A Rapid and Improved Method to Generate Recombinant Dengue Virus Vaccine Candidates

Dengue is one of the most important mosquito-borne infections accounting for severe morbidity and mortality worldwide. Recently, the tetravalent chimeric live attenuated Dengue vaccine Dengvaxia^® was approved for use in several dengue endemic countries. In general, live attenuated vaccines (LAV) are very efficacious and offer long-lasting immunity against virus-induced disease. Rationally designed LAVs can be generated through reverse genetics technology, a method of generating infectious recombinant viruses from full length cDNA contained in bacterial plasmids. In vitro transcribed (IVT) viral RNA from these infectious clones is transfected into susceptible cells to generate recombinant virus. However, the generation of full-length dengue virus cDNA clones can be difficult due to the genetic instability of viral sequences in bacterial plasmids. To circumvent the need for a single plasmid containing a full length cDNA, in vitro ligation of two or three cDNA fragments contained in separate plasmids can be used to generate a full-length dengue viral cDNA template. However, in vitro ligation of multiple fragments often yields low quality template for IVT reactions, resulting in inconsistent low yield RNA. These technical difficulties make recombinant virus recovery less efficient. In this study, we describe a simple, rapid and efficient method of using LONG-PCR to recover recombinant chimeric Yellow fever dengue (CYD) viruses as potential dengue vaccine candidates. Using this method, we were able to efficiently generate several viable recombinant viruses without introducing any artificial mutations into the viral genomes. We believe that the techniques reported here will enable rapid and efficient recovery of recombinant flaviviruses for evaluation as vaccine candidates and, be applicable to the recovery of other RNA viruses.

Development of nucleic acid vaccines: use of self-amplifying RNA in lipid nanoparticles

Self-amplifying RNA or RNA replicon is a form of nucleic acid-based vaccine derived from either positive-strand or negative-strand RNA viruses. The gene sequences encoding structural proteins in these RNA viruses are replaced by mRNA encoding antigens of interest as well as by RNA polymerase for replication and transcription. This kind of vaccine has been successfully assayed with many different antigens as vaccines candidates, and has been shown to be potent in several animal species, including mice, nonhuman primates, and humans. A key challenge to realizing the broad potential of self-amplifying vaccines is the need for safe and effective delivery methods. Ideally, an RNA nanocarrier should provide protection from blood nucleases and extended blood circulation, which ultimately would increase the possibility of reaching the target tissue. The delivery system must then be internalized by the target cell and, upon receptor-mediated endocytosis, must be able to escape from the endosomal compartment into the cell cytoplasm, where the RNA machinery is located, while avoiding degradation by lysosomal enzymes. Further, delivery systems for systemic administration ought to be well tolerated upon administration. They should be safe, enabling the multiadministration treatment modalities required for improved clinical outcomes and, from a developmental point of view, production of large batches with reproducible specifications is also desirable. In this review, the concept of self-amplifying RNA vaccines and the most promising lipid-based delivery systems are discussed.

[Elaboration and evaluation of a candidate to the DNA vaccine using synthetic genes derived from the peptídeo SBm7462 against the carrapato Rhiphicephalus (Boophilus) microplus]

Rhiphicephalus (Boophilus) microplus is one of the most important arthropods in veterinary medicine due economic losses and health problems caused in cattle production. The vaccination represents optimum method evaluated with effective cost to prevent economic losses and to increase the duration and quality of life of the production animals. A synthetic peptide, SBm 7462, derived from Bm86, has been shown great results in control of ticks. The construction and synthesis of one nucleotide sequence based on this peptide might be useful for design a DNA vaccine that has many advances than peptide vaccine. A gene, called seq1, was constructed with a three repetition of nucleotide sequence of SBm 7462. It was cloned into a pCIneo vector expression in mammals and injected in BALB/c mouse. When mice were inoculated with the expression cassette they did not response in ELISA. They elevated antibody titles only when vaccinated with the synthetic peptide SBm7462®. And, the best titles of immunoglobulins were seen when the SBm7462® was administered subcutaneously.

