Project Summary Recent data from clinical trials with humanized or fully human mAbs targeting Aβ suggest that immunotherapy could clear/reduce brain amyloid plaques and even slow cognitive decline in vaccinated subjects when initiated as a preventive measure. However, passive immunotherapy with even the most effective anti-Aβ mAb is not practical and cost-effective as a preventive measure in healthy subjects due to the need for frequent (monthly) administrations of high concentrations (~800mg IV injections/each time) of this immunotherapeutic in a substantial patient population. At the same time, high doses of mAb frequently (~30%) induce ARIA-E and ARIA- H. In contrast, AD vaccine, similar to the vast majority of vaccines in general, could be very effective when used as a preventive/early intervention measure. Today, only limited results are available from ACC001, CAD106, and UB311 epitope vaccine clinical trials, but fortunately, comprehensive data on AN-1792 are published. These data demonstrated that the AN-1792 vaccine has induced antibodies specific to N-terminus of amyloid in ~19% immunized AD patients without causing ARIA-E and ARIA-H abnormalities. Importantly the follow-up analysis revealed that even after 14 years post-vaccination, the vaccinated subjects were plaque-free, and there was a significant inverse correlation between peripheral blood anti-Aβ antibody titers and the plaque counts. Despite the reduction of Aβ pathology, vaccination did not improve cognitive functions likely due to tau pathology buildup. These data support our long-standing proposal of starting anti-Aβ vaccination with AV-1959D as a prophylactic measure in subjects at risk for AD to inhibit/reduce oligomerization of Aβ and delay downstream pathological processes. However, based on an ethical imperative raised by the FDA during our pre-IND meeting, they recommended us to test our Aβ vaccine AV-1959D in participants with early-stage AD patients prior to initiating the preventive tri