Engineering a dimeric single-domain antibody for improved detection and neutralization of amyloid-β oligomers.

Soluble Aβ oligomers are regarded as major neurotoxic agents in Alzheimer's disease. Several monoclonal antibodies have been developed to target Aβ oligomers, but most of them show limited specificity binding also to monomers and fibrils. To generate an antibody with high specificity for the oligomers, we aimed to increase the efficiency and sensitivity of a human VH-derived Aβ-oligomer-specific single domain antibody, called DesAb-O. We engineered a dimeric DesAb-O variant, DiDesAb-O, which showed significantly higher binding affinity for Aβ oligomers as compared to the monomeric sdAb. DiDesAb-O selectively detected Aβ42 oligomers not only in vitro and in cultured cells using synthetic preparations, but also in the cerebrospinal fluid from Alzheimer's patients. Moreover, it inhibited the binding of these toxic species to cellular membranes and neutralized their neurotoxicity both in cells and in patient-derived cerebrospinal fluid at lower concentrations compared to DesAb-O. These results indicate that rational dimerization of single-domain antibodies can substantially enhance target engagement and functional efficacy, providing a promising strategy for the development of improved diagnostic and therapeutic molecules for Alzheimer's disease.