CpG DNA, a novel immune enhancer for systemic and mucosal immunization with influenza virus

A CpG-containing oligodeoxynucleotide as an efficient adjuvant counterbalancing the Th1/Th2 immune response in diphtheria-tetanus-pertussis vaccine

Adjuvants in vaccines are immune stimulants that play an important role in the induction of effective and appropriate immune responses to vaccine component(s). Diphtheria-tetanus-pertussis (DPT) vaccine contains not only aluminum hydrate (alum) to enhance the immune response to the vaccine ingredients, but also, both for that purpose and as a principal ingredient, pertussis toxin (PT). However, both adjuvants strongly promote T helper (Th) 2 type immune responses. Th1 and Th2 type immune responses are counterbalanced in vivo, and a Th2-prone immune response is not effective against intracellular infections but promotes IgE production, which is related to allergic disease. In this study, we used the CpG motif contained in oligodeoxynucleotide (CpG-ODN), which has an adjuvant effect and also induces the Th1 response, as an adjuvant to this vaccine, and we investigated its adjuvanticity and its potential to modulate immune responses to DPT vaccine. Administration of DPT vaccine with CpG-ODN (DPT-alum/ODN) to mice significantly reduced the total IgE levels and increased the anti-PT specific IgG2a titer in serum, in comparison with ordinary DPT vaccine (DPT-alum). Moreover, we investigated the antibody response to orally administrated ovalbumin (OVA) after vaccine administration. In the DPT-alum/ODN-administered group, the OVA specific IgE production in serum greatly decreased in comparison with that in the DPT-alum-administered group. These data indicate that CpG-ODN was not useful only as an efficient vaccine adjuvant but also shifted the immune responses substantially toward Th1 and modulated the Th1/Th2 immune response in DPT vaccine. These data suggested new applications of CpG-ODN as adjuvants in DPT vaccine.

Effects of multiple copies of CpG on DNA vaccination

It has previously been demonstrated that a dose-dependent enhancement of immune response is derived from immunization with several copies of the CpG motif. Following that lead, we sought to incorporate a higher copy number of CpG motifs into an expression construct to evaluate the augmentation of immune responses. By multiple insertions, 30 copies of the CpG motif were cloned into the backbone of an expression construct encoding the foot-and-mouth disease virus (FMDV) capsid protein VP1. After intramuscular immunization, an augmented immune response with significantly increased levels of the specific antibody, T-cell proliferation, and IFN-gamma in Balb/c mice was observed. Compared to chemically synthesized CpG ODN, application of such a multicopy of CpG sequences within the expression backbone for DNA vaccination strategy is feasible and warranted.

The Mucosal Adjuvant Macrophage-Activating Lipopeptide-2 Directly Stimulates B Lymphocytes via the TLR2 without the Need of Accessory Cells

The macrophage-activating lipopeptide-2 (MALP-2) is an agonist of the TLR heterodimer 2/6, which exhibits potent activity as mucosal adjuvant, promoting strong humoral and cellular responses. Although B cells expressing TLR2/6 are potential targets, very little is known about the effect of MALP-2 on B cells. Studies were performed using total spleen cells or purified B cells from WT mice or animals deficient in TLR2, T cells, B cells, or specific subpopulations of B cells. They demonstrated that MALP-2 promotes a T cell-independent activation and maturation of B cells (mainly follicular but also B-1a and marginal zone B cells) via TLR2. MALP-2 also increased the frequency of IgM- and IgG-secreting cells, but bystander cells were required for IgA secretion. Activated B cells exhibited increased expression of activation markers and ligands that are critical for cross-talk with T cells (CD19, CD25, CD80, CD86, MHC I, MHC II, and CD40). Immunization of mice lacking T cells showed that MALP-2-mediated stimulation of TLR2/6 was unable to circumvent the need of T cell help for efficient Ag-specific B cell activation. Immunization of mice lacking B cells demonstrated that B cells are critical for MALP-2-dependent improvement of T cell responses. The knowledge emerging from this work suggests that MALP-2-mediated activation of B cells through TLR2/6 is critical for adjuvanticity. B cell stimulation by pattern recognition receptors seems to be a basic mechanism that can be exploited to improve the immunogenicity of vaccine formulations.

Resistance to influenza A virus infection by antigen-conjugated CpG oligonucleotides, a novel antigen-specific immunomodulator

Oligodeoxynucleotides (ODN) containing CpG motifs (CpG) act as modulators that bias the immune response towards a Th1-dominant phenotype. To investigate this effect further, we examined the protective effects of a covalently linked conjugate between CpG-ODN and HA-2kd antigen in mice infected with influenza A virus. The conjugated form of CpG-ODN and HA-2kd was more efficient in regulating influenza A virus than the unconjugated mixture of CpG-ODN and HA-2kd. The antigen-conjugated CpG-ODN induced an immune response with a Th1-dominant cytokine pattern characterized by the secretion of high levels of HA-2kd-specific interferon-gamma and IgG2a (Th1), which were only slightly induced by HA-2kd alone. These findings support the use of CpG-ODN-Ag conjugates as novel Ag-specific immunomodulators and suggest that CpG-ODN-HA-2kd might be a promising immune therapy for patients with influenza virus.

CD8+ T-cell-mediated cross-clade protection in the genital tract following intranasal immunization with inactivated human immunodeficiency virus antigen plus CpG oligodeoxynucleotides

Human immunodeficiency virus (HIV) is a mucosally transmitted infection that rapidly targets and depletes CD4+ T cells in mucosal tissues and establishes a major reservoir for viral persistence in gut-associated lymphoid tissues. Therefore, vaccines designed to prevent HIV infections must induce potent and durable mucosal immune responses, especially in the genital tract. Here we investigated whether intranasal (i.n.) immunization with inactivated gp120-depleted HIV-1 antigen (Ag) plus CpG oligodeoxynucleotide (ODN) as an adjuvant induced local immune responses in the genital tract and cross-clade protection against intravaginal (IVAG) challenge. Lymphocytes isolated from the iliac lymph nodes (ILNs) and genital tracts of female mice i.n. immunized with HIV-1 Ag plus CpG showed significant HIV-specific proliferation and produced significantly higher levels of gamma interferon (IFN-gamma) and beta-chemokines than mice immunized with HIV-1 Ag alone or mixed with non-CpG ODN. CD8+ lymphocytes were dramatically increased in the genital tracts of mice immunized with HIV-1 Ag plus CpG, and protection following IVAG challenge with recombinant vaccinia viruses (rVVs) expressing HIV-1 gag was shown to be CD8 dependent. Finally, cross-clade protection was observed between clades A, C, and G but not B following IVAG challenge with rVVs expressing HIV-1 gag from different clades. These studies provide evidence that mucosal (i.n.) immunization induced strong local T-cell-mediated immune responses in the genital tract and cross-clade protection against IVAG challenge.

