A Cochrane review published this week suggested that anti-amyloid beta monoclonal antibodies produce “trivial effects” on cognitive function and dementia severity while increasing the risk of amyloid-related imaging abnormalities (ARIA). The authors concluded that successful removal of amyloid from the brain does not appear to translate into clinically meaningful benefit, and suggested future research should focus on alternative mechanisms. These findings, and the review’s methodology, have been swiftly rebutted by researchers affiliated with the UK Dementia Research Institute.
The Cochrane review findings
The Cochrane review evaluated 17 randomized controlled trials involving 20,342 patients with mild cognitive impairment or mild Alzheimer’s disease, assessing seven anti-amyloid beta monoclonal antibodies against placebo, namely: aducanumab (n = 3), bapineuzumab (n = 4), crenezumab (n = 2), donanemab (n = 1), gantenerumab (n = 4), lecanemab (n = 1), and solanezumab (n = 2).
The analysis found that while these therapies effectively reduce amyloid levels in the brain, their impact on clinical outcomes is minimal. Across trials, effects on cognitive decline and dementia severity were characterized as trivial, with functional benefits described as small at best and below commonly accepted thresholds for clinical meaningfulness.
The review also identified consistent safety concerns. Treatment with anti-amyloid antibodies was associated with a significantly increased risk of amyloid-related imaging abnormalities (ARIA), including brain edema and microhemorrhages, detected on MRI scans. While many cases were asymptomatic, the long-term consequences remain uncertain, and reporting of both adverse events and clinical outcomes was inconsistent across studies, limiting confidence in some estimates.
Overall, the authors concluded that successful removal of amyloid plaques does not translate into clinically meaningful benefit for patients at these early disease stages, challenging the assumption that amyloid is a sufficient therapeutic target. On this basis, the review recommends that future Alzheimer’s drug development should shift toward alternative biological mechanisms beyond amyloid, reflecting growing uncertainty about the centrality of the amyloid hypothesis in driving disease progression.
Researcher response
Researchers affiliated with the UK Dementia Research Institute at UCL, Imperial College London, Cardiff University, and the University of Edinburgh published a formal response contesting the review’s analytical approach. Their central objection is that combining antibodies with mechanistically distinct targets and divergent clinical track records produces a pooled estimate that reflects neither the failures nor the successes accurately.
Prof. Sir John Hardy of the UK DRI at UCL framed the issue in mechanistic terms, noting that the review conflates therapies with different mechanisms. Drug-specific data within the review showed lecanemab slowing cognitive decline by approximately 27% on the CDR-SB scale and donanemab by approximately 35%, both reaching statistical significance. The five antibodies that did not advance past clinical trials showed minimal or no effect.
The mechanistic distinction matters for interpreting the amyloid beta treatment evidence. Lecanemab preferentially binds soluble amyloid protofibrils before they deposit as plaques, targeting the cascade at an earlier stage. Donanemab engages already-deposited plaques via an N3pG epitope, triggering microglial phagocytic clearance through Fc receptor engagement. Solanezumab, which targeted monomeric soluble amyloid beta and failed in trials, operates through a different binding strategy. Grouping these biologics into a single meta-analytic pool treats mechanistically heterogeneous interventions as interchangeable, which the UK DRI researchers argue is scientifically unjustified given the substantial trial heterogeneity the review itself acknowledges.
Lecanemab, developed by Eisai and Biogen, received traditional FDA approval in July 2023. Donanemab, an Eli Lilly product marketed as Kisunla, received FDA approval in July 2024. Aducanumab received accelerated FDA approval in 2021 but was subsequently withdrawn from the market. The regulatory divergence between these three antibodies — two approved, one withdrawn — illustrates why the responding researchers argue that a pooled analysis treating all seven as a single class obscures clinically relevant distinctions.
The safety data in the review remain a point of serious consideration regardless of the analytical dispute. ARIA-E rates of approximately 35% in lecanemab-treated patients, elevated microhemorrhage rates across active treatment arms, serious ARIA events including deaths, and greater brain volume loss in treatment arms than in placebo arms are findings that apply specifically to the licensed agents, not only to the failed ones. Prof. Paul Morgan of the UK DRI at Cardiff University acknowledged the findings will generate vigorous debate and identified an urgent need to understand the drivers of continued disease progression after successful amyloid clearance, in order to identify complementary therapeutic targets.
That translational question — what happens after amyloid is cleared — is now a primary focus of next-generation Alzheimer’s clinical trials. Eli Lilly has registered a Phase II Alzheimer’s Tau Platform master protocol (NCT06957418) designed to test tau-directed therapies alone and in combination with donanemab. A separate study (NCT07456462) is using 3T MRI and blood sampling to optimize monoclonal antibody treatment selection and monitoring. These programs reflect the field’s recognition that amyloid clearance alone does not halt disease progression, and that tau pathology, neuroinflammation, and synaptic loss represent additional targets.