Methods of treating or delaying onset of a neurodegenerative disorder with α-synuclein pathology in an individual comprise administering an antibody which is produced from a stabilized soluble α-synuclein oligomer and capable of binding a stabilized soluble α-synuclein oligomer, the stabilized soluble α-synuclein oligomer having a lower formation rate to a non-soluble aggregated form than a non-stabilized soluble oligomer of the α-synuclein. The antibody has been collected from a non-human animal to which stabilized soluble α-synuclein oligomer had been administered or has been produced by hybridoma technology, phage display, ribosome display, mammalian cell display or bacterial display, and the disorder with α-synuclein pathology is characterized by deposition of Lewy bodies and Lewy neurites or is selected from the group consisting of Parkinson's disease (PD), dementia with Lewy bodies (DLB), the Lewy body variant of Alzheimer's disease, and multiple system atrophy (MSA).