Disclosed is the use of an immunoconjugate in the manufacture of a medicament for treating a disease associated with target cells expressing CD138 in a human subject, the immunoconjugate comprising at least one engineered targeting antibody targeting CD138 expressing cells, and at least one effector molecule, wherein said engineered targeting antibody is functionally attached to said effector molecule to form said immunoconjugate, wherein at least a part of the engineered targeting antibody confers IgG4 isotype properties, wherein the disease associated with target cells expressing CD138 is a plasmaproliferative disorder or a solid tumour, wherein said treating comprises administering the immunoconjugate in a multiple dose regimen comprising at least two doses, wherein the aggregate dose to be administered within an active treatment cycle is an aggregate maximum tolerable dose (AMTD) or a fraction of the AMTD and wherein said AMTD or said fraction exceeds the dose resulting in dose limiting toxicity (DL T) when the immunoconjugate is administered as a single dose, including as part of a multiple single dose regimen or exceeds the maximum tolerable dose (MTD) when the immunoconjugate is administered as a single dose, including as part of a multiple single dose regimen within said active treatment cycle.
