DNA In Saline Research Articles

Ichthyoplankton metabarcoding as a tool for studying fish reproductive dynamics

The study of ichthyoplankton composition, abundance and distribution is paramount to understand the reproductive dynamics of local fish assemblages. The analysis of these parameters allows the identification of spawning sites, nursery areas and migration routes. However, due to the lack of characters in early life stages, the morphological identification of ichthyoplankton is often impractical and many studies identify only fish larvae. Additionally, its accuracy shows great variation between taxonomists and laboratories according to their experience and specialty. DNA barcoding emerged as an alternative to provide assertive identification of fish eggs and larvae, but it becomes too expensive and laborious when the study demands the processing of huge amounts of organisms. DNA metabarcoding can overcome these limitations as a rapid, cost-effective, broad and accurate taxonomy tool, allowing the identification of multiple individuals simultaneously. Here, we present the identification of a sample containing 68 fish eggs and another containing 293 fish larvae from a single site in the São Francisco River Basin, Eastern Brazil, through DNA metabarcoding. We used a low-cost saline DNA extraction followed by PCR amplification with three primer sets targeting the 12S rRNA gene: MiFish (~170bp), Teleo_1 (~60bp), and NeoFish (~190bp). The latter was recently developed by our research group specifically for the identification of Neotropical fishes. All the amplified samples were sequenced in a single multiplexed Illumina MiniSeq run. We performed the filtering steps and assigned Amplicon Sequence Variants (ASVs) using a DADA2/Phyloseq based pipeline and a custom 12S reference sequence database including 101 species and 70 genera from the Jequitinhonha and São Francisco basins. The species Cyphocharax gilbert, Leporinus taeniatus, Megaleporinus elongatus, Prochilodus argenteus, P. costatus and Psalidodon fasciatus were detected by all three primer sets in the larva pool, while Pterygoplichthys etentaculatus was detected solely by NeoFish (Fig. 1). Within the egg pool, all three markers detected the species Characidium zebra, Curimatella lepidura, M. elongatus, Pimelodus fur and P. costatus, but Brycon orthotaenia was detected only by NeoFish, P. maculatus only by Teleo, and P. pohli by MiFish and Teleo (Fig. 1). The consistency in species detection among all three markers underpins the credibility of this method to accurately describe the sample composition. Considering that most of species were exclusive to the larvae or egg pool, our experiment highlights the importance of including the identification of fish eggs in reproduction studies, as it can provide additional information about which species are spawning in an area. Furthermore, the application of DNA metabarcoding to the study of ichthyoplankton can help decision makers create more informed guidelines for conservation of economically and ecologically important fish species.

Priming but not boosting with plasmid DNA encoding mycolyl-transferase Ag85A from Mycobacterium tuberculosis increases the survival time of Mycobacterium bovis BCG vaccinated mice against low dose intravenous challenge with M. tuberculosis H37Rv

DNA vaccination is a potent means for inducing strong CD4 + (Th1) and particularly CD8 + mediated immune responses and protective immunity against tuberculosis infection in mice. Here we have analyzed the potential of a DNA vaccine encoding the immunodominant mycolyl-transferase Ag85A for increasing the efficacy of the current tuberculosis vaccine Mycobacterium bovis Bacille Calmette-Guérin (BCG) in three long-term survival experiments. BALB/c mice were vaccinated with BCG either following DNA priming or prior to DNA boosting. Ag85A specific CD4 + and CD8 + mediated IFN-γ responses were increased in mice primed with DNA prior to BCG, and in BCG vaccinated mice subsequently boosted with DNA. In the latter immunization protocol, antigenic stimulation also induced significant levels of IL-17. Mice were monitored for cachexia and survival following a low dose intravenous challenge with M. tuberculosis H37Rv. Priming with Ag85A but not control DNA increased significantly the protective efficacy of the BCG vaccine as indicated by reduced cachexia and prolonged survival time: 32 weeks versus 23 weeks in one experiment and 33 weeks versus 26 weeks in another experiment (MST in control, TB infected mice: 17 weeks in both experiments). On the other hand, boosting of BCG by subsequent Ag85A DNA in saline or vaxfectin™ – or recombinant 85A protein or MVA-85A for that matter – did not augment the efficacy of BCG (MST 19–21 weeks in all vaccinated groups versus 11 weeks in control, TB infected mice). Our results demonstrate that Ag85A DNA priming can increase efficacy of BCG and that boosting protocols of BCG may possibly be hampered by the induction of Th IL-17 cells.

