Influence of DNA encoding cytokines on systemic and mucosal immunity following genetic vaccination against herpes simplex virus

A recombinant plasmid containing CpG motifs as a novel vaccine adjuvant for immune protection against herpes simplex virus 2

The aim of the present study was to evaluate the efficacy of a herpes simplex virus type 2 (HSV-2) DNA vaccine co‑immunized with a plasmid adjuvant containing CpG motifs. A novel eukaryotic expression plasmid vector containing kanamycin resistance gene (pcDNA3Kan) was acquired from pET‑28a(+) and pcDNA3 plasmids. A gene encoding full length HSV‑2 glycoprotein D (gD) was amplified from the pcDNA3‑gD plasmid, which was cloned into pcDNA3Kan resulting in the construction of the recombinant plasmid pcDNA3Kan‑gD (pgD). A DNA segment containing 8 CpG motifs was synthesized, and cloned into pcDNA3Kan, resulting in the recombinant plasmid pcDNA3Kan‑CpG (pCpG). Mice were co‑inoculated with pgD (used as a DNA vaccine) and pCpG (used as an adjuvant) by bilateral intramuscular injection. Mice inoculated with pgD+pCpG showed higher titers of antibodies than those inoculated with the DNA vaccine alone (P<0.05). In addition, mice inoculated with pgD+pCpG showed the highest percentage of CD4+ T cells in the blood of all the groups (P﹤0.05). Thus, the present study demonstrated that pCpG could stimulate the HSV‑2 DNA vaccine to induce a stronger cell‑mediated immune response than the DNA vaccine alone. The aim of the present study was to evaluate the efficacy of a HSV‑2 DNA vaccine (pgD) co‑immunized with a plasmid adjuvant containing CpG motifs (pCpG). Whether the pCpG would be able to stimulate the pgD to induce a stronger immune response compared with pgD alone.

Innate endogenous adjuvants prime to desirable immune responses via mucosal routes

Vaccination is an effective strategy to prevent infectious or immune related diseases, which has made remarkable contribution in human history. Recently increasing attentions have been paid to mucosal vaccination due to its multiple advantages over conventional ways. Subunit or peptide antigens are more reasonable immunogens for mucosal vaccination than live or attenuated pathogens, however adjuvants are required to augment the immune responses. Many mucosal adjuvants have been developed to prime desirable immune responses to different etiologies. Compared with pathogen derived adjuvants, innate endogenous molecules incorporated into mucosal vaccines demonstrate prominent adjuvanticity and safety. Nowadays, cytokines are broadly used as mucosal adjuvants for participation of signal transduction of immune responses, activation of innate immunity and polarization of adaptive immunity. Desired immune responses are promptly and efficaciously primed on basis of specific interactions between cytokines and corresponding receptors. In addition, some other innate molecules are also identified as potent mucosal adjuvants. This review focuses on innate endogenous mucosal adjuvants, hoping to shed light on the development of mucosal vaccines.

Generation of antigen-specific immunity following systemic immunization with DNA vaccine encoding CCL25 chemokine immunoadjuvant

A significant hurdle in vaccine development for many infectious pathogens is the ability to generate appropriate immune responses at the portal of entry, namely mucosal sites. The development of vaccine approaches resulting in secretory IgA and mucosal cellular immune responses against target pathogens is of great interest and in general, requires live viral infection at mucosal sites. Using HIV-1 and influenza A antigens as models, we report here that a novel systemically administered DNA vaccination strategy utilizing co-delivery of the specific chemokine molecular adjuvant CCL25 (TECK) can produce antigen-specific immune responses at distal sites including the lung and mesenteric lymph nodes in mice. The targeted vaccines induced infiltration of cognate chemokine receptor, CCR9+/CD11c+ immune cells to the site of immunization. Furthermore, data shows enhanced IFN-λ secretion by antigen-specific CD3+/CD8+ and CD3+/CD4+ T cells, as well as elevated HIV-1-specific IgG and IgA responses in secondary lymphoid organs, peripheral blood, and importantly, at mucosal sites. These studies have significance for the development of vaccines and therapeutic strategies requiring mucosal immune responses and represent the first report of the use of plasmid co-delivery of CCL25 as part of the DNA vaccine strategy to boost systemic and mucosal immune responses following intramuscular injection.

