Methods: The Red Maple Trials (RMT) Allergen Challenge Theatre (ACT) is a 4-zone facility holding up to 100 seats in a series of elevated rows. Grass pollen (Phleum pratense) was injected into the air supply and blown into the facility through ducts located across the top of the front wall. A technical validation was performed to determine stability and uniformity of pollen concentrations in the room. Pollen counts were measured by a laser particle counter (LPC) positioned 5 ft above floor level and by impact samplers (IS) set at face level. IS were installed in 5 sections of a T-shaped quadrant and measurements taken every 30 minutes for 180 minutes. To evaluate the clinical response to grass pollen exposure, subjects with a history of grass allergy and positive skin prick test underwent two 3-hour challenges to grass pollen. Nasal and ocular symptom scores were recorded at baseline and every 30 min during the challenge.
Results: For the technical validation, pollen counts measured by LPC were stable for 3 hours at 4,800 ± 500 g/m3. LPC pollen counts correlated well with IS counts over a range from 1,500 to 7,500 g/m3 (LPC =0.849IS -269.0, r2=0.85). Mean pollen counts in each of the 5 sections of the quadrant ranged from 2,821 ±303 to 5,726 ±249. For the clinical validation, 17/32 patients had at least one Total Nasal Symptom Score (TNSS) ≥5 at challenge 1. In these subjects, mean change from baseline TNSS was 4.35±2.32 for challenge 1 and 4.94±2.41 at challenge 2, p=0.48. Total ocular symptom scores (TOSS) were 1.29±1.31 and 2.29±2.17, p=0.029, respectively.
Conclusion: The Red Maple Trials ACT demonstrated the capacity to achieve and maintain a stable grass pollen concentration associated with the ability to induce nasal and ocular symptoms of appropriate intensity upon a three-hour allergen challenge.