Immune Response of Individuals Vaccinated With Hypoallergenic Derivatives of the Major Birch Pollen Allergen, Bet v 1

The only disease-modifying treatment for allergic disorders nowadays is allergen-specific immunotherapy (SIT). To induce hyporesponsiveness increasing doses of the disease-eliciting allergens are applied. One major problem of this treatment is, that it has to combat with an already established immune response against the disease-eliciting allergen. To circumvent this problem the investigators want to perform the proof of principle study towards prophylactic treatment. Prophylactic vaccination is used since many years for many infectious diseases. The investigators want to adopt this successful principle for the treatment of type I allergies.

For this purpose non-allergic healthy individuals will be immunized with adjuvant-bound hypoallergenic derivatives of the major birch pollen allergen, Bet v 1. As usual for allergen-specific immunotherapy, injections will be applied subcutaneously. Three injections in one-monthly intervals will be given to establish the immune response and a further injection after one year will determine how the vaccine-induced immune response can be boosted.

The vaccine will be composed of an equimolar mixture of two adjuvant-bound hypoallergenic derivatives of the major birch pollen allergen, Bet v 1. The first investigational product (IP) designated as Bet v 1aF1 is a protein of 73 amino acid residues and represents the first half (1-73aa) of the Bet v 1 molecule. The second IP, Bet v 1aF2, is a protein of 86 amino acid residues and represents the second half (74-160aa) of Bet v 1. Both proteins are expressed in Escherichia coli. The hypoallergenic derivatives lost their IgE binding capacities by the disruption of the conformational IgE epitopes of the Bet v 1 molecule.

In several preclinical and clinical studies it has been shown that the two hypoallergenic fragments, Bet v 1aF1 and Bet v 1aF2 have a strongly reduced allergenic reactivity and almost no sensitization potential, requisite for a prophylactic treatment. In a multi-centre placebo-controlled double blind clinical trial including 124 allergic patients no relevant sensitization against new epitopes could be observed after vaccination of the Alum-bound Bet v 1 derivatives.

In contrast, the vaccine induced a strong IgG response in animals as well as in clinical studies. Vaccine-induced antibodies showed protective properties as they could inhibit the binding of allergic patients' IgE. An improvement of clinical symptoms and a reduction of the skin reactivity was correlated with an increase of IgG antibodies and could be shown only in actively treated patients in a multi-centre placebo-controlled double blind clinical trial.

The investigational products will be tested in a Phase I clinical trial for prophylactic allergy vaccination in healthy non-allergic subjects. The two IPs will be coupled either to Alum and an equimolar mixture will be injected subcutaneously. The immune responses will be compared to placebo. In total 20 non-allergic healthy male subjects (10 per group) will be included in this clinical trial. For safety precautions the subjects will be monitored by skin prick testing using the two uncoupled IPs and commercial birch pollen extract in short intervals to recognize possible vaccine-induced sensitizations. The primary endpoint of phase I clinical trial is the evolution of Bet v 1-specific and Bet v 1 fragment-specific IgG1-4, IgE and IgM antibody levels in serum and in nasal fluids after vaccination of rBet v 1 derivatives.