Posdinemab
Posdinemab is an investigational monoclonal antibody developed by Johnson & Johnson for the treatment of Alzheimer's disease. It is designed to target phosphorylated tau protein, specifically binding to phosphorylated amino acid 217 in the proline-rich domain of tau.
Mechanism of action
Posdinemab is a humanized IgG1/kappa monoclonal antibody that binds with high affinity to phosphorylated amino acid 217 in the proline-rich domain of tau protein. The parent molecule, designated PT3, was originally raised against Alzheimer's disease brain-purified paired helical filaments. Preclinical studies with the humanized version have demonstrated reductions in tau seeding, the process by which toxic tau spreads through the brain.The antibody works by targeting abnormal tau proteins that accumulate in the brains of patients with Alzheimer's disease. Unlike therapies that target amyloid beta, posdinemab specifically addresses tau pathology, which is closely associated with neuronal dysfunction and cognitive decline in Alzheimer's disease.
Clinical development
Phase I studies
The first-in-human clinical trials of posdinemab included both healthy participants and participants with Alzheimer's disease. These Phase 1 studies evaluated the safety, tolerability, pharmacokinetics, pharmacodynamics, and immunogenicity of the antibody. A separate single ascending dose study was also conducted in Japanese participants.The Phase 1 trials demonstrated no safety or tolerability concerns and showed dose-dependent reductions in phosphorylated tau protein at position 217 in cerebrospinal fluid following administration of posdinemab. The safety and biomarker profiles from these studies supported the continued investigation of the compound.
Phase II studies
AuTonomy study
Posdinemab is currently being evaluated in a Phase 2b clinical trial called "AuTonomy". This study is investigating the efficacy and safety of posdinemab in patients with early Alzheimer's disease, including those with prodromal Alzheimer's disease and mild Alzheimer's dementia.The AuTonomy study evaluates the effect of two doses of posdinemab compared to placebo, administered every 4 weeks over a 104-week treatment period. The study includes patients with symptomatic Alzheimer's disease who meet clinical criteria and have elevated plasma phosphorylated tau-217 levels, followed by intermediate levels of tau burden on tau PET imaging. As of August 2025, the Phase 2b AuTonomy study is fully enrolled and ongoing.
This trial represents the first to employ a plasma biomarker approach for participant selection in anti-tau therapy studies.