Strong expression of foreign genes following direct injection into fish muscle

Two bicistronic DNA vaccines against Vibrio anguillarum and the immune effects on flounder Paralichthys olivaceus

Chemokines are cytokines that can promote the activation and migration of immune cells, and increase the recognition of antigen by antigen-presenting cells (APC). Previous studies showed that a DNA vaccine can induce humoral and cellular immune responses of flounder after immunization. To explore the improvement of chemokines on the efficiency of OmpK vaccine, two bicistronic DNA candidate vaccines were constructed and the immune responses they induced in the flounder were investigated by reverse transcription polymerase chain reaction (RT-PCR), indirect immunofluorescent assay (IFA), H&E staining, flow cytometry (FCM), and quantificational real-time polymerase chain reaction (qRT-PCR). pBudCE4.1 plasmid as an expression vector, bicistronic DNA vaccines encoding OmpK gene and CC-motif ligand 4 gene (p-OmpK-CCL4), or Ompk gene and CC-motif ligand 19 gene (p-OmpK-CCL19) were successfully constructed. The results showed that two bicistronic DNA vaccines expressed Ompk protein of Vibrio anguillarum and CCL4/CCL19 proteins of flounder both in vitro and in vivo. After immunization, a large number of leucocytes in muscle were recruited at the injection site in treatment groups. The constructed vaccines induced significant increases in CD4-1⁺ and CD4-2⁺ T lymphocytes, and sIgM⁺ B lymphocytes in peripheral blood, spleen, and head kidney. The percentage of T lymphocytes peaked on the 14^th post-vaccination day whereas that of B lymphocytes peaked in the 6^th post-vaccination week. Moreover, the expression profiles of 10 immune-related genes increased in muscles around the injection site, spleen, and head kidney. After the challenge, p-OmpK-CCL4 and p-OmpK-CCL19 conferred a relative percentage survival (RPS) of 74.1% and 63.3%, respectively, higher than p-OmpK alone (40.8%). In conclusion, both CCL4 and CCL19 can improve the protection of p-OmpK via evoking local immune response and then humoral and cellular immunity. CCL4 and CCL19 will be potential molecular adjuvants for use in DNA vaccines.

Wnt10b Participates in Regulating Fatty Acid Synthesis in the Muscle of Zebrafish

There are 19 Wnt genes in mammals that belong to 12 subfamilies. Wnt signaling pathways participate in regulating numerous homeostatic and developmental processes in animals. However, the function of Wnt10b in fatty acid synthesis remains unclear in fish species. In the present study, we uncovered the role of the Wnt10b signaling pathway in the regulation of fatty acid synthesis in the muscle of zebrafish. The gene of Wnt10b was overexpressed in the muscle of zebrafish using pEGFP-N1-Wnt10b vector injection, which significantly decreased the expression of glycogen synthase kinase 3β (GSK-3β), but increased the expression of β-catenin, peroxisome proliferators-activated receptor γ (PPARγ), and CCAAT/enhancer binding protein α (C/EBPα). Moreover, the activity and mRNA expression of key lipogenic enzymes ATP-citrate lyase (ACL), acetyl-CoA carboxylase (ACC) and fatty acid synthetase (FAS), and the content of non-esterified fatty acids (NEFA), total cholesterol (TC), and triglyceride (TG) were also significantly decreased. Furthermore, interference of the Wnt10b gene significantly inhibited the expression of β-catenin, PPARγ, and C/EBPα, but significantly induced the expression of GSK-3β, FAS, ACC, and ACL. The content of NEFA, TC, and TG as well as the activity of FAS, ACC, and ACL significantly increased. Thus, our results showed that Wnt10b participates in regulating fatty acid synthesis via β-catenin, C/EBPα and PPARγ in the muscle of zebrafish.

Aquaculture role in global food security with nutritional value: a review

Food security is the main path to develop the socioeconomic status in any country in the world to defeat malnutrition. The present scenario in an under developed countries are still facing this problem. Hence the human nutrition deficiencies focus on the importance of animal protein in their regular diet. To overcome this problem, fisheries contribute a significant amount of animal protein to the diets of people worldwide. The aquatic animals are the highly nutritious and cheapest protein sources, which serves as a valuable supplement in diets by providing essential vitamins, proteins, micronutrients, and minerals, for the poor people. Aquaculture is playing a vital role in the developing countries in national economic development, and global food supply. Food and agricultural organization (FAO) declared that this aquaculture has the continuous potentiality to create a developmental goals for the country economy and better human welfare.

GSK-3β at the Crossroads in Regulating Protein Synthesis and Lipid Deposition in Zebrafish

In this study, the mechanism by which GSK-3β regulates protein synthesis and lipid deposition was investigated in zebrafish (Danio rerio). The vector of pEGFP-N1-GSK-3β was constructed and injected into the muscle of zebrafish. It was found that the mRNA and protein expression of tuberous sclerosis complex 2 (TSC2) was significantly increased. However, the mRNA and protein expression of mammalian target of rapamycin (mTOR), p70 ribosomal S6 kinase 1 (S6K1), and 4E-binding protein 1 (4EBP1) was significantly decreased by the pEGFP-N1-GSK-3β vector in the muscle of zebrafish. In addition, the mRNA and protein expression of β-catenin, CCAAT/enhancer binding protein α (C/EBPα), and peroxisome proliferators-activated receptor γ (PPARγ) was significantly decreased, but the mRNA expression of fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), ATP-citrate lyase (ACL), and HMG-CoA reductase (HMGCR) was significantly increased by the pEGFP-N1-GSK-3β vector. The activity of FAS, ACC, ACL, and HMGCR as well as the content of triglyceride (TG), total cholesterol (TC), and nonesterified fatty acids (NEFA) were significantly increased by the pEGFP-N1-GSK-3β vector in the muscle of zebrafish. The content of free amino acids Arg, Lys, His, Phe, Leu, Ile, Val, and Thr was significantly decreased by the pEGFP-N1-GSK-3β vector. The results indicate that GSK-3β may participate in regulating protein synthesis via TSC2/mTOR signaling and regulating lipid deposition via β-catenin in the muscle of zebrafish (Danio rerio).