Systemic immunization with CCL27/CTACK modulates immune responses at mucosal sites in mice and macaques

Plasmid DNA is a promising vaccine platform that has been shown to be safe and able to be administered repeatedly without vector interference. Enhancing the potency of DNA vaccination through co-delivery of molecular adjuvants is one strategy currently under investigation. Here we describe the use of the novel chemokine adjuvant CCL27/CTACK to enhance immune responses to an HIV-1 or SIV antigen in mice and rhesus macaques. CCL27 has been shown to play a role in inflammatory responses through chemotaxis of CCR10+ cells, and we hypothesized that CCL27 may modulate adaptive immune responses. Immunizations in mice with HIV-1gag/CCL27 enhanced immune responses both at peripheral and, surprisingly, at mucosal sites. To confirm these findings in a large-animal model, we created optimized CCL27 and SIV antigenic plasmid constructs for rhesus macaques. 10 macaques (n=5/group) were immunized intramuscularly with 1mg/construct of antigenic plasmids+/-CCL27 with electroporation. We observed significant IFN-gamma secretion and CD8+ T-cell proliferation in peripheral blood. Interestingly, CCL27 co-immunized macaques exhibited a trend toward greater effector CD4+ T cells in the bronchiolar lavage (BAL). CCL27 co-delivery also elicited greater antigen-specific IgA at unique sites including BAL and fecal samples but not in the periphery. Future studies incorporating CCL27 as an adjuvant in vaccine or therapy models where eliciting immune responses in the lung are warranted.

Effective vaginal DNA delivery with high transfection efficiency is a good system for induction of higher local vaginal immune responses

Objectives

To investigate the local vaginal and systemic immune responses of effective vaginal DNA delivery with high transfection efficiency, we determined the effects on Th1-dependent cytokine (interferon-γ) production in spleen and inguinal lymph node cells and antibody responses of vaginal pDNA immunization with a cell-penetrating peptide, and compared our vaginal immunization with intradermal and intranasal immunizations.

Methods

Mice were immunized by vaginal, nasal or dermal administration of pCMV-OVA with or without peptide carriers, and serum, vaginal fluids, spleen and inguinal cells were harvested. The serum immunoglobulin (Ig)G2a and vaginal IgA antibody responses were determined by sandwich enzyme-linked immunosorbent assay (ELISA). The interferon-γ production from spleen cells or inguinal lymph node cells was determined by an ELISA kit.

Key findings

The direct vaginal immunization strongly induced IgA in the vaginal fluids and interferon-γ production in the local lymph node draining from the vagina. In addition, co-vaccination with the peptide carriers elevated these immune responses compared with vaccination with pCMV-OVA alone. Vaginal immunization with high transfection efficiency promoted vaginal IgA production to a significantly greater extent than intradermal or nasal immunization.

Conclusions

These results suggested that direct vaginal DNA vaccines under high transfection conditions induced higher local vaginal antibody than that by intranasal or intradermal administration, and peptide carriers effectively elevated mucosal immune responses. Therefore, this vaginal DNA vaccination method may be expected to be useful in the prevention and treatment methods for vaginal infectious diseases such as HIV infection.

Plasmids encoding the mucosal chemokines CCL27 and CCL28 are effective adjuvants in eliciting antigen-specific immunity in vivo

A hurdle facing DNA vaccine development is the ability to generate strong immune responses systemically and at local immune sites. We report a novel systemically administered DNA vaccination strategy using intramuscular codelivery of CCL27 or CCL28, which elicited elevated peripheral IFN-gamma and antigen-specific IgG while driving antigen-specific T-cell secretion of cytokine and antibody production in the gut-associated lymphoid tissue and lung. This strategy resulted in induction of long-lived antibody responses that neutralized influenza A/PR8/34 and protected mice from morbidity and mortality associated with a lethal intranasal viral challenge. This is the first example of the use of CCL27 and CCL28 chemokines as adjuvants to influence a DNA vaccine strategy, suggesting further examination of this approach for manipulation of vaccine-induced immunity impacting both quality and phenotype of responses.

