Characterization of humoral immune responses induced by an influenza hemagglutinin DNA vaccine

Adjuvant effects of β-defensin on DNA vaccine OmpC against edwardsiellosis in flounder (Paralichthys olivaceus)

β-defensin of flounder plays an important role in immunomodulation by recruiting immune cells and has a potential vaccine adjuvant effect in addition to its bactericidal activity. In this study, adjuvant effects of β-defensin on DNA vaccine OmpC against edwardsiellosis in flounder (Paralichthys olivaceus) were investigated. The bicistronic eukaryotic expression plasmid pBudCE4.1 plasmid vector with two independent coding regions was selected to construct DNA vaccine of p-OmpC which express only the gene for the outer membrane protein of Edwardsiella tarda and the vaccine of p-OmpC-βdefensin which express both the outer membrane protein of the bacterium and β-defensin of flounder. In vitro and in vivo studies have shown that the constructed plasmids can be expressed in flounder embryonic cell lines and injection sites of muscles. After vaccination by intramuscular injection, both p-OmpC and p-OmpC-βdefensin groups showed significant upregulation of immune-response. Compared to the pBbudCE4.1 and the p-OmpC vaccinated groups, the p-OmpC-βdefensin vaccinated group showed significantly more cell aggregation at the injection site and intense immune response. The proportion of sIgM+ cells, as well as the CD4-1+ and CD4-2+ cells in both spleen and kidney was significantly higher in the p-OmpC-βdefensin vaccinated group at peak time point than in the control groups. The relative survival rate of the p-OmpC-βdefensin vaccine was 74.17%, which was significantly higher than that of the p-OmpC vaccinated group 48.33%. The results in this study determined that β-defensin enhances the responses in cellular and humoral immunity and evokes a high degree of protection against E. tarda, which is a promising candidate for vaccine adjuvant.

A Comparison of Plasmid DNA and mRNA as Vaccine Technologies

This review provides a comparison of the theoretical issues and experimental findings for plasmid DNA and mRNA vaccine technologies. While both have been under development since the 1990s, in recent years, significant excitement has turned to mRNA despite the licensure of several veterinary DNA vaccines. Both have required efforts to increase their potency either via manipulating the plasmid DNA and the mRNA directly or through the addition of adjuvants or immunomodulators as well as delivery systems and formulations. The greater inherent inflammatory nature of the mRNA vaccines is discussed for both its potential immunological utility for vaccines and for the potential toxicity. The status of the clinical trials of mRNA vaccines is described along with a comparison to DNA vaccines, specifically the immunogenicity of both licensed veterinary DNA vaccines and select DNA vaccine candidates in human clinical trials.

Evaluation of a xenogeneic vascular endothelial growth factor-2 vaccine in two preclinical metastatic tumor models in mice

In this study, a xenogeneic DNA vaccine encoding for human vascular endothelial growth factor receptor-2 (hVEGFR-2) was evaluated in two murine tumor models, the B16-F10 melanoma and the EO771 breast carcinoma model. The vaccine was administered by intradermal injection followed by electroporation. The immunogenicity and the biological efficacy of the vaccine were tested in (1) a prophylactic setting, (2) a therapeutic setting, and (3) a therapeutic setting combined with surgical removal of the primary tumor. The tumor growth, survival, and development of an immune response were followed. The cellular immune response was measured by a bioluminescence-based cytotoxicity assay with vascular endothelial growth factor-2 (VEGFR-2)-expressing target cells. Humoral immune responses were quantified by enzyme-linked immunosorbent assay (ELISA). Ex vivo bioluminescence imaging and immunohistological observation of organs were used to detect (micro)metastases. A cellular and humoral immune response was present in prophylactically and therapeutically vaccinated mice, in both tumor models. Nevertheless, survival in prophylactically vaccinated mice was only moderately increased, and no beneficial effect on survival in therapeutically vaccinated mice could be demonstrated. An influx of CD3+ cells and a slight decrease in VEGFR-2 were noticed in the tumors of vaccinated mice. Unexpectedly, the vaccine caused an increased quantity of early micrometastases in the liver. Lung metastases were not increased by the vaccine. These early liver micrometastases did however not grow into macroscopic metastases in either control or vaccinated mice when allowed to develop further after surgical removal of the primary tumor.

Advances in novel influenza vaccines: a patent review

The threat of a major human influenza pandemic such as the avian H5N1 or the 2009 new H1N1 has emphasized the need for effective prevention strategies to combat these pathogens. Although egg based influenza vaccines have been well established for a long time, it remains an ongoing public health need to develop alternative production methods that ensures improved safety, efficacy, and ease of administration compared with conventional influenza vaccines. This article is intended to cover some of the recent advances and related patents on the development of influenza vaccines including live attenuated, cell based, genomic and synthetic peptide vaccines.

Construction of a catsper1 DNA vaccine and its antifertility effect on male mice

Cation channel of sperm 1 (CATSPER1) is a unique sperm cation channel protein, and essential for sperm function and male fertility. CATSPER1 exclusively expresses in meiotic and postmeiotic spermatogenic cells, thus belongs to the spermatogenesis-specific antigen that escape central tolerance. We have previously demonstrated the immunocontraceptive potential of its transmembrane domains and pore region, and reported the antifertility effects of its B-cell epitopes on male mice. Aiming to develop DNA vaccine targeting CATSPER1 for male contraception, here the whole open reading frame of mouse Catsper1 was cloned into the plasmid pEGFP-N1 to obtain a DNA vaccine pEGFP-N1-Catsper1. The vaccine was confirmed to be transcribed and translated in mouse N2a cell in vitro and mouse muscle tissue in vivo. Intramuscular injection with the vaccine on male mice induced specific immune reaction and caused significant inhibition on sperm hyperactivated motility and progressive motility (P<0.001 for both), and consequently reduced male fertility. The fertility rate of experimental group was 40.9%, which was significant lower (P=0.012) than control group (81.8%). No significant change in mating behavior, sperm production and histology of testis/epididymis was observed. Given that Catsper1 exhibits a high degree of homology among different species, Catsper1 DNA vaccine might be a good strategy for developing an immunocontraceptive vaccine for human and animal use.

On the efficacy of malaria DNA vaccination with magnetic gene vectors

We investigated the efficacy and types of immune responses from plasmid malaria DNA vaccine encoding VR1020-PyMSP119 condensed on the surface of polyethyleneimine (PEI)-coated SPIONs. In vivo mouse studies were done firstly to determine the optimum magnetic vector composition, and then to observe immune responses elicited when magnetic vectors were introduced via different administration routes. Higher serum antibody titers against PyMSP119 were observed with intraperitoneal and intramuscular injections than subcutaneous and intradermal injections. Robust IgG2a and IgG1 responses were observed for intraperitoneal administration, which could be due to the physiology of peritoneum as a major reservoir of macrophages and dendritic cells. Heterologous DNA prime followed by single protein boost vaccination regime also enhanced IgG2a, IgG1, and IgG2b responses, indicating the induction of appropriate memory immunity that can be elicited by protein on recall. These outcomes support the possibility to design superparamagnetic nanoparticle-based DNA vaccines to optimally evoke desired antibody responses, useful for a variety of diseases including malaria.

