【Purpose】PF-06823859 is a potent, selective, humanized immunoglobulin G1 antibody against the interferon β (IFNβ) cytokine that is currently being investigated in several subtypes of idiopathic, inflammatory myopathies, including dermatomyositis. This study assessed the safety, tolerability, immunogenicity, and pharmacokinetics (PK) of PF-06823859 in healthy Japanese participants.【Methods】This randomized, double-blind, Phase 1 study (NCT05037409) enrolled healthy Japanese participants. The study consisted of two cohorts in which participants were randomized at a ratio of 5:1 to receive a single intravenous (IV) infusion of PF-06823859 (300 mg or 900 mg) or placebo. The primary endpoint was the incidence of treatment-emergent adverse events (TEAEs) and serious adverse events, and clinically significant changes in vital signs, electrocardiograms (ECGs), and laboratory tests. Serum PF-06823859 PK parameters and immunogenicity will also be assessed.【Results/Considerations】Twelve participants (66.7% male; 21-52 years of age) completed treatment (PF-06823859 300 mg, n=5; PF-06823859 900 mg, n=5; placebo, n=2). In total, five (41.7%) participants experienced nine TEAEs (PF-06823859 300 mg, n=5 events in four participants; PF 06823859 900 mg, n=4 events in one participant). The majority of TEAEs were mild in severity. No significant changes in vital signs or ECGs were reported during the study. There were no infusion-related reactions or infusion-site reactions reported during the study. One participant in the PF-06823859 900 mg group reported a mild viral infection of nasopharyngitis; however, this was deemed to be unrelated to the study treatment. No herpes zoster infections were reported in the study. 【Conclusion】PF-06823859 up to 900 mg as a single IV infusion demonstrated an acceptable safety profile in healthy Japanese participants, which supports the further clinical development in Japan as a treatment for diseases caused by increased IFNβ levels.