Adjuvant activity of cytokines

The activity of several potent adjuvants, including incomplete Freund's adjuvant, CpG oligodeoxynucleotides, and alum, has been shown to be due at least in part to the induction of cytokines, including type I interferons (IFNs), IFN-gamma, interleukin-2 (IL-2), and IL-12, that play key roles in the regulation of innate and adaptive immunity. The relatively short half-life of recombinant homologues of cytokines has limited their use as vaccine adjuvants. These difficulties have been overcome by encapsulation into liposomes and the use of cytokine expression vectors co-administered with DNA vaccines. Although a number of cytokines including IFN-alpha, IFN-gamma, IL-2, IL-12, IL-15, IL-18, IL-21, GM-CSF, and Flt-3 ligand have been shown to potentiate the immune response to vaccination in various experimental models, the full potential of cytokines as vaccine adjuvants remains to be established.

A novel adjuvant, the general opioid antagonist naloxone, elicits a robust cellular immune response for a DNA vaccine

While many adjuvants have been discovered and used in research, only a few adjuvants have been permitted for use with human vaccination. We have previously shown that the administration of naloxone (NLX), a general opioid antagonist, during infection with a non-virulent strain of herpes simplex virus type 1 (HSV-1) could enhance protection against HSV-1 challenge. Here, the adjuvant activity of NLX has been evaluated using a DNA vaccine for HSV-1 as a model. BALB/c mice were divided into four groups; for experimental groups, mice received the glycoprotein D1 (gD1) DNA vaccine alone or in combination with the adjuvant NLX. A positive control group received the KOS strain of HSV-1, and a negative control group received PBS. All mice were immunized three times on days 0, 21 and 42. Three weeks after the last immunization, immune responses against HSV-1 were assessed. Our results indicate that the administration of NLX as an adjuvant increased the ability of the gD1 DNA vaccine to enhance cytolytic T lymphocyte activity, lymphocyte proliferation, delayed-type hypersensitivity and shifting the immune response toward a T helper (Th)1 pattern and improved protective immunity against HSV-1. NLX also increased the IgG2a/IgG1 ratio, though it did not affect the production of HSV-1 antiserum. In conclusion, administration of NLX as an adjuvant in combination with the gD1 DNA vaccine can enhance cell-mediated immunity and shift the immune responses to Th1.

Prospects for use of interleukin-12 as a mucosal adjuvant for vaccination of humans to protect against respiratory pneumococcal infection

Mucosal vaccination against pneumococcal disease offers potential protection against otitis media, pneumonia and invasive disease, including providing herd benefit by reducing pathogen carriage. The major obstacle, however, remains the lack of a suitable adjuvant for use in humans. Animal models have demonstrated success of interleukin-12 (IL-12) as an adjuvant for mucosal vaccines using recombinant pneumococcal protein antigens. This review examines the biology of the IL-12 cytokine family, the toxicity of IL-12 in human studies and suggests approaches by which IL-12 could be developed as a mucosal adjuvant with pneumococcal protein based vaccines, for use in humans.

Comprehensive evaluation of positional candidates in the IL-18 pathway reveals suggestive associations with schizophrenia and herpes virus seropositivity

Interactions between genetic variation and environmental factors have been invoked in schizophrenia genesis, but pathways linking them are uncertain. We used a pathway-oriented approach to evaluate six genes mediating IL18 function (IL-18, IL18BP, IL18R1, IL18RAP, IL12B, and IL12A). The first five are also localized to regions previously linked with schizophrenia. Fifty-four representative tag SNPs were selected from comprehensive sequence data and genotyped in 478 patients with schizophrenia/schizoaffective disorder (DSM IV criteria) and 501 unscreened control individuals. Exposure to three herpes viruses previously suggested as risk factors for schizophrenia was estimated simultaneously among the cases. Five SNPs in four genes were associated with schizophrenia, most prominently rs2272127 at IL18RAP (P = 0.0007, odds ratio for C allele 1.49, 95% CI: 1.18-1.87; P = 0.03 following correction for multiple comparisons). Exploratory analysis revealed that rs2272127 was also associated with herpes simplex virus 1 (HSV1) seropositivity in cases (P = 0.04, OR for G allele 1.58, 95% CI: 1.04-2.39). Similar patterns were observed at another correlated SNP (rs11465702, P = 0.005 and 0.006, respectively for associations with schizophrenia and HSV1 seropositivity). We suggest plausible, testable hypotheses linking IL-18 signaling and HSV1 in schizophrenia pathogenesis.

