A Study of Single and Multiple Doses of KHK6640 in Subjects With Prodromal or Mild to Moderate Alzheimer's Disease

Inclusion Criteria: * Patients with prodromal AD or mild to moderate AD * Clinical Dementia Rating (CDR) score of 0.5, 1.0, or 2.0 * Have a cognitive impairment * Low Aβ and high Tau in Cerebrospinal fluid (CSF) * Mini Mental State Examination (MMSE) score \> 16 at Screening Exclusion Criteria: * Previous active treatment with an AD immunotherapy in an investigational study * Use of another investigational drug within 30 days of screening * History or presence of clinically significant seizures, brain trauma, transient ischemic attack, and/or cerebrovascular disease * Presence of a neurological condition that could be contributing to cognitive impairment above and beyond that caused by the subject's AD * Evidence of infection, tumor, or other clinically significant lesions that could indicate a dementia diagnosis other than AD