Internalization of tau antibody and pathological tau protein detected with a flow cytometry multiplexing approach.

Introduction: Tau immunotherapy has emerged as a promising approach to clear tau aggregates from the brain. Our previous findings suggest that tau antibodies may act outside and within neurons to promote such clearance.

Methods: We have developed an approach using flow cytometry, a human neuroblastoma cell model overexpressing tau with the P301L mutation, and paired helical filament (PHF)-enriched pathologic tau to effectively screen uptake and retention of tau antibodies in conjunction with PHF.

Results: The flow cytometry approach correlates well with Western blot analysis to detect internalized antibodies in naïve and transfected SH-SY5Y cells (r = 0.958, and r = 0.968, P = .021 and P = .016, respectively). In transfected cells, more antibodies are taken up/retained as pathologic tau load increases, both under co-treated conditions and when the cells are pretreated with PHF before antibody administration (r = 0.999 and r = 0.999, P = .013 and P = .011, respectively).

Discussion: This approach allows rapid in vitro screening of antibody uptake and retention in conjunction with pathologic tau protein before more detailed studies in animals or other more complex model systems.