Chitosan microparticles containing plasmid DNA as potential oral gene delivery system

The potential of chitosan as a polycationic gene carrier for oral administration has been explored since 1990s. Chitosan has been shown to effectively bind DNA in saline or acetic acid solution and protect DNA from nuclease degradation. In this study, pDNA (plasmid DNA) was encapsulated in chitosan microparticles. Chitosan–DNA microparticles were prepared using a complex coacervation process and stability of plasmid DNA was investigated in this complex. The chitosan–DNA microparticles could protect the encapsulated plasmid DNA from nuclease degradation. Release of pDNA from microparticles was studied in simulated gastric, simulated intestinal medium and acidic PBS (phosphate buffer saline) (pH 4.5) buffer at 37 °C, and released pDNA was assayed spectrophotometrically. In vitro release of pDNA from chitosan microparticles was dependent on pH, as the pH of the release medium increased release profile decreased. In in vivo-animal studies blue color was observed with X-gal (4-chloro-5-bromo-3-indolyl-β-galactosidase) staining of histological stomach and small intestine sections after oral administration of pDNA–chitosan microparticles as an indicator of exogeneous gene expression.

Increased stability and specificity through combined hybridization of peptide nucleic acid (PNA) and locked nucleic acid (LNA) to supercoiled plasmids for PNA-anchored “Bioplex” formation

Low cellular uptake and poor nuclear transfer hamper the use of non-viral vectors in gene therapy. Addition of functional entities to plasmids using the Bioplex technology has the potential to improve the efficiency of transfer considerably. We have investigated the possibility of stabilizing sequence-specific binding of peptide nucleic acid (PNA) anchored functional peptides to plasmid DNA by hybridizing PNA and locked nucleic acid (LNA) oligomers as “openers” to partially overlapping sites on the opposite DNA strand. The PNA “opener” stabilized the binding of “linear” PNA anchors to mixed-base supercoiled DNA in saline. For higher stability under physiological conditions, bisPNA anchors were used. To reduce nonspecific interactions when hybridizing highly cationic constructs and to accommodate the need for increased amounts of bisPNA when the molecules are uncharged, or negatively charged, we used both PNA and LNA oligomers as “openers” to increase binding kinetics. To our knowledge, this is the first time that LNA has been used together with PNA to facilitate strand invasion. This procedure allows hybridization at reduced PNA-to-plasmid ratios, allowing greater than 80% hybridization even at ratios as low as 2:1. Using significantly lower amounts of PNA–peptides combined with shorter incubation times reduces unspecific binding and facilitates purification.

Characterization of immune response in mice to plasmid DNA encoding human sperm associated antigen 9 (SPAG9)

To examine the immunogenicity of the plasmid DNA encoding human sperm associated antigen 9 (hSPAG9), the cDNA corresponding to hSPAG9 was cloned in mammalian expression vector pcDNA 3.1 down stream of cytomegalovirus promoter. Immunization of female BALB/cJ mice with pcDNA–hSPAG9 plasmid DNA in saline by intramuscular (i.m.), by adsorbing onto gold microcarriers (delivered by gene gun) and by recombinant hSPAG9 (r-hSPAG9) protein generated antibody response against Escherichia coli expressed r-hSPAG9 protein and native SPAG9 in human sperm. Although mice immunized with r-hSPAG9 protein exhibited highest antibodies titres ( P < 0.001), the difference in the antibody titres seen by the two modes of plasmid DNA delivery were not significant ( P > 0.05). A dominant IgG1 isotype response was observed in mice immunized with pcDNA–hSPAG9 plasmid DNA delivered by gene gun as compared to a mixed IgG1–IgG2a isotype response in mice immunized with r-hSPAG9 protein and pcDNA–hSPAG9 plasmid DNA delivered by i.m. Further, antibodies generated by pcDNA–hSPAG9 plasmid DNA localized acrosomal compartment of human sperm and inhibited sperm adherence to or penetration in zona-free hamster egg penetration test. These studies for the first time, demonstrate the feasibility of generating an immune response to sperm specific hSPAG9 protein by DNA vaccine and that antibodies thus generated recognize native SPAG9 in human sperm.

The origin and identification of unknown events associated with low-level leucocyte counting by flow cytometry.