DNA vaccination for finfish aquaculture

In fish, DNA vaccines have been shown to give very high protection in experimental facilities against a number of viral diseases, particularly diseases caused by rhabdoviruses. However, their efficacy in generating protection against other families of fish viral pathogens is less clear. One DNA vaccine is currently in use commercially in fish farms in Canada and the commercialisation of another was authorised in Europe in 2017. The mechanism of action of DNA vaccines, including the role of the innate immune responses induced shortly after DNA vaccination in the activation of the adaptive immunity providing longer term specific protection, is still not fully understood. In Europe the procedure for the commercialisation of a veterinary DNA vaccine requires the resolution of certain concerns particularly about safety for the host vaccinated fish, the consumer and the environment. Relating to consumer acceptance and particularly environmental safety, a key question is whether a DNA vaccinated fish is considered a Genetically Modified Organism (GMO). In the present opinion paper these key aspects relating to the mechanisms of action, and to the development and the use of DNA vaccines in farmed fish are reviewed and discussed.

Generation and functional evaluation of a DNA vaccine co-expressing Cyprinid herpesvirus-3 envelope protein and carp interleukin-1 beta

Cyprinid herpesvirus 3 (CyHV-3) infection in carp causes a fatal and highly contagious disease that results in huge economic losses in common and koi carp aquaculture worldwide. Thus the development of an effective vaccine to protect carp stocks against the CyHV3 virus is imperative. In this study, we immunized common carps with a DNA vaccine consisting of a plasmid that co-expresses the CyHV-3 envelope protein ORF25 and the carp IL-1β gene in order to evaluate the adjuvant potential of IL-1β. Our result shows that antibodies specific to ORF25 can be detected as early as one week after intramuscular injection of the DNA vaccine at low dosage. Moreover, the co-expression of IL-1β can enhance the potency of the vaccine, as demonstrated by a higher antibody level after the third immunizations. Importantly, the DNA vaccine reduced mortality in carps when they were immunized prior to a CyHV-3 challenge, as compared to negative control groups. However, despite being able to induce higher neutralizing antibody titres, the co-expression of IL-1β in the DNA vaccine did not significantly improve the overall survival of immunized fish following virus challenge. Furthermore, the DNA vaccine can protect carps from tissue damage and histopathological alteration caused by viral infection. These strongly suggests that the vaccine can efficiently elicit protective immunity against CyHV-3 infection. In conclusion, the DNA vaccine formulated with the pIRES-ORF25-IL-1β DNA construct can protect carp against CyHV-3 infection and has potential applicability in the aquaculture industry.

In Vivo Transfection of Naked DNA into Xenopus Tadpole Tail Muscle

In vivo gene transfer systems are important to study foreign gene expression and promoter regulation in an organism, with the benefit of exploring this in an integrated environment. Direct injection of plasmids encoding exogenous promoters and genes into muscle has numerous advantages: the protocol is easy, efficient, and shows time-persistent plasmid expression in transfected muscular cells. After injecting naked-DNA plasmids into tadpole tail muscle, transgene expression is strong, reproducible, and correlates with the amount of DNA injected. Moreover, expression is stable as long as the tadpoles remain, or are maintained, in premetamorphic stages. By directly expressing genes and regulated promoters in Xenopus tadpole muscle in vivo, one can exploit the powerful experimental advantages of gene transfer systems in an intact, physiologically normal animal.

Plasmid Biopharmaceuticals

Plasmids are currently an indispensable molecular tool in life science research and a central asset for the modern biotechnology industry, supporting its mission to produce pharmaceutical proteins, antibodies, vaccines, industrial enzymes, and molecular diagnostics, to name a few key products. Furthermore, plasmids have gradually stepped up in the past 20 years as useful biopharmaceuticals in the context of gene therapy and DNA vaccination interventions. This review provides a concise coverage of the scientific progress that has been made since the emergence of what are called today plasmid biopharmaceuticals. The most relevant topics are discussed to provide researchers with an updated overview of the field. A brief outline of the initial breakthroughs and innovations is followed by a discussion of the motivation behind the medical uses of plasmids in the context of therapeutic and prophylactic interventions. The molecular characteristics and rationale underlying the design of plasmid vectors as gene transfer agents are described and a description of the most important methods used to deliver plasmid biopharmaceuticals in vivo (gene gun, electroporation, cationic lipids and polymers, and micro- and nanoparticles) is provided. The major safety issues (integration and autoimmunity) surrounding the use of plasmid biopharmaceuticals is discussed next. Aspects related to the large-scale manufacturing are also covered, and reference is made to the plasmid products that have received marketing authorization as of today.

Molecular cloning, characterization and functional assessment of the myosin light polypeptide chain 2 (mylz2) promoter of farmed carp, Labeo rohita

We cloned the 5'-flanking region (1.2 kb) of a muscle-specific gene, encoding myosin light chain 2 polypeptide (mylz2) of a farmed carp, Labeo rohita (rohu). Sequence analysis using TRANSFAC-database search identified the consensus cis acting regulatory elements of TATA-box and E (CANNTG)-box, including the monocyte enhancer factor 2 motif, implying that it is likely to be a functional promoter. The proximal promoter (~620 bp) was highly homologous with that of Danio rerio (zebrafish) as compared to Channa striatus (snakehead murrel) counterparts and showed less identity with Sparus auratus (gilthead sea bream), Xenopus laevis (African clawed frog) and Rattus norvegicus (Norway rat). Direct muscular (skeletal) injection of the construct containing the mylz2 promoter (0.6 kb) fused to a green fluorescent protein (GFP) reporter gene showed efficient expression in L. rohita, validating its functional activity. Further, the functional activity was confirmed by the observation that this promoter drove GFP expression in the skeletal muscle of transgenic rohu. The promoter may have potential applications for value-addition in ornamental fishes and studying gene regulatory functions.

Strategies and hurdles using DNA vaccines to fish

DNA vaccinations against fish viral diseases as IHNV at commercial level in Canada against VHSV at experimental level are both success stories. DNA vaccination strategies against many other viral diseases have, however, not yet yielded sufficient results in terms of protection. There is an obvious need to combat many other viral diseases within aquaculture where inactivated vaccines fail. There are many explanations to why DNA vaccine strategies against other viral diseases fail to induce protective immune responses in fish. These obstacles include: 1) too low immunogenicity of the transgene, 2) too low expression of the transgene that is supposed to induce protection, 3) suboptimal immune responses, and 4) too high degradation rate of the delivered plasmid DNA. There are also uncertainties with regard distribution and degradation of DNA vaccines that may have implications for safety and regulatory requirements that need to be clarified. By combining plasmid DNA with different kind of adjuvants one can increase the immunogenicity of the transgene antigen – and perhaps increase the vaccine efficacy. By using molecular adjuvants with or without in combination with targeting assemblies one may expect different responses compared with naked DNA. This includes targeting of DNA vaccines to antigen presenting cells as a central factor in improving their potencies and efficacies by means of encapsulating the DNA vaccine in certain carriers systems that may increase transgene and MHC expression. This review will focus on DNA vaccine delivery, by the use of biodegradable PLGA particles as vehicles for plasmid DNA mainly in fish.

