Microcrystalline Tyrosine and Aluminum as Adjuvants in Allergen-Specific Immunotherapy Protect from IgE-Mediated Reactivity in Mouse Models and Act Independently of Inflammasome and TLR Signaling.

Allergen immunotherapy (AIT) is the only modality that can modify immune responses to allergen exposure, but therapeutic coverage is low. One strategy to improve AIT safety and efficacy is the use of new or improved adjuvants. This study investigates immune responses produced by microcrystalline tyrosine (MCT)-based vaccines as compared with conventional aluminum hydroxide (alum). Wild-type, immune-signaling-deficient, and TCR-transgenic mice were treated with different Ags (e.g., OVA and cat dander Fel d 1), plus MCT or alum as depot adjuvants. Specific Ab responses in serum were measured by ELISA, whereas cytokine secretion was measured both in culture supernatants by ELISA or by flow cytometry of spleen cells. Upon initiation of AIT in allergic mice, body temperature and further clinical signs were used as indicators for anaphylaxis. Overall, MCT and alum induced comparable B and T cell responses, which were independent of TLR signaling. Alum induced stronger IgE and IL-4 secretion than MCT. MCT and alum induced caspase-dependent IL-1ß secretion in human monocytes in vitro, but inflammasome activation had no functional effect on inflammatory and Ab responses measured in vivo. In sensitized mice, AIT with MCT-adjuvanted allergens caused fewer anaphylactic reactions compared with alum-adjuvanted allergens. As depot adjuvants, MCT and alum are comparably effective in strength and mechanism of Ag-specific IgG induction and induction of T cell responses. The biocompatible and biodegradable MCT seems therefore a suitable alternative adjuvant to alum-based vaccines and AIT.

Intraperitoneal administration of aluminium-based adjuvants produces severe transient systemic adverse events in mice.

Vaccines typically come with adjuvants that trigger the innate immune system in order to prepare best possible inflammatory conditions as to allow the adaptive immune system to become activated, generally for the induction of antibodies. The oldest approved and most abundant immunological adjuvants are salts of aluminium, which are also frequently used in animal models of immunisation and allergy desensitization. In rodents, the intraperitoneal administration of aluminium adjuvants is commonly performed and considered safe. In the current investigation, we show that intraperitoneal administration of aluminium adjuvants is associated with a dose-dependent hypothermic reaction within 10 min of the injection. The body temperature of mice dropped as much as 4 °C, and the clinical symptoms included apathy, hunched posture, and piloerection. The temperature normalised and other clinical manifestations disappeared within 60-80 min of the intraperitoneal aluminium injection, which caused strong infiltration of neutrophil and eosinophil granulocytes into the peritoneal cavity, a clinical manifestations typically associated with inflammasome activation. However, the observed reactions to aluminium adjuvants were independent of NALP3, caspase-1, and interleukin-1ß, but dependent on histamine. Hence, aluminium adjuvants may have potential local and systemic side effects, which warrants further investigations into the nature of these side effects, but also into the possible implications on health in man.