A mimotope gene encoding the major IgE epitope of allergen Phl p 5 for epitope-specific immunization.

A gene vaccine based on a mammalian expression vector containing the sequence of a peptide mimotope of Phl p 5 was constructed. To test whether mimotope gene vaccines can induce allergen-specific antibody responses via molecular mimicry, BALB/c mice were immunized using the mimotope construct with or without a tetanus toxin T-helper epitope. Moreover, intradermal injection was compared to epidermal application via gene gun immunization. Immunization with both mimotope gene constructs elicited allergen-specific antibody responses. As expected, gene gun bombardment induced a Th2-biased immune response, typically associated with IgG1 and IgE antibody production. In contrast, intradermal injection of the vaccine triggered IgG2a antibody expression without any detectable IgE levels, thus biasing the immune response towards Th1. In an RBL assay, mimotope-specific IgG antibodies were able to prevent cross-linking of allergen-specific IgE by Phl p 5. A construct coding for the complete Phl p 5 induced T-cell activation, IFN-gamma and IL-4 production. In contrast, the mimotope-DNA construct being devoid of allergen-specific T-cell epitopes had no capacity to activate allergen-specific T cells. Taken together, our data show that it is feasible to induce blocking IgG antibodies with a mimotope-DNA construct when applied intradermally. Thus the mimotope-DNA strategy has two advantages: (1) the avoidance of IgE induction and (2) the avoidance of triggering allergen-specific T-lymphocytes. We therefore suggest that mimotope gene vaccines are potential candidates for epitope-specific immunotherapy of type I allergy.

Characterization of the protective and therapeutic efficiency of a DNA vaccine encoding the major birch pollen allergen Bet v 1a.

BACKGROUND: An estimated 100 million individuals suffer from birch pollen allergy. More than 95% of birch pollen-allergic subjects react with the major birch pollen allergen Bet v 1a, and almost 60% of them are sensitized exclusively to this allergen. OBJECTIVE: DNA immunization using the Bet v 1a gene was evaluated with respect to its prophylactic and therapeutic efficacy. METHODS: A DNA vaccine containing the entire Bet v 1a cDNA under the control of a CMV-promoter was constructed. In order to estimate the protective efficiency, animals received three injections of this vaccine prior to sensitization with recombinant Bet v 1a. Vice versa, in a therapeutic approach, sensitization was followed by treatment with the DNA vaccine. RESULTS: The Bet v 1a DNA vaccine induced strong Bet v 1-specific antibody responses with a Th1-biased response type. Animals which received the DNA vaccine were protected against a following allergic sensitization with Bet v 1a. The protective effect was characterized by suppression of Bet v 1-specific immunoglobulin (Ig)E production, lack of basophil activation and enhanced interferon (IFN)-gamma expression. In a therapeutic situation, treatment of sensitized animals with DNA vaccines decreased IgE production, IgE-mediated basophil release and drastically reduced anaphylactic activity as measured by passive cutaneous anaphylaxis assays. Concerning the cellular immune response, DNA immunization induced a sustaining and dominant shift from a Th2 type response towards a balanced Th1/Th2 type response as indicated by increased IFN-gamma but unchanged IL-5 levels in lymphoproliferation assays. CONCLUSION: The results demonstrate the allergen-specific protective and therapeutic efficacy of a DNA vaccine encoding the clinically highly relevant allergen Bet v 1a indicating the suitability of this concept for the treatment of allergic diseases.