Beneficial Effect of ACI-24 Vaccination on A Plaque Pathology and Microglial Phenotypes in an Amyloidosis Mouse Model

Amyloid-beta (A beta) deposition is an initiating factor in Alzheimer's disease (AD). Microglia are the brain immune cells that surround and phagocytose A beta plaques, but their phagocytic capacity declines in AD. This is in agreement with studies that associate AD risk loci with genes regulating the phagocytic function of immune cells. Immunotherapies are currently pursued as strategies against AD and there are increased efforts to understand the role of the immune system in ameliorating AD pathology. Here, we evaluated the effect of the A beta targeting ACI-24 vaccine in reducing AD pathology in an amyloidosis mouse model. ACI-24 vaccination elicited a robust and sustained antibody response in APPPS1 mice with an accompanying reduction of A beta plaque load, A beta plaque-associated ApoE and dystrophic neurites as compared to non-vaccinated controls. Furthermore, an increased number of NLRP3-positive plaque-associated microglia was observed following ACI-24 vaccination. In contrast to this local microglial activation at A beta plaques, we observed a more ramified morphology of A beta plaque-distant microglia compared to non-vaccinated controls. Accordingly, bulk transcriptomic analysis revealed a trend towards the reduced expression of several disease-associated microglia (DAM) signatures that is in line with the reduced A beta plaque load triggered by ACI-24 vaccination. Our study demonstrates that administration of the A beta targeting vaccine ACI-24 reduces AD pathology, suggesting its use as a safe and cost-effective AD therapeutic intervention.