661 - Efficacy and safety of amlitelimab, an anti-OX40 ligand antibody, in patients with moderate-to-severe atopic dermatitis (AD): a phase 2b trial (STREAM-AD)

Abstract Background Amlitelimab is a fully-human, non-depleting, anti-OX40 ligand (OX40L) monoclonal antibody that binds to OX40L on antigen-presenting cells. Amlitelimab blocks the interaction of OX40L with OX40 on activated T-cells, inhibiting T-cell dependent inflammation without depleting T-cells. Objective To evaluate the efficacy and safety of amlitelimab (Part 1), and explore the maintenance of clinical response over a 28-Week period (Part 2) in patients with moderate-to-severe AD. Methods STREAM-AD (NCT05131477), was a randomized, double-blind, placebo-controlled Phase 2b trial, that included a 24-Week, double-blind, treatment period (Part 1), a 28-Week maintenance/withdrawal period (Part 2), and a 16-Week safety follow-up. In Part 1, adult participants were randomized 1:1:1:1:1 to subcutaneous amlitelimab Q4W (250mg with 500mg loading dose [+ LD], n=77; 250mg, n=78; 125mg, n=77; 62.5mg, n=79) or placebo Q4W (n=79). In Part 2, Clinical responders (defined as those achieving EASI-75 and/or IGA 0/1 at Week-24) in Part 1, were rerandomized 3:1 to withdraw or continue pre-Week 24 Q4W dose (250mg + LD, n=34 [withdrawal]/n=13 [continuing]; 250mg, n=28/n=12; 125mg, n=33/n=12; 62.5mg, n=35/n=7; placebo responders continuing placebo, n=16), and were followed to Week-52 to evaluate maintenance of clinical response. Primary efficacy endpoint was percent change in EASI from baseline at Week-16. Key secondary endpoints were proportion of patients achieving IGA 0/1, EASI-75, PP-RNS≥4. The statistical analysis was performed using two methods: 1) imputing the endpoint as nonresponder after rescue medication use (NRI); and 2) including all measurements regardless of rescue use (treatment policy). Results Out of 390 participants enrolled in Part 1, 190 entered Part 2. In Part 1, all four doses of amlitelimab demonstrated statistically significant improvements in percent change in EASI from baseline to Week-16 vs placebo; the highest response was seen with 250mg + LD group. Clinically meaningful improvements in key secondary endpoints were observed at Week-16, with continued improvements through Week-24. In Part 2, maintenance of EASI-75 and/or IGA 0/1 response at Week-52 was observed in 59%, 63%, 55%, and 66% of clinical responders withdrawn from 250mg + LD, 250mg, 125mg, and 62.5mg, respectively (NRI). Using treatment policy, 77%, 82%, 67%, and 74% maintained response off-drug, respectively. Those continuing amlitelimab treatment had numerically higher maintenance response rates. AD-related biomarkers were reduced during Part 1 and remained decreased over Part 2. Amlitelimab was well tolerated across all dose groups, with no new safety concerns identified during the 52-Weeks. Conclusion Clinically meaningful efficacy with amlitelimab was demonstrated over 52-Weeks, with an acceptable safety profile. Clinical responses were maintained in most patients 28-Weeks after treatment discontinuation.