A method for enhancing an immune response to a nucleic acid vaccine comprising administering to an animal a nucleic acid construct encoding a fusion protein comprising a processing component and an antigenic polypeptide of interest wherein said processing component provides heterogeneous processing of the antigenic polypeptide when the nucleic acid construct is expressed in a host cell and a resulting enhancement of the immune response. The processing component is derived from an N-terminal portion of PORF2 of Hepatitis E virus.