Safety and immunogenicity of CPG 7909 injection as an adjuvant to Fluarix influenza vaccine

CPG 7909, a 24-mer B-Class CpG oligodeoxynucleotide (ODN), was tested for safety, tolerability and its ability to augment the immunogenicity of a commercial trivalent killed split influenza vaccine (Fluarix containing A/Beijing/262/95, A/Sydney/5/97 and B/Harbin/7/94; SmithKline Beecham) in a phase Ib blinded, randomized, controlled clinical trial. Sixty healthy volunteers were recruited in two consecutive cohorts of 30 subjects, who were randomly assigned to receive Fluarix plus 1mg CPG 7909 or Fluarix plus saline control (15 subjects each). Vaccines were administered by intramuscular injection on a single occasion with subjects in the first cohort receiving a 1/10th dose of Fluarix and those in the second cohort receiving the full-dose. All safety measures including physical evaluation, laboratory blood assays, and assays for DNA autoimmunity were within normal values except for transient and clinically inconsequential decreases in total white blood cell counts in groups receiving CPG 7909. All vaccines were found to be generally well tolerated with similar frequency and intensity for most adverse reactions for groups receiving CPG 7909 as controls. Exceptions were injection site pain and headache, which were reduced in frequency in subjects receiving the 1/10th Fluarix dose without CpG, compared to the frequency in all other groups. There was a lack of pre-existing immunity, defined as hemagglutinin inhibition (HI) activity < or =20, for all subjects to the influenza strains A/Beijing/262/95 and B/Harbin/7/94 and for some subjects to A/Sydney/5/97. Post-vaccination humoral immune responses, as determined 2 and 4 weeks later by assay of HI activity and ELISA to detect antibodies against hemagglutinin (anti-HA) were similar for both full and reduced Fluarix doses but the cellular immune responses (measured as PBMC antigen-specific IFN-gamma secretion) were reduced in the 1/10th Fluarix dose group. Humoral responses were not significantly enhanced by the addition of CPG 7909, except in individuals with pre-existing immunity to A/Sydney/5/97 strain (baseline HI activity titre >20), where there was a trend to higher HI activity with CPG 7909 (P = 0.06). The addition of CPG 7909 to the 1/10th dose of Fluarix did however result in significantly higher levels of IFN-gamma secretion from peripheral blood mononuclear cells recovered at 4 weeks and restimulated ex vivo with A/Beijing/262/95 (P = 0.048) and B/Harbin/7/94 (P = 0.0057), restoring these to the level seen with full-dose vaccine. These results suggest that addition of CPG 7909 to Fluarix may allow the use of reduced vaccine doses without reduced immunogenicity.

Intravaginal immunization with viral subunit protein plus CpG oligodeoxynucleotides induces protective immunity against HSV-2

Although the genital tract has been considered a poor inductive site for immunization with non-replicating antigens, genital immunization may be important for protection against sexually transmitted infections. Recently, we and others showed that CpG oligodeoxynucleotides (ODNs) serve as potent adjuvants for mucosal immunization. The purpose of this study was to determine whether intravaginal (IVAG) immunization with recombinant glycoprotein B (rgB) of herpes simplex virus type 2 (HSV-2) plus CpG ODN can induce specific immunity and protect against genital HSV-2 challenge. C57BL/6 mice were immunized IVAG with rgB plus CpG ODN, rgB plus non-CpG ODN, or rgB alone and challenged IVAG with HSV-2. Mice immunized with rgB + CpG had higher levels of anti-gB IgA and IgG in the vaginal washes and serum compared to mice immunized with rgB alone. Mice immunized with rgB + CpG also had the highest levels of gB-specific IgG in the nasal washes, however no specific IgA was detected in the nasal washes of any group. Mice immunized IVAG with rgB + CpG showed higher survival and lower pathology scores following genital HSV-2 challenge than mice immunized with rgB + non-CpG ODN or rgB alone. Additionally, vaginal viral titers were lower in the rgB + CpG group after infection. These results clearly show that the genital tract is capable of generating a protective immune response after local intravaginal immunization and that a non-replicating antigen is able to induce such a response when administered with an appropriate adjuvant.

CpG oligonucleotides improve the protective immune response induced by the anthrax vaccination of rhesus macaques

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, improving the immune response elicited by co-administered vaccines. Combining CpG ODN with anthrax vaccine adsorbed (AVA, the licensed human vaccine) increased the speed, magnitude and avidity of the resultant anti-anthrax response. The protective activity of these Abs was established by passive transfer to anthrax-challenged mice. The ability of CpG ODN to accelerate and magnify the immune response to AVA suggests this strategy may contribute to the development of prophylactic and therapeutic vaccines against biothreat pathogens.

The arthritogenic and immunostimulatory properties of phosphorothioate oligodeoxynucleotides rely on synergy between the activities of the nuclease-resistant backbone and CpG motifs

Experiments with immunostimulatory unmethylated CpG-containing DNA are usually conducted with nuclease-protected phosphorothioate oligodeoxynucleotides (S-ODNs), rather than phosphodiester oligodeoxynucleotides (O-ODNs). We compared the murine immune responses to S-ODNs and O-ODNs that either contained or lacked CpG motifs. Both CpG and non-CpG S-ODNs induced synovitis, as did sequence-matched CpG O-ODN, but not GpC O-ODN. There was a minimum length requirement for arthritogenic S-ODNs since a CpC dinucleotide S-ODN did not induce arthritis. There were both sequence- (CpG > non-CpG) and backbone-dependent (S-ODN > O-ODN) differences in the levels of DNA-induced arthritis upon intra-articular injection with the ODNs. However, CpG O-ODN being an exception, induced more severe arthritis than the GpC S-ODN. The levels of in vitro proliferation and production of IL-6, TNF-alpha, IL-12, and RANTES by splenocytes following exposure to CpG S-ODN were significantly higher than those induced by CpG O-ODN. In addition, both proliferative responses and cytokine production induced by S-ODN-stimulated splenocytes increased significantly when the S-ODN contained a CpG motif. Transcription factor NFkappaB was activated by both CpG S-ODN and CpG O-ODN but interestingly not by GpC S-ODN. This indicates that the NFkappaB signal pathway modulates CpG-mediated immunostimulation, while sequence-independent immune activation by the phosphorothioate backbone is probably signalled via a different pathway.

CpG-oligodeoxynucleotides enhance porcine immunity to Toxoplasma gondii

Protection against a challenge infection with Toxoplasma gondii VEG strain oocysts was examined in pigs after vaccination with T. gondii RH strain tachyzoites with or without a porcine specific synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs. Six groups of pigs were immunized with incomplete Freund's adjuvant (IFA) and either vehicle, tachyzoites alone or in combination with three different doses of CpG ODN or with CpG ODN alone. Protection from challenge was significantly (P < 0.05) improved in pigs vaccinated using CpG ODN as an adjuvant with tachyzoites compared to all other groups. The CpG ODN tachyzoite-immunized pigs also had higher serum parasite specific IgG antibody, no clinical signs of disease, and 52% had no demonstrable tissue cysts after the challenge infection. These data indicate that CpG ODN is a potential safe and effective adjuvant for the T. gondii RH strain vaccine in pigs.

