A composition for the co-delivery to a cell of a nucleic acid and an assistor protein, comprising vesicles, nucleic acid and protein, wherein the nucleic acid operatively encodes an antigenic protein or portion thereof which shares at least one epitope with the assistor protein, the composition comprising said nucleic acid and said assistor protein associated with the same vesicles as one another. A preferred embodiment is a composition comprising liposomes formed from liposome forming materials and, associated with the liposomes, nucleic acid operatively encoding an antigenic protein and an assistor protein, wherein the assistor protein shares at least one epitope with the antigenic protein. The composition is for use as a vaccine and provides improved immune response compared to non-vesicular compositions, or mixtures of liposomes some of which are associated with nucleic acid and some of which are associated with assistor protein.