Flow cytometric enumeration of residual leucocytes (WBC) in leucocyte-depleted components occasionally reveals a population of events that stain with propidium iodide, but which are outside the main counting region. These extraregional events may result in discrepancies in residual WBC counts. To identify the origin of these unknown events, separate populations of mononuclear cells and polymorphonuclear neutrophils (PMNs) (prepared by density-gradient centrifugation) were spiked into leucocyte-depleted red cell concentrates (RCC) to a concentration of 150 cells/ microl and assessed, using LeucoCount and DNA Prep reagents, by flow cytometry. In addition, isolated WBC nuclei, DNA in saline, or enzymatically digested free DNA, was spiked into diluted whole blood (final concentration 5 microg/ml). Isolated WBC nuclei fell in the main counting region of the dot plot. Extraregional events were generated in leucocyte-depleted RCC spiked with PMN (17/ microl by day 4), but not with mononuclear cells, and increased with sample storage (4 days). A significantly (P < 0.01) greater number of extraregional events was observed using the LeucoCount reagent, compared with the DNA Prep reagent. Enzymatically digested WBC nuclei or free DNA, added to diluted whole blood, generated extraregional events using LeucoCount, but not the DNA Prep reagent. When free DNA was enzymatically digested, no extraregional events were observed. These previously unidentified events are probably fragmented nuclei or free DNA originating from PMN owing to a combination of ageing and reagent addition. Currently, in our protocols, the region used for WBC enumeration counts intact WBC nuclei. To achieve WBC counting consistency, flow cytometric gating protocols must be standardized, and a decision taken as to whether to include extraregional events in the count.

Mechanisms of increased immunogenicity for DNA-based vaccines adsorbed onto cationic microparticles

Investigation into the mechanism of action of vaccine adjuvants provides opportunities to define basic immune principles underlying the induction of strong immune responses and insights useful for the rational development of subunit vaccines. A novel HIV vaccine composed of plasmid DNA-encoding p55 gag formulated with poly-lactide-co-glycolide microparticles (PLG) and cetyl trimethyl ammonium bromide (CTAB) elicits both serum antibody titers and cytotoxic lymphocyte activity in mice at doses two orders of magnitude lower than those required for comparable response to plasmid DNA in saline. Using this model, we demonstrated the increase in potency requires the DNA to be complexed to the PLG–CTAB microparticles. Furthermore, the PLG–CTAB–DNA formulation increased the persistence of DNA at the injection site, recruited mononuclear phagocytes to the site of injection, and activated a population of antigen presenting cells. Intramuscular immunization with the PLG–CTAB–DNA complex induced antigen expression at both the injection site and the draining lymph node. These findings demonstrate that the PLG–CTAB–DNA formulation exhibits multiple mechanisms of immunopotentiation.

Optimization of DNA-based Vaccination in Cows Using Green Fluorescent Protein and Protein A as a Prelude to Immunization Against Staphylococcal Mastitis

Staphylococcus aureus is a contagious pathogen that often results in chronic intramammary infections in dairy cows. Current vaccine formulations are ineffective in preventing this infection. The objective of this study was to stimulate an immune response in dairy cows through injection of plasmid DNA designed to express staphylococcal Protein A in transfected cells. Intramuscular and intradermal vaccination sites were evaluated using a plasmid containing the human cytomegalovirus (CMV) promoter/enhancer directing expression of green fluorescent protein (pcDNA3/GFP). DNA was delivered by needle and syringe, or by high-, intermediate-, or low-pressure jet injections (Ped-o-Jet and LectraJet). Five cows per treatment were injected with 0.5mg of plasmid DNA at 6, 4, and 2 wk prepartum. Serum antibody levels determined by ELISA indicated that intradermal high-pressure jet injection elicited a greater immune response compared to needle and syringe injection. Differences in antibody production among low-pressure and needle and syringe treatment groups were not significant. An expression plasmid containing the CMV promoter/enhancer driving expression of the Fc-binding domain of S. aureus Protein A was coinjected into cows by vulvamucosal vaccination using the high-pressure Ped-o-Jet. Beginning 6 wk prepartum, groups of cows (n = 5) were injected three times at 2-wk intervals with DNA in saline, DNA in aluminum phosphate adjuvant, or served as noninjected controls. A cellular immune response to Protein A was detected in 4 of 10 animals, while cellular responses to GFP were not detected. Humoral responses to Protein A were observed in 6 of 10 animals and to GFP in 2 of 10 animals. Aluminum phosphate adjuvant appeared to enhance antibody production in response to Protein A. In experiment 3, a protein boost injection of Protein A was given to six animals approximately 5 mo postpartum. Three animals were nonvaccinated controls, and three were among those stimulated to produce antibody in response to the DNA-based vaccine. These results showed that Protein A specific antibodies remained elevated as compared to nonvaccinated controls and were stimulated in response to the protein boost. However, the magnitude of the response in animals previously vaccinated with DNA was not different than that observed in the nonvaccinated controls. We have shown that a humoral and cellular immune response to abbreviated Protein A can be raised in dairy cows using intravulvamucosal jet injection of a DNA-based vaccine.