Upstream processing of plasmid DNA for vaccine and gene therapy applications

The demand for plasmid DNA has increased vastly in response to rapid advances in its use in gene therapy and vaccines. These therapies are based on the same principle, i.e. the introduction of nucleic acids in human/non-human cells receptor to restore, cancel, enhance or introduce a biochemical function. Naked plasmid DNA as a vector has attracted a lot of interest since it offers several advantages over a viral vector, especially weak immunogenicity, better safety and easy to manufacture, but low transfection efficacy. Non-viral gene therapy may require considerable amounts (milligram scale) of pharmaceutical-grade pDNA per patient since the efficacy and duration of gene expression is presently relatively low. Reliance on fermentation, which generates large lysate volumes, for producing the needed quantities of pDNA is becoming more widespread. Through optimization of the biological system, growth environment and the growth mode, improvements can be achieved in biomass productivity, plasmid yield, plasmid quality and production costs. The information on large-scale plasmid production is scarce and usually not available to the scientific community. This review summarizes recent patents and patent applications relating to plasmid upstream processing manufacturing, ranging from plasmid design to growth strategies to produce plasmid-bearing E. coli.

Allergenicity and antigenicity of wild-type and mutant, monomeric, and dimeric carrot major allergen Dau c 1: destruction of conformation, not oligomerization, is the roadmap to save allergen vaccines

BACKGROUND

Carrot allergy is caused by primary sensitization to birch pollen. Continuous carrot exposure results in additional Dau c 1-specific allergic responses. Thus, immunotherapy with birch pollen may not improve the food allergy.

OBJECTIVE

Evaluation of mutation and oligomerization of the major carrot allergen, Dau c 1, in regard to alteration of antibody binding capacities, structure, and the ability to induce blocking IgG antibodies.

METHODS

Measurement of IgE reactivities to monomers, dimers of wild-type and mutant Dau c 1.0104 and Dau c 1.0201, and Dau c 1.0104 trimer, their ability to induce blocking antibodies in mice, and their allergenic potency by histamine release.

RESULTS

The reactivity of human IgE to the mutant dimer was reduced on average by 81%. Sera of immunized Balb/c mice showed specific IgG similar to the human IgE antibody response; Dau c 1.01 was more antigenic than Dau c 1.02. Both wild-type and mutant Dau c 1 variants induced cross-reacting IgG, which blocked binding of human IgE. The mutants were more antigenic than the wild-type forms, and the dimers induced higher IgG responses in mice than the monomers. The results of the histamine release experiments corroborated the findings of the antibody binding studies.

CONCLUSION

Destruction of native conformation rather than oligomerization is the appropriate strategy to reduce the allergenicity of Bet v 1-homologous food allergens.

CLINICAL IMPLICATIONS

The dimer composed of mutants of Dau c 1.0104 and Dau c 1.0201 is a promising candidate vaccine for treatment of carrot allergy because of its high immunogenicity and drastically reduced allergenicity.

Adjuvant properties of listeriolysin O protein in a DNA vaccination strategy

The use of infectious agents as vaccine adjuvants has shown utility in both prophylactic and therapeutic vaccinations. Listeria monocytogenes has been used extensively as a vaccine vehicle due to its ability to initiate both CD4(+) and CD8(+) immune responses. Previous work from this laboratory has used transgenic Listeria to deliver vaccine constructs. A chimeric protein composed of tumor antigen and a non-hemolytic variant of the Listeria protein, listeriolysin O (LLO), has demonstrated effective tumor protection beyond that of antigen alone expressed in the same system. To address the question of how fusion with LLO improves vaccine efficacy, we constructed a number of DNA plasmid vaccines to isolate this effect in the absence of other endogenous Listeria effects. Here we have analyzed the ability of these vaccines to induce the regression of previously established tumors. A vaccine strategy using DNA vaccines bearing the tumor antigen either alone or in combination with LLO in addition to plasmids encoding MIP-1alpha and GM-CSF was examined. Further, LLO was used either as a chimera or in a bicistronic construct to address the importance of fusion between these elements. Notably, the strategies employing both chimeric and bicistronic vaccines were effective in reducing tumor burden suggesting that LLO can act as an adjuvant that does not require fusion with the tumor antigen to mediate its effect.