Strategies and hurdles using DNA vaccines to fish

DNA vaccinations against fish viral diseases as IHNV at commercial level in Canada against VHSV at experimental level are both success stories. DNA vaccination strategies against many other viral diseases have, however, not yet yielded sufficient results in terms of protection. There is an obvious need to combat many other viral diseases within aquaculture where inactivated vaccines fail. There are many explanations to why DNA vaccine strategies against other viral diseases fail to induce protective immune responses in fish. These obstacles include: 1) too low immunogenicity of the transgene, 2) too low expression of the transgene that is supposed to induce protection, 3) suboptimal immune responses, and 4) too high degradation rate of the delivered plasmid DNA. There are also uncertainties with regard distribution and degradation of DNA vaccines that may have implications for safety and regulatory requirements that need to be clarified. By combining plasmid DNA with different kind of adjuvants one can increase the immunogenicity of the transgene antigen - and perhaps increase the vaccine efficacy. By using molecular adjuvants with or without in combination with targeting assemblies one may expect different responses compared with naked DNA. This includes targeting of DNA vaccines to antigen presenting cells as a central factor in improving their potencies and efficacies by means of encapsulating the DNA vaccine in certain carriers systems that may increase transgene and MHC expression. This review will focus on DNA vaccine delivery, by the use of biodegradable PLGA particles as vehicles for plasmid DNA mainly in fish.

The immune-adjuvant effect of Japanese flounder Paralichthys olivaceus IL-1β

IL-1β is known as a pro-inflammatory cytokine and plays a pivotal role in regulating immune response. IL-1β has been shown to influence immune responses in Japanese flounder Paralichthys olivaceus. To investigate the immune responses, a plasmid construct of pcDNA3.1-driven Japanese flounder IL-1β (pcDNA3.1-JFIL-1β) was co-injected into the muscle with Bovine serum albumin (BSA), as an antigen model, or pCI-neo driven with GFP (pCI-neo-GFP) as a vaccine model compared with the antigen or vaccine model alone, respectively. The IL-1β expression in the muscle was dramatically elevated in fish injected with pcDNA3.1-JFIL-1β on a day after injection, and the induction level was significantly higher than control groups. Moreover, pcDNA3.1-JFIL-1β significantly stimulated the gene expression of IL-1β in the kidney. The pcDNA3.1-JFIL-1β enhanced the antibody titer against BSA at 30 days after injection. In the DNA vaccine model, the antibody titer against GFP was also higher in the fish injected with pcDNA3.1-JFIL-1β than the group that injected pCI-neo-GFP alone. These results suggest that the pcDNA-driven Japanese flounder IL-1β could have potential immunoadjuvant effects.

Protection of Japanese flounder (Paralichthys olivaceus) against Vibrio anguillarum with a DNA vaccine containing the mutated zinc-metalloprotease gene

Vibrio anguillarum is one of the causative agents of vibriosis, a systemic disease of fish characterized by acute hemorrhagic septicemia. The extracellular zinc metalloprotease (EmpA) is a putative virulence factor involved in pathogenicity of V. anguillarum. Here we described the results of immunization against V. anguillarum with the plasmid expressing the mutated EmpA (m-EmpA7), which had no protelytic activity or cytotoxicity. In vitro protein expression of m-empA7 gene was determined by fluorescent microscopy and Western-blot after transfection of Chinese hamster ovary (CHO) and human embryonic kidney (HEK293T) cell lines. All three groups of fish immunized with a single intramuscular (i.m.) injection of different doses of the m-EmpA7 DNA vaccine showed significant serum antibody levels after vaccination, compared with the fish injected with the control eukaryotic expression vector pEGFP-N1 and PBS. In addition, fish receiving the DNA vaccine developed a protective response to a live V. anguillarum challenge 4 weeks post-inoculation, as demonstrated by increased survival of vaccinated fish over the control and by decreased histological alterations in vaccinated fish. Furthermore, humoral immune responses and protective effects were significantly increased at higher vaccine doses using a single intramuscularly injection route.

Potential use of chitosan nanoparticles for oral delivery of DNA vaccine in Asian sea bass (Lates calcarifer) to protect from Vibrio (Listonella) anguillarum

In recent years, attention has been focused on the possibility of utilizing DNA vaccines in fish aquaculture. A successful regime for intramuscular injection of naked DNA into fish has been developed and novel methods to deliver this DNA to fish are under investigation. The potential of chitosan as a polycationic gene carrier for oral administration has been explored since 1990s. The present study examines the potential efficacy of DNA vaccine against Vibrio anguillarum through oral route using chitosan nanoparticles encapsulation. The porin gene of V. anguillarum was used to construct DNA vaccine using pcDNA 3.1, a eukaryotic expression vector and the construct was named as pVAOMP38. The chitosan nanoparticles were used to deliver the constructed plasmid. In vitro and in vivo expression of porin gene was observed in sea bass kidney cell line (SISK) and in fish, respectively by fluorescent microscopy. The cytotoxicity of chitosan encapsulated DNA vaccine construct was analyzed by MTT assay and it was found that the cytotoxicity of pVAOMP38/chitosan was quite low. Distribution of gene in different tissues was studied in fish fed with the DNA (pVAOMP38) encapsulated in chitosan by using immunohistochemistry. The results indicate that DNA vaccine can be easily delivered into fish by feeding with chitosan nanoparticles. After oral vaccination Asian sea bass were challenged with Vibrio anguillarum by intramuscular injection. A relative percent survival (RPS) rate of 46% was recorded. The results indicate that Sea bass (Lates calcarifer) orally vaccinated with chitosan-DNA (pVAOMP38) complex showed moderate protection against experimental V. anguillarum infection.