Cloning, expression and immunoassay detection of ferret IFN-gamma

Ferrets (Mustela putorius furo) develop symptoms upon influenza infection that resemble those of humans, including sneezing, body temperature variation and weight loss. Highly pathogenic strains of influenza A, such as H5N1, have the capacity to cause severe illness or death in ferrets. The use of ferrets as a model of influenza infection is currently limited by a lack of species-specific immunological reagents. Interferon gamma (IFN-gamma) plays a key role in the development of innate and adaptive immunity and the regulation of Th1-type immune responses. Here we describe the cloning of the full-length cDNA for ferret IFN-gamma. Multiple sequence alignment of the predicted amino acid sequence with those of other species indicates that the predicted ferret protein shares the highest identity with Eurasian badger IFN-gamma. We raised two hybridoma clones expressing monoclonal antibodies against recombinant ferret IFN-gamma capable of detecting IFN-gamma protein derived from mitogen-stimulated ferret PBMCs by immunoblotting, ELISA and ELISPOT assay. Finally, an ELISA utilizing the ferret-specific antibodies detected elevated levels of IFN-gamma in serum samples from H3N2 influenza A-infected ferrets.

Evaluation of γ-interferon kinetics in HSV-1 infected mice in different days post infection (in vivo) and post re-stimulation (in vitro)

Gamma interferon (IFN-gamma) is among the most important immune factors for limiting of herpes simplex virus (HSV) infections. However, our knowledge about the kinetics of IFN-gamma production after HSV infection is limited. The present study examines the kinetics of IFN-gamma expression following secondary infection with HSV-1. Using semiquantitative RT-PCR assay, the expression of IFN-gamma in spleen lymphocytes was significantly detected on 14 days but not 7 days after intraperitoneal inoculation of HSV-1, while ELISA detected IFN-gamma on both days. At various hours after in vitro re-stimulation of spleen cells, RT-PCR showed a decreasing pattern of mRNA transcripts, whereas, ELISA assayed an increasing amount of secreted protein through the experiment. Despite the contrast results of ELISA and RT-PCR, regarding the short half-life of mRNA, the data are in correlation with each other and need to interpret.

Elicitation of T cell responses to histologically unrelated tumors by immunization with the novel cancer-testis antigen, brother of the regulator of imprinted sites

Brother of the regulator of imprinted sites (BORIS) was previously described as a transcription factor for epigenetic reprogramming the expression of which is strictly confined to germ cells of adult testes but is aberrantly activated in the vast majority of neoplastic cells. Considering the critical role of BORIS in cancerogenesis and the fact that its expression pattern may preclude thymic tolerance, we generated DNA- and protein-based mouse BORIS antitumor vaccines using a non-DNA-binding version of the BORIS molecule. Clinical use of BORIS as a vaccine Ag would require that certain safety concerns be met. Specifically, administration of the functional BORIS protein would hypothetically pose a risk of BORIS accelerating the progression of cancer. To alleviate such safety concerns, we have developed vaccines based on the BORIS molecule lacking the DNA-binding zinc fingers domain. To enhance anti-BORIS cellular immune responses, we used a standard molecular adjuvant approach. It consisted of plasmids encoding murine IL-12 and IL-18 for a DNA-based vaccine and conventional Th1 type adjuvant, Quil A, for a protein-based vaccine. Both DNA- and protein-based vaccines induced Ag-specific CD4(+) T cell proliferation with Th1 and Th2 cytokine profiles, respectively. Protein-based, but not DNA-based, BORIS vaccine induced a significant level of Ab production in immunized animals. Importantly, potent anticancer CD8(+)-cytotoxic lymphocytes were generated after immunization with the DNA-based, but not protein-based, BORIS vaccine. These cytolytic responses were observed across a wide range of different mouse cancers including mammary adenocarcinoma, glioma, leukemia, and mastocytoma.

