Allergies are an increasing health problem and a large economic burden in industrialized countries, affecting up to 30% of the whole population.
Allergen-specific immunotherapy is still the only causative treatment that alters the disease-eliciting hypersensitivity reaction of the immune system but has various disadvantages. Therefore, more knowledge about intrinsic characteristics of allergens could help to improve allergy vaccines. Furthermore, novel adjuvants that foster the counter-regulation of the disease-eliciting Th2-like response in allergic individuals may contribute to higher efficacy of allergy vaccines.
Here, we compared a potent allergen, Bet v 1, the major birch pollen allergen, with birch GST, a member of the glutathione-S-transferase protein family recently found in high amounts in birch pollen. We demonstrated that birch GST was of low allergenic relevance in a large cohort of birch pollen-allergic patients although it showed a comparable immunogenicity as Bet v 1 in mice. Therefore, we checked both proteins for their release from hydrated birch pollen and found a limited release of birch GST. We concluded that the limited availability of birch GST upon contact of birch pollen with mucosal surfaces results in its low sensitizing capacity. These findings contribute to answer the question what makes an allergen an allergen.
Ligands for Toll-like receptors (TLR) have revealed promising results as adjuvants in allergy vaccines in pre-clinical trials. This tempted us to compare different TLR-ligands regarding their immunomodulatory potential in allergic patients in vitro. We found that different TLR ligands functionally matured monocyte-derived dendritic cells with varying degrees resulting in marked differences in the differentiation of naïve T cells. Thus, not all TLR are equally well suited to be used as adjuvants in allergen-specific immunotherapy. This finding is an important contribution to the development of novel allergy vaccines.
Deduced from our insights we designed different fusion proteins consisting of Bet v 1 and [alpha]A Crystallin, a TLR2/4 ligand, since the direct conjugation of allergens and immunomodulatory agents has several advantages over the mixture of both components. We learnt that various parameters need to be taken into account when engineering such fusion proteins that shall display a reduced IgE-reactivity combined with retained T cell stimulatory activity and immunomodulatory capacity.
Together, this thesis provides new information about factors influencing the allergenicity of proteins as well as on the immune shaping functions of TLR-stimulation.
These findings represent an important contribution to the development of novel vaccines for allergen-specific immunotherapy.