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

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

Specific uptake of plasmid DNA without reporter gene expression in Atlantic salmon (Salmo salar L.) kidney after intramuscular administration

In this study we investigated tissue distribution of pDNA after intramuscular and intravenous administration, cellular localisation, receptor-specific uptake, integrity of pDNA and transgene expression in Atlantic salmon (Salmo salar L). Anatomical distribution of plasmid DNA was determined using both radiotracing and fluorescence microscopy. Cellular uptake was studied in cultures of adherent anterior kidney leucocytes. The integrity of the pDNA in vivo was investigated by Southern blot analysis. Transcription of plasmid DNA encoded luciferase gene and protein synthesis were investigated in salmon tissues by means of real-time reverse transcription-polymerase chain reaction and enzyme activity measurements, respectively. Approximately 50% of the total recovered radioactivity was redistributed from the carcass 168h after intramuscular administration and accumulated mainly in the kidneys (37% of total). The majority of radiolabelled plasmid DNA administered intravenously was taken up within the first 15min mainly by the kidney. Intravenous co-administration of trace amounts of radiolabelled plasmid DNA with excess amounts of unlabelled plasmid DNA or formaldehyde treated albumin (a ligand for the scavenger receptors) significantly inhibited accumulation of the radiotracer in the kidney. Fluorescence microscopy demonstrated that fluorescence was localised intracellularly in cells lining the sinusoids of the kidney after intravenous administration of rhodamine-labelled plasmid DNA. Southern blot analysis demonstrated presence of supercoiled plasmid DNA in all organs and tissue samples 168h after intramuscular administration, but degradation products were only revealed at the administration site. Luciferase transcript and activity were only detectable at the administration site 24-168h after intramuscular administration of plasmid DNA. After incubation with trace amounts of radiolabelled plasmid DNA, only minor amounts of radiolabelled plasmid DNA were cell associated in cultures of adherent anterior kidney leucocytes. These results suggested that a substantial portion of radiolabelled plasmid DNA was redistributed from the carcass and was mainly cleared by a receptor-specific uptake in the kidney. Although intact plasmid DNA was detected in the kidney and other tissues, no luciferase transcripts or activity were detected in these samples at any time points investigated (24-168h), except for the administration site following intramuscular administration.

Towards a metalloprotease-DNA vaccine against piscine cryptobiosis caused by Cryptobia salmositica

Cysteine protease is a metabolic enzyme, whereas metalloprotease is the virulent factor in cryptobiosis caused by Cryptobia salmositica. Recombinant DNA vaccines were produced with the insertion of either the metalloprotease or cysteine protease gene of C. salmositica into plasmid vectors (pEGFP-N). As expected, fishes (Oncorhynchus mykiss and Salmo salar) injected intramuscularly with the metalloprotease-DNA (MP-DNA) vaccine (50 microg/fish) were consistently more anemic (lower packed cell volume, PCV) than controls (injected only with the plasmid) at 3-5 weeks post-inoculation. Also, there were no difference in PCV between fish injected with the cysteine-DNA plasmids and the controls. In addition, agglutinating antibodies against Cryptobia were detected only in the blood of MP-DNA-vaccinated fish at 5-7 weeks post-vaccination and not in cysteine-DNA plasmids and the control groups. MP-DNA-vaccinated fish when challenged with the pathogen had consistently lower parasitemia, delayed peak parasitemia, and faster recovery compared with the controls. All fish vaccinated with attenuated strain were protected when challenged with the pathogen; this positive control group confirmed that the two vaccines operate through different mechanisms.

Expression and antiviral activity of a beta-defensin-like peptide identified in the rainbow trout (Oncorhynchus mykiss) EST sequences

The in silico identification of a beta-defensin-like peptide sequence (omBD-1) in the rainbow trout (Oncorhynchuss mykiss) database of salmonid EST is reported here. We have studied the transcript expression of this beta-defensin-like sequence in different organs and expressed the recombinant peptide in a fish cell line. Finally, we have demonstrated the in vitro antiviral activity of the recombinant trout beta-defensin-like peptide against viral haemorrhagic septicaemia rhabdovirus (VHSV), one of the most devastating viruses for worldwide aquaculture. Thus, the resistance to VHSV infection of EPC cells transfected with pMCV 1.4-omBD-1 has been shown. Since EPC cells transfected with omBD-1 produced acid and heat stable antiviral activity and up regulation of Mx, a type I IFN-mediated mechanism of antiviral action is suggested. To our knowledge, this is the first report showing biological activity of a beta-defensin-like peptide from any fish.

DNA vaccination can protect Cyprinus Carpio against spring viraemia of carp virus

Several DNA constructs containing the spring viraemia of carp virus (SVCV) glycoprotein (G) gene were investigated for their ability to induce protection against SVCV following injection into myofibres. The constructs were pooled into four groups and co-injected with a plasmid encoding murine granulocyte-macrophage colony-stimulating factor. Group 1 contained one full-length and two truncated G constructs under the control of the cytomegalovirus (CMV) promoter. Group 2 contained full-length constructs with the CMV promoter, the simian virus 40 promoter and a muscle-specific promoter. Group 3 contained constructs in which the G-gene was fused with a second gene in order to improve secretion of the G-protein or to enhance destruction of transfected myocytes by T cells. Group 4 contained constructs with the CMV-Intron A promoter in plasmids with or without CpG motifs. A small-scale trial in goldfish showed that antibody responses in at least half the fish were induced by three injections of plasmids from Groups 1 and 3 whereas T-cell like responses with stimulation indices of above 3 were induced in at least half the fish by Groups 2 and 4. A single-dose of each plasmid mix was then used to protect carp in a large-scale trial. Following challenge with a heterologous strain of SVCV that killed 64% of fish, the strongest protection was observed in carp that received the full length G-gene expressed by two plasmids driven by the CMV-Intron A promoter (Group 4), with a relative percentage survival of 48% (p=0.00008).

Protection of flounder against hirame rhabdovirus (HIRRV) with a DNA vaccine containing the glycoprotein gene

Hirame rhabdovirus (HIRRV) is an important virus of cultured flounder (Paralichthys olivaceus). We tested the protective immunogenicity of DNA-based vaccines against this virus. Genes encoding the nucleocapsid protein (N) and the C-terminal half of the glycoprotein (G) were amplified by RT-PCR and separately cloned into the eukaryotic expression vector pcDNA 3.1. The G protein expressed by transfected cells was detected by western blot analysis. PCR analyses demonstrated the presence of injected plasmids in fish muscle tissue at 14 days post injection. Immunocytochemistry of muscle tissue injected with the plasmid DNA showed expression of the target protein in myofibrils and sarcoplasm. Flounder fry with an average weight of 3 g were injected with 5 microg of plasmid DNA and challenged at 21 days after immunization. Fish injected with vector DNA or PBS showed >95% cumulative mortality by 16 days after inoculation with the virus. In contrast, fish injected with plasmids containing the N gene, G gene, or N + G gene mixture showed 70, 5, and 2.5% cumulative mortality, respectively. These results show that the G gene is effective for the induction of protective immunity against HIRRV infection in injected fish.

