. Following FITC-oligo administration, fluorescence was detected in all the tissues examined. In terms of the fluorescent intensity, accumulation was greatest in liver and kidney, intermediate in spleen and bone marrow, and very low in peripheral blood mononuclear cells (PBMC). At 4 hours after administration, the level of oligonucleotide uptake in PBMC, spleen lymphocytes, and bone marrow cells revealed the following pattern: monocytes/macrophages > B cells > T cells. Confocal microscopy detected intracellular fluorescence in PBMC prepared under the same conditions as those for flow cytometry. These studies provide a rationale for designing cell targets for antisense therapeutics.

Optimization of Codon Usage of Plasmid DNA Vaccine Is Required for the Effective MHC Class I-Restricted T Cell Responses Against an Intracellular Bacterium

In an attempt to study codon usage effects of DNA vaccines on the induction of MHC class I-restricted T cell responses against an intracellular bacterium, Listeria monocytogenes, we designed two plasmid DNA vaccines encoding an H-2Kd-restricted epitope of listeriolysin O (LLO) of L. monocytogenes, LLO 91–99. One DNA vaccine, p91wt, carries the wild-type DNA sequence encoding LLO 91–99, and the other one, p91mam, possesses the altered DNA sequence in which the codon usage was optimized for murine system. Our read-through analyses with LLO 91–99/luciferase fusion genes confirmed that the optimized 91mam DNA sequence showed extremely higher translation efficiency than the wild-type sequence in murine cells. Consistent with this, i.m. injections of p91mam, but not of p91wt, into BALB/c mice were capable of inducing specific CTL- and IFN-γ-producing CD8+ T cells able to confer partial protection against listerial challenge. Taken together, these observations suggest that optimization of codon should be taken into consideration in the construction of DNA vaccines against nonviral pathogens.