Induction of immune tolerance in asthmatic mice by vaccination with DNA encoding an allergen-cytotoxic T lymphocyte-associated antigen 4 combination

Allergen-specific immunotherapy is a potential treatment for allergic diseases. We constructed an allergen–cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)-encoding DNA vaccine, administered it directly to antigen-presenting cells (APCs), and investigated its ability and mechanisms to ameliorate allergic airway inflammation in an asthmatic mouse model. An allergen-CTLA-4 DNA plasmid (OVA-CTLA-4-pcDNA_3.1) encoding an ovalbumin (OVA) and the mouse CTLA-4 extracellular domain was constructed and transfected into COS-7 cells to obtain the fusion protein OVA-CTLA-4, which was able to bind the B7 ligand on dendritic cells (DCs), and induced CD25⁺ Foxp3⁺ regulatory T (Treg) cells by the coculture of naive CD4⁺ T cells with DCs in vitro. In an animal study, BALB/c mice were sensitized and challenged with OVA to establish the asthmatic model. Vaccination with a high dose of OVA-CTLA-4-pcDNA_3.1 significantly decreased interleukin-4 (IL-4) and IL-5 levels and eosinophil counts and prevented OVA-induced reduction of the gamma interferon level in the bronchoalveolar lavage fluid. In addition, these mice suffered less severe airway inflammation and had lower levels of OVA-specific IgE and IgG1 titers in serum. Also, high-dose OVA-CTLA-4-pcDNA_3.1 vaccination inhibited the development of airway hyperreactivity and prevented OVA-induced reduction of the percentages of Foxp3⁺ Treg cells in the spleen. Our results indicate that a high dose of allergen-CTLA-4-encoding DNA vaccine was more effective in preventing an allergen-induced Th2-skewed immune response through the induction of Treg cells and may be a new alternative therapy for asthma.