Generating Differentially Targeted Amyloid-β Specific Intrabodies as a Passive Vaccination Strategy for Alzheimer's Disease

Amyloid-β (Aβ) has been identified as a key component in Alzheimer's disease (AD). Significant in vitro and human pathological data suggest that intraneuronal accumulation of Aβ peptides plays an early role in the neurodegenerative cascade. We hypothesized that targeting an antibody-based therapeutic to specifically abrogate intracellular Aβ accumulation could prevent or slow disease onset. Aβ42-specific intracellular antibodies (intrabodies) with and without an intracellular trafficking signal were engineered from a previously characterized single-chain variable fragment (scFv) antibody. The intrabodies, one with an endoplasmic reticulum (ER) targeting signal and one devoid of a targeting sequence, were assessed in cells harboring a doxycycline (Dox)-regulated mutant human amyloid precursor protein Swedish mutant (hAPPswe) transcription unit for their abilities to prevent Aβ peptide egress. Adeno-associated virus (AAV) vectors expressing the engineered intrabodies were administered to young adult 3xTg-AD mice, a model that develops amyloid and Tau pathologies, prior to the initial appearance of intraneuronal Aβ. Chronic expression of the ER-targeted intrabody (IB) led to partial clearance of Aβ42 deposits and interestingly, in reduced staining for a pathologic phospho-Tau epitope (Thr231). This approach may provide insights into the functional relevance of intraneuronal Aβ accumulation in early AD and potentially lead to the development of new therapeutics.