Immunological Effects of Treatment with STG320 Sublingual Tablets of House Dust Mite Allergen Extracts in Subjects with HDM-Associated Allergic Asthma

Rationale: A clinical development program investigating the efficacy and safety of house dust mite (HDM) sublingual tablets (STG320) in adults with HDM-associated allergic asthma is ongoing. Here we present immunological data from a phase II study evaluating the effect of three doses of STG320 compared to placebo.

Methods: This DBPC, dose-ranging study enrolled subjects (18-50 years) whose asthma was partly controlled [Asthma Control Test™ (ACT) 16-19] while receiving asthma therapies consistent with GINA treatment Steps 2 to 4. Eligible subjects were to have a positive skin prick test to HDM and HDM-specific serum IgE ≥0.7 kU/L. Participants were randomized to receive 100IR, 500IR or 1000IR of STG320 or placebo, daily for about 13 months. The primary endpoint was the ACT score after the treatment period. HDM-specific IgE and IgG₄assessed before and after treatment and fold-changes were analyzed descriptively in each group. Safety data were analyzed descriptively.

Results: Of 386 randomized subjects, 344 were included in the analysis (100IR: 88, 500IR: 87, 1000IR: 81, placebo: 88). The primary endpoint was not met. At baseline, HDM-specific IgE and IgG₄ were similar in the four treatment groups. After treatment, HDM-specific IgE increased by 1.5- to 2-fold in the active groups, and was unchanged in the placebo group. Changes in IgG₄ increased with the dose, from 3-fold (100IR) to 6-fold (1000IR), and were unchanged for placebo. No unexpected adverse events were observed.

Conclusions: In this study, the HDM sublingual tablet showed a dose-dependent effect based on its immunological activity.