Immune responses induced in HHD mice by multiepitope HIV vaccine based on cryptic epitope modification

CD8+ T cells play an important role in early HIV infection. However, HIV has the capacity to avoid specific CTL responses due to a high rate of mutation under selection pressure. Although the HIV proteins, gag and pol, are relatively conserved, these sequences generate low-affinity MHC-associated epitopes that are poorly immunogenic. Here, we applied an approach that enhanced the immunogenicity of low-affinity HLA-A2.1-binding peptides. The first position with tyrosine (P1Y) substitution enhanced the affinity of HLA-A2.1-associated peptides without altering their antigenic specificity. More importantly, P1Y variants efficiently stimulated in vivo native peptide-specific CTL that also recognized the corresponding naturally processed epitope. The potential to generate CTL against any low-affinity HLA-A2.1-associated peptide provides us with the necessary technique for identification of virus cryptic epitopes for development of peptide-based immunotherapy. Therefore, identification and modification of the cryptic epitopes of gal and pol provides promising candidates for HIV immunotherapy dependent upon efficient presentation by virus cells. Furthermore, this may be a breakthrough that overcomes the obstacle of immune escape caused by high rates of mutation. In this study, bioinformatics analysis was used to predict six low-affinity cryptic HIV gag and pol epitopes presented by HLA-A*0201. A HIV compound multi-CTL epitope gene was constructed comprising the gene encoding the modified cryptic epitope and the HIV p24 antigen, which induced a strong CD8+ T cell immune response regardless of the mutation. This approach represents a novel strategy for the development of safe and effective HIV prophylactic and therapeutic vaccines.

A DNA prime-protein boost vaccination strategy targeting turkey coronavirus spike protein fragment containing neutralizing epitope against infectious challenge

The present study was undertaken to determine immune response and protection efficacy of a spike (S) protein fragment containing neutralizing epitopes (4F/4R) of turkey coronavirus (TCoV) by priming with DNA vaccine and boosting with the recombinant protein from the corresponding DNA vaccine gene segment. Turkeys were vaccinated by priming with either one dose (G1-750DP) or two doses (G3-750DDP) of 750 μg DNA vaccine expressing 4F/4R S fragment and boosting with one dose of 200 μg 4F/4R S fragment. One dose of 100 μg DNA vaccine mixed with polyethyleneimine (PEI) and sodium hyaluronate (HA) followed by one dose of 750 μg DNA vaccine and one dose of 200 μg 4F/4R S fragment were given to the turkeys in group G2-100DPH. After infectious challenge by TCoV, clinical signs and TCoV detected by immunofluorescence antibody (IFA) assay were observed in less number of turkeys in vaccination groups than that in challenge control groups. TCoV viral RNA loads measured by quantitative real-time reverse transcription-PCR were lower in vaccinated turkeys than those in challenge control turkeys. The turkeys in G3-750DDP produced the highest level of TCoV S protein-specific antibody and virus neutralization (VN) titer. Comparing to the turkeys in G1-750DP, significantly less TCoV were detected by IFA in the turkeys in G2-100DPH receiving an extra dose of 100 μg DNA mixed with PEI and HA. The results indicated that DNA-prime protein-boost DNA vaccination regimen targeting TCoV S fragment encompassing neutralizing epitopes induced humoral immune response and partially protected turkeys against infectious challenge by TCoV.

Salmonella enterica as a vaccine carrier

Salmonella enterica is an invasive, facultative intracellular gastrointestinal pathogen causing human diseases such as gastroenteritis and typhoid fever. Virulence-attenuated strains of this pathogen have interesting capacities for the generation of live vaccines. Attenuated live typhoidal and nontyphoidal Salmonella strains can be used for vaccination against Salmonella infections and to target tumor tissue. Such strains may also serve as live carriers for the development of vaccination strategies against other bacterial, viral or parasitic pathogens. Various strategies have been developed to deploy regulatory circuits and protein secretion systems for efficient expression and delivery of foreign antigens by Salmonella carrier strains. One prominent example is the use of type III secretion systems to translocate recombinant antigens into antigen presenting cells. In this review, we will describe the recent developments in strategies that utilize live attenuated Salmonella as vaccine carriers for prophylactic vaccination against infectious diseases and therapeutic vaccination against tumors. Considerations for generating safe, attenuated carrier strains, designing stable expression systems and the use of adjuvants for live carrier strategies are discussed.

DNA vaccines: an historical perspective and view to the future

This review provides a detailed look at the attributes and immunologic mechanisms of plasmid DNA vaccines and their utility as laboratory tools as well as potential human vaccines. The immunogenicity and efficacy of DNA vaccines in a variety of preclinical models is used to illustrate how they differ from traditional vaccines in novel ways due to the in situ antigen production and the ease with which they are constructed. The ability to make new DNA vaccines without needing to handle a virulent pathogen or to adapt the pathogen for manufacturing purposes demonstrates the potential value of this vaccine technology for use against emerging and epidemic pathogens. Similarly, personalized anti-tumor DNA vaccines can also readily be made from a biopsy. Because DNA vaccines bias the T-helper (Th) cell response to a Th1 phenotype, DNA vaccines are also under development for vaccines against allergy and autoimmune diseases. The licensure of four animal health products, including two prophylactic vaccines against infectious diseases, one immunotherapy for cancer, and one gene therapy delivery of a hormone for a food animal, provides evidence of the efficacy of DNA vaccines in multiple species including horses and pigs. The size of these target animals provides evidence that the somewhat disappointing immunogenicity of DNA vaccines in a number of human clinical trials is not due simply to the larger mass of humans compared with most laboratory animals. The insights gained from the mechanisms of protection in the animal vaccines, the advances in the delivery and expression technologies for increasing the potency of DNA vaccines, and encouragingly potent human immune responses in certain clinical trials, provide insights for future efforts to develop DNA vaccines into a broadly useful vaccine and immunotherapy platform with applications for human and animal health.

