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What is the aim of the study?

Alzheimer's disease (AD) is a type of dementia that affects memory, thinking and behaviour. Symptoms usually develop slowly and get worse over time, becoming severe enough to interfere with daily tasks.

It is believed that changes in two proteins in the brain, beta-amyloid and tau, cause AD. Plaques (clumps of beta-amyloid) and tangles (twisted threads of tau) are the main reasons that brain cells are damaged. These two proteins are the focus of many researchers working on treatments that could help slow down or stop AD.

This study is testing a new medicine called trontinemab. It is designed to help remove amyloid plaques from the brain, which may help slow down early symptoms of Alzheimer’s disease.

Trontinemab is an experimental medicine. This means health authorities (like the U.S. Food and Drug Administration and European Medicines Agency) have not approved trontinemab for the treatment of AD.

The aim of this study is to compare trontinemab with a placebo (a dummy medicine) to see:

• How well it works
• How safe it is in people who have early signs of Alzheimer’s disease.

Participants will be randomly assigned (50/50 chance) to receive either:

• Trontinemab, or
• A placebo (a treatment with no active medicine)

Trontinemab or placebo is given by intravenous (IV) infusion, which is a drip into a vein in the arm. The first infusion takes about 4 hours. If it is well tolerated, future infusions may be shortened to about 2 hours.

Find more information about why studies use blinding, randomisation and placebo controls.

How long the study lasts

Total time of participation in the study will be about 1 year and 7 months. Participants have the right to stop study treatment and leave the study at any time, if they wish to do so. After this study ends, participants, if eligible, will be offered the option to join an open label extension study where everyone will receive trontinemab.

The total treatment period lasts 72 weeks (approx. 18 months) and is divided into two phases:

• Induction Phase (first 6 months): participants will receive an infusion every 4 weeks (Weeks 0, 4, 8, 12, 16, 20, and 24)
• Maintenance Phase (after 6 months): participants will switch to receiving an infusion every 12 weeks (Weeks 36, 48, and 60) until the end of the study.

Brain Scans (Imaging)

Participants will have a number of brain scans to check brain health and to measure amyloid and tau throughout the study:

Magnetic resonance imaging (MRI)

• Shows the structure of the brain.
• Helps check for safety changes, like swelling or tiny bleeds (called ARIA).
• When: screening, Weeks 4, 12, 24, 48, and 72.

Positron emission tomography (PET) scans

Amyloid PET scan

• Uses a small amount of a radioactive tracer to measure amyloid plaques in the brain.
• When: screening, one mid study scan (Week 12 or Week 28), and Week 72.

Tau PET scan (optional)

• Measures tau tangles in the brain.
• Participants can choose whether to take part.
• When: Baseline and Week 72.

This study is testing a new investigational medicine called RO7812653.

The aim of this study is to compare RO7812653 with a placebo (a dummy medicine) to see:

• How well RO7812653 works
• How safe RO7812653 is in people who have early signs of Alzheimer’s disease.

RO7812653 is an experimental medicine. This means health authorities (like the U.S. Food and Drug Administration and European Medicines Agency) have not approved RO7812653 for the treatment of AD.

How the study is carried out

This study is a double-blind placebo-controlled trial. This means:

• Some people will get RO7812653.
• Some people will get a placebo (a dummy treatment that has no medicine in it).

Neither the participant, their study doctor, nor the study team will know who is getting which treatment during the first part of the study. This helps make the results fair.

People in the study will be put into their treatment groups by chance, like flipping a coin. Most participants will have a 3 in 4 chance of receiving RO7812653 (the study drug) and a 1 in 4 chance of receiving a placebo (a dummy treatment).

For the very first group taking part, the chances are slightly different: they will have a 2 in 3 chance of getting the study drug and a 1 in 3 chance of getting a placebo.

Find more information about why studies use blinding, randomisation and placebo controls.

How is the study treatment given?

RO7812653 or placebo is given as an injection into the space around the spine so it can reach the brain more directly. Participants will be given RO7812653 or placebo once in the study.

What will participants be asked to do during the study?

During the study, participants will:

• Have some laboratory tests, such as blood tests. These tests help doctors check for any new side effects, such as symptoms or health changes that might happen after receiving the study medicine.
• Have brain scans called magnetic resonance imaging (MRI) scans. These scans take detailed pictures of the brain to help doctors check brain health and safety.
• Wear a heart monitor that records your heartbeat so doctors can spot any problems that a quick heart test might miss, like your heart beating too fast, too slow, or feeling like it skips a beat.
• Be admitted to hospital to be monitored immediately before, and for 24 hours after receiving RO7812653 or placebo.
• Complete tests that look at memory, thinking, and emotional wellbeing.

If participants would like more details about the tests, procedures, or number of visits, the study team can provide full information.