Described is a prion protein, wherein said prion protein is a homodimer or heterodimer. The prion protein dimers are highly immunogenic capable of inducing an immune response in a mammal, thus useful for prophylactic or therapeutic vaccination against diseases associated with the infectious forms of prion proteins, PrP.sup.Sc, i.e. transmissible spongiform encephalopathies. Moreover, antibodies generated by using the prion protein diners as an antigen, pharmaceutical composition containing the prion protein dimers or antibodies directed against said diners as well as DNA sequences encoding the prion protein diners are described.