Provided herein are methods of reducing clinical decline in a subject having early Alzheimer's disease, methods of converting an amyloid positive subject having early Alzheimer's disease to amyloid negative, methods of reducing brain amyloid level in a subject, and methods of preventing Alzheimer's disease, the methods comprising administering a composition comprising a therapeutically effective amount of at least one anti-Aβ protofibril antibody. In some embodiments, the subject is ApoE4-positive. In some embodiments, the at least one anti-Aβ protofibril antibody is BAN2401.本發明提供減少患有早期阿茲海默症之個體之臨床衰退的方法；將患有早期阿茲海默症之澱粉狀蛋白陽性個體轉變成澱粉狀蛋白陰性之方法；降低個體之腦澱粉狀蛋白量之方法；及預防阿茲海默症之方法，該等方法包含投與包含治療有效量之至少一種抗Aβ基原纖維(protofibril)抗體的組合物。在一些實施例中，該個體呈ApoE4陽性。在一些實施例中，該至少一種抗Aβ基原纖維抗體為BAN2401。
