Subcutaneous allergen immunotherapy for asthma: A randomized, double-blind, placebo-controlled study with a standardized Blomia tropicalis vaccine

Abstract

BackgroundSensitization to Blomia tropicalis (Bt) is very frequent in the tropics, and particularly in Cuba, being a significant cause of allergic asthma. Allergen immunotherapy (AIT) with Bt can be a therapeutic option, however, placebo-controlled clinical trials have not been reported. ObjectiveTo assess the therapeutic effect and safety of AIT for asthma using a standardized allergen vaccine of B. tropicalis by subcutaneous route, in allergic asthmatic patients exposed and sensitized to this mite species. MethodsA double-blind, placebo-controlled Phase II trial was conducted in 35 adults (18 with treatment and 17 with placebo), with mild to moderate asthma, predominantly sensitized to Bt. AIT was administered subcutaneously in increasing doses from 4 to 6000 Biological Units using a locally manufactured standardized extract (BIOCEN, Cuba). Patient assessment was performed using symptom-medication score (SMS), peak expiratory flow and skin reactivity relative to Histamine as measured by skin prick test (SPT). ResultsThe 12-month treatment achieved a significant (p < 0.001) decrease of SMS. Symptom score showed only 41% (CI: 26–61) of placebo values, whereas medication was 34.5% (22.4%–63.3%). Treatment was regarded clinically effective in 67% of patients (OR 32; 95%CI: 17 to 102). The effect size on symptoms and medication was higher than has been reported with equivalent allergen dosages of D. pteronyssinus and D. siboney in Cuban asthmatic patients. Skin reactivity to Bt was also significantly reduced (p = 0.0001), increasing 148-fold the allergen threshold to elicit a positive skin test. This desensitization effect was specific to Bt and did not modify the reactivity to Dermatophagoides. The change of specific skin reactivity was significantly (p < 0.05) correlated to clinical improvement. All adverse events were local with a frequency of 2.4% of injections. ConclusionsSubcutaneous AIT with Blomia tropicalis was effective and safe in asthmatic adults exposed and sensitized to this mite species in a tropical environment. Trial registrationCuban Public Registry of Clinical Trials: RPCEC00000026 (WHO International Clinical Trial Registry Platform ICTRP).