Analysis of DNA-vaccinated fish reveals viral antigen in muscle, kidney and thymus, and transient histopathologic changes

A highly efficacious DNA vaccine against a fish rhabdovirus, infectious hematopoietic necrosis virus (IHNV), was used in a systematic study to analyze vaccine tissue distribution, persistence, expression patterns, and histopathologic effects. Vaccine plasmid pIHNw-G, containing the gene for the viral glycoprotein, was detected immediately after intramuscular injection in all tissues analyzed, including blood, but at later time points was found primarily in muscle tissue, where it persisted to 90 days. Glycoprotein expression was detected in muscle, kidney, and thymus tissues, with levels peaking at 14 days and becoming undetectable by 28 days. Histologic examination revealed no vaccine-specific pathologic changes at the standard effective dose of 0.1 mug DNA per fish, but at a high dose of 50 mug an increased inflammatory response was evident. Transient damage associated with needle injection was localized in muscle tissue, but by 90 days after vaccination no damage was detected in any tissue, indicating the vaccine to be safe and well tolerated.

Time course study of in situ expression of antigens following DNA-vaccination against VHS in rainbow trout (Oncorhynchus mykiss Walbaum) fry

The present study was performed as a time course study of fish vaccinated with 20 microg plasmid DNA vaccine encoding either the VHSV G-protein or the VHSV N-protein. Samples of the injection site were collected sequentially over a 7-week period. The study revealed an intense positive staining by immunohistochemistry for the viral G-protein mainly in the membrane of intact myocytes, most prominent by days 10-27, and with concomitant infiltration of inflammatory cells by days 13-38 that subsequently lead to a marked reduction in the number of myocytes expressing the G-protein. By immunofluorescence, infiltrating cells positive for MHC II, IgM, and C3 were demonstrated. By contrast, in fish vaccinated with the VHSV-N construct, fewer, diffusely positive myocytes were found, most prominent by days 13-38, these having a positive reaction for the N-protein mainly in the cytoplasm and variably in the membrane. N-protein positive myocytes did not attract infiltrating cells to the same degree. Positive reaction for the N-protein almost ceased by day 48 post-vaccination.

Gene expression in tilapia following oral delivery of chitosan-encapsulated plasmid DNA incorporated into fish feeds

DNA delivery into fish is important for transient gene expression, (e.g., DNA vaccination). Previous studies have generally focused on intramuscular injection of DNA vaccines into fish. However, this method is obviously impractical and laborious for injecting large numbers of fishes. This study reports oral delivery of a construct expressing the beta-galactosidase reporter gene into fish by encapsulating the DNA in chitosan and incorporating it into fish feeds. We found that beta-galactosidase expression could be observed in the stomachs, spleens, and gills of fishes fed with flakes containing the chitosan-DNA complex. These results suggest that DNA vaccines and other constructs can be easily and cheaply delivered into fishes orally by use of carriers and incorporation into fish feeds.

Expression of luciferase in selected organs following delivery of naked and formulated DNA to rainbow trout (Oncorhynchus mykiss) by different routes of administration

In the present work, the expression of luciferase in selected organs following administration of DNA delivered as naked, liposome-formulated or chitosan-formulated by different routes of administration (intramuscular, intraperitoneal and intravenous injection, immersion and anal intubation) was studied in rainbow trout (Oncorhynchus mykiss). The different formulations and routes of administration both influenced in which organs luciferase was expressed and the magnitude of expression. The highest expression levels of luciferase in the head kidney and liver were found after an intraperitoneal injection of lipoplex 2. In the spleen, the highest levels were detected after injection of naked DNA (intraperitonal or intramuscular) and lipoplex 2 (intraperitoneal). Following intravenous injection, naked DNA gave higher expression levels in the organs than the formulated plasmids and immersion and anal intubation were not effective routes of delivery as no expression of luciferase could be detected in any of the organs tested. Additionally, PCR using a primer specific for a 600 bp region of the luciferase gene pcDNA3-luc was used to assess the distribution of the plasmid itself after intramuscular and intraperitoneal injection. Positive amplification was obtained in spleen, head kidney, liver and muscle at the injection site following injection of formulated plasmids, while only muscle tissue from the injection site was positive when naked DNA was used.

Assessment of DNA vaccine potential for gilthead sea bream (Sparus aurata) by intramuscular injection of a reporter gene

Naked circular plasmid DNA containing the cytomegalovirus (CMV)-promoter-driven lacZ reporter gene (pCMV-LacZ) was injected in the epaxial muscle of gilthead sea bream (Sparus aurata). A mosaic pattern of expression of beta-galactosidase (beta-gal) in the myofibres at the site of injection was visualised by in situ histochemical staining using 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside. As measured by o-nitrophenyl-beta-D-galactopyranoside assay, beta-gal enzymatic activity was found to steadily increase for at least 50 days post injection (p.i.) in pCMV-LacZ-injected muscle. In parallel, foreign DNA was detected by polymerase chain reaction in injected muscles (but not in other tissues) up to 60 days p.i., persisting most probably in an extrachromosomal, non-replicative, circular form. Neither beta-gal activity nor pCMV-LacZ-related amplification products were found 90 days p.i. Antibodies against beta-gal were demonstrated in pCMV-LacZ-injected fish sampled 45 days p.i. The results suggest that intramuscular delivery of foreign genes represents a realistic approach for DNA vaccine technology for the prevention of infectious diseases in gilthead sea bream.

Fish can be first--advances in fish transgenesis for commercial applications

Over the past 15 years researchers have generated stable lines of several species of transgenic fish important for aquaculture. 'All-fish' growth hormone (GH) gene constructs and antifreeze protein (AFP) genes have been successfully introduced into the fish genome resulting in a significant acceleration of growth rate and an increase in cold and freeze tolerance. However, neither gene modification is completely understood; there are still questions to be resolved. Expression rates are still low, producing variable growth enhancement rates and less than desired levels of freeze resistance. Transgene strategies are also being developed to provide improved pathogen resistance and modified metabolism for better utilization of the diet. Additional challenges are to tailor the genetically modified fish strains to prevent release of the modified genes into the environment.