Prime-Boost with Alternating DNA Vaccines Designed to Engage Different Antigen Presentation Pathways Generates High Frequencies of Peptide-Specific CD8+ T Cells

The route for presentation of Ag to CD8+ or CD4+ T cells following DNA vaccination is critical for determining outcome, but the pathways involved are unclear. In this study, we compare two different DNA vaccine designs aimed to elicit CD8+ T cell responses against a specific peptide-epitope either by direct- or cross-presentation. Each carries sequences from tetanus toxin (TT) to provide essential CD4+ T cell help. In the first already proven design, the peptide-epitope is fused to the N-terminal domain of fragment C from TT. This appears to act mainly by cross-presentation. In the second design, the peptide-epitope is encoded by a minigene, with induction of Th responses mediated by coexpression of a hybrid invariant chain molecule, incorporating a single determinant from TT (p30) in exchange for class II-associated invariant chain peptide. This design appears to act mainly via direct presentation from transfected APCs. Both vaccines mediated Th-dependent priming of CD8+ T cells in mice, but the kinetics and level of the responses differed markedly, consistent with engagement of distinct pathways of Ag presentation. Importantly, the vaccines could be combined in an alternating prime-boost regime, in either order, generating substantially expanded memory CD8+ T cells, with potent effector function. Taken together, these results demonstrate that vaccination protocols involving different modes of Ag presentation at prime and boost can significantly improve the effectiveness of immunization.

DNA vaccines: progress and challenges

In the years following the publication of the initial in vivo demonstration of the ability of plasmid DNA to generate protective immune responses, DNA vaccines have entered into a variety of human clinical trials for vaccines against various infectious diseases and for therapies against cancer, and are in development for therapies against autoimmune diseases and allergy. They also have become a widely used laboratory tool for a variety of applications ranging from proteomics to understanding Ag presentation and cross-priming. Despite their rapid and widespread development and the commonplace usage of the term "DNA vaccines," however, the disappointing potency of the DNA vaccines in humans underscores the challenges encountered in the efforts to translate efficacy in preclinical models into clinical realities. This review will provide a brief background of DNA vaccines including the insights gained about the varied immunological mechanisms that play a role in their ability to generate immune responses.

Developing vaccines to counter bioterrorist threats

Large and innovative research programs are underway to define the immune parameters for vaccines against a wide array of pathogens considered to represent a potential bioterrorist threat. However, the development and utilization of such vaccines presents a number of predicaments that have not previously been addressed by the field of vaccinology.

Fusion of Two Malaria Vaccine Candidate Antigens Enhances Product Yield, Immunogenicity, and Antibody-Mediated Inhibition of Parasite Growth In Vitro

A Plasmodium falciparum chimeric protein 2.9 (PfCP-2.9) was constructed consisting of the C-terminal regions of two leading malaria vaccine candidates, domain III of apical membrane ag-1 (AMA-1) and 19-kDa C-terminal fragment of the merozoite surface protein 1 (MSP1). The PfCP-2.9 was produced by Pichia pastoris in secreted form with a yield of 2600 mg/L and approximately 1 g/L of final product was obtained from a three-step purification process. Analysis of conformational properties of the chimeric protein showed that all six conformational mAbs interacted with the recombinant protein were reduction-sensitive, indicating that fusion of the two cysteine-rich proteins retains critical conformational epitopes. PfCP-2.9 was found to be highly immunogenic in rabbits as well as in rhesus monkeys (Macaca mulatta). The chimeric protein induced both anti-MSP1-19 and anti-AMA-1(III) Abs at levels 11- and 18-fold higher, respectively, than individual components did. Anti-PfCP-2.9 sera from both rabbits and rhesus monkeys almost completely inhibited in vitro growth of the P. falciparum FCC1/HN and 3D7 lines when tested at a 6.7-fold dilution. It was shown that the inhibition is dependent on the presence of Abs to the chimeric protein and their disulfide bond-dependent conformations. Moreover, the activity was mediated by a combination of growth-inhibitory Abs generated by the individual MSP1-19 and AMA-1(III) of PfCP-2.9. The combination of the extremely high yield of the protein and enhancement of its immune response provides a basis to develop an effective and affordable malaria vaccine.

Construction and immunogenic characterization of a fusion anti-caries DNA vaccine against PAc and glucosyltransferase I of Streptococcus mutans

Glucosyltransferases (GTFs) and A cell-surface protein (PAc) are two important virulence factors of the cariogenic organism Streptococcus mutans. They may mediate sucrose-independent or sucrose-dependent attachment of Streptococcus mutans to tooth surfaces, respectively. Thus, inhibiting both virulence factors is predicted to provide better protection against caries than inhibiting a single factor. To develop a highly efficient vaccine against caries, we constructed a fusion DNA vaccine, pGLUA-P, by cloning the GLU region of GTF into a DNA vaccine, pCIA-P, which encodes two highly conservative regions of PAc. In this report, we provide evidence that fewer caries lesions were observed in rats following subcutaneous injection of pGLUA-P, compared with pCIA-P, near the submandibular gland. Our findings suggest that a multigenic DNA vaccine may be more caries-preventive than a single-gene DNA vaccine.

