In Vivo Electroporation Enhances the Immunogenicity of Hepatitis C Virus Nonstructural 3/4A DNA by Increased Local DNA Uptake, Protein Expression, Inflammation, and Infiltration of CD3+ T Cells

Abstract

The mechanisms by which in vivo electroporation (EP) improves the potency of i.m. DNA vaccination were characterized by using the hepatitis C virus nonstructural (NS) 3/4A gene. Following a standard i.m. injection of DNA with or without in vivo EP, plasmid levels peaked immediately at the site of injection and decreased by 4 logs the first week. In vivo EP did not promote plasmid persistence and, depending on the dose, the plasmid was cleared or almost cleared after 60 days. In vivo imaging and immunohistochemistry revealed that protein expression was restricted to the injection site despite the detection of significant levels of plasmid in adjacent muscle groups. In vivo EP increased and prolonged NS3/4A protein expression levels as well as an increased infiltration of CD3+ T cells at the injection site. These factors most likely additively contributed to the enhanced and broadened priming of NS3/4A-specific Abs, CD4+ T cells, CD8+ T cells, and γ-IFN production. The primed CD8+ responses were functional in vivo, resulting in elimination of hepatitis C virus NS3/4A-expressing liver cells in transiently transgenic mice. Collectively, the enhanced protein expression and inflammation at the injection site following in vivo EP contributed to the priming of in vivo functional immune responses. These localized effects most likely help to insure that the strength and duration of the responses are maintained when the vaccine is tested in larger animals, including rabbits and humans. Thus, the combined effects mediated by in vivo EP serves as a potent adjuvant for the NS3/4A-based DNA vaccine.

Serum amyloid P component facilitates DNA clearance and inhibits plasmid transfection: implications for human DNA vaccine

“…We therefore suggest that electroporationadjuvant strategies may have better efficacy in increasing the expression level of DNA vaccines in human applications, which are consistent with the previous reported results. 44,45 However, the electroporation can also induce cytokine secretion and inflammatory cell infiltration in the muscle hours after the treatment, 46,47 which may also facilitate SAP-mediated clearance and limits the efficacy of DNA vaccines. We therefore suggest that electroporation should be preformed immediately after DNA inoculation.…”

DNA Vaccines against Infectious Diseases and Cancer

“…It has been suggested that the main reason for this might be resulting from a lack of APCs at the DNA injection site in humans as there are very few professional APCs in muscles after DNA immunization (Barouch et al, 2002). However, EP, the administration of electrical pulses to muscle or dermal tissue following DNA injection, has been shown to enhance the immunogenicity of DNA vaccines in a wide variety of small and large animal models (Buchan et al, 2005;Folgori et al, 2006;Ahlén et al, 2007;Hooper et al, 2007;Luckay et al, 2007;Hirao et al, 2008b;Rosati et al, 2009). EP functions partially by increasing myocyte permeability and thus facilitating plasmid uptake and antigen expression by host cells (Aihara and Miyazaki, 1998;Rizzuto et al, 1999;Widera et al, 2000;Gronevik et al, 2005).…”

“…It is thought that danger signals caused by EP's needle probes and the electric pulses might be possibly responsible for this immune cell infiltration. These localized effects likely help to insure that the strength and duration of the responses are maintained when the vaccine is tested in larger animals, including rabbits and humans (Ahlén et al, 2007). Thus, it seems likely that EP can induce a more potent immune response through both more uptake of DNA to host cells, leading to more antigen expression, and more recruitment of APCs to the injection site (Fig.…”

“…This improved immunogenicity also showed a more rapid priming of CTL as demonstrated by an NS3/4A-specific tumor-inhibiting immunity. The same group further tested this vaccine in EP delivery, showing that DNA vaccines induce functional CD8+ responses in vivo, resulting in elimination of HCV NS3/4A-expressing liver cells in transiently transgenic mice (Ahlén et al, 2007). It was also reported that EP of a novel candidate DNA vaccine encoding an optimized version of the nonstructural region of HCV (from NS3 to NS5B) induced substantially more potent, broad, and long-lasting CD4+ and CD8+ cellular immunity than naked DNA injection in mice and in rhesus macaques .…”

Noncarrier naked antigen-specific DNA vaccine generates potent antigen-specific immunologic responses and antitumor effects

“…13 DNA vaccine technology also eliminates the need for biocontainment and the risk of exposure to live viral agents. Several modalities have been employed to deliver DNA vaccines, including intramuscular injection using conventional needle and syringe, 3 electroporation, 14 intradermally by the needle-free biojector 15 and epidermally through a gene gun. 16,17 However, one of the concerns regarding DNA vaccines is their limited potency.…”