Methods: House dust mite allergen extract (ALK lyophilised SQ503 Der p, ALK-Abello, Wedel, Germany) was diluted in an aqueous solution of 10% lactose. The solution was spray-dried at various liquid feed rates leading to allergen aerosols with different pre-defined concentrations but a constant mass mean aerodynamic particle diameter of 13.5 µm. Particle size is dependent on the solute (lactose) concentration and can thereby be adjusted accordingly. In a single-blind, five-way cross-over pilot study 18 subjects with allergic rhinitis and sensitization to HDM were allergen-exposed for 4 hours at either 250 SQE/m3, 500 SQE/m3, 1000 SQE/m3, or lactose alone (0 SQE/m3) seven days apart. The dose of 500 SQE/m3 was repeated to investigate reproducibility. Total nasal symptom score (TNSS), anterior rhinomanometry, nasal secretions, exhaled NO, FEV1, and adverse events were assessed prior to and during the exposures.
Results: Allergen exposure was safe and significantly elicited symptoms of AR compared to room air exposure with a mean total nasal symptom score (TNSS) of 3.6±2.0 (mean±SD) at the highest allergen concentration. Lactose alone did not change TNSS (0.7±0.6) compared to pre-challenge level. Repeated exposure to 500 SQE/m3 induced a TNSS which was not different between the two challenge sessions. Objective measures of nasal flow and nasal secretions were in line with clinical symptoms.
Conclusions: We conclude that this universal allergen particle generation is safe, specific, and reproducible and can therefore be used for efficacy testing of immunotherapy.