Needle-free jet injection of a mixture of Japanese encephalitis DNA and protein vaccines: a strategy to effectively enhance immunogenicity of the DNA vaccine in a murine model

Devices for drug delivery in the gastrointestinal tract: A review of systems physically interacting with the mucosa for enhanced delivery

The delivery of macromolecules via the gastrointestinal (GI) tract remains a significant challenge. A variety of technologies using physical modes of drug delivery have been developed and investigated to overcome the epithelial cell layer of the GI tract for local and systemic delivery. These technologies include direct injection, jetting, ultrasound, and iontophoresis, which have been largely adapted from transdermal drug delivery. Direct injection of agents using needles through endoscopy has been used clinically for over a century. Jetting, a needle-less method of drug delivery where a high-speed stream of fluid medication penetrates tissue, has been evaluated pre-clinically for delivery of agents into the buccal mucosa. Ultrasound has been shown to be beneficial in enhancing delivery of macromolecules, including nucleic acids, in pre-clinical animal models. The application of an electric field gradient to drive drugs into tissues through the technique of iontophoresis has been shown to deliver highly toxic chemotherapies into GI tissues. Here in, we provide an in-depth overview of these physical modes of drug delivery in the GI tract and their clinical and preclinical uses.

HER2/neu DNA vaccination by intradermal gene delivery in a mouse tumor model: Gene gun is superior to jet injector in inducing CTL responses and protective immunity

DNA vaccines are potential tools for the induction of immune responses against both infectious disease and cancer. The dermal application of DNA vaccines is of particular interest since the epidermal and dermal layers of the skin are characterized by an abundance of antigen-presenting cells (APCs). The aim of our study was to compare tumor protection as obtained by two different methods of intradermal DNA delivery (gene gun and jet injector) in a well-established HER2/neu mouse tumor model. BALB/c mice were immunized twice with a HER2/neu-coding plasmid by gene gun or jet injector. Mice were then subcutaneously challenged with HER2/neu⁺ syngeneic D2F2/E2 tumor cells. Protection against subsequent challenges with tumor cells as well as humoral and T-cell immune responses induced by the vaccine were monitored. Gene gun immunization was far superior to jet injector both in terms of tumor protection and induction of HER2/neu-specific immune responses. After gene gun immunization, 60% of the mice remained tumor-free until day 140 as compared with 25% after jet injector immunization. Furthermore, gene gun vaccination was able to induce both a strong T_H1-polarized T-cell response with detectable cytotoxic T-lymphocyte (CTL) activity and a humoral immune response against HER2/neu, whereas the jet injector was not. Although the disadvantages that were associated with the use of the jet injector in our model may be overcome with methodological modifications and/or in larger animals, which exhibit a thicker skin and/or subcutaneous muscle tissue, we conclude that gene gun delivery constitutes the method of choice for intradermal DNA delivery in preclinical mouse models and possibly also for the clinical development of DNA-based vaccines.

Improvement of antibody responses by HIV envelope DNA and protein co-immunization

BACKGROUND

Developing HIV envelope (Env) vaccine components that elicit durable and protective antibody responses is an urgent priority, given the results from the RV144 trial. Optimization of both the immunogens and vaccination strategies will be needed to generate potent, durable antibodies. Due to the diversity of HIV, an effective Env-based vaccine will most likely require an extensive coverage of antigenic variants. A vaccine co-delivering Env immunogens as DNA and protein components could provide such coverage. Here, we examine a DNA and protein co-immunization strategy by characterizing the antibody responses and evaluating the relative contribution of each vaccine component.

METHOD

We co-immunized rabbits with representative subtype A or B HIV gp160 plasmid DNA plus Env gp140 trimeric glycoprotein and compared the responses to those obtained with either glycoprotein alone or glycoprotein in combination with empty vector.

RESULTS

DNA and glycoprotein co-immunization was superior to immunization with glycoprotein alone by enhancing antibody kinetics, magnitude, avidity, and neutralizing potency. Importantly, the empty DNA vector did not contribute to these responses. Humoral responses elicited by mismatched DNA and protein components were comparable or higher than the responses produced by the matched vaccines.