IL-18 bridges innate and adaptive immunity through IFN-gamma and the CD134 pathway

IL-18 induces inflammation resulting in either enhanced protection from pathogens or exacerbation of autoimmunity, and T cells are profoundly activated during these responses. How IL-18 influences T cell activation is unknown, but this study in mice shows that IL-18 boosted Ag-specific T cell clonal expansion of effector T cells and induced a subpopulation of IFN-gamma superproducing T cells. Commitment to IFN-gamma production through IL-18 was independent of NK cells and IL-12 but dependent on host-derived IFN-gamma. To determine how expansion of these effectors occurred, IL-18 was shown to induce OX40L on dendritic cells, whereas peptide stimulation induced CD134 (OX40) on specific T cells. CD134 blockade inhibited T cell effector expansion thereby reducing the number of IFN-gamma superproducers by 12-fold. Thus, independent of IL-12, IL-18 impacts T cell immunity throughout lymphoid and nonlymphoid tissue by bridging the innate and adaptive arms of the immune system through IFN-gamma and the CD134 costimulatory pathway.

Developments in herpes simplex virus vaccines: old problems and new challenges

Vaccination has remained the best method for preventing virus spread. The herpes simplex virus (HSV) candidate vaccines tested till now were mostly purified subunit vaccines and/or recombinant envelope glycoproteins (such as gB and gD). In many experiments performed in mice, guinea pigs and rabbits, clear-cut protection against acute virus challenge was demonstrated along with the reduction of the extent of latency, when established in the immunized host. The immunotherapeutic effect of herpes vaccines seems less convincing. However, introduction of new adjuvants, which shift the cytokine production of helper T-cells toward stimulation of cytotoxic T-cells (TH1 type cytokine response), reveals a promising development. Mathematical analysis proved that overall prophylactic vaccination of seronegative women, even when eliciting 40-60 % antibody response only, would reduce the frequency of genital herpes within the vaccinated population. Even when partially effective, immunotherapeutic vaccination might represent a suitable alternative of chronic chemotherapy in recurrent labial and genital herpes.

Role of mucosal immunity in preventing genital herpes infection

The female genital tract is immunologically unique because it must be tolerant to spermatozoa, pregnancy, and vaginal flora, but also protect the host from pathogen challenge. The mucosal response to herpes simplex viruses (HSV), a major cause of genital ulcerative disease and critical co-factor in the HIV/AIDS epidemic, is complex and consists of the normally acidic vaginal environment, constitutively secreted and induced antimicrobial peptides, complement, and cellular responses mediated by epithelial and immune cells. This review summarizes our current understanding of the mucosal response to HSV focusing on those factors that may prevent initial infection. Understanding how each of these components contribute to innate immunity, mechanisms of antiviral activity, and whether the virus has evolved strategies to evade their effects may lead to the development of novel vaginal microbicides.

Direct application of plasmid DNA containing type I interferon transgenes to vaginal mucosa inhibits HSV-2 mediated mortality

The application of naked DNA containing type I interferon (IFN) transgenes is a promising potential therapeutic approach for controlling chronic viral infections. Herein, we detail the application of this approach that has been extensively used to restrain ocular HSV-1 infection, for antagonizing vaginal HSV-2 infection. We show that application of IFN-alpha1, -alpha5, and -beta transgenes to vaginal mouse lumen 24 hours prior to HSV-2 infection reduces HSV-2 mediated mortality by 2.5 to 3-fold. However, other type I IFN transgenes (IFN- alpha4, -alpha5, -alpha6, and -alpha9) are non effectual against HSV-2. We further show that the efficacy of IFN-alpha1 transgene treatment is independent of CD4+ T lymphocytes. However, in mice depleted of CD8+ T lymphocytes, the ability of IFN-alpha1 transgene treatment to antagonize HSV-2 was lost.

The cell-mediated immune response induced by plasmid encoding bovine herpesvirus 1 glycoprotein B is enhanced by plasmid encoding IL-12 when delivered intramuscularly or by gene gun, but not after intradermal injection

Bovine herpesvirus 1 (BHV-1) causes respiratory and genital infections in cattle. Previously we demonstrated that a DNA vaccine encoding a truncated, secreted form of BHV-1 glycoprotein B (tgB) induces cytotoxic T lymphocyte (CTL) responses in C3H mice. In this study we investigated the potential of interleukin 12 (IL-12) to further enhance the CTL response. C3H mice were immunized with a plasmid encoding tgB or with plasmids encoding tgB and murine IL-12. When the plasmid encoding tgB was delivered intramuscularly or epidermally by a gene gun, co-administration with IL-12 plasmid stimulated the synthesis of more IgG2a, the production of higher levels of IFN-gamma, and more effective killing by CTLs. In contrast, after intradermal delivery no effect of co-administration of IL-12 encoding plasmid was observed. Further investigation suggested that antigen and IL-12 need to be expressed in the draining lymph nodes, where IL-12 can have a direct effect on T cells.

