Donanemab in Japanese Patients with Early Alzheimer’s Disease: Subpopulation Analysis of the TRAILBLAZER-ALZ 2 Randomized Trial

Introduction Donanemab, a monoclonal antibody directed against an insoluble, modified, N-terminal truncated form of amyloid beta, demonstrated efficacy and safety in patients with early, symptomatic Alzheimer’s disease (AD) in the phase 3 TRAILBLAZER-ALZ 2 trial. Here, we report clinical outcomes, biomarkers, and safety results for the Japanese subpopulation. Methods TRAILBLAZER-ALZ 2 ( N = 1736) was conducted in eight countries, including Japan (enrollment June 2020–November 2021; database lock April 2023). Participants (60–85 years) with early, symptomatic AD (mild cognitive impairment/mild dementia), Mini-Mental State Examination score 20–28, and confirmed amyloid and tau pathology were randomized 1:1 (stratified by tau status) to intravenous donanemab (700 mg for three doses, then 1400 mg/dose) or placebo every 4 weeks for 72 weeks. Primary outcome was change from baseline to week 76 in integrated Alzheimer’s Disease Rating Scale (iADRS) score. Other outcomes included clinical measures of cognitive and functional impairment, biomarkers, and safety. Results Of 88 Japanese participants (43 placebo, 45 donanemab), 7 in each group discontinued. Least-squares mean (LSM) change from baseline in iADRS score at week 76 was smaller with donanemab than with placebo in the combined (low-medium tau and high tau) and low-medium tau ( N = 76) subpopulations (LSM change difference: 4.43 and 3.99, representing 38.8% and 40.2% slowing of disease progression, respectively). Slowing of AD progression with donanemab was also observed for other clinical outcomes. Marked decreases in amyloid plaque and plasma phosphorylated tau 217 were observed; amyloid clearance (