Characterization of immune response in mice to plasmid DNA encoding dog zona pellucida glycoprotein-3

To investigate the immunogenicity of plasmid DNA encoding dog zona pellucida glycoprotein-3 (dZP3), the cDNA corresponding to dZP3, was cloned in mammalian expression vector VR1020 downstream of tissue plasminogen activator signal sequence under cytomegalovirus promoter (VRdZP3). In vitro transfection of COS-1 mammalian cells with VRdZP3 plasmid DNA led to its cytosolic expression. The expressed dZP3 has an apparent molecular weight of 45 kDa as compared to calculated molecular weight of 38.4 kDa, suggesting possible glycosylation. Immunization of male BALB/cJ mice with VRdZP3 plasmid DNA in saline, by electroporation or adsorbed onto gold microcarriers (delivered by gene gun) generated antibody response against Escherichia coli expressed recombinant dZP3 (r-dZP3). Administration of r-dZP3 in saline following immunization with plasmid DNA led to boosting of the antibody response. Although mice immunized with gene gun exhibited highest antibody titres, the differences in the antibody titres seen by the three modes of plasmid DNA delivery were not statistically significant ( P>0.05). Interestingly, female mice immunized with VRdZP3 plasmid DNA using gene gun also generated antibodies against r-dZP3. A dominant IgG1 isotype response was observed in mice immunized with VRdZP3 plasmid DNA using gene gun as compared to a mixed IgG1–IgG2a isotype response when delivered in saline or by electroporation. Immunization with VRdZP3 plasmid DNA also generated cell mediated immune response. The antibodies generated by VRdZP3 plasmid DNA recognized dog native zona pellucida. These studies for the first time, demonstrate the feasibility of generating an immune response to ZP3 by DNA vaccine and that the antibodies thus generated recognize native zona pellucida.

A DNA vaccine containing an infectious Marek's disease virus genome can confer protection against tumorigenic Marek's disease in chickens.

A DNA vaccine containing the infectious BAC20 clone of serotype 1 Marek's disease virus (MDV) was tested for its potential to protect against Marek's disease (MD). Chickens were immunized at 1 day old with BAC20 DNA suspended either in PBS, as calcium phosphate precipitates, incorporated into chitosan nanoparticles, in Escherichia coli DH10B cells, or bound to gold particles for gene-gun delivery. Challenge infection with MDV strain EU1 was performed at 12 days old, and four out of seven birds immunized with BAC20 DNA in saline by the intramuscular route remained free of MD until day 77 after challenge infection. A delay in the development of the disease could be observed in some animals vaccinated with other BAC20 DNA formulations, but clinical MD and tumour formation were evident in all but one bird. Five out of seven animals immunized with the vaccine virus CVI988 were protected against MD, but none out of seven birds survived EU1 challenge infection after injection of negative-control plasmid DNA. In a second animal experiment, five out of 12 chickens immunized with BAC20 DNA and six out of eight birds immunized with virus reconstituted from BAC20 DNA remained free of MD after challenge infection. In contrast, none out of 12 chickens survived challenge infection after immunization with BAC20 DNA lacking the essential gE gene or with gE-negative BAC20 virus. The results suggested that an MDV BAC DNA vaccine has potential to protect chickens against MD, but that in vivo reconstitution of vaccine virus is a prerequisite for protection.

