Rationally designed antibodies selective for pathogenic tau aggregates

Abstract

Background Tauopathies are neurodegenerative disorders characterized by the abnormal aggregation of tau protein in the brain. Soluble toxic tau aggregates have the ability to transfer from cell‐to‐cell and to induce newly formed aggregates in recipient cells, thereby propagating tau pathology across the brain in a prion‐like manner. We used computational modeling to identify conformational “disease‐specific” epitopes predicted to become exposed on misfolded tau aggregates. Selectivity of antibodies for tau pathogenic species, as opposed to pan‐tau reactivity, is needed both in order to preserve normal tau function and to minimize the diversion of active antibody from the target through unproductive binding to more abundant non‐toxic forms of the protein. Method The ability of predicted disease‐associated conformational peptide epitopes to induce tau aggregation on their own was tested in a Thioflavin‐T fluorescence(ThT)‐based seeding assay. Mouse monoclonal antibodies raised against selected epitopes were screened by surface plasmon resonance (SPR) for binding to synthetic tau monomers, toxic oligomers, and soluble pre‐formed fibrils (PFFs). Recognition of naturally occurring tau species in Alzheimer’s disease (AD) brain was also confirmed by SPR. The ability of selected antibodies to inhibit induction of tau aggregation by AD brain seeds was assessed in a seeding assay using TauRD P301S FRET Biosensor Cells expressing tau constructs with different fluorescent labels producing a FRET signal when aggregated. Result Predicted conformational peptide epitopes capable of seeding activity in the ThT assay were used to immunize mice. SPR screening of hybridoma supernatants was used to identify antibody clones with the desired profile of preferential binding to a preparation of toxic tau oligomers vs non‐toxic tau monomers. A majority of these antibodies also bound soluble tau PFFs, a species believed to play a role in propagation of disease. Antibodies selected for further testing were found to recognize tau from AD brain extract by SPR and to inhibit seeding activity in a FRET assay. Conclusion Computational modeling for identification of predicted disease‐associated epitopes together with in vitro screening methods allowed for the generation of monoclonal antibodies with selectivity and activity against pathogenic, aggregated species of tau.