CONCLUSION

Our data show that co-delivering DNA and protein can augment antibodies to Env. The rate and magnitude of immune responses suggest that this approach has the potential to streamline vaccine regimens by inducing higher antibody responses using fewer vaccinations, an advantage for a successful HIV vaccine design.

Nanotechnological Approaches for Genetic Immunization

Genetic immunization is one of the important findings that provide multifaceted immunological response against infectious diseases. With the advent of r-DNA technology, it is possible to construct vector with immunologically active genes against specific pathogens. Nevertheless, site-specific delivery of constructed genetic material is an important contributory factor for eliciting specific cellular and humoral immune response. Nanotechnology has demonstrated immense potential for the site-specific delivery of biomolecules. Several polymeric and lipidic nanocarriers have been utilized for the delivery of genetic materials. These systems seem to have better compatibility, low toxicity, economical and capable to delivering biomolecules to intracellular site for the better expression of desired antigens. Further, surface engineering of nanocarriers and targeting approaches have an ability to offer better presentation of antigenic material to immunological cells. This chapter gives an overview of existing and emerging nanotechnological approaches for the delivery of genetic materials.

HIV/SIV DNA vaccine combined with protein in a co-immunization protocol elicits highest humoral responses to envelope in mice and macaques

Vaccination with HIV/SIV DNAs elicits potent T-cell responses. To improve humoral immune responses, we combined DNA and protein in a co-immunization protocol using in vivo electroporation in mice and macaques. DNA&protein co-immunization induced higher antibody responses than DNA or protein alone, or DNA prime/protein boost in mice. DNA&protein co-immunization induced similar levels of cellular responses as those obtained by DNA only vaccination. The inclusion of SIV or HIV Env gp120 protein did not impair the development of cellular immune responses elicited by DNA present in the vaccine regimen. In macaques, the DNA&protein co-immunization regimen also elicited higher levels of humoral responses with broader cross-neutralizing activity. Despite the improved immunogenicity of DNA&protein co-immunization, the protein formulation with the EM-005 (GLA-SE) adjuvant further increased the anti-Env humoral responses. Dissecting the contribution of EM-005, we found that its administration upregulated the expression of co-stimulatory molecules and stimulated cytokine production, especially IL-6, by dendritic cells in vivo. These terminally differentiated, mature, dendritic cells possibly promote higher levels of humoral responses, supporting the inclusion of the EM-005 adjuvant with the vaccine. Thus, DNA&protein co-immunization is a promising strategy to improve the rapidity of development, magnitude and potency of the humoral immune responses.

Induction of humoral and cellular immune responses by antigen-expressing immunostimulatory liposomes

Recently we have shown that liposomes can be used as artificial microbes for the production and delivery of DNA-encoded antigens. These so-called antigen-expressing immunostimulatory liposomes (AnExILs) were superior in inducing antigen-specific antibodies compared to conventional liposomal protein or DNA vaccines when tested in mice after i.m. immunization. In this study, we investigated the capacity of AnExILs to induce T-cell responses. By using a plasmid vector encoding a model antigen under control of both the prokaryotic T7 and the eukaryotic CMV promoter we hypothesized that antigen production could lead to CTL activation via two distinct routes: i. production of antigens inside the AnExILs with subsequent cross-presentation after processing by APCs and ii. endogenous production of antigens after AnExIL-mediated transfection of the pDNA. Although we were not able to demonstrate transfection-mediated expression of luc-NP in mice, i.m. injection of AnExILs producing luc-NP resulted in T-cell responses against the encoded NP epitope, as determined by tetramer staining. T-cell responses were comparable to the responses obtained after i.m. injection of naked pDNA. In order to find out whether CTL activation was caused by cross-presentation of the exogenous antigens produced inside AnExILs or by endogenous antigen production from transfection with the same pDNA source a second study was initiated in which the contribution of each of these effects could be separately determined. These results demonstrate that the observed T-cell responses were not exclusively caused by cross-presentation of the AnExIL-produced antigens alone, but were rather a combination of dose-dependent antigen cross-presentation and low levels of endogenous antigen production.

