A Study to Assess THN391 in Subjects With Alzheimer's Disease

This is a Phase 1b, randomized, double-blind, multi-center, placebo-controlled, multiple ascending dose trial in male and female participants, aged 60 to 85 years with Early Alzheimer's disease and cSVD. For the 3 dose administration group, the study duration is approximately 8 months: first screening to assess eligibility, then 2 months' treatment period (3 monthly doses), followed by a 6 month follow-up period. For the 6 dose administration group (starting in January 2026), the study duration is approximately 11 months: first screening to assess eligibility, then 5 months' treatment period (6 monthly doses), followed by a 6 month follow-up period. The trial will investigate THN391 in at least 3 dose cohorts, Depending on preliminary, blinded results of the first two cohorts, the sample sizes of the following dose cohort may be increased and/or additional dose cohorts may be added. Eligible participants will be randomized to receive either THN391 or placebo. Three or six dose administrations will be provided monthly. Participants will undergo clinical and laboratory-based safety-related assessments, as well as Pharmacodynamics (PD), immunogenicity, and blood Pharmacokinetic (PK) collections at different time points. Assessments will include 5-7 brain MRIs (Magnetic Resonance Imaging), 3 spinal taps, electrocardiograms (ECGs), vital signs, physical and neurological examinations, adverse event recordings, monitoring of mental health, and tests to determine the severity of Alzheimer's disease.