MoonLake Immunotherapeutics

On September 28, 2025, MoonLake Immunotherapeutics announced disappointing Phase 3 results for its only drug candidate, sonelokimab (“SLK”), revealing that SLK failed to match the efficacy of its competitor, Union Chimique Belge’s bimekizumab-bkz (“BIMZELX”). The Company had repeatedly promoted SLK’s nanobody structure as superior to other monoclonal antibodies—while allegedly failing to disclose it targeted the same molecules and lacked proven advantages.

Following the news, MoonLake’s stock fell $55.74, or 89.9%, to close at $6.24 per share on September 29, 2025, and thereby harming investors.

The complaint filed in this class action alleges that throughout the Class Period, Defendants made materially false and/or misleading statements, as well as failed to disclose material adverse facts about the Company’s business, operations, and prospects. Specifically, Defendants failed to disclose to investors that: (1) that SLK and BIMZELX share the same molecular targets (the inflammatory cytokines IL-17A and IL-17F); (2) that SLK’s distinct Nanobody structure would not confer a superior clinical benefit over the traditional monoclonal structure of BIMZELX; (3) SLK’s distinct Nanobody structure supposed increased tissue penetration would not translate to clinical efficacy; and (4) as a result, Defendants’ positive statements about the Company’s business, operations, and prospects were materially misleading and/or lacked a reasonable basis at all relevant times.