Generation of Toxoplasma gondii GRA1 protein and DNA vaccine loaded chitosan particles: preparation, characterization, and preliminary in vivo studies

Chitosan microparticles as carriers for GRA-1 protein vaccine were prepared and characterized with respect to loading efficiency and GRA-1 stability after short-term storage. Chitosan nanoparticles as carriers for GRA-1 pDNA vaccine were prepared and characterized with respect to size, zeta potential, and protection of the pDNA vaccine against degradation by DNase I. Both protein and pDNA vaccine preparations were tested with regard to their potential to elicit GRA-1-specific immune response after intragastric administration using different prime/boost regimen. The immune response was measured by determination of IgG2a and IgG1 antibody titers. It was shown that priming with GRA1 protein vaccine loaded chitosan particles and boosting with GRA1 pDNA vaccine resulted in high anti-GRA1 antibodies, characterized by a mixed IgG2a/IgG1 ratio. These results showed that oral delivery of vaccines using chitosan as a carrier material appears to be beneficial for inducing an immune response against Toxoplasma gondii. The type of immune response, however, will largely depend on the prime/boost regimen and the type of vaccine used.

Development of a DNA vaccine designed to induce cytotoxic T lymphocyte responses to multiple conserved epitopes in HIV-1

Epitope-based vaccines designed to induce CTL responses specific for HIV-1 are being developed as a means for addressing vaccine potency and viral heterogeneity. We identified a set of 21 HLA-A2, HLA-A3, and HLA-B7 restricted supertype epitopes from conserved regions of HIV-1 to develop such a vaccine. Based on peptide-binding studies and phenotypic frequencies of HLA-A2, HLA-A3, and HLA-B7 allelic variants, these epitopes are predicted to be immunogenic in greater than 85% of individuals. Immunological recognition of all but one of the vaccine candidate epitopes was demonstrated by IFN-gamma ELISPOT assays in PBMC from HIV-1-infected subjects. The HLA supertypes of the subjects was a very strong predictor of epitope-specific responses, but some subjects responded to epitopes outside of the predicted HLA type. A DNA plasmid vaccine, EP HIV-1090, was designed to express the 21 CTL epitopes as a single Ag and tested for immunogenicity using HLA transgenic mice. Immunization of HLA transgenic mice with this vaccine was sufficient to induce CTL responses to multiple HIV-1 epitopes, comparable in magnitude to those induced by immunization with peptides. The CTL induced by the vaccine recognized target cells pulsed with peptide or cells transfected with HIV-1 env or gag genes. There was no indication of immunodominance, as the vaccine induced CTL responses specific for multiple epitopes in individual mice. These data indicate that the EP HIV-1090 DNA vaccine may be suitable for inducing relevant HIV-1-specific CTL responses in humans.

Immunogenicity of DNA vaccines that direct the coincident expression of the 120 kDa glycoprotein of human immunodeficiency virus and the catalytic domain of cholera toxin

Passive antibody studies unequivocally demonstrate that sterilizing immunity against lentiviruses is obtainable through humoral mechanisms. In this regard, DNA vaccines represent an inexpensive alternative to subunit vaccine for mass vaccination programs designed to induce such responses to human immunodeficiency virus type I (HIV-1). At present, however, this vaccine modality has proven relatively ineffective at inducing humoral responses. In this report, we describe the immunogenicity of DNA vaccines that direct the coincident expression of the cholera toxin catalytic domain (CTA1) with that of the human immunodeficiency virus type I gp120 through genes either encoded in individual plasmids or in a single dicistronic plasmid. In BALB/cJ mice, coincident expression of CTA1 in either a separate plasmid or in the dicistronic plasmid in the DNA vaccines induced serum IgG responses to gp120 that were at least 1000-fold greater, and remained elevated longer than, the analogous responses in mice vaccinated with a DNA vaccine that expressed gp120 alone. In addition, mice vaccinated with CTA1 and gp120 produced significantly more gp120-specific IFN-gamma ELISPOTs than mice vaccinated with the gp120 DNA vaccine. Combined, these data show that the adjuvant properties of cholera toxin can be harnessed in DNA vaccine modalities.

