Long‐term safety and immunogenicity of ABvac40 active immunotherapy in mild cognitive impairment and very mild Alzheimer's disease: Results from AB1601 phase 2 extension study

INTRODUCTION: ABvac40 is an active immunotherapy targeting Aβ40, the main component of cerebrovascular deposition in Alzheimer's disease (AD). A 24-month randomized, placebo-controlled phase 2 study (Part A) showed favorable safety and robust immunogenicity, with exploratory signals of clinical efficacy. Here, we report results from Part B, an 18-month extension evaluating long-term safety and immunological memory. METHODS: Participants treated with ABvac40 in Part A received placebo plus a delayed booster, whereas previous placebo participants received ABvac40. Exploratory endpoints included safety, tolerability, and immunogenicity. RESULTS: Seventy-seven participants entered Part B. Treatment-emergent adverse events (TEAEs) occurred in 75.0% of participants in placebo + booster group and 81.1% in ABvac40 group; serious TEAEs were 5.0% and 16.2%, respectively. No ARIA-E or meningoencephalomyelitis were observed, with one ARIA-H event. ABvac40 induced robust antibody responses following delayed booster, with detectable anti-Aβ40 antibodies in CSF. DISCUSSION: ABvac40 showed favorable long-term safety and durable immunogenicity, supporting further clinical development. TRIAL REGISTRATION: ClinicalTrials.gov: NCT03461276, registered March 2, 2018. EudraCT: 2016-004352-30, registered March 10, 2017.