Isolation and characterisation of tilapia beta-actin promoter and comparison of its activity with carp beta-actin promoter

The regulatory sequence including proximal promoter, untranslated exon 1 and intron 1 of the beta-actin gene from tilapia (Oreochromis niloticus) has been isolated and spliced to a beta-galactosidase reporter gene to test its activity. Comparisons of promoter activity have been carried out with three different constructs: (1) 1.6 kb tilapia beta-actin regulatory sequence, (2) 1.5 kb carp beta-actin regulatory sequence, and (3) 4.7 kb carp beta-actin regulatory sequence. Although the 1.6 kb tilapia beta-actin regulatory sequence gave slightly different expression patterns in tilapia embryos assayed by in situ X-gal staining, no difference was observed in expression level when the tilapia sequence was compared with the 4.7 kb carp beta-actin regulatory sequence by quantitative assay. In comparison with the 1.5 kb carp beta-actin regulatory sequence, the 1.6 kb tilapia beta-actin regulatory sequence gave higher expression levels in tilapia embryos, while a reverse result was observed in zebrafish embryos. In cell transfection experiments, the 1.6 kb tilapia beta-actin regulatory sequence showed three to four times better activity in blue gill cells than either the 4.7 kb carp beta-actin or the 1.5 kb carp beta-actin regulatory sequences. The 1.6 kb tilapia beta-actin regulatory sequence also drove higher reporter gene activity in somatic cells of tilapia than did the 4.7 kb carp beta-actin regulatory sequence following direct injection of constructs into muscle. Therefore, taken together, the data demonstrate that the tilapia beta-actin promoter can be used as an efficient regulatory sequence to produce autotransgenic tilapia.

The immune responses of common carp, Cyprinus carpio L., injected with carp interleukin-1beta gene

The function of the common carp, Cyprinus carpio L., interleukin-1beta (IL-1beta) gene was studied by DNA injection. To investigate the immune responses to IL-1beta, a plasmid construct of cytomegalovirus (CMV)-driven carp IL-1beta was injected into the epaxial muscle of carp. IL-1beta protein expressed in serum on 1, 3, and 5 days after plasmid injection was quantified by ELISA and immunohistochemistry. IL1-beta gene injection increased proliferation of the lymphocytes by phytohemagglutinin (PHA). Macrophage functions, such as production of superoxide anion and phagocytosis, also were stimulated by IL-1beta gene injection. Moreover, an increase in resistance to Aeromonas hydrophila infection was recorded in IL-1beta-injected fish compared with control fish. Thus, the cloned homolog of IL-1beta from carp has all the functional similarities to the mammalian IL-1beta gene.

Improvement of DNA transfection with cationic liposomes

The increasing use of cationic liposomes as vectors for DNA transfection of eukaryotic cells is due to its high efficiency and reproducibility. After the interaction of the DNA cationic-liposome complexes (DNA-CLC) with the plasma membrane, the entry into the cells delivers the DNA-CLC to the endosome-lysosome pathway where some of the DNA-CLC are degraded. The non-degraded DNA that escapes to the cytoplasm, still has to transverse the nuclear membrane to be transcribed and then translated. To improve the efficiency of the whole process, we can manipulate the DNA (sequences, promoters, enhancers, nuclear localisation signals, etc), the DNA-CLC (lipids) or the plasmatic, endosomal and/or nuclear cellular membranes (ultrasound, electroporation, Ca++, pH of the endosomes, mitosis, fusogenic peptides, nuclear localisation signals, etc). Most of these methods have been generally used individually but in combination, may greatly improve the efficiency and reproducibility of in vitro transfection. While much of this work remains yet to be done and present results further explored, the application of these efforts is essential to the future development of new gene therapy strategies.

Assessment of DNA vaccine potential for juvenile Japanese flounder Paralichthys olivaceus, through the introduction of reporter genes by particle bombardment and histopathology

Genetic immunisation potential, following DNA bombardment for juvenile Japanese flounder, Paralichthys olivaceus was examined. GFP plasmids bombarded at two pressures, 150 and 300psi were sampled at 1, 7, 14 and 28 days, greater immunofluorescence was observed at the higher bombardment pressure. Histopathology, at 3 h post bombardment showed considerable damage to fish epithelial and dermal tissues when bombarded at pressures greater than 200 psi, with many DNA-coated gold particles present. At 150psi there was little pathology and no DNA-coated particles. Histopathology, up to 28 days again showed little pathology at 150 psi with few DNA-coated particles, whereas at 300 psi there was significant pathology observed with many DNA-coated particles seen in conjunction with the cytoplasm of inflammatory cells. By day 28 epithelial coverage was observed with tissue damage restricted to the dermal layer. Chloramphenicol acetyltransferase (CAT) assay showed long term and stable expression of the CAT protein from day 1 to day 60. The transcription activity of two promoters; pCMV-CAT and pSV2-CAT showed greater activity in the former. It was concluded that DNA vaccination potential for juvenile flounder is a viable option.

Epitope-tagged insulin-like growth factor-I expression in muscle

Development of a recombinant insulin like growth factor I (IGF-I) that is distinguishable from its endogenous counterpart would provide a powerful tool for delineating the role of IGF in myogenesis. Therefore, the objective of this study was to create an epitope-tagged IGF-I that retains biological activity and determine whether expression of this construct is possible in muscle tissue following direct DNA injection. Expression vectors were created that encoded porcine IGF-I containing a T7 (11-amino acid) epitope-tag (TIGF). Immunoreactivity of the purified recombinant TIGF was confirmed using monoclonal antibodies. Biological activity was evaluated by examining differentiation of myoblasts cultured with TIGF or transfected with TIGF plasmid DNA. Addition of purified TIGF to myoblast cultures stimulated (P < 0.05) muscle creatine kinase levels similar to insulin (10(-5) M). Likewise, transfection of L6A1 with TIGF DNA hastened (P < 0.01) differentiation compared to control pcDNA-transfected myoblasts. The integrity of the recombinant protein was confirmed using a sandwich-configured enzyme linked immunosorbent assay. Finally, recombinant TIGF DNA was injected in porcine muscle and the ability to detect TIGF protein was evaluated. TIGF expression was detected in muscle fibers of injected porcine muscle. These data show that a T7 amino acid tag placed on the amino terminus of the IGF-I protein remains intact during processing and does not interfere with the biological activity of the molecule. Use of this DNA construct is an excellent tool for investigating the role of IGFs in control muscle development and provides a model to investigate other regulators of animal growth.

DNA vaccines: technology and application as anti-parasite and anti-microbial agents

DNA vaccines have been termed The Third Generation of Vaccines. The recent successful immunization of experimental animals against a range of infectious agents and several tumour models of disease with plasmid DNA testifies to the powerful nature of this revolutionary approach in vaccinology. Among numerous advantages, a major attraction of DNA vaccines over conventional vaccines is that they are able to induce protective cytotoxic T-cell responses as well as helper T-cell and humoral immunity. Here we review the current state of nucleic acid vaccines and cover a wide range of topics including delivery mechanisms, uptake and expression of plasmid DNA, and the types of immune responses generated. Further, we discuss safety issues, and document the use of nucleic acid vaccines against viral, bacterial and parasitic diseases, and cancer. The early potential promise of DNA vaccination has been fully substantiated with recent, exciting developments including the movement from testing DNA vaccines in laboratory models to non-human primates and initial human clinical trials. These advances and the emerging voluminous literature on DNA vaccines highlight the rapid progress that has been made in the DNA immunization field. It will be of considerable interest to see whether the progress and optimism currently prevailing can be maintained, and whether the approach can indeed fulfil the medical and commerical promise anticipated.

