Compositions and methods for blood-brain barrier delivery

Monoclonal anti-TfR antibodies and antigen-binding fragments thereof for delivering an agent to the brain of a subject in need thereof are described. Also described are conjugates and fusion constructs containing the anti-TfR antibody or antigen-binding fragment thereof coupled to a therapeutic or diagnostic agent, such as a second antibody and antigen-binding fragment thereof, for treating or detecting a neurological disorder and/or delivering a therapeutic or diagnostic agent across the blood-brain barrier. Also described are nucleic acids encoding the antibodies, conjugates and fusion constructs and related recombinant host cells.