Immunological properties of bacterial DNA

In vitro induction of T regulatory cells by a methylated CpG DNA sequence in humans: Potential therapeutic applications in allergic and autoimmune diseases

BACKGROUND

Allergic and autoimmune diseases comprise a group of inflammatory disorders caused by aberrant immune responses in which CD25+ Forkhead box P3-positive (FOXP3+) T regulatory (Treg) cells that normally suppress inflammatory events are often poorly functioning. This has stimulated an intensive investigative effort to find ways of increasing Tregs as a method of therapy for these conditions. One such line of investigation includes the study of how ligation of Toll-like receptors (TLRs) by CpG oligonucleotides (ODN) results in an immunostimulatory cascade that leads to induction of T-helper (Th) type 1 and Treg-type immune responses.

OBJECTIVE

The present study investigated the mechanisms by which calf thymus mammalian double-stranded DNA (CT-DNA) and a synthetic methylated DNA CpG ODN sequence suppress in vitro lymphoproliferative responses to antigens, mitogens, and alloantigens when measured by [3H]-thymidine incorporation and promote FoxP3 expression in human CD4+ T cells in the presence of transforming growth factor (TGF) beta and interleukin-2 (IL-2).

METHODS

Lymphoproliferative responses of peripheral blood mononuclear cells from four healthy subjects or nine subjects with systemic lupus erythematosus to CT-DNA or phytohemagglutinin (PHA) was measured by tritiated thymidine ([3H]-TdR) incorporation expressed as a stimulation index. Mechanisms of immunosuppressive effects of CT-DNA were evaluated by measurement of the degree of inhibition to lymphoproliferative responses to streptokinase-streptodornase, phytohemagglutinin (PHA), concanavalin A (Con A), pokeweed mitogen (PWM), or alloantigens by a Con A suppressor assay. The effects of CpG methylation on induction of FoxP3 expression in human T cells were measured by comparing inhibitory responses of synthetic methylated and nonmethylated 8-mer CpG ODN sequences by using cell sorting, in vitro stimulation, and suppressor assay.

RESULTS

Here, we showed that CT-DNA and a synthetic methylated DNA 8-mer sequence could suppress antigen-, mitogen-, and alloantigen-induced lymphoproliferation in vitro when measured by [3H]-thymidine. The synthetic methylated DNA CpG ODN but not an unmethylated CpG ODN sequence was shown to promote FoxP3 expression in human CD4+ T cells in the presence of TGF beta and IL-2. The induction of FoxP3+ suppressor cells is dose dependent and offers a potential clinical therapeutic application in allergic and autoimmune and inflammatory diseases.

CONCLUSION

The use of this methylated CpG ODN offers a broad clinical application as a novel therapeutic method for Treg induction and, because of its low cost and small size, should facilitate delivery via nasal, respiratory, gastrointestinal routes, and/or by injection, routes of administration important for vaccine delivery to target sites responsible for respiratory, gastrointestinal, and systemic forms of allergic and autoimmune disease.

What happens to the DNA vaccine in fish? A review of current knowledge

The primary function of DNA vaccines, a bacterial plasmid DNA containing a construct for a given protective antigen, is to establish specific and long-lasting protective immunity against diseases where conventional vaccines fail to induce protection. It is acknowledged that less effort has been made to study the fate, in terms of cellular uptake, persistence and degradation, of DNA vaccines after in vivo administration. However, during the last year some papers have given new insights into the fate of DNA vaccines in fish. By comparing the newly acquired information in fish with similar knowledge from studies in mammals, similarities with regard to transport, blood clearance, cellular uptake and degradation of DNA vaccines have been found. But the amount of DNA vaccine redistributed from the administration site after intramuscular administration seems to differ between fish and mammals. This review presents up-to-date and in-depth knowledge concerning the fate of DNA vaccines with emphasis on tissue distribution, cellular uptake and uptake mechanism(s) before finally describing the intracellular hurdles that DNA vaccines need to overcome in order to produce their gene product.