An equine herpesvirus 1 (EHV-1) vectored H1 vaccine protects against challenge with swine-origin influenza virus H1N1

In 2009, a novel swine-origin H1N1 influenza A virus (S-OIV), antigenically and genetically divergent from seasonal H1N1, caused a flu pandemic in humans. Development of an effective vaccine to limit transmission of S-OIV in animal reservoir hosts and from reservoir hosts to humans and animals is necessary. In the present study, we constructed and evaluated a vectored vaccine expressing the H1 hemagglutinin of a recent S-OIV isolate using equine herpesvirus 1 (EHV-1) as the delivery vehicle. Expression of the recombinant protein was demonstrated by immunofluorescence and western blotting and the in vitro growth properties of the modified live vector were found to be comparable to those of the parental virus. The EHV-1-H1 vaccine induced an influenza virus-specific antibody response when inoculated into mice by both the intranasal and subcutaneous routes. Upon challenge infection, protection of vaccinated mice could be demonstrated by reduction of clinical signs and faster virus clearance. Our study shows that an EHV-1-based influenza H1N1 vaccine may be a promising alternative for protection against S-OIV infection.

Influenza: a unique problem in vaccination

The genetic attributes of the influenza virus lead to unique problems in vaccination. First, a highly mutable RNA genome, resulting in sequential antigenic variation, could potentially manifest as a vaccine failure or epidemic influenza. Second, a segmented genome that engenders the virus with the capacity for genetic reassortment and the introduction of new antigens into a host population could possibly result in a pandemic. The core problem in combating influenza is the need for continual vaccine revision and induction of broader heterovariant immunity. Current vaccines – the conventional inactivated vaccine and the live attenuated vaccine – rely on technology of strain selection and production methods that is decades old. The immunity induced by these vaccines is dominated by the response to hemagglutinin (HA) and, therefore, the vaccines are most effective when there is sufficient antigenic relatedness between the vaccine strain HA and the circulating wild-type virus HA. Consequently, these vaccines are susceptible to failure when an antigenically distinct virus emerges after the selection of the vaccine candidate strain. New vaccine strategies need to include immunization with other viral antigens in addition to HA, thereby broadening the immune response against influenza. Inclusion of the more slowly evolving neuraminidase and/or M2e in a vaccine against influenza could reduce the vulnerability to antigenic changes, and conserved antigens from internal proteins – nucleoprotein and M1 – delivered to induce T-cell helper and cytotoxic T cells, could ensure the presence of activated T cells that facilitate clearance of pandemic strains. Alternative production technologies, such as recombinant baculovirus and yeast, and different delivery methods, such as virus-like particles, should be explored to decrease vaccine production times and reduce reliance on embryonated eggs.

Analysis of three plasmid systems for use in DNA A beta 42 immunization as therapy for Alzheimer's disease

In an effort to optimize DNA immunization-elicited antibody production responses against A beta 1-42 (A beta 42) as a therapy for Alzheimer's disease (AD), comparisons were made between three distinct plasmid systems using gene gun delivery. Plasmids encoding A beta 42 monomer and a novel A beta 42 trimeric fusion protein were evaluated in conjunction with CMV or Gal4/UAS promoter elements. It was found that vaccination A beta 42 trimer under the Gal4/UAS promoter elicited high levels of anti-A beta 42 antibody production. Serum antibody levels from Gal4/UAS-A beta 42 trimer immunized mice were found to be 16.6+/-5.5 microg/ml compared to 6.5+/-2.5 microg/ml with Gal4/UAS-A beta 42 monomer or even less with CMV-A beta 42 trimer. As compared to monomeric A beta 42 or A beta 42 trimer expressed under the CMV promoter, injection of the Gal4/UAS-A beta 42 trimer induced high levels of A beta 42 antigen expression in tissue suggesting a mechanism for the increase in anti-A beta 42 antibody. Antibodies were found to be primarily IgG1 suggesting a predominant Th2 response (IgG1/IgG2a ratio of 9). Serum from A beta 42 trimer-vaccinated mice was also found to identify amyloid plaques in the brains of APP/PS1 transgenic mice. These results demonstrate the potential therapeutic use of Gal4/UAS DNA A beta 42 trimer immunization in preventing Alzheimer's disease.

The Toll-like receptor adaptor molecule TRIF enhances DNA vaccination against classical swine fever

To evaluate the effects of the Toll/interleukin-1 receptor domain-containing adaptor-inducing interferon-beta (TRIF) on immune responses induced by DNA vaccines, mice were immunized with the eukaryotic expression plasmid pcDNA/E2 encoding classical swine fever virus (CSFV) E2 alone or in combination with the TRIF genetic adjuvant. Immune responses were examined in immunized mice. Our data demonstrates that co-delivery of the DNA vaccine pcDNA/E2 with the TRIF adjuvant augmented specific humoral and cellular immune responses in a mouse model. Vaccination of pigs confirmed that the pcDNA/E2 in combination with TRIF conferred total protection against lethal challenge with highly virulent CSFV. We conclude that TRIF enhances the effects of the DNA vaccine against CSFV infection and could be used as a potential genetic adjuvant for DNA vaccines in large animal species.

A pcDNA-Ehcpadh vaccine against Entamoeba histolytica elicits a protective Th1-like response in hamster liver

DNA vaccines are promising tools to fight parasitic diseases, including amoebiasis caused by the protozoan Entamoeba histolytica. Here we studied the immunogenicity and protective efficacy of a DNA vaccine against this parasite composed by the EhCPADH surface complex encoding genes (Ehcp112 and Ehadh112). EhCPADH is formed by an adhesin (EhADH112) and a cysteine proteinase (EhCP112), both involved in the parasite virulence. We evaluated transcription, protein expression, immunological response and protection against hepatic amoebiasis in hamsters intradermally and intramuscularly immunized with a mixture of pcDNA-Ehadh112 and pcDNA-Ehcp112 plasmids. RT-PCR and immunohistochemical assays showed that both antigens were differentially expressed in spleen and liver of immunized animals. No significant antibody immune response was induced by either route. However, intradermally inoculated hamsters presented a robust Th1-like immune response, characterized by high levels of INF-gamma and TNF-alpha cytokines, detected in the liver of animals challenged with virulent trophozoites. Animals showed significant protection against amoebiasis manifested by a higher survival rate and a significant prevention of liver abscess formation. We conclude that a refinement of this DNA vaccine could be a good choice to control hepatic amoebiasis.

A single immunization with HA DNA vaccine by electroporation induces early protection against H5N1 avian influenza virus challenge in mice

Background

Developing vaccines for the prevention of human infection by H5N1 influenza viruses is an urgent task. DNA vaccines are a novel alternative to conventional vaccines and should contribute to the prophylaxis of emerging H5N1 virus. In this study, we assessed whether a single immunization with plasmid DNA expressing H5N1 hemagglutinin (HA) could provide early protection against lethal challenge in a mouse model.

Methods

Mice were immunized once with HA DNA at 3, 5, 7 days before a lethal challenge. The survival rate, virus titer in the lungs and change of body weight were assayed to evaluate the protective abilities of the vaccine. To test the humoral immune response induced by HA DNA, serum samples were collected through the eye canthus of mice on various days after immunization and examined for specific antibodies by ELISA and an HI assay. Splenocytes were isolated after the immunization to determine the antigen-specific T-cell response by the ELISPOT assay.

