Tau oligomers as potential targets for immunotherapy for Alzheimer's disease and tauopathies.

The aggregation and accumulation of the microtubule-associated protein (Tau) is a pathological hallmark of Alzheimer disease (AD) and many neurodegenerative diseases. For a long time research has focused on neurofibrillary tangles (NFTs) and other large meta-stable inclusions composed of aggregated hyperphosphorylated tau protein. The correlation between these structures and disease progression produced conflicting results; moreover, the mechanism of their formation remains poorly understood. Lately, the significance and toxicity of NFTs have been challenged and a new aggregated tau entity has emerged as the true pathogenic species in tauopathies and a possible mediator of Aβ toxicity in AD; specifically, aggregates of a size intermediate between monomers and NFTs the so-called tau oligomers. Tremendous efforts have been devoted toward the optimization of a safe vaccine for AD by targeting Aβ peptide; despite the disappointing results, these studies produced a wealth of useful knowledge, which should be considered in developing tau-based immunotherapy. Herein, we discuss the evidence supporting the critical role of tau oligomers in AD, the potential and challenges for targeting them by immunotherapy as a novel approach for AD treatment.