Protection of chickens against a lethal challenge of Escherichia coli by a vaccine containing CpG oligodeoxynucleotides as an adjuvant

Synthetic oligodeoxynucleotides (ODN) containing cytosine-phosphodiester-guanine (CpG) motifs (CpG-ODN) have been shown to be effective immunoprotective agents and vaccine adjuvants in a variety of bacterial, viral, and protozoan diseases in different animal species. The objective of this study was to compare the immune response of chickens to a killed Escherichia coli vaccine combined with oil in water emulsion or with CpG-ODN. Birds were vaccinated with killed E. coli antigens with either 10 or 50 microg of CpG-ODN on days 10 and 20 of age. At day 30, a virulent isolate of homologous E. coli was applied on a scratch site on the caudal abdominal region. Birds were examined for 10 days post-E. coli challenge, and pathologic and bacteriologic assessments were conducted on all birds that were either found dead or euthanized. The E. coli vaccine group that received no CpG-ODN had a survival rate of 65%. In contrast, groups that received the vaccine with CpG-ODN adjuvant had significantly higher survival rate of 92% (P < 0.01) with isolation of low numbers of E. coli from internal organs. Total IgG against E. coli antigens was highest in groups that received CpG-ODN as an adjuvant. Birds that received vaccine containing CpG-ODN had minimal inflammatory reaction without tissue necrosis at the injection site. Severe tissue necrosis was present in birds that received vaccine containing oil in water emulsion adjuvant. This study demonstrated that CpG-ODN is an effective vaccine adjuvant in chickens and results in minimal tissue destruction. This study is the first study in which CpG-ODN has been demonstrated to produce an adaptive immune response, at a significant level, against an extracellular bacterial infection in chickens.

Immunological analysis of a Lactococcus lactis-based DNA vaccine expressing HIV gp120

For reasons of efficiency Escherichia coli is used today as the microbial factory for production of plasmid DNA vaccines. To avoid hazardous antibiotic resistance genes and endotoxins from plasmid systems used nowadays, we have developed a system based on the food-grade Lactococcus lactis and a plasmid without antibiotic resistance genes. We compared the L. lactis system to a traditional one in E. coli using identical vaccine constructs encoding the gp120 of HIV-1. Transfection studies showed comparable gp120 expression levels using both vector systems. Intramuscular immunization of mice with L. lactis vectors developed comparable gp120 antibody titers as mice receiving E. coli vectors. In contrast, the induction of the cytolytic response was lower using the L. lactis vector. Inclusion of CpG motifs in the plasmids increased T-cell activation more when the E. coli rather than the L. lactis vector was used. This could be due to the different DNA content of the vector backbones. Interestingly, stimulation of splenocytes showed higher adjuvant effect of the L. lactis plasmid. The study suggests the developed L. lactis plasmid system as new alternative DNA vaccine system with improved safety features. The different immune inducing properties using similar gene expression units, but different vector backbones and production hosts give information of the adjuvant role of the silent plasmid backbone. The results also show that correlation between the in vitro adjuvanticity of plasmid DNA and its capacity to induce cellular and humoral immune responses in mice is not straight forward.

Alternative codon usage of PRRS virus ORF5 gene increases eucaryotic expression of GP5 glycoprotein and improves immune response in challenged pigs

Pigs exposed to GP(5) protein of PRRSV by means of DNA immunization develop specific neutralizing and protecting antibodies. Herein, we report on the consequences of codon bias, and on the favorable outcome of the systematic replacement of native codons of PRRSV ORF5 gene with codons chosen to reflect more closely the codon preference of highly expressed mammalian genes. Therefore, a synthetic PRRSV ORF5 gene (synORF5) was constructed in which 134 nucleotide substitutions were made in comparison to wild-type gene (wtORF5), such that 59% (119) of wild-type codons were replaced with known preferable codons in mammalian cells. In vitro expression in mammalian cells of synORF5 was considerably increased comparatively to wtORF5, following infection with tetracycline inducible replication-defective human adenoviral vectors (hAdVs). After challenge inoculation, SPF pigs vaccinated twice with recombinant hAdV/synORF5 developed earlier and higher antibody titers, including virus neutralizing antibodies to GP(5) than pigs vaccinated with hAdV/wtORF5. Data obtained from animal inoculation studies suggest direct correlation between expression levels of immunogenic structural viral proteins and immune response.