DNA-antiviral vaccines: new developments and approaches--a review

Current vaccines can be divided into "live," "recombinant" and "killed" vaccines. Live vaccines are traditionally composed of attenuated viruses or bacteria, selected for their reduced pathogenicity. Recombinant vaccines, driven by a viral or bacterial vector express foreign antigens, or only recombinant proteins injected as antigen. Killed vaccines consist of inactivated whole pathogens. But all these traditional vaccines have some disadvantages: Attenuated live vaccine are able to undergo mutation and as mutated viruses or bacteria can now provoke the diseases against which the vaccine should protect the organism. A further disadvantage of live vaccines is the possibility of shedding which is a real problem especially in veterinary medicine. Clearly, there is a need for better vaccines to protect against diseases without the disadvantages associated with vaccines presently in use. Modern vaccines might be characterized as safe, no risk of reversion to pathogenicity, and they should be stable without the necessity of a "cold chain." Production should be simple, standardized and inexpensive. Vaccine development has now been improved by the ability to use direct inoculations of plasmid DNA encoding viral or bacterial proteins. One of the major benefits of DNA-vaccines, variously termed "DNA-, genetic- or nucleic acid-immunization," is the endogenous synthesis of the encoded protein. Therefore DNA vaccines mimic natural infection and provoke both strong humoral and cellular immune response. This review summarizes new developments and approaches of DNA vaccination and explains the construction of expression plasmids as well as possible mechanisms of immune responses.

The safety and longevity of DNA vaccines for fish

A plasmid that contained the cytomegalovirus (CMV)-promoter-driven lacZ reporter gene (pCMV-lacZ) remained in the epaxial muscle of five of eight goldfish as covalently closed circles, the most functional form of plasmid, for at least 70 days at 22 degrees. It was not present in the gills or elsewhere by polymerase chain reaction and was not integrated. Its expressed protein, Escherichia coli beta-galactosidase (beta-gal), which was in the injected myofibres, was detected in all the fish at 4-21 days and in about half the fish from 28 days until the end of the experiment at 70 days. The numbers of cells that secreted antibody to beta-gal in the kidney peaked at 14 days. Serum antibody and proliferating kidney cells to beta-gal were in all fish from 14 days with a plateau of the responses from 21 days onwards. The plasmid did not induce autoimmune-like antibodies to itself or to single- or double-stranded salmon testis DNA. Plasmids can therefore induce long-term foreign protein expression whilst inducing humoral and cell-mediated immunity without autoimmunity or integration in goldfish.

DNA vaccines

In just a few years, injection of plasmid DNA to elicit immune responses in vivo has developed from an interesting observation to a viable vaccine strategy. DNA vaccines have been shown to elicit both cellular and humoral immune responses and to be effective in a variety of preclinical bacterial, viral, and parasitic animal models. This review will discuss the current knowledge of vector design, methods of plasmid delivery, immune responses elicited by various DNA vaccines, safety issues, and production and release of plasmid as a vaccine product. The potential of this new vaccine strategy and its future prospects is summarized.

Cloning of the rainbow trout (Oncorhynchus mykiss) Mx2 and Mx3 cDNAs and characterization of trout Mx protein expression in salmon cells

Two rainbow trout (Oncorhynchus mykiss) Mx cDNAs were cloned by using RACE (rapid amplification of cDNA ends) PCR and were designated RBTMx2 and RBTMx3. The deduced RBTMx2 and RBTMx3 proteins were 636 and 623 amino acids in length with molecular masses of 72 and 70.8 kDa, respectively. These proteins, along with the previously described RBTMx1 protein (G. D. Trobridge and J. A. Leong, J. Interferon Cytokine Res. 15:691-702, 1995), have between 88.7 and 96.6% identity at the amino acid level. All three proteins contain the tripartite GTP binding domain and leucine zipper motif common to Mx proteins. A monospecific polyclonal antiserum to an Escherichia coli-expressed fragment of RBTMx3 was generated, and that reagent was found to react with all three rainbow trout Mx proteins. Subsequently, endogenous Mx production in RTG-2 cells induced with poly(IC) double-stranded RNA was detected by immunoblot analysis. The cellular localization of the rainbow trout proteins was determined by transient expression of the RBTMx cDNAs in CHSE-214 (chinook salmon embryo) cells. A single-cell transient-transfection assay was used to examine the ability of each Mx cDNA clone to inhibit replication of the fish rhabdovirus infectious hematopoietic necrosis virus (IHNV). No significant inhibition in the accumulation of the IHNV nucleoprotein was observed in cells expressing either trout Mx1, Mx2, or Mx3 in transiently transfected cells.

An improved plasmid DNA expression vector for direct injection into skeletal muscle

In previous work, the direct injection of 50 micrograms of a plasmid DNA vector encoding firefly luciferase (VR1205) into murine quadriceps muscle produced an average of 6.5 ng of luciferase per muscle at 7 days postinjection. In this report, various elements of the VR1205 vector were modified to increase gene expression levels or to eliminate undesired viral sequences. Expression of the modified vectors was then compared to VR1205 using the intramuscular injection assay. In general, modifications to promoter, enhancer, and intronic sequences either decreased luciferase expression levels or had no effect. However, modifications to the polyadenylation and transcriptional termination sequences, plasmid backbone elements, and the luciferase gene itself each increased luciferase expression levels. The best-expressing vector, designated VR1255, contained a combination of these incrementally beneficial changes. A single intramuscular injection of 50 micrograms of VR1255 produced 300 ng of luciferase at 7 days postinjection, an expression level 46-fold higher than the VR1205 vector (or 22-fold higher, excluding modifications to the luciferase gene) and 154-fold higher than a commercially available luciferase expression vector. Thus, VR1255 represents an improved plasmid DNA vector that may be useful for gene therapy applications.

Regulation and expression of transgenes in fish -- a review

Transgenic fish, owing to a number of advantages which they offer over other species, are proving to be valuable model systems for the study of gene regulation and development genetics in addition to being useful targets for the genetic manipulation of commercially important traits. Despite having begun only a decade ago, the production of transgenic fish has become commonplace in a number of laboratories world-wide and considerable progress has been made. In this review, we initially consider the various regulatory elements and coding genes which have been used in fish, and subsequently discuss and compare both the transient and long-term fate and expression patterns of injected DNA sequences in the context of the different factors which are likely to have an effect on the expression of transgenes.