Results

Challenge experiments revealed that a single immunization of H5N1 virus HA DNA is effective in early protection against lethal homologous virus. Immunological analysis showed that an antigen-specific antibody and T-cell response could be elicited in mice shortly after the immunization. The protective abilities were correlated with the amount of injected DNA and the length of time after vaccination.

Conclusion

A single immunization of 100 μg H5 HA DNA vaccine combined with electroporation was able to provide early protection in mice against homologous virus infection.

West Nile virus seroconversion in penguins after vaccination with a killed virus vaccine or a DNA vaccine

To investigate the serologic response of penguins to West Nile virus (WNV) vaccines, four species of exclusively indoor-housed penguins, negative for WNV by serology, were evaluated: Humboldt (Spheniscus humboldti), Magellanic (Spheniscus magellanicus), Gentoo (Pygoscelis papua), and Rockhopper (Eudyptes chrysoscome) penguins. Birds were inoculated with either a killed virus vaccine or a plasmid-mediated DNA WNV vaccine, and postinoculation serology was evaluated. Both vaccines induced seroconversion in all four species, and no adverse reactions were noted. Postvaccination serology results varied across species and vaccine types. However, in all four species, the killed virus vaccine resulted in a greater seroconversion rate than the DNA vaccine and in a significantly shorter time period. Additionally, the duration of the seropositive titer was significantly longer in those birds vaccinated with the killed virus vaccine compared with those vaccinated with the DNA vaccine. A subset of unvaccinated penguins serving as negative controls remained negative throughout the duration of the study despite the presence of WNV in the geographic locations of the study, suggesting that indoor housing may minimize exposure to the virus and may be an additional means of preventing WNV infection in penguins.

DNA vaccines against influenza viruses

As an attractive alternative to conventional vaccines, DNA vaccines play a critical role in inducing protection against several infectious diseases. In this review, we discuss the advantages that DNA vaccines offer in comparison to conventional protein-based vaccines. We discuss strategies to improve the potency and efficacy of DNA vaccines. Specifically, we focus on the potential use of DNA-based vaccines to elicit broad-spectrum humoral and cellular immunity against influenza virus. Finally, we discuss the advances made in the use of DNA vaccines to prevent avian H5N1 influenza.

Enhanced protective efficacy of H5 subtype avian influenza DNA vaccine with codon optimized HA gene in a pCAGGS plasmid vector

H5N1 influenza viruses have caused significant disease and deaths in various parts of the world in several species, including humans. Vaccination combined with culling can provide an attractive method for outbreak containment. Using synthesized oligos and overlapping extension PCR techniques, we constructed an H5 HA gene, optiHA, containing chicken biased codons based on the HA amino acid sequence of the highly pathogenic H5N1 virus A/goose/Guangdong/1/96 (GS/GD/96). The optiHA and wild-type HA genes were inserted into plasmids pCI or pCAGGS, and designated as pCIoptiHA, pCAGGoptiHA, pCIHA and pCAGGHA, respectively. To evaluate vaccine efficacy, groups of 3-week-old specific pathogen free (SPF) chickens were intramuscularly injected with the four plasmids. Sera were collected on a weekly basis post-vaccination (p.v.) for hemagglutination inhibition (HI) assays and neutralization (NT) antibody detection. All chickens receiving pCAGGoptiHA and pCAGGHA developed high levels of HI and NT antibodies at 3 weeks p.v., and were completely protected from lethal H5 virus challenge, while only partial protection was induced by inoculation with the other two plasmids. A second experiment was conducted to evaluate if a lower dose of the pCAGGoptiHA vaccine could be effective, results indicated that two doses of 10 microg of pCAGGoptiHA could induce complete protection in chickens against H5 lethal virus challenge. Based on our results, we conclude that construction optimization could dramatically increase the H5 HA gene DNA vaccine efficacy in chickens, and therefore, greatly decrease the dose necessary for inducing complete protection in chickens.

Inhibition of type I allergic responses with nanogram doses of replicon-based DNA vaccines

BACKGROUND

Allergic diseases have become a major public health problem in developed countries; yet, no reliable, safe and consistently effective treatment is available. DNA immunization has been shown to prevent and balance established allergic responses, however, the high dose of conventional DNA vaccines necessary for the induction of anti-allergic reactions and their poor immunogenicity in primates require the development of new allergy DNA vaccines. We evaluated protective and therapeutic effects of a Semliki-Forest Virus replicase-based vs a conventional DNA vaccine in BALB/c mice using the model allergen beta-galactosidase.

METHODS

Immunoglobulin (Ig)E suppression was determined by a basophil release assay as an in vitro correlate for allergen-specific crosslinking capacity of IgE reflecting the in vivo situation in an allergic individual. Th1 memory responses were measured by cytokine detection via enzyme-linked immunosorbent assay (ELISA) and enzyme-linked immunospot assay (ELISPOT).

RESULTS

Nanogram amounts of a replicase-based vector triggered a Th1 response comparable with that achieved with the injection of 20,000-times more copies of a conventional DNA plasmid, and induced IgE suppression in both a protective and a therapeutic setting.

CONCLUSIONS

Replicase-based DNA vaccines fulfill the stringent criteria for an allergy DNA vaccine, i.e. low dose, strong Th1 immunogenicity and memory, lack of 'therapy-induced' IgE production and anaphylactic side effects. Moreover, by triggering apoptosis in transfected cells, their unique 'immunize and disappear' feature minimizes the hypothetical risks of genomic integration or induction of autoimmunity.

Transcutaneous immunization with inactivated influenza virus induces protective immune responses

The recent outbreaks of highly pathogenic avian influenza in Asia and spread of the disease worldwide highlight the need to redefine conventional immunization approaches and establish effective mass vaccination strategies to face global pandemics. Transcutaneous immunization (TCI) is a novel route for vaccination, which uses the topical application of vaccine antigens on the skin. In this study, we investigated the potential of TCI using inactivated whole influenza virus. We found that TCI with whole inactivated influenza virus induced influenza virus-specific antibodies with hemagglutination inhibition and neutralizing activities as well as cellular immune responses, even without an adjuvant, and conferred protective immunity to virus challenge. Co-administration with cholera toxin (CT), a potent adjuvant for TCI, significantly enhanced immune responses against the influenza virus antigen. To enhance penetration of the skin barrier to the particulate influenza viral antigens, we tested the effects of the potential penetration enhancers/immunomodulators oleic acid (OA) and retinoic acid (RA). Pretreatment of mouse skin with OA elicited increased levels of influenza virus-specific binding and neutralizing antibodies to levels equivalent to those induced by intranasal immunization with inactivated influenza virus. OA and RA treatments differentially affected the pattern of cytokine production upon stimulation with influenza viral antigen and provided enhanced protection. These results reveal a promising perspective for the application of transcutaneous immunization to prevent influenza epidemics as well as a range of other infectious diseases.