Protection of neonatal chicks against a lethal challenge of Escherichia coli using DNA containing cytosine-phosphodiester-guanine motifs

Oligodeoxynucleotides (ODN) containing cytosine-phosphodiester-guanine (CpG) motifs have been shown to be effective immunoprotective agents in murine models for a variety of viral, intracellular bacterial, and protozoan infections. We recently have shown that CpG ODN protects against extracellular bacterial infections in mature chickens. The objective of this study was to investigate the effect of CpG ODN on Escherichia coli septicemia in neonatal broiler chicks. Two-day-old chicks, or embryonated eggs that had been incubated for 18 or 19 days, received 50 microg CpG ODN. Three days after exposure to CpG ODN, a virulent isolate of E. coli was inoculated subcutaneously in the neck of each bird. Birds were examined for 7 days post-E. coli challenge and dinical, pathologic, and bacteriologic assessments were conducted. The control group of birds that received no CpG ODN had a survival rate of 0% to 20%. In contrast, groups that received CpG ODN, either by intramuscular or in ovo routes, had significantly higher survival rates (P < 0.0001). Bacterial counts in air sacs were significantly lower when birds or embryos were treated with CpG ODN as compared with controls. A dose as low as 10 microg of CpG ODN, administered intramuscularly, was able to protect birds significantly against E. coli challenge. Formulation of CpG ODN with 30% Emulsigen did not enhance the protection. This study demonstrates that CpG ODN has systemic protective effects in broiler chicks against E. coli infections. This is the first time that CpG ODN has been demonstrated to have an immunoprotective effect against a bacterial infection in chicks following in ovo delivery.

Regulation of CpG-induced immune activation by suppressive oligodeoxynucleotides

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated "CpG motifs" stimulate an innate immune response characterized by the production of cytokines, chemokines, and polyreactive Igs that promote host survival following infectious challenge. Yet CpG-driven immune activation can have deleterious consequences, such as increasing the host's susceptibility to autoimmune disease. The immunomodulatory activity of CpG DNA can be blocked by DNA containing "suppressive" motifs. This work explores the rules governing cellular recognition of stimulatory and suppressive motifs, and the resultant modulation of the immune system. Results suggest that both CpG and suppressive ODN may find use as therapeutic agents.

Effect of cytofectins on the immune response of murine macrophages to mammalian DNA

DNA, depending on base sequence, can induce a wide range of immune responses. While bacterial DNA is stimulatory, mammalian DNA is inactive alone and can, moreover, inhibit the response to bacterial DNA. To determine whether the mode of cell entry affects the immune properties of mammalian DNA, we have investigated the effects of the cytofectin agents Fugene 6 (Roche Diagnostics Corp., Indianapolis, IN), Lipofectin and Lipofectamine (Life Technologies, Grand Island, NY) on the responses of murine macrophages to DNA from calf thymus and human placenta. Whereas calf thymus and human placenta DNA alone failed to stimulate J774 or RAW264.7 cell lines or bone marrow-derived macrophages, these DNAs in complexes with cytofectin agents stimulated macrophages to produce nitric oxide but not interleukin 12. Both single-stranded and double-stranded DNAs were active in the presence of cytofectins. Macrophage activation by the DNA-cytofectin complexes was reduced by chloroquine, suggesting a role of endosomal acidification in activation. As shown by flow cytometry and confocal microscopy, the cytofectins caused an increase in the uptake of DNA into cells. Our findings indicate that macrophages vary in their response to DNA depending on uptake pathway, suggesting that activation by DNA reflects not only sequence but also context or intracellular location.