Coccidioidomycosis: host response and vaccine development

Coccidioidomycosis is caused by the dimorphic fungi in the genus Coccidioides. These fungi live as mycelia in the soil of desert areas of the American Southwest, and when the infectious spores, the arthroconidia, are inhaled, they convert into the parasitic spherule/endospore phase. Most infections are mild, but these organisms are frank pathogens and can cause severe lethal disease in fully immunocompetent individuals. While there is increased risk of disseminated disease in certain racial groups and immunocompromised persons, the fact that there are hosts who contain the initial infection and exhibit long-term immunity to reinfection supports the hypothesis that a vaccine against these pathogens is feasible. Multiple studies have shown that protective immunity against primary disease is associated with T-helper 1 (Th-1)-associated immune responses. The single best vaccine in animal models, formalin-killed spherules (FKS), was tested in a human trial but was not found to be significantly protective. This result has prompted studies to better define immunodominant Coccidioides antigen with the thought that a subunit vaccine would be protective. These efforts have defined multiple candidates, but the single best individual immunogen is the protein termed antigen 2/proline-rich antigen (Ag2/PRA). Studies in multiple laboratories have shown that Ag2/PRA as both protein and genetic vaccines provides significant protection against mice challenged systemically with Coccidioides. Unfortunately, compared to the FKS vaccine, it is significantly less protective as measured by both assays of reduction in fungal CFU and assays of survival. The capacity of Ag2/PRA to induce only partial protection was emphasized when animals were challenged intranasally. Thus, there is a need to define new candidates to create a multivalent vaccine to increase the effectiveness of Ag2/PRA. Efforts of genomic screening using expression library immunization or bioinformatic approaches to identify new candidates have revealed at least two new protective proteins, expression library immunization antigen 1 (ELI-Ag1) and a beta-1,3-glucanosyltransferase (GEL-1). In addition, previously discovered antigens such as Coccidioides-specific antigen (CSA) should be evaluated in assays of protection. While studies have yet to be completed with combinations of the current candidates, the hypothesis is that with increased numbers of candidates in a multivalent vaccine, there will be increased protection. As the genome sequences of the two Coccidioides strains which are under way are completed and annotated, the effort to find new candidates can increase to provide a complete genomic scan for immunodominant proteins. Thus, much progress has been made in the discovery of subunit vaccine candidates against Coccidioides and there are several candidates showing modest levels of protection, but for complete protection against pulmonary challenge we need to continue the search for additional candidates.

Two distinct pathways of immuno-modulation improve potency of p53 immunization in rejecting established tumors

The p53 gene product is overexpressed by almost 50% of cancers, making it an ideal target for cancer immunotherapy. We previously demonstrated rejection of established p53-overexpressing tumors without stimulating autoimmunity by immunization with modified vaccinia Ankara-expressing murine p53 (MVAp53). Tumor rejection was enhanced through antibody-mediated CTL-associated antigen 4 (CTLA-4) blockade. We examined the role of synthetic oligodeoxynucleotides (ODN) containing unmethylated cytosine-phosphate-guanine (CpG) motifs (CpG ODN) in enhancing MVAp53-mediated tumor rejection. CpG ODN with MVAp53 resulted in tumor rejection in BALB/c mice bearing poorly immunogenic 11A-1 murine mammary carcinomas or Meth A sarcomas and C57Bl/6 mice bearing MC-38 colon carcinomas. The effect was similar to that seen in tumor-bearing mice treated with MVAp53 along with CTLA-4 blockade. Monoclonal antibody depletion experiments demonstrated that the adjuvant effects of CpG ODN and CTLA-4 blockades were CD8 dependent. CpG ODN were partially natural killer cell dependent and ineffective in Toll-like Receptor 9(-/-) and interleukin 6(-/-) mice, whereas CTLA-4 blockade was partially CD4 dependent and functional in Toll-like Receptor 9(-/-) and interleukin 6(-/-) mice. In addition, when administered with MVAp53, both adjuvants enhanced p53-specific cytotoxicity and demonstrated an additive effect when combined. The combination of CpG ODN and CTLA-4 blockade worked synergistically to reject palpable 11A-1 and MC-38 tumors. These experiments demonstrate the potential for augmenting MVAp53-mediated antitumor immunity using CpG ODN and CTLA-4 blockade. This cell-free immunotherapy approach is a candidate for evaluation in cancer patients.

A candidate DNA vaccine elicits HCV specific humoral and cellular immune responses

AIM: To investigate the immunogenicity of candidate DNA vaccine against hepatitis C virus (HCV) delivered by two plasmids expressing HCV envelope protein 1 (E1) and envelope protein 2 (E2) antigens respectively and to study the effect of CpG adjuvant on this candidate vaccine.

METHODS: Recombinant plasmids expressing HCV E1 and E2 antigens respectively were used to simultaneously inoculate mice with or without CpG adjuvant. Antisera were then collected and titers of anti-HCV antibodies were analyzed by ELISA. One month after the last injection, animals were sacrificed to prepare single-cell suspension of splenocytes. These cells were subjected to HCV antigen specific proliferation assays and cytokine secretion assays to evaluate the cellular immune responses of the vaccinated animals.

RESULTS: Antibody responses to HCV E1 and E2 antigens were detected in vaccinated animals. Animals receiving CpG adjuvant had slightly lower titers of anti-HCV antibodies in the sera, while the splenocytes from these animals showed higher HCV-antigen specific proliferation. Analysis of cytokine secretion from the splenocytes was consistent with the above results. While no antigen-specific IL-4 secretion was detected for all vaccinated animals, HCV antigen-specific INF-γ secretion was detected for the splenocytes of vaccinated animals. CpG adjuvant enhanced the secretion of INF-γ but did not change the profile of IL-4 secretion.

CONCLUSION: Vaccination of mice with plasmids encoding HCV E1 and E2 antigens induces humoral and cellular immune responses. CpG adjuvant significantly enhances the cellular immune response.

Nasal Flt3 ligand cDNA elicits CD11c+CD8+ dendritic cells for enhanced mucosal immunity

Nasal immunization is an effective way to induce both mucosal and systemic immune responses. In this study, we assessed a cDNA vector for Flt3 ligand (FL) for its potential to enhance mucosal immunity or tolerance. Interestingly, tolerance was avoided and elevated levels of OVA-specific Ab responses were induced in nasal washes, fecal extracts, and saliva as well as in plasma when compared with mice given nasal OVA plus DNA plasmid without the FL gene. In addition, significant levels of OVA-specific CD4+ T cell proliferative responses and OVA-induced IL-4 and IL-2 production were noted in spleen and cervical lymph nodes. Further, marked increases in FL protein occurred in the nasal lamina propria and submandibular glands and the frequencies of CD11c+CD8+ dendritic cells (DCs) significantly increased in the mucosal tissues. Moreover, these DCs expressed high levels of CD40, CD80, CD86, and MHC class II molecules. Nasal delivery of plasmid FL with OVA resulted in FL expression in both mucosal inductive and effector sites and resulted in expanded activated lymphoid DCs. Thus, nasal plasmid FL prevents mucosal tolerance and enhances active immunity when given by a mucosal route.