Epidermal DNA vaccine for influenza is immunogenic in humans

A phase I clinical trial was conducted to evaluate a monovalent influenza DNA vaccine containing the HA gene from A/Panama/2007/99 delivered by particle-mediated epidermal delivery (PMED). Three groups of 12 healthy adult subjects received a single dose on day 0 of either 1, 2 or 4 microg of DNA vaccine, delivered as 1, 2 or 4 PMED administrations. The PMED influenza DNA vaccine elicited serum hemagglutination-inhibition (HAI) antibody responses at all three dose levels, with the highest and most consistent responses in subjects vaccinated with the highest dose level. Antibody responses were greatest at the last time point tested, day 56. Treatment-related reactions were mild to moderate, and included skin reactions at the vaccine site. These results provide a preliminary indication of the safety and immunogenicity of a prototype epidermal DNA vaccine for influenza.

Immunization with a DNA chimeric molecule encoding a hemagglutinin peptide and a scFv CD21-specific antibody fragment induces long-lasting IgM and CTL responses to influenza virus

Killed viral vaccines are known to induce primarily antibody responses. By contrast DNA vaccination using naked DNA encoding viral antigens induces both humoral and cellular immune responses. Various approaches have been used to construct DNA vaccines with build-in adjuvanticity. We hypothesized that sequences encoding a common epitope of influenza A virus hemagglutinin jointed to sequences encoding a single-chain variable fragment (scFv) antibody fragment to a costimulatory B cell surface receptor would result in the in vivo expression of a chimeric viral peptide with increased immunogenicity. Such a hybrid DNA molecule was constructed by us, encoding a T and B cell epitope-containing influenza hemagglutinin peptide and a scFv antibody fragment binding to mouse complement receptors I and II (CR1 and CR2). A single immunization with a plasmid containing the described construct induced a strong anti-influenza cytotoxic response lasting for more than six months and a weak antibody response.

Dissecting the components of the humoral immune response elicited by DNA vaccines

Although DNA vaccines appear to be efficient at inducing strong cellular immune responses, a number of questions remain regarding their ability to induce humoral immunity. The essential components for generating an antibody response include B and T cell recognition of antigen, subsequent activation, clonal expansion of each lymphocyte type and migration of T cells into B cell follicles to provide help, all leading to germinal centre formation and antibody production. We have employed a double adoptive transfer system based on ovalbumin (OVA)-specific CD4+ DO11.10 T cells and hen egg lysozyme (HEL)-specific MD4 B cells to assess all of these parameters in the context of DNA vaccination in vivo. We find that vaccination with DNA constructs expressing an OVA-HEL gene fusion (encoding contiguous T and B cell epitopes) can induce T cell activation, clonal expansion and migration into B cell follicles accompanied by B cell activation, blastogenesis, expansion and antibody production. These findings show that DNA vaccination can induce all of the components required for humoral immunity and also provide a system for in depth analysis of factors that influence the development of antibody responses. Such strategies may facilitate the rational design of vaccines capable of inducing effective humoral immunity.

Protective effects of a DNA vaccine expressing the infectious salmon anemia virus hemagglutinin-esterase in Atlantic salmon

Infectious salmon anemia (ISA) is a disease, caused by an orthomyxovirus, which has considerable economic impact on farming of Atlantic salmon. Here we describe the results of immunization against ISA using plasmids expressing the ISA virus hemagglutinin-esterase (HE). Immunized Atlantic salmon demonstrated moderate protection after challenge with ISA virus, with relative percent survival of 39.5 and 60.5 in two parallel groups. No protection was seen after immunization using a plasmid expressing the ISA virus nucleoprotein. Fish in the HE-immunized group had earlier onset of clearance of the virus than control fish. There was no detectable ISA virus specific humoral response after immunization. After challenge a specific humoral response could be demonstrated in the fish in all groups, but no correlation between this response and protection was found.

Protection against dengue type 2 virus induced in mice immunized with a DNA plasmid encoding the non-structural 1 (NS1) gene fused to the tissue plasminogen activator signal sequence

Dengue is one of the most important arboviral diseases in humans, and although efforts over the last decades have dealt with the development of a vaccine, this vaccine is not available yet. In order to evaluate the potential of a DNA vaccine based on the non-structural 1 (NS1) protein against dengue virus (DENV), we constructed the pcTPANS1 plasmid which contains the secretory signal sequence derived from human tissue plasminogen activator (t-PA) fused to the full length of the DENV-2 NS1 gene. Results indicate that pcTPANS1 promotes correct expression of NS1 in eukaryotic cells and drives secretion of the recombinant protein to the surrounding medium in a dimeric form. Balb/c mice, intramuscularly inoculated with this plasmid, presented high levels of antibodies, recognizing mainly surface-exposed conformational epitopes present in the NS1 protein expressed by insect cells. Long-term antibody response was observed in animals 56 weeks after the first plasmid inoculation, and a rapid, efficient secondary response was observed after a DNA boost. Vaccinated animals were challenged against DENV-2 in two murine models, based on intracerebral (i.c.) and intraperitoneal (i.p.) virus inoculations, and in both cases, pcTPANS1-immunized mice were protected. Overall, these results provide further support for the use of such a plasmid in a possible approach for the development of a vaccine against DENV.

Protection against influenza virus infection in BALB/c mice immunized with a single dose of neuraminidase-expressing DNAs by electroporation

The ability of a single dose of plasmid DNA encoding neuraminidase (NA) or hemagglutinin (HA) from influenza virus A/PR/8/34 (PR8) (H1N1) to protect against homologous virus infection was examined in BALB/c mice. In the present study, mice were immunized once with 30 microg of NA or HA DNA by electroporation. Four weeks or 28 weeks after immunization, mice were challenged with a lethal dose of homologous virus and the ability of NA or HA DNA to protect the mice from influenza was evaluated. We found that a single inoculation of NA DNA could provide protection against influenza virus challenge as well as long-term protection against viral infection. Whereas, the mice immunized with a single dose of HA DNA could not be protected. In addition, neonatal mice immunized with a single dose of 30 microg of NA DNA could be provided with significant protection against viral infection.