Protection of chickens against Escherichia coli infections by DNA containing CpG motifs

Synthetic oligodeoxynucleotides (ODN) containing CpG motifs (CpG-ODN) have been shown to be effective immunoprotective agents in murine models for a variety of viral, intracellular bacterial, and protozoan infections. Until now, the use of CpG-ODN to protect against extracellular bacterial infections has not been reported. The objective of this study was to investigate the effect of CpG-ODN against cellulitis and colibacillosis in broiler chickens, using a well-established model. At 22 days of age, birds received CpG-ODN by either the subcutaneous or intramuscular route. Three days later, a virulent isolate of Escherichia coli was applied to a scratch site on the caudal abdominal skin. Birds were examined for 10 days after the E. coli challenge, and pathological and bacteriological assessments were conducted on all birds. The control group of birds receiving no CpG-ODN((2007)) had a survival rate of 15%. In contrast, groups that received CpG-ODN((2007)), by either subcutaneous or intramuscular injection, had significantly higher survival rates (P < 0.0001). Furthermore, the size of the cellulitis lesion was significantly smaller in groups that received CpG-ODN((2007)) by the subcutaneous route (P < 0.01). A dose of as little as 3.16 micro g of CpG-ODN((2007)), delivered 3 days prior to challenge by either the subcutaneous or intramuscular route, significantly protected birds against E. coli infection (P < 0.01). This study demonstrates that CpG-ODN((2007)) has both local and systemic protective effects in broiler chickens. This is the first time that CpG-ODN((2007)) has been demonstrated to have an immunoprotective effect against an extracellular bacterial infection in any food animal species.

Effect of suppressive DNA on CpG-induced immune activation

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs stimulate a strong innate immune response. This stimulation can be abrogated by either removing the CpG DNA or adding inhibitory/suppressive motifs. Suppression is dominant over stimulation and is specific for CpG-induced immune responses (having no effect on LPS- or Con A-induced activation). Individual cells noncompetitively internalize both stimulatory and suppressive ODN. Studies using ODN composed of both stimulatory and suppressive motifs indicate that sequence recognition proceeds in a 5'-->3' direction, and that a 5' motif can block recognition of immediately 3' sequences. These findings contribute to our understanding of the immunomodulatory activity of DNA-based products and the rules that govern immune recognition of stimulatory and suppressive motifs.

B cells express Ly-6C in a Th1 but not Th2 cytokine environment

Interferon-alpha (IFN-alpha) is the primary regulator of transient Ly-6C expression on T cells. B cells, which do not express Ly-6C in the resting state, have been reported to express Ly-6C following exposure to proinflammatory stimuli. This study examined the factors controlling Ly-6C expression on B cells and the kinetics of Ly-6C expression in the presence of these factors. In vivo studies demonstrated that proinflammatory (Th1) cytokines transiently upregulate B cell Ly-6C expression. In vitro studies identified Th1 cytokines, particularly IFN-alpha and IFN-gamma, as the principal cytokines responsible for this induction. Polyclonal B cell activators (anti-IgM and recombinant CD40 ligand trimer) showed minimal ability to independently induce Ly-6C expression on B cells but did enhance the ability of IFNs to induce expression. Th2 cytokine environments did not result in B cell Ly-6C expression, and interleukin-4 (IL-4) actually antagonized the IFN-driven induction of Ly-6C. Ly6.1 strains of mice consistently demonstrated a greater ability to express Ly-6C on B cells than did Ly-6.2 strains. Together, these studies demonstrate the ability of Th1 but not Th2 cytokine environments to transiently induce the expression of Ly-6C on B cells and provide additional evidence for differences in the regulation of Ly-6C expression in Ly6.1 and Ly6.2 strains.

Role of the heat shock protein 90 in immune response stimulation by bacterial DNA and synthetic oligonucleotides

To elucidate the mechanisms of immunostimulation by bacterial DNA and synthetic oligonucleotides, the effects of heat shock protein 90 (Hsp90) inhibitors on the activation of murine spleen cells and macrophages by these molecules were investigated. Murine spleen cells and J774 and RAW264.7 macrophages responded to a CpG-containing oligodeoxynucleotide (CpG ODN) and Escherichia coli DNA by increased production of interleukin 6 (IL-6), IL-12, tumor necrosis factor alpha, and nitric oxide (NO). Pretreatment with any of the three Hsp90 inhibitors geldanamycin, radicicol, and herbimycin A resulted in a dose-dependent suppression of cytokine production from the spleen cells and macrophages and of NO from macrophages stimulated with CpG ODN or E. coli DNA. These Hsp90 inhibitors, however, had no effect on Staphylococcus aureus Cowan strain 1-induced IL-12 production from either the murine spleen cells or macrophages. CpG ODN and E. coli DNA induced increased intracellular levels of phosphorylated extracellular signal-regulated kinases (ERK1 and -2), which are members of the mitogen-activated protein (MAP) kinase family, while geldanamycin and radicicol blocked the phosphorylation of ERK1 and -2 in J774 and RAW264.7 cells. These data indicate that DNA-induced activation of murine spleen cells and macrophages is mediated by Hsp90 and that Hsp90 inhibitor suppression of DNA-induced macrophage activation is associated with disruption of the MAP kinase signaling pathway. Our findings suggest that Hsp90 inhibitors may provide a useful means of elucidating the mechanisms of immunostimulation by bacterial DNA and CpG ODN as well as a strategy for preventing adverse effects of bacterial DNA as well as lipopolysaccharide.