Critical components of a DNA fusion vaccine able to induce protective cytotoxic T cells against a single epitope of a tumor antigen

DNA vaccines can activate immunity against tumor Ags expressed as MHC class I-associated peptides. However, priming of CD8(+) CTL against weak tumor Ags may require adjuvant molecules. We have used a pathogen-derived sequence from tetanus toxin (fragment C (FrC)) fused to tumor Ag sequences to promote Ab and CD4(+) T cell responses. For induction of CD8(+) T cell responses, the FrC sequence has been engineered to remove potentially competitive MHC class I-binding epitopes and to improve presentation of tumor epitopes. The colon carcinoma CT26 expresses an endogenous retroviral gene product, gp70, containing a known H2-L(d)-restricted epitope (AH1). A DNA vaccine encoding gp70 alone was a poor inducer of CTL, and performance was not significantly improved by fusion of full-length FrC. However, use of a minimized domain of FrC, with the AH1 sequence fused to the 3' position, led to rapid induction of high levels of CTL. IFN-gamma-producing epitope-specific CTL were detectable ex vivo and these killed CT26 targets in vitro. The single epitope vaccine was more effective than GM-CSF-transfected CT26 tumor cells in inducing an AH1-specific CTL response and equally effective in providing protection against tumor challenge. Levels of AH1-specific CTL in vivo were increased following injection of tumor cells, and CTL expanded in vitro were able to kill CT26 cells in tumor bearers. Pre-existing immunity to tetanus toxoid had no effect on the induction of AH1-specific CTL. These data demonstrate the power of epitope-specific CTL against tumor cells and illustrate a strategy for priming immunity via a dual component DNA vaccine.

Inhibition of adjuvant arthritis by a DNA vaccine encoding human heat shock protein 60

Adjuvant arthritis (AA) is an autoimmune disease inducible in rats involving T cell reactivity to the mycobacterial 65-kDa heat shock protein (HSP65). HSP65-specific T cells cross-reactive with the mammalian 60-kDa heat shock protein (HSP60) are thought to participate in the modulation of AA. In this work we studied the effects on AA of DNA vaccination using constructs coding for HSP65 (pHSP65) or human HSP60 (pHSP60). We found that both constructs could inhibit AA, but that pHSP60 was more effective than pHSP65. The immune effects associated with specific DNA-induced suppression of AA were complex and included enhanced T cell proliferation to a variety of disease-associated Ags. Effective vaccination with HSP60 or HSP65 DNA led paradoxically to up-regulation of IFN-gamma secretion to HSP60 and, concomitantly, to down-regulation of IFN-gamma secretion to the P180-188 epitope of HSP65. There were also variable changes in the profiles of IL-10 secretion to different Ags. However, vaccination with pHSP60 or pHSP65 enhanced the production of TGFbeta1 to both HSP60 and HSP65 epitopes. Our results support a regulatory role for HSP60 autoreactivity in AA and demonstrate that this control mechanism can be activated by DNA vaccination with both HSP60 or HSP65.

Influenza vaccines: new developments

Current inactivated influenza vaccines are being produced with three influenza virus strains that are recommended annually by the World Health Organization on the basis of information obtained from global influenza surveillance. The use of these vaccines, for which the antigens are produced in embryonated chicken eggs, can result in a significant reduction of influenza-related morbidity and mortality. Nevertheless, there is still a demand for vaccines with a higher efficacy that can be produced more rapidly and more flexibly in response to an epidemic or a pandemic. New developments in the field of influenza vaccine preparation include novel vaccine production technologies, reverse genetics technology for the generation of vaccine strains and novel adjuvants for the improvement of vaccine immunogenicity.