Diverse Plasmid DNA Vectors by Directed Molecular Evolution of Cytomegalovirus Promoters

Genetic vaccinations, gene therapy, and manufacturing of therapeutic proteins would benefit from promoter sequences that provide improved or prolonged expression levels. The cytomegalovirus (CMV) promoter is one of the most potent promoters known to date, and no previous examples of improved activity of this promoter by sequence mutagenesis have been reported. This study describes directed molecular evolution of CMV promoters derived from two human and two nonhuman primate strains of CMV by DNA shuffling and screening. Libraries of chimeric promoters were screened and analyzed for expression levels and immune responses, using plasmid DNA vectors encoding luciferase and beta-galactosidase. The results indicate that high functional diversity among CMV promoters can be generated, and the chimeric promoters selected after two rounds of DNA shuffling and particularly designed screening assays provided approximately 2-fold increased luciferase reporter gene expression and anti-beta-galactoside antibody response in vivo when compared with wild-type promoters. Sequence analysis of the shuffled promoters identified several mutations potentially contributing to the observed enhanced or reduced promoter activities and identified a 42-nucleotide region that appears obsolete for the functioning of the CMV promoter. Taken together, these data demonstrate the feasibility of generating diverse promoter sequences by DNA shuffling and screening methods, and provide novel structure- function information about CMV promoters. DNA shuffling and screening technologies provide a new approach to promoter optimization and development of optimal expression vectors for genetic vaccinations, gene therapy, and protein expression.

Intranasal immunization with liposome-encapsulated plasmid DNA encoding influenza virus hemagglutinin elicits mucosal, cellular and humoral immune responses

BACKGROUND

Influenza viral infections are a significant global public health concern due to the morbidity and mortality associated with acute respiratory disease, associated secondary complications and pandemic threat. Currently, the most effective preventative measure is an annual intramuscular (i.m.) injection of a trivalent vaccine. Intramuscular immunization induces strong systemic humoral responses but not mucosal immune responses which are important in the first line of defense against influenza.

OBJECTIVES

A plasmid encoding influenza A/PR/8/34 (H1N1) hemagglutinin (HA; pCI-HA10) was evaluated with respect to the mucosal, cellular and humoral immune responses generated and to its efficacy in protection against a challenge with a lethal dose of influenza.

STUDY DESIGN

BALB/c mice were immunized with pCI-HA10 DNA or liposome-encapsulated pCI-HA10 by either an intranasal (i.n.) or i.m. route. Sera and bronchoalveolar lavage (BAL) fluid were collected at various times and evaluated for HA-specific IgG and IgA antibodies and T cells, isolated from draining lymph nodes and spleens, were analyzed for their proliferative ability. Immunized mice were challenged with a lethal dose (5LD(50)) of influenza and monitored for survival.

RESULTS AND CONCLUSIONS

Intranasal immunization with liposome-encapsulated pCI-HA10 stimulated both IgG and IgA humoral responses and increased IgA titers in BAL fluid, whereas immunization with naked pCI-HA10 had no effect on the antibody response. Intramuscular immunization with both naked and liposome-encapsulated pCI-HA10 elevated serum IgG levels, but had no effect on IgA levels in either the serum or BAL fluid. Both i.n. and i.m. administration of HA vaccine (naked and liposome-encapsulated) elicited T cell proliferative responses. These results suggest that i.n. administration of liposome-encapsulated HA-encoding DNA is effective at eliciting mucosal, cellular and humoral immune responses. Mice immunized i.n. were able to withstand a lethal challenge of influenza virus, confirming that the immune responses mediated by the vaccine were protective.

DNA vaccine

The DNA vaccine has proven to be one of the most promising applications in the field of gene therapy. Due to its unique ability to readily induce humoral as well as cellular immune responses, it attracted great interest when the concept was first confirmed in the early 1990s. After thousands of articles related to the DNA vaccine were published, scientists began to realize that although the DNA vaccine is very effective in small animal models, its effectiveness in recent clinical trails is rather disappointing. Therefore, current effort has been shifted to understanding the different performance of the DNA vaccine in mouse and large animal models and on how to transfer the success of the DNA vaccine in small animals to large animals and humans.

DNA immunization for the production of monoclonal antibodies to Blo t 11, a paramyosin homolog from Blomia tropicalis

BACKGROUND

Blo t 11 is a high molecular weight allergen from Blomia tropicalis with significant immunoglobulin (Ig)E binding frequency. Native and recombinant Blo t 11 are susceptible to degradation and the isolation and expression of the allergen is problematic thus obtaining sufficient amounts of purified Blo t 11 for antibody production is limiting. DNA-based immunization is an attractive alternative strategy that bypasses antigen purification for antibody production.

OBJECTIVES

To use a DNA-based immunization protocol for the production and characterization of Blo t 11 monoclonal antibodies (mAbs).

METHODS

The 2625 bp cDNA coding for Blo t 11 was cloned into a mammalian expression vector and immunized intramuscularly with electroporation into mice. Monoclonal antibodies to Blo t 11 were generated using a methylcellulose-based hybridoma cloning kit. These mAbs were utilized for native Blo t 11 isolation and the development of sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

Six mAbs recognizing the native and recombinant Blo t 11 were generated and characterized. Native Blo t 11 was affinity purified from Bt extract and its identity was confirmed by matrix assisted laser desorption/ionization - time of flight mass spectrometry. The native Blo t 11 showed IgE reactivity with 67% of mite allergic sera. A two-site ELISA developed showed a detection limit of 100 pg/ml of Blo t 11.

CONCLUSION

A DNA-based immunization protocol was successfully used to generate Blo t 11 mAbs with a spectrum of distinct epitopes located throughout the whole molecule, and they are useful for immunoaffinity purification and immunoassays.

DNA immunization followed by a single boost with cells: a protein-free immunization protocol for production of monoclonal antibodies against the native form of membrane proteins

Recent advancements in antibody-based therapies require the development of an efficient method for generation of monoclonal antibodies (MAbs) against the native form of membrane proteins. We examined DNA immunization followed by a single boost with cells as a protein-free immunization protocol for production of MAbs. Mice immunized with plasmid cDNAs encoding human CD30 or Ret tyrosine kinase were given a single boost with cells expressing the corresponding antigen prior to cell fusion. A total of nine cell fusion experiments revealed that the cell boost is necessary for efficient generation of hybridomas and the DNA-cell boost method gave good yields of specific MAbs (5-59 MAbs from one mouse). All IgG isotypes except IgG3 were generated, although IgG2a was the dominant isotype. All the MAbs reacted with native antigens expressed on cells in a fluorescence-activated cell sorter (FACS) analysis as well as with recombinant CD30 or Ret protein genetically fused with human Fc in an enzyme-linked immunosorbent assay (ELISA). The affinities of the anti-CD30 MAbs to CD30-Fc protein ranged from 0.9 to 12.4 nM Kds, which were comparable to existing MAbs to these proteins, which range from 3.0 to 13.0 nM. Western blot analysis and topographical epitope mapping experiments based on the mutual competition of pairs of the anti-CD30 MAbs revealed that about 40% of the epitopes were linear epitopes and that each epitope was topographically classified into one of six groups. The large number of MAbs that react with high affinities to a variety of epitopes on the native form of antigens indicates that the method presented in this paper could be generally useful for generating MAbs to other membrane proteins.

