A method for the treatment of a disease in a mammal by administering a therapeutically effective amount of a conjugate comprising a biospecific affinity counterpart and a peptide, wherein the peptide contains an amino acid sequence that is derived from staphylococcal enterotoxin A, binds to a V.beta. of a T cell receptor, and has a D227A mutation so that the peptide has a modified ability to bind to MHC class II antigens.