Background: ACC-001 is an investigational therapeutic vaccine designed to elicit antibodies against the N-terminal peptide 1-7 of the amyloid-beta peptide, believed to be important in the pathogenesis of Alzheimer's disease.
Objectives: To evaluate safety, immunogenicity, impact on brain amyloid, and other exploratory endpoints in participants receiving ACC-001.
Design: Randomized, phase 2, interventional study.
Trial registration: Clinicaltrials.gov ID NCT01227564.
Participants: Individuals with early Alzheimer's disease (Mini-Mental State Examination scores ≥25, a global Clinical Dementia Rating of 0.5, and evidence of elevated baseline brain amyloid burden).
Intervention: Participants were randomized to ACC-001 3 µg or 10 µg with QS-21 adjuvant (50 µg), or placebo.
Measurements: The primary endpoint was change in brain amyloid burden by 18F-florbetapir positron emission tomography in composite cortical standard uptake value ratio.
Results: A total of 63 participants were randomized and 51 completed the study. At week 104, no significant differences were observed in 18F-florbetapir positron emission tomography composite cortical standard uptake value ratio between either ACC-001 dose compared with placebo. In both ACC-001 + QS-21 treatment groups, following the initial immunization, the anti-amyloid-beta geometric mean titers increased after each subsequent vaccination and then declined, with less apparent decline after the later compared with earlier immunizations. The majority of treatment-emergent adverse events in the ACC-001 + QS-21 groups were injection site reactions, which occurred at a greater rate in active treatment groups than in the placebo group. No amyloid-related imaging abnormalities of edema or effusion were reported.
Conclusion: No statistically significant differences were observed between groups in the change from baseline brain amyloid burden despite apparently robust systemically measured anti-amyloid-beta antibody response at both dose levels. Insufficient antibody titers, poor quality immune response, short duration of treatment, or small sample size may have resulted in these findings. The safety and tolerability profile was acceptable.
Keywords: Alzheimer’s disease; PET; amyloid; early AD; vaccine.