Enhanced hepatitis C virus NS3 specific Th1 immune responses induced by co-delivery of protein antigen and CpG with cationic liposomes

Mice were immunized intramuscularly with free recombinant hepatitis C virus (HCV) NS3 (non-structural protein 3) protein, liposomes encapsulating rNS3 or rNS3 and CpG mixture, liposomes co-encapsulating rNS3 and CpG or liposomes co-encapsulating rNS3 and GpC. Liposomes co-encapsulating rNS3 and CpG induced a much higher titre of anti-HCV NS3 IgG and the dominant IgG subtype was IgG2a. Liposomes co-encapsulating rNS3 and GpC also induced high levels of anti-HCV NS3 IgG antibody, but the dominant IgG subtype was still IgG1, the same as in free HCV/NS3 immunized mice. Liposomes encapsulating rHCV NS3 and the mixture of rHCV NS3 and CpG did not increase the antibody response but switched the IgG subtype. A cytokine profile analysis revealed that the levels of Th1 cytokines in the mice immunized with liposomes co-encapsulating rHCV NS3 and CpG were significantly higher than in other mice while the levels of Th2 cytokine were significantly lower than in the mice immunized with naked rNS3. IL-12 in the mice immunized with liposome-NS3-CpG was significantly higher than in other mice. In conclusion, liposomes co-encapsulating HCV NS3 and CpG are a good candidate vaccine to induce strong Th1 immune responses against hepatitis C viruses.

CpG oligodeoxynucleotides improve the survival of pregnant and fetal mice following Listeria monocytogenes infection

Listeria infection during pregnancy can cause the death of both mother and fetus. Previous studies established that immunostimulatory CpG oligodeoxynucleotides (ODN) increase the resistance of healthy adult mice to many infectious pathogens, including Listeria monocytogenes. This study examines whether the innate immune response elicited by CpG ODN can reduce the susceptibility of pregnant mice to lethal listeria challenge. The results indicate that CpG ODN treatment significantly improves maternal survival and reduces pathogen transmission to offspring. CpG ODN administered during pregnancy did not induce abortion, birth defects, or reduce the size or health of litters. These findings suggest that CpG ODN may provide a safe and effective means of improving the health of mothers and fetuses during pregnancy.

Safety of CpG oligodeoxynucleotides in veterinary species

Bacterial DNA and synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs in particular sequence contexts (CpG ODN) are recognized as a danger signal by the innate immune system of vertebrates. For this reason, CpG ODNs have a potential application as both an adjuvant and nonspecific immune modulator and are currently being evaluated in a number of human and veterinary clinical trials. Given their potent immunostimulatory activity, CpG ODNs could possibly induce adverse reactions. As all adjuvants and immune modulators must be nontoxic to meet safety requirements, it was essential to address the safety aspects of CpG ODNs. The current review summarizes experiments carried out to date to establish the safety of CpG ODNs in animals.

Immunization of rats against Fasciola hepatica using crude antigens conjugated with Freund's adjuvant or oligodeoxynucleotides

Chronic Fasciola hepatica infection is correlated with the development of a T helper (Th2)-predominant immune response. To determine whether immunostimulatory CpG-containing oligodeoxynucleotides (CpG-ODN) or Freund's complete adjuvant (FCA), known to promote a Th1 (T helper 1) immune responses, could provide protection from F. hepatica infection, total homogenate (TH) of F. hepatica mixed with CpG-ODN or FCA were injected subcutaneously (s.c.) into Wistar rats. A F. hepatica-specific Th1-predominant immune response was induced with CpG-ODN or FCA in lymph nodes of immunized animals. Lymph node cells from TH-CpG-ODN or TH-FCA immunized rats showed increased antigen-specific proliferation with high levels of INFgamma, compared to lymphocytes from rats injected with TH alone. In contrast, these two groups of immunized animals did not modify IL-4 release by draining lymph node cells, when they were subsequently stimulated with TH in vitro. However, a significant reduction in the burden of flukes (76.7%) was only observed in rats immunized with TH-FCA. Conversely, immunization of rats with TH-CpG-ODN did not promote protection against the parasite. Therefore, even though CpG-ODNs and FCA induced Th1 type responses, only FCA provided a significant protection to rats infected with F. hepatica.

Cytotoxic-T-lymphocyte human papillomavirus type 16 E5 peptide with CpG-oligodeoxynucleotide can eliminate tumor growth in C57BL/6 mice

Previously, we identified human papillomavirus type 16 (HPV-16) E5 as a tumor rejection antigen that can induce cytotoxic T lymphocytes (CTLs) to protect against tumor growth (D. W. Liu et al., J. Virol. 74:9083-9089, 2000). In the present study, we further mapped the CTL epitope of E5 protein by analyzing E5-specific CD8(+) gamma interferon-positive (IFN-gamma(+)) double-positive cells in C57BL/6 mice with flow cytometry. The results showed the region spanning amino acids 25 to 33 (VCLLIRPLL) contained the potential D(b)-restricted CTL epitope. Subsequently, to determine whether peptide E5 25-33-based vaccination could induce E5-specific CTL activity, syngeneic animals received E5 25-33 emulsified with either CpG oligodeoxynucleotide (CpG ODN 1826) or Freund's adjuvant, and the growth of the tumors was monitored. The results showed that although both adjuvants induced E5-specific CD8(+) IFN-gamma(+) T cells and eradicated E5-containing tumor growth, CpG ODN was found to stimulate stronger CTL response than Freund's adjuvant. We also compared the immune response of the effector/memory/recall phase induced by E5 25-33 peptide or by E5 protein that was synthesized in vivo by adenovirus-based E5 gene delivery. E5 25-33 peptide plus CpG ODN was shown to be a superior vaccine compared to the adenovirus-based E5 gene. Interestingly, their chronological patterns of immune response were similar, suggesting that E5 25-33 is a major CTL peptide of E5 protein.

Efficacy of DNA vaccines against infectious bursal disease virus in chickens enhanced by coadministration with CpG oligodeoxynucleotide

The objective of the present study was to investigate the feasibility of a DNA vaccine and CpG oligodeoxynucleotide (ODN) to protect chickens against infectious bursal disease virus (IBDV) infection. Two plasmids DNA carrying VP2 genes of the very virulent (vv) strain of IBDV were constructed with reverse transcription-polymerase chain reaction and designated as pcDNA3.1-VP2 and pCI-VP2. The VP2 protein expressed in COS-7 cells transfected with the plasmid was confirmed by indirect immunofluorescence assay. Seven-day-old chickens were intramuscularly injected with the plasmids alone or plus commercial attenuated infectious bursal disease (IBD) vaccine or synthetic CpG ODN twice at weekly intervals. Chickens at 5 wk old were orally inoculated with vvIBDV strain 99J1 and observed for 7 days after challenge. Immunization with plasmid plus commercial attenuated IBD vaccine or CpG ODN conferred protection for 70%-80% of chickens, as evidenced by the absence of dinical signs, mortality, and atrophy in the cloacal bursa. About 25%-45% of chickens vaccinated with commercial attenuated IBD vaccine or pcDNA3.1-VP2 or pCI-VP2 plasmid alone had dinical signs and died after challenge. Furthermore, there were significantly different histopathologic lesion scores in the clocal bursae between the pcDNA3.1-VP2 or pCI-VP2 plus CpG or live vaccine and pcDNA3.1-VP2, pCI-VP2, or live vaccine vaccinated group. Enzyme-linked immunosorbent assay antibody titers in chickens vaccinated the constructs DNA plus live vaccine or CpG ODN were significantly higher than in those inoculated with the constructs or the live vaccine alone. These results suggest that coadministration of the constructed plasmid pcDNA3.1-VP2 or pCI-VP2 with CpG ODN or commercial attenuated IBD vaccine could protect chickens efficiently from direct vvIBDV challenge.

