Ellen F. Fynan

Protection of ferrets against influenza challenge with a DNA vaccine to the haemagglutinin

Immunization of ferrets with a plasmid DNA expressing influenza virus haemagglutinin (pCMV/H1 DNA) provided complete protection from challenge with the homologous A/PR/8/34 (H1N1) influenza virus. Delivery of DNA-coated gold beads by gene gun to the epidermis was much more efficient than intramuscular delivery of DNA in aqueous solution. The antibody response induced by DNA delivered by gene gun was more cross-reactive than DNA delivered in aqueous solution or after natural infection. This novel approach to vaccination against influenza may afford broader protection against antigenic drift than that provided by natural infection.

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.

Protective immunity induced by rotavirus DNA vaccines.

It is estimated that Group A rotavirus diarrhea causes as many as one million deaths per year in children worldwide, and effective vaccines will be essential for their control. Plasmid DNA vaccines encoding murine rotaviral proteins VP4, VP6, or VP7 were tested in adult BALB/c mice for their ability to induce immune responses and provide protection against rotavirus challenge. The vaccines were administered by inoculation into cells of the epidermis with an Accell gene gun. (Auragen, Inc., Middleton, WI, USA). Each vaccine elicited rotavirus-specific serum antibodies as measured by ELISA. Virus neutralizing antibodies were detected in mice receiving plasmid DNAs encoding for outer capsid proteins VP4 and VP7, but not for VP6, an inner capsid protein, and all of the vaccines generated virus-specific CTL responses. Each vaccine was effective in protecting mice against infection after homotypic rotavirus (100 ID50) challenge, showing reductions (P < 0.0002) in viral excretion measured over a 9 day period. Increased rotavirus-specific intestinal IgA antibodies were seen in vaccinated mice after rotavirus challenge, particularly in mice that received the VP6 DNA vaccine. This suggests that intracellular IgA-mediated neutralization may be involved in protective immunity induced by the VP6 DNA vaccine, and may represent a new mechanism for protection by DNA vaccines.

Immunity obtained by gene-gun inoculation of a rotavirus DNA vaccine to the abdominal epidermis or anorectal epithelium.

We have previously shown that gene-gun delivery of murine rotavirus DNA vaccines to the epidermis induced protection against rotavirus challenge in mice. In this study, we used a rotavirus group antigen (VP6)-specific DNA vaccine to compare epidermal immunization with immunization to the anorectal epithelium for efficacy in inducing protective immunity. The vaccine was administered into cells of the abdominal epidermis or anorectal epithelium of adult BALB/c mice with an Accell gene-gun (PowderJect, Inc). Vaccines administered by either route elicited rotavirus-specific ELISA antibodies and analysis of the IgG subtypes indicated Th2-type responses were generated by both routes of administration, in contrast to Th1-type responses generated by live rotavirus. Protection against virus challenge was obtained in mice inoculated by either route, as shown by significant reduction of virus excreted in stools. The protection obtained by immunization of the anorectal epithelium was greater than that for epidermal immunization at the same vaccine dose. These results suggest that mucosal immunization of DNA vaccines may be an effective means to generate protective immunity against mucosal pathogens.