The selective cytotoxic activity of WT nBT062-DM4, stable nBT062-DM4, half nBT062-DM4 and bispecific nBT062-natalizumab-DM4 was investigated using a cytotoxicity assay towards NCI-H929 (CD138+/ CD49d+) multiple myeloma cells. Here, ITGA4 is linked to plasma cell myeloma.