The invention relates to a conjugate comprising (a) an amatoxin comprising (i) an amino acid 4 with a 6-deoxy position and (ii) an amino acid 8 with an S-deoxy position (b) a BCMA-binding moiety comprising (i) the variable domains of humanized antibody J22.9-ISY, and (ii) a heavy chain constant region comprising a D265C mutation and (c) a protease-cleavable linker linking said amatoxin and said target-binding moiety. The invention furthermore relates to a pharmaceutical composition comprising such conjugate, particularly for use in the treatment of multiple myeloma.