Improved Tuberculosis DNA Vaccines by Formulation in Cationic Lipids

Mice were vaccinated with plasmid DNA (pDNA) encoding antigen 85A (Ag85A), Ag85B, or PstS-3 from Mycobacterium tuberculosis either in saline or formulated for intramuscular injections in VC1052:DPyPE (aminopropyl-dimethyl-myristoleyloxy-propanaminium bromide-diphytanoylphosphatidyl-ethanolamine) (Vaxfectin; Vical, Inc., San Diego, Calif.) or for intranasal instillations in GAP-DLRIE:DOPE (aminopropyl-dimethyl-bis-dodecyloxy-propanaminium bromide-dioleoylphosphatidyl-ethanolamine). These two novel cationic and neutral colipid formulations were previously reported to be effective adjuvants for pDNA-induced antibody responses. The levels of Ag85-specific total immunoglobulin G (IgG) and IgG isotypes were all increased 3- to 10-fold by formulation of pDNA in Vaxfectin. The level of production of splenic T-cell-derived Th1-type cytokines (interleukin-2 and gamma interferon) in response to purified Ag85 and to synthetic peptides spanning the entire Ag85A protein was also significantly higher in animals vaccinated with pDNA formulated in Vaxfectin. Cytolytic T-lymphocyte responses generated by pDNA encoding phosphate-binding protein PstS-3 in Vaxfectin were better sustained over time than were those generated by PstS-3 DNA in saline. Intranasal immunization with Ag85A DNA in saline was completely ineffective, whereas administration in GAP-DLRIE:DOPE induced a positive Th1-type cytokine response; however, the extent of the latter response was clearly lower than that obtained following intramuscular immunization with the same DNA dose. Combined intramuscular and intranasal administrations in cationic lipids resulted in stronger immune responses in the spleen and, more importantly, in the lungs as well. Finally, formulation in Vaxfectin increased the protective efficacy of the Ag85B DNA vaccine, as measured by reduced relative light unit counts and CFU counts in the spleen and lungs from mice challenged with bioluminescent M. tuberculosis H37Rv. These results may be of importance for future clinical use of DNA vaccines in humans.

Antibodies generated in response to plasmid DNA encoding zona pellucida glycoprotein-B inhibit in vitro human sperm-egg binding.

To investigate the immunogenicity of plasmid DNA encoding bonnet monkey (Macaca radiata) zona pellucida (ZP) glycoprotein-B (bmZPB), the cDNA corresponding to bmZPB, excluding the N-terminal signal sequence and C-terminus transmembrane-like domain, was cloned in mammalian expression vector VR1020 downstream of tissue plasminogen activator signal sequence under cytomegalovirus promoter (VRbmZPB). In vitro transfection of COS-1, COS-7, CHO, HEK-293, and UM-449 mammalian cells with VRbmZPB plasmid DNA led to the expression of bmZPB. Expression of bmZPB in transfected cells was cytosolic. Flow cytometry analysis of COS-1 cells transfected with VRbmZPB revealed that approximately 15% cells expressed bmZPB. The expressed bmZPB has an apparent molecular weight of 57 kDa. Immunization of male BALB/cJ mice with VRbmZPB plasmid DNA in saline as compared to VR1020 immunized group, elicited significant antibodies against E. coli expressed recombinant bmZPB as evaluated in ELISA. The antibodies generated by VRbmZPB plasmid DNA recognized bonnet monkey as well as human ZP. The immune sera obtained from mice immunized with VRbmZPB plasmid DNA also inhibited, in vitro, the binding of spermatozoa to the ZP in the hemizona assay. These studies, for the first time, demonstrate the feasibility of DNA vaccine to generate antibodies against ZP that recognize native protein and inhibit human sperm-oocyte binding.

Enhancements in Gene Expression by the Choice of Plasmid DNA Formulations Containing Neutral Polymeric Excipients

Formulations containing maltodextrin (2% w/v) were identified to facilitate intramuscular (im) delivery of plasmid DNA in mice using the reporter genes luciferase and chloramphenicol acetyltransferase (CAT) and the therapeutic gene of erythropoietin (EPO) as monitors of transfection efficiency. Even though considerable variability in gene expression was observed in animals, a 5–8-fold enhancement of reporter gene expression was observed with this excipient compared with saline formulations of DNA. In a therapeutically significant experiment, a single im injection of an EPO plasmid formulation containing 2% (w/v) maltodextrin resulted in a significant and prolonged elevation of the hematocrit levels of mice compared with control DNA in saline. Biophysical studies with Fourier transform infrared (FTIR) spectroscopy, isothermal titration, and differential scanning calorimetry (DSC) suggested a weak interaction between DNA and maltodextrin as well as a thermal stabilizing effect on the DNA. These in vivo and biophysical results with maltodextrin are comparable to those reported previously with other nonionic polymers, such as poly(vinyl pyrrolidone) and poloxamers, and indicate that maltodextrin is an additional nonionic excipient that displays the property of gene expression enhancement. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 1371–1381, 2002

DNA vaccines: basic mechanism and immune responses (Review).