Needle-free jet injection of small doses of Japanese encephalitis DNA and inactivated vaccine mixture induces neutralizing antibodies in miniature pigs and protects against fetal death and mummification in pregnant sows

Japanese encephalitis (JE) virus causes abortion and stillbirth in swine, and encephalitis in humans and horses. We have previously reported that immunogenicity of a DNA vaccine against JE was synergistically enhanced in mice by co-immunization with a commercial inactivated JE vaccine (JEVAX) under a needle-free injection system. Here, we found that this immunization strategy was also effective in miniature pigs. Because of the synergism, miniature pigs immunized twice with a mixture of 10 μg of DNA and a 1/100 dose of JEVAX developed a high neutralizing antibody titer (1:190 at 90% plaque reduction assay). Even using 1 μg of DNA, 3 of 4 pigs developed neutralizing antibodies. Following challenge, all miniature pigs with detectable neutralizing antibodies were protected against viremia. Pregnant sows inoculated with 10 or 1 μg of DNA mixed with JEVAX (1/100 dose) developed antibody titers of 1:40-1:320. Following challenge, fetal death and mummification were protected against in DNA/JEVAX-immunized sows.

Evaluation of extracellular subviral particles of dengue virus type 2 and Japanese encephalitis virus produced by Spodoptera frugiperda cells for use as vaccine and diagnostic antigens

New or improved vaccines against dengue virus types 1 to 4 (DENV1 to DENV4) and Japanese encephalitis virus (JEV), the causative agents of dengue fever and Japanese encephalitis (JE), respectively, are urgently required. The use of noninfectious subviral extracellular particles (EPs) is an inexpensive and safe strategy for the production of protein-based flavivirus vaccines. Although coexpression of premembrane (prM) and envelope (E) proteins has been demonstrated to produce EPs in mammalian cells, low yields have hindered their commercial application. Therefore, we used an insect cell expression system with Spodoptera frugiperda-derived Sf9 cells to investigate high-level production of DENV2 and JEV EPs. Sf9 cells transfected with the prM and E genes of DENV2 or JEV secreted corresponding viral antigens in a particulate form that were biochemically and biophysically equivalent to the authentic antigens obtained from infected C6/36 mosquito cells. Additionally, equivalent neutralizing antibody titers were induced in mice immunized either with EPs produced by transfected Sf9 cells or with EPs produced by transfected mammalian cells, in the context of coimmunization with a DNA vaccine that expresses EPs. Furthermore, the results of an enzyme-linked immunosorbent assay (ELISA) using an EP antigen derived from Sf9 cells correlated significantly with the results obtained by a neutralization test and an ELISA using an EP antigen derived from mammalian cells. Finally, Sf9 cells could produce 10- to 100-fold larger amounts of E antigen than mammalian cells. These results indicate the potential of Sf9 cells for high-level production of flavivirus protein vaccines and diagnostic antigens.

Possibility and effectiveness of drug delivery to skin by needle-free injector

We evaluated a needle-free injector (NFI), which has been studied as an administration device to the subcutaneous tissue, as a device to deliver drugs into skin tissues. ShimaJet used for self-injection of insulin was selected as a spring-powered NFI in this study. Weak (NFI-w) and strong (NFI-s) injectors were evaluated. Rhodamine 6G, as a model compound, was injected onto the skin surface of hairless rats and the skin distribution and amount released from the skin of the compound were followed. A modified nozzle (able to inject at an angle of 45 degrees ) was prepared in addition to the conventional dedicated nozzle. The spring constants, nozzle shapes and penetration enhancer, 1-[2-(decylthio)ethyl] azacyclopentane-2-one (HPE-101), affected not only the skin distribution, but also the release profiles of rhodamine 6G. In addition, the release profiles of rhodamine 6G after injection using NFI-w or NFI-s obeyed diffusion-controlled or membrane-controlled kinetics, respectively. This difference was probably due to the skin site (depth) of rhodamine 6G delivered by the NFI. Furthermore, HPE-101 increased the retention time of rhodamine 6G in the epidermis. The present results suggested that an NFI can be a useful tool for enhanced drug delivery into skin.

