Validation of an environmental exposure unit for controlled human inhalation studies with grass pollen in patients with seasonal allergic rhinitis

Background There is an increasing need for allergen inhalation systems to perform basic clinical research and test anti-allergic drugs under well-controlled conditions. This requires stability of environmental conditions like temperature and humidity, as well as allergen concentration and reproducible induction of allergic symptoms. Objective The aim of this study was to validate an environmental exposure unit for controlled human pollen inhalation studies in participants with seasonal allergic rhinitis. Methods Temperature, relative humidity, and air flow rate were kept constant with an air conditioning system. Pollen atmosphere was generated using a specially designed feeding system and monitored online by laser counter and offline using rotating rod samplers. Efficacy (total nasal symptom score, nasal air flow rate, nasal secretion) and safety (lung function) parameters were evaluated at different pollen concentrations and repeated allergen challenges. Results Temperature, humidity, and air flow rate in the environmental exposure unit remained constant within a range of <2%. The spatial distribution and the temporal stability of the pollen concentration varied only slightly over 4 h (+/-10% and <4%, respectively). Dose-dependent induction of allergic rhinitis symptoms, reduction in nasal air flow rate, and increase in nasal secretion were observed over time. These effects were reproducible from day to day. Lung function remained clinically normal at all concentrations and from day to day. Conclusions Thus, pollen exposure in the environmental exposure unit is an effective, reproducible, safe, and suitable method for single-centre clinical studies on the efficacy of anti-allergic treatment or basic clinical research.