Long-Term Administration of BTH2 Hypoallergenic Vaccine Candidate Induces Hallmarks of Allergen Immunotherapy in Murine Model of Blomia tropicalis-Induced Asthma

<b>Background/Objectives</b>: Allergen-specific immunotherapy remains the only disease-modifying treatment for allergic diseases, and the use of recombinant hypoallergenic derivatives is a promising therapeutic approach. Among these, BTH2 has previously shown efficacy in an acute murine model of allergy induced by <i>Blomia tropicalis</i>. The present study aimed to evaluate both the efficacy and safety of BTH2 in a chronic asthma model induced by <i>B. tropicalis</i>. <b>Methods</b>: A/J male mice (<i>n</i> = 6) were sensitized and chronically challenged with <i>B. tropicalis</i> extract over four months. One group repeatedly received subcutaneous doses of BTH2 (25 µg) for three months (65 doses). Parameters of allergic airway inflammation, antibody profiles, cytokine levels, and markers of AIT success were evaluated in bronchoalveolar lavage fluid, lung tissue, serum, and splenocyte cultures. <b>Results</b>: Repeated BTH2 administration was well tolerated, with no signs of systemic toxicity. BTH2 significantly reduced neutrophilic and eosinophilic airway inflammation, while increasing lymphocytes and regulatory cytokines in the lungs. It suppressed IgE against <i>B. tropicalis</i> allergens, while inducing mucosal IgA responses and systemic IgG, which may be linked to the observed blocking antibody activity in BTH2-treated mice. The treatment also led to downregulation of Th2 cytokines and enhanced expression of regulatory and Th1-associated cytokines, especially IL-10, TGF-β and IFN-γ. Correlation matrix analyses indicated that regulatory cytokines were correlated with beneficial antibody responses and reduced inflammation. <b>Conclusions</b>: BTH2 shows strong therapeutic and immunomodulatory effects in a chronic asthma model induced by <i>B. tropicalis</i>, with a favorable safety profile. These findings support its potential for future clinical trials, including those involving patients with allergic asthma.