TFRC and Alzheimer disease: For example, anti-transferrin receptor (TfR) × BACE1 bsAbs leverage TfR-mediated transcytosis to deliver therapeutic antibodies across the blood-brain barrier, thereby reducing β-amyloid (Aβ) accumulation in the treatment of Alzheimer’s disease [243]; (5) Immune checkpoint synergy: This modality involves concurrent targeting of multiple immune checkpoint molecules (e.g., PD-1 and CTLA-4) in order to attenuate the immunosuppressive tumor microenvironment.