Improving recombinant MVA immune responses: Potentiation of the immune responses to HIV-1 with MVA and DNA vectors expressing Env and the cytokines IL-12 and IFN-gamma

Recombinants based on vaccinia virus vectors, especially on the highly attenuated modified vaccinia virus Ankara (MVA) strain, are now being tested in clinical trials for safety and immunogenicity, using prime/boost heterologous regimes of vaccination. Due to the limited replication capacity of MVA, it is necessary to develop procedures that can enhance the specific cellular immune responses to the recombinant antigen delivered by the MVA vector. In this investigation, we have characterized the systemic immune responses in BALB/c mice using interferon-gamma (IFN-gamma) or interleukin-12 (IL-12) in an adjuvant-like manner elicited by MVA recombinants or naked DNA vectors expressing one of those cytokines in combination with the human immunodeficiency virus type 1 (HIV-1) envelope (Env) as antigen. In infected mice, virus gene expression in splenocytes and levels of cytokines IFN-gamma and IL-12 in serum were maximal by 6h post-infection (hpi) with MVA recombinants expressing IFN-gamma (MVAIFN-gamma) or IL-12 (MVAIL-12). In the infected animals, co-expression of HIV-1 env (MVAENV) and either IFN-gamma or IL-12 from MVA recombinants produced a two and three-fold increase of anti-env CD8+ T cell response, respectively. When priming was carried out with DNA vectors expressing HIV-1 env and either IFN-gamma or IL-12, the magnitude of the specific anti-env CD8+ T cell stimulation after MVAENV booster was further enhanced. Our findings revealed that IFN-gamma or IL-12 can be used to potentiate the cellular immune response to HIV-1 env, when delivered either from a single MVA recombinant or from a DNA vector. The increment of the CD8+ T cell response was higher in a DNA/MVA prime/boost protocol. Thus, the immune response of MVA vectors can be improved with the co-delivery of the cytokines IFN-gamma or IL-12.

CpG oligodeoxynucleotide augments HSV-2 glycoprotein D DNA vaccine efficacy to generate T helper 1 response and subsequent protection against primary genital herpes infection in mice

The present study was undertaken to evaluate the efficacy of a combined use of DNA vaccine of HSV-2 glycoprotein D (gD DNA) and CpG oligodeoxynucleotide (ODN) in comparison to gD DNA vaccine alone in inducing immunity against genital HSV-2 infection. Intramuscular vaccination of C57Bl/6 mice with gD DNA followed 48 h later by CpG ODN administration conferred a strong immunity against genital herpes infection. This was concomitant with development of a robust specific IgG2c (an indicator of Th1-type response in C57Bl/6 mice) antibody response as well as IFN-gamma production by genital lymph node and spleen cells in vitro. Administration of CpG ODN prior to gD DNA immunization, on the other hand, was inferior to immunization with gD DNA alone in providing protection against macroscopic signs of the disease. Consistent with the in vivo protection data, mice immunized with CpG ODN followed by gD DNA vaccine showed decreased specific lymphoproliferative and IFN-gamma responses compared to gD DNA vaccinated mice. In conclusion, these results indicate that timely administration of CpG ODN augments the immunity elicited by gD DNA vaccine, resulting in augmented Th1-type immunity against genital herpes infection in mice. These findings emphasize the value of using CpG ODN in a DNA vaccination scheme against genital herpes and merit also further evaluation in genetic vaccination approaches against other sexually transmitted infections.

Current developments in viral DNA vaccines: shall they solve the unsolved?

