A therapeutic composition comprising: (a) a yeast vehicle； and (b) a fusion protein expressed by the yeast vehicle, the fusion protein comprising: (i) at least one antigen or immunogenic domain thereof； and (ii) a peptide linked to the N-terminus of the antigen or immunogenic domain thereof, the peptide consisting of at least two amino acid residues that are heterologous to the antigen, wherein the peptide stabilizes the expression of the fusion protein in the yeast vehicle or prevents posttranslational modification of the expressed fusion protein； wherein the peptide linked to the N-terminus of the antigen, or immunogenic domain thereof, comprises an amino acid sequence of M-X 2 -X 3 -X 4 -X 5 -X 6 ； wherein X 2 is any amino acid except methionine, glycine, proline, lysine or arginine； wherein X 3 is any amino acid except methionine, lysine or arginine； wherein X 4 is any amino acid except methionine, lysine or arginine； wherein X 5 is any amino acid except methionine, lysine or arginine； and wherein X 6 is any amino acid except methionine,.