DNA fusion vaccine designed to induce cytotoxic T cell responses against defined peptide motifs: implications for cancer vaccines

DNA vaccination offers a strategy to induce immune attack on cancer cells, but tumor Ags are often weak. Inclusion of a "foreign" protein increases immunogenicity, and we found previously that fusion of the fragment C (FrC) of tetanus toxin to the tumor Ag sequence promotes Ab and CD4(+) responses against B cell tumors. For CTL responses, use of the full two-domain FrC may be less helpful, because known immunogenic MHC class I-binding peptides in the second domain could compete with attached tumor-derived epitopes. Therefore, we removed the second domain, retaining the N-terminal domain, which contains a "universal" helper epitope. We investigated the ability to induce CTL responses of candidate peptides placed at the C terminus of this domain. As test peptides, we repositioned the two known CTL motifs from the second domain to this site. Strong CTL responses to each peptide were induced by the engineered construct, as compared with the native FrC construct. Induced CTLs were able to specifically kill tumor cells transfected with FrC as a surrogate tumor Ag both in vitro and in vivo. Further reduction of the domain to a short helper epitope generated only weak CTL responses against fused peptides, and synthetic peptides mixed with the plasmid containing the first domain were ineffective. The single FrC domain-peptide vaccine design also was able to induce high levels of CTLs against a known epitope from carcinoembryonic Ag. Response to peptide was suppressed if two FrC domains were present, consistent with immunodominance. These principles and designs may have relevance for cancer vaccines delivered via DNA.

Immunostimulatory DNA-based vaccines elicit multifaceted immune responses against HIV at systemic and mucosal sites

Immunostimulatory DNA sequences (ISS, also known as CpG motifs) are pathogen-associated molecular patterns that are potent stimulators of innate immunity. We tested the ability of ISS to act as an immunostimulatory pathogen-associated molecular pattern in a model HIV vaccine using gp120 envelope protein as the Ag. Mice immunized with gp120 and ISS, or a gp120:ISS conjugate, developed gp120-specific immune responses which included: 1) Ab production; 2) a Th1-biased cytokine response; 3) the secretion of beta-chemokines, which are known to inhibit the use of the CCR5 coreceptor by HIV; 4) CTL activity; 5) mucosal immune responses; and 6) CD8 T cell responses that were independent of CD4 T cell help. Based on these results, ISS-based immunization holds promise for the development of an effective preventive and therapeutic HIV vaccine.

Intramyocardial injection of DNA encoding vascular endothelial growth factor in a myocardial infarction model

In a previous study, we observed that one injection of 500 microg of DNA for the plasmid encoding for vascular endothelial growth factor (ph VEGF(165)) into one site in a rat myocardial infarction model resulted in neovascularization confined to angiomatous structures that did not contribute to regional myocardial blood flow. The purpose of the present study was to determine whether a lower dose (125 microg DNA), which is the same as that being used in some clinical trials, injected into four separate sites could enhance collateral flow and vascularity to the ischemic bed without inducing angiomas. Rats received injections of 125 microg DNA of the plasmid encoding phVEGF(165) or control DNA at four separate sites within the anterior free wall of the left ventricle (LV) supplied by the left coronary artery. The left coronary artery was ligated and hearts analyzed at 4 weeks. In vitro studies confirmed that the phVEGF(165) used was capable of producing VEGF polypeptide in mammalian cells. The infarct size (percentage of endocardial circumference that infarcted) was similar in controls (42+/-6%) and treated hearts (39+/-7%); the LV cavity area did not differ between groups. The number of vascular structures per high-power field within the infarct scar was 10.50+/-0.68 in controls and 10.00+/-0.85 in phVEGF(165)-treated rats. Relative regional myocardial blood flow determined by radioactive microspheres and expressed as a ratio of radioactive counts within the scar divided by radioactive counts in the noninfarcted ventricular septum was similar in control (0.74+/-0.25) and treated hearts (0.88+/-0.30) (p=not significant). No angiomatous structures were observed. Injections of 125 microg of DNA of phVEGF(165) into myocardium to become ischemic had no effect on infarct size or LV cavity size. Unlike higher doses of 500 microg of DNA, it did not cause gross angiomatous structures; however, it failed to improve neovascularization or regional myocardial blood flow in this rodent model of acute myocardial infarction.

Downstream processing of plasmid DNA for gene therapy and DNA vaccine applications

Interest in producing large quantities of supercoiled plasmid DNA has recently increased as a result of the rapid evolution of gene therapy and DNA vaccines. Owing to the commercial interest in these approaches, the development of production and purification strategies for gene-therapy vectors has been performed in pharmaceutical companies within a confidential environment. Consequently, the information on large-scale plasmid purification is scarce and usually not available to the scientific community. This article reviews downstream operations for the large-scale purification of plasmid DNA, describing their principles and the strategy used to attain a final product that meets specifications.