Effect of CpG oligodeoxynucleotides on the immunogenicity of Pfs25, a Plasmodium falciparum transmission-blocking vaccine antigen

Antibodies directed against Pfs25, a protein present on the surface of zygotes and ookinetes of Plasmodium falciparum, completely block pathogen transmission. We evaluated the immunomodulatory effect of CpG oligodeoxynucleotides (ODN) on the immunogenicity of recombinant Pfs25 (rPfs25) formulated in alum (Al). Immunization of mice with rPfs25 plus CpG ODN improved both the antibody titer (a 30-fold-higher antibody response than that with rPfs25-Al alone) and avidity. Coadministration of CpG ODN dramatically enhanced the titer of immunoglobulin G2A (IgG2a) compared to the titer of the IgG1-dominant response caused by rPfs25-Al alone, and the sera from the CpG ODN-coadministered group completely blocked the transmission of P. falciparum parasites to mosquitoes, as determined by membrane feeding assays. However, transmission-blocking experiments revealed that blocking efficacy was dependent on high-titer antibody levels, independent of isotypes. These results suggest that CpG ODN can be used as an adjuvant to enhance the immunogenicity of rPfs25 as a malaria transmission-blocking vaccine.

Strong cytosine-guanosine-independent immunostimulation in humans and other primates by synthetic oligodeoxynucleotides with PyNTTTTGT motifs

Synthetic oligodeoxynucleotides (ODNs) containing cytosine-guanosine (CpG) motifs stimulate B and plasmacytoid dendritic cells of the vertebrate immune system. We found that in primates strong stimulation of these cells could also be achieved using certain non-CpG ODNs. The immunostimulatory motif in this case is a sequence with the general formula PyNTTTTGT in which Py is C or T, and N is A, T, C, or G. Assays performed on purified cells indicated that the immunostimulatory activity is direct. The use of a nuclease-resistant phosphorothioate backbone is not a necessary condition, since phosphodiester PyNTTTTGT ODNs are active. It was also demonstrated that ODN 2006, a widely used immunostimulant of human B cells, possess two kinds of immunostimulatory motifs: one of them mainly composed of two successive TCG trinucleotides located at the 5' end and another one (duplicated) of the PyNTTTTGT kind here described. Even though PyNTTTTGT ODNs are mainly active on primate cells, some of them, bearing the CATTTTGT motif, have a small effect on cells from other mammals. This suggests that the immunostimulatory mechanism activated by these ODNs was present before, but optimized during, evolution of primates. Significant differences in the frequency of PyNTTTTGT sequences between bacterial and human DNA were not found. Thus, the possibility that PyNTTTTGT ODNs represent a class of pathogen-associated molecular pattern is unlikely. They could, more reasonably, be included within the category of danger signals of cell injury.

Immunization with Th-CTL fusion peptide and cytosine-phosphate-guanine DNA in transgenic HLA-A2 mice induces recognition of HIV-infected T cells and clears vaccinia virus challenge

We evaluated immunogenicity of a novel Th-CTL fusion peptide composed of the pan DR Th epitope and a CTL epitope derived from HIV-pol in two transgenic HLA-A*0201/K(b) mouse models. The immunogenicity of peptides of this structure is highly dependent on coadministered cytosine-phosphate-guanine DNA. Initial evaluations of peptide-specific immunity are based on results of chromium release assay, intracellular cytokine, and tetramer staining. Significant cytotoxic T cell responses are found upon a single immunization with as low as 0.1 nmol both peptide and cytosine-phosphate-guanine DNA. Splenocytes from immunized mice recognize naturally processed HIV-pol expressed from vaccinia virus (pol-VV). Translation of immunologic criteria into more relevant assays was pursued using systemic challenge of immunized mice with pol-VV. Only mice receiving both peptide and DNA together successfully cleared upward of 6 logs of virus from ovaries, compared with controls. Challenge with pol-VV by intranasal route of intranasal immunized mice showed a significant reduction in the levels of VV in lung compared with naive mice. A convincing demonstration of the relevance of these vaccines is the robust lysis of HIV-infected Jurkat T cells (JA2/R7/Hyg) by immune splenocytes from peptide- and DNA-immunized mice. This surprisingly effective immunization merits consideration for clinical evaluation, because it succeeded in causing immune recognition and lysis of cells infected with its target virus and reduction in titer of highly pathogenic VV.

Mucosal immunity: overcoming the barrier for induction of proximal responses

Vaccination represents one of the most efficacious and cost-effective medical interventions. It is the only medical intervention proven to eliminate disease at a global level. Many of the pathogens against which we most require adequate vaccines infect via the highly exposed mucosal surfaces. For this reason the mucosa is often considered the first, and sometimes only, line of defense. Therefore, responses that protect the local mucosa are vital. In this review, we first explore the immunological mechanisms that protect the mucosa. We then review the literature of mucosal vaccines within the principles of antigenic composition, dose, and danger, highlighting the need and niche for the next generation of mucosal vaccines.

Oral pretreatment of mice with CpG DNA reduces susceptibility to oral or intraperitoneal challenge with virulent Listeria monocytogenes

Listeria monocytogenes is an enteroinvasive intracellular bacterial pathogen that infects humans and other animals, including mice, sometimes resulting in severe systemic infections. Previous studies showed that intraperitoneal (i.p.) pretreatment of susceptible BALB/c mice with immune-stimulatory CpG DNA 48 to 96 h prior to i.p. challenge with virulent L. monocytogenes reduces bacterial numbers in livers by greater than 100-fold, correlating with recovery from infection. Here we show that oral pretreatment of BALB/c mice with CpG DNA results in decreased susceptibility to either oral or i.p. challenge with L. monocytogenes. A single dose of 200 microg of CpG DNA administered to BALB/c mice orally by gavage 48 h or 7 days before oral challenge with virulent L. monocytogenes reduces bacterial numbers approximately 10- to 100-fold in livers and spleens. Lymphotoxin alpha knockout mice lacking Peyer's patches (PPs) and pretreated orally with CpG DNA 48 h prior to oral challenge with L. monocytogenes also have reduced susceptibility to infection, suggesting that PPs are required neither for oral infection nor for CpG-induced resistance against oral infection with L. monocytogenes. Surprisingly, 48-h oral pretreatment of BALB/c mice with 100 to 200 microg of CpG DNA results in approximately 100-fold-decreased bacterial numbers in livers following i.p. challenge with L. monocytogenes, suggesting, along with other data in this report, that orally delivered CpG DNA induces systemic resistance to infection. These results indicate that oral administration of CpG DNA induces systemic innate immune defenses against either oral or systemic infection with virulent L. monocytogenes.

CpG DNA in the prevention and treatment of infections

Microbial infection is sensed by Toll-like receptors (TLRs) on innate immune cells. Among the ten so far defined TLRs, TLR9 and its ligand are peculiar. TLR9 recognises bacterial DNA characterised by the abundance of unmethylated CpG dinucleotides, which distinguish bacterial DNA (CpG DNA) from mammalian DNA. Moreover, TLR9 shows a restricted cellular and subcellular pattern of expression. In contrast to other TLR agonists, CpG DNA is superior in activation of dendritic dells and induction of costimulatory cytokines such as interleukin (IL)-12 and IL-18. This qualifies CpG DNA as a Th1-promoting adjuvant. During infection, recognition of CpG DNA of intracellular pathogens skews and fine-tunes the ongoing immune response and induces long-lasting Th1 milieus. Thus, CpG DNA might play an important role in driving the immune system to a Th1 profile, preventing undesired Th2 milieus that might favour induction of allergic responses. Since CpG DNA can be synthesised with high purity and sequence fidelity, synthetic CpG DNA will become an important agent for Th1 instruction and be an effective adjuvant during vaccination.

