NCT04639050

Who might be able to join this trial:

• You are able to give written consent to participate in the study yourself
• You have a "study partner" (such as a family member or close friend) who agrees to take part, has regular contact with you, and speaks the language used at the study site
• You are willing and able to complete all parts of the study, including brain scans (MRI and PET), a lumbar puncture (spinal tap), and genetic testing
• You are able to complete memory and thinking tests either on your own or with help from your study partner
• You have good enough vision and hearing to complete thinking and memory tests (glasses and hearing aids are allowed)
• You have been diagnosed with mild to moderate Alzheimer's disease (AD) dementia, or an early stage called mild cognitive impairment due to AD
• You scored between 18 and 28 on a standard memory test (MMSE) within about 3 months before the study start
• You received a specific score (0.5, 1, or 2) on a standard dementia rating scale within about 3 months before the study start
• A brain scan confirmed the presence of amyloid protein (a hallmark of Alzheimer's) within the 12 months before the study start
• If you are already taking Alzheimer's medication, your dose has been stable for at least 8 weeks before the study starts
• You agree not to donate blood or blood products during the study and for 1 year after your last dose
• You agree not to join any other research studies while taking part in this trial
• You agree to have a genetic test related to a gene called APOE

For the optional extension phase (Part 4) only:

• You completed the full treatment period in an earlier part of this same study

Who may not be able to join:

• You have another brain or nervous system condition besides Alzheimer's disease, such as another form of dementia, a history of seizures, a stroke-related condition, or a brain infection or injury
• You have certain other serious health conditions, including significant blood disorders, certain eye diseases, or very poor vision in either eye (confirm with trial site)
• You have significant heart or kidney disease, unexplained liver problems, or an abnormal thyroid condition (confirm with trial site)
• You have previously had a serious allergic reaction to a biological medicine or any ingredient in the study drug
• You have significantly abnormal results on blood, urine, or spinal fluid tests, as judged by the study doctor
• Your MRI scan shows certain types of brain damage, such as more than 2 small strokes, a larger stroke, or significant white matter changes in the brain
• Your MRI scan shows more than 4 tiny bleeds in the brain, or certain signs of bleeding around the surface of the brain
• Your MRI scan shows other significant brain abnormalities, including a type of brain swelling sometimes associated with Alzheimer's treatments (called ARIA-E)
• You are unable to have an MRI scan, or it is medically unsafe for you to do so
• You are unable to have an eye examination
• It is medically unsafe for you to have a lumbar puncture (spinal tap)
• It is medically unsafe for you to have a PET scan

For the optional extension phase (Part 4) only:

• You left the earlier part of the study early, before completing the treatment period
• You received another experimental treatment (other than the study drug RO7126209) during or after the earlier part of the study
• You received a type of antibody therapy (passive immunotherapy) aimed at preventing memory decline since finishing the earlier part of the study
• You are taking blood-thinning (anticoagulant) medications
• You currently have brain swelling (ARIA-E) or are having an ongoing reaction to a study drug infusion (though you may be able to join once these have resolved — confirm with trial site)
• Your MRI scan at the start of Part 4 shows certain brain abnormalities (including swelling, bleeding, or stroke-related changes) that meet specific limits (confirm with trial site)
• Your blood count (hemoglobin) has dropped significantly or is below a certain level (confirm with trial site)

Important: Always verify eligibility with the trial site directly before applying.