The invention relates to soluble CTLA4 molecules which bind a B7 antigen and comprise an amino acid sequence that corresponds to a mutant CTLA4 extracellular domain, wherein the amino acid sequence corresponding to the mutant CTLA4 extracellular domain comprises the sequences Met-Tyr-Pro-Pro-Pro-Tyr and Ala-Ser-Pro-Gly-Lys-Ala-Thr-Glu.The invention further relates to pharmaceutical compositions comprising such a molecule and the use of such a molecule in therapy. Also, the invention relates to methods for regulating binding and interactions wherein such a molecule is used.