CpG oligodeoxynucleotide enhances immunity against blood-stage malaria infection in mice parenterally immunized with a yeast-expressed 19 kDa carboxyl-terminal fragment of Plasmodium yoelii merozoite surface protein-1 (MSP1(19)) formulated in oil-based Montanides

The 19kDa carboxyl-terminal fragment of Plasmodium yoelii merozoite surface protein-1 (MSP1(19)), an analog of the leading falciparum malaria vaccine candidate, induces protective immunity to challenge infection when formulated with complete/incomplete Freund's adjuvant (CFA/IFA), an adjuvant unsuitable for use in humans. In this study, we investigate Montanide ISA51 and Montanide ISA720 as well as CpG oligodeoxynucleotide (ODN) as adjuvants for induction of immunity to MSP1(19). Mice immunized with MSP1(19) adjuvanted with Montanide ISA51 were protected even though some mice experienced low-grade parasitemia before resolving the infection. Mice immunized with MSP1(19) adjuvanted with Montanide ISA720 showed delayed patent parasitemia with all mice ultimately succumbing to infection. Interestingly, when the synthetic CpG ODN 1826 was included in either Montanide formulation, mice were completely protected with no parasites detected in the blood. MSP1(19)-specific antibodies in MSP1(19)-immunized mice adjuvanted with Montanide ISA51 or Montanide ISA720 showed predominantly IgG1 antibody and low levels of IgG2a. CpG ODN 1826 significantly enhanced both IgG1 and IgG2a antibody responses in Montanide ISA51-adjuvanted mice but significantly enhanced only the IgG2a antibody response in Montanide ISA720-adjuvanted mice. To investigate the relative roles of antibody and CD4(+) T cells in protection, MSP1(19)-immunized mice adjuvanted with Montanide ISA720 and CpG ODN 1826 were depleted of CD4(+) T cells just prior to challenge. Results showed that three of nine immunized/T cell depleted mice died following infection. These results suggest that antibody and CD4(+) T cells are critical for protection following immunization with MSP1(19) adjuvanted with Montanide and CpG ODN and that the formulation of a human malaria vaccine candidate in Montanide ISA720 or ISA51 together with human compatible CpG ODN would be useful for improving efficacy.

Molecular approaches to disease control

Recent advances in molecular biology, genomics, and immunology are revolutionizing our approach to managing infectious diseases of humans, livestock, and poultry. One of the most interesting additions to the armamentarium of research focusing on controlling infectious diseases has been a better understanding of how the host's innate immune system recognizes "danger" signals. Additionally, there has been recognition of the relationship between the innate and the specific arms of the immune system. For example, the recent discovery that CpG motifs can modulate immune responses has been used both as an adjuvant to enhance the responses to vaccines, as well as a direct immunostimulant to prevent infections. Using an Escherichia coli chicken model, we have been able to prevent cellulitis in chickens with CpG alone. Thus, CpG can be used immunoprophylactically to reduce infectious diseases. In addition, we will describe how CpG formulations with various antigens; recombinant proteins, peptides, and conventional vaccines can enhance immune responses to each of these different vaccine combinations. What is even more interesting is that CpG incorporation in vaccines can shift the immune response from a predominant T helper 2 (Th2)-like immune response generally induced by killed or subunit proteins to a much more balanced Th1-Th2 response. These immunomodulatory effects have significant implications for management of infectious diseases of all vertebrates.

Effective mucosal immunity to anthrax: neutralizing antibodies and Th cell responses following nasal immunization with protective antigen

Mucosal, but not parenteral, immunization induces immune responses in both systemic and secretory immune compartments. Thus, despite the reports that Abs to the protective Ag of anthrax (PA) have both anti-toxin and anti-spore activities, a vaccine administered parenterally, such as the aluminum-adsorbed anthrax vaccine, will most likely not induce the needed mucosal immunity to efficiently protect the initial site of infection with inhaled anthrax spores. We therefore took a nasal anthrax vaccine approach to attempt to induce protective immunity both at mucosal surfaces and in the peripheral immune compartment. Mice nasally immunized with recombinant PA (rPA) and cholera toxin (CT) as mucosal adjuvant developed high plasma PA-specific IgG Ab responses. Plasma IgA Abs as well as secretory IgA anti-PA Abs in saliva, nasal washes, and fecal extracts were also induced when a higher dose of rPA was used. The anti-PA IgG subclass responses to nasal rPA plus CT consisted of IgG1 and IgG2b Abs. A more balanced profile of IgG subclasses with IgG1, IgG2a, and IgG2b Abs was seen when rPA was given with a CpG oligodeoxynucleotide as adjuvant, suggesting a role for the adjuvants in the nasal rPA-induced immunity. The PA-specific CD4(+) T cells from mice nasally immunized with rPA and CT as adjuvant secreted low levels of CD4(+) Th1-type cytokines in vitro, but exhibited elevated IL-4, IL-5, IL-6, and IL-10 responses. The functional significance of the anti-PA Ab responses was established in an in vitro macrophage toxicity assay in which both plasma and mucosal secretions neutralized the lethal effects of Bacillus anthracis toxin.

Enhancement of immune responses to an HIV env DNA vaccine by a C-terminal segment of listeriolysin O

An effective vaccine against AIDS should induce both cellular and humoral immune responses. Here we report that immunization of mice with a DNA plasmid encoding a chimeric protein consisting of HIV89.6 Env gp140 and the listeriolysin O (LLO) C-terminal segment (59 amino acids) significantly enhanced both humoral and cellular immune responses against the HIV89.6 Env protein. Plasmid DNA expression vectors with genes codon-optimized for mammalian expression were synthesized for HIV89.6 gp140 as well as for chimeric protein gp140-LLO, in which the coding sequence for the C-terminal 59 amino acids of LLO were fused in frame to the 3' end of the codon-optimized gene for gp140. All plasmid vectors produced high levels of protein expression, and the gp140-LLO chimeric protein was cleaved and secreted as efficiently as gp140. Analysis of humoral immune responses by ELISA showed that the chimeric gp140-LLO construct induced higher antibody responses than the gp140 construct in immunized mice, more notably in the IgG2a antibody subtype. Intracellular cytokine staining and flow cytometry analysis showed that the gp140-LLO construct induced significantly higher levels of cytotoxic T lymphocyte immune responses against the HIV 89.6 Env protein than those observed with the gp140 construct. Our results thus demonstrate that the C-terminal segment of LLO can be effectively employed to enhance both cellular and humoral immune responses against the HIV89.6 Env antigen in the context of a DNA vaccine.

