Tau immunotherapy and imaging.

Disappointing findings from recent phase III trials on amyloid-β (Aβ) immunotherapy for Alzheimer's disease (AD) have shifted the focus of such treatments to the tau protein. As tau pathology correlates better with the degree of dementia than Aβ plaque burden, it is a more attractive target once cognitive impairments are evident, while Aβ therapies may be better suited for the presymptomatic phase of the disease. Over 12 years ago, we initiated a tau immunotherapy program, seeking to alleviate the functional impairments associated with tau lesions in tauopathies. We have reported that various active and passive tau immunizations diminish tau pathology and improve function, including cognition, in different mouse models. Both extra- and intracellular pathways are likely involved. The antibodies may block the spread of tau pathology via microglial phagocytosis of the antibody-tau complex and facilitate lysosomal tau clearance in neurons after endosomal uptake. We have observed such antibody internalization following intracarotid injection in mice and in various culture models. These include brain slices and primary neurons from tangle mice as well as human neuroblastoma cell lines. Antibody targeting of different intracellular protein aggregates, including α-synuclein, Aβ and superoxide dismutase has been reported by others. Now, several laboratories have confirmed and extended our findings using various active and passive tau immunizations in different models, thereby clearly establishing the feasibility of this approach for clinical trials. We are also working on imaging approaches to monitor tau pathology, its consequences and the efficacy of treatments. Dire need exists for such diagnostic methods for tauopathies. Overall, therapies and diagnostic tools targeting tau pathology have a great potential for AD and other tauopathies.