Parkinson's disease (PD) is characterized by a progressive loss of dopaminergic neurons, linked to aggregation of alpha-synuclein (αSYN) into Lewy bodies. Current treatments are symptomatic and do not halt or reverse the neurodegeneration. Immunotherapy targeting aggregated αSYN shows potential, but therapeutic efficacy is limited by poor brain penetration of antibodies. We developed a bispecific antibody, RmAb38E2-scFv8D3, based on αSYN oligomer selective RmAb38E2 fused to a transferrin recepto...