DNA vaccines: ready for prime time?

Since the discovery, over a decade and a half ago, that genetically engineered DNA can be delivered in vaccine form and elicit an immune response, there has been much progress in understanding the basic biology of this platform. A large amount of data has been generated in preclinical model systems, and more sustained cellular responses and more consistent antibody responses are being observed in the clinic. Four DNA vaccine products have recently been approved, all in the area of veterinary medicine. These results suggest a productive future for this technology as more optimized constructs, better trial designs and improved platforms are being brought into the clinic.

Co-immunization with West Nile DNA and inactivated vaccines provides synergistic increases in their immunogenicities in mice

West Nile virus is now distributed throughout many temperate, subtropical and tropical areas: vaccines need to be developed that are affordable for developed and developing countries. Here, we constructed and evaluated a DNA vaccine expressing the premembrane and envelope proteins of West Nile virus (pcWNME). Mice immunized twice with 100 or 10 microg of pcWNME developed high or moderate levels of neutralizing antibodies, respectively. These mice were protected from viremia and death after lethal challenge. Mice immunized with a mixture of 1 microg of pcWNME and a small amount (1/10 dose) of a commercial inactivated vaccine developed moderate levels of neutralizing antibodies, whereas immunization with pcWNME or the inactivated vaccine alone induced only low or undetectable levels: co-immunization with the DNA and protein vaccines synergistically increased their own immunogenicities. The synergism reduced the amount of DNA sufficient to induce neutralizing antibodies: a single immunization with doses as low as 0.1 microg induced a titer of 1:40 at a 90% plaque reduction 6 or 9 weeks after immunization. Both IgG1 and IgG2a antibodies were induced in mice by co-immunization with the DNA and protein vaccines.

Needle-free liquid jet injections: mechanisms and applications

Liquid jet injections employ a high-speed jet to puncture the skin and deliver drugs without the use of a needle. They have been used to deliver a number of macromolecules including vaccines and insulin, as well as small molecules, such as anesthetics and antibiotics. This article reviews liquid jet injectors with respect to their historical perspective, clinical applications, mechanisms and future prospects. An overview of the use of jet injectors for delivery of vaccines, insulin and growth hormones is presented. Particular attention is paid to the mechanistic understanding of jet injections, especially the dependence of jet penetration on parameters such as nozzle diameter, velocity and jet power. Finally, gaps in the current understanding are presented and suggestions for future research and development are made.

Dengue tetravalent DNA vaccine increases its immunogenicity in mice when mixed with a dengue type 2 subunit vaccine or an inactivated Japanese encephalitis vaccine

We previously developed a dengue tetravalent DNA vaccine that can induce neutralizing antibodies against four dengue viruses in mice. Here, we demonstrated that immunogenicity of our tetravalent vaccine is synergistically increased in mice by co-immunization with dengue type 2 virus (DENV2) subviral extracellular particles (D2EPs) or inactivated Japanese encephalitis vaccine (JEVAX). A single immunization with a mixture of 100 microg of the tetravalent vaccine and 150 ng of D2EPs or a 1/10 dose of JEVAX induced moderate levels of neutralizing antibodies in a 90% plaque reduction assay. Immunized mice were protected from "artificial" viremia created by intravenous injection with DENV2.

Current status and future prospects of needle-free liquid jet injectors

Needle-free liquid jet injectors have been used for more than 50 years for parenteral delivery of vaccines and drugs. Although excellent bioavailability has been reported for a number of drugs, occasional pain and bruising have limited wide acceptance of jet injectors. This article reviews jet injectors with respect to their current clinical applications, emerging applications, mechanistic understanding and future prospects.

DNA vaccines: successes and limitations in cancer and infectious disease

Vaccination with plasmid DNA is an active area of investigation that is being applied to diseases including cancer and microbial pathogens associated with infectious diseases. Since its discovery, great progress has been made with the administration of DNA vaccines to initiate specific and effective immune responses against targeted illnesses. However, many obstacles still face its use in prophylactic and therapeutic vaccination scenarios. The nature of these difficulties alongside the successes and future of plasmid DNA will be discussed.