DNA vaccines raise immune responses by expressing proteins in vaccinated hosts. Responses are raised by nanogram levels of protein expression. Popular methods of DNA delivery include intramuscular (i. m.) injections of DNA in saline and gene gun delivery of DNA-coated gold beads to the epidermis. Professional antigen-presenting cells derived from the bone marrow present DNA-expressed antigens to T-cells. Following gene gun immunizations directly transfected dendritic cells present antigens, whereas following i.m. immunizations both directly transfected dendritic cells and macrophages can present antigen. For both methods of DNA delivery, non-lymphoid cells can serve as factories of antigen for professional antigen presenting cells. Gene gun immunizations depend on antigen expression at the skin target whereas i.m. immunizations are largely independent of DNA expression in the muscle target. For both methods, antigen expression capable of initiating an immune response persists for about one month. intramuscular deliveries of DNA tend to raise type 1 T-cell help for intracellular and plasma membrane antigens but type 2 T-cell help for secreted antigens. Gene gun immunizations tend to raise type 2 T-cell help for both cell-associated and secreted antigens. In mice, DNA-raised immune responses can be equivalent to those raised by viral infections for both the height and longevity of antibody and cytotoxic T-cell responses.

DNA is as effective as protein at inducing antibody in fish

Antiviral vaccines are needed for fish. 50 μg plasmid DNA in saline by the intramuscular route and 10 μg β-gal protein in a commercial oil adjuvant by the peritoneal route induced serum antibody of the same titre and avidity in goldfish. The DNA expressed β-gal under control of the immediate early promoter/enhancer gene of human cytomegalovirus. Commercial bacterin vaccines are administered to fish by the intraperitoneal route with oil and this route for DNA induced only 2-fold less antibody than DNA by the intramuscular route. Bacterin vaccines and antiviral plasmid DNA could therefore be co-injected into the peritoneum of fish in an oil adjuvant as a single dose.

Immune Response to a Hepatitis B DNA Vaccine in Aotus Monkeys: A Comparison of Vaccine Formulation, Route, and Method of Administration

Attempts to optimize DNA vaccines in mice include using different routes of administration and different formulations. It may be more relevant to human use to carry such studies out in nonhuman primates. Here we compare different approaches to delivery of a DNA vaccine against the hepatitis B virus (HBV) in Aotus monkeys. Thirty-two adult Aotus l. lemurinus monkeys divided into 8 groups of four were immunized with 400 microg of a DNA vaccine which encoded hepatitis B surface antigen (HBsAg). DNA in saline was administered by intradermal (ID) or intramuscular (IM) injection with needle and syringe, IM injection with the Biojector needleless injection system or combined ID (needle) and IM (Biojector). DNA formulated with cationic liposomes (CellFECTIN) was injected IM with needle or Biojector. DNA with added E. coli DNA (100 microg) was injected IM with the Biojector or ID. A ninth group of 4 monkeys was injected IM (needle) with Engerix-B, a commercial vaccine containing recombinant HBsAg (10 microg) adsorbed onto alum. Monkeys were boosted in an identical fashion to their prime at 8 weeks, but all received the protein vaccine (Engerix-B) at 16 weeks. Sera was assessed for antibodies against HBsAg (anti-HBs) by enzyme-linked imunosorbent assay (ELISA). The primary humoral response induced by IM delivery of the DNA vaccine was very poor. In most cases there was no detectable anti-HBs even after 2 DNA doses but the kinetics of the response to subsequent protein indicated that a memory B cell response had been induced. In contrast, following IM-administration of DNA using the Biojector, detectable anti-HBs were observed in 3 of 8 animals and evidence for immunological priming was apparent in an additional 4 of the 8 monkeys. ID injection of DNA vaccine in saline induced a potent antibody response which was augmented 6-fold by the addition of E. coli DNA. Combining ID and IM administration did not improve humoral immunity over ID injection alone. For immunization of primates with DNA vaccines, ID may be a preferable route to IM, although it is not clear whether the Aotus monkey is a relevant model for humans in this respect. Nevertheless, the use of the Biojector needleless injection system may improve responses with IM delivery of DNA vaccines. As well, the immunostimulatory action of E. coli DNA may be used to augment the humoral response induced by a DNA vaccine.