Vaccination and systemic lupus erythematosus: the bidirectional dilemmas

Vaccination has been perhaps the most important achievement in medicine of the last century. A hoard of infectious diseases that used to claim the lives of many, especially children, have been prevented and some even eradicated. However, it is possible that within this gift there is hidden a 'Trojan Horse'. During the last decade increasing numbers of reports regarding possible autoimmune side effects of vaccination, have been published. The existing data does not link the vaccines and the autoimmune phenomena observed in a causal relationship, nevertheless a temporal connection has been described. In this article we wish to address in particular the possible link between vaccines and systemic lupus erythematosus (SLE), namely two aspects of this inter-relationship: the occurrence of SLE following vaccination and outcome of immunization of known SLE patients.

The role of the macrophage scavenger receptor in immune stimulation by bacterial DNA and synthetic oligonucleotides

To assess the role of the macrophage scavenger receptor type A (SRA) in immune activation by CpG DNA, cytokine induction and DNA uptake were tested in vitro and in vivo using SRA knockout (SRA-/-) and wild type (WT) mice. As a source of CpG DNA, Escherichia coli DNA (EC DNA) and a 20-mer phosphorothioate oligodeoxynucleotide with two CpG motifs (CpG ODN) were used. In vitro, both EC DNA and the CpG ODN induced dose-dependent increases of interleukin (IL)-12 production by spleen cells and bone-marrow-derived macrophages (BMMPhi) from both SRA-/- and WT mice. The levels of cytokines produced by SRA-/- spleen cells and BMMPhi were similar to those of WT spleen cells and BMMPhi. When injected intravenously with CpG ODN and EC DNA, both SRA-/- and WT mice showed elevated serum levels of IL-12. To investigate further the role of the SRA, flow cytometry and confocal microscopy were performed to examine the uptake of fluorescently labelled oligonucleotides. SRA-/- and WT BMMPhi showed similarity in the extent of uptake and distribution of oligonucleotides as assessed by these two techniques. Together, these findings indicate that, while the SRA may bind DNA, this receptor is not essential for the uptake of CpG DNA or its immunostimulatory activity.

Responses of human B cells to DNA and phosphorothioate oligodeoxynucleotides

Emerging information has documented that certain DNA and sODNs can be both immunogenic and immunostimulatory. sODNs, but not DNA, induce T-cell-independent polyclonal activation of human B cells by engaging cell-surface receptors. Manifestations of sODN-induced human B-cell activation include expression of activation markers, proliferation, Ig production and anti-DNA antibody production. IL-2 and intact T cells enhanced B-cell responses to sODNs but were not required. Monocytes also provided a modest enhancement of human B-cell responses induced by sODNs. The chemical nature of sODNs capable of stimulating human B cells and the specific cell-surface receptors involved have not been completely delineated. Further studies will be necessary to elucidate the potential role of stimulatory sODNs in disease pathogenesis and to develop a means to employ ODNs as therapeutic agents in humans.

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.

