This study will assess the effects of each of the two therapies given separately, both targeting amyloid, on cognition, global clinical status, and underlying pathology in participants at risk for the onset of clinical symptoms of Alzheimer's disease (AD). Cognitively unimpaired individuals with two APOE4 genes and age 60 to 75 years, inclusive, are selected as they represent a population at particularly high risk of progression to Mild Cognitive Impairment and/or dementia due to Alzheimer's disease.

The study follows a randomized, double-blind, placebo-controlled, two-cohort, parallel group design in which participants receive one of the investigational treatments or their matching placebo for at least 60 months up to a maximum of 96 months and no longer than when the target number of events for the TTE endpoint has been observed and confirmed in either cohort.

An unbalanced randomization (active: placebo) of 5:3 ratio in Cohort I (430 CAD106 :260 Placebo) and 3:2 ratio in Cohort II (390 CNP520 : 260 Placebo) will be applied. Randomization will be stratified by age group (60-64 years, 65-75 years) and region (North America/Other , Europe).

Participants who meet study entry requirements will be required to undergo at least one PET scan during the course of the study. Additional PET scans, blood and CSF collection will be voluntary. The study (also known as the Generation Study 1) is conducted as part of the Alzheimer's Prevention Initiative (API) program.