The present invention relates to fusion polypeptides comprising (a) a 4-oxalocrotonate tautomerase (4-OT)-based polypeptide scaffold which is capable of forming multimers, and (b) a polypeptide antigen； and homo- and hetero-multimers thereof. The invention also provides nucleic acid molecules and vectors encoding the fusion polypeptides and multimers； and methods of using the fusion polypeptides, multimers, nucleic acid molecules and vectors to produce an immunogenic response against the polypeptide antigen.
