Molecular mechanisms underlying amyloid lowering by aducanumab: differential and comparative effects of sex and IgG reveal the post-treatment disease brain

INTRODUCTIONImproving the predictive validity of preclinical studies for Alzheimers disease (AD) requires rigorous evaluation of therapeutic efficacy, safety, and sex-specific responses in translationally relevant models. As amyloid-targeting monoclonal antibodies continue to advance clinically, there is an urgent need to define the molecular milieu that persists after amyloid is reduced and disease progression continues. Leveraging the NIA-funded MODEL-AD Preclinical Testing Core, we investigated the biochemical, functional, and multi-omic signatures associated with chronic administration of murine chimeric aducanumab (chAdu) in 5XFAD mice, including the contribution of IgG-mediated effects. METHODSMale and female 5XFAD mice were treated weekly with chAdu beginning at 8 months of age and compared to age-and sex-matched murine IgG2a{kappa} isotype (IgG) and saline controls. Plasma and brain pharmacokinetics, amyloid-beta (A{beta}), behavioral assessments, and treatment-emergent anti-drug antibodies (ADAs) were quantified. Post-treatment transcriptomic and proteomic analyses were performed to assess molecular pathways associated with chAdu and IgG exposure following 17-week treatment. RESULTSchAdu produced sex-dependent changes in A{beta}, including increased plasma A{beta}42:40 and reductions in brain A{beta} which were associated with mild behavioral impairments in the absence of improvements in cognitive function. IgG control treatment produced similar reductions, indicating biologically active IgG-mediated processes independent of A{beta}-targeted specificity. Treatment-emergent ADAs occurred in 10% of chAdu-treated mice and were associated with reduced drug exposure and efficacy. Multi-omics analyses confirmed sex-dependent and IgG-mediated effects at both the transcriptomic and proteome level revealing disease-associated genes and proteins not altered despite reductions in amyloid with treatment. DISCUSSIONThese findings demonstrate sex-dependent PK and pharmacodynamic responses to chAdu, identify biologically meaningful IgG-driven effects, and reveal molecular signatures that persist after amyloid reduction. This work provides biological insights into pathways that may remain insufficiently addressed following amyloid lowering; revealing novel targets for future drug discovery to prevent and treat disease.