Mucosal adjuvants and anti-infection and anti-immunopathology vaccines based on cholera toxin, cholera toxin B subunit and CpG DNA

The mucosal immune system consists of an integrated network of lymphoid cells that work in concert with innate host factors to promote host defence. Mucosal immunization can be used both to protect the mucosal surfaces against colonization and invasion by microbial pathogens and to provide a means for immunological treatment of selected autoimmune, allergic or infectious-immunopathological disorders through the induction of antigen-specific tolerance. The development of mucosal vaccines, whether for prevention of infectious diseases or for oral tolerance immunotherapy, requires efficient antigen delivery and adjuvant systems. Significant progress has recently been made to generate partly or wholly detoxified derivatives of cholera toxin (including the completely nontoxic cholera toxin B subunit) and the closely related Escherichia coli heat-labile enterotoxin, with retained adjuvant activity. Cholera toxin B subunit is a protective component of a widely registered oral vaccine against cholera, and has proven to be a promising vector for either giving rise to anti-infective immunity or for inducing peripheral anti-inflammatory tolerance to chemically or genetically linked foreign antigens administered mucosally. Promising advances have also recently been made in the design of efficient mucosal adjuvants based on bacterial DNA that contains CpG-motifs and various imidazoquinoline compounds binding to different Toll-like receptors on mucosal antigen-presenting cells.

CpG DNA as a vaccine adjuvant

Synthetic oligodeoxynucleotides containing unmethylated CpG motifs act as immune adjuvants, accelerating and boosting antigen-specific antibody responses by up to 500-fold. CpG motifs promote the production of T-helper 1 and pro-inflammatory cytokines and induce the maturation/activation of professional antigen-presenting cells (including macrophages and dendritic cells). These effects are optimized by maintaining close physical contact between the CpG DNA and the immunogen. Coadministering CpG DNA with a variety of vaccines has improved protective immunity in animal challenge models. Ongoing clinical studies indicate that CpG oligodeoxynucleotides are safe and well-tolerated when administered as adjuvants to humans and in some cases increase vaccine-induced immune responses.

Enhancement of mucosal immunization with virus-like particles of simian immunodeficiency virus

Cholera toxin (CT) is the most potent known mucosal adjuvant, but its toxicity precludes its use in humans. Here, in an attempt to develop safe and effective mucosal adjuvants, we compared immune responses to simian immunodeficiency virus (SIV) virus-like particles (VLPs) after intranasal coimmunization with RANTES, CpG oligodeoxynucleotides (ODN), or CT. Antibody analysis demonstrated that RANTES and CpG ODN had capacities for mucosal adjuvanticity, i.e., for enhancing serum and vaginal antibodies specific to SIV Env, similar to those for CT. RANTES and CpG ODN skewed serum antibodies predominantly to the immunoglobulin G2a isotype. Most importantly, RANTES and CpG ODN were more effective than CT in increasing neutralizing titers of both serum and vaginal antibodies. After intranasal coadministration with VLPs, RANTES or CpG ODN also induced increased levels of gamma interferon (IFN-gamma)-producing lymphocyte and cytotoxic T-lymphocyte activities in both spleen and lymph nodes but did not increase the levels of interleukin-4-producing lymphocytes. The results suggest that RANTES and CpG ODN enhance immune responses in a T-helper-cell-type-1 (Th1)-oriented manner and that they can be used as effective mucosal adjuvants for enhancing both humoral and cellular immune responses in the context of VLPs, which are particulate antigens.

CPG ODN allows lower dose of antigen against hepatitis B surface antigen in BALB/c mice

We have evaluated alum, immunostimulatory cytosine guanine dinucleotide-containing oligodeoxy-nucleotides (CPG ODN), and an alum/CPG ODN combination as adjuvants with hepatitis B surface antigen, to compare their potential to allow lower doses of antigen to be used for induction of humoral responses. BALB/c mice were immunized by intramuscular injection with 0.01, 0.1 or 1.0 micro g recombinant hepatitis B surface antigen without adjuvant or with alum and/or CPG ODN added. When given without adjuvant or with alum, each 10-fold decrease in amount of antigen resulted in a similarly reduced titre of antibody against hepatitis B surface antigen. In contrast, CPG ODN, on its own or combined with alum, allowed high anti-hepatitis B surface antigen titres even with a 1000-fold reduction in amount of antigen. These findings may have important immunological and economical consequences for vaccine development.

Biological activity of immunostimulatory CpG DNA motifs in domestic animals

Bacterial DNA contains a much higher frequency of CpG dinucleotides than are present in mammalian DNA. Furthermore, bacterial CpG dinucleotides are often not methylated. It is thought that these two features in combination with specific flanking bases constitute a CpG motif that is recognized as a "danger" signal by the innate immune system of mammals and therefore an immune response is induced when these motifs are encountered. These immunostimulatory activities of bacterial CpG DNA can also be achieved with synthetic CpG oligodeoxynucleotides (ODN). Recognition of CpG motifs by the innate immune system requires engagement of Toll-like receptor 9 (TLR-9), which induces cell signaling and subsequently triggers a pro-inflammatory cytokine response and a predominantly Th1-type immune response. CpG ODN-induced innate and adaptive immune responses can result in protection in various mouse models of disease. Based on these observations, clinical trials are currently underway in humans to evaluate CpG ODN therapies for cancer, allergy and infectious disease. However, potential applications for immunostimulatory CpG ODN in species of veterinary importance are just being explored. In this review, we will highlight what is presently known about the immunostimulatory effects of CpG ODN in domestic animals.

Mucosal immunization with helicobacter, CpG DNA, and cholera toxin is protective

The mucosal delivery of antigens requires an effective adjuvant to induce mucosal immunity. Current mucosal adjuvants include cholera toxin (CT) and Escherichia coli heat-labile toxin. Unmethylated CpG immunostimulatory oligodeoxynucleotides (ODNs) have been proposed as novel mucosal adjuvants. In this study, mice were immunized with sonicated Helicobacter felis with CT and/or CpG ODN adjuvants. All groups receiving either adjuvant singly or in combination developed increased serum anti-H. felis immunoglobulin G (IgG). The addition of either CpG or CT, or both, produced a specific fecal anti-H. felis IgA response, with the highest IgA levels occurring in animals immunized intranasally with sonicated H. felis with CT and CpG. Following H. felis challenge, addition of the adjuvant CpG ODN provided no significant protection, while groups given CT showed a high degree of protection, although not complete. When CpG ODN was combined with CT and the vaccine combination was delivered intranasally, no bacterial colonization was detected by quantitative PCR, providing "sterile immunity" and demonstrating synergy between CpG ODN and CT.

Recombinant GroES in combination with CpG oligodeoxynucleotides protects mice against Mycobacterium avium infection

The groES gene of Mycobacterium avium strain 485 was cloned and expressed in Escherichia coli and the recombinant GroES protein was purified by affinity chromatography. The GroES preparation showed high purity by electrophoresis and immunoblotting. Immuno-electron microscopy showed that GroES was located both in the cytoplasm and on the surface of the mycobacterial cells and thus is readily available to interact with the host immune system. BALB/c mice were immunised intranasally with recombinant GroES, alone or in combination with a synthetic oligodeoxynucleotide containing unmethylated CpG motifs, and tested for protection against infection with M. avium. Neither GroES nor CpG alone provided any protection against subsequent challenge with M. avium, whereas a combination of the two significantly protected the lungs and spleen against colonisation by M. avium after intranasal challenge with a low dose of the organism. This indicates that intranasal administration of GroES and CpG oligodeoxynucleotides increases the resistance of BALB/c mice to M. avium infection.

