AV-1980R (Tau Vaccine) in Preclinical Alzheimer's Disease (TAURUS-1980)

Inclusion Criteria: Male or postmenopausal or surgically sterile female, 65 to 80 years of age, inclusive. Cognitively unimpaired participant with preclinical Alzheimer's disease who meets all of the following: Clinical Dementia Rating global score of 0 at Screening. Mini-Mental State Examination score ≥26, with education adjustment at Screening. Plasma p-tau217/Aβ42 ratio ≥0.00738 measured using Lumipulse (Fujirebio). A prior positive result obtained within 12 months before Screening may be accepted but must be confirmed by the central laboratory. Sight and hearing, including use of a hearing aid, sufficient to comply with study procedures. Stable concomitant medications. Participants receiving fluctuating medication or treatment may be considered if the underlying condition is controlled. Signed informed consent before any study-related procedure. Ability, in the Investigator's opinion, to understand the study and comply with protocol requirements. Exclusion Criteria: Screening MRI showing any of the following: More than one noncortical lacunar infarct greater than 1.5 cm. Any territorial infarct greater than 1.5 cm. Combined microbleeds and areas of leptomeningeal hemosiderosis greater than 5, or disseminated leptomeningeal hemosiderosis. Any other significant cerebral abnormality, including ARIA-E. Contraindication to MRI, including non-MRI-safe implanted metallic devices or clinically significant claustrophobia. Serious illness requiring systemic treatment or hospitalization within 4 weeks before study entry. Clinically relevant cardiovascular, respiratory, gastrointestinal, endocrine, immunologic, hematologic, systemic disease, or major surgery that could interfere with participation or follow-up. Insulin-dependent diabetes. Clinically relevant cardiac arrhythmia, palpitation, conduction abnormality, prolonged QT interval, or bundle branch block. Pre-existing autoimmune disease. C-SSRS score of 3 or higher. History of seizure disorder, except permitted stable use of certain antiepileptic medications for chronic pain. Any medical, psychological, or social condition that could interfere with participation, compliance, or participant 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 tau or amyloid-beta immunotherapy within 1 year before Screening. Use of specified immunomodulatory or growth-stimulating treatments within 30 days before study entry. Chronic use for more than 3 months of warfarin, other coumarin derivatives, anticoagulants, or an antiplatelet agent such as clopidogrel. Parenteral immunoglobulin preparations, blood products, or plasma derivatives. History of severe local or systemic vaccination reactions or significant allergic reactions. Clinically significant laboratory abnormalities at Screening, including ALT or AST greater than 1.5 times the upper limit of normal. Positive testing for HIV-1 or HIV-2, hepatitis B surface antigen, or hepatitis C.