TREM2 and Alzheimer disease: Bispecific antibodies outperform mAbs in AD mouse models and are classified into two categories: (a) Pathology-targeting bispecific antibodies, engaging AD-related targets (e.g., Aβ/tau, Aβ/TREM2) for synergistic effects; and (b) BBB-shuttling bispecific antibodies, combining CNS-active antibodies with brain-penetrating modules (e.g., TfR1, CD98hc) to enhance delivery [59,63].