Deviation of the Allergic IgE to an IgG Response by Gene Immunotherapy

Abstract

The Th1/Th2 type immune response to E. coli β-galactosidase (β-gal) was compared to that to gene vaccination with plasmid (p) DNA encoding β-gal. BALB/c mice were immunized with β-gal in alum or a pDNA construct consisting of a CMV-based promoter and the β-gal gene (pCMV-LacZ). β-gal in alum induced IgGl and IgE antibodies and the CD4+ T cells from these mice secreted interleukin 4 (IL-4) and IL-5 but no interferon-γ (IFN-γ) after in vitro antigen stimulation. In contrast, mice immunized with pCMV-LacZ formed predominantly IgG2a antibodies and their CD4+ T cells secreted IFN-γ but no IL-4 and IL-5. These data indicate that β-gal induced a Th2 and the pCMV-LacZ a Th1 response to β-gal. The pDNA induced Th1 response dominated over the Th2 response. Mice primed with pCMV-LacZ failed to produce IgE antibodies after a booster injection of β-gal in alum. Boosting of mice primed with β-gal in alum with pCMV-LacZ resulted in a 75% decrease in the IgE antibody liter within 6 weeks and IgG2a antibody formation and CD4+ T cells that secreted IFN-γ in amounts similar to T cells from pDNA primed mice. As shown by adoptive cell transfer, both CD4+ and CD8+ T cells from pDNA immunized mice inhibited an IgE response to β-gal in alum in the recipient mice. pDNA immunization also inhibited the eosinophilic infiltration of the lung of ovalburnin (OVA) immunized mice after OVA inhalation challenge in an animal model of the late phase reaction. The mechanism of the pDNA induced Th1 immune response was shown to be the result of stimulation by distinct non-coding immunostimulatory DNA sequences (ISS) in the backbone of the pDNA. The ISS induced antigen presenting cells to secrete cytokines that cause naive T cells to differentiate into Th1 cells (e.g. IFN-α, IL-12). The data indicate that gene vaccination induces a Th1 immune response that is capable of down-regulating a preexisting Th2 response and IgE antibody formation. Thus, immunization with pDNA encoding for allergens may provide a novel type of immunotherapy for allergic diseases.

Key Words:

• Gene immunotherapy
• Th1 immune response
• IgE
• DNA
• immunostimulatory sequences
• Gene vaccination