AV-1959R Vaccine in Individuals With Preclinical Alzheimer's Disease

Inclusion Criteria: Male or female participants 55 to 80 years of age, inclusive, at screening. Signed informed consent before initiation of study-related procedures. Cognitively unimpaired participants with preclinical Alzheimer's disease meeting all of the following: CDR global score = 0 at screening. MMSE score ≥26 at screening, with education adjustment. Plasma p-tau217/Aβ1-42 ratio ≥0.00738. Vision and hearing sufficient to comply with study procedures, in the investigator's judgment. Stable concomitant medications for management of existing medical conditions, as appropriate. Women must be of non-childbearing potential as defined in the protocol. Men must meet protocol-defined contraception and sperm donation requirements. Ability, in the investigator's opinion, to understand the study and comply with study requirements. Exclusion Criteria: Screening MRI showing clinically significant abnormalities, including protocol-defined infarcts, excessive microbleeds, leptomeningeal hemosiderosis, superficial siderosis, or ARIA-E. Contraindication to MRI. Serious illness requiring systemic treatment and/or hospitalization within 4 weeks before study entry. Clinically relevant cardiovascular, respiratory, gastrointestinal, endocrine, immunologic, hematologic, neurologic, or other systemic disease that could interfere with participation or follow-up. Insulin-dependent diabetes. Clinically significant ECG abnormalities, including protocol-defined conduction abnormalities or QTc abnormalities. Pre-existing autoimmune disease. History of seizure disorder, except protocol-permitted use of certain antiepileptic medications for chronic pain. Any medical, psychological, or social condition that may interfere with participation, compliance, or safety. Participation in another investigational drug study or use of an investigational drug within 30 days or 5 half-lives, whichever is longer, before dosing. Prior amyloid-beta or tau immunotherapy, including vaccine or monoclonal antibody, within 1 year before screening. Recent use of protocol-defined immunomodulatory or growth-stimulating agents. Chronic use of protocol-defined anticoagulants or antiplatelet agents; aspirin is permitted. Parenteral use of immunoglobulin preparations, blood products, or plasma derivatives. History of severe local or systemic vaccine reactions or significant allergic reactions. Clinically significant laboratory abnormalities at screening. Positive testing for HIV-1/2, hepatitis B surface antigen, or hepatitis C virus.