Arialys Therapeutics, a clinical-stage biotechnology company pioneering precision medicines for autoimmune neuropsychiatric diseases, today announced clinical and regulatory progress for ART5803, a novel therapeutic candidate designed using structural biology to specifically inhibit the pathogenic effects of autoantibodies that target the NMDA receptor.
The first patient with anti-NMDA receptor encephalitis (ANRE) has been treated with ART5803 in ART5803-201, an open-label Phase 2a signal-seeking study actively enrolling in the Republic of Korea. In addition, the U.S. Food and Drug Administration (FDA) has cleared Arialys’ investigational new drug (IND) application for ART5803-202, a separate randomized Phase 2 study.
Arialys has also completed Phase 1 single-ascending-dose (SAD) and multiple-ascending-dose (MAD) studies of ART5803 in healthy volunteers. Data presented recently at the American Academy of Neurology 2026 Annual Meeting demonstrated a safety and pharmacokinetic profile, including evidence of blood-brain barrier penetration, supportive of further clinical development in patients with autoimmune neuropsychiatric disease.
“ART5803 is the first therapeutic of its kind and is designed to directly inhibit the pathogenic effects of autoantibodies targeting the NMDA receptor, providing the potential for a precise and rapid treatment for autoimmune neuropsychiatric patients,” said Peter Flynn, Ph.D., President and CEO of Arialys Therapeutics. “With Phase 1 complete, a Phase 2 study actively enrolling in Korea, FDA clearance to advance a randomized Phase 2 study in the U.S., and Orphan Drug and Rare Pediatric Disease designations, Arialys is well positioned to efficiently assess ART5803’s therapeutic potential in ANRE and related autoimmune neuropsychiatric conditions.”
“ANRE is a rare but extremely serious condition for which there are currently no approved therapeutics,” said Dr. Soon-Tae Lee, Professor of Neurology at Seoul National University Hospital. “Patients can exhibit a range of serious and protracted neurological and psychiatric symptoms, often requiring intensive care and ICU hospitalization. ART5803 has a novel therapeutic mechanism of action, and we are motivated to evaluate whether it can support more rapid and complete recovery for patients.”
About ART5803
Arialys scientists used crystallographic structures and pharmacological assessments to develop ART5803, the first precision therapeutic designed to directly inhibit the pathological effects of autoantibodies on the NMDA receptor. ART5803 is a humanized, monovalent monoclonal antibody. In preclinical models, ART5803 rapidly reversed behavioral symptoms caused by NMDAR autoantibody pathogenicity. Arialys has completed Phase 1 SAD and MAD clinical assessments in healthy volunteers. ART5803 demonstrated safety, pharmacokinetic, and CNS penetration profiles supportive of further clinical assessment. Arialys has received Orphan Drug Designation and Rare Pediatric Disease Designation from the U.S. FDA for ART5803.
- Study ART5803-201 is an open-label Phase 2a signal-seeking study in acute and chronic ANRE patients and psychosis patients who exhibit anti-NMDAR autoimmunity. The study is actively enrolling patients in Korea.
- Study ART5803-202 is a randomized, placebo-controlled Phase 2 study in patients with ANRE and is planned to initiate in the United States in the second half of 2026.
About ANRE
Anti-NMDA receptor encephalitis (ANRE) is a rare, life-threatening, 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 disease can cause debilitating neuropsychiatric symptoms, including psychiatric and behavioral alterations, cognitive decline, seizures, coma, and autonomic dysfunction. A significant percentage of ANRE patients are pediatric, and NMDA receptor-specific autoantibodies can also contribute to neurological development deficits. There are no approved therapies for ANRE, and current treatments rely on broad immunosuppressive agents, which are associated with delayed efficacy and significant side effects.
About Autoimmune Neuropsychiatric Disease
Recent findings have identified anti-NMDA receptor autoantibodies in additional neurological and psychiatric diseases, including schizophrenia, depression, bipolar disorder, and dementia. Arialys is initiating clinical assessment of ART5803 in ANRE and anti-NMDA receptor autoantibody-positive psychosis, with plans to evaluate future development in a subpopulation of schizophrenia patients. The company has developed a proprietary high-throughput and highly sensitive assay to screen patient samples for NMDA receptor autoantibodies, supporting the identification of disease indications and patient subpopulations for clinical development.
About Arialys Therapeutics
Arialys was founded by Avalon Bioventures, Catalys Pacific, and MPM BioImpact 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.
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