Anti-amyloid immunotherapy drives APOE4 specific increases in glial reactivity, perivascular immune activation, and ARIA-like events.

Anti-amyloid antibodies represent the first disease modifying therapeutics for Alzheimer's disease (AD). Adoption of these novel treatments has been slowed by the occurrence of amyloid related imaging abnormalities (ARIA) - treatment-associated edema (ARIA-E) or microhemorrhages (ARIA-H) that disproportionately affect carriers of the E4 allele of apolipoprotein E (APOE). With E4 carriers comprising nearly 70% of the AD population, there is a critical need to understand the unique vulnerability of E4 carriers to these events. To address this gap, we utilized the EFAD mouse model - which expresses human APOE isoforms on the 5xFAD background of amyloidosis - to directly compare the effects of anti-amyloid therapy across APOE genotypes. 9-month-old E2, E3, and E4FAD mice received weekly injections of chimeric Aducanumab (chAdu) or IgG control for 12 weeks, to assess APOE isoform-specific effects on amyloid dynamics, ARIA-H-like microhemorrhages, and underlying cellular and transcriptomic responses. E4FAD mice demonstrated plaque reductions with accompanying increases in microhemorrhages (measured on both MRI and histology), and increases in microglial and astrocyte reactivity - especially in the perivascular compartment. Additionally, vascular branching analysis and parallel single cell and spatial transcriptomics revealed a loss of vascular plasticity and increased inflammatory and immune signaling in the neurovascular units of E4FAD mice. Together, these findings suggest the cerebrovasculature of E4s is uniquely susceptible to antibody mediated vascular damage and provide immunological targets for the assessment or mitigation of ARIA risk in this highest need population.