Immunization with a dicistronic plasmid expressing a truncated form of bovine herpesvirus-1 glycoprotein D and the amino-terminal subunit of glycoprotein B results in reduced gB-specific immune responses

As an approach to create a divalent DNA vaccine, a truncated secreted version of bovine herpesvirus-1 (BHV-1) glycoprotein D (tgD) and the amino-terminal subunit of glycoprotein B (gBb) were expressed from a dicistronic plasmid, designated pSLIAtgD-IRES-gBb. Intradermal immunization of mice with pSLIAtgD-IRES-gBb or a mixture of plasmids encoding tgD (pSLIAtgD) and gBb (pSLIAgBb) by needle injection or gene gun elicited strong tgD-specific immune responses. However, a significant reduction in gBb-specific immune responses was observed upon immunization of mice with pSLIAtgD-IRES-gBb or a mixture of pSLIAtgD and pSLIAgBb in comparison to immunization with pSLIAgBb alone. This reduction in gBb-specific immune responses induced by pSLIAtgD-IRES-gBb was due to production of low amounts of gBb from pSLIAtgD-IRES-gBb, inefficient processing and transport of gBb, and possibly competition for antigen-presenting cells by tgD and gBb. These results indicate that, although divalent plasmids may be used to express different antigens, the efficacy of vaccination with such plasmids may be influenced by the plasmid design and the characteristics of the expressed antigens.

Analysis of epitope recognition of antibodies induced by DNA immunization against hemagglutinin protein of influenza A virus

In an effort to find efficient DNA vaccine candidates, cDNA of influenza A virus hemagglutinin (HA) gene and several derived mutants were injected into mice using a gene gun. Mice immunized with HA1 DNA, with or without a membrane domain, showed a humoral immune response and the survival rate against homologous virus challenge was comparable to that of mice injected with HA DNA. In order to analyze epitopes recognized by antibodies induced by gene gun immunization, we used a binding assay employing the chimeric HA protein method. Serum antibodies of mice immunized with HA DNA recognized the HA1 domain but not the HA2 domain. In addition, antisera obtained from mice immunized with HA1 DNA reacted with each of the known antigenic sites on the HA1 domain, similar to the results obtained with HA DNA immunization.

Vaccination of mice with MUC1 cDNA suppresses the development of lung metastases

C57BL/6 mice were immunized intradermally with various doses of purified pCEP4 plasmid DNA containing full-length MUC1 cDNA (22 tandem repeats). Mice immunized with MUC1 DNA three times at weekly intervals had serum antibodies to a synthetic peptide corresponding to the tandem repeats of MUC1. The antibody titer correlated with the plasmid DNA dose. After the third immunization mice were injected intravenously with 5 x 10(5) 16-F10 melanoma cells that had been stably transfected with MUC1 cDNA (F10-MUC1-C8 clone cells). The number of lung metastatic nodules three weeks after inoculation of F10-MUC1-C8 cells was significantly lower in mice immunized with MUC1 plasmid DNA than in mice immunized with the vector DNA alone. Thus, the suppression of lung metastasis was antigen-specific. In vivo depletion of lymphocyte subpopulations by specific antibodies revealed that natural killer cells are the major effector cells responsible for the suppression of lung metastasis. CD4+ cells and CD8+ cells apparently played some roles too.

The combination of DNA vectors expressing IL-12 + IL-18 elicits high protective immune response against cutaneous leishmaniasis after priming with DNA-p36/LACK and the cytokines, followed by a booster with a vaccinia virus recombinant expressing p36/LACK

Protocols of immunization based on the DNA prime/vaccinia virus (VV) boost regime with recombinants expressing relevant antigens have been shown to elicit protection against a variety of pathogens in animal model systems, and various phase I clinical trials have been initiated with this vaccination approach. We have previously shown that mice immunized with a DNA vector expressing p36/LACK of Leishmania infantum followed by a booster with VVp36/LACK induced significant protection against Leishmania major infection. To further improve this protocol of immunization, here we investigated whether the cytokines interleukin-12 (IL-12) and IL-18 could enhance protection against L. major infection in BALB/c mice. We found that priming with DNA vectors expressing p36/LACK and either IL-12 or IL-18, followed by a booster with a VV recombinant expressing the same L. infantum LACK antigen, elicit a higher cellular immune response than by using the same protocol in the absence of the cytokines. The cytokine IL-12 triggered a higher number of IFN-gamma-secreting cells specific for p36 protein than IL-18. When immunized animals were challenged with promastigotes, the highest protection against L. major infection was observed in animals primed with DNAp36 + DNA IL-12 + DNA IL-18 and boosted with VVp36. This protection correlated with a Th1 type of immune response. Our findings revealed that in prime/booster protocols, co-expressing IL-12 and IL-18 during priming is an efficient approach to protect against leishmaniasis. This combined prime/booster immunization regime could have wide use in fighting against parasitic and other infectious diseases.

New technology platforms in the development of vaccines for the future

The desire for improved quality of life in both industrialised and under-developed nations has led to the quest for greater understanding and subsequent prevention and treatment of diseases. Here we discuss some of the latest of modern medicine's approaches to vaccination and disease treatment. Our main subject of discussion being the novel antigen delivery systems termed immunopotentiating reconstituted influenza virosomes (IRIVs) and their use as vaccines. Particular attention is paid to the currently licensed Epaxal and Inflexal V, good examples of the improvements being made in vaccinology. Alternative uses of virosomes such as peptide delivery, cytosolic drug delivery and gene delivery are also considered, highlighting the flexibility of the IRIV formulation and method of action. The paper concludes with consideration of alternative novel approaches to vaccinology including bacterial carriers for DNA vaccines, recombinant MV vaccines and polysaccharide-protein conjugates.

Antibody responses and protection against influenza virus infection in different congenic strains of mice immunized intranasally with adjuvant-combined A/Beijing/262/95 (H1N1) virus hemagglutinin or neuraminidase

Antibody (Ab) responses and protection against influenza virus infection in mice immunized intranasally with hemagglutinin (HA) or neuraminidase (NA) purified from the A/Beijing/262/95 (A/Beijing) (H1N1) virus were compared among B10 congenic mouse strains. Mice were immunized intranasally with 0.1, 0.3 or 1microg of HA or NA together with the cholera toxin adjuvant, and then boosted intranasally with 0.3 microg of the adjuvant-combined HA or NA 4 weeks later. Two weeks after the second immunization, the mice were challenged by an infection of the upper respiratory tract with the homologous virus. After 3 days, nasal wash and serum specimens were collected for virus and Ab titration. The HA immunization induced HA-specific IgG Ab responses against A/Beijing HA, which depended on the H-2 haplotype of the strain: The B10.A (H-2(a)), B10.D2 (H-2(d)), B10.BR (H-2(k)) and B10 (H-2(b)) strains were the highest, high, intermediate and low responders, respectively. The nasal IgA responses were induced in the B10.A, B10.D2 and B10.BR strains, but not in the B10 strain. In parallel with Ab responses, the B10.A, B10.BR and B10.D2 strains were conferred significant protection at any dose of primary immunization, but the B10 strain was provided protection only at 1microg of HA. On the other hand, the NA immunization induced NA-specific Ab responses, which depended on the the H-2 haplotype of the strain: the B10.A, B10.D2, B10 and B10.BR strains were the highest, high, intermediate and low responders, respectively. In parallel with Ab responses, all the strains were conferred significant protection at any dose of primary immunization. These results indicate that the MHC-restricted responsiveness of mice to HA is different from that to NA, suggesting that the use of high-HA dose or NA as a component of the nasal influenza A (H1N1 subtype) virus vaccine improves the protective efficacy against influenza among low responder populations.

