Microcrystalline tyrosine as a novel depot-forming agent in venom immunotherapy: a pre-clinical evaluation in bee-venom allergic mice.

Background: Venom immunotherapy (VIT) with aqueous venom extracts is a standard treatment for severe insect venom allergies. In other fields of allergen immunotherapy (AIT), depot adjuvants have been used for decades, with benefits for both safety and efficacy. Biodegradable microcrystalline tyrosine (MCT), is well-established in AIT, and has proven both safe and effective through sustained release and adjuvancy. The objective of the current study was to evaluate MCT as a depot-forming agent in VIT using a murine model of bee venom allergy. Materials and methods: Mice were sensitised with bee venom extract and then received subcutaneous immunotherapy (SCIT) with 10, 50, or 100 µg aqueous venom extracts or venom formulated with MCT or aluminium hydroxide (alum) as depot-forming agents. Systemic reactions upon VIT and challenge were assessed by measuring body temperature, while antigen-specific IgE and IgG responses were analysed by ELISA. Mast cell degranulation was evaluated by serum MCPT-1 levels. Results: VIT with MCT significantly improved survival, reduced body temperature changes, and promoted robust IgG1 and IgG2b responses. While antibody responses were comparable between MCT and alum at higher VIT doses (50 and 100 µg), MCT also induced significant IgG responses at lower doses (10 µg), indicating enhanced sensitivity of the immune response to MCT. MCT-treated mice further exhibited reduced mast-cell degranulation compared to untreated controls, consistent with a reduced risk of anaphylaxis. Conclusion: VIT with bee venom extract and MCT enabled safe and effective VIT by promoting protective IgG responses and reducing systemic reactions. These findings further support the evaluation of MCT as a complement to aqueous allergen extracts in VIT for human use.