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-X2-X3-X4-X5-X6； wherein X2 is any amino acid except methionine, glycine, proline, lysine or arginine； wherein X3 is any amino acid except methionine, lysine or arginine； wherein X4 is any amino acid except methionine, lysine or arginine； wherein X5 is any amino acid except methionine, lysine or arginine； and wherein X6 is any amino acid except methionine,.
