Sanofi (Nasdaq: SNY) announced on July 24, 2026 that it will not submit amlitelimab (SAR445229, KY1005), its OX40-ligand monoclonal antibody, for regulatory review in moderate-to-severe atopic dermatitis anywhere in the world, and is discontinuing clinical development of the drug in that indication. The decision ends a multi-year program that had generated positive Phase III data as recently as March 2026.
Sanofi said the totality of efficacy and safety evidence does not support further development in atopic dermatitis, and that amlitelimab "would not represent a meaningful improvement to the standard of care." The ESTUARY Phase III long-term extension study (NCT06407934) demonstrated maintenance of clinical response without relapse in patients aged 12 and older, but those results were insufficient to justify a filing. Full data from ESTUARY will be presented at a forthcoming medical meeting.
The decision is a reversal of the company's stated position as recently as April 2026, when management defended amlitelimab's regulatory submission timeline for H2 2026 on the Q1 earnings call, citing physician and payer enthusiasm and characterizing two cases of Kaposi's sarcoma across approximately 4,500 exposed patients as manageable. That safety signal — two cutaneous cases in patients with known risk factors, both resolving after treatment discontinuation — had drawn analyst scrutiny given that Kyowa Kirin and Amgen had previously discontinued their OX40-pathway program on similar grounds.
The abandoned program had produced statistically significant Phase III results across three trials. Data presented at the American Academy of Dermatology in March 2026 from COAST 1, COAST 2, and SHORE showed amlitelimab met primary endpoints in monotherapy and combination settings, with vIGA-AD 0/1 response rates of 21–32% across active arms versus 9–17% for placebo at Week 24. The drug's once-every-12-week dosing schedule had been positioned as a potential differentiator against approved biologics that require two- to four-weekly injections.