Involvement of an ATP-dependent peptide chaperone in cross-presentation after DNA immunization

Immunization with plasmid DNA holds promise as a vaccination strategy perhaps useful in situations that currently lack vaccines, since the major means of immune induction may differ from more conventional approach. In the present study, we demonstrate that exposure of macrophages to plasmid DNA encoding viral proteins or OVA generates Ag-specific material that, when presented in vitro by dendritic cells to naive T cells, induces primary CTL response or elicits IL-2 production from an OVA peptide-specific T-T hybridoma. The immunogenic material released was proteinaceous in nature, free of apoptotic bodies, and had an apparent m.w. much larger than a 9-11-aa CTL-recognizable peptide. The macrophage-released factor(s) specifically required a hydrolyzable ATP substrate and was inhibited by procedures that removed or hydrolyzed ATP; in addition, anti-heat-shock protein 70 antiserum abrogated the activity to a large extent. These results indicate the possible involvement of a heat-shock protein 70-linked peptide chaperone in a cross-priming method of immune induction by DNA vaccination. Such a cross-priming process may represent a principal mechanism by which plasmid DNA delivered to cells such as myocytes effectively shuttle Ag to DC or other APC to achieve CTL induction in vivo.

Effective construction of DNA vaccines against variable influenza genes by homologous recombination

We demonstrate the potential of cloning by homologous recombination as a rapid method to construct DNA molecules encoding newly developing hemagglutinins (HA) of influenza A virus. The variable parts of the HA genes were cloned into a basic construct containing the HA gene from an H3N2 strain. The recombinant DNAs thus created encode different variable domains with neutralising epitopes from four recently circulating influenza A H3 strains. The technology allows rapid production of DNA constructs for vaccines that can induce antibody and, particularly, cellular immune responses. These new constructs were also capable of conferring protection to challenge in mice. The technology may hence be a valuable tool for rapid adaptation of influenza vaccines to changes in the circulating influenza strains.

A DNA immunization model study with constructs expressing the tick-borne encephalitis virus envelope protein E in different physical forms

We have conducted a DNA immunization study to evaluate how the immune response is influenced by the physical structure and secretion of the expressed Ag. For this purpose, we used a series of plasmid constructs encoding different forms of the envelope glycoprotein E of the flavivirus tick-borne encephalitis virus. These included a secreted recombinant subviral particle, a secreted carboxyl-terminally truncated soluble homodimer, a nonsecreted full-length form, and an inefficiently secreted truncated form. Mice were immunized using both i.m. injection and Gene Gun-mediated application of plasmids. The functional immune response was evaluated by determining specific neutralizing and hemagglutination-inhibiting Ab activities and by challenging the mice with a lethal dose of the virus. As a measure for the induction of a Th1 and/or Th2 response, we determined specific IgG subclasses and examined IFN-gamma, Il-4, and Il-5 induction. The plasmid construct encoding a secreted subviral particle, which carries multiple copies of the protective Ag on its surface, was superior to the other constructs in terms of extent and functionality of the Ab response as well as protection against virus challenge. As expected, the type of Th response was largely dependent on the mode of application (i.m. vs Gene Gun), but our data show that it was also strongly influenced by the properties of the Ag. Most significantly, the plasmid encoding the particulate form was able to partially overcome the Th2 bias imposed by the Gene Gun, resulting in a balanced Th1/Th2 response.

DNA immunization with HIV-1 tat mutated in the trans activation domain induces humoral and cellular immune responses against wild-type Tat

