This study is testing a new vaccine called AV-1959D for Alzheimer's disease, a condition that affects memory and thinking. The study will check if the vaccine is safe and how well people can handle it. Participants will be divided into three groups, each receiving different doses of the vaccine, or a placebo (a harmless substance with no medical effect). People between 60 and 85 years old, with mild memory problems, can join. They need a partner to help with visits and must have a recent brain scan showing signs of Alzheimer's. Participants must be stable on any current Alzheimer's medications for at least 3 months.

Some people cannot join, like those who have been in another trial recently, have certain medical conditions, or have had other specific treatments. The study will check for any health issues that might interfere with participation.

• The study involves multiple visits, so a study partner is needed to accompany patients.
• Participants must be stable on current Alzheimer's medications for at least 3 months.
• Some medical conditions or recent participation in other studies may restrict eligibility.