Salivary gland delivery of pDNA-cationic lipoplexes elicits systemic immune responses

OBJECTIVE

To test the ability of two cationic lipoplexes, Vaxfectin and GAP-DLRIE/DOPE, to facilitate transfection and elicit immune responses from plasmid DNAs (pDNAs) after retrograde instillation into salivary glands.

METHODS

Two pDNA expression vectors encoding either the influenza NP protein or human growth hormone (hGH) were complexed with the cationic lipid transfection reagents, GAP-DLRIE/DOPE or Vaxfectin, and delivered to the submandibular glands of rats. Samples from rats receiving the influenza NP protein pDNA and cationic lipoplexes were analyzed for anti-influenza NP-specific IgG1, IgG2a, and IgG2b in serum, and IgA in saliva, by an enzyme- linked immunosorbent assay (ELISA). Cytotoxic T-cell lymphocyte (CTL) assays were also performed. Transgene protein expression (hGH) was determined from extracts of submandibular glands of rats receiving hGH lipoplexes.

RESULTS

Serum antibodies (IgG) against the NP protein developed and were highest in all rats vaccinated with GAP-DLRIE/DOPE or Vaxfectin. The major serum IgG subclass stimulated by this route of immunization was IgG2b, followed by IgG2a. CTL assay results showed statistically significantly higher percentage killing in the Vaxfectin group than controls (P < 0.05). No rats developed IgA antibodies to NP protein in saliva. Animals receiving plasmid encoding hGH and either lipoplex expressed significantly higher amounts of hGH compared with those receiving the hGH plasmid and water. Although hGH expression was higher in the animals receiving pDNA/Vaxfectin (approximately 30-fold > pDNA/water), the difference with those receiving pDNA/GAP-DLRIE/DOPE (approximately 10-fold > pDNA/water) was not significant.

CONCLUSIONS

Retrograde instillation of pDNA complexed with Vaxfectin into the salivary glands can stimulate cytotoxic and humoral responses to the influenza NP protein antigen. Optimization of the conditions required to stimulate humoral and secretory antibody formation may facilitate use of this tissue for specific clinical applications of pDNA immunization.

Enhanced immune responses after DNA vaccination with combined envelope genes from different HIV-1 subtypes

In a multisubtype approach to HIV-1 vaccination, mice were immunized with HIV-1 envelope gp160 genes from subtypes A, B, and C. Subsequently the mice were challenged with syngeneic primary splenocytes infected with a HIV-1/MuLV pseudovirus carrying a subtype B genome. HIV-specific immune responses and protection were strongest in the group of animals immunized with a combination of subtype A, B, and C specific gp160 genes as compared to subtype B only. Immunization with the combination of the cross-reactive subtypes A and C envelope genes induced HIV-specific immune responses but did not result in significant protection to challenge with subtype B infected cells. From this we conclude that immunization with the envelope genes from several HIV-1 subtypes may indeed enhance immune responses. This study shows that by using a mix of subtype envelope genes, an enhanced protective immunity can be obtained experimentally, potentially also in humans.

Stable and long-lasting immune response in horses after DNA vaccination against equine arteritis virus

Equine arteritis virus (EAV) is the causative agent of the equine viral arteritis. It is a small RNA virus with a linear, non-segmented plus RNA genome. EAV is a member of the Arteriviridae family that includes porcine reproductive and respiratory syndrome virus (PRSSV), simian haemorrhagic fever virus (SHFV) and lactate dehydrogenase virus (LDV). The viral transmission is via respiratory and reproductive routes. Clinical signs in horses vary, and severe infection can lead to abortions in pregnant mares or neonatal foal death. The aim of this study was to investigate the development of the immune response in horses after immunization with a DNA vaccine harbouring and expressing EAV Open Reading Frames (ORF) 2, 5, and 7, in combination with equine interleukin 2 (eqIL2). Three boosters followed the basic immunization in two-week intervals. Each immunization was a combination of gene gun and intramuscular injection. All horses developed a high titer of neutralizing antibodies after basic immunization within 2 weeks. Remarkably, this immune response was found to be independent of the age of animals. The youngest horse was six-years old, and the oldest twenty-two years old. A remarkable difference in the immune response between the young and old were not observed. The duration of immunity was investigated during a period of one year. After 12 months, neutralizing antibodies were still detectable in all the vaccinated horses.

HER2 peptide-specific CD8(+) T cells are proportionally detectable long after multiple DNA vaccinations

We prepared a plasmid encoding 147 amino acid residues from the N terminus of c-erbB-2/HER2/neu (HER2), which included both a cytotoxic T lymphocyte (CTL) epitope (HER2p63) and a helper epitope (HER2p1), using the mammalian expression vector pCAGGS-New (pCAGGS147HER2). In a parallel analysis with a Tetramer assay and CTL assay, good specificity and sensitivity of a quantitative enzyme-linked immunospot (ELISPOT) assay to detect functional HER2p63-specific CD8(+) T cells were demonstrated after intramuscular immunization of pCAGGS147HER2. In an ELISPOT assay for HER2p63, spots of IFN gamma-producing cells were first detected 10 days after the first immunization, and additional immunizations increased the number of spots. HER2p63-specific CD8(+) T cells were detected over a period of more than 10 months after the last immunization. In hosts receiving more than three immunizations, surprisingly high numbers of specific CD8(+) T cells were persistently detectable. HER2 protein-specific antibodies of IgG class with dominance of IgG2a remain detectable 6 months after single or multiple immunizations. The antibodies however, were not reactive with cell surface HER2 antigens. Total suppression of tumor growth was observed when syngeneic HER2(+) tumor cells (2 x 10(6)) were injected subcutaneously 14 days after a single immunization with pCAGGS147HER2. Furthermore, the number of pulmonary metastases decreased significantly when DNA vaccination was initiated on the day of, or 3 days after, intravenous injection (1 x 10(6) cells).