Intramuscular immunization of mice with plasmids encoding two transdominant negative mutants of the HIV-1 Tat protein (Tat22 and Tat22/37) elicited a humoral response to wild-type Tat that is comparable to that induced by inoculation of wild-type tat DNA or Tat protein. The percentage of the responders and the Ab titers continued to increase after three additional DNA boosts and pretreatment with bupivacaine at the site of inoculation, without a significant difference (p > 0.05) among the three groups of mice immunized with mutant and wild-type tat genes. By utilizing synthetic peptides representing the amino acid sequence of Tat, one major B cell epitope was defined within the cysteine-rich domain of Tat. Anti-Tat IgG Abs directed against this epitope were found in mice immunized with all tat DNA constructs, whereas different Tat epitopes were detected in mice immunized with the Tat protein. Similarly, IgG2a was the predominant isotype in DNA-immunized mice, with both mutants and wild-type tat genes, as compared with protein immunization, which induced mostly IgG1 and IgG3. Sera from most immunized mice neutralized the effect of extracellular Tat in activating HIV-1 replication. A cellular response was also elicited as indicated by the proliferation of splenocytes when stimulated with wild-type Tat. These results indicate that the wild-type Tat Ag is recognized by Abs and T cells induced by DNA immunization with mutated tat genes, suggesting the possible use of these Tat transdominant mutants, lacking viral trans activation activity and capable of blocking wild-type Tat activity, in the development of an anti-HIV-1 vaccine.

New technologies for vaccines

The impact of vaccination on the health of the world's people has been considerable. With the possible exception of clean water, no other development has had such a major effect on mortality reduction and population growth. During the last 200 years vaccination has controlled nine major diseases and has led to the eradication of one, i.e. smallpox. However, in many instances, the exact mechanisms of successful vaccines are not fully understood. Almost all of the vaccines in use today are of three types: live attenuated microorganisms, inactivated whole microorganisms, or split or subunit preparations. These have different strengths and weaknesses with respect to safety and efficacy, but traditional vaccine development methodologies have not yet led to the generation of a vaccine with all the characteristics required of the ideal vaccine. Thus the development of improved vaccines that overcome the difficulties associated with many of the currently available vaccines is a major goal of biomedical sciences. In addition, there is an urgent need for new vaccines against the many infectious agents that still cause considerable morbidity and, in some cases, mortality. As has been the case in many areas of biology, the application of recombinant DNA approaches to vaccinology has opened up whole new areas of possibilities. The details of these and other technologies and their application to vaccine development are described in this review.

DNA vaccines: vector design, delivery, and antigen presentation

Inoculations with antigen-expressing plasmid DNAs (DNA vaccines) in the production of protective immune responses. Since the initial development of DNA vaccines more than 5 years ago, major strides have been made in the design of efficient vaccine vectors and in the process of vaccine delivery. However, many questions remain regarding the mechanism of cellular transfection and in the development of immune responses. This review addresses functional aspects of DNA vaccines, including vector design and delivery, as well as cellular transfection and antigen presentation.

DNA cancer vaccines: a gene gun approach

A wide variety of approaches, all using gene transfer, have been tested experimentally as alternative means to vaccinate against cancer, either prophylactically or therapeutically. These include both ex vivo and in vivo gene transfer to tumour and/or non-tumour cells, using both viral and non-viral vectors. The transferred DNA has varied widely as well, including genomic or cDNA encoding tumour-associated or oncofoetal antigens, cytokines, histocompatibility molecules, and costimulatory molecules. Several of these approaches have been applied in human clinical trials. This review summarizes those approaches, then compares and evaluates various methods using cytokine DNA in conjunction with autologous tumour cells, with particular emphasis on particle-mediated gene transfer via a gene gun. Finally, prospects and needs for further development are discussed.

Development of a multicomponent candidate vaccine for HIV-1

Nucleic acid or DNA immunization represents a novel approach to both vaccine and immune therapeutic development. DNA vaccination induces antigen-specific cellular and humoral immune responses through the delivery of non-replicating transcription units which drive the synthesis of specific foreign proteins within the inoculated host. We have previously reported on the potential use of DNA immunization as a novel vaccine strategy for HIV-1. We found that both antigen-specific cellular and humoral immune responses could be induced in vivo with various DNA vaccine constructs against different antigenic targets within HIV-1. In order to enhance the DNA vaccine's ability to elicit cell-mediated immune responses, we co-delivered plasmids encoding costimulatory molecule B7 and interleukin-12 genes with DNA vaccine for HIV-1. We observed a dramatic increase in both antigen-specific T helper cell proliferation and CTL response. Eventual development of successful vaccines for HIV-1 would likely involve targeting multiple antigenic components of the virus to direct and empower the immune system to protect the host from viral infection. We present here the utility of multicomponent DNA immunization to elicit specific humoral and cell-mediated immune responses against different antigenic targets of HIV-1 as well as the ability of this immunization strategy to achieve significant enhancements of antigen-specific cellular immune responses.