This review describes the mechanisms of immune response following DNA vaccination. The efficacy of DNA vaccines in animal models is highlighted, especially in viral diseases against which no widely accepted vaccination is currently available. Emphasis is given to possible therapeutic vaccination in chronic infections due to persisting virus genomes, such as recurrent herpes (HSV-1 and HSV-2), pre-AIDS (HIV-1) and/or chronic hepatitis B (HBV). In these, the problem of introducing foreign viral DNA may not be of crucial importance, since the immunised subject is already a viral DNA (or provirus) carrier. The DNA-based immunisation strategies may overcome several problems of classical viral vaccines. Novel DNA vaccines could induce immunity against multiple viral epitopes including the conservative type common ones, which do not undergo antigenic drifts. Within the immunised host, they mimic the effect of live attenuated viral vaccines when continuously expressing the polypeptide in question. For this reason they directly stimulate the antigen-presenting cells, especially dendritic cells. The antigen encoded by plasmid elicits T helper cell activity (Th1 and Th2 type responses), primes the cytotoxic T cell memory and may induce a satisfactory humoral response. The efficacy of DNA vaccines can be improved by adding plasmids encoding immunomodulatory cytokines and/or their co-receptors.

An interferon gamma-gp120 fusion delivered as a DNA vaccine induces enhanced priming

Nucleic acid vaccination has many potential advantages over traditional methods, but suffers from the fact that DNA vaccines tend to be relatively poorly immunogenic. Attempts to enhance DNA vaccine immunogenicity have included the addition of cytokine-encoding plasmids into the formulation, as well as the use of heterologous prime-boost regimes and the addition of conventional adjuvants, such as alum. We have previously shown that interferon gamma fusions have enhanced immunogenicity as recombinant protein vaccines. We have assessed here the immunogenicity of an interferon gamma-gp120 fusion delivered as a DNA vaccine, in the context of a prime-boost strategy and in the presence of absence of aluminium phosphate. Fusion of gp120 DNA to interferon gamma-encoding DNA resulted in strongly enhanced priming, especially of Th1 responses, including IgG2a responses to a protein boost.

Tumor immunity and prolonged survival following combined adenovirus-HSP72 and CEA-plasmid vaccination

We have studied the effects of recombinant adenoviruses as immune adjuvants for DNA vaccination. In a mouse model, using the weak immunogen carcinoembryonic antigen (CEA), anti-CEA IgG production was significantly higher and occurred earlier when immunization included a recombinant adenovirus together with CEA-plasmid DNA. Combined immunization with a recombinant adenovirus expressing the immunomodulatory molecule heat shock protein 72 (ADHSP72) and CEA-plasmid DNA resulted in CEA-specific T-cell activation capable of protecting mice from tumor formation with CEA expressing cells. Additionally, animals with CEA expressing tumors showed diminished tumor growth and prolonged survival when immunized with ADHSP72 and CEA-plasmid DNA compared to controls. Recombinant adenoviruses expressing immunomodulatory molecules such as HSP72 may be useful adjuvants for DNA vaccination.

Mucosal adjuvants and delivery systems for protein-, DNA- and RNA-based vaccines

Almost all vaccinations today are delivered through parenteral routes. Mucosal vaccination offers several benefits over parenteral routes of vaccination, including ease of administration, the possibility of self-administration, elimination of the chance of injection with infected needles, and induction of mucosal as well as systemic immunity. However, mucosal vaccines have to overcome several formidable barriers in the form of significant dilution and dispersion; competition with a myriad of various live replicating bacteria, viruses, inert food and dust particles; enzymatic degradation; and low pH before reaching the target immune cells. It has long been known that vaccination through mucosal membranes requires potent adjuvants to enhance immunogenicity, as well as delivery systems to decrease the rate of dilution and degradation and to target the vaccine to the site of immune function. This review is a summary of current approaches to mucosal vaccination, and it primarily focuses on adjuvants as immunopotentiators and vaccine delivery systems for mucosal vaccines based on protein, DNA or RNA. In this context, we define adjuvants as protein or oligonucleotides with immunopotentiating properties co-administered with pathogen-derived antigens, and vaccine delivery systems as chemical formulations that are more inert and have less immunomodulatory effects than adjuvants, and that protect and deliver the vaccine through the site of administration. Although vaccines can be quite diverse in their composition, including inactivated virus, virus-like particles and inactivated bacteria (which are inert), protein-like vaccines, and non-replicating viral vectors such as poxvirus and adenovirus (which can serve as DNA delivery systems), this review will focus primarily on recombinant protein antigens, plasmid DNA, and alphavirus-based replicon RNA vaccines and delivery systems. This review is not an exhaustive list of all available protein, DNA and RNA vaccines, with related adjuvants and delivery systems, but rather is an attempt to highlight many of the currently available approaches in immunopotentiation of mucosal vaccines.