Immunostimulatory CpG Oligodeoxynucleotides Enhance the Immune Response to Vaccine Strategies Involving Granulocyte-Macrophage Colony-Stimulating Factor

Immunostimulatory oligodeoxynucleotides containing the CpG motif (CpG ODN) can activate various immune cell subsets and induce production of a number of cytokines. Prior studies have demonstrated that both CpG ODN and granulocyte-macrophage colony-stimulating factor (GM-CSF) can serve as potent vaccine adjuvants. We used the 38C13 murine lymphoma system to evaluate the immune response to a combination of these two adjuvants. Immunization using antigen, CpG ODN, and soluble GM-CSF enhanced production of antigen-specific antibody and shifted production towards the IgG2a isotype, suggesting an enhanced TH1 response. This effect was most pronounced after repeat immunizations with CpG ODN and antigen/GM-CSF fusion protein. A single immunization with CpG ODN and antigen/GM-CSF fusion protein 3 days before tumor inoculation prevented tumor growth. CpG ODN enhanced the production of interleukin-12 by bone marrow-derived dendritic cells and increased expression of major histocompatibility complex class I and class II molecules, particularly when cells were pulsed with antigen/GM-CSF fusion protein. We conclude that the use of CpG ODN in combination with strategies involving GM-CSF enhances the immune response to antigen and shifts the response towards a TH1 response and that this approach deserves further evaluation in tumor immunization approaches and other conditions in which an antigen-specific TH1 response is desirable.

Immunostimulatory CpG Oligodeoxynucleotides Enhance the Immune Response to Vaccine Strategies Involving Granulocyte-Macrophage Colony-Stimulating Factor

Immunostimulatory oligodeoxynucleotides containing the CpG motif (CpG ODN) can activate various immune cell subsets and induce production of a number of cytokines. Prior studies have demonstrated that both CpG ODN and granulocyte-macrophage colony-stimulating factor (GM-CSF) can serve as potent vaccine adjuvants. We used the 38C13 murine lymphoma system to evaluate the immune response to a combination of these two adjuvants. Immunization using antigen, CpG ODN, and soluble GM-CSF enhanced production of antigen-specific antibody and shifted production towards the IgG2a isotype, suggesting an enhanced TH1 response. This effect was most pronounced after repeat immunizations with CpG ODN and antigen/GM-CSF fusion protein. A single immunization with CpG ODN and antigen/GM-CSF fusion protein 3 days before tumor inoculation prevented tumor growth. CpG ODN enhanced the production of interleukin-12 by bone marrow-derived dendritic cells and increased expression of major histocompatibility complex class I and class II molecules, particularly when cells were pulsed with antigen/GM-CSF fusion protein. We conclude that the use of CpG ODN in combination with strategies involving GM-CSF enhances the immune response to antigen and shifts the response towards a TH1 response and that this approach deserves further evaluation in tumor immunization approaches and other conditions in which an antigen-specific TH1 response is desirable.

Cationic Lipids Enhance Cytokine and Cell Influx Levels in the Lung Following Administration of Plasmid: Cationic Lipid Complexes

Administration of plasmid/lipid complexes to the lung airways may be associated, in addition to expression of transgene, with a range of other responses. We report here the induction of cytokines and cellular influx in the lung airway following intratracheal administration of an N-[1-(2–3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride/cholesterol/plasmid positively charged complex in mice. We show that 1) the appearance of the Th1-associated cytokines IFN-γ and IL-12 in bronchoalveolar lavage fluid is caused by unmethylated CpG dinucleotide sequences present within the plasmid, and is enhanced by the lipid formulation; 2) cationic lipids by themselves do not induce IL-12 or IL-12p40; 3) TNF-α is rapidly induced by cationic lipids and plasmid/lipid complex, but not by plasmid alone; 4) an acute cellular influx is induced by cationic lipid alone and by a plasmid/lipid complex, but to a much lesser extent by plasmid alone; and 5) plasmid methylation does not influence the degree of inflammatory cell influx. The induction of the innate immune responses by plasmid/lipid complexes may be advantageous to gene therapy of lung diseases. In particular, induction of the Th1 cell-promoting cytokines by plasmid/lipid complexes could, in conjunction with an expressed transgene, be used to modulate immune responses in the lung airways in disease conditions that are deficient in Th1 cell responses or that have a dominant Th2 phenotype. Alternatively, the elimination of immunostimulatory sequences in plasmids may improve the tolerability and/or efficacy of nonviral gene therapy, especially for diseases requiring chronic administration.

