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September 25, 2025

Arialys Therapeutics Receives FDA Rare Pediatric Disease Designation for ART5803 to Treat Anti-NMDA Receptor Encephalitis

La Jolla, Calif., September 25, 2025 – Arialys Therapeutics, a clinical-stage biotechnology company pioneering new precision medicines for autoimmune neuropsychiatric diseases, today announced that the U.S. Food and Drug Administration (FDA) has granted Rare Pediatric Disease Designation to ART5803 for the treatment of pediatric patients with anti-NMDA receptor encephalitis (ANRE). ART5803 is a novel precision therapeutic candidate designed using structural biology to specifically inhibit the pathogenic effects of autoantibodies that target the NMDA receptor. Dosing of Phase 1 single- and multiple-ascending dose (SAD and MAD) studies in healthy volunteers has been completed, and Phase 2 evaluation in both ANRE and autoimmune psychosis patients is currently being initiated.

“ANRE is a rare autoimmune condition affecting both adults and children for which there is currently no approved therapy,” said Peter Flynn, Ph.D., President and CEO of Arialys Therapeutics. “The Rare Pediatric Disease Designation recognizes the severity of ANRE as well as the potential of ART5803, a precision medicine specifically designed to rapidly reverse the symptoms of anti-NMDA receptor autoimmunity, to meet a significant unmet medical need for these rare pediatric patients.”

The FDA grants Rare Pediatric Disease Designation for serious and life-threatening diseases that primarily affect children ages 18 years or younger and fewer than 200,000 people in the United States. If a Biologics Licensing Application (BLA) for ART5803 for the treatment of pediatric ANRE is approved by the FDA as a rare pediatric disease application, Arialys may be eligible to receive a Priority Review Voucher (PRV) that can be redeemed to receive a priority review for any subsequent marketing application or may be sold or transferred. This program is intended to encourage the development of new drugs and biologics for the treatment of rare pediatric diseases.

About ART5803

ART5803 is a humanized, monovalent monoclonal antibody therapeutic. Arialys scientists used crystallographic structures and pharmacological assessments to develop ART5803 as a precision therapeutic that reverses the pathological effects of autoantibodies that target the NMDA receptor. In preclinical models, ART5803 exhibited rapid reversal of behavioral symptoms caused by NMDAR autoantibody pathogenicity. Arialys has completed dosing in Phase 1 SAD and MAD clinical assessments in healthy volunteers. ART5803 was well tolerated, demonstrating safety, pharmacokinetics, and CNS penetration conducive to further clinical assessment (ClinicalTrials.gov Identifier: NCT06575153). The company expects to share detailed clinical data in early 2026. Phase 2 evaluation of ART5803 in both ANRE and autoimmune psychosis patients is being initiated in Australia (ClinicalTrials.gov Identifier: NCT07093333). Arialys has received Orphan Drug Designation and now Rare Pediatric Designation from the U.S. FDA for ART5803.

About ANRE

Anti-NMDA receptor encephalitis (ANRE) is a rare, potentially lethal, poorly managed, and often misdiagnosed neurological disease. ANRE is caused by pathogenic autoantibodies that bind to and crosslink NMDA receptors in the brain, leading to receptor internalization and synaptic dysfunction. The result is a range of debilitating neuropsychiatric symptoms including psychiatric and behavioral alterations, cognitive decline, seizures, coma, and diminished autonomic function. A significant percentage of ANRE patients are pediatric, where NMDA receptor-specific autoantibodies can also result in neurological development deficits. There are no approved therapies for this disease, and current treatments rely on broad immunosuppressive agents, which are associated with delayed efficacy and significant side effects.

Recent findings have also identified anti-NMDA receptor autoantibodies in other neurological and psychiatric diseases such as schizophrenia, depression, bipolar disorder and dementia. Arialys is initiating clinical assessment of ART5803 in both ANRE and anti-NMDA receptor autoantibody-positive psychosis patients. Further, the company is currently testing patient samples using a proprietary high-throughput screen for NMDA receptor autoantibodies to identify disease indications and subpopulations for future clinical development.

About Arialys Therapeutics

Arialys was founded by Avalon Bioventures, Catalys Pacific, and MPM to meaningfully expand the treatment possibilities for neuropsychiatric disorders driven by autoimmune disease. Using a combination of highly sensitive autoantibody detection, patient sampling and receptor structural biology, Arialys has developed a first-in-class precision therapy to specifically block pathogenic autoantibodies in the brain. Arialys is headquartered in La Jolla, California. For more information, visit www.arialysrx.com.

Contacts

Media: Jessica Yingling, Ph.D., Little Dog Communications Inc., jessica@litldog.com

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