Induction of CD8 T-cell-specific systemic and mucosal immunity against herpes simplex virus with CpG-peptide complexes

Oligodeoxynucleotides (ODN) containing unmethylated CpG motifs exert powerful adjuvant activity in vivo and in vitro. Administered with antigen they induce a population of antigen-specific CD8+ T cells. In this study we immunized C57BL/6 mice with bioactive CpG ODN combined with an immunodominant epitope derived from herpes simplex virus (HSV) glycoprotein B (amino acids 498 to 505; SSIEFARL) and analyzed the magnitude and durability of the peptide-specific response. The effectiveness of the CD8+ T-cell response as measured by peptide-specific tetramers, peptide-induced intracellular gamma interferon expression, and resistance to systemic and mucosal challenge during the acute and memory phases was compared with the response induced by immunization with recombinant vaccinia virus encoding SSIEFARL as a minigene (VvgB(498-505)). Confirming the reports of others, our results demonstrate that the CpG ODN-peptide approach generates an antigen-specific CD8+ T-cell population, but the frequency of CD8+ T cells is lower than that induced by VvgB(498-505). Nevertheless, the protection level was comparable when mice were systemically and mucosally challenged during the acute phase. However, such responses by both groups waned with time and were functionally less effective. Still, our results indicate that the CpG ODN-peptide immunization system holds promise as a means of selectively inducing a CD8+ T-cell response against HSV.

The development and use of vaccine adjuvants

Interest in vaccine adjuvants is intense and growing, because many of the new subunit vaccine candidates lack sufficient immunogenicity to be clinically useful. In this review, I have emphasized modern vaccine adjuvants injected parenterally, or administered orally, intranasally, or transcutaneously with licensed or experimental vaccines in humans. Every adjuvant has a complex and often multi-factorial immunological mechanism, usually poorly understood in vivo. Many determinants of adjuvanticity exist, and each adjuvanted vaccine is unique. Adjuvant safety is critical and can enhance, retard, or stop development of an adjuvanted vaccine. The choice of an adjuvant often depends upon expensive experimental trial and error, upon cost, and upon commercial availability. Extensive regulatory and administrative support is required to conduct clinical trials of adjuvanted vaccines. Finally, comparative adjuvant trials where one antigen is formulated with different adjuvants and administered by a common protocol to animals and humans can accelerate vaccine development.

Immunogenicity of anti-Haemophilus influenzae type b CRM197 conjugate following mucosal vaccination with oligodeoxynucleotide containing immunostimulatory sequences as adjuvant

Most vaccines are delivered by injection. Mucosal vaccination would increase compliance and decrease the risk of spread of infectious diseases due to a reduction of mucosal colonization and of contaminated syringes. However, most vaccines are unable to induce immune responses when administered mucosally, and require the use of strong adjuvant or effective delivery systems. Synthetic oligodeoxynucleotides (ODN) containing CpG immunostimulatory sequences (ISS) have been shown to act as potent adjuvants of type-1 immune responses also when mucosally co-administered with protein or peptide vaccines. We have shown that ISS can increase the anti-polysaccharide polyribosyl ribitol phosphate (PRP) antibody titres and anti-diphtheria toxin neutralizing antibody, if used as adjuvant of anti-Haemophilus influenzae type b (Hib) PRP vaccine conjugated with cross-reacting material (CRM) of diphtheria toxin in mice. Here, we show that ISS have the potential to increase host local and systemic antibody response against both the PRP and the protein component of a conjugated vaccine when mucosally administered in mice. Mucosal administration of Hib-CRM vaccine induced anti-PRP and neutralizing anti-diphtheria toxin antibodies of all the IgG subclasses, with a predominance of type-1 immune response-associated IgG2a and IgG3. At odds with systemic administration, the mucosal delivery of Hib-CRM induced anti-PRP and anti-diphtheria toxin mucosal IgA. These data envisage the feasibility of a mucosal vaccination with an already licensed Hib-CRM vaccine to achieve both an anti-H. influenzae and -diphtheria effective protection.

Activation of nonspecific cytotoxic cells (NCC) with synthetic oligodeoxynucleotides and bacterial genomic DNA: binding, specificity and identification of unique immunostimulatory motifs

We have analyzed the effects of synthetic oligodeoxynucleotides (sODNs) and bacterial DNA (bDNA) on the in vitro activation of NCC. Teleost NCC recognition of DNA appeared to differ from that which occurs in higher vertebrates. NCC contain at least two different receptor specificities for DNA. Both oligodeoxyguanosine 20-mers (dG20) and 5'-TGCTGCTTGTGCTTGTGCTT-3' (4GC-2T) bound specifically to NCC. The existence of different receptor specificities was indicated by reciprocal cold target inhibition experiments. dG20 competed with 4GC-2T binding but sODNs composed of GpC or CpG nests did not compete with recognition by NCC of the dG20. ODN binding by NCC primarily depended on the presence of GpC or CpG nests with a preference for -G- serving as the anchor nucleotide. Secondarily, and similar to models of ODN activation in mammals, palindrome sequences of pu-pu-CpG-py-py activated NCC cytotoxicity. Additional analysis of the requirements for ODN activation indicated that guanosine could not substitute for adenosine as a purine spacer and that CpG motifs containing flanking thymidine (i.e.-GTCpGTT-) augmented the activity of the sODN containing this flanking base. Other evidence for the participation of both G and C in the recognition of specific nucleotides by NCC was that poly-dC20, dA20 or dT20 had no activating properties. Methylation of all cytosine nucleotides within an ODN abrogated activation. A canonical ODN motif of 5'-C/AT/AGCTT-3' can now be suggested for teleosts. Additional studies were done to examine the effects of in vitro treatment of NCC with bDNA. bDNA from three different disease isolates of Streptococcus iniae activated NCC cytotoxicity. Treatment of the bDNA with DNase abrogated the enhancement of cytotoxicity. Also, treatment of NCC with eukaryotic DNA had no effects on cytotoxicity. These studies suggested that NCC recognize bacterial nonmethylated DNA. The consequences of these interactions may be increased innate and acquired anti-bacterial immunity.

Enhancement of rat tear IgA antibody responses following intranasal immunization with antigen and CpG ODN

PURPOSE

To determine the effect of unmethylated oligodeoxynucleotides containing bacterial CpG motifs (CpG ODN) on the induction of rat tear IgA antibody responses.

METHODS

Rats were immunized intranasally with either soluble dinitrophenylated bovine serum albumin (DNP-BSA) or poly(lactide-co-glycolide) (PLG) encapsulated DNP-BSA in combination with CpG ODN. The animals received two immunizations 21 days apart. Following the second immunization, tear, saliva and serum samples were collected for 28 days and analyzed for antigen specific antibodies. Tear IgA, saliva IgA and serum IgG antibody concentrations were determined by ELISA.

RESULTS

Co-administration of CpG ODN with either soluble or encapsulated antigen resulted in significantly elevated levels of both tear and salivary IgA antibodies as well as levels of serum IgG antibodies. Microencapsulated DNP-BSA plus CpG ODN elicited higher levels of IgA antibodies in tears than did soluble antigen plus CpG ODN.

CONCLUSIONS

CpG ODN is an effective mucosal immune modulator for enhancing rat tear IgA antibody responses to both soluble and microencapsulated antigens.