Non-anaphylactic surface-exposed peptides of the major birch pollen allergen, Bet v 1, for preventive vaccination (1)
The clinical efficacy of specific immunotherapy may have two major disadvantages that must be overcome: first, systemic administration of allergens can induce life-threatening anaphylactic side-effects. Second, immunotherapy is performed with allergen extracts consisting of mixtures of allergenic and non-allergenic components that cannot be tailored to the individual patients’ sensitization profile. The major birch pollen allergen, Bet v 1, contains most of the IgE epitopes present in pollens of trees belonging to the Fagales order (birch, alder, hazel, oak, hornbeam) and in plant-derived food (e.g. apple, carrot, nuts). The recognition of Bet v 1 depends on conformational epitopes and hence requires a folded molecule.
Two of the peptides (P5, P6) comprised sequence motifs that were described to stimulate Bet v 1-specific human T cells, whereas the other four peptides (P1, P2, P3, P4) did not contain relevant Bet v 1-specific human T cell epitopes. only peptide 5 contains a major T cell epitope (BV 139: MGETLLRAVESY), whereas the other five peptides had failed to induce significant T cell proliferation in BALB/c mice.
Neither the individual peptides nor an equimolar mix of the peptides induced release of histamine up to concentrations of 10mg/mL whereas complete rBet v 1 wild-type induced a dose-dependent release of histamine with a maximum release already at a concentration of 1 ng/mL.
Mice in the P – /S – group received a subcutaneous injection of CFA at day 1 and one with Al(OH)3 at day 32. The P – /S+ group received CFA at day 1 and was sensitized with rBet v 1 adsorbed to Al(OH)3 at day 32. Mice of the P+/S – group were treated with CFA-adsorbed peptides at day 1 and received Al(OH)3 at day 32. The P+/ S+ group was treated with CFA-adsorbed peptides and sensitized with Al(OH)3-adsorbed rBet v 1 at day 32.
Prophylactic vaccination with a mix of the six peptides led to a reduction of Bet v 1-specific IgE production in mice. The prophylactic treatment was accompanied by a strong and highly significant induction of Bet v 1-specific IgG responses, whereas almost no induction of Bet v 1-specific IgE levels and skin sensitivity were noted.
RBL degranulation was also blocked when Bet v 1 was added in the presence of rabbit IgG obtained by immunization with the complete Bet v 1 allergen. Addition of preimmune IgG from peptide- or rBet v 1-immunized rabbits did not reduce Bet v 1-induced RBL degranulation.
None of the Bet v 1 allergic patients showed IgE reactivity to the peptides and the peptides did not induce histamine release or skin reactions in patients. The lack of allergenic activity of the Bet v 1-derived peptides can be explained by the absence of secondary structure of the peptides because birch pollen-allergic patients IgE antibodies primarily recognize conformational epitopes.