DNA immunization: Effects of vehicle and route of administration on the induction of protective antiviral immunity

The effectiveness of DNA immunization has been demonstrated in several model systems, usually following intramuscular injection of DNA in saline, or topical administration to the skin. In this study we have compared DNA delivered by three routes (intramuscular, intravenous, and intraperitoneal) and, for each route, in two vehicles (cationic liposome complex and pH sensitive liposome). These two lipid vehicles were evaluated because they are frequently used in gene therapy studies, but their immunogenicity has not been extensively studied. Each of these six combinations has been evaluated not only by assay of marker gene expression in a variety of tissues, but also by measurement of biologically-relevant parameters of immunity induction of antibodies, cytotoxic T lymphocytes, and protection against viral challenge. By both criteria (marker gene expression and induced immunity), the outcomes vary markedly among the six combinations. The combination leading to maximal marker gene expression (DNA with cationic lipid, administered i.v.) also induces detectable antibodies and CTL, and is the only one of the six combinations to induce immune responses comparable to those seen following i.m. injection of DNA in saline. However, marker gene expression can be detected in other combinations in the absence of induced immunity thus the value of marker gene expression in predicting the protection induced by a microbial antigen is questionable suggesting that, when evaluating various promoter constructs, marker gene expression may not adequately replace the direct measurement of biological outcomes.

DNA immunization: Effects of vehicle and route of administration on the induction of protective antiviral immunity

The effectiveness of DNA immunization has been demonstrated in several model systems, usually following intramuscular injection of DNA in saline, or topical administration to the skin. In this study we have compared DNA delivered by three routes (intramuscular, intravenous, and intraperitoneal) and, for each route, in two vehicles (cationic liposome complex and pH sensitive liposome). These two lipid vehicles were evaluated because they are frequently used in gene therapy studies, but their immunogenicity has not been extensively studied. Each of these six combinations has been evaluated not only by assay of marker gene expression in a variety of tissues, but also by measurement of biologically-relevant parameters of immunity induction of antibodies, cytotoxic T lymphocytes, and protection against viral challenge. By both criteria (marker gene expression and induced immunity), the outcomes vary markedly among the six combinations. The combination leading to maximal marker gene expression (DNA with cationic lipid, administered i.v.) also induces detectable antibodies and CTL, and is the only one of the six combinations to induce immune responses comparable to those seen following i.m. injection of DNA in saline. However, marker gene expression can be detected in other combinations in the absence of induced immunity thus the value of marker gene expression in predicting the protection induced by a microbial antigen is questionable suggesting that, when evaluating various promoter constructs, marker gene expression may not adequately replace the direct measurement of biological outcomes.

DNA vaccines: A novel approach to immunization

Direct DNA inoculations are being developed as a method of subunit vaccination. Plasmid DNAs encoding influenza virus hemagglutinin glycoproteins have been tested for the ability to provide protection against lethal influenza challenges. In immunization trials using inoculations of purified DNA in saline, 67–95% of test mice and 25–63% of test chickens were protected against the lethal challenge. Good protection was achieved by intramuscular, intravenous and intradermal injections. In mice, 95% protection was achieved by gene gun delivery of 250–2500 times less DNA than the saline inoculations. Successful DNA vaccination by multiple routes of inoculation and the high efficiency of gene-gun delivery highlight the potential of this promising new approach to immunization.

DNA vaccines: protective immunizations by parenteral, mucosal, and gene-gun inoculations.

Plasmid DNAs expressing influenza virus hemagglutinin glycoproteins have been tested for their ability to raise protective immunity against lethal influenza challenges of the same subtype. In trials using two inoculations of from 50 to 300 micrograms of purified DNA in saline, 67-95% of test mice and 25-63% of test chickens have been protected against a lethal influenza challenge. Parenteral routes of inoculation that achieved good protection included intramuscular and intravenous injections. Successful mucosal routes of vaccination included DNA drops administered to the nares or trachea. By far the most efficient DNA immunizations were achieved by using a gene gun to deliver DNA-coated gold beads to the epidermis. In mice, 95% protection was achieved by two immunizations with beads loaded with as little as 0.4 micrograms of DNA. The breadth of routes supporting successful DNA immunizations, coupled with the very small amounts of DNA required for gene-gun immunizations, highlight the potential of this remarkably simple technique for the development of subunit vaccines.