Structure of the cAC10-vcMMAE system. Conjugates were prepared by controlled partial reduction of internal cAC10 disulfides with DTT, followed by addition of the maleimide-vc-linker-MMAE. Stable thioether-linked ADCs were formed with the addition of the free sulfhydryl groups on the mAbs to the maleimides present on the drugs. cAC10-vcMMAE and the cIgG-vcMMAE used in these studies contained approximately 8 drugs/mAb.