Increased immune response elicited by DNA vaccination with a synthetic gp120 sequence with optimized codon usage

DNA vaccination elicits humoral and cellular immune responses and has been shown to confer protection against several viral, bacterial, and parasitic pathogens. Here we report that optimized codon usage of an injected DNA sequence considerably increases both humoral and cellular immune responses. We recently generated a synthetic human immunodeficiency virus type 1 gp120 sequence in which most wild-type codons were replaced with codons from highly expressed human genes (syngp120). In vitro expression of syngp120 is considerably increased in comparison to that of the respective wild-type sequence. In BALB/c mice, DNA immunization with syngp120 resulted in significantly increased antibody titers and cytotoxic T-lymphocyte reactivity, suggesting a direct correlation between expression levels and the immune response. Moreover, syngp120 is characterized by rev-independent expression and a low risk of recombination with viral sequences. Thus, synthetic genes with optimized codon usage represent a novel strategy to increase the efficacy and safety of DNA vaccination.

DNA vaccines: safety and efficacy issues

DNA technology has been harnessed to produce a variety of plasmid-based vaccines designed to prevent viral, bacterial and parasitic infections. The rapid adoption and implementation of this novel vaccine strategy carries with it important safety and efficacy concerns. This review will focus on whether DNA vaccines (1) are likely to induce systemic or organ-specific autoimmune disease, (2) have the potential to induce tolerance rather than immunity, and (3) are as effective in individuals with depressed immune function as they are in healthy adults.

Immunostimulatory oligodeoxynucleotides containing the CpG motif are effective as immune adjuvants in tumor antigen immunization

Recent advances in our understanding of the immune response are allowing for the logical design of new approaches to cancer immunization. One area of interest is the development of new immune adjuvants. Immunostimulatory oligodeoxynucleotides containing the CpG motif (CpG ODN) can induce production of a wide variety of cytokines and activate B cells, monocytes, dendritic cells, and NK cells. Using the 38C13 B cell lymphoma model, we assessed whether CpG ODN can function as immune adjuvants in tumor antigen immunization. The idiotype served as the tumor antigen. Select CpG ODN were as effective as complete Freund's adjuvant at inducing an antigen-specific antibody response but were associated with less toxicity. These CpG ODN induced a higher titer of antigen-specific IgG2a than did complete Freund's adjuvant, suggesting an enhanced TH1 response. Mice immunized with CpG ODN as an adjuvant were protected from tumor challenge to a degree similar to that seen in mice immunized with complete Freund's adjuvant. We conclude that CpG ODN are effective as immune adjuvants and are attractive as part of a tumor immunization strategy.

RNA recognition by autoantigens and autoantibodies

The La, Ro, Sm and RNP autoantigens have been intensely studied over the past decade since cDNAs encoding autoantigens have been available. Most of these autoantigens are closely associated with RNA in RNP particles and molecular studies have provided insights into their modes of recognition and binding to RNA. For example, a common RNA Recognition Motif (RRM) was found to be a critical component of the RNA-binding domain of these autoantigens and the three dimensional structure of the RRM has been solved. As described in other articles in this series, the presence of La, Ro, Sm and RNP autoantibodies correlates with disease subsets, such as Sjogren's syndrome, systemic lupus erythematous and other connective tissue diseases. Immunological analysis of sera from autoimmune patients using recombinant autoantigens has revealed that multiple epitopes reside along the proteins and these represent both continuous and discontinuous (conformational) autotopes. Findings to date support a model of autoantibody induction which involves the direct presentation of proteinaceous autoantigens to the immune system. Circumstantial evidence has suggested that immunological crossreactivity between systemic autoantigens and structural components of infectious agents may play an initial role in the autoimmune response to certain antigens. However, the etiology of autoimmune diseases is probably multifactoral with genetic and other immune features acting on the organismal level. In addition, RNA molecules themselves can be autoantigens with higher order structural conformations which are recognized by RNP-type autoantibodies. Immune crossreactivity and/or direct presentation may generate autoantibodies reactive with conformational RNA epitopes. If crossreactivity with components of cellular or infectious agents give rise to RNA epitopes, they may represent structural or functional mimetics of the primary epitopes that actually drive the response. These ideas are discussed with respect to the role of mimetic processes in molecular recognition during autoimmunity.