ABvac40 Alzheimer's Vaccine Shows Strong Safety and Immune Response in Phase 2 Trial

Alzheimer's disease research has long focused on Aβ42 aggregating in brain plaques, but Aβ40 — the predominant amyloid species deposited in cerebral blood vessel walls — has received far less therapeutic attention. Cerebral amyloid angiopathy (CAA), driven largely by Aβ40, affects approximately 80% of Alzheimer's patients and independently accelerates cognitive decline. ABvac40 is a peptide-based active immunotherapy (vaccine) designed specifically to target Aβ40. It conjugates the C-terminal Aβ33-40 fragment to keyhole limpet hemocyanin (KLH) as a carrier protein, formulated in a Th2-biased adjuvant intended to elicit robust B-cell antibody production while avoiding the Aβ-specific T-cell activation that caused fatal meningoencephalitis in earlier AN1792 vaccine trials.

The AB1601 phase 2 trial enrolled 124 patients aged 55–80 with amnestic mild cognitive impairment (a-MCI) or very mild Alzheimer's disease (vm-AD), defined by MMSE scores of 24–30 and CDR global score of 0.5. Participants were randomized 1:1 to ABvac40 (n=64) or placebo (n=60) across 23 sites in France, Italy, Spain, and Sweden. The dosing schedule comprised five monthly subcutaneous injections of 0.2 mg immunogenic peptide, followed by a booster at month 10, with 18–24 months of follow-up. Notably, amyloid PET positivity was not required for enrollment, reflecting a pragmatic early-stage population.

On the primary safety endpoints, treatment-emergent adverse events (TEAEs) occurred in 90.6% of ABvac40 recipients versus 93.3% of placebo recipients — statistically comparable. Serious TEAEs were also similar: 26.6% (ABvac40) versus 26.7% (placebo). Critically, no cases of ARIA-edema (ARIA-E) or meningoencephalomyelitis were observed in either group. ARIA-hemorrhage (ARIA-H) rates were 12.5% in the ABvac40 group and 15.0% in the placebo group, with no significant between-group difference. This safety profile is notably cleaner than that seen with approved anti-Aβ42 monoclonal antibodies lecanemab and donanemab, which carry meaningful ARIA-E risks.

On immunogenicity — the primary efficacy endpoint — ABvac40 induced a specific, sustained antibody response in plasma against Aβ40. Importantly, anti-Aβ40 antibodies were also detectable in cerebrospinal fluid (CSF), confirming CNS penetration of the immune response. The antibodies were highly specific for Aβ40 and recognized multiple aggregation states of the peptide. This CSF penetration is clinically meaningful because it suggests the immune response can reach the vascular amyloid deposits in the brain.

Secondary exploratory endpoints showed favorable trends for ABvac40 over placebo on cognitive scales and MRI-based volumetric measures of brain atrophy, though the trial was not powered for definitive efficacy conclusions on these outcomes. The authors note these signals are hypothesis-generating and warrant investigation in larger, adequately powered trials. Limitations include the absence of mandatory amyloid PET confirmation at baseline, the relatively small sample size for efficacy conclusions, and the fact that the study was funded by Araclon Biotech-Grifols, the vaccine developer. Part B of the trial (18-month crossover extension) results are not yet reported. Overall, ABvac40 represents a mechanistically distinct approach to Alzheimer's immunotherapy that may complement existing anti-Aβ42 strategies by addressing the vascular amyloid component of disease.