An isolated peptide or polypeptide containing the sequence VSIGLSFPMLP (SEQ ID NO:1), found in the secreted form of human MUC1, that enhances an immune response when administered to a mammal, compositions containing the peptide, host cells producing the peptide and methods of use. The peptide or polypeptide may be conjugated to a carrier protein and administered as part of a vaccine or immunogenic composition for prevention or treatment of a disease or disorder.