QXL138AM targets CD138 on tumor cells; protease unmasking enables IFN-α to trigger IFNAR–JAK/STAT apoptosis/antiproliferation in CD138+ cells, and the IgG1 Fc engages Fcγ receptors (including CD32a) on immune effectors to mediate ADCC/ADCP/CDC against CD138+ targets. CD32a+ cells are effectors, not killed by the drug.