Passive tau-based immunotherapy for tauopathies

: Tauopathies are heterogeneous clinicopathological entities characterized by abnormal neuronal and/or glial inclusions of the microtubule-binding protein tau. In secondary tauopathies, i.e., Alzheimer's disease (AD), tau deposition can be observed, but tau may coexist with another protein, i.e., amyloid-β. In the last 20 years, little progress has been made in developing disease-modifying drugs for primary and secondary tauopathies and available symptomatic drugs have limited efficacy. Treatments are being developed to interfere with the aggregation process or to promote the clearance of tau protein. Several tau-targeted passive immunotherapy approaches are in development for treating tauopathies. At present, 12 anti-tau antibodies have entered clinical trials, and 7 of them are still in clinical testing for primary tauopathies and AD (semorinemab, bepranemab, E2814, JNJ-63733657, Lu AF87908, PNT00, and APNmAb005). However, none of these seven agents have reached Phase III. The most advanced anti-tau monoclonal antibody for treating AD is semorinemab, while bepranemab is the only anti-tau monoclonal antibody still in clinical testing for treating progressive supranuclear palsy syndrome. Two other anti-tau monoclonal antibodies have been discontinued for the treatment of primary tauopathies, i.e., gosuranemab and tilavonemab. Further evidence will come from ongoing Phase I/II trials on passive immunotherapeutics for treating primary and secondary tauopathies.