A3 and A45 Studies

Thank you for your interest in the A3 and A45 Studies!

The A3 and A45 studies are clinical trials aimed at preventing memory loss due to Alzheimer's disease, designed and conducted by the Alzheimer's Clinical Trials Consortium (ACTC) in collaboration with Eisai. Funding is through a public-private partnership with National Institute on Aging/NIH, Eisai, and several philanthropic organizations.

We anticipate enrollment will begin in early 2020.

We are in the process of working on the design details and launch of these two studies, and will provide periodic updates on this site.


A3 Study

The A3 Study aims to get closer to primary prevention of AD, through preventing amyloid build-up in the brain. The study targets cognitively normal individuals who are currently below the threshold for amyloid elevation on amyloid PET but are at high risk for further Aβ accumulation. The A3 study will be a global, multicenter, double-blind, randomized trial to compare the effects of two doses of elenbecestat vs. placebo, to test whether a BACE inhibitor can slow brain amyloid accumulation at this very early stage of disease. The A3 Study will also measure accumulation of tangle pathology using tau PET and exploratory cognitive outcomes.

A45 Study

The A45 study will target the preclinical (pre-symptomatic) stage of AD. The study will enroll clinically normal participants (little to no cognitive impairment) who have elevated levels of amyloid in brain and are at high risk for progression to mild cognitive impairment and AD dementia. The A45 study will be a global, multicenter, double-blinded, placebo-controlled, randomized trial of a treatment regimen consisting of an anti-Aβ antibody and a BACE inhibitor to prevent cognitive decline and delay biomarkers of pathological progression versus placebo. In the active arm, individuals will be treated first with BAN2401 to clear amyloid deposits and Aβ protofibrils from the brain, after which they will be maintained on elenbecestat with the aim of decreasing the production of Aβ and preventing the reaccumulation of amyloid plaques and protofibrils.

Study Leadership

The A3 and A45 Studies are led by three academic principal investigators: Dr. Paul Aisen from University of Southern California, and Drs. Reisa Sperling and Keith Johnson from Brigham and Women’s Hospital and Massachusetts General Hospital, Harvard Medical School.


The Alzheimer's Prevention Trials (APT) Webstudy is an online memory and thinking research tool aimed at accelerating enrollment for Alzheimer’s clinical trials, including the A3 and A45 Studies, by identifying and tracking individuals who may be at higher risk for developing Alzheimer's disease.

Learn more about the APT Webstudy: www.aptwebstudy.org

The APT Webstudy is being conducted by the University of Southern California Alzheimer's Therapeutic Research Institute and funded by the National Institute on Aging (NIA).

IRB #HS-17-00746

The ACTC is an NIA-funded clinical trial network with 35 primary clinical study sites across the United States, with aims to accelerate and expand studies for therapies in AD and related dementias across the spectrum from pre-symptomatic to more severe stages of disease. ACTC was established with grant funding from the NIA/NIH in December 2017.