Muscle growth and muscle function: a molecular biological perspective

Molecular biological methods are pervading all biomedical fields and it is likely that they will soon introduce new techniques to veterinary diagnostics and have a major impact on food and fibre production in animal agriculture. The ability to manipulate muscle growth and phenotype will present new ethical problems, particularly if the techniques are used to manipulate muscle development in greyhounds and racehorses where the financial rewards could be very substantial. Muscle has been a useful tissue for the study of the molecular control of tissue development because terminal differentiation results in the production of large quantities of highly specialised proteins. Now that the functional anatomy of structural genes in muscle is being elucidated, a coherent picture is beginning to emerge of the way in which post-natal muscle growth and phenotype are regulated at the gene level. The hormones and growth factors involved in regulating the quantitative and qualitative changes in gene expression are now better understood, together with the ability of the tissue to adapt to physical signals and hence new activity patterns. The myosin heavy chain isoform genes which encode the myosin cross-bridges (the force generators for muscular contraction) exist as a large multigene family. The contractility and other characteristics of muscle depend to a large extent on the differential expression of members of this and other gene families. Muscle fibres adapt for increased power output by expressing a subset of "fast' genes and for increased economy of action by expressing a slow subset of genes and producing more mitochondria. With the increasing understanding of gene expression in muscle, there are prospects for manipulating the mass, contractility and other characteristics of muscle and also to change its phenotype and understand certain disease states.

The characterisation of the 5' regulatory region of a temperature-induced myosin-heavy-chain gene associated with myotomal muscle growth in the carp

We have isolated and characterised the 5' region of a member of the carp myosin heavy chain gene family. Expression of this gene has previously been shown to be induced by an increase in environmental temperature and is restricted to the small-diameter white myotomal muscle fibres which are associated with growth. The whole isoform gene, including potential regulatory sequence 5' to the transcription start site and the 3' untranslated region was cloned in a lambda2001 bacteriophage vector. Studies of the structure of the 5'-end of the gene revealed high amino acid sequence similarity with translated exons 3-7 of mammalian myosin heavy chain genes indicating identical exon/intron boundaries. The overall length of the gene was however only about one half of that in mammals and birds due to shorter introns. The region 5' to the transcription unit was sequenced and revealed the presence of putative TATA and CCAAAT boxes. In order to study the regulation of expression, a series of endonuclease-generated fragments from the 5' flanking sequence were spliced to chloramphenicol acetyltransferase reporter vectors and used in cell transfection assays or direct gene injection into carp skeletal muscle. The 5' flanking region, which contains a consensus sequence known as an E-box (CANNTG) and a MEF2 binding site, was shown to improve the expression of the reporter gene in fish acclimated at 18 degrees C or 28 degrees C. Unlike the coding region, there was little similarity between the 5'-upstream sequence (promoter region) when compared with sequences flanking the 5'-end of the other myosin heavy chain genes in mammals or chicken.

Induction of mucosal anti-HIV antibodies by facilitated transfection of airway epithelium with lipospermine/DNA complexes

BACKGROUND

Expression of microbial protein sequences in eukaryotic cells transfected by transcriptional/translational permissive cDNA constructs can induce systemic humoral and cellular responses in vivo. Two methods of in vivo transfection have been described to date. One method uses large quantities of naked DNA injected into skeletal muscle. The second method uses relatively small quantities of DNA complexed to gold particles for bollistic penetration of the plasma membrane of keratinocytes. The major disadvantage of the bolistic method is that instrumentation is required which is not generally available.

OBJECTIVES

The objectives of this study were to determine whether the use of DNA complexed with a cationic lipopolyamine could reduce the quantity of DNA required to induce systemic humoral responses following muscle transfection and whether similar DNA/lipopolyamine complexes could induce mucosal humoral responses following airway exposure.

STUDY DESIGN

Balb/c mice were exposed by nasal aerosol or intramuscular inoculation to a mammalian transcriptional/translational permissive DNA construct containing the entire sequence for the HIV-1 envelope polyprotein. Experimental animals were further segregated by the number of exposures at 3-week intervals and whether the DNA was complexed to dioctadecylamidoglycylspermine (DOGS) at a 5:1 molar charge ratio of DOGS/DNA.

RESULTS

DOGS facilitated in vivo transfection of mouse muscle reduced the quantity of DNA required for a systemic humoral response to surface expressed HIV-envelope proteins by one order of magnitude. Exposure of airway mucosa to both 10 micrograms and 1 microgram quantities of DNA complexed to DOGS produced systemic humoral responses to HIV-envelope as well as mucosal antibodies in pulmonary and colonic epithelia. Molecular modeling of DOGS/DNA complexes at the 5:1 charge ratio used in this study indicates that the DNA component is not exposed to aqueous solvents and may be relatively resistant to degradation under common biological environments.

CONCLUSION

Facilitated transfer of DNA by DOGS to transcriptional/translational competent cells offers several distinct advantages to the use of DNA alone. Since significantly smaller amounts of DNA are required, the potential for the induction of antibodies against DNA itself lessens the likelihood for the development of a lupus-like syndrome. More importantly, however, is the apparent ability to transfect mucosal cells which results in the development of specific mucosal immune responses. This procedure may allow the development of general methods for the induction of mucosal immunity at the level of entry for mucosal pathogens without the disadvantages inherent in live attenuated vectors.

Obtaining marketing authorization for nucleic acid vaccines in the European Union

Nucleic acid vaccines are promising candidates for easy-to-handle and cost-effective vaccines that combine the safety of subunit vaccines with the efficacy of live virus vaccines. In order to obtain marketing authorization for a nucleic acid vaccine in all member states of the European Union, a single application dossier has to be filed with the European Agency for the Evaluation of Medicinal Products. Notes for Guidance on the data necessary to support applications are available. The preclinical development of nucleic acid vaccines has to follow procedures of contained use according to the relevant EC directives which were translated into the German Gene Law. Clinical trials in Germany would follow the known procedures defined in the German Drug Law, whereas the Gene Law is not applicable. Clinical trials should be started only after having obtained consent of the Commission for Gene Therapy Trials formed under the auspices of the Federal Chamber of Physicians. Experience in intramuscular nucleic acid inoculation of animals has been gained using expression constructs comprising single and multiple genes of simian immunodeficiency virus. Specific antibodies were induced against multiple antigens. No adverse effects of nucleic acid inoculations were found, but more rigorous testing of specific safety problems will have to be performed.