Prodromal Alzheimer's Disease

The purpose of this study is to assess the safety, tolerability, immunogenicity and pharmacodynamic effects of ACI-24.060 in subjects with prodromal Alzheimer's disease and in non-demented adults with Down syndrome.

The Alzheimer's Tau Platform (ATP) is a multi-center platform trial to evaluate the safety and effectiveness of tau-directed therapies, alone or in combination with donanemab, in adults aged 50-80 with late preclinical or early prodromal Alzheimer's disease. Regimen A will evaluate the safety and efficacy of AADvac1, alone or in combination with donanemab.

The goal of the Alzheimer's Tau Platform (ATP) is to evaluate the safety and effectiveness of tau-directed therapies, alone or in combination with the anti-amyloid monoclonal antibody, donanemab, in adults aged 50-80 with late preclinical or early prodromal Alzheimer's disease. This platform trial allows for the simultaneous testing of multiple tau therapies under a shared master protocol. This means that multiple investigational products will be tested simultaneously or sequentially. Each investigational product will be tested in a regimen. The main questions the platform trial aims to answer are: * Does a tau-directed therapy, alone or in combination with donanemab, reduce tau buildup in the brain compared to donanemab alone? * Does a tau-directed therapy, alone or in combination with donanemab, slow disease progression based on brain imaging, fluid biomarkers, and measures of memory and thinking? Participants will: * Be randomized to a treatment regimens, each containing different tau therapies. The exact number of treatment regimens that will active at the time of screening will change over time. * Receive donanemab or placebo for 6 months, followed by 24 months of tau therapy alone or in combination with donanemab. * Undergo regular cognitive testing, brain scans (MRI/PET), and biomarker assessments over 30 months Participants will have an equal chance to be randomized to all regimens that are active at the time of screening. Once randomized to a regimen, participants will be randomized to one of three arms: (1) tau therapy alone, (2) a combination of donanemab and tau therapy, or (3) donanemab alone. New regimens will be continuously added as new investigational products become available. The Alzheimer's Tau Platform Trial will enroll additional participants as each new regimen becomes available. ATP will launch with one regimen: Regimen A: AADvac1. In the future, Regimen B ("Tau2") will launch with a second tau directed therapy.

Neurodegenerative diseases are a major health concern due to their growing societal implications and economic costs. The identification of early markers of pathogenic mechanisms is one of the current main challenges. The gut-brain axis has become a primary target because of its transversal role across the neurodegenerative spectrum and its effect on cognition. However, despite recent progress, how changes in the gut-microbiota composition can affect the human brain is still unclear. The goal of this observational study is to characterise the gut-microbiota composition associated with alterations in brain structure and function during the ageing process and across neurodegenerative disorders. This is based on recent studies showing that changes in the human brain and in the microbiota composition, can indicate very sensitively and in a predictive way pathological development and, consequently, be used as markers of neurodegenerative diseases. The main questions it aims to answer are: * How variation in the gut-microbiota composition correlates with the normal brain ageing trajectory? * How dysregulation in the gut-microbiota correlates with pathological changes in brain regions in specific neurodegenerative disorders? * Can the impact of the gut-microbiota on the brain be modulated by blood biomarkers? The investigators will recruit 40 young healthy participants, 40 old healthy participants, 40 participants with prodromal Alzheimer's Disease, 40 participants with Parkinson's Disease and 40 participants with Multiple Sclerosis. Participants will undergo the following examinations: * Magnetic Resonance Imaging * Analysis of a stool sample * Analysis of a blood sample * Neuropsychological assessment * Questionnaires on eating habits