A new study in Nature Communications reports clonal expansion of cytotoxic CD8+ T cells in association with ARIA (amyloid‑related imaging abnormalities) observed in patients treated with lecanemab, the Alzheimer’s anti‑amyloid antibody. The investigators mapped immune cell clonotypes and linked local cytotoxic signatures to imaging abnormalities. The findings provide mechanistic insight into ARIA, a known safety signal for anti‑amyloid immunotherapies, and suggest monitoring strategies and potential biomarker development to stratify risk. Authors recommend integrating immunoprofiling into future lecanemab and anti‑amyloid trials to better anticipate and mitigate ARIA events. For developers of Alzheimer’s biologics, the study underscores the need to balance target engagement with immune safety profiling and may inform both trial design and post‑marketing surveillance.