Cytokine genetic adjuvant facilitates prophylactic intravascular DNA vaccine against acute and latent herpes simplex virus infection in mice

Intravascular plasmid DNA (pDNA) vaccine encoding herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) effectively induces prophylactic immunity against lethal HSV-1 infection in mice. We investigated whether the vaccine potency is further improved by coadministration of cytokine genes together with a low dose of genetic vaccine. pDNA encoding IL-12, IL-15, IL-18 or IL-21 was capable of elevating survival rates of HSV-1-infected mice when coinjected with 1 microg of gB pDNA, while IL-10 gene delivery failed to affect the effectiveness of the genetic immunization. Although only 17% of mice survived acute HSV infection after the gB pDNA vaccination at a dose of 1 microg, all mice coadministered with 1 microg each of gB and IL-12 pDNAs not only survived the acute infection but also escaped latent infection. In these animals, the neutralizing antibody against HSV-1 was abundantly produced, and CTL activity against the gB antigen was augmented. Coadministration of the gB and IL-12 genes also elevated the serum level of interferon-gamma. Adaptive transfer experiments indicated that soluble factors contributed to preventive immunity, while cell components alone were not capable of protecting mice from fatal viral infection. These results strongly suggest potential usefulness of Th1 cytokine genes as effective molecular adjuvants that facilitate specific humoral as well as cellular immune responses elicited by intravascular molecular vaccination.

Molecular adjuvants for mucosal immunity

Mucosal surfaces represent the entry route of a multitude of viral pathogens. For many of these viruses, such as the herpes simplex viruses and human immunodeficiency virus, no effective vaccine exists. Hence, it is important that prospective vaccines engender maximal immunity at these susceptible sites. Genetic vaccines encoding adjuvant molecules represent one approach to optimize mucosal as well as systemic immunity. Promising candidates include various inflammatory cytokines and chemokines that might be used to enhance the primary response to a level sufficient for protection. Encouraging studies involving cytokines such as granulocyte/macrophage colony-stimulating factor, interleukin-2 (IL-2), IL-12, IL-18, and many others are examined. Notable chemokines that may offer hope in such efforts include IL-8, RANTES, CCL19, CCL21, and a few others. Combinatorial approaches utilizing several cytokines and chemokines will most likely yield the greatest success. In addition, as more is discovered regarding the requirements for memory development of T cells, boosters involving key cytokines such as IL-15 and IL-23 may prove beneficial to long-term maintenance of the memory pool. This review summarizes the progress in the use of genetic vaccines to achieve mucosal immunity and discusses the needed strategies to maximize long-term prospective immunity at this vulnerable entry site.

The host response to herpes simplex virus infection

PURPOSE OF REVIEW

Infection with herpes simplex virus remains a significant cause of disease. The host immune system plays an important role in containing viral replication, and there has been considerable progress in defining which components of immunity are key to the resolution of infection. Nevertheless, effective immunoprophylaxis or immunotherapy has not yet been achieved.

RECENT FINDINGS

Recent work has focused on understanding the early events leading to the herpes simplex virus-specific immune response, in particular on the role of antigen-presenting dendritic cells. Herpes simplex virus has evolved a number of ways of interfering with antigen presentation by dendritic cells, thus presumably impeding or delaying the host immune response. Nevertheless, herpes simplex virus triggers strong cellular and humoral immunity. The ability of dendritic cells to take up dead or dying infected cells and cross-present them to cognate T cells may be the key to resolving this apparent paradox. Interaction between dendritic cell subsets, and particularly the virus-induced release of type I interferons may be essential to drive efficient antigen cross-presentation and subsequent T-cell activation.

SUMMARY

A greater understanding of the importance of dendritic cells in driving viral immunity, and of the ligands that activate these cells and the cytokines they secrete, has provided novel vaccination strategies. The delivery of immunomodulatory genes together with viral antigens, for example by DNA vaccination, may harness the full potential of dendritic cells, and achieve the goal of effective immunological control of herpes simplex virus.