Coadministration of gamma interferon with DNA vaccine expressing woodchuck hepatitis virus (WHV) core antigen enhances the specific immune response and protects against WHV infection

Abstract

DNA vaccinations are able to induce strong cellular immune responses in mice and confer protection against infectious agents. However, DNA vaccination of large animals appears to be less effective and requires repeated injections of large amounts of plasmid DNA. Enhancement of the efficiency of DNA vaccines may be achieved by coapplication of cytokine-expressing plasmids. Here we investigated, with woodchucks, whether coadministration of an expression plasmid for woodchuck gamma interferon (IFN-gamma), pWIFN-gamma, can improve DNA vaccination with woodchuck hepatitis virus core antigen (WHcAg). Animals were immunized with pWHcIm (a plasmid expressing WHcAg) alone or with a combination of pWHcIm and pWIFN-gamma using a gene gun. Six weeks postimmunization, all animals were challenged with 10(5) genome equivalents of woodchuck hepatitis virus (WHV). The antibody and lymphoproliferative immune responses to WHV proteins were determined after immunization and after challenge. Vaccination with pWHcIm and pWIFN-gamma led to a pronounced lymphoproliferative response to WHcAg and protected woodchucks against subsequent virus challenge. Two of three animals vaccinated with pWHcIm alone did not show a detectable lymphoproliferative response to WHcAg. A low-level WHV infection occurred in these woodchucks after challenge, as WHV DNA was detectable in the serum by PCR. None of the pWHcIm-vaccinated animals showed an anti-WHcAg antibody response after DNA vaccination or an anamnestic response after virus challenge. Our results indicate that coadministration of the WIFN-gamma gene with pWHcIm enhanced the specific cellular immune response and improved the protective efficacy of WHV-specific DNA vaccines.

FIG. 1

Serological profiles of woodchucks after immunization and WHV challenge. (A) Woodchucks immunized with pWHcIm. (B) Woodchucks immunized with pWHcIm and pWIFN-γ. (C) Woodchucks immunized with the control plasmid pcDNA3. The woodchucks were immunized at week −6 and challenged at week 0, as indicated. Antibody reactivity of woodchuck sera to WHsAg (open square) or WHcAg (black square) is shown. The presence of WHV DNA is indicated by a black plus sign for PCR positive and by a white plus sign for PCR and dot blot hybridization positive. Dot blot hybridization was carried out using the titration of a standard (10¹⁰ to 10⁶ copies/ml) and comparing the signals to the experimental signals. All detected signals were in the 10⁶ range except for those of animal 9936 in week 4 (10⁷ copies/ml) and animal 9993 in week 4 (10⁷ copies/ml).

FIG. 1

Serological profiles of woodchucks after immunization and WHV challenge. (A) Woodchucks immunized with pWHcIm. (B) Woodchucks immunized with pWHcIm and pWIFN-γ. (C) Woodchucks immunized with the control plasmid pcDNA3. The woodchucks were immunized at week −6 and challenged at week 0, as indicated. Antibody reactivity of woodchuck sera to WHsAg (open square) or WHcAg (black square) is shown. The presence of WHV DNA is indicated by a black plus sign for PCR positive and by a white plus sign for PCR and dot blot hybridization positive. Dot blot hybridization was carried out using the titration of a standard (10¹⁰ to 10⁶ copies/ml) and comparing the signals to the experimental signals. All detected signals were in the 10⁶ range except for those of animal 9936 in week 4 (10⁷ copies/ml) and animal 9993 in week 4 (10⁷ copies/ml).

FIG. 1

Serological profiles of woodchucks after immunization and WHV challenge. (A) Woodchucks immunized with pWHcIm. (B) Woodchucks immunized with pWHcIm and pWIFN-γ. (C) Woodchucks immunized with the control plasmid pcDNA3. The woodchucks were immunized at week −6 and challenged at week 0, as indicated. Antibody reactivity of woodchuck sera to WHsAg (open square) or WHcAg (black square) is shown. The presence of WHV DNA is indicated by a black plus sign for PCR positive and by a white plus sign for PCR and dot blot hybridization positive. Dot blot hybridization was carried out using the titration of a standard (10¹⁰ to 10⁶ copies/ml) and comparing the signals to the experimental signals. All detected signals were in the 10⁶ range except for those of animal 9936 in week 4 (10⁷ copies/ml) and animal 9993 in week 4 (10⁷ copies/ml).

FIG. 2

Lymphoproliferative responses to WHcAg and WHcAg-derived peptides during the immunization study. Positive results (SI > 3) are indicated by boxes. Numbers stand for peptides as shown in Table 2. C, WHcAg.

FIG. 3

Magnitude of T-cell proliferation induced by the combination vaccination. Lymphocytes derived from vaccinated and challenged woodchucks were stimulated with WHcAg and WHcAg-derived peptides. Results for PBMCs (triplicates) are presented as mean SI.