Despite successfully removing amyloid plaques from the brain, widely anticipated antibody therapies fail to deliver meaningful cognitive improvements, raising critical questions about the future direction of Alzheimer’s treatment.
Study: Amyloid‐beta‐targeting monoclonal antibodies for people with mild cognitive impairment or mild dementia due to Alzheimer’s disease. Image credit: Kateryna Kon/Shutterstock.com
Scientists have recently systematically reviewed articles to assess the efficacy and harms of amyloid‐beta‐targeting monoclonal antibodies in people with mild cognitive impairment or mild dementia due to Alzheimer’s disease. This review is available in the Cochrane Database of Systematic Reviews.
Alzheimer's disease: Epidemiology, pathology, and diagnosis
Alzheimer’s disease (AD) is a progressive, irreversible neurodegenerative disorder affecting millions of people worldwide. It is defined neuropathologically by the accumulation of extracellular amyloid-beta (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) of hyperphosphorylated tau protein, leading to synaptic dysfunction, neuronal loss, and cognitive deterioration.
Onset typically occurs in older adults, and prevalence is projected to rise sharply as global populations age. AD progresses along a continuum from mild cognitive impairment (MCI) to mild, moderate, and severe dementia. MCI is characterized by objective memory difficulties with preserved functional independence. About 15 % of people with MCI develop dementia due to Alzheimer’s disease within two years.
Anti-amyloid monoclonal antibodies: rationale and evidence gaps
Amyloid-beta-targeting monoclonal antibodies (Aβ-mAbs) have been developed as potential therapies for AD. Mechanistically, monoclonal antibodies bind to forms of Aβ and promote clearance via microglial phagocytosis or peripheral mechanisms. This strategy aims to reduce plaque burden and may slow disease progression, although clinical benefits remain uncertain.
Repeated amyloid PET imaging has demonstrated that Aβ-mAbs can reduce aggregated amyloid burden; however, the clinical significance of this finding remains uncertain. Evidence from randomized controlled trials suggests these treatments probably result in little to no difference in cognitive function and may have little to no effect on dementia severity at 18 months.
Overall, the net clinical benefit of Aβ-mAbs remains uncertain, with limited clinical efficacy and safety concerns, including amyloid-related imaging abnormalities (ARIA). Long-term safety data beyond 18 months remain limited, and evidence in underrepresented populations remains insufficient.
Assessing the efficacy and safety of Aβ-mAbs in AD patients with MCI
The current review addressed the lack of a comprehensive, GRADE-informed systematic review of Aβ-mAb efficacy and safety in MCI and mild AD dementia. All relevant research articles were obtained from CENTRAL, MEDLINE (PubMed), Embase, and two clinical trial registries, with additional reference checking and citation searches. The most recent search was conducted in August 2025. RCTs of at least 12 months comparing Aβ-mAbs with placebo in MCI or mild AD dementia (parallel-group and cluster designs) were considered.
Critical outcomes included cognitive function, dementia severity, functional ability, amyloid-related imaging abnormalities (ARIA), symptomatic brain hemorrhage, serious adverse events, and all-cause mortality, assessed at 12, 18, 24, and over 24 months. Results were pooled using an inverse-variance random-effects meta-analysis, and certainty of evidence was rated using GRADE.
Included randomized controlled trials reveal modest efficacy and persistent safety tradeoffs
Of the identified records, 17 placebo-controlled randomized controlled trials (RCTs) were ultimately included, enrolling a total of 20,342 participants. All trials used parallel-group randomization and were conducted across multiple countries, lasting between 18 and over 24 months.
Participants had a mean age in the early to mid-70s, with women comprising a substantial proportion. Studies enrolled individuals with either MCI, mild Alzheimer's dementia, or a combination of both. Most participants were receiving standard-of-care cognitive medications, such as cholinesterase inhibitors or memantine. All included studies were funded by the pharmaceutical industry.
Across 13 studies at 18 months, Aβ-mAb treatment probably resulted in little to no difference in cognitive function compared with placebo as measured by the ADAS-Cog (Alzheimer’s Disease Assessment Scale-Cognitive Subscale), with moderate certainty of evidence. Results at longer time points were similarly modest and less certain.
On the CDR-SB (Clinical Dementia Rating-Sum of Boxes) scale, treated patients may have experienced little to no difference in dementia severity compared with placebo at 18 months, with low certainty of evidence. This pattern persisted at 24 months and beyond.
Functional outcomes, measured across several validated scales, showed little to no difference overall, although some measures suggested small improvements in certain aspects of daily functioning, indicating that any benefit is small at best and that the evidence ranges from low to moderate certainty depending on the scale used. Evidence on behavioral symptoms was not consistently reported across studies, limiting firm conclusions.
The most notable safety concern is amyloid-related imaging abnormalities (ARIA) on brain MRI (Magnetic Resonance Imaging), which can be asymptomatic or, in more serious cases, cause neurological symptoms. At 18 months, ARIA-E (edema/effusion) was more frequent in treated patients, though the absolute increase in symptomatic cases was small, with moderate certainty of evidence.
Evidence on ARIA-H (microhemorrhages) was limited and heterogeneous, preventing firm conclusions about differences between groups. At longer follow-up, ARIA-E rates may remain elevated, though this evidence is less certain. Rates of serious adverse events and death were comparable between treatment and placebo groups at 18 months and across all other time points assessed, with high certainty.
Conclusions
Current evidence does not support a clinically meaningful benefit of Aβ-mAb for cognitive function, dementia severity, or functional ability in people with MCI or mild Alzheimer’s disease. These agents carry a notable risk of amyloid‐related imaging abnormalities, and successful amyloid clearance does not appear to translate into meaningful clinical improvement. Future disease‐modifying research should explore alternative therapeutic mechanisms of action.
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