Adjuvant effects of aluminium hydroxide-adsorbed allergens and allergoids - differences in vivo and in vitro.

Allergen-specific immunotherapy (SIT) is a clinically effective therapy for immunoglobulin (Ig)E-mediated allergic diseases. To reduce the risk of IgE-mediated side effects, chemically modified allergoids have been introduced. Furthermore, adsorbance of allergens to aluminium hydroxide (alum) is widely used to enhance the immune response. The mechanisms behind the adjuvant effect of alum are still not completely understood. In the present study we analysed the effects of alum-adsorbed allergens and allergoids on their immunogenicity in vitro and in vivo and their ability to activate basophils of allergic donors. Human monocyte derived dendritic cells (DC) were incubated with native Phleum pratense or Betula verrucosa allergen extract or formaldehyde- or glutaraldehyde-modified allergoids, adsorbed or unadsorbed to alum. After maturation, DC were co-cultivated with autologous CD4(+) T cells. Allergenicity was tested by leukotriene and histamine release of human basophils. Finally, in-vivo immunogenicity was analysed by IgG production of immunized mice. T cell proliferation as well as interleukin (IL)-4, IL-13, IL-10 and interferon (IFN)-γ production were strongly decreased using glutaraldehyde-modified allergoids, but did not differ between alum-adsorbed allergens or allergoids and the corresponding unadsorbed preparations. Glutaraldehyde modification also led to a decreased leukotriene and histamine release compared to native allergens, being further decreased by adsorption to alum. In vivo, immunogenicity was reduced for allergoids which could be partly restored by adsorption to alum. Our results suggest that adsorption of native allergens or modified allergoids to alum had no consistent adjuvant effect but led to a reduced allergenicity in vitro, while we observed an adjuvant effect regarding IgG production in vivo.

Gram-positive bacteria on grass pollen exhibit adjuvant activity inducing inflammatory T cell responses.

BACKGROUND: Recently, it has been established that pollen grains contain Th2-enhancing activities besides allergens. OBJECTIVE: The aim of this study was to analyse whether pollen carry additional adjuvant factors like microbes and what immunological effects they may exert. METHODS: Timothy pollen grains were collected and disseminated on agar plates, and the growing microorganisms were cultivated and defined. Furthermore, the immunologic effects of microbial products on DC and T cell responses were analysed. RESULTS: A complex mixture of bacteria and moulds was detected on grass pollen. Besides Gram-negative bacteria that are known to favour Th1-directed immune responses, moulds were identified as being sources of allergens themselves. Herein, we focused on Gram-positive bacteria that were found in high numbers, e.g. Bacillus cereus and Bacillus subtilis. Contact of immature dendritic cells (DC) from grass pollen allergic donors with supernatants of homogenized Gram-positive bacteria induced maturation of DC as measured by up-regulation of CD80, CD83 and CD86 and by enhanced production of IL-6, IL-12p40 and TNF-α, which was less pronounced compared with effects induced by lipopolysaccharide (LPS). Consequently, stimulation of autologous CD4(+) T cells with supernatants of homogenized Gram-positive bacteria plus grass pollen allergen-pulsed DC led to an enhanced proliferation and production of IL-4, IL-13, IL-10, IL-17, IL-22 and IFN-γ production compared with T cells that were stimulated with allergen-pulsed immature DC alone, whereas production of the transcription factor for regulatory T cells FoxP3 was not significantly affected. CONCLUSIONS AND CLINICAL RELEVANCE: These data indicate that grass pollen is colonized by several microorganisms that influence the immune response differently. Similar to LPS, supernatants of homogenized Gram-positive bacteria may serve as adjuvants by augmenting DC maturation and inflammatory Th1, Th2 and Th17 responses helping to initiate allergic immune responses.

An alternative allergen:adjuvant formulation potentiates the immunogenicity and reduces allergenicity of a novel subcutaneous immunotherapy product for treatment of grass-pollen allergy.

BACKGROUND: Subcutaneous specific immunotherapy (SCIT) has proven sustained clinical efficacy against allergy. The recommended regimen for SCIT is a gradual updosing over a period of weeks. Commonly, in commercial products for SCIT, the specific allergen is formulated with an adjuvant, most often in the form of aluminium hydroxide (AlOH). It has been shown that allergen-specific IgG antibodies are induced as a result of successful SIT. OBJECTIVE: To investigate the possibility of optimizing the formulation of AlOH-based grass-pollen allergy vaccines for SCIT in a way that allows for shorter updosing regimens while maintaining the immunogenicity of the vaccine. METHODS: Mice were immunized with various concentrations of Phleum pratense (Phl p) allergen extract and AlOH or a fixed dilution of the maintenance doses of one conventional and one alternatively formulated vaccine. The kinetics of Phl p-specific IgG antibody responses in serum and spleen T cell responses were determined. Allergenicity, measured as the ability of the formulations to activate human basophils, was also determined. In addition, human T cell responses and the expression of dendritic cell surface markers after vaccine challenge in vitro were analysed. RESULTS: Specific IgG antibody responses were shown to depend on the AlOH concentration, but not on the allergen concentrations. The immunogenicity of the conventional formulation and the alternative formulation was shown to be similar with regard to the in vivo-induced IgG and T cell responses. In contrast, the allergenicity of the alternative formulation was significantly reduced compared with the conventional formulation. CONCLUSION: The optimization of the formulation allows for administration of a lower dose of allergen while maintaining the immunogenicity of the product and at the same time reducing allergenicity. CLINICAL RELEVANCE: This study indicates that the optimization of the allergen and the adjuvant